Thorium-tungsten electrode is the first to use the rare earth tungsten electrode, is by far the best varieties of tungsten electrode welding performance, therefore, varieties of the tungsten electrode on a global scale the highest market share, but because the thorium-tungsten electrode in the process of powder metallurgy and rolling grinding &polishing radioactive pollution will happen, so the European and American countries limit production of varieties of the electrode, but because of its excellent welding performance, its use is not restricted.

FIG. 1  thorium tungsten electrode

Currently, cerium tungsten electrode ranks the second in usage. It has no radioactive pollution and belongs to the green environmental protection product. It can start arc easily with a very small current, and the arc maintaining current is also relatively small. Cerium tungsten electrodes are very popular under low direct current conditions. However, it is not as burn-resistant as thorium tungsten, and it wears out faster. If it wears out faster, the investment will be large, and the cost will be high. This is what many manufacturers who use argon tungsten arc welding do not want to see.

FIG. 2  Cerium tungsten electrode

Therefore, it can be seen that lanthanum tungsten electrode is the most suitable alternative to thorium tungsten electrode. At least in the present technology, this is the most suitable. It has the most similar properties to thorium tungsten electrode. Even in the use of small and medium current, the arc performance and burn resistance of thorium tungsten electrode are better than that of thorium tungsten electrode. Moreover, lanthanum tungsten electrode has no radioactivity, durable current and minimum burning rate.

FIG. 3  Lanthanated tungsten electrodes

Thorium tungsten pole contains 1-1.2% thorium oxide, which is a radioactive material that is affected by radiation during welding and in contact with thorium tungsten bar.

Radiation ACTS on the body in two forms:

First the external irradiation

Second the through the respiratory and digestive system into the body to occur in vivo irradiation. A large number of investigations and measurements on argon mask arc welding and plasma arc welding have proved that their radioactive hazards are small, because the consumption of thorium tungsten rod is only 100-200 mg per day, and the radiation dose is very small, which has little impact on human body.

However, there are two situations that must be paid attention to: 

first, when welding in the container, the ventilation is not free, the radioactive particles in the smoke may exceed the sanitary standards;

Second, the concentration of radioactive aerosol and radioactive dust can reach or even exceed the hygienic standard when grinding thorium tungsten rod and where thorium tungsten rod exists. Radioactive substances into the body can cause chronic radiation disease, the main performance in the general functional state weakened, can see obvious weakness, the resistance to infectious diseases significantly reduced, weight reduction and other symptoms.

The thorium tungsten electrode contains thorium oxide (Th02 or thorium oxide), which is the most commonly used tungsten electrode and has become a standard for judging other tungsten electrodes. However, because of the low-level radioactive hazard of the tungsten electrode, many users have switched to other options. In general, a 2% thorium tungsten electrode is a good tungsten electrode with the lowest amount of work and works well even at overload voltage. Thorium tungsten electrode is superior to pure tungsten electrode in many aspects. Thorium oxide provides about 20 percent more current carrying capacity than pure tungsten and generally has a longer life and helps prevent welding contamination.

With the thorium tungsten electrode, arc initiation is easier and the arc is more stable than pure tungsten or zirconium tungsten electrodes. Both thorium tungsten electrode 1%(EWTh -- 1) and thorium tungsten electrode 2%(EWTh -- 2) can be used for DCEN.

Thorium tungsten electrode is usually used in dc negative electrode or carbon steel, stainless steel, nickel alloy, titanium alloy and other positive electrode applications. They work well and weld well even under overload currents.