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 are closer in characteristics to steel alloys, but at the same time they are spared from the shortcomings of the metal, one of which is corrosion. At the same time, a complete rejection of the traditional material is not possible in all sectors, therefore, they remain relevant and the means to eliminate rust processes. One of the most popular methods of this type is hot dip galvanizing, which forms a durable and reliable protective layer on the surface of the product.
Galvanized protection principle
After passing through a series of preparatory procedures, the products or structure are subjected to application by molten zinc. This is usually done by dipping the preform into the liquid mass so 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 facilitate the independent penetration of zinc into the structure of the material already during the operation of the product. The speed of filling uncovered areas is an average of 2 mm per year.
However, threaded places and nuts may subsequently become sources of corrosion. These processes can be prevented by the initial use of rust-proof hardware. This is especially important to consider if hot-dip galvanizing of metal structures is performed, the bolts in which carry a high power load.
Preparation for surgery
At the preparation stage, the main task is to clean the surfaces of the product and ensure potential uniformity in the reactions of zinc and iron when immersed in a container with an active mass. This is achieved through several technological steps, including degreasing and washing. Subsequently, etching and fluxing operations will follow. Degreasing is reduced to removing particles of dirt and oil - the efficiency of zinc penetration into the metal structure will depend on this.
As a rule, this operation is carried out by means of degreasing reagents in order to subsequently obtain high-quality hot-dip galvanizing. The flushing technology is implemented after degreasing. At this stage, it is important to remove all excess that was used to rid the surface of traces of oil. In particular, foam is removed from solutions and reagents that dissolve chemistry.
Workpiece pickling
This procedure can also be attributed to the steps of cleaning a metal surface. But if in previous cases the material got rid of deposits of dirt and oil, then this time it is necessary to deal with dross formed during heat treatment. In the process of etching, hydrochloric acid is used, the chemical action of which allows 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 different proportions may include the 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 base. Therefore, technologists strive 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 for basic galvanizing procedures. In particular, oxides that can be re-formed during washing are dissolved. In addition, fluxing provides material protection through passivated film. This coating in some way begins to create a protective base that will continue to continue the hot galvanizing of the metal, and in particular its internal structure. But if zinc will protect 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 Stage
At this stage, the product is immersed in a bath in which molten zinc is located. The processes that are carried out at this stage will be represented by the destruction of the flux and the interaction of the structures of the two metals. The duration of the dive depends on the size of the structure. This usually takes 5 to 10 minutes. It is much more important to determine the optimal 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 residual salts on the surface, which inevitably reduces the quality of the result. The optimal speed is selected based on the size of the object, the duration of immersion and surface characteristics.
Quality control of hot dip galvanizing
Basically, the quality of the resulting product is judged by two characteristics: strength and coating thickness. To evaluate these parameters, experts analyze threaded joints and welded assemblies, which are considered the most technically vulnerable areas. As for checking the thickness, here it should be based on the requirements that GOST imposes. In accordance with the standards, hot-dip galvanizing must be performed in such a way that the thickness in the places away from knurling, angles and threads by 5 mm corresponds to the design. The specific values of the layer parameters are determined on the basis of the requirements for a particular product, but the verification method should be carried out precisely in free areas.
How much does hot dip galvanizing cost?
On average, the cost of hot dip galvanizing is 30-35 thousand rubles. for 1 t. In this case, deviations from this corridor are also encountered, if we are talking about non-standard orders. Affects the price tag and condition of products. Often, enterprises 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, the use of high-quality reagents, drying of the processed products in special chambers and confirmation of the work performed by expert documentation is suggested.
Advantages and disadvantages of the method
For large plants that work with large volumes of metal, this method of corrosion protection 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 indicators of thermal and electrical conductivity of the material. As for the shortcomings, 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-dip galvanizing include the limitations of its use in relation to small parts - a thin layer in this case is simply not practical to apply.
Conclusion
Galvanizing metal protection technology has been used for many years, and to this day there is no worthy alternative to it. The prevalence of the method is due to the fact that hot dip galvanizing qualitatively copes with the main task - preventing the formation of rust. This reliable method has proved itself both in industry and in construction.
Where precisely the issues of achieving the strength and durability of metal structures come to the fore, zinc coating also justifies itself.