Michael Provost, age 15, of Monroe, La., for his question:
HOW DO YOU WELD METAL?
Welding is a way of joining pieces of metal together, usually by melting or heating their adjacent surfaces. There are almost 40 different ways to weld metal with the best, perhaps, being either arc welding, gas welding, resistance welding, brazing, induction welding or thermite welding.
Arc welding is the most widely used process. It uses heat from an electric arc between the parts to be joined and a metal rod. As the metal rod is moved along the joint, a strip of molten metal is created. When the metal cools, the joined parts become one solid piece of metal.
Gas welding employs the heat from burning gas and oxygen. The gas is usually either acetylene or natural gas. The welder usually holds a welding rod or filler metal in one hand and a torch in the other. The rod melts as the flame moves over the surfaces to be joined, and a solid bond is formed. In resistance welding, heavy electrodes are used to press the parts together and to send a surge of electric current through the area where the parts are in contact. This process is used in assembly lines and in mass production of sheet metal products.
Brazing requires a prepared filler metal and a carefully prepared joint. The filler material is put at or in the joint so that when it is melted it will flow throughout the joint. Even though a brazing filler metal has a lower melting point than the parts being welded together, a fusion takes place to make a strong joint.
Induction welding makes use of an induction coil, an electrical device that is shaped to fit the work piece. Then the work piece is heated by its resistance to the high frequency current induced by the coil. The process is used for certain shapes, such as small diameter, thin walled steel tubing.
Thermite welding uses a chemical reaction that produces molten filler metal that in turn goes into a mold surrounding the joint. The reaction comes from a mixture of powdered aluminum and a metal oxide.
In the thermite welding method, when the chemicals are ignited, the oxide is almost immediately reduced to a hot liquid metal that fuses the joint. This type of welding is used primarily to join thick pieces of metal.
In the popular arc welding method, the rod is usually a straight wire electrode that measures from 9 to 18 inches in length. The electrode is held in a clamp, or electrode holder, and has a covering of flux, which melts with the electrode and protects the weld pool by covering it with a slag.
In submerged arc welding, a high speed process, the electrode is a continuous coil of wire automatically fed from a reel. A powdered flux is put in a small mound over the arc, completely covering it.
In gas metal arc welding, the electrode is also fed from a coil, but instead of a flux, a special gas is used to cover the arc and weld pool.
Gas tungsten arc welding uses electrodes that are made of a tungsten rod that does not melt at ordinary welding temperatures.