Tungsten is a rare metal element used to make gas tungsten arc welding (GTAW) electrodes. The GTAW process relies on the hardness and high-temperature resistance of tungsten to transfer the welding current to the arc. Tungsten has the highest melting point of any metal at 3,410 degrees Celsius.
These non-self-consuming electrodes come in a variety of sizes and lengths and are composed of pure tungsten or an alloy of tungsten with other rare earth elements and oxides. The choice of welding rod for GTAW depends on the type and thickness of the substrate and whether alternating current (AC) or direct current (DC) is used for welding. Choosing which of the three final formulations to be spherical, pointed, or truncated is critical to optimizing results and preventing contamination and rework.
Each electrode is color-coded to eliminate confusion about its type. The color appears at the tip of the electrode.
Pure tungsten (color code: green)
Pure tungsten electrodes (AWS classification EWP) contain 99.50% tungsten, have the highest consumption rate of any electrode, and are generally cheaper than their alloy counterparts.
When heated, these electrodes form a clean, spherical tip and provide a large arc stabilization and equilibrium wave for AC welding. Pure tungsten also provides good arc stability for AC sine wave welding, especially aluminum and magnesium. It is not typically used for DC welding because it does not provide a strong arc to start with an electrode of thorium or cerium. Pure tungsten is not recommended for inverter-based machines for best results. Use electrodes of sharp spinel or lanthanides.
Thorium (color code: yellow, red)
Thorium-containing tungsten electrodes (AWS classifications EWTH-1 and EWTh-2) contain at least 97.30% tungsten and 0.8% to 2.20% thorium and come in two types: EW TH-2 and EW TH-1, containing 1% and 2%, respectively. They are commonly used electrodes and are favored for their longevity and ease of use. Thorium increases the electron emission mass of the electrode, improves arc starting, and allows for higher current-carrying capacity. This electrode operates at a much lower temperature than its melting temperature, which results in a fairly low consumption rate and eliminates greater stability from arc loitering. Compared with other welding rods, thorium-containing welding rods deposit less tungsten into the weld pool, so they pollute the weld seam less.
These electrodes are primarily used for DC negative electrode (DCEN) welding of carbon steel, stainless steel, nickel, and titanium, as well as for certain special AC welding (e.g. thin gauge aluminum applications).
During the manufacturing process, thorium is evenly dispersed across the electrode, which helps tungsten maintain its sharp edge after grinding – the ideal electrode shape for welding thin steel. Note: Thorium is radioactive, so you must always follow the manufacturer’s warnings, instructions, and Material Safety Data Sheet (MSDS) for its use.
Waxy (color code: gray, previously orange)
Cerium tungsten electrodes (AWS classification EWCe-2) contain at least 97.30% tungsten and 1.80% to 2.20% cerium and are known as 2% cerium tungsten electrodes. These electrodes perform best in DC welding at low current settings but can be used proficiently in AC processes. Cerium tungsten has excellent arcing properties at low amperage, so it is becoming increasingly popular in applications such as orbital tube and pipe manufacturing, thin sheet metal fabrication, and machining involving fine parts. Like it, it is best for welding carbon steel, stainless steel, nickel alloys and titanium, and in some cases it can replace 2% ori welding electrodes. Cerium tungsten has slightly different electrical properties than pure tungsten, but most welders cannot tell the difference.
Porous electrodes with higher amperage are not recommended because higher amperage can cause oxides to migrate rapidly to the heat at the tip, removing oxide content and invalidating their process benefits.
Lanthanum treatment (color codes: black, gold, blue)
Tungsten lanthanide electrodes (AWS classifications EWLa-1, EWLa-1.5, and EWLa-2) contain at least 97.30% tungsten and 0.8% to 2.20% lanthanum or lanthanum, known as EWLa-1, EWLa-1.5, and lanthanum. EWLa-2 was lanthanum-treated. These electrodes offer excellent arcing, low burnout, good arc stability, and excellent ignition characteristics, many of which offer the same benefits as electrodes with electrodes. Lanthanide electrodes also have a conductivity of 2% tungsten. In some cases, lanthanum tungsten can be used in place of tungsten without major welding program changes.
If you want to optimize welding performance, lanthanum-based tungsten electrodes are ideal. They can work well on AC or DCEN with a pointed tip, or they can be made into a ball shape for use with AC sine wave power. Lanthanum tungsten maintains a sharp tip, which is advantageous for welding steel and stainless steel on DC or AC with square wave power supplies.
Unlike th-tungsten, these electrodes are suitable for AC welding and, like C-welded welding rods, can arc and keep the arc at a lower voltage. The addition of lanthanides increases the maximum current-carrying capacity by about 50% for a given electrode size compared to pure tungsten.
Zirconia (color code: brown)
The zirconia tungsten electrode (AWS classification EWZr-1) contains at least 99.10% tungsten and 0.15% to 0.40% zirconium. The zirconia tungsten electrode produces an extremely stable arc and is resistant to tungsten splashes. It is ideal for AC welding because it retains the spherical tip and is highly resistant to contamination. Its current-carrying capacity is equal to or greater than that of TH tungsten. Under no circumstances is zirconia recommended for DC soldering.
Rare Earths (color code: various colors not yet in use, previously gray)
Rare earth tungsten electrodes (AWS classification EWG) contain unspecified rare earth oxide additives or mixed combinations of different oxides, but manufacturers need to determine each additive and its percentage on the packaging. Depending on the additive, desired results can include stable arcing during AC and DC processes, longer life than thorium tungsten, the ability to use smaller diameter electrodes in the same job, the ability to use higher currents in similarly sized electrodes, and less tungsten spatter.
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