MANUFACTURE OF INSULATED ELECTRIC CABLES

摘要

1462431 Sheathing cans of non-circular section BICC Ltd 15 July 1975 [16 July 1974] 31456/74 Heading B5A An extrusion die head, for applying a sheathing to a continuously advancing core of sectorshaped section, comprises an annular orifice defined between an outer die and an inner die having a part 1, Figs. 1 and 2, which has a bore 6 of the same shape as the section of the core, and which protrudes downstream of the die to provide an outer surface 5 of decreasing section in the downstream section and over which the extruded sheath can slide on to the core. The port is preferably replaceably attached. The surface 5 may commence at, and preferably upstream of the orifice and may be of circular section throughout its length, with a diameter decreasing at a rate which is either uniform, or increases continuously, or in stages, but which preferably changes in shape and size to that of the bore at the downstream extremity. The part 1 may comprise molybdenum disulphide loaded nylon 66, and in the Fig. 1 and 2, and in the Fig. 3 and 4 embodiment (not shown), the sector shaped bores are of defined angle, and of a projection beyond the die defined in terms of the major and minor diameters of the shape. In the Fig. 5 embodiment (not shown), the point is detachably and stationarily mounted on the downstream end of a core tube, and an intermediate die member is provided to define a pair of passages from each of which the materials of a pair of layers, of a composite sheathing, are delivered into juxtaposition upstream of the orifice. In the Fig. 6 embodiment, the composite covering is extruded around a pre-spiralled core, with which the part 61 rotates as the core passes through the bore 60 thereof. For its rotation, the part 61 is secured by a threaded member 56 to a sleeve 46, which rotates within the point 44 at bearings 51 secured by a circlip 49, and which is secured by a circlip 55 to rotate against thrust bearings 57. As described, the point projects into a treatment chamber which is hermetically sealed to the die, and contains a fluid medium at superatmospheric pressure, which urges the downstream end of the part 1 radially inwardly. The medium may comprise steam or water which collapses the sheath on to the core, and forcing of the sheath back along the core tube may be prevented by admitting a fluid through the core tube to maintain a pressure difference across the sheath, as in Specification 1,201,528. Various materials are specified, which may include electrically conductive additives, and may be cured by the fluid medium. The conductor may be a bare or previously covered wire or strand, or a group thereof.