Tungsten Electrodes

Tungsten Electrodes

Tungsten electrodes are often used in electric discharge machining and gas tungsten arc welding. Usually a heavy-metal tungsten alloy is used, composed of mostly tungsten and a small amount, usually 2%, of thorium oxide. Using ThO2 enhances the thermionic electron emission, which improves the starting characteristics of gas tungsten arc welding electrodes. Tungsten is highly electrically conductive and is chemically inert, making it an ideal metal for electrode fabrication. It can also withstand very high temperatures, which an electrode is regularly subjected to during the welding process. The electrodes themselves are made from a tungsten rod. Since tungsten is so hard, only a select few materials-silicon carbide and diamond-are able to machine them. They are usually ground by diamond tools into a round rod with a pointed tip at one end. Tungsten thorium oxide alloy is the first choice for electrodes in arc welding because it is able to carry more current than pure tungsten, allowing for higher temperatures, consequently a more efficient welding process.

The 2% of thorium oxide is very important in tungsten electrodes because it allows them to more efficiently resist sagging and deformation that generally happens to pure tungsten in extremely high temperatures, which are common during arc welding. It also makes it easier for the tungsten to emit electrons. Tungsten electrodes are able to weld many different types of metals, but mostly steel grades and aluminum are welded by this electrically conductive tool. Gas tungsten arc welding is the most common application for tungsten electrodes. It uses a shielding gas, usually helium, to protect the welding area from atmospheric contamination. Filler metals, which are strips of metal material that help bind the two metal components together more effectively, are usually used in this welding process. The tungsten electrode's polarity must always be changed from positive to negative to eliminate the risk of tungsten particles transferring to the welded parts. During the welding process, the tungsten electrode is heated until white-hot, at temperatures very few metals can handle without melting or chemically changing.