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 iron. With hammers and sledgehammers, they also flattened metal blanks, turning them into tin, and this was the first sheet steel. The process was long and laborious.
Progress did not stand still, and therefore more and more thin iron was required, appropriate equipment was created, on which sheets were first forged, and later began to be rolled at 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 dimensions. Therefore, they gradually switched to rolling sheets with a size of 1000 mm by 2000 mm and a thickness of 0.6 mm, and later - 1250 mm by 2500 mm and a thickness of up to 0.5 mm, while modern machines allow rolling a sheet from 0.25 mm thick and unlimited length.
And everything would be fine, but the metal, as you know, is subject to oxidation (rusts), at first they couldn’t think of anything, they just painted it, but gradually people learnedcover metal with zinc.
First, sheet steel is cleaned, and scale is removed from it using acid pickling. Then the hot-rolled strip is subjected to annealing in order to give it certain properties, physical and chemical. Not only sheet steel can be processed in this way, it can be applied to steel products: pipes, strips, and so on. Its process can be performed using various methods, they depend on the type of product. There are methods of hot dip galvanizing, electrolytic galvanizing and thermal diffusion.
In the method of hot galvanizing, sheet steel is immersed in molten zinc, where the thickness of the coating is fixed, resulting in galvanized sheet steel. The thermal diffusion method is used for products that have a complex shape, including threaded ones. When applying a zinc coating, zinc follows the contours of the product. With the electrolytic method of galvanizing, a layer is applied using conductive rollers. Some users call this the cathode method. With it, a steel part is loaded into a bath in which a saline solution is located, then an electric current is passed through it. With this deposition of zinc, a layer is formed, the thickness of which is 0.5-10 microns.
Such work in modern rolled metal is in great demand, it is difficult to overestimate it, after its completion the surface becomes protected from any influences.
Galvanization gives steel products corrosion resistance, after which they can be used for solving critical tasksproduction. It is used in the automotive, construction, oil and gas industries. With the use of zinc, steel sheet weight changes slightly, but acquires the properties of protection from corrosion processes for a rather long period, it can be up to 50 years.
The quality of the surface of the processed sheets must be in accordance with GOST 16523-89, the width of the sheet - from 710 mm to 1800 mm, its thickness can be from 0.5 mm to 5 mm.
Steel sheet is divided into 3 classes, it depends on the thickness of the zinc on the sheets:
- class "P" has a thickness of coatings from 40 microns to 60;
- class "1" - from 18 microns to 40;
- class "2" - from 10 µm to 18 µm.
Steel types of sheets can be ordinary and XIII sheets, they are used for cold stamping purposes. There are types of steel sheets for cold forming: "H" for the manufacture of parts by the normal method; "G" for the method of manufacturing deep drawing parts; for the very deep drawing method, the marking "VG" is used; for cold profiling - "HP"; for subsequent painting use sheets "PC"; for general purpose products, the marking "OH" is used.
