Drafty conditions are bad for welders and their GTAW arcs.

Richard Harris, consulting editor

According to CK Worldwide, its Gas Saver front-end kit lets welders save up to 40% of shieldinggas consumption, while improving shielding-gas coverage.

Controlling air movement is critical with GTAW because the argon shielding-gas is heavier than air so it can quickly drift away from the arc. Gardner and his crew used tarps to protect their work from the breeze along the Lake Erie shore.

After plugging in his portable Lincoln Electric V200T inverter power source to a 220-V line at the dock, Gardner sets the argon shielding-gas at 15 ft 3 /hr, which maintains an even shielding around the arc despite the slight lake breeze.

Gardner matched a 316 stainless steel filler metal to repair the Type 316 stainless steel, thin-wall stanchion rails. He set the power source at 100 amp, but most of the welds were well-under that.

Gardner's tool kit for GTAW includes a number of cups, or nozzles, that direct the shielding gas for specific applications.

The V200T inverter power source from Lincoln Electric is portable, even fitting into some car trunks.

Meticulous welders know to stay out of drafts because windy conditions can make shielding gas drift, leading to porosity and metallurgically poor weld quality. Just ask Bob Gardner, who tests welding products for WELDING DESIGN & FABRICATION. He selected torch tips, tarps, and tape to minimize the impact of wind on a recent job repairing a power boat's stainless steel railings.

The 34-ft craft, built in 1985, had broken welds where the rail stanchions had been fusion-welded to a base plate bolted to the deck. Most broken welds were on the left (port) side of the boat, where passengers boarded and exited via the gangplank. As people crossed, they put pressure on the railing, and, eventually, some welds cracked.

Gardner, who holds a certified welding instructor certificate from the American Welding Society, had to make the weld repairs in place. The bolts holding the plates were fastened with nuts on the underside of the deck. But, access to the nuts required removing cabinets and paneling, an expensive solution that could potentially damage woodwork.

"I would have preferred to lift the rail and make the repair weld from the bottom of the plate for a safer repair job and more eye-appealing finish," says Gardner, owner of a fabrication shop near Cleveland.

Because this wasn't possible, he chose the gas tungsten arc welding (GTAW) process because it gave him the accuracy and delicate touch needed to deal with the poor fitup caused by welding in place and using a thin material. Also, with GTAW, he could make cosmetically pleasing welds without sparks that might burn the deck or start a fire.

Unlike weld processes using self-shielding weld metal or flux, many other GTAW applications such as track-side repairs for motorsports or offshore power boats require protection from the wind.

Beware of oxidation
The GTAW process, according to Jefferson's Welding Encyclopedia, produces an electric arc as current passes through a conductive, ionized shielding gas feeding through the torch. The arc, which travels between the tip of the electrode and the work, generates heat to melt the base metal. Once a welder establishes the weld pool, he moves the torch along the joint and the arc progressively melts the faying surfaces. If he needs filler metal, he usually adds it to the leading edge of the weld pool to fill the joint.

Shielding gas (argon or helium or a mix of the two, and argon and hydrogen for 300 series stainless steel) is a protective gas that helps prevent or reduce atmospheric contamination of the molten weld metal. Some procedures call for a backup purge gas to protect the underside of the weld and its adjacent base metal surfaces from oxidation during welding.

At the molten temperature, most metals exhibit a strong tendency to form oxides, and to a lesser extent, nitrides. Oxygen also reacts with carbon in molten steel to form carbon monoxide and carbon dioxide. These reactions may cause weld deficiencies, such as porosity and metallurgically poor weld quality.

In addition to this protection, shielding gas and flow rate also effect:

• Arc characteristics
• Penetration and weld bead profile
• Welding speed
• Undercutting tendency
• Weld-metal mechanical properties.

Sea gulls and hot water
"I matched a 316 stainless steel filler metal to repair the Type 316 stainless steel, thin-wall stanchion rails," states Gardner, "with the power source set at 100 amp, but most of the welds were well-under that amperage."

The prep was minimal: no joint prep and the stainless steel was clean, except for wiping off sea-gull droppings.

"I could only weld for short durations because the heat from the arc might damage the fiberglass deck and the rubber gasket under the plate. The gasket seals out water and reduces wear between the plate and the deck."

Still, the heat from the arc started the rubber on fire a few times. And water had seeped in some of the weld cracks so he had to watch for hot water geysers.

Gardner continues, "There is almost always a breeze along the Lake Erie shore. There was minimal wind that day, so my helpers and I used a tarp and taped it in place. As I moved to a new stanchion, we adjusted the tarp position so I could work around the plate."

Check the weather vane
Air-movement control is critical with GTAW because the argon shielding gas is heaver than air so a slight breeze can quickly remove the gas from the arc. Even a shop's slow-moving ceiling fan can disrupt the gas shielding.

When this happens, the welder sees a blue-gray discoloration and maybe a soot-like deposit near the weld joint and the arc is usually hard to start because the tungsten oxidizes.

"My tool kit for GTAW includes a number of cups, or nozzles, designed to direct the shielding gas for specific applications," says Gardner. Gas nozzles, or cups, fit into the head of torch, directing the shielding gas to the weld zone. Within the torch body, diffusers feed the gas to the nozzle.

"In this case I needed to reach the back side, which had an acute angle, so I used a number four cup ( ¹ /4 in. across the orifice face). It also worked for the other angles of the weld zones," says Gardner.

"Had the wind been stronger I would have tried a flow straightener lens. It has a mesh screen that takes out the turbulence of the gas stream. This turbulence can pick up air, creating oxidation on the weld bead."

Gardner says he picks the cup for the application — usually the amount of space to work in — and the conditions — inside with no breeze or out-side with some degree of wind.

This is critical when welding titanium, which is very reactive to oxygen in the arc. Here, welders typically use a cup that provides an elongated or trailing shielding to cover the weld until it cools to 400°F to 500°F, minimizing contamination.

Gardner's toolbox includes CK Worldwide's Gas Saver front-end kit. The kit saves up to 40% of shielding gas consumption while improving shielding-gas coverage. With better coverage, welders can extend the tungsten up to 6 the diameter of the electrode beyond the edge of the gas cup. (This is achieved in draft-free areas using argon gas.)

Gas lenses ensure a laminar flow of shielding gas. (A laminar flow is a streamline flow in a viscous fluid near solid boundaries.) The lenses contain a porous barrier diffuser and fit inside the gas nozzle and around the electrode or collet. The lens lets operators weld with the nozzle one inch or more from the work, improving their view of the weld pool and allowing them to reach places with limited access, such as inside corners.

CK offers Alumina or Pyrex glass cups to retrofit its CK 2 and 3 series torches or competitive brand equivalents. Alumina cups handle high-temperature welding applications. The glass cups aid visibility for inside corners, inside pipes, and around tubing.

Gardner plugged his portable Lincoln Electric V200T inverter power source, which runs in single phase, to a 220-V line at the dock. He set the argon shielding gas at 15 ft ³ /hr, which helps maintain an even shielding around the arc despite the slight breeze. Too much pressure can pull air into the arc creating oxygen contamination.

"I used a CK rotary-amperage hand controller so I could vary the current, a real advantage for delicate welds," notes Gardner. "I can use the controller with either hand to weld when access is limited. This is a simple-touse controller, helping me do a good job."

In addition, the unit's remote amperage controls provide welding machine contactor on-off, activate gas and/or water solenoids, and handle current output control. The fingertip controls come in either rotary or linear-slide-potentiometer configurations.

For more information call Bob Gardner, Willoughby Tech, Willoughby, Ohio, phone: (440) 946-7085, or CK Worldwide Inc., Auburn, Wash., phone: (800) 426-0877 or (253) 854-5820; fax: (800) 327-5038 or (253) 939-1746, e-mail: ckworldwide.com.