What size tungsten rod do I need?

Tungsten inert gas (TIG) welding, otherwise known as gas tungsten arc welding (GTAW), is known for producing a clean and precise weld, and tungsten electrodes play a central role in it. From providing excellent thermal conductivity to ensuring precision arc control, using tungsten electrodes adds to the various benefits of TIG welding. Thus, it is important that the TIG tungsten size be selected carefully to add to the quality of the weld. 

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This article will discuss the different selection criteria for TIG tungsten electrodes. 

TIG Tungsten Size Selection Criteria

There are many factors that affect the choice of the right tungsten size when TIG welding—the weld amperages, material thickness, and tungsten type, to name a few.

• Amperage: High amperage corresponds to the need for a larger tungsten diameter to handle the high heat and current level. A larger tungsten size means a wider area to dissipate heat and prevent issues like overheating and ensure arc stability. 

• Material thickness: A general rule of thumb is that the TIG tungsten size should roughly be slightly smaller than the thickness of the material being welded to ensure proper heat input and adequate weld penetration.

• Tungsten type: Different tungsten types have different current-carrying capacities. For example, pure tungsten has a low current carrying capacity (typically up to 150 amps) compared to thoriated (≈ 300 amps) or ceriated (≈ 200 amps) tungsten. The size of the tungsten electrode must, thus, be based on the choice of tungsten electrode type.

The table below is the recommended TIG tungsten size for welding material of a wide range of thicknesses. 

TIG Tungsten Size

Tungsten Diameter (mm)

Material Thickness (mm)

Amperage (Amps)

1.6

Up to 0.8

< 50A

2.4

0.8 to 3.2 

50 – 150A

3.2

3.2 to 6.4

150 – 300A

4.0

6.4 to 9.5

300 – 400A

4.8

9.5 to 12.7

400 – 500A

6.4

12.7 to 19.1

> 500A

These GTAW torch parts are common across most types of GTAW welding machines, with the differences being in how these elements are adapted to different roles. Narrow groove GTAW is meant for big bore pipe welding and similarly heavy-duty tasks which require a lot of heat and steady current flow. Narrow groove tungsten electrodes incorporate what is effectively a collet into the electrode itself to ensure an even flow of current and heat into the electrode to help keep the arc and weld fusion symmetrical. Other heavy-duty GTAW torches are water-cooled to deal with excess heat. This is accomplished by modifying the collet body into a coolant sleeve that transfers heat from the collet and the tungsten it contains. Although somewhat unnervingly, these modified collet bodies retain their job of ensuring the collet receives enough current and frequently use the same lead for the current input and the coolant outflow or inflow.

The key takeaway from these GTAW torch parts is their commonality of function between different types of GTAW torches. This includes automated or semi-automated GTAW torch parts. However, these parts’ size, position, and functionality can be substantially altered. Although very different, they are still recognizable and performing what are recognizably the same roles they usually do.

Orbital Weld Head GTAW Torch Parts

One of the most surprising things to welders who have performed manual GTAW welding is how recognizable the components of most automated orbital GTAW weld heads are. Ceramic nozzles are prominent features of most of these weld head types. The exception is closed weld heads used in autogenous welding. This is because the body of the weld head effectively acts as a gas nozzle that surrounds the workpiece and the joint with shielding gas. The other familiar GTAW torch parts are still present and still recognizable.
In larger models meant for interior diameter welding or cladding, things are even more immediately recognizable as GTAW torch parts are mounted in an unusual configuration on machinery that allows them to be mobile and operate as directed via a weld parameter that is input through a power supply. This illustrates what is most likely the most significant difference between GTAW torch parts made for manual welding and those meant for automated processes. Automated GTAW torch parts like those meant for orbital welding are part of an integrated system. So while an operator can switch out all manual GTAW torch parts on a whim, automated or semi-automated systems like orbital welders need to account for these differences in the welding parameters, and need to use GTAW torch parts from the manufacturer to ensure their suitability.

Arc Machines, Inc. has been leading the welding industry with high-quality orbital welding solutions that provide reliable and consistent outcomes. For inquiries regarding products, contact sales@arcmachines.com. For service inquiries, such as how to select the right TIG tungsten size, contact service@arcmachines.com. Arc Machines welcomes the opportunity to discuss your specific needs. Contact us to arrange a meeting.

Tungsten electrodes for welding

One of the reasons TIG welding is favored for sensitive welding applications is because it gives the welder superlative control. The heat for welding comes from an electric arc that streams from a tungsten electrode in the torch. Over the years, welding engineers have found many ways to tailor these electrodes for specific applications by adding small amounts of exotic elements to the tungsten. The different types of electrodes are identified by a band of color at one end. 

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In the early days of TIG welding there were only two types of tungsten that were commonly used. Pure tungsten was favored for aluminum and magnesium, and 2% thoriated tungsten was used for everything else. While these worked well for generations, research and development led to a broad range of tungsten electrodes, each with unique properties. It can be somewhat bewildering for a beginning welder to sort through all the options, so we’ll take a look at the most widely used types of tungsten electrodes. This should help you make an informed decision about which one is best for your welding projects.

Pure tungsten was used as a welding electrode at the beginning of the TIG process, back in the 1940s. TIG welding was developed to efficiently join aluminum and magnesium alloys, and pure tungsten made sense at the time, since it has the highest melting temperature of all metals. In those days power sources were transformer based, and pure tungsten could accommodate welding in the AC mode, which is the standard for aluminum and magnesium. Back then, it was common practice to prepare the tungsten by “balling” the tip. This was done by briefly running a burst of current through the electrode with the power source set to the “reverse polarity” (electrode positive) mode. This would melt the tip of the electrode, and when the current was terminated the tungsten would solidify into a smooth, shiny ball. The shielding gas prevented the electrode from oxidizing, and the size of the ball could be controlled by the amount of current that was run through the electrode in the EP mode. This balled electrode would shape the arc into a wide cone, and the electrode could carry fairly high current without “spitting,” or transferring tiny amounts of tungsten into the weld puddle. Note that with modern inverter power sources, pure tungsten electrodes are not recommended.

For DC welding (used for all metals other than aluminum and magnesium) a small amount of thorium was added to the tungsten electrode, usually 2%. This made arc starts more consistent, and increased the current carrying capacity of the electrode.

Even though these two types of electrodes handled the needs of TIG welders for decades, they are not commonly used with modern welding equipment, for some good reasons. When the industry migrated from transformer to inverter power sources, balling the electrode for AC welding was no longer required, and pure tungsten electrodes gave way to superior blends.

Thorium is slightly radioactive and handling thoriated tungsten electrodes poses health and environmental risks at elevated exposure levels. Consult the AWS Safety and Health Fact Sheet on Thoriated Tungsten Electrodes for more information.

Other elements have proven to be superior to thorium for electrodes in every way. As you’ll see, there are a couple types of tungsten electrodes that are well suited for virtually any TIG welding task, either AC or DC

2% lanthanated tungsten (color-coded blue) is at the top of the list. This is a true all-purpose electrode, with excellent arc starting characteristics and the ability to transmit high current without spitting. It provides a stable arc at both high and low current, and works very well on all metals.

2% Ceriated tungsten (grey) is another good choice for all types of welding; providing good arc start and restart characteristics with no spitting. It is ideal for low- and medium-current welding on all metals.

Rare earth tungsten (chartreuse) has the very best low-current arc starting characteristics, and it can be used on all metals. This type is often preferred for automated welding.

Zirconiated tungsten (white) is good for welding aluminum and magnesium alloys. It has high current-carrying capacity, and it provides better arc starts and stability than pure tungsten.

Tungsten electrodes come in a wide range of diameters — from .020-inch diameter up to ¼-inch. You need to select a diameter large enough to accommodate the maximum current used for each welding job. Smaller diameter electrodes will start the arc more readily at very low amperage settings. For the work I do, which involves a broad range of shapes and sizes, I use a 3/32-inch diameter electrode. I have no problem with arc starts, even for light-gauge sheet metal, and I can weld metals ¼-inch thick, or more.

The most common length for tungsten electrodes is 7 inches. For working in restricted areas, it may be beneficial to cut them down, allowing a shorter back cap to be used on the torch. 

Tungsten can be cut with an abrasive cutoff wheel or ground through with the corner of a grinding wheel. Do not cut the electrodes with a wire cutter or break them by bending. This may result in unseen fractures at the cut ends, which can cause an erratic arc.

Tungsten electrodes usually come with blunt ends that need to be sharpened before use. The angle of the point determines the shape of the arc that streams from the electrode. There is an inverse relationship between the electrode point angle and the arc — a sharply pointed electrode will produce a cone-shaped arc with a broad base where it hits the metal, creating a wide puddle. This can be beneficial for edge-welding thin materials.

Conversely, a stubby point on your tungsten will produce a narrow cone with a small base, focusing the energy into a smaller area. This can help you get deep penetration on thicker materials. With some experimentation, you can find the point angle that gives you the characteristics best suited for a particular job.

For very high-amperage welding, it can help to grind a small flat at the tip of the tungsten electrode. This will help prevent the electrode from spitting small particles into the workpiece.

There are lots of tools made specifically for sharpening tungsten electrodes, but you can do a good job with a stone, belt or disc grinder. To avoid contaminating the electrode, use a dedicated grinder for tungsten, and be sure that all of the grinding scratches are parallel with the electrode centerline. If you leave angled or spiral grinding scratches, the arc may be unstable.

It is not uncommon for electrodes to get contaminated. This can happen when the tip is accidentally touched to the molten puddle, or if the filler rod contacts the hot electrode. Sometimes impurities in or on the metal can fly out and contaminate the electrode, too. It is essential that the electrode be absolutely free from any contamination, so be ready to swap it out whenever this happens. It can help to have several pre-sharpened electrodes handy as you weld.

Even though there are many choices for tungsten welding electrodes, after you have selected an appropriate type and diameter for your application, you shouldn’t have to think much about it. A good all-purpose electrode, like a 3/32-inch diameter, 2% lanthanated, should be an excellent choice for most welders.

 

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