Machine Design

Bearing Load Rating

Basic dynamic load rating is the load at which 90% of a group of bearings can survive 1 million inner-race revolutions. However, some manufacturers use 90 million inner-race revolutions as the rating basis. In either case, basic load rating is the figure of merit used to evaluate bearing life in applications where fatigue -- rather than inadequate lubrication, excessive temperature, overloading, or overspeeding -- is the primary failure mechanism. Relationships for predicting bearing fatigue life under both constant and sinusoidally varying radial loads are given elsewhere in this chapter.

Relations for calculating basic dynamic load rating for conventional bearings are given in Sections 9 and 11 of the AFBMA Standards. The calculated ratings tend to be low because of recent advances in bearing technology.

Basic static-load rating is the maximum radial or thrust load a bearing can endure without excessive permanent deformation. Maximum deformation of a rolling element or race that does not significantly degrade bearing performance is 0.0001 times the diameter of the rolling element. Equations for basic static load for standard bearings are given in Sections 9 and 11 of the AFBMA Standards.

TAGS: Bearings
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