Prevent Premature Mounted Bearing Failure
Do you know what it means for a bearing to fail prematurely? Hint: it has nothing to do with material fatigue.
A mounted bearing’s life expectancy can be determined if certain factors, like working load and speeds, are known. Overtime, it’s normal for the materials that constitute a bearing to wear down. However, a bearing is said to fail prematurely when the causes that contributed to its failure aren’t associated with material fatigue.
Most premature bearing failures are caused by a faulty mounting, improper lubrication, contamination, improper handling, or improper maintenance. These factors contribute to these failures: fatigue, brinelling, misalignment, electric arcing, particle contamination, thrust, lubrication, false brinelling, and moisture contamination. Luckily, there are preventative measures you can take to prevent bearing failure.
Bearing fatigue failure is cause by overload on the bearing. To prevent overload, there are a number of measures that can be taken. A redesign of the system to incorporate a bearing with greater load capacity is one option. Another is to decrease the load. Housings can be gauged for out of roundness and machined for proper symmetry and size. If failure is caused by inner ring expansion, the shaft fit may be made looser or, in the event of a thermal expansion, a bearing with a looser fit can be installed. Finally, if the failure is caused by end loading, the cause of the end loading must be corrected.
Particle contamination causes scoring pitting and scratching. If moisture is allowed to enter the bearing, it can cause rust, etching, and staining. Most contamination is cause by dirty surroundings, abrasive waste materials, or moisture in the surrounding environment. Preventing contamination of moisture is achieved by having efficient sealing. To prevent particulate contamination, it’s critical to maintain clean work surroundings.
Brinelling, deformation of the bearing surfaces where the rollers contact the races, is caused either by incorrectly exerted force or radial shock load. To prevent these, proper mounting procedure must be followed. This means that force should always be exerted against the ring being mounted. Additionally, identifying and removing any source of overload is also effective.
False brinelling is caused directly by vibration or oscillation. To prevent harmful vibration, correct its source, lock the bearing, adequately lubricate all surfaces, tighten internal fits, or use a low viscosity lubricant. To prevent oscillation, increase the angle of rotation, adequately lubricate all surfaces, or select a different bearing type.
Thrust failure is caused either by improper mounting or counterbore failure. To prevent thrust failure, select the right bearing for the job, ensuring that it’s not overloaded, and to mount it correctly so that the balls have full shoulder support on both the inner and outer rings.
Misalignment is caused by shaft misalignment, housing misalignment, or shaft bowing. To prevent shaft or housing misalignment, insure that both the housing and bores are true to each other. To prevent shaft bowing, the shaft should be gauged to make sure that it is concentric and straight.
Electric arcing is caused by static electricity emanating from charged belts or the manufacturing process, electric leakage from faulty wiring or inadequate insulation, or a short circuit. Where there is a passage of current through a bearing and the source can’t be current, a shunt in the form of a slip ring assembly can be used to by-pass the current around the bearing. Corrective maintenance should be performed to insure that wiring, insulation, or rotor windings are sound. Grounding belts can be used to eliminate static charges. Insulating bearings with sleeves of nonconductive material can be used. And, finally, utilizing electrically conductive grease will provide a path for the current to minimize or cease damage to your bearings.
Lubrication failure is the final kind of failure discussed here. Dirty lubricants, too much lubricant, inadequate, or the wrong kind of lubricant are all causes. Avoiding contamination can prevent dirty lubricant. Using the correct amount of lubrication can prevent surplus lubricant. And, finally, using a lubricant with sufficient viscosity can properly separate the rolling contact surfaces.