Abstract: A process for grinding materials comprises driving a plurality of unground particles in a grinding zone in a predetermined direction, abruptly reversing the direction of motion of part of the particles in a subsequent grinding zone so that they impact with each other and reversing the direction of motion of the particles as they pass from one grinding zone to the next, until the size of the particles is reduced to the desired level. A grinder for carrying out such process essentially comprises first and second rotors, the first rotor being provided with a plurality of first perforate members and the second rotor being similarly provided with a plurality of second perforate members alternately arranged between each pair of first perforate members. The first rotor is rotatable in a predetermined direction, while the second rotor is rotatable in the opposite direction.

Abstract: A rotary mill for micronic grinding comprising an impelling mechanism for the solid materials to be ground, such as minerals and the like, consisting of a disc, the walls of which are perforated in such manner that the materials are discharged through the perforations, and flung against the peripheral wall of the mill, thus effecting the grinding. Both around the perforations in the disc and upon the peripheral wall a protective layer is formed of the material being ground, so that the grinding is effected by the impact of the material upon the material, thus forming a self-generated grinding process.