Surface roughness changes during rolling

The changes in surface topography of a rolled strip have been examined after sequential passes giving various total reductions of cross-sectional area. A relocation technique has been used to reveal details of individual surface hills and valleys, and the data have been digitised for computation of selected surface parameters.It is found that the hills are very easily flattened, but that the valleys persist much longer, even after 40% reduction when a grease lubricant is used. A thin layer of MoS₂ provides lubrication but allows a smooth shiny surface to be produced by rolling.