Hot-dip galvanizing is up-to-date and advanced method of protection of the finished metal and steel constructions from atmosphere, water and ground corrosion.
What is hot-dip galvanizing
For a long time it has been generally known that zinc was used to protect products against corrosion. There is produced millions tons of zinc every year. Half of this volume is used to protect steel against rust. There are also used other metals such as magnesium, aluminium and cadmium to protect products against corrosion. From an ecological point of view the usage of zinc is advantageous, because 80% of it is reused. Zinc does not weaken its physical and chemical properties. If protecting steel with zinc it helps to safe natural resources, such as metal and energy. As it is known, every year 10% of steel becomes useless due to corrosion.
The method of hot-dip galvanizing is very popular. It is widely known in the whole world as the method that is used to protect steel products against corrosion. The process of coating steel structures with a zinc layer, which is resistant against mechanical damage, is performed with the help of immersion of the steel element into molten zinc ( at bath temperature – 445-460 °C). Zinc shell serves as a protective barrier, which minimizes the environment impact and is also resistant against mechanical damage. Zinc also serves as an electrochemical protection, because when steel is dipped into zinc there is formed an electrochemical (galvanic) cell. The stress that appears in the element leads to the corrosion of zinc, not steel. It happens even if a zinc layer cracks. When using other corrosion preventing systems there forms either protective barrier, or galvanic cell. Only the method of hot-dip galvanizing combines these two methods and offers an effective and economic product, which protects steel for many years. Metal constructions pass a complete cycle of surface preparation, treating and drying. The process of hot-dip galvanizing takes place in the bath into which the fabrications are dipped. The bath has zinc and aluminium composition. This guarantees the high European quality.
The advantages of hot-dip galvanizing method
Hot-dip galvanizing is a simple and effective method of protection steel constructions against corrosion. Nevertheless, metallurgical processes that run during hot-dip galvanizing are very complicated. Zinc coating forms due to reaction that takes place between iron and zinc. As a result of this reaction there forms a durable alloy. At the bath temperature – 440 – 450°C, this reaction runs fast. It takes a few minutes. Then a construction is extracted from zinc. The coating is already formed, but its internal structure continues to change till steel acquires its normal temperature. Today, when the matter of quality heads the list, zinc is more and more in demand despite the relatively high price of this material. The advantage for consumers lies in the fact that they can relay on the quality of our protective coating that will last for many years. They do not need to spend money for inspection of constructions, control and maintenance of the protective coating in a proper state. That’s why hot-dip galvanizing is the most economic method from all of the methods that acquired wide practical application.
Hot-dip galvanizing is the best corrosion protection technology
Zinc coating forms an alloy with steel surface. It covers all internal and external units of the element that is galvanized.
The article is immersed into the bath with molten zinc at 450˚ C. After the treatment there forms an oxide carbonate layer on the galvanized article. It protects safety layer from further oxidation.
Annual consumption of the coating makes 2mm.
Service life of galvanized in such a way metal with thickness – 80-100mm makes 20-65 years. Service life of the coating also depends on aggressiveness of the environment.
Technology:
The technological process consists of 6 stages:
- Degreasing — At this stage fat stains, oils and other synthetic layers, which slow down and worsen the pickling process are removed from metal constructions.
- Pickling — The pickling process is an important stage of preparation of metal surface for the hot-dip galvanizing. At his stage rust and dross are removed from the fabrication surface. There is also done chemical activation of steel surface (removal of an oxidative layer) without the surface damage.
- Rinsing — During the rinsing process solid metal particles are washed off from the fabrication surface that is galvanized. This prevents the transference of hydrochloric acid solution into the flux bath.
- Fluxing — This is the final stage of surface preparation which is necessary for coating the metal surface with a protective zinc layer. During the fluxing oxides are removed from the surface and later they do not form on the metal surface that is hot-dip galvanized.
- Drying — During the drying process moisture is removed from the surface of metal constructions. The fabrications are heated to 100°C. This stage serves as a temperature preparation for the hot-dip galvanizing process.
- Hot-dip galvanizing — During this process due to reaction between metal and zinc, which together form an alloy, forms zinc coating.
All processes take place in special bathes.
Hot-dip galvanizing services include:
- Truck unloading and loading
- Chemical treating of the fabrications
- Hot-dip galvanizing according to State Standard (GOST 9.307-89)
- Treating of fabrications after the hot-dip galvanizing process.
