Welding is a method used to permanently join two pieces of metal. Heat is applied to two of the metal surfaces or edges, usually with a gas torch or an 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 fuse, or flow together.
During the welding process, the heated metals must be protected from the oxygen and nitrogen in the air, for both these gases cause the weld to become weak and brittle. This protection is provided by spraying other gases on the metal during the welding process.
Once two pieces of metal are welded together and the weld cools and hardens, the joint is as strong as any other part of the metal. Welding is used in the manufacture of cars, buildings, bridges, airplanes, and large appliances.
The heat generated by welding is often more than 4,000° Fahrenheit!