Neale Consulting Engineers - Rolling Bearing Failure - Premature Fatigue - False brinnelling

ROLLING BEARING FAILURE

Rolling bearing failure index

Premature fatigue index

3.4 False brinnelling

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	Figure 3.4a
	Figure 3.4b
	Figure 3a
	Figure 3b
	Figure 3c
Main Characteristics	If a bearing is subject to vibration when stationary, fretting damage occurs at the points of contact, giving rise to what is known as 'false brinnelling' (figures 3.4a , b). (Note: It is different from fitting damage in that material is removed rather than displaced.) This can occur to large bearings even before they are installed.
Cause	A characteristic of all the above mechanisms is that the damage occurs when the bearing is stationary and is thus at rolling element spacing. Premature fatigue is readily distinguished from normal fatigue in that it occurs in discrete patches at rolling element spacing, rather than as a continuous band starting from the initial point of failure as is the case with normal fatigue (figures 3a, b). Premature fatigue also occurs with angular contact bearings incorrectly fitted so that the axial load is taken on the low shoulder side of the race (figure 3c).
Note
Possible Confusion with Other Types of Damage
Comment	With separable bearings, e.g. cylindrical roller, taper roller bearings, it is good practice to store the bearing with the two parts separated. Non-separable bearings should be stored with the axis of rotation vertical so that the gravity loading is uniformly distributed over the rolling elements. Standby machines and machines in store should be rotated slightly once per week to change the points of contact. Where there are installed standby machines, it is good practice to run the machines alternately to reduce the risk of fretting. This is particularly important in the case of two machines mounted on the same pedestal.