The breakage induced by a single grinding ball dropped onto a randomly packed particle bed

This paper describes some computer simulations of the breakage induced in a two-dimensional particle bed by the descent of a single large grinding ball. These are approximate experiments related to ball-milling that are tractable by the simulation technique (i.e., involve relatively few particles). As a result of the impact of the grinding ball, the particles in the bed are broken and/or scattered away from the grinding ball as it falls. Simulations were performed for four different bed depths and three different frictions. Generally, the deeper the bed, the less the total amount of breakage. The results show also show the dual role that friction plays in the breakage process. On one hand, the majority of the grinding ball's energy is lost to friction so that increasing the friction increases this energy loss. On the other hand, the friction holds the bed together and the larger the friction, the longer the bed stays in place for the grinding ball to do its work. It appears that this latter effect is the stronger of the two in that increasing the particles' coefficients of surface friction greatly increases the amount of breakage; that extra energy for breakage appears to come from a reduced kinetic energy of the scattered fragments. (C) 2000 Elsevier Science S.A. All rights reserved.