In FCAW, what provides shielding for the weld?

• A. Shielding gas from an external source only
• B. Shielding from gas evolved during flux decomposition only
• C. Shielding from gas evolved during flux decomposition and sometimes by an auxiliary shielding gas
• D. No shielding is required for FCAW

Answer: (C)

In FCAW the weld is protected by two possible sources of shielding. First, the flux coating on the filler wire decomposes when heated and releases gases that blanket the molten pool, keeping air from causing oxidation and porosity. Second, in many FCAW setups an auxiliary shielding gas from an external bottle is used in addition to the flux gas to provide extra coverage and to help stabilize the arc and weld bead. That combination—gas from flux decomposition and, sometimes, an external shielding gas—best explains how FCAW shielding is provided. The other possibilities are incomplete: some FCAW processes rely solely on flux gas (self-shielded), while others use an external gas, but not always both, and shielding is always required for a proper weld.