Patent GB-1207448-A (GB)
Title: Extrusion apparatus for the production of tubes and tubular films of synthetic organic thermoplastic polymeric material
IPC: B29C48/885
Filed: 1968-01-29
Abstract: 1,207,448. Producing tubular films. SEPROMA G.m.b.H. 29 Jan., 1968 [17 Jan., 1968], No. 4464/68. Heading B5B. An apparatus for producing tubular films by the " blown tube " method is provided with an extrusion die comprising a die body 1 (Fig. 1) and a core or mandrel 2 which define an annular extrusion orifice through which a tubular film 3<SP>1</SP> is melt extruded. The die body has mounted thereon a sizing and cooling sleeve comprising three sections 4, 5 and 6 bolted together to form a tube through which and in contact with the inner surface of which the tubular film is drawn. During its passage through the cooling sleeve the tubular film is cooled to a temperature below the crystalline melting point of the film material by the passage of a cooling medium through the jackets of the sections, 4, 5 and 6. After leaving the cooling sleeve the part 8 of the tubular film is expanded by compressed air at a pressure P1 supplied through an axial bore 7 in the core 2 into a tube 16 coaxial with the core and screwed thereto. The tube 16 increases in diameter towards its free end up to about the inside diameter of the portion 3<SP>1</SP> of the tubular film and is provided at its free end with a hollow mandrel 11 having a passage 20 through which the compressed air supplied at pressure P1 passes into the portion 8 of the tubular film and expands it. The mandrel 11 is cooled by means of a cooling medium which is supplied to and discharged from the hollow interior 21 of the mandrel by means of pipes 14 and 15. The portion 3<SP>1</SP> of the tubular film is urged against the internal surface of the cooling and sizing sleeve 4, 5, 6 by compressed air at pressure p2 introduced into the space 24 between the tube 16 and the portion 3<SP>1</SP> of the tubular film. In order to prevent the air at pressure p2 in the space 24 from escaping into the portion 8 of the tubular film, air at pressure p3 is introduced into the annular recess 12 in the nozzle section 6, said recess surrounding the portion 3<SP>1</SP> of the tubular film whereby the portion 3<SP>1</SP> is urged by the pressure p3 of the compressed air against the sealing body 11. The outlet 13 of the cooling and sizing sleeve 4, 5, 6 is slightly constricted towards its outer end to minimize the escape of air at pressure p3 from the recess 12. After leaving the cooling and sizing sleeve 4, 5 6, the tubular film is inflated by the air at pressure p1 introduced into its interior, passed between two mutually inclined members initially to flatten it and hauled off and completely flattened by a pair of driven nip rolls in the usual manner. In the alternative embodiment shown in Fig. 3, the tubular film 3 is drawn intermittently in the direction of the arrow between the final portion 31 of the cooling and sizing sleeve and a mandrel 30. Directly adjacent to the inside surface of the section 32 of the tubular film is a temperature adjusting device 33 mounted on the mandrel 30 and supplied with a heating or a cooling medium through a conduit 35 in the mandrel 30. When the temperature of the tubular film section 32 has been adjusted to a required level by the device 33, air at pressure p4 is introduced through a duct 40 in the mandrel into the interior of the section 32 and inflates this section until it assumes the shape shown at 32<SP>1</SP> which is subsequently drawn out of the inflation zone by the nip rolls 42.