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Gas Assisted Injection Moulding

SpecialChem / Feb 21, 2007

The first GAIM processes targeted the production of parts with large cross-sectional areas that had the potential for being hollow for all but a couple of millimetres of thermoplastic outer wall section. The gas, in the first instance pure Nitrogen was injected through a modified injection machine nozzle when the mould was approximately 80% filled. The nitrogen displaced the molten polymer in the centre of the sprue, runner and gates and into the mould cavity. The melt so displaced moved to fill the remainder of the mould. If the timings, volumes and pressures were controlled in the right way the polymer just filled the mould before the gas reached the end of the flow. The gas, now totally sealed inside the polymer was maintained at a set pressure until the polymer froze. Subsequently the gas pressured was released and the mould opened and the hollow part ejected. The only evidence of the gas was that when the gate was cut there would be a small hole and that the part was significantly lighter than a solid part would have been.

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