When drawing metals as wires, a hot-rolled rod having an uneven diameter is first cleaned in an acid pickling tub, which helps in removing scaly outer corrosion.
After the metal is further washed in a rinsing tub to get rid of the acid coating, next follows the water wash, making the metal absolutely free from all unwanted coatings.
After the water wash, the metal is treated with air so that a thin layer of rust gets deposited over it, which later on helps the drawing operations to be done more smoothly.
The next step involves dipping of the rod in lime water, followed by force drying of the metal at about 300 degree F. The dried rod is then forwarded to the drawing bench, where the rod end is made into a point like shape by hammering.
This end is then used to “feed" the die tapered opening, and the drawing process is initiated with the help of a power rod. This power rod starts drawing the metal until the entire metal passes through the die slot smoothly due to the actions of the lime and the rust layers. Other forms of external lubricants like grease, tallow or soap are also sometimes utilized.
Through some controlled number of drawing passes, the degree of metal reduction or shaping and through regular in between annealing of the metal, literally any possible level of strength and toughness can be induced into the metal.
With mild steel, the above procedure can be used for producing wire rods with significantly enhanced strengths.
This method is fundamentally used throughout the world to produce copper wires used as electrical conductors.