The KingsWeld exothermic welding process is a simple, self-contained, efficient way of welding copper-to-copper or copper-to-steel.
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Each connection uses a KingsWeld weld metal which, when ignited, creates an exothermic reaction between copper oxide and aluminium powder.
The connections are produced inside a graphite mould, specifically designed to suit the size of conductors to be welded as well as the specific joint configuration.
Each exothermic connection requires a specific mould designed to suit the joint configuration and conductors being used. Each mould type requires a specific weld metal size. This can be found in our weld metal selection table.
Once the correct mould and weld metal have been selected, the process is simple and straightforward.
The conductors are positioned in the graphite mould. A steel retaining disc is then inserted into the mould before any weld metal is added. Only after the disc is in place and properly seated can the main weld metal (under the green cap) be poured into the reaction crucible. The ignition temperature of the main weld metal is approximately °C. This is difficult to achieve and so we use a starter powder to start the exothermic reaction, this is contained under the red cap. The starter powder is similar to the main weld metal, but finer, allowing ignition at around 450°C (through using the spark from a flint ignitor).
The resultant exothermic reaction produces high temperature molten copper (in excess of °C) and aluminium slag.
The molten copper melts the steel retaining disc and flows down the tap hole into the joint cavity. In doing so, the molten copper melts and welds the conductors into a solid homogenous joint.
The whole process takes no more than a few seconds. The aluminium oxide produced stays on top of the joint and is easily removed.
What process welds at °C without applying a power source? Meet thermit welding—fascinating, century-long technology that’s still revolutionizing industries today. Hailed for its smooth, durable joints, thermit welding (or exothermic welding) uses an internal heat source to melt and bond metals together.
Thermit welding is an exothermic fusion welding process that uses a reaction between a metal oxide (typically iron oxide) and aluminum powder to generate molten metal for joining.
It does not require or use external energy in the form of an arc or gas—it takes only a spark to ignite the mixture, or thermite. What is generated is a pool of highly superheated liquid metal that fills a mold, fusing parts when it cools.
The process originated in , when German chemist Hans Goldschmidt developed the aluminothermic process – the basis for the thermit welding process.
By , railway maintenance was transformed using this method, allowing workers to weld rail ends in the field without the need for cumbersome machinery.
Picture 20th-century crews casting fire-embers on Europe’s expanding railroad network. Its heyday was during the s–30s with millions of welds documented worldwide. Nowadays, it is not utilized as much anymore—60% less since , as revealed by a report by the rail industry—but still utilized for distant repair and specialized applications.
Thermit welding hinges on a controlled chemical reaction:
8Al + 3Fe3O4 → 9Fe + 4Al2O3 + heat
Here’s how it works: 8 units of aluminum combine with 3 units of magnetite (Fe₃O₄) to produce 9 units of molten iron and 4 units of aluminum oxide slag, along with a burst of heat—at up to °F (°C) at the reaction center.
The resulting molten iron, about °C, is poured into a mold to bond metal pieces. The typical thermite combination is 1 part aluminum powder to 3 parts iron oxide by weight, ground into a light, gray powder.
To specialized welds, alloying elements like manganese (for toughness) or nickel (for corrosion resistance) may be added, changing the iron’s properties.
This self-sustaining exothermic reaction emits about 850 kJ/mol of energy when ignited—far more than necessary to melt steel edges without a torch or generator. Fun fact: Thermite heat was even utilized in WWII to melt tank armor. It is now precision-recalled to weld.
Clean the metal surfaces (e.g., rail ends) with a wire brush to remove rust and dirt. Align them with a 1–2 inch gap, depending on joint size.
Build a mold around the gap using refractory sand or ceramic, shaped to match the weld profile (e.g., rail head).
Preheat the area around with a propane torch 10–15 minutes to 300–500°C, making moisture burn off and allow fusing. The foe is moisture—steam explosion is danger if trapped. (For rail welds, preheating to 500°C ensures the molten iron bonds deeply, reducing cracks.)
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Place a crucible (normally graphite-lined steel) over the mold, connected by a tapping hole. A typical crucible holds 5–10 kg of thermite for a rail weld.
Charge the mixture of thermite, topped with ignition powder (barium peroxide or magnesium ribbon).
Clamp the setup in place—any tilt risks spillage of °C metal.
Ignite the powder with a flint gun or sparkler. The reaction is 20–30 seconds long, giving a brilliant flash and a hiss as the thermite ignites.
When done, tap the crucible to fill the mold with molten iron, filling within seconds. Excess metal is caught by the mold, forming a collar at the joint.
Thermit welding isn’t one-size-fits-all. Each type tweaks the reaction for specific metals, making thermit welding versatile beyond steel.
Thermit welding shines in practical, high-stakes scenarios:
Railway Welding: Binds rail ends together to create uninterrupted track, appreciated for unbroken strength.
Electrical Joints: Copper thermite joins busbars, transmission lines, and grounding systems. One weld carries + amps, with no seams to corrode.
Heavy Machinery: Fixes massive steel components—think 10-ton ship propeller shafts or steel mill rolls. In a project, a thermit weld fixed a broken press frame in less than 2 hours, avoiding weeks of downtime.
Other Uses: Historically, thermite incendiary bombs disabled artillery in WWI and WWII. Today, it’s an emergency fix for out-of-the-way pipeline repair or developing world structural steel.
Thermit welding has unique pros and cons. It’s a trade-off between rugged simplicity and modern efficiency.
Thermit welding’s heat and materials demand caution. Here’s how to stay safe:
1. Risks: Burns from metal at °C, eye injury from intense light, inhaling fumes.
2. Protocols:
Thermit welding is a chemistry and engineering wonder—converting powder to molten metal to form unbreakable bonds. From its roots in railroads to modern-day niche uses, it marries simplicity with power, despite encroachment from newer methods.
Want more about welding applications? Read our blogs on: “Welding Applications and Their Advantages”. Or you can learn more about different types of welding on “Different Types of Welding: A Comprehensive Guide”.
Yes, they’re two names for the same reaction-based process.
No—the reaction requires compatible metals like steel or copper, not aluminum itself.
From setup to finish, about 30–60 minutes, and the size depending.
The method begins with mixing and igniting the thermite mixture. When ignited, the reaction produces intensely high temperatures (typically to approximately °C–°F).
The metal is then poured into an existing mold or gap between the workpieces, and when it hardens, it forms a firm, permanent bond.
It is predominantly used for ferrous metals (for example, steel) like rail welding. There are also variations of the thermite process in non-ferrous metals (for example, copper), where the metal oxide within the thermite mixture is adjusted accordingly based on the proposed application.
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