# WHAT IS MAGNETIC BLOW?

Arc blow is the deflection of the welding arc in shielded metal arc welding (SMAW), where the arc becomes erratic and is directed toward one side of the groove, causing lack of fusion defects. This phenomenon occurs most frequently when welding with direct current (DC) on magnetic materials (iron and nickel).

Arc blow can occur with alternating current (AC) under certain conditions, but these cases are uncommon and the intensity of the blow is always less severe. Direct current, as it flows through the electrode and base metal, creates magnetic fields around the electrode that tend to deflect the arc from its intended path. The arc may deflect laterally, but most commonly it deflects forward or backward along the joint.

Backward arc blow occurs when welding toward the workpiece connection near the end of the joint or at a corner.

Forward arc blow occurs when welding away from the work lead cable at the beginning of the joint.

HOW TO PREVENT ARC BLOW?

Reduce the amperage, move the work clamp as far away from the weld as possible. If arc blow occurs in the direction opposite to travel, position the work connection at the start of the weld; if it blows in the direction of travel, position the work connection at the end of the weld. Keep the arc as short as possible and switch from direct current to alternating current.

The ideal solution to prevent arc blow is to demagnetize the base material that has become magnetized from a particular operation. Another method is to wrap the work lead cable along the base material in order to generate a magnetic field that counteracts the arc deflection and stabilizes the arc.

If the equipment allows, switching to alternating current will also help neutralize the magnetic effects due to the continuous and rapid reversal of current direction.

Another approach is to angle the electrode into the workpiece in the direction of the arc blow, or to use the backstep welding technique.