Diagnosing Roller Bearing Failures

When a rolling bearing is damaged during machine operation, the entire machine or equipment may seize or malfunction. Since bearings that fail prematurely or unexpectedly cause trouble, it is important to be able to identify and predict failure beforehand, if possible, so that preventive measures can be adopted.

Generally, bearing inspection or housing inspection can identify the cause of the problem. Often the cause of the bearing damage is attributable to poor lubrication, improper handling, contamination, excessive loading, misalignment, selecting the wrong bearing, or improper shaft and housing fit or some combinations of these. Usually the cause can be determined by considering operation of the bearing before the failure, investigating the lubrication conditions and the mounting condition, and carefully observing the damaged bearing itself.

Sometime bearings are damaged and fail both quickly and unexpectedly. Such premature failure is different from material fatigue failure, which is the result of shear stresses cyclically appearing immediately below the load-carrying surface. After a period of time, these stresses cause cracks that gradually extend up to the surface. As the rolling elements pass over the cracks, fragments of material break away and this is known as flaking (see Table 1 and Figs. 1 & 2).

Basically, bearing life can be separated and categorized into two types: premature failure and normal rolling contact fatigue. The tables here cover typical bearing damages and countermeasures.

This article provides a general overview of bearing failure, but this problem entails so much more than what can be described here. There are many more bearing diagnoses to be viewed by visiting www.tec.nsk.comor contact NSK Canada at www.ca.nsk.comfor engineering assistance.

NSK Canada Inc.