What Is Thermite Welding? Is Thermite Welding Still Used?
What Is Thermite Welding?
Thermite Welding, also called exothermic bonding, Exothermic welding or Thermit welding is a process that uses molten metal to join conductors permanently. It uses an exothermic reaction of a thermite mixture to heat the metal without an external source of heat or electricity.
The chemical reaction is an aluminothermic reaction between aluminum powder and a metal oxide typically iron oxide. The reaction creates aluminum oxide, elemental iron, and a lot of heat. The reactants are usually powdered and mixed with a binder.
The process is commonly used to weld railway rails, and the reaction must take into account that the actual molten metal is at the bottom of the crucible and covered by floating slag. Copper thermite, using copper oxide, can also be used for creating electric joints.
The reaction reaches high temperatures and the reactants are usually supplied in the form of powders, with the reaction triggered using a spark.
The aluminum oxide slag that it produces is discarded. When welding copper conductors, a semi-permanent graphite crucible mold is used, which forms an electrically conductive weld between them.
How Does Thermite Welding Work?
Thermite reaction is a process where metal powders are oxidized by a localized and exothermic reaction, generating enough heat to melt the metals and create a weld.
This reaction starts by mixing metal oxide and iron(III) oxide powders, which generates heat without the need of a spark or flame. Thermite welding uses aluminum powder mixed with other metallic fuels such as magnesium strip or zinc dust, with a small amount of water added before ignition.
The reaction continues until all the metal-fuel is consumed or the aluminum powder is burned off. There are two types of thermite reactions used in welding, gasless welding which uses magnesium as fuel and aluminum or zinc powder as metal oxide, and ignited welding which requires air or oxygen mixed with metal-fuel and aluminum oxide.
Hand-held graphite crucibles can also be used, they are portable, cost-effective and flexible.
History Of Thermite Welding
In the mid-1890s, Hans Goldschmidt developed modern thermite rail welding as an application of the thermite reaction he was researching for producing high-purity chromium and manganese.
The first rail line was welded using this process in Germany in 1899 and it gained popularity due to its increased reliability for new electric and high-speed rail systems.
In 1904, Goldschmidt established his company in New York City to bring the process to railways in North America. George E. Pellissier an engineering student, oversaw the first installation of the track using this process in the United States in 1904 and went on to improve it further.
Although not all rail welds are done using the thermite process it remains a standard procedure worldwide.
Properties Of Thermite Welding
An exothermic weld is stronger and more resistant to corrosion than other types of welds. It is also durable and stable under short-circuit pulses.
However, it is more expensive than other welding methods and requires replaceable moulds. It also has low repeatability and can be affected by wet or bad weather conditions.
Applications Of Thermite Welding
Exothermic welding is a technique that is commonly used to join copper conductors, but it can also be used to weld a variety of other metals, including stainless steel, cast iron, common steel, brass, bronze, and Monel.
It is particularly useful for joining different types of metal. The process is known by many different names such as AIWeld, American Rail Weld, AmiableWeld, Ardo Weld, ERICO Cadweld, FurseWeld, Harger Ultrashot, Quikweld, StaticWeld, Techweld, Tectoweld, TerraWeld, Thermoweld and Ultraweld. Due to its good electrical conductivity and stability, exothermic welding is specified by §250.7 of the United States National Electrical Code for grounding conductors and bonding jumpers.
It is the preferred method for bonding copper to galvanized cable, and it is the only acceptable method for doing so.
The NEC does not require that these exothermically welded connections be listed or labeled, but some engineering specifications require that completed exothermic welds be examined using X-ray equipment.
Advantages Of Thermit Welding
Thermit welding is an efficient and cost-effective method of joining metals, both similar and dissimilar, as it does not require a costly power supply and can be performed in locations without access to electricity.
Disadvantages Of Thermit Welding
The drawbacks of Thermit welding include its limited applicability to only ferrous metal components of substantial size and its inefficiency for welding inexpensive or small metal pieces.
Is Thermite Welding Still Used?
Thermite welding is a specialized process which is still used today to address any issues with railroads. It involves the use of a special compound comprised of iron oxide and aluminum which, when combusted, creates an incredibly hot flame – up to 2,500 degrees Celsius.
This flame melts the metal together at the joint and creates an incredibly strong bond once it cools. The thermite welding process is known for its versatility: it can be used on any type of railroad track – from standard steel rails to more modern high-speed track systems – and even for different types of metals including copper, brass, stainless steel or cast iron.
Today, it remains a fairly common solution for fixing railroad line problems quickly, economically and efficiently.
Why Thermite Rail Welding?
Thermite rail welding is an effective and highly mobile method used for joining heavy section steel structures, such as rails. This process utilizes a special thermit steel that has been heated to extremely high temperatures, allowing it to weld together two components with impressive metallurgical properties.
This makes it the ideal choice for joining high strength and high hardness steels that are commonly used in modern rails.
The thermal energy generated through the reaction of the thermit steel produces an exceptionally strong joint, making thermite rail welding one of the most popular options for track construction projects.