Hot rolled coils are large pieces of metal that that have been passed through a series of machining steps in order to make them a certain size and thickness. As the name suggests, hot rolled coils are heated up to about 100 degrees Celsius whilst being formed. The heat of the metal must remain consistent throughout the entire hot rolling process because if the metal was to cool during hot rolling, the resulting coil would not be consistent or usable.
Similarly, the rollers that are used by the mill during hot rolling have to be properly maintained and examined for any defects caused by general wear. Wear and tear on the rollers during hot rolling are generally caused by elements such as a lubricant, chemical or water as well as the speed of the metal passing through the rollers, the pressure on the rollers, the heat and so forth.
Rolling mills differ with the number of rolls in the machine and the manner in which they rotate. Some machines have two rollers which rotate in different directions in order for the hot rolled coil to pass between them. When another roll is added to the top or bottom of a machine, the mill is termed a three high roller. The hot rolled coil passes through the bottom and middle roller first, and then through the middle and top rollers whilst being formed.
Some rolling mills have more than one roller on top of each other for added pressure. These rolls turn in alternate directions. The outer rolls are larger and are used to stabilise and give more pressure to the smaller inner rolls. Hot rolled coils are passed through these rollers or a series of these rollers in tandem whilst being formed. Rolling mills may also have a cluster of rollers, such as two or more above the smaller working roll that is actually in contact with the hot rolled coil.