Tungsten electrode
Because of the characteristics of tungsten, it is very suitable for TIG welding and other electrode materials similar to this kind of work. Adding rare earth oxide to tungsten metal to stimulate its electron work, the welding performance of tungsten electrode can be improved: the arc starting performance of electrode is better, the stability of arc column is higher, and the electrode burning rate is smaller. Common rare earth additives include cerium oxide, lanthanum oxide, zirconia, yttrium oxide and thorium oxide.
1 Introduction
The tungsten electrode is made of materials with high melting point, corrosion resistance, high density, good thermal conductivity and conductivity. Tungsten electrodes are widely used for welding in their properties. Tungsten electrodes are ground or polished with black rods. The final color is different, can distinguish the difference. In the tungsten electrode, more importantly, their final color is different, the tungsten content is also different. When welding, choose the right tungsten electrode to make welding easier, the important thing is to get high quality welding. Some important factors to consider in making the right choice are the type of power supply (inverter or transformer), welding material (steel, aluminum or stainless steel) and material thickness.
2 English name
English Name: tungsten electrodes
3 research status
Tungsten has high melting point (3683 ℃± 20 ℃), strong electron emission ability, high elastic modulus and low vapor pressure
It's used as a thermionic emission material. The emission efficiency of pure metal tungsten electrode is very low, and the equiaxed grain structure is formed by Recrystallization at high temperature, which makes the tungsten wire droop and fracture. In order to overcome the above shortcomings and adapt to the development of modern industrial new technology and new process, material workers in various countries are committed to the research and development of various new electrode materials. Doping some rare earth oxides with low electron work function can not only increase the recrystallization temperature, but also activate the electron emission. Rare earth metal oxides have excellent thermal electron emission ability, and rare earth tungsten electrode materials have always been the development direction to replace 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 related application of electrode materials, and prospects the broad application prospect of tungsten electrode, in order to provide reference for the research and application of rare earth tungsten electrode materials in China.
4 scope of application
Tungsten electrode is used for TIG welding. It is a tungsten alloy bar made by adding 0.3% - 5% rare earth elements such as cerium, thorium, lanthanum, zirconium and yttrium into the tungsten matrix by powder metallurgy method, and then processed by pressure. The diameter is from 0.25 to 6.4mm, and the standard length is from 75 to 600. The most commonly used specifications are diameter 1.0, 1.6, 2.4 and 3.2. The shape of the electric pole is an important parameter for TIG welding Important factors: when using DCSP, the electrode end needs to be ground into a sharp shape, and its tip angle changes with the application scope, electrode diameter, and welding current. A narrow joint needs a small 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, and an appropriate grounding electrode can ensure easy arc striking and good electric performance Arc stability and appropriate weld bead width. When AC power source is used for welding, it is unnecessary to grind the electric pole, because when proper welding current is used, the electrode end will form a half spherical shape. If the welding current is increased, the electric pole will turn into a bulb shape and may melt and pollute the molten gold.
With the development and application of tungsten inert gas welding, the research of tungsten electrode is more and more in-depth. In the past, thorium tungsten electrode was used in plasma arc welding, cutting and non consumable argon arc welding. However, due to the radioactive effect of thorium (the radiation dose is 3.60 × 105 Curie / kg), it will damage human health and pollute the environment. Therefore, cerium tungsten electrode with cerium oxide content of 2-4% was used instead of thorium tungsten electrode. In direct current direct argon arc welding, the cerium tungsten electrode is easy to start the arc, the electrode burning loss is small, and the allowable welding current density is larger than that of thorium tungsten electrode; while in AC argon arc welding, the cerium tungsten electrode burning loss is larger than that of thorium tungsten electrode, and the allowable welding current range of cerium tungsten electrode is smaller than that of thorium tungsten electrode.
Thorium tungsten electrode is easy to operate and can work well even under overload current. Many people still use this material. It is regarded as a part of high-quality welding. However, people gradually turn their attention to other types of tungsten electrodes, such as cerium tungsten and lanthanum tungsten. Because the thorium oxide in the tungsten thorium electrode produces a small amount of radiation, some welding personnel do not want to get close to them.
5 characteristics
Tungsten electrode plays an important role in the starting, stability and welding quality of TIG arc. The mass loss of tungsten electrode under the action of high temperature of arc is called ablation of tungsten electrode. In order to discuss the ablation mechanism of tungsten electrode, ablation can be divided into ablation with oxide and ablation of tungsten itself.
