Thermo-mechanical aging during churning in grease lubricated bearings and its impact on grease life

Grease aging in a rolling bearing happens primarily during the churning phase due to high shear and temperature caused by macroscopic flow. This study utilizes a temperature profile to quantify the impact of thermo-mechanical aging on grease. Two different methods are explored to evaluate the energy dissipated in the grease during churning: one estimates the imposed energy density and the other calculates the heat transfer entropy density. Both models show a good correlation with the measured grease life. Grease life test results show that a high imposed energy density or heat transfer entropy density during churning results in shorter grease life. Therefore, a low energy density or heat transfer entropy density is preferred during churning.