Effect of Silicon Nitride Balls and Rollers on Rolling Bearing Life

Three decades have passed since the introduction of silicon nitride rollers and balls into conventional rolling-element bearings. For a given applied load, the contact (Hertz) stress in a hybrid bearing will be higher than an all-steel rolling-element bearing. The silicon nitride rolling-element life as well as the lives of the steel races were used to determine the resultant bearing life of both hybrid and all-steel bearings. Life factors were determined and reported for hybrid bearings. Under nominal operating speeds, the resultant calculated lives for deep-groove, angular-contact, and cylindrical-roller hybrid bearings are respectively, 3.8, 3.3, and 5.5 times that using the Lundberg-Palmgren equations. An all-steel bearing under the same load and nominal operating speeds will always have higher life than the equivalent hybrid bearing operating under the same conditions. Under these conditions, hybrid bearings are predicted to have a lower fatigue life than the all-steel bearings by 58 percent for deep-groove bearings, 41 percent for angular-contact bearings and 28 percent for cylindrical roller bearings.