Hot-Dip Galvanizing is a very popular and highly effective corrosion protection method for steel components.
The technology of hot-dip galvanizing was developed over 250 years ago, and nowadays it meets the most severe requirements to anticorrosion protection of the critical structures.
Steel is coated with a zinc layer as a result of immersion of the steel component into the liquid zinc (temperature 440-460 `С)
The technology of hot-dip galvanizing was invented by a French chemist Paul Jacques Malouin in 1742. About a century later, in 1836, his colleague, also a French scientist S. Soreil patented this method with addition of preliminary treatment of steel surface with 9% solution of sulfuric acid and fluxing in ammonium chloride. These operations significantly increased adhesion of zinc coating to the base, ensuring heavy-duty and stable coating. The first hot-dip galvanizing workshop was commissioned already in 1742 in the city of Solingen, Germany.
As a result of the reaction a layer of iron-zinc alloy develops on the surface of the workpiece, consisting of four layers with different specific ratio of iron and zinc. The lowest Г-layer is an alloy of 25% iron and 75% zinc. It is followed by a δ-layer containing 10% of iron. The following layer is a ζ-layer, which consists of 6% of iron and 94% of zinc. Finally, the surface layer is an almost pure zinc layer. This structure of hot-dip galvanized surface ensures high adhesion between steel and zinc, which cannot be achieved by any other paint, polymer or metalized coating. The arising tension in the element even in case of cracking of zinc shell will result in corrosion of zinc, but not steel. Other anticorrosion systems create either a safety barrier, or a wet cell. Only hot-dip galvanizing combines these two methods in one.
Loading of metalware on jig. Wires of different thickness are used for this purpose. Correspondingly, the wares should have service openings used for hanging.
Degreasing. Different contaminants and oil films are removed from the surface of metal during this process. Paint coating is not allowed, since it cannot be removed by this method.
Acid pickling. It is used to remove scaling, generated in the course of thermal processing, and rust from the surface of metal. However, this method cannot provide complete cleaning for metals with high degree of rusting.
Rinsing. Removes residues of pickling solutions from the surface.
Fluxing. The surface of metal is covered with water chemical composition, ensuring uniformity of zinc coating.
Drying. Metal structures are placed to the drying oven, where the flux is dried and metal is heated up to 120 С.
Hot-Dip Galvanizing. Dipping of structure into the zinc melt. When the structure is withdrawn from the melt, the excess of zinc flows back to the kettle. In order to ensure unhampered flowing of zinc, most metal structures should have specially prepared service openings. If there are no such openings, it is not possible to obtain high quality of zinc coating.
Cooling. The structure, withdrawn from the zinc kettle, has a temperature close to 450 0С. It is cooled down to the ambient temperature either in the basin with clear water, or in the open air.
Unloading of metalware from jig. The galvanized products are removed from the jig, and if required, packed and carried to the warehouse.