Introduction:

Galvanizing is an economical and effective method to prevent steel corrosion. The thickness of galvanized steel sheet is generally 0.35 ~ 3 mm.. "galvanizing" in English means that the galvanized layer can protect the steel plate electrochemically. In 1742, Melomin, a Frenchman, succeeded in studying the hot dip galvanizing method. In 1836, Sorel, a Frenchman, applied the hot dip galvanizing method to industrial production. In 1837, British H. W.Grawford obtained a patent for hot dip galvanizing by flux method. In 1935, T.Sendzimir, an American, proposed the continuous hot dip galvanizing of strip steel by protective gas reduction method, which is commonly known as "Sendzimir method". In 1937, the first continuous hot dip galvanizing line by Sendzimir method was built in the United States. China began to produce hot-dip galvanized sheet in Anshan in the 1940s, and the first continuous hot-dip galvanizing line for strip steel was built in Wuhan in 1979.

Production method:

calorizingThere are two kinds of zinc plating for thin plates: hot plating and electroplating. The thickness of hot-dip galvanized zinc layer is generally 60 ~ 300 g/m2 (single side), which is used for parts requiring strong corrosion resistance. The galvanized zinc layer is 10 ~ 50g/m2 (single side), which is mostly used for painted parts or unpainted parts with low requirements on corrosion resistance. Hot plating method is divided into flux method and protective gas reduction method according to pretreatment method. The flux method is pickling the annealed steel plate to remove the oxides on the surface, then passing through a flux bath containing ZnCl2 _ 2 and NH4Cl, and then entering a molten zinc bath for zinc plating. Protective gas reduction method is widely used in continuous hot dip galvanizing of strip steel. The strip steel first passes through a flame-heated preheating furnace to burn off the residual oil on the surface, and at the same time, an iron oxide film is formed on the surface; Then enters a reduction annealing furnace containing mixed gas of H2 and N2, and is heated to 710-920 DEG C to reduce the iron oxide film into sponge iron. After the surface purified and activated strip steel is cooled to a temperature slightly higher than that of molten zinc, it enters a zinc pot at 450 ~ 460℃, and the thickness of zinc layer is controlled by an air knife. Finally, it is passivated by chromate solution to improve the white rust resistance.

Electroplating method

According to the plating solution used, it can be divided into alkaline method and acidic method. Alkaline plating bath is expensive, pollutes the environment, has low production efficiency and poor coating quality, so it is actually not used. The main components of the acidic plating solution are ZnSO _ 4 7H2O, NH4Cl and Al _ 2 (SO _ 4) 3 18H2O, etc. With pure zinc as anode and strip steel as cathode, under the action of current, the zinc anode plate is dissolved into Zn2+ and enters the plating solution, while Zn2+ is reduced to metallic zinc at the cathode and deposited on the surface of strip steel. The coating is treated with mixed solution of phosphate and chromate, which can improve the paintability, and the surface of galvanized steel plate is bright and smooth, which was mainly used in automobile industry in the past. In recent years, the application scope has been extended to the electrical industry and other aspects, which has promoted the development of galvanized sheet industry. Single-sided galvanized sheet was also developed in the 1970s.

Use:

Galvanized steel plate is mainly used in construction, light industry, automobile, agriculture, animal husbandry and fishery, commerce and other industries. Among them, the construction industry is mainly used to manufacture roof panels and roof grilles of anti-corrosion industries and civil buildings. Light industry uses it to make household appliance shells, civil chimneys, kitchen utensils and so on. The automobile industry is mainly used to manufacture corrosion-resistant parts of automobiles. Agriculture and animal husbandry are mainly used for food storage and transportation, frozen processing tools for meat and aquatic products, and commercial materials storage and transportation, packaging equipment, etc.