What is cold rolling process

- Jan 09, 2019-

Cold rolling usually takes the form of longitudinal rolling. The process of cold rolling production generally includes raw material preparation, pickling, rolling, skimming, annealing (heat treatment), finishing and so on. Cold rolling products as raw materials, cold rolling before the raw materials to remove phosphorus, in order to ensure that the surface of cold rolled products clean. Rolling is the main process that deforms the material. The purpose of skimming is to remove the lubricant grease attached to the rolling material during rolling, so as not to pollute the steel surface when annealing, stainless steel is also to prevent carbon enhancement. Annealing includes intermediate annealing and finished heat treatment, intermediate annealing is the process hardening produced by recrystallization to eliminate cold deformation, in order to restore the plasticity of the material and reduce the deformation resistance of the metal. The purpose of heat treatment of finished products is to eliminate hardening beyond recrystallization. It is also based on the technical requirements of the product to obtain the required organization (such as various textures) and product performance (such as deep punching, electromagnetic performance, etc.). Finishing includes inspection, shearing, straightening (leveling), printing, sorting and packaging. Cold-rolled products have high packaging requirements to prevent products from being scratched on the surface during transport. In addition to the above processes outside the production of some special products, there are their own special processes.

Such as rolling silicon steel plate, in the cold rolling before the decarbonization annealing, after rolling to carry out coating film, high temperature annealing, tensile straightening (see tension straightening) and tempering.

The rolling mill used in cold rolled strip has two roll mill, four-roll rolling mill and multi-roll rolling mill. The most widely used is the four-roll mill. Rolling rolling mill should be used to roll thinner products. There are many kinds of multi-roll rolling mill, such as six roll mill, partial eight roll mill, 12 roll mill, 20 roll mill, etc. (see Rolling Mill). With the improvement of plate shape requirements, many techniques to improve the shape of the plate have been developed, such as bending roller technology, roller technology and cross roll technology. The cold rolled strip mill can be divided into two types, single-machine reversible or irreversible and multi-aircraft continuous, according to the frame arrangement. The former is suitable for many varieties, less batches or alloy steel products in a large proportion of the situation. It invests low and builds fast, but yields are low and metal consumption is large. Multi-rack continuous rolling is suitable for the case of single product variety or small change, it has the advantages of high production efficiency and large output, but the investment is larger.

Compared with hot-rolled strip (see Hot continuous rolling broadband steel production process, Hot rolled narrowband steel production), the rolling process of cold rolled strip (see cold rolled plate belt production) has the following characteristics:

(1) The use of process lubrication and cooling to reduce the deformation resistance and cooling roll during rolling;

(2) The use of large tension rolling, in order to reduce deformation resistance and maintain the stability of the rolling process. The average unit tension value is the 10%~60% of the yield strength of the material, which generally does not exceed 50%;

(3) The use of multi-rolling rolling. Because cold rolling makes the material produce hardening, when the total deformation reaches 60%~80%, it becomes very difficult to continue to deform. For this reason, intermediate annealing should be carried out so that the material softens and the rolling can continue. In order to get the required thin strip, such intermediate annealing may have to be carried out several times. Two times the rolling between intermediate annealing is called a rolling process. Annealing of cold-rolled strip is carried out in a continuous annealing furnace or cover annealing furnace with protective gas (see cold rolled plate with annealed). The minimum thickness of cold rolled strip can reach 0.05mm at present, and cold rolled foil can reach 0.001mm.