Wire Selection, Shielding Gas, and Machine Setup

What Is FCAW and Why Wire Selection Matters

Flux-Cored Arc Welding (FCAW) uses a continuously fed tubular wire electrode whose hollow core contains flux ingredients. Those ingredients shield the arc, control the weld chemistry, and determine what positions and base metals the wire suits. Choosing the wrong wire for the job produces porosity, cracking, or mechanical properties that fall short of the Welding Procedure Specification (WPS). Your first task on any FCAW job is to match the wire classification to the base metal, joint position, and shielding gas already written into the WPS.

Reading an AWS A5.20 or A5.36 Classification

AWS A5.20 covers carbon-steel FCAW electrodes; AWS A5.36 is a newer, open-classification standard that allows manufacturers more flexibility in reporting optional designators. Both use the same basic prefix structure.

Take E71T-1C-H8 as an example and read it digit by digit:

• E — electrode
• 7 — minimum tensile strength in units of 10 ksi (70 ksi minimum)
• 1 — usability position: 1 = all positions; 0 = flat and horizontal only
• T — tubular (flux-cored)
• -1 — usability designator; indicates flux type, polarity, and shielding gas family (T-1 wires run DCEP with external gas)
• C — shielding gas: C = 100% CO₂; M = 75% Ar / 25% CO₂ (C25); some classifications list both (e.g., T-1C/M)
• H8 — optional diffusible hydrogen designator: maximum 8 mL of hydrogen per 100 g of deposited weld metal; lower numbers (H4, H2) indicate even drier deposits and reduce the risk of hydrogen-induced cracking

Under A5.36, an open-classification wire may carry designators such as T15-M21-A8-CS1-H4, encoding flux type, gas group, composition, and hydrogen level in a slightly expanded format. Your classification chart decodes each field.

Gas-Shielded (FCAW-G) vs. Self-Shielded (FCAW-S)

FCAW-G wires (T-1, T-2, T-9, T-12, and others) require external shielding gas. Common choices:

• 75% Ar / 25% CO₂ (C25): lower spatter, smoother bead, good for out-of-position work
• 100% CO₂: deeper penetration, slightly more spatter, lower cost, preferred by some codes for certain groove welds

Check the wire classification — the letter after the dash (C or M) tells you which gas the wire is qualified for. Using the wrong gas voids the electrode's classification and can violate the WPS.

FCAW-S wires (e.g., E71T-8, E70T-7) contain all shielding in the core; they run without any cylinder gas. They are useful in wind or outdoors where external gas would blow away, but they typically generate more fume and require strict attention to electrode extension (stickout) to maintain adequate self-shielding. Never apply external shielding gas to an FCAW-S wire — it disrupts the core chemistry.

Machine Setup on a CV Power Source

FCAW runs on a constant-voltage (CV) power source. The machine holds voltage essentially steady while wire feed speed (WFS) controls amperage. The three essential variables you will set are:

1. Voltage (V): controls arc length and bead width. Too low = stubbing, cold lap. Too high = excessive spatter, undercut.

2. Wire Feed Speed (WFS, in inches per minute, ipm): directly sets amperage for a given wire diameter. Higher WFS = higher amperage = deeper penetration.

3. Inductance (if available): controls how quickly current rises at arc start. Higher inductance softens the arc and reduces spatter; lower inductance gives a crisper, faster-freezing puddle useful for out-of-position work.

Always set voltage and WFS to the values written in the WPS before you strike an arc. A typical starting range for .045 in. E71T-1C on 3/8 in. plate in the flat position is roughly 26–29 V and 350–450 ipm, but your WPS is the authority — not memory.

Loading Wire and Setting Electrode Extension

1. Verify the drive roll groove size matches the wire diameter (knurled rolls for flux-cored wire).

2. Feed the wire through the inlet guide, drive rolls, cable liner, and contact tip. Trim the wire flush at the tip, then pull out 3/4 in. (approximately 19 mm) as your initial electrode extension (stickout). Electrode extension for FCAW-G is typically 3/4 in. to 1 in.; FCAW-S may require longer extension per the manufacturer.

3. Set gas flow with a flowmeter. Most FCAW-G procedures call for roughly 35–50 CFH; confirm your WPS value. Check for drafts — even a light breeze can disrupt shielding.

4. Verify contact tip size matches wire diameter. A mismatched tip causes erratic feeding and arc instability.

Safety Points

• Fume extraction: FCAW produces more fume than GMAW. Use local exhaust ventilation (LEV) or a fume extraction gun. Never weld over galvanized or coated steel without engineering controls and awareness of toxic oxide risks.
• PPE: minimum shade 10 lens for most FCAW amperages (verify ANSI Z87.1 / AWS F2.2 filter shade table); leather gloves, flame-resistant jacket, and leather boots.
• Cylinder safety: chain all cylinders upright; keep caps on when not in use; never use cylinders as rollers or stands.
• Wire and drive rolls: de-energize and follow lockout/tagout (LOTO) procedures before changing drive rolls, liners, or contact tips — the wire feeder can feed unexpectedly if the trigger is bumped.
• Spatter burns: FCAW-G with CO₂ can throw spatter several feet. Clear the area and use spatter-resistant spray on fixtures.