Effect of surface roughness of roll on coefficient of friction in hot rolling

In order to understand the tribological behavior at the interface between roll and workpice in hot steel rolling, it is important to measure the coefficient of friction and examine the effect of the tribological factors on the coefficient of friction. In this paper, the effects of the surface roughness of roll on the coefficient of friction are investigated by using the tribo-simulatior testing machine for hot rolling developed by the authors. The workpice material used is SPHC. The roll material is SKD11 and the surface roughnesses are 0.1, 0.2, 0.4 and 0.8 mu m Ra. The rolling tests are carried out at a temperature of 800 degrees C during a rolling distance of 400 mm, changing the rolling speed from 50 to 70 m/min. The colza oil is used as a base oil and the emulsion concentrations are 0.1 and 3.0%. The coefficient of friction at an emulsion concentration of 3.0% dose not depend on the surface roughness of roll. However, the coefficient of friction at an emulsion concentration of 0.1% decreases with increasing surface roughness of roll up to a surface roughness of 0.3 mu m Ra and over 0.3 mu m Ra it increases with increasing surface roughness of roll.