The effects of lubricant starvation on ball bearing cage pocket friction

Abstract

This paper presents an experimental and analytical investigation into the lubrication of deep groove ball bearing (DGBB) cage pockets. A custom acrylic replica of a cage segment was designed, developed, and installed on a cage friction test rig for the simultaneous measurement of frictional torque and visualization of oil flow inside of the cage pocket. A broad set of experiments was conducted with different lubrication methods, oil viscosities, cage positions, and ball speeds to characterize the state of lubrication inside of the cage pocket. The quantity of oil inside of the pocket was found to correlate closely with the measured frictional torque. Videos of oil flow were subsequently analyzed to estimate the volume of oil present within the cage pocket at each operating condition. This oil volume information was then used to define an equivalent fluid to be used in a numerical cage pocket lubrication model. The model solves the Reynolds equation over a spherically defined cage pocket domain and produces estimates of frictional torque. Predictions from the model agree well with experimental friction measurements. The cage pocket friction results exhibit a dichotomous relationship – first increasing with speed then decreasing due to the dominating evacuation of lubricant from the cage pocket. Curve fit equations are presented to describe both behaviors, allowing for the prediction of cage pocket friction spanning a range of Reynolds numbers from 2 to 5000.