Tungsten electrode selection
Which tungsten, at what diameter, ground to what angle — and which gas cup and flow rate go with it.
Choosing the type
Lanthanated (blue or gold) and ceriated (grey) electrodes will do almost everything: they strike easily, run on both AC and DC and keep their point. Pure tungsten (green) is the traditional choice for AC aluminium, where it forms the balled end the process wants.
Thoriated electrodes — the red ones — are left out of the calculation on purpose. The thorium is mildly radioactive and the grinding dust is the problem, not the electrode itself. Lanthanated types replace them with no loss of arc performance, and there is no reason left to buy them.
| Designation | Tip colour | Oxide | Current | Where it is used |
|---|---|---|---|---|
| WP | green | W ≥ 99.95 % | AC | Aluminium, magnesium and their alloys |
| WT-20 | red | 2 % ThO₂ | DC | Steel, stainless, titanium, copper |
| WT-10 | yellow | 1 % ThO₂ | DC | Steel, low and medium current |
| WT-30 | purple | 3 % ThO₂ | DC | Steel, high current |
| WC-20 | grey | 2 % CeO₂ | AC / DC | General purpose, excellent at low current |
| WL-15 | gold | 1.5 % La₂O₃ | AC / DC | General purpose |
| WL-20 | blue | 2 % La₂O₃ | AC / DC | General purpose, the most common choice |
| WZ-8 | white | 0.8 % ZrO₂ | AC | Aluminium where weld contamination is unacceptable |
| WY-20 | dark blue | 2 % Y₂O₃ | DC | Critical joints, titanium, deep penetration |
The colour is a standard, not a brand: the code comes from ISO 6848 (EN 26848), so a red tip means 2 % thoria whoever made it.
Grinding
Grind lengthwise, never across: the grinding marks guide the arc, so circumferential marks make it wander. A sharp point, about 20–30°, concentrates the arc for thin material and low current; a blunter 45–60° point carries more current and lasts longer on thicker work. On AC the tip balls over by itself, so the angle matters less.
Diameter follows the current, with a margin on AC because the electrode runs hotter there. Too large a tungsten at low current gives an arc that wanders across the tip; too small at high current melts it into the pool, and then the weld gets ground out.
Frequently asked questions
Why are thoriated electrodes left out?
Because their grinding dust is slightly radioactive and it is breathed in at the bench. Lanthanated (blue, gold) and ceriated (grey) reach the same currents and last as long. There is no longer a technical reason to buy red ones.
Point or ball?
A point on DC, a ball on AC for aluminium — where it forms by itself if you strike briefly on a piece of copper. Pure tungsten (green) makes the cleanest ball; lanthanated will take AC with a slightly rounded point.
How far should the tungsten stick out?
Roughly the nozzle diameter divided by three, and more in a fillet. The further it protrudes, the worse the gas covers it — a grey, dull start to the bead is the first sign of that.
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