Robert Dray, a well-known screw designer and builder, has long held that there’s no such thing as a “general-purpose” injection molding screw—calling it rather a “no-purpose” screw because, in his view, it can’t do an adequate job of plasticating any polymer. Now Dray is offering a screw design that he says can properly process a wide range of polymers. His firm, R. Dray Mfg., Hamilton, Tex., is offering the APS, or “All Purpose Screw” (patent pending). The key to this screw is a mixing section with one or more removable dams that can be interchanged to alter the balance of distributive and dispersive mixing, depending on the viscosity of the material. The dams are keys inserted into slots and held by cap screws. This development also is suited to extrusion applications where a variety of resins are processed, according to Dray. (More details on the APS next month.)
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