Rolling Temperature

Rolling is a metalworking technique that involves compressing a part between two rotating cylinders, called rollers, to reduce its thickness and make it more uniform. Rolling can be classified into three types, depending on the temperature of the part: hot, warm or cold. Hot rolling is performed at temperatures above the recrystallization point of the metal, which allows for large deformations without increasing the strength or hardness of the material. Warm rolling is done at intermediate temperatures, where some recrystallization occurs but not enough to prevent strain hardening. Cold rolling is done at room temperature or below, where the metal becomes stronger and harder due to work hardening, but also more brittle and prone to cracking.

One example of a rolling process is the production of billets from cast ingots. Billets are long bars with a constant rectangular cross section, which can be further processed into various shapes and products, such as I beams, tubes, rods, bars and so on. To make billets, cast ingots are first heated to a high temperature and then passed through a series of rollers that gradually reduce their thickness and width. The final product has a smooth surface and a uniform grain structure. Billets can also be rolled into different shapes by changing the shape of the rollers or by using additional tools, such as mandrels or dies.

Cold rolling can be used to create shapes that are similar to those obtained by extrusion, which is another metalworking technique that involves forcing a part through a die to create a cross-sectional profile. However, unlike extrusion, cold rolling requires that the wall thickness of the part be uniform throughout, otherwise the rollers will not be able to apply equal pressure and cause defects. Cold rolling can produce high-quality products with tight tolerances and smooth surfaces, but it also requires more energy and causes more wear on the tools.

When a part undergoes multiple stages of rolling, from hot to cold, it may develop surface oxides and scales due to exposure to air and heat. These impurities can affect the quality and appearance of the final product, as well as interfere with subsequent processes such as welding or coating. To remove them, a process called pickling is performed, which involves immersing the part in an acid solution that dissolves the oxides and scales. Pickling also helps to improve the corrosion resistance and adhesion of the metal surface.

Hot Rolling

Factory producing a variety of stocks and components using Hot rolling (and come cold work as well)

Cold Rolling

Reduce sheet thickness using cold rolling: