126.96.36.199 Ball mills. The ball mill is a tumbling mill that uses steel balls as the grinding media. The length of the cylindrical shell is usually 11.5 times the shell diameter ( Figure 8.11). The feed can be dry, with less than 3% moisture to minimize ball coating, or slurry containing 2040% water by weight. The ball mill-hydrocyclone circuit and the ball mill-screen circuit were sampled in order to measure and compare the performance of the circuits. The ball mills are different in design.