The power supply classification features. The potential distribution in the arc. The welding arc properties (Part 2).

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 = U+ 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;  (U= Ес·lд).

he maximum temperature at the arc column is at least 5000-6000 оС.

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