The welder’s activities may be divided into two operations—welding and cutting.
Welding
In welding, metals, like or unlike, are joined together by melting them until they fuse, “adding material” being used where it is required. The welder also builds up worn parts or adds metal where it is lacking. Common metals which can be treated by this process include the following: Cast iron, steel, malleable iron, aluminum, copper, brass, bronze, lead, and nickel. Precious metals also can be welded. Each metal has its peculiar characteristics and mode of treatment, and the welder who would turn out a good job must master the special technique for handling each metal.
Welding forms the larger part of the welder’s activities. It is much more difficult than cutting, and also has a wider field of application.
Cutting
Cutting can be learned in a few hours. It is restricted in its scope, as it can be used only on steel and wrought iron. The cutting torch is similar to the welding torch with the difference that it is equipped with a special outlet for oxygen under pressure. The operator turns on his usual welding flame until the object is heated to a cherry red, and then presses a device which turns on the oxygen, causing the metal to burn away rapidly. The torch is then advanced slowly along the line of the cut to be made. By practice comes the knack of steadiness and of moving the torch at just the right speed to cut clear through the metal—not too fast for complete penetration, nor too slow, causing loss of oxygen.
Work in the Open and in the Shop
Where the job can not be brought into the shop, welding and cutting are done out of doors, and may be carried on under all conditions of weather. Very commonly the process is used in cutting scrap, wreckage, and piling, and in welding piping and mains.
Inside work varies from shop to shop according as the shop is part of a manufacturing plant or of a foundry, or is purely a job welding shop.
Some account of the common uses of the processes in different industries is given in the section below on “Industrial Applications.” In steam and electric railway shops and yards, in shipbuilding, in the manufacture and repair of automobiles, in installing pipes and mains, in sheet-metal and metal plate work, in the manufacture of furniture, containers and other metal products, and in foundry work, welding and cutting is being extensively used to-day, and each day the welder’s field of operations is still further extended.