湿式水中プラズマ溶接の横向姿勢への適用性

抄録

The applicability of underwater wet plasma welding in the horizontal position was examined by using a welding attachment developed. This assembly, which is designed simply, is attached to the front face of plasma torch.
Welding was carried out in pressurized city water. Appearances of weld beads, cooling cycles at weld bonds and hardnesses of weld metals and HAZ's were investigated by varying weld rotation and welding conditions.
The use of the developed attachment stabilizes a gas cavity formed by plasma jet and protects any molten pool in this cavity from the invasion of environmental water in the horizontal wet welding. This leads to good welds.
Molten metal tends to hang down with increasing in the angle of rotation from 0 deg. (flat position) to 90 deg. (horizontal position). Therefore, from the standpoint of welding procedure, multi-pass welding with a reduced amount of weld metal may be advantageous in the horizontal position.
The ranges of adaptable plasma arc current and plasma gas flow rate in the horizontal position become narrow comparing with those in the flat position.
Cooling of welds in the horizontal position is rapid comparing with that in the flat position. This difference is caused by the fact that the dissipation of heat is accelerated by the repetition of contact with water flowing in immediately after the floating of steam bubbles formed on the backside of base plate.