The first buying question is whether your wire feeder will use shielding gas. ER70S-6 is a solid carbon-steel MIG (GMAW) wire that needs external shielding gas. E71T-GS is a self-shielded flux-cored wire intended for single-pass work on suitable thin mild steel. Both feed through a welding gun, but they are not drop-in substitutes: gas requirements, polarity, drive-roll setup and application limits differ. Start with the exact wire classification and your machine manual before choosing a spool.
ER70S-6 vs. E71T-GS at a glance
| Selection check | ER70S-6 solid MIG wire | E71T-GS self-shielded flux core |
|---|---|---|
| Process | GMAW / solid wire | FCAW-S / flux-cored wire |
| External shielding gas | Required; confirm approved gas with wire and machine instructions | Not required for this classification |
| Typical DC polarity | DCEP (electrode positive) | DCEN (electrode negative) for the Washington Alloy E71T-GS identified here |
| Common environment | Controlled shop setup, protected from drafts | Portable/outdoor work where a gas cylinder is impractical |
| Feed hardware | Normally suitable smooth V-groove rolls | Often knurled rolls appropriate for the selected tubular wire |
| Surface and cleanup | Clean base metal; minimal slag to remove | Still clean base metal; expect flux slag removal |
| Procedure limits | Depends on approved gas, diameter, position and WPS | Washington Alloy specifies single-pass, nonstructural applications |
These are purchasing checks, not a generic welding procedure. Washington Alloy lists ER70S-6 under AWS A5.18 and E71T-GS under AWS A5.20. Miller explains the underlying solid-wire versus flux-cored process differences.
1. Check shielding gas before changing wire
ER70S-6 is a solid electrode. Its weld pool relies on an external gas shield, commonly an approved argon/CO2 mixture or CO2 for suitable mild-steel applications. The gas cylinder, regulator, hose and machine gas-control arrangement must be in place and working. A wire carton marked ER70S-6 does not become "gasless" when a cylinder is disconnected. Wind can displace the shield and lead to porosity, so outdoor work may need effective wind protection or a different approved process.
Self-shielded E71T-GS uses flux within a tubular electrode to form its own shielding system. It does not need an external gas cylinder, which can simplify portable work. But flux-cored is not always gasless: other classifications, including some gas-shielded flux-cored products, explicitly require gas. Read the complete AWS classification and manufacturer data, not just the words "flux core" on a shopping page. See Miller’s flux-cored process guide.
2. Confirm the actual polarity terminals
For these specific wire families, the polarity change matters. ER70S-6 solid MIG commonly operates DCEP, while Washington Alloy identifies its E71T-GS as DCEN, also called straight polarity. Check the power-source diagram for the exact model and follow the wire data sheet. Some compact machines have polarity-change connections inside the wire-drive compartment; others require a different approved connection procedure. Never move leads or open equipment while energized.
Before treating spatter, sticking or erratic arc behavior as a bad spool, verify wire classification, selected process mode, voltage/wire-feed settings within the manufacturer's range, and the actual terminal configuration. A label reading "MIG/flux-core capable" does not prove the machine supports every diameter or polarity arrangement.
3. Match the drive rolls, contact tip and spool hub
Solid ER70S-6 wire generally feeds well with the correct smooth V-groove drive roll. The more easily deformed tubular construction of self-shielded wire often calls for the manufacturer's recommended knurled roll. Excessive feed tension can distort wire and cause jams; too little tension can cause slipping. Use the feeder's tension-adjustment procedure rather than guessing. The linked MIG drive-roll and wire-feed troubleshooting guide addresses related feeder checks.
Match contact-tip bore to wire diameter and inspect the liner and drive path for wear or contamination. Also verify spool hub/bore, outside diameter, weight capacity, spindle brake and machine clearance. A machine that accepts a 2-lb spool may not accept an 11-lb spool without an approved hub or spindle arrangement. Confirm the selling unit, too: two small spools and one large spool are not interchangeable package descriptions.
4. Choose the wire by the joint and procedure
ER70S-6 is commonly selected for shop fabrication of mild steel with controlled gas shielding. Washington Alloy describes its manganese/silicon deoxidizers for less-than-ideal fit-up, but this is not permission to weld over grease, paint or unknown coatings. Clean and prepare the joint as required. Final selection depends on material grade, thickness, welding position, joint design, procedure and inspection requirements—not the appealing promise in a retailer title.
Washington Alloy describes E71T-GS for single-pass, nonstructural work, including suitable thin sheet-metal repairs where external gas is inconvenient. Do not quietly substitute it into a structural, pressure-retaining or multipass job. A 70-class-looking designation does not make two products equally approved for the same service. For important work, the applicable WPS and manufacturer qualification data control.
5. Compare exact stocked Arc Weld options
For an ER70S-6 setup, the current catalog has .023-inch solid MIG wire on a 2-lb spool, .030-inch solid MIG wire on an 11-lb spool and .035-inch solid MIG wire on an 11-lb spool. These are different physical packages and wire diameters. Choose only after checking the machine output, drive rolls, contact tip, spool mounting, approved gas and the work's welding procedure.
For self-shielded work where E71T-GS is permitted, compare .030-inch E71T-GS supplied as a two-spool 2-lb package with .035-inch E71T-GS on an 11-lb spool. The first listing contains two small spools, not a single 4-lb roll. Confirm the exact package label and current availability before ordering. These live inventory examples are not a recommendation to change classification on an approved job.
6. A short troubleshooting checklist
- Porosity with solid wire: inspect gas supply, regulator/hose integrity, nozzle condition, drafts, base-metal cleanliness and the approved flow setup before changing wire.
- Excessive spatter or a harsh arc after switching: verify DCEP versus DCEN, selected mode, manufacturer operating range and work connection.
- Birdnesting or inconsistent feeding: confirm spool brake, correct drive-roll type/groove, pressure, liner and tip for the actual wire diameter.
- Unexpected slag: confirm whether the spool is tubular self-shielded flux core rather than solid wire; remove slag between operations as applicable.
- Unclear identification: stop and inspect the spool/carton and batch information. Do not identify a wire classification by color alone.
Safety and procedure boundaries
"No external gas" does not mean "no harmful fumes." Both processes require appropriate ventilation and a worksite hazard assessment, and flux-cored welding can introduce additional fume considerations. Coatings, especially zinc galvanizing, can create hazardous fumes when heated. Follow OSHA 29 CFR 1910.252 welding ventilation and protection requirements, applicable workplace rules and the manufacturer's safety data. Remove contaminants safely under the approved work plan; do not rely on a wire's tolerance of surface rust to make coated steel safe to weld.
Frequently asked questions
Can I use ER70S-6 without a gas bottle?
No. ER70S-6 is a gas-shielded solid MIG wire. Without the required shielding, the weld pool can become contaminated and the resulting weld may be defective.
Is every flux-cored wire DCEN?
No. Washington Alloy specifies DCEN for the E71T-GS considered here, but other flux-cored classifications can have different requirements. Check the exact wire sheet and machine manual rather than applying a blanket polarity rule.
Can E71T-GS replace ER70S-6 for a structural repair?
Not on the basis of their names. Washington Alloy describes its E71T-GS as a single-pass, nonstructural product. Critical joints require a suitable qualified procedure and an electrode that meets its applicable requirements.
Bottom line: choose the approved wire class for the work, then verify shielding method, polarity, drive rolls, diameter and spool fit. A correct wire-and-machine match prevents many apparent "bad spool" problems before they start.