Hot-rolled coils are used as feedstock to produce cold-rolled coils. The processing begins by pickling the feedstock in acid and washing on continuous pickling lines to remove scale and impurities from the strip surface.
The coils are then transferred to continuous and reversing cold-rolling mills, where plastic deformation without pre-heating is applied until the cold-rolled coil reaches the customer's required thickness. The external deformation force causes changes in the structure and, therefore, properties of the steel, which is called cold hardening. The structure of cold-hardened metal is characterised by the predominant orientation of crystals (texture) towards the rolling direction. While cold hardening promotes greater strength and hardness, as well as lower plasticity and viscosity, these properties may differ along the cross section of the coil. Therefore, once discharged from the rolling mill, most merchant cold-rolled coils go through heat treatment, ie annealing, in bell-type furnaces or on continuous lines.
cold-rolled coils are transported to coiling, skin-pass and straightening facilities, slitting or cutting machines, followed by inspection, packing and placing the cold-rolled coils in the finished goods storage area to be shipped to customers.
Today, the following main equipment is used to produce cold-rolled coils:
- Modern continuous-rolling mills with 6-7 mill stands providing a rolling speed of up to 50 metres per second and a coil weight of up to 60 tonnes;
- A high level of process automation by using sensors for automatic in-line control of strip tension, gauge and width;
- Use of vertical or horizontal continuous heat-treatment lines.
