Recommended Techniques for Washing Glass

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					    Glass Technical Document                                                           TD-144

           Recommended Techniques for Washing Glass

Prologue                                              Whatever the job and whichever glass
                                                      product is chosen, the attractive and efficient
This document is a reproduction of the
                                                      use of glass requires a clean glass surface.
original publication, with only minor
                                                      With more than 120 years in glass
changes and updating.         The original
                                                      manufacturing and fabrication, PPG offers
publication was introduced over 20 years
                                                      the recommendations in this document to
ago and remains one of the most requested
                                                      assist glass fabricators successfully wash the
and helpful resources on techniques for
                                                      glass products that PPG is pleased to furnish
washing glass. While most of the principles
                                                      them. The included recommendations are
and recommendations for the machine
                                                      based on detailed research, years of first-
washing of glass remain applicable, Table 1
                                                      hand production experience, and work in
has been deleted, since the glass cleaning
                                                      solving hundreds of customer related glass-
product information shown was obviously
                                                      cleaning problems.
dated. In addition, the introduction of new
performance enhancing low-e coatings, such            Included in this document is a detailed
as Solarban® 60, Solarban 70, Solarban 80             review of:
Solarban z50 coated glass, have led to
                                                          x    Dirt types that affect glass
additional recommendations that are noted
in this update.                                           x    Glass surface protection
Introduction                                              x    Water and detergent requirements
                                                          x    Mechanical washers
The durability and beauty of glass, coupled
with its transparency, make it one of the                 x    Prewashing
world’s most utilized building materials.                 x    Requirements for Low-E glass
Glass allows light to enter the building,                 x    Washing system maintenance
while providing protection from the
                                                          x    Troubleshooting
elements. And, it allows occupants the
connection to the outside environment that
                                                      Glass Surfaces: Cleanliness & Protection
has been proven to improve morale and
productivity.                                         Because dirt negatively affects glass
                                                      undergoing any type of processing, glass
Glass is available in a wide variety of tints         surfaces must be clean. Proper cleanliness
that provide aesthetic variety, as well as            requires that the glass surfaces be washed
improved energy efficiency and occupant               effectively.
comfort. In addition, aesthetics, comfort
and energy efficiency can be further
enhanced through the use of the many types
of coatings that have been developed for
application to the glass.

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                                        PPG Industries, Inc.
    Glass Technical Document                                                              TD-144

When glass is “dirty”, both its aesthetic and            units, or for fabricators who coat, temper, or
performance quality may be diminished. If                etch glass and require exceptional glass
dirt is not removed effectively, it will inhibit         cleanliness prior to final processing.
processes where the adhesion of other
materials (sealants, coatings, etc.) to glass is         Dirt on glass surfaces can be grouped into
necessary. For example, when glass is used               four general categories:
for mirror and architectural coating                         x    particulates
applications, the surface must be clean in
order to permit metals or metal oxides to                    x    surface residues
bond to the glass. Insulating glass                          x    reaction contaminants
fabrication processes require clean glass for                x    surface corrosion
the sealants to adhere properly to the glass,
since this bond provides the required long-              Glass fabricators usually encounter only the
term performance of the hermetic seal.                   first two types of dirt and these will be the
Glass processes such as heat-strengthening,              primary focus of this document.
tempering, and bending require clean glass               Particulates are solid materials, loosely
to minimize bull’s-eyes distortion, burn, and            deposited on the glass surface, that can best
other “dirt” influenced effects.                         be removed with non-abrasive mechanical
                                                         methods such as a high pressure water
                                                         spray. Typical glass surface particulates
What Makes Glass Dirty                                   include paper interleaving fibers, acrylic
“Dirt” on glass can best be defined as “any              beads, wood flour and other powder
unwanted material on the glass surface”.                 interleaving materials, glass handling chips,
Consider glass interleaving, for example.                wood splinters, cardboard pieces, and other
Interleaving materials are essential for the             packaging materials. See Figure 1 for an
protection of glass surfaces and coatings                example of a typical particulate.
during transport and storage. However,                   Surface residues are contaminants that may
when glass is prepared for any fabricating               be cleaned from glass using detergent
process, the interleaving becomes an                     washing solutions and/or mechanical
unwanted contaminant, or “dirt”, that must               scrubbing techniques. Examples of such
be removed from the glass surface.                       residues are fingerprints, paper scum, and
                                                         cutting oils. An example of paper scum is
The degree of “dirtiness” or cleanliness of              shown in figure 2.
glass that is acceptable is dependent on the
end-use of the glass. For example, glass
cleanliness that is sufficient for picture
frame applications (in which the surface
remains accessible for repeated future
cleaning) may not be acceptable to the
insulating glass fabricator, who permanently
seals glass surfaces within insulating glass

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                                           PPG Industries, Inc.
    Glass Technical Document                                                              TD-144

Reaction Contaminates are more tenacious               inventory, and practice stock rotation. With
than surface residues and may physically or            the increased use of MSVD low-e products,
chemically bond or interact with the glass             such as Solarban 60 low-e coated glass, the
surface. For this reason, their removal may            proper storage of glass inventory becomes
require chemical “undercutting” with a                 even more important, as these types of glass
cleaning solution tailored for specific                are more sensitive to moisture.
dissolution or bondbreaking.                           In its initial stage, glass surface corrosion is
Hard-water salts are a commonly                        visible only under critical light (or
encountered reaction contaminant. In some              occasionally after coating application) and
parts of the country, water supplies contain           cannot be observed by the naked eye. At
                                                       this stage, with uncoated glass, it may be
large quantities of inorganic compounds. If            possible to remove the corroded glass
glass is washed with this water, care must be          layer(s) with an abrasive such as cerium
taken to rinse the glass surfaces thoroughly           oxide. Obviously, coated glass that is
with demineralized water before drying or              corroded – even in its earliest stage - cannot
further processing (coating, tempering, etc.).         be cleaned without destroying the coating.
The use of demineralized water to rinse the
glass will prevent the deposition of hard-             Once glass corrosion becomes severe, a
water salts that may be visible in the final           heavy blue or white stain is visible on the
product. If hard water is allowed to dry on            glass surface, the glass matrix has
glass surfaces, the chemical nature of these           undergone degradation, and glass
salts may require the use of off-line cleaning         transparency cannot be restored. The only
with acid solutions for their effective                practical remedy at this stage of surface
removal. This type of aggressive cleaning              damage is to replace the glass.
may not be safe, environmentally correct, or
economically feasible in a production                  Figures 1 – 4 are examples of the different
environment. In addition, with coated                  types of “dirt” discussed.
glasses, such cleaning procedures will most
likely lead to coating damage.
Surface corrosion is not really a type of
“dirtiness”, although a corroded glass
surface will exhibit a semi-opaque
appearance that can be and often is mistaken
for deposited dirt. Surface corrosion is an
irreparable physical degradation of the glass,
usually resulting from inappropriate storage
conditions of high temperature and
humidity. To prevent surface corrosion,
PPG strongly recommends that customers
store glass properly, maintain a detailed

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                                         PPG Industries, Inc.
Glass Technical Document                                                      TD-144

                                           Figure 1 – Particulates
                                           A magnified (40x) view of particulates
                                           removed from incoming primary glass
                                           by a prewash system. Interleaving
                                           beads and glass chips are seen here.

                                           Figure 2 – Surface Residue
                                           Typical paper scum on glass (note the
                                           duplication of the paper ridges and
                                           wrinkles in the scum pattern.) This
                                           residue can be removed using a 50/50
                                           isopropanol alcohol and water mixture,
                                           or a detergent solution.

                                           Figure 3 – Reaction Contaminant
                                           Acid rain/masonry/glazing material
                                           run-down on the glass surface.
                                           Removal requires an acidic solution, or
                                           may not be practically possible.

                                           Figure 4 – Surface Corrosion
                                           Glass corrosion is typically caused by
                                           prolonged exposure to high humidity
                                           and temperature and is often not

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                           PPG Industries, Inc.
    Glass Technical Document                                                          TD-144

PROTECTING GLASS                                      MECHANICAL GLASS WASHING
To protect glass surfaces from corrosion and
                                                      The key elements involved in mechanically
scratching, a chemical and physical barrier           cleaning glass are:
must be maintained between adjacent lites
of glass when stacked for shipment and                    x    Water Quality
storage. This dual function is performed by               x    Detergent
an interleaving material. While other types
                                                          x    The Washer System
of interleaving (such as paper) are still
occasionally used, the major form of                  All of these critical elements must be
interleaving currently used in the flat glass         carefully selected so that they will work
industry for uncoated glass consists of               together effectively to clean the glass.
plastic beads to provide the physical                 Water
separation, combined with acidic corrosion
inhibitors on the glass surface. With PPG             Water is the foundation of the washer
MSVD coated glass, corrosion inhibitors               system. Used at high pressures, it physically
are not applied to the glass. Interleaving            removes particulates. When mixed with an
consists of only the plastic separator beads.         appropriate detergent, it removes surface
                                                      residues, acts as a “lubricant” between the
PPG’s powder interleaving (with or without            washer brushes and the glass surface, and
the corrosion inhibitors) is compatible with          ultimately carries away dirt and debris.
mechanical packing, which reduces
packaging related glass surface issues such           Because water plays many important roles
as scratches, handling chips and packing              in the cleaning system, water quality is
rubs encountered with manual packing                  critical. Water used in glass cleaning should
procedures. The powder interleaving is also           have minimal turbidity (solid material
compatible with automated “pick”                      content), and a suitable hardness or softness
equipment used by many glass optimizer                for two reasons:
                                                          x    To allow detergent dissolution and
At some point in glass processing, any                         easy rinsing
interleaving becomes an undesirable surface               x    To prevent build-up of excessive
contaminate that must be removed. Powder                       washer scale
interleaving can be removed by cleaning
procedures previously recommended for                 If required, water treatment equipment
particulate contaminants, namely, non-                should be installed to furnish water with
abrasive mechanical action (e.g. high                 suitable quality. The initial investment will
pressure water spray). The water soluble              ultimately provide more efficient glass
corrosion inhibitors will dissolve and be             cleaning and reduce the potential for the
carried away, along with the separator beads          formation of reaction contaminants on glass

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    Glass Technical Document                                                              TD-144

Appropriate filters installed on main water             the washer, since such water minimizes or
supply lines and within the wash system                 eliminates the possible streaking/spotting
flow lines will remove inherent water                   that occurs from mineral residue deposits.
turbidity and internally generated washer               However, this type of water treatment
debris (broken brush bristles, scale, glass             sometimes increases water corrosiveness
chips, etc.). Based on PPG production                   that may damage some metal parts in the
experience, a 25 micron replaceable                     washer. PPG recommends that the washer
cartridge filter is recommended. These                  manufacturer be consulted prior to installing
filters will reduce glass surface scratches,            and using such water treatment systems.
recontamination in the washer, and lower
                                                        Generally, heated rinse water provides a
the incidence of nozzle blockage from water
                                                        more effective rinse and facilitates drying.
borne particulates.
                                                        However, rinse water should not be heated
The pH (acidity/alkalinity) of the water used           beyond 140°F. and, if the rinse water is
in the wash section of glass washers will be            treated, it should not be heated beyond
altered if a detergent is used. Therefore, the          110°F.
pH range of the incoming wash water cannot
be practically specified. However, PPG has
traditionally recommended that detergents               The use of a detergent, while recommended,
be used that maintain a wash solution pH                is not necessary in all washer systems.
that is slightly acidic to achieve the best
                                                            x    Surface residues are removed most
glass cleaning. While this recommendation
                                                                 effectively with detergent solutions,
remains valid, there are detergents that yield
                                                                 not plain water.        In addition,
slightly basic solutions that are successfully
                                                                 detergents decrease the potential for
used. Detergents that yield a pH of 11 or
                                                                 glass surface scratching in washing
higher should be used with care, as they can
lead to scale and deposits in the washer, as
well as on the glass. If a water soluble                    x    It is important that the correct
cutting fluid is used, the use of a detergent is                 concentration of detergent in water is
not always necessary.                                            used for the wash solution. Most
                                                                 detergent suppliers recommend
Warm water dissolves detergents more                             optimum concentrations for their
readily, and enhances cleaning efficiency.                       products.
Wash water temperature recommendations                      x    Introducing       detergents     into
for various washer equipment is typically in                     previously water only systems will
the 100 to 140°F. range.                                         initially liberate accumulated dirt
The rinse section water quality is extremely                     and scale. Therefore, it should be
important because it is the last liquid to                       done during non-production periods.
contact the glass before final processing.                       Draining and refilling the wash tank
The use of water treatment systems such as                       may have to done more than once in
reverse osmosis (RO) or Deionized (DI) is
recommended to provide high quality, low
mineral content water to the rinse section of

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                                          PPG Industries, Inc.
    Glass Technical Document                                                           TD-144

order to “flush out” the system before                         acidity)?      Does the resulting
beginning actual production processing.                        discharge comply with local, state
                                                               and federal EPA requirements? Will
There is no universally effective glass
                                                               it be necessary for washer personnel
cleaning detergent! A detergent that works
                                                               to wear protective equipment
well at one facility may be inappropriate at
                                                               (gloves, face shield, etc.)?
another due to differences in water hardness
or temperature.         Therefore, specific               x    Local Availability: Is the detergent
detergent    recommendations       are    not                  locally or readily available, or is a
practical. Rather, trials by the fabricator                    large inventory required?
will provide more specific results and useful
                                                          x    Supplier reliability:       Will the
information for his operation.
                                                               supplier go out of business or change
For a given water type and operating                           the detergent formulation without
temperature, the selection of a suitable                       notifying customers?
detergent requires answers to the following
                                                      In general, acidic detergents are more
                                                      readily rinsed from glass surfaces than
   x   Solubility: Will the detergent foam            those that are basic (or alkaline).
       excessively in your washer?        A           However, acidic detergents may cause
       quick, easy method to screen                   etching of some metal components of the
       detergents         for       foaming           washer, and perhaps an all-stainless steel
       characteristics involves pouring 50cc          construction would be required.        PPG
       of a one-percent detergent solution            recommends that the washer manufacturer
       into a 250cc graduated cylinder,               be consulted to determine if this acid
       agitating vigoursly, and observing             condition will have an adverse effect on the
       the resulting foam volume. For a               washer equipment.
       low-foaming detergent, the total
       foam volume should not exceed                    Some coated glass products may be
       80cc.                                            acid (or base) sensitive and require
   x   Rinsing Characteristics: If a small              special detergent consideration. See
       (12” x 12” is suitable) glass sample             Precautions for Coated Glass on p. 17
       is hand washed with a one-percent
                                                      After a detergent has been selected, PPG
       detergent solution, is excessive
                                                      recommends trial runs in the washer. Full
       rinsing necessary to remove all
                                                      scale production should not be attempted
       traces of the detergent?
                                                      until the user is satisfied from these trials
   x   Environmental/Safety                           that the detergent will perform satisfactorily.
       Considerations: Does the chemical
                                                      Detergents that are currently in use in the
       composition of the detergent serve
                                                      fabricator’s washer may be perfectly
       the      specific    environmental
       requirements     for your    water
       treatment area (e.g., phosphates,

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                                        PPG Industries, Inc.
    Glass Technical Document                                   TD-144

While PPG continues to recommend the use
of detergents, the increased use of MSVD
low-e coated glass products (Solarban 60,
Solarban 70, etc.) has allowed many
fabricators to successfully clean glass
without the use of detergents. As previously
mentioned, PPG’s MSVD coated glass
products are shipped with only the separator
beads as interleaving. The glass is typically
very clean when it is shipped and does not
typically remain in inventory, either at PPG
or the customer’s shop, for extended
periods. In addition, the glass may be
protected with a plastic wrap, which
minimizes incidental accumulations of dirt
and contaminants. For these reasons, a
detergent free wash can be successful,
provided that the washer is well maintained
and adequate water flow is used. The use of
high quality, low mineral content water in
the rinse section is recommended for all
glass, but it is critical when processing
PPG’s MSVD low-e coated glass products.
It is important to understand that
detergents that are used be evaluated for
compatibility with PPG’s MSVD low e
coated products. PPG offers a behavioral
evaluation of the detergent as a service to
its customers.
The following detergents have           been
evaluated and found to be acceptable:
   x   Dart 210
   x   Billco Glass Washing Detergent
   x   Basic H
   x   I.G.S. 55:1
   x   Sommer & Maca Low E Detergent
   x   Buckeye Blue

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    Glass Technical Document                                                          TD-144

                                                        Mechanical brush action may be
                                                        detrimental to PPG’s MSVD low e
 Automatic glass washers cannot
                                                        coated glass that may be easily
 remove all water insoluble surface
 residues. Sometimes, identification of
 a contaminant’s chemical nature can                    PPG recommends that brushes with a
 save production time wasted by                         bristle diameter between 0.006” and
 repeatedly washing glass in attempts to                0.009” be used to process its MSVD
 remove such residues. For example,                     low e coated glass. In addition,
 deposition of an adhesive from tape or                 brushes must be properly adjusted to
 a label on glass surfaces may require                  avoid excessive brush contact.
 special off-line pre-cleaning with                     The washer conveyer system should
 organic solvents to remove this water                  never be stopped while these coated
 insoluble tacky residue prior to line                  glasses are beneath the brushes.
 washer entry.                                          See “precautions for Coated Glass on
                                                        p. 17
Automatic glass washers are designed to
remove water-soluble surface residues.
These washers consist of a detergent                  While a typical glass washer is appropriate
application (or washing) section, one or              for cleaning surface residues from glass,
more rinse sections, and a drying section             particulate “dirt” can cause significant
(e.g., air knives). In the washing section of         system problems, especially in re-circulating
a system, cylindrical or oscillating cup              washers that are not equipped with
brushes provide mechanical action that                appropriate water-flow filters.         Glass
operates with the detergent’s chemical                handling chips or other gritty particulates
action to clean the glass.                            that enter the washing section will be
                                                      mobilized on the glass surface by the washer
Optimum washer performance requires                   brushes causing scratches.       Even non-
proper glass loading. Glass spacing should            abrasive particulates pose a problem as they
be greater than the roll circumference.               accumulate on washer brushes and in
Conveyer speeds should provide suitable               solution    tanks,    decreasing     cleaning
washer dwell time, and conveyors should               efficiency and increasing the need for
not be stopped while glass is under the               washer maintenance.
brushes or air knives. In fact, it is best to
not stop glass in any part of the washer.

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                                        PPG Industries, Inc.
    Glass Technical Document                                                             TD-144

PPG PRE-WASH SYSTEM                                     glass forms narrow streams and channels).
                                                        Second, the detergent solution decreases
Recognizing the need to optimize washer
                                                        attractive forces the particulates may have
performance by preventing particulate entry,
                                                        for one another (e.g., interleaving plastic
PPG conducted research in glass cleaning
                                                        bead static charges) or for the glass surface
that led to the development of a simple,
                                                        or system components. This facilitates
compact, economical washer add-on that is
                                                        particulate removal and ultimate disposal.
called the “pre-wash”.
                                                        There is no minimum specified time that the
Just as optimum performance is obtained
                                                        detergent must remain on the glass to
from automatic dishwashers by rinsing solid
                                                        accomplish these actions, which are
foods from dishes prior to loading the
                                                        instantaneous. Glass surfaces do not have to
washer, the pre-wash system provides
                                                        soak in this solution, since its purpose is to
optimum glass washer performance by
                                                        “wet”, not clean; therefore, the distance
effectively removing all particulates from
                                                        between the detergent pipe and high
the glass surface prior to entry into a
                                                        pressure rinse can be as little as 24 inches.
standard line washer.
                                                        Any typical glass-cleaning detergent
The PPG pre-wash is a two-phase system.                 designed for the production line washer may
In the first phase, a dilute detergent solution         be used for this pre-wash wetting solution.
is applied to the glass surface, as shown in
                                                        If the pre-wash is installed on a production
Figure 5. In the second phase, this detergent
                                                        line that is not continuously loaded with
residue and particulate debris are removed
                                                        glass, the wetting detergent delivery system
with a high pressure, filtered water rinse,
                                                        can be designed to conserve detergent
also shown in Figure 5.
                                                        solution by the installation of a feedback
Figure 6 provides a schematic of the PPG                loop, conveyor limit switch, and solenoid
pre-wash system.                                        valves. The detergent solution will then
The dilute, filtered detergent solution can be          pump through hoses, bypass the delivery
applied with a low pressure (10 to 15psi)               pipe, and return to solution holding tanks
spray as shown in figure 7, or a gravity-feed           when no glass is on the conveyor. When
drip pipe. The choice depends on conveyor               glass moves under the delivery pipe, the
line speed. The detergent solution must                 limit switch activates solenoid valves to
completely cover (wet) the glass surface. If            close the bypass circuit and divert the flow
conveyor speeds are slow enough to                      of solution into the pipe, spraying the glass
accomplish this coverage through drip-pipe              surface.
application, no pumps are necessary.                    In the second phase of the pre-wash shown
Detergent solution application is essential to          in figure 5, the glass enters a metal sheeting
the pre-wash system.         It serves two              enclosure fitted with spray-pipes delivering
purposes. Most important, it “wets” the
glass so that the following high pressure
water rinse will flow readily over the entire
glass surface (plain water applied to dry

                                            Page 10 of 19
                                          PPG Industries, Inc.
    Glass Technical Document                                                           TD-144

filtered water at a pressure of around 150            *Prewash parameters relating to pipe
psi.     If water is recirculated in the              position/alignment, nozzle spray pattern,
production washer that follows the pre-               orfice size and spacing, etc. are given as
wash, it may be necessary to place a high             guidelines based on PPG experience.
pressure pipe below the conveyor to remove            Since all line configurations vary for a
the few particulates that transfer to the             given production facility, experimentation
bottom surface of the glass during stacking.          with these parameters must be conducted
This prevents the potential accumulation of           to devise the most effective system for a
these particulates in a re-circulated system.         specific installation.
Otherwise, one or two high pressure pipes
                                                      When the pre-wash water is discarded, it can
spraying only on the glass top surface will
                                                      be included with all other plant effluent for
suffice for the pre-wash on a line with a non
                                                      normal sewage disposal. The particulates
re-circulating washer.
                                                      suspended in the water will require normal
Water used in the high pressure spray may             solid-waste treatment (as would cerium
be from any convenient source (well, tap,             oxide, for example).       If operators are
washer rinse overflow), as long as it is              concerned with particulates in their effluent,
filtered through at least a 25 micron                 a screen (or tandem series of screens) can be
replaceable cartridge filter before being             placed beneath the high pressure enclosure
pumped through the delivery pipes. This               to retain solid matter rinsed from the glass
room temperature water must be particulate-           surfaces.     Based on the particle size
free to prevent glass surface recontamination         distribution of PPG’s typical powder
and nozzle blockage. If the water source is           interleaving, a 120-mesh screen will retain
acidic (e.g., some demineralized water),              approximately 99 percent of this material for
stainless steel pipes, nozzles, and pumps are         alternative disposal. These screens should
recommended to prevent corrosion of these             be installed so that they can be easily
system components.                                    removed for cleaning as necessary. These
                                                      effluent collection methods are not
The spray pipes shown in Figure 8 in the              necessarily complete or comprehensive.
high pressure enclosure are mounted 3 to 4            EPA, state and local requirements should be
inches* from the glass surface in an                  considered before dumping any effluent.
orientation to provide the spray with a 45
degree angle of incidence with the incoming           There are no brushes in the pre-wash
glass surface. Stainless steel nozzles (fan           system. They are unwarranted since the
type 65 to 110 degrees, orfice diameter               system performs well without them. More
0.026 inch) are suitable for use in both the          importantly, particulates can collect on a
detergent and high pressure spray pipes.              brush and re-deposit on a glass surface,
These nozzles are spaced on 3 or 4 inch               defeating the purpose of the pre-wash.
centers across the width of the conveyor.             Use of a pre-wash system provides a debris-
                                                      free glass surface for subsequent line washer

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  Glass Technical Document                                                                    TD-144

Figure 5 – Pre-wash System in Operation. Detergent Application and High Pressure Rinse sections.
Distance between detergent and rinse sections is for clarity only; they can be as little as two feet apart.

                                Figure 6 – Schematic of Pre-Wash System

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Glass Technical Document                                                   TD-144

               Figure 7 – Close-up of Low Pressure Detergent Application

                Figure 8- High Pressure Section of the Pre-Wash System

                                    Page 13 of 19
                                  PPG Industries, Inc.
    Glass Technical Document                                                         TD-144

    RECOMMENDATIONS FOR                               Main Line Washer
        MAINTENANCE                                     Note:
Routine maintenance of all washing system               The best source for maintenance
components is essential for providing                   requirements and procedures is from
optimum glass cleanliness. While some                   your equipment manufacturer. PPG
maintenance functions will be performed on              offers the following recommendations in
a demand basis, others should be scheduled              good faith and in an effort to provide
periodically or in response to production               some useful information, NOT as a
volume.                                                 replacement      for    the equipment
                                                        manufacturer’s recommendations.
PPG’s recommended pre-wash system                     Daily
requires only three basic maintenance                    x Replenish the detergent and rinsing
procedures:                                                 tanks with fresh solution and water
1. Filter cartridges on detergent solution               x Rinse out inline filters (Replace as
   and high pressure water lines must be                    necessary)
   changed whenever exhausted. Filter
                                                         x Check rubber rollers and ensure that
   replacement frequency is based on
                                                            they are free of dirt and oil
   several parameters, including supplier
   recommended       pressure    differential            x Check spray pipes to ensure that they
   across filter sumps, visual filter                       are not clogged
   inspection, or as dictated by production           Weekly
   experience.                                           x Replace air filters in the airknife
2. Occasional cleaning or replacement of                    blower unit
   blocked or corroded nozzles may be                    x Clean the spray pipe nozzles
   required; a visual system inspection will             x Clean airknife slots
   generally reveal the need. If nozzles are
   not stainless steel, a general system                 x Lubricate necessary components per
   pressure drop may occur after prolonged                  manufacturer’s guidelines. Avoid
   production. This pressure change could                   lubricant contact with pinch rolls
   indicate     aperture    corrosion     or          Monthly
   enlargement.                                          x Clean all water pipes with a wire
3. For a pre-wash system using re-                          brush
   circulating high pressure rinse water,                x Thoroughly inspect all moving parts
   holding tanks must be drained and rinsed              x Completely clean the washer, inside
   at least every 24 hours.                                 and out, with a high pressure washer.

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If production problems occur that seem
related to glass cleanliness, an unscheduled
check of some or all of these system
parameters may be indicated. In addition, a
quick     reference    to    the   following
troubleshooting guide may prove helpful.
There are a variety of washer associated
cleaning defects that can be readily resolved
by taking appropriate corrective action.
The guide shown on p. 16 is provided as a
convenient reference for locating potential
causes of observed washer system-related
defects. Although this guide is based on
PPG’s experience and is offered in good
faith, it is only a guide. PPG cannot accept
any responsibility for its effectiveness in
solving specific individual glass washer
problems. PPG recommends that the guide
be used to supplement the manufacturer’s
instructions for washer operation.
When production rejects occur, an effort
should be made to examine glass that has
passed through the line washer, but has not
yet experienced further processing. If this
examination reveals any of the glass
conditions listed below, the corresponding
potential causes should be investigated.
This procedure should identify those
production problems originating in the
washing section of the processing line.
Since abnormal surface conditions on
incoming glass (i.e., stain or corrosion) will
also be discerned in this examination, these
have been included in the list of potential

                                           Page 15 of 19
                                         PPG Industries, Inc.
Glass Technical Document                                                                                 TD-144

                                   General Troubleshooting Guide

        Observed                          Primary
     Glass Condition                  Potential Causes                                     Key
                                                                     a - Air Knife: poor alignment insufficient
Washing has failed to remove                                             air velocity
spots/streaks of dirt visible on   d, g, j, k, o, p, r, w            b - Air Knife: dirty filters and/or ductwork
glass as received                                                    c - Air Knife: conveyors stopped while
                                                                         glass under blowers
                                                                     d - Brushes: dirty, poor contact, non-uniformly
Surface scratches                  e, k, n, o, q
                                                                         worn, losing bristles
                                                                     e - Conveyor Rolls: dirty
Washing       has  deposited                                         f - Conveyor Loading: glass too close together
                                   b, d, e, h, I, m, n, o q, s,
particulate contaminants on                                          g - Conveyor Speed: too fast
                                   t, u
the glass surfaces                                                   h - Detergent: too much being used
                                                                     i - Detergent: solubility/rinsing inappropriate
                                                                         for water conditions
Water droplets on surface(s)       a, f, g, t
                                                                     j - Detergent: substandard cleaning capability
                                                                     k - Detergent – none in use
                                   a, b, e, f, g, h, I k, l, m, n,   l - Detergent: contains de-foaming agent
Spot defects on surface(s)
                                   o, p, r, s, t, u, v, w, x         m - Detergent: recent change to new detergent
                                                                         causing release of accumulated dirt (scale)
                                                                     n - Filters (Pre-wash, Washer, Air Knife):
Surface streaks that are                                                 expended, wrong size, or not in place
                                   a, b, c, h, i, k, l, m, n, o,
random in occurrence and                                             o - Nozzles     (Pre-wash,     Washer,     Rinse):
                                   p, r, s, t, u, v, w, x
orientation                                                              blocked      or   corroded     Resulting    in
                                                                         insufficient    water Volume or velocity
                                                                     p - Organic solvent pre-cleaning necessary to
Relatively uniform surface                                               remove water insoluble contaminants
streaks oriented parallel to       b, d, e, o, s, u                  q - Particulate contamination of washer system
direction of glass travel                                            r - Reaction contaminant dirt on glass require-
                                                                         ing alternative cleaning procedures
Surface      streaks oriented                                        s - Rinse Water Quality: high turbidity or
perpendicular to direction of                                            hard water salts content
                                   c, e, f
glass travel                                                         t - Rinse Water Temperature: too cold
                                                                     u - Rinse Water Volume: insufficient
                                                                     v - Solution Hold Tanks (Pre-wash or Washer):
Visible film or haze over glass                                          dirty, scrubbing and/or steam cleaning
surface(s) or subsurface(s)                                              needed
                                   b, d, h, I, j, k, l, m, n, o,     w - Stained (corroded) glass
exhibiting                  poor
                                   s, t, u, v, w, x
wetting/adhesion in- dicative                                        x - Water in Pre-wash: dirty from prolonged
of an invisible surface film                                             re-circulation

                                                  Page 16 of 19
                                                PPG Industries, Inc.
Glass Technical Document                                                               TD-144

   COATED GLASS PRODUCTS                                PPG MSVD COATED GLASS

Coated glass can act differently from              x   Install brushes that have a bristle diameter
uncoated glass in a washing system.                    between 0.006 and 0.009”. When ordering
Precautions will be necessary when                     brushes, specify the actual bristle diameter
washing coated glass products.                         size; do not simply order “low-e brushes”.
                                                   x   Keep washer brushes clean and free of grit
Pyrolytic coated glass, such as PPG                    and abrasives.
Solarcool®, Vistacool®, or Sungate®                x   Use minimum brush pressure required to
500 coated glass incorporate coatings                  provide effective cleaning.
that are “fired” onto the glass surface by         x   If a detergent is used, select one that maintains
a pyrolytic method at elevated                         a wash water pH that it is not excessively low
temperatures. These products, when                     or high.
cleaned in a washer system as outlined             x   Never allow glass to be stopped in a fixed
in this document, can be treated in the                position beneath the washer brushes.
washer the same as uncoated glass.
                                                   x   All brushes must have sufficient water flow
                                                       in order to prevent the brush from
Magnetic Sputtered Vacuum                              scratching the coating. A “rule of thumb” is
Deposition (MSVD) coatings such as                     to have ¾ GPM per foot of pipe for each pipe
PPG SUNGATE 100, Solarban® 60,                         within the washer. Flow meters on each
SOLARBAN 65, SOLARBAN 70,                              header should be installed to monitor the water
SOLARBAN 80, and SOLARBAN z50                          flow.
coated glass are not as durable as                 x   Keep pinch rolls clean and free of debris
pyrolytic coatings. In addition, these                 such as process labels.
coatings involve materials that may be             x   Do not allow washer components, such as
more chemically reactive than pyrolytic                splash curtains, to drag on the coated
coatings.                                              surface.
                                                   x   The total dissolved solids in the final rinse
The following recommendations are                      water must be 20ppm or less.
offered to aid in the successful washing
                                                   x   If remedial hand-cleaning is necessary, use a
of MSVD coated glass. While all of the                 solution of 50 -50 demineralized water and
following      recommendations         are             isopropyl alcohol and a clean cotton cloth.
important, those that are in bold print                Patting, rather than rubbing, is recommended
are considered critical. And, of course,               to avoid coating damage.
implementing these recommendations                 x   Implement a regular and comprehensive
will also improve the efficiency and                   preventive maintenance program for the
quality involved with all glass products.              washer.

                                       Page 17 of 19
                                     PPG Industries, Inc.
Glass Technical Document                                                            TD-144

             GLOSSARY                              Particulates – solid material loosely
                                                   deposited on a surface. They can be
These definitions pertain to the words as          removed by using non-abrasive,
they are used in this document.                    mechanical methods such as high
Adhesion Chips – chips of glass bonded             pressure water.
to the glass surface                               Powder Interleaving – granular
Alkaline – having the properties of an             particles purposely placed on the glass to
alkali: capable of neutralizing an acid.           act as a mechanical separator that may or
Having a pH greater than7; also referred           may not contain acidic compounds to
to as basic.                                       prevent corrosion between lites of glass.
                                                   Acrylic beads and wood flour are
Deionize – the process by which ion                examples.
exchange resins are used to remove hard
water salts.                                       Reaction Contaminants – residues that
                                                   have some degree       of physical or
Demineralize – the removal of mineral              chemical bonding or interaction with the
constituents from water                            glass surface. These cannot be removed
Esters – any of a class of organic                 with practical, standard washing
compounds formed by the reaction of an             procedures.
acid with an alcohol                               Scale - a deposit of mineral compounds
Hardness – the amount of calcium                   present in water.
carbonate dissolved in water.                      Softness – the degree to which
Hermetic Seal – an airtight seal.                  magnesium and calcium ions have been
                                                   removed from water.
Interleaving - a packaging material that
is placed between adjacent lites of glass.         Solubility – the ability of a substance
                                                   such as detergent, to dissolve in water.
pH – a scale of 1 through 14 that
designates relative acidity or alkalinity          Surface Corrosion – irreparable,
of liquids. 7 is neutral, 1 is the acidic          moisture initiated, chemical erosion of a
extreme, and 14 is the alkaline extreme.           glass surface.
                                                   Turbidity – Opaqueness or cloudiness
Paper Interleaving – paper that is used
                                                   of a liquid caused by suspended
to separate two lites of glass.
Paper Scum – a glass surface residue
resulting from the transfer of paper
interleaving esters to the glass surface
during storage. If this residue is allowed
to remain on the glass, reaction with
surface alkali may result in formation of
permanent reaction contaminants.

                                       Page 18 of 19
                                     PPG Industries, Inc.
Glass Technical Document                                                                                                TD-144

                                                    HISTORY TABLE
              ITEM                           DATE                                 DESCRIPTION
TD-144                                  11/6/2006                   Electronic version of “Recommended
                                                                    Techniques for Washing Glass” with minor
                                                                    modifications and additons..

This document is intended to inform and assist the reader in the application, use, and maintenance of PPG Flat Glass products. Actual
performance and results can vary depending on the circumstances. PPG makes no warranty or guarantee as to the results to be
obtained from the use of all or any portion of the information provided herein, and hereby disclaims any liability for personal
injury, property damage, product insufficiency, or any other damages of any kind or nature arising from the reader's use of
the information contained herein.

                                                        Page 19 of 19
                                                      PPG Industries, Inc.

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