Patent GB-1188817-A (GB)
Title: Method and Apparatus for Making Thermoplastic Resinous Film.
Inventor: HEISTERKAMP HERBERT WALTER
IPC: B29C48/10
Filed: 1967-04-21
Abstract: 1,188,817. Tubular film making apparatus. DOW CHEMICAL CO. 21 April, 1967 [27 April, 1966], No. 18391/67. Heading B5B. In the production of tubular films by the trapped bubble process a liquid coolant is circulated through a heat exchanger which is disposed in the interior of the trapped bubble and the air or other gas in the bubble is caused to circulate sequentially over the cooling elements of the heat exchanger and the internal surface of the bubble in two adjacent vortical flow patterns. The process may be carried out in an apparatus for producing tubular films comprising a die having an annular extrusion orifice, a means for flattening tubular film extruded by the die positioned at a distance from the die on the extrusion axis, the die having disposed therein a passageway for the introduction of a gas at superatmospheric into the interior of the film and an inlet conduit and an outlet conduit in communication with a source of a liquid coolant (not shown) passing therethrough and in communication with the interior of the tubular film, two annular liquid-gas heat exchanger means disposed within the tubular film in coaxial end-to-end relationship with each other and supported by the die and in communication with the inlet and outlet conduits, means to cause the air or other gas within the tubular film to flow over the cooling members of the heat exchangers and then over the internal surface of the freshly extruded tubular film, and means for rotating an annular gas distributer about the axis of the tubular film. As shown in Fig. 1, heated film-forming material is fed to a die 12 for extruding tubular films from an extruder 11 through a conduit 13 to form a tubular film 16 which is cooled externally by an air ring 15 and is drawn upwards and flattened by the nip rolls 18 and 19 in the usual manner. The tubular film is inflated and maintained in an inflated form by means of internal gas pressure in the usual manner, gas at a pressure somewhat above atmospheric being introduced into the space 36 within the tubular film from a source 38 through a conduit 39 and a duct passing through the die 12. Disposed within the bubble or interior of the film 36 and mounted on the die 12 is a cooling assembly 30 comprising a support and gas flow distributer 32, a first gas cooler 33 mounted on the distributer 32 and a second gas cooler mounted on the first gas cooler 33. The units 32, 33 and 35 are adapted to cause the gas in the bubble 36 to flow over cooling coils within the coolers 33 and 35 and thence to flow in an annular vortical flow pattern between the external walls of the coolers and the internal wall of the tubular film 16, as shown by the arrows. The impeller motors within the units 32, 33 and 35 are supplied with power through the lines 45 to 47 passing through the die and a cooling liquid is circulated in the coolers 33 and 35 by means of pipe-lines 51 and 52 and a refrigeration unit 50. A pair of liquid-gas heat exchange cooling assemblies 60 (Fig. 2) comprise a first cooling assembly 61 arranged in series with a second cooling assembly 62. The heat exchanger 61 comprises a core 64 mounted on the distributer (shown at 32 in Fig. 1) and supporting the finned heat exchanger tubes 70 to 72 which are supplied with refrigerated liquid from the header 80 and the conduits 81 to 83. The finned tubes 70 to 71 are helically disposed within a cylindrical housing 65, the top and bottom of which are closed by a perforated plate and a filter 85 respectively. An impeller 89 driven by an electric motor 88 is adapted to cause gas within the bubble 36 to flow through the housing 65 over the cooling tubes 70 to 72 and through the filter 85 in the direction shown by the arrows. Refrigerated liquid flows from the outlet ends 76 to 78 of the tubes 70 to 72 through the line 90 to the inlets 101 to 103 of the cooling tubes 98 to 100 of the second cooler 62 and from the outlet ends 105 to 107 of the cooling tubes through the return line 108 to an external refrigeration and circulation unit (not shown). An impeller 111 driven by the motor 110 causes the gas in the bubble 36 to flow over the tubes 98 to 100 in the direction shown by the arrows. The cooled gas flows through an upper distributer 112 and out of the apertures 16 into the bubble 36. The gas distributer 32 is adapted to be rotated about its vertical axis by an electric motor in order to provide a sufficient distribution of minor irregularities in the air flow from an annular discharge orifice at the bottom of the distributer.