Study on Stabilization of Welding Arc under Hyperbaric Condition

在高压TIG焊中，电弧往往是不稳定的，很难获得良好的焊缝。本文主要研究了磁场和交变磁场频率对焊接过程中的电弧现象和焊接效果的影响。主要研究结果如下：1)高压下施加磁场可以解除焊接电弧的收缩，增大其直径；2)高压下施加静电场，可以防止电弧电压的不规则波动，但电弧电压的振荡周期约为0.5ms。因此，电弧可以在2 kHz的频率下旋转或振动。3)对高压下的电弧施加交流磁场，可以防止电弧电压的波动，但电弧电压的振动取决于励磁电流的频率。4)对高压下的电弧施加交流磁场，可以获得相对稳定的电弧，获得笔直、声音良好的焊缝。5)在较高的磁场频率下，为了在较低的频率下获得相同的磁通密度，必须使用较大的励磁电流。6)La_2O_3-W电极的烧蚀比ThO_2-W电极的烧蚀小得多。在焊接过程中，La_2O_3-W电极尖端的表面存在La_2O_3，使功函数减小，防止了电极尖端的过热。因此，电极的烧蚀可能会变得比其他电极更小。

In hyperbaric TIG arc welding, the arc tends to be unstable and accordingly it is difficult to obtain sound welds. Therefore the effects of magnetic field and the frequency of alternating magnetic field on the arc phenomena and welding results were investigated.Main results obtained are summarized as follows : 1)Applying magnetic field to a welding arc under high pressure, the constriction of the arc is released and its diameter increases.2)Applying static field to an arc under high pressure, irregular fluctuation of arc voltage is prevented, but the arc voltage vibrates in a period of 0.5ms approximately. Accordingly, the arc may turn or vibrate in a frequency of 2 kHz.3)Applying alternating magnetic field to an arc under high pressure, fluctuation of arc voltage is prevented, but the arc voltage vibrates depending on a frequency of excitation current.4)Applying alternating magnetic field to an arc under high pressure, straight and sound welds can be obtained by a relatively stable arc. However, effect of frequency of magnetic field on welding result is not observed.5)In a higher frequency of magnetic field, a higher excitation current must be used in order to obtain a same magnetic flux density in a lower frequency. As the result, the excitation coil has a tendency to be heated in operation.6)The erosion of La2O3-W electrode is much less than that of ThO2-W electrode. At the tip of the La2O3-W electrode during welding, La2O3 exists at the surface and it makes the work function decrease and prevents superheat of the electrode tip. As the result, erosion of the electrode may become smaller than those of other electrodes.