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The melting point and boiling point of tungsten is highest in all metals, while the vapor pressure in metal is the lowest. Chemical properties of tungsten is very stable, is a chemical inert metal, widely used in aerospace, military, steel, energy, automotive, machinery manufacturing, chemical, electronics and other important areas, is an important strategic metal elements. China is a major producer and producer of tungsten resources. Tungsten reserves account for about 70% of the world's total reserves. More than 80% of the world's tungsten resources are consumed by China. At present, China's tungsten industry from mining, smelting, processing has been to international trade, has formed a complete industrial system in China's national economic development plays a very important role.
First, the tungsten electrode in industrial production and the status of the national economy
Tungsten has a high melting point, high temperature strength, thermal electron emission capability and other characteristics, has long been used as a hot electron emission material. Tungsten-based thermionic emission material is a key industrial material, often used as electronic equipment cathode and argon arc welding electrode. Tungsten electrodes are widely used in inert gas shielded welding, plasma welding, cutting, thermal spraying and electrical vacuum and other fields. Among them, the most widely used to the number of inert gas welding. As an important connection method of metal materials, inert gas shielded welding has become one of the basic manufacturing technologies indispensable in the manufacturing industry, and plays an important role in the national economy. In a number of inert gas welding, the TIG is the fastest growing at home and abroad, the most widely used welding technology, has become an indispensable means of welding a variety of metal structures. Tungsten electrode is one of the main heat source materials used in argon arc welding. Its appearance and development have led to the development of welding technology. The construction of large structural parts such as skyscrapers, long-span bridges, pressure piping vessels and ships are inseparable from argon arc welding technology. At present, China tungsten electrode annual consumption of about 2000t. The main products of tungsten electrodes are pure tungsten, thorium tungsten, lanthanum tungsten, yttrium tungsten, cerium tungsten, zirconium tungsten and multiple composite tungsten electrodes.
Second, tungsten electrode type, characteristics and its main application areas
Tungsten as a hot electron emission material in the industry has been widely used as a filament used in the lighting industry. However, pure tungsten as electrode material, its emission efficiency is low, the work function of high (4.52eV), current capacity is small, in the high current burning more serious, high temperature conditions for a long time recrystallization phenomenon, the formation of equiaxed Like grain structure, the material becomes brittle and fracture. Pure tungsten electrode does not add any rare earth oxides, the minimum emission of electrons, it is only suitable for AC under heavy load conditions, such as welding of aluminum and aluminum-magnesium alloy welding.
Thorium tungsten electrode material was invented in 1913, is pure tungsten doped with about 2% of the thorium dioxide (ThO2). The thorium tungsten electrode has the advantages of easy arc-starting, stable arc, high current carrying capacity and anti-weld pollution, and its work function is lower than pure tungsten by 2.62eV. Thorium tungsten electrode is a traditional electrode, has excellent welding properties, usually used for carbon steel, stainless steel, nickel alloy and titanium welding DC. However, thorium is a natural radioactive element, in the processing and recycling of waste materials when the human body and the environment can easily cause radioactive pollution, which the environment and the human body harm.
At home and abroad for a single tungsten electrode welding consumables annual consumption has reached thousands of tons, improper handling is likely to cause serious environmental pollution. The United States, the EU-related manufacturers due to government restrictions, has stopped the production of thorium tungsten material or production transferred to developing countries. As countries on environmental protection and occupational health concerns, the global stop the production and use of thorium tungsten is an inevitable trend.
In recent 20 years, with the continuous development of science and technology, welding technology, cutting material varieties, specifications and shape of the increasingly numerous in modern TIG (tungsten inert gas welding) and PLASMA (plasma) and other areas are emerging automatic welding, Plasma spraying, plasma cutting and high-precision welding and a series of new technologies, new technology, the reliability and stability of the electrode material put forward higher requirements. At the same time, in order to adapt to the development of human civilization, tungsten electrode materials in the production and use of the impact on the environment have a higher and more demanding requirements. To this end, national materials researchers are working to develop a variety of new tungsten electrode materials.
So far, progress in the replacement of radioactive thorium tungsten electrode, basically concentrated in rare earth (cerium, lanthanum, yttrium and its composite rare earth oxide) tungsten electrode materials.
At present, in the absence of radioactive thorium electrode products, the use of more electrodes are cerium tungsten electrode. Since the 20th century, the seventies and eighties, China's Shanghai bulb factory, Beijing tungsten and molybdenum materials plant has invested in the development and production of cerium tungsten materials, cerium tungsten electrode has been included in the International Organization for Standardization non-melting pole international standards. Cerium tungsten electrode with a good arc effect, resistance to burning, long life and so on. Because the cerium tungsten electrode is to replace the radioactive thorium tungsten material and developed at home and abroad have a wider application market, especially in small size tungsten electrodes used in welding successfully replaced the thorium tungsten electrode, won the user's wide acclaim . However, in the exchange of hydrogen electrode, high-power ultra-high pressure spherical atmosphere lamp cathode material, etc. can not completely replace the thorium tungsten electrode, there are still welding current instability. At the same time, cerium tungsten electrode arc performance is also poor, short life and so on.
80 years of the 20th century, researchers will be rare earth oxide yttrium oxide (Y2O3) directly doped into the tungsten oxide, the reduction, sintering and processing into a variety of specifications of the yttrium tungsten electrode. Yttrium tungsten electrode in working condition, the arc arc slender, the degree of compression, especially in the large current working conditions, the maximum penetration depth, mainly for military and aerospace industry. The results show that the electrodes can only be limited to small current welding, the electrode burns badly under high current load, and the stability of electron emission is poor. The results show that the performance of the electrode is good, the arc static characteristic, the anti-burning ability and the welding process test .
Since the 90s of the 20th century, Beijing Institute of Mining and Metallurgy and Beijing University of lanthanum tungsten electrode has also been studied. It was found that tungsten oxide added with lanthanum oxide has a lower operating temperature and higher electron emission capability than thorium tungsten wire, and has a longer service life than tungsten wire with other rare earth oxides. Lanthanum tungsten oxide Migration rate and evaporation rate is low, easy to form a swallow-tailed lap metallographic structure, thereby improving the high temperature creep resistance. In addition, the lanthanum tungsten electrode high current, burning the smallest, but its processing performance and arc stability is not enough. At present, the lanthanum tungsten electrode is mainly used for DC welding. Since the lanthanum-tungsten electrode has the closest electrical performance to the thorium tungsten electrode of 2%, the TIG operator can quickly replace the thoriated tungsten electrode without the need to change the welding procedure to protect against thorium radioactivity. In AC conditions and DC conditions are feasible. At present, the lanthanum tungsten electrode in Europe and Japan to become the most popular thorium tungsten electrode alternatives.
Zirconium tungsten electrode contains a small amount of zirconium dioxide (ZrO2). Zirconium tungsten electrode welding special energy between pure tungsten electrode and thorium tungsten electrode, is to improve the tungsten electrode in high load welding conditions easy to melt and then pollute the drawbacks of the workpiece and the development of tungsten electrode products. Zirconium tungsten electrode in AC current conditions performed well, the tip of the electrode when welding to maintain a spherical shape, and the arc than the pure tungsten electrode stability. Zirconium tungsten electrode is characterized by the maximum load current in the case of welding, this electrode ball-like structure can reduce the phenomenon of tungsten, and has good corrosion resistance. Zirconium tungsten electrode for magnesium and its alloys AC welding, the current domestic manufacturers are mainly Beijing Mining and Metallurgy Research Institute under the North Mine new materials.
The use of rare earth oxides as dispersion strengthening of the second phase into the tungsten matrix, can improve the tungsten electrode recrystallization temperature, reduce the work function of the electron to extend the service life, improve the comprehensive performance of materials, especially a variety of rare earth compound added, can Electrode carrying current range is wider, welding performance is better than thorium tungsten electrode. Application practice has proved that the unit of rare earth tungsten electrode material welding characteristics can not be comparable with thorium tungsten electrode, can only be used in small current welding and other occasions, can not completely replace the thorium tungsten material. Beijing Institute of Mining and Metallurgy Research and Beijing University of Technology to develop and produce multi-composite rare earth tungsten electrode by the international and domestic markets favor, the main export-oriented environmental protection of the European Union and the United States and other regions.
Third, the future development of tungsten electrode direction - green electrode
North mine new material is the earliest research and development of rare earth refractory alloy material system and its application to the welding unit, to achieve the rare earth tungsten and molybdenum products, high efficiency, low energy consumption preparation, tungsten electrode product development and production technology level in the peer always Leading. Since the 20th century, 90 years, the North began a new material on the unit and multiple rare earth tungsten electrode research, respectively, the development of cerium tungsten, lanthanum tungsten, yttrium tungsten and a series of products, including three electrode products were China Nonferrous Industry Corporation scientific and technological progress second prize and third prize. Especially in the early 21st century, the North Mine new materials and the Beijing University of Technology joint system to explore a variety of rare earth tungsten arc welding mechanism and burn mechanism to study the complex effects and the law to develop multiple composite rare earth tungsten materials, new technologies, and integrated Forming a multi-rare earth tungsten electrode APT direct doping, large temperature gradient reduction, low current smelting sintering and other industrial new technologies, the formation and improvement of the rare earth tungsten electrode industry Production of technical regulations; developed a production line of key equipment to achieve a highly efficient production and key process quality control, industrial production rate than the current products such as thorium tungsten electrode more than 5%, China Nonferrous Metals Industry Association organization identified as "the overall technology to the international Leading level "," multiple composite rare earth tungsten electrode and its preparation technology "won the 2008 National Technology Invention Award. North mine new material also established the world's first multi-composite rare earth tungsten electrode industrial production line, a series of green electrodes used in domestic and foreign manufacturing, and guide the realization of metal welding cutting material non-radioactive production and use of our carrier rocket, advanced fighters, "Shenzhou V" spacecraft launch has made contributions. In 2011, the Beijing Municipal Science and Technology Commission, under the support of equity investment, the new materials and focus on the North to carry out the transformation of scientific and technological achievements in Beijing project - no radioactive rare earth tungsten electrode-scale manufacturing.
North mine new materials of multi-composite rare earth tungsten electrode products with technical and economic advantages, market competitiveness. The total chemical composition of rare earth tungsten electrode is the same as that of unit tungsten electrode. At present, the cost of raw materials added by three kinds of rare earth compound is half of the cost of adding the same amount of thorium raw materials. Especially, the new technology makes the yield higher, the production cost is obviously lower than Thorium tungsten, generally with the existing cerium tungsten and other units rare earth tungsten electrode quite. Multi-composite rare earth tungsten electrode welding performance is extremely excellent, able to adapt to different welding current range and the needs of welding base metal. From the price point of view, multi-compound rare earth tungsten electrode has obvious technical and economic advantages, strong market competitiveness, widely used in industrial manufacturing, national defense and civilian commodity areas such as aircraft, "Shenzhou" series, power plants, various types of metal structures, Boats, cars and bicycles and other national key projects and social areas of life, leading to the field of green production and use, the use of the product performance gradually recognized by the user. At present, the export of new products of North Mine is mainly exported to Europe, Japan and other regions with high environmental requirements. It is a substitute for thorium tungsten and other grades of electrodes. It is the only multi-compound rare earth tungsten electrode industrial product in the world. Around the world recognized.
Fourth, the conclusion
In summary, we can see that through the study of non-radioactive rare earth tungsten electrode preparation technology, the production of a variety of specifications, multi-purpose rare earth - tungsten electrode material, will achieve environmental protection rare earth tungsten product development and application, To further enhance the level of preparation of tungsten electrodes in China to achieve the rapid increase of tungsten electrode production. China is rich in tungsten resources and rich in rare earth resources (80% of the world's total), if according to the nature of different welding base metal, size, shape and different welding process requirements, continue to develop different welding With tungsten electrode materials, relying on China's resource advantages, the formation of tungsten electrode products, China's tungsten electrode industry will have greater industry prospects, a broader market potential.
