The influence of oscillation sequences on rolling bearing wear

Oscillating applications for rolling bearings include construction machinery like cranes and excavators and wind turbine pitch and yaw bearings. Due to the widespread use and the specific challenges of wind energy, oscillating applications have gained increased attention by the scientific community in the last years. In wind turbines, the amplitudes, their mean values and external loads of oscillations vary. In this paper, the authors examine the effect of different sequences of oscillations on rolling bearing wear by the means of tests with 7220 type bearings. Loads and kinematic parameters are downscaled from wind turbine applications; the lubricant is a fully formulated grease. To compare different sequences of oscillations, a reference test with 40.000 cycles of 3.95° double amplitude and 2.5 GPa contact pressure was varied. Constant, small amplitudes produced clearly visible damage patches on the bearing rings. The bearing rings had no visible surface damage if larger movements of 79° each 10 cycles interrupted the small-amplitude movements. We named such large movements protection runs. Protection runs are effective, even if their movement is interrupted by pauses or small reverse movements. These results show that the sequence of varying oscillations has a significant influence on wear risk.