A Novel Test Rig for the Investigation of Ball Bearing Cage Friction

This article presents a novel experimental test rig for the investigation of friction between a ball and cage of a deep groove ball bearing (DGBB). The experimental apparatus was designed and developed to replicate the orientation and dynamics of a full bearing in steady-state operation while collecting measurements of cage friction. A six-axis load cell was used to record force and torque values generated due to a rotating ball inside of a rigidly fastened cage segment. The test rig can be set up in two different configurations to collect cage friction measurements: (a) A position control configuration where measurements of friction torque on the ball are collected for specific positions of the ball and the cage and (b) a load control configuration where a constant force is applied between the ball and the cage and a friction coefficient is calculated from the results. The test rig was used to investigate four different DGBB cage varieties: (a) a snap-on polymeric cage, (b) a low-profile polymeric cage, (c) a stamped steel cage, and (d) a machined brass cage. The friction performance of each cage type is shown to be related to the shape of the lubricating film between the ball and the cage wall. In addition, measurements of friction torque at specific positions provide insight into the mixture of oil and air inside the cage pockets. Friction coefficients from experiments in the load control configuration are shown to increase with speed and reduce with applied load for all four cage varieties.