Friction in grease lubricated rolling/sliding contacts: Influence of thickener type and a comparison among grease, bled oil, and base oil

The influence of thickener type on grease lubrication was examined by comparing six greases formulated with the same base oil (PAO10) and NLGI grade. Friction curve, traction curve, and film thickness were measured in rolling/sliding point contacts over a broad range of entrainment speeds and temperatures. Under mixed lubrication conditions, clear differences in friction behavior were observed among the greases, particularly at low speeds and higher temperatures. In this regime, several greases showed lower friction coefficients than both the base oil and their corresponding bled oils. With increasing entrainment speed, the friction and traction responses of the greases progressively approached those of the base oil. In addition, temperature markedly affects the frictional behavior of greases compared to the base oil and bled oils. Film thickness measurements further showed that both greases and bled oils produced thicker films than the base oil, with the extent depending on thickener morphology and oil release behavior. The results indicate that thickener-related effects play an important role in grease lubrication and should be considered when assessing performance across different lubrication regimes.