TAILIEUCHUNG - Mold Design Fundamentals P2

In the insulated runner system, the runner diameter is oversized (say, 15~30mm) in order to maintain the molten state of the material. The large diameter runner allows an inner molten melt to pass through during the molding cycle because of the insulation effect of frozen skin shell surrounding the melt core. The insulation runner system has the advantage of extremely simple construction, low cost tooling, and high efficiency, provided the system can be left running undisturbed for long periods. This design is suitable for most olefinic plastics (such as polyethylene (PE), polypropylene (PP). ) and polystryene (PS) | Insulated Runner System CoreTech System In the insulated runner system the runner diameter is oversized say 15 30mm in order to maintain the molten state of the material. The large diameter runner allows an inner molten melt to pass through during the molding cycle because of the insulation effect of frozen skin shell surrounding the melt core. The insulation runner system has the advantage of extremely simple construction low cost tooling and high efficiency provided the system can be left running undisturbed for long periods. This design is suitable for most olefinic plastics such as polyethylene PE polypropylene PP . and polystryene PS . The disadvantages of the insulated runner system includes - it requires fast cycle to maintain molten state within runner at least 5 shots min . - it requires long start-up periods 15-25min to stabilize the runner temperature up to 150 oC - it needs a long color change time - it needs very accurate gate temperature control in order to have a satisfactory production rate. - Additional emergency parting line is required to facilitate the removal of the frozen runner in the case of prolonged delay in the cycle time. 16 A Internally Heated Hot Runner System - Material is heated by the heating element in the center of the runner - Annular gap for melt flow Melt Heater Cartridge Heated Probe Torpedoe Vlocity Profile Tempertature Profile CoreTech System In the internally heated hot runner system the material is heated and kept at a molten state by the heated probe torpedoe in the center of the runner. The melt is allowed to flow in the cross section of the annular gap of the runner. The advantages of the internally heated hot runner systems include -Less heat loss and lower heating power required since the thermal insulation of polymer melt -Less mold components mis-matching problem arising from thermal expansion -Inexpensive as compared with the external heated runner system -Little space required. The disadvantages

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