Understanding the ability of fully formulated industrial oils to protect the contacting surfaces requires techniques revealing the effect of tribofilm growth on the EHL film. This was achieved by employing sliding/rolling smooth contact in a ball-on-disc test for two industrial EAL gear oils and two industrial mineral oils. Friction and electrical contact resistance (ECR) of three stribeck stages at different running-in periods were studied besides measuring the tribofilm thickness evolutions by Spacer Layer Interferometry Method (SLIM). In the end, a wear test was performed and wear scars were measured. Results showed that lower pressure-viscosity coefficient of EALs does not necessarily lead to high metal-metal contact, and their thin tribofilm serves to keep the friction low in mixed and boundary regimes.
Open access article by Reza Bayat and Arto Lehtovaara: EHL/mixed transition of fully formulated environmentally acceptable gear oils, Tribology International, Volume 146, 2020, https://doi.org/10.1016/j.triboint.2020.106158