Production of multi-wall plastic tubing and tubular film by melt extrusion

摘要

992,930. Making multi-wall tubular film; extruding multi-layer thermoplastic tubes. UNION CARBIDE CORPORATION. Sept. 3, 1963, No. 34674/63. Headings B5A and B5B. An apparatus for continuously producing integral, multi-wall tubing and tabular film by concurrently melt-extruding two or more thermoplastic organic materials comprises an extruder 10 (Fig. 2) from which the plastic melt flow is discharged through the elbow 32 into the lower end of the tube 80 which is screwed into the bottom port of tha triple ported tee fitting 34, a second port of which communicates with the discharge end of a second extruder 20. The third port of fitting 34 communicates with the cylindrical central passage 78 of a vertical die holder 36. A multiported cylindrical core member or plug 75 for channeling the flow of melt from extruder 10 into a stream 16 of annular cross-section (Fig. 9) and of a melt from extruder 20 conjointly into a stream 27 of annular cross-section exteriorly encircling stream 16 and a central core stream 26 of circuair cross-section interiorly of stream 16 (Figs. 6 and 9) is positioned within the lower portion of central passage 78 in die holder 36 (Fig. 2) and extends downwardly through tee fitting 34. Core plug 75 comprises the tube 80 provided near its upper end with three equidistant spaced streamlined spiders 81 to centre the tube in passage 78 (Figs. 7 and 11). Positioned within tube 80 and fastened thereto is an inner tube 84 centred inside tube 80 by three spiders 85 and having on its lower end a proportioning chamber. Tube 84 has an axial cylindrical passage 88 and a communicating transverse passage 90 aligned with passage 92 of tube 80 and also with passage 76 of tee fitting 34. The melt 25 flowing from the second extruder 20 towards the proportioning chamber is divided at the entrance to conjoined passages 92 and 90 thereof, a portion of the melt 25 rising as a cylinder 27 of annular cross section in the passage 93 of annular cross-section between the tube 80 and passage 78, and the balance of the flow rising as a cylinder in passage 88. The relative rates of flow of melt in passages 93 and 88 is adjusted by flow means of the valve 86. The proportioning chamber at the lower end of tube 84 has its lower and outer walls flattened on two sides parallel to each other and to passage 90 and its lower extremity streamlined to form a truncated wedge which bifurcates and guides the melt fed thereto from extruder 10 about the proportioning chamber. The passage 95 (Figs. 4, 5, 6 and 12) formed by the flattened outer walls of 84 and the inner wall of tabs 80 guides the two streams 161, 1611 about the proportioning chamber and reunites them in combined flow rising as a cylindrical tube in the upper extension of passage 95 formed by the outer surface of tube 84 and the inner surface of tube 80. The die assembly 38 (Fig. 2) comprises a conical die cup 41 and a depending cone 40 spaced therefrom to form a tapered hollow cone passageway 37 having an annular crosssection for supplying melt from cylindrical passage 78 to an annular die orifice 42. An apparatus for forming triple wall tubing or tubular film and comprising three extruders and an extrusion die of the above type is shown in Fig. 14.