Effect of lubricating oils on cage failure of ball bearings

Ball Speed Variation (BSV) and cage clearances affect the cage life of ball bearings. Vibration and impact of the moving surfaces of a bearing under high pressure conditions also affects the cage life. Moreover, large forces at the cage-ball and cage-race contacts cause cage failure. Therefore, cage design is improved by increasing the looseness at the ball pocket and race. However, in many cases, cage failure still is occurring. To investigate the causes of cage failure, thrust ball bearing life testing was done using eight kinds of lubricant. The general feature found was that bearing life with synthetic naphthenic oils, polybutene and fluoro silicon oil increases with increasing film parameter in the ball-race contacts. Flaking occurred in the inner and outer ring and ball. In the case of dimethyl silicon oil that has mechanical shear thinning (permanent viscosity loss), poor oil film formation and poor boundary lubrication performance, all stoppage of the experiments occurred due to cage damage. Cage-ball contact fluid film characteristics were investigated by testing the high pressure rheology of the lubricants under the impact of a ball on a lubricated surface. Impact indentations were analyzed and compared with the bearing life experiment results. It was found that abrasion of the cage at the ball-cage contact was not the only determining factor. Surface chemistry also had a great influence on the cage failure.