Effect of thermorheological properties on tribological behaviors of lubricating grease

Abstract Lubricating grease has increased thermorheological properties during heating, which may affect the lubrication of the friction pair. And a friction pair usually heats up in the working process. This study explored the effect of surface temperature of the friction pair on the lubrication performance under lubrication conditions. The thermorheological properties of lubricating grease were analyzed using a rotational rheometer, and the variations and mechanisms of the thermo- rheological properties were explored. The friction-wear test on lubrication was conducted at different temperatures to examine the effects of thermorheological properties on the tribological behaviors of lubricating grease. Wear scar morphology, composition change, and friction-lubrication mechanisms at different temperatures were probed through SEM and X-ray spectrometer analysis. The results showed that lubricating grease has significant thermorheological properties. Moreover, its soap fiber entanglement decreases with rising temperature, and the entanglement properties are slowly lost at high temperature. The soap fiber structure of lubricating grease plays a vital role in lubrication. As temperature rises, the soap fiber entanglement of lubricating grease decreases and the base oil is more easily released under shear, exhibiting a trend of friction coefficient decreasing with the rising temperature. High temperatures weaken the soap fiber entanglement of lubricating grease, the film-forming property, and the surface friction-abrasion resistance of the friction pair and even cause oxidative wear.