Verfahren und Vorrichtung zur kontinuierlichen Herstellung von Formteilen oder Profilsträngen aus thermoplastischen Kunststoffen mit Zellstruktur

摘要

1,018,178. Moulding expanded synthetic resins. T. ENGEL. Oct. 1, 1964 [Nov. 29, 1963], No. 40013/64. Heading B5A. In a process of moulding expanded thermo - plastic synthetic resin, e.g. polythene, the resin is plasticized by a screw 2 and a blowing agent, e.g. ammonium carbonate, is introduced into cylinder 1 by means of a screw 3, the blowing agent being stored in a reservoir 4, where it is subjected to air or other gas pressure. Heat and pressure conditions within the cylinder are maintained such that although the resin remains liquefied, expansion does not occur until the resin leaves nozzle 6, and according to the invention, the cooling that then takes place results in the formation of an extensible outer skin within which the expansion occurs. The reservoir 4 may contain a quantity of powdered thermoplastic material, dyestuffs, lubricants and other additives, such as stabilizers, as well as the expanding agent, and the use of a gas under pressure to act as expanding agent is also considered. In the embodiment shown, extrudate is fed in turn to open-ended moulds 10 mounted on a rotatable plate 9, the mould bottoms being covered by a fixed plate 18 provided with a gap so that the formed mouldings may be ejected by a pin 11. Extrusion is continuous, the motion of plate 9 from one position to the next cutting off the flow to a particular mould and determining together with the rate of extrusion the extent to which each mould is filled. In a modification, Fig. 3 (not shown), a cleaner cutoff of the extrudate is achieved by the provision of a reciprocable apertured thimble 12 positioned over nozzle 6, the base of the thimble being convex and sliding over the surface of plate 9 when the latter is rotated. Both cylinder 1 and moulds 10 may be cooled and the nozzle may extend into the mould and be withdrawn progressively therefrom, or the mould may be rotated during filling. In further embodiments (not shown) the resin is extruded either in the form of a strip from an elongated nozzle and is cut and shaped by mating cavity dies, or in the form of a tube which may be blow moulded. In a two-stage process the extrudate is cooled sufficiently to prevent complete expansion, expansion being completed subsequently by heating the resin in a mould. A rotary mixer may be provided between screw 2 and nozzle 6.