of teeth which are in each case formed by a groove 39 running helically in the peripheral direction of the opening roller 21 and indents 40 extending substantially parallel to the axis of rotation 41 fig3 shows an opening roller 21 in a side view partially in section as can be seen an opening roller 21 of this type consists of a central roller body 33 which is non rotationally arranged on a shaft 32 by means of a press fit a drive wharve 23 also being fixed to the shaft 32 the clothing ring 27 according to the invention is preferably non positively fixed in its installation position on the roller body 33 between annular collars 36 37 the annular collar 37 is detachably arranged here and can be fixed on the roller body 33 by means of a screw bolt 49 or the like the opening roller 21 which can be freely rotated about the rotational axis 41 is also as usual supported by means of roller bearings 34 in a bearing housing 35 which can in turn be fixed in the bearing bracket 19 of the cover element 8 as shown in fig4 the clothing ring 27 according to the invention which is preferably manufactured as a solid ring and produced from steel for example consists substantially of a tubular basic body 45 with an annular centring shoulder 46 in the region of its internal diameter as can be seen the clothing ring 27 is configured as a tearing tool on its outer periphery in other words in the region of the outer periphery of the clothing ring 27 a large number of teeth 38 are arranged which are formed by milling in a groove 39 running helically in.