What is Exothermic Welding?- Process & Uses

What Is Exothermic Welding?

Exothermic welding, which may also be known as exothermic bonding, thermite welding (TW), or thermit welding, is a welding process that uses molten metal to forever join the conductors.

Exothermic welding one of the few processes used for bonding similar metals, such as copper to steel, or copper to copper. It uses an exothermic reaction to create a molecular bond between two pieces.

The connection is created in a purpose-built graphite mold. The weld uses a exothermic reaction of thermite (powdered metal) to heat the metal. In the simplest terms, an exothermic uses a sort of chemical reaction that creates heat and requires no external heat source.

The chemical reaction producing the heat is an aluminothermic reaction of a metal oxide and aluminum powder.

Exothermic Welding Process

Exothermic Welding is a way to make connections of copper to copper or copper to steel that requires no outside heat or power source. In Exothermic welding, a specific weld material is put into a special mold that can withstand high-temperature and is ignited.

Igniting the particles creates super high heat and molten metal (exothermic reaction) up to 1400 celsius and makes a molten metal slag. This liquid copper metal pours into the weld cavity filling all free space, completing the weld.

The weld is allowed to cool to solidify then removed from the mold. The mold is ready for the next weld after a quick cleaning with a brush. The process takes only seconds to complete.

Exothermic Welded connections are permanent and better performing than any known mechanical or pressure type surface-to-surface contact connector.

Since the connection made is a molecular bond, an exothermically welded connection would not loosen or gain resistance, over the life of the installed connection.

FEATURES

• It has a higher electrical conductivity than the conductors.
• It does not corrode oxide or deteriorate over time and is resistant to galvanic coupling.
• It is able to stand repeated electrical discharges.
• It does not increase its resistance.
• It has greater mechanical and squeezing resistance than the conductors.
• It provide permanent melting and a low resistance connection; necessary for achieving long-wearing and reliable earthing results.

It specifically guarantees the most common connections not only between copper cables, but also for welding tapes and metallic pieces made of brass, stainless steel and copper coated steel earth rods.

When Exothermic Welding is used?

Exothermic welding has the predominant purpose of providing a permanent connection or weld between copper conductors. It is the only method of bonding copper to galvanized cable.

It can also be used on stainless steel, cast iron, steel, brass, bronze, and other metals. So, it is a good option if it is necessary to join two dissimilar metals.

Process for Exothermic Welding

Step 1: Always wear protect safety glasses and gloves while working with exothermic welding materials.

Step 2: Prepare all essential and correct materials and equipment/accessories for the type of connection being made. The normal weld system requires a graphite mold, handle clamp, weld metal, a natural bristle brush for cleaning the mold, a wire brush for cleaning/preparing conductors, a flint igniter, and a propane torch. Inspect the graphite mold for wear or cracked material which could allow molten weld metal to leak.

Step 3: Slide the handle clamp through the pre-drilled holes with proper orientation for the thumbscrews. Tighten the clamp thumbscrews onto the mold to close the grips to tightly lock the mold. Make adjustments to tighten/loosen the handles.

Step 4: The material being welded (cable, rod, tape) must be clean and dry using the brush which was included in the kit accessories. In this way, the oxide layer and superficial impurity is removed. Since the graphite mold also absorbs moisture, it should also be removed by pre-heating with gas welding torch to prevent porous welding. When the first weld is finished there is no reason to re-heat the mold if the next weld is completed within 15 minutes as the prior residue heat is preserved.

Step 5: Place the conductors in the mold and tighten the handle clamp to avoid material losses during the reaction.

Please Note – In the event a gap of any kind is created by the components, apply a Sealing Compound at the points where the conductors are exiting at the time of Welding as the Powder will outlay a flame resulting in an improper joint

Step 6: Block off the tap hole with the brass disk. Empty the contents of the weld mixture packet.

Step 7: Empty 50% of the Starting Powder above the Exothermic Weld Powder (Don’t Mix, just scatter) and then close the Mold Mouth, then empty the remaining 50% Starting Powder to on the Mold Mouth at the providing small hole on the top of the Mold Mouth.

Step 8: Light the starting powder extended on the top/side of the mold using the flint igniters. Once started, allow 3-4 seconds for the reaction to take place, during this time you are recommended to stand clear from the mold.

Step 9: After at least two minutes of bonding, open the mold by loosening the handle grip. Draw off the mold from the joint and then clean the joint for any slag. Once open, remove the slag sticking to the mold with the appropriate tool and clean the ingress. The mold is now ready to use again and does require reheating as it is already hot.

MAINTENANCE & STORAGE

• The molds can typically provide 50-60 connections in field conditions.
• The equipment is fragile and should be used with care.
• Molds should be cleaned with a suitable brush/material when the mold has cooled off a reasonable amount from the welding process. Do not clean molds while hot.
• Cavity-cleaning should be done in a way that make sure not to damage/chipped.
• After completing work, the molds should be cleaned from the inside and outside using a soft cloth and well wrapped with bubble plastic packing when stored.
• Molds and weld powder should always be stored in a cool & dry area.
• Tools and accessory should always be cleaned prior to packing, where possible, for safe reuse.

Applications

Exothermic welding is typically used for welding copper conductors, but can be used for other metals including stainless steel, cast iron, common steel, brass, bronze, and Monel. It is also a very good method for joining dissimilar metals.

Exothermic welds are one of the options specified by §250.7 of the United States National Electrical Code for grounding conductors and bonding jumpers.

This is due in part by the good electrical conductivity and high stability to short-circuit pulses. Exothermic welding is a preferred bonding method and is additionally the only acceptable bonding method when bonding copper to galvanized cable.

While the NEC does not require that these exothermically welded connections be listed or labeled, some engineering specifications require that an exothermic weld must be evaluated by either the use of X-ray equipment after completion.

Exothermic welding has greater mechanical strength than other forms of welding and has great corrosion resistance.

It has very high stability to repeated short-circuit pulses, and unlike other bonding methods, there will not be a degradation of electrical resistance during the use of the bonded installation.

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