Fretting wear is often the case when ball-and-roller bearings oscillate under grease lubrication. Against the backdrop of fretting wear on the wheel bearings of automobiles caused by rail transportation, the ASTM D4170 fretting test method was developed to evaluate the fretting protection property of lubricating grease. The ASTM test is conducted under a fixed load, but the load condition for industrial machines usually fluctuates. Currently, there is no international standard to evaluate the fretting wear under fluctuating load. In this study, using thrust ball bearings the authors examined 14 kinds of commercially produced greases and three kinds of originally prepared greases on fretting protection evaluation under both the ASTM test and the impact fretting test. Consequently, the authors found out the inversion of the order of fretting protection superiority between the ASTM test and the impact fretting test. As for the kinematic viscosity of base oil of grease, the amount of wear of ASTM test increases with increasing the kinematic viscosity, on the other hand the wear of impact fretting test decreases with increasing the kinematic viscosity.
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