There are three basic profiles that are used on the end of a tungsten electrode. A balled end, a tapered end, and a truncated end. The choice of which one to use is based on the type of welding that you are doing. A rough guideline is; for AC use a balled end, for DC, use a tapered or truncated end. One thing to note is that it’s possible to use a tapered point when welding with square wave AC for instance, but it’s dependent upon the waveform and balance settings and is beyond the scope of what’s outlined below.
For welding with AC, you’ll you’ll normally use a balled end electrode; It will ball up on it’s own. If you’ve got a previously used electrode, it’s best to clean it up to remove the oxide layer first before you start welding with it. Pure tungsten – green band, Ceriated – orange band, or zirconiated – brown band electrodes and certain gray band rare earth electrodes are all suitable for use with AC welding. Thoriated – red band electrodes are not recommended for AC welding. You can learn more about the different types of tungsten electrodes here.
The ball on the end of the electrode should be uniform in appearance, and shouldn’t be any larger than 1.5 times the diameter of the tungsten. Any larger than that and you run the risk of the ball melting off and contaminating the weld. At low currents, a larger ball will also produce a more unstable arc that has a tendency to wander.
Tapered and Truncated End
To weld with DC, you’ll need a tapered end or a truncated end. A tapered end is most commonly used at low to average current levels. If you’re welding at higher currents, you may want to use a truncated end. This helps to prevent contamination of the weld if the tip overheats and melts, falling into the weld.
A couple rules of thumb apply to grinding or sharpening a taper. The first is that you should grind along the length of the electrode, not perpendicular to it as shown below:
The thought behind this is that if ground perpendicular, you’ll get grooves on the tip that will cause the arc to wander. Personally, I’ve never noticed a difference between grinding along the axis, or perpendicular to it. On most job sites, at least in the construction field, you’ll see welders grinding their tungsten with a hand grinder, using a drill motor to spin the tungsten when they grind it, or both. And yet they still produce good welds. And yes, I’m guilty of all the above. In my opinion I don’t see this as being an ultra-critical detail, but I do try to do it the correct way whenever possible. But when you’re hanging from the ceiling making a tie-in and you screw up your last good tungsten, it’s not always possible to do it the ‘correct’ way.
Another general rule of thumb is to grind the taper back to around 2.5 times the diameter of the electrode. Depending on how you want to concentrate the heat, you can change this some. The farther back you grind your tungsten, the wider your arc will be. This has the effect of dispersing the heat more and providing less penetration with a wider bead. This is useful when welding very thin metal. It keeps the heat spread out and reduces the risk of burning through. Grinding a blunt taper concentrates your heat and provides a deeper penetrating arc with a narrower bead. This is useful on thicker metals, or when running a larger filler wire for a root pass for instance. With experience, you’ll find what you like best, and works best for you.
While you can use normal grinding wheels to sharpen your tungsten, there are better choices. They’re not as hard as tungsten so they don’t really cut the tungsten, they break it or chip it off. Often you’ll see a bench grinder set up with what’s called a green wheel. This is a silicon carbide (carborundum) wheel that works pretty well for grinding tungsten. You could also use a diamond wheel, or a borazon (cubic boron nitride) wheel. Another option is to use a tungsten grinder. These work great, provide a consistent taper, and are much safer. The only downside is that they’re very expensive. Remember, a smoothly sharpened electrode works best. Below are some sharpeners and green wheels for sharpening tungsten.
Tags: ac, aluminum, dc, stainless, steel, thoriated, tungsten, welding