Metals to be made into wire are first cast (or rolled in the case of wrought iron) into long square billets. A billet intended for wire is about 4 x 4 x 56 inches. Brass and copper billets are also called "wire bar," when cast for making wire.

The first operation is to break down these billets in billet and rod mills. A billet is run hot through a continuous mill of about eight sets of rolls, which break it down to about 1 1/8-inch square cross section. It then goes at once through the looping rod-mill which delivers it as coiled rod varying from 3/16 to % inches diameter, and a hundred or more feet in length.

These coils are sent to the wire mills and the remainder of the process of reducing them to the diameter of wire required is accomplished by drawing them cold through dies.

At the wire mill, coils must first be pickled to remove all scale. After this they are dipped in lime water and dried in a steam-drying room where they remain until removed to be drawn.

Fig. 60 shows in cross section a steel die for wire drawing. The work of drawing is clone on the draw bench, as shown in Fig. 61, which is a long bench against the shop wall. Along this bench are mounted, on vertical spindles, a row of short cylindrical drums about 22 inches in diameter. These drums, known as "drawing blocks," are made to revolve by being geared to a long shaft under the bench. A drum resembles somewhat a car wheel, with the flange at its lower edge, and each drum may be stopped at will while the remainder on the bench continue in motion. Near each drum, at the edge of the bench, is a small vise, or "frame," which holds the die.

Fig. 60. Wire Drawing Die.

Fig. 61. - Wire-Drawing Bencn.

A coil of rod from the drying room is placed on a reel fastened to the. floor near each frame on the draw bench, and a rod end is filed or hammered so that it will pass through the die. An appliance on the bench pulls about 6 feet of this end through the die. A workman fastens this end to the drawing block and starts the block in motion. The revolutions of the block draw the rod through the die and the wire is wound on the block, which continues in motion until the entire rod is drawn through.

The percentage of reduction in diameter accomplished by the die depends upon the softness of the rod. Drawing must necessarily pull a metal beyond its elastic limit, else the metal would not remain in the shape drawn, but the metal cannot be pulled too near its tensile strength, else it would break.

After one or more drawings, the coil must be taken from the block and annealed to soften it and relieve it of brittleness. To prevent scale forming on the wire in annealing, several coils are placed in an annealing pot which is sealed and heated in the annealing furnace. Successive drawings and annealings are continued until the wire is reduced to the diameter required.

Manufacturers lubricate wire dies with oil, solid grease or a ferment of bran and yeast in water. Common wire is made usually of acid Bessemer steel. Sounding wire, piano wire and other high-grade wires are made of crucible steel or of open-hearth steel refined in the electric furnace.