Experimental Investigation in to Lubricant Properties and Surface Features on Thrust-ball Bearing Skidding and Friction Torque

In severe operating conditions, skidding has emerged as a primary factor aggravating the rolling bearing failure, particularly for thrust ball bearings, where the skidding phenomenon is especially pronounced. Current research on bearing skidding mainly focuses on measuring the skidding rate of rolling elements or cages in radial bearings. However, due to the non-uniform load distribution in radial bearings and the coupling effects of numerous influencing factors, it remains challenging to accurately elucidate the mechanism of bearing skidding. Nevertheless, bearing skidding is intrinsically linked to bearing lubrication, bearing life, and even the reliability of the entire equipment. Therefore, under practical working conditions, clarifying the mechanism of rolling bearing skidding is an essential issue that must be addressed in bearing research. In this study, using the features of uniform load distribution and considerable skidding in thrust ball bearings, a custom thrust bearing test bench was designed. This setup was used to investigate the skidding behavior and lubrication characteristics of thrust ball bearings under actual working conditions. Specifically, it could be employed to examine the lubricant properties, rolling element surface properties, surface roughness, and applied loads influenced skidding and friction torque. Additionally, the relationship between the skidding rate of rolling elements and film-forming properties, friction torque, lubricant properties, and surface properties was analyzed, aiming to establish a comprehensive relationship among these factors. Thus an evaluation method was established to analyze the lubricant performance and surface performance of contacting pairs based on the skidding rate test of thrust ball bearings, providing a reference for selecting rolling bearing lubricants and assessing bearing lubrication performance. The test results indicated that PAO oil, due to its weak polarity, was prone to cause rolling element skidding, leading to a reduced trend in film thickness growth and increased friction torque. In contrast, naphthenic oil with strong polarity exhibited a lower rolling element skid rate, had almost no effect on film thickness, and demonstrated lower friction torque at higher speeds. PAO oil adsorbed poorly on ceramic ball surfaces, resulting in higher friction torque at low speeds compared to steel balls but also causing a higher skidding rate for the contact pair. Due to the lower thermal conductivity of ceramic balls, friction torque showed a slower increase under high-speed conditions. Increase in surface roughness led to an overall rise in friction torque and prolongs the mixed lubrication interval. Higher loads increase the contact area, which could suppress the degree of skidding.