CONSTRUCTION OF FAST-RESPONSE HEATING ELEMENTS FOR INJECTION-MOLDING APPLICATIONS

A new type of heating element was developed capable of changing the mold surface temperature by about 70 K in 0.2 s, thus enabling reduction of frozen-in orientation and stresses in injection molded products without undue increase in cycle time. The heater, which consists of two insulation layers with a resistance layer in between, is discussed in this paper. The thickness of this insulation layer proves to be the most important design parameter. Too thick an insulation layer increases the cooling time too much, whereas with a thin layer the surface temperatures will stay too low. Temperature measurements at the heater surface and in the mold wall are reported and demonstrate the extreme fast response characteristics.