Patent GB-756045-A (GB)
Title: Tubular extruded products of thermoplastic film-forming material
Inventor: STIMSON EDWARD ERIC
IPC: B29C48/12
Filed: 1953-05-20
Abstract: 756,045. Extruding tubes from thermoplastic material. BRITISH CELANESE, Ltd. May 19, 1954 [May 20, 1953], No. 14177/53. Class 87(2) Thermoplastic film forming material is extruded in a heat fluidized condition in such a way as to form a product comprising a plurality of parallel tubes, the walls of which are integral with one another. The die head comprises an adaptor 10, which may be bolted to the front end 11 of an extruder, with a conical passage 12 which registers with the outlet and leads to a rectangular passage 14. A die-core assembly, fits in a slot 16 in the adaptor in such a manner that the direction of movement of the material changes through 90 degrees becoming vertically downwards instead of horiontal. Hexagonal cores 21, of gradually increasing section towards the outlet and spaced to form passages 26, are welded to a plug 22 which is flanged at 23 to seat on the upper face 28 of the adaptor. A cover plate 30 rests on the flanges and has an inlet pipe 32 which admits air to a recess 31, from which it passes to holes 27 in the cores. A die-plate 19 is bolted to the lower face of the adaptor and has an aperture 20 shaped to fit round the outside perimeter of the cover to give the honeycomb pattern of die apertures shown in Fig. 2, which shows three rows of aperture as an example. The material is soft as it leaves the die apertures and stretches slightly due to its weight, acquiring a thickness 10-25 per cent less than the width of the aperture and of the order of 3-12 mils. Air is supplied through the bores 27 to the interior of the extruded tubes at a pressure regulated to prevent collapse and avoid undue inflation. Alternatively, the -material may change direction in the horizontal plane and leave the die horizontally, in which case it is stretched by draw-rollers profiled to give an opening corresponding to the aperture 20. A ring of air jets cools the material as it leaves the die. Alternatively, it may be sprayed with cooling water, as extruded into a cooling bath, or in some cases the atmosphere is sufficient. Beyond the draw rollers (where used), the tubing may be cut into lengths, e.g. 6-8 feet. Internal support for the extruded tubes may also be provided by a mandrel, as described in Specification 691,125. This is a hollow ex-' pansion hexagonal in section of a tubular stem which projects from each core and which provides a passage for air which passes into the space between the extended tube and the stem to keep the tube out of contact with the mandrel until it reaches the expansion, the air then passing through suitable outlets into the hollow expansion. Also an arrangement similar to that described in Specification 702,176 may be used to support the extruded tube, employing a series of hexagonal discs in a staggered arrangement, each having part of its edge meeting the inside of the tube, the remainder of the edge being out of contact. In some cases the internal air support may be dispensed with and solid cores used. Suitable materials are cellulose acetate plasticized with diethyl phthalate and triphenyl phosphate, or with other plastiizers e.g. as mentioned in the Specification; cellulose propionate and other thermoplastic cellulose derivatives; polyvinyl compounds; acrylic acid derivatives, and thermoplastic linear condensation polymers. An example is given with dimensions and physical conditions of extruding cellulose acetate. The products are suitable for thermal insulation or, when containing, e.g. colouring agents, for decorative purposes