Page:EB1911 - Volume 28.djvu/759

Rh 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. 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. In the case of submarine cables, coverings of jute-served gutta-percha are employed, upon which a protective covering of steel wires is laid, subsequently treated with jute yarns or tapes and protected with coatings of compound. Messrs Johnson & Phillips, Ltd., of Charlton, Kent, make combination machines which lay the steel wires, apply the tapes and cover with the preservative compound, in one continuous operation. The wire is carried on bobbins in two rotating cages, having twelve bobbins each, and the jute bobbins, seventy-two in number, are mounted on disks, while the compound is supplied from steam-heated tanks, through which the cable is passed by rollers. A machine of this class will turn out as much as 8 m. of finished cable in a day of twelve hours. When a supply of steel wire has been used up, the next portions are united by electric welding.

Tapes of paper, rubber or jute are served from bobbins on disks and also in some designs from independent bobbins, each mounted on its own pin, set at a suitable angle in a frame, to give the spiral lead. In some instances seventy-two layers of paper are applied to high-tension cables. These cables are subsequently put into steam-heated tanks, hermetically sealed and connected to a vacuum pump, by which the moisture is drawn off as quickly as possible. When the cable is thoroughly dry a quantity of compound is admitted to the tank and so permeates the insulation. Lead is put on the outside of the paper in a press, which has dies through which the cable passes, and is covered with a uniform coating or tube of lead, forced into the dies and around the cable by hydraulic pressure. Steel tapes are in some cases used to armour cables and protect them from external injury; the tape is wound in a similar manner to the other materials already described.

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.

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

Wire Gauges.—In commerce, the sizes of wire are estimated by gauges which consist of plates of circular or oblong form having notches of different widths round their edges to receive wire and sheet metals of different thicknesses. Each notch is stamped with a number, and the wire or sheet, which just fits a given notch, is stated to be of, say, No. 10, 11, 12, &c., of the wire gauge. But it is always necessary to state what particular gauge is used, since, unfortunately, uniformity is wanting. Holtzapffel investigated the subject, and published a valuable collection of facts relating thereto in 1846. A more exhaustive report was published by a committee of the Society of Telegraph Engineers in 1879 (Journ. Soc. Tel. Eng. viii. p. 476), a result of which was the sanctioning by the Board of Trade, in 1884, of the New Imperial Standard Wire Gauge. That report stated: “The different gauges in use might be counted by hundreds. . . . Every wire-drawer has gauges adjusted to suit special objects. When competition is keen, wire is commonly drawn by one gauge and sold by another; half sizes and quarter sizes are in constant use among the dealers, the wire being sold as whole sizes. Sometimes four or five different gauge plates have been made by one maker—some by which the workmen are paid, and others by which the wire is sold. . . . The whole system is in confusion, and lends itself to those who desire to use fraudulent practices.” Thomas Hughes (The English Wire Gauge, London, 1879) stated that, “In

the same town some use Stubs, some the Warrington, some the Lancashire, some the Yorkshire, some the Birmingham, some the iron wire gauge and some their own made wire gauge, all maintaining the gauge in their own possession to be the correct one.”

Gauges may be broadly divided into two groups, the empirical and the geometrical. The first include all the old ones, notably the Birmingham (B.W.G.) and the Lancashire or Stubs. The origin of the B.W.G. is lost in obscurity. The numbers of wire were in common use earlier than 1735. It is believed that they originally were based on the series of drawn wires No. 1 being the original rod, and succeeding numbers corresponding with each draw, so that No. 10, for example, would have passed ten times through the draw plate. But the Birmingham and the Lancashire gauge, the latter being based on an averaging of the dimensions collated from a large number of the former in the possession of Peter Stubs of Warrington, have long held the leading position, and are still retained and used probably to a greater extent than the more recent geometrical gauges. There is no need, therefore, to give an account of the other and less known gauges which have been used by manufacturers. In no case is there any regular increment of dimensions from which a regular curve could be drawn.

The first attempt to adopt a geometrical system was made by Messrs Brown & Sharpe in 1855. They established a regular progression of thirty-nine steps between the English sizes, No. 0000 (460 mils) and No. 36 (5 mils). Each diameter was multiplied by 0.890522 to give the next lower size. This is now the American gauge, and is used to a considerable extent in the U.S.A.

The Imperial Standard Wire Gauge, which has been sanctioned by the British Board of Trade, is one that was formulated by J. Latimer Clark. Incidentally, one of its recommendations is that it differs from pre-existing gauges scarcely more than they differ among themselves, and it is based on a rational system, the basis being the mil. No. 7/0, the largest size, is 0.50 in. (500 mils) in diameter, and the smallest, No. 50, is 0.001 in. (1 mil) in diameter. Between these the diameter, or thickness, diminishes by 10.557%, and the weight diminishes by 20%.

But the fact remains that a large number of gauges are still in common use, and that gauges of the same name differ and are therefore not authoritative. Sheet iron wire gauge differs from Stubs' steel wire gauge. Gauges for wire and plate differ. Accuracy can only be secured by specifying precisely the name of the gauge intended, or, what is generally better, the dimensions in decimals, which can always be tested with a micrometer. A decimal gauge has been proposed. Tables of decimal equivalents of the wire gauges have been prepared, and are helpful.

The circular forms of gauge are the most popular, and are generally 3¾ in. in diameter, with thirty-six notches; many have the decimal equivalents of the sizes stamped on the back. Oblong plates are similarly notched. Rolling mill gauges are also oblong in form. Many gauges are made with a wedge-like slot into which the wire is thrust; one edge being graduated, the point at which the movement of the wire is arrested gives its size. The graduations are those of standard wire, or in thousandths of an inch. In some cases both edges are graduated differently to serve for comparison between two systems of measurement. A few gauges are made with holes into which the wire has to be thrust. All gauges are hardened and ground to dimensions.  WIREWORM, a popular name for the slender, hard-skinned grubs or larvae of the click-beetles or Elateridae, a family of the Coleoptera (q.v.). These larvae pass a long life (two or three years) in the soil, feeding on the roots of plants, and they often cause much damage to farm crops of all kinds, but especially to cereals. A wireworm may be known by its broad, quadrate head and cylindrical or somewhat flattened body, all of whose segments are protected by a firm, chitinous cuticle. The three pairs of legs on the thoracic segments are short and the last abdominal segment is, as is frequently the case in beetle grubs, directed downwards to serve as a terminal proleg. The hinder end of the body is acutely pointed in the larvae of the species of Agriotes (A. obscurus and A. lineatus) that are the best knows of the wireworms, but in another common form (the grub of Athous haemorrhoidalis) the tail is bifid and beset with sharp processes. The subterranean habits of wireworms make it hard to exterminate them when they have once begun to attack a crop, and the most hopeful practice is, by rotation and by proper treatment of the land, to clear it of the insects before the seed be sown. Passing easily through the soil on account of their shape, wireworms travel from plant to plant and thus injure the roots of a large number in a short time. (See .) Other subterranean creatures—such as the “leather-jacket” grub of crane-flies—which have no legs, and geophilid centipedes, which may have over two hundred, are often confounded with the six-legged wireworms.