Cold rolling of flat products

The minimum thicknesses achieved industrially by continuous hot strip mills are of the order of 1.2 mm. To achieve lower thicknesses, cold rolling is currently indispensable. With this process, a thickness of 0.18 mm can be achieved on continuous strip mills under good lubrication conditions. In addition to the possibility of achieving lower thicknesses, cold rolling offers other advantages over hot rolling: excellent surface appearance, improved dimensional tolerances and better metallurgical properties (particularly for deep drawing).

The cold mill operations cycle applies to hot-rolled coils and comprises four main stages:

• pickling, which prepares the strip for the next operation by removing the oxide formed on its surface during hot rolling and subsequent cooling;

• Laminating, whose role is to reduce the strip thickness to the desired value;

• annealing to regenerate the metal's crystalline structure;

• skin-passing, which removes the yield point remaining after annealing (except on decarburized steels), imparts the desired roughness and improves flatness.

Other operations in the cold mill for uncoated sheet include degreasing the rolled strip with a high saponification oil prior to annealing, as well as product finishing: surface inspection, cutting sheets to length, coil slitting, packaging, etc.

In the following, we will only deal with pickling and rolling operations on continuous plants.