Cold rolling is a process by which the sheet metal or strip stock is introduced between rollers and then compressed and squeezed. The amount of strain introduced determines the hardness and other material properties of the finished product.
The advantages of cold rolling are good dimensional accuracy and surface finish.
Cold rolled sheet can be produced in various conditions such as skin-rolled, quarter hard, half hard, full hard depending on how much cold work has been performed. This cold working (hardness) is often called temper, although this has nothing to do with heat treatment temper.
In skin rolling, the metal is reduced by 0.5 to 1% and results in a surface that is smooth and the yield point phenomenon--excessive stretching and wrinkling in subsequent operations, is eliminated. This makes the metal more ductile for further forming and stretching operations.
Quarter Hard, Half Hard, Full Hard stock have higher amounts of reduction, upto 50%. This increases the yield point; grain orientation and material properties assume different properties along the grain orientation. However, while the yield point increases, ductility decreases.
Quarter Hard material can be bent (perpendicular to the direction of rolling) on itself without fracturing. Half hard material can be bent 90º; full hard can be bent 45º. Thus, these materials can be used for in applications involving great amounts of bending and deformation, without fracturing.