SKF’s Information Bulletin
Troubleshooting for Noisy Bearings
A 5-page document has been prepared for you listing 30 symptoms and solutions with respect to noisy bearings. Trou-
bleshooting related to lubrication, internal clearance, contamination, housing bore, seal failure, adapter sleeve, unbal-
anced load, incorrect mounting and vibration are highlighted.
To receive (in electronic form) simply request via return email.
Crushed stone producer saves € 27,000 with hydraulic assist maintenance tools.
Increased worker safety contributed to the bottom line.
Bearings on the horizontal impact crusher needed replacement. This primary crusher producers 400 tonnes/hour and
the plant’s production stops when it is out of service. Bearing replacement took the maintenance crew 26 hours to rig
tools to dismount and mount new spherical roller bearings on the tapered shaft.
The solution was a SKF hydraulic assist nut, fittings and a hydraulic pump to mount new bearings onto the shaft. Hy-
draulic assist drives the bearings onto the shaft with quick, easy and efficient hydraulic pressure. The stead force of
the hydraulic pressure enables the bearing clearance to be measured accurately and set precisely. This eliminates the
need for hammers, spanners or bars and virtually eliminates the need to remount the bearing because clearance is
not correct - a common occurrence when using a hammer to mount a bearing. With the SKF hydraulic assist tools the
remounting of the bearing took 4 hours. Total downtime was 13 hours - half the time of the previous outage.
Caution: The most common causes of injury in the mining and mineral processing industry are doing machine mainte-
nance and repair and the improper use of hand-tools. The use of hydraulic assist tools substantially reduces the risk of
injury by eliminating the hammers, drive bars and torches too often used to mount and dismount bearings.
Savings by minimizing downtime and labour costs - €33,000
Investment in SKF hydraulic nut, fittings and pump - - €6,000
Total Savings - €27,000
Typical applications include: conveyors, crushers, mills, kiln supports, fans, gearboxes and motors.
To receive more information on SKF Hydraulic Techniques” (in electronic form), simply request via return email.
Ensuring Quality in Plastic Film Manufacturing
The plant produces “breathable” plastic films with thicknesses between 15µm - 200µm. The production line has a series
of 3.2m wide rollers the first six of which are heated to 140°C in order to preheat the plastic, which is then stretched
over the remaining rollers until it reaches the required thickness.
Many factors affect the quality and consistency of the film, but the most important is tension, which is strongly influ-
enced by the bearings used to support the rollers. To maintain constant tension, the friction torque of the bearings
must also be constant. Achieving this presents a considerable challenge as the axial expansion of the heated rollers can
significantly increase the friction torque of traditional bearing arrangements.
With these arrangements, the non-locating bearing must be able to move axially in the housing
to accommodate thermal expansion of the shaft. When sliding occurs, friction between the outer
ring of the bearing and the housing produces a thrust load on the bearing arrangement, increas-
ing frictional torque to the point where product quality may suffer.
To eliminate internal thrust loads, the non-located bearings were replaced with SKF CARB toroidal
roller bearings, which accommodate axial expansion internally. This allowed consistent product
quality to be achieved with the added benefit that as CARB bearings are self-aligning, there is no
reduction in bearing life if minor misalignment of the rollers occurs.
If SKF can assist in your application, please advise. To receive more information on SKF CARB
Bearings, please request via return email.
Seals - Frequently Asked Questions
Section 1 - V-Rings
• What are the shaft requirements for V-ring Seals?
In general, the surface roughness of the shaft should not exceed 250 µin (micro inch). When sealing fluids
and fine particles, a maximum of 125 µin, is recommended.
• How are V-rings installed?
The V-ring seal is an all rubber seal that mounts directly on the shaft and seals axially against a counter
face, housing, seal case, or similar surface. Because it is all rubber and very elastic, it can be stretched over
flanges or other assemblies for positioning with minimal disassembly.
• Do V-rings require lubrication?
No, the V-ring performs well in dry applications and is capable of a greater amount of eccentricity and mis-
alignment than most radial lip seals.
• What is the pressure capability of V-rings?
In certain applications, V-rings can handle up to 10 psi (pounds per second inch) on the body side only.
V-rings should not be used on shafts mounted below the sump oil level.
• What is the high-speed capability of a V-ring?
When the V-ring is fitted on the shaft, the body of the V-ring is subject to a centrifugal force that could pos-
sibly move or lift off from the shaft at extremely high speeds. At shaft speeds of 10 to 12 m/s (meters per
second) 1969 - 2362 ft/min (feet per minute) the V-ring generally requires radial retention, depending on
the V-ring material and construction.
Section 2 - Teflon Seals
• What are the shaft requirements for Teflon Seals?
PTFE (“Teflon”) lip seals are usually more aggressive and abrasive to the shaft than standard elastomeric
lip seals, therefore, they require a hardened sealing surface. For best results, Chicago Rawhide generally
recommends a shaft hardness of 55 to 65 Rockwell C scale, and a surface finish of 8 to 16 µin (micro inch)
with a machine lead angle less than 0±0.05 degrees. The final surface finish should be achieved by using
the plunge ground finishing method.
• Do Teflon Seals require lubrication?
No, Teflon has dry running characteristics.
• What is the temperature capability of Teflon Seals?
PTFE can accept a wide thermal range of -200 to over 500° F (-128 to 260°C).
• What is the chemical resistance of Teflon Seals?
PTFE is chemically inert, which means it resists degradation by lubricants or agents that can destroy other
• What is the high-speed rating for Teflon?
SKF PTFE seals offer reliable sealing performance even where surface speeds exceed 6,000 fpm (30 m/s)
Monitoring of Screw Compressor Bearings and Rotational Elements
Monitoring screw compressors can be very different from monitoring other types of equipment such as pumps, fans,
and motors. The primary difference is the extremely high noise level caused by the gas pulse that is generated as
the compressed gasses are discharged from the unit. This is compounded if the unit is a two-stage compressor with
two discharge gas pulses. The gas pulse frequency will be equal to the female rotor speed (or speeds), and enveloped
acceleration amplitudes will be high. Under normal operating conditions amplitudes in excess of 15 gE have been ob-
served. One problem users may encounter is that of perception. Many employ the autorange feature in their monitoring
software. With a gas pulse amplitude of 15gE, a bearing fault signal will often be “down in the dirt” even though it may
have a high amplitude that would indicate a fault.
Shown in this spectrum, the Ball Pass Frequency Outer race (BPFO) exceeds 1.5gE. This definitely indicates a serious
problem. However, since the signal’s overall value is over 15gE, the 1.5gE peak does not “stand out”.
Two techniques may be used to help prevent overlooking these “hidden” enveloped acceleration amplitudes. The first
and easiest, is to use the Frequency Analysis Module (FAM) and assign the installed bearing’s fault frequencies to the
measurement POINT. When the data is collected, overlay the FAM markers on the spectrum, regardless of how the
spectrum looks, and look for energy spikes at the marker positions.
The second technique will provide you with the same information in a different way, but will allow you to alarm on the
bearing fault frequencies more easily. Again, using FAM fault frequencies, build a spectrum alarm band around the BPFO
and BPFI frequencies. Set each band’s frequency limits at 10 Hz below and 10 Hz above the FAM value. Set the band’s
peak alarm levels for 0.5gE for an alert and 1.0gE for the danger alarm.
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Distributors. Please make your comments via return email.
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