The studies have shown that the extent of the cathode and anode zones of the arc is very small: : lк = 1·10-5 см; lа = 1·(10-3…10-4) cm. Then the length of the column of the arc: lс ≈ lд (equal to the length of the arc), and
Uд = Ua + Uк + Uс ,
Lд = lа + lк + lс .
The power released in the 3 zones of the arc Pд = Icв·Uа + Icв·Uк+Icв·Uс, is completely determined by the values Uа,Uк,Uс, Uа = 2..5 V; Uк = 4..20 V. For steel electrodes Uа = 4..5 V.
The charged particles in the arc arise due to the emission of electrons from the surface of the cathode (thermal and field-electron) and ionization of gases located in the arc gap (these are positive ions).
To evaluate the properties of the arc column, the concept is introduced: the gradient of the potential of the arc column – Ес.
Since the function Uc = f(lc) is linear,
For the welding arcs: Ес = 1 – 5 V/mm.
Ес depends on the composition of the arc gas. For most arcs with the steel electrode:
а) when melting in air – Ес ≈ 3 – 4 V/mm;
b) in СО2 – Ес ≈ 5 V/mm;
c) for W welding in the argon medium – Ес ≈ 1 V/mm.
d) when welding in vacuum: Ес≈ 0,1 V/mm.
When the welding current (its value) changes, the value of Ес (for the given welding method) changes little. As a result, when welding, linearity is observed on the graph of the voltage dependence on the arc from its length (Fig. 1).
Uд = Uк + а + Ес · lд; (Uc = Ес·lд).
he maximum temperature at the arc column is at least 5000-6000 оС.