Tungsten electrodes: colours, designations and use
The colour code of ISO 6848: which oxide, for which current and which metal, how to grind it, and how much current an electrode of a given diameter will take.
Colour and composition
| Designation | Tip colour | Oxide | Current | Materials |
|---|---|---|---|---|
| WP | Green | Pure tungsten | 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 code comes from ISO 6848 (EN 26848 in Europe), so a red tip means 2 % thoria whoever made it. Unpainted and repainted counterfeits do turn up, though: if the arc behaves unlike it should, this is often why.
Current by electrode diameter
| Diameter, mm | DC−, A | AC, A | Filler rod, mm |
|---|---|---|---|
| 1.0 | 15–80 | 15–55 | 1.0–1.6 |
| 1.6 | 70–150 | 60–120 | 1.6–2.0 |
| 2.0 | 100–200 | 80–160 | 1.6–2.4 |
| 2.4 | 150–250 | 120–210 | 2.0–3.0 |
| 3.2 | 220–350 | 180–280 | 2.4–4.0 |
| 4.0 | 300–450 | 240–350 | 3.0–4.0 |
Grinding
| Included angle | Current | What it gives |
|---|---|---|
| 15–30° | Low | Easy striking, narrow arc, deep narrow penetration. Wears quickly. |
| 30–60° | Medium | The compromise: steady arc and acceptable life. |
| 60–90° | High | Wide arc, longest life, less risk of melting the tip off. |
| Balled end | AC (WP, WZ-8) | Forms by itself on AC and holds the cathode spot steady. |
Common mistakes
- Grinding across. Marks perpendicular to the axis make the arc wander. Grind along the axis, on a wheel kept for tungsten only.
- Dipping into the pool. A contaminated tip gives an unstable arc and tungsten inclusions in the weld — regrind it rather than trying to burn it clean.
- WT-20 on AC. Thoriated tungsten cracks and spits on alternating current. For aluminium use WP, WZ-8 or WL-20.
- Too much stick-out. Outside the gas shield the tungsten oxidises and turns blue. Keep the stick-out no longer than the cup diameter.
Frequently asked questions
Which tungsten for aluminium?
On AC, WP (green) or WZ-8 (white): both hold the balled end that AC wants. On square-wave inverters WL-20 (blue) also works well, and it is ground to a point rather than balled.
What replaces thoriated WT-20?
WL-20 (lanthanated, blue) is the closest match for arc behaviour on DC, without the weak radioactivity of thorium. WC-20 (ceriated, grey) strikes better at low current and suits thin material.
What angle do I grind to?
Rule of thumb: make the ground length two to three times the electrode diameter. A sharp grind (15–30°) gives a narrow arc and reliable striking at low current; a blunt one (60–90°) gives a wider arc and lasts longer at high current. Grind along the axis, never across — transverse marks pull the arc sideways.
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