Abstract
In the behaiviours of magnetically driven arc in the pipe welding, the following phenomena are observed.
In early period of arc, in which the cold cathode state takes place, the cathode spot tends to move into the internal surface of the pipe due to the existence of an oxide film and the magnetic force acting on the component of the arc current, while the anode spot moves round smoothly on the pipe end from the beginning of arc initiation.
The experiment shows that the melting rate of anode is larger than that of the cathode. This is presumed to he caused by the cathode behaiviours above mentioned.
Fig.11 shows the relation of the arc current and the exciting current to obtain a uniform molten layer at the pipe end.
