Exothermic welding (also known as aluminothermic welding) is a method of bonding metals by heating them with superheated molten metal resulting from an exothermic reaction between the metal oxide and the aluminum metal. Exothermic welding was founded at the end of the 19th century when H. Goldschmidt discovered that aluminum powder and metal oxide can be made to start an exothermic reaction by an external heat source and that once the reaction has taken place it can be sustained on its own, the general formula for this reaction being: metal oxide + aluminum (powder) → aluminum oxide + metal + heat. Exothermic fusion welding can mainly weld pure copper, brass, bronze, copper, copper-clad steel, pure iron, stainless steel, wrought iron, galvanized steel, cast iron, and so on. The welding process is easy to operate, does not require external power and heat source, the welding cost is low, the quality is stable and reliable, the conductivity is the same as the parent material, very suitable for the welding of cables and other metal components in the field, suitable for the installation process of cathodic protection system copper core cable and steel structure welding or connection between copper core cable.

Exothermic welding process features and advantages

(1) The current cut-off at the welding point is equal to that of the wire.
(2) The welded joint is permanent and will not cause high resistance due to loosening or corrosion.
(3) The solder joint is like copper, but tougher than the copper itself, and is not affected by corrosive products.
(4) The solder joint can withstand repeated large inrush (fault) currents many times without degradation.
(5) The welding operation method is simple and easy to learn.
(6) The equipment is lightweight and easy to carry.
(7) welding, no external power or heat source; (8) from the appearance of the verification can be verified.
(8) The quality of the weld can be verified from the appearance.
Can be used to weld copper, copper alloy, copper-plated steel, various alloy steels including stainless steel, and high resistance heating heat source materials.

Key points of the exothermic welding process

(1) Influencing factors
A good welded joint surface plump and bright, with no porosity, or slag, cut its profile into a whole without porosity and defects. The main reason affecting the welding effect is moisture or water, because the mold, welding powder, and the welded object may adsorb moisture, so how to prevent or drive away moisture, is the most important step that must be taken when welding. Another factor that affects the welding effect is the cleanliness of the mold and the welded object, such as the surface of the welded object must be cleared of dust, grease, oxides, or other adhesions, so that it is clean and bright before welding operations, otherwise the conductive properties of the welded joint and mechanical properties will be affected. If the residue left in the mold is not completely removed, will cause the surface of the welded joint to be not smooth, not bright.

In summary, the main points of attention.
1, drive away the moisture (available torch baking).
2、Clean the soldered object.
3、Clean the mold.

(2) Precautions

(a) Each packet of solder powder corresponds to a solder joint, and the brand number of the solder powder should correspond to the mold, which should be carefully checked before use.
(b) The solder powder is protected from moisture by multiple layers when it leaves the factory, but it is recommended to store it properly to avoid moisture.

(3) Preparation work

(a) Bake and dry the die with a heating tool (torch or drying box) before each work to drive out the moisture.
(b) Clean the mold after each use, using a soft brush or another soft object to avoid damaging the mold.
(c) Check the tightness of the contact surface of the mold to prevent the copper liquid from leaking out from the gap during operation.
(d) The die clamp is used to open and close the mold, and the tightness of the die clamp affects the effect of welding, so please check the die clamp carefully and make appropriate adjustments before the welding starts.
(e) The mold is made of graphite, which is fragile and cannot withstand throwing and strong impact, so do not force the weld beyond the size of the mold into the mold, or use hard substances and tools to remove the residue.
(f) The service life of the mold can generally be more than 50-100 times.

Application areas

Applicable to the connection of conductors in cathodic protection, electric power, grounding, railroad, and other industries.

Classification

I. Exothermic solder for copper conductors. It uses the heat of chemical reaction of metal compounds as a heat source, through the superheated (reduced) molten metal, directly or indirectly heated work, in the cavity of the specially designed graphite mold to form a certain shape and size, in line with the engineering needs of the molten welded joint. The chemical reaction formula is expressed as
M O + Al ===== M + AlO + high temperature (where M is the required available metal)
Second, is the thermite welding of aluminum conductors, also known as flux-coated welding. Flux-coated welding can not only weld aluminum strands with a cross-sectional area of 3-240mm 2 but also aluminum bus bars with a cross-sectional area of 1000mm 2.
Third, iron and iron connection, steel and steel connection, and steel and iron connection of exothermic flux, such as the welding of steel rails.

Advantages: 1. The current-carrying capacity (melting point) of the fusion joint is the same as that of the conductor, with good electrical conductivity, and the rate of change of the DC resistance ratio before and after welding is close to zero after testing. This is not comparable to any of the traditional connection methods.
2、The welded joints are molecularly bonded, permanent, and do not age.
3、The welded joints are not affected by corrosion like copper.
4, will not be damaged by high inrush current. Tests have shown that in a short period of high current impact, the conductor melts before the fusion welding joint.
5、Convenient and easy to operate. No need for professional personnel.