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Gas Assist, Foam and Water Injection
Valve gating is a key component for injection molding processes involving gas assist, foaming agents or water injection. An initial melt injection through the valve gate nozzle fills the cavity only partially, the valve gates then close rather than applying to hold or pack pressure as would be the case for a conventional injection molding process. After the gates close, the gate pressure is applied (by injecting nitrogen gas) or the reaction of the foaming agent (via additive) will develop foam cells to expand the melt volume. This expansion will counteract the volumetric shrinkage for the melt during the cooling phase of the cycle.
Dog houses molded using cascade fill, gas assist and foam. Objectives achieved - 20% less material through reduction of wall thickness, improved structural strength and cost savings through lower clamp tonnage.
In other applications where the goal is to create large hollow sections or channels inside molded parts for structural functions or for design aesthetics, valve gate nozzles can close the gates to prevent melt back flow (flow back) while the melt displacement with gas pressure, foam cell pressure or water injection takes place.
Tough, Reliable Performance
Rheo-Pro® valve gate hot runner nozzles and Rheo-Pro® CV-Series sequence controllers provide reliable and accurate control of the gates for these special molding applications.
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Case Study
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