Glossary 875 Microhardness testers: Testers used to test the hardness on a very small area of a part. MIG: A nonstandard term. See Gas metal arc welding. Mildly active (RMA) fl uxes: Fluxes used on highly solder- able surfaces. They clean better and faster than nonac- tive fl uxes. Mixing chamber: The part of the welding or cutting torch in which the welding gases are mixed prior to combustion. Modulus of rupture: In a bend or torsion test, the stress at which fracture occurs, expressed as a constant. Molecular theory of heat: The speed of the motion of mole- cules in a substance determines the temperature of the substance. The amount of the substance and the temper- ature of that substance determine the total heat energy. Monochromatic: Type of light energy that has one frequency. Monolithic: Massively uniform. Movable core reactor: Type of transformer that uses a primary and a secondary coil. In addition, a third coil with a movable core is used to control the current output. Movable shunt transformer control: A type of transformer output control in which output current is adjusted by moving a shunt into or out of the space between the primary and secondary coils. N Narrow groove welding: GMAW process that was devel- oped to weld thick sections using a groove that is much narrower than normal. Also called narrow gap welding. National Pipe Thread Tapered Thread (NPT): A type of tapered thread typically used for pipes and pipe fi ttings. Natural gas: Naturally occurring mixture of hydrocarbons in gaseous form. NEMA: Acronym for the National Electrical Manufac- turers’ Association. Neutral fl ame: The fl ame resulting from combustion of perfect proportions of oxygen and the welding gas. Neutral gases: Gases, such as carbon monoxide or hydrogen, that prevent oxygen in the air from combining with molten metal. Newton: The SI Metric unit of force. A force of 9.8 newtons is required to lift a mass of 1 kilogram. Nickel-based electrode: An electrode that contains from 45% to 85% nickel, depending on its designation. Nitriding: A casehardening process that involves adding nitrogen to a solid ferrous alloy by keeping the alloy at a suitable temperature while in contact with a material rich in nitrogen. Nodular cast iron: Cast iron containing primary graphite that is in a ball-like or globular form, rather than in fl akes as in gray cast iron. Also known as spheroidal graphite iron, it is more ductile and has greater strength than ordinary iron. Nonactive (R) fl uxes: Soldering fl uxes that consist of rosins dissolved in alcohol or turpentine and are used only on highly solderable surfaces. Nondestructive evaluation: A nonstandard term. See Nondestructive examination. Nondestructive examination (NDE): The act of determining the suitability of materials or parts, using techniques that do not affect the serviceability of the part or material. Nondestructive testing (NDT): Tests performed to check a weld’s quality without damaging it. Nonessential variables: Variables that, when changed from the approved welding procedure specifi cations, do not require requalifi cation of the procedure. Nonferrous metal: A metal that contains no iron. Nonmetallic: Term that indicates a material does not contain metal. Nontransferred: Term that means the pilot arc is formed between different parts of the torch rather than between the torch and the work. Nontransferred arc: A pilot arc between the negative electrode and a positive constricting nozzle of a plasma arc torch. Normalizing: The process of heating steel above the temperature used for annealing and then cooling it in still air at room temperature. Used as a preparation for further heat treatment. Normalized steel has a uniform unstressed condition with a grain size and refi nement that makes the metal more suitable for heat treating. Notch brittleness: Tendency of a material to break at points where stress is concentrated. Notch sensitivity: A measure of the extent of reduction of strength in a metal after introducing stress concentra- tion (by notching). Nozzle: A device that directs a shielding medium or gas. Number drill sets: Drill sets that begin with No. 1 (0.228″) and go to No. 80 (0.0135″). In number drills, the higher the number, the smaller the drill. O Object line: A solid black line that defi nes the outline of an object. Occupational Safety and Health Administration (OSHA): Federal agency responsible for setting and enforcing regulations regarding workplace health and safety. Off time: In resistance welding, the time that the elec- trodes are off the work. It can also be defi ned as the time between repeating cycles. One-atmosphere pressure vessel: A chamber built around an underwater welding project. The chamber has a passageway or tube to the surface. Pressure inside the vessel is one atmosphere. Open bottom chamber: A chamber built around an underwater welding project. Water is forced out of the chamber using pressurized air. The chamber is open on the bottom for the welder/diver to enter. Optical pyrometer: Temperature-measuring device that compares the incandescence (white, glowing heat) of a heated object with an electrically heated fi lament whose incandescence can be regulated. Organic fl uxes: Soldering fl uxes that contain carbon, are moderately active, and have a medium level of cleaning ability. Orifi ce: The opening or hole(s) in a torch tip through which a gas fl ows.