Gas tungsten arc welding (GTAW) is an electric arc welding process that produces an arc between a nonconsumable tungsten electrode and the products to be welded. Besides, the weld is shielded from the shielding. GTAW has widely used range. On one hand, it can be used on ferrous and nonferrous metals welding, depending on the base metal, in all welding positions. On the other hand, it also can be used to weld thin or thick materials with or without a filler metal.

Using GTAW for thin or thick material welding is not the same. When welding thinner materials, edge joints, and flange, filler metals are not used. For thicker materials, an externally fed filler wire is generally used. The type of filler metal wire to be used is based on the chemical analysis of the base metal. The size of the filler metal wire depends on the thickness of the base metal, which usually dictates the welding current. Besides, the methods of operation for GTAW can be manual or automatic.

Tungsten electrode is an important part in GTAW welding. Tungsten has high temperature property, so it can be used in high temperature environment for long time without deformation. There are many tungsten electrode types including pure tungsten electrode, thoriated tungsten electrode and certiated tungsten electrode and so on. Besides, it also has different size, and the size of an electrode to be used is determined by the welding current required. Larger electrodes permit higher currents to be used. Smaller diameter electrodes may be used for welding thinner materials or while welding out of position.

Pure tungsten electrode used on nonferrous metals, such as aluminum and magnesium, and is typically used with a balled-end preparation on AC.

Thoriated tungsten electrode is the most widely used type and it usually use on carbon and stainless steel. It can be purchased with 1 or 2 percent thorium. The thoriated tungsten starts readily and maintains a stable arc. It has a greater resistance to contamination and will maintain a sharp point and will not break down as readily as pure tungsten.

Zirconiated tungsten electrode is welding with higher AC currents on nonferrous metals.

2% thoriated tungsten electrode still have widely used, at least for DC welding. Because compared with other type tungsten electrodes it always has been the best all-around electrode. It lasts the longest, holds the sharpest point, and has the strongest arc and other advantages, so even it has radiation welders like to use it for TIG welding.

Compared pure tungsten electrode and thorium tungsten electrode welding aluminum on AC performance found pure tungsten electrode is softer and balls up easier for aluminum welding on AC, but it doesn’t handle heat as well. I preferred having electrodes that wouldn’t split at heat as opposed to one that balled up quickly. On the other hand, thorium tungsten electrodes stay sharp for so long and are so hard that there’s no way they can give off anything significantly harmful to breathe in during the welding process or to absorb while handling.

Besides, recently, some researchers released an article, “There is almost no release of radioactive material during arcing,” and “a welder holding an electrode for a whole year a very small fraction of the maximum permissible radiation dose, and it is concluded that the external radiation hazard is likely to be negligible.” They think that fears of radiation coming from the thoriated tungsten electrode had led the welding industry to look for alternatives electrode witch is unnecessary. 

In fact, the only real danger in using 2 percent thoriated is inhalation of dust during grinding. Because during the grinding process, tungsten particles may produce with thoria on the surface and dust particles may be inhaled to cause harm TIG welders health. But these researchers insisted that the risk of cancer in due to thoria exposure is very low, since the exposure times to individuals are invariably small.

As the main tungsten product, tungsten crucible is widely applied in smelting of rare earths and the demand of it is also increasing for rare earth industry. However, the crack of tungsten crucible bottom will directly influence in the rate of finished tungsten crucible products during the productive process. Operating engineer should pay attention to the reasons for the crack of tungsten crucible bottom and find out the solution to solve those problems, so that the rate of finished tungsten crucible products can be improved. According to researchers, they show that reasons for the crack of tungsten crucible bottom mainly lie in the pressing step and sintering step.

During the pressing process, if people select the thicker tungsten powder which would be difficult to suppress. It would result that the pressed compact higher needs a higher sintering temperature or more holding time in the next step sintering. What’s more, the thicker tungsten powder would waste much energy and time and has a great impact on the life time of the equipment. In the selection of the powder, in general, the thicker the tungsten powder is，the worse the compressibility is. And it would cause that users should choose a more large size of the mold cavity while filling it. A large powder needs for more pressure during the pressing. Except that, its compression is poor and it would directly reduce the density of the pressed compact. Therefore, when choosing the size of the powder, users should choose different sizes. The small size particles can fill the space leaving by large particles in the process of pressing to increase the density of compacts to avoid being cracked. In addition, the pressure of the pressing process also affects the qualified rate of the tungsten crucible compacts. Moreover, the qualified rate of the tungsten crucible compact is also affected by the hardness of the rubber sleeve, the greater the hardness, the more likely cause cracks.

During the sintering process, the selection of equipment and the sintering atmosphere has a greater impact on the qualified rate of the tungsten crucible. It’s required that tungsten crucible should be under a anaerobic condition, but there still exist oxygen on the surface of tungsten powder, the oxide film of its surface would hinder the sintering process. Oxygen of tungsten powder will be greatly removed in a hydrogen atmosphere which would increase the density of the product. In the selection of the sintering equipment, electric resistance furnace would be better than the induction furnace. The temperature of the upper and lower ends of the induction furnace is much lower than the middle part because of its structure, which would result in  nonuniform sintering of tungsten crucible bottom.

China is one of the richest tungsten resources storage countries in the world. Therefore, as deep processing product of tungsten, tungsten crucible industry has been continuously developed in China. The main applications of tungsten crucible in China are rare earth smelting, quartz glass, electronic spraying, crystal growth, etc.

Nowadays, our country has a production capacity for some conventional tungsten crucible, but there still exist some problems for the high-tech products. For example, the manufacturing technique for complex shape of the tungsten crucible is relatively rare, but such products play an important role in the area of high technology. And for instance, quartz glass has been widely applied in laser technology, astronomy and sophisticated technology. With the rapid development of modern technology, as the core components of quartz glass, tungsten crucible has a wide range prospects for development. The next few years, the development direction of the tungsten crucible will be large-size, high-quality, low-cost characteristics of tungsten crucible

With the rise of the tungsten industry in our country, the exploitation of tungsten resources has become a major problem. Our country has been exporting tungsten raw materials for a long time, which will affect the production of tungsten crucible. On the other hand, the utilization of the tungsten crucible is not enough. Tungsten Crucible has a long life time for using so that users can reuse it for many times. It can not only save costs but also protect the ecological environment. In addition, changing the export structure of the tungsten crucible which can save a lot of foreign exchange and improve our economy.

In recent years, the rapid development of chemical vapor deposition of can produce complex shape tungsten products in China. This is an important research direction of pure tungsten manufacturing technique. Such tungsten crucible that made by chemical vapor deposition process will be gradually on the market. Isostatic - sintering process in our country has reached the international advanced level and the scale of China's tungsten crucible development would be expanded with continuously improvement of the process. With the deepening of China's tungsten crucible research, international influence of domestic tungsten crucible is gradually rising, the tungsten crucible industry of China will occupy a major position in the international area in the future.

The main raw material of tungsten crucible is tungsten, and it is mainly formed through the deep processing of tungsten. Thanks to the high melting point and boiling point, a good thermal conductivity, low thermal expansion coefficient, a strong abrasion and corrosion resistance and other excellent properties of tungsten, tungsten crucible is widely applied in smelting of rare earth, quartz glass and crystal growth industries.

As an important member in the smelting of rare earth, functional performance and life time of tungsten crucible is very important. In the past, smelting of rare earth mainly use crucible which is welded by tungsten, molybdenum, or tantalum slab. But because there are many problems of this kind of crucible which would have seriously impact on their life time. The problems of welded crucible are more serious for high temperature or high purity rare earth metals. welding production out of the crucible short life is even more obvious. To solve this problem, the researchers developed a sintered tungsten crucible which can deal with the problem of crack of welding process. Sintered tungsten crucible has a high density, a high purity, long life time and other properties which make the rare earth smelting industry pay more attention to it. Compared with other types of crucibles, on the one hand, tungsten crucible would produce less pollution when smelting metal. On the other hand, its life time is longer, so the tungsten crucible is widely applied in rare earth industry.

Because of the melting point of tungsten can reach 3600℃, tungsten crucible can be considered as the cord cage and widely applied to the furnace of sapphire products. And the temperature tungsten crucible is generally above 2000 ℃ while working. Especially for sapphire products furnace, characteristics of a high purity, high density, crack-free, precise size, smooth inner and outer walls of the tungsten crucible can greatly improves the success rate of seed of the growth of sapphire crystal. In addition, tungsten crucible also plays a key role in controlling the quality of crystal pulling and the life time of sapphire products.

Quartz glass is an amorphous material which is only made of silica. The raw materials of it are crystal, silica and silicide, and quartz glass can be formed by high temperature melting or chemical vapor deposition. Therefore, it need for a high melting point and boiling point tungsten crucible as the core cage. In addition, the tungsten crucible can also greatly improve the rate of finished quartz glass.