Apparatus for moulding heat-expandable thermo-plastics material
OwnerRobert Frederick Joseph Cotterellinventor
Life of this patent
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Abstract
Heat-expandable beads of thermo-plastic material such as polystyrene are moulded by steam heating in a metal mould and venting the interior of the mould through apertures in plugs set into ports in the wall of the mould. The plugs are made of low heat conductivity material, for example nylon, to prevent the apertures being blocked by fusion of the beads in contact with the plugs due to heat conduction from the wall of the mould. The steam may be introduced into the mould through apertures in nylon plugs set in ports in the wall of the mould, the low heat conductivity of the nylon preventing the steam raising the plugs to a temperature at which the beads would burn onto the plugs. The same plugs may be used to introduce steam into the mould and then vent the interior of the mould.
Claims9
Apparatus for moulding relatively thick articles from heat expandable beads of synthetic thermoplastic resinous material such as polystyrene, said apparatus comprising a mould having metal walls which define a cavity wherein beads can be confined and the cavity surfaces of which correspond to the shape of an article to be moulded, means cooperating with the walls of the mould to define a chamber external to said cavity, means for introducing a hot gaseous medium under pressure into said chamber so that the medium is applied to the walls of the mould for heating the same, and means for conducting hot gaseous medium from said chamber through the mould walls and into the cavity for expanding and fusing beads therein, said apparatus being characterized by means for assuring good fusion of beads within the interior of articles moulded in the apparatus notwithstanding that such articles may have substantial thickness and, when finished, may have a substantially hard external crust, the last mentioned means comprising:
- means for assuring continued venting of hot gaseous medium out of the cavity to enable continued flow of hot gaseous medium from said chamber into the cavity, comprising a plug set into a metal wall of the mould, said plug
- 1. having an inner surface defining part of the cavity surface of the mould,
- 2. having an aperture therethrough which is surrounded by said inner surface and through which fluid can pass out of the cavity, and
- 3. being made of a nonmetallic material capable of withstanding a pressure of 20 p.s.i. under a temperature equal to that of steam at said pressure, and having a coefficient of thermal conductivity substantially lower than that of the metal of the mould wall to ensure that beads in contact with said plug are not fused due to heat conduction therethrough prior to fusion of beads in the center of the cavity.
Apparatus for moulding articles from heat expandable beads of synthetic thermoplastic polymeric resinous material, which apparatus is of the type comprising a mould having metal walls formed with internal surfaces defining a cavity that conforms to the shape of an article to be moulded and in which beads can be confined, means cooperating with said mould to define a chamber that substantially surrounds the mould and is communicable with the cavity through inlet apertures in the mould walls, means for introducing a hot gaseous medium into said chamber under pressure so that the mould walls can thereby be heated from their outer surfaces, and means for venting the cavity so that gaseous medium can be circulated therethrough from said chamber, by way of said inlet apertures, and in passing through the cavity can expand and fuse beads confined therein, said apparatus being characterized by means for assuring good fusion of beads within the interior of articles moulded in the cavity notwithstanding that such articles may have substantial thickness and, when finished, may have a substantially hard external crust, the last mentioned means comprising:
- plugs in the mould walls that define outlet apertures through which the cavity is communicated with said means for venting the same, said plugs
- a. having inner surfaces which surround said outlet apertures and cooperate with the internal surfaces of the metal mould walls in defining the cavity, and
- b. being of nonmetallic material capable of withstandng pressures up to at least 20 pounds per square inch under a temperature equal to that of steam at said pressure, and having a thermal conductivity substantially lower than that of the metal of the mould walls, and on the order of that of nylon, so that said plugs do not conduct sufficient heat from the metal walls to beads adjacent to said outlet apertures to fuse said beads, thus ensuring that gaseous medium can continue to pass out of the cavity until beads at the interior of the mould have fused.
Dependencies are inferred from the claim text.