Arc column, located between the anode and cathode regions, has the greatest length in the arc gap. The main process here is ionization, or the formation of charged gas particles. This process occurs in result of collision of electrons and neutral gas particles. When sufficient energy collision gas particles lose electrons and form positive ions. Such ionization is called ionization collision. Collision may occur without ionization, whereas the collision energy is released as heat and is a rise in temperature arc column. Formed in the arc column charged particles move to the electrodes: electrons – to the anode, the ions – to cathode. Part of the positive ions reach the cathode spot, the other part of them reaches the cathode, and by attaching itself to the negatively charged electrons, forming neutral atoms.
This process of neutralization of particles called recombination. In the arc column at all combustion conditions there is a sustainable balance between ionization and recombination processes. In general, the arc column is neutral, since in each of its cross section are simultaneously equal number of oppositely charged particles. The temperature of the arc column reaches 6000 8000 C or more – depending on the density of the welding current. Voltage drop in the column varies between 10 50 V / cm, depending on the gas medium and decreases with the introduction of the components. These include alkaline and alkaline-earth metals (Ca, Na, K, etc.).
The total voltage drop in the arc Ua – uk + Uz + U &. Voltage drop in the arc column can be represented as Ue = E1, where E – the tension along the length, / cm – the length of the arc column. Values of uk, Ua, E practically depend only on the electrode material and the composition of the medium arc gap, and with the unchanged sion remain constant under different conditions welding. Due to the small length of the cathode and anode regions can be considered as practically / o = / d, where d is the length of the arc. Then the expression Un = a + – b where a = uk + Ua; b = E. It follows that the arc voltage directly depends on its length. Welding arc classified into: the applied electrodes – with mig and tig, the degree of compression of the arc – and a free compression scheme for supplying a welding current – direct and indirect, by the nature of the current – dc and ac (single phase or three-phase current); to the polarity of dc – direct and reverse polarity. Arc is called short if its length is 2 4 mm. The length of the normal arch is 4 6 mm. Arc length more than 6 mm long call.