EFFECT OF IMPACT ON THE GRINDING MEDIA AND MILL LINER IN A LARGE SEMIAUTOGENOUS MILL

The introduction of large semiautogenous mills to grind larger pieces of ore necessitates the use of large diameter grinding balls. Grinding balls as large as 127 mm (5 in) in diameter are not rare. The increased height of fall of such grinding balls in these larger mills results in severe impact between the grinding balls and also between the grinding balls and the mill liners. Severe impact also resulted in fatigue failure of the mill liners and a phase transformation below the surface of the grinding balls due to the generation of high temperature. In smaller mills, using smaller grinding balls, considerable work hardening was observed beneath the surface of the grinding balls. The extent of the work hardening increased with increase in the ball and mill diameter.