Magnetic Blowing Phenomenon and Countermeasures in Welding

During DC arc welding, the phenomenon of partial blow caused by electromagnetic force is called magnetic partial blow, which has an adverse impact on the welding process and quality. Only by overcoming it can we ensure the welding quality. There are many factors leading to magnetic partial blow, specifically:

When arc striking and arc ending are welded at the edge of the workpiece, the magnetic flux density is extruded and deformed, resulting in different magnetic flux density before and after the arc. The magnetic flux density at the edge of the workpiece is higher than that far away from the workpiece. According to the law of current force, the magnetic bias blowing phenomenon of arc leaning towards the front and towards the rear during arc striking and arc ending occurs; Elimination measures: add arc striking plate and arc stopping plate to change the walking angle of welding rod.

The position of the ground wire is wrong with the welding direction, and the magnetic flux density in front of the arc is less than that in the rear, so it is biased towards the front; Elimination measures: the ground wire shall be connected to the arc end, and the non-magnetic ground wire clamp shall be used.

When welding T-joints, in order to reduce welding deformation, the method of simultaneous welding on both sides of the vertical plate is generally adopted, but this process measure is easy to cause magnetic bias blowing; Elimination measures: adopt AC and DC power supply for welding at the same time, and change the walking angle of welding rod.

When welding workpieces with different thicknesses, magnetic bias blowing will also occur, because the magnetic field attraction of thick workpieces is large and attractive to charged arc particles; Elimination measures: use short arc welding, the angle between the welding rod and the flat plate is large, and the ground wire is clamped on one side of the thick plate.

The arrangement of welds has a great impact on magnetic bias blowing. The groove depth of butt welds and internal fillet welds are prone to magnetic bias blowing. Elimination measures: adopt short arc welding, increase the number of tack welds and use AC power supply.

Welding direction and sequence when the weld is long, straight through welding will produce welding deformation and magnetic partial blow. In this case, back welding method can be used to avoid magnetic partial blow.

Fixture and backing plate fixture and backing plate also have a great impact on magnetic bias blowing. Fixture and backing plate adopt non-magnetic materials, and additional plates and other process methods can reduce magnetic bias blowing.

Keywords:Welded pipe, LSAW pipe