China scholars call 1837 Saulier patent and 1937 Sendzimir process the two most important turning points and milestones in the history of hot dip galvanizing. The former invented the solvent hot-dip galvanizing process a century after the doctoral report, and this method is still used for batch hot-dip galvanizing. The latter invented the gas reduction method after the invention of the solvent method 100, thus laying the foundation for modern continuous hot dip galvanizing. The solvent hot-dip galvanizing process has not changed significantly in the 20th century, but the gas reduction process is constantly improving. At present, the improved Sendzimir process is mainly adopted. The former can produce general galvanized steel plates, while the latter can produce high-quality galvanized steel plates.
Hot dip coating materials have made great progress in the past half century. In 1950s and 1960s, the United States, Japan, Britain, Germany, France, Canada and other countries successively produced aluminized steel plates. In the early 1970s, Bethlehem Iron and Steel Company of the United States invented the Al-Zn-Si coating material with the trade name Galvalume, and its alloy composition was 55% Al? -43.4% Zn- 1.6% Si, with corrosion resistance 2~6 times that of pure zinc coating, is widely used in the production of coated strip steel. In 1980s, the international lead-zinc research organization (ILZRO) funded the Belgian Liege Metallurgical Research Center (CRM) to develop a zinc-aluminum rare earth coating material with the trade name Galfan. Its alloy composition is Zn-5% Al-Re, and its corrosion resistance is 2-3 times that of pure zinc coating. It is widely used in the production of strip steel and steel wire.
In 1960s, Canada took the lead in studying the inhibition of nickel in zinc on hot-dip galvanizing of silicon-containing active steel, which was supported by ILZRO. In 1980s, the hot-dip zinc-nickel alloy process was rapidly popularized in Europe, North America and Australia, and its process was named Technigalva. At present, Zn-Ni-Sn-Bi has been developed on this basis, which is suitable for steel with Si content below 0.5% and can obviously inhibit the Saint Linde effect when hot-dip coating silicon steel.
In 1990s, Nisshin Iron and Steel Company of Japan developed a Zn-Al-Mg coating material with the trade name ZAM and the chemical composition Zn? —6% Al—3% Mg, its corrosion resistance is 18 times that of traditional zinc plating (Zn-0.2% Al), and it is called the fourth generation of high corrosion-resistant coating materials after the third generation of high corrosion-resistant coatings Galvalume and Galfan. In addition, Zn-4.5% Al? -0.1%mg; Zinc-0.5% magnesium; Zinc-15% aluminum -0.5% tin; Zinc-aluminum-lead; Zn-Zn-0.1%Bi alloy is also used to some extent, and the development of alloy coating is the most important progress of hot dip plating in the second half of the 20th century.
Compared with other metal anticorrosion methods, hot-dip galvanizing process has incomparable advantages in electrochemical protection, compactness, durability, maintenance-free, adhesion between coating and substrate, economy, adaptability of hot-dip galvanizing process to steel shape and size, and high production efficiency. According to the atmospheric exposure test of Japan Galvanizing Association 10, the service life of the hot-dip galvanized coating with a coating thickness of 86 microns in heavy industry, ocean, suburbs and urban areas is 13, 50, 104 and 30 years respectively. Generally speaking, the maintenance-free service life of galvanized layer with zinc content of 600g/m2 is 20~50 years, the service life of color plate with galvanized base material for building is 3~5 years, and the service life of color plate with galvanized base material can reach 20~30 years.
2 Current situation of hot dip galvanizing in China
Hot dip galvanized steel is widely used in basic industries of national economy. Since the Eighth Five-Year Plan, China has made great efforts to develop electric power, transportation, communication, energy and urban infrastructure. From 65438 to 0999, the central government put forward the strategy of developing the western region. With the development of projects such as Power Transmission from West to East, National Networking, Power Transmission from West to East, Three Gorges Project, South-to-North Water Diversion Project, Second Network Reconstruction, Five Vertical Lines and Seven Horizontal Lines, and Railway Speed-up, with the start of building steel structure market and the development of household appliances and automobile industries. Galvanizing is the subsequent process of steel production. The development of zinc plating industry depends on the production of steel and zinc, and the development of zinc plating industry is basically synchronous with the development of steel and zinc industry. On the one hand, since 1996, China's steel output has exceeded 1 100 million tons for seven consecutive years, ranking first in the world (see Figure 2); On the other hand, since 1994, China's zinc production has exceeded one million tons, making it the largest zinc producer in the world. In the consumption structure of zinc, the consumption of zinc for galvanizing has always occupied the first place, and the consumption of zinc for galvanizing in developed countries abroad accounts for 40%~70% of the total zinc consumption. According to the statistics of relevant departments, the consumption structure of zinc in China is shown in Figure 3, in which zinc for galvanizing accounts for about 34%. Generally speaking, the consumption of zinc for galvanizing accounts for 30% of all kinds of galvanizing.
Hot dip galvanizing technology is widely used in steel plate, steel strip, steel wire, steel tube, structural parts, spare parts and other products. Galvanizing enterprises in China can be roughly divided into two categories: one is a professional galvanizing factory, which only engages in hot galvanizing process by outsourcing steel or strip processing; The other is a non-professional factory, and hot dip galvanizing is only a process in the whole production process. Most steel wire and steel pipe galvanizing enterprises are non-professional factories, most structural steel and parts are professional factories, and the rest are.