Influence of Shaft Scratch on Static and Transient Behavior of Water-Lubricated Bearing

When sand enters the gap between the shaft and water-lubricated bearing, it will nick surfaces of shaft and bearing bush, and the scratch will appear. The variations of static and transient performance with the number and depth of scratches are studied in the paper. The results show that scratches have a significant effect on the critical load and critical speed of the transformation of bearing lubrication state. The existence of scratches reduces the critical load from elastohydrodynamic lubrication to mixed lubrication. The shaft with scratches vibrates more strongly than the shaft with no scratch at the moment of start-up. The contact area, contact time, and bush-burning probability are directly proportional to the number of scratches. Shaft center movement orbits under step load have the similar “L” shape, whether the shaft has scratch or not. But the scratched shaft has longer movement orbit and lower equilibrium point than the shaft with no scratch. This paper can provide a reference for structure design and service life evaluation of bearing-shaft system.