Kneading disc for a single screw extruder
Kneading disc for a single screw extruder.In order to improve the wear-resistance of highly stressed surfaces of a kneading disc in a helical twin screw extruder, the exposed tips of the kneading disc are provided with inserts of an extremely wear-resistant, hard material. In a variety of embodiments, the tips of the lenticular kneading disc are provided with bores and recesses for receiving the hard inserts. Advantageously, the recesses are cylindrical wells in which cylindrical inserts are soldered or cemented. The inserts may be made from hard metals or ceramics, for example tool steel or tungsten carbide or the like.
Screw extruders employing kneading discs of the type to which this sheet production extruder relates are known. Such kneading discs may be employed in single-shaft or multi-shaft screw extruders wherever a particularly thorough kneading action and shearing of the material to be transported is required. The dimensions of the kneading discs generally conform to similar dimensions in the associated helical screw.
FIG. 1 shows a typical kneading disc of a twin- screw extruder in a perspective view illustrating its lenticular cross section substantially defined by two circular segments 2,3. The external surfaces 4,5 of the disc are parallel to its central axis 6. Coaxially with the central axis 6, there is formed within the kneading disc a bore 7 having several keyways 8 for the purpose of placing the disc 1 onto the shaft of a helical extruder so as to impart co-rotation thereto. Kneading discs of the type illustrated are normally disposed between sections of the conveyor helix. The extent of their large diameter, i.e., the axis 9 shown vertically in FIG. 9, is substantially equal to the overall diameter of the associated screw or helix.
In the general area of intersection of the circular surfaces 4 and 5, there are formed areas 17 and 18, respectively, which are at the greatest radial extent from the central axis 6 and which thus will be closest to the interior wall 15 of the extruder housing 16. In the vicinity of these so-called kneader edges 17, 18, the force exerted onto the material to be treated by the screw conveyor will be the greatest as will be the wear and tear on the surface of the kneading disc 1. Advantageously, there are formed in that area flat surfaces 19, 20, respectively, which are parallel to the central axis 6 as well as to the short axis 10, i.e., substantially parallel also to the interior wall 15 of the housing 16.
In a first exemplary embodiment of the twin screw extruder as illustrated in FIGS. 1 and 2, the wear-resistance is imparted to the kneading disc 1 by the placement of substantially radial bores 21, 22 which have blind bottoms and which are open at the corresponding flat surface 19 or 20. As may be seen from FIGS. 1 and 2, the diameter D of these bores 21 and 22 are somewhat smaller than the width b of the flat surfaces 19, 20. The distance between the extent of adjacent bores is labeled a in FIG. 2 and this distance will be seen to be definitely smaller than the bore diameter D but in all cases greater than O. Bores 21, 22 serve to receive inserts which, in this embodiment, are cylindrical inserts 23. Kneading disc for a single screw extruder.