Abstract:
In a grinding machine comprising a stationary wall part and a plate part which rotates about an axis of rotation, between which a gap is formed, the gap is limited from above by a ceramic part and from below by an elastic part.

Description:
This application claims Paris Convention priority of DE 200 18 805.4 filed Nov. 3, 2000 the complete disclosure of which is hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     The invention concerns a grinding machine having a stationary wall part and a plate part, which can rotate about an axis of rotation, wherein a gap is formed between the stationary wall part and the plate part. 
     A grinding machine of this type is disclosed in DE 196 06 117 A1. Such a grinding machine operates under the influence of centrifugal force. Workpieces to be treated and grinding material are disposed within the inner space formed by the wall and the plate part, and rotated through rotation of the plate part to effect a polishing effect through the influence of centrifugal forces and the relative speeds between the workpieces and grains of grinding material. 
     In a known embodiment, the annular gap between the rotary plate part and the stationary wall part is limited from the upper side by an elastic lining of the wall part, and, on the lower side, by a ceramic ring disposed on the rotary plate. The ceramic ring has a rectangular cross-section. The plate part is formed directly below the ceramic ring and tapers inwardly towards the bottom. While the elastic lining, due to its elasticity, is hardly worn by the grinding material bodies, it has turned out that the ceramic ring experiences large wear as a result of continuous exposure to grinding bodies, wherein, in particular, grinding material bodies collect in the gap and, through their abrasive effect, grind down the ceramic ring in the region of its inner upper edge thereby forming a step having a depth of 3 mm to 5 mm, within a short period of time. Grinding material can collect therein and accumulates up to the lower edge of the lining of the stationary wall to cause further wear of the ceramic part in response to the relative motion between the wall and the plate parts. The ceramic part must therefore be replaced after a short period of time. 
     It is the underlying purpose of the present invention to further develop a grinding machine of the above-mentioned type which has a longer service life. 
     SUMMARY OF THE INVENTION 
     This object is achieved in accordance with the invention by a grinding machine of the above-mentioned type, characterized in that the gap is limited from the top by a ceramic part and from the bottom by an elastic part. It has surprisingly turned out that, compared to prior art, the abrasive effect of the grinding material bodies on the ceramic part is much less if the ceramic part is disposed on the lower side of the stationary wall, wherein the ceramic ring limits the gap from above. The gap is limited from below by the elastic lining of the rotary plate part. The reason for the reduced wear may be that, although a small step also forms in the region of the inner lower edge of the ceramic ring due to the abrasive effect of the grinding material bodies, grinding material cannot collect and accumulate therein, since it is constantly removed by the undamaged opposite edge of the elastic lining of the plate part. 
     The invention therefore provides for a much longer service life compared to prior art. The ceramic ring must only be replaced after a much longer period of use. 
     The elastic part of the plate part is preferably a lining thereof while the ceramic part is a ceramic ring. Preferably, surfaces are provided between the two opposite planes which are preferably oriented horizontally and perpendicularly with respect to the axis of rotation. They can also incline slightly towards the inside with respect to the horizontal, e.g. in a range of 10° to 30°. The axis of the grinding machine is usually vertical. A particularly preferred embodiment of the invention is characterized in that the ceramic part has a nose-like projection extending downwardly, wherein, in particular, the inner wall of the plate part and wall part are formed substantially conically, tapering from the top towards the bottom above and below the gap. The conical inclination of the inner wall with respect to the vertical axis of rotation can thereby be 30° to 45°. Both, this inclination of the plate part directly below the gap as well as the conical inclination extending inwardly and downwardly of the inner wall of the wall part, support the abrasion-preventing arrangement of the gap-limiting ceramic part on the upper wall part and the elastic part of the rotary plate limiting the lower side of the gap. 
     Further advantages and features of the invention can be extracted from the claims and the following description which show, in detail, an embodiment of the invention with reference to the drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     FIG. 1 shows a vertical section through a preferred embodiment of the inventive grinding machine, partly cut; and 
     FIG. 2 shows an enlarged detailed representation of the device of FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows a vertical longitudinal section of a preferred embodiment of an inventive grinding machine  1 . The grinding machine is symmetrical about its axis of rotation A such that substantially only the right part of the vertical section is shown. The inventive grinding machine  1  comprises a stationary wall part  2  below which a plate part  4  is provided which is rotated about the axis A by a drive shaft  3 . Outside of the plate part  4  and surrounding same a stationary lower part  6  can be adjacent to the lover side of the wall part  2 . These components are substantially metallic, e.g. aluminum. The wall part  3  and the bottom part  4  have an elastic lining  7 ,  8  on their inner side, preferably of polyurethane. The lower side of the wall part  2  comprises a ceramic ring  9  which is firmly connected to the wall part  2 . 
     The lower region of the inner wall of the elastic lining  7  and thereby of the wall part  2  exhibits a tapered inclination with respect to the vertical line defined by the axis of rotation A, wherein the angle of inclination can be in the range of e.g. 30° to 45°. The ceramic ring  9  has an inner wall  11  which substantially extends at that same inclination and an upper wall side  12  and rear wall  13  which are directed substantially perpendicular to each other and perpendicular and parallel with respect to the axis A, respectively. The lower inner side of the ceramic ring has a nose-like downwardly extending projection  14  which merges in its rear region, via an inclination  16  slanting upwardly from an edge  16   a  and outwardly, into an outer lower wall region  17  extending horizontally, perpendicular with respect to the axis of rotation A, up to the outer edge  17   a  of the ceramic ring  9 . The inclination  16  can also extend continuously from the edge  16   a  to the edge  17   a , wherein the horizontal region  17  is omitted. 
     The upper side  19  of the elastic lining  8  of the plate part  4  angles outwardly to form a projection  18 , which extends substantially along the upper side  19  of the plate part  4 . The upper surface of the projection  18  is flat and extends parallel to the lower side of the nose  14   a.    
     The grinding machine  1  is operated by inserting workpieces, such as rings or the like, and grinding material into the inner space formed by the wall  2  and plate  4  and rotating the plate part  4  at a high speed thereby grinding the workpieces with the grinding material. During operation, the grinding material reaches the region of the gap S. Due to the elasticity of the elastic lining  8 , the abrasive effect on it is relatively small. The abrasive effect is larger on the ceramic ring, in particular in the region of its inner lower edge  21 . 
     It has turned out that the abrasive effect and therefore the wear of the ceramic ring is considerably smaller with the inventive design compared to that of prior art. 
     List of Reference Numerals 
       1  Grinding machine 
       2  wall part 
       3  drive shaft 
       4  rotary plate part 
       6  stationary lower part 
       7  elastic lining 
       8  elastic lining 
       9  ceramic ring 
       11  inner wall 
       12  upper wall side 
       13  rear wall 
       14  nose-like projection 
       14   a  nose 
       16  inclination 
       17  lower wall region 
       18  projection 
       19  upper side 
     A axis of rotation 
     S gap