EFFECT OF SURFACE-ROUGHNESS ORIENTATION ON PITTING RESISTANCE OF LUBRICATED ROLLERS

A two-roller rolling contact fatigue test machine was used to study the effect of orientation of the surface roughness on pit ting resistance. The driving disk had either longitudinal or transverse roughness while the specimen always had longitudinal roughness. The test results indicated that the roughness orientation was not an independent parameter on pitting. Fitting was related to other parameters, such as the hardness, viscosity, roughness amplitude, and slide-to-roll ratio. In pure rolling tests, the crack orientation on the specimen followed the roughness orientation on the driving disk, but only transverse cracks were observed if sliding was present. Reducing the amplitude of the roughness had a greater effect on pitting life than did increasing the lubricant viscosity. With lower hardness and smaller film thickness parameter (Lambda < 0.3) conditions, the transverse roughness on the disk caused more damage on the specimen surface than did longitudinal roughness, but the effect was reversed if the specimen had a higher hardness. In the case of Lambda larger than 1, the transverse roughness on the disk made less damage than did the longitudinal one.