Effects of different grain sized sands on wear behaviours of NBR/casting copper alloys

Nitrile Butadience Rubber (NBR) is widely used in marine water-lubricated stern tube bearings. The sand in water, especially in a river (e.g., Yangtze River), is a key factor affecting the tribological properties and lubrication performance of the rubber stern tube bearings. Studying the wear performance of rubber stern tube bearings under different grain sized sands will provide a guide for rational design of the rubber stern tube bearings to reduce wear and prolong service life. In this study, a CBZ-1 tribo-tester was used to conduct sliding wear tests under the sand water with different grain sizes (i.e., 4.5 µm, 23 µm, 48 µm, 75 µm), distilled water-lubricated conditions and the same mass concentration of 1.1%. The comparison analyses of friction coefficient, wear volumes and the worn surface morphologies were conducted. The results showed that the grain size of sands, sliding velocity and applied load had significant effects on the wear performance of NBR/ZCuSn10Zn2 cast copper. The friction coefficient, wear volumes and worn surface morphologies of most samples increased as the applied load and grain size increased. The sand particles destroyed the water-film to reduce the properties of NBR/ZCuSn10Zn2 cast copper. Meanwhile, the higher the sliding velocity, the easier the water-film formed between the NBR/ZCuSn10Zn2 cast copper. The friction coefficient, wear volumes and worn surface morphologies of rubbing pairs decreased as the sliding velocity increased. It is believed that the knowledge obtained in this study provides the real practical basis for running condition selection of water-lubricated rubbing stern tube bearings in marine propulsion systems.