WIRE-DRAWING is the art of drawing out any of the ductile metals into long and regular threads of an uniform diameter, and of any size and shape.
The process by which this is effected is extremely simple, the apparatus employed consisting only of a draw plate and a draw bench. The Brow plate is a thick plate of the finest steel, perforated with holes of various sizes from that of the largest to that of the smallest wire required. These holes are punched in the plate while hot by well pointed punches of German steel. Four heats are gene rally required, and at every heat a finer punch is employed, so as to make the hole taper or take a form slightly conical. The holes are made to differ from each other in diameter, by very imperceptible gradations, The draw bench is a simple machine, consisting of a horizontal roller or axis turned by four vertical levers like a rolling press. A strong strap or chain is coiled round the roller, and at the end of the strap is a pair of pincers for taking hold of the end of the piece of metal to be drawn. The draw plate is then made to bear against two strong iron pins placed in the draw bench, and the piece of metal seized by the pincers is put into the hole in the plate immediately less in diameter than the piece of metal. By turning the levers, the pincers at the end of the strap pull the piece of metal through the hole in the draw plate, and thus lengthens it a cer tain quantity. It is then drawn through smaller and smaller holes till it is reduced to the proper degree of fineness, the wire being coiled up on the roller as it is drawn out.
In drawing thick wires, or pipes, or any other bodies which cannot be coiled up as they are drawn, the pincers are placed upon a movable frame which recedes from the draw plate.
In the wire mills in France the wire is not coiled round a barrel, but the pincers are attached to a lever which draws them backwards, and advances them forwards alternately, the pincers opening and quitting the wire when they advance, and shutting and seizing the wire when they begin to draw back wards. The operation is exactly like that of a man drawing a rope out of the water. When he has drawn it out a certain quantity he ceases to grasp it, and advances his hands to give a fresh pull. By this method of drawing wire, its surface is covered with pincer marks at the distance of two inches on the great wires, and five inches in the smaller wires.
Iron wire is principally used in the construction of cards and carding machinery, and so great is the demand for it, that Messrs. Minchel of Aigle in France manufacture annually a hundred thousand quintals of iron wire of 100 lbs. each. Most of it is consumed in France, and the rest exported to Spain, Portugal, Italy, and•the Archipelago.
The drawing of wire out of the more ductile me tals, sufficiently fine for the purpose of micrometers, has always been a desideratum in France. The French were celebrated for having produced the finest wire for such purposes; and we have been informed by the late James Watt, Esq. that the draw plates by which such wire was produced were lost during the revolution. The art, however, has been well supplied, and even greatly perfected, by a most ingenious process invented by the late Dr. Wollaston, the whole of whose paper* we lay before Our readers, as it is incapable of abridgement.
" It is recorded by Muschenbroek," says he, " that an artist of Augsburg drew a wire of gold so slender that 500 feet of it weighed only one grain; but the method by which this was effected is not mentioned, and indeed it has been doubted whether it could really have been done. I shall, however, show that a wire of gold may without much diffi culty be obtained finer than that spoken of by Muschenbroek, and that wire of platina may be drawn much more slender with the utmost facility.
Those who draw silver wire in large quantities for lace and embroidery, sometimes begin with a rod that is about 3 inches in diameter, and ulti mately obtain wires that are as small as thdth of an inch in thickness. If in any stage of this pro cess a rod of silver wire be taken, and a hole be drilled through it longitudinally, having its diame ter part of that of the rod, and if a wire of pure gold be inserted so as to fill the hole, it is evident that by continuing to draw the rod the gold within it will be reduced in diameter exactly in the same proportion as the silver; so that if both be thus drawn out together till the diameter of the silver is Til-'oath of an inch, then that of the gold will be only and of such wire five hundred and fifty feet would be requisite to make one grain.