The paper discusses a way of choosing the design features (geometry, the rate of grinding and thrust) of ring-ball mills. Various methods of calculating the optimal rate of grinding have been compared. Basing on experimental investigations on the pilot-plant and industrial scale, the influence of the angular velocity and the thrust on the mill have been verified, and the interdependence between the rate of grinding and the thrust of the grinding elements have been explained.

The empirical-analytic model of milling in a ring-ball mill has been presented. It concerns the interaction of the basic design features of the grinding unit (geometry, rate of grinding and thrust of the balls) on the maximum efficiency of the mill. The production of pulverized coal was expressed by the product of the flux of material drawn in by the balls and the so-called "grinding effect of the balls" (defined by the increase of the mass fraction of dust in its flux). The kinematic quantities (among others, the flux of loose material drawn in by the balls) have been calculated on the basis of a simple analytical description of the flow of particles and some parametrical assumptions. The grinding properties of coal have been determined making use of laboratory tests of its cruising by the rollers. Some verifications of the grinding model on the experimental test stand with a ring-ball mill have been presented. The test stand is installed at the Institute of Power Engineering and Turbomachinery of the Silesian University of Technology.