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Fought & Company’s 340,000 sq ft facility in Tigard, OR is the birthplace of many recognizable structural steel and bridge projects in the Pacific Northwest. Founded in 1949, Fought is responsible for portions of the retractable roof on Safeco Field in Seattle, a 120,000 sq ft steel and glass canopy at Portland International Airport, and over 12,000 tons of steel bridges on I-15 in Salt Lake City, UT.

Fought relies on automatic submerged arc welding (or sub arc) to fabricate 90 percent of each bridge that comes through its facility. Sub arc, like all welding processes, joins metals by fusion. Sub arc differs, however, because its shielding is provided by a granular flux material.

Fought has traditionally performed this process with a solid electrode (AWS A5.17, classification: EM12K), yet recently explored switching to Tri-Mark’s Metalloy EM13K-S (AWS A5.17, classification: EC1) composite metal-cored electrode in an effort to increase productivity without impacting key quality elements of the weld. That exploration led to a complete wire changeover on the sub arc process in which weld travel speed increased 40 percent.

“We’ve gone from running a single pass, 5/16 in fillet weld with a travel speed of 12 ipm to running that single pass 5/16 in fillet weld anywhere from 16-17 ipm,” says Steve Fugate, quality assurance manager, Fought & Company. “That was unachievable with the solid electrodes without getting bead profile problems or undercutting at the top toe of the fillet weld.”

BUILDING A BETTER BRIDGE
Fought fabricates each bridge in its yard then disassembles it for shipping to its final erection site. Each full penetration weld undergoes volumetric testing (either x-ray or ultrasonic) to ensure integrity. Projects currently in Fought’s yard include the new Sixth Avenue rail bridge in Denver and the Nisqually River trestle for Tacoma, WA.

The majority of bridge girder welds, such as the web to the flange, are welded with automatic sub arc. Automatic welding eliminates starts and stops over the course of a weld, thus eliminating potential sources of discontinuities and weld failure. Automatic sub arc welding also offers a high deposition rate and requires all welds to be performed in the flat or horizontal position.

“Sub arc offers us high deposition and extremely good mechanical properties,” notes Fugate. “And not having the welder wearing a hood as he welds for 140 feet is a big benefit (minimizing physical strain).”

Fought set out to increase its productivity without impacting key elements. Considerations for a new electrode included a need to increase speed and deposition while preventing top leg undercut on fillet welds and maintaining and/or improving the required impact properties (D1.5 Bridge Code) on full penetration welds. The company also tests to Zone 3 Charpy requirements to work on Alaska’s North Slope.

COMPOSITE METAL-CORED WIRE PREVENTS UNDERCUTTING FOR FOUGHT
In searching for a new electrode, one of Fought’s greatest concerns was preventing undercut in fillet welds. Undercutting is a groove melted into the base metal adjacent to the weld toe or weld root and left unfilled by weld metal.

Composite metal-cored electrodes, like Metalloy EM13K-S, have better starting characteristics and greater wetting action compared to solid electrodes. The new electrode also provides excellent arc characteristics, smaller molten droplet transfer and a wider weld projection area. This typically helps to bridge gaps better, but in Fought’s particular application it helps improve the fillet weld profile, thus eliminating undercutting.

Composite metal-cored electrodes also provide higher deposition rates compared to solid electrodes of equal size (assuming the same amperage, electrical stick-out and flux are applied). Since composite metal-cored electrodes are made using a steel sheath with alloying powders and materials inside, the current is primarily conducted through the outer sheath. This results in higher burn-off rates and translates into the potential for increased deposition rates, typically resulting in faster travel speeds.

Fought’s welding parameters went from 450 amps at 32 volts with its previous solid electrode to 550 amps at 34 volts with composite metal-cored Metalloy EM13K-S. “With our full penetration welds, we’ve gone from topping out at about 450 amps to 600 amps,” adds Fugate.

The material contained in the core of a composite metal-cored electrode includes deoxidizers and scavengers that scavenge the weld pool of mill scale and other impurities. Alloying materials are added to some electrodes to achieve additional properties in the finished weld, such as CVN toughness, post weld heat treatment, long term creep resistance and corrosion resistance.

“We run the dual head sub arc process for welding the stiffener to the web,” says Fugate. “We weld on both sides of that stiffener at the same time. On thinner members, where the fillets actually fully penetrate the web and overlap, we get porosity problems because you don’t get your traditional hot degassing from both sides, but we’re not finding that here with this electrode. So having these characteristics actually helps us, even on clean materials.”

Another area that concerned Fugate was how a composite metal-cored electrode would feed through the system. Past experience with a composite metal-cored electrode led Fugate to believe that these were soft and, when increased drive-roll tension was applied, the wire would crush or deform.

“We had nothing but feeding problems with other composite metal-cored electrodes we tried because the guys’ first thought is to increase the drive roll tension, and that can deform the wire and lead to feeding problems,” states Fugate. “We don’t have that problem with this electrode, and we’ve been running it for four or five months now.”

ELECTRODE CHANGE PROVES PRODUCTIVE
Fought & Company regularly has numerous bridge and structural steel projects being staged in its yard. The ability to process each project efficiently and send it into the field for erection is paramount to their success. The 40 percent increase in travel speed resulting from the transition to a composite metal-cored electrode is the definition of minimal effort/maximum reward.

“We had reached a certain level of expectation of where we would be if we stuck with the solid sub arc electrodes,” explained Fugate. “We reached a plateau in terms of deposition. Hobart brought in the composite metal-cored electrode and we found it to have spectacular properties. We worked with it and found that we could improve travel speed by 40 percent, which was a huge change over where we peaked with solid electrodes. And we could still keep the upper toe of the fillet leg undercut under control and get our desired properties at those high heat inputs. We’re in and out 40 percent faster at the start of a project, which is our traditional log jam.”

The new composite metal-cored electrode has made a believer out of Fugate and his staff of foremen and welders, who remained skeptical until shown just what an electrode change could do. “It’s a mind-boggling improvement,” says Fugate. “We like to make 10 percent changes. We’re happy with that. We’ve never had an improvement that has been this dramatic.”

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Fought & Company, Inc., 14255 SW 72nd Avenue, Tigard, OR 97224-8042, 503-639-3141, Fax: 503-620-3279, www.fought.org.

Tri-Mark, Hobart Brothers, 101 Trade Square, Troy, OH 45373, 937-332-4000, www.hobartbrothers.com .