Influence of MoS₂ and PTFE in oil film characteristics and tribological performance in EHL point contacts

ABSTRACT

The use of improvers of viscosity index mixed with engine oil to enhance film thickness of lubricant, have been tribologically studied by the optical interferometry technique. The viscosity index improvers (PTFE and MoS₂) effect on the mixed engine oil, were experimentally studied and compared with benchmark engine oil without added viscosity improvers. The outcome of the improvers, rolling velocity and contact pressure on the engine oil film formation in a steel ball, loaded on a flat glass surface in point contact, was investigated. The two-beam light source optical interferometry principle was used in this experiment. The Hamrock and Dowson's numerical methods for EHL film formation was compared with the tribo-test results. The base engine oil for this study is SAE 30 while PTFE and MoS₂ powdered lubricants were blended with the engine oil. The viscosities of the lubricants ranged from 0.0109 Pa s to 0.255 Pa s. The rolling speed and the loads were distinctly selected between 0.189 m/s to 0.641 m/s and 1 N to 2.6 N, respectively. The steady and rolling state was used to evaluate the stability of the film thickness at contact point. The viscosity improvers were observed to have significant positive influence on the film thickness behaviour.

KEYWORDS:

• PTFE additive
• film thickness
• liquid-solid lubricant

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the China Post-Doctoral Fund [grant number 2015M582357], National Natural Science Foundation of China [grant numbers 51575190, 51675105 and 51575113]. Special gratitude to the Special Support Fund of Guangdong Province (2014TQ01X542) and Fundamental Research Funds for Central Universities (2015ZZ080) for supporting this work.