ã€China Aluminum Industry Networkã€‘ 1. Electrolytic aluminum bath has high temperature and high gas content. The electrolytic aluminum production process is an electrochemical process under high temperature conditions. Nowadays, with the development of science and technology, the capacity of electrolytic cells is getting larger and larger, the current intensity is as high as 350-500 kA, and the current efficiency is 94-95%. The electrolysis cell uses the carbon block as the anode and the semi-graphitizing carbon block as the cathode. The general temperature is between 950-960Â°C. Electrolyte composition is very complex, in addition to the main ingredient cryolite, but also added Al2O3, CaF2, MgF2, etc., their content were 1.38-2.88%, 4.88-5.88% and 0.47-0.87%; moisture content in addition to AlF3 â‰¤ 7.5% Others are all less than or equal to 1.0%. The moisture in the above materials is adhered water and crystal water, and the attached water is easily evaporated under high temperature conditions, while the crystal water is chemically reacted in the electrolytic cell 3H2O+2ALâ†’Al2O3+6[H], [H] dissolved In the electrolytic aluminum liquid, the higher the temperature of the aluminum liquid, the greater the saturation concentration of atomic hydrogen. In addition to hydrogen, electrolytic aluminum liquids also contain CO2, CO, CH4, and N2. The electrolytic aluminum liquid has a wide gas composition range, H2: 53-96%, CO2: 2.5-30%, CO: 20%, CH4: 2.5%, and N2: 2.5%. For electrolytic aluminum liquids with high gas content, effective degassing measures must be taken to eliminate their hazards.
2. Electrolytic aluminum liquid impurity content The impurities in the liquid primary aluminum are mainly non-metallic impurities, but also a small amount of metal impurities. Non-metallic impurities are more aluminum oxide, followed by fluoride salts, aluminum carbide and aluminum nitride. In the electrolytic process, the alumina added to the electrolytic cell is sand-like alumina. Sand-like alumina consists of Î±-Al2O3 and Î³-Al2O3, Î±-Al2O3 â‰¥ 25%; Î±-Al2O3 is spherical, large in specific gravity, compact in texture, and small in surface area. In the electrolyte, the dissolution rate is slow, and the Î±-Al2O3 is too late to dissolve. Precipitate at the bottom of the tank and mix a small amount into the cathode aluminum liquid. However, Î³-Al2O3 has a large activity and a fast dissolution rate and is generally not deposited on the bottom of the electrolytic cell. Generally speaking, the electrolytic cell draws aluminum liquid once in 24 hours, and Î±-Al2O3 mixed in the molten aluminum enters into the aluminum liquid together with the molten aluminum and is poured into the smelting furnace of the casting production system.
The metal impurities in the electrolyzed aluminum bath are silicon, iron, zinc, titanium, sodium, etc., but the main metal impurities are silicon and iron. There are two main sources of these impurities: First, raw materials and materials. For example, alumina raw materials produced by the alkaline method contain impurities such as SiO2, Fe2O3, TiO2, ZnO, Na2O, etc., and Si, Fe, and Ti are produced through electrolysis. Zn, Na and other metals. The second is from the electrolytic tank lining, tools, equipment, dust and other.
Incidentally, in high-temperature liquid aluminum, carbon reacts with titanium to form TiC. TiC is a very good non-spontaneous nucleus in the solidification process of liquid aluminum alloy. The nucleation of TiC is better than that of TiB2 particles, which favors the crystallization of aluminum alloy liquid. When the grain is refined, it is a pity that the content is too low.
China is a country with a large amount of primary aluminum production in the world. It uses a short process to use electrolysis of aluminum liquid solar cells to directly produce slabs and round ingots required for aluminum processing. This is the only way for the development of the aluminum industry and has also caused the relevant departments to highly valued. Some large-scale electrolytic aluminum enterprises, such as Guizhou Aluminum Plant, Qinghai Aluminum Plant, Baotou Aluminum Plant, Qingtongxia Aluminum Plant, etc., have introduced advanced technologies and advanced equipment from Europe and the United States in recent years, and successively built a high-tech first-class fusion casting production line The main equipments include large smelting furnaces, large-scale hydraulic tilting furnaces, high-power electromagnetic stirrers, on-line argon gas degassing systems, hydraulic casting machines and ingot homogenization equipment. Through trial production, the product quality is good, and good economic and environmental benefits have been achieved.
There are also some companies that invest millions of dollars to build three 15-ton smelting furnaces, two wire rope casting machines, a monorail crane, and a set of vomiting, low-grade, low-temperature, low-temperature, 5,000 tons/year. . However, the equipment is too simple, technology and equipment are poor, and disciplines are not respected, management is neglected, production is tedious, product quality is poor, and problems are piled up. For this type of enterprise, how to carry out equipment transformation, strengthen technical management, improve process technology measures, improve the process system, and produce qualified products.
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