An Introduction to metal-cored wire
6 questions to ask
Metal-cored wire is a tubular electrode that consists of a metal sheath and a core of various powdered materials, primarily iron. The core of metal-cored wire contributes almost entirely to the deposited weld metal.
Following are six important questions to ask before you decide whether metal-cored wire is right for you.
1. What applications benefit from metal-cored wire?
Good candidates include:
- Single-pass, solid-wire welds more than 3 inches long.
- Solid wire in the flat and horizontal positions where spray transfer is being used.
- Many gas-shielded, flux-cored, and some submerged-arc applications.
- Multiple-pass robotic and automatic welding.
- Other applications determined by weld cost calculations or weld quality issues (compensating for poor fit-up, bead appearance, burn-through).
2. Why do welders use metal-cored wire?
For the right applications, switching to metal-cored wire can save $100 to $200 for every 100 pounds of weld metal deposited. Typical benefits include:
- High deposition rates and travel speeds.
- No slag and almost no spatter.
- Little to no postweld cleanup or cleaning between passes.
- Excellent side-wall fusion and root penetration.
- Ability to bridge part gaps without burn-through.
- Ability to weld thin materials at high amperages without burn-through.
- Ability to use next larger electrode diameter.
- Capability to weld out-of-position with pulsed spray or short-circuit transfer.
- Compliance with the American Bureau of Shipping (ABS), Det Norsk Veritas (DNV) offshore standards, the American Petroleum Institute (API), the Lloyds Register of Shipping (LRS), American National Standards Institute (ANSI), and American Welding Society (AWS D1.1) standards.
3. How does metal-cored wire differ from solid wire?
Solid wire's entire cross section carries the welding current, and the molten droplets are large. Metal-cored wire's current is concentrated on the outside sheet; the metal powders inside are less conductive because of their granular nature. Focusing current on the wire's outer diameter creates a broader, bowl-shaped arc cone. It also can create finer molten droplets and a less turbulent weld pool.
4. Does metal-cored wire provide good fusion?
Metal-cored wire's spray transfer pattern can bridge gaps and help eliminate cold lap. Even if an operator doesn't point the arc directly at the joint, or if parts in an automated application have less than optimal fit-up, metal-cored wire might be able to compensate. Its broader, more tolerant arc still could catch the toe of the joint and make an acceptable weld.
5. Do I have to worry about burn-through with metal-cored wire?
Metal-cored wire can weld thin materials without burn-through because it lacks a "deep finger" of penetration. Also, spray transfer requires less amperage with metal-cored wire. On thinner metals (1/8 in. or less), metal-cored wire may let you switch from short-circuit to spray transfer to improve travel speeds, bead appearance, and bead quality.
6. Do metal-cored wires cost more than solid wires and require expensive gas mixes?
Yes, but you also should look beyond the cost of consumables. Filler metals make up 10 percent of a weld's cost and gas 3 percent. Labor accounts for 85 percent of welding costs. Any significant productivity increase from using metal-cored wire can outweigh an increase in consumables cost.
Steve Barhorst is tubular wire marketing manager for ITW Hobart Brothers Co., 400 Trade Square East, Troy, OH 45373, 800-346-2529, fax 937-332-5808, www.hobartbrothers.com. ITW Hobart Brothers Co. is a manufacturer of welding filler metals.
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