On one of my early stick welding jobs, I was running beads on mild steel and couldn’t figure out why the arc kept spattering and the weld looked rough. I didn’t realize that flux was doing far more than just coating the rod—it was protecting the molten puddle from oxygen, stabilizing the arc, and even adding helpful alloys to the weld.
Whether you’re burning 6011 rods on rusty farm equipment, comparing MIG vs TIG for stainless welding, or adjusting heat for different metal thicknesses, understanding flux can make or break your weld quality. It’s not just about laying down a cleaner bead—it’s about strength, safety, and saving time on joint prep. In this guide, we’ll dig into what flux really does and why it’s a game-changer in real-world welding.
Image by red-d-arc
Why Flux Matters in Welding
Welds are only as good as their integrity. A weak weld can crack, leak, or fail, leading to costly repairs, safety hazards, or scrapped projects. I’ve seen a rookie welder skip flux-cored wire on a windy outdoor job, only to end up with porous, brittle welds that failed inspection. Flux protects the weld pool from oxygen, nitrogen, and other atmospheric nasties that cause defects like porosity or slag inclusions.
It also improves arc stability, controls the weld pool’s flow, and even adds alloying elements to strengthen the weld. Whether you’re welding mild steel in a shop or stainless in the field, flux is critical for quality, safety, and efficiency.
What Is Flux and How Does It Work?
Flux is a chemical compound used in many welding processes to protect the molten weld pool. It’s found in stick electrodes, flux-cored wires, and submerged arc welding (SAW). When heated, flux melts and forms a protective slag or gas shield that keeps air out of the weld pool, preventing oxidation and contamination.
How Flux Functions
Picture this: you’re welding a steel plate with a stick electrode like E7018. As the electrode burns, the flux coating melts, releasing gases like carbon dioxide that push away air. The molten flux also forms a slag layer over the weld bead, acting like a blanket to shield it as it cools.
This dual action—gas shield and slag—keeps your weld clean and strong. I’ve watched flux save welds on dirty steel in less-than-ideal conditions, like a dusty construction site. Without it, you’re fighting a losing battle against defects.
Types of Flux
- Stick Electrodes: The coating on rods like E6010 or E7018 contains flux. Each type has a specific formula for different applications (more on that later).
- Flux-Cored Wire: Used in flux-cored arc welding (FCAW), these wires have flux inside the core, eliminating the need for external gas in some cases.
- Submerged Arc Welding (SAW): Granular flux is poured over the weld area, melting to form a protective layer. Common in heavy industrial welding.
- Flux in MIG/TIG: While MIG and TIG often use inert gas for shielding, some processes (like flux-cored MIG) rely on flux for extra protection.
Why Use Flux in Welding?
Flux isn’t just a nice-to-have; it’s a game-changer. Here’s why it’s essential, based on my time in the shop and field.
Shields the Weld Pool
Oxygen and nitrogen in the air are weld killers. They cause porosity (tiny gas holes) and weaken the weld. Flux creates a barrier—either as a gas cloud or slag—that keeps these elements out. I’ve welded in windy conditions where flux-cored wire saved the day by providing its own shield, no gas bottle needed.
Stabilizes the Arc
A shaky arc makes for ugly welds and poor penetration. Flux helps maintain a consistent arc, especially in stick welding or FCAW. For example, E6010 electrodes have a cellulose-based flux that gives a snappy, digging arc—perfect for pipe welding. I’ve used it to burn through rust and still get a solid bead.
Improves Weld Quality
Flux can add alloying elements to the weld, like manganese or silicon, to boost strength and toughness. It also controls the weld pool’s flow, preventing it from running or sagging. On a structural job, I switched to E7018 for its low-hydrogen flux to avoid cracking on high-strength steel—worked like a charm.
Cleans the Weld
Some fluxes are designed to “clean” by floating impurities like oxides or dirt to the surface, where they become part of the slag. This is a lifesaver when welding dirty or rusty steel, though I always preach cleaning the metal first for best results.
Common Welding Processes That Use Flux
Not all welding processes rely on flux, but the ones that do are workhorses in the industry. Let’s break down the main ones and how flux plays a role.
Stick Welding (SMAW)
Shielded Metal Arc Welding (SMAW), or stick welding, is where flux shines. The electrode’s coating provides both shielding gas and slag. Common rods include:
- E6010: Cellulose flux for deep penetration, great for pipe or root passes.
- E7018: Low-hydrogen flux for strong, crack-resistant welds on structural steel.
- E6013: General-purpose flux for smooth beads on thin materials.
I’ve used E7018 on countless jobs for its versatility, but it needs dry storage to prevent moisture pickup, which can ruin the flux’s low-hydrogen properties.
Flux-Cored Arc Welding (FCAW)
FCAW uses a wire with flux inside, fed through a MIG welder. It comes in two flavors:
- Self-Shielded FCAW: The flux core generates its own shielding gas, ideal for outdoor work. I’ve used it on farm repairs where dragging a gas bottle wasn’t an option.
- Gas-Shielded FCAW: Uses external gas (like CO2) plus flux for extra protection, common in shops for thicker materials.
Submerged Arc Welding (SAW)
SAW buries the weld under a pile of granular flux, which melts to form a thick slag layer. It’s used for heavy plate welding, like shipbuilding or pressure vessels. I’ve seen SAW in action on massive structural beams—super efficient but not practical for small shops.
Photo by grecianmagnesite
Choosing the Right Flux for Your Weld
Picking the right flux depends on your material, welding process, and job conditions. Here’s a quick guide based on my experience.
Material Type
- Mild Steel: E6013 or E7018 for stick, or E71T-11 flux-cored wire for FCAW. These handle general-purpose jobs well.
- Stainless Steel: Use low-hydrogen electrodes like E308L-16 or stainless flux-cored wire to prevent corrosion and cracking.
- High-Strength Steel: E7018 or E70T-5 flux-cored wire to avoid hydrogen-induced cracking.
Job Conditions
- Outdoor Welding: Self-shielded FCAW or E6010 stick electrodes. Their flux handles wind and dirty surfaces better than gas-shielded processes.
- Shop Welding: Gas-shielded FCAW or E7018 for cleaner, controlled environments.
- Thick Materials: SAW or E7018 for deep penetration and strong slag protection.
Code Requirements
If you’re welding to AWS D1.1 (structural steel) or ASME Section IX (pressure vessels), check the code for flux requirements. Low-hydrogen fluxes like E7018 are often mandatory to prevent cracking. I’ve had to switch rods mid-job to meet code—always read the specs first.
Comparison Table: Common Flux Types
| Electrode/Wire | Flux Type | Best For | Pros | Cons |
|---|---|---|---|---|
| E6010 (Stick) | Cellulose | Pipe, root passes | Deep penetration | Rough bead appearance |
| E7018 (Stick) | Low-Hydrogen | Structural steel | Crack-resistant | Needs dry storage |
| E6013 (Stick) | Rutile | Thin materials | Smooth beads | Limited penetration |
| E71T-11 (FCAW) | Self-Shielded | Outdoor welding | No gas needed | More spatter |
| E70T-5 (FCAW) | Gas-Shielded | Thick plates | High deposition | Requires gas |
Step-by-Step Guide to Welding with Flux
Let’s walk through how to weld with flux, using stick welding with E7018 as an example. This is based on countless hours I’ve spent in the shop.
Step 1: Prep the Metal
Clean the base metal with a wire brush or grinder to remove rust, oil, or dirt. Flux can handle some impurities, but don’t rely on it. I once skipped cleaning on a “quick job” and ended up with porosity—lesson learned.
Step 2: Select and Store Electrodes
Choose E7018 for structural or high-strength steel. Store rods in a heated oven (250°F) to keep flux dry. Wet flux causes hydrogen cracking, and I’ve seen welds fail inspection because of it.
Step 3: Set Up Your Welder
For a 1/8-inch E7018 rod on 1/4-inch steel:
- Amperage: 90-120 amps (DC+ polarity).
- Arc Length: Short, about 1/8 inch, to maintain arc stability.
- Travel Speed: Steady, to avoid slag inclusions.
Test settings on scrap metal first. I always dial in my machine on a practice piece to avoid messing up the real weld.
Step 4: Strike the Arc and Weld
Strike the arc by tapping or scratching the rod on the metal. Hold a consistent angle (10-15° from vertical) and move steadily. The flux will form a slag layer as you weld—don’t rush, or you’ll trap slag in the bead.
Step 5: Remove Slag
Once the weld cools, chip off the slag with a chipping hammer and wire brush. Inspect the bead for smoothness and uniformity. I’ve caught tiny slag inclusions by taking my time here—don’t skip it.
Step 6: Inspect the Weld
Use visual inspection or NDT (like UT or RT) to check for defects. For DIYers, a magnifying glass and good lighting can spot surface issues. Pros, follow your project’s code for formal inspection.
Practical Tips and Common Mistakes
Here’s some hard-earned know-how to make your flux welds shine.
Tips for Success
- Dry Electrodes: Keep stick rods in a rod oven or sealed container. Moisture in flux is a weld killer.
- Angle and Speed: Maintain a consistent electrode angle and travel speed. Too fast, and you’ll get slag inclusions; too slow, and the bead sags.
- Clean Between Passes: For multi-pass welds, chip and brush slag thoroughly between passes. I’ve seen multi-pass welds fail because of trapped slag.
- Machine Settings: Start with manufacturer-recommended amps and adjust based on your weld’s look. For FCAW, tweak wire feed speed for smooth feeding.
Common Mistakes and Fixes
- Mistake: Wet flux on E7018 rods. Fix: Store rods properly and bake them at 250°F if they’ve been exposed.
- Mistake: Poor slag removal. Fix: Use a chipping hammer and brush, and check for inclusions before the next pass.
- Mistake: Wrong flux for the job. Fix: Match flux to material and conditions (e.g., E6010 for dirty steel, E7018 for clean structural work).
- Mistake: Inconsistent arc length. Fix: Practice a short, steady arc to avoid porosity or burn-through.
Safety Considerations When Using Flux
Flux makes welding safer by reducing spatter and stabilizing the arc, but you still need to play it smart.
- Ventilation: Flux creates fumes, especially in FCAW. Use a fume extractor or weld in a well-ventilated area. I’ve felt woozy from poor ventilation—don’t skip this.
- Eye Protection: The bright arc and flying slag demand a quality welding helmet (shade 10-12 for stick/FCAW). I’ve seen guys try to “tough it out” with cheap shields—bad idea.
- Gloves and Clothing: Wear flame-resistant gloves and a jacket. Molten slag can burn through regular clothes in seconds.
- Slag Removal: Let the weld cool before chipping slag to avoid burns or flying debris. I’ve got a scar from a hot slag chip—learn from my mistake.
Flux in Action: Real-World Examples
Let’s see how flux plays out in practical scenarios I’ve encountered.
Scenario 1: DIY Trailer Repair
You’re fixing a cracked trailer frame in your garage. You grab a 110V stick welder and E6013 rods for their easy-to-use flux and smooth beads. Clean the metal, set 80-100 amps, and weld with a steady drag. The flux shields the weld from your drafty shop, giving you a strong repair.
Scenario 2: Structural Steel on a Job Site
You’re welding beams for a building under AWS D1.1. E7018 rods are your go-to for their low-hydrogen flux, preventing cracks on A36 steel. You store rods in a heated oven, set your machine to 110 amps, and weld in a controlled shop. The flux ensures clean, code-compliant welds.
Scenario 3: Pipeline Welding
You’re on a pipeline job with API 1104 specs. E6010 rods with cellulose flux dig through rust and provide deep penetration for root passes. You follow with E7018 for filler passes. The flux handles outdoor conditions, and your welds pass RT inspection.
Conclusion
You’re now ready to harness the power of flux in your welding projects. What is the purpose of flux in welding? It shields the weld pool, stabilizes the arc, improves bead quality, and cleans impurities, ensuring strong, defect-free welds. Whether you’re a DIYer, hobbyist, or pro, choosing the right flux—E7018 for structural steel, E6010 for pipe, or flux-cored wire for outdoor work—sets you up for success. Prep your metal, dial in your settings, and weld with confidence knowing flux has your back.
Pro Tip: Always test your setup on scrap metal first—it saves time and prevents costly rework. Now, fire up that welder and lay down some beads you can be proud of!
FAQ
What does flux do in welding?
Flux protects the molten weld pool from air contamination, stabilizes the arc, and forms a slag layer to shield the cooling weld. It also cleans impurities and can add alloys to strengthen the weld.
Can you weld without flux?
Yes, but only with processes like TIG or gas-shielded MIG, which use inert gas for shielding. Without flux or gas, welds are prone to porosity and weakness due to atmospheric contamination.
What’s the best flux for outdoor welding?
Self-shielded flux-cored wire (like E71T-11) or E6010 stick electrodes are best for outdoor welding. Their flux generates a strong shield, handling wind and dirty surfaces without needing external gas.
How do I store flux-coated electrodes?
Store stick electrodes like E7018 in a heated rod oven (250°F) or sealed container to prevent moisture pickup. Wet flux can cause hydrogen cracking, ruining your weld.
Why is slag removal important?
Slag protects the weld as it cools but must be removed to inspect the bead and prevent inclusions in multi-pass welds. Chip and brush thoroughly to ensure a clean, strong weld.
