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Current Situation And Future Development Trend Of China Tungsten Electrode Industry

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.

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