Effect of thermal aging on the grease film thickness in ball bearings

In this paper the effect of thermal aging of grease on the film thickness in a ball bearing is studied by aging two different types of greases in an oven for various duration and by measuring their film thicknesses in a sealed for life ball bearing and single contact. The results show that the bearing film thickness initially remains constant for a very long time. Thermal aging leads to evaporation and oxidation. Tests with thermally aged grease show that the film thickness will only change in the case oxidation has occurred. After this, the level of starvation decreases despite an increase of viscosity and decrease of bleed properties. Traction increases, which would result in a loss of lubricity.