Abstract
The formation of an anodic spot on the molten pool is caused by a floating slag bit on the pool. The necessary conditions to change a slag bit into an anodic spot were discussed. The anodic spot current is a part of the whole arc current and the remaining current forms an anodic region dispersed within a certain range on the pool. The anodic spot exists within the region and is located in balance between the outward force of the plasma stream and the magnetic force between the spot current and the remaining current.
Sometimes multiple anodic spots are formed around the circular molten pool in a stationary GTA on a steel plate. The anode configuration changes in shape with the passage of time. The formation mechanism of the multiple spots was clarified.
The penetration profile is shaped as the pool is deeper around the periphery than at the center on the arc condition to form the multiple spots.
