1,245,302. Extrusion dies. NRM CORP. 3 Jan., 1969 [16 Jan., 1968], No. 494/69. Headings B5A and B5B. In an extrusion die, particularly intended for the extrusion of plastics blown film, a mandrel 5 is supported within die body 2 on, as shown, diamond-shaped fins 14 which divide the flow of material during its travel from inlet 3 to outlet slot 7, the flow on one side of each fin 14 meeting that on the other such that the flows overlap and blend and the resultant joinder line extends diagonally from the outer to the inner surface of extrudate T. Such overlapping is accomplished by confining flow channels 11 along the downstream sides of fins 14 to be substantially either in body 2, shown in solid line, Fig. 3, with a clockwise force being exerted upon the material as indicated by the solid arrows, or substantially in mandrel 5, shown in phantom line, with an anticlockwise force being exerted upon the material as indicated by the phantom arrows. See also Figs. 4-7 (not reproduced). In the embodiment of Figs. 8-13 (not shown), flow in combined channel portions (23SP1/SP, 24SP1/SP) meets flow in combined channel portions (2311, 2411) substantially tangentially and such combined flows also meet one another substantially tangentially. Fins (25) have concave edges and edge (26) of mandrel (21) is bevelled to define a channel(27). In the embodiment of Figs. 14-21 (not shown), channels (34) are each provided with a radial channel (34SP11/SP) which communicates with an adjacent channel (34) at a point where channel portion (34SP1/SP) terminates, see Fig. 15 (not reproduced). In Fig. 2, mandrel 5 is provided with a spreader 10 and pressure equalizing chambers 9.
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