When plasma arc cutting, DC positive connection is usually used, that is, the electrode is connected to the negative level and the workpiece is connected to the positive level. When selecting electrode materials, you should choose materials with strong electron emission capabilities, small work function, and small electrode burnout during cutting. Practice has proved that when high melting point tungsten is used as an electrode, the burning loss is still quite serious. The thoriated tungsten electrode made by adding a small amount of thorium oxide to tungsten has a much smaller burning loss than pure tungsten and a stable arc. However, thoriated tungsten electrodes contain 1.2% to 2.0% thorium oxide. Since thorium is a radioactive element, it is harmful to both manufacturers and users. It is no longer used in China. In recent years, cerium tungsten electrodes (containing cerium oxide with a mass fraction of 3%) have been widely produced and used in China. The electron emission capability and burning resistance of electrodes made of this material are better than those of thorium tungsten. After it is burned, the electrode end can still maintain a sharp point, which is useful for maintaining long-term stable cutting and maintaining the arc compression effect, and improves Cutting efficiency is beneficial. At the same time, cerium tungsten electrodes are not radioactive, which is beneficial to the labor protection of operators. Therefore, cerium tungsten electrodes should be used as much as possible.
There are two types of electrodes for plasma arc cutting: pencil-shaped and mosaic structures. In addition to the properties of the electrode material, the diameter and shape of the electrode also affect the burning loss of the electrode and the stability of the arc. The electrode ends should not be too sharp or too blunt. If the tungsten is too sharp, it is easy to burn. If it is too blunt, the cathode spots will easily drift, affecting the stability of cutting, and even causing double arcs or burning the nozzle. The pencil electrode is shown in Figure-Pen electrode tip shape. Some users also grind the electrodes into a pointed shape and then burn off the pointed ends to naturally form the most suitable electrode shape.
The inlaid structure electrode is composed of a pure copper base and an electron-emitting electrode metal. Its structural form is shown in Figure -The shape and structure of direct water-cooled embedded electrodes. The electrode metal uses cerium tungsten, yttrium tungsten alloy, zirconium and hafnium, etc. It usually uses direct water cooling and can withstand large loads. operating current and reduce electrode loss.
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