Fundamental Processes of the Short Arc: With Applications to Contact Erosion and Percussion Welding

When charged electrodes are brought together, an electric arc is formed before they touch. For potentials below about 300 volts, the arc is both initiated and maintained by field emission currents. The initiation and sustaining mechanisms are quite well understood and have been treated in considerable detail in papers by L. H. Germer and his coworkers. Recently Germer and Boyle1 have presented experimental evidence that two distinct types of short arcs exist. One of them, called the cathode arc, obtains the predominant supply of ions necessary to maintain an arc by continuously exploding small points on the cathode surface. This type of arc does not weld the electrodes together and will not be treated in this paper. The second type of arc, which derives its ions from metal vaporized from the anode by electron bombardment, is appropriately called an anode arc. If sufficient energy is supplied to this arc, the electrodes will be welded together. We have obtained experimental information which clarifies the physical processes that give rise 537