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 (Δ V). 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 Δ V are largely dependent on the initial surface texture of the workpiece. For a smooth workpiece, the friction coefficient decreases with increasing sliding velocity Δ V 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 Δ V 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 Δ V, the rubbed portions become more conspicuous. For a rough workpiece, galling occurs at high sliding velocity Δ V. The critical condition for galling outbreak is shown on the V–Δ V graph. The galling outbreak process is observed by interrupting the rolling process.