To correctly prepare your tungsten electrode for welding you must first select the composition and diameter best suited for your application. Below listed are the 5 most commonly produced tungsten welding electrodes for TIG DC, TIG-AC, and Plasma welding:

PURE TUNGSTEN (EWP Classification)
(Green Stripe)

2% CERIATED TUNGSTEN (EWCe Classification)
(Orange Stripe)

1% ZIRCONIATED TUNGSTEN (EWZr Classified)
(Brown Stripe)

1% THORIATED TUNGSTEN (EWTh-1 Classification)
(Yellow Stripe)

2% THORIATED TUNGSTEN (EWTh-2 Classification)
(Red Stripe)

TABLE 1.2: TYPICAL CURRENT RANGES FOR TUNGSTEN ELECTRODES?

Electrodes are produced with either a clean finish or ground finish. Electrodes with a clean finish have been chemically cleaned to remove surface impurities after the forming operation. Those with a ground finish have been centerless ground to remove surface imperfections.

ELECTRODE SIZES AND CURRENT CAPACITIES

Tungsten and thoriated tungsten electrode sizes and current ranges are listed in Table 1.2, along with shield-gas cup diameters recommended for use with different types of welding power. This table provides a useful guide for selecting the correct electrode for specific applications involving different current levels and power supplies. Current levels in excess of those recommended for a given electrode size and tip configuration will cause the tungsten to erode or melt. Tungsten particles may fall into the weld pool and become defects in the weld joint. Current too low for a specific electrode diameter can cause arc instability. Direct current with the electrode positive requires a much larger diameter to support a given level of current because the tip is not cooled by the evaporation of electrons but heated by their impact. In general, a given electrode diameter on DCEP would be expected to handle only 10 percent of the current possible with the electrode negative. With alternating current, the tip is cooled during the electrode negative cycle and heated when positive. Therefore, the current carrying capacity of an electrode on AC is between that of DCEN and DCEP. In general, it is about 50 percent less than that of DCEN.

EPP Electrode Classification (Green Stripe).

Pure tungsten electrodes (EWP) contain a minimum of 99.5 percent tungsten, with no intentional alloying elements. The current-carrying capacity of pure tungsten electrodes is lower than that of the alloyed electrodes. Pure tungsten electrodes are used mainly with AC for welding aluminum and magnesium alloys. The tip of the EWP electrode maintains a clean, balled end, which provides good arc stability. They may also be used with DC, but they do not provide the arc initiation and arc stability characteristics of thoriated, Ceriated, or Lanthanated electrodes.

EWTh-1 (Yellow Stripe) Electrode Classifications

EWTh-2 (Red Stripe) Electrode Classifications

The thermionic emission of tungsten can be improved by alloying it with metal oxides that have very low work functions. As a result, the electrodes are able to handle higher welding currents without failing. Thorium oxide is one such additive. To prevent identification problems with these and other types of tungsten electrodes, they are color coded. Two types of thoriated tungsten electrodes are available. The EWTh-1 and EWTh-2 electrodes contain 1 percent and 2 percent thorium oxide (THO2) called thoria, respectively, evenly dispersed through their entire lengths. Thoriated tungsten electrodes are superior to pure tungsten electrodes in several respects. The thoria provides about 20 percent higher current-carrying capacity, generally longer life, and greater resistance to contamination of the weld. With these electrodes, arc starting is easier, and the arc is more stable than with pure tungsten or Zirconiated tungsten electrodes.

The EWTh-1 and EWTh-2 electrodes were designed for DCEN applications. They maintain a sharpened tip configuration during welding, which is desirable for welding steel. They are not often used with AC because it is difficult to maintain the balled end, which is necessary with AC welding, without splitting the electrode.

Thorium is a very low-level radioactive material. The level of radiation has not been found to represent a health hazard. However, if welding is to be performed in confined spaces for prolonged periods of time, or if electrode grinding dust might be ingested, special precautions relative to ventilation should be considered. The user should consult the appropriate safety personnel

EWCe Electrode Classification (Orange Stripe)

Tungsten electrodes were first introduced into the United States market in the early 1980's. These electrodes were developed as possible replacements for thoriated electrodes because cerium, unlike thorium, is not a radioactive element. The EWCe-2 electrodes are tungsten electrodes containing 2 percent cerium oxide (CEO2), referred to as ceria. Compared with pure tungsten, the Ceriated electrodes exhibit a reduced rate of vaporization or burn-off. These advantages of ceria improve with increased ceria content. EWCe-2 electrodes will operate successfully with AC or DC.

EWLa Electrode Classification.

The EWLa-1 electrodes were developed around the same time as the Ceriated electrodes and for the same reason, that lanthanum is not radioactive. These electrodes contain 2 percent lanthanum oxids (La203), referred to as lanthana. The advantages and operating characteristics of these electrodes are very similar to the Ceriated tungsten electrodes, also called rare earth.

EWZr Electrode Classification (Brown Stripe).

Zirconiated tungsten electrodes (EWZr) contain a small amount of zirconium oxide (ZrO2). Zirconiated tungsten electrodes have welding characteristics that generally fall between those of pure and thoriated tungsten. They are the electrode of choice for AC welding because they combine the desirable arc stability characteristics and balled end typical of pure tungsten with the current capacity and starting characteristics of thoriated tungsten. They have higher resistance to contamination than pure tungsten.

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