False brinelling is fretting occurring in bearings
When fretting wear occurs in bearings, it is referred to as false brinelling. A bearing will experience false brinelling when it is not turning but subjected to vibrations of some sort. Because the bearing is not turning, the grease or oil will be gradually removed from the ball or roller contacts ending in metal to metal contact. Next wear takes place and the damage will cause the bearing to fail sooner after start up.
False brinelling is different from true brinelling. Brinelling is caused by a large impact on a bearing which causes the rolling elements to leave large dents in the raceway. False brinneling leaves a very similar wear scar, but it comes from a series of small impacts instead of one large impact. False brinelling marks are usually wider than brinelling marks and there may be two marks for each roller because of the slip zones occurring on either side of the roller.
Bearings often experience false brinelling damage in an assembled machine in storage. Only very small vibrations are needed for false brinelling to take place and usually vibration is not considered while deciding upon where to leave a machine. If a machine it stored near where it will be used, it is very likely that there will be vibrations present from the machine it will replace.
False brinelling caused one of the most famous cases of fretting. Automobiles in the 1930s were being shipped from Detroit to the west coast on trains. During shipment, their storage location–a train car–experienced vibration leading to the failure of wheel bearings. Unfortunately, similar mistakes have been be made many times since.
False brinelling causes bearings to fail because the rolling element and raceway come into metal-on-metal contact. When the asperities touch one another both wear and oxidation take place. This is bad on for several reasons:
- The wear debris formation leaves a wear scar in its wake which will interfere with the normal rotation of the bearing when a machine is started.
- Because bearing races and rolling elements are very hard, hard wear particles are formed which cause abrasive wear.
- Because the bearing is not turning, the particles remain in the contact area instead of being distributed evenly or removed by a filter.
False brinelling is a failure due to fretting wear not fretting fatigue. A bearing will fail due to the geometric changes of the wear scars not from fatigue cracks nucleating at the rolling-element contacts.default