The arc is part of an electric welding circuit. When welding with direct current electrode connected to the positive pole of the power source of the arc, called the anode and the negative – cathode. If the welds are on the ac, then each electrode is alternately an anode or cathode. The gap between the electrodes, called the domain of arc, or arc gap, the length of the arc gap – the length of the arc. Arc, burning between the electrode and the object of welding is an arc of direct action. Such an arc is called a free arc in contrast to the compressed cross-section of a force reduced by the torch nozzle, the gas flow and electromagnetic field. Excitation of the arc is as follows.

Short-circuit the electrode and contact details in the field of sti sur heated. On opening of the electrodes with a heated cathode is the emission of electrons – the electron emission. Electron yield is primarily attributed to the thermal effect (thermionic emission) and the presence of high intensity electric field (field electron issue). The presence of electron emission from the cathode surface considered an indispensable condition for the existence of arc discharge. Ignition of the arc welding consumable electrode also begins with a short circuit.

Because surface roughness of the electrode contact with the base metal is selected prominent sites that instantly melt under the action of the released heat, forming a fluid jumper between the ground metal and the electrode. With the rapid dilution of the electrodes fused jumper stretched and narrowed, resulting in the current density in them comes at break up of such magnitude that turns them into pairs. At high temperature metal vapor ionization interval is so significant that a relatively small potential difference between the ends of the electrodes occurs arc. The discharge is supported on the stationary stable arc in the event that saved the factors that support the ionization of the arc gap.