Hot-dip galvanizing. The process of galvanizing of metal products

In the construction industry and industry, there is a tendency to move from metallic materials to high-strength plastics and modern composites. This is due to the fact that synthetic substitutes approximate the characteristics of steel alloys, but they are spared from the disadvantages of metal, one of which is corrosion. At the same time, a complete rejection of the traditional material is not possible in all industries, therefore, the relevance and the means to remove the rust are preserved. One of the most popular methods of this type is hot-dip galvanizing, which forms on the surface of the product a durable and reliable protective layer.

Principle of protection by zinc coating

After undergoing a number of preparatory procedures, the products or structure are subjected to molten zinc plating. This is usually done by dipping the preform in a liquid mass in such a way that all the pores of the metal structure are filled. There are some nuances that must be considered before performing hot-dip galvanizing. The technology assumes that the high anodicity of zinc in relation to the base metal will promote the independent penetration of zinc into the structure of the material already during the operation of the product. The rate of filling of uncovered areas is on average 2 mm per year.

However, places with threads and nuts can later become sources of corrosion. Prevent such processes can be by using the original use of metalware with protection against rust. This is especially important to take into account if hot-dip galvanizing of metal structures, bolts in which carry a high power load.

Preparing for an operation

At the stage of preparation, the main task is to clean the product surfaces and to ensure a potential homogeneity in the reactions of zinc and iron when immersed in a container with an active mass. This is achieved through several technological steps, among which degreasing and washing. Later, etching and fluxing operations will follow. Degreasing reduces to removing particles of dirt and oil - this will determine the effectiveness of zinc penetration into the metal structure.

As a rule, this operation is carried out by means of degreasing reagents in order to obtain high-quality hot-dip galvanizing in the future. The washing technology is realized after degreasing. At this stage, it is important to remove all the surpluses that were used to remove surfaces from oil traces. In particular, foam is removed from solutions and reagents that dissolve chemistry.

Etching of workpiece

This procedure can also be attributed to the stages of cleaning the metal surface. But if in previous cases the material got rid of mud and oil deposits, then this time it will be necessary to deal with the scale formed during the heat treatment. In the etching process, hydrochloric acid is used, the chemical action of which makes it possible to obtain not only a clean but also a shiny surface. Almost every hot dip galvanizing plant develops its own unique recipes for active media, which in various proportions can include inclusion of inhibitors to eliminate hydroxyls and oxides. Observance of clear proportions is necessary for the reason that, in addition to scale, such solutions also affect the structure of the substrate. Therefore, technologists tend to limit the excessive effect of chemistry on the metal, preventing the risks of hydrogen saturation.

Fluxing

In the process of fluxing, several tasks are performed. The main one is the completion of the preparation of the metal surface to the basic procedures of galvanizing. In particular, dissolution of oxides occurs, which can be re-formed during washing. In addition, fluxing provides protection of the material through passivated film. This coating in some way begins to create a protective base, which will further continue the hot- dip galvanizing of the metal, and in particular its internal structure. But if zinc protects the material from external influences during its use, the passivated layer prevents oxidation in the framework of galvanizing, and at the same time increases the wettability of the molten mass.

Galvanizing step

At this stage, the product is immersed in a bath containing molten zinc. The processes that are performed at this stage will be represented by the destruction of the flux and the interaction of the structures of the two metals. The length of the dive depends on the size of the structure. Usually it takes from 5 to 10 minutes. It is much more important to determine the optimum speed of immersion and extraction of the workpiece. For example, hot dip galvanizing with a slow immersion speed will help release the metal from the previously applied passivated coating.

On the other hand, high speed leads to the capture of salt residues on the surface, which inevitably lowers the quality of the result. The optimum speed is chosen based on the size of the object, the duration of immersion and the characteristics of the surfaces.

Quality control of hot-dip galvanizing

Basically, the quality of the product obtained is judged by two characteristics: the strength and thickness of the coating. To assess these parameters, specialists perform analysis of threaded joints and welded joints, which are considered to be the most vulnerable areas from a technical point of view. As for checking the thickness, we should rely on the requirements of the GOST. Hot-dip galvanizing in accordance with the standards should be carried out in such a way that the thickness in places remote from knurling, corners and threads by 5 mm, corresponded to the design. Specific values of the parameters of the layer are determined on the basis of the requirements for a particular product, but the method of verification should be carried out on free areas.

How much does hot-dip zinc?

On average, the cost of hot-dip zinc coating is 30-35 thousand rubles. For 1 ton. In this case, there are deviations from this corridor, if it is a question of non-standard orders. Affects the price tag and the condition of the products. Often companies offer a full service cycle, which implies multi-stage hot-dip galvanizing. The price of the full cycle, in which there will be preparatory operations, can reach 50 thousand. For this amount, as a rule, it is proposed to use quality reagents, to dry processed products in special chambers and to confirm the quality work performed by expert documentation.

The advantages and disadvantages of the method

For large industries that work with large volumes of rolled metal, this method of protection against corrosion is optimal primarily for economic reasons. In addition, the technology provides a reliable barrier to corrosion processes and at the same time does not reduce the heat and electrical conductivity of the material. As for the disadvantages, the hot-dip galvanizing of metal structures requires a high consumption of components for the active mass and careful organization of the overall processing process. The disadvantages of hot galvanizing include restrictions on its application to small parts - a thin layer in this case is simply impractical to apply.

Conclusion

The technology of galvanizing metal protection has been used for many years, and to this day it does not have a worthy alternative. The prevalence of the method is due to the fact that hot-dip galvanizing copes qualitatively with the main task - preventing the formation of rust. This reliable method has proved itself in both industry and construction.

Wherever the issues of achieving the strength and durability of metal structures come to the forefront, zinc coating justifies itself.