How to Exothermic Weld
Exothermic welding is also known as thermite welding, thermit welding or exothermic bonding. This process uses a copper alloy that is superheated to create the weld. Exothermic welding uses a chemical reaction to create heat, and it does not require an external heating source or source of current. Exothermic welding offers excellent electrical conductivity and is very stable. For this reason, the National Electric Code specifies exothermic welding as one method for bonding jumpers or grounding conductors. Does this Spark an idea?
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Things You'll Need
- Torch
- Thermite
- Alloy metal
- Crucible
- Mold
- Mold clasps
- Weld catch basins
- Hot chisel
- Grinder
Instructions
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Prepare the materials to be welded. Preparation methods vary by each material's makeup and the application of the finished weld. Clean the pieces to be welded, and position them for welding. Make sure the spacing between the two pieces is appropriate for your weld. Also ensure the ends of the pieces are level.
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Place the weld mold. Because of the nature of the welding process, exothermic welds require a mold at the weld site, to capture and form the molten metal. The most common mold types are sand and graphite molds. Clamp all the mold pieces in place. Double-check that they are in the correct position and securely fastened to the pieces to be welded. Place catch basins to capture any weld overflow. Use the torch to preheat the two pieces, to ensure the molten metal bonds with them. Then use the torch to preheat the mold. If the mold isn't preheated, the weld can cool too quickly, which will negatively affect the strength.
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Prepare the molten metal for the weld. In the crucible, place the thermite and the alloying metal. Ignite the termite with the torch, and allow the chemical reaction to melt the alloying metal. Pour the molten metal into the sand mold, or into the weld area. The molten metal bonds to the two pieces to be welded, joining them. The slag created from the smelting process, during the thermite's chemical reaction with the alloying metal, rises to the top of the molten metal and is captured in the catch basins, as the mold is overfilled. Allow to cool.
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Remove the mold and finish the weld. Carefully remove the mold and catch basins. Use a hot chisel to remove any large areas of excess weld material. The hot chisel remelts the metal to facilitate the chiseling process. Use the grinder to further smooth out the weld, until you reach the desired finish.
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Tips & Warnings
* Double check your materials before you weld. Once welded, the only way to correct a bad weld is to cut and remove the section that was welded.
* Remote welding can be performed in some instances, where the ignition of the thermite charge happens from a distance.
* Always wear protective clothing when welding.
* Due to the high temperatures, exothermic welding should be performed only by properly trained welders.
References
Resources
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