The Influence of Static Thermal Degradation on Microstructure and Rheological Properties of Lithium-Calcium Base Grease

Simple static thermal ageing tests have been carried out to simulate the thermal degradation of the Lithium-Calcium base grease used in a rolling element bearing. The microstructure and rheology of Lithium-Calcium base grease after thermal degradation were analyzed by Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and rheometer. The results show that both oil and thickener were degraded, i.e. FT-IR absorbance at 1700 cm^-1 and the enhanced strength of absorbance with the increasing aging time, and the gradually destroyed net structures of fiber with chain ruptured, degraded crystal structure of Lithium-Calcium base grease. After ageing time reached the critical value of 288 hours , the ageing of grease accelerated, the stability of the grease structures deteriorated sharply with prolonged ageing time, and the net structures of fiber rebuilt slowly after shearing, resulted that the samples cannot adhere and function well in movable joints with 288 hours ageing.