Welding is a method that permanently joins two pieces of metal. Heat is applied to two of the metal edges or surfaces, usually with a gas torch or electric welding tool.
However, when large surfaces are to be welded, large machines are used. The heat applied by the machines melts the two surfaces or edges until they melt into one piece.
During the welding process, the heated metal must be protected from oxygen and nitrogen in the air, as these gases cause the weld to be weak and brittle. This protection is provided by spraying other gases into the metal during the welding process.
Once the two pieces of metal are welded together and the weld cools and hardens, the assembly is as strong as any other part of the metal. Welding is used in the manufacture of cars, buildings, bridges, airplanes, and large electrical appliances.
The heat generated by welding is often more than 1,500° Celsius.
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