When it comes to rolled goods, there are generally two different kinds of methods behind this: hot rolling and cold rolling. Cold rolling generally focuses on products that do not need to be heated in order to roll the material, such as toilet paper. Hot rolling is necessary for harder items, like metal, in order to make it possible to roll the item. While the exact temperature and certain specifics can vary from one hot rolling process to another, it generally is going to utilize the same basic procedure. This way, the metal can be heated, stretched and rolled up, all so it is possible to provide the highest quality product in a roll that is easy to transport.
During the process, slabs of metal are heated inside of a slab furnace in order to reach a necessary rolling temperature. This is where the metal is hot enough to be flattened out when pressure is applied to it, but still not hot enough to turn into liquid. The heat is going to vary depending on the material, but in the case of steel, the temperature is usually placed at 1100 degrees Celsius.
Once heated, the metal is pushed through a roughing mill. This mill flattens out the metal into much thinner strips. It can often take a 220 mm thick slab and force it down to a 30mm slab. This also allows the coil length to grow. When using these measurements, an 11 meter slab is able to extend out to 80 meters, due to the flattening process.
After traveling through the roughing mill, the plate is cleaned out in order to remove any sort of mill scale that might have taken place to the metal. The metal is then flattened again in order to reach a desired thickness. The hot rolling process can vary, depending on what the desired thickness, but it is often possible to take the 30mm slab until 1.8 mm. This is a fast moving process in order to prevent the metal from sticking to the rollers. As an example, if the metal is forced out to a 2 mm thickness, it allowed the 80 meter sheet to now have a length of 1,300 meters.
The sheet of metal is now cooled and then coiled. Once coiled, it is possible to transport the finished product to its next destination.