METHOD AND APPARATUS FOR INJECTION MOULDING
An injection moulded plastics article is produced by introducing a stream of molten plastics material from an injection moulding machine cylinder into an article forming mould space (13). Pressurised gas is supplied into the interior of the molten plastics material to form a gas containing cavity (2...
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Format: | Patent |
Sprache: | eng |
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Zusammenfassung: | An injection moulded plastics article is produced by introducing a stream of molten plastics material from an injection moulding machine cylinder into an article forming mould space (13). Pressurised gas is supplied into the interior of the molten plastics material to form a gas containing cavity (25) therein. The plastics material is then allowed to solidify and cool sufficiently so that the article can itself sustain the form dictated by the mould surface. The cavity is vented to reduce the pressure within the cavity to ambient pressure prior to opening of the mould. The step of venting the cavity is achieved by providing at at least one position which is separate from the plastics inlet and the gas inlet a vent passage (30) in the mould open at its inner end to a part of the interior of the mould at which the gas containing cavity (25) is formed, and a retractable closure (31) for opening and closing the vent passage at its inner end, maintaining the closure in its closed position during the forming of the article whereby the cavity wall is formed over the inner end of the vent passage and the closure therefor, and subsequently retracting the closure to allow the creation of a vent opening in the cavity wall in the area of the inner end of the vent passage through which vent opening gas from the cavity passes into the vent passage. Apparatus for carrying out the above process is also described. |
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