Patent GB-1438514-A (GB)
Title: Extrusion
IPC: B29C48/06
Filed: 1973-06-07
Abstract: 1438514 Cross-head sheathing die WESTERN ELECTRIC CO Inc 7 June 1973 [7 June 1972 3 Nov 1972] 27182/73 Heading B5A [Also in Division H1] In the coating, by a cross-head extruder die, of a copper or aluminium conductor filament core 22 with specified polymeric materials, e.g. polypropylene, which may be foamed, the material is delivered to around the conductor 22 as a tubular stream, at uniform pressure formed at 91<SP>1</SP> around the cross-head mandrel, Fig. 8, from two pairs of equi-circumferentially spaced streams 87<SP>1</SP> flowing in the direction of conductor travel through the crosshead and from which streams the material is discharged at equal and steady state flow. The streams 87<SP>1</SP> may converge at a confluence 91<SP>1</SP>, as in the Fig. 2-4 embodiment (not shown), and are formed, from an inlet stream 73<SP>1</SP> from a screw extruder, by a stream 58<SP>1</SP> flowing in the direction of conductor travel and dividing into two streams 61<SP>1</SP> extending circumferentially around the conductor. Each stream 61<SP>1</SP> bends to flow as a stream 62<SP>1</SP> flowing in the reverse direction to that of conductor travel, and then as a stream 72<SP>1</SP> flowing radially inwardly and which divides into a pair of circumferentially extending streams, each bending into a stream 87<SP>1</SP>. Steady state flow in the streams 87<SP>1</SP>, as well as in the streams 611 and 62<SP>1</SP>, is obtained by each stream division being symmetrical with respect to the principal plane in which a preceding stream bend occurs, to ensure the same flow conditions in each division, and by the streams 61<SP>1</SP>, 621 and 87<SP>1</SP> having sufficient and stated ratios of length to "diameter" to produce the steady state flow downstream of a bend. In the Fig. 1-4 embodiment (not shown), the flow paths are defined in the cross-head body with an assembly screw threadedly retained therein and comprising concentric outer and inner tubular members (48), (78) with a core guide (93) within the member (78). The outer member (48) is aligned within the die head at a slot and set screw connection. The material streams 58<SP>1</SP>, 611 and 62 are formed by semicircular, V-shaped, or rectangular channels in, and the stream 72 by a channel through, the outer member (48). The streams downstream thereof are formed by channels in the outer surface of the inner member (78). The channels may also be formed in opposed surfaces of the crosshead body, outer tubular part, and inner tubular part, to define streams of symmetrical cross-section, which may be circular or elliptical. In the Figs. 2-4 embodiment, the core guide (93) projects downstream of the inner member (78), but in the Fig. 9 embodiment (not shown) the core guide terminates upstream thereof with the core being additionally guided by a passage (132) through the inner member (178). In the Fig. 10 (not shown) modification of the Fig. 9 embodiment, the inner member (278) is machined to sequential frusto-conical contours to remove the confluence, and so that the core tube (293) projects downstream thereof. In the Fig. 11 embodiment, the channels are formed in outer and inner members 348, 378, and the core guide is eliminated by employing a bored diamond die 138 within the inner member 378. In the Fig. 12 embodiment, the core guide 493 is extended into, or downstream of, the extrusion passage of the die 403 to define therewith a tubular orifice from which a tubular sheath 408 is drawn down on to the core 422. The extruded materials may also comprise high density polypropylene, high, medium or low density polyethylene, foamed plastics such as cellular polyethylene or polypropylene, or polyvinyl chloride, and nylon, or rubber.