Tungsten needle

Tungsten needle can be divided into pure tungsten needle, rare earth tungsten needle, doped tungsten needle. Tungsten needles are mainly used to make electrodes for arc tubes of high-intensity gas discharge lamps.

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Due to the properties of tungsten, it is very suitable for tiG welding and other similar electrode materials for this work. Adding rare earth oxides to metal tungsten to stimulate its electronic work function makes the welding performance of tungsten electrodes improved: the arcing performance of the electrode is better, the stability of the arc column is higher, and the electrode burning rate is smaller. Common rare earth additives include cerium oxide, lanthanum oxide, zirconium oxide, yttrium oxide and thoria.

Tungsten needle is used for TIG welding. Tungsten alloy strip is made by adding about 0.3-5% rare earth elements such as cerium, thorium, lanthanum, zirconium, yttrium, etc. into tungsten substrate by powder metallurgy method. It is then processed by pressure. Its diameter ranges from 0.25 to 6.4mm, and its standard length ranges from 75 to 600. The most commonly used specifications are 1.0, 1.6, 2.4 and 3.2 in diameter, the shape of the electrode end is an important factor for TIG. When DCSP is used, the electrode end needs to be ground into a pointed shape, and its tip angle changes with the application range, electrode diameter, and welding current. Narrow joints need a smaller tip angle. When welding very thin materials, it needs to be carried out with a low current, needle-like minimum electrode to stabilize the arc, the proper grounding electrode can ensure easy arc ignition, good arc stability and proper weld bead width. When welding with an AC power source, it is not necessary to grind the electrode terminal because the electrode terminal forms a half ball when a proper welding current is used, and if the welding current is increased, the electrode terminal becomes bulb-shaped and may melt to contaminate the molten gold.

Tungsten has a high melting point (3683 ℃ ± 20 ℃), strong electron emission ability, high elastic modulus, and low vapor pressure, so it has been used as a thermionic emission material very early [. The emission efficiency of pure metal tungsten electrode is very low, and it recrystallizes at high temperature to form an equiaxed grain structure, which makes the tungsten wire sag and break. In order to overcome the above shortcomings and adapt to the development of new technologies and new processes in modern industry, materials workers in various countries are committed to the research and development of various new electrode materials. Some rare earth oxides with low electron work function doped with tungsten can not only increase the recrystallization temperature, but also activate the electron emission. Rare earth metal oxides have excellent thermionic emission ability, and rare earth tungsten electrode materials have been the development direction of replacing traditional radioactive thorium tungsten electrode materials. This paper introduces the preparation and research results of several rare earth tungsten electrode materials, as well as the application of electrode materials, and looks forward to the broad application prospects of tungsten electrodes, aiming to provide reference for the research and application of rare earth tungsten electrode materials in China.

Tungsten needle plays an important role in arc starting, arc stability and welding quality in TIG welding. The loss of mass of the tungsten electrode under the action of the high temperature of the arc is called the ablation of the tungsten electrode. In order to facilitate the discussion of the ablation mechanism of the tungsten electrode, the ablation can be divided into the ablation of the added oxide and the ablation of the tungsten itself.