Effect of microstructure and rheology on the grease EHL film thickness at medium speeds

In this study the parameters influencing the film thickness of six greases in a rolling elastohydrodynamically lubricated contact under fully flooded conditions are analyzed. The grease film thickness was found to be higher than their corresponding bled oil suggesting the presence of thickener in the contact. The film thickness of the greases were found to be independent of rheological properties characterized by steady and dynamic shear. AFM measurements of the thickener micro-structure showed that the relative increase in the film thickness due to entrainment of the thickener was proportional to the ratio of thickener volume fraction and the size of the thickener. Hence, with the same concentration, smaller thickener particles create thicker films than larger thickener particles. With the limited number of greases that we studied this varied between 1 % and 70%.