Rolling bearing failure index

7.0 Wear

Click on photograph to enlarge
	Figure 7a Matt track caused by wear with abrasive particles
	Figure 7b Heavily corroded ball
	Figure 7c Hollow ball
Main Characteristics	Abrasive particles in the lubricant will cause wear. This is normally most severe with the softer cage material and can lead to cage fracture. Wear damage can be distinguished from lubrication breakdown by the appearance of the tracks. Either these take on a specular polish if the abrasive particles are very fine, or become matt and scored with larger particles (figure 7a).
Cause	Wear also occurs as a secondary result of corrosion, the iron oxides so produced acting as jeweller's rouge (figure 7b). Under extreme conditions with high speed bearings this can lead to the formation of hollow balls (figure 7c) where there is some internal discontinuity in the ball that allows it to expand to fit the gap between the races to compensate for the wear. Wear, of course, can be caused by the particles released by fatigue pitting, but this is secondary to the fatigue damage.
Note
Possible Confusion with Other Types of Damage
Comment	Care should be taken to ensure that, when electric induction heaters are used to ease the fitting of races with an interference fit, the bearing is properly demagnetised. A magnetised bearing tends to collect steel particles and this will increase the amount of wear.

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