Tungsten Insert Electrodes - RWMA Class 13
Refractory Metal Faced Electrodes for resistance welding of electrical contacts, copper terminals and silver components. Used by manufacturers of contactors, switches and automotive electrical components in medium-frequency welding machines.
Specifications per AWS J1.3 • ISO 6848 • RWMA Class 13 • Precision Metrology
What is Tungsten?
Tungsten, also known as wolfram, is a transition metal with extraordinary properties that make it indispensable in high-demand industrial applications. Its name comes from the Swedish "tung sten" meaning "heavy stone".
Unique Physical Properties
Tungsten has the highest melting point of all metals: 3,422°C (6,192°F). To put this in perspective, this is more than double the melting point of steel (1,370°C) and higher than any other known metallic element. Its boiling point reaches 5,555°C.
In addition to its exceptional thermal resistance, tungsten has a density of 19.25 g/cm³, virtually identical to gold (19.30 g/cm³). This characteristic makes it one of the densest metals in the periodic table, surpassed only by metals like osmium and iridium.
Fun Fact: As Dense as Gold
Tungsten's density (19.25 g/cm³) is so similar to gold's (19.30 g/cm³) that conventional densimeters cannot distinguish them. In 2012, Australian company ABC Bullion discovered counterfeit gold bars with tungsten cores that had passed all authenticity tests - the fraud was only detected when a bar weighed 2 grams less than expected.
Name Origin: Wolfram vs Tungsten
This metal has two internationally accepted names. "Tungsten" comes from the Swedish tung sten (heavy stone), while "wolfram" derives from the German wolf rahm, which medieval Saxon miners translated as "wolf's foam" or "wolf drool," because the mineral interfered with tin extraction, "devouring" the metal like a wolf.
The chemical symbol W comes from wolfram, the name preferred in Spanish and German, while English uses tungsten. The IUPAC officially accepts both names.
1783 Discovery in Spain
Brothers Juan Jose and Fausto de Elhuyar, Spanish scientists born in Logrono, isolated tungsten for the first time on September 28, 1783 at the Royal Seminary of Vergara (Basque Country, Spain). They obtained it through carbon reduction of wolframite mineral. It is the only chemical element discovered in Spain and one of the few isolated without existing in free form in nature.
Industrial Uses of Tungsten
Thanks to its unique properties, tungsten is irreplaceable in multiple industries:
- Incandescent light bulb filaments: In 1910, William Coolidge developed the method to convert tungsten into filaments, revolutionizing electric lighting.
- Welding electrodes: Both in TIG (GTAW) welding and resistance welding, where its high melting point prevents alloying with the base material.
- Cutting tools: Tungsten carbide (WC) reaches hardness 9 on the Mohs scale, surpassed only by diamond.
- Shielding and counterweights: Its high density makes it ideal for projectiles, aviation counterweights and radiation shielding.
- Aerospace components: Resistance to extreme temperatures in rocket nozzles and turbine components.
Tungsten in Resistance Welding per AWS J1.3
In resistance welding, tungsten is classified as RWMA Class 13 per AWS J1.3/J1.3M:2020-AMD1 "Specification for Materials Used in Resistance Welding Electrodes and Tooling." Its combination of high density, extreme melting point and low electrical conductivity (30% IACS) makes it ideal for welding highly conductive metals like copper, silver and aluminum.
"According to AWS J1.3/J1.3M:2020-AMD1, RWMA Class 13 tungsten electrodes must have a minimum purity of 99.9% W, minimum hardness of 69 HRA, electrical conductivity of 30% IACS (17.4 MS/m), and ultimate compressive strength of 200 ksi (1,379 MPa)."
— AWS J1.3/J1.3M:2020-AMD1, An American National Standard
| AWS J1.3 Class 13 Minimum Requirements (Rod & Bar) | |
|---|---|
| Composition | 99.9% W minimum |
| Hardness | 69 HRA minimum |
| Electrical Conductivity | 30% IACS [17.4 MS/m] |
| Ultimate Compressive Strength | 200 ksi [1,379 MPa] |
| ISO 5182 Equivalent | B14 or W |
Source: AWS J1.3/J1.3M:2020-AMD1, Table 1 & Table 2 - Group B Refractory Metals
Unlike conventional copper electrodes (Classes 1-3), tungsten does not alloy with the base material during welding, ensuring clean joints and long-lasting electrodes in applications such as:
- Copper terminal welding (busbars, connectors)
- Cross-wire welding (grids, filters)
- Silver contact welding
- Copper braids to terminals joining
Alloy Catalog by Color Code (ISO 6848)
Color codes reference ISO 6848 standard (originally for TIG welding). In resistance welding we use this nomenclature to identify composition.
Pure Tungsten (WP)
ISO Code: GreenFor general welding applications of materials with good conductivity: copper, silver inserts, cross-wire welding and resistance brazing.
Lanthanated Tungsten (WLa) - Replace pure tungsten with superior performance
WLa10 - 1% Lanthanum
ISO Code: BlackMedium volume copper terminal welding. Electrical connectors and busbars.
WLa15 - 1.5% Lanthanum
ISO Code: GoldNon-radioactive replacement for WTh20. High volume copper terminals. Braided wire to connectors. Silver components.
WLa20 - 2% Lanthanum
ISO Code: BlueHigh current copper busbars. Intensive 24/7 production. Power switch silver components.
Tungsten vs Elkonite: Correct Application
Tungsten Class 13 should NOT be used for nut projection welding on steel - its brittleness causes thermal shock fracture. For nut welding use Elkonite (CuW) Classes 10-12. Tungsten is specific for highly conductive materials: copper, brass, silver, aluminum.
Comparison Table - Tungsten Class 13 Family
| Property | WP | WLa10 | WLa15 | WLa20 |
|---|---|---|---|---|
| Lanthanum Oxide | 0% | 0.8-1.2% | 1.3-1.7% | 1.8-2.2% |
| Density (g/cm³) | 19.25 | 19.20 | 19.18 | 19.15 |
| Thermal Shock Resistance | Baseline | Good | Very Good | Excellent |
| Production Volume | Low | Medium | High | Intensive |
| Typical Application | Basic cross-wire | Cu terminals | High volume | 24/7, high current |
Technical Documentation
Frequently Asked Questions about Tungsten Electrodes
What are tungsten insert electrodes used for?
Tungsten insert electrodes are used in resistance welding of highly conductive metals: copper, brass, silver and aluminum. Their high density (19.25 g/cm³) and melting point (3,422°C) prevent the electrode from alloying with the base material, ensuring clean welds on electrical terminals, cross-wire welding and contact components.
What is the difference between pure tungsten (WP) and lanthanated tungsten (WLa)?
Pure tungsten (WP) is ideal for low volume applications. Lanthanated tungstens (WLa10, WLa15, WLa20) contain lanthanum oxide that improves thermal shock resistance, allowing higher production volume. WLa15 (1.5% La₂O₃) is the non-radioactive replacement for thoriated tungsten WTh20. Higher lanthanum percentage means greater durability in intensive production.
Can Class 13 tungsten be used for nut projection welding?
No. Class 13 tungsten is brittle and can fracture from thermal shock when welding nuts on steel. For nut welding and stud welding, use Elkonite (copper-tungsten) Classes 10, 11 or 12, which combines copper conductivity with tungsten resistance per AWS J1.3.
What standard applies to tungsten electrodes in resistance welding?
AWS J1.3 (Specification for Materials Used in Resistance Welding Electrodes) classifies tungsten as RWMA Class 13. Color codes (green, black, gold, blue) follow ISO 6848 standard originally for TIG, but adopted in resistance welding to identify material composition.
ALCAVIL Manufacturing Capabilities
We manufacture tungsten and molybdenum insert electrodes with precision technology. EDM machining for exact cuts in refractory materials and certified metrology to ensure tolerances.
Need tungsten or molybdenum insert electrodes for your application?
Request QuoteIndustrial Applications of Insert Electrodes
Contactors & Switches
Silver contact welding in industrial contactors for Schneider, Siemens, ABB.
Automotive Electrical Terminals
Copper terminal welding for wire harnesses (Phoenix, BorgWarner, Milwaukee).
Cross-Wire Welding
Cross-wire welding for grids, filters and copper/brass meshes.
Projection Welding
Projection welding of copper components where electrode contamination must be avoided.
Resistance Brazing
Resistance brazing with refractory electrodes that don't alloy with filler material.
Hot Crimping
Hot crimping of cables and connectors where high temperature without adhesion is required.