As stated previously, most small bearings are used in applications where rotational accuracy and low torque are primary requirement and loads are light. Therefore the operating lifetime of the bearing is relatively long, and, if properly operated, failure is rare. Nevertheless, all bearings have a finite life under use and will eventually fail to perform satisfactorily due to an increase in noise and vibration, loss of running accuracy, deterioration of lubricant, or fatigue flaking of the rolling surfaces. Such failure modes are considered “normal” and can be predicted using standardized techniques.

In addition to normal deterioration, bearings may fail due to heat seizure, fracture, scoring of the rings and other conditions caused by improper use, selection or maintenance of the bearing. Such failures are not normal and can only be avoided by careful handling and correct operation of the bearing in a given application.

BASIC BEARING FATIGUE LIFE

a₂ = Life correction factor for operating conditions. It has been empirically determined to have a value between 2.0 under ideal operating conditions and 0.2 where one or more of the following conditions may apply:

• The lubricant film thickness between the raceways and the rolling elements is low
• Bearing raceways are excessively misaligned
• Oscillatory motion
• Rotation speed of the bearing elements is very low
• Contamination or water is present in the bearing

When subjected to an excessive load or shock, rolling bearings may incur a permanent damage to the raceways, called brinelling. This occurs when the elastic limit of the raceway material is exceeded and will permanently effect the smooth rotation of the bearing.