Thoriated electrodes both 1 and 2% are very commonly used electrodes since they were the first to show better arc performance over pure tungsten for DC TIG welding. However, thoria is a low-level radioactive material, thus vapours, grinding dust and disposal of thorium raises health, safety and environmental concerns.
The relatively small amount present has not been found to represent a health hazard. But if welding will be done in confined spaces for prolonged periods of time, or if electrode grinding dust might be ingested, special precautions should be taken concerning proper ventilation. The welder should consult informed safety personnel and take the appropriate steps to avoid the thoria.
The thoriated electrode does not ball as does the pure tungsten, cerium or lanthana electrodes. Instead, it forms several small projections across the face of the electrode when used on alternating current. When used on AC sine wave machines, the arc wanders between the multiple projections and is often undesirable for proper welding. Should it be absolutely necessary to weld with these type machines, the higher content lanthana or thoria electrodes should be used. The thoriated electrodes work well with the Advanced Squarewave power sources and should be ground to a modified point.
These electrodes are usually preferred for direct current applications. In many DC applications, the electrode is ground to a taper or pointed. The thorium electrode will retain the desired shape in those applications where the pure tungsten would melt back and form the ball end. The thoria content in the electrode is responsible for increasing the life of this type over the pure tungsten.
