Lubricant additives for improved pitting performance through a reduction of thin-film friction

• Effects of VMs, AW, and EP additives on pitting are analysed.
• The pitting lives of four oils are investigated using rolling four-ball tests.
• The pitting lives correspond well with measured friction levels for the oils.
• The mechanism proposed for improved life is due to a lowering of thin-film friction.

This paper describes an investigation into possibilities of enhancement of pitting lives of rolling components by using additive combinations with low thin-film friction. Various viscosity index improvers, anti-wear and extreme-pressure additive combinations were analysed in terms of their frictional behaviour, which in turn was compared to the oils pitting lives. For the pitting studies, a rolling four-ball test was employed. Friction was measured using a ball on disc machine as well as indirectly through “near contact” temperature measurements performed during rolling four-ball tests. The results show that additive combinations that result in low friction at the specific running condition can enhance pitting performance.