Plastic Injection Molding Manufacturing For The Automotive Industry
Runner-less or Hot-Runner of Bumper Mould When the plastic melt is thermally stable, it is possible to completely eliminate the need to regrind runners by using runnerless molds. One common type is the hot runner mold. In this bumper mould, the plastic is injected into an insulated runner plate...
When the plastic melt is thermally stable, it is possible to completely eliminate the need to regrind runners by usingrunnerless molds.One common type is thehot runner mold.In this bumper mould, the plastic is injected into an insulated runner plate that is kept slightly above melt temperature by a separate set of electric cartridge heaters and then through the runner channels and insulated nozzles into each cavity . In effect, this is a runnerless operation since there is no runner regrind. The hot runner plate is thermally insulated by an air gap.
Hot-runner car bumper moulds have numerous advantages as a consequence of elimination of sprue and runner regrind. There is no material loss or contamination from regrinding and no extra cost in blending regrind with virgin resin for automotive company. There is no degradation of polymer, especially in optical and electrical properties, due to regrind usage. No energy is wasted in regrinding or in melting and cooling regrind. There is an effective increase in shot capacity and reduction in required mold-opening stroke. Cold runners have a tendency to catch on other mold parts during ejection, and this problem is eliminated. The bumper mould fills faster and balanced flow to the cavities is more readily accomplished.
To control drool and yet prevent freezing, hydraulically operated gate valves orvalve gatesystems have been developed . Valve gates are compact hydraulic cylinder/valve pin assemblies for positive individual gate shutoff. At a preset time, the hydraulic cylinders retract at each gate, permitting melt flow. Secondary timers set the positive closure of each valve to occur after optimum preset fill time has expired. This eliminates overpacking or underfilling at each gate. The system manifold and nozzles are temperature controlled to prevent thermal degradation of the melt. This complex system helps control cavity filling and end bumper product properties, especially for large, multigated parts andfamily moulds.Family moulds make different parts for a common assembly, and inherently have unbalanced flow. Valve gate systems can be adjusted by tool maker to compensate for unbalanced flow and to run with minimum rejects in these situations. This is vital where regrind is not allowed because of rigid product specifications, such as in medical or optical products.