EP0309257A2
Expired / Lapsed
EP
⏱️ 0.0 years remaining
Method and apparatus for injection moulding
Assignee: Cinpres Ltd
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Filing: 1988-09-23
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Granted: —
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Expires: 2008-09-23
Abstract
Abstract 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.
Inventors
- 👤 Matthew Emmett Sayer
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-03 08:56
CPC Classifications
B; B29; B29C; B29C45/00; B29C45/17; B29C45/76; B29C45/1703; B29C45/1704; B29C45/26; B29C45/34; B29C45/46; B29C45/57; B29C2045/1729; Y; Y10; Y10S; Y10S425/00; Y10S425/058; Y10S425/812
Claims Analysis
Total Claims: 24
Claim 1
Independent Claim
252 words
A method of producing an injection moulded plastics article comprising introducing a stream of molten plastics material from an injection moulding machine cylinder into an article forming mould space (13), supplying pressurised gas into the interior of the molten plastics material to form a gas containing cavity (25) therein, allowing the plastics material to solidify and cool sufficiently so that the article can itself sustain the form dictated by the mould surface, and venting the cavity to reduce the pressure within the cavity to ambient pressure prior to opening of the mould, the step of venting the cavity being achieved by providing at least one position which is separate from the plastics 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, characterised by providing the vent passage (30) at a position which is also separate from the gas inlet (26), maintaining the closure (31) 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 (25) passes into the vent passage.
Claim 2
Independent Claim
252 words
A method of producing an injection moulded plastics article comprising introducing a stream of molten plastics material from an injection moulding machine cylinder into an article forming mould space (13), supplying pressurised gas into the interior of the molten plastics material to form a gas containing cavity (25) therein, allowing the plastics material to solidify and cool sufficiently so that the article can itself sustain the form dictated by the mould surface, and venting the cavity to reduce the pressure within the cavity to ambient pressure prior to opening of the mould, the step of venting the cavity being achieved by providing at least one position which is separate from the plastics 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, characterised by providing the vent passage (30) at a position which is also separate from the gas inlet (26), maintaining the closure (31) 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 (25) passes into the vent passage.
Claim 3
Dependent Claim
41 words
A method as claimed in Claim 1, characterised in that on retraction of the closure (31) the cavity wall is unsupported and the pressure of the gas within the cavity (25) ruptures the cavity wall and thereby creates the vent opening.
Claim 4
Dependent Claim
61 words
A method as claimed in Claim 1 or Claim 2, characterised by immersing a part of the closure (31) in the cavity wall as it is formed to produce weak lines in the cavity wall whereby on retraction of the closure the weak lines assist the pressure of the gas to rupture the cavity wall and thereby create the vent opening.
Claim 5
Dependent Claim
59 words
A method as claimed in Claim 1, characterised by immersing a part of the closure (31) in the cavity wall as it is formed to produce weak lines in the cavity wall whereby on retraction of the closure the weak lines assist the removal of a section of the cavity wall and thereby the creation of the vent opening.
Claim 6
Dependent Claim
33 words
A method as claimed in Claim 4, characterised in that the part of the closure (31) to be immersed is undercut whereby retraction of the closure pulls said section from the cavity wall.
Claim 7
Independent Claim
35 words
A method as claimed in any one of the preceding claims, characterised by the step of applying heat at the inner end of the vent passage (30) to assist the creation of the vent opening.
Claim 8
Dependent Claim
19 words
A method as claimed in Claim 6, characterised in that the heat is applied by heating the closure (31).
Claim 9
Dependent Claim
166 words
Apparatus for producing an injection moulded plastics article comprising means (17) for introducing a stream of molten plastics material from an injection moulding machine cylinder into an article forming mould space (13), means for supplying pressurised gas into the interior of the molten plastics material to form a gas containing cavity (25) therein, and at at least one position which is separate from the plastics inlet (19) a vent passage (30) in the mould (10) open at its inner end to a part of the interior of the mould at which the gas containing cavity is to be formed, a retractable closure (31) 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 (32) for moving the closure between its extended and retracted positions, characterised in that the position of the vent passage is also separate from the gas inlet (26).
Claim 10
Dependent Claim
166 words
Apparatus for producing an injection moulded plastics article comprising means (17) for introducing a stream of molten plastics material from an injection moulding machine cylinder into an article forming mould space (13), means for supplying pressurised gas into the interior of the molten plastics material to form a gas containing cavity (25) therein, and at at least one position which is separate from the plastics inlet (19) a vent passage (30) in the mould (10) open at its inner end to a part of the interior of the mould at which the gas containing cavity is to be formed, a retractable closure (31) 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 (32) for moving the closure between its extended and retracted positions, characterised in that the position of the vent passage is also separate from the gas inlet (26).
Claim 11
Dependent Claim
26 words
Apparatus as claimed in Claim 8, characterised in that the inner end of the vent passage (30) is open to the article forming mould space (13).
Claim 12
Dependent Claim
39 words
Apparatus as claimed in Claim 8, characterised in that the inner end of the vent passage (30) is open to a part of the interior of the mould (10) which is upstream of the article forming mould space (13).
Claim 13
Dependent Claim
48 words
Apparatus as claimed in any one of Claims 8 to 10, characterised in that the closure (31) has a conical surface (34) which engages a correspondingly shaped valve seat (35) in the vent passage (30) when the closure is in its extended position thereby closing the vent passage.
Claim 14
Dependent Claim
34 words
Apparatus as claimed in any one of Claims 8 to 11, characterised in that a part of the closure (31), in its extended position, becomes immersed in the cavity wall as it is formed.
Claim 15
Dependent Claim
26 words
Apparatus as claimed in Claim 12, characterised in that said part of the closure (31), in its extended position, protrudes into the interior of the mould.
Claim 16
Dependent Claim
37 words
Apparatus as claimed in Claim 12 or Claim 13, characterised in that said part of the closure (31) is shaped to assist the removal of a section from the cavity wall when the closure (31) is retracted.
Claim 17
Dependent Claim
34 words
Apparatus as claimed in any one of Claims 12 to 14, characterised in that the closure (31) is undercut to provide a head which becomes immersed in the cavity wall as it is formed.
Claim 18
Dependent Claim
26 words
Apparatus as claimed in any one of Claims 8 to 15, characterised in that the closure is a pin (31) extending lengthwise of the vent passage.
Claim 19
Dependent Claim
31 words
Apparatus as claimed in any one of Claims 8 to 25 16, characterised in that means (36) are provided for applying heat at the inner end of the vent passage (30).
Claim 20
Dependent Claim
20 words
Apparatus as claimed in Claim 17, characterised in that the heating means (36) are provided internally of the closure (30).
Claim 21
Dependent Claim
27 words
Apparatus as claimed in any one of Claims 8 to 18, characterised in that the means (32) for moving the closure (31) is a piston and cylinder.
Claim 22
Dependent Claim
26 words
Apparatus as claimed in any one of Claims 8 to 19, characterised in that the outer end of the vent passage (30) is open to atmosphere.
Claim 23
Dependent Claim
24 words
Apparatus as claimed in any one of Claims 8 to 19, characterised in that the vent passage (30) is connected to a factory vent.
Claim 24
Dependent Claim
26 words
Apparatus as claimed in any one of Claims 8 to 9, characterised in that the vent passage (30) is connected to means for collecting the gas.
References Cited (Backward Citations)
No citation records indexed.
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