Especially for conventional abrasives, crushing and milling are applied to change the size and shape of the abrasive grits [KLOC05a, p. 24]. For this purpose, jaw crushers, roll mills (roll crushers), gyratory crushers, ball mills, or pipe mills are utilized [LIET08]. Crushing with rollers can create needles in extreme cases; crushing with impact mills (hammer mills) produces cubical, blocky grits; crushing with roll mills causes grit splintering [MARI07, p. 79]. The crushing and milling processes are always carried out so that the abrasive grits remain sharp-edged [STAD62, p. 7].
Abrasion of the crushing equipment cannot be avoided [LIET08]. Steel equipment is preferred because the abraded particles can be removed by magnetic separators [LIET08].
Heat treatment in general increases toughness in conventional abrasives [SCHT81]. However, the grit toughness in one-phase systems such as white corundum and SiC is not affected much, whereas regular corundum shows a larger toughness increase at temperatures up to 1350 °C [SCHT81]. Heat treatment takes place at temperatures of 1100-1400 °C in an oxide containing, oxidizing atmosphere. The cracks and flaws created by the crushing process anneal and the containing TiO2 converts [MARI07, p. 79, TYRO03]. Above 1350 °C grit toughness is rapidly decreased [SCHT81]. During heating, regular corundum changes its color from dark brown to dark blue and grey [SCHT81].