What is thermite welding

Thermite welding technology, preparation of the required mixture

Welding processes when working with metals are an integral component. At the same time, the welding modes that are familiar to us, including manual arc and semi-automatic welding, are not always appropriate, and not always feasible.

When connecting metal structures of large dimensions, special conditions must be created, and often such a need arises outside populated areas. Naturally, there can be no talk about power supplies, inverters and gas equipment.

The only option is thermite welding.


When connecting parts, a special powder mixture is used as a consumable material, which includes elements such as aluminum, magnesium and iron oxides. These powders are called termites. When they burn, energy is released. This energy is enough to transform the edges of the parts being joined into a semi-liquid state. The metal is mixed with the mixture material and subsequent crystallization occurs.

To carry out the welding process, at the initial stage it is necessary to ignite the mixture. Its combustion temperature reaches 1350°C degrees. Several effective methods of arson have been developed. The specified temperature can be achieved by receiving an electric discharge, exploding a squib, or burning a special cord.

When thermite burns, the temperature inside the mixture rises to 2400-2700°C degrees. Most metals have a melting point below this value.

What is noteworthy about this technology is that combustion does not require the supply of atmospheric oxygen. There is enough oxidizing agent inside the mixture itself. If necessary, thermite welding can be carried out in an inert gas environment.


If aluminum powder is used as thermite, then the welding procedure involves fusing the ends of the parts. It is suitable for joining workpieces made of cast iron and other brittle alloys.

In the railway transport industry, thermite welding is in demand when repairing or joining rails. GOST R 57181-2016 specifies all the requirements for the welding process.

Thermite welding is used in mechanical engineering; it is indispensable in the production of propellers for marine transport or crankshafts for automobiles.

This type of welding has also found application in metalworking enterprises. It is often necessary to repair rolling mills, rotor shafts, various presses or buckets. All of the above are considered large equipment, so only one type of welding is possible. It must be emphasized that it is thanks to the combustion of thermite that high-quality connections of wires on power and communication lines are possible. In this case, compositions containing magnesium are used.


There is a classification that distinguishes two types of thermite welding: muffle and crucible. They are used depending on the external conditions.

Crucible welding is most often called aluminothermic welding and is used when connecting elements of grounding loops, as well as other metal structures that require repair by surfacing. Thermite contains aluminum powder and iron oxide.

The approximate ratio of the proportion is 23 to 70. When the composition burns, scale is formed, which in molten form connects the parts.

An important advantage of aluminothermic welding is the ability to connect cast iron workpieces without noticeable joints. But aluminum parts are connected in a different way - muffle welding. Due to the evaporation of aluminum at high temperatures, magnesium is used as thermite in muffle welding. The molten composition is absorbed into the surfaces without spreading over them. But when working with aluminum, it is necessary to remove the oxide film. To do this, add a special flux.

There are four ways to conduct thermite welding.

  1. The first method is characterized by a butt connection. But first, the ends of the parts are processed and cleaned. To avoid deformation from uneven heating of the metal, the welded areas are wrapped in thermal insulation film. After the thermite burns, the resulting liquid metal, located in the crucible, is poured into the gap left between the workpieces. After this, the blanks are pressed against each other and joined.
  2. Intermediate casting is considered less expensive and technologically easier. Molten metal from the crucible is poured into the gap. In this case, the parts are not prepared in advance, which greatly simplifies the process.
  3. Combined welding is characterized by the fact that it combines the technology of butt connection and intermediate casting. It is usually used when welding rails. The ends of the workpieces are cleaned, and a metal plate is placed between them. After the alloy is poured, the rails are pressed against each other. If possible, the seam around the perimeter is re-welded.
  4. The duplex method involves subsequent compression of the workpieces after pouring the alloy.


As mentioned above, iron-aluminum thermite welding has become the most popular. The bulk of thermite is iron oxide. There is only 25% aluminum in the mixture, but additional components can be found in the composition. Flux, alloying additives and iron trimming are added. Thermite combustion and melting of the mixture occurs in a magnesite crucible. In addition to aluminum, it is possible to combine the following elements:

  • Magnesium (31%) and iron oxide (69%).
  • Calcium (43%) and iron oxide (57%).
  • Titanium (31%) and iron oxide (69%).
  • Silicon (21%) and iron oxide (79%).

Depending on the welding application, different types of mixtures are prepared. Iron dross and aluminum powder provide an elemental mixture. Proportions must be strictly observed.

For connection and repair on the railway, a special rail train is created. During aluminothermic welding, a steel filler is introduced into the charge, which consists of ferromanganese and graphite chips.

Alloy steels are joined using a special composition. It contains ferrotitanium or ferrovanadium additives.

Cast iron products, as a rule, have special requirements for welding. Thus, thermite for cast iron must contain silicon. If you follow the technology, you can get a fairly high-quality and durable connection. Manganese is not used in such additives.

Aluminothermic rail welding

The entire procedure can be divided into separate stages. First, the total amount of heat released is calculated. It should be sufficient for the welding process. The optimal composition of the thermite mixture is selected. The mixture should be uniform in composition. Use any available method to ignite the mixture. It is necessary to reach a temperature of 1350°C degrees.

Subsequently, the temperature in the thermite mixture increases. Molten metal is obtained from thermite in 20-30 seconds. Its mass is approximately half the mass of the mixture. The remaining half is slag. The metal will settle at the bottom of the crucible, and the slag, due to its lower density, will float to the top.

The difficulty of repairing rails is that all work has to be done in the field. The rail welding machine is quite massive, but its use is the only opportunity to carry out repair work. The first step is to prepare the ends. They must be even, and the gap between them is 2-3 cm. The elements to be welded are aligned and fixed in one position. After installing the refractory mold, the welding itself takes place.

Every welder wants to get a high-quality result. Unlike manual arc welding, thermite welding requires precise calculations. It is necessary to correctly select the total amount of powder so that the resulting metal completely fills the gap. When preparing the mixture, it is important to thoroughly mix all the ingredients. The initial start of the process should occur at a temperature of 1400°C degrees. Lower values ​​will not cause thermite fires.


Thermite welding technology seems elementary at first glance. However, it requires careful preparation and the availability of the necessary tools and equipment. Thermite is poured into a crucible; it must be made of a refractory material, for example, ceramic. The crucible is equipped with a special device that allows you to drain the molten metal.

To ensure that the casting turns out neat and fits the free space, matrices and molds are made. In some cases they can be reused, but often the forms are disposable. A special clay coating will not allow the metal to spread over the surface.

An important point in thermite welding is to ensure the immobility of the workpieces and their fixation. It is carried out using various devices and devices, which include a vice or clamps. The tool for surface treatment depends on the type of metal and the degree of its contamination. Usually they work with an abrasive wheel or a wire brush.

Additional work may be required after thermite welding. The welder's arsenal must include an oxygen torch, a torch and a hacksaw for metal.

Advantages and disadvantages of the method

Using thermite welding, it is possible to weld ferrous and non-ferrous metals without the use of expensive equipment. Compared to other welding methods, this technology is favorably distinguished by a number of qualities.

  • Thermite welding is less time-consuming. If we take into account the massiveness of the parts being welded, this benefit is sometimes decisive.
  • The quality of the seams reaches a high degree, since partial penetration of the metal of the workpieces occurs. In addition, the seam is quite aesthetic and neat.
  • It should also be noted that the work is relatively low in labor intensity.
  • A certain skill is required from the welder, but it rather concerns the preparatory stage and preparation of the mixture. The welding process itself does not require special skills, unlike electrode welding.
  • The availability and low cost of consumables will significantly save money and simplify the task.
  • Welding equipment can be used away from populated areas.

At the same time, thermite welding installation is considered quite dangerous. Precautions must be taken when using it. It is important to remember that termites are considered flammable. Liquids must not be allowed to enter the mixture, as this may lead to an explosion.

Thermite welding has not become as widespread as arc welding, but in some cases it is irreplaceable. In small workshops, repairs are carried out using a thermite pencil. A novice master should first master this tool, and only then begin to study the real equipment.

Source: https://svarkoy.ru/teoriya/termitnaya-svarka.html

Thermite welding ECP

Pipelines in the ground and running on the surface are subject to corrosion by an electrochemical mechanism, and anodic and cathodic zones are formed on the metal surface. An electrical potential is formed between them, current begins to flow, and corrosive destruction occurs.

Thermite welding of ECP terminals

One of the ways to protect pipelines from corrosion is electrochemical protection. Protective coatings applied to pipes do not provide sufficient protection against corrosion. Therefore, regulatory and technical documents contain requirements to provide oil and gas pipelines with electrochemical protection means of electrochemical protection.

The most technologically advanced and reliable method of fastening ECP terminals is thermite welding. Thermite welding of ECP leads has the following advantages over other methods:

  •  convenience, applicability in any place;
  •  mobility, no power sources required;
  •  high quality welded joint.

: Designations of welded joints in drawings

The essence of thermite welding

The thermite welding method is based on the production of heat during a chemical reaction, as a result of which the materials being welded are heated to the melting point and welded.

For thermite welding, powdered flammable mixtures of metals with metal oxides are used, which release large amounts of heat during combustion. Such materials in thermite mixtures are metals with high heat of oxide formation, such as aluminum and magnesium.

For thermite welding of ECP terminals, copper thermite is used, which contains aluminum powder, copper powder and copper scale.

To start the welding process, the thermite mixture must be ignited. The thermite mixture burns quite actively. The mixture burns in 5 - 10 seconds, producing a large amount of heat; the temperature can reach 3000 degrees. The principle of thermite welding of ECP terminals is based on burning the thermite mixture in a special fireproof form - a crucible.

At the end of the combustion process, the reaction products - liquid copper and slag - will be divided into layers depending on density. The liquid mixture melts the membrane in a crucible and is poured onto the metal being welded, melting it and forming a welded joint.

The liquid slag serves as a protection for the welded joint and retains heat to complete the welding process.

In addition to the main components, various additives and alloying components are added to thermite mixtures to improve the technological properties of thermite and impart special properties to the welded joint.

Equipment and materials for thermite welding of ECP terminals

For thermite welding of electrochemical protection of pipelines the following are used:

  • disposable or reusable crucible molds;
  • thermite mixture;
  • thermal pencils;
  • soldering and welding rods;
  • special matches or remote ignition device.

Thermite mixture is used for welding steel and copper ECP leads with a diameter of 2-5 mm to steel pipelines with a wall thickness of at least 5 mm. It is prohibited to use thermite welding on pipelines with a wall thickness of less than 5 mm, as there is a high probability of burn-through. Strict requirements are established for the storage of thermite mixture: in a dry room with humidity up to 80%, and a temperature of no more than 30 degrees, away from heating devices.

Crucible molds are usually made of graphite and ceramic materials with high heat resistance, equipped with special fasteners to hold them on the pipe during welding. Inside the crucible mold there is a membrane that separates the thermite mixture from the welded material.

Crucible mold for thermite welding

The thermite mixture is placed inside the crucible mold, compacted and ignited using special matches, which are inserted into the ignition hole of the crucible mold lid or using thermal ignition.

Thermite matches are designed for igniting thermite mixture and thermite cartridges.

Matches for thermite welding

Thermal ignition is made from a slow-burning fire cord, which is ignited with ordinary matches or wires and an igniter; ignition occurs at a distance. Ignition can be done at a distance using a radio transmitter and a radio receiver-switch.

Soldering and welding rods are copper thermite mixtures packed in a cylindrical shell made of laminated paper. Soldering and welding rods of the EKhZ-1150A brand are intended for welding EKhZ-1150A on pipes with a wall thickness of 3.5 to 10.0 mm, EKhZ-1150 - on pipes with a wall thickness of walls from 4.0 to 10.0 mm, EKhZ-1152 - on pipes with a wall thickness from 10.1 to 40.0 mm, used for welding all types of electrochemical protection on pipelines with a diameter of up to 1420 mm.

Thermite pencil

It is a cylindrical product made from a copper thermal mixture into which an igniting element and a delayed combustion cord are pressed. The thermal pencil is placed in a reusable crucible mold made of heat-resistant graphite.

The end of the cord coming out of the thermal pencil is led into the hole in the lid of the crucible mold. Ignition is carried out with ordinary matches, which distinguishes thermal pencils from the usual mixture.

In addition, they are more convenient to store and do not require dosing the mixture, calcining or stirring.

Technology of thermite welding of ECP terminals

The surface of the pipe at the welding site of the ECP leads and at a distance of at least 50 mm from the welding site must be cleaned to a metallic shine and degreased. On the cable there is an ECP terminal, the insulation is removed at a distance of 120 mm, the terminals must be cleaned to a metallic shine.

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Welding of ECP terminals using copper thermite mixtures in a reusable crucible mold is performed in the following order:

1 Before starting work on thermite welding of ECP leads, you need to inspect the crucible mold. It is not allowed to use defective crucible molds with cracks or chips.

2 To ensure a tight fit of the crucible mold to the pipe, grinding is carried out using sandpaper on a pipe of the same diameter.

3 The crucible mold is installed on the cleaned section of the pipe

4 The ends of the ECP output wire are inserted into the sprue chamber of the crucible mold

5 When using a copper thermite mixture with a reusable graphite crucible mold of two half-crucibles for welding ECP terminals, a steel or copper membrane with a thickness of 0.3 ± 0.02 mm is first installed on the bottom of the combustion chamber. In order to prevent the thermal mixture from entering the cavity of the crucible mold, the membrane must be installed evenly, without distortions.

6 Before opening the sealed package of thermite mixture mass, you need to mix the package by shaking. The thermite mixture is poured into the central channel of the crucible mold using a measuring container (glass) included in the kit, corresponding to one weight portion (from 54 to 56 g), in two stages with layer-by-layer compaction.

7 Soldering and welding rods are installed in the central channel of a graphite mandrel or crucible mold.

8 The fire cord for igniting the thermal mixture is led out through the ignition hole of the crucible mold cover or through the slag removal channel of the graphite mandrel.

9 Ignition of a slow-burning fire cord is carried out with a match, a thermal match, or through a transmitter and receiver of a remote ignition device.

10 After welding the ECP leads and cooling, the crucible mold is removed by shaking in different directions.

11 The welding area is cleaned to a metallic shine.

12 The strength of thermite welding will be checked by repeated bending of the welded ECP terminal.

The quality of welding depends almost exclusively on the preparation of the pipe surface and does not depend on the qualifications of the welder.

Typical defects in thermite welding of ECP terminals

Source: https://svarkka.ru/%D1%82%D0%B5%D1%80%D0%BC%D0%B8%D1%82%D0%BD%D0%B0%D1%8F-%D1% 81%D0%B2%D0%B0%D1%80%D0%BA%D0%B0-%D1%8D%D1%85%D0%B7/

Thermite welding. Application in industry and everyday life. Thermite pencil

Thermite reaction (from the ancient Greek therm - heat) is the process of combustion of thermite, consisting of a mixture of aluminum (or magnesium) powder with various oxidized metals (most often iron).

The reaction proceeds with intense heat release. Thermite combustion temperature is more than 2300 degrees Celsius and as a result of its combustion, metal and aluminum slag are formed. If you delve into the history of the discovery of the process, the reaction was first obtained by the Russian researcher N.N. Beketov.

The scientist saw the practical use of thermite mainly in the production of steel. However, the thermite reaction became popular almost half a century later thanks to the work of the German chemist Hans Goldschmidt (literally “goldsmith”), who proposed using it for welding railway rails.

Goldschmidt developed a welding technology and drew drawings of a crucible in which the high-temperature mixture is burned.

The use of thermite welding made it possible to obtain a strong and reliable weld without technological lack of penetration, and the effectiveness of the method made it possible to implement it on an industrial scale.

Welding by means of an aluminothermic reaction is still used today in the construction of railway tracks. Thermite welding is a simple and effective way to obtain continuous welded joints at minimal cost.

It can also be used for welding reinforcing bars in construction, power transmission line wires, and for the repair and restoration of large parts made of steel and cast iron. Metal surfacing is used to repair worn parts of parts.

For example, this is how you can “build up” a worn or chipped gear tooth.

The thermite reaction is written with the following formula:

Fe2O3 + 2Al =>Al2O3 +2Fe + 760 kJ, where

Fe2O3 – trivalent iron oxide (visually looks like ordinary rust); 2Al – aluminum powder; Al2O3 – slag composition;

Fe – pure iron.

The reaction proceeds very violently and lasts 15-30 s. From one kilogram of thermite, 0.55 kg of metal and 0.45 kg of slag are obtained. For welding work, the thermite mixture is prepared mainly in the following proportions: 1/4 powdered Al and ¾ iron oxide. Thermite is additionally alloyed to obtain a welded joint with the specified fur. properties and filled with steel scraps to increase the quantitative yield of molten reaction products.

To form liquid metal, molds consisting of two detachable halves are used. Welding is performed with cast metal, which melts the edges of the parts and fills the gap between them. The gap size is 10-15 mm.

There are two welding methods: the first allows you to save thermite consumption, the second allows you to increase the speed of work.

In the first case, the connection on which the mold is pre-installed is heated with a burner, which is supplied through its upper part, to T-(850-900) degrees Celsius. Once the temperature is reached, the molten composition is held for 5-6 seconds and lowered into the mold.

The second case does not involve the use of preheating (which saves time of 15-20 minutes) of the product being welded with a gas-flame torch.

The metal of the welded joint is heated by the thermite itself, which is burned in increased quantities (in foundry production a similar technique is also used when the chill mold is heated by the metal itself, for example, in aluminum gravity casting).

Here, the welded joint is formed by casting superheated metal. The crucible part is separated from the poured volume by a metal shutter. The thickness of the damper is calculated so that it melts before the end of the process.

Parts must not contain moisture. The water will cause metal to splash out. Thermite welding operators must be familiar with safety procedures. They must use PPE: high-temperature-resistant transparent glasses, special shoes, clothing treated with a fire-resistant compound (read the article “Welder PPE”).

 In one of the episodes of the action-packed series “Breaking Bad,” a thermite composition helped the main characters open the door of a warehouse where barrels of a substance for the synthesis of methamphetamine were stored.

We in no way suggest that you follow Walter White and commit any illegal/illegal actions (unless you cannot open your personal safe using traditional methods).

Nevertheless, this is a striking Hollywood example of the fact that the thermite reaction can be used not only for industrial/production purposes, but also for domestic purposes. If thermite can be used to melt metal (cutting), then the reverse process - welding - is also valid.

For example, with the help of a completely simple invention called a “thermite pencil”, two iron parts can be welded in the field without electricity. The method is convenient in the country if the electricity is turned off or if you need to cook something without having to purchase an inverter and spend some money on it.

Making a pencil with your own hands is very simple. We find or buy a metal rod on the farm (most likely you will come across ferrous metal - low-carbon steel, since it is most often found), or we cut it from wire.

Take a rod ø2-5 mm depending on the thickness of the product (the thicker it is, the larger the diameter of the rod) and apply a coating mixed with glue on it. The coating consists of 23-24% aluminum powder and 76-77% ferric oxide.

The particles of these two components should be of a fine fraction no more than 0.5 mm.

In order for the mixture to stick to the metal rod, you need to add nitrocellulose or synthetic glue (quick-drying) to it and stir it all to a paste.

The coating is applied as follows

You need to roll a cylinder from tracing paper. Its internal diameter should be 3 times larger than the diameter of the rod. Next, it is filled with a paste-like composition, into which a steel rod is inserted in the center. After the coating dries and adheres to the metal part, you can cut the paper with a stationery knife and use a thermite pencil.

Previously, the template was made from tracing paper, which was a transparent paper used by draftsmen to copy drawings on a draloscope (light table). Due to the development of copying technology, draloscopes have become a thing of history, as has tracing paper. Although some may still have it from their student days. Be that as it may, if you don’t have tracing paper, we think you can use foil instead

You can apply a seed to the end of the pencil, which will make it easier to ignite. The seed consists of berthollet salt and aluminum powder in a ratio of 2:1. The seed can be done separately in the form of a pilot match, or you can not use it at all, using a sparkler to ignite. The easiest way to light a pencil is with a gas torch, which have now become very portable.

As mentioned above, thermite combustion temperature is very high. The reaction will proceed with intense heat release and spattering of molten metal. And this is no longer a joke. You need to think about your health and stock up on personal protective equipment. Use safety glasses (read about UVEX) and clothing made of thick fabric (under no circumstances should you wear synthetics - read the article on this topic).

Source: https://svarka-master.ru/termitnaya-svarka/

Thermite welding: what it is, the essence of the method, where it is used, advantages and disadvantages

Depending on the objectives of the project, different types of welding are used in construction and other areas of industry and mechanical engineering.

It connects parts firmly and reliably and is accessible to everyone.

Later in this article we will look at the entire process in detail. Go!

The essence of the method

This is a procedure that uses metal in powder form. When it burns, it produces a lot of thermal energy. This is a termite. It contains aluminum and iron.

When these elements combine, a catalyst is formed. That is, using a chemical method, the metal is restored from the oxide.

How the process works

Thermite welding procedure

The edges of the parts melt due to molten metal from the thermite and intense heat. The flow of this heat (its temperature is 2400-2700C) replaces the amount of heat that arises from a gas welding torch or an electric arc welding electrode.

Thermite powder ignites on its own. Why is this happening? Everything depends on the presence of oxygen, which appears as a result of a chemical reaction. Therefore, this method can be used in environments with non-flammable gases.

What are the types?

To create an ideal and durable seam, the following thermite welding options are used:

  • intermediate casting,
  • end to end
  • duplex,
  • combined.

Let's look at each of them.

  1. Intermediate casting is a technology where powder turns into liquid metal. This method is used when installing pre-fixed structures.
  2. The “end-to-end” method is used for plate products, cathode and drainage leads.
  3. Combined welding combines the first and second methods. How is everything going? Almost all work is done using liquid fused deposition (intermediate casting). Only at the end the “butt” option is used for the edges.
  4. The essence of the “duplex” technique is to add one more step to the process - pressing the melted gap of the structure.

According to another classification, thermite welding is of two types: crucible (or aluminum-thermite) and muffle. What is their difference?

The crucible is suitable for fastening small electrical cables and for creating ground loops. The mixture contains iron and aluminum.

They have a ratio of 70 to 23. How does the process work? First, the thermite burns to ashes, then iron forms and connects the joints.

The main task of such welding is to make a surfacing on the product. This type is used in the repair of tram rails. This technology allows you to connect cast iron without joints.

But it cannot create a seam on aluminum parts. Then muffle welding is used. At the melting temperature, the aluminum parts of the joints evaporate.

In muffle welding, the thermite is magnesium in powder form.

Muffle and crucible technologies differ in that the first of them does not produce liquid welding products. Magnesium does not spread at high temperatures, so it connects the necessary parts without seams.

As soon as we start work, it is important to immediately apply flux to our area.

Remember about safety

Thermite welding, although often used, is quite dangerous. Still, when coming into contact with chemical elements, it is important to carefully monitor the entire process. What should you pay attention to?

  1. Store the powder in a dry and warm place. Because moisture and dampness negatively affect its composition.
  2. You can start the procedure only when the temperature is above 10C.
  3. Before the process, do not forget to clean, and if necessary, degrease the connecting areas.

It's not difficult to do this kind of work. It is important to follow all precautions. Then you will get a durable, high-quality seam.

Source: https://prosvarku.info/tehnika-svarki/termitnaya-svarka

What is thermite welding. Types and scope

Any production related to metal cannot do without welding. However, traditional methods are not always cost-effective and applicable. For example, creating a strong connection between parts of large structures requires lengthy preparation, and in the field there are no power sources and gas welding equipment. An alternative in such cases is thermite welding.

Application area

Thermite, based on aluminum powder, is used for surfacing on parts and joining products made of cast iron and brittle alloys. In railway transport, this is a reliable, fast way to repair rails. To regulate it, GOST R 57181-2016 was developed.

 In mechanical engineering, thermite technology is used in the manufacture of propellers for sea ships, car crankshafts, etc. At metallurgical and metalworking enterprises, rolling mills, presses, rotary shafts, casting ladles and other large-sized equipment are repaired using this method.

 To splice cables used in communication and power lines, welding is used, thermite for which is made of magnesium.

Thermite welding technology

The joining of parts by this method is carried out using powder mixtures of aluminum, magnesium, iron oxides, called thermites, the combustion of which generates a lot of heat.

Under its influence, the surfaces being welded become semi-liquid and, combining with the metal of the mixture, are fused into a single whole. To fully understand what thermal welding is, mention should be made of the method of igniting the mixture.

For ignition, a temperature of at least 1350⁰C is required. The ignition is produced by an electric discharge, a squib, or a special cord.

The combustion temperature reaches 2400 - 2700⁰C. This is enough to melt most materials. Combustion does not require an influx of oxygen from the atmosphere, since there is enough of it in the mixture. Therefore, thermite can be used in an inert gas environment.

Types of thermite welding

Depending on the material and application conditions, crucible or muffle welding is used. The first is better known as aluminothermic welding. It is used when installing grounding loops and metal structures. Thermite is prepared from a mixture of iron oxide and aluminum powder in a ratio of 70:23. When it burns, the joints of the parts are connected by molten iron reduced from scale.

Source: https://svarkaprosto.ru/tehnologii/chto-takoe-termitnaya-svarka-vidy-i-oblast-primeneniya

Thermite welding: what is it, thermal process diagram and types of connections

Thanks to the thermal effect on various parts of metal equipment, it is possible to ensure high strength of their connections.

Thermite welding is a popular and simple job that you can easily do yourself at home with minimal experience and if you are new to welding.


What is thermite welding?

Thermite welding also has another name - powder welding. It implies a subtype of welding processes where thermite is the energy source. It is used for welding rails, electrochemical protection and other structures.

Thermite, in turn, is a mixture in the form of a powder made from metals. Aluminum, magnesium and scale are often used.

After the question: what is thermite welding, you need to understand its types and main features.

There are two main types:

  • crucible or aluminum-thermic;
  • muffle

To use the second method, you must additionally take an overlay or a thermite cartridge, which will greatly facilitate the task of welding single- or multi-core wires.

Advantages and disadvantages

Welding using thermite has its advantages and disadvantages.

The advantages of this process include the following:

  1. Thanks to the thermite substance, a high-quality seam is ensured at the joint.
    The joint has increased strength and durability. If aluminum is present, this ensures minimal risk of corrosion.
  2. Economy.
    When operating the equipment, you do not need to waste a large amount of electricity.
  3. Ease.
    Absolutely anyone, even a beginner in the welding field, can weld steel, aluminum, cast iron and other metals. The work process takes a little time, is carried out with a compact tool, with the ability to store it in your apartment or house.

The disadvantages of thermite welding are as follows:

  1. To carry out this type of welding, it is necessary to perform additional and preparatory processing of the metal product and the cable separately.
  2. The welding process is not monitored, which is why it is necessary to use seamless equipment, which can only be operated by an experienced professional with NAKS certification.

Cooking process

Thermite welding requires the presence of a special tool.

Crucible for thermite welding.

In addition, to carry out the work, the master will need:

  • crucible with attached drain;
  • A thermite pencil is necessary to perform thermite welding at home. It does not require heating, firing or melting. Once the equipment is connected to the network, work can begin;
  • fasteners for parts being welded to support and hold them together;
  • a metal saw, a torch for a welding machine, a thermometer and other items that may be needed for work.

A diagram of welding work with thermite for rails, cables and other elements may look like this:

  • duplex;
  • end to end;
  • mixed;
  • with intermediate injection.

The thermite welding process is used in cases where it is necessary to attach different surfaces, cathode and drain leads, or other similar parts to each other. Before you start welding metal, the parts themselves must be fired in a furnace.

It is important to note that the thermite must be fired separately. Then the parts to be welded are put under a press and treated with a special thermite substance. At this stage, the edges and ends of the surfaces are carefully processed, which makes it possible to use it at home.

To weld rails, switch mechanisms and other parts, you can use mixed technology. It combines butt welding and infusion welding. Before starting the process, the part to be welded must be protected with a steel plate using a press.

A gap will appear at this place, into which thermite of a liquid consistency is poured. After it hardens, the seam is processed and welded.

Process safety

Despite the fact that thermite welding may seem quite simple at first glance, in fact this work is dangerous and difficult.

It is necessary to adhere to the safety rules established by regulations when operating such welding equipment:

  1. Thermite substance must be stored in warm and ventilated rooms.
  2. Do not apply thermite with moisture.
  3. When operating welding equipment while outdoors, it is necessary to clean the surface within half a meter of dirt, dust and other unnecessary substances and objects.
  4. Do not ignite the charge from the welding arc.
  5. It is not recommended to start welding work if the thermometer shows less than 10 degrees.
  6. The master performing the work process must have special clothing, in particular overalls.
  7. When using a thermite inverter, it is necessary to fill the thermite with sand during combustion, create a line using an additional safety valve for oxygen supply, and turn off the fuel overflow if the burner is damaged.

Bottom line

To summarize, from all of the above, we can say that thermal welding is a fairly promising option for welding several parts in a metal structure.

The more often it is used, the more it appears in the production sphere of different directions. In order to do a quality job, a thermite welder must have good knowledge of chemistry.

Source: https://tutsvarka.ru/vidy/termitnaya

Thermite welding at home: instructions

Thermal effects on individual parts of metal structures allow them to provide high-strength connections. Thermite welding is a well-known and simple type of work that can be easily performed at home even by craftsmen with minimal experience.

Technological features

Thermite or powder welding GOST 2601-84 is a type of welding work in which thermites serve as a heat source; it is used to connect rails, electrochemical protection, etc. Thermite is a powdered mixture of various metal materials, in particular aluminum and magnesium and iron scale.

There are the following types of thermite welding:

  1. Crucible (aluminium-thermic);
  2. Muffle.

The crucible is used to create grounding loops and when connecting small-diameter electrical cables. The technology involves the use of a thermite mixture in an aluminum / iron ratio of 23 / 70.

When the thermite burns completely, iron is released, which is used to connect the joints together. The combustion process itself depends on the grain size of the thermite powder.

When working with copper or other compounds, compounds of other metals are sometimes added to the powder to increase the strength of the weld.

Photo - working on rails

Aluminum is used when it is necessary to create a surfacing on the surface of a certain structure, for repairing tram rails or when working with fragile materials. One of the key advantages of this technology is the possibility of welding cast iron using a weldless method.

Photo - schematic diagram

At the same time, crucible welding cannot be used to join aluminum, so muffle welding is used here. The peculiarity of muffle work is such that, upon direct contact, the high melting temperatures of thermites cause certain areas of the aluminum compounds to evaporate.

Therefore, to create such fastenings it is necessary to use linings or thermite cartridges. These sockets make working with single-core and stranded wires much easier. They are a tip equipped with a metal mold. The difference between the muffle type and the crucible type is that liquid welding products do not appear during operation.

When exposed to high temperatures, magnesium does not spread over the surface to be joined, but is absorbed into it, forming a seamless connection.

Photo - seam

For aluminum cables, exposure to flux is required before performing thermite welding. It will dissolve the oxide film that prevents the welding of individual parts of aluminum, but can cause rusting of the wires. Therefore, professionals rarely use this technique. To connect this type of cable, molds or filler rods are used, into which the ends of the wires are inserted and heated to the required temperature.

Photo - types of thermal effects

Welding with thermite, which contains magnesium, is used for processing small-section wires (telephone, Internet cables), various electrical connections, etc. To create thermite, about 20% magnesium or aluminum in the mixture and 80% iron (its scale) are required ). At the same time, the main source of oxygen in the process is iron oxide, and heat is generated by pure metal.


  1. Simplicity. This technology for joining joints of steel, aluminum, cast iron and other metals can be used even by beginners in welding. The work does not take much time and is carried out with compact equipment that is convenient to store at home;
  2. Termites provide excellent quality joints. The joints are strong and durable. When working with aluminum, VAMI type fluxes are used to reduce corrosion processes;
  3. Availability. Thermite welding equipment does not require a large amount of electrical energy.

Photo - thermite mixture

But this type of welding work also has certain disadvantages :

  1. To carry out this type of welding, auxiliary and preparatory processing of metal structures and cables will be required;
  2. The welding process cannot be tracked, so only professionals with NAKS certification will be able to work with seamless technology.


Thermite welding requires special equipment. This:

  1. Crucible equipped with drain;
  2. Thermite pencil. A very convenient device for doing work at home. It does not need to be heated, fired or melted. After connecting to the network, the device is ready for use;
  3. Devices for supporting and clamping welded structures;
  4. Cutter, metal saw, inverter burner, thermometer;
  5. Other additional tools (abrasive wheel, wire brush).

Let's look at an example of how thermite welding is carried out on an aluminum base. To ignite such a powder, a minimum temperature of 1300 degrees is required. Under its influence, metal structures evaporate and microcracks form on their surface.

Heated aluminum can not only restore the metal, but also provide a tight and durable connection of individual parts. The parts to be connected are fixed in a form that can be made from improvised materials or bought in a special store.

The parts are processed using the selected type of welding, cooled and cleaned.

Photo - thermite powder

Thermite welding for rails, cables, etc. is of the following types:

  1. With intermediate casting;
  2. Back to back;
  3. Combined;
  4. Duplex.

During intermediate casting, thermite powder becomes liquid metal under the influence of high temperatures. The mixture produced by melting has the same characteristics as its solid (powder) form.

During this, the connected parts of a separate metal structure are fixed in a special form. Thermite is poured into it, due to which the metal parts melt and join. It should be noted that the duplex circuit is very similar to intermediate casting.

The process is identical, except that after the thermite is poured into the mold and hardened, the resulting joint is additionally pressed.

Photo - welding process

Thermite butt welding is used to connect various plates, cathode and drain leads, and other similar elements. Before starting work, parts of the structure are fired in a kiln, while the thermite is fired in another crucible. Afterwards, the metal structures are pressed and welded with fired thermite powder. The technique involves careful processing of the edges and ends of the plates, so it is rarely used at home.

For welding rails, switch mechanisms, etc., a combined technique is used. This combines butt welding and casting. Before work begins, the rails are cut to create sharp edges. A steel plate is installed between the individual parts of the rails, which is pressed into them using a powerful press. Accordingly, a small gap is formed at this place, into which liquid thermite is poured under pressure. After it hardens, the seam is further processed and welded.

Photo - mold for rails

how to do thermite welding

Source: https://asutpp.ru/termitnaya-svarka.html

Thermite welding: features of the process and its advantages

Many people know this type of welding as electric arc and gas. They are widely used both in production and in construction. But thermite welding is not known to many people. Therefore, we will talk about her. Thanks to the use of thermite welding, the results are no worse in terms of joint quality than with electric or gas welding, and no power source or gas cylinders are required.

Areas of use

As mentioned above, thermite welding is applicable in field conditions, or in cases where other traditional methods are not financially profitable.

This method of joining metals has found application in the repair of railway tracks, communication cables or electrical wires.

Aluminothermic welding of rails is, in principle, the only way to quickly carry out repairs at minimal cost.

But thermite welding of parts is also used in production. This connection method is especially relevant in the manufacture of large-sized parts: blades in river and sea vessels, crankshafts of cars and others.

Thermite is also widely used in the repair of large equipment in metallurgy and metalworking: rolling mills, rotary shafts, forging presses and others.

How does this happen technologically?

Advantages and disadvantages

Let us note the main advantages highlighted in the process of joining parts using thermite for welding:

First of all, it is worth noting that the process is not complicated. Even if you do not have much experience in creating seams, if you follow all the rules and requirements, you can perform high-quality welding work with your own hands, and the procedure will not take much time.

Thermite for welding promotes high quality joints that are reliable and durable. The equipment does not require a large amount of electricity to operate.


To perform this procedure, it is necessary to carry out preparatory work on the processing of metal products and cables. It is simply impossible to monitor the accuracy of the welding process. In this regard, only professionals can perform a seamless technique.

Features of the technology

Welding metal parts using thermite is based on melting the edges of the parts being joined during the combustion process and directing the molten metal obtained due to high temperatures.

A rather interesting method was used in blacksmithing a long time ago. Sulfur mixed with scale was poured into the container. The first was set on fire and a melt of metal was obtained, which could be used to join parts. The quality, of course, was not very high.

Of course, modern thermite welding is more advanced. It works as follows.

The joint of the parts to be joined is poured with a melt obtained by burning the thermite mixture in a crucible. The combustion temperature is very high and allows you to quickly melt steel.

The mixture is ignited electrically or, if powder welding is used, by detonating the squib.

Technologically, thermite welding is carried out in several stages:

  • At the junction of parts.
  • Casting in gaps (in the gap between the parts to be welded).
  • Combined.
  • Duplex (two receptions at once).

Areas of application

Thermite welding today is used for welding cast iron, electrical and telephone communications, pipes, engine parts, and so on. Thermite is especially often used for welding railway rails. The connections are quite reliable. The repair site can be on any section of the road, even several hundred kilometers from a populated area.

How these tricks work

The thermite butt welding method requires careful preparation of the surfaces to be joined. Then a thermite film is installed in the gap. Separately from the parts, a melt is prepared in crucibles, which is poured end-to-end, while the workpieces themselves are compressed for a high-quality connection.

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Casting into the gap is a simpler technique. The melt is prepared by burning thermite in a separate mold and pouring it into the gaps between the parts.

The combined technology is used in welding railway rails. The ends are first cleaned, then a steel plate is placed between them. When poured, the rails are compressed and high-quality connections are obtained.

Duplex involves the use of thermite welding with pressing of the joined parts.

What advantages of such technology should be highlighted?

If we talk about the main advantages of the process under consideration, they include:

  • High speed of work completion. It should be noted that this is one of the fastest methods of joining metal products. For example, joining railway rails takes an average of about 50 minutes. Moreover, if several teams work simultaneously, the efficiency of such work will only increase (in just 2 hours, three teams can weld up to 12 joints).
  • Good quality seams. The joints between parts are highly resistant to mechanical loads and chemicals. In addition, such seams look aesthetically attractive.
  • Ease of completing the task. This technology does not require special skills and knowledge, since any specialist can cope with it, subject to short training. The number of workers involved is also small.
  • Availability of materials. The powder mixtures and additional materials required for this can be purchased in specialized stores, and their price will not be high.
  • No need to use expensive equipment. Unlike methods of resistance welding of metal elements, when using thermite mixtures it is not necessary to use expensive welding equipment. This is especially true for working at remote sites, when it is not possible to find a source of electric current or transport bulky gas cylinders.

However, there are some disadvantages, which include the need to comply with strict safety regulations. First, thermite itself is highly flammable, so special care should be taken when transporting and storing it. Secondly, while performing the task, care must be taken to ensure that water or any other liquids do not get into the burning mixture, as this may cause an explosion.

Features of wire welding

Thermite welding has become widespread when connecting various types of non-insulated cables.

With this technology, the main thing is accurate calculation and compliance with all rules. At the junction of the wire, the cross-section of the wire increases, but at the same time the electrical resistance decreases.

For welding, a special thermite cartridge is used, consisting of sheet copper (thickness 1.25 millimeters), copper-phosphorus liners for filling the gap, and the thermite block itself for melting the metal with further joining of the parts.

What is thermite welding?

This is a method of joining metal parts, based on the use of thermite - a special powder mixture that contains aluminum and metal oxides.

The essence of the procedure is that the ends of the elements to be connected are given the desired shape through the use of heat-resistant materials, and then they are heated by filling the joint with a pre-ignited thermite mixture.

As a result, the hot iron is welded with the metal of the parts themselves, which leads to the creation of a strong, reliable and durable connection with high technical characteristics.

Currently, this technique is used to connect a wide variety of metal products, including pipes, cables, wires, ground loop elements and others. A special place is given to the work carried out during the installation of railway rails.

Thermite technology allows rails to be reliably connected to each other, without the need to use the electric arc method, which requires a nearby power source. At the same time, the capabilities of gas welding equipment would be insufficient for welding such thick and dense parts as rails.

By the way, for the described process there is GOST R 57181-2016 (Thermite welding of rails).

preparation of the process

For cable:

In general, the technique of using thermite based on aluminum and metal oxides is in demand, but, like explosion welding, it is used only in cases where there is a special need for it.

What alternative methods exist?

Of course, in terms of popularity and prevalence, this technology is inferior to the electric arc method. To obtain additional information about it, you can read the material on the use of gases and welding mixtures to create a protective environment when using an electric arc.

We also invite you to explore the range of products of our company "PROMTEHGAZ". You can do this by following this link. Contact us!

Source: https://xn--80affkvlgiu5a.xn--p1ai/termitnaya-svarka-osobennosti/

Thermite welding technology

Currently, all kinds of welding are actively used in construction. One of the most accessible and inexpensive technologies that allows you to obtain a high-strength connection is thermite welding. We will talk about what thermite welding is and what its main distinctive features are in this article.

What is the essence of the thermite welding process?

“Thermite welding” involves the use of special powder metal compositions, which during the combustion process generate a fairly large amount of thermal energy. Most often, these metal mixtures are called termites.

In other words, thermal welding is a procedure in which the product being welded is heated to a semi-liquid substance and at the same time fused into an integral composition using a special powder.

The most commonly used powder (welding thermite) is composed of iron and aluminum.

When these elements are mixed, a high-quality catalyst is formed based on an aluminothermic reaction at the welding site. The essence of the reaction is that the metal is reduced from the corresponding oxide by a chemical method.

Welding of products is carried out as a result of the fact that their edges melt in the area where they are welded under the influence of molten metal from thermite (acts as a filler material) and powerful heat.

This powerful heat flow (2400-2700°C), resulting from thermal welding, well replaces the heat generated by a gas welding torch or an electric arc welding electrode.

A distinctive feature of this technology is that powdered thermite can ignite on its own. This is due to the presence of oxygen in its composition, which is released during a chemical reaction from iron oxide.

Thanks to these features, thermal welding can be performed in an environment filled with non-flammable gases, such as carbon dioxide, and even in a complete vacuum.

Types of thermite welding

Today there are four main techniques for obtaining a seam using thermite for welding:

  • intermediate casting,
  • end to end
  • duplex,
  • combined.

The intermediate pouring technique is based on the fact that the powder composition passes into the state of liquid metal and this does not in any way affect the characteristics of thermite. Most often, this technology is used for the installation of metal structures that are pre-installed in the desired position.

To work with plate products, cathode and drainage leads, thermite butt welding is used, the composition for which must initially be fired in a furnace. Combined welding consists of combining the casting method and butt welding. This means that the thermite welder performs the entire main process of work by means of liquid deposition, and finishes the edges by butt welding.

The duplex technique involves one more stage, which consists of pressing the melted gap of the structure.

Thermite welding has two main types:

  • Crucible (aluminium-thermic).
  • Muffle.

Crucible is used to create grounding loops and when connecting small-diameter electrical cables. This technology is based on the use of a thermite mixture in an iron/aluminum ratio of 70/23. When the thermite burns completely, iron is formed, which binds the joints together.

Aluminum-thermic welding is used in cases where surfacing needs to be done on the surface of the product. It has also found its active use in repair work on tram rails. The main advantage of this technology is the ability to weld cast iron using a weldless method. Its disadvantage is that it is not suitable for creating a seam on aluminum parts, so in this case muffle welding is used.

Its essence is that at high temperatures at which thermite melts, some places in the aluminum joints evaporate. That is why, in muffle welding, powdered magnesium, which is characterized by a high melting point, is used as thermite.

The main difference between muffle welding and crucible welding is that during the first type of joining of parts, liquid welding products are not formed. Under the influence of high temperatures, magnesium does not spread, but is well absorbed into the surface and forms a seamless connection.

Before connecting aluminum cables using thermite welding, flux should be applied to the area to be welded.

Thermite welding technology: scope and equipment

In all types of construction and industry, different types of welding are widely used, they all have individual differences, but thermite welding has the most labor-intensive technology. After its use, a high-strength connection appears, so this type of welding is used to connect rails.

Briefly about the history of development

For the first time, thermal welding was used to repair rails in 1915, and already 8 years later in the capital, all tram overpasses were repaired only by this method, using imported thermite. In 1925, Russian engineer Mikhail Aleksandrovich Karasev patented domestic thermite and organized its production in Moscow .

Thanks to domestic thermite, which was much better than imported options, the rails were welded to a higher quality, and the seam lasted much longer. As a result, over 100 thousand joints on tram tracks were restored.

In those distant times, repairs were carried out in two ways: by wedging and by a combined method. The first option quickly failed under constant load, so they abandoned it and began to use duplex - intermediate casting with pressing of molten metal.

The quality was constantly improving - the number of burst joints over 10 years of operation did not exceed 0.8%, so similar methods began to be used during the construction of the Moscow metro. The original technique began to be used for welding joints of high-pressure pipes, where special strength alloy steel was used . Thermites were used to repair large diameter shafts and other large metal parts.


Thermite welding has two main types:

  1. Aluminum thermite or crucible . The second option is used when connecting wires, as well as for creating grounding loops; it is based on the use of a mixture of iron and aluminum in a ratio of 70 to 23. The first option is suitable for repairing rail tracks, for firmly connecting structures and parts made of cast iron.
  2. Muffle , when magnesium-based thermite is used, it does not spread, but is absorbed into the molten joints, forming a seamless connection.

The following methods of thermite welding are used in technology:

  • Butt welding , when the surfaces to be welded are thoroughly cleaned, wrapped in a thermite film, and molten metal from the crucible fills the gap, after which the parts are tightly pressed with their ends.
  • An intermediate option is used for parts that are firmly fixed in the desired angle. It is distinguished by its simple design, since the molten thermite enters the gap, where it hardens.
  • Combined is a symbiosis of both options, successfully used to repair rails, then the joint is welded again from above.
  • Duplex is performed using the crucible welding method, but crimping of the joints is used.

The powder for the manufacture of thermite cartridges (pencils) consists of aluminum powder and iron oxide with a ratio of 25/75%; other metals can be used instead of aluminum: magnesium, titanium, silicon or calcium. Cylindrical structures made from compressed mixtures have an accurate dosage, are ready for use, and are easy to store and transport to the work site.


They are extremely simple:

  • the volume of thermite required to completely melt the joints and all components involved in the chemical reaction is calculated in advance;
  • when using a charge (a loose form of the thermite mixture), you should make sure that all ingredients have a similar consistency and are mixed until homogeneous;
  • the temperature pulse must be at least 1350 °C.

The active phase of the chemical reaction lasts no more than 30 seconds : liquid metal fills the gap, and unburned residues form slag.

Basic equipment

This is a crucible where the combustion process of a thermite cartridge or prepared mixture occurs, as well as the smelting of the contained metal . At the lowest point of the structure there is a drain made of refractory metal or shockproof ceramics. The technology provides for the presence of matrices and molds to work with molten components. Such devices are available for single or reusable use.

You will need clamps, various clamps, as well as an oxygen torch to remove excess and thermal matches to activate the cartridges.

Household use

For this use, a pencil is used with a combustion temperature of at least 1300 0C ; if the technological nuances are observed, a fairly strong connection of large parts is obtained. A variety of thermal mixtures will allow the home craftsman to achieve high quality and strength during repairs.

When performing work, you must strictly observe safety measures:

  • face and hand protection is required;
  • When thermite burns, it releases a lot of heat energy and bright light, so dark glasses are needed.

Industrial Application

For such purposes, high-power thermite cartridges are used , which have a greater melting efficiency compared to pencils, so work is carried out in an open area or in large rooms, for example, in a metro station. The performers are at a safe distance and are not exposed to high temperatures.

For example, in the electrical industry, powerful inverters, thermostats and other devices are used that allow monitoring all parameters of the production process. When thermal welding is performed, reinforced equipment is used to secure structures in the desired position, crucibles made of high-strength material, and specially designed clamps.

Welding wires

Non-insulated metal cables require a strong connection, and for this it is necessary to perform preliminary accurate calculations, since the cross-section at the junction increases, but the electrical resistance decreases. For such work, a cartridge made of sheet copper with a thickness of no more than 1.25 mm is used, inside of which there are liners pressed from copper and phosphorus.

Safety regulations

The process of thermal joining of metal structures is simple to perform, but requires strict adherence to safety precautions:

  1. Strict measures for organizing the storage of cartridges and mixtures, which must be located in dry, well-heated warehouses.
  2. Do not use damp mixtures or cartridges, as the quality of welding will be reduced.
  3. The conditions of use are quite strict: the ambient temperature is not allowed below +10 °C; Degrease the joints and clean them to a shine.


Of all types of welding, the thermite method is characterized by simple equipment, but an increased danger to the health of performers, therefore only those with special permission work. Carrying out similar welding work at home is unprofitable and dangerous.

Source: https://svarka.guru/vidy/thermo/termitnaya.html

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