Electrical heater for heating cylindrical injection molding nozzles comprises a metal tube with low heat transmission compared to heated part and a longitudinal slot along tube for heater element

摘要

A tubular metal body (1) has a longitudinal slit (2) and forms a carrier for a heating element. The body is made of a metal with a lower heat expansion coefficient than the cylindrical part to be heated. The tubular body is pushed onto the cylindrical part to be heated and forms a close fit. Grooves (3) in the outer cover hold a heating element with axial or radial connectors. An expanding tool for positioning the tubular body (1) is placed in the longitudinal slit (2). After locating the expanded body onto the part to be heated the expanding tool is removed. A widened area (6) of the longitudinal slit receives the expanding tool without stressing or widening of the slit body. Movement of the tool along the slit expands the tubular body. The longitudinal slit has a rhombus shape in plan view, whose longitudinal tips lie on an extension of the middle line of the axial slit. Transverse tips (8) of the rhombus lie at the center of the slit. The expanding tool has a rounded shape conforming to that of the tubular body and is attached to one end of a slim shaft whose diameter is less than that of the narrowest point of the slit. Shaft length ensures the shaft protrudes axially beyond the slit body. Wall thickness of the tubular body around the slit is greater, preferably twice as thick, as in other areas and in particular is 4 mm. Restriction of the longitudinal slit at the axial ends forms a guide for the expanding tool shaft.