Common Causes of Premature Wear or Failure in Industrial Bearings
Proper bearing maintenance and repair will help ensure your bearings meet or exceed the expected service life. However, for most industrial applications, bearings are considered a wear item. That means no matter how rigorously you keep up with maintenance, internal components and/or seals will wear out under normal use. As wear develops, overall performance will progressively deteriorate.
In other words – knowing when to service your bearings is crucial to maintaining the performance and productivity of your equipment.
As one of the industry’s leading bearing manufacturers and distributors, BSC can often save you the cost of a full replacement through our comprehensive bearing remanufacturing and repair services. We can also provide you with complete sets of quality replacement bearings when necessary. In either case, we’ll give you a cost-optimized solution that keeps your equipment up and running with minimum downtime.
Diagnosing Common Modes of Bearing Failure and Performance Issues:
Improper Fitment or Misalignment
Some bearings can tolerate minor misalignments between shaft and bearing housing – namely spherical bearing configurations. However, in most serious cases, even minor misalignment substantially increases wear and/or impedes bearing performance.
Bearing misalignment is exactly what it sounds like. If one of the rings is out of alignment in relation to the other, the ball or roller path will run from one side of the race to the other around half of the circumference on the non-rotating ring. That means the rotating ring will have a wider roller path in operation. The extra pressure (and friction) imposed on the bearing due to misaligned conditions typically results in excessively high temperatures. Extended use at such elevated temperatures tends to discolor the roller tracks and the rollers while destroying the lubricant.
Similarly, there’s also retainer ring misalignment. The purpose of the retainer is to space the rolling elements and guide them in a true path around the raceway. When a ring is misaligned, the rollers are driven up against the race shoulder. That creates a stress point between the roller and its retainer pocket. The pocket is forced to flex, increasing friction as well as the possibility of retainer fracture.
For example, misalignment of the shaft in relationship to the housing causes an overload of the balls or rollers. Similarly, housing misalignment may be caused either by the housing being cocked in relation to the plane of the shaft or the housing shoulder being ground out-of-square so that it forces the outer ring to cock in relation to the inner.
Improper Lubrication
For proper lubrication of rolling element bearings, adequate viscosity at operating temperature is crucial. Insufficient lubricant is the most obvious issue, but excessive levels of lubricant can also result in excessive frictional heat.
Highly polished or discolored bearing raceways and rolling elements indicate improper lubrication. Surface roughening in contact, the result of insufficient oil film, is another indication of metal-to-metal contact wear conditions. Typically, an early indication of lubricant failure is a rapid rise from the normal operating temperature. Excessive or abnormal noise is also a common side effect.
If the grease is stiff or caked and changed in color, it indicates lubrication failure. The original color will usually turn to a dark shade or jet black. The grease will have an odor of burnt petroleum oil. Lubricity will be lost as a result of lack of oil. In cases of lithium greases, the residue appears like a glossy, brittle varnish which will shatter when probed with a sharp instrument.
Contamination and Corrosion
A failure caused by the entrance of foreign objects into the bearing, may show a number of identifying marks. Contamination with large particles of dirt or dust results in scratches and pits around the periphery of the race with corresponding scoring of the rolling elements. When the contamination is in the form of very fine abrasives such as glass powder, graphite, or dust-impregnated lubricants, the impurities will act as a lapping agent, damaging the surfaces of rolling elements and raceways.
Naturally, rust is a common example of corrosion failure. When rust forms on the O.D. of the outer ring, it will not usually interfere with the bearing’s performance in standard application. On the other hand, rust in the bore is more serious because of the importance of inner-ring to shaft fit. Rust in the raceways or on the roller elements precludes any further use of the bearings.
However, rust isn’t the only contamination issue. If moisture is allowed to enter a bearing it can damage the bearing in several different ways. The internal surfaces may become corroded or etched. A stationary bearing exposed to moisture is likely to exhibit individual staining on the race in locations of contact between rolling elements and raceway, or random spots of corrosion on exposed surfaces. Either pattern of corrosion deters proper bearing performance and results in excessive noise, inadequate clearance, or premature fatigue damage of the corroded areas.
Bearing Overloading
Exceeding the bearing’s maximum weight/load capacity, or overloading, can lead to generally poor performance, excessive wear/fatigue, and premature failure.
Premature failure of the bearings may result from the bearing being either radially or axially loaded beyond its normal capacity. Excessive operating load is not, however, the only reason for bearing overload. Overload may also occur due to numerous other abusive operating conditions:
- If a bearing with insufficient internal clearance (space between rolling elements and races) is mounted on a shaft with an excessively heavy press fit, the bearing is forced to operate under increased friction and torque. Basically, with the outer ring held firmly, the inner ring expands and pinches the rolling elements between the two rings.
- If the bearing housing is out-of-round, the outer ring will tend to conform to the shape of the housing. This will exert a localized pressure on the rolling element contact area, in addition to the normal pressure imposed by the operating work load.
- When a roller bearing is end loaded (due to misalignment, shaft slope, etc.) the load on the bearing is no longer uniformly distributed over the bearing’s full width. This overloads a portion of the races and rolling elements resulting in localized fatigue.
Committed to Quality Industrial Bearings Since 1933
BSC is one of America’s leading independent manufacturers and repair sources for industrial bearing projects. Founded in 1933, we provide industry-leading experience in virtually all bearing types – ball, cylindrical, thrust, and standard interchange bearings.
Through our full-service repair, refurbishment, and reconditioning options, we aim to provide customers with the most sustainable, cost-effective solution to their unique industrial bearing needs.
