Polishing Process of Ceramic Tiles - Variation of Contact Pressure

The contact pressure is one of the most important parameter in the industrial polishing process of ceramic tiles. The contact pressure is asically a function of the elasticity moduli of both tile and abrasive tool, the applied load, and also the curvature of the abrasive tool. Due to the wear, this curvature decreases during the polishing process, causing an increase in the contact pressure. The purpose of this work is to research the influence of contact pressure on the evolution of gloss and roughness of the polished ceramic tiles and to improve the quality of generated surface. The variation of curvature was replaced with the direct increment of three different normal forces onto the abrasive tool. It is known from literature that for fine abrasive grits higher tool loads increase gloss gain and decrease roughness. However, there are not many works that research the whole sequence of abrasives for different loads and compare the quality of the final surface. Polishing tests on a laboratory scale CNC-Tribometer have been used to study the industrial polishing process for unglazed porcelain ceramic tiles. Tests were carried out for three different tool loads with a sequence of progressively smaller silicon carbide abrasive particles embedded in a magnesia cement matrix. Tile surface quality was evaluated by roughness and optical gloss. The removed work piece material and the used abrasive were measured with a coordinate measuring machine. The distribution of gloss and roughness of the tile was measured before and during the experiments until a saturation of gloss and roughness for each grit number was achieved, respectively. The topography of the tile was measured before and after the polishing process with particularly grit number. The used abrasives show a general trend of increasing gloss and decreasing roughness during the process. The coarse abrasives caused the major effect on surface roughness and almost no effect on gloss. In opposite finer abrasives caused the major gloss enhancement and almost no effect on surface roughness. The results show the evolution of roughness and gloss for each load as a function of abrasive grit number and polishing time, as well as the material removal rate for each grit number and load.