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Exothermic welding uses a chemical reaction to create a permanent bond between metal components, producing heat and filler metal. It is durable, maintains good electrical conductivity, and can be used with various metals. Safety precautions are necessary due to the high temperatures involved.
Exothermic welding is a joining technique used to create a permanent connection between two metal components. This is a chemical reaction that generates heat, known as an exothermic reaction. This process is particularly known for the durability of the bond produced and for maintaining good electrical conductivity between the joined components.
Creating a bond by exothermic welding typically involves heat created by a chemical reaction between some type of heavy metal oxide and a reducing agent. For example, iron oxide is a commonly used metal oxide and aluminum is a common reducing agent. These reagents produce heat extremely rapidly when ignited, thus reaching the high temperatures necessary for soldering.
Such heating is generally initiated once the parts to be joined are fitted together in a mold which contains the materials and the reaction as it occurs. Filler metal in liquid form is produced from this reaction and mixes with the molten metal of the parts to be joined to form a bond shaped by the die. The dies used in exothermic welding can be made of graphite, ceramic or other appropriate materials.
Welds formed by this method have two particularly useful characteristics. First, they form permanent molecular bonds between materials. The resulting joint, therefore, does not loosen over time, nor does it corrode at a different rate than the joined components. Push-fit connections, on the other hand, are highly susceptible to loosening and corrosion. Welds between sections of railroad track or segments of reinforcing steel rod in concrete can be made exothermically to take advantage of this durability.
The joints thus formed also maintain good electrical performance. They typically have uniform electrical conductivity and do not increase in electrical resistance over time. Exothermic welding is, therefore, commonly prescribed by professional industry standards for use in joining electrically conductive components used in grounding systems.
Another benefit of this welding method is its portability. No external power source or heat source is needed for exothermic welding, so it can be done almost anywhere. It can be used with a variety of materials, ranging from common metals like copper or steel to rare metals like niobium. These characteristics make exothermic welding suitable for a wide variety of applications.
While the exothermic reaction that occurs in this welding method is not explosive, it is very rapid and occurs at high temperatures. Safe operation begins with proper operator equipment, including a full-face mask, protective clothing, and gloves, all designed to withstand contact with hot metal. All materials and molds involved in the operation must be completely dry to avoid the buildup of steam, which has the potential to eject hot metal onto the user. The added precaution of operating remotely is also prudent whenever practicable.
