Introduction
Rolling, also known as strain hardening, is a metal forming process in which metal pieces, typically round or flat, are passed through a set of rolls, or between two rotating cylindrical rolls, under pressure. Rolling changes the shape and surface of the metal, and can reduce its thickness as well as increase its hardness and strength. Rolling is used to create metal sheets and plates, create rods, create and shape metal bars and pipes, and manufacture metal coins, bolts and screws.
Types of Rolling
There are two main types of rolling - hot and cold rolling. Hot rolling is used to form smaller and more complex shapes, while cold rolling is used to create more precise shapes and features.
Hot Rolling
Hot rolling is the process of forming metal at temperatures between 700 and 900 degrees Celsius, or at temperatures above the metal’s recrystallization temperature. At these temperatures, the metal is more malleable and can be rolled into a variety of shapes. This is often done by passing the metal between a pair of rolls rotating in opposite directions. The higher temperatures reduce the thickness of the metal and increase its strength.
Hot rolling is suitable for forming round and flat bars, as well as creating shapes with sharp bends. It is also used to turn billets, or long pieces of carbon steel that have been heated and heated, into finished products. Hot rolling is used to create rods and sheets, and also to create complex car or airplane parts.
Cold Rolling
Cold rolling is the process of forming metal at temperatures below recrystallization temperatures. This involves passing the metal between two opposed rolls, but at significantly lower temperatures than hot rolling. The outputs of cold rolling are very precise, and the process does not cause any strain hardening.
Cold rolling is used to create more precise shapes than hot rolling, and more intricate shapes, such as wires, pipes, tubing and small shaped bars. The process can also be used to make rod and sheet metal, which can then be further processed to create products.
Finishing Rolling and Coiling
Once the rolling process has finished, the metal must be further processed before it can be used to make products or pieces. This is usually done through finishing rolling and coiling. Finishing rolling uses the same principles of rolling (strain hardening the metal) to further shape and size it. Coiling involves winding the metal into a roll, which makes it easier to ship or transport.
Conclusion
Rolling is an important metal forming process that can be used to create sheets and plates, rods, bars and pipes, and even coins, bolts and screws. Rolling is used in both hot and cold forms, with the main difference being that hot rolling involves working with the metal at temperatures above recrystallization temperatures, while cold rolling involves working with the metal at low temperatures. After rolling, the metal is usually finished through additional rolling or coiling, which shapes it even further and prepares it for use.
