The overhead plate butt welding of gas shielded welding is difficult to operate stably because people are in an unnatural position during overhead welding. At the same time, heavy welding guns and cables should be lifted to increase the difficulty of operation. In addition,

the molten iron in the molten pool is easy to sag during overhead welding, and it is easy to form convex weld beads, which may cause molten iron to flow in serious cases. Therefore, welding parameters should be strictly controlled to obtain good weld formation.

First, ensure that the butt gap between the two plates is 3mm, which cannot be too large or too small. If it is too large, it will cause breakdown, overlap and concave weld bead. If it is too small, it will cause incomplete penetration and fusion at the back.

Backing weld

Welding process: the welding parameters are set as voltage 18.5V and current 130A.

Angle before welding: the angle between the welding gun and both sides of the groove shall be 90 °, and the included angle with the rear side shall be 80-90 °. The sawtooth or lunar tooth type shall be used for the strip manipulation, and the strip shall be stopped at both sides

and crossed at the middle to prevent undercut at both sides, excessive height in the middle or threading.

Filler welding

Before welding, the spatter and welding slag generated by backing welding shall be cleaned up.

Welding process: the welding parameters are set to voltage of 19V and current of about 140A.

Angle before welding: the angle between the welding gun and both sides of the groove shall be 90 °, and the included angle with the rear side shall be 75-85 °. Sawtooth or crescent shaped electrode shall be used for electrode manipulation, and the gap between the two sides

shall be stopped to avoid excessive undercut between the two sides. Short arc welding shall be used for welding. Cover welding shall be started when the filler weld bead is about 1mm lower than the base metal.

Cover welding

Before welding, the spatter and welding slag generated by backing welding shall be cleaned up.

During welding, the welding parameters are set to voltage of 18V and current of 110-120A.

Angle before welding: the angle between the welding gun and both sides of the groove shall be 90 °, and the included angle with the rear side shall be 75-85 °. The saw tooth or crescent tooth type shall be used for the strip manipulation. The strip shall be stopped at both sides

and crossed in the middle. The left and right sides shall be fully integrated with the base metal before swinging, so as to prevent the occurrence of excessive undercut at both sides.