Correlation of grinding rate of gibbsite with impact energy in tumbling mill with mono-size balls

Dry grinding of a gibbsite powder was conducted in air using a tumbling bal l mill with mono-size of media (balls) ranging from 4.8 to 31.7 min diamete r to investigate ball size effect on grinding rate. The impact energy of ba lls during grinding was calculated by the method proposed previously in ord er to correlate with the grinding rate. The grinding rate increases with an increase in the rotational speed of the mill, subsequently, it falls aroun d the critical speed. The maximum grinding rate shifts toward higher rotati onal speed range as the ball size becomes large. In the range of rotational speed before the grinding rate falls, the grinding rate is improved when g rinding with balls of 12.7 mm or less, while it is reduced when larger ball s over 15.9 mm are used. A similar trend can be seen in the relation betwee n the specific impact energy of balls and the rotational speed of the mill. The grinding rate is proportional to the specific impact energy of balls r egardless of the ball size. Therefore, the specific impact energy of balls plays a significant role in governing the grinding rate in tumbling ball mi lling of the sample powder. (C) 2001 Published by Elsevier Science Ltd. All rights reserved.