Arc Performance Affected By Tungsten Electrode Chemical Composition

Tungsten electrode arc performance is affected by physical and chemical property, mechanical properties, chemical composition and organizational structure. The following will analyzes the influence of tungsten electrode chemical composition on arc performance in welding process.

Pure tungsten electrode has high electron work function and it is not conducive to high electron stream emission, so the service life and arc performance is poor, which directly affect the welding performance. In order to improve the disadvantages of pure tungsten electrode, with further research, manufacturers developed rare earth tungsten electrode and multiple rare earth tungsten electrodes. According to the current density formula of physics emission mechanism Je = AT₂exp (-eφ / kT) shows that, in order to reduce eφ (electronic charge), we can add rare earth oxides or other elements in tungsten electrodes to low eφ’s value. Different types of rare earth tungsten electrodes having a particular Je value, so they arc performance are relatively stable.

Tungsten electrodes chemical composition’s type, content, distribution and high temperature characteristics determine the ignition and stability of the arc. In terms of content, taking single rare earth doped tungsten electrode as example, rare earth oxide content is higher, the better the arc performance of the electrodes. In addition, the uniformity distribution and high temperature evaporation and diffusion behavior of rare earth oxides also affected arc performance to some extent. The main reason for arc performance deterioration is caused by doped rare earth’s evaporation and decomposition. Different type rare earth tungsten electrode under different conditions has difference arc performance, tungsten electrode doped with two rare earth oxides is better than pure tungsten electrode and tungsten electrode doped with three rare earth oxides is better than tungsten electrode doped with two rare earth oxides.

Tungsten electrode during operation, the ends of the electrodes will produce ring mushroom nodules, called "Rim" phenomenon. This is because tungsten electrode surface has more added rare earth oxide content than the central portion, in favor of arc in a short time. When the protective gas is mixed with a small amount of O₂ or welding parameters transferred to short-term overload state, it will occurs "Rim" phenomenon. This phenomenon is still under study, some scholars believe that this is due to the tungsten oxide and rare earth oxides evaporation, decomposition, precipitation and segregation at the high temperature to occur dephlegmation and segregation precipitation. In fact, it is the chemical composition of the tungsten electrode changed at high temperatures. "Rim" phenomenon is good for arc in short time, but for a long time will lead to surface additives concentration reduction affected arc electrode performance and increased consumption.

• < Prev
• Next >