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Gas-assisted compression moulding of glass reinforced polypropylene

By Ian Brzeski

Abstract

A new process of combining gas injection with compression moulding was developed\ud and studied in this research work. The process is called Gas Assisted Compression\ud Moulding (or GasComp). The principle is based on the injection of nitrogen gas\ud during a conventional compression moulding cycle. The flow of the material due to\ud the compressive force of the press is assisted by the injection of gas into the centre\ud of the molten material. The gas assists in the flow by coring out the material,\ud reducing the weight by up to 45 percent and increasing the dimensional stability of\ud the component.\ud Novel glass matt thermoplastic mould tools were designed and developed during the\ud course of the research program for use with the process. These designs were of a\ud flash compression mould tool design with a horizontal clamping face, rather than the\ud conventional positive plug compression mould tool with a vertical shear edge. This\ud created a fixed volume mould tool, which when used in conjunction with a short shot\ud of material, would allow the gas to flow the material to fill the remaining volume.\ud Several materials were investigated for their suitability with the process. Their\ud characterisation showed that they contained different glass fibre contents and\ud architectures. A material with a short, dispersed glass fibre content of 11 percent\ud proved to consistently contain a significant gas cavity. The glass architecture proved\ud to be the most significant contributing factor in the creation of a successful gas cavity.\ud The most significant processing parameter in the creation of a large volume cavity\ud proved to be the gas injection delay time. The gas pressure and gas ramp time\ud affected the cavity shape, length and extent of gas fingering.\ud The shrinkage was reduced in the presence of a gas cavity, along with the visible\ud reduction of sink marks. The presence of other moulding features, such as hesitation\ud marks, gas packing and the change in fibre orientation were also discussed

Topics: TP
OAI identifier: oai:wrap.warwick.ac.uk:3627

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