Apparatus for moulding heat-expandable thermo-plastics material

Claim 2

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

Claim 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.

Claim 4

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.

Claim 5

The apparatus of claim 1 wherein said means for conducting hot gaseous medium from said chamber into the cavity comprises another plug set into a metal wall of the mould and having the characterizing features of the first mentioned plug.

Claim 6

The apparatus of claim 1, wherein said plug is made of a synthetic polymeric resinous material having a co-efficient of thermal conductivity within the range 2-8 × 10 - 4 cal./sec./sq.cm./1(°C/cm.).

Claim 7

The apparatus of claim 3 wherein said plug is made of nylon.

Claim 8

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.

Claim 9

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.

Claim 10

The apparatus of claim 5, further characterized in that said inlet apertures are formed in inlet plugs set into the metal walls of the mould, said inlet plugs being of a nonmetallic material capable of withstanding a pressure of at least 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 walls to ensure that beads do not "burn on" to said inlet plugs and block said inlet apertures.

Claim 11

The apparatus of claim 5, wherein said venting means includes exhaust duct means connected to said plugs and extending to the outside of said chamber, further characterised by: A. each of said plugs comprising: 1. a tubular portion set into a port in a wall of the mould and open at one end, the tubular portion projecting beyond the outer surface of the metal wall of the mould at said end thereof, 2. an apertured end wall extending across the other end of that tubular portion and lying substantially flush with the interior surface of the mould wall; and B. screw threaded means connecting the tubular portion of the plug, at the first mentioned end thereof, with the exhaust duct means.

Claim 12

The apparatus of claim 7 further characterised by: each of said plugs: 1. being made of plastic material having substantial resilience, and 2. having its tubular portion screwed into the wall of the mould, the resilience of the plug insuring a fluid tight fit between it and the wall of the mould.

Claim 13

The apparatus of claim 5, wherein said plugs are made of nylon.