Study On Wind Field Structure Of Local Dry Cover And Arc Characteristics In Local Dry Method Welding

Underwater welding technology has been widely applied in the building and repairing of underwater construction in recent years. Among the underwater welding technologies, local dry welding method which adopts local dry chamber to prevent the effect of water to the welding process has some advantages such as better joint quality and ease to realize automatic welding, so it has a good application prospect in marine construction.High-pressure gas is pushed in the local dry chamber to push the water out in local dry welding method, however the high-pressure gas is hard to avoid horizontal flow in the local dry chamber, affecting the arc characteristics and the stability of welding process.It is a good thing if we can use the horizontal flow to restrain the stay of welding pool under gravity in horizontal welding, the weld can be improved from two aspects of mechanical and energy suppression.Firstly this paper studied the wind structure of high-pressure gas in the local dry chamber with different structures, and through optimizing the structure of the local dry chamber, found out the speed of outlet can be greatly increased by setting a baffle in outlet, and with a porous barrier at top of local dry chamber will reduce the speed of wind as well as decrease the circulation, resulting in a stable upward wind at the bottom of local dry chamber. Then integrated its advantages above, we identified specific structure of the local dry chamber, and processed it.Secondly based on MHD theory and Secondary Development of CFD software Fluent by UDF/UDS, mathematical model of 3D stable rotating arc of MIG welding was established, and then the impacts of the wind field and ambient pressure in the local chamber to the welding process and arc characteristics such as the temperatures,velocities and pressures of arc plasma are simulated and get the changing rules:with the raise of the ambient pressure, arc had a phenomenon of shrink, the temperatures and velocities of arc plasma decreased slightly, arc column area pressures field intensityincreased; under the lateral wind blowing arc deflected one side, temperature, pressure,velocity changes were consistent, the declination of arc column displays a linear relationship with the increasing of lateral wind speed. and the increasing slope is quite.Then a high-speed camera is used in the welding experiments to photograph the arc shape under different lateral wind. It is found that the experimental results are consistent with the simulation results.Lastly, two sets of lateral wind farm or not corresponding welding experiments under different parameters were did, and calculated its static sensor characteristics mathematical model. Then compared with the experimental data, deviations within a reasonable range, it said the model is genuine and believable. Found that under the influence of lateral wind field, the current signal fluctuations increased, welding parameters require more stringent, wire extension keep a bigger slope with the current changes.