Injection molding nozzle with partially unheated heating element

摘要

An injection molding nozzle and method of making it having an electrical heating element extending in a pair of alternating coils in a spiral channel around a central melt passage. The heating element has a U-shaped bend near the forward end of the nozzle and two ends at an external terminal near the rear end. A central wire in the heating element has a fine coiled heating portion extending between two larger diameter conductive portions which extend to the terminal. One of the conductive portions of the central wire is a predetermined length longer than the other and extends in one of the alternating coils of the heating element along a rear portion of the nozzle adjacent the terminal. The heating portion of the wire extends in both of the alternating coils of the heating element along a forward portion of the nozzle so the heating element provides substantially less heat along the rear portion than along the forward portion of the nozzle.