Mechanism of graphene lubricating oil cooling effect on Si3N4-GCr15 friction pair

Abstract

Si3N4-GCr15 (silicon nitride-bearing steel) friction pair is often used in high-speed bearings. The molecular dynamics model of graphene additive lubricating oil (mixed oil) is developed to study the effect of graphene as a nano lubricant additive on the thermal conductivity of the lubricating oil. With the research temperature range of 298~532 K, the results of internal molecular dynamics simulation show that the thermal conductivity of mixed oil increases with the increase in the graphene mass fraction at 298 K. When the temperature is higher than 298 K, the thermal conductivity of the mixed oil increases first and then decreases with the increase of the graphene mass fraction. When the mass fraction of graphene is constant, the thermal conductivity of the mixed oil increases first and then decreases with the increase of temperature. An experiment was designed to investigate the heat transfer coefficient for mixed lubricating oil at test specimen surface. Experiments show that an appropriate amount of graphene is added to improve the convective heat transfer between the lubricating oil and the test piece. However, as the amount of graphene added increases, the viscosity of the mixed oil increases, thereby inhibiting the fluid flow behaviour, resulting in a decrease in the convective heat transfer coefficient. This shows that only an appropriate amount of graphene additive has a cooling effect on Si3N4-GCr15 friction pair.