As soon as people learned to melt metal and produce products from it, they were able to appreciate the useful properties of steel (strength, durability, wear resistance). Creating their first masterpieces, blacksmiths felt the need for thin sheet metal. With hammers and sledge hammers, they flattened metal blanks, turning them into tin, this was the first sheet steel. The process was long and time consuming.
Progress did not stand still, and therefore more and more thin iron was required, the corresponding equipment was created on which the sheets were first forged, and later they began to be rolled on rolling mills. The first rolled sheets had a minimum thickness of 0.8 mm and dimensions of 710 mm by 1420 mm, it was extremely difficult to work with them due to their large thickness and small size. Therefore, we gradually switched to the rental of sheets with a size of 1000 mm by 2000 mm and a thickness of 0.6 mm, and subsequently - 1250 mm by 2500 mm and a thickness of up to 0.5 mm, but modern machines allow rolling sheets from 0.25 mm thick and unlimited lengths.
And everything would be fine, but the metal, as you know, is susceptible to oxidation (rust), at first they could not think of anything, it was just painted, but gradually people learned to coat the metal with zinc.
Initially, the sheet steel is cleaned, and the scale is removed from it by acid etching. Then, the hot-rolled strip is subjected to annealing in order to give it certain properties, physical and chemical. Thus, not only sheet steel can be processed, it can be applied to steel products: pipes, strips, etc. Its process can be performed using various methods, they depend on the type of product. There are methods of hot galvanizing, electrolytic galvanizing and thermal diffusion.
In the hot dip galvanizing method, sheet steel is immersed in molten zinc, where the coating thickness is fixed, resulting in galvanized sheet steel. The thermal diffusion method is used for products having a complex shape, for threaded ones as well. When applying a zinc coating, zinc follows the contours of the product. With the electrolytic galvanizing method, a layer is applied using conductive rollers. Some users call this the cathode method. With it, the steel part is loaded into the bath in which the saline solution is located, then an electric current is passed through it. With this deposition of zinc, a layer is formed whose thickness is 0.5-10 microns.
Such work in modern metal rolling is very popular, it is difficult to overestimate it, after its implementation the surface becomes protected from any influences.
Galvanizing gives corrosion resistance to steel products, after which they can be used to solve critical production problems. It is used for the automotive, construction, oil and gas industries. With the use of zinc, steel changes its sheet weight slightly, but acquires the properties of protection against corrosion processes for a rather long period, it can be up to 50 years.
The surface quality of the processed sheets should be in accordance with GOST 16523-89, the width of the sheet is from 710 mm to 1800 mm, its thickness can be from 0.5 mm and reach up to 5 mm.
Sheet steel is divided into 3 classes, it depends on the thickness of the zinc on the sheets:
- class "P" has a coating thickness of 40 microns and up to 60;
- class "1" - from 18 microns to 40;
- class "2" - from 10 microns to 18 microns.
Steel types of sheets can be ordinary and XH-sheets, they are used for cold stamping. There are types of steel sheets for cold stamping: "N" for the manufacture of parts by the normal method; "G" for the method of manufacturing deep drawn parts; for the method of very deep drawing apply the marking "VG"; under cold profiling - "HP"; for subsequent painting using sheets of "PC"; for general purpose products, the marking "OH" is used.