• INTERRUPTED SPOT WELDING

    A nonstandard term for MULTI-IMPULSE WELDING. 

  • INVERTER POWER SUPPLY

    A welding power supply that utilizes solid-state components to change the incoming 60 Hz power to a higher frequency, nominally 18 to 100 kHz. Changing the frequency results in greatly reduced size and weight of the transformer. Inverters can be used with all of the arc welding processes. 

  • ION

    An atom, or group of atoms, of matter which has gained or lost one or more outer shell electrons, and which therefore carries an electrical charge. Positive ions, or cations, are deficient in outer shell electrons. Negative ions, or anions, have an excess of outer shell electrons. The ion or charged atom provides an electrical conductor for the arc welding current to follow from the electrode to the workpiece. 

  • IONIC BOND

    A primary bond arising from the electrostatic attraction between two oppositely charged ions. 

  • IONIZATION POTENTIAL

    The energy necessary to remove from or add one or more electrons to an atom, thereby making it an ion. The potential energy requirement varies, depending on the material involved. The term ionization potential is generally used when referring to shielding gases with the GMAW or GTAW welding processes. See ION. 

  • IRON

    (Chemical symbol: Fe). The most abundant of metallic elements, known and used since very early times. Pure iron, which is practically unknown in industry, is silver-white, very ductile, malleable, and magnetic. It is the basis for many important alloyed structural materials. It has a specific gravity of 7.87; atomic weight, 55.84; melting point, 1536°C (2797°F); boiling point, 3000°C (5432°F).

    Iron ores occur in large deposits in many parts of the world in the form of various iron oxides. The ore is heated in a blast furnace with limestone and coke to produce molten pig iron, and with further treatment, is converted into steel. 

  • IRON LOSS

    The hysteresis and eddy current losses in the iron cores of electrical machinery. 

  • IRON SOLDERING (INS)

    A soldering process in which the heat required is obtained from a soldering iron. 

  • IRON, PIG

    See CAST IRON. 

  • ISOTHERMAL TRANSFORMATION DIAGRAM

    A diagram which graphically describes the time delay and the reaction rate of austenite transformation to pearlite, bainite or martensite. It also shows the temperature at which these transformations take place. 

  • ISOTOPE RADIOGRAPHY

    The production of radiographs using an isotope as a source of radiation.

    Radioactive isotopes have largely replaced radium and X-ray machines for inspecting welds, castings, and finished products for voids and cavities. Isotopes such as cobalt-60, cesium- 137, and iridium- 192 are used in radiographic testing of lead, steel, and iron castings.

    Procedures using isotopes are similar to the techniques used with X-ray machines. A radiation source is placed on one side of the material to be tested, and photographic film on the other. After exposure, the film is developed and interpreted.

    Isotope radiography has proven safe, reliable, and versatile. Inspection of complicated machinery can be made without dismantling. Radiation sources can be of any desired shape or size, and they offer high radioactivity at relatively low cost. 

  • ISOTOPES

    Atoms of the same element which are identical in their chemical behavior but different from one another in the number of neutrons contained in their nuclei, and thus have different atomic weights. In common usage, isotopes that are radioactive are known as radioisotopes.

    Isotopes have an important role in industry as production aids, serving in three basic fields: (1) as tracers and gauges, “super-detectives” for monitoring and controlling a wide variety of industrial operations; (2) in place of X-ray machines, as cameras for spotting machinery faults and wear; and (3) as catalysts or active agents in creating and modifying materials.

    Isotopes also act as flow tracers for detecting leaks in buried or inaccessible equipment. In a typical case, a leak was suspected in the copper tubing of a heating system buried in the concrete floor of a factory. A small amount of a radioisotope (iodine-131) was added to the water of the heating system. A Geiger counter quickly located the increased radioactivity at the leak; the break was repaired by removing a section of flooring only 15 cm (6 in.) long. 

  • IZOD TEST

    An impact test performed on a specimen of a metallic material to evaluate resistance to failure at a discontinuity and to evaluate the resistance of a comparatively brittle material during extension of a crack.

    In an Izod test, a small bar of round or square cross section is held as a cantilevered beam in the gripping anvil of a pendulum machine. The specimen is broken by a single overload of the swinging pendulum, and the energy absorbed in breaking the specimen is recorded by a stop pointer moved by the pendulum. The Izod specimen can be tested as an unnotched bar, or it can be prepared with a 45” V-notch in the face struck by the pendulum. The energy absorbed in breaking Izod specimens is reported in joules (1 joule = .0737 ft/lb). Standard methods for impact testing can be found in ASTM E23, Notched Bar Impact Testing of Metallic Materials.

    The Izod test of the notched specimen is particularly useful for detecting the presence of embrittling constituents, which might be caused by nitrides that take form during aging or in slow cooling after annealing, and for locating the brittle zone. This test does not reflect the tensile properties of the weld or the parent metal. See CHARPY TEST. See Figure C-4. 

  • I²R LOSS

    The power loss due to current flowing through a conductor which has resistance. This loss is converted into heat; its units are watts.