This Glossary of Terms explains the meaning of terms most used by welders. Technical engineering terms have been simplifi ed. For additional defi nitions, refer to the publication Standard Welding Terms and Defi nitions (ANSI/AWS A3.0). It is available from the American Welding Society. A Abrasion: Wear produced by rubbing. Abrasive wear: Deterioration of metal due to a rubbing or scraping action. Absolute zero: The temperature (–273°C, or 0K) at which all molecular motion stops. Accelerating voltage: A voltage difference between an emitter and anode. Accident: An unintentional and unexpected undesirable event. Acetylene (C2H2): Gas composed of two parts of carbon and two parts of hydrogen. When acetylene is burned in an atmosphere of oxygen, it produces one of the highest fl ame temperatures obtainable. Acetylene cylinder: Specially built container manufac- tured according to ICC standards. Used to store and ship acetylene (sometimes called “tank” or “bottle”). Acetylene generator: A device that brings the proper amounts of water and calcium carbide together at the rate required to safely generate acetylene. Acetylene hose: See Hose. Acetylene regulator: A device used to control the fl ow of acetylene. The regulator reduces acetylene cylinder pressures to torch pressures and keeps the pressures constant. Acoustic emission: Sound produced by a material as it undergoes some change. Actual throat: Shortest distance from the root of the weld to the face of the weld. Actuator: A device (usually an electric motor or a hydraulic cylinder) that is used to move a robot about its base or to move the robot arm. Adhesion: Act of sticking or clinging. Air carbon arc cutting (CAC-A): Arc cutting process that uses a carbon arc to heat the metal and an air blast to remove the molten metal and form the cut or gouge. Air purifying respirator: A device worn over the face to fi lter harmful or toxic particles or chemicals from the air breathed. This device is not powered. Air supplied respirator: A device that provides clean air to the helmet through a long hose from a central source. Also referred to as an air-line respirator. Alloy: An alloy is a pure metal that has additional metal or nonmetal elements added while molten. The alloy has mechanical properties that are different (usually improved) from the pure metal. Alloy brass: An alloy created when a third or fourth element is added to brass to improve its physical properties. Alloy bronze: An alloy created when a third or fourth element is added to bronze to improve its physical properties. Alloy steel: An alloy produced by adding additional elements, such as nickel, chromium, or manganese, to plain carbon steel. Alternating current (ac): Electric current that changes direction at regular intervals. Alternating current (ac) power sources: Welding machines that produce alternating current. Aluminizing: A process used to coat a surface with aluminum. Aluminum electrodes: Electrodes that have aluminum as the major alloying ingredient. Ambient pressure chamber: A chamber that creates a dry environment for underwater welding through the use of air pressure or a background gas mixture, which forces the water out of the chamber. Ampere: Unit of electrical current. One ampere is required to fl ow through a conductor having a resistance of one ohm at a potential (pressure) of one volt. Ampere-turns: A term used with electromagnets. It is equal to the number of turns of wire in a coil times the number of amperes fl owing in the coil. Annealed: Heated and cooled to soften and make less brittle. 861