Surface Roughness Effect on the Friction and Wear Behaviour of Acrylonitrile–Butadiene Rubber (NBR) Under Oil Lubrication

Recently, the tribological characteristics of rubber elastomers have attracted widespread attention of researchers due to its destructive character and its high frequency of occurrence. However, most experiments were performed by using relatively smooth mating surfaces and did not consider the effect of the surface roughness of the harder counter surface, which could be important in practical applications. This study is devoted to investigate the effect of surface roughness on friction and wear behaviour of elastomer. Various kinds of rough mating surfaces with different surface roughness from R _a = 0.5 to R _a = 0.003 on the steel plates were attained, and the reciprocating sliding tests were performed on a NBR pin against a steel plate. The friction coefficients obtained when the rubber slid against the different textured surfaces were analysed and compared. The morphologies of the NBR worn surface were examined by using scanning electron microscopy. On the basis, the optimal surface roughness values of the metal counterpart are proposed for the rubber sliding against the metal. In addition, Stribeck-like curves are obtained and their characteristics are discussed. A series of experimental results are presented to examine the effect of surface roughness on the Stribeck curves. The results show that surface roughness had a significant effect on the lubrication regime and tribological behaviours of the NBR. Overall, the rougher the surface of the counterpart is, the more easily the friction pairs enter into the ML regime. The surface damage of rubber depends on coupling action of surface roughness of the harder counter surface and lubrication regime. The knowledge gained herein provides a better understanding for the tribological characteristics of rubber elastomers associated with surface roughness, and it is useful to reduce sealant wear and lengthen their service life.