Tungsten Electrode Selection
The selection and preparation of tungsten electrodes for TIG Welding or Gas Tungsten Arc Welding (GTAW) to use for a particular application depends on many variables, including the type of material to be welded, the welding amperage and the type of weld, among other factors.
Tungsten Electrode Diameters and Lengths
Tungsten Electrodes are available in a variety of standard diameters and lengths.
|1/16”||(.062” and .060”) 1.6 mm|
|3/32”||(.093”) 2.4 mm|
|1/8”||(.125”) 3.2 mm|
|5/32”||(.156”) 4.0 mm|
|3/16”||(.187”) 4.8 mm|
The most common length is 7.00” (175 mm). Tungsten is normally sold in boxes of 10 pieces.
TIG arc starting and arc stability from a consistently prepared tungsten electrode are beneficial to the TIG welder.
In most applications, TIG welders use tungsten electrodes that contains an emission-enhancing oxide such as Thorium, Cerium, or Lanthanum. These oxides naturally migrate from inside the tungsten electrode to the heat at the point of the tungsten, where they give off their oxide element in the arc, and leave a film of the metal alloy on the tip. This causes the electrode to have a different temperature at the tip based on the work function of that element. The oxides that are emitted at the tip serve to improve arc starting and stability. They also cause the electrode to provide the same level emission as pure tungsten at much lower temperatures. Lower temperatures improve the longevity of the tungsten and keep the grains within the tungsten smaller for improved arc stability. Thus, oxides are a very important part of tungsten. Each oxide has unique physical characteristics that affect tungsten performance. In addition, the technique used in manufacturing the tungsten will also affect its performance.
Tungsten Electrode Grain Size and Structure
The molecular structure inside the point of a tungsten electrode is divided into smaller groups called grains. Oxides migrate to the tip of the tungsten electrode, primarily along the boundaries or borders of these grains. It is much easier for the oxides to migrate from inside the tungsten to the tip on the grain boundaries than it is for them to migrate within the crystallized grains. In manufacturing the tungsten, smaller sized grains are better, because they produce more paths and therefore the oxides can more easily migrate to the tip. However, it is a difficult manufacturing process to minimize the size of the grains while maximizing the consistency of the oxide distribution and maintaining the proper quantity of oxides. This difficulty in the manufacturing process is the primary reason for the differences in tungsten performance quality that is produced by the different manufacturers.
Tungsten Electrode Oxide Distribution and Size
Oxide distribution is a key indicator of tungsten electrode quality. Oxides should be distributed homogenously throughout the tungsten. Uneven distribution results in poor performance: areas with little or no oxides will tend to suffer from grain growth, whereas areas with too much oxide will tend to “bottleneck” and prevent the oxides from getting to the point. Higher quality oxides are smaller in size, which allows them to migrate to the tip easier.
The more of an oxide added to tungsten, the lower the work function that tungsten will have, and thus the better it will arc start. A 2% lanthanated tungsten electrode will arc start more easily than a 1% lanthanated tungsten electrode (assuming they were made using the same manufacturing process).
Even if electrodes are the same type, electrodes of different manufacturers cannot be compared using only the work function and volume of oxides, because this comparison would not take into account the important manufacturing
variables such as grain size and structure of the oxide size and distribution.
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