GB1450990A - Method and apparatus for the manufacture of extrudates of structural foam thermoplastic material - Google Patents

Abstract

1450990 Controlling dimensions of extruded foam SOC CHIMIQUE DES CHARBONNAGES 13 March 1974 [16 March 1973] 11252/74 Heading B5A [Also in Division C3] A thermoplastic polymer containing a foaming agent, is extruded to foam upon issuing from an extrusion die and, at the exit of the die, is differentially cooled around its periphery by fluid pressure jets to effect expansion differentially to a shape at least similar to that of the shape of a sizing die through which it passes, so that friction is reduced in drawing the shape through the sizing die. The sized shape is cooled in passage through water tanks. The fluid may comprise cold compressed air, e.g. at 20‹ C., or other gas, or a suspension of water in air. The differential cooling may be effected by differing pressure and/or temperature of the fluid. In Example (1), the polymer comprises high impact polystyrene containing polybutadiene foamed with zeolite, the extrusion die shape 1 being as shown in Fig. 3, or in Fig. 1 (not shown), and the sizing die shape being as shown in Fig. 2. The fluid cooling is effected by two (or four or eight) compressed air or water suspension blowing devices 3 and 4, each comprising one or more orifices, with the upper device 3 operating at a higher pressure than the lower device 4. Figs. 5 and 6 (not shown) show variations of shape effected by varying the fluid pressures. In Example (2), a similar high impact polystyrene foamed with azodicarbonamide is extruded from the Fig. 7 die shape, to produce a rectilinear sided "L"-section, the cooling fluid being directed at different pressures from three locations across the top of the extruded section, and locations at either side and at the bottom of the section. In Examples (3) and (4), crystal polystyrene, or rigid P.V.C., containing azodicarbonamide is extruded from the die 1a of Fig. 10, to produce a rectangular section, using upper and lower 3, 4, and opposite lateral fluid blowing devices operating at different pressures. Foam densities are stated. The differential cooling may produce a variable surface around the article comprising a smooth skin, a rough skin and/or the absence of a skin.