Consumables Corner: Advancements in SAW
Q: What role does flux and wire play in submerged arc welding?
A: It is important to choose the right flux and wire combination for submerged arc welding (SAW) processes. This will allow you to gain efficiency while meeting your performance requirements.
Basic submerged arc welding uses a single wire and a DC power source. Twin-wire SAW uses two smaller-diameter wires with a single power source and feeder, which can increase deposition rates by 20 percent or more without significantly increasing heat input. It does this by pushing the current through the smaller cross-section area of wire to achieve greater current density.
SAW with negative-polarity DC can increase deposition rates by 20 percent to 30 percent; however, it risks shallow penetration and lack of fusion. Welding with AC provides a better deposition than positive-polarity DC and better penetration than negative-polarity DC. Square-wave AC output provides a more stable arc than conventional sine-wave AC.
Tandem SAW uses two wires that feed into the same molten puddle. Each wire has its own power source and feeder, doubling the deposition rate of single-wire SAW. It is possible to combine tandem welding with twin wires using a combination of DC positive/AC or AC/AC. Using 1,250-amp square-wave power supplied with tandem twin-wire SAW will provide the highest possible deposition rates.
All these processes seek to increase weld travel speed while decreasing the number of passes needed to complete a weld. High travel speed requires high amperage, while decreasing the number of passes requires greater heat input per pass. This puts high demand on the flux and wire. If the flux breaks down under high current, the weld can become ropy and slag inclusions may occur. At high heat input the mechanical properties of the base metal HAZ and weld metal can decrease. The best flux choice is one that is designed for welding at these high heats and travel speeds and offers easy slag removal and low bead profile. These fluxes are currently used in wind tower, pipe mill, and other welding-intensive industries.
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