multiple preferably four parallel flutes orbit helically in order to achieve an adequate helix angle u03b1 the flutes 29 are designed open at their beginning and end due to the rotational motion of the lower seal half with the helical flutes 29 a certain transport of air from the interior of the eccentric drive through the sealing gap s1 towards the exterior of the crushing space occurs a penetration of dust laden air in the opposite direction into the interior of the eccentric drive is thereby reliably prevented a circumnavigent annular groove 32 is disposed in the inner wall of the cylindrical ring 25 of the upper seal half in the lower range thereof the groove 32 can be filled with grease from the outside by way of a grease fitting 33 in operation the grease is pressed into the annular groove 32 or respectively against the interior wall as a result of centrifugal force and reduces the sealing gap s1 to the smallest possible dimension excess grease is transported downwardly out of the sealing gap s1 by the serrate flute shoulders should despite the air flowing out of the sealing gap isolated superfine dust particles penetrate into the sealing gap from below then the same are hurled toward the exterior by the centrifugal force and adhere to the grease in the annular groove 32 however the dust particles are repeatedly stripped from the surface of the grease.