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GUIDE FOR SELECTING AND PREPARING TUNGSTEN ELECTRODES
Tungsten is the main metal used in Gas Metal Arc Welding (GTAW) or TIG electrodes. This has to be selected with care. Tungsten is hard and has high temperature resistance and the highest melting point of 3,410degrees C. The tungsten electrodes are available in various sizes and lengths. They can be of pure tungsten or a combination of tungsten with other rare earth elements and oxides. A number of factors need to be considered while choosing the right tungsten electrode. They depend on the type and thickness of the base material used and whether AC or Dc current is used.
Some of the varieties of tungsten and its combinations that can be used are:
Pure Tungsten (color code – green) – This is less expensive than the alloyed varieties and has 99.50 % tungsten and is widely used. When it is heated a clear, balled tip is formed. This gives good arc stability for aluminum and magnesium with AC current. It should not be used for DC welding.
2% Thoriated (color code – red) – This is easy to use and has longevity. It is commonly used. The use of thorium increases electron emission qualities. It is used for AC welding. It is exceptional for DC electrode negative (straight polarity) on carbon and stainless steel, nickel and titanium applications. It has lower weld contamination. It sharpened edge is good for thin steel. As it is has low level of radioactivity, the manufacturer’s warnings and instructions and the MSDS (Material Safety Data Sheet) should be followed correctly.
2% Ceriated ( color code – orange) – It is best for DC welding. It can be used in AC or DC processes. It is used in orbital tunes, pipe manufacturing, thin sheet metal work and small and delicate jobs. It can be used to weld carbon, stainless steel, nickel alloys and titanium. Pointed ceriated tungsten starts very well and has more current capacity than the same diameter of pure tungsten. It does not contain radioactive materials.
1.5% Lanthanated – (color code – gold) – It is best for AC and DC electrode negative with pointed end or can be balled for use with AC sine wave power source. The sharpened point is good for welding steel and stainless steel.
Zirconiated (color code – brown) – It is good for AC welding as it has high resistance to contamination and can retain a balled tip. It current carrying capacity is equal to or greater than that of thoriated tungsten. It is under any circumstances recommended for DC welding.
Rare Earth (color code – gray) – Unspecified additives of rare earth oxides or hybrids are used and the manufacturers are required to identify each addition and its percentage on the package.
The preparation of Tungsten requires that the tip should be prepared. The tip can be balled, pointed or truncated.
If you apply AC amperage that is recommended for a given electrode diameter a ball will form at the tip. This is used in AC process on sine wave and conventional square waveTIG welders. For a pointed or truncated tip, you should use a grinding wheel that is specially designed, made of borazon or diamond. The manufacturer’s warnings should be followed. To ensure that the grind marks run the length of the electrode, the grinding should be done straight and not at 90 degrees. It is used in pure tungsten, ceriated, lanthanatd and thoriated tips. It should be used for inverter AC and DC welding processes. When using on thinner materials the taper should be ground on tungsten to a distance of no more than 2.5 times the electrode diameter. This helps in forming a focused arc formation and prevents distortion of aluminum. When higher current has to be used, a truncated tip is needed. This can be made by first grinding to a thin taper and then grinding a 0.10″ – 0.30″ flat land on the end of the tungsten. This will prevent ball formation.
The main thing to take into account while selecting and preparing tungsten electrodes is to know whether AC or DC current is being used, the type of material welded and the right type of tungsten for it.