FEM COMPARISON OF BALL AND ROLLER BULLGEARS

A structural finite element model has been developed for calculating t he forces transmitted through the rolling elements (fond distribution) in a bullgear assembly. The elastic structural model consists of 3-D beam elements used to approximate the global race deflection. and non- linear springs that approximate the combined rolling element/raceway c ontact deflections. For rollers, an upperbound on the contact stress ( assuming linear variation of force along the length of the roller) is estimated by modeling the rollers as pairs of nonlinear springs. The f inite element approach iteratively solves the Contact forces al each r olling element. Contact stresses are then calculated from the contact forces using Hertz contact theory. This approach is applied to analyze two Proposed designs of hall and crossed roller hearing bullgear asse mblies used for relating the radar antenna on top of a ship's mast. Th e lends analyzed include those arising from wind lending and from out- of-flatness of the inner race of the bearings due to deflection of the mast. The distribution of the load and the maximum contact stresses f or the proposed bullgear assemblies are estimated and compared. It is found that the maximum contact stress in the crossed roller bearing is less than that in the ball bearing for both types of loads. Furthermo re, the analysis shows that the out-of-flatness loading produces signi ficantly higher stresses than wind loading.