Kingsweld (Exothermic) Welding

Introduction to Exothermic Welding

“Exothermic” is a chemical term used to describe a reaction that produces heat.

Exothermic Welding, also known as “thermit welding” or “aluminothermic welding” is a welding process for permanently joining materials (usually copper conductors) that employs the exothermic reaction.

An exothermic reaction requires no external heat or power source, reactant powders and a spark is all that is needed for the high energy reaction.

For Kingsweld exothermic welding, it is the reaction occurring between copper oxide and aluminum powder (weld metal) creating molten super-heated copper and aluminum oxide slag. When a spark first reaches the weld metal it causes the reaction within the weld metal, melting and separating the metals. The aluminum rises to the top of the connection creating slag leaving the copper to flow around the joint creating the actual weld.

The weld or connection is a permanent, maintenance-free connection that will not loosen overtime or deteriorate with age. The connection’s current carrying capability is equal to or greater than that of the conductors being joined. In other words, there is no increase in resistance in an exothermically welded connection as there is in most pressure connections.

Throughout the world, exothermic welding has been shown to be the best choice where safety, reliability, current carrying capacity and longevity are critical.

Advantages of Exothermic Welding:

  1. The current carrying capacity of the connection is greater than or equal to that of the conductor.
  2. Has a lower electrical resistance than a mechanical connection.
  3. Does not deteriorate with age.
  4. Does not loosen over time.
  5. Can withstand repeated high current surges without deterioration.
  6. Does not require an external power source.
  7. Used to weld copper, copper alloys, copper bonded steel, various steel alloys, including stainless steel.
  8. Quick and easy to install.
  9. Exceptional corrosion resistance due a very high copper content (97%+).
  10. Fusion temperature is in excess of 2000°C forming a molecular bond.

This adds up to a superior connection when compared to mechanical or pressure type (crimp) connectors.

The KingsWeld exothermic connection is the best choice, especially in safety critical environments where reliability, longevity and current carrying capacity are paramount.

The Kingsweld Process

The KingsWeld exothermic process is a simple, self-contained, efficient way of welding copper-to-copper or copper-to-steel.

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 connection requires a specific mould designed to suit the joint configuration and conductors being used. Each mould type requires a specific weld metal size.

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 1000°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 2000°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.

Making a

Items required to make a connection:

  • KingsWeld mould
  • Handle clamp
  • Weld metal
  • Flint gun

Before making a KingsWeld connection:

  • Always wear proper clothing, gloves and safety glasses when exothermic welding.
  • Read the general safety instructions and the positioning of conductors sheet supplied with each KingsWeld mould to familiarise yourself with the procedure you are going to perform.
  • Make sure the conductors that are to be welded are dry, dirt-free and clean.
  • Use the wire brush to clean the conductor surfaces being placed inside the mould – the cleaner the surface the better the connection will be.
  • Attach the handle clamp to the KingsWeld mould and check it will open & close freely.
  • Make sure that the KingsWeld mould is dry and moisture free. The best way to do this is by pre-heating the mould with a blow torch or by making a test connection.

How To Order

The most common Kingsweld exothermic connections are listed in our dedicated Kingsweld product catalogue for your easy reference. However, it would not be feasible to place all the possible connections, configurations and sizes of conductor in this catalogue as the amount is simply too vast (and constantly growing.) With a database of approximately 15,000 moulds the chances are we would already of supplied a mould you require in the past. In the unlikely event that we haven’t supplied the mould in the past then we will design and produce the required mould.

If you do not see the connection, configuration or size of conductor required by you mentioned in the Kingsweld product catalogue then please contact our sales office with the below relevant information and we will advise you accordingly.

  1. Know the materials to be welded (Copper, Steel etc)
  2. Determine the weld type (configuration) using the selector charts in the catalogue
  3. Find the required weld type and turn to the relevant catalogue page
  4. Determine the material sizes and types (mm, mm2, stranded, solid etc.)
  5. Locate the above information on the correct catalogue page to find the correct mould stock code
  6. Verify you have the following information:
    – Kingsweld mould stock code
    – Price key – This will determine the cost of the Kingsweld mould
    – Weld metal (size) required to perform each connection
    – Handle clamps required for the Kingsweld mould
    – Packing materials required (if any)
    – Notes for any other accessories/information that may be required to perform the connection

Contact our sales office with the above information for current prices and lead times.

Kingsweld Moulds

The KingsWeld exothermic mould is manufactured from high quality graphite. This lends itself to easy machining as well as being able to withstand the high thermal and mechanical shocks produced during the exothermic welding process. Heat obtained in such reactions is in excess of 2000°C.

Our moulds are designed to have an average lifetime of 50 to 60 connections. But, if treated with care, it is possible to obtain a significantly longer life.

Graphite is both brittle and soft, therefore it is important that the operator takes care whilst handling the product.

Worn-out or damaged moulds should not be used.

Each mould has a nameplate, detailing the connection type, part code and the correct weld metal size to be used.

Weld Metal (Weld Powder)

The weld metals are packed into plastic inner cartons, each of which contains metal discs, a moisture absorbing sachet and a box label, clearly identifying size, quantity and batch information.

The weld metal container has two compartments.

The main weld metal is under the green cap and the starter powder is under the red cap.

Part no.DescriptionInner pack qty
#015Weld metal 1520
#025Weld metal 2520
#032Weld metal 3220
#045Weld metal 4520
#065Weld metal 6510
#075Weld metal 7510
#090Weld metal 9010
#115Weld metal 11510
#150Weld metal 15010
#200Weld metal 20010
#250Weld metal 25010

Handle Clamps

Handle Clamps

For most connections involving lugs, cable or rectangular bar, Kingsweld Handle Clamps are used.

Kingsweld Handle Clamps make possible the use of many different sizes and types of moulds with only two different clamps. The two handle clamps are Kingsweld HCD and HCE. These will fit 95% of all standard Kingsweld moulds.

  1. Use HCD on D type moulds.
  2. Use HCD on E type moulds.
kingsweld handle clamp

Special Handle Clamps

Horizontal & Vertical Chain Clamps

Special chain clamps are used to hold a mould in position on a horizontal or vertical pipe.

Vertical Magnetic Clamps

Special magnetic clamps are used to hold a mould in position on a vertical steel surface.

Tools and Accessories

kingsweld exothermic welding accessories

The Flint Ignitor is used to ignite the staring powder.

Spare flints for use with IGN Flint Ignitor.

The Cable Cleaning Brushes are used to clean cable conductors before making a connection. Do not use the cable cleaning brush to clean the mould.

The Mould Cleaning Brush is used to clean the graphite mould without causing any damage to the mould.

The Mould Cleaning Scrapers are used to clean the slag from the moulds that are not split through the crucible.
MS34 – to suit type C moulds
MS55 – to suit type D moulds
MS65 – to suit type E/F moulds
RSC – rail crown scraper
RWSC – rail web scraper
RFSC – rail foot scraper

Sealing Putty is used to prevent the molten weld metal from leaking out of the mould. When cable opening becomes worn from heavy use, the Sealing Putty may be used to prolong mould use.

For use with moulds that require more support than is provided by the standard Handle Clamp.

HD35 – Hammer Die 35mm²
HD50 – Hammer Die 50mm²
HD70 – Hammer Die 70mm²
HD97 – Hammer Die 97mm²
HD120 – Hammer Die 120mm²
HD150 – Hammer Die 150mm²
HD185 – Hammer Die 185mm²
HD240 – Hammer Die 240mm²

kingsweld exothermic welding hammer dies

All essential safety and operational items to carry out an exothermic weld.

Toolkit comprising: conductor cleaning brush, safety goggles, plastic tool box, spare flints, sealing putty, safety gloves, mould cleaning brush, minor burn kit, flint ignitor, safety apron (leather), earth rod driving cap (M16), handle clamp (cathodic protection), handle clamp (for type D moulds), handle clamp (for type E/F moulds), mould scraper (to suit C moulds), mould scraper (to suit D moulds) and mould support clamp.


kingsweld exothermic welding toolkit

For use with MCPT joint.

Exothermic welding must be used in accordance with instructions and with all safety precautions taken. This includes the use of personal protective equipment (PPE). We run operator training courses to train field operatives on how to safely carry out an exothermic weld.

SAFEG – Safety goggles
SAFEGL – Safety gloves
SAFEA – Leather safety apron

kingsweld exothermic welding safety accessories
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