Extrusion with Ceramic Screws
Metal screws are used almost exclusively in the plastics industry when melting plastics. As part of a research project, ceramic screws have now been developed to the stage where they are suitable for use in production.
The ceramic materials are corrosions- and wear-resistant. This provides definite benefits when processing highly filled materials: the availability of the equipment is increased significantly, since less time must be devoted to screw maintenance. Fewer spare parts are needed. Since the screw material does not corrode, no decomposition products accumulate in the melt or end up in the final product.
The particular characteristics of ceramic materials, however, require that a new approach be taken. Ceramic screws cannot be manufactured in a single piece. As a result, the individual sections must be assembled through use of suitable joining techniques. Ceramic materials withstand tensile stress to only a limited degree, while exhibiting an extremely high compressive strength. Accordingly, tensile stresses must be transformed into compressive stresses as much as possible.
The use of ceramic components in the field of extrusion is about to become commonplace. With further optimisation, regular use in injection moulding is also quite conceivable.
Several companies and research institutes participated in the development of the new screw concept. These include the Institute for Ceramic Components in Machinery at the RWTH Aachen, H.C. Starck Ceramics GmbH, Selb, the German Plastics Institute, Darmstadt, Battenfeld GmbH, Meinerzhagen, Dronco AG, Wunsiedel, ECT Extrusion for Ceramic Technology GmbH, Mühlacker, and the Hermsdorfer Institute for Technical Ceramics, Hermsdorf.
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