WIRE, Manufacture of. At the present time all wire is made by the drawing process, and while permitting the production of a much thinner wire than could be obtained from the rolls, it also gives a wire of greater tensile strength, so much so that the smaller the size to which the wire is drawn down, the greater is its ultimate breaking strength per square inch. The breaking strength of English piano wire ranges from 225 pounds for Nn. 12 music i wire, which is 0.029 inch in diameter, to 650 pounds for No. 22, which is 0.052 inch in diam eter, indicating an ultimate tensile strength, ranging from 300.000 to 240,000 pounds per square inch. This wire shows a content of carbon, 0.570 per cent; silicon, 0.090 per cent; sulphur, 0.011 per cent; phosphorus, 0.018 per Lent; and manganese, 0.425 per cent In the past all classes of iron wire were made entirely from wrought iron and required very careful preparation of the raw material to insure toughness and high tensile strength; but, with the discovery of the Bessemer and the open hearth converting processes, and the con sequent lowering of the cost of production ac companied by an enormous increase in the strength of the raw material, wrought iron was quickly supplanted by mild steel The great increase in the strength of steel wire over that of wrought iron may be better appreciated from the following statement of facts: The ultimate tensile strength of the best bright, hard-drawn wrought-iron wire is about 70,00() pounds to the square inch while that of ordi 'Lary Bessemer steel is 8000 pounds, and that of ooin-hearth steel is 120,000 pounds to the square inch. In the special grades of wire man ufactured from high carbon, open-hearth steel, the values range from 200,000 pounds to 340, 000 pounds per square inch.
A description of the process of manufacture may be begun with the billets. The bulk of the wire of commerce is made from Besse mer steel billets, while open-hearth billets are worked up into rods for the manufacture of chain, for special grades of wire and for vari ous finished products requiring great tensile strength. The reduction of the billets to the rods which are the raw material of the wire drawer is done by a rolling-mill (q.v.). The billets are generally stored near the continuous heating furnaces located at the upper end of the rod mill. In the larger plants, when the mill is in full op Lion_ four furnaces are con tinually at v.0 1 fifth held in reserve.
The billets ? 4 X 4 inches in section, and 36 inc:ie. 11, are fed into the fur nace transvers • by side, and are pushed through thy for • by a hydraulic charg ing machine. After they have been heated to the right temperature for rolling, they are pushed out, one after the other, through the rear door of the furnace on to a conveyor which takes them to the rod mill, where they are passed through the roughing rolls. This mill consists of eight pairs of rolls, and by its opera tion reduces the billet from its section of 4 X 4 inches to a rod of three-fourths of an inch square and of great ultimate tensile strength. The alternate pairs of rolls are provided with different shaped grooves so as to press the rods into shapes alternately square and oval, oval and round, etc., thus working the metal thor
oughly and improving its qualities. In the eighth pair of rolls the grooves are one-fourth of an inch square, and from them the rods are carried to the finishing mill where they are given 10 more passes and brought down to the required dimensions.
The finishing mill lies at right angles to the roughing mill with its 10 pairs of rolls ar ranged side by side. As the rods issue from one pair of rolls, they are seized with a pair of tongs by workmen who bend them around and feed them into the next pair. The rapid in crease in length is accommodated by the in creased speed of the successive pairs of rolls, that of the 10th pair being about 1,350 feet per minute, or about 15 miles per hour. The en tire operation of rolling down the billet to a fin ished rod one-fourth inch square and about a quarter of a mile long, is accomplished in one heat. The smallest size of rod produced in the rolling mill is three-sixteenths of an inch in di ameter. As the rods issue from the last pair of rolls, their ends arc seized and attached to the drums of the reels on which they are wound into coils of convenient size, and then dropped upon a conveyor, by which they are carried to the wire mill In the wire mill, the coils are thoroughly cleaned of scales. oil and dirt by being placed in wooden tanks containing a weak solution of sulphuric acid. They are then placed in lime. and then in the bakeries and dried thoronghl• Up to this point the product is technically known as •rods," and only after it has been to a smaller diameter, at least to one-fifth of an inch, is it known under the commercial de•ignatio 11 of "w ire." The wire-drawing machine consists of stout bench upon which is mounted a cast-iron drum, around which the wire is wound as it 1. drawn through the dies. In drawing. the cod of rod is placed on a spool fastened to the tloor of the shop near the end of the bench, and the end of the wire having been swaged down. it is inserted in the larger end of the hole in the .die-plate, passed through and caught by the tongs attached to the drum which is revolved until the entire coil has been drawn down. The die-plate is a heavy block of cast steel in which arc set several dies of various sizes. the latter made of the hardest chrome steel. The hole to the die is conical, the smaller end being the size to which the wire is drawn. In forming the die this opening is made smaller than required and enlarged to the correct size by driving suitable punch into it — the compression thus exerted increasing the hardness of the drawinc surface in the die. The sockets in the & plate into which the dies are set are slight conical and as the dies wear to a point at %filch the wire becomes too large, the dies are driven further into the die-plate, thus reducing the opening and are again sized with the punch Once started the speed of the drum must fit constant or the wire will he of uneven diameter becoming slightly smaller when the mill is stopped.