If you buy resistance welding electrodes in North America, sooner or later a drawing or a quote says “RWMA Class 11” — and if you have never had the system explained, the number tells you nothing. The classification is genuinely useful once decoded: it sorts electrode materials by family and duty, so that a buyer in one plant and a supplier on another continent mean the same metal. This guide walks through the system and shows exactly where tungsten copper sits.
What RWMA classes are
The Resistance Welding Manufacturers Alliance (formerly the Resistance Welder Manufacturers’ Association, hence “RWMA”) publishes a classification of electrode and holder materials. The classes group materials into families, roughly in order of increasing strength and decreasing conductivity:
- Classes 1–3 — wrought copper alloys for general electrode duty, from high-conductivity work through harder, stronger grades.
- Classes 4 and up through the copper-alloy range — increasingly specialized strengthened coppers for holders, fixtures and high-strength duty.
- Classes 10–12 — refractory composites, dominated by tungsten copper and related sintered materials.
- Class 13 — pure tungsten.
- Class 14 — pure molybdenum.
Two cautions before the details. First, the class number specifies a family and nominal composition range, not a certified property set — two suppliers’ Class 10 material can differ in density and hardness within tolerance. Second, class designations describe the material, not the electrode shape or the schedule.
The refractory classes in detail
This is where tungsten copper lives, and where buyers most often need precision:
| RWMA class | Material family | Typical use |
|---|---|---|
| Class 10 | Tungsten copper composite (roughly CuW70-type, ~70% W) | Flash and upset welding dies, high-wear facings |
| Class 11 | Tungsten copper composite (roughly CuW75-type, ~75% W) | Seam wheels, high-force facings, projection dies |
| Class 12 | Higher-tungsten refractory composite | Specialized erosion-resistant duty |
| Class 13 | Pure tungsten | Extreme-heat inserts, cross-wire welding facings |
| Class 14 | Pure molybdenum | Flash welding dies, specialized high-temp duty |
The useful pattern: from Class 10 to 13, tungsten content and wear resistance rise while conductivity falls. Class 10 is the more conductive, faster-dressing end of the CuW range; Class 11 is the harder, more wear-resistant end that holds profile longer. That is precisely the W70Cu30 vs W75Cu25 trade-off described elsewhere on this site.
A note on precision: supplier literature occasionally assigns nominal percentages to these classes with more confidence than the standard itself does. Treat “Class 10 ≈ 70% W–Cu” and “Class 11 ≈ 75% W–Cu” as the practical mapping the industry actually trades on — and always confirm the actual composition and properties on the mill certificate, which is what your quality system will audit anyway.
How to use classes as a buyer
- Quote in both languages. Put the class designation on the RFQ (“RWMA Class 11 equivalent, W/Cu 75/25”) — the class for your quality system, the composition for the mill.
- Never let the class substitute for properties. If your process depends on conductivity or hardness limits, specify the numbers, not just the class.
- Check certificates, not catalogues. Reputable suppliers ship with material test reports; third-party stamped reports to ASTM B702 are available on our material on request.
- Match the class to the failure mode. Heat-limited stations want the more conductive end; wear-limited stations want the harder end. Forging the class number onto the drawing without that analysis is how lines end up with the wrong member of the family.
Where the classes meet our catalogue
ArcTung manufactures the two workhorse CuW grades: W/Cu 75/25 electrode wheels and rods, blocks and threaded electrodes in both grades — corresponding to Class 11 and Class 10 duty respectively. Class 13 and 14 materials (pure tungsten and molybdenum) are outside our line, and the reasons are in our pure tungsten comparison: for resistance welding electrodes carrying current under thermal cycling, the infiltrated composite outperforms the pure refractory metals where it matters.
Common questions
Is a higher RWMA class always better? No. Higher refractory classes trade conductivity for wear. The right class is the one matched to your failure mode, not the highest number.
Do EU and Asian suppliers use RWMA classes? The class system is North American in origin but widely recognized; most international suppliers can map their grades to it. Composition and certificate still beat the label.
What class is chromium copper? It falls among the wrought copper-alloy classes (Class 2 in common supplier usage) — see our chromium copper comparison for when the copper-alloy family stops being enough.
Get a quote
Send us your drawing with the RWMA class called out — or just the worn part — and request a quote. We will confirm the grade, price it within 24 hours (quotes valid 7 days), and ship standard shapes in 10–14 days with no minimum order.