PTFE and MoS2 Additives for Mineral Oil Film Formation in EHL Point Contacts

Lubricant film-forming viscosity index improvers blended with commercial engine oil have been developed and studied by using optical interferometry. The influence of the viscosity index improvers (PTFE and MoS₂) mixed with oil were experimentally studied and compared with engine oil without the index improvers as the baseline. The effect of the viscosity index improvers on lubricant film thickness, contact pressure and rolling speed for the case of a steel ball loaded on a flat glass surface in point contact condition was investigated. An optical interferometry technique which utilized a monochromatic two-beam interferometry light source, a microscope and a high-speed video recording device was used for the investigation. Hamrock and Dawson calculations for EHL film thickness were also used for comparative analysis. The lubricants used were commercial SAE #30 engine oil and PTFE and MoS₂ mixed with commercial SAE #30 engine oil. The oil viscosities ranged from 0.0109 Pa.s to 0.255 Pa.s. The rolling speed and the loads were varied between 0.189 m/s to 0.641 m/s and 1 N to 2.6 N respectively. The lubricant film thickness stability at the point of contact between the steel ball and the glass disc was investigated for both steady and rolling state conditions. The viscosity index improvers were found to have a significant effect on the film thickness behavior under pure rolling point contact conditions.