Patent GB-1417312-A (GB)
Title: Method and apparatus for making structural elements
IPC: B29C48/92
Filed: 1973-01-04
Abstract: 1417312 Extruding foamed plastics ARCO POLYMERS Inc 4 Jan 1973 [18 Feb 1972] 652/73 Heading B5A [Also in Divisions A4 C3 and G3] An extruded foamed thermoplastics section, simulating wood grain and having a denser or unfoamed structure adjacent its surface than in its interior, is produced by pulling the extrudate from the extrusion die, e.g. by an opposed belt mechanism, through a sizing die which is cooled by a surrounding water jacket and is spaced apart from the extrusion die to permit partial foaming of the extrudate between the dies to a cross-section greater than that of the sizing die passage, and continuation of the foaming in the sizing die passage. The greater cross-section is maintained at a constant value, preferably by adjustment of the speed of the puller mechanism, either manually or automatically. The denser skin initially formed by contact with the cooled sizing die passage, progressively increases in thickness during continued expansion of the interior of the extrusion in passing through a refrigerated coolant or water cooling bath immediately downstream of the sizing die. The extrusion die may be of the same, or different shape from that of the section. Pigment may be added at the extruder hopper to accentuate the wood grain effect, and calcium carbonate and glass fibre fillers may be employed. Numerous conventional thermoplastics and blowing agents, and mixed blowing agents are specified, and these may comprise thermoplastics in which the blowing agent is incorporated during polymerization. The thermoplastics to be extruded may comprise expandable polystyrene beads together with specified hydrates, and with specified non-expandable thermoplastics powders which form an outer unexpanded layer in the section. An exemplary composition comprises expandable polystyrene beads containing decomposable blowing agent, or pentane, citric acid and sodium carbonate, together with either a graft polymer of styrene on butadiene, or a blend of polystyrene and butadiene. or low or high density polyethylene, or acrylonitrilebutadiene-styrene resin, or with polystyrene. In the Fig. 1 embodiment (not shown) a circular section rod is obtained employing a similar shaped extrusion die passage, and with the sizing die comprising a water circulating jacket throughout its length. In the Fig. 8 embodiment, the passage of the extrusion die 43 and sizing die 44 are of the same shape as the section produced, Fig. 9, for use as a drawer side wall with grooves 34, 35 respectively serving for sliding engagement with a furniture piece side rail and for retaining the drawer base by means of adhesive or nails. In this embodiment, the sizing die 44 has an upstream chamber to which vacuum is applied, at 54, to draw water from ports 59a in a downstream water circulating cooling jacket and from the water bath 50, to function as a cooling and lubricating agent between the extrusion and the sizing die passage which is provided with transverse slots 60 to further reduce friction. The water bath 50, is provided with spaced supports, Fig. 4 (not shown), for the extrusion, and at its outlet with a rubber seal around the extrusion. In the Fig. 10 embodiment (not shown) a sizing die of otherwise similar construction to the Fig. 8 embodiment, produces a square section rod from an extrusion passage of circular section. In the Fig. 14 embodiment (not shown) a tubular section is employed using a tubular extrusion die passage, and a sizing die provided with a surrounding circulating water passage throughout its length, and with a circulating water cooled mandrel supported either at lugs to the upstream face of the sizing die, or by the extrusion die mandrel. The greater cross-sectional area of the extrusion 30, Fig. 16, intermediate the extrusion and sizing dies 22, 23, may be automatically maintained constant, as in either the Figs. 16 or 17 embodiments. In the Fig. 16 embodiment, increase or decrease of the area of the extrusion 30 correspondingly alters the amount of light passing, from a light source 73, to a photoelectric cell 74 which is connected to a controller 76 which acts to alter the speed of motor 72 driving the opposed belt drawing mechanism 29. In the Fig. 17 embodiment (not shown) the speed of the electric motor driving the opposed belt drawing mechanism, is altered by varying the electric current supplied thereto, by a control device (86) which is responsive to fluid pressure in a delivery line (85) from a piston valve (80), which is actuated mechanically, by one arm of a bell crank lever (82), the other arm (78) of which acts as a feeler to be displaced by the area of the extrudate (30).