A rolling-element bearing, also known as a rolling bearing, is a bearing which carries a load by placing round elements between the two pieces. The relative motion of the pieces causes the round elements to roll with very little rolling resistance and with little sliding
Typical Failures
- Flaking: depict the condition that develops when ball bearing surfaces disintegrate Into irregular particles, known as flaking. The bearing surface becomes scaly and literally peels off due to contact loading as pothole-like flaws develop. This phenomenon is caused by rapid metal fatigue in cyclically stressed surfaces subject to excessive loads or exposed to excessive temperatures caused by insufficient clearances. Another name for this condition is spalling.
- Seizing: Seizing is one of the most common fallure modes when bearings are first put O service The lack of rolling element rotation results in a rapid and excessive rise in temperature. The surface hardness of the bearing races and rollers or balls is reduced, and the bearing is quickly rendered unsuitable for use. The rollers usually are the first indicators of damage, as their comers change color due to loss of temper associated with excess temperatures. Metal to metal contact takes place between rolling elements and raceways, and then micro-welding and overheating occur As this phenomenon progresses ever more rapidly, seizing takes place.
- Race Fracture: Improper mounting insufficient internal clearance among bearing parts, or shock loads can result in fracture of bearing races. The fracture often comes about as a result of sharp impacts during rotation caused by previous flaking. If flaking is found in the split race, it should be suspected as the primary cause of bearing failure. In some cases a crack may not be readily visible, but large enough to create fine metal chips that will deteriorate the bearing Axial direction, Le parallel to the shaft center line, cracks on a bearing inner race can be caused by too tight of a fit between the race and shaft. Figure above depicts this condition. The shaft mounting surface is probably oversize, resulting in this conditions, which often appears shortly after the improper installation, Precise measurement of the shaft, establishing the correct fit tolerances, and proper installation are essential to ensuring a full useful bearing life. Preventive measures to avoid a recurrence of race fracture include proper mounting, correct fits, and eliminating shock loads.