7018 welding rods (classified as E7018 under AWS A5.1 standards) are renowned for their high strength (70,000 psi tensile strength) and low-hydrogen properties, making them ideal for structural steel welding, heavy machinery, and critical joints. However, their low-hydrogen flux coating demands precise handling to avoid defects like porosity or cold cracking. Below is a detailed guide to mastering 7018 welding.
1. Prepare the 7018 Rods: Moisture is the Enemy
7018 rods are "low-hydrogen" (≤0.4% hydrogen), but their flux coating absorbs moisture quickly from air, humidity, or improper storage. Moisture introduces hydrogen into the weld, causing cold cracking-especially in thick steel or high-carbon alloys.
Baking: Always bake new or exposed 7018 rods before use.
Temperature: 500–600°F (260–315°C) for 1–2 hours .
Purpose: Evaporates trapped moisture in the flux.
Storage: After baking, store rods in a rod oven set to 250–300°F (120–150°C) to prevent reabsorption of moisture. Never leave rods exposed to air for more than 1 hour-re-bake if they sit out longer .
Handling: Use clean, dry gloves to handle rods; avoid touching the flux with bare hands (skin oils contaminate the weld) .
2. Prepare the Base Metal: Cleanliness Ensures Fusion
7018 requires a clean base metal to achieve strong, defect-free welds. Contaminants like rust, paint, oil, or mill scale block fusion and trap hydrogen.
Cleaning Steps:
Use a wire brush, grinder, or sandblaster to remove rust, scale, or paint from the weld area (at least 1–2 inches on both sides of the joint) .
Wipe the surface with a solvent (acetone or denatured alcohol) to remove oils or greases.
For thick steel (≥1/2 inch), preheat the base metal to 250–400°F (120–200°C) to reduce cooling rates and prevent cold cracking .
3. Set Up Your Welding Machine: DC Reverse Polarity is Critical
7018 performs best with DC reverse polarity (DCEP: Direct Current Electrode Positive). This polarity concentrates heat at the electrode tip, ensuring the flux melts evenly, forms a protective slag, and deposits filler metal smoothly .
Machine Settings:Current: Adjust based on rod diameter and welding position (flat, vertical, overhead).
1/8 inch (3.2mm) rod: 90–130 amps (flat); 80–110 amps (vertical/overhead) .
5/32 inch (4mm) rod: 140–180 amps (flat); 120–150 amps (vertical/overhead) .
Too low: Poor penetration, "cold" welds with incomplete fusion.
Too high: Burn-through, spatter, or flux breakdown (exposing the weld to hydrogen).
Arc Voltage: Typically 22–28 volts (varies with machine type). A stable arc sounds like a "crisp sizzle"-not a harsh pop or buzz .
4. Welding Technique: Control the Arc and Travel Speed
7018's flux forms a thick slag layer that protects the weld pool as it cools. Mastering arc length, travel speed, and rod angle is key to a smooth, strong bead.
Arc Length: Keep the arc short-about the same as the rod diameter (e.g., 1/8 inch arc for a 1/8 inch rod). A long arc causes:
Flux breakdown (loss of shielding).
Porosity (gas bubbles in the weld).
Uneven bead shape .
Rod Angle: Tilt the rod 5–15° toward the direction of travel (a "push" angle) for flat or horizontal welds. For vertical uphill welds, tilt slightly upward (10–15°) to control the molten pool .
Travel Speed: Move steadily to avoid:
Too slow: Overheating, excessive slag, or "piling up" metal (weakening the joint).
Too fast: Shallow penetration, narrow bead, or incomplete fusion.
Aim for a bead width 2–3 times the rod diameter (e.g., 1/4–3/8 inch wide for a 1/8 inch rod) .
Slag Removal: After each pass, let the weld cool slightly, then chip away slag with a hammer or chisel. Slag left on the metal can cause "slag inclusions" in subsequent passes .
5. Welding in Different Positions: Adjust for Gravity
7018 is an "all-position" rod (the "1" in 7018 indicates this), but techniques vary by position:
Flat Welding: Easiest position. Use a slight push angle, steady speed, and medium amperage for a flat, even bead.
Vertical Uphill: Critical for structural welds. Lower amperage (10–15% less than flat) to control the molten pool. Use a "weave" pattern (small side-to-side motions) to build up the bead without sagging .
Overhead Welding: Most challenging. Keep amperage low to prevent the molten pool from dripping. Use a tight arc and slow, steady travel-focus on short, controlled rod movements .
6. Post-Weld Checks: Inspect for Defects
After welding, inspect the bead for:
Porosity: Small holes (sign of moisture, long arc, or dirty metal).
Cold Cracks: Fine, jagged cracks (often caused by hydrogen, rapid cooling, or underheating).
Incomplete Fusion: Gaps between the weld and base metal (from low amperage or fast travel speed).
Slag Inclusions: Dark, irregular spots (from failing to remove slag between passes) .
Safety First
Wear a welding helmet with a shade 10–12 lens to protect eyes from UV/IR radiation.
Use flame-resistant gloves, a leather jacket, and pants to shield from sparks.
Work in a well-ventilated area-7018 flux emits fumes (including manganese) that can irritate lungs .
Final Tips
Always use fresh, properly stored 7018 rods-moisture ruins their low-hydrogen benefit.
Practice on scrap steel first to dial in amperage and travel speed.
For critical welds (e.g., bridges, pressure vessels), follow AWS D1.1 standards and perform non-destructive testing (NDT) like X-rays or ultrasonic checks .
By following these steps, you'll leverage 7018's strength and reliability to create welds that meet structural standards and withstand heavy loads. Remember: preparation (rod baking, clean metal) and control (arc length, speed) are the keys to success.
