Non-refractory Metals Research Articles

The magnetic stabilization of low pressure d.c. arcs

Self-sustaining d.c. arc discharges between solid metal electrodes at pressures down to 104 mm of mercury have been investigated. At pressures below a few millimetres of mercury, arcs on both refractory and non-refractory metals behaved like cold arcs. Spot-splitting and reverse of the cathode spot were observed and a form of instability is described. Reverse driving of the cathode spot or spots by the magnetic field set up by the current in the electrodes themselves is suggested as the cause of the instability. A magnetic method of stabilizing the discharge is described, requiring an axial magnetic field of at least 500 G. A marked constriction of the positive column was caused with this value of field. The magnetically stablized discharge has been used experimentally to produce short welds on 1/8 in thick mild steel plate at 1 μ of mercury pressure using about 40 A at 30 V.