Gage Length

The original length of that portion of the specimen over which strain or change of length is determined.

Gage Marks

Reference marks; in tensile testing, the marks which indicate the gage length, used in determination of tensile elongation.

Gagger

A metal piece of irregular shape (usually an L shape) used to reinforce and support sand in deep pockets of molds. There are two types; straight or hooked (cast or steel rods).

Gaging

Checking dimensional requirement by means of a gage.

Gamma iron

One of the allotropic (polymorphic) forms of iron which crystallizes in the face-centered-cubic lattice form. When pure, its range of stability is from 1,670°F to 2,552°F (910°C to 1400°C).

Gannister

An acid (silicious) refractory often used in furnace linings.

Gas Holes

Rounded cavities caused by generation or accumulation of gas or entrapped air in a casting; holes may be spherical, flattened or elongated.

Gas Porosity

A condition existing in a casting caused by the trapping of gas in the molten metal, or by mold gases evolved during the pouring of the casting.

Gate

Specifically, the point at which molten metal enters the casting cavity. Sometimes employed as a general term to indicate the entire assembly of connected columns and channels carrying the metal from the top of the mold to that part forming the casting cavity proper. This term is also applied to pattern parts that form the passages, or to the metal that fills them.

Gated Patterns

One or more patterns with gating systems attached. See Gate, Pattern.

Gating System

The complete arrangement of gates, runners, and sprues through which molten metal flows into the cavity of the mold. See Cavity, Gate, Molds, Runners, Sprues.

Gilsonite

Natural black lustrous asphalt found in the Uinta Mountains in Utah and also known as uintaite. It is used as a carbonaceous addition to foundry sands.

Gooseneck

The pressure vessel or metal injection mechanism in a hot-chamber-type die-casting machine.

Gouging Abrasion

Abrasion involving gross surface indentation and possible removal of sizable metal fragments.

Grade

The grade of an iron, usually given by three successive numbers, the first being the tensile strength (KSI), the second the yield strength (KSI), and the third the elongation (%).

Grain Fineness Number

A system developed by AFS for rapidly expressing the average grain size of a given sand. It approximates the number of meshes per inch of that sieve that would just pass the sample if its grains of uniform size. It is approximately proportional to the surface area per unit of weight of sand, exclusive of clay.

Grain Refiner

Any material added to a liquid metal or alloy or treatment which produces a finer grain size in the subsequent solid.

Grains

Crystals in metals and alloys.

Granular Fracture (Crystalline fracture)

A type of irregular surface produced when metal is broken.

Granular Pearlite

A structure formed from ordinary lamellar pearlite by long annealing at a temperature below but near to the critical point, causing the cementite to spheroidize in a ferrite matrix.

Graphite

Native carbon in hexagonal crystals, also foliated or granular massive, of black color with metallic luster, and soft. Used for crucibles, foundry facings, lubricants, etc. Also made artificially by passing alternating current through a mixture of petroleum coke and coal tar pitch. See Coke, Crucible.

Graphite, Primary

Carbon precipitated as graphite flakes while the iron cools through the freezing eutectic in which austenite, graphite, molten iron, and carbide exist together. Usually with reference to white fracture cast iron.

Graphite, Secondary

Graphite formed by decomposition of austenite during slow cooling of cast iron.

Graphitization

The decomposition of carbide to give free carbon as graphite or as temper carbon.

Graphitizer

Any substance, such as silicon, titanium, aluminum, etc., which promotes the formation of graphite in cast iron compositions.

Gray Iron

Iron in which a large percentage of the carbon content is in the form of graphite flakes. Traditionally referred to as “Cast Iron”. The graphite flakes cause it to have low shock resistance, but high damping ability. It has a gray fracture. Gray Iron is by far the oldest and most common form of cast iron. As a result, it is assumed by many to be the only form of cast iron and the terms "cast iron" and "gray iron" are used interchangeably. Cast iron containing graphite in flake form and typically consisting of 2 to 4 percent carbon and 1 to 3 percent silicon. Gray iron is widely used for engine components in automobiles and trucks. See Cast Iron.

Gray Iron Meltimg

The process of melting gray iron, especially as it is done in a foundry on a commercial scale. See Gray Iron.

Gray Iron Quality Control

The application of quality control practices to the manufacture of gray iron. See Gray Iron.

Green Permeability

Property of a molded mass of sand in its tempered condition which is a measure of its ability to permit the passage of gases through it.

Green Sand

Natural sands combined with water and organic additives, such as clay, to proper consistency for creating molds. See Core, Molds, Natural Sand.

Green Sand Core

A core that is made of molding sand but not baked.

Green Strength

Tenacity (compressive, shear, tensile, or transverse) of a tempered sand mixture at room temperature.

Grinding

Removing gate stubs, fins, and other projections on castings by an abrasive wheel. See Casting, Gate, Fins.

Growth

With reference to cast iron, permanent increase in volume that results from continued or repeated cyclic heating and cooling at elevated temperatures. For unalloyed iron, temperature is in excess of 900° F, and growth is cause by decomposition or graphitization of carbides and by oxidation of the graphite. See Cast Iron.

Guide Pin

The pin on a flask used to locate the cope in the proper place on the drag; also used to locate cheeks. See Cope, Cheek, Drag, Flask.

Gypsum Cement

Calcined calcium sulfate, commonly called plaster of Paris.