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.

The commonly known effects of both the rotating speeds and external loads on the bearing dynamics or life behaviors are mostly caused by its cage dynamics, because of the complicated contact and collision interactions between the cage and other parts such as the inner or outer rings and balls. In this paper, experimental investigation of dynamic motions of a cage is carried out under various rotating speeds and external loads in a ball bearing. On a bearing test rig, the cage motions in axial and radial directions are measured by use of eddy transducers installed inside the bearing house and the subpanel. Then the measured results are analyzed by fast Fourier transform and compared at different operating conditions including rotating speeds, axial and radial forces, or moments. The three-dimensional space motions of the cage are also constructed to illustrate its different modes. Results reveal that the cage motions are typically periodic in the three directions. The motion frequencies consist of the cage rotating frequency and its multi-frequency, the inner ring rotating frequency, and also some combination frequencies of the cage and inner ring. The obtained characteristic frequencies of the cage motion in axial are similar to that in radial, but different in the variety of amplitudes under the same operating conditions. The increment of rotating speeds and axial loads of the bearing gradually make the whirl trajectories of the cage mass center regular, and enlarge its whirl radii. Instead, the whirl trajectories change from well-defined patterns to complicated ones, and its whirl radii decrease on increasing the radial loads and moments of the bearing. All the obtained experimental results are useful references for dynamic design and life prediction of high-speed and low-load bearings commonly used in many machines.

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Clearances of cages in ball bearings, including pocket and guiding clearances, play a vital role in the stability and reliability of bearings. In this paper, experiments on the cage motion and wear were carried out to investigate the influence of clearances in ball bearings. Firstly, the cages with a series of pocket and guiding clearances were specially designed and tested for prescribed operating conditions on a bearing test rig in which the cage motions were measured, and corresponding wear was also observed. Then, the normalized trajectory, waveform, and spectra of cage motion were constructed and compared to illustrate the effects of clearances on the cage motion and then to establish the relationship between cage motion and wear. Results reveal that the cage motion and wear are both significantly affected by its clearances. The increment of cage guiding clearance makes the whirl trajectories of the cage regular and the motion frequency of cage motion significantly change. However, the increment of cage pocket clearance make the whirl trajectories change from well-defined patterns to complicated ones, and the frequency of cage motion apparently changes. Additionally, the bearing wear is closely related to the cage motion. If the inner ring frequency is of domination for the cage motion, the cage guiding surface will wear seriously. While cage motion is dominated by two times cage frequency in spectrum domain, the cage pocket will wear more seriously.

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