Study on removal mechanism at the tool rotational center in bonnet polishing of glass

Preston's law is a widely used equation that expresses time-dependency of material removal in polishing process. In this research, it is experimentally found that Preston's law does not hold at the tool rotational center in glass polishing. Material removal observations point to a mechanical phenomenon accelerated by chemical reaction. To identify the underlying phenomenon, experiments are conducted that isolate the contribution from each constituent factor in Preston's law. By observing the motion of loose-abrasive particles during polishing, it is found that they travel as expected on concentric trajectories around the tool rotational center. By measuring the pressure distribution in static situation as well as the contact force during polishing, it can be concluded that no hydrodynamic increase in pressure occurs at the tool rotational center. Finally, experiments are performed to investigate the relationship between distance from tool rotational center and removal depth by a single abrasive particle. The depth of removal is observed to reach a maximum value at the tool rotational center in all polishing conditions tested, from which a modified expression of Preston's law is derived. Finally, hypotheses based on fracture and material mechanics are proposed to explain abrasion mode transitions in single particle abrasion.