At the RHI grinding plant (Site: Veitsch), differing materials of varying comminution behaviour are ground to the necessary particle size. The milling process in use consists of a ball mill designed for a capacity of 9 tons material per hour in closed circuit with an air classifier. The required particle size of the ground product depends on the subsequent process and is thus variable. Some of the products are too fine for optimum utilization. Within a shift of 8 hours up to 4 different materials are ground back to back in the ball mill. Within this tesis the comminution behaviour of selected materials are determined by the OCS method. The grinding plant is characterized by sampling the mass flows and by detailed analysis of the appartus involved. The influence of the frequent feed material changes on the process stability is investigated. Possibilities to shift the size distribution to the coarse with the existing apparatus are discussed.