Patent GB-1467477-A (GB)
Title: Extrusion moulding method
IPC: B29C48/11
Filed: 1974-07-16
Abstract: 1467477 Extruding articles with closed cavities SUMITOMO CHEMICAL CO Ltd 16 July 1974 [18 July 1973] 31523/74 Heading B5A A thermoplastics article 21, Fig. 5, having a plurality of discrete closed cavities 20 is produced by extruding into a water cooled sizing die 5, a thermoplastics section having a plurality of bores defined between partitions extending in the extrusion direction, and sequentially admitting pressure air to and from different bores, e.g. by alternately admitting and venting the pressure to the different bores, to sequentially expand different partitions transversely into fusing contact 23 with adjacent partitions. The article may be employed in construction, heat insulation, wrapping, and cushioning, and various known thermoplastics are specified. The partitions and outer surface of the section may comprise materials from different extrusion sources delivered to an extrusion die from which the section is extruded or, as shown, Fig. 1, may comprise material from the same extrusion source 8, extruded from a die 2 defining the article exterior surfaces and which surrounds a plurality of mandrels 3 defining the partitions. The extruded section is drawn by means 7 from the die 2 and through the water-cooled sizing die 5, and the expanding air is sequentially admitted to different bores from mandrel passages 4, sequential ones, e.g. alternate ones 4a, 4b, Fig. 4a, of which are connected to different mandrel passages 9, 10, through which the air is alternately delivered and vented by a switching electromagnetic valve. The process is initiated by a mechanism 11 which crushes the extruded section together, and the section is cut downstream of the means 7. The mandrels 3 defining the bores at the edges of the section are preferably half the width of the intermediate mandrels. The section may be externally flat, as in Figs. 1-5, or as in Fig. 6 (not shown), in which the expansion from a similarly configured die is sequentially effected from adjacent mandrel bores, of sets of three bores repeating across the width of the die. Alternatively, the flat section may be extruded from a die having upper and lower sets of co-extensive mandrels from each of which sets the expansion is alternately effected from adjacent mandrels; so that with the expansion also being alternately effected from each of upper and lower co-extensive mandrels, Fig. 10, a section is produced having diagonal fused partitions; and with the expansion being simultaneously effected from each of upper and lower co-extensive mandrels, Fig. 11 (not shown), the partitions are horizontally and vertically fused. Alternatively, an "L" section may be produced, Fig. 7 (not shown), in which the expansion is alternately effected from adjacent mandrels, or a circular section in which the expansion is alternately effected from each of a pair of semicircular mandrels, Fig. 8 (not shown), or from diagonally opposed pairs of four mandrels 4a, 4b, Fig. 9. The extrusion die is heated and provided with bolts for adjusting for extrusion uniformity. To prevent adhesion of the thermoplastics, the sizing die 5 comprises aluminium having a roughed surface.