Ball bearing skidding and over-skidding in large-scale angular contact ball bearings: Nonlinear dynamic model with thermal effects and experimental results

From a kinematic point of view, rolling elements should continuously roll on the raceways of rolling element bearings. When the dynamic behaviour is also considered, pure rolling occurs if the bearing is properly loaded and the system is correctly lubricated. In the absence of these conditions, the rolling elements may slide, or skid, from time to time. In the literature, this behaviour is well documented and occurs generally for low-load roller bearings. During a long-lasting experimental test on a large-scale industrial angular contact ball bearing (ACBB), not only skidding behaviour but also so-called over-skidding behaviour was observed on the rolling elements of the bearing. The term over-skidding, or negative-skidding, means that the cage/rotor speed ratio exceeds the value calculated under pure rolling kinematic conditions. To the best of authors’ knowledge, this phenomenon has not been fully described or analysed before. Therefore, a comprehensive model considering the kinematics of the bearing components, the Hertzian contact between the rolling elements and raceways, the interaction between the rolling elements and cage, the hydro-dynamic lubrication, and the thermal effects is introduced in this paper to study and forecast the over-skidding and skidding mechanisms. The model acronym is KH-THD, that is the kinematic-Hertzian-thermo-hydro-dynamic model. The empirical existence of over-skidding indicates that the use of the theoretical value for the cage/rotor speed ratio is inaccurate for determining whether the bearing rolling elements are slipping or not on the raceways, especially for large-scale industrial bearings. The results of the experimental tests on such kinds of bearings obtained by varying the load and under three different operating rotational speeds and two lubricant supply conditions suggest that the KH-THD model is more accurate than existing models, which neglect the thermal effects due to friction. The analysis of the friction thermal effects due to skidding shows that a considerable temperature gradient forms in the bearing. The increase in the lubricant flow rate can somehow mitigate the increase in temperature even though it can worsen the skidding. The proposed model is useful for determining this trade-off for a given load.