2% Thoriated (color code: red)
Preferred for their longevity and ease of use, 2% thoriated tungsten electrodes are the most commonly used electrodes today. They contain a minimum of 97.30% tungsten and 1.70% to 2.20% thorium, and they have an AWS classification of EWTh-2.

These electrodes offer good arc starts and provide a higher current-carrying capacity than many other types. 2% thoriated tungsten also operates far below its melting temperature, which results in a considerably lower rate of consumption, minimizes arc wandering and lessens instances of weld contamination.

These electrodes can be used for AC welding, and they are exceptional for DC electrode negative (straight polarity) on carbon and stainless steel, nickel and titanium applications.

During manufacturing, thorium is evenly dispersed throughout the electrode. This evenness allows the electrode to maintain a sharpened edge — the ideal electrode shape for welding thin steel. Sharpening the electrode’s point, however, should be done with great care. Thoriated tungsten contains low levels of radioactivity. Therefore, operators must always follow manufacture’s warnings, instructions, and the MSDS (Material Safety Data Sheet) for its use.

Proper tungsten preparation
There are three main ways to prepare tungsten electrodes for welding — balled, pointed or truncated — each of which depends on the type of tungsten electrode you choose to use. For example, pure tungsten generally requires a balled tip and works well when using the AC process on sine wave and conventional squarewave TIG welders.

Figure 1: Typical current ranges for electrodes with argon shielding.
Click to enlarge

To ball the end of the tungsten, apply the AC amperage recommended for a given electrode diameter (see Figure 1); the ball on the end of the tungsten will form itself. As a rule of thumb, the diameter of the balled end should not exceed 1.5 times the diameter of the electrode, as having a larger sphere at the tip of the electrode can reduce arc stability and/or can fall off and contaminate the weld. As an example, a 1/8-in. electrode should form a 3/16-in. diameter end maximum.

You should use a pointed and/or truncated tip (for pure tungsten, ceriated, lanthanated and thoriated types) for inverter AC and DC welding processes, and also when welding with lower currents on thinner materials (those ranging from .005- to .040-in). A pointed tungsten allows the welding current to transfer in a focused arc and helps prevent thinner metals, such as aluminum, from becoming distorted. As a note, using pointed tungsten for higher-current applications is not recommended, as the higher current can blow off the tip of the tungsten and cause weld puddle contamination.

Figure 2: Preparing tungsten for DC electrode negative welding and AC with wave-shaping power sources.

To grind the tungsten to a point, use a grinding wheel specially designated for tungsten grinding, to help prevent contamination. A grinding wheel made of borazon or diamond works well to resist tungsten’s hardness. Note: iIf you are grinding thoriated tungsten, make certain you control and collect the dust, have an adequate ventilation system at the grinding station, and follow manufacture’s warnings, instructions, and MSDS.

Grind the tungsten straight on the wheel (not at a 90-degree angle) to ensure that the grind marks run the length of the electrode. Doing so reduces ridges on the tungsten that can lead to arc wandering or melt into the weld puddle. Grind the taper on the tungsten to a distance of no more than 2.5 times the electrode diameter (for example, with a 1/8-in. electrode you would grind a surface 1/4 to 5/16-in. long). Grinding the tungsten to a taper eases arc starting and creates a more focused arc for better welding performance.

For higher-current applications, grind your tungsten to a truncated tip by first grinding the tungsten to a taper (as explained above) and then grinding a 0.010- to 0.030-in. flat land on the end of the tungsten. This flat land helps prevent the tungsten from being transferred across the arc and/or from balling.

In any application, the type and shape of tungsten you use helps to determine the arc quality and welding performance you will achieve. Each of the five types of tungsten discussed here brings with it distinct advantages and disadvantages. That’s why, regardless of type of material you are TIG welding or whether you are using an AC or DC process, it is always important to choose your tungsten carefully for each application. Doing so can maximize your TIG welding success and is one of the best defenses against contamination and rework.

Joshua Sprinkle is a regional sales manager for Weldcraft, a full-spectrum supplier of TIG welding products and accessories.