To prevent arc blow, what can be used?

• A. Use DC polarity
• B. Use AC polarity
• C. Increase shielding gas flow
• D. Use a larger electrode

Answer: (B)

Arc blow is caused by the magnetic field around the welding arc interacting with residual magnetism in the metal, which can cause the arc to wander off course. Using alternating current reverses the polarity repeatedly, so the magnetic field around the arc changes direction and, over time, cancels out the steady magnetic bias from the metal. This stabilizes the arc and prevents blow. Keeping DC polarity would maintain a constant magnetic field that can drive the arc away; increasing shielding gas flow doesn’t address the magnetic cause; and a larger electrode changes arc characteristics but doesn’t directly stop the magnetic wandering.