Effect of Surface Conditions of the Electrode on TIC Arc Starting

Abstract

Effect of surface conditions of the electrode on TIG arc starting is investigated and electrode surface is observed microscopically.
The normal arc starting decreases with the number of times of tests. The tip of its electrode (YWTh-2) is covered by solidified tungsten film and the rate of normal arc starting is reduced because particles of thorium oxide (thoria) disappear.
When slightly oxigen is added to shielding gas, the ability of arc starting is maintained at normal arc starting. Because tungsten oxide film is formed on electrode surface and its film vaporizes at lower temperature and thoria particles appear.
Electrolytical etching is conceived and thoria particles appear on tungsten surface by etching. The proportion of thoria particles is over primary content (2%), then ability of arc starting is improved by etching treatment.