Frictional Instabilities in Ball Bearings

Abstract

Computer modeling techniques are used to investigate instabilities in the motions of ball and cage in a ball bearing. As the friction at ball/race and ball/cage contacts increases, the cage mass center whirl orbit changes from circular to polygonal and then to a rather erratic shape under excessive friction. The corresponding variations in whirl velocities also increase to represent bearing squeal. It is shown that cage instabilities are directly dependent on the ball/race traction slope, under low slip velocities, and the friction coefficient at the cage interfaces. Under steep traction slopes, the variation in traction at higher slip rates is also significant in high-speed bearings. In particular, it is found that a negative traction slope, in the high-slip region, may produce appreciable ball skid which promotes excessive interaction in the cage pockets and, perhaps, the most damaging instability of the cage, where the mechanical interactions progressively increase to indicate significant potentials for cage failure. Under stable conditions of operation, the computer results also provide correlations between time-averaged wear rates of the cage and the frictional behavior.