Wear has been found in the Hertz tracks of fluid lubricated, high quality angular contact ball bearings which spin too slowly to generate an elastohydrodynamic lubricating film. Often a taper section or profile of the track shows a “W” or a “U” shaped groove. A mechanism is proposed to account for these shapes.

This wear has been detected by destructive long term life tests in expensive bearings. A bench test is described which gives accelerated results on easily rejuvenated plates. Connections between the ball on plate tester and any angular contact bearing are outlined.

Ball on plate tests using two perfluorinated and one synthetic hydrocarbon lubricant are interpreted in terms of a slow buildup of an electrically insulating, chemically derived film on the Hertz track. Details of the film buildup and its wear protection ability are specific to each lubricant.