Cold rolling is most often used to decrease the thickness of plate and sheet metal.
If enough grains split apart, a grain may split into two or more grains in order to minimize the strain energy of the system. When large grains split into smaller grains, the alloy hardens as a result of the Hall-Petch relationship. If cold work is continued, the hardened metal may fracture.
During cold rolling, metal absorbs a great deal of energy, some of this energy is used to nucleate and move defects (and subsequently deform the metal). The remainder of the energy is released as heat.
While cold rolling increases the hardness and strength of a metal, it also results in a large decrease in ductility. Thus metals strengthened by cold rolling are more sensitive to the presence of cracks and are prone to brittle fracture.
A metal that has been hardened by cold rolling can be softened by annealing. Annealing will relieve stresses, allow grain growth, and restore the original properties of the alloy. Ductility is also restored by annealing. Thus, after annealing, the metal may be further cold rolled without fracturing.
Foil rolling is a continuous deformation process compressing metal between a pair of rollers called work rolls .
Foil is produced for several applications:
Foil stock is reduced in thickness by a rolling mill, where the material is passed several times through metal work rolls. As the sheets of metal pass through the rolls, they are squeezed thinner and extruded through the gap between the rolls. The work rolls are paired with heavier rolls called backup rolls, which apply pressure to help maintain the stability of the work rolls. The work and backup rolls rotate in opposite directions. As the foil sheets come through the rollers, they are trimmed and slitted with circular or razor-like knives installed on the rolling mill. Trimming refers to the edges of the foil, while slitting involves cutting it into several sheets .
Aluminum alloys are most commonly produced in the foil rolling process because the raw materials necessary for its manufacture are abundant. Aluminum foil is inexpensive, durable, non-toxic, and greaseproof. Iron, Silicon, and Manganese are all major alloying elements. Sheet metals with a thickness below 200 micrometers are considered foils (Some foils may be as thin as 6.3 micrometers) . It is very useful in metal processing.
Reed-Hill, Robert, Et. Al. "Physical Metallurgy Principles", 3rd Edition, PWS publishing, Boston, 1991. ISBN 978-0534921736.
Callister Jr., William D., "Materials Science and Engineering - an Introduction", 6th Edition, John Wiley & Sons, New York, Ny, 2003. ISBN 0-471-13576-3
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