A model for batch rod milling

Abstract A model for rod milling is proposed which states that the top sizes present in the distribution are broken preferentially. For the small mill used in the tests the enhancement of specific rate of breakage is about 1.4, that is, when a particle is in the top 15% by weight it breaks 1.4 times as fast as when it is in the bottom 85% by weight. Under normal breakage conditions, the preferential action of the rod mill on larger sizes makes relatively minor changes to the shapes of the size distributions produced. On the other hand, for large feed sizes where a ball mill would give inefficient abnormal breakage of the large particles, the rod mill still gives normal, approximately first-order breakage on these large size. Thus, compared to such ball milling, the rods appear to have a preferential action on larger particles. This is more accurately stated as: ball milling breaks too large particles slower than expected, rather than rod milling breaks large particles faster than expected.