A B C DE F G H I J K L M N O P Q R Sa-Sq St-Sy T U V W X Y Z
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gage
(1) The thickness of sheet or the diameter of wire. The various standards are arbitrary and differ with regard to ferrous and nonferrous products as well as sheet and wire. (2) An aid for visual inspection that enables an inspector to determine more reliably whether the size or contour of a formed part meets dimensional requirements. (3) An instrument used to measure thickness or length.
gage length
The original length of that portion of the specimen over which strain, change of length and other characteristics are measured.
gall
To damage the surface of a powder metallurgy compact or die part, caused by adhesion of powder to the die cavity wall or a punch surface.
galling
(1) A condition whereby excessive friction between high spots results in localized welding with subsequent spalling and a further roughening of the rubbing surfaces of one or both of two mating parts. (2) A severe form of scuffing associated with gross damage to the surfaces or failure. Galling has been used in many ways in tribology; therefore, each time it is encountered its meaning must be ascertained from the specific context of the usage. See also scoring and scuffing.
galvanic cell
(1) A cell in which chemical change is the source of electrical energy. It usually consists of two dissimilar conductors in contact with each other and with an electrolyte, or of two similar conductors in contact with each other and with dissimilar electrolytes. (2) A cell or system in which a spontaneous oxidation-reduction reaction occurs, the resulting flow of electrons being conducted in an external part of the circuit.
galvanic corrosion
Corrosion associated with the current of a galvanic cell consisting of two dissimilar conductors in an electrolyte or two similar conductors in dissimilar electrolytes. Where the two dissimilar metals are in contact, the resulting reaction is referred to as couple action.
galvanic couple
A pair of dissimilar conductors, commonly metals, in electrical contact. See also galvanic corrosion.
galvanic current
The electric current that flows between metals or conductive nonmetals in a galvanic couple.
galvanic series
A list of metals and alloys arranged according to their relative corrosion potentials in a given environment. Compare with electromotive force series.
galvanize
To coat a metal surface with zinc using any of various processes.
galvanneal
To produce a zinc-iron alloy coating on iron or steel by keeping the coating molten after hot dip galvanizing until the zinc alloys completely with the basis metal.
gamma iron
The face-centered cubic form of pure iron, stable from 910 to 1400 °C (1670 to 2550 °F).
gamma ray
Short-wavelength electromagnetic radiation, similar to x-rays but of nuclear origin, with a range of wavelength from about 10-14 to 10-10 m. See also electromagnetic radiation.
gamma structure
Structurally analogous phases or electron compounds having ratios of 21 valence electrons to 13 atoms. This is generally a large, complex cubic structure.
gang milling
Milling with several cutters mounted on the same arbor or with workpieces similarly positioned for cutting either simultaneously or consecutively during a single setup.
gang slitter
A machine with a number of pairs of rotary cutters spaced on two parallel shafts, used for slitting metal into strips or for trimming the edges of sheets.
gangue
The worthless portion of an ore that is separated from the desired part before smelting is commenced.
gap-frame press
A general classification of press in which the uprights or housings are made in the form of a letter C, thus making three sides of the die space accessible.
gas atomization
An atomization process whereby molten metal is broken up into particles by a rapidly moving inert gas stream.
gas classification
The separation of a powder into its particle size fractions by means of a gas stream of controlled velocity flowing counterstream to the gravity-induced fall of the particles. The method is used to classify submesh-size particles.
gaseous corrosion
Corrosion with gas as the only corrosive agent and without any aqueous phase on the surface of the metal. Also called dry corrosion. See also hot corrosion , oxidation , and sulfidation.
gas holes
Holes in castings or welds that are formed by gas escaping from molten metal as it solidifies. Gas holes may occur individually, in clusters, or throughout the solidified metal.
gas metal arc cutting
An arc cutting process used to sever metals by melting them with the heat of an arc between a continuous metal (consumable) electrode and the work. Shielding is obtained entirely from an externally supplied gas or gas mixture.
gas metal arc welding (GMAW)
An arc welding process that produces coalescence of metals by heating them with an arc between a continuous filler metal electrode and the workpieces. Shielding is obtained entirely from an externally supplied gas.
gas pocket
A cavity caused by entrapped gas.
gas porosity
Fine holes or pores within a metal that are caused by entrapped gas or by the evolution of dissolved gas during solidification.
gas shielded arc welding
A general term used to describe gas metal arc welding, gas tungsten arc welding, and flux cored arc welding (when gas shielding is employed).
gassing
(1) Absorption of gas by a metal. (2) Evolution of gas from a metal during melting operations or upon solidification. (3) Evolution of gas from an electrode during electrolysis.
gas torch
See preferred terms cutting torch (arc) , cutting torch (oxyfuel gas) , welding torch (arc) , and welding torch (oxyfuel gas).
gas tungsten arc cutting
An arc-cutting process in which metals are severed by melting them with an arc between a single tungsten (nonconsumable) electrode and the workpiece. Shielding is obtained from a gas or gas mixture.
gas tungsten arc welding (GTAW)
An arc welding process that produces coalescence of metals by heating them with an arc between a tungsten (nonconsumable) electrode and the work. Shielding is obtained from a gas or gas mixture. Pressure may or may not be used and filler metal may or may not be used.
gas welding
See preferred term oxyfuel gas welding.
gate
The portion of the runner in a mold through which molten metal enters the mold cavity. The generic term is sometimes applied to the entire network of connecting channels that conduct metal into the mold cavity. See also gating system.
gated pattern
In foundry practice, a pattern that includes not only the contours of the part to be cast but also the gates.
gathering
A forging operation that increases the cross section of part of the stock; usually a preliminary operation.
gathering stock
Any operation whereby the cross section of a portion of the forging stock is increased beyond its original size.
gating system
The complete assembly of sprues, runners, and gates in a mold through which metal flows to enter casting cavity. The term is also applied to equivalent portions of the pattern.
gear cutting
Producing tooth profiles of equal spacing on the periphery, internal surface, or face of a workpiece by means of an alternate shear gear-form cutter or a gear generator.
geared press
A press whose main crank or eccentric shaft is connected by gears to the driving source.
gear hobbing
Gear cutting by use of a tool resembling a worm gear in appearance, having helically spaced cutting teeth. In a single-thread hob, the rows of teeth advance exactly one pitch as the hob makes one revolution. With only one hob, it is possible to cut interchangeable gears of a given pitch of any number of teeth within the range of the hobbing machine.
gear milling
Gear cutting with a milling cutter that has been formed to the shape of the tooth space to be cut. The tooth spaces are machined one at a time.
gear shaping
Gear cutting with a reciprocating gear-shaped cutter rotating in mesh with the work blank.
general corrosion
(1) A form of deterioration that is distributed more or less uniformly over a surface. (2) Corrosion dominated by uniform thinning that proceeds without appreciable localized attack. See also uniform corrosion.
gibs
Guides or shoes that ensure the proper parallelism, squareness, and sliding fit between metalforming press components such as the slide and the frame. They are usually adjustable to compensate for wear and to establish operating clearance.
glazing
Dulling the abrasive grains in the cutting face of a wheel during grinding.
glide
(1) Same as slip. (2) A noncrystallographic shearing movement, such as of one grain over another.
globular transfer
In consumable-electrode arc welding, a type of metal transfer in which molten filler metal passes across the arc as large droplets. Compare with short-circuiting transfer and spray transfer.
gold filled
Covered on one or more surfaces with a layer of gold alloy to form a clad or composite material. Gold-filled dental restorations are an example of such materials.
gooseneck
In die casting, a spout connecting a molten metal holding pot, or chamber, with a nozzle or sprue hole in the die and containing a passage through which molten metal is forced on its way to the die. It is the metal injection mechanism in a hot chamber machine.
gouging
In welding practice, the forming of a bevel or groove by material removal. See also arc gouging and oxygen gouging.
gouging abrasion
A form of high-stress abrasion in which easily observable grooves or gouges are created on the surface. See also abrasion.
G-P zone
A Guinier-Preston zone.
graded abrasive
An abrasive powder in which the sizes of the individual particles are confined to certain specified limits. See also grit size.
grain
An individual crystal in a polycrystalline material; it may or may not contain twinned regions and subgrains.
grain boundary
A narrow zone in a metal or ceramic corresponding to the transition from one crystallographic orientation to another, thus separating one grain from another; the atoms in each grain are arranged in an orderly pattern.
grain-boundary corrosion
Same as intergranular corrosion. See also interdendritic corrosion.
grain-boundary sulfide precipitation
An intermediate state of overheating of metals in which sulfide inclusions are redistributed to the austenitic grain boundaries by partial solution at the overheating temperature and reprecipitation during subsequent cooling.
grain coarsening
A heat treatment that produces excessively large austenitic grains in metals.
grain flow
Fiberlike lines on polished and etched sections of forgings caused by orientation of the constituents of the metal in the direction of working during forging. Grain flow produced by proper die design can improve required mechanical properties of forgings. See also flow lines and forged structure.
grain growth
(1) An increase in the average size of the grains in polycrystalline material, usually as a result of heating at elevated temperature. (2) In polycrystalline materials, a phenomenon occurring fairly close below the melting point in which the larger grains grow still larger while the smallest ones gradually diminish and disappear. See also recrystallization.
grain refinement
The manipulation of the solidification process to cause more (and therefore smaller) grains to be formed and/or to cause the grains to form in specific shapes. The term refinement is usually used to denote a chemical addition to the metal but can refer to control of the cooling rate.
grain refiner
A material added to a molten metal to induce a finer-than-normal grain size in the final structure.
grain size
(1) For metals, a measure of the areas or volumes of grains in a polycrystalline material, usually expressed as an average when the individual sizes are fairly uniform. In metals containing two or more phases, grain size refers to that of the matrix unless otherwise specified. Grain size is reported in terms of number of grains per unit area or volume, in terms of average diameter, or as a grain-size number derived from area measurements. (2) For grinding wheels, see preferred term grit size.
grain size distribution
Measures of the characteristic grain or crystallite dimensions (usually, diameters) in a polycrystalline solid; or of their populations by size increments from minimum to maximum. Usually determined by microscopy.
granular fracture
A type of irregular surface produced when metal is broken that is characterized by a rough, grainlike appearance, rather than a smooth or fibrous one. It can be subclassified as transgranular fracture or intergranular fracture. This type of fracture is frequently called crystalline fracture; however, the inference that the metal broke because it “crystallized” is not justified, because all metals are crystalline in the solid state. See also fibrous fracture and silky fracture.
granulated metal
Small pellets produced by pouring liquid metal through a screen or by dropping it onto a revolving disk, and, in both instances, chilling with water.
graphitic carbon
Free carbon in steel or cast iron.
graphitic corrosion
Corrosion of gray iron in which the iron matrix is selectively leached away, leaving a porous mass of graphite behind; it occurs in relatively mild aqueous solutions and on buried pipe and fittings.
graphitic steel
Alloy steel made so that part of the carbon is present as graphite.
graphitization
The formation of graphite in iron or steel. Where graphite is formed during solidification, the phenomenon is termed primary graphitization; where formed later by heat treatment, secondary graphitization.
graphitizing
Annealing a ferrous alloy such that some or all the carbon precipitates as graphite.
gravity hammer
A class of forging hammer in which energy for forging is obtained by the mass and velocity of a freely falling ram and the attached upper die. Examples are the board hammer and air-lift hammer.
gravity segregation
Variable composition of a casting or ingot caused by settling out of heavy constituents, or rising of light constituents, before or during solidification.
gray cast iron
See gray iron.
gray iron
A cast iron characterized by a gray fracture surface due to the presence of flake graphite.
green compact
An unsintered powder metallurgy or ceramic compact.
green density
The density of a green compact.
green rot
A form of high-temperature attack on stainless steels, nickel-chromium alloys, and nickel-chromium-iron alloys subjected to simultaneous oxidation and carburization. Basically, attack occurs first by precipitation of chromium as chromium carbide, then by oxidation of the carbide particles.
green sand
A naturally bonded sand, or a compounded molding sand mixture, that has been “tempered” with water and that is used while still moist.
green sand core
(1) A core made of green sand and used as-rammed. (2) A sand core that is used in the unbaked condition.
green sand mold
A casting mold composed of moist prepared molding sand. Contrast with dry sand mold.
green strength
(1) The strength of a tempered foundry sand mixture at room temperature. (2) The ability of a green compact to maintain its size and shape during handling and storage prior to sintering. (3) The tensile or compressive strength of a green compact.
grindability
Relative ease of grinding, analogous to machinability.
grindability index
A measure of the grindability of a material under specified grinding conditions, expressed in terms of volume of material removed per unit volume of wheel wear.
grinding
Removing material from a workpiece with a grinding wheel or abrasive belt.
grinding burn
See burning.
grinding cracks
Shallow cracks formed in the surfaces of relatively hard materials because of excessive grinding heat or the high sensitivity of the material. See also grinding sensitivity.
grinding fluid
An oil- or water-based fluid introduced into grinding operations to (1) reduce and transfer heat during grinding, (2) lubricate during chip formation, (3) wash loose chips or swarf from the grinding belt or wheel, and (4) chemically aid the grinding action or machine maintenance.
grinding oil
An oil-type grinding fluid; it may contain additives, but not water.
grinding relief
A groove or recess located at the boundary of a surface to permit the corner of the wheel to overhang during grinding.
grinding sensitivity
Susceptibility of a material to surface damage such as grinding cracks; it can be affected by such factors as hardness, microstructure, hydrogen content, and residual stress.
grinding stress
Residual stress, generated by grinding, in the surface layer of work. It may be tensile or compressive, or both.
grinding wheel
A cutting tool of circular shape made of abrasive grains bonded together. See also diamond wheels.
grit
Crushed ferrous or synthetic abrasive material in various mesh sizes that is used in abrasive blasting equipment to clean castings. For materials used for grinding belts or grinding wheels, see the preferred term abrasive.
grit blasting
Abrasive blasting with small irregular pieces of steel, malleable cast iron, or hard nonmetallic materials.
grit size
Nominal size of abrasive particles in a grinding wheel, corresponding to the number of openings per linear inch in a screen through which the particles can pass.
Grossmann number (H)
A ratio describing the ability of a quenching medium to extract heat from a hot steel workpiece in comparison to still water defined by the following equation: where h is the heat transfer coefficient and k is the conductivity of the metal.
gross porosity
In weld metal or in a casting, pores, gas holes, or globular voids that are larger and in much greater numbers than those obtained in good practice.
groundbed
A buried item, such as junk steel or graphite rods, that serves as the anode for the cathodic protection of pipelines or other buried structures.
ground connection
In arc welding, a device used for attaching the work lead (ground cable) to the work.
growth (cast iron)
A permanent increase in the dimensions of cast iron resulting from repeated or prolonged heating at temperatures above 480 °C (900 °F) due either to graphitizing of carbides or oxidation.
Guerin process
A rubber-pad forming process for forming sheet metal. The principal tools are the rubber pad and form block, or punch.
guided bend
The bend obtained by use of a plunger to force the specimen into a die in order to produce the desired contour of the outside and inside surfaces of the specimen.
guided bend test
A test in which the specimen is bent to a definite shape by means of a punch (mandrel) and a bottom block.
guide mill
A small hand mill with several stands in a train and with guides for the work at the entrance to the rolls.
Guinier-Preston (G-P) zone
A small precipitation domain in a supersaturated metallic solid solution. A G-P zone has no well-defined crystalline structure of its own and contains an abnormally high concentration of solute atoms. The formation of G-P zones constitutes the first stage of precipitation and is usually accompanied by a change in properties of the solid solution in which they occur.
gun drill
A drill, usually with one or more flutes and with coolant passages through the drill body, used for deep hole drilling.
gutter
A depression around the periphery of a forging die impression outside the flash pan that allows space for the excess metal; surrounds the finishing impression and provides room for the excess metal used to ensure a sound forging. A shallow impression outside the parting line.