Effects of Lubricant Viscosity on Creep in Thrust Washers of Needle Roller Bearings

Abstract

In recent years, there has been increasing demand in the fields of industrial equipment and automobiles for lighter and more compact units to save energy. The use of low-viscosity lubricant with high fluidity is known to reduce stirring resistance and decrease energy loss, delivering notable improvements in unit efficiency. As rolling bearings provide essential support to rotating components, the use of lightweight units incorporating slim and thin-section bearings has increased due to their smaller outer ring outside diameter at the same inner ring bore diameter. However, there are concerns that the bearing outer ring (the fixed ring) in these units will rotate in the same direction as the inner ring, a harmful phenomenon known as creep. In a previous study [1], we investigated the cause of creep in the thin fixed thrust washers of thrust needle roller bearings. Experimental evaluations and FEM analysis revealed that creep occurs in fixed thrust washers when circumferential strain on their back face exceeds a certain limit. In this study, a test method was established to assess the creep speed of fixed thrust washers using three types of lubricants with different kinematic viscosities. In addition, detailed observation of the thrust washer surface after testing and X-ray analysis techniques were used to verify the contribution of creep speed to rolling contact fatigue. Results indicate that although creep speed exhibits slight variation depending on differences in lubricant viscosity, lubricant additives represent a critical factor. Furthermore, controlling creep speed could significantly enhance the bearing life of thrust needle roller bearings under conditions involving substantial inclination of the support surface, which contrasts with conventional rolling contact fatigue theory.