The wire drawing process is quite simple in concept. The wire is prepared by shrinking the beginning of it, by hammering, filing, rolling or
swaging, so that it will fit through the die; the wire is then pulled through the die. As the wire is pulled through the die, its volume remains the same, so as the diameter decreases, the length increases. Usually the wire will require more than one draw, through successively smaller dies, to reach the desired size. The
American wire gauge scale is based on this. This can be done on a small scale with a
draw plate, or on a large commercial scale using automated machinery. Often intermediate anneals are required to counter the effects of cold working, and to allow further drawing. A final anneal may also be used on the finished product to maximize
ductility and
electrical conductivity. An example of product produced in a continuous wire drawing machine is telephone wire. It is drawn 20 to 30 times from hot rolled rod stock.
Lubrication Lubrication in the drawing process is essential for maintaining good surface finish and long die life. The following are different methods of lubrication: • Wet drawing: the dies and wire or rod are completely immersed in lubricants • Dry drawing: the wire or rod passes through a container of lubricant which coats the surface of the wire or rod • Metal coating: the wire or rod is coated with a soft metal which acts as a solid lubricant • Ultrasonic vibration: the dies and mandrels are vibrated, which helps to reduce forces and allow larger reductions per pass • Roller die Drawing (also referred as
Roll drawing): roller dies are used instead of fixed dies to convert shear friction to rolling friction with dramatic reduction in the drawing forces as reported by Lambiase. When roller dies are adopted, the drawing stages are composed by 2-4 idle rolls and the wire is pulled within the rolls clearance. This type of solution can be easily adopted also to produce flat or profiled drawn wires. Various lubricants, such as
oil, are employed. Another lubrication method is to immerse the wire in a
copper(II) sulfate solution, such that a film of copper is deposited which forms a kind of lubricant. In some classes of wire the copper is left after the final drawing to serve as a preventive of
rust or to allow easy
soldering.
Mechanical properties The strength-enhancing effect of wire drawing can be substantial. The highest strengths available on any steel have been recorded on small-diameter cold-drawn austenitic stainless wire. == Drawing dies ==