Study on effects of the deformable supporting structure and differential thermal expansions on fatigue life of slewing ring ball bearings– a multibody dynamics approach

Large diameter bearings or slewing rings are used in Prototype Fast Breeder Reactor (PFBR) to facilitate rotation of large and small rotatable plugs for fuel handling. The performance and life of these bearings are a function of load distribution among the rolling elements such as bearing balls or rollers. Undulations – wave like deformations – forms in the large diameter bearings due to elastic deformation of bearing supporting structure, manufacturing errors and differential thermal expansions along the bearing races occurring during reactor operation. These undulations adversely affect the load distribution in the bearing resulting in non-uniform load distribution among the rolling elements during rotation of the bearing. An estimation of the load distribution during bearing operation will help in assessment of bearing performance and life. Towards this, a Multi Body Dynamic (MBD) simulation is carried out. Performing MBD simulation of the large diameter bearing is a novel approach to study the effects of undulations and differential thermal expansions on bearing performance as no open literature is available on a similar study. With this approach load distribution in the bearing, kinematics and dynamics of rolling elements motion during bearing rotation is studied which is not feasible by conventional static finite element analysis approach. A general purpose commercial multi body dynamic simulation tool – Recurdyn - with capability to simulate flexible bodies is used to study the effect of undulations on bearing performance. In this study, maximum load taken by the bearing balls under the individual influence of undulations and differential thermal expansions as well as the combined influences were estimated. Along with these estimates, spacer ball to load ball interaction forces during bearing operation are also estimated. Estimated maximum loads on the bearing balls are used to estimate the fatigue life of bearing to study the effect of undulations on the bearing performance. These estimates provide inputs to make design recommendations for PFBR large diameter bearings.