Wire

A wire is a single, usually cylindrical, elongated strand of drawn metal. Wires are used to bear mechanical loads and to carry electrical energy and/or communications signals.

Finishing, covering, and insulating

Wires and cables for electrical purposes are covered with various insulating materials, such as cotton, rubber, or plastic, wrapped in concentric fashion and further protected with, substances such as paraffin, some kind of preservative compound, bitumen or lead sheathing or steel taping. The stranding or covering machines employed in this work are designed to carry supplies of material and wind it on to the wire which is passing through at a rapid rate. Some of the smallest machines for cotton covering have a large drum, which grips the wire and moves it through toothed gears at a definite speed; the wire passes through the centre of disks mounted above a long bed, and the disks carry each a number of bobbins varying from six to twelve or more in different machines. A supply of covering material is wound on each bobbin, and the end is led on to the wire, which occupies a central position relatively to the bobbins; the latter being revolved at a suitable speed bodily with their disks, the cotton is consequently served on to the wire, winding in spiral fashion so as to overlap. If a large number of strands are required the disks are duplicated, so that as many as sixty spools may be carried, the second set of strands being laid over the first.

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For the heavier cables, used for electric light and power, and submarine cables, the machines are somewhat different in construction. The wire is still carried through a hollow shaft, but the bobbins or spools of covering material are set with their spindles at right angles to the axis of the wire, and they lie in a circular cage which rotates on rollers below. The various strands coming from the spools at various parts of the circumference of the cage all lead to a disk at the end of the hollow shaft. This disk has perforations through which each of the strands pass, thence being immediately wrapped on the cable, which slides through a bearing at this point. Toothed gears having certain definite ratios are used to cause the winding drum for the cable and the cage for the spools to rotate at suitable relative speeds which do not vary. The cages are multiplied for stranding with a large number of tapes or strands, so that a machine may have six bobbins on one cage and twelve on the other.

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Rubber covering of wires and cables is done by passing them through grooved rollers simultaneously with rubber strips above and below, so that the rubber is crushed on to the wires, the latter emerging as a wide band. The separate wires are parted forcibly, each retaining its rubber sheathing. Vulcanizing is afterwards done in steam-heated drums. However, the conductor needed to be tinned to provide some relief to stripping away the natural rubber. Since the mid1960s, the insulation has been plastic or polymers exhibiting properties simular to rubber.

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Many auxiliary machines are necessary in connection with wire and cable-covering, as plant for preparing the rubber and paper, etc., cutting it into strips, winding it, measuring lengths, etc.

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