Arc blow refers 1 the metal stream 2 deflected from its intended path. Rather than follow the shortest path from the electrode to the work, the metal is deflected forward or backward from the direction of travel, or less 3 to the side. Arc blow results 4 excessive spatter, incomplete fusion, reduced welding speed, and generally lowered weld quality.
Arc blow is caused by 5 magnetic or thermal conditions in the arc area. Magnetic blow comes from an unbalanced magnetic field surrounding the arc. Magnetic fields are set up in a continuous series of circles perpendicular to the current path. When the fields are unbalanced, the arc bends away 6 the greater concentration, resulting in arc blow. This condition exists particularly with direct current 7 the induced fields are constant in direction. It is only minor for ac because the magnetic fields collapse as the current reverses.
Thermal arc blow results from the physics of the electric arc, 8 requires a hot spot on both the electrode and the workpiece to maintain a continuous flow of current in the arc stream. As the electrode moves relative to the work, the arc will tend to lag 9 because it is reluctant to move to a cold spot. 10 manual weld, thermal arc blow is not likely to become a problem, but with higher speeds of automatic welding, thermal and magnetic arc blow are likely to become more frequent.
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