CO2 Gas-Shielded Flux Cored Welding Wire

A1: Its flux core eliminates the need for separate flux, enabling continuous wire feeding. The deposition rate (10-15kg/h) is much higher than solid wires or manual electrodes, and it tolerates rusty base metals—reducing pre-weld cleaning time.

A2: Flux cored wire has a flux core (deoxidizes, forms slag) and relies on dual protection (gas + slag), while solid wire only uses gas. Flux cored wire is more adaptable to rusty surfaces and windy conditions but may leave slag (needs cleaning). Solid wire is cleaner but requires stricter base metal cleaning.

A3: No. The flux core alone can’t fully prevent oxidation—CO₂ is necessary to isolate air and stabilize the arc. Without gas, the weld will have severe porosity, oxidation, and spatter. Some "self-shielded" flux cored wires exist, but they’re not CO₂-dependent and have different performance.

A4: Excessive slag is caused by high flux content, slow welding speed (slag accumulates), or low current (incomplete slag fusion). Reduce it by: increasing current (promote slag melting); speeding up travel (avoid accumulation); choosing low-slag wires (e.g., E71T-8) for thin plates.

A5: E71T-8 is for low-alloy steel, all-position welding, and requires better base metal cleanliness (suitable for structural parts). E71T-11 is for mild steel, tolerates rust/oil, and is cheaper (ideal for outdoor rough welding like pipe piles).

A6: Generally 20-25L/min. For thin plates (＜5mm) or indoor welding: 15-20L/min. For thick plates (＞10mm) or outdoor/windy conditions: 25-30L/min (prevent air intrusion). Too low: porosity; too high: turbulent gas flow (also causes porosity).

A7: Slag entrapment occurs when slag from the previous layer isn’t cleaned. Prevent it by: using a chisel or wire brush to remove slag between layers; ensuring the next layer’s arc melts the previous layer’s edge (1-2mm overlap); tilting the gun forward to push slag ahead.

A8: Too fast: wire jams or doesn’t melt, causing incomplete fusion. Too slow: insufficient filler, leading to concave welds. Match speed to current (e.g., 1.2mm wire + 200A = 5-7m/min). Stable wire feeding is critical—use a well-maintained wire feeder.

A9: Yes, but choose matching wires. For Q690 (tensile strength ≥690MPa), use E91T1-K2 (≥620MPa) or E111T1-K3 (≥760MPa). Ensure the wire’s alloy elements (Cr, Mo) match the base metal to avoid strength mismatch.

A10: Cracks are caused by hydrogen from moisture (flux absorbs water, rust, or oil). Avoid them by: using low-hydrogen wires (E81T1-Ni1, hydrogen ≤8ml/100g); storing wires in dry cabinets (humidity ≤60%); preheating rusty base metals (100-150℃ to remove moisture).

A11: Grind out porous areas, then re-weld. To prevent recurrence: check gas flow and purity (≥99.5%); ensure flux core isn’t damp (bake damp wires at 250℃ for 2h); clean heavy oil/rust (flux can’t handle excessive contaminants).

A12: Preheat to 150-250℃. For low-alloy steel (Q355): 150-200℃. For high-alloy steel (Q690): 200-250℃. Preheating reduces cooling rate, avoids martensite formation (brittle) and hydrogen-induced cracks. Use a temperature gun to monitor.

A13: Yes, choose all-position wires like E71T-8. Key tips: use small-diameter wire (1.2mm); lower current (180-220A) to control molten pool; keep short arc length; tilt the gun slightly upward to prevent slag falling into the pool.

A14: Store in airtight packaging in a dry cabinet (temperature 10-30℃, humidity ≤60%); after opening, use within 48 hours (flux absorbs moisture quickly); unused wire must be sealed in a moisture-proof bag with desiccant; damp wire needs baking (250℃ for 2-3h) before use.

A15: Gas-shielded (e.g., E71T-8) requires CO₂/argon-CO₂ gas, with better weld quality (low spatter, smooth surface) for structural parts. Self-shielded (e.g., E71T-8NS) has flux that generates shielding gas, no need for external gas—used for outdoor field welding but with more spatter.

A16: Increase gas flow by 5-10L/min (to 25-30L/min); use a wind shield (blocks crosswinds); choose larger-diameter nozzles (20-25mm) for broader gas coverage; slow travel speed to ensure fusion—wind disrupts gas protection, so prioritize stability over speed.

A17: Undercut is due to excessive current (melts base metal edges) or high voltage (arc blows to edges). Fix by: reducing current/voltage by 10%; increasing wire feed speed (adds more filler); tilting the gun 5-10° toward the weld (focuses arc on the pool).

A18: Tensile test (strength, elongation); impact test (low-temperature toughness for LPG tanks); bending test (180° bend to check plasticity); hardness test (avoids brittle heat-affected zones). For pipelines, add pressure tests (leak detection).

A19: Yes. Choose a wire with intermediate strength, e.g., E71T-8 (matches mild steel) or E81T1-Ni1 (for low-alloy). Control heat input to avoid overheating the low-alloy side (prevents grain coarsening); preheat to 100℃ if the thickness difference is large.

A20: Deoxidizers (Mn, Si) reduce porosity; slag formers (TiO₂) control slag flow; alloying elements (Ni, Cr) improve strength/toughness; hydrogen binders (F, Ca) reduce hydrogen content. For example, E81T1-Ni1’s nickel enhances low-temperature toughness.

A21: 0.8-1.2mm for thin plates (3-8mm); 1.2-1.6mm for medium plates (8-20mm); 1.6-2.0mm for thick plates (＞20mm). Larger diameters require higher current but increase deposition efficiency—match to the welding machine’s capacity.

A22: 48 hours in dry conditions (≤60% humidity); 24 hours in high humidity (＞60%); 12 hours if exposed to rain/fog. Flux absorbs moisture quickly, leading to hydrogen cracks—don’t use expired wire even if stored sealed.

A23: Adjust current/voltage to optimal range (stable arc, quiet pool); use anti-spatter spray on the base metal; ensure wire feeding is smooth (no jams); choose low-spatter wires (E71T-8 is better than E71T-11).

A24: Causes: insufficient heat input (low current/speed), rust/oil at the root, or small groove angle. Fix by: increasing current by 10-15%; cleaning the root thoroughly; using a 60° groove angle (for thick plates) to improve access.

A25: Yes, it’s ideal for repairs due to high efficiency and rust tolerance. For small defects: use 1.2mm wire, low current (150-180A) to avoid burning through. For large defects: multi-layer welding (clean slag between layers) to ensure strength.

A26: Slag sticks if cooling is too slow (slag fuses with weld) or flux is damp. Fix by: increasing travel speed (faster cooling); using a wire brush while the weld is warm (slag is brittle); ensuring wire is dry (damp flux changes slag properties).

A27: Weld from the center to both ends (reduces stress); use symmetrical welding (e.g., weld left and right of the beam alternately); skip weld (weld 50mm, skip 100mm, then fill) to avoid heat accumulation; finish with continuous weld to close gaps.

A28: Preheat base metal to 100-150℃ (raises cooling temperature); use low-hydrogen wire (E81T1-Ni1); avoid high current (prevents excessive heat input); post-weld wrap in insulation blankets (slow cooling to reduce stress).

A29: "T-8" indicates rutile flux (good slag detachability, low spatter) for all-position welding, suitable for structural parts. "T-11" indicates high-titania flux (tolerates rust, low cost) for flat/horizontal welding, ideal for rough welding.

A30: Bend a 300mm wire—dry wire bends smoothly; damp wire is brittle (may crack). Trial weld: damp wire produces excessive smoke, porous welds, or "pop" sounds (hydrogen escaping). Bake damp wire at 250℃ for 2h before use.

A31: Yes, but take precautions. Zinc evaporates at 907℃ (causes porosity and fumes). Use E71T-11 (flux absorbs zinc vapor); reduce heat input (low current + fast speed); ventilate well (zinc fumes are toxic); grind galvanized layer 5-10mm from the groove.

A32: Too much reinforcement: reduces fatigue strength. Control by: matching wire feed speed to travel speed (avoid over-filling); adjusting gun angle (10° forward tilt to spread filler); using a straight edge to check—reinforcement should be ≤3mm.

A33: Worn tips (enlarged aperture) cause unstable wire feeding and arc deviation, leading to uneven welds or undercut. Replace tips when: wire feeding is jerky; arc sparks are irregular; tip has visible wear (replace every 8-10 hours of use).

A34: Choose wires with corrosion-resistant elements, e.g., E81T1-Ni1 (nickel improves seawater resistance) or E91T1-K2 (chromium/molybdenum). Post-weld: remove slag and paint (or galvanize) to enhance corrosion resistance.

A35: Flux cored wire has a higher unit price but lower overall cost: it reduces pre-cleaning labor (rust tolerance), increases deposition efficiency (faster welding), and requires less skilled labor. For large projects, flux cored wire saves 15-20% in total costs.