On the Thermally Induced Failure of Rolling Element Bearings

Abstract

This dissertation is devoted to the investigation of thermally induced seizure of rolling element bearings. A comprehensive thermal model of the rolling element bearings is developed which can predict the operating temperature of the bearing components in a wide range of operating conditions. The validity of this thermal model is verified by comparing the simulation results with a set of experiments. The results of simulations reveal that the rotational speed, oil viscosity and cooling rate of the housing have a significant influence on the operating temperature of the rolling bearings. To provide detailed information about all of the contact forces between the bearing components, a dynamic model of rolling element bearings is developed that can utilize different rheological models and traction curves in order to calculate the traction coefficient between the rollers and the raceways. The validity of this dynamic model is verified by comparing the simulation results with the previously published experimental results. The simulation results show that the simplified traction curves can be utilized in dynamic simulations only in operating conditions with low slide-to-roll ratios. This dynamic model is also employed to investigate the effect of surface roughness on the dynamic behavior of roller bearings operating at low rotational speeds and large radial loads. It was shown that an increase in the radial load results in a proportional increase in the wear rate and an exponential increase in the heat generation, although it does not affect the film thickness noticeably. Finally, the developed thermal and dynamic models are combined in a unified simulation approach to investigate two types of thermally induced failure in rolling element bearings. The simulations results revealed that the cage failure can occur during the thermal failure in radially–loaded rolling bearings operating at high temperatures, while a severe surface damage and disruption of the lubricant film can occur during the thermally induced failure of spindle bearings in high speed machine tools.