Effects of entraining velocity of lubricant and sliding velocity on friction behavior in stainless steel sheet rolling

Abstract

A series of experiments was carried out using a rolling-type tribometer to investigate the effects on friction behavior of the entraining velocity of the lubricant (ν) at the inlet to the contact zone and sliding velocity during deformation (Δν). Experiments with stainless steel sheets of two different surface roughness show that the variations in the friction coefficient with entraining velocity and sliding velocity are largely dependent on the initial surface texture of the workpiece. For a smooth workpiece, the friction coefficient decreases with increasing sliding velocity but keeps almost constant with increasing entraining velocity. However, for a rough workpiece, the friction coefficient initially decreases slowly and increases largely with increasing sliding velocity or decreasing entraining velocity. Observation of the rolled surface for a smooth workpiece shows that, with increasing entraining velocity, the slip band becomes more marked, and with increasing sliding velocity, the rubbed portions become more conspicuous. For a rough workpiece, galling occurs at high sliding velocity. The critical condition for galling outbreak is shown on the ν-Δν graph. The galling outbreak process is observed by interrupting the rolling process.