Influence of ambient pressure on the electrode arc stability of local dry underwater welding

In order to investigate the arc characteristic of local dry underwater welding, various pressure of compressed air was inflated into a chamber to simulate the various water depths. The arc signals were acquired and analyzed in time and frequency domain, respectively. Results show that the metal transfer mode of iron powder low-hydrogen potassium electrode is large droplet short circuiting transfer. The increase of the pressure results in the increase of droplet size. The average short circuiting time was changed from 5-7 ms under atmospheric pressure to 8-10 ms under pressure condition. Under pressured condition, the electrode melting rate increases and meanwhile the stable working point of the arc voltage feedback control system moves upward leading to the increase of arc voltage. The frequency domain analysis shows that the main characteristic frequency is less than 10 Hz under atmospheric pressure, whereas large amounts of the characteristic spectrums with frequency of more than 10 Hz appeared under high pressure condition, indicating an instability of the welding process.