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CounterpressureCounterpressure Structural Foam is a variation of the structural foam process. The purpose is to control the pressure drop at the leading edge that occurs during resin injection. Normally the pressure drop allows the blowing agent to expand during mold filling causing a visual defect called "swirl".
The Counterpressure in the mold cavity controls blowing agent expansion at the leading edge of the flow front. Nitrogen gas pre-pressurizes the mold cavity prior to plastic injection. Controlled venting and a pressure tight mold are essential elements of the process. Further information can be obtained from The SPI's Structural Plastics Division. They offer a CD of the best papers from their collection of 35 annual conferences.
Counterpressure actually works well with EGM. Counterpressure is a valuable tool employed during the mold filling phase of the injection molding process. EGM uses the same mold sealing techniques and kicks during the packing or resin shrinkage phase.
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Steve Ham
Plastics 537 Hickory Street Highlands, NC 28741 USA |
