Basic operation technology of CO₂ gas shielded welding

1、Arc striking of CO₂ gas shielded welding

There is a little difference between the methods of arc striking between CO₂ gas shielded arc welding and shielded metal arc welding. There is no need to lift the welding gun when starting the arc.

The specific operation steps are as follows:

1). Before starting arc, press the control switch on the welding gun and send out a section of welding wire by inching. The extension length of welding wire is less than the distance between nozzle and weldment, and the extra long part should be cut off. As shown in the figure.

If the ball appears at the end of the welding wire, it must be cut off in advance, otherwise it is difficult to start the arc.

2). Place the welding gun at the arc striking position according to the requirements (keep proper inclination angle or nozzle height) (see Fig. Note that the end of the welding wire does not contact with the weldment, and the nozzle height is determined by the welding current.

3). Press the control switch on the welding gun, the welding machine will automatically supply gas in advance, turn on the power supply after a delay, maintain high voltage and slow wire feeding, and automatically ignite the arc when the welding wire collides with the short circuit of the weldment. When striking the arc, press down the welding gun with a little force to prevent the torch from being extinguished because the torch is lifted too high and the arc is too long.

2、Swing mode of welding gun for CO₂ gas shielded welding

When butt welding of plate flat welding with CO gas protection, different swing mode shall be adopted according to the groove gap,

When the groove clearance is smaller than 0.2-1.4mm, straight-line welding or small amplitude swing is generally used.

When the groove clearance is 1.2-2.0mm, the small amplitude swing of serrated shape is adopted, and the welding bead center moves slightly faster, while the groove stays about 0.5-1s on both sides of the groove, as shown in the figure.

When the groove gap is larger, the swing mode should swing back and forth while swinging horizontally. At this time, the welding arc should not act on the gap directly, as shown in the figure.

In order to get larger welding foot, the method of swinging back and forth with small current can be used in single pass flat position fillet welding.

When welding the fillet weld of the ship position, the method of swinging the crescent before and after is done.

When vertical downward welding, the molten iron in the molten pool is easy to flow downward. Small standard current should be used. The welding torch can be moved in a straight line or small swing method. The metal in the molten pool can be pushed up by the blowing force of the arc. The angle of the welding gun is shown in the figure.

The arc should always be kept in front of the metal in the molten pool, and molten iron should not flow to the front of the arc

When welding upward, the angle of welding gun is shown in the figure below.

In the case of small amplitude, the welding leg should be sawtooth.

Due to the heat concentration at this time, the weld bead is easy to bulge, so in the case of uniform swing, it should move up quickly.

If larger welding feet are required, the crescent swing mode shown in the figure above shall be adopted, and the center part of weld bead shall be moved rapidly, while the two sides shall be kept for 0.5 ~ 1s to prevent undercut.

But at this time, it should be noted that the angle of the welding torch should not be swayed with a downward curved crescent, because this swing will easily cause molten iron flow and undercut.

It is easy to get flat and smooth weld bead when single pass welding is carried out by vertical upward welding. Usually, the maximum weld leg size can reach 12mm.

When larger leg size is required, multi-layer welding shall be used. In multi-layer welding, the first layer adopts small swing, while the second layer adopts crescent shaped swing.

If large welding feet are required, triangle swing can be used for the first layer. Both sides and root three points should stay for 0.5-1s and move up evenly. After that, the tooth shape swing can be used in each layer.

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