Glossary 871 Groove weld: Welding rod fused into a joint that has the base metal removed to form a V, U, or J trough at the edge of the metals to be joined. Groove weld size: The depth to which the weld penetrates into the base metal. Gross porosity: Large pores, gas holes, or globular voids in a weld or casting. Called gross because they are bigger and more numerous than would be found in good practice. Guided bend test: Bending a specimen in a defi nite way by using a fi xture. Guided side bend test: A test, used on thick materials, in which a side bend test sample is removed from the test weld and bent using a jig. Gun set-up jig: A tool used in the robotic workcell to locate a predetermined point in space (set-up point). Gun welders: Portable spot welding machines. Also called PSW guns or gun welding machines. Gun welding machines: Portable spot welding machines. Also called gun welders or PSW guns. H Half-scale: Drawn one-half of actual size. Half-wave rectifi ed ac: Simplest manner of rectifi cation in which the reverse half of the cycle is blocked out completely. Result is a pulsating direct current with intervals when no current is fl owing. Hall process: The production of aluminum by electrolysis of a molten solution of purifi ed alumina in cryolite. Halogen gas leak test: Locating leaks by putting halogen gas (refrigerant) into a pipe or tube under pressure. Any leak is detected by a very sensitive electronic ionizing sniffer and is indicated by a meter reading or by a buzzer sound. Hammer forging: Process involving deforming of the work- piece by repeated blows. Hammer welding: Forge welding done using power hammers, fi xtures, and presses. Hand shield: An approved arc welding helmet designed to be hand held. Often used by instructors or observers. Hardening: Making metal harder by a process of heating and cooling. Hardfacing: Surfacing material deposited on a surface so that it will resist abrasion, erosion, wear, corrosion, galling, or impact wear. Hardness: Ability of metal to resist plastic deformation. The same term may refer to stiffness or temper, resis- tance to scratching or abrading. Hard-surfacing: Laying beads of comparatively hard alloys side-by-side on the surfaces of a softer base metal. HAZ: See Heat-affected zone. Heat: Molecular energy of motion. Heat-affected zone (HAZ): That part of the base metal altered by heat from welding, brazing, or cutting operations. Heat-checking: Crazing of a die surface, especially one subjected to alternate heating and cooling. Heat conductivity: Speed and effi ciency of heat energy movement through a substance. Heat of combustion: The heat released by the process of burning. Heat shield: A shield installed on some plasma arc cutting torches in order to protect the torch from the high heat of the cutting process and to direct shielding gas in a dual fl ow torch. Heat-treatable alloys: Aluminum alloys that reach maximum strength by solution heating and quenching. Heat treatable low alloy (HTLA) steels: Highly hardenable steels with a carbon content of .25% to .45% plus manga- nese, nickel, chromium, and molybdenum. Require heat treating after welding to develop high strength. Helium (He): Inert, colorless, gaseous element used as a shielding gas in welding. Helmet: Protective hood that fi ts over the arc welder’s head, provided with an approved fi ltering lens through which the operator may safely observe the electric arc. Hertz: Unit of frequency equal to one cycle per second. Hexagonal close-packed structure: A metallic structure with hexagonal crystals. Hidden edge lines: Dashed lines that represent any line of an object that is hidden from view by material in front of it. High-pressure gauge: The gauge on a pressure regulator that shows the cylinder pressure. High-strength low-alloy (HSLA): Structural steels that typically have a low carbon content of .15% to .20% and only 1% to 3% alloying elements, but are 10% to 50% stronger than mild steel. High-voltage starting: A starting method in which a high- voltage surge causes the arc to jump the gap and start. Hold time: Time that force continues to be applied to elec- trodes in resistance welding after the current is turned off. Home point: See Set-up point. Hopper: Bell-shaped opening at the top of a blast furnace. Horizontal (2G) welding position: A welding position in which the weld axis is horizontal and the weld face is vertical or near vertical. Horn: The arm of a resistance welding machine that carries the current and applies the electrode pressure. Horn spacing: In a spot welding machine, the distance between the electrode arms when the electrodes are closed. Hose: A fl exible, usually reinforced, rubber tube used to carry pressurized gases or water to a torch. Hot forming: Term for operations performed on metal while it is above its recrystallization temperature. Hot forming operations may include bending, drawing, forging, heading, piercing, and pressing. Hot pass: The second pass or layer of a multiple pass weld. Hot shortness: A weakness of metal that occurs in the hot forming temperature range. Hot working: Shaping of metal at a temperature and rate that does not cause strain hardening. Housekeeping: Cleaning and organizing the work area. Hydrogen: A gaseous element. When ignited in the pres- ence of oxygen, it forms a very clean fl ame.