On the Stress Concentration Factors of Rolling Element Bearing Cages

Abstract

In high-speed rolling element bearings, cage hoop stress is one of the critical design considerations. The cages in these bearings are typically simple solid rings with a series of equally spaced radial holes for ball bearings or square slots for roller bearings. There are stress concentrations caused by this series of holes or slots and thus the hoop stress is not uniform in the circumferential direction. These stress concentrations in the presence of combined centrifugal and dynamic loading can lead to cage failure. In the design process these stress concentration factors (SCF) are typically obtained from standard references. However, due to the unique geometry of a bearing cage, significant extrapolation is required and these stress concentration factors tend to overestimate the actual stress level.

In this study, FEM models with critical parametric geometric variables were developed for typical roller and ball bearing cages. Stress concentration factors were derived for various combinations of cage design variables. The design of experiments (DoEs) techniques were used to study the variation of design parameters or variables and then the stress concentration factors as functions of critical design variables were developed. These transfer functions can provide a much more accurate and realistic estimation of the maximum cage stresses than traditional methods, and they can be used for cages of any reasonable geometric proportions. Furthermore, the effects of radial balance slots on maximum stress were also studied and recommendations on slot size and locations were provided.

KEY WORDS:

• Rolling Element Bearing
• Bearing Cage
• Stress
• Stress Concentration
• Stress Concentration Factor

ACKNOWLEDGEMENTS

The authors would like to acknowledge Messrs. R. Ganiger and A. Vijarvargiya for building the FEM models and running the DoEs.

Review led by Mike Hoeprich