Injection molding method and equipment

Abstract

A method of molding an element from liquid synthetic resin wherein liquid resin is introduced into a mold cavity through a first gate and liquid resin is concurrently introduced into the mold cavity through a second gate with portions of the resin received through each of the gates meeting at a joint interface. The resin in the second gate is caused to solidify sooner than the resin in the first gate so that the leading surface of the resin received through the first gate projects into a leading surface portion of the resin received through the second gate during the mold packing operation to provide an enlarged weld line area and improved strength in the joint. Apparatus for carrying out this method includes structure for causing the temperature in the gate of one of the resin streams to be different from that of the temperature in the gate of the other of the resin streams as a result of preselected characteristics of the respective gates through which the resin streams are passed. In an illustrated embodiment, a first gate passage may have a different cross-sectional configuration than that of a second gate passage so that the resin in the first gate may be cooled or heated to a different degree than the resin in the second gate, through differences in the heat transfer characteristics of the walls defining the respective passages. Alternatively, the first and second gate structure materials may have different thermal diffusivities. Further alternatively, the flow through the first gate may be terminated prior to the termination of flow through the second gate. In an illustrated embodiment, the invention is employed in an injection molding apparatus having more than two gate structures.

Dependencies are inferred from the claim text.