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

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 at the inlet to the contact zone (V) and sliding velocity during deformation (ΔV). Experiments with stainless steel sheets of two different surface roughnesses showed that the variations in the friction coefficient with entraining velocity V and sliding velocity ΔV are largely dependent on the initial surface texture of the workpiece. For a smooth workpiece, the friction coefficient decreases with increasing sliding velocity ΔV but keeps almost constant with increasing entraining velocity V. However, for a rough workpiece, the friction coefficient initially decreases slowly and increases largely with increasing sliding velocity ΔV or decreasing entraining velocity V. Observation of the rolled surface for a smooth workpiece shows that, with increasing entraining velocity V, the slip band becomes more marked, and with increasing sliding velocity ΔV, the rubbed portions become more conspicuous. For a rough workpiece, galling occurs at high sliding velocity ΔV. The critical condition for galling outbreak is shown on the V–ΔV graph. The galling outbreak process is observed by interrupting the rolling process.