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 Continue reading →

The metal structure basis (Part 4).

The metal melting in a small area, leads to the appearance of shrinkage stress. Even if the external fixation of the sample was ensured during the heating and cooling cycle, the tension caused by uneven heating and cooling persists in the cooling part. This voltage is called the residual voltage. Due to the residual stress, the sample remains curved. However, the sample will not continue to bend further, since it has already cooled to room temperature and has acquired sufficient strength to resist residual stress forces. The residual stress remains in the sample if Continue reading →

The crystallization process mechanisms.

The crystallization takes place in two stages: in the beginning, nucleation center arise, and then nucleation center grow. There are two mechanisms for the nucleation of the nuclei: crystallization centers:

  1. Homogeneous (spontaneous, spontaneous without extraneous particles);
  2. Heterogeneous (not spontaneous, with the participation of foreign impurities at the ready interfaces.)

The growth of crystallization centers does not depend on the method of nucleation of crystallization centers and obeys general laws.

  The homogeneous crystallization theory.Continue reading →

The isolation of the excess phase from the supersaturated solid solution (Part 1).

The metals in the solid state can only dissolve other metals and nonmetals. As the pressure and temperature change, the solubility changes, this leads to the separation or dissolution of excess phases. If the alloy is in an unstable state, these processes can occur without changing the external conditions. Structural changes due to the limited solubility of the components in the solid state are widely used in the technique of heat treatment.

Let us consider the system whose components are bounded soluble in one another in the solid state. In this case, the field of the diagram below the solidus line is Continue reading →

The amount of metal evaporating from the cathode spot (Part 1).

When welding with the direct polarity, the dimensions of the anode spot determine the width of the weld. At the same time, at the given current and voltage, on the arc from the width of the seam depends on the depth of penetration of the product, since it is determined by the arc pressure on the weld pool. Thus, the size of the anode spot affects not only the technological parameters of the welding process, but also the strength properties of the welded joint. The size of the anode spot is directly influenced by the diameter of the column of the arc, which in turn depends on the composition of the arc gas, which is significantly influenced by metal vapor from the cathode spot on the electrode. Similarly, when welding on the reverse Continue reading →

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