an electric arc formed in the weld zone joint or in the area of thermal cutting when an electric current passes between electrodes through a gas. A welding arc is the most developed form of electric discharge in gases. It is characterized by a low voltage, a high current, and the presence of an ionized gas in the arc gap. The ionized gas column of the arc discharge glows brightly and has a temperature of 6,000°-10,000°C along the axis of the arc column. The principal factor responsible for ionization is the high temperature maintained by the flow of energy from a power supply.
The voltage of a welding arc, that is, the voltage between the electrode tips, depends mainly on the length of the arc, the strength of the current, the materials and dimensions of the electrodes, the gas composition, and gas pressure. The properties of a welding arc are controlled by changing the length of the arc (between 0.01 and 1 cm), the strength of the current (between 0.5 and 3,000 amperes), the pressure of the gas (between 102 and 105 newtons/m2, that is, between 0.001 and 1 kg force/cm2), or the material, shape, or dimensions of one of the electrodes. In addition, the arcing zone can be shielded by the flow of a gas, or the arc can be compressed.
The thermal power of a welding arc ranges from 10 to 105 watts at concentrations from 102 to 105 watts/cm2. The wide power range makes it possible to use welding arcs to weld and cut various materials ranging in thickness from 0.05 to 100 mm in one or more passes.