Bearing load distribution and fatigue life analysis for a tilted overhung agitator

Agitators with tilted overhung rotors are widely used in the pharmaceutical and bioengineering industries; however, the accurate evaluation of bearing loads and fatigue life for such systems remains a challenging problem in engineering practice. In this study, a tilted agitator rotor was investigated. Based on a detailed mechanical analysis, the coupled effects of rotor tilt on the gravitational load distribution and operating loads were considered. Bearing elastic deformation is incorporated by introducing Hertzian contact theory and a nonlinear bearing load model, leading to a set of equilibrium and differential deflection equations. The displacements and angular misalignments of the bearing inner rings were solved using the Newton–Raphson method, which enabled the determination of the actual contact loads acting on individual rolling elements. On this basis, a bearing system life prediction method suitable for tilted agitator rotors was developed by combining ISO 281:2007 with the Ioannides–Harris (IH) life theory and rolling element–raceway contact fatigue theory. A HCQ50 agitator is selected as a representative case for the numerical investigation. The results indicate that, compared with the lower bearing B, the upper bearing A carries the majority of the axial load and therefore exhibits a shorter fatigue life. Bearing preload has the most significant influence on bearing life, whereas the effect of bearing span is relatively minor. An optimal bearing life is achieved at a preload of approximately 230 N. The bearing life reaches a maximum when the agitator shaft inclination angle is approximately 10°. In addition, reducing the overhung length and agitator rotational speed are also beneficial for extending bearing life.