Structural Degradation of a Lithium Lubricating Grease after Thermal Ageing

抄録

Due to the potential structural degradation when the lubricating grease was heated to improve its fluidity and pumpability, fresh NLGI 3 lithium grease was heated to simulate the static thermal ageing by using drying oven. The microstructure and infrared spectra of grease samples were studied by using field emission scanning electron microscopy (FESEM) and Fourier transform infrared spectroscopy (FTIR) technique respectively. And by using rotational rheometer, the frequency sweep and controlled-stress tests were carried out to estimate its entanglement and structural strength. At last, the mechanical reversibility was studied by carrying out triple-step-shear stress tests. It is found that the original structure of grease sample could be basically maintained after being aged at 120°C within 24 h, while the irreversible structure hardening and degradation are shown after being aged at 150°C.