Injection moulding die with heavy-duty sprue bush

Claim 1

In an injection moulding die for moulding thermoplastic material, the die having a heavy-duty sprue bush of higher temperature than the die for a spruing through tunnel gating to at least one mould chamber, the heavy-duty sprue bush being: oriented generally perpendicularly to the jointing plane of the die; fixedly located within a receiving chamber in the die; and heated by a first electric heater portion coiled around it, the improvements comprising: (a) an orifice head attached to a front end of the sprue bush and received in the receiving chamber, the orifice head having a generally cylindrical outer wall; (b) means in the orifice head defining sprue runners, the axis of each runner extending generally parallel to, but displaced from the jointing plane of the die; (c) a second electric heating coil portion wrapped around the generally cylindrical outer wall of the orifice head, the first and second heating coil portions serving to heat the sprue bush and the orifice head so as to maintain the moulding material in a plastic, free-flowing state throughout the length of the sprue bush and the sprue runners, the dimensions of the cylindrical outer wall and the second electric heating coil portion being such as to leave an insulating air gap between them and the receiving chamber to minimize heat transfer to the die; and, (d) means defining an injection opening through a side wall of each of the moulding chambers tightly abuting said sprue runners, the axis of each injection opening extending generally parallel to the jointing plane of the die, but displaced therefrom.