How to Weld Copper Grounds With Thermite
Thermite welding is commonly used in the construction trade to bond heavy copper electrical ground wires to the iron rebar in a building's foundation. Also known as exothermic welding, the process uses an aluminum-oxide based welding powder that burns at high temperature to melt a reactant metal, such as copper. The molten metal flows into a lightweight graphite mold that shapes the joint and holds the ground wire and rebar in place throughout the reaction.
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Things You'll Need
- Wire brush
- Copper cladding, 1/16-inch thick
- Metal snips
- Graphite welding mold
- Mold sealing compound
- Copper reactant metal
- Thermite
- Thermite igniter
- Blowtorch or match
- Safety glasses
- Welding gloves
Instructions
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1
Clean the rebar of dirt and rust by scrubbing it thoroughly with a wire brush. Make sure the rebar is dry. Wrap both sides of the join area on the rebar with a strip of copper cladding to ensure the weld bonds completely to the rebar's irregular surface.
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2
Place the copper ground wire parallel to the rebar. Make sure the welding mold is free of slag from previous welds, then press both the rebar and the ground wire into their guide grooves in the welding mold.
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3
Clamp and lock the welding mold around the ground wire and rebar, with the mold's crucible facing up. Apply mold sealant along the bottom and side seams of the mold to keep molten metal from escaping during the welding reaction.
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4
Open the top of the crucible. Place the reactant metal in the bottom of the crucible, followed by the thermite. If you're using a packaged product that contains the reactant metal and the thermite, open the correct end of the container -- which will be clearly marked -- so the metal pours into the bottom of the crucible first.
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5
Insert an igniter strip into the thermite. Position the igniter's fuse so it protrudes through the ignition slot on top of the crucible. Close the top of the crucible.
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6
Light the igniter's fuse with a blowtorch or match, then move at least 6 feet away from the mold while the fuse burns down. Most fuses have a burn time of three to five seconds, but don't dawdle. If any metal or slag escapes the crucible, you don't want to be in the neighborhood.
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7
Stay well back from the crucible while the thermite burns. Allow one minute for the reaction to complete and the weld to cool.
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8
Open the top of the crucible, then inspect the mold to ensure the reaction has stopped and no molten metal is present. Unlock the mold and open it. Pull the mold away from the welded ground connection.
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Tips & Warnings
Cut or file away any aluminum slag that forms on top of the joint. Clean your welding mold thoroughly with a wire brush after each use.
Always wear safety glasses and welding gloves when working with thermite welding compounds.
