Start with the basics: Understanding flux-cored wires

WWW.THEFABRICATOR.COM JANUARY 2008

January 15, 2008

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Arming yourself with basic information about flux-cored wires can help you decide if these consumables are right for your welding application. Available in gas-shielded and self-shielded, flux-cored wires require less skill to use than other filler metals and commonly are used for general fabrication, pressure vessels, petrochemical piping, and heavy-equipment manufacturing

Flux cored welding

By arming yourself with some basic knowledge, you can choose and use flux-cored wires for your own welding applications confidently.

Flux-cored arc welding (FCAW) wires certainly aren't new, but like any part of the welding process, understanding them can be confusing—without the right information. Becoming acquainted with some basics, including the most appropriate applications, general classifications and characteristics, and advantages and limitations, of flux-cored wires can yield significant results. With more knowledge you can choose and use flux-cored wires confidently for your own welding applications.

Flux-cored wires have been around since the 1950s and are available in two main versions: gas-shielded and self-shielded. Both types are composed of an outer sheath and are filled with flux, a compound that is a mixture of alloys and deoxidizers, the latter of which are necessary to protect the weld from contaminants.

As their name implies, gas-shielded flux-cored wires require an external shielding gas supply to protect the weld; self-shielded wires do not. The flux in self-shielded wires generates the shielding gas, which makes these wires highly portable and ideal for outdoor welding applications, such as structural steel, shipbuilding, and bridge construction. Common applications for gas-shielded flux-cored wires include general fabrication, pressure vessels, petrochemical piping, and heavy-equipment manufacturing.

Start at the Beginning

Gas-shielded and self-shielded flux-cored wires are available for flat/horizontal or all-position welding on base materials ranging from mild and low-alloy steel to stainless steel and special alloyed metals like chrome-moly. Flux-cored wires also are available for hardsurfacing new parts to protect them from impact and abrasion and for rebuilding old or worn-out parts. Note that hardsurfacing wires do not have a classification according to the American Welding Society (AWS), but all other gas- and self-shielded flux-cored wires do.

As an example, a gas-shielded flux-cored wire designed for welding mild steel has the AWS classification E70T-1C. In this classification:

  • E signifies electrode
  • 7 indicates tensile strength (here, 70,000 pounds per square inch [PSI])
  • 0 indicates flat and horizontal positions (1 would imply a wire has all-position welding capabilities)
  • T signifies a tubular (flux-cored) wire
  • 1 indicates the wire's usability and performance capabilities, including its operating parameters
  • C designates that the product is to be used with 100 percent CO2,shielding gas only

Gas-shielded flux-cored wires require either pure CO2, as in the previous example, or a mixture of argon/CO2,(indicated by an M at the end of the classification). Using CO2,offers good penetration, but may create more spatter and a less stable arc; a mixture of argon/CO2,provides good arc quality and lower spatter levels, but typically provides less penetration. Self-shielded flux-cored wires, again, do not require an external shielding gas supply. SeeFigure 1for other flux-cored wire classifications and operating specifications.

AWS
Classification

Shielding
Gas

Welding Position

Current &
Polarity

Minimum Tensile
Strength (PSI)

E70T-1C

CO2,

Flat/Horizontal

DCEP

70,000

E71T-1C/M

CO2,or Ar/CO2,

All

DCEP

70,000

E70T-2C/M

CO2,or Ar/CO2,

Flat/Horizontal

DCEP

70,000

E70T-3

None

Flat/Horizontal

DCEP

70,000

E70T-4

None

Flat/Horizontal

DCEP

70,000

E70T-5C/M

CO2,or Ar/CO2,

Flat/Horizontal

DCEP

70,000

E70T-7

None

Flat/Horizontal

DCEN

70,000

E71T-8

None

All

DCEN

70,000

E71T-9C/M

CO2,or Ar/CO2,

All

DCEP

70,000

E71T-11

None

All

DCEN

70,000

E71T-12C/M

CO2,or Ar/CO2,

All

DCEP

70,000

Figure 1

Other factors to consider about both gas-shielded and self-shielded flux-cored wires are their slag systems, which are classified as either rutile (T-1) or basic (T-5). A flux-cored wire with a rutile slag provides good weldability (low spatter, good arc quality, and decent weld puddle control), but its mechanical properties generally are not as good as those of a wire with a basic slag system.

Both gas-shielded and self-shielded flux-cored wires are available in multiple industry-standard diameters, including 0.035, 0.045, 0.052, 1/16, 5/64, and 3/32 inch, and operate at wire stick-out (also called electrical stick-out or electrode extension) ranging from to 1 in.

A few notes on wire diameter and stick-out: First, a larger-diameter wire does not necessarily mean a bigger, better weld or, more specifically, greater deposition (how much weld metal is placed in a given amount of time). Follow the manufacturer's recommendation for achieving the desired deposition for a given flux-cored wire and application. In many cases, a smaller-diameter wire can provide a better result.

Second, smaller-diameter wires typically require less stick-out, but the exact classification of the given flux-cored wire and the amperage at which it is used also determine stick-out length.

Flux-cored wires operate on constant-voltage (CV) DC power sources. Depending on the composition of the wire, the power source needs to be set for straight polarity (direct current electrode negative, or DCEN) or reverse polarity (direct current electrode positive, or DCEP). The composition of the wire also determines whether it can be used for single- or multiple-pass welding. It is best to consult with the filler metal manufacturer or distributor and read the packaging label or the wire's specification sheet for exact operating parameters.

You also can consult these resources for storage and handling directions. As a rule, however, gas-shielded and self-shielded flux-cored wires should be well-protected from moisture, as exposure to moisture can lead to poor welding performance and likely void the manufacturer's warranty.

Consider the Advantages and Disadvantages

Like any welding wire or welding process, flux-cored wires (both gas-shielded and self-shielded) have advantages and disadvantages. Advantages of both include higher deposition rates than solid wire or stick electrode, nice weld bead appearance, and the ability to weld thick materials.

Flux-cored wires also provide good mechanical properties, such as high-strength welds and strong impact values, and can be alloyed to match different base materials. These wires tend to be more tolerant of dirt and mill scale and can weld through such contaminants with less precleaning than other types of welding wires or stick electrodes. Note, however, that precleaning is always recommended as a best practice on any welding application. And, finally, flux-cored wires are relatively forgiving, meaning that they generally do not require operators to be as skilled or well-trained as those who weld with other types of filler metals.

The primary disadvantage of flux-cored wires is the post weld cleaning that is required. Both gas-shielded and self-shielded wires produce slag, which must be removed by chipping and/or wire brushing between weld passes or after the final pass is completed. In some cases, these wires also can be more expensive per pound than solid wires.

Bottom Line

Before choosing either a gas-shielded or self-shielded flux-cored wire for an application, consider some of this basic information. Or, when in doubt, remember that welding distributors and filler metal manufacturers always are good resources for helping make an informed decision about flux-cored wires or any other part of the welding process.



Keith Packard

Marketing Segment Manager - Oil and Gas
Hobart Brothers Co.
101 Trade Square East
Troy, OH 45373
Phone: 937-332-5435

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