Effect of Gas Pressure on the Formation Mechanism of Welds Based on Local Dry Underwater Welding

Abstract

During the local dry underwater welding process, the gas pressure in the micro drainage cover plays a key role in the formation of welds, but the relationship among the stability of the underwater arc, the formation of welds and the gas pressure has not been clarified. In this study, a micro drainage cover with dual-gas curtain based on the Lafar tube was used in the local dry underwater MIG welding experiments at a depth of 20 cm to explore the influence of gas pressure on the formation of underwater welds. The results showed that when the arc shielding gas was only 0.1 MPa in the micro drainage cover, the welding process was interrupted and the width of welds was not uniform; while the drainage gas was added, both the welding process and formation effect were improved. However, when both the shielding gas and the drainage gas pressure reached 0.4 MPa, the process and formation effect performed worse. The photos of arc combustion and metal transfer under different gas pressure were shot using high-speed photography. It turned out that the most ideal condition was both 0.2 MPa of the shielding gas pressure and drainage gas pressure at the water depth of 20 cm.