片面狭開先MAG溶接法の研究(第1報)

直流棒マイナス極性における裏波ビード形状の観察

抄録

A new technique of high efficiency one-side narrow-gap MAG welding was developed using simple I-groove and soft backing, and 'Uranami welding' was carried out easily with this technique. It is principal characteristic of this welding technique that 'Uranami welding' is carried out easily with DC electrode negative polarity.
In case of high current welding, backing does not melt down because of using DC electrode negative polarity, therefore high speed 'Uranami welding' can be achieved. In addition, the bead surface is Ushaped and penetration into side walls is increased owing to the change of molten metal flow in molten pool to a desirable pattern by directing control gas against the tail area of the molten pool.
In this report, using mild steel plate (thickness: 22 mm) and I-groove (root gap: 10 mm) the range of welding conditions for achieving suitable 'Uranami beads' was searched for by observing many 'Uranami bead' shapes and the practical utility of this welding technique is discussed.
The results are as follows;
1) Using this welding technique, suitable 'Uranami bead' is achieved easily over a wide range of welding conditions. The optimum welding conditions of this welding technique is as follows; welding current arc 450A - arc voltage 35V - welding speed 26cm/min
wire dia.: 1.6 mm distance between contact tip-groove bottom: 35 mm
primary shielding gas: 30%Ar+70%CO₂ (401/min)
secondary shielding gas: 100%CO₂ (30l/min)
control gas: 80%Ar+20%CO₂ (12.5l/min)
2) The changeable root gap range and the range of misfit of base plate within which suitable 'Uranami bead' can be achieved with this welding technique are 6-13 mm and 0-3 mm respectively.
3) Using this welding technique, 'Uranami bead' can be achieved without defects.