Edge rounding of brittle materials by low velocity erosive wear

The finishing of sharp brittle edges frequently has the objective of achieving uniform edge rounding with low roughness, while avoiding the formation of relatively large chips. In the present work, detailed observations were made on the edge chipping and rounding of borosilicate glass and silicon nitride due to the low velocity erosive wear generated in a vibratory tub and a vibratory bowl finisher. Large-scale chipping was measured as function of the included angle of the edge and of the width of edge chamfers. Given the observed strengthening effect of edge blunting against chip formation, a processing approach was developed to achieve smooth edges in the vibratory finishing of brittle materials. In addition to the observations made on the large-scale edge chipping in vibratory finishing, it was found that all the processed glass and ceramic specimens exhibited a narrow wear band of abraded material on the curved edges of the specimens, and that the adjacent flat surfaces were unaffected or minimally affected by the erosive wear process. A fracture-based erosive wear mechanism is presented in which edge wear is attributed to micro-scale edge chipping, caused by the indentation of abrasive particles protruding from the finishing media. The rate of edge wear was found to be closely related to the evolving microtopography of the edge as reflected by measurements of a roughness parameter that is proportional to the density of peaks and the average included angle of the peaks. The suggested erosion mechanism is compared with the observed trends and rates of edge rounding.