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Material Selection

For quite some time, tungsten manufacturers have added an oxide to pure tungsten to improve the arc starting characteristics and the longevity of pure tungsten electrodes. Below is a chart that lists the major commercially sold tungsten types, their American Welding Society (AWS) and International Standards Organization (ISO) classifications, and the amount and type of oxide contained in the electrode.

Material AWS Class ISO Class Oxide Content
2% Thoriated EWTh-2 WT20 1.7-2.2% ThO2
2% Ceriated EWTh-2 WC20 1.8-2.2% CeO2
1½% Lanthanated EWLa-1.5 N/A 1.3-1.7% La2O3
1% Lanthanated EWLa-1 WL10 0.8-1.2% La2O3
Zirconiated EWZr-1 WZ3 0.15-0.40% ZrO2
Pure Tungsten EWP W None


Below is a description of each of these types and their uses:

2% Thoriated Tungsten

This is the most commonly used tungsten material because it was the first to display a significant improvement over pure tungsten. This is a good general use tungsten for DC applications, because it has a low work function and operates well even when overloaded with extra amperage. While many companies still use this material because it is specified as part of a qualified weld program, there is a definite migration to other tungsten types, namely 2% Ceriated and 1½% Lanthanated, due to their superior performance in most applications and the fact that they are non-radioactive. The thoria contained in 2% Thoriated tungsten is slightly radioactive and many welders and safety officers are leading the move away from this material. The American Welding Society, in their A5.12 "Specification for Tungsten and Tungsten-Alloy Electrodes for Arc Welding and Cutting" state the following on this issue:

Thoria is a low-level radioactive material. 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 appropriate safety personnel.

The primary concern in using this material is in ingesting the dust produced while grinding points on them. The AWS goes on to say,

...during the grinding of electrode tips there is generation of radioactive dust, with the risk of internal exposure. Consequentially, it is necessary to use local exhaust ventilation to control the dust at the source, complemented if necessary by respiratory protective equipment.

2% Ceriated Tungsten

This non-radioactive alternative to 2% Thoriated Tungsten is best when used primarily in DC welding at low currents. It has excellent arc starting capabilities at low currents and therefore it has become the standard for many orbital tube and pipe welding equipment manufacturers. In addition, it is often used in other low amperage applications where small or delicate parts are being welded. It would not be good for higher amperage applications, because the oxides migrate very quickly to the heat at the tip under these conditions and the oxide content and benefits are then removed.

1½% Lanthanated Tungsten

This has been a very popular new material internationally and has recently been introduced in the United States. The 1½% content (as opposed to 2%) was chosen by two of the largest manufacturers as the optimum content amount based on scientific studies which showed that this content amount most closely mirrors the conductivity characteristics of 2% Thoriated Tungsten. Therefore, welders can usually easily replace their radioactive 2% Thoriated material with this tungsten and not have to make any welding program changes. It makes the switch quick and easy. In addition, one major manufacturer had an independent study performed on this material and it was presented at the 1998 American Welding Society Exhibition in Detroit, Michigan. In summary, 2% Thoriated, 2% Ceriated and two manufacturer's ½% Lanthanated were compared by observing tip erosion after 300 DC arc strikes at both 70 amps and 150 amps. In both cases, the 1½% Lanthanated tungsten showed the least amount of tip erosion. This material is also suitable for AC welding. Therefore, if you are considering optimizing your welding, this is an excellent material to consider.

Zirconiated

This material is used primarily for AC welding. The AWS states, "This electrode performs well when used with alternating current as it retains a balled end during welding and has a high resistance to contamination." This electrode has reduced in importance as other alternatives have become available. Pro-Fusion's recommendation is to try 1½% Lanthanated tungsten for your AC welding. Zirconiated tungsten has very poor performance in DC welding.

Pure Tungsten

Like Zirconiated Tungsten, this tungsten is also only used for AC welding and there are better alternatives available. Try 1½% Lanthanated instead of this material.

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