Abstract: Three mill units are mounted axially in series in a mill housing with a cover. Each mill unit has a rotor disc between two stator discs. The rotor discs are secured to the rotor shaft at their radially interior region. The stator discs are secured to the housing wall at their radially outer region. Individual pulverization gaps are formed between the stator discs, which gaps run around the rotor discs and in longitudinal cross section extend sequentially with a serpentine shape. The outer parts of the pulverization gaps form individual gap loops the inner ends of which are connected or "short-circuited" via ball return channels. During operation, the grinding elements are accelerated outward by centrifugal forces, and are concentrated into the gap loops. The grinding elements in each of the individual stages may be kept separated from the grinding elements in other stages; and they may have different sizes from stage to stage. The individual mill stages can be replaced as units.