METAL REMOVAL FLUIDS
A GUIDE TO THEIR MANAGEMENT AND
This proposal has been developed over the past two years by ORC Staff working with a task
force of safety and health professionals from ORC member companies, and other concerned
industrial organizations, in particular the American Automobile Manufacturers Association and
the Independent Lubricant Manufacturers Association. These individuals and their employers
have generously contributed of their time and professional skills to make this Guide a reality.
ORC thanks them for their dedication and commitment to the effort.
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Counselors Inc., and does not necessarily represent the opinions of member companies or the
This guide is intended to be an information document for the effective management, use and
maintenance of metal removal fluids (“MRF”). It is not within the scope of this guide to analyze
specific technical or legal issues. Each company should consult with its own legal counsel as to
any legal or compliance issues. Organization Resources Counselors, Inc. (“ORC”) and the Metal
Working Fluids Product Stewardship Group (“MWFPSG”) do not make any warranty or
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TABLE OF CONTENTS
Introduction .................................................................................................................... 1
Purpose of this Guide ................................................................................................... 1
Scope ........................................................................................................................... 2
A Multifactorial Problem ............................................................................................. 2
Management of Metal Removal Fluid Systems ............................................................ 3
Composition of Metal Removal Fluids ......................................................................... 5
Product Selection ........................................................................................................... 7
Reduction of Employee Exposure to Metal Removal ................................................. 9
Reduce Contamination and Degradation of Metal Removal Fluid .............................. 11
Control And Maintenance of Metal Removal Fluids ................................................... 13
Changing Metal Removal Fluids .................................................................................. 16
Health And Hygiene Considerations for Metal Removal Fluids ................................. 17
What Is An Appropriate Goal for Airborne Concentration of MRF? ......................... 18
APPENDIX A - Definitions .......................................................................................... 20
APPENDIX B - Health Effects .................................................................................... 22
APPENDIX C - Check Lists ......................................................................................... 31
APPENDIX D - Enclosure and Ventilation as Controls .............................................. 32
APPENDIX E - Polymer Additives for Metal Removal Fluids .................................... 38
APPENDIX F - Filtration Systems ................................................................................ 39
APPENDIX G - Way Oils And Hydrostatic Systems .................................................... 72
APPENDIX H - Metal Removal Systems Model Test Schedule ................................... 74
APPENDIX I - Metal Removal Fluid Compatibility ...................................................... 75
APPENDIX J - Factors Affecting the Performance of Metal Removal Fluids ............ 80
APPENDIX K - Procedures for Changing Metal Removal Fluids ................................ 83
APPENDIX L - Key Elements from OSHA‟s Formaldehyde Standard ........................ 84
APPENDIX M - Velocity Trenches and Flumes ........................................................... 90
APPENDIX N - References ........................................................................................ 93
The intent of this document has been to gather in one spot some basic, practical information to
allow individuals in shops both large and small to more effectively manage metal removal fluid
(MRF) systems and reduce employee exposures. The material contained in “Metal Removal
Fluids, A Guide To Their Management and Control” is a distillation of the personal views and
practical observations of many individuals and organizations with long experience in metal
machining operations of all sizes. In the preparation of this document, care has been taken to
retain the intent of individual recommendations. However, because of the multiplicity of
sources, and the integration of recommendations, ORC has not attempted to identify individual
This document is not intended to be used as an authoritative guide or sole resource for employers
seeking to improve the management of MRF systems or reduce exposures to MRFs. The
“Guide” is not a “cookbook”, but instead it is a starting point for gathering additional information
and analyzing the particular circumstances in each workplace necessary to reach independent
judgement about appropriate MRF management practices.
For the reader wishing more information, we have included appendices that present a very basic
overview of some of the key elements associated with understanding and controlling MRF
systems. The appendices of this document are not intended to be a comprehensive review of
technical or scientific literature, but are intended only to acquaint the reader with some of the
basic information about MRFs and their relationship to worker health issues, and ORC makes no
claim, explicit or implicit, for completeness. Finally, in Appendix N, References, ORC has listed
a variety of sources that the reader may turn to for additional information, but this list is not
comprehensive, and must not be regarded as complete.
METAL REMOVAL FLUIDS
A GUIDE TO THEIR MANAGEMENT AND CONTROL
Over the past several years concerns have been expressed over the potential health effects
associated with exposure to metal removal fluids (MRFs). These concerns are shared by
employers, many of whom have made significant commitments of financial resources to the
improvement of health and safety conditions in machining operations. The most obvious
method for further reducing MRF exposure levels is to enclose and ventilate all machine tools
that generate aerosols of MRF. Enclosure and ventilation are, however, extremely expensive
and, when pursued on a retrofit basis, often not completely effective. The most effective
enclosures are those that are designed and installed on the tool by the original equipment
manufacturer, but many employers simply cannot afford to replace their machine tools on
anything other than a long term basis.
In addition, the idea of totally enclosing machine tools is just not realistic for many employers
who must purchase used equipment because of economic circumstances. However, the inability,
in the short-term, to totally enclose and ventilate machine tools does not mean that nothing
significant can be done to reduce employee exposure to MRF. There are many ways that have
been proven effective in reducing both the generation of MRF mists and concern over health
effects that may result from such exposures. Usually, the cost of implementing such changes is
nominal and quickly recouped in the form of more efficient operations, fewer employee
complaints and a higher quality final product. The authors of this document believe that, through
the use of informed, systematic approaches to the management of MRF systems, all employers
can take actions now to both effectively reduce airborne concentrations of MRF and improve
working conditions for their employees.
1.0 PURPOSE OF THIS GUIDE
This guide is intended to provide general guidance for the effective management, use and
maintenance of MRF in a variety of operations. Employers use many different
approaches to successfully manage and maintain MRF. This guide presents techniques
and management tools that have been applied over a broad range of control approaches,
fluid types and machining conditions. Some of the listed methods may be useful or
essential for certain approaches or conditions, but may be unnecessary for, or inconsistent
MRFs, are generally safe to work with and around. However, like most tools, they have
the potential to cause problems if not handled or cared properly. Most problems with
MRFs are caused by a failure to follow simple common sense rules for their use and
maintenance. This guideline supplies an overview of basic methods and procedures that
have proven effective in properly maintaining MRFs and preventing unnecessary human
exposure. This document is not intended to be comprehensive in scope or mandatory in
nature. There are a number of useful documents available to assist those wishing to learn
more about the proper use, handling, care and maintenance of cutting fluids. A listing of
these sources can be found in Appendix N.
This guide applies to fluids used to facilitate the wet removal of metal in machining
operations that include both cutting and grinding. Fluids used to facilitate wet metal
removal operations are primarily intended to control temperature build-up in the work
piece and cutting tool, and to provide lubrication. Iimportant secondary uses include
removing swarf and dust, and preventing corrosion of the work piece and machine tools.
MRFs that are properly handled and maintained last longer, perform their intended job
better, have less potential to cause health problems for exposed workers, and save money.
3.0 A MULTIFACTORIAL PROBLEM
The production of MRF mists (MRF mist, oil mist, oil vapor and oil smoke) cannot be
isolated to a single cause and is a synergy of several factors including:
MRF nozzle size, type and position.
Pump size, type and condition.
Tool type and speed.
Velocity trench design and condition.
Use of chip drags and other means of transporting chips and swarf.
Fixture and part configuration and shape.
Exhaust ventilation, air supply design, volume, configuration and location.
Amount of supply or exhaust air recirculated.
Air cleaner/collector design, appropriateness and efficiency.
Condition of MRF.
Continuous vs non-continuous application of MRF.
General housekeeping around machining lines.
Metal removal rate.
Grinding speeds and feeds.
Amount of entrained air.
Effect of tankside additions.
Control of tramp oil and other contamination.
The increased reliance on higher tool speeds and fluid pressures could amplify issues
associated with MRF aerosol generation. The introduction of computer-controlled
machinery will further mandate more effective control of plant air quality. Solving these
issues will positively impact product quality, worker satisfaction and environmental
3.2 A Systems Approach Is Needed
Since issues relating to MRF mist generation are interdependent, a systemic approach to
these issues will be the most productive and cost-effective one. While addressing only
one or a few of the relevant issues is likely to be ineffective, dealing with all of the issues
in a systematic manner will benefit the machine builder or rebuilder, MRF supplier, and
the machine user.
4.0 MANAGEMENT OF METAL REMOVAL FLUID SYSTEMS
4.1 The Importance of Having a Written Management Program
A key element in controlling employee exposure to MRFs is the development and
implementation of a written MRF management plan. An MRF management plan can be
simple or complex, but it should define how the systems involved will be maintained.
MRF systems are complex, dynamic, biologically active and constantly changing in
response to conditions of use. MRF systems can be maintained in a stable condition over
relatively long periods of time, but this requires a well thought-out and consistently
enforced management plan. Such a plan should be in written form and should
specifically identify key elements of the program and the individual(s) responsible for
their implementation. Such a plan should consider at least the following elements:
4.1.1 A Statement of Goals and Commitment: This indication of management
commitment and what it wants to achieve should include a broad reference to
managing and controling MRF, promoting of product quality and preventing
health problems. It could also contain a definition of what is considered
4.1.2 Designation of Overall Responsibility for Performance of the System: This
generally should be an individual, but may be a team. The person(s)
coordinating the fluid management program should receive input from all
available sources along with information on finished part quality, production
quantity and production cost data. For those with overall responsibility for a
system‟s performance, a thorough understanding of the chemistry involved is
4.1.3 Designation of an Individual or Team Who is Responsible for Adding
Materials to the System: All system additions of any kind should be controlled
and recorded by this individual or team. Such additions may include fresh
biocides, MRF fluid additives or concentrates and water or oils to make up
volume lost through normal operation of the system.
4.1.4 A Written Standard Operating Procedure (SOP) For Testing the Fluid:
Such an SOP should include where and when the samples to be tested should be
collected, how they should be treated after collection, which tests should be
performed, a specific protocol for each test performed and who is responsible
for performing and recording them.
4.1.5 A Data Collection and Tracking System: The data should include
observations made at the system, laboratory analyses and addition data. This
data should be tabulated in a manner that reveals relationships and trends in the
data and this information should be used to improve the fluid management
techniques. These techniques can often be generalized to smaller machines and
systems with reduced laboratory testing to allow their successful management.
Production and quality data may also supply useful information on the
performance of the system.
This system should have a response time that allows feedback on system
condition so that corrective actions, if needed, may be taken before the system
experiences significant problems. Factors recorded and tracked should be up to
the discretion of the MRF manager. These factors should be prioritized and
customized for specific facility situations. For example:
3. Foaming tendency.
4. Water quality.
5. System stability.
6. Biological contamination.
7. Tramp oil and invert emulsions “cream” contamination.
8. Biocide levels.
9. Corrosion resistance.
10. Emulsified oils.
4.1.6 Employee Participation: The only way to effectively manage MRF is to enlist
the aid of the people who work with the system every day. This should include
personnel from manufacturing, maintenance, technical support groups, and MRF
lubricant and machine tool suppliers. Workers who operate the machines are the
real experts on the operation of the system, but usually they are not scientifically-
trained observers. They should be trained to understand how a MRF works and
what affects it. System personnel should have a basic understanding of the
laboratory tests and have the results available to them in an easy to read and
understandable form. There should be a simple way that workers can submit their
observations to those responsible for system maintenance. Worker observations
should be documented and correlated with the laboratory data and any chemical
4.1.7 Training Programs: These should be designed to help workers understand the
basic functioning of the system. For instance, what can affect the proper
functioning of a particular MRF system and shorten or prolong its useful life?
What are the warning signs of impending problems and what happens when a
system goes bad? Other elements of a basic training program should include
information on potential hazards from exposure to MRFs and how to avoid them,
as well as standards of personal conduct and their impact on both the employee
and the system. Employees should understand that hazards are reduced, but not
eliminated, as MRF concentrations are diluted. MRFs, additives, and enhancers
should always be used in accordance with instructions on labels or on MSDSs.
All containers used to transport or administer a labeled product should themselves
be labeled. All manufactured and formulated MRF constituents should have a
current MSDS on file and readily available to employees. All MSDSs, and
employee training associated with their use and distribution, should comply with
the requirements spelled out in the Occupational Safety and Health
Administration (OSHA) Hazard Communication Standard, 29 CFR 1910.1200. It
should be noted, however, that most MSDSs are written for the concentrated fluid,
and the contents of these MSDSs may be very general.
4.1.8 When A System Has Come to the End of Its Useful Life: Even well-managed
systems eventually reach the end of their useful life. System managers should
develop guidance on when a system needs to be dumped, and how this should be
5.0 COMPOSITION OF METAL REMOVAL FLUIDS
5.1 Straight Oils
These products generally consist of a severely solvent-refined or hydro-treated petroleum
oil, a synthetic oil, or other oils of animal or vegetable origin. The oldest type of MRF,
straight oils, provide excellent lubricity, good rust control and long sump life. These oils
are not intended to be diluted with water prior to use. In many cases oil is the major
component, but often additives are included to:
increase lubricity (oiliness) such as vegetable oils or polyolesters;
impart extreme temperature and pressure characteristics to the oil, such as
sulfurized fatty materials or chlorinated paraffins;
control oxidation, such as alkylated phenols;
passivate metals in the system, such as triazole;
control corrosion, such as calcium sulfonates;
control mists, such as various polymers;
keep the additives in suspension;
control odors, such as copper compounds; and
make the presence of MRFs more easily visible, such as dyes.
5.2 Soluble Oils
These are a combination of 35-85% severely refined petroleum base oils, emulsifiers, and
water. In addition, they may contain soaps, sulfonates and coupling agents to help keep
the oil emulsified. They may also contain additives such as biocides to retard spoilage,
and alkanolamines for “reserve alkalinity” to react with short-chain fatty acids produced
by bacterial action. They are intended to be mixed with good quality water in various
concentrations, and are used as oil-in-water emulsions. “Commodity” grade straight oils
offer good lubricity, better cooling than straight oils, but draw backs may include poor
corrosion control, formation of by-products that coat tools and are difficult to remove,
may have poor mix stability and short sump life. Here, as with other products, the
“premium” formulations offer improved performance and longer sump life when
compared to less complex formulations. However, a more complicated chemistry may
make a premium product more difficult to maintain. Because of the tendency for
microorganisms to grow in soluble MRF, effective management requires close attention
to system maintenance.
5.3 Semi-synthetic Fluids
These fluids contain small amounts of severely refined base oil (usually less than ten
percent) as well as a number of organic and inorganic materials such as alkanolamines,
borates, fatty acid soaps, phosphates, amines, amides, alcohols, surfactants, and biocides
in an aqueous solution. These products as designed include 30-50% water, and working
fluids will be diluted further. Typical semi-synthetic MRFs are transparent or translucent,
offer good lubrication, cooling capacity and rust control, longer sump life and generally
are easier to remove from tools and the surrounding environment than soluble oils.
However, semi-synthetic MRFs also have a greater tendency to foam when the water is
soft and may be unstable in hard water. These products may contain amine salts of boric
acid for extra corrosion control and sometimes a chelator, such as ethylenediamine tetra
acetic acid (EDTA). Because of the potential for forming nitrosamines, the use of
materials that contain both nitrites and secondary amines should be avoided.
5.4 Synthetic Metal Removal Fluids
These are aqueous solutions of chemicals similar to semi-synthetics, but without mineral
oil. Like the semi-synthetic, the use of materials that contain both secondary amines and
nitrites should be avoided. True synthetics consist of solutions of polymers and a variety
of organic and inorganic chemicals mixed with water. They have the capacity to supply
exceptional cooling properties, especially in very high-speed cutting applications.
Synthetic MRFs do not break down as do soluble oils and semi-synthetics. Since they
contain no mineral oil, they generally do not smoke. Because they lack emulsifiers,
synthetic MRFs reject so-called “tramp oil,” such as leaking hydraulic oils. These
products are transparent, which allows machine operators to see their work better, and
they are generally unaffected by dissolved minerals in water. However, synthetic MRFs
typically offer poor physical lubrication, may be more difficult to dispose of, and may
have a tendency to foam under some circumstances. Also they tend to form gummy
residues that do not readily resolubilize. There may be poor worker acceptance of
synthetic MRF because of some attendant respiratory irritation. Synthetics offer other
benefits that may be significant. Additives may include, but are not limited to, ethylene
oxide or propylene oxide polymers, amides and/or organic esters as lubricants, mono and
dicarboxylic and boric acids as corrosion inhibiters, plasticizers such as glycol ethers, as
well as chelators, defoamers, odorants, biocides and dyes. Because of the potential for
forming secondary amines, the use of materials that contain both nitrites and secondary
amines should be avoided.
5.5 Additives for Metal Removal Fluids
In addition to the original chemical contents of the MRF, other substances are added to
the fluids at the machines to retain the properties of the original fluid. Some additives
may have unanticipated effects on a system. For instance, some additives will release
entrained air and generate mist. Regardless of the type and the presence or absence of
added chemicals, all MRFs have a potential for producing adverse health effects,
depending on conditions of use. Decisions regarding the selection and maintenance of
MRFs should include consideration of health and environmental impact, as well as
economic and performance factors. Only those MRFs and additives approved for use in
specific systems or operations should be used. Records should be kept of the type,
manufacturer, amount of material added and the date of the addition.
6.0 PRODUCT SELECTION
MRFs are manufactured for many kinds of operations, some quite specialized. The MRF
selected should be carefully matched to assure compatibility of the MRF with the
machining operations, alloy being machined and tools used.
6.1.1 Evaluating the Compatibility of Materials
Chemicals which are likely to be added to the MRF should be screened for
compatibility. (See Appendix I, Metal Removal Fluid Compatibility.)
6.1.2 Possible combinations of MRFs, biocides, additives, machine cleaners, floor
soaps, hydraulic oils, way lubricants, seal greases, machine paint, rustproofing
agents and carry-over materials should be evaluated. Compatible materials are
those that will not react with each other to change, neutralize or alter desired
chemicals, or create unwanted chemicals or conditions.
6.1.3 Make use of commercially available tests to determine the compatibility with the
other fluids in your system. (See Appendix I.)
6.1.4 To assure the highest level of compatibility, the following factors should be
(1) MRF from which the water has evaporated should be soluble or at least easily
dispersible in the lubricants used on the machine tools. The residue of the MRF
and water should be non-tacky when evaporated. The MRF should be capable of
providing both deep-hole corrosion protection and stability in the presence of
chemical or biological contaminants.
(2) Ideally, lubricating oils and hydraulic fluids used in machine tools should be
non-emulsifiable in dilute MRF; no surfactants should be present. Lubricating
oils and hydraulic fluids should readily and completely separate from dilute MRF
even after severe mechanical mixing. However, this is almost impossible to
achieve with soluble oil MRFs, which contain emulsifiers as an integral
component. (See Appendix G, Way Oils & Hydrostatic Systems.)
(3) Users should be aware of the possible creation of galvanic cells where copper,
aluminum and zinc metals may come into contact with MRFs. Alternatively,
users may select an MRF that contain “yellow metal” or bimetallic corrosion
inhibitors when machining copper, brass or aluminum material. The selection of
the proper MRF is critical to the success of an operation.
6.1.5 Compatibility tests of MRF should extend to all system components that may
come into contact with it such as valve seats, elastomers and seal material.
All products used in MRF should be tested to ensure they function effectively with the
particular MRF filtration equipment in use. (See Appendix F, Filtration Systems.)
6.3 Waste Treatment System Compatibility
All products should be tested to ensure that they function appropriately in the waste
treatment process in use at a particular site.
7.0 REDUCTION OF EMPLOYEE EXPOSURE TO METAL REMOVAL FLUIDS
Systems handling MRFs should be designed or modified to minimize factors that may
contaminate or adversely alter the MRFs or needlessly expose the worker to the fluid.
There are a number of basic steps that can be taken to reduce employee exposure to mist
7.1 The Minimum Adequate Fluid Pressure Should Be Used
A generous, low-pressure flow of MRF delivered directly to the cutting zone, where it
floods and cools the workpiece and cutting tool, is normally most effective. A high-
pressure delivery of MRF may create mists, may not supply adequate cooling or
lubrication, and may not have sufficient flow to properly remove swarf or chips from the
7.2 Avoid the Generation Of Mists
Mechanically formed dispersions of MRF droplets in air are usually referred to as "mist"
in the shop, and are effected by the surface tension and cohesive properties of the MRF.
Where possible, enclose and ventilate mist generating operations.
7.3 Select MRFs With An Understanding of Their Misting Characteristics
Some research has shown that soluble oils tend to produce less mechanically induced
mist than semi-synthetic MRFs, which produce less mist than synthetic MRFs. Consult
with your fluid suppliers. Polymeric additives have been found useful in reducing mist
from straight oils. Polyoxyethylene additives have been found to be useful in some water
dilutable MRF operations. (See Appendix E, Polymer Additives.)
7.4 Cover the Sump With A Moderate Foam Blanket
While excessive foam is undesirable, a foam blanket can act as a trap to capture mist
released from bursting bubbles of entrained air (in the MRF). Destroying this foam (with
an antifoam) can cause immediate and severe misting at the system.
7.5 Minimize Accumulation of Tramp Oil Into the System
Tramp oil can “plate out” on hot tool surfaces and, due to its low thermal conductivity
(when compared to water), it vaporizes and condenses to oil mist. While it is virtually
impossible to prevent all tramp oil leakage into the system, tramp oil from leaking seals
or broken lines is detrimental to the proper operation of any MRF. Tramp oil can extract
from MRF some oil-soluble constituents such as emulsifiers, short-chain fatty acids and
biocides. More importantly, excessive tramp oil enhances microbiological growth which
can lead to offensive odors and excessively high bacteria counts. (See Appendix G, Way
Oils And Hydrostatic Systems.)
7.6 Interrupt or Reduce the Flow of MRF When Feasible
The flow of MRF should be interrupted when machining is not occurring. This not only
reduces mechanically generated mist, it also reduces degradation of the MRF and
oxidation of the biocides. An intermittent flow (or change in pressure) of the MRF (e.g.
30 seconds on, then 2 minutes off) may often be more effective at moving chips than a
continuous flow (with fixed turbulence etc.).
7.7 Sluice/Flume Systems Should Be Vented
The use of sluice/flume systems to move chips should be minimized. Where sluices are
used, an enclosed sluice spillway can cause the mechanically generated mist to be blown
back at the machine operator. Venting the sluice (e.g. into the pit) will reduce this
phenomenon. (See Appendix M, Velocity Trenches And Flumes.)
7.8 Where "Smoke" Is Being Generated, Increase MRF Flow
Smoke is a sign of excessive heat. Vapor and smoke are reduced by increasing the
pressure and/or flow to the part/tool interface, or adjusting the speed of the operation or
the feed-rate of the material being machined. High oil MRF and large amounts of tramp
oil will increase smoke.
7.9 Removal of Vapors and Smoke
Vapors cannot be removed from the plant air by common mist removal techniques such
as coalescence, impaction, impingement, or centrifugal and electrostatic separators. They
can only be removed by absorption, adsorption or condensation, e.g. scrubbers, charcoal
filters or refrigeration. Smoke, depending on its nature, can often be removed by filters
and electrostatic precipitators.
7.10 Effective Enclosure and Splash Guarding Should Be Provided
The provision of well-designed enclosures and splash guards can alleviate many
employee exposure problems, as well as avoid loss of MRF and improve the general
cleanliness of the operation. Where effective splash guards are lacking, machine operators may
avoid being splashed by reducing the flow of fluid to levels not adequate to control heat
generated by the machining process. Overheating of cutting tools and work pieces can lead to the
generation of fumes or vapors, and may damage both. (See Appendix D, Enclosure And
Ventilation As Controls.)
7.11 Local Exhaust Ventilation at the Site of Mist Generation Should Be Incorporated as
A well-designed local exhaust system can remove a large percentage of the mist and
fumes generated by an operation, keeping it away from the machine operator and concentrating
it for more effective removal and disposal. Local exhaust systems are especially effective
when combined with appropriately designed enclosures.
7.12 Assure that Recirculated Air is Clean
Where recirculation of exhaust ventilation is used, assure that the air is adequately
cleaned of contaminants prior to being recirculated. Equipment used to clean air that is to
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be recirculated should meet rigorous minimum collection efficiencies. Monitoring of
recirculated air should be performed often enough to assure that contaminant levels do
not exceed established limits. The manual, Industrial Ventilation, available from the
American Conference of Governmental Industrial Hygienists (ACGIH) has much useful
information concerning the proper design and operation of ventilation systems. (See
Appendix D, and Appendix N, References.)
7.13 Remote Operating Stations Should Be Considered
Control panels or stands moved a short distance from the actual machining operation
reduce employee exposure.
7.14 Use Simple Checklists to Track Safe Working Practice
The use of simple one or two page safety checklists that employees can fill out and turn in
to managers is an effective way to remind employees of safe practices and keep track of
conditions in the shop. (See Appendix C, Checklists, for examples.)
7.15 Plan Additions of MRF Maintenance Chemicals
The addition of sump maintenance chemicals such as biocides should be timed for
periods when they will least affect operators and area personnel.
8.0 REDUCE CONTAMINATION AND DEGRADATION OF METAL REMOVAL
8.1 Provisions Should Be Taken to Maintain the Cleanliness of MRF
The removal of very small metal particles resulting from machining operations is an
important requirement in MRF maintenance because such contamination is an important
source of MRF degradation. Small, clean metal particles are highly reactive and have
enormous aggregate surface area. The greater the surface area, the greater the reactivity
with emulsifiers, biocides and other MRF components. Filtration is the best way to
assure that particulate matter is removed from the MRF before it is recirculated. (See
8.2 Large Systems Should Have Their Own Cleaning Equipment To Remove
Contaminants from the MRF
Smaller stand-alone systems should make use of portable cleaning and filtering
equipment. Contamination of MRF can come from many sources in an operation.
For instance, hydraulic fluids leaking from machine tools, rust preventatives, way
lubricants, metal chips and swarf, food particles, floor cleaners and human wastes.
8.3 Effective Removal of Particulates is Important
There are six basic methods for removing particulate matter: (1) straining, (2) settling,
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(3) skimming, (4) centrifugation, (5) cyclone separation and (6) filtration. Straining can
remove many larger particles before the fluid enters a sump. After it is strained, the MRF
is usually collected in a settling tank (sump). In the sump, the MRF should be allowed to
sit for a period of time to allow the heavier particles such as swarf, metal chips and dirt to
settle out. A central sump should be located away from heavy traffic areas, and should
hold from 10 to 15 times the flow rate (per minute) of the MRF pumps to give the swarf
and chips time to settle out and the fluid a chance to cool before it is again pumped to the
machine tools. (See Appendix F.)
8.4 Remove Tramp Oil Before Recirculating MRF
As the fluid rests in the sump, tramp oil will often float to the surface where it can be
removed by skimming. Where tramp oil is allowed to form a surface layer, it may seal a
stagnant sump from aeration, encouraging the growth of anaerobic bacteria. Agitation of
the fluid in the tank will improve aeration and help avoid the growth of anaerobic
bacteria. Depending on the nature of your operation, consider the use of mechanical oil
removal systems such as: air floatation systems to float solids and tramp oil to the surface
of sumps where they can be skimmed away; belt skimmers that attract oil from a sump
and scrape it off the belt into containers; centrifuge cleaning that uses centrifugal forces to
separate solids and tramp oil from MRF; a coalescer which uses plastic media that attracts
oil to promote formation of oil “floats” that can be skimmed off; or a disc skimmer where
a disk rotates in MRF, attracting oil to its surface, then scrapes the oil off into a container.
(See Appendix F, Filtration Systems.)
8.5 Keep Chips and Swarf from Accumulating in Trenches
Flumes should be designed so that chips and swarf do not accumulate. An adequate
grade should be maintained to assure good flow and sharp curves and corners avoided.
The sooner that chips and swarf are effectively removed from the MRF, the less chance
that the system will become physically blocked. There are many mechanical means used
to remove chips etc., but one of the most effective chip removal methods requires an alert
machine operator who notes and corrects problems before the system is blocked. (See
Appendix M, Velocity Trenches and Flumes.)
8.5.1 In-floor trenches should be designed with a U-shaped cross section
to maintain good flows at low volumes.
8.5.2 Nozzles supplying MRF to move chips and swarf should have outlets that are in
good condition. They should be aimed so that a uniform stream of MRF travels
several feet down the sluice before contacting the walls.
8.5.3 Dead spots should be avoided because they allow chips and swarf
to accumulate, retard fluid exchange and allow microbial growth.
8.5.4 Flumes and trenches should be covered to exclude dirt and large objects which
could physically block fluid flow, and to minimize the release of mists.
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8.5.5 Where metal removal is minimal, as in grinding, or lightweight metal (aluminum)
is being machined, the use of a high-volume low-pressure trench flush should be
8.6 Control Potential Sources of Contamination
8.6.1 Seals, greases and paints should be compatible with the fluid so that they are not
degraded by the MRF.
8.6.2 Seals that fit properly and do not fail are important to reduce contamination with
hydraulic fluid. Repairing leaks in hydraulic systems is imperative.
8.6.3 Avoid splashing MRF onto machine ways unless the MRF is specifically designed
to replace way lubricants. (See Appendix G.)
8.6.4 The use of zinc-based hydraulic fluids and greases should be avoided as they can
accelerate MRF degradation.
8.7 Keep Machines Clean
Machines should be cleaned once a shift to remove chips etc.
9.0 CONTROL AND MAINTENANCE OF METAL REMOVAL FLUIDS
The successful control of MRFs is an exercise in good management that involves
communication and common sense. Do all the testing that is required to keep systems
stable. Keep files on changes within systems and keep a concerned working relationship
with your people. Fluid suppliers can assist in designing an effective control and
Management should be aware of what is happening on the shop floor and be involved
with operators and machining operations. If a system develops an irritating odor, or an
operator complains of an uncomfortable condition, each complaint should be addressed
individually and expediently. Don‟t wait for concerns or complaints to accumulate; if an
exposure situation is irritating, the problem should be dealt with and minimized or, if
possible, eliminated. If machine operators understand that management is concerned and
that problems will be dealt with promptly, you will have established an important
foundation for successful management. (See Appendix J, Factors Affecting the
Performance of Metal Removal Fluids.)
9.1 Once in Use, the MRF Should Be Maintained in Good Condition
Factors that should be controlled include MRF concentrations, pH, suspended
particulate matter, tramp oil, microbe levels and biocide concentrations.
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9.2 The Following Measurements Should Be Performed, Recorded and Adjusted as
9.2.1 On a daily basis: pH, MRF concentration, suspended particulate matter.
9.2.2 At a regular interval, for instance, weekly or more frequently: microbial activity
and, if possible, biocide levels. Refer to ASTM 1497 for guidelines.
(See Appendix N, References.)
9.3 The Following Levels Should Be Maintained
9.3.1 pH should be kept below 9.5, but generally above 8.5, with some systems
requiring a pH above 8.7-8.9. Consult the fluid supplier for specific guidelines.
9.3.2 MRF concentration should not exceed the manufacturer‟s recommended levels.
9.3.3 Suspended particulate matter should be kept below 50 ppm. (See Appendix F for
a discussion of appropriate levels of particulate matter for different systems.)
9.3.4 Tramp oil should be kept at no more than two percent, and preferably below one
9.3.5 Bacteria should be kept preferably below 100,000 (105 ) colonies/cc but should
not exceed 1 million (106 ) colonies/cc. Consult your fluid or biocide supplier for
recommendations. (See Appendix J for a discussion of the dissolved oxygen test
for managing bacterial concentration and the effects of copper on microbial
9.3.6 Yeast and fungus should be absent, but are often difficult to detect prior to the
growth of visible mold or fungus. Your fluid supplier can give assistance if this
problem is suspected. (See Appendix H.)
9.3.7 Biocide levels should not exceed the manufacturer‟s recommended level. (See
Appendix B, Health Effects, and Appendix L, OSHA Formaldehyde Standard.)
9.4 Laboratory Analysis Should Be Chosen to Generate Data Useful for MRF
9.4.1 The real value of the analyses lies in the effects of the actions they cause, such as
chemical additions, skimming, pump-outs etc.
9.4.2 The particular analysis used should be evaluated on a regular basis and modified
as conditions dictate.
9.4.3 New analyses should be developed as the need arises.
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9.5 Sampling and Sample Preparation and the Order Of Analysis Can Be as Important
as the Analyses Themselves
9.5.1 The sample should be representative of the bulk fluid in the system and the
analyses should be done before the sample changes. This usually means that the
analyses should be started in the first 24 hours after it was collected.
9.5.2 A number of the tests are much more informative when run on a centrifuged
sample. The refractive index, acid break, cationic titration, pH, conductivity and
total alkalinity can give entirely different answers on an uncentrifuged sample. In
these cases the results of tests run on the centrifuged sample produce more
9.6 Any Additions or Changes to an MRF Should Be Controlled
The decision to add chemicals or biocides should be made by the individual or team
designated by management as having responsibility for the maintenance of the MRF.
Any addition of chemicals to the MRF should be done by, or under the direction of, the
designated person or team.
9.7 All Additions and Changes Should Be Recorded
The maintenance of good records allows an accurate determination of the condition of the
MRF and what the trends are. Good records can assist in determining why a system went
bad, or why it has lasted so long.
9.8 The Use of Reodorants (Masking Agents) to Cover the Smell of "Spoiled" Systems
Should Be Prohibited
Reodorants are sometimes used to make the work environment more pleasant. However,
the use of reodorants to cover the smell of “spoiled” systems should be minimized, and
additions of these agents should be made only by authorized individuals . (See Appendix J.)
9.9 Production Changes, Unusual Events, Accidents, Actual or Alleged Adverse Health
Effects and Miscellaneous Observations on the System Should Be Recorded on a
Only designated individuals should be allowed to make log entries, and the identity of the
individual making the entry should also be recorded.
9.10 Use of "Dip Sticks" to Determine Biological Growth
Where dipstick methods are used for determination of the biological growth in an MRF
system, the analysis should be done at the facility. Some have found that biological
growth determinations done by suppliers (on identical samples) at the supplier‟s
laboratories have shown significant decreases in growth from samples tested at the
9.11 Biocide Additions Should Be Carefully Controlled
9.11.1 Concentrations should never exceed the manufacturer‟s recommended levels;
“more” is not better!
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9.11.2 To maintain microbe control, biocides may need to be changed occasionally.
9.11.3 Only biocides registered with the EPA and approved by the individual in charge
should be added. Biocide additions should be based upon known concentrations
of existing biocides and microbes.
9.11.4 Where triazine biocides are used, the possibility exists of exceeding the 0.5 ppm
action level of OSHA‟s Formaldehyde Standard, 29 CFR 1910.1048, and
initiating medical surveillance, or exceeding 0.1 ppm and triggering hazard
communication and training requirements of that standard. (See Appendix L.)
9.12 System Clean-outs Should Be Routinely Scheduled
Part of any MRF control program should be a routine, scheduled clean-out of the system
following standard operating procedures. (See Appendix K.)
10.0 CHANGING METAL REMOVAL FLUIDS
10.1 The preferred method is to completely remove or recycle the original fluid, thoroughly
clean and disinfect the system, then recharge with a clean MRF. Caution should be
exercised because one of the most common sources of contaminants in a fresh system is
residue left from the previous charge. After a system has been recharged, the MRF should
be treated with appropriate biocides and monitored very carefully. This is perhaps the most
critical period in the useful life of MRF. How a system is treated for the first month it is in
use will often determine its level of performance and working life. (See Appendix J.)
10.2 The quality of the water used to mix MRF can affect its ultimate performance more than
any other single factor. When mixing fresh MRF or adding water to make up evaporation
losses, which can be as much as 5-20% of the total volume per day, use only water of low
hardness and dissolved solids, uncontaminated with bacteria. If possible, it is preferable
to use water purified by deionization, distillation or reverse osmosis. Zeolite softening
may cause problems because it usually increases the total salt content of the system.
Where purified water is not available, the system may be treated with a water conditioner
such as EDTA, which will tie-up the hard water salts and reduce their destabilizing effect.
(See Appendix J.)
11.0 HEALTH AND HYGIENE CONSIDERATIONS
11.1 Typical Routes of Exposure
Dermal (skin) contact, eye contact, inhalation, ingestion and injection are all
potential routes of exposure. Exposure can take place through direct contact with
a fluid from splashes, through airborne mists and vapors, or fluid residues on parts
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and production equipment. (See Appendix B, Health Effects.)
(a) Prolonged exposure to water-reducible MRF may cause skin irritation that can
be difficult to control, and some MRFs and their additives may induce
sensitization in some individuals. MSDSs for MRF and additives of all kinds
should be carefully reviewed, and their potential toxicity in the particular system
of concern evaluated periodically.
(b) A prime cause of dermatitis and respiratory system complaints is lack of care
and maintenance of MRF systems. Tramp oil is one of the main causes of
dermatitis because it is a prime carrier of fines, which are a key cause of skin
irritation due to mechanical abrasion with the skin.
(c) A water-based MRF that is not carefully controlled for concentration of
additives can, be much more irritating than one that is operating at the
manufacturers recommended concentration.
(d) Bacterial growth in MRF can be a secondary source of dermatitis and lung
problems, and is also a major contributor to degradation of the MRF. Proper
maintenance and cleaning of the MRF system, and especially the sumps, can have
a highly beneficial impact on the incidence of dermatitis and respiratory problems
reported by employees.
(e) Personal hygiene is important if dermatitis problems are to be avoided. One
of the key troublemakers is suspended solids which may include fine metallic
swarf (fine chips), grinding wheel debris, oxide scale and rust particles. All of
these, combined with MRF, can cause problems if allowed to remain on the skin.
If dirt is removed from the skin in such a way that it causes the dirt to be rubbed
in, it will make the problem worse. Workers should use a good quality cream or
gel hand cleaner.
(f) The use of good quality barrier creams on exposed skin areas can offer
significant protection against the development of dermatitis if used consistently
and renewed as necessary throughout the shift.
(g) Clothing that becomes thoroughly soaked with MRF should be changed
immediately! Work clothes that become soaked with MRF during the day, and
are hung up over night to dry out will concentrate the salts in the MRF. If worn
again the next day, the clothes start out with a pre-load of salts that can soon
increase to levels that may cause skin irritation.
(h) Protective equipment must be used in compliance with the requirements of
OSHA‟s Personal Protective Equipment Standard, 29 CFR 1910.133, 138.
11.3 Preventive Steps
(a) Where possible avoid contact with MRF.
(b) Maintain MRF concentration within manufacturer‟s recommendations. High
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concentrations can and do cause dermatitis.
(c) MRF residues should not be allowed to accumulate.
(d) Clothing and rags should be cleaned as needed. Shop rags should be free of
abrasive dirt, metal fines and contaminant chemicals.
(e) Correct fluid flow rates and adequate splash guards should be used.
(f) If contact cannot be avoided, an impervious apron and gloves made of a
material such as nitrile or PVC should be considered. Disposable or washable
inner gloves should also be considered to eliminate perspiration. Great caution
must be exercised when using gloves around rotating or moving machinery.
(g) Where gloves are used they should be changed routinely, especially when wet
(h) When washing, do not wash in the MRF tank/sump, and avoid the use of
solvents that remove natural oils and cause dry skin which is more susceptible to
irritation and infection.
(i) At each break, before eating or going to the toilet, exposed skin should be
washed with a mild gel-type hand cleaner or a mild non-abrasive soap, using hot
water and drying gently but thoroughly.
(j) Observance of good personal hygiene should be made part of established shop
12.0 WHAT IS AN APPROPRIATE GOAL FOR AIRBORNE CONCENTRATIONS
It is clear that the lower the concentration of airborne particulates in a workplace, the less
likely the worker is to have an adverse reaction. The best advice seems to be attempting
to maintain an 8-hour Time Weighted Average (TWA) below 2 mg/m3 at all times, and to
aim at staying below 1.0 mg/m.3 Many plants in the U.S. routinely operate near or below
1.0 mg/m3 (total MRF mist) and there is anecdotal evidence that, whenever
concentrations exceed 3 mg/m3, complaints and problems multiply rapidly. Lowering the
airborne concentration can be accomplished in many different ways but, in the final
analysis, enclosure and ventilation should play a major part. These are expensive options
and for many smaller operations, are not feasible. Economic and technical feasibility
dictate limits on what can be accomplished and how quickly. There are other approaches
that can be effective and these should be considered. There is some evidence that
bacterial endotoxin may play a significant role in the development of respiratory irritation
and sensitivity, and a plant with low airborne concentrations of MRF could still have a
problem. Such problems can often be addressed by more effectively managing the MRF.
In other words, by controlling pH, microbiological growth, fines and fluid application
pressures, by assuring that all additions to the system are controlled by one person or a
team and good records are being kept, by following on a daily basis the condition of the
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MRF, and by making good use of filters, significant reductions in both airborne
particulate concentrations and employee complaints can be achieved. (See Appendices,
D, F, and N.)
The use of MRFs in metal machining operations, as well as the assessment and control of
employee exposures is an exceedingly complicated one. To date, no single causal factor or
putative agent has been identified. What should be clear to the reader of this guide is that a
“systems” approach to the overall management of your MRFs should be employed. Safe and
effective MRF usage is a series of intertwined variables, and effective management of these
variables as a total system can lead to dramatic improvement for both employee and employer.
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“Metal Working Fluids” is often used as a generic term to
describe four categories of fluids (straight oils, soluble oils,
semi-synthetic and synthetic) that facilitate a wide variety of
operations involving the working or modification of metals.
Metal removal fluids are used in machining and grinding and
honing operations. Metal forming fluids are used in stamping,
forging, drawing, coining, rolling, piercing, cold heading and
wire/bar/rod drawing operations. Metal protecting fluids are
used primarily for fingerprint displacing and indoor/outdoor
storage. Metal treating fluids are used primarily for metal
quenching operations. Drawing and forming fluids are similar or
identical in composition to MRFs but are used in an entirely
Close Capture Enclosure
This is a device mounted near the source, before the breathing
zone of the operator. By design it will have a high entrainment
velocity and lower air volume requirement. This is a very
effective method of enclosure.
Slides prepared with appropriate growth media, dipped into MRF,
and incubated to measure microbial growth in MRFs. Relatively
inexpensive, easy to use, and available commercially.
A mixture of liquids that do not dissolve in each other to form a
true solution, but have droplets of one liquid dispersed
throughout the other. For MRF it is generally an oil in water
A mechanical device that creates a separation or barrier between
the process and the worker's environment. Enclosures may be
designed as close capture, total enclosure or tunnel enclosures.
A hood is a generic term for a device designed to capture
contaminated air and conduct it into an exhaust duct system. The
term may include enclosures, canopy hoods, push-pull hoods, down
draft hoods, side draft hoods or others.
Metal Removal Fluid (MRF)
A fluid applied to a tool and workpiece while cutting or removing
material. This fluid may be water or oil based. Its principal
functions are: to cool the tool/workpiece interface, to provide
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lubrication, and to flush chips or contaminants generated in the
metal cutting or removal process.
Fine liquid droplets suspended in or falling through a moving or
stationary gas atmosphere.
Straight Oil MRF
An oil-based MRF that contains no water and is not mixed with
water in normal working conditions.
Soluble Oil MRF
A water-based (reducible) MRF composed of an emulsion of oil (or
oil-like material) in water. It may or may not include
performance enhancing additives.
A water-based (reducible) MRF composed of both water-soluble
components and emulsifiable components. It may or may not
include performance enhancing additives, and generally contains 5
to 30% (by volume) of oil. In mixed form semi-synthetic MRF may
contain 5% or less of oil.
A water-based (reducible) MRF composed of a true solution of
water-soluble organic and/or inorganic components. It may or may
not include performance enhancing additives.
Fine particles of metal, graphite and carbide that result from
Non-homogeneous oil either introduced into the MRF system from
machine tool oils (e.g. way oils) hydraulic fluids or by
destabilization of emulsified product oil.
A box or housing around the machine or process. The housing is
not intended to be airtight. Openings are limited to the minimum
required to allow for part entry/egress, maintenance or utility
A continuous total enclosure over two or more connected work
stations or machining processes. The design principles are
similar to those applied for total enclosure.
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MRFs have been implicated in a variety of health problems where
exposures are sufficiently high. These problems include
irritation of the pulmonary system, skin and eyes, and equivocal
links to a variety of cancers. Perhaps the most common problem
is the development of skin and lung irritation, with the
seriousness of the problem being dependent on many variables,
e.g. the kind of fluid, the nature and duration of the exposure,
and the type of metal being machined. Another variable involves
individual sensitivity to a particular fluid in a particular
MRFs typically vary widely in chemical makeup as manufactured.
However, after a MRF has been in use for several days, it is
usually significantly different from what it was when first
added. This is due to conditions such as the metals being
machined, machine oil leaks, sources of make-up water, additives
and microbial flora that are unique to a particular system and
workshop. This tremendous variability makes it difficult for
scientists to pinpoint specific “bad actors” in MRF. While some
of the known components of historical MRF compositions have been
shown to cause problems, we can only speculate as to what the
actual composition was, and what shop floor exposures really were
in the past.
Much of the best work on MRF and cancer has relied heavily on
retrospective epidemiology for exposures that took place decades
ago when airborne concentrations of MRF were assumed to be much
higher than today. The composition of MRF has also changed
dramatically over the years since many of the exposures that were
studied took place. Many toxic substances present in MRF during
the 1920's-1940's have been removed from commercially-available
MRF, and are no longer a problem. This does not mean, however,
that there are no problems with MRF used currently, only that the
nature of the problems has changed.
Toxicological and health effects information related to MRF
exposure is voluminous and extremely complex. This Appendix
provides only a very basic overview of some of the worker health
issues most frequently associated with exposure to MRFs. Summary
descriptions are provided for a few of the potentially harmful
components of various types of MRFs. These are followed by brief
discussions of some of the health conditions most commonly linked
to MRF exposures. This Appendix is not intended to be a
comprehensive review of technical or scientific literature, but
only to acquaint the reader with some of the basic information
about MRFs and their relationship to worker health issues.
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POTENTIALLY HARMFUL MRF COMPONENTS
These compounds, many of which have been shown to be
carcinogenic, may be generated during use from the combination of
nitrites and secondary amines present in the MRF, biocides and
rust inhibitors. Prior to 1976, some water-based MRFs included
sodium nitrite as a corrosion inhibitor. Nitrite, even under
alkaline conditions, has the potential to react with secondary
amines to form N-nitrosamines. In October of 1976 NIOSH issued
Current Intelligence Bulletin 15, “Nitrosamines In Cutting
Fluids.” Shortly thereafter, MRF manufacturers began to remove
nitrite from their products, and many employers stopped using MRF
that contained nitrites. By about 1985 the process was
essentially complete. However, it was shown as recently as 1990
that some MRF concentrates were contaminated with N-
Nitrosodiethanolamine (NDELA). It is possible that carry-over of
nitrite containing in-process cleaners into an MRF containing a
secondary alkanolamine may be responsible for the NDELA found.
In May 1993 the U.S. Environmental Protection Agency issued a
Significant New Use Rule for nitrites intended for MRF. (Federal
Register Vol. 58, 27940-27944.)
Nitrosamines are readily formed under acidic conditions by the
reaction of secondary amines, such as diethanolamine, with a
nitrosating agent, such as nitrous acid. The rate of the
reaction decreases dramatically as pH increases; at pH values of
10-11 which are typical of metalworking fluid concentrates, the
formation of nitrosamines is extremely slow. Nevertheless, when
a fluid containing both nitrite and diethanolamine is stored for
extended periods of time, detectable levels (> 100 ppm) of NDELA
can form. Studies have shown that the amount of NDELA present in
an aged fluid is determined by the amount of DEA present in the
fluid. The presence of other proposed precursors or promoters,
such as TEA, formaldehyde-release biocides, C-nitro biocides or
heavy metals, has not been demonstrated to have a measurable
effect on NDELA content.
The formation of a stable nitrosamine requires the presence of a
secondary amine and a nitrosating agent. Tertiary amines cannot
be nitrosated. Primary amines can be nitrosated, but they react
with additional nitrosating agent to form diazonium salts which
decompose immediately. Many routes to nitrosamines formation,
other than the reaction of nitrite and DEA, have been proposed.
Most of these speculations invoke the presence of an exotic
nitrosating agent. Some bacteria which may be present in a used
MRF can reduce nitrate to nitrite. However, these same bacteria
also further reduce nitrites and there is generally no build-up.
This is why it was so hard to keep nitrite at the desired levels
in older nitrite-containing fluids. Notwithstanding all the
proposed theories, only one has been shown to actually operate in
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a working MRF. NDELA levels have been found to increase in
fluids cooled in evaporation towers where the fluid was exposed
to N0x .
Once formed, nitrosamines react rapidly with the reactive
surfaces of the metal chips formed in metal removal operations.
Workplace studies by NIOSH found that NDELA was stripped from a
MRF within a few hours of use. Build-up of NDELA in a used fluid
happens only if the DEA content is high enough to make the rate
of NDELA formation greater than the rate of destruction.
Polycyclic Aromatic Compounds (PAC) and Polycyclic Aromatic
The acronyms PAC and PAH are frequently used as if they are
identical, but they are not. PAHs are composed of multiple
aromatic benzene rings and typically contain only carbon and
hydrogen. PACs, while similar, may also contain molecules of
nitrogen, sulfur and oxygen attached to the ring structures. In
other words, all PAHs are PACs, but not all PACs are PAHs.
Historical formulations of mineral base oils used in MRFs have
been shown to have the potential to cause dermatitis, oil acne,
folliculitis and skin cancer. Some studies have linked exposure
to unrefined mineral oil lubricants to lung and rectal cancer.
The International Agency for Research on Cancer (IARC) has found
sufficient evidence from human epidemiology that mineral oils of
various formulations that have been used in metal machining
operations can be carcinogenic to humans. Credible animal
studies, often using the mouse as a test subject, have confirmed
the carcinogenic potential of many of the early mineral oil
lubricants. Analytical work performed over the years has
identified certain polycyclic aromatic compounds as the causative
agents. Historical formulations of mineral oils used in metal
removal operations were often derived from both shale and
petroleum oils and, prior to about 1950, many of these oils were
essentially raw distillates or only mildly refined. These early
oil-based MRFs contained significant amounts of PACs that
resulted in cancer hazards to those exposed to them. Work
practices in the 1920s and 1930s were significantly different
from those prevailing today and often resulted in heavy dermal,
inhalation and ingestion exposures.
Since the late 1950s, most mineral oils used in the formulation
of MRFs have undergone severe solvent extraction and/or severe
hydro treatment and, where properly used, these treatments
essentially eliminate the carcinogenic potential of the base oil.
Modern severe refining techniques of solvent extraction
selectively remove PACs from base oils, and the hydrogen
treatment chemically disrupts the ring structures of PACs,
producing non-ring compounds. It should be noted, however, that
some lubricants, including bearing and gear lubes, greases,
- 25 -
hydraulic fluids, cleaning fluids and degreasers typically do not
undergo the same severe refining process as base oils used for
formulating MRFs. Where they are allowed to contaminate the main
body of the MRF, they can be a source of PACs. Acid-treated
base oils are generally considered to have higher levels of PACs
than severely solvent refined and hydro-treated oils. The
recycling of used industrial oils is becoming more popular as it
avoids much of the cost of purchasing new oils and almost all
disposal costs. However, research has demonstrated that some
reprocessed oils may have unacceptably high levels of PAHs.
Unless the oil reprocessing involves severe refining techniques,
it is important that all reclaimed oil destined for reprocessing
be tested; any showing high levels of PAH should be segregated,
and not processed for reuse as a manufacturing lubricant.
It is now possible to routinely produce base oils for MRFs that
have been shown, through a variety of bioassays and screening
tests, to be non-carcinogenic. However, oil-based MRFs may be
manufactured from a variety of sources, including reprocessed
oils. Therefore, it is recommended that organizations purchasing
base oils for use in MRFs request information from suppliers on
the severity of treatment of those products prior to their
purchase and use. Analytical methods which measure the
concentrations of polycyclic aromatic compounds in base oils are
the Institute of Petroleum IP 346 test, ASTM Method E-1687-95,
“Determining Carcinogenic Potential of Virgin Base Oils in
Metalworking Fluids,” the Food and Drug Administration
ultraviolet absorbance test and other tests for total polycyclic
aromatic content. The March 11, 1997 issue of Lubes’n’Greases
Magazine discusses a recent review of the scientific literature
concerning the potential for used MRFs to develop and accumulate
levels of PACs that might represent a hazard. Based on available
data, the article concludes that there is little scientific basis
for health concerns from the generation of carcinogenic PACs in
straight oils used in metalworking. (See Appendix N,
Of the chemicals commonly found in MRF, the short-chain, highly
chlorinated paraffins would seem to pose the greatest cancer
hazard. The National Toxicology Program (NTP) Seventh Annual
Report on Carcinogens has listed chlorinated paraffins (C12 60%
Cl) as “reasonably anticipated to be carcinogenic to humans.”
The physical characteristics of this viscous liquid, however,
may limit exposure to workers. For C23 43% Cl, there was no
evidence of carcinogenicity in male rats in high-dose two-year
studies, but there was equivocal evidence of carcinogenicity in
female rats. Male mice, however, showed significantly increased
malignant lymphomas and were rated by the NTP as showing clear
evidence of carcinogenicity.
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Synthetic and semi-synthetic MRFs may contain diethanolamines and
triethanolamines. Exposure to these compounds can take place
during the machining process either through skin contact or
inhalation/ingestion. Extensive testing of ethanolamines over
the last 45 years has well characterized the potential oral,
dermal and/or inhalation toxicities of monoethanolamines,
diethanolamines and triethanolamines. In general, ethanolamines
have limited acute oral toxicity, can cause skin irritation at
high concentrations, and have not been proven to be sensitizers
in laboratory testing. Target organs identified in prolonged
studies include skin, liver and/or kidneys. Ethanolamines have
been shown to be negative in teratogenicity assays and, as a
family, lack genotoxic activity, this could be interpreted to
indicate a general lack of potential to cause cancer in animals
at concentrations below those capable of causing chronic tissue
damage. It is known that diethanolamine can react with nitrite
compounds to form the nitrosamine, N-nitrosodiethanolamine, which
has been shown to be both carcinogenic and mutagenic. Standard
bioassays of TEA have not demonstrated genotoxicity, and
generally have failed to present unequivocal evidence of
carcinogenicity. However, some studies of liver tumor data in
female mice and renal tubular adenomas in male rats have been
interpreted as supplying some evidence of TEA’s potential
carcinogenicity. Skin irritation has been reported in animals
treated dermally, as would be expected given the potential
irritant properties of these very alkaline materials at high
concentrations. Tests for reproductive hazards using high
dosages have not (reproducibly) resulted in birth defects.
Biocides are chemicals used in MRFs to control microbial
contamination which, if not controlled, leads to rapid
biodegradation of the MRF. Signs of deterioration in MRFs
include emulsion destabilization, the production of noxious odors
and “slime,” and failure of the MRF to perform as designed. The
Federal Insecticide, Fungicide and Rodenticide Act (FIFRA)
regulates the use of industrial biocides, and requires that their
manufacture, packaging, distribution and use meet strict
requirements. FIFRA requires extensive labeling of biocides and,
as a result, users often assume that biocides present higher
hazards than many other chemicals commonly used in the metal
removal process. Only EPA-registered biocides should be used as
Selection of the most effective biocide for a particular
operation is a key decision, and should depend on an analysis of
the most important considerations involved. For instance, is
microbial contamination the source of a particular problem and,
if so, is a biocide the right way to control it? Knowledge about
the specific microbiological population and the effect of
specific biocides on each microbial species would be useful, but
is usually not available. What is the cost effectiveness of
other means to control biological growth compared to the use of
biocides? And, finally, what are the risks presented to
- 27 -
potentially exposed employees by various biocide products?
Many biocides have as a key component chemicals known as
formaldehyde-condensates which release formaldehyde during use,
and these products have received close attention since
formaldehyde was identified as a suspect carcinogen.
Formaldehyde and formaldehyde- condensates are in general quite
toxic, but all biocides should be considered potentially toxic to
humans at high concentrations. One thorough, recent study of the
release of formaldehyde by triazine used in MRF found that
employees working with MRF containing triazines in a variety of
metal removal operations were not exposed to formaldehyde at or
above the OSHA Action Level of 0.5 ppm or to concentrations that
would exceed the Short-Term Exposure Level of 2 ppm. The
exception to this general finding was for employees working for
extended periods of time around poorly ventilated sumps. (H.
Cohen, 1994, unpublished.)
Where employees are exposed to formaldehyde gas, its solutions,
and materials that release formaldehyde, OSHA’s Formaldehyde
Standard, Code of Federal Regulations Title 29, Part 1910.1048,
applies. Employers are required to make Medical Surveillance
(1910.1048(l)) programs available for all employees exposed to
formaldehyde at concentrations at or above the Action Level of
0.5 ppm, or the Short-Term Exposure Level of 2 ppm (1910.1048(l).
All mixtures or solutions capable of releasing formaldehyde into
the air under reasonably foreseeable conditions of use, at
concentrations reaching or exceeding 0.1 ppm, trigger the Hazard
Communication (1910.1048(m)) and Training (1910.1048(n))
provisions of OSHA’s Formaldehyde Standard. Requirements under
Hazard Communication include informing employees of specific
health hazards including cancer, irritation and sensitization of
the skin and respiratory system, eye and throat irritation, acute
toxicity, labeling provisions, MSDSs, and a written hazard
communication program. Training requirements require that ALL
employees assigned to workplaces where there is exposure to
formaldehyde must participate in a training program unless the
employer can demonstrate, through the use of objective data, that
employees are not exposed to formaldehyde at or above 0.1 ppm.
(See Appendix L, OSHA Formaldehyde
Many biocides are human sensitizers and, depending on individual
variation and conditions of exposure, may have the potential to
cause problems even if concentrations are not excessive. It
should be noted that toxicological dose responses are typically
not linear. A thorough understanding of the particular
conditions a biocide is intended to correct is important in
determining the most effective product and concentration that
will do the intended job and not have potentially adverse
consequences among exposed workers. This is especially important
as some biocides may destroy bacteria and fungi, but not their
associated endotoxins. Since bacteria are in general more
- 28 -
susceptible to some biocides than fungi and yeasts, it is
important to be sure that both the correct biocide and
appropriate concentrations are used. Too low a concentration of
biocide may result in differential growth of fungi. A common
practice, the mixing of multiple biocides in MRF systems, may
complicate management of systems and should be avoided.
HEALTH EFFECTS ASSOCIATED WITH MRFS
This is the most commonly reported medical condition resulting
from exposure to MRFs. It has been estimated that between 0.3
and 1% of machinists are afflicted by either contact dermatitis
or allergic contact dermatitis. For most machinists, simple
exposure to MRF under normal working conditions does not result
in dermatitis. There are a few well-known conditions that
predispose machinists to the development of dermatitis, including
high salt concentration in the MRF, too high a concentration of
the active ingredients in MRF, continued excessive exposure, the
use of abrasive soaps, use of solvents that remove natural skin
oils, poor personal hygiene, dirty shop rags, filter malfunction,
seasonal conditions, wearing of clothing soaked by MRF (either
fresh or dried), contamination of the fluid by dissolved metals
or excessive concentration of fine metal particles in the MRF,
and off-the-job activities. There can also be contact
sensitization to the chemical components of the MRF. This kind
of allergic dermatitis is often more difficult to treat than
straight chemical or abrasive irritation of the skin, and its
resolution will require close cooperation between worker,
management, and physician.
Generally, problems with dermatitis can be resolved by focusing
on ways to reduce exposures, management of the fluid, education
of workers, use of appropriate protective equipment and/or
barrier creams and close cooperation between employer, fluid
manufacturer and medical personnel. Elevated levels of
dermatitis among machine operators may be an indication that a
system is out of control. Free standing machines may present
greater problems than central systems because of intermittent
patterns of use or casual operators, and because it is often more
difficult to analyze and treat many individual sumps which may
each have their own unique problems. (See Appendix F, Filtration
Upper and Lower Respiratory Tract Irritation
Many studies have demonstrated that workers exposed to airborne
concentrations of MRF in the workplace can show both acute and
chronic respiratory responses. Exposure to airborne MRF mists
may aggravate the effects of existing respiratory infections and
cigarette smoking. The chronic effects include an increased
incidence of sinus problems, persistent cough, and possibly
asthma, increased upper and lower airway secretions and airway
constriction that may result in shortness of breath. These
- 29 -
responses have been linked with essentially all types of fluid.
There is also solid evidence of decreased Forced Expiratory
Volume in one minute (FEV1) across a shift, among machinists
exposed to soluble MRF, which is usually reversible. There are,
however, significant differences in the degree of reaction of
those exposed to different kinds of MRFs. Workers exposed to
emulsified, semi-synthetic or synthetic MRFs exhibited a greater
degree of symptomatic response than those individuals exposed to
straight oil MRFs.
An important factor that should be considered in evaluating the
development of lower respiratory tract irritation in workers
exposed to MRFs is the impact of microbial contamination, and the
role of bacterial endotoxin in sensitivity reactions. The
endotoxin producing microbes in a water-based system are mainly
gram-negative bacteria, and endotoxin levels represent both
living and dead bacteria. Many researchers have come to believe
that the presence of bacterial endotoxin in MRFs is an important
predictor of lower respiratory tract irritation among exposed
workers. Endotoxins have the potential to stimulate alveolar
macrophage release of cytokine mediators that are involved in
broncho-constriction and the initiation of airway inflammatory
Airborne endotoxin has been shown to be present in some
automotive machining plants at concentrations that exceeded
threshold response levels in humans. While lowering human
exposure to concentrations of MRFs is always the right place to
start when addressing a respiratory irritation and sensitization
problem, this approach may not always, by itself, eliminate the
problem. Once a population has become sensitized to a particular
endotoxin, exposure to even low levels may elicit a response in
the human respiratory tract. Hypersensitivity pneumonitis has in
some cases been associated with exposure to airborne molds and
gram-positive bacteria. The control of microbial contamination
in MRFs should be seriously considered when addressing
respiratory irritation problems in workers exposed to MRFs.
Hypersensitivity Pneumonitis (HP)
The July 19, 1996 issue of Morbidity And Mortality Weekly Report
(MMWR) carried a report of “Biopsy-confirmed Hypersensitivity
Pneumonitis in Automobile Production Workers Exposed to Metal
Removal Fluids-Michigan, 1994-1995" (pp 606-610). Other
outbreaks have been reported in diverse industries. Also known
as extrinsic allergic alveolitis, HP is a diffuse interstitial
granulomatous lung disease thought to involve an immunologic
reaction of the lung to repeated inhalation of foreign antigens.
In June, 1994 the UAW requested a NIOSH Health Hazard Evaluation
(HHE) to evaluate whether occupational exposures might be
responsible for the problem. NIOSH performed an evaluation, and
its report is the basis for the Center for Disease Control (CDC)
report in the MMWR. HP is thought to reflect a physiological
reaction to exposure to components of bacterial cell wall or
endotoxin in MRFs.
- 30 -
There is experimental evidence in animals that exposure to
endotoxin and mold wall 1.3 B-glucan may act synergistically in
the development of a condition resembling hypersensitivity
pneumonitis with the formation of granulomas. Diagnosis of HP is
difficult because its symptoms mimic those of other common
illnesses such as bronchitis or pneumonia, and differentiation
can be difficult. In this instance, no specific antigen has been
associated with these cases. HP-like illnesses associated with
workers exposed to MRFs have been reported in the United Kingdom
and the U.S. auto industry. The diagnosis of HP should be
considered where pneumonia-like symptoms keep recurring without a
logical explanation. Recurrent episodes of acute HP can lead to
progressive, irreversible lung impairment. The main treatment
for HP is to avoid exposure to the source of antigens. (An
antigen is a substance, usually of biological origin, foreign to
the human body, which stimulates the body’s defensive mechanisms
to produce antibodies designed to neutralize the foreign
material. Pollen is an common example of an antigen.)
A workshop on “Pneumonitis In The Machining Environment” was held
January 28-29, 1997, sponsored by the UAW-Chrysler National Joint
Committee on Health and Safety, and facilitated by NIOSH. This
workshop gathered together some of the most knowledgeable experts
in the country on HP who discussed the present understanding of
the cause, effect, diagnosis and treatment of HP. The
proceedings of this workshop will be published by NIOSH and
should be available from their publications division. (See
Appendix N, References.)
Over the years a number of studies have found an association
between working with MRF and a variety of cancers, including
stomach, rectal, pancreatic, laryngeal and skin. The biggest and
by far the best of these studies were done at GM and Ford in
cooperation with the UAW. These studies, depending on
interpretation, found exposure-response associations for cancer
of the larynx, esophagus, pancreas and rectum of exposed workers.
Epidemiology based on smaller and earlier studies found an
increase in stomach, rectal, pancreatic and laryngeal cancers
associated with exposure to MRF. However, the earlier smaller
studies were not supported by the results of the large GM-UAW and
Ford studies which had a more rigorous design and were
analytically more thorough. There are, however, multiple
confounding factors that work to modify the conclusion that there
were increases in stomach cancer. In a follow-up case control
study of the stomach cancers at Ford more detailed information
was obtained on work histories, ethnicity and a surrogate for
diet, and the increase in stomach cancer was not supported.
Increased rates of esophageal and colon cancers have been
reported by the GM-UAW study in relation to grinding with
synthetic or soluble fluids, but data relating to exposure
- 31 -
concentrations are not available. These studies presented data
showing excess risk with a 10-20 year lag period which means that
deaths which took place from 1940 to 1984 would be the result of
exposures that took place in the previous 10-20 years. For the
relationship between this data and exposure to synthetic or
soluble MRF in grinding operations to be accepted, it should be
demonstrated that the plants in this study had significant use
of soluble or synthetic MRF between 1920 and 1964 with the risk
due to exposure during those periods.
Straight oils and soluble fluids were the most common MRF used in
the plants studied during the period 1920-1940. Synthetics
started to become more common in the 1970s. When considering the
significance of the GM-UAW study for laryngeal, prostate and
rectal cancers, one should also take into account the change in
base oil refining practices which began removing PACs around
1950. Over 60% of the deaths in the GM-UAW study came out of the
oldest plant, which started operations in the 1920s and primarily
used straight oils and soluble fluids. Two of the three plants
in this study started operations in the 1920s. The average time
from first exposure for individuals from this oldest plant was 29
years, which means that, on average, first exposure occurred
prior to 1954. Among those who died, the average year of first
exposure would be even earlier. Another confounding factor would
be the gradual removal of nitrites from semi-synthetic and
synthetic MRF starting in the middle 1970s.
Historical exposures to MRF containing non-severely refined base
oils can be related to the development of laryngeal, prostate and
rectal cancers. Both the Ford and GM/UAW studies found an
increased incidence of pancreatic cancers in black but not white
employees, and these seem related to historical grinding
operations. The GM-UAW study also found some small to moderate
increases of several kinds of cancers not observed in the Ford
study. These findings relate to historical patterns of MRF use
and exposure patterns which, for the most part, are no longer
valid. What they tell us about the risk of cancer from exposure
to very different modern synthetic fluids at much lower
concentrations can only be speculated upon until appropriate
follow-up studies have been done.
Much of the material included in this Appendix can be found in
greater detail in appropriate sections of The Industrial
Metalworking Environment: Assessment and Control; Proceedings
from the AAMA Metalworking Fluids Symposium, November 13-16,
1995, and the December 1996 issue of the American Industrial
Hygiene Association Journal, Vol. 57, No. 12. ( For information
on obtaining a copy of these documents, see Appendix N,
- 32 -
This appendix contains examples of three practical checklists
that can be used by machine operators to assist in the
maintenance and upkeep of their equipment and the surrounding
work areas. These examples were developed in three different
shops, and so they differ in their details, but overall the
thrust is very much the same: keep the machines clean, and make
sure that everything is working the way it is supposed to. These
forms could be used as the basis for development of checklists
customized for a particular operation or workplace.
Metal Removal Fluid
- 33 -
Worksheet Instructions: Place a (_ ) in the appropriate boxes in the
left hand column (yes/no) for each safety item. If a check mark is
placed in the “no” column, fill in the appropriate safety code to the
right and add any comments/corrective actions. Direct any questions
regarding the worksheet to your supervisor or the safety department.
Yes No tly being used as per the Material
Safety Data Sheets (MSDS) and G) Is floor dry
instructions for safe use? required around the
base of the
B) Are metal removal fluid containers machine(s)?
labeled properly and are employees
using product as per label? C-2
C) Are the MRF pH at the required levels? Actions/Comments:
D) Are metal removal fluids disposed of
E) Are absorbent materials saturated with
machine cutting fluids
F) Is your hard piping, which contains
metal removal fluid labeled ?
G) Have the employees been trained on the
type of metal removal fluid they are
H) Is personal protective equipment (PPE)
required (gloves, respirator, etc.)?
If so, are employees using them?
Yes No I) Are metal removal fluid containers
being stored according to
A) Are the metal removal fluids creating
a slip hazard? (puddles laying on
B) Are the machines washed down on a
regular basis to keep stagnate metal
fluids from building up?
C) When the machines are cleaned are the
trenches, drip pans, metal fluid pits
D) Is trash (cigarette butts, paper,
Hazard cups, etc.) being thrown in the metal
Communica removal fluid catch basins?
A) Are E) Are metal removal fluid drip
the pans/catch basins in good condition
metal and pumped out regularly to avoid
fluids F) Are absorbent socks required around
curren the machine(s)?
wiped up promptly and if necessary B) Is the volume of
called in for repairs? MRF usage being
regulated to reduce
I) Are there any saturated absorbent employee aerosol
materials on the plant floor? If so, exposure?
C) Is new equipment
J) Have you observed chip accumulation being purchased
prohibiting proper circulation of MRF? with the MRF
K) Do you see MRF fluids dripping off containment build
building structure? in.
L) Do the plant/dept have adequate floor D) Is the proper MRF
scrubbing equipment to keep the floor being used?
Yes No free of oil airborne?
C - 3
A) Are the ventilation hoods in good
B) Is the exhaust ventilation effectively
removing air containments away from
C) If fans are being used is the air from
the fan being directed towards the
operator without hindering exhaust
D) Are fan cords creating a tripping
Yes No hazard?
E) Is the supply air ventilation working
F) Are the meter readings on collectors
at acceptable levels?
A) Are guards in place and in good
Yes No B) Are there OK mist containment
mechanisms at each machine station?
C) Are there any visible emissions of
D) Are the flap extensions working
correctly? (Skirting: panel-to-floor)
Yes No Preventive Maintenance
A) Are MRF oil skimmers being maintained?
B) Are mist collectors functioning as per
manufacturer’s specifications and
preventive maintenance performed?
C) Are mist collectors filter being
changed per manufacturers
H) Are General
spills A) Is MRF pipe pressure being regulated
and to meet compliance?
Wet Metal Removal Operations
Enclosure & Ventilation
Purpose: Observe Enclosure and Ventilation Systems to Assure
and Capture of Fluid Mist Associated with Wet Metal Removal
Date: Bay (Col. Nos.):
Production Volume Today:
Enclosure/Panels (Elements - Missing, Damaged,
Effective Containment of Fluid Mist?
Any Visible Emissions of Fluid Mist?
Local Exhaust Ventilation
Hoods: Hood Placement?
Smoketube Capture Effective?
Ducetwork: Smooth Transitions?
Collector: Magnehelic Reading?
Diffusers: Placement / Position / Height
Confirm Air Discharge?
Smoketube Ribbon at Register
„Stagnant‟ Fluid Accumulations on Floor?
Saturated Absorbent Materials on Floor? How long?
Comments / Observations
MRF System Management Checklist
(milling, drilling, boring reaming, broaching, honing, grinding)
(page 1 of 2)
Instructions: Place a check in the appropriate boxes below. If “No” is checked, make comments and recommend
corrective actions if possible. If an item does not apply to the plant/department/operation, check the “NA” box.
Yes No NA Housekeeping Corrective Actions/Comments
A) Do metal removal fluids and/or other machine
fluids (e.g. hydraulic fluids) create a slip hazard?
B) Are machines washed down regularly to
prevent stagnation of metal removal fluids?
C) Is trash (e.g. cigarette butts, paper, cups, etc.)
thrown on floor or into drip pans, trenches, etc?
D) Are drip pans and other fluid reservoirs in
good condition and cleaned out regularly to avoid
E) Any absorbent socks around the machines? If
yes, are they required because of continuous leaks
or splashing coolant?
F) Any “Floor Dry” around base of machines? If
yes, is it required because of continuous leaks or
G) Any accumulations of chips on floor or inside
machines? If yes, do chips interfere with proper
circulation of coolant?
H) Do you see MRF dripping off building
structure? (e.g. trusses, columns, pipes)
Yes No NA Ventilation Corrective Actions/Comments
A) Are exhaust ventilation hoods in good
B) Does the exhaust ventilation adequately
capture coolant mist?
C) Do main cooling fans, if present, interfere with
the exhaust ventilation?
D) Can you detect airflow from the supply air
E) Are the supply air diffusers/boxes and supply
air ductwork in good condition?
F) Do mist collector pressure gauge (e.g.
Magnehelic) readings fall within the desired
G) Any visible emissions of aerosol from mist
collector(s)? (e.g. leakage out of ductwork,
enclosure; from outlet)
H) Is a record of mist collector maintenance (e.g.
filter changes) attached to the collector(s)?
Yes No NA Machine Guarding Corrective Actions/Comments
A) Are guards in place and in good condition?
B) Is additional guarding needed?
C) Is coolant mist contained effectively at each
D) Do flap extension guards (i.e. skirting, bottom
of machine to floor) contain coolant mist?
ENCLOSURE AND VENTILATION AS CONTROLS
Retrofit vs OEM Enclosures
Enclosure and ventilation are important controls for MRF mist. Where feasible, it is
recommended that machine enclosures be phased in with new machinery or machinery rebuilds
rather than depending on retrofitting enclosures to existing machines. There is considerable
difference in the efficacy and cost of enclosure and exhaust for control of MRF mist for
machinery brought into a plant with an enclosure (Original Equipment Manufacturer [OEM])
when compared to an existing machine with a "retrofit" enclosure. Upon inspection, OEM
enclosures are visibly cleaner than retrofit ones with less evidence of MRF on the floors of OEM
areas and less visible mist in the air. Ventilated OEM enclosures have shown the capability to
control to lower mist levels, in many cases to 0.5 mg/m3 or less. Even without ventilation, some
OEM enclosures can approach 1.0 mg/m3 of mist. Retrofit enclosures are much less efficient
and, even with ventilation, have difficulty controlling consistently to 1.0 mg/m3. Some studies
show little or no benefit for retrofit enclosures compared to non-enclosed machines.
In addition, retrofitting takes considerable time and effort, and involves disrupting production,
trying to fit to predetermined "footprints," custom fitting to varied shapes, tying into existing
ventilation systems and working in crowded surroundings. The additional effort shows up in
costs as well, with retrofits costing approximately twice as much as OEM enclosures.
General Considerations for the Design of Machine Tool Enclosures
(a) Reasonable access should be planned for the operator, the work pieces and tool changes.
Access ports should be either hinged or sliding. Removable panels are generally not
recommended because they are too often not replaced after being removed.
(b) Where access ports are installed, provisions should be made for electrically operated
interlocks to prevent operation while the ports are open.
(c) An efficient design will limit the free access of outside air into the enclosure to both
minimize exhaust volume, and to maintain the designed airflow inside the enclosure. Special
attention should be paid to areas such as MRF entry and egress, chip removal systems, and
other areas where air may enter or leave the enclosure.
(d) Some make-up (replacement) air is necessary for the system to function properly.
However, care should be taken in the design to maximize the capture of contaminants by
filters etc., at the working face of the tool prior to their being exhausted into the air collection
system. If possible, avoid placing replacement air ducts where the air flow will be
interrupted by contact with non-contaminant generating parts of the machine prior to
reaching the workface.
- 32 -
(e) Mist collection exhaust ducts should be located where they are unlikely to capture either
liquid MRF or chips. Airflow velocity at the collection duct should not be so high as to
facilitate capture of chips or liquid MRF.
(f) Design of the enclosure should include provision of a slope or pitch to the top of the
device to avoid dripping.
(g) When enclosures are mounted on the machine, care should be taken not to interfere with
the operation of the equipment through increased vibration or capture of heat.
Types of General Enclosure Design
(a) Close Capture: Involves the mounting of a contaminant capture enclosure very close to
the point of mist generation and away from the breathing zone of the operator. This device is
open to the ambient air at some point, has a high air (capture) velocity, and relatively lower
volume requirements than some systems. This is the preferred method for contaminant
capture when total enclosure is not feasible, provided it controls mist emissions adequately.
It should be noted that, when close capture is used with MRF, there may be a significant loss
of the MRF into the exhaust system, causing excessive make-up fluid to be added and
consequent emulsion destablization.
b) Total Enclosure: Involves the complete enclosure of a particular machine or operation
and proper exhaust of the enclosure. The enclosure or housing is designed to allow make-up
air into the housing, and to limit openings to the minimum required. This is the preferred
method of enclosure.
(c) Tunnel Enclosure: Involves a continuous enclosure encompassing several
interconnected machining operations. The same design considerations applied to close
capture and total enclosure should also be used here.
(d) Push-Pull Hood: Has the capture (exhaust) hood at the side of the machine operator,
with make-up air being directed in front of the worker, past the workpiece, toward the
exhaust hood. Not recommended unless other capture designs are not effective.
(e) Side Draft Hood: The capture (exhaust) hood is located to one side, or behind the
worker, but without a specifically directed stream of make-up air as in (d). Not
(f) Canopy Hood: The canopy hood is located above the machine operator's breathing zone.
Large volumes of exhaust air are required for the operation of this design. Not
(g) Down Draft Hood: This device is located in the floor or at the base of the machine and
is intended to capture and exhaust contaminants pulled down vertically from the machine
and away from the operator. Requires large volumes of exhaust air and is sensitive to the
- 33 -
thermal effects of heat generated by metal removal operations. Not recommended.
Design Considerations for Enclosures
(a) All enclosures intended to capture MRF mist should be designed and constructed with
materials known to effectively resist degradation by the MRF it will be used with.
(b) Enclosure design should avoid sharp corners or protrusions and allow easy operator
access to working parts of the machine.
(c) Enclosure design should take into account access by cranes so that major parts of the
machine tool may be removed for repair or replacement without destruction of the enclosure.
(d) Enclosure design should allow for effective removal of chips and swarf.
(e) Enclosure openings should be limited to those necessary for operator access, exhaust
make-up air and utility entries.
(f) Exhaust ducting should make use of tapered entries to minimize excessive duct takeoff
velocity. Suggested duct entry velocity should be in the vicinity of 2000 FPM or less for
heavy materials such as cast iron, with lower velocities for lighter materials such as
aluminum or plastics.
(g) Safety of the operator during normal operation of the machine should be a primary
consideration in design of all enclosures. Safety reviews should be conducted during design
and installation periods. Compliance with confined space regulations and safety lock-out
capability should be given serious consideration where operators or repair personnel may be
required to enter the enclosure.
(h) Windows may be a design requirement and, where they may be impacted by splash and
spray, consideration should be given to the use of automatic wipers to clean the windows
during operation of the machine.
(i) Seals, gaskets and sound absorption materials used in construction of enclosures for
metal removal tools should be known to resist degradation by the specific kinds of MRF
used. Seals should be designed to hold position and not shift or roll as entry ports are opened
(j) Depending on the type of MRF in use, fire alarms and suppression systems may need to
be part of the design considerations.
(k) Enclosures designed to capture MRF mist may also provide considerable noise
abatement depending on the design and the materials used in the construction.
(l) For some metal removal operations, permanent lights may need to be fitted inside the
- 34 -
enclosure. Where lighting is a factor, design should be consistent with NEC and NFPA as
well as applicable local or plant-specific codes. Under some conditions, portable lighting
systems may be the optimum solution.
Design Considerations for Enclosure Exhaust Ductwork
(a) There are two main types of systems: the plenum system and tapered main system. A
plenum system utilizes a main duct of constant cross-sectional area. A tapered main
system utilizes ducts that gradually change in cross-sectional areas to maintain a
relatively consistent air velocity.
(i) Advantages of the plenum system:
Ease of machine tool relocation.
Ease of ductwork expansion, but design capacity of enclosure may
May provide some coalescing and condensation prior to collection.
Ease of cleaning.
(ii) Disadvantages of the plenum system:
May require duct drains.
(iii) Advantages of tapered main system:
May have lower initial cost.
May require lower total power to operate.
(iv) Disadvantages of tapered main system:
Not flexible for machine relocation or duct extensions.
(b) Exhaust ductwork should be constructed from materials known to resist degradation
by the MRF intended for use in that system.
(c) Exhaust ductwork should be designed with all welded seams or with mechanical
seams. The use of ductwork intended for HVAC is NOT recommended.
(d) Ductwork should be designed with consideration given to maintaining proper
drainage angles to collection points.
(e) Exhaust ductwork for metal removal machines should be designed with
adequate access for maintenance or it will rarely be cleaned.
(f) Air velocity in exhaust ductwork should be adequate for the transport of MRF
mist, but not so high that chips and MRF are also entrained.
- 35 -
(g) During design and construction of exhaust ductwork, consideration should be
given to the need to monitor system flow rates, pressures and temperatures. This
could include ports for pitot tubes and/or other instruments that can be readily
opened and tightly closed after use.
(h) Flexible ductwork may at times be necessary on some enclosures, but it should be
limited as to length and should never be used in a horizontal position.
(i) When designing traps for ductwork drains, the static pressure of the system at
the location of the drain must be considered. All drains and traps should be
accessible for maintenance. Standard plumbing traps should not be used.
(j) MRF-compatible gaskets or sealants should be used between connecting sections of
Types of Filters
(a) Primary and secondary filters:
Open cell foam designed to coalesce MRF particles.
Metal mesh filters of various sizes designed to remove large
droplets through coalescence and impaction.
Centrifugal filters which are designed to remove airborne
droplets through centrifugal forces and drain them out of the
Helical tube systems, with many helical elements housed in a
tube and mounted in a common frame.
Electrostatic precipitators which impart an electrostatic charge
to droplets and attract them to a collection element, where they
coalesce and drain out of the system.
Disposable filters designed to be replaced on a regular basis.
Pyramidal polypropylene filters designed to remove large
(b) Final filters
Media bags with an air-to-media ratio of 10 CFM/square foot at a
- 36 -
Rigid cell: 250-500 FPM face velocity.
Cartridge filters: with an air-to-media ratio of 10 CFM per square foot
Mist Collection Systems
There are many commercial mist collection systems available but the best design for a
given application is dependent on many factors unique to a specific application. In
general, commercial filters have multiple stages with a relatively inefficient first stage
followed by a higher efficiency second stage that may make use of pocket or cartridge
filters, and usually a 95% efficient DOP or HEPA final stage. In some cases, centrifugal
cells and/or electrostatic precipitators may be used as early stages. Most filters are
effective when new, but may rapidly lose effectiveness as they become loaded with
liquid. Filter efficiency increases with solids loading and decreases with liquid loading.
Filters with high liquid loading may experience substantial re-entrainment of MRF
droplets or vapor. As filter loading increases, the pressure drop increases and the power
required to move air through the system increases, as does operating cost.
First Stage Filters
Experimental work has demonstrated that, for first stage filters, metal mesh filters were as
efficient as the other designs but experienced lower pressure drop. Efficiencies for metal
mesh filters can be significantly increased with only modest increases in pressure drop.
Second Stage Filters
Electrostatic precipitators have generally been found to be as efficient as pocket filters,
and experience very low pressure drops, have only moderate maintenance, and provide
long service life. Other filters such as pocket filters lose their efficiency more rapidly, but
in some applications can last up to a year. For mineral oil, up to 30 % of the mist
entering the system can be expected to evaporate and pass through the filter as vapor. For
some mineral oils, collectors with multiple stages had the lowest overall efficiency (still
quite acceptable), but the electrostatic precipitator provided the highest overall efficiency,
perhaps because the oil droplets were removed from the air stream and drained away
before they could evaporate.
Third Stage Filters
All 95% DOP filters have high efficiency for droplets of all sizes, but the lifetime
efficiency of these final stage filters is dependent on the efficiency of the first and second
A useful discussion of the costs of controlling MRF mists can be found in the
Proceedings of the November 13-16, 1995 AAMA symposium, The Industrial
Metalworking Environment Assessment & Control (page 321). Ford Motor Company has
estimated that it would cost over $ 8.5 million per million square feet of plant to control
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exposures down to 0.5 mg/m3, plus another half million dollars a year in operating costs.
Several tables are presented that compare costs for new and existing machines.
POLYMER ADDITIVES FOR METAL REMOVAL FLUIDS
The generation of oil mist levels in association with high-speed machine tool operations
where straight oils are used as a major component of the MRF can be a serious health and
safety problem. Straight oils atomize readily and produce aerosols that remain in the
ambient air for long periods of time. Straight oils are often necessary to achieve a high-
quality surface finish, and thus are an important component of modern quality machining
operations. One promising approach to reducing the amount of oil mist generated by
machining operations involves the use of high molecular weight polymers which are
dissolved in the MRF in very low concentrations.
It should be noted that this technique has not worked equally well in all systems.
Experimental work performed on dilute solutions of polyisobutylene in mineral oil
demonstrated that, when atomized, they produced droplets that were on average much
larger than oil without the polymer. With a larger average size of droplet there are fewer
drops generated and their settling rate is greatly increased. In one study, where 20 parts
per million of polyisobutylene were added to oil-based MRFs, oil mist concentrations
were reduced by 80-90% with no adverse effects on the quality of the machining. This
mist suppression can be achieved at a cost of $10 to $100 per week for a 10,000 gallon
system. Work is progressing on a similar system for water-based MRF. Current work
indicates that polyethylene oxide may be as effective with a water-based MRF as
polyisobutylene was with oil-based.
A useful discussion of this topic can be found in “Polymer Additives as Mist
Suppressants in Metalworking Fluids: Laboratory and Plant Studies,” by Esin Gulari,
Charles W. Manke, Joseph Smolinski, Richard S. Marano, and Louis Toth in The
Industrial Metalworking Environment: Assessment and Control, Symposium
Proceedings, November 13-16, 1995, pp. 294-300.
Lubes’n’Greases Magazine published an interesting article on this topic in its May 1996
issue entitled “Chrysan Blossoms” (p. 22) in which author Lisa Tocci discusses the
technology developed by Chrysan Industries (Plymouth, MI) to automatically blend anti-
mist polymers into MRF in precise amounts to keep the concentration of polymer within
limits required for effective mist reduction.
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- 39 -
1. Design Principle........................................................................................... 39
2. Types of Materials/Chip Characteristics ................................................... 40
2.2 Cast Iron
2.4 Grinding Operations
3. Types of MRF Clarifiers .............................................................................. 41
3.1 Methods of Separation
3.2 Methods of Filtration
4. MRF Monitoring and Management............................................................. 50
4.1 Test Procedure
4.2 MRF Clarity Reporting
5. Typical Central System Sizing...................................................................51
5.1 Determining System Size
5.2 Typical Aluminum Machining System
5.3 Typical Cast Iron Machining System
5.4 Typical Steel Machining System
6. Disposable Media Selection and Management .......................................... 57
6.1 Media Selection
6.2 Media Management
7. Self-Contained MRF Systems ...................................................................... 59
8. Chip Handling.............................................................................................60
9. MRF System Selection Matrix ..................................................................... 63
9.1 Aluminum Systems - Water-Based MRF
9.2 Cast Iron Systems - Water-Based MRF
9.3 Steel Systems - Water-Based MRF
9.4 Steel Systems - Straight Mineral Oil MRF
10. Definitions .................................................................................................... 67
1.0 DESIGN PRINCIPLES
1. Straight oil MRFs are generally used only when the process has critical
surface finishes and/or size tolerances that cannot be met with soluble oil and
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2. Straight oil MRF systems require larger filters and may require fire protection,
making them more costly than soluble oil systems. Straight oil MRF is
usually more costly per gallon than soluble oil and water mixtures.
3. Synthetic MRFs form true solutions with water that are difficult to break down
for disposal. Waste treatment plants often are not equipped to handle
synthetic and water solutions.
4. Coordinate with facilities engineering and maintenance to standardize on
pump and motor selection. Standard pumps reduce parts inventory and
5. For energy conservation variable speed pump control should be considered for
all new central systems over 2000 GPM.
6. Central systems can be equipped with a liquid level indicator - float, bubbler
or electronic. Automatic high/low alarms with automatic water make-up are
7. When designing a new MRF system, help reduce filter media inventory by
selecting a media (type, weight, width and length [roll diameter]) that is in
stock in your plant. Select the largest practical roll diameter to save labor in
8. New system design should include a reserve capacity of a minimum of 25%
over machining and flush requirements.
9. Plant layout should provide space for maintenance (drum and pump removal
etc.), media replacement and chip handling.
10.The clarity specification determines media weight, decision to use pre-coat, and the
flux rate of the filter required (GPM/sq/ft. of filter area). Avoid over-
specifying which can add unnecessary cost to the system.
11. The process tooling and MRF engineers should work together to prevent
unusual chip configurations (chip bundles) that can block machine discharge
12. The process engineer should supply the MRF engineer with complete
MRF, foundation and utility requirements, as well as machine and layout drawing
- 41 -
13. System pumps should be selected to operate in the most efficient range on the
manufacturer's pump curve.
14. Filters should not be manually indexed at daily start-up. Filtration is
with an established chip cake. The system should be designed to monitor and maintai
15. When high-pressure MRF is required for special operations on a machining
line, the machine tool supplier should furnish all necessary pumps, valves,
2.0 TYPES OF MATERIALS
Cast aluminum, cast or nodular iron and steel are the primary metals used in
manufacturing. Each material has characteristics which affect the decision as to
the type of MRF, filtration, trench flushing and chip handling to be used for a
specific manufacturing process.
Most aluminum used is cast aluminum alloys ranging from SAE 308 to SAE 390.
The type of chip generated depends on the type of operation (turning, boring,
milling, etc.). Most aluminum chips do not present major handling problems,
although ductile aluminum may form bundles in turning operations. Water-
soluble MRF is normally used when machining aluminum. The most notable
exception is where a light mineral oil is used to aid in holding micro-finish and
critical tolerances. Due to the light weight of aluminum (approx. 1/3 of steel), the
use of settling tanks is ineffective, as the aluminum chips tend to float or stay in
suspension. To remove heavy aluminum chip loads prior to filtration, a flow-
through wedge-wire tank with a drag conveyor is required.
2.2 CAST IRON/NODULAR IRON
Water-soluble MRF is used for most cast iron machining. Cast iron breaks up
into small, heavy granular chips that settle out readily. An overflowing settling
tank with a drag conveyor is used to remove heavy chip loads prior to filtration.
Most steel machining is done with a water-soluble MRF. Some operations
(especially gear machining) are done with a mineral oil to provide lubricity for
heavy stock removal. Steel, when machined, produces a wide range of chips,
depending on the type of machining being done and material composition.
Turning and boring usually produce a long stringy chip which is the most difficult
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to handle. Often stringy chips will entangle and form large bundles which are
difficult to move through the flumes. The use of a chip breaker at the tool may
help prevent the formation of large bundles. An overflowing hinge pan or screw
conveyor can be used to remove the large bundles and strings prior to the main
filter. If long stringy chips are not expected, an overflowing settling tank with
drag conveyor can be used prior to the filter.
2.4 GRINDING OPERATIONS
Grinding operations performed on all three materials (aluminum, cast iron and
steel) present different problems than machining operations which generate large
chips. Rough grinding can produce a chip large enough to build a filter cake on
the media through which finer filtration can be obtained. Finish grinding and
honing usually produce chips that are too fine to form a good filter cake. Instead,
they blind off the pores in the media. Without a filter cake the pore size of the
media determines the clarity of the MRF.
Grinding also produces "swarf" which is an accumulation of fine chips and fine
abrasive particles and bonding material from the grinding wheel. Swarf consists
of very fine particles which tend to float and collect on the surface. Swarf will be
carried out by the media or can be manually skimmed.
3.0 TYPES OF MRF CLARIFIERS
The primary methods of MRF clarification are separation and filtration.
Separation is the process of removing particles through settling out, magnetic
attraction, centrifugal force, etc., rather than a mechanical barrier. Filtration is the
most widely used method and offers the most positive results. Dirty MRF is
passed through a septum with a known porosity range which traps and removes
3.1 METHODS OF SEPARATION
3.1.1 Settling - A settling tank is a very effective method of allowing the
larger, heavier chips to settle out through gravity. Systems are usually
sized for 3-5 minutes retention time. The chips accumulated in the
settling tank are carried up a ramp by a drag conveyor for either automatic
or manual chip handling. A settling tank is usually used prior to the
primary filter to reduce the chip load and media usage.
1. No media to be replaced or disposed of.
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1. Not true filtration since there is no septum to trap and remove particles.
Clarity is dependent on retention time and the weight of the chips.
2. Not effective on aluminum chips or grinding swarf which tend to float or
stay in suspension.
3.1.2 Magnetic Separation
A number of types of magnetic separators are available. The larger units
usually have magnetic plates or bars which collect the ferrous particles as
the MRF flows over. The fines are then scraped off and removed by a
drag or screw conveyor.
1. No media to replace or dispose of.
1. Cannot be used on aluminum or other non-ferrous materials.
2. Will not remove non-magnetic materials or grinding swarf.
3. Requires low flow rate which increases floor area required.
3.1.3 Cyclonic Separation
Dirty MRF is pumped into a cone-shaped, vertically-mounted vessel. The
liquid is directed into the cyclone so it spins at high velocity around the
cone wall. The solids (contaminant) are thrown outward by centrifugal
force and downward by back pressure. The contaminant is discharged
through an underflow orifice back into the dirty tank while the clean MRF
follows a vortex column in the center and is discharged through an
overflow orifice into the clean tank.
1. No moving parts in the unit.
2. No media to be replaced.
1. Flow rate is limited, requiring many cyclones which require extensive piping
2. High maintenance required to keep underflow orifices unplugged.
3. Will not produce as consistent quality MRF as most filtration methods.
4. This system requires (2) sets of pumps; one pumps dirty MRF through the
cyclones to the clean tank, the second pumps clean MRF from the clean tank
to the system.
3.1.4 Dissolved Air Separation
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Plant compressed air is injected into the MRF forming bubbles. The bubbles provide a
large surface area in which the surface tension of the working fluid attracts the
contaminants. The contaminants and bubbles form a foam on the MRF
surface. A wiper blade then skims the foam from the surface into a disposal
1. Removes tramp oil without stripping MRF from water.
2. No media or pre-coat to dispose of.
3. Works on fine particulates.
1. Large footprint to capacity ratio (6.5' x 6.5' of floor space for 25 GPM).
2. Increases usage of plant compressed air.
3.2 METHODS OF FILTRATION
3.2.1 Automatic Vacuum Filtration
One of the most common types of filtration. A vacuum is created on one side of a
septum, usually by means of pump suction. As the dirty MRF is drawn
through the septum the contaminant is trapped and forms a filter cake. The
filter media is used to trap contaminants and form a filter cake, and the actual
fine filtration is obtained by drawing the MRF through the filter cake. As the
filter cake increases, the vacuum required to draw the MRF through rises and
the pump output decreases. At a pre-selected point, usually 10" hg.
(approximately 5 psi), an index cycle is initiated to purge the accumulated
contaminant. The filtration media (septum) can be disposable media,
permanent belt, wedge wire drums, micro-screen drums or micro-screen discs
depending on the application.
1.Only one set of pumps is required for this system.
2. Since the pumps are located on the clean side of the filtration media, they pump
clean MRF and will not be subjected to wear caused by chips and contaminants.
1.Limited to approximately 10" hg.vacuum differential, will index more frequently than a
2.Some chip migration can occur when filter indexes.
A. Disposable Media - A roll of disposable fabric is carried over perforated plate
to form the septum. When an index cycle is started, a drag conveyor pulls the
dirty media and chips up a ramp and discharges them into a chip hopper or
onto a rewinder for disposal. The media is indexed a preset distance (usually
12"-15"), exposing clean media. The pumps supply MRF from the clean tank
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to the system while this index cycle is in progress.
1.Disposable media is available in a wide range of weights (oz./sq. yd.) to satisfy most
2. Media selection can be quickly changed to optimize clarity without affecting other
1.Ongoing cost of buying disposable media.
2. Disposal of media could become an environmental issue.
3. Media can tear or bunch on one side of the vacuum box causing unfiltered MRF
to be supplied to the machine tool.
B. Permanent Belt - A continuous belt made of a fine mesh woven synthetic
fiber is the septum on which the contaminant is trapped. When the filter cake
reaches the maximum useful thickness, the belt is indexed a preset distance
(usually 12"-15"), exposing clean media. As the belt is indexing, the chips
and tramp oil are removed from the belt by either scraping, brushing, blow-off
nozzles, flush nozzles or a combination of these methods.
1.No ongoing cost for disposable media.
2. The salvage value of chips is greater when disposable media is not present.
1.Cannot be tightly woven so until a filter cake is established, MRF clarity will not be as
good as with disposable media.
2. Contaminant can become embedded in the belt and blind off the pores.
3. More susceptible to blinding off by tramp oil.
4. Susceptible to tracking problems which can damage the belt and prevent
creation of a vacuum.
C. Wedge -ire Drum - Drums are available with slotted openings down to 0.003
inches thick; however, 0.007 - 0.010 inch slots are the most common. Drums
with slots less than 0.007 inches tend to become plugged with chips. A filter
cake is built up on the outside of wedge-wire through a vacuum created by
pump suction. When the vacuum differential reaches 10" hg. an index cycle is
initiated. The drum is rotated a preset increment (usually 6" to 10") while a
doctor blade scrapes the chips from the drum. The chips fall to the bottom of
the tank where they are carried away and discharged by a drag conveyor.
1.No ongoing cost for disposable media.
2. Chips are not mixed with disposable media so the chip salvage value is higher.
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1.Some long thin chips (shavings) could pass through the slots before a filter cake is
2. Average MRF clarity will not be as good as with a disposable media.
3. If vacuum is broken (index, shut down periods, etc.) the filter cake may come off
the drum, requiring the formation of a new cake when vacuum is re-established.
4.More susceptible to MRF problems associated with poor MRF control.
5.Not recommended for aluminum machining applications. Aluminum chips tend to
"smear" and plug the slots.
D.Micro-Screen Drum - Identical to a wedge-wire drum in construction and operation
except the drum is made of thin plate with very small holes. Holes are usually
0.005 -0.010 inches in diameter. Micro-screen is often used with a filter aid
on honing, finish grinding, test stands, etc., where small amounts of chips are
being generated. Micro-screen has been used on rough steel grinding without
a filter aid.
Micro-screen is a relatively new development with few applications in operation. As
more performance information becomes available, additional advantages and
disadvantages of this method can be determined.
1.Smaller openings than wedge-wire. Provides finer filtration while building a chip cake.
Chip cake build-up is faster than wedge wire.
1.Lighter construction than wedge-wire, may require more frequent replacement.
E. Micro-Screen Discs - A series of discs made of micro-screen. A vacuum is
created inside the discs and a chip cake is formed on the outside, providing
fine filtration. Can be used with pre-coat or as a self-coat filter. Chip cake is
scraped off by doctor blades.
1. Discs provide three times as much filter area as a micro-screen drum.
1.Lighter construction than wedge wire, may require more frequent replacement.
2. More complex doctor blade system may require more maintenance.
3.2.2 Automatic Pressure Filtration
Filters which collect contaminant on a septum as the MRF is pumped through
the septum under pressure. The filter media is used to trap contaminant and
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form a filter cake. The actual fine filtration is obtained by pumping the MRF
through the filter cake. As the filter cake increases, the pressure required to
pump the MRF through increases and the pump output decreases. At a
preselected pressure, an index cycle is started which purges the accumulated
filter cake and exposes a clean septum.
A.Flat Bed Filter - The filter media is sealed between two horizontally opposed shells.
The dirty MRF is pumped into the upper shell under pressure and forced
through the media. The contaminant is trapped on the media, forming the
filter cake while the MRF is discharged to a clean tank for recirculation by the
system pumps. At a preset point, usually 12-17 psi, the incoming dirty MRF
is stopped and plant compressed air is forced through the upper shell, blowing
the remaining MRF through the media into the clean tank. The compressed
air is stopped, the seal is broken and the media is indexed until the entire
septum is covered with clean media. Flat beds can utilize either disposable
roll media or a permanent belt.
1.Since they can operate at higher pressures than vacuum filters, flat bed filters can build
up a thicker chip cake before an index is required.
2. Less susceptible to chip migration.
3. Disposable media is moved through a flat bed on a belt, not dragged through by
conveyor flights. This reduces the possibility of torn media.
4. Provides good filtration at a higher flow rate per sq/ft. of media.
1.Flat beds require two sets of pumps.
2. The filter pumps are pumping dirty MRF and may require more maintenance.
3. More sensitive to media blinding off from tramp oil.
4. During index blow-down this system places additional demands on plant
compressed air supply.
B. Disposable Media - A roll of disposable fabric is carried through the filter by
a media conveyor belt. When the filter cake reaches the maximum useful
thickness, the conveyor is indexed until the entire septum is covered with
Same as Section 3.2.1. A.
Same as Section 3.2.1 A.
C. Permanent Belt - A continuous belt made of a fine mesh woven synthetic
fiber is the septum on which the contaminant is trapped. When the filter
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indexes the accumulated contaminant is removed from the belt by either
scraping, brushing, blow-off, flush-off or a combination of these methods.
Same as Section 3.2.1. B
Same as Section 3.2.1. B
D.Pre-Coated Tubes - A series of perforated tubes covered with wire mesh act as the
septum and are mounted in a pressure vessel. A slurry of the clean liquid and
a pre-coat powder is circulated through the vessel resulting in a cake of pre-
coat powder on the outside of the filter tubes. After a preset time the slurry
pump shuts off and the filter pump starts. The filter pump forces the dirty
MRF through the pre-coat cake, up through the tubes and into the clean tank
for delivery to the system. As contaminant builds up on the filter cake,
pressure increases in the vessel. When the differential pressure reaches a
preset point, usually 25 psi, the filter pump is stopped and plant compressed
air is used to blow the liquid, contaminant and spent pre-coat into a secondary
vacuum filter. With the primary filter vessel empty and all tubes clean, the
filter automatically starts a pre-coat cycle while the system pump continues to
supply liquid from the clean tank to the system. The secondary filter
automatically processes the blown-down liquid from the primary vessel. The
used pre-coat powder and contaminants are deposited in a waste hopper by
means of a drag conveyor while the liquid is returned to the dirty tank.
1.Filtration through diatomaceous earth pre-coat can remove particles as small as ½
2. Can use multiple primary vessels with one secondary filter for large system
3. Large amount of filter area can handle high GPM system requirements.
4. Closed system emits less odors.
1.The use of pre-coat often causes housekeeping and environmental problems.
2. Diatomaceous earth pre-coat cannot be used on water soluble MRF because the
filtration is so fine it will strip out the oil which is in suspension.
3. More complex system requires more maintenance.
4. Higher cost to purchase and operate.
E. Automatic Back-Washing Tube Filter - A vessel containing a tubular filter
element as the septum to trap contaminant as the MRF is forced through by
pump pressure. When the differential pressure builds up to a preset point, an
automatic valve diverts flow to a second vessel while flow through the
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contaminated vessel is reversed. The back flow dislodges the contaminant
and is discharged to a trench. The vessel is now ready to go back on line
1.Eliminates the expense of frequent cartridge changes.
2. Best suited for secondary filtration.
1.MRF clarity (usually particles of 100 microns or more) usually cannot match disposable
media filtration. When elements with finer particle retention are used, the life of
the elements is significantly reduced.
2. Not available with the capacity to be the primary filter on large systems.
F. Automatic Back-Washing Strainer - Similar in operation to the automatic
back-washing filter. This unit is classified a strainer because its function is to
remove only large particles, usually 250 microns and above. This unit is most
often used as a sentinel (back-up) on automatic filtration to provide some
protection in the event of a system failure such as torn media or allowing the
system to run out of disposable media.
3.2.3 Manual Pressure Filtration
A system where contaminant is collected on the septum as the MRF is pumped through.
The system has no means of expelling the contaminant so the septum element
should be cleaned or replaced. These units are mounted in tandem so flow
can be diverted to one while the other is being serviced.
A. Disposable Cartridges - A vessel containing one or more elements
(usually a series of elements) made of polypropylene, polyester, nylon,
etc. mounted over perforated tubes. The cartridges are usually
constructed in a pleated pattern to expose as much filter area as
possible. The MRF passes through the outside of the cartridge where
the contaminant is trapped, while the clean MRF flows into the tubes
and to the system. Cartridges are made of a porous material with the
pore sizes determining the clarity obtained.
1. Available in a wide range of micron ratings.
2. Available with Beta and ISO ratings to verify cartridge efficiency.
3. Used primarily as secondary filtration after automatic filtration has removed larger
4. Cartridges usually have more filter area than bags.
1. The contaminant is accumulated on the outside of the cartridges. When dirty
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cartridges are being removed, the contaminant falls into the vessel. The vessel
must be cleaned manually, which increases maintenance costs.
2. If the contaminant input is greater than expected, the cartridge replacement cycle
will be shortened and maintenance cost will be excessive.
B. Disposable Bags - A pressure vessel with a basket or series of baskets
suspended from a plate. Disposable bags are placed inside the baskets to
collect the contaminant. Dirty MRF is introduced in the upper chamber of the
vessel and pumped through the bags out the bottom chamber to the system.
Bags are available in a variety of materials such as polypropylene, polyester,
1.All contaminant is trapped in bags that can be removed without contaminating the
lower chamber of the vessel. The bags of contaminant are removed, new bags
installed and the cover replaced in much less time than with cartridge
2.Available in a wide range of micron ratings.
3. Pleated bags, which increase the filter area and bag life, are available for some
1.Less filter area than similar cartridge vessels, will require more frequent changing.
C. Basket Strainers - Similar to bag filters except that baskets are not lined with
a disposable bag. The baskets are usually a fine mesh stainless steel wire.
The baskets are removed from the vessel and cleaned, then reinstalled in the
1. No disposable bags or cartridges to purchase.
1. Limited use. Used as a back-up on automatic filtration systems.
2. Not capable of fine filtration, usually 250 microns and above.
4.0MRF MONITORING AND MANAGEMENT
Soluble oil systems should be monitored on a regular basis. MRF samples should be
drawn and tested in the same manner each time, with samples taken at the same time of day when po
vacuum or pressure should be recorded when the sample is taken (contaminant levels
may be higher if the filter has just indexed).
4.1 Test Procedure
Tests should be conducted to monitor a number of properties of the MRF. Some tests are
not required as often as others. The following test procedures are recommended:
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·Centrifuge - A sample is spun on a low-speed centrifuge (3000 RPM) for 15 minutes.
The tramp oil will separate at the top of the liquid, the cream will separate to form
the next level and the suspended solids will settle to the bottom. A translucent or
watery looking layer at the lower part of the tube indicates a weak (unstable)
emulsion. The particulate collected in the bottom of the tube is then reported in
parts per million by volume. This procedure should be done daily until the results
are consistent enough to reduce the frequency. Tests should be done a minimum
of twice a week.
· Centrifuge/acid split - Sulfuric acid is added to the sample and both are placed in
a winthrop tube. The tube is spun in a low-speed centrifuge for 15 minutes. The
oil will form a layer at the top of the tube which indicates the concentration (ratio
of water to oil). Concentration should be monitored daily on most systems, but
not less than twice a week.
· pH test - Sample should be tested with a pH meter. MRF should be maintained at
a pH of 8.8 to 9.2. Proper pH level will inhibit bacteria growth and minimize
odor problems. Sodium borate can be added to raise system pH. pH should be
monitored at the same frequency as concentration.
· Bacteria Count - Bacteria cultures can be run to determine the presence of
bacteria in the system. Biocides should be added to control bacteria when
necessary. Bacteria should be checked weekly or more frequently when a
suspected bacteria problem exists.
· Gravimetric - A 100 ml MRF sample is filtered through a membrane of known
micron size (usually 8 micron). The dirt captured on the membrane is weighed
and reported in parts per million by weight.
4.2MRF Clarity Reporting
In the past the filtration industry in general has used the gravimetric test with an 8-micron
membrane to verify system clarity. This test is simple and the results reproducible, but
particles less than 8 microns pass through the membrane and are never included in the
ppm results. In cast iron and cast aluminum, a significant amount of the contaminant
may be less than 8 microns and will go undetected. Previously, it was thought that
small particles below 8 microns were not as detrimental to machining operations as
larger particles. Recent studies have indicated this is not true, and sub-8 micron
particles may cause more problems than larger particles. Most filter systems for
machining operations are effective at removing particles over 20 microns. Efficiency of
particulate removal drops as particle size decreases. When the centrifuge testing
method reports total solids in ppm it is including many particles in the 1 to 10-micron
range that the filter cannot efficiently remove.
Plants are encouraged to use both methods of testing, gravimetric and centrifuge. The
centrifuge method should be used regularly to monitor the stability and quality of the
MRF. The gravimetric method should be used periodically and when quality
- 52 -
problems arise to verify filter function. A gravimetric test through a series of
different membranes (1, 8, 20, 40 microns for example) is a better indication of filter
performance. The presence of a great amount of large particles would indicate a filter
or media problem.
New filtration equipment should be tested and MRF clarity recorded as a benchmark for
the capability of this type of equipment. This clarity benchmark will also be valuable
to verify satisfactory filter operation if part quality problems occur.
5.0 TYPICAL CENTRAL SYSTEM SIZING
The following information should be available to determine system size and type of
Type of material and amount of stock being removed.
The type of machining operations and profile of chips being generated.
Type of MRF to be used. This decision should be made at the inception of the
program by the process engineer, machine supplier, tooling engineer and
Clarity required. This requirement will determine the type of filtration used and
the flow rate through the filter.
Quantity of MRF (GPM) required for machining operations, flush stations and
flush nozzles internal to the machine (machine and pallet flushing). OEM
SHOULD PROVIDE DATA SHOWING CALCULATIONS, SINCE
HISTORY SHOWS ORIGINAL NUMBERS ARE OFTEN
Temperature control requirements. If MRF is to be temperature controlled,
additional MRF is required for circulation in the chiller loop.
Floor plan layout. A layout showing approximate location of machine(s) is
necessary to determine trench length for trench flushing requirements.
5.1The following steps are followed in determining system size
· Machining, flush stations and machine flush = GPM
High-pressure stations or other unique operations = GPM
Side arm polishing filter if required = GPM
MRF for trench flushing = GPM
MRF for temperature control = GPM
BASE TOTAL = GPM
*Rule of thumb. When estimating MRF requirements for trench flushing, use the
Aluminum machining: 1-1/2 to 2 GPM MRF required per linear foot of trench.
Cast iron machining: 2 to 2-1/2 GPM MRF per linear foot of trench.
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Steel machining: 2-1/2 to 5 GPM MRF per linear foot of trench. When long stringy chips
which form bundles are expected, 5 GPM/ft. may be required with large-volume
nozzles to dislodge and move the bundles. Additional nozzles may be required at
machines producing chip bundles.
The amount of MRF required for the chiller loop is 12-15% of the total MRF required for all
machining, high-pressure stations, polishing filters and flushing.
· An additional 10% of clean MRF is required for clean tank refill - base total x
·As a chip cake is built up on the septum it becomes more difficult for the MRF to pass
through and the pump output decreases. To compensate for this reduction, an
additional 5% capacity is built into the base system - base total x 5%.
· Experience has shown that when new systems are launched, it is usually necessary
to add flush nozzles in areas where chips are building up or to increase MRF flow
to some tools. To provide reserve MRF for these problem areas an additional
10% of the base requirement should be provided - base total x 10%.
Clean Tank Refill 10%
Pump Output Reduction due to vacuum increase 5%
Reserve MRF 10%
Total Additional = 25%
Minimum System Requirement = base total x 1.25.
5.2 Typical Aluminum Machining System
Material - ALUMINUM
Operations - TRANSFER LINE (Drilling, reaming, turning, boring, etc.)
MRF - WATER SOLUBLE @ 12:1
Temperature Controlled - 72 F +/- 1
High Pressure Stations or Critical Operations - NONE
MRF Clarity - 200 ppm
·Total MRF required for machining, machine flush and flush stations. - 2,000 GPM
(Specified by the machine supplier.)
· MRF required for trench flushing - 400 feet of trench required as shown on system
400 Feet @ 2 GPM/ft. - 800 GPM
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· MRF required for temperature control - (machine requirements plus trench
requirements) x 15% = 2800 x .15 = 420 GPM
· Base System Requirement = 2,000 + 800 + 420 = 3,220 GPM
· Additional MRF required for clean tank refill, pump output reduction and reserve
capacity = 25%.
3,220 GPM x 1.25 = 4,025 GPM total MRF required
The pump of choice for this system is a vertical turbine 1,400 GPM @ 110' hd with 50 HP
4,025 GPM Req‟d. = 2.875 = (3) pumps required
3 x 1,400 = 4,200 GPM system size
Filter supplier should verify 110' hd is sufficient to meet pressure requirements at all drops.
·Since the MRF clarity requirement is 100-200 ppm, a vacuum disposable media filter
will be used. A flow-through wedge-wire panel primary conveyor will be installed
ahead of the filter to remove the larger chips. The primary conveyor will normally
remove 80-90% of the chip load. This increases the time between filter cycles which
improves filtration and reduces media usage.
Flow-through wedge-wire primary conveyor:
4,200 GPM = 60 Sq/ft. min. wedge-wire required.
Primary conveyor to have a min. of 60 Sq/ft. of wedge-wire.
Disposable Media Filter: flow rate for aluminum machining = 15 GPM/Sq/ft. of
4,200 GPM = 280 Sq/ft. of filter area req‟d. (min)
15 GPM/sq. ft.
Note: On large systems (2) filters may be required to provide the necessary filter area.
5.3 Typical Cast Iron Machining System
Material: Cast Iron.
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Operations: General machining (turning, milling, drilling, tapping). MRF required =1,800 GPM pe
High-Pressure or Critical Operations: Critical tolerances and micro-finish on boring
MRF required: 320 GPM per machine tool manufacturer.
MRF: water-soluble @ 12:1 concentration.
Temperature Control: None.
MRF Velocity Trench: 400 ft. as shown on layout.
System Equipment Determination
General machining on cast iron usually requires MRF clarity in the 400-500 ppm range.
A wedge-wire drum system can be used.
Critical boring operations require MRF in the 100-200 ppm range. A vacuum
disposable media polishing filter will be used.
320 GPM required for precision machines.
10% required for clean tank make-up
5% required to make up for pump output reduction
10% reserve capacity = 25%
Polishing filter minimum requirement = 320 x 1.25 = 400 GPM
Use 400-420 GPM end suction pump
The recommended flow rate through the polishing filter is 10 GPM/Sq/ft. of filter area.
420 GPM = 42 Sq/ft. min. filter area
10 GPM/ Sq/ft.
Wedge-Wire Drum Filter
MRF required for general machining 1,800 GPM
MRF required for polishing filter: Provide 450 GPM to polishing filter
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MRF required for trench flush:
400 ft. @ 2-1/2 GPM/ft. = 400 x 2.5 = 1,000 GPM
3,250 GPM = base system requirement
Additional MRF required for clean tank refill, pump output reduction and reserve
capacity = 25%.
1.25 x 3,250 = 4,062 GPM required.
Use Vertical Turbine 1,400 GPM pumps for this system.
4,062 GPM required = 2.9 = (3) pumps required
3 pumps x 1,400 GPM/pump = 4,200 GPM system size
Wedge-wire drums should operate at a flow rate of approximately 20 GPM/Sq/ft. of filter
area for best results.
4,200 GPM = 210 Sq/ft. of wedge-wire required
Drums are built in standard sizes (diameter and length) which contain a specific amount of
Example: One supplier produces the following series of drums:
3'-0" Diameter 4'-6" Diameter
1'-0" Lg. = 18 Sq.ft. w/wire area 2'-0" Lg. = 56 Sq/ft.
2'-0" Lg. = 38 Sq/ft. w/wire area 3'-0" Lg. = 84 Sq/ft.
3'-0" Lg. = 56 Sq/ft. w/wire area 4'-0" Lg. = 112 Sq/ft.
4'-0" Lg. = 74 Sq/ft. w/wire area 5'-0" Lg. = 140 Sq/ft.
To obtain a minimum of 210 square feet of drum filter area,either (3) 3' diameter x 4' long (3
x 74 S.F. = 222 S.F.) or (2) 4'-6" dia. x 4' lg. (2 x 112 S.F. = 224 S.F.) can be used. It is
recommended the (3) 3' diameter drums be used so if one drum must be removed for
maintenance the system can continue to operate (at reduced efficiency) until that drum is
5.4TYPICAL STEEL MACHINING SYSTEM
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Operations: General machining (turning, milling, boring, drilling and tapping) MRF
required per machine tool supplier = 1,500 GPM 25 psi min.
High-Pressure or Critical Operations: None.
MRF: water-soluble @ 12:1 concentration.
Temperature Control: None.
MRF Velocity Trench: 300 ft. as shown on layout.
System Equipment Determination:
·General machining will produce mostly large chips; turning and boring will produce
some long stringy chips which will entangle and form bundles. To handle these
bundles a submerged hinge pan conveyor will be used. The hinge pan will overflow
into a vacuum media filter. If long stringy chips and bundles are not expected, a
wedge-wire drum primary filter with a disposable media polishing filter can be used.
MRF required for machining, machine flush and flush stations = 1,500 GPM specified
by machine supplier).
MRF required for trench flush - 300 ft. of trench @ 5 GPM/ft. (use 5 GPM/ft. to handle
expected bundles from turning and boring operations)
300 ft. @ 5 GPM/ft. = 1,500 GPM.
Base system requirement: = 1,500 + 1,500 = 3,000 GPM.
Additional MRF required for clean tank refill, pump output reduction and reserve
capacity = 25%.
3000 GPM x 1.25 = 3,750 GPM total MRF required.
Use vertical turbine 1,400 GPM @ 110' hd pumps. Filter supplier should verify adequate
system pressure at machines.
3,750 = 2.68 (3) pumps @ 1,400 GPM required.
Vacuum Disposable Media Filter:
Flow rate for steel machining: = 20 GPM/Sq/ft.
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4,200 = 210 Sq/ft. of filter area required.
Hinge Pan Conveyor W/Tank:
Hinge pan conveyors are available in a wide range of widths. Common widths used in
T&C Operations filtration systems are 36" to 60." The selection of the hinge pan
conveyor width should be a joint decision between engineering and the filtration
equipment supplier based on chip load and similar existing applications. The hinge
pan conveyor tank should be sized to provide approximately (1) minute settling time
6.0DISPOSABLE MEDIA SELECTION AND MANAGEMENT
Depth filtration is the goal of all roll media filtration applications. If the dirt load forms a
filter cake on the media (cast iron, aluminum and steel machining, and some coarse
grinding) then the media serves as a septum for the filter cake and we have depth
filtration using the filter cake as the filter. Clarity is determined by a combination of the
media weight, filter cake formed and the time to form a satisfactory filter cake.
While the filter cake is forming, the media pore size determines the clarity of the MRF
and the media should be heavy enough to do a satisfactory job of filtering to prevent
objectionable particles from passing through the media. The media selection is a trade-
off - lightweight media that forms a filter cake slowly but does not plug easily or
heavyweight media that forms a filter cake rapidly but tends to plug up easily. Then there
is also the problem of wet strength - the heavier the weight, the stronger the media. The
media should be heavy (strong) enough to index without tearing.
If the media cannot form a filter cake (honing, fine grinding - cast iron, hardened steel,
etc.) then the media must serve as the primary filter. The media should be heavy enough
to produce the desired clarity and yet not plug too rapidly and result in excessive media
usage. With no filter cake, the media usage will naturally be higher than with depth
filtration using a filter cake as a filter. Without a filter cake, the pore size of the media
determines the clarity of the MRF.
In cartridge filtration there is generally no depth filtration. Polishing and sentinel filters
do not see a coarse enough dirt load to form a filter cake.
6.1 MEDIA SELECTION
One of the most widely-used roll media is a polyester blend. This media provides a good
combination of strength, efficiency, cake retention capacity and cost. Polyester does not
have an affinity for oil like polypropylene and nylon fibers, which can cause the media to
blind off and index prematurely.
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Roll media is specified by weight (ounces per square yard) with heavier media being
stronger than lighter media of the same fiber. Fiber diameter (denier) has a significant
effect in determining the physical properties of a filter media. A fine denier fiber
produces a tighter, more uniform media at the same weight than a larger diameter fiber.
This tighter porosity will produce finer, more efficient filtration. Cost should be
considered in media selection. While a heavier media provides finer filtration, it also
costs more. Since a heavier media traps more fine particles before the filter cake is
formed, media usage usually increases.
The following table shows machining operations and typical media used:
Polyester blends give the best overall media results on vacuum filters. You can switch
from polyester blends to nylon of the same weight and get similar filter results.
Aluminum and Steel Machining
· 1.5 oz and heavier on large filters.
· 1.0 oz. and heavier on small filters.
Cast Iron Machining
· 1.5 oz. - 1.8 oz.
· 1.5 oz. media is recommended as a starting point because 1.0 oz. media may not
build a filtering cake fast enough and the media will pass too many fine particles
before the filter cake is formed.
Soft Steel - (coarse) grinding
· 1.5 oz. - 2.0 oz. Produces a steel wool-like swarf - relatively easy to filter -
builds a good filter cake.
Hard Steel - (fine) grinding
· 1.5 oz. - 2.0 oz. Difficult to filter - does not build a good filter cake.
Cast Iron - (fine) grinding
· 1.5 oz. - 2.5 oz. Difficult to filter - does not form a filter cake - produces a
black smear. A heavy (tight) media is required.
6.2 MEDIA MANAGEMENT
Polyester blends, while excellent filter materials, are somewhat weak in the transverse
(width) direction. At times it may be necessary to go to a heavier media or even a PBN
(pattern bonded nylon) media for strength. PBN has excellent strength and the heat-
formed square pattern reduces the tendency for the nylon to blind off. On new jobs being
run in, it is advisable to use PBN for the first few months to wear off rough points in the
filter that may tend to tear the media. If PBN tears on a new job, the filter should be
reworked to remove the rough spots causing the tear.
If PBN is used and the filter fails to pull the media, it may be necessary to go to a heavy,
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thicker polyester blend. PBN is difficult to pull because it does not provide a soft surface
for the flights to dig into. If the filter cannot pull a heavy polyester blend, then check the
flights for straightness and sharp corners as well as the ramp for flatness in the transverse
direction. On some of the wider filters it is necessary to use media re-winders to aid in
pulling the media on index. Delay time consuming media replacements by using jumbo
rolls. 1000 yards is common for 72" and 92" filters and 500 yards for 51" filters. Check
media roll diameter with supplier and check maximum permitted roll diameter with filter
manufacturer. The heavier the media, the larger the media roll diameter.
7.0. SELF-CONTAINED MRF SYSTEMS
Self contained MRF systems are small units that service one or two operations. Self-
contained clarifiers can be filters or separators. Filters are usually small vacuum
disposable media or wedge-wire drums. A wide variety of separators are available such
as chip conveyors, magnetic conveyors, spiked belt conveyors and roller filter conveyors.
It should be noted that the separators do not provide positive filtration and may not be
suitable for many final operations. For finish grinding, honing, polishing, etc., a vacuum
disposable media filter is recommended. Usually the MRF drains directly from the
machine into the clarifier or from the machine through a short chute into the clarifier.
Special attention should be paid to machine discharge height to avoid unnecessary pit
installation. In some cases, where accessibility is a problem, the MRF is drained into a
sump and pumped over to the filter with a sump mounted transfer pump. However, this
method often creates a clean out problem in the sump. On small machines the sump is
too small to include a drag conveyor and chips build up requiring manual clean out.
Small individual filters work well for isolated machines or operations that require a
unique MRF, but if a number of similar operations are in the same area, a central system
is usually more functional and provides greater economy of scale. Small filters take up
more floor space per GPM than larger filters used in central systems. Individual filters
are more expensive per GPM because each unit requires its own controls, drive
mechanism, pumps, service drops and maintenance. Adequate space should be left open
around all filters (large or small) for chip removal, media replacement and maintenance.
8.0 CHIP HANDLING
The efficient handling, processing and salvage of chips presents a continuous house-
keeping and economic issue for many plants. The amount of chips processed by a single
plant can be as much as 4,000 tons per month. This huge volume of chips along with
their oily carry-off create housekeeping and environmental issues in plant aisles, salvage
cart and chip storage areas which require constant monitoring. Currently, virtually all
chips are handled manually. This means chip carts stationed at the point of process
discharge are towed across the plant to a salvage area. Chip carts are marshaled by
material type and allowed to drain. The chips are then emptied into salvage cars and
removed from the site. Chips should be segregated by material type to maintain salvage
Manual chip handling, while creating housekeeping problems and requiring extensive cart
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handling, is widely used due to its very low facility cost investment. The primary
requirements for manual handling are a conscientious program to maintain leak-proof
chip carts and a disciplined program for timely replacement of full chip carts at
process discharge points. Additionally, as process locations change, the material
handling plans should be revised to ensure all pick-up points are scheduled into
specific salvage routes. Manual chip handling can be successful if management
enforces a rigid program to eliminate oily and chip-laden floors.
The alternative to manually handling chips is to install automated systems that process
chips from their point of origin to the point of removal from site. The driving force to
install an automatic chip handling system comes from better housekeeping, increased
salvage value from dry chips and stricter environmental concerns over the chip oil lost
in transit. These systems employ chip shredders/crushers, wringers (to remove oil by
centrifugal separation), and blowers that transport the chips through thick-walled
piping to the removal site.
A well-designed, well-tuned automatic system will provide a complete "Hands Off"
approach to chip removal. Since this seems like the optimum answer to handling
large volumes of chips, the question is why these systems have not been installed in
more plants? Like all potential solutions these systems also have limitations. The
major disadvantage is the high initial capital investment. Also, different chip
materials (aluminum, steel, or cast iron) pose different problems as does the type of
MRF (soluble or straight oil). Additionally, these systems are subject to high abrasive
wear and will "self-destruct" over time requiring a relatively high amount of
maintenance and downtime. Despite the disadvantages, the continuous drive for
cleaner and more environmentally-conscious facilities dictates the investigation of
automated chip handling as a means of achieving this goal.
A summary of advantages and disadvantages of manual and automatic chip handling is as
Manual Chip Handling
· Low initial capital investment.
· Simple equipment - less risk of down time.
· Reduced equipment maintenance.
Less need for MRF flushing and less mist generation.
· Chip carts should be changed frequently.
· When carts are allowed to over-fill, chips and MRF are spilled throughout the
· Chip carts should be monitored and repaired to eliminate leaking.
· Chip carts contain excessive oil which should be allowed to drain before dumping
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into salvage carts.
· Material in chip carts could be a fire hazard.
· Requires plant area to marshal chip carts.
· Open chip carts tend to accumulate miscellaneous trash from employee discards.
· Frequent shuttling/handling of carts.
Automatic Chip Handling
· Eliminates many housekeeping problems associated with chip and oil spillage.
· Eliminates labor required to shuttle chip carts.
· Salvage value is greater for dry chips (with oil removed).
· Excessive MRF from chips is returned to system.
· Reduced chip cart maintenance.
· High initial capital investment.
· System is inclined to "self-destruct;" high maintenance potential.
· Provisions for manual handling should be provided for times when automatic
system is down.
· May be less effective when used on straight oil system.
Often requires much larger MRF sumps.
Potential for dead areas where MRF can “spoil” (bacterial growth).
Much greater energy costs. (A sluice pump can cost over $30,000/year for a 60
HP pump -- sluice systems often have multiple pumps.)
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9.0 GUIDELINES FOR MRF SELECTION
9.1 ALUMINUM MACHINING OPERATIONS WITH WATER-BASED MRF
OPERATION SURFACE MACHINE PRIMARY APPROX. MACHINE FLUSH TRENCH
FINISH MRF CLARITY CHIP PRIMARY SUPPLY SUPPLY FLUSH RATE
REQUIRED REQUIRED REMOVAL RETENTION FILTER FILTER
Rough > 32 u In. Wedge-wire 70-100 GPM Vacuum perm. Same as 2 GPM per
Machining- 400 ppmv bottom flow- per Sq/ft. belt or disp. machine lin. ft.
> .8 u M thru drag of wedge-wire. media filter supply.
200 u max. conveyor with w/1.5 oz.
.030 slots polyest.
General 16 - 32 u In. 200 ppmv Wedge-wire 70-100 GPM Vacuum perm. Same as 2 GPM per
Machining- .4 - .8 u M 50 u max. bottom flow per Sq/ft. belt or disp. machine lin. ft.
thru drag of wedge-wire. media filter supply.
Boring, conveyor with w/1.5 oz.
Turning .030 slots. polyest.
Finish 8 - 16 u In. 100 ppmv Not required. N/A Vacuum or Same as 1 - 2 GPM per
Machining- pressure disp. machine lin. ft.
.2 - .4 u M 15 u max. media filter supply.
Gun Drilling & polyest.
Reaming 7 GPM/Sq/ft.
Gun drill &
Grinding 8 - 16 u In. 100 ppmv Not required. N/A Vacuum or Same as 1 - 2 GPM per
.2 - .4 u M 25 u max. pressure disp. machine lin. ft.
media filter supply.
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w/1.5 - 2.5
Super 4 - 8 u In. 50 ppmv Not required. N/A Vacuum or Same as 1 GPM per
Finishing - 10 u max. pressure disp. machine lin. ft.
1 - .2 u M media filter supply.
Honing, w/2.5 Oz.
9.2 CAST IRON MACHINING OPERATIONS WITH WATER-BASED MRF
OPERATION SURFACE MACHINE MRF PRIMARY APPROX. MACHINE FLUSH TRENCH
FINISH CLARITY CHIP PRIMARY SUPPLY SUPPLY FLUSH RATE
REQUIRED REQUIRED REMOVAL RETENTION FILTER FILTER
> 32 u In. 400 ppmv
Rough Settling tank 3-5 min. Wedge-wire Same as 3 GPM per
Machining- > .8 u M 200 u max. w/drag drum machine lin. ft.
conveyor. .007 slots supply.
Mill, Drill, 20 GPM/Sq/ft.
General 16 - 32 u In. 200 ppmv Settling tank 3-5 min. Vacuum perm. Wedge-wire 2 - 3 GPM per
Machining- w/drag belt or disp. drum lin. ft.
.4 - .8 u M 50 u max. conveyor. media filter .007 slots
w/1.5 oz. 20 GPM/Sq/ft.
Turning 15 GPM/Sq/ft.
Finish 8 - 16 u In. 100 ppmv Usually not Vacuum disp. Vacuum disp. 1 - 3 GPM per
Machining- required. media filter media filter lin. ft.
w/1.5 oz. w/1.5 oz.
.2 - .4 u M 15 u max. 3-5 min. 11 GPM/Sq/ft.
Gun Drilling & Can use
Reaming settling tank Gun drill &
- 65 -
if necessary. ream cart.
Grinding 8 - 16 u In. 100 ppmv Not required. N/A Vacuum disp. Same as 1 - 2 GPM per
media filter machine lin. ft.
.2 - .4 u M 25 u max. w/2.5 oz. supply.
Super 4 - 8 u In. 50 ppmv Not required. N/A Vacuum disp. Same as 1 GPM per
Finishing - media filter machine lin. ft.
.1 - .2 u M 10 u max. w/2.5 oz. supply.
Micro-sizing 7 GPM/Sq/ft.
9.3 STEEL MACHINING OPERATIONS WITH WATER-BASED MRF
OPERATION SURFACE MACHINE MRF PRIMARY APPROX. MACHINE FLUSH TRENCH
FINISH CLARITY CHIP PRIMARY SUPPLY SUPPLY FLUSH RATE
REQUIRED REQUIRED REMOVAL RETENTION FILTER FILTER
Rough > 32 u In. 400 ppmv Settling tank 3-5 min. Wedge-wire Same as 3 - 5 GPM per
Machining- w/hinge pan drum machine lin. ft.
> .8 u M 200 u max. conveyor. .007 slots supply.
General 16 - 32 u In. 200 ppmv Settling tank 3-5 min. Vacuum perm. Wedge-wire 3 - 5 GPM per
Machining- w/hinge pan belt or disp. drum lin. ft.
.4 - .8 u M 50 u max. conveyor. media filter .007 slots.
Turning 20 GPM/Sq/ft.
Finish 8 - 16 u In. 100 ppmv Settling tank 3-5 min. Vacuum disp. Vacuum disp. 2 - 3 GPM per
Machining- w/drag media filter media filter lin. ft.
conveyor. w/ 1.5 oz. w/1.5 oz.
- 66 -
.2 - .4 u M 15 u max. polyest. polyester
Not required 15 GPM/Sq/ft.
Gun Drilling & if light chip Gun drill &
Reaming load. ream cart.
Grinding 8 - 16 u In. 100 ppmv Not required. N/A Vacuum disp. Same as 1 - 2 GPM per
media filter machine lin. ft.
.2 - .4 u M 25 u max. 1.5 - 2.0 oz. supply.
Super 4 - 8 u In. 50 ppmv Not required. N/A Vacuum or Same as 1 GPM per
Finishing - pressure disp. machine lin. ft.
.1 - .2 u M 10 u max. media filter supply.
Micro-sizing 4 - 5
9.4 STEEL MACHINING OPERATIONS WITH STRAIGHT MINERAL OIL MRF
OPERATION SURFACE MACHINE MRF PRIMARY APPROX. MACHINE FLUSH TRENCH
FINISH CLARITY CHIP PRIMARY SUPPLY SUPPLY FLUSH RATE
REQUIRED REQUIRED REMOVAL RETENTION FILTER FILTER
Rough > 32 u In. 400 ppmv Settling tank 6-8 min. Vacuum Same as 3 - 5 GPM per
Machining- w/hinge pan Wedge-wire machine lin. ft.
> .8 u M 200 u max. conv. for long drum supply.
stringy chips. .015 slots
Mill, Drill, 5-7 GPM/Sq/ft.
Broach - not
- 67 -
General 16 - 32 u In. 200 ppmv Settling tank 6-8 min. Vacuum wedge- Same as 3 - 5 GPM per
Machining- w/drag wire drum machine lin. ft.
.4 - .8 u M 50 u max. conveyor or 5-7 GPM/Sq/ft. supply.
Boring, conv. for long
Turning stringy chips.
Finish 8 - 16 u In. 100 ppmv Settling tank 3-5 min. Vacuum disp. Vacuum disp. 2 - 3 GPM per
Machining- w/drag media filter media filter lin. ft.
conveyor. w/ 1.5 oz. w/1.5 oz.
.2 - .4 u M 15 u max. polyest. polyester
Not required 3 GPM/Sq/ft.
Gun Drilling & if light chip Gun drill &
Reaming load. ream cart.
Grinding 8 - 16 u In. 100 ppmv Not required. N/A Vacuum disp. Same as 1 - 2 GPM per
media filter machine lin. ft.
.2 - .4 u M 25 u max. 1.5 - 2.0 oz. supply.
Super 4 - 8 u In. 50 ppmv Not required. N/A Vacuum or Same as 1 GPM per
Finishing - pressure disp. machine lin. ft.
.1 - .2 u M 10 u max. media filter supply.
Micro-sizing 2-3 GPM/Sq/ft.
BAG FILTER A pressure filter where fabric bags are installed inside a cylindrical housing (pressure vessel) and the
filtered liquid is pumped through the bag walls. Liquid flow is from the inside to the outside of the
bag - dirt is trapped inside the bag. These pressure vessels must be ASME (American Society of
Manufacturing Engineers) coded.
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BETA RATIO Ratio of the number of particles greater than a specified size in the upstream (dirty) fluid divided by the
number of the same size particles in the downstream (clean) fluid. Example: Beta10 = 75 shows that, for
every 75 particles greater than 10 microns in size entering the filter (upstream), only one particle
will not be removed. This shows this element to be 74/75 = 98.67% efficient at removing particles over
BLIND OFF Condition where the media pores are plugged or coated to the point MRF will not flow through.
A pressure filter where paper or fabric cartridges are installed inside a cylindrical housing (pressure
vessel) and the filtered liquid is pumped through the cartridge walls. Liquid flow is usually from the
outside of the cartridge wall through to the inside core - dirt is deposited on the OD of the cartridge.
These pressure vessels must be ASME coded.
A large MRF system for a transfer line or group of related machines using a common MRF and usually
machining the same metal.
CHILLER Mechanical refrigeration unit used to generate chilled water that is used to control the temperature of
MRFs used on critical machining operations.
CLARIFIER Equipment used to remove contaminant from MRF.
CLARITY Nebulous term referring to the amount of contaminant in the MRF. Clarity should include weight or volume
of particulate in parts per million (ppm). A description of particle count by size may also be
determined. A description or specification of the test method is also required.
MRF Soluble oil and water, synthetic and water, or straight oil used in machining operations to provide
lubricity, heat removal and chip flushing.
MRF SYSTEM Usually includes a clarifier, electrical controls, pumps and a trench return for chips and spent MRF.
May also include water make-up, chiller for temperature control, tramp oil skimmer, variable speed pump
System to separate light floating liquid (tramp oil) from a heavier liquid (water-soluble MRF).
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Usually a roll of non-woven fabric through which the dirty MRF is passed. This porous fabric filters the
contaminant from the MRF.
Filtering through a bed or cake of dirt (particulate) removed from the MRF as it is established on the
A decant system with a method of introducing compressed air into the MRF air. The dissolved air bubbling
up through the MRF picks up fines and improves the clarity in the submicron range.
DRAG TANK MRF tank with flight conveyor to scrape out chips that have settled. Dirty liquid flows into tank and
overflows a relatively clear liquid to the next stage in the filtration process.
EMULSIFIER A substance added to petroleum oil to form neat oil. The emulsifier allows the neat oil to form a stable
emulsion (go into suspension) with water.
FILTER A porous medium (disposable media, wedge-wire or mesh screen) through which liquid is passed to separate
and trap particles held in suspension.
Conveyor consisting of a motorized drive, (2) sections of heavy duty chain, and a series of bars or
sections of angle iron (flights) bolted between the chains at regular intervals. As the conveyor moves,
the flights are dragged across the bottom of the tank carrying accumulated contaminant out for disposal.
Similar to a drag tank, having a flight conveyor, except that the bottom is made of wedge-wire panels
(.020 to .040 inch slot width) and relatively clear liquid flows through the wedge-wire. Used primarily
on aluminum machining jobs where aluminum chips float and would not settle out in a drag tank. Flow-
through conveyors are designed to pass 75 to 100 GPM per square foot of wedge-wire panel.
HEAD Discharge pressure of a pump in feet of liquid being pumped.
HEAD x SG = psi discharge pressure
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HINGE PAN CONVEYOR
Conveyor consisting of a motorized drive, (2) sections of heavy-duty chain, and a series of pans with
pusher bars mounted between the chains. Hinge pans are used to remove bundles of stringy chips. Chips
accumulate on the hinge pan and are carried out for disposal while the MRF overflows into the filter
INDEX In automatic media filters (vacuum and flat bed), advancing the media to remove a dirty and plugged
section. In automatic wedge-wire drum and wedge-wire septum filters, to scrape the wedge-wire and remove
a portion of the dirt load that forms the filter cake.
Refers to that part of the filter upon which the contaminant is actually trapped as the fluid passes
through. Usually disposable media, permanent belt, wedge-wire, etc.
MICRON 1 = 1 meter ; 1 millimeter = 0.000039 In.
(micrometer) 1,000,000 1,000 (39 millionths of an inch)
NEAT OIL As it comes from the drum - not diluted. Usually refers to soluble oil before mixing with water to
form soluble oil and water MRF mixtures.
Rating for roll media, filter cartridges and filter bags. Nominal rating is mean flow pore size of media
- half the flow is through pores smaller than the nominal rating and half the flow is through pores
greater than the nominal rating. Not an explicit specification.
PARTICULATE Small dirt particles in MRF.
PPM Parts per million - must state test used and whether by weight or by volume.
A filter where the filtered liquid is pumped under pressure through the media. Examples are automatic
flat bed filters, cartridge and bag filters.
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Usually refers to an oil used as an MRF. Could be a mineral seal oil (40 to 50 SSU) used for honing, a
light oil (90 to 100 SSU) used for aluminum machining (valve bodies) or a heavy oil with high-pressure
additives used for broaching (250-450 SSU).
An accumulation of machine hydraulic and lubricating oils which leaks into the MRF system. Tramp oil is
the major source of soluble MRF deterioration.
TRAMP OIL SKIMMER
A device for removing floating tramp oil. Common types are endless tube, disc, belt, and decant systems.
All tramp oil removal systems require regular maintenance - systems remove fines as well as floating
tramp oil and tend to plug up. Must be installed in a still or quiescent part of the filter dirty tank.
TURNOVER TIME or
Related to particulate settling rate. The more viscous the MRF, the lower the settling rate; thus the
turnover time should be increased by increasing the system tank volume.
Flow rate gal x turnover time min = tank vol gal
Turnover time min = tank vol gal
flow rate gal
Soluble oil and water systems generally have 3 to 5 min. turnover time, while light oil systems have 7 to
10 min. turnover time.
VACUUM Negative pressure measured in units below atmospheric pressure. Normally measured in inches of mercury,
and is convertible to psi below atmospheric pressure as follows:
ATMOSPHERIC PRESSURE (Barometric Pressure)
14.7 psi x 2.31 ft. water = 33.96 ft. water
33.967 ft. water = 2.50 ft hg = 30" hg
13.57 sg hg
NORMAL INDEX PRESSURE (10" hg Vacuum)
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10" hg x 14.7 psi = 4.90 psi
4.90 psi x 2.31 ft. water = 11.32 ft water
A filter where a vacuum is created on one side of the media, usually by means of the pump suction.
Atmospheric pressure then pushes the dirty
liquid through the media.
Solid state device to control (change) frequency of AC power frequency and the fixed number of poles in
Wire drawn to a wedge shape - used primarily for strainer and filter applications. Standard materials
are the 300 series stainless steels.
Wedge-wire drums are made by spirally wrapping wedge wire over a mandrel with longitudinal support rods.
The wedge wire is automatically resistance welded to the support rods forming a drum. As the wire is
wrapped, a precise dimension is maintained between each wrap to form precision slots. Slots are usually
in .007 to .010 range for vacuum filtration applications.
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WAY OILS AND HYDROSTATIC SYSTEMS
Hydrostatic ways, used on some machines, are neither a way
application nor a hydraulic application. The oil used for this
application is continuously pumped between the moving ways and
prevents metal-to-metal contact. It actually floats the ways.
It is collected in troughs and is continuously recirculated.
Hydrostatic way systems have made it much more difficult to keep
the oil and the MRF separated. Sprayed MRF is likely to enter
the recirculating way oil troughs, thus contaminating the way
oil, and any blockage of the return troughs and lines can cause
major "dumps" of the hydrostatic oil into the MRF. The polar
additives in most way oils (used to improve stick-slip and wear
characteristics) cause any MRF contaminating the way oil to stay
emulsified. These same additives also severely destabilize
emulsifiable MRFs (by changing the HLB of the surfactant package)
if they leak into the MRF. Even if the MRF is not an emulsion,
these contaminating way oils create invert emulsions which makes
biological control of the in-use MRF much more difficult.
Many of the problems associated with hydrostatic systems could be
remedied by utilizing the appropriate oil. Other than pump
requirements, the only requirement on the oil used for
hydrostatic way applications is its hydrodynamic viscosity.
Polymers and stick-slip additives are not necessary. A primary
requirement of these oils is compatibility with the MRFs they may
eventually encounter. The oils the machine tool manufacturers
normally recommend (and the end users use) for hydrostatic
applications are way lubricants or anti-wear hydraulic oils.
Neither of these oils are compatible with emulsifiable MRFs due
to destabilization of the emulsion. Furthermore, synthetic and
low oil semi-synthetic MRFs are not compatible with most way
lubricants or anti-wear hydraulic oils; their evaporated residues
are not soluble in these oils and either foul the hydrostatic
system or dissolve/degrade non-ferrous components of these
systems. The situation is further complicated when the oil
reservoir also services a lost-lube way system1 which may place
stick-slip and anti-wear requirements on the oil.
Hydraulic applications can be categorized as either high-pressure
or low-pressure. Anti-wear hydraulic oils may be necessary to
reduce wear at pressures above 1500 psi. Anti-wear oils are
Lost-Lube system. A traditional once-through way lube system where the oil lubricates the surfaces of a vertical or
horizontal way (and associated bearing, if present) and is not recovered and recycled.
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designed to be unstable at elevated temperatures (greater than
140 degrees Centigrade). These temperatures occur at the wear
points in the system when the system is stressed. The thermal
breakdown products are not only great boundary lubricants but
they are insoluble tarry residues. The dispersants are necessary
to "disperse" these tarry residues and the demulsifiers are
necessary to demulsify any extraneous water which would also be
These dispersants and demulsifier packages impact the stability
and quality of the MRF. Higher hydraulic pressures in some of
the newer machine tools have required the use of these anti-wear
hydraulic oils that are inherently unstable.
In many plants the low-pressure applications predominate. Yet
the common adage is: "A premium oil is superior for all
applications." However, where pressures of less than 1000 psi
occur, non-anti-wear hydraulic oils are completely adequate --
and they are much less detrimental to the MRFs.
Between pressures of 1000 and 1500 psi a value assessment should
be made as to which oil, anti-wear, or R & O should be used.
Low oil semi-synthetic MRFs and synthetic MRFs are much easier to
manage than high oil MRFs, particularly in the presence of way
oils and anti-wear hydraulic oils. But their residues are not
soluble in the lubricating oils that allow the machine tool ways
and other moving parts to move uniformly. This can wreak havoc
with a complicated machine tool and cause significant downtime
and even loss of tool life. These synthetic MRF residues are
often incompatible with non-ferrous and polymeric components of
the machine tools. This effect is most predominant in areas that
are not flushed with dilute MRF -- where MRF mist may accumulate
and evaporate to a concentrate, or in the hydrostatic oil where
MRF may leak in and the water evaporate.
High oil emulsifiable MRFs prevent rust by a different mechanism
than synthetic and low oil semi-synthetic MRFs. The anionic
surfactants in the high oil MRFs attach a barrier film of oil to
the metal surface. This blocks oxygen from the surface, thus
preventing oxidation from occurring. The synthetic rust
inhibitors form a thin film on the metal surface that maintains a
pH above 8.0. Either biological growth which lowers the pH, or
concentration of salts through evaporation of water (increasing
the conductivity) will allow rust to occur. Both of these
conditions often occur where the MRF can become isolated, e.g. on
set screw threads or inside collets.
Machine tool builders should develop a basic understanding of MRF
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and lubricant composition. This knowledge should be coupled with
an understanding of the interactions with materials used to
construct the machine tool. This will allow them to select
materials that are compatible with the MRFs and lubricants. Some
of the component manufacturers are capable of helping machine
tool builders evaluate these interactions.
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METAL REMOVAL SYSTEMS MODEL TEST SCHEDULE
MRFS CLEANERS MRFS CLEANERS
CONCENTRATION DROPS TWICE WEEKLY WEEKLY
RATIO - % TWICE WEEKLY WEEKLY
TWICE WEEKLY WEEKLY
TOTAL ALKALINITY TWICE WEEKLY WEEKLY
CONDUCTIVITY WEEKLY WEEKLY WEEKLY
CHIP CORROSION MONTHLY WEEKLY
RUST INHIBITOR LEVEL WEEKLY
SOLIDS MONTHLY WEEKLY
BACTERIA WEEKLY WEEKLY WEEKLY
FUNGI WEEKLY WEEKLY WEEKLY
OPERATING LEVEL WEEKLY
FORWARD SAMPLE TO WEEKLY
METAL REMOVAL FLUID COMPATIBILITY
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A New Test for MRF Compatibility
It is difficult to know in advance whether a new MRF or additive
will be compatible with an existing system, or whether it may
cause a system failure. John M. Burke and Dawn Becher from the
Eaton Corporation, Manufacturing Technologies Center are in the
process of developing a system that can test the compatibility of
MRFs and additives in laboratory scale. Work done by Eaton has
shown that it can effectively test different MRF emulsions for
compatibility with freshly machined metals.
For this test system to work, Eaton says that you will need only
a few man-hours in the lab, samples of your actual tramp oil,
metals being machined, water used to make up or adjust the system
and similar items. Eaton, which has offered to share their
experimental protocol with any interested parties, estimates
costs to set up the test of around $3,000.
Those who are interested in this system and would like to see the
protocol should contact Mr. John Burke by fax or e-mail. Fax:
216-523-6784. E-mail: JBURKE@VINES.ETN.COM.
Material in this discussion was excerpted from an article written
by Nancy DeMarco and published in Lubes’n’Greases Magazine, June
1996, page 29.
The Impact of Metal Removal Fluids on Carbide Tools
The use of carbide tools in machining and grinding operations
should be taken into consideration when choosing a MRF. While a
variety of MRFs can be used, some cause cobalt to leach from the
metal or the carbide tool. Carbide leaching has three aspects
that should be considered:
1. Cobalt in the airborne mist or spray is suspected of causing
respiratory ailments and serious skin irritation in workers.
2. Leaching may reduce the quality, efficiency and life of the
tool as the cobalt is needed as a binder for the other
alloying elements in the hard metal.
3. Wastewater containing cobalt may be regulated because of
environmental effluent discharge regulations that strictly
limit the levels of heavy metals. Even if the material is
removed by the waste treatment, it may still be regulated and,
thus, be more costly to dispose of than other dissolved
metals. Some MRFs contain an inhibitor to prevent leaching
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which, in many cases, can be effective. Yet these inhibitors
can often be depleted over time, and cobalt will dissolve into
the MRF. At present there are a number of tests such as the
Kennametal test that are designed to test a MRF’s ability to
resist cobalt leaching. The results of these tests however
may not be an accurate reflection of what is really happening
in your MRF systems.
In 1994 the Berol Company came up with a better test they
called the “swarf test” which more accurately determines the
levels of cobalt in MRFs. This test can be a reasonably
accurate indicator of whether or not a MRF will cause leaching
of carbide. Tests performed by the D.A. Stuart Co. and an
additive supplier, Angus Chemical, found that, in carbide
grinding operations where the MRF had been in use for several
months, the carbide leaching inhibitors had been used up, and
the swarf test showed significant levels of cobalt in the MRF.
Working together, the two companies developed an MRF with a
limited ability to leach cobalt out of carbide. Initial
testing was positive, and ultimately led to production of a
commercially available synthetic MRF called Dascool Nobalt.
Information about Dascool Nobalt can be obtained from Colin
White, Product Manager (708) 655-4595. Information about
additives that inhibit cobalt leaching can be obtained from Angus
Chemical at (800)362- 2580 or (847) 215-8600. It should be
noted that most MRF suppliers have developed specific products
to avoid the leaching of cobalt from tools. Consult your MRF
supplier for more information this subject.
The material in this discussion on MRF and carbide tools was
excerpted from an article entitled: “Fluids That Won’t
Attack Carbide Tools” published in Lubes’n’Greases Magazine,
June 1996, page 17.
Compatibility: Identifying The Problem
The number one priority of any manufacturing operation is to
machine an acceptable quantity of parts at the least cost in a
safe environment. This can be accomplished only if the machining
process is designed as a total system where the elements and
their interactions are optimized. In spite of dramatic advances
in the functional design of machine tools, MRFs and process oils
(lubricants and hydraulic fluids), extensive problems have
occurred when these tools must work together. Compatibility of
all three tools in their working environment has not been
considered in their individual design. In each of these domains,
the designer demonstrates little knowledge of the other two
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areas. For this reason, the total system has flaws which cannot
be solved by singularly modifying any one of the component parts.
This article details specific examples of shop problems and their
resolution. It also details the development of the rationale
for these solutions.
In the quest for solutions it has become apparent to some Metal
Working Fluid Process Engineers (MFPEs) that the MRF, contrary to
popular perception, is not always the problem, but that the
interactions between MRFs and machine tool lubricants often
result in destabilization of both the MRF and the lubricant.
Recognition of this phenomenon has led to the realization that
all elements of the machining process - - the MRFs, the machine
tool, the lubricant, and the hydraulic fluid - - should be
considered as a total system.
IDENTIFYING THE PROBLEMS
A significant barrier to optimizing the total machining process
can be described as harmful interactions between the machine
tool, process oils (machine tool lubricants and hydraulic
fluids), and the MRF. Resulting problems, as perceived on the
shop floor, can be grouped into three types of interactions:
Between the Machine Tool and Metal Removal Fluid
1. Deep hole corrosion (set screws, collets, etc.).
2. Sticking of switches, tooling and other moving parts.
3 Corrosion of non-ferrous machine elements (electrical
components, tool holders, etc.).
4. Degradation of polymeric components of the machine tool
(seals, gaskets, etc.).
5. Decreased tool life and cut rate.
6. Softening/peeling of paint on machine tool.
Between the Machine Tool Process Oils and Metal Removal Fluid
1. Destabilization of emulsifiable MRFs contaminated with
2. Objectionable odors in MRFs contaminated with certain
3. Insoluble residues formed in some lubricants when
contaminated with MRF.
4. Evaporated MRF residues which are insoluble in the
5. Loss of lubricant tacky properties.
6. Uncontained MRF mist.
7. Uncontrollable foam.
Between the Machine Tool and Machine Tool Process Oils
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1. Insoluble residues in hydraulic and hydrostatic oil systems.
2. Attack on non-ferrous components in hydrostatic oil systems
(e.g. brass pump gears).
3. Way lubricant not functioning acceptably, inadequate
lubrication and resultant wear.
4. Over-application of way lube in lost-lube systems (once-
through lubrication systems).
5. Inadequate containment of lubricant in hydrostatic way
systems and other recirculating oil systems.
AN IDEAL COMPATIBLE SYSTEM WOULD HAVE THE FOLLOWING PROPERTIES:
MRF Used: High Oil Semi-Synthetic MRFs or High Quality Soluble
1. The evaporated MRF (without the water) should be totally
soluble in the lubricants used.
2. The MRF should provide a positive barrier film (to oxygen)
on the machine tool to prevent deep-hole and mist- actuated
3. This MRF should be extremely stable to both chemical and
Way Lubes and Hydraulic Oils Used: Non-Emulsifiable Type
1. The oils should be non-emulsifiable in the dilute MRF used
in the machine tool.
2. They must separate readily and completely from the MRF,
even after severe mechanical mixing.
3. They should be hydrolytically, thermally, and biologically
stable and designed specifically for their intended
Machine Tools Designed to Minimize Fluid Usage
1. Machine tools should be designed to minimize the leakage of
oil into the MRF and MRF into the oil reservoirs.
Machine Tools Designed from Materials Compatible with MRFs
1. Copper, aluminum and zinc should not be used where they may
come in contact with the MRF.
2. Where MRFs come in contact with metal components, potential
galvanic cells should be considered.
This discussion is based upon an article published by Douglas P.
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Hunsicker and Jeanie S. McCoy in the May, 1996 issue of
Lubrication Engineering, pp. 366-373. This article is an
excellent, in-depth discussion of some of the compatibility
problems experienced with large, flexible manufacturing systems
and how they were, at least in part, resolved. Highly
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National Center for Manufacturing Sciences
Metalworking Fluids Evaluation Guide
Section 4. Compatibility
Section 4, Compatibility, of this Guide has an excellent
discussion and references on compatibility issues. For each
criterion heading, important issues, why important, and tests
available are discussed. A listing of the criterion headings is
3. Galvanic Corrosion
5. Mechanical Properties
7. Diffusion/Capillary Action
8. Residue Formation/Removal
9. Service Performance
A copy of this document can be obtained from:
Manufacturing Information Resource Center, NCMS
Ann Arbor, Michigan 48108-3266
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FACTORS AFFECTING THE PERFORMANCE OF METAL REMOVAL FLUIDS
I. Conditions of the MRF that are important to maintain.
A. Homogeneity: The MRF should be homogeneous. If it is
composed of more than one phase (e.g. invert emulsion in MRF),
biological control can become nearly impossible.
B. Steady state: The MRF should achieve a steady state where
chemical, biological, and physical changes are minimal. This
condition must be reached to have a functional MRF maintenance
C. Appropriate chemical properties:
1. Lubrication and wear reduction.
2. Corrosion protection.
3. Biological growth resistance.
II. Contaminants causing detrimental conditions.
A. Water quality
1. Hardness (Ca, Mg, Fe, etc.).
2. Dissolved salts.
3. Biological contaminants.
4. Biological nutrients.
B. Tramp oil
1. If present, an invert (water-in-oil emulsion) provides
many discrete pockets of MRF (which are separated from
the bulk MRF) where bacteria and fungi can hide. If
significant invert (cream) is present, it can become
nearly impossible to maintain biological control of the
2. Extracts lipophilic biocides.
C. Suspended Solids
1. Adsorbs and removes components of the MRF.
2. Provides areas for isolated biological growth.
D. Dissolved Solids
1. Can make corrosion inhibition impossible.
2. Can destabilize the MRF.
E. Biological Growth
1. Biological growth destabilizes the MRF, changes its
chemical properties, and makes the system dynamic (not
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2. Biological growth also creates endotoxins which may have
the potential to cause adverse physiological reactions in
Effects of Copper on Microbial Control
The addition of copper ions to MRFs has been reported to improve
microbial control. There appear to be two modes of action for
1. The malodorous chemical compounds associated with rancidity
are compounds of sulfur or nitrogen. These compounds are
complexed by copper ions and held in the fluid rather than
escaping into the air. Microbial degradation of the fluid
continues but does not call attention to itself through odor
generation. The workplace may be more pleasant but may
actually be less healthy if exposures to high levels of
organisms result. This is of special concern in view of the
recent speculation about endotoxin exposures and
hypersensitivity pneumonitis. Emphasis should be on
preventing rancidity and odors rather than on hiding the
2. There is evidence that copper can help to prevent the
chemical degradation of some biocides in an MRF. The
ability of copper to complex with chemicals that would
otherwise react with and destroy a biocide molecule leads to
higher biocide concentrations in a fluid and, thus, an
extended trouble-free working life. There is also some
evidence that copper can act synergistically with the same
The actual benefits of copper by either mode will be limited
because copper will be depleted from an in-use fluid through
precipitation as insoluble salts or by galvanic exchange with
more electrochemically active metals like iron or aluminum. As
with biocides, to maintain the benefits of copper, it should be
added to MRF when its concentration is depleted.
Dissolved Oxygen Test for Metal Removal Fluids
A large Midwestern engine manufacturing facility uses a dissolved
oxygen test to monitor the stability of MRFs. This is an
especially useful test with several advantages:
1. It is fast and simple. Dissolved oxygen probes are readily
available and are used like a pH meter probe. This is a
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common water pollution test method. When applied to MRFs
systems it can be used on a daily basis.
2. The dissolved oxygen reading is an effective leading
indicator of bacterial concentration change. When the
dissolved oxygen concentration dips, the bacteria count is
rising and will be noticeable within a day or two. The
reading itself is not important because it depends upon many
variables unique to the metal and fluid, but the change is
the key. By the time a traditional bacteria colony test is
incubated and read, the fluid system may already be out of
control. A stable dissolved oxygen count of around 8
ppm/200C indicates minimal bacterial activity, but a drop in
dissolved oxygen can be due to chemical reactions as well as
microbial activity. It should be noted also that a modest
population of yeasts or mold can consume O2 at least as
rapidly as bacteria.
3. By getting a fast leading indicator of bacterial growth,
adjustments can be rapid and minimal. This avoids the up-
down cycle of high bacteria counts and massive bacteria
destruction which, when repeated over and over, leaves
massive amounts of endotoxin in the system.
It has been the experience of this plant that the dissolved
oxygen test is the best tool they have to control the biology of
their MRF systems. This engine plant has several large central
systems over 10,000 gallons and daily testing has avoided many
A useful discussion of things that can be done to improve
efficiency and cost-effectiveness of machining operations can be
found in the December 1995 issue of Lubes’n’Greases, p. 30. The
article, entitled “Real World Lubrication,” authored by Dan
Jones, looks at efforts by the Haliburton Energy Services Co. to
take control of their MRF systems and solve MRF-related problems.
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PROCEDURES FOR CHANGING METAL REMOVAL FLUIDS
(1) Add a biocide that will work effectively with your
contaminated (dirty) fluid and circulate thoroughly before
pumping out and disposing of the old MRF.
(2) Remove all chips and swarf from flumes, trenches, lines
(3) Add sump cleaner first, then fill the system with fresh
water and a good machine tool/sump cleaner and agitate.
Circulate this solution and high-pressure clean all
contaminated surfaces, spraying it onto machine tool surfaces
that are not wetted by the normal flow of the circulating MRF.
(4) Pump out the cleaning solution, refill with fresh water,
circulate thoroughly, and rinse off all surfaces. Dump the
rinse water and refill with fresh water, again circulating and
thoroughly washing/rinsing down all appropriate equipment.
This should be done as often as necessary to assure complete
removal of the cleaning solution.
(5) The addition of a small amount of MRF concentrate to the
rinse water may help to protect against rapid rusting while it
is being rinsed.
(6) Immediately after the last rinse has been pumped out,
refill with fresh MRF, circulate the MRF and wet those
surfaces that may rust.
A useful discussion dealing with the disposal and recycling of
used MRF can be found in the January, 1996 issue of
Lubes’n’Greases Magazine. “Zero Pollution Discharge,” written by
Nancy DeMarco, reports on progress by the Eaton Corporation in
developing a nanofiltration system for metalworking fluid
wastewater treatment. Eaton uses a membrane separation process
that can handle the waste stream from metalworking operations,
and is simple to use and install.
The September 1996 issue of Lube’n’Greases reports on “Rethinking
Recycling” (p.20), written by Lisa Tocci. The article addresses
the progress made in reclaiming used oil-based industrial
lubricants and gives some hints about what to look for in a
quality reprocessing operation.
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Another useful source of information is the National Center for
Manufacturing Sciences Metalworking Fluids Evaluation Guide,
Section 3, Environment, which discusses three issues (criterion):
contamination, disposability and waste minimization.
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SELECTED KEY ELEMENTS FROM OSHA’S FORMALDEHYDE STANDARD
29 CFR 1910.1048 revised by 57 FR 22290, May 27, 1992
(Effective date - June 26, 1992)
(a) Scope and Application
This standard applies to all occupational exposures to
formaldehyde, i.e. from formaldehyde gas, its solutions and
materials that release formaldehyde.
For purposes of this standard, the following definitions shall
apply: "Action level" means a concentration of 0.5 part
formaldehyde per million parts of air (0.5 ppm) calculated as an
eight (8)-hour time-weighted average (TWA) concentration.
"Emergency" is any occurrence such as, but not limited to,
equipment failure, rupture of containers, or failure of
control equipment that results in an uncontrolled release of a
significant amount of formaldehyde.
"Employee exposure" means the exposure to airborne
formaldehyde which would occur without corrections for
protection provided by any respirator that is in use.
"Formaldehyde" means the chemical substance, HCHO, Chemical
Abstracts Service Registry No. 50-00-0.
(c) Permissible Exposure Limit (PEL)
(1) TWA: The employer shall assure that no employee is exposed
to an airborne concentration of formaldehyde which exceeds 0.75
parts formaldehyde per million parts of air (0.75 ppm) as an
(2) Short-Term Exposure Limit (STEL): The employer shall
assure that no employee is exposed to an airborne
concentration of formaldehyde which exceeds two parts
formaldehyde per million parts of air (2 ppm) as a
(d) Exposure monitoring
(i) Each employer who has a workplace covered by this standard
shall monitor employees to determine their exposure to
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(ii) Exception: Where the employer documents, using objective
data, that the presence of formaldehyde or
formaldehyde-releasing products in the workplace cannot result in
airborne concentrations of formaldehyde that would cause any
employee to be exposed at or above the action level or the STEL
under foreseeable conditions of use, the employer will not be
required to measure employee exposure to formaldehyde.
(i) Medical surveillance
(1) Employees covered.
(i) The employer shall institute medical surveillance
programs for all employees exposed to formaldehyde at
concentrations at or exceeding the action level or exceeding the
(ii) The employer shall make medical surveillance available
for employees who develop signs and symptoms of
overexposure to formaldehyde and for all employees exposed to
formaldehyde in emergencies. When determining whether an
employee may be experiencing signs and symptoms of
possible overexposure to formaldehyde, the employer may
rely on the evidence that signs and symptoms associated with
formaldehyde exposure will occur only in exceptional
circumstances when airborne exposure is less than 0.1 ppm
and when formaldehyde is present in material in concentrations
less than 0.1 percent.
(2) Examination by a physician. All medical procedures,
including administration of medical disease
questionnaires, shall be performed by or under the supervision of
a licensed physician and shall be provided without cost
to the employee, without loss of pay, and at a reasonable
time and place.
(3) Medical disease questionnaire. The employer shall make the
following medical surveillance available to employees
prior to assignment to a job where formaldehyde exposure is at or
above the action level or above the STEL and annually
thereafter. The employer shall also make the following
medical surveillance available promptly upon determining that an
employee is experiencing signs and symptoms indicative of
possible overexposure to formaldehyde:
(i) Administration of a medical disease questionnaire, such
as in Appendix D, which is designed to elicit information
on work history, smoking history, any evidence of eye, nose,
or throat irritation; chronic airway problems or hyper
reactive airway disease; allergic skin conditions or
dermatitis; and upper or lower respiratory problems.
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(ii) A determination by the physician, based on evaluation
of the medical disease questionnaire, of whether a
medical examination is necessary for employees not required
to wear respirators to reduce exposure to formaldehyde.
(4) Medical examinations. Medical examinations shall be
given to any employee who the physician feels,
based on information in the medical disease questionnaire,
may be at increased risk from exposure to formaldehyde, and
given at the time of initial assignment and at least
annually thereafter, to all employees required to wear a
respirator to reduce exposure to formaldehyde. The medical
examination shall include:
(i) A physical examination with emphasis on evidence of
irritation or sensitization of the skin and respiratory
system, shortness of breath or irritation of the eyes.
(ii) Laboratory examinations for respirator wearers
consisting of baseline and annual pulmonary function tests.
At a minimum, these tests shall consist of forced vital capacity
(FVC), forced expiratory volume in one second (FEV1), and
forced expiratory flow (FEF).
(iii) Any other test which the examining physician deems
necessary to complete the written opinion.
(iv) Counseling of employees having medical conditions that
would be directly or indirectly aggravated by
exposure to formaldehyde, on the increased risk of
impairment of their health.
(m) Hazard Communication
(1) General. Communication of the hazards associated with
formaldehyde in the workplace shall be governed by the
requirements of paragraph (m). The definitions of 29 CFR
1910.1200 (c) shall apply under this paragraph.
(i) The following shall be subject to the hazard communication
requirements of this paragraph: formaldehyde gas, all
mixtures or solutions composed of greater than 0.1 percent
formaldehyde, and materials capable of releasing formaldehyde
into the air, under reasonably foreseeable conditions of
use, at concentrations reaching or exceeding 0.1 ppm.
(ii) At a minimum, specific health hazards that the employer
shall address are: cancer, irritation and sensitization of the
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skin and respiratory system, eye and throat irritation, and
(2) Manufacturers and importers who produce or import
formaldehyde-containing products shall provide downstream
employers using or handling these products with an objective
determination, through the required labels and MSDSs, if these
items may constitute a health hazard within the meaning of 29 CFR
1910.1200(d) under normal conditions of use.
(3) Labels. (i) The employer shall assure that hazard warning
labels complying with the requirements of 29 CFR 1910.1200(f)
are affixed to all containers of materials listed in paragraph
(m)(1)(I), except to the extent that 29 CFR 1910.1200(f) is
inconsistent with this paragraph.
(ii) Information on labels. At a minimum, for all materials
listed in paragraph (m)(1)(I) capable of releasing
formaldehyde at levels of 0.1 ppm to 0.5 ppm, labels shall:
identify that the product contains formaldehyde; list the name
and address of the responsible party; and state that physical and
health hazard information is readily available from the employer
and from material safety data sheets.
(iii) For materials listed in paragraph (m)(1)(I) capable of
releasing formaldehyde at levels above 0.5 ppm, labels shall
appropriately address all hazards as defined in 29 CFR 1910.1200
(d) and 29 CFR 1910.1200 Appendices A and B, including
respiratory sensitization, and shall contain the words
"Potential Cancer Hazard."
(iv) In making the determinations of anticipated levels of
formaldehyde release, the employer may rely on objective
data indicating the extent of potential formaldehyde release
under reasonably foreseeable conditions of use.
(v) Substitute warning labels. The employer may use warning
labels required by other statutes, regulations, or
ordinances which impart the same information as the warning
statements required by this paragraph.
(4) Material safety data sheets. (i) Any employer who uses
formaldehyde-containing materials listed in paragraph (m)(1)(I)
shall comply with the requirements of 29 CFR 1910.1200(g) with
regard to the development and updating of material safety data
(ii) Manufacturers, importers, and distributors of
formaldehyde-containing materials listed in paragraph (m)(1)(I)
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shall assure that material safety data sheets and updated
information are provided to all employers purchasing such
materials at the time of the initial shipment and at the time
of the first shipment after a material safety data sheet is
(5) Written hazard communication program. The employer shall
develop, implement, and maintain at the workplace a written
hazard communication program for formaldehyde
exposures in the workplace, which at a minimum describes how
the requirements specified in this paragraph (for labels and
other forms of warning, and material safety data sheets, and
paragraph (n) for employee information and training) will be
met. Employers in multi-employer workplaces shall comply with
the requirements of 29 CFR 1910.1200(e)(2).
(n) Employee Information and Training
(1) Participation. The employer shall assure that all employees
who are assigned to workplaces where there is exposure to
formaldehyde participate in a training program, where the
employer can show, using objective data, that employees are not
exposed to formaldehyde at or above 0.1 ppm, except that the
employer is not required to provide training
(2) Frequency. Employers shall provide such information and
training to employees at the time of initial assignment, and
whenever a new exposure to formaldehyde is introduced into the
work area. The training shall be repeated at least annually.
(3) Training program. The training program shall be conducted in
a manner which the employee is able to understand and shall
(i) A discussion of the contents of this regulation and the
contents of the Material Safety Data Sheet;
(ii) The purpose for and a description of the medical
surveillance program required by this standard, including:
(a) A description of the potential health hazards associated
with exposure to formaldehyde and a description of the
signs and symptoms of exposure to formaldehyde;
(b) Instructions to immediately report to the employer the
development of any adverse signs or symptoms that the
employee suspects is attributable to formaldehyde exposure;
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(iii) Description of operations in the work area where
formaldehyde is present and an explanation of the safe work
practices appropriate for limiting exposure to formaldehyde in
(iv) The purpose for, proper use of, and limitations of
personal protective clothing and equipment;
(v) Instructions for the handling of spills, emergencies, and
(vi) An explanation of the importance of engineering and work
practice controls for employee protection and any necessary
instruction in the use of these controls; and
(vii) A review of emergency procedures including the specific
duties or assignments of each employee in the event of an
(4) Access to training materials. The employer shall inform all
affected employees of the location of written training materials
and shall make these materials readily available, without cost,
to the affected employees.
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To return spent MRF and chips generated by the machining operations,
central systems utilize trenches (flumes) in the plant floor. To
promote MRF and chip flow, the trenches are sloped down to the
filter tank. Flush nozzles piped from the MRF system pumps are
used to assist in carrying the chips through the flumes. Flumes
are installed so the top surface of the liners and the cover
plate are flush with the surrounding floor or deck.
Flumes should be located immediately below the machine discharge chute
and should be wide enough to contain the chip and MRF discharge.
Flumes are usually supplied in standard widths of 9", 12", 15",
18", 24" and 36". Flume width should also be based on the
quantity of MRF flowing through the flumes. Flumes should be
sized and pitched to maintain an MRF velocity of 6-10 ft./sec.
depending on the material being machined.
Most flume systems are installed with a 1/8"/ft. slope to the
filter tank. Flush nozzles are installed at intervals (usually
every 20'-32' depending on the application) throughout the flume
system to move chips and maintain MRF velocity. The flume
sections at these nozzles are built so the flow from the nozzle
is discharged below the MRF flowing through the flume. Each of
these step-flush boxes results in a 2" to 2-1/2" drop in trench
The pitch of the flumes, number of step-flush nozzles and length
of the trench runs will determine the depth of the MRF pit. The
pit construction cost increases significantly with increased
depth. Deep pits usually require sheet piling and de-watering.
Pit depth can be minimized if the pit can be located in the
center of long trench runs rather than at the end.
Flumes are constructed of a 10-gage steel liner formed into a "U"
shape. The "U" type construction should transition from a round
cross-section, to a half-round, to a rectangular cross-section at
all changes in direction. Changes in direction should be
accomplished with 3 ft. (inside) radius turns. Flumes are
constructed in approximately 20-foot sections. Flume sections
should be welded water-tight (no stitch welding), including curb
angles. Section joints should be ground to provide smooth MRF
Flume cover plates are required in all areas not covered by
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machines. Covers should be made from 3/8", 1/2" or 5/8" thick
non-slip ("Slip-Not", "E-Z Weld", etc.) safety plate capable of
supporting 250 PSF. When crossing an aisle, the top of the
trench should be recessed 8 inches and a 10-gage cover welded to
the liner. Reinforced concrete is then poured over the trench to
complete the aisle.
When engineering flumes for a central system, the primary
consideration is the type of material being machined. Flume
systems are usually classified as either aluminum, cast iron or
steel. Each material has its own characteristics and related
problems. The following sections show typical requirements and
considerations for each material.
Aluminum chips are light and, therefore, easier to transport
through the flumes. While aluminum turning operations produce
some long stringy chips, they usually do not form large springy
bundles. MRF velocity should be maintained at 6-8 ft./sec.
Flush nozzles are usually spaced at 30-foot intervals with a
trench slope of 1/16" to 1/8"/ft. MRF required for trench flush
is approximately 1-1/2 to 2 GPM/ft. of trench.
Cast iron and nodular iron break up into small, heavy granular
chips which move readily through the trench if MRF velocity is
adequate. MRF velocity should be maintained at approximately 10
ft./sec. MRF required for trench flush is approximately 2 to 2-
1/2 GPM/ft. of trench. Normal spacing for flush nozzles is
approximately 20 feet.
Steel chips can vary in size and shape from very small granular
to long stringy curls on turning operations. It is the long
stringy curls which intertwine and accumulate to form large
bundles which are very difficult to move through the trench. The
problem with bundles usually starts with the machine not
discharging the chips efficiently. Often long stringy chips are
hung up in the machine discharge and are allowed to accumulate
from a number of parts before the operator manually clears the
machine. The operator usually uses a stick or rake to push the
accumulated bundle through the machine into the trench. When the
bundle is forced through the machine discharge, it compresses
until it enters the trench where it springs back out and may, at
that point, become lodged in the trench. The trench should be
wide enough to accept the bundles as they spring back out after
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MRF velocity should be maintained at 10 ft./sec. through the
trench. MRF flow required for trench flush is 2-1/2 to 5 GPM/ft.
of trench depending on the type of chips expected. Flush nozzles
are usually spaced every 20 ft., but should be located near
operations where bundles are expected.
High-Volume/Low-Pressure Trench Flushing
Recently, high-volume low-pressure end flushes have been used in
lieu of stepped flushes and flush nozzles for aluminum machining
and even ferrous fine grinding operations. This method provides
easier trench installation and fabrication with lower mist
generation. Normally, total GPM is not reduced by this method.
These systems have only high-volume MRF supply pipes at the
shallow end of each trench run; there are no intermediate flush
nozzles. The trench slope is varied from 0 to 3/8"/ft.
throughout the system to maintain 6 ft./sec. MRF velocity. These
systems have performed satisfactorily to date.
1. Piping costs are lower because there are very few flush drops.
2. Trench liners are less expensive to build because there are no
step flush boxes to fabricate.
3. Low-pressure flushing should reduce MRF misting problems and
1. If problems moving the chips are encountered at certain
operations, there are no intermediate nozzles where flow can
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A Note To Readers
Except where otherwise indicated, the material in this document
has been derived from the collective experience of ORC member
companies. Therefore, in most cases, there is no specific
reference given for a particular discussion. The discussions
contained in this “Guide” are meant to be generally useful and
informative, but no attempt has been made to produce an
exhaustive work, and no claim for completeness is made. The
subject of metalworking fluids is both interesting and large, and
much useful material is published in many different journals on a
regular basis. It would be impossible, in this document, to give
a comprehensive listing of books, articles or studies that relate
to metalworking fluids. However, as a service to readers, we
have attempted to provide an annotated short listing of useful
1. The Industrial Metalworking Environment: Assessment & Control.
Symposium Proceedings, Dearborn, Michigan November 13-16, 1995.
Sponsored by the American Automobile Manufacturers Association in
cooperation with an impressive list of organizations including
OSHA, UAW, AIHA, API, AFL-CIO, EPA, NIOSH, CMA IAMAW and ASSE,
these Symposium Proceedings are perhaps the most useful and up-
to-date collection of scientific discussions available on MRF.
The articles, shortened versions of presentations made at the
symposium, cover virtually every important issue in the
metalworking world. This 409-page volume can be purchased from
the AAMA for $50.00 U.S. or $55.00 Canada or Mexico, and $95.00
overseas. Only prepaid orders will be accepted. Send request
with check or money order payable in U.S. funds to: American
Automobile Manufacturers Association, P.O. Box 11170, Detroit,
An additional Symposium Proceedings from Metalworking Fluids
Symposium II, The Industrial Metalworking Environment: Assessment
& Control of Metal Removal Fluids will be available in late 1997.
The symposium will take place in Detroit, Michigan, September
2. Pneumonitis in the Machining Environment. A workshop
facilitated by NIOSH and sponsored by the UAW-Chrysler National
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Joint Committee on Health and Safety held January 28-29, 1997 in
Detroit, Michigan. Meeting Report: Kathleen Kreiss, M.D. and
Jean Cox-Ganser, Ph.D. Metalworking Fluid-Associated
Hypersensitivity Pneumonitis. American Journal of Industrial
Medicine 32(4) pp. 423-432, October, 1997.
BOOKS AND BOOKLETS
1. Metalworking Fluids Evaluation Guide, National Center for
“This guide was created by participants in National Center for
Manufacturing Sciences (NCMS) Project No. 17-0301, a cooperative
research project involving manufacturers of metalworking
equipment, suppliers of metalworking fluids, and end users who
depend on metalworking processes in their operations.” This
guide focuses on the many tests that are available to help users
select the right MRF for the job. The intent of the guide is to
help readers sort the tests out, choose the right ones for their
needs, and interpret the results.
At this time the Guide is available only as an industry review
copy, but the final is expected to be available early in 1997.
Copies of the Guide and the test methods listed in it can be
Manufacturing Information Resource Center
Ann Arbor, Michigan 48108-3266
2. Metalworking Fluids, J.P. Byers, Marcel Dekker, New York,
1994. An excellent, up-to-date resource on most aspects of the
use of metalworking fluids.
3. Standard Practice for Safe Use of Water-Miscible Metalworking
Fluids, ASTM E 1497 - 94, American Society for Testing and
Materials, 1994. Guidelines for the safe use and handling of
water-miscible metalworking fluids. This 4-page document covers
product selection, storage, dispensing and maintenance. Useful.
4. Ventilation Consideration for the Design, Installation and
Use of Machine Tools Using Metalworking Fluids, The Machine Tool
Safety Standards Committee of the American Standards Institute
(ANSI) B-11 Subcommittee. This document should be available by
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June-July of 1997, and can be ordered by calling 212-642-4900, or
by faxing your order to: 212-302-1286, or by mailing your order
to the address below. ANSI’s web site is:
American National Standards
Attn. Customer Service
11 West 42nd Street
New York, NY 10036 USA
5. Talking About Cutting Fluids, Castrol Industrial Lubricants,
Castrol North America.
A very helpful manual that covers the history (why needed, why
used), composition (all kinds and why used), the kinds of metals
commonly machined and the tools used, different machining
practices, and how that impacts the kind of MRF used, handling of
MRFs, and problems associated with MRF contact. Clearly written
and only 30 pages long, this booklet has a wealth of useful
information for both the accomplished machinist and the novice.
To obtain a copy of this booklet, write to Castrol North America,
1001 West 31st Street, Downers Grove, Illinois 60515. Highly
6. Guide to MRF System Maintenance and Management, E.F. Houghton
& Co., Madison & Van Buren Avenues, Valley Forge, Pennsylvania
19482. A thorough discussion of all the factors that go into the
care and maintenance of MRF systems. Clearly written, with many
useful photos, this booklet is a great source of practical
information on what affects the quality and life expectancy of an
MRF, and what is necessary to maintain its efficiency. Highly
7. Biology and Your Metalworking Process, E.F. Houghton & Co.,
Madison & Van Buren Avenues, Valley Forge, Pennsylvania 19482.
An insightful discussion of the dynamics of the biological system
that is always present in MRFs, and how to understand and control
the growth of microorganisms. Highly recommended.
8. Cutting and Grinding Fluids: Selection and Application,
Silliman, JD ed:, Second Edition. Dearborn, MI.: Society of
Manufacturing Engineers (1992).
9. Introduction to Metalworking Fluids: Industrial
Formulations, Components, Contaminants and Additives,
Steigerwald, JC; JK Howell, and WE Lucke: ILMA: Alexandria,
10. Dermatitis in Machinists, Bennett, EO: Angleton, Texas:
Biotech Publishing (1993).
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11. Industrial Ventilation: A Manual of Recommended Practice,
22nd Edition. American Conference of Governmental Industrial
Hygienists, 1330 Kemper Meadows Drive, Cincinnati, Ohio 45240,
phone: (513) 742-2020. This is the industrial hygienists’
ventilation “bible” and contains much useful and practical
information on the design, operation, and testing of effective
industrial ventilation systems. This valuable resource can be
purchased from the ACGIH at the above address for $55.00.
12. Shop Guide to Reduce the Waste of Metalworking Fluids. A
Competitive Advantage Manual for the Metal Fabricating and
Machining Industry, the Institute of Advanced Manufacturing
Sciences, (800) 345-4482, and the Waste Reduction and Technology
Transfer Foundation, (205) 386-3869. This manual has been
produced to assist metalworking and metal fabrication companies
to meet new standards for waste disposal and to show how a
company may decrease the amount and type of wastes it may need to
discharge. Offering a wealth of practical information on the
effective management of all aspects of the use of metalworking
fluids and lubricants, this document will be particularly useful
for companies involved in broaching, turning, milling, threading,
tapping, drilling, forming, stamping, drawing and honing. “The
right to copy, in part or as a whole, with appropriate credit is
freely given.” The language used is simple and easy to
MAGAZINES AND JOURNALS
1. Lubes’n’Greases. Published monthly, this magazine is aimed at
the producers and users of industrial lubricants of all kinds,
including MRFs. Well-written, with solid coverage of all
segments of industry, Lubes’n’Greases reports on cutting edge
technology development, systems management, industry standards
and trends, and government regulatory efforts. Most issues have
at least one article related to some aspect of MRFs. Highly
recommended. Lubes’n’Greases staff can be contacted at 2809
North Brandywine Street, Arlington, Virginia 22207 USA. Phone:
(703)-532-8240, Fax: (703) 532-5694.
2. Lubrication Engineering. Journal of the Society of
Tribologists and Lubrication Engineers.
A professional journal with useful information on both the
scientific/technical and practical aspects of MRF development and
3. Compoundings. Published by the Independent Lubricant
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Manufacturers Association, Compoundings is directed toward
producers and users of industrial lubricants, including MRFs.
For more information contact the Independent Lubricants
Manufacturers Association, 651 South Washington Street,
Alexandria Virginia 22314.
1. Criteria for a Recommended Standard: Occupational Exposures
to Metalworking Fluids (Draft). U.S. Department of Health And
Human Services, Public Health Service, Centers for Disease
Control and Prevention, National Institute for Occupational
Safety and Health, Division of Surveillance, Hazard Evaluations
and Field Studies, Education and Information Division, Division
of Physical Sciences and Engineering, Division of Respiratory
Disease Studies, February 1996. The final version of this
document should be available by September 1997, and can be
Publications Dissemination, EID
National Institute for Occupational Safety and Health
4676 Columbia Parkway
Cincinnati, Ohio 45226
2. 29 CFR Part 1910. 1048, Occupational Exposure to Formaldehyde;
57 FR 22290, May 27, 1992. Occupational Safety and Health
Administration, (OSHA) 200 Constitution Avenue, N.W., Washington,
D.C. 20210. Virtually all documents published by OSHA over the
last five years can be accessed through the Department Of
Labor/OSHA web site: http://www.osha.gov.
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