Title: Sprue bushing for a single cavity or center sprued mold

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Abstract: Plastics material is injected into a single cavity mold through a sprue bushing which has a cylindrical base portion with a semispherical seat within one end for receiving the nozzle of an injection molding machine. A cylindrical nose portion of smaller diameter, projects from the base portion and includes a flat end or tip surface which is adapted to be positioned flush with the cavity and has a discharge orifice connecting with an axially extending cylindrical chamber within the body. A valve member is supported for axial movement within the chamber and has a cylindrical tip portion which normally closes the discharge orifice under the bias of a series of spring washers confined within the chamber adjacent the opposite end of the valve member. The plastics material is directed from the nozzle seat to the chamber through a plurality of passages which extend around the spring washers. An elongated heating element is located within the valve member and is supplied with power through leads which extend rearwardly through the washers and through an outwardly extending hole within the body. A band type electrical heating element surrounds the base portion of the body.


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