Production technology of hot dip galvanizing and alloy of steel wire

Abstract

This paper introduces the hot-dip plating process of zinc and zinc alloy for hot-dip galvanizing of steel wire in China, including the composition and chemical composition of zinc for hot plating and Zinc-5% Al-mixed rare earth alloy for hot plating. The forming process and corrosion resistance of hot dip galvanizing layer of steel wire are described in detail, and the advantages of alloy coating and pure zinc coating in corrosion resistance are compared. At the same time, the traditional technology and green production technology of hot dip galvanized steel wire, and the development of production technology and equipment of hot dip galvanized steel wire alloy are discussed. Finally, it is urgent to accelerate the research of aluminum coating technology and hot dip aluminum plating technology of steel wire.

1. Zinc for hot plating

1.1 Zinc for hot plating

GB/T470-2008 "Zinc Ingot" stipulates the selection of Zn99995 and Zn9999, and its chemical composition is shown in Table 1. The national standard stipulates that the surface of zinc ingot is not allowed to have melting holes, shrinkage holes, slag inclusion, delamination, external interlayer, scum and natural oxide film, but natural oxide film is allowed. The melting point of zinc is 419.5 ° C and the boiling point is 907 ° C. The strength and hardness are larger than copper and aluminum, but smaller than tin and lead.

1.2 Zinc-5% aluminum-mixed rare earth alloy for hot plating

GB/T20492-2006 specifies Galfan alloy coated steel wire, steel strand, steel core aluminum strand, its chemical composition is shown in Table 2. Aluminum is the main alloying element in the alloy, which can significantly improve the fluidity and casting performance of the zinc liquid. For the one-step method, the aluminum content in the melt in the alloy plating bath should be controlled at 4.2%~6.2%; For the two-step plating method, first galvanized (hot dip galvanized) or electric galvanized, and then plated 5%-5% aluminum-mixed rare earth alloy coating, the aluminum content in the alloy plating tank is allowed to reach 7.2%. GB/T20492-2006 specifies that the aluminum content in the alloy coated steel wire coating is not less than 4.2%.

2. Formation process and corrosion resistance of hot dip coating of steel wire

2.1 Formation process of galvanized layer

When the steel wire enters the zinc liquid, because its surface is cold, a layer of zinc shell is condensed immediately; With the increase of temperature, the zinc shell begins to melt, and the solvent layer falls off from the surface of the steel wire. The zinc liquid is infiltrated and diffused on the steel matrix to form an iron-zinc alloy layer. The zinc liquid is further wetted, adhered, dispersed and solidified on the surface of the iron-zinc alloy layer, and the solid zinc is further cooled and crystallized.

2.2 Corrosion resistance of alloy coating

The dense AI2O3 film on the surface of the alloy coating greatly slows down the corrosion rate, and the uniform barrier layer established in the alloy coating can effectively prevent corrosion. In addition, the effects of La and Ce in the alloy increase the wettability of the steel surface and reduce the tendency of intergranular corrosion.

2.3 Steel wire hot-dip galvanizing process

The traditional hot-dip galvanizing process includes the steps of paying off, degreasing, hot water washing, pickling, washing, plating aid, drying, hot-dip galvanizing, wiping, take-up and so on. The traditional process uses solvent drying, degreasing, pickling and plating aid are the key processes.

2.4 Green production process of hot dip galvanized steel wire

The green production process includes: ultrasonic degreasing, composite agent rust removal method, closed acid-fog pickling, air strong stirring of washing water, recovery of hot dip galvanized slag and other measures to reduce environmental pollution.

3. Steel wire hot-dip galvanizing -5% aluminum - mixed rare earth alloy production process and equipment

3.1 One-Step Method

The process includes pay-off, alkali washing, cleaning, pickling, cleaning, dip plating agent, drying, hot dip plating, wiping, cooling, coating protection, take-up. The domestic production process of single-dip galvanizing -5% aluminum-rare earth alloy coating has been mature, and has the advantages of short process and low energy consumption.

3.2 Two-step plating method

The process includes pay-off, surface treatment, plating aid, drying, pure zinc bath, Galfan alloy bath, wiping, cooling, take-up. The advantage of the two-step plating method is that it can prevent the leakage plating problem, the coating is thicker, and the corrosion resistance is long.

3.3 Production Equipment

Pay-off equipment adopts double flower basket frame or I-wheel continuous pay-off; Surface treatment equipment includes degreasing furnace degreasing, electric degreasing, electrolytic alkali washing, ultrasonic cleaning, etc. The hot plating equipment is heated by ceramic galvanized pot.

4. Aluminum coating technology of steel wire

The process of producing aluminum clad steel wire includes heating the aluminum rod and steel wire with clean surface to a certain temperature, compressing the aluminum strip through the extrusion wheel groove, making it combine with the steel wire under the control of the wire die and the sizing die in the shoe to form a seamless aluminum tube layer. Tianjin Metallurgical Group ZhongXingxingda Steel Co., Ltd. has introduced foreign advanced equipment and realized intelligent aluminum clad steel production line.

5. Hot dip aluminum plating technology of steel wire

The process and properties of hot dip aluminum plating by solvent method of steel wire have been studied in China, including pre-treatment, water washing, assisted plating treatment, drying and preheating, hot dip aluminum plating and water cooling. Although there are no reports of successful application in industrial production, it is of great significance to strengthen the research in this area to enhance the competitiveness of Chinese enterprises in the international future market.