CraftsTechnology has introduced a new core pin made from a special grade of tungstencarbide that directly addresses the problems of thermal conductivity anddeflection in the plastic injection molding process. The tungsten carbide corepin has a very high thermal conductivity with extreme rigidity. In suchapplications as medical parts and consumer components, the use of tungstencarbide core pins has resulted in cycle-time savings of as much as 20 to 40percent without sacrificing the quality of the molded part.

In high-volume production of plastic injection molded components, cycletime is critical to profitability, and one of the limiting factors is theremoval of heat from the mold. Some plastic injection molded parts have deepinternal features that require the use of long core pins. During solidificationand cooling, the plastic contracts on the core pin; thus, the rate of coolingis controlled by the heat transfer through the core pin. Whether the core pinhas a bubbler, heat transfer is dependent upon the thermal conductivity of thecore pin material.

Before the development of tungsten carbide core pins, hardened copperalloys typically were selected as the material of choice for long core pins.However, the copper alloys are not very rigid, and for high-aspect ratioconfigurations, they will deflect during the injection phase. The deflection results in unacceptabledimensional stability. In situations where deflection occurs, hardened tool steelis used. But because steel does not havehigh thermal conductivity, cycle times suffer.