Figure 8-3. - Power supply unit specifically designed for gas tungsten-arc welding.

tungsten electrode. The arc, the electrode, and the weld zone are surrounded by an inert gas (usually either helium or argon or a mixture of the two) that displaces the air and eliminates the possibility of weld contamination by the oxygen and nitrogen present in the atmosphere. The tungsten electrode has a high melting point that makes it virtually nonconsumable.

Specific advantages of gas tungsten-arc welding include the following:

Welding can be done in all positions.

The weld is usually equal to the base metal in composition.

Flux is not used; therefore, finished welds do not require cleaning of corrosive residue.

Smoke or fumes are not present to obscure vision; therefore, you can easily see the welding process.

Distortion of the base metal is minimal because the heat is concentrated in a small area.

No splatter is produced because metal is not transferred across the arc.

GTA WELDING EQUIPMENT AND SUPPLIES

The equipment and supplies required for gas tungsten-arc welding consist of an electric power unit, shielding gas, a pressure-reducing regulator and flow- meter, an electrode holder (commonly called a torch), nonconsumable tungsten electrodes, filler rods, a supply of cooling water (when required), and personal protective gear.

Electric Power Unit

Most welding power sources can provide the current needed for GTA welding. The common welding machines, whether alternating current (at) or direct current (de), have their advantages in certain welding applications; however, they can be cumbersome and their hose and cable connections can create difficulties. Because of this, specially designed machines with all the necessary controls are available for gas tungsten-arc welding (fig. 8-3).

GTA power units are equipped with solenoid valves that turn the flow of shielding gas and cooling water on and off. They are also equipped with a hand- or foot- operated remote-control switch that turns the water and gas on and off. Some of these remote-control devices