Jan 07, 2015· 2. Shape, size, and weight of the grinding media. 3. Friction between the lining and the grinding media. 4. Internal friction mill charge. Figure: Grinding media 4.4.1 Grinding Ball Charge in Mills: According to Levenson, the optimum grinding ball charge should be r - 0.16D The degree of ball charge varies with in the limit of 25 and 45%.