Abstract
The electric current flowing from an anodic spot was obtained by measurement of the amplitude of the electric potential difference between two points on the back of a thin plate, when the anodic spot was rotating on the circular weld pool formed in a stationary GTA welding.
As a result, the anodic spot current on the molten pool in an austenitic stainless steel plate was at most 10% of the welding current and was not more than that of the steel plates in which at least Cr was not included. When welding current was increased more than 180-200 A, the anodic spot current in the stainless steel plate decreased to a few amperes.
When the tip of a composite oxides rod (55%Al2O3+41%SiO2) is touched to the arc from a side of the pool and the melting and vaporizing oxides bit is being transferred on the pool surface to the opposite side, a part of welding current flows from the oxides. The current depends on the composition of the base metal. The order of the base metals in which the current flowing from the oxides bit was higher was cold rolled mild steel, pure iron, stainless steel with high S content, stainless steel with low S content, and Ti-alloy(8Al-Mo-V).
From those experimental results, it was clear that the anodic spot current was greatly influenced by the lowest ionization potential in the main elements of the base metal and the vaporization behaviour on the molten pool.
In the GTA welding of cold rolled steel plates in which the anodic spot current was higher, the possibility of periodic variation in temperature near the weld pool and irregular weld bead formation caused by the anodic spot movement on weld pool were estimated from thermal conduction analysis, and several examples were given for a thin plate welding.
