Abstract: The grinding unit comprises a grinding rotor unit, incorporating a inlet screw member, a conical grinding tool member, a delivery dish member and a gear unit. A dog clutch is operationally inserted between the delivery dish member and the gear unit. A safety clutch is operationally inserted between delivery dish member and grinding tool which limits the torque to be transmitted. The safety clutch is provided with ball members located in axially running bores of the delivery dish member and being axially displaceable in these bores. The ball members are forced against the front face of the grinding tool and partially engage apertures provided therein under the influence of spring members assigned to each ball member. The delivery dish member is provided at its surface which faces the grinding tool member with a metallic disc member in which are located the mouths of axial bores containing the spring pressure loaded ball members.