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US 4,923,667 AGranted
Method and apparatus for injection moulding
AssigneeCinpres Limited
InventorMatthew E. Sayer
Life of this patent
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AssigneeCinpres Limited
InventorMatthew E. Sayer
Estimating the term…
An injection molded plastic article is produced by introducing a stream of molten plastic material from an injection molding machine cylinder into an article forming mold space. Pressurized gas is supplied into the interior of the molten plastic material to form a gas containing cavity therein. The plastic material is then allowed to solidify and cool sufficiently so that the article can itself sustain the form dictated by the mold surface. The cavity is vented to reduce the pressure within the cavity to ambient pressure prior to opening of the mold. The step of venting the cavity is achieved by providing at least one position which is separate from the plastic inlet and the gas inlet a vent passage in the mold open at its inner end to a part of the interior of the mold at which the gas containing cavity is formed, and a retractable closure 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.
A method of producing an injection molded plastic article comprising introducing a stream of molten plastic material from an injection molding machine cylinder into an article forming mold space, supplying pressurized gas into the interior of the molten plastic material to form a gas containing cavity therein, allowing the plastic material to solidify and cool sufficiently so that the article can itself sustain the form dictated by the mold surface, and venting the cavity to reduce the pressure within the cavity to ambient pressure prior to opening of the mold, the step of venting the cavity being achieved by providing at at least one position which is separate from the plastic inlet and the gas inlet a vent passage in the mold open at its inner end to a part of the interior of the mold at which the gas containing cavity is formed, and a retractable closure 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 producing an injection molded plastic article comprising means for introducing a stream of molten plastic material from an injection molding machine cylinder into an article forming mold space, means for supplying pressurized gas into the interior of the molten plastic material to form a gas containing cavity therein, and at at least one position which is separate from the plastic inlet and the gas inlet a vent passage in the mold open at its inner end to a part of the interior of the mold at which the gas containing cavity is to be formed, a retractable closure positioned in the inner end of the vent passage for movement between an extended position in which the vent passage is closed and a retracted position in which the vent passage is open, and means for moving the closure between its extended and retracted positions.
Dependencies are inferred from the claim text.