is a long, thin, flexible metal rod that has a uniform cross section. Only ductile metals,
or metals that can be easily drawn out, can be used for making wire. The chief ductile
metals are copper, steel, brass, tungsten, gold, silver, and aluminum.
How wire is made. From early ages until the 1300's, wire was made by
hammering metal into plates. These plates were then cut into strips and rounded by
beating. Then crude methods of "drawing" wire were introduced. Machine-drawn
wire was first made in England in the mid-1800's. Today, all wire is machine-made. Steel
or iron billets, 2-inch (5-centimeter) square blocks of metal, are heated and run through
rollers that press them into smaller, longer shapes. They come out as long rods about 1/4
inch (6 millimeters) in diameter. The rods are cast into coils and cleansed in sulfuric
acid and water.
Pulling the rods through a series of tungsten carbide dies draws them out to form wire.
The die has a funnel-like shape with a round opening smaller than the rod. The rod, which
is pointed at one end by hammering, may be run into the die as thread runs through the eye
of a needle. When the pointed end passes through the die, it is seized with a pair of
pincers, which are operated mechanically or by hand, and drawn far enough to be attached
to an upright drum. The drum rotates, pulling the wire through the die. The wire winds on
the drum. Fine wire is drawn through a series of dies of continuously decreasing
diameters. Drawn wire tends to harden, and so it is softened and made less brittle by
being heated in a furnace. For drawing the finest wires, extremely hard dies made of
diamonds are used.
Sizes of wire. The size of wire differs according to its gauge, or
diameter. American, or Brown and Sharpe, is the standard gauge used in the United States
for copper and other nonferrous wire. This gauge varies from No. 000000, which is 0.58
inch (15 millimeters) in diameter, to No. 51, which is 0.000878 inch (0.022301
millimeter). Sometimes other U.S. standards or the imperial gauge of England are used.
France and Germany use gauges based on the millimeter. The steel wire gauge is the U.S.
standard gauge for steel wire. Wire may be drawn through specially shaped dies to be made
square, oval, flat, or triangular. But most wire is round.
Uses of wire. Manufacturers make telephone and electric-power wires of
copper and aluminum, which are unusually ductile as well as good conductors of
electricity. The very thin wires used in telescopes are made of platinum. People use wire
in making nails, fences, watch springs, screens, and strings for musical and scientific
instruments. Wire is also used in automobile springs, bolts, nuts, paper clips, screws,
and staples. Magnet wire is used in generators and motors. Wire netting, gauze, and cloth
are woven from wire. Wire ropes and cables consist of wires twisted together. Large
suspension bridges are supported by steel-wire cables, which consist of many wires bunched
together. Wire ropes are used in mining and oil drilling. Optical fibers, a type of wire
made from glass, are used for high-speed data transmission.
Contributor: I. Melvin Bernstein, Ph.D., Vice
President, Arts, Sciences, and Technology, Tufts Univ.