Arc characteristics are summarized and relationships to the welding arc are brought in.
The "welding arc" is so called as a matter of convenience. Actually, it differs from other short, high-pressure, heavy-current arcs mainly in application. The welding arc is a relatively steady-state phenomenon which is used to melt or transfer molten material. The basic phenomena involved in this arc are not essentially different from those occurring in many circuit interrupters or the short steady-state arcs used for illumination. The material presented in this paper relates to the high-pressure, short arc in general, but is equally applicable to the welding arc. It is, of course, quite impossible to cover adequately the complex phenomena occurring in an arc in a paper of this length, and the reader is referred to books on the subject.
Before going into the atomic details of arc phenomena, it may be well to review the more general characteristics of the discharge. The arc is defined as a discharge having a voltage drop at the cathode that is of the order of the least ionization potential of the gas or vapor in which it burns. This drop may in some cases be as low as the least excitation potential of the gas. Table 1 gives these critical potentials for some of the atoms found in welding arcs. The arc is distinguished as a low-voltage, high-current discharge as compared with the glow and corona discharges that are low-current, relatively high-voltage discharges, and the spark discharge which is a high-voltage, transient discharge.
For the short arc, the voltage across the entire discharge is of the same order of magnitude as that of the cathode. For low current, of the order of 10 amp., the arc has a falling V-I characteristic. At higher currents, the arc voltage is nearly independent of the current. However, magnetic fields, confining walls, air blasts, etc., may cause the arc voltage to increase with current due to lengthening of the column or other energy loss effects. The high pressure arc is characterized by high temperatures both in the column and at the electrodes. The arc may be divided into three sections for the purpose of this discussion. These sections are the column, the cathode region and the anode region.
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| Number of Pages : | 12 |
| Published : | 1949 |
