Cold rolling increases the strength via strain hardening, further improving the surface finish of the metal and allows for higher tolerances. Common cold-rolled products include sheets, strips, bars, and rods. The output from a strip mill is coiled and, subsequently, used as the feed for a cold rolling mill or used directly by fabricators. Cold-rolled sheets and strips come in various conditions: full-hard, half-hard, quarter-hard, and skin-rolled. Full-hard rolling reduces the thickness by 50%, while the others involve less of a reduction. Quarter-hard is defined by its ability to be bent back onto itself along the grain boundary without breaking. Half-hard can be bent 90°, while full-hard can only be bent 45°, with the bend radius approximately equal to the material thickness. Skin-rolling (also known as a skin-pass), involves the least amount of reduction: 0.5-1%. It is used to produce a smooth surface, a uniform thickness.
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