Cold Rolling
Jeffry S. Asher
DT1410 Unit 4 Assignment 2
ITT Technical Institute
January 18, 2016

Cold rolling is a metal forming process in which the shape and the structure of steel are altered through drawing, extruding, hammering, pressing, rolling, spinning, and stretching at temperatures below the steel's recrystallization point, usually room temperature. These processes result in changes to the metal's composition which permanently increases its hardness and tensile strength, and improve the surface finish, but decrease ductility and impact resistance. After hot rolling, many steel products undergo a further processing in the cold state. This stage of processing may not necessarily alter the shape of the steel, but it does reduce its thickness and significantly improve its performance characteristics. Hot rolled coil is commonly known as cold rolled, also known as cold reduced. 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. Quarter Hard, Half Hard, Full Hard stock have higher amounts of reduction, up to 50%. This increases the yield point; grain orientation and material properties undertake different properties along the grain orientation (Efunda 2016). 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 and full hard can be bent 45º. Resulting in these materials being used for applications involving great amounts of bending and deformation, without fracturing the metal. From the beginning the strip is first uncoiled from a big roll and then passed through a series of rolling mill stands which apply pressure to the strip and progressively reduce its thickness down to as low as 0.15 mm, the strip is then recoiled. Cold rolling processes are also used to improve the surface quality of the steel. Cold rolling also has the effect of hardening steel, so cold reduced strip is consequently hardened, a process of very carefully controlled heating and cooling to soften it. Cold reduced strip and sheet is able to withstand subsequent forming and pressing operations without the steel cracking (UK Steel 2016). The process has become so sophisticated that modern steelmaking and rolling techniques can now shape a complete can, including the bottom and sides by pressing it from sheet steel, leaving only the lid to be sealed on after being filling. Many drink cans are formed this way now. The other uses are the intricate shapes often used to make car body panels that are pressed out of cold reduced sheets, known also as black plate, after coated the sheet with a thin layer of tin, it can also be used to make food and drink cans. Both of the articles covered all the processes from the start of forming the sheet steel to the final product and gave me a lot of informative. I found the information to enlightening and helped me understand cold rolling and what different applications there are for the sheet steel in today’s industries.

References
Efunda, (2016) Cold Rolling Retrieved from http://www.efunda.com/processes/metal_processing/cold_rolling.cfm.
UK Steel, (2016) Cold Rolling. Retrieved from http://www.eef.org.uk/uksteel/About-the-industry/How-steel-is- made/step-by-step/Cold-rolling-drawing.htm.