TIG welding often uses tungsten electrodes and an inert gas (usually argon and helium) to form an arc with the workpiece. A properly sized electrode is essential for producing a consistent or accurate electrode and also has a great impact on arc stability, continuous working time and welding quality. Its specific performance requirements are as follows:
1. Excellent high temperature resistance. The electrode will not melt and burn during welding. Otherwise, not only the electrode itself will be consumed quickly, but also the arc will drift, resulting in arc instability. In addition, once the electrode is melted, the electrode material entering the weld pool will pollute the weld, produce welding defects, and affect the quality of the weld.
2. Strong ability to emit electrons. The escape work of the electrode material is small. Especially at high temperatures, it should have a strong ability to emit hot electrons.
3. Large current carrying capacity. The electrode should have good electrical and thermal conductivity and can carry large current without overheating.
4. Good grinding performance. The surface of the electrode needs to be ground to have a certain dimensional accuracy and end Angle, so as to ensure the clamping accuracy of the electrode and reliable conduction, maintain the stability of the arc, and improve the concentration of the arc heat.
5. Low radioactivity. Some substances used to improve the ability of electrodes to emit electrons are radioactive, which is harmful to the human body, so electrode materials with small radioactivity should be selected.
At present, our company can provide tungsten electrode materials such as pure tungsten, thorium tungsten, cerium tungsten and lanthanum tungsten. Among them, pure tungsten electrode has better grinding performance and higher escaping work. In the DC positive electrode welding (tungsten is extremely negative), the welding current is large because of the strong thermal electron emission ability. In DC negative polarity welding (tungsten is extremely positive), tungsten can not play the advantage of hot electron emission, the current is very small. Ac welding, between the two, the current value is also centered.
Secondly, thorium tungsten electrode can be formed by adding 1% ~ 2% thorium oxide (ThO) to pure tungsten. This can greatly reduce the escape work of the electrode, significantly enhance the electron emission ability, and improve the arc initiation and arc stability of the electrode, but also improve the current carrying capacity of the electrode and extend the service life of the electrode. However, the small amount of ThO2 contained in thorium tungsten electrode is highly radioactive, so it is not used much at present.
Finally, to reduce the radioactivity of the electrode, we use less radioactive cerium (Ce) instead of thorium. Practice has proved that adding cerium oxide (CeO) with a mass fraction of about 2% to pure tungsten can also significantly reduce the escape work of the electrode and improve the arc initiation and arc stability of the electrode. Especially in the small current welding, the arc heat of cerium tungsten electrode is more concentrated, and the burning rate of electrode is reduced. However, in high current welding, the anti-overheating ability of cerium tungsten electrode is not as good as that of pin tungsten electrode. Cerium tungsten electrode is a promising electrode material because of its weak radioactivity and little harm to human body.
