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 polarity, when the cathode spot is on the product, the processes in it also ultimately influence the technological features of the welding process and the strength properties of the welded joint. Consequently, the determination of the amount of metal evaporating at the cathode is an important task, not only from a theoretical point of view, but also from a practical point of view. Therefore, we will consider the amount of metal evaporating from the cathode.

The ions carrying ion current in the cathode zone are formed in the ionization part of this zone. At present, the various methods for the formation of ions from neutral atoms are known, but which ones are predominant in the cathode zone is not known. However, for all ionization mechanisms it is characteristic that even the small difference in ionization potentials (Ui) of atoms has the significant effect on the ionization probability, and the smaller the Ui, the greater the ionization probability of the atom. In the cathode zone, in addition to the metal atoms of the electrode, the atoms of the shielding gas can also be present, for example, when welding Ar in Ar atoms, and when welding in CO2, C and O atoms, since at an average arc temperature of 7000 K, the characteristic for CO2 welding, The molecules of CO2 must completely decompose into atomic oxygen and atomic carbon. The ionization potentials of these atoms are UiAr = 15.8 eV, UiO = 13.6 eV, UiC = 11.3 eV and much larger than the ionization potential of iron atoms UiFe = 7.9 eV. This indicates that, when found in equal conditions, the probability of ionization of iron atoms is many times greater than that of the atoms of the protective gas. Consequently, the ions formed in the ionization part of the cathode zone will be almost completely formed from the iron atoms, which will be facilitated not only by a lower Ui, but also by a much larger concentration of iron atoms in the cathode zone compared to the concentration of protective gas atoms.

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