Investigation of cage motions affected by its unbalance in a ball bearing

Cage rotating and whirling inside rolling bearings involve conical motion and easily lead to excessive wear if the cage exists unexpected unbalances. In this study, the cage motions affected by its unbalance in a ball bearing are investigated analytically and experimentally, which helps to understand the bearing dynamics and cage wear. Firstly, a dynamic model of angular contact ball bearing with the unbalanced cage is established to simulate the cage motions as a function of typical cage unbalances over a range of operating speeds. Then, an experimental approach is proposed to measure the spatial motions of the cage with various prescriptive unbalances on a test rig. Finally, the trajectories, waveforms, and spectra of cage motions are constructed and compared to elucidate its diversified patterns under various cage unbalances. The experimental observations of the cage motions agree well with the theoretical predictions and reveal that the whirl motions of cage are evidently affected by its unbalances. The increment of cage unbalance mass makes the trajectories of cage center more regular and enlarges the whirl radii. It is also observed that the amplitudes of the axial and radial motions of the cage, particularly corresponding cage rotating frequency and the wear extent of the cage guiding surface increase with the increment of cage unbalance