Common types of grinding mills include Ball Mills and Rod Mills. This includes all rotating mills with heavy grinding media loads. This article focuses on ball and rod mills excluding SAG and AG mills. Although their concepts are very similar, they are not discussed here.
Photographs of a glass ended laboratory ball mill show action of ball mass within the mill. The action of other grinding media is similar.
As the mill revolves, lifters assist in picking up the grinding charge and elevate it to an angle at which gravity overcomes friction and centrifugal force. The charge then cascades downward