The basic principle of plasma arc

In 1955, the United States first successfully developed plasma arc cutting technology. The principle of plasma arc is to allow the continuously ventilated discharge arc to pass through a nozzle hole, and under the three compression effects generated in its channel, strong compression is obtained. Under the condition of maintaining balance with the internal expansion pressure of the arc column, the central gas of the arc column is highly ionized, forming a mixture of electrons, ions, and some atoms and molecules, which is called plasma arc.

The compression effect on a plasma arc is called the compression effect. There are three forms of compression effect:

(1) Mechanical compression effect. A high voltage is applied between the tungsten electrode (negative electrode) and the welding element (positive electrode) to ionize the gas and form an arc. When the arc column passes through a special hole shaped nozzle, a certain pressure of working gas is applied to force the arc column to pass through the fine hole. Due to the mechanical compression of the arc column, the cross-sectional area is reduced, which is called the mechanical compression effect.

(2) Thermal shrinkage effect. When the arc passes through the nozzle, high speed cooling gas flow (nitrogen or hydrogen, etc.) is continuously sent to the periphery of the arc to make the periphery of the arc column be strongly cooled, and the Degree of Dissociation degree is greatly reduced, forcing the arc current to pass through the center of the arc column, resulting in further reduction of the conductive section. At this time, the current density of the arc is greatly increased, which is the heat shrinking effect.

The basic principle of plasma arc

(3) Magnetic contraction effect. Due to the same direction of current, under the electromagnetic force generated by the current itself, it attracts each other and generates a force that compresses from around the arc column towards the center, further reducing the diameter of the arc column. The compression effect caused by the magnetic field of the conductor itself is called the "magnetic contraction effect". The greater the arc current, the stronger the magnetic contraction effect.

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