WIRE AND WIREDRAWING. The facility with which any metal can be drawn into wire depends upon its ductility. Most metals have this property; but some, like bismuth and antimony, are so brittle that they can only be drawn out with difficulty, and wire made from such metals is useless, from want of tenacity. See DuCTLL1TY.
Metals largely used for making wire, such as iron, brass, and copper, are drawn by essentially the same process. We may take iron as an example. It is prepared by cut ting up fiat rolled plates into square rods of a given thickness. This is done by means of a pair of slitting rollers; one of these has grooves, equal to the breadth of the rods wanted, fitting into corresponding grooves in the other, which cut up the metal like scissors. The rods are cleaned of scales of oxide, either by mechanical rubbing, or bx chemical treatment with dilute sulphuric acid. If time rod is thick, it has its square edge taken off by rollers. It is then drawn into wire by forcing it through the hole of a draw-plate. This is an oblong piece of hard. steel pierced with conical holes, gradually diminishing in diameter, and having the smallest ends of these tapering holes carefully prepared to the required size- Sometimes cubical shaped dies, each with a single trumpet shaped bole, are used. Motion is given to the drawing-block or cylinder by means of beveled wheels connected with a shaft driven by steam or waterpower.
The workman commences by making a point on the rod, so as to allow it to pass through the bole, and be grasped by a pair of pincers attached to a chain• which draws it out till the length is sufficient to pass round the cylinder. This much is done by hand, and then the cylinder, being put in gear, is made to revolve and pull the wire through the draw-plate—coiling it round itself as the drawing proceeds. After being once drawn, it is again passed through a smaller hole, and so time process ie repeated till it has been reduced to the size required. Fine wire may require from 20 to 30 drawings. The cylinder revolves slowly with a thick wire, and the speed is increased as the size dinminishes. After being passed a few times through the draw plate the metal becomes brittle, and requires to be annealed. Sometimes, a lubricat• ing substance—as was, grease, or soap—is employed during the drawing, especially for fine wires.
For some very accurate purposes, such as chronometer springs, and for gold and silver lace, the wire is drawn through jeweled holes, that is, holes perforated in rubies and other hard gems. A silver wire 170 m. long, and about of an inch in diameter,
has been drawn through a hole in a ruby, and found, by a micrometer, to be of exactly the same size at the end as at the beginning; whereas the drawing of a length of 16 m. of brass wire through a steel draw-plate necessitates a readjustment of the hole.
Platinum wire can be drawn as thin as Ten of an inch in diameter by first encas ing it in silver, drawing down the compound wire, and then dissolving off the sil ver with nitric acid. By the same process gold wire can be obtained only of an inch in diameter. It has been shown by Babbage, as an illustration of how greatly labor increases the value of a raw material, that one pound of iron, which costs twopence, will yield 50,000 wire pendulum springs for watches, each weighing about one-seventh of a grain, and selling at the retail price of twopence.
Wire, although mostly cylindrical in form, is drawn of many different sections, such as oval, half-round, flat, triangular, molded, and the grooved pinion-wire from which the small toothed pinions for clocks and watches are cut. Copper wire of different forms is used to form patterns in the blocks used by calico printers.
The following table (given by Dr. Tomlinson) of weights, omitting fractions of a pound, which were sustained by wires 0.787 of a line in diameter, shows the compara tive tenacity of a few of the metals: Iron, 549 lbs.; copper, 302 lbs.; platinum, 274 lbs. ; silver, 187 lbs.; gold, 151 lbs.; zinc, 110 lbs. ; tin, 35 lbs.; lead, 28 lbs. It may be re marked here that some kinds of brass wire have been noticed to become extremely brittle in the course of time, especially if subjected to vibration, and even to bieak when used to support objects, without any assignable cause.
The quantity of wire used in the English manufacturing districts must be enormous, steel and iron wire being required for the manufacture of needles, fish-hooks, hooks and eyes, carding-machines, serew-nails, fencing, and basket-work; brass wire for the manu facture of pins, wire cloth for paper making and other machines, and chain-making; and copper wire for bell-hanging. Nothing, however, has increased the production of wire, both iron, and copper, more than the electric telegraph. Belgium, which a few years ago exported none, now exports 1200 tons annually of iron wire.