Millstar Ball Load Estimator Millstar Mill Power Filter MillStar Intelligent Filtering and Fault the varying size and hardness of the mill feed material affects the residence time in the mill and the power drawn. feeder to determine the size distribution of feed material.Exploring ball size distribution in coal grinding mills - ResearchGate. ABSTRACT Tube mills use steel balls as grinding media. new balls periodically to maintain a steady balanced ball charge in the mill. of the calculation of the size distribution of the equilibrium mixture of balls in a ball mill is developed.