Development of surface finish during the polishing of porcelain ceramic tiles

Abstract

Polishing tests on a laboratory scale have been used to simulate and study the industrial polishing process for unglazed porcelain ceramic tiles. Tile surface quality was assessed in terms of roughness and optical gloss. Tests with a sequence of progressively smaller silicon carbide abrasive particles showed a general trend of decreasing roughness and increasing gloss during the process. The coarser abrasives (larger than 400 grit number) caused the major change in surface roughness, while the finer abrasives (smaller than 400 grit number) produced the major change in gloss. In these materials the maximum gloss achievable by polishing is limited by the porosity of the ceramic. The rate of material removal during polishing with a coarse abrasive obeyed an Archard-type wear law, being linearly proportional to applied load, although load had little effect on the surface roughness attained after different durations of polishing. In contrast, load had a significant effect on gloss, with higher loads leading to higher values of gloss. The development of both roughness and gloss with polishing time is well described by quantitative empirical models involving a simple exponential function. The same model for gloss evolution is also shown to apply to data reported from industrial-scale polishing experiments in previous work.