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Cold Galvanizing

Corrosion is an inevitable phenomenon that affects all metal goods. Metal components rust as a result of exposure to the elements, being less stable and, as a result, unfit for further use. Nowadays, there are many ways to protect metal from rust, the most common of which is galvanizing, which involves covering objects (or individual products) with a protective film of zinc. Corrosion protection

Zinc coatings are well known for providing the longest (up to 25-50 years) corrosion resistance for steel. This is due to the unique characteristics of metallic zinc and a variety of chemical and electrochemical processes that occur through its contact with the atmosphere and the steel substrate.

Zinc is a silvery-white, porous metal with a density of -7.1 g/cm3 and a melting point of 420 ° C under natural conditions. Zinc, like iron, is one of a group of metals with greater thermodynamic volatility, with an electrode potential less than that of a hydrogen electrode at pH = 7. (- 0.413 V). Air, on the other hand, has virtually no effect on zinc. This is because when zinc reacts with water, it produces a hydroxide on its surface that is essentially insoluble and stops the reaction from progressing. Pure zinc corrosion is delayed even in a weakly acidic environment, which is linked to a relatively high value of the overvoltage of hydrogen evolution on zinc (-1V). As zinc comprises a few hundredths in a percent of impurities of metals like copper and iron, which have lower hydrogen evolution overvoltages (0.6 and 0.5 V, respectively), the rate of zinc contact with acids increases hundreds of times.

Zinc oxidizes in the presence of oxygen, producing a thin yet solid oxide layer or simple zinc carbonate. This film effectively prevents zinc from further oxidation and ensures the metal's high corrosion resistance.

In contrast, rust, for example, does not form a continuous film on the surface of iron and between individual crystals of hydrated iron oxide III; there are large gaps, the presence of which explains the tendency of iron to progressive corrosion.

The strong anticorrosive properties of zinc when added to iron (steel) are also attributed to the fact that zinc has a lower electrochemical potential than iron (-760 and -440 mV, respectively), because in an electrochemical pair, zinc is iron, occurring in the presence of water (moisture), zinc acts as an anode and dissolves, and the metal substrate (iron) acts as a cathode, as a result of which the steel is passivated due to alkalization. Carbon dioxide in the air reacts with zinc ions. This is followed by the creation of thick layers of insoluble zinc carbonates, which prevent the corrosion process from progressing further.

Zinc protects iron (steel) both as a barrier (insulating) type (which is more common for hot-dip galvanizing, where zinc forms a continuous moisture-proof coating immediately) and electrochemical (protective) type (where zinc, serving as an anode in relation to iron, is ingested to shield in the presence of moisture) and the resulting zinc compounds "heal" coating defects, preventing iron corrosion.

Traditional zinc coating processes, such as hot-dip galvanizing or electrochemical deposition, are physically challenging to introduce when shielding massive metal systems and are seldom used in use.

Cold galvanizing, which was invented relatively recently, in the 1980s of the twentieth century, is the most usable, easiest, and often only process available as compared to conventional methods. scientists from the Russian Academy of Sciences' Ural Branch (Ural Branch of the Russian Academy of Sciences).

Cold galvanizing is the process of applying a specific zinc-containing composition to a primed surface using the same techniques as ordinary paints, resulting in a coating with the same anti-corrosion properties as a hot-dip galvanized coating.

The tread type of safety is more common in cold galvanizing, particularly during the initial formulation of the coating, since it has a porous structure that allows moisture to penetrate the steel surface, resulting in the forming of an electrochemical zinc-iron pair. The coating's shape is compacted and its defensive action is enhanced during subsequent operations from protective to barrier.

Thus, the coating obtained by cold galvanizing covers the steel by the same process as the coating added by hot method after a certain time, depending on the working conditions (primarily humidity). The further action of zinc on the electrochemical form of protection (as well as on hot-dip galvanized surfaces) occurs only when the purity of the applied coating is damaged for one reason or another, including mechanical purposes, and moisture penetrates the steel surface.

Cold galvanizing: features of the method

A zinc coating is produced when a zinc-containing composition, also known as zinc-rich paint (ZNK), is sprayed (pneumatic or airless), brushed, or rolled onto a metal surface.

A defensive (electrochemical) form of protection is effective at first.

The coating defects (pores) are "healed" with insoluble zinc compounds during subsequent operations, the coating structure is compacted, and the defensive action transitions to a shield level of protection. Thus, for a certain amount of time, the coating obtained by the cold galvanizing process, depending on the working conditions, covers the steel by the same mechanism as the coating applied by the hot method. The electrochemical form of zinc coating protection, installation, operation, thermal expansion-contraction, is renewed. According to ISO 3549 (DIN 55969) requirements for cold galvanizing, offering active electrochemical safety over the entire surface (e.g. pervasive and unrestricted movement of electrons between zinc particles within the coating and from zinc to the steel surface) must be at least 94 per cent pure zinc Zinc-rich (zinc-containing) paints which do not comply with the above specification do not belong to cold-galvanized formulations and do not form an electrically conductive zinc coating suitable for the properties and service life of hot-dip galvanized paints. Zinc, present in them, plays only the function of a specific (including color-forming) pigment that improves the defense of the barrier (film) due to its oxidation and "clogging of pores" in the paint layer.

Hot Galvanizing

Hot-dip galvanizing is a method whose essence is to shield iron and steel from corrosion. Specialists have been involved in metal galvanizing for more than 150 years and have now transformed the process into a highly technical and regulated process. At the heart of the galvanizing process is the immersion of a metal structure (previously cleaned) into a container of molten zinc, where a chemical is reaction of the latter with iron occurs. As a result, a protective layer is formed that does not cause the surface to rust. The pre-cleaning of the metal surface is also necessary. If, for example, steel or metal is coated with oil or scale, the zinc will not react to the polluted surface. That's why the surface must be pre-cleaned by degreasing, acidic etching, sandblasting. After washing, the surface is coated with a flux that stimulates it and facilitates stronger contact with zinc.

Today, one of the leading components used to stabilize monolithic concrete frames, giving them additional properties, is galvanized reinforcement. Thanks to its basic but irreplaceable qualities, the reinforcement is an integral part of the support system for high-rise buildings and assures the durability and dignity of the concrete frame. The key advantage of this method of reinforcement is the zinc coating, which avoids the accumulation of corrosion on the reinforcement bars. Property of resistance to natural deformation enables the use of galvanized mortar in conditions of high humidity and also offers a wide variety of grades of concrete and filler. It is difficult to safeguard against the manifestation of corrosion, because the deformation mechanism starts with the fastening components – anchors and clamps – and, after a while, approaches areas covered by concrete, which impair the integrity of the construction. However, the use of galvanized reinforcement decreases the risk of corrosion spread on steel mesh bars. The zinc layer is an efficient part of a solid reinforced concrete construction. Galvanized fittings are still in high demand, being a durable material that can withstand the impact of a hostile climate. Depending on the form of the profile, it is subdivided into flat, sickle-shaped and ring-shaped.

Reinforcement is distinguished by the test load criterion:

• prestressed - used in structures with regular mechanical stress;
• stress-free - used in structures with alternating mechanical stress.

 The following classification is also considered depending on the profile of the reinforced concrete structure:

• longitudinal reinforcement - prevents the formation of a split in concrete;
• transverse reinforcement - restrains lateral mechanical stresses;

Information on the reinforcement, the choice of which is attributable to the precise requirements of the supporting structure, and the grade of the steel, is most commonly expressed in the labeling of the metal component and the associated papers. It is important to note that many forms of reinforcing may be used during the building of the building.

Order

You can order Galvanized on the website by leaving an online application. You can also call directly by phone. Managers will help you place an order. We work with large and small wholesale clients. We organize deliveries to anywhere in Uzbekistan. We also export products to Russia, CIS countries and foreign countries. In your order, you can vary the delivery time, order quantity, color and size of the product.