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Everything You Ever Wanted to Know About Aluminum Casting

Aluminum casting comes with a lot of questions. What does green permeability mean? What is an insulating sleeve used for? And what role does a gate play in the pouring process?

We hope to answer all of these questions and more by sharing an industry glossary of terms we’ve created, just for our customers who’d like to have a better understanding of the aluminum casting process.  

worker cutting molds down by hand

Casting 101: A Glossary of Aluminum-Casting Terms


A change in properties of metals and alloys which occurs slowly at room temperature and will proceed rapidly at higher temperatures. A change in the metal or alloy by which its structure recovers from an unstable condition produced by quenching, quench aging, or by cold working, strain aging. The change in structure consists. The change in properties is often, but not always, due to a phase change, precipitation, but never involves a change in chemical composition of the metal or alloy.


A reverse taper from the designed direction of draw from a pattern or corebox; prevents removal of a pattern from a mold without damage to the mold-tear ups.

Blind Riser

A riser not opened to the atmosphere or does not reach to the exterior of the mold.


A casting defect due to trapping of gas in molten or partially molten metal.

Blow Hole

A hole, or void, left in the casting caused by trapped air or gases

Brinell Hardness

The value of hardness of a metal on an arbitrary scale representing kg/mm2 determined by measuring the diameter of the impression made by a ball of given diameter applied under a known load. Values are expressed in Brinell Hardness Numbers, BHN


Bulging of a large flat face of a casting; in investment casting, caused by dip coat peeling from the pattern. Defect on a casting surface, appearing as an indention resulting from an expansion scab. An indentation in a casting, resulting from expansion of the sand, may be termed the start of an expansion defect.


A misnomer usually indicating metal penetration into sand resulting in a mixture of sand and metal adhering to the surface of a casting. Sand adhering to the surface of the casting which is extremely difficult to remove. This condition may be due to soft molds, poor sand compaction, insufficient mould coating (graphite) paint, or high pouring temperature.

Cast Plate

Metal plate, usually aluminum, cast with the cope pattern on one side and the drag pattern on the other.


A process where molten metal is poured into a mold and solidification is allowed to take place. The act of pouring metal.


A metal object obtained by pouring molten metal into a mold. The metal shape, exclusive of gates and risers, that is obtained as a result of pouring metal into a mold.

Casting Layout

A check of dimensions against applicable drawings and specifications.


Metal supports or spacers used in molds to maintain the cores, or parts of a mold, which are not self-supporting. Chaplets maintain these dimensions during the casting process, they then become part of the casting itself as the molten metal solidifies around the chaplet and fuses it into the finished casting


Metal, graphite or carbon blocks that are incorporated into the mold or core to locally increase the rate of heat removal during solidification and reduce shrinkage defects, include directional solidification and reduce shrinkage defects. A device used to cool an isolated area of a mold.


Restriction in the gating system that controls the flow rate of metal into the mold cavity.

Choke or Primary Choke

The part of the gating system that most restricts or regulates the flow of metal into the mold cavity

Close Over

The operation of lowering a part of the mold over some projecting portion such as a core.

Cold Box Process

A rapid coremaking process which does not require application of heat to cure the cores. Hardening of the cores is accomplished by chemical reaction rather than by conventional baking. A phenolic resin is added to the sand used to make the core. This resin reacts chemically when exposed to an accelerator, typically an active organic gas, and hardens very quickly, forming an organic bond in the core sand. This reaction occurs at room temperature and does not require special coreboxes or equipment. Additionally, since the bond is organic, the sand collapses readily during shakeout and can be recovered easily from the casting.

Cold Lap

Wrinkled markings on the surface of an ingot or casting from incipient freezing of the surface.


The top half of a horizontally parted mold. The upper or topmost section of a flask, mold, or pattern.


A bonded sand insert placed in the mold to form an undercut or hollow section in the casting which cannot be shaped by the pattern. A core is frequently used to create openings and various shaped cavities in the casting. The shaped body of sand which forms interior of casting and also selected external features.

Core Box

A mold in which a core is formed. A wood, metal or plastic box, whose cavity has the shape of the desired core which is to be made therein.

Core Fin

A casting defect, a depression in the casting caused by a fin on the core that was not removed before the core was set, or by paste that has oozed out from between the joints

Core Float

A casting defect caused by core movement towards the cope surface of the mold, as a result of core buoyancy in liquid steel, resulting in a deviation from the intended wall thickness.

Core Shift

A defect resulting from the movement of the core from its proper position in the mold cavity. A variation from specified dimensions of a cored section due to a change in position of the core or misalignment of cores in assembling


A projection on a pattern which leaves an impression in the mold for supporting the core.


A casting defect, such as buckling or breaking, of a section of mold due to incorrect register when closing. Also, an indentation in the casting surface due to displacement of sand in the mold when the mold is closed.

Crush Strip or Bead

An indentation in the parting line of a pattern plate which ensures that cope and drag have good contact by producing a ridge of sand which crushes against the other surface of the mold or core


Usually a chemical reaction resulting from a compound added to molten metal to remove gases from the metal. Often inert gases are used in this operation.


Indefinite term referring to any extraneous material entering a mold cavity and usually forming a blemish on the casting surface

Dirt Trap

A well employed in a gating system to entrap the first metal poured, which may contain dirt or unwanted particles (ineffective).

Dispersed Shrinkage

Small shrinkage cavities dispersed through the casting, which are not necessarily cause for rejection.


A pin used between the sections of parted patterns or core boxes to locate and hold them in position, registering them correctly


Lower or bottom section of a mold, pattern or flask.


A term used to temper, to remove pattern from mold, as an external contraction defect on surface of mold. To remove a pattern from a mold

Drop (Dropout)

A casting defect caused by sand dropping from the cope or other overhanging section.

Drop Gate

A term for a pouring gate or runner leading directly into the top of the mold.


Metal oxides and other scum on the surface of molten metal or in a metal or alloy (mostly a non-ferrous term).

Dye Penetrant

Penetrant is used to crack detection, which has a dye added to make it more readily visible under normal or black-lighting conditions. In the case of normal lighting, the dye is usually red and nonfluorescent. With black lighting, the dye is fluorescent and yellow-green in color.


A measure of a material’s ductility. Given in a percent, it indicates the amount a material will deform before permanent deformation. The higher the number, the more ductile. See Ductility.

Expansion, Sand

Dimensional increase that sand undergoes when subjected to elevated temperature conditions.


A concave corner piece, often a preformed strip of leather or wax, used on foundry patterns used at the intersection of two surfaces to round out a sharp corner.


The filtering out of unwanted gases in the casting, at pouring off portion of making the casting.


A thin projection of metal from the casting, formed as a result of imperfect mold or core joints. See Casting, Core.

Finish (machine)

Amount of metal allowed for machining.


Thin fin or web of metal extending from the casting along the joint line due to the cope and drag not matching completely or where core and coreprint do not match

Flat Back

A pattern with a flat surface at the joint of the mold. It lies wholly within the drag or cope, and this joint of the mold is a plane surface. See Cope, Drag, Mold, Pattern.


Any substance used to promote fusion. Also any material which reduces, oxidizes, or decomposes impurities so that they are carried off as slags or gases.

Foundry Ladle

A vessel for holding molten metal and conveying it from cupola to the molds.

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.


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.

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.

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 Strength

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


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

Hard Sand Match (Match Plate)

A body of sand shaped to conform to the parting line upon which a pattern is laid in starting to make a mold. Sand is made hard by addition of linseed oil and litharge, Portland cement, etc. See Match.


Resistance of a material to indentation as measured by such methods as Brinell, Rockwell, and Vickers. The term hardness also refers to stiffness of a material, or its resistance to scratching, abrasion, or cutting. See BHN, Brinell Hardness, Vickers Diamond.


Relative term referring to the resistance of a metal to plastic deformation from a given standard load applied on a standard penetration head. See BHN, Brinell Hardness, Vickers Diamond.


A single furnace charge of metal to be used for pouring directly into mold cavities; a heat may be all of part of a master heat. See Mold Cavity.

Heat Treatment 

A combination of heating and cooling operations timed and applied to a metal or alloy in the solid state in a manner which will produce desired properties.

Hot Spots

Areas of extra mass usually found at the junction of sections.

Hot Tear

Irregularly shaped fracture in a casting formed prior to completion of metal solidification resulting from stresses set up by steep thermal gradients within the casting during solidification and too much rigidity of the core or mold material. See Core, Solidification.


Cavity in a die-casting die or in a mold. See Cavity, Mold.


Particles of slag, refractory materials, sand or deoxidation products trapped in the casting during solidification. See Dirty Casting, Solidification.


The channels through which molten metal enters the mold cavity. See Gate.


Casting to be later forged or hot worked. Also, a form used for convenient handling of cast iron, aluminum, and other commercial metals. i.e., Pigs.


A part usually formed from metal, which is placed in a mold and may become an integral part of the casting. See Casting, Mold.

Insulating Sleeve

Hollow cylinders or sleeves formed of gypsum, diatomaceous earth, pearlite, vermiculite, etc. Placed in the mold at sprue and riser locations to decrease heat loss and rate of solidification of the metal contained in them. See Riser, Sprue.

Invest, Core Invest

Knock Out

To remove sand and casting from a flask

Liquid Penetrant Testing

A nondestructive testing method suitable for evaluating the surface integrity of non-magnetic and ferro-magnetic parts.

Loose Piece

Part of a pattern so attached that it remains in the mold, and is removed after the body of the pattern is drawn. In die-casting, a type of core, (which forms the undercuts, positioned in, but not fastened to, a die and so arranged as to be ejected with the die-casting, from which it is removed and used repeatedly for the same purpose. See Core Box, Pattern.

Machine Finish (Machine Stock)

Allowance of stock on the surface of the pattern to permit the machining of the casting to the required dimensions

Master Pattern

An original pattern made to produce castings which are then used as metal patterns. See Casting.


A metal or other plate on which patterns split along the parting line are mounted back to back with the gating system to form an integral piece.

Metal Penetration

Defect in the casting surface which appears as if the metal has filled the voids between the sand grains without displacing them.


Extremely fine porosity in castings caused by shrinkage or gas evolution and apparent on radiographic film as mottling. See Microshrinkage.


Very finely divided porosity resulting from interdendritic shrinkage resolved only by use of the microscope; may be visible on radiographic films as mottling. Etching shows they occur at intersections of convergent dendritic directions.


The structure and characteristic condition of metals as revealed on a ground and polished (etched or unetched) specimen at magnifications above 10 diameters. See Microsection.


Denotes an irregularity of the casting surface caused by incomplete filling of the mold due to low pouring temperature, gas back-pressure from inadequate venting of the mod, and inadequate gating.


Normally consists of a top and bottom form, made of sand, metal, or any other investment material which contains the cavity into which molten metal is poured to produce a casting of definite shape and outline. See Mold Cavity.

Mold Cavity

The impression in a mold produced by removal of the pattern. It is filled with molten metal to form the casting. Gates and risers are not considered part of the mold cavity. See Casting, Gates, Risers.

Mold Shift

Casting defect resulting when the two cavities in the cope and drag molds do not match properly. See Cavity, Mold Cavity, Cope, Drag.

Molding Machine

Hand or pneumatically operated machine on which molds are made and which rams the sand by squeezing or jolting or both.

Molding Sand

Mixture of sand and clay suitable for mold making.
Sands containing over 5% natural clay, usually between 8 and 20%. See Naturally Bonded Molding Sand.


Type of foundry-sand-mixing machine. See Foundry Sand.


The thorough mixing of sand, water and binding ingredients to form tempered ready-to-use molding or core sand. See Core Sand.

Nobake Binder

A synthetic liquid resin sand binder that hardens completely at room temperature, generally not requiring baking, used in the Cold Setting process. See Cold Setting Process.

No-Bake Process 

Molds/cores produced with a resin bonded air setting sand. Also known as the air set process because molds are left to harden under normal atmospheric conditions. See Core, Mold.

Non-destructive Testing (Inspection, NDT) 

Testing or inspection that does not destroy the object being tested or inspected.


A negative term, refers to alloy in which the predominate metal or solvent is not iron. See Alloy.

Open Riser

Riser whose top is open to the atmosphere through the top of the mold. See Riser.


Any reaction whereby an element reacts with oxygen


The joint, dividing line, where mold separates to permit removal of the pattern

Parting Line

A line on a pattern or casting corresponding to the separation between the cope and drag portions of a sand mold. The joint where mold separates to permit removal of pattern. See Casting, Cope, Drag, Mold, Pattern.


An original used as a form to produce duplicate pieces. Pattern dimensions are slightly enlarged to counteract the shrinkage of the casting as it solidifies and cools in the mold. Although patterns can be made in one piece, a complicated casting may consist of two or more parts. The pattern may be made out of wood, plastic, metal, or other material. See Casting, Mold, Solidification.

Pattern Draft

The taper allowed on the vertical faces of a pattern to permit easy withdrawal of pattern from the mold or die.

Pattern Shrinkage

The shrinkage allowance made on all patterns to compensate for the change in dimensions as the solidified casting cools in the mold from freezing temperature to room temperature. Pattern is made larger by the amount of shrinkage characteristic of the particular metal in the casting and the amount of resulting contraction to be encountered. Rules or scales are available for use. Also known as a Shrink Rule

Pattern, Split

Pattern usually made in two parts, sometimes in more than two.


A craftsman engaged in production of foundry patterns from wood, plastic, or metals, such as aluminum, brass, etc. See Pattern.


Peening action obtained by impact of metal shot, often used to improve fatigue properties by putting the surface in compression. Also the small end of a molder’s hammer.


The property of a mold material to allow passage of gases. The property in sand molds which permits the passage of gases.

Physical Properties

Properties of matter such as density, electrical and thermal conductivity, expansion, and specific heat. This term should not be used interchangeably with “mechanical properties.”


Small hole under the surface of a casting. See Casting.


A body of sand surrounded on all but one side by molten metal.


Unsoundness in castings appearing as blowholes and shrinkage cavities.

Porosity (Blow-Holes)

Holes in the casting due to gases trapped in the mold, reaction of molten metal with moisture in the molding sand, or imperfect fusion of chaplets with molten metal. (Surface porosity may be due to overheating of the mold or core faces, but should not be confused with sand inclusions.) See Blow Hole, Blow Holes, Inclusion, Molding Sand.


Filling the mold with molten metal. Transfering the molten metal from the furnace to the ladle, ladle to ladle, or ladle into the molds. See Molds, Ladle.

Pouring Basin, Cup, Well

Located on top of sprue or downgate. That portion of the gating.

Primary Choke (Choke)

That part of the gating system which most restricts or regulates the flow of metal into the mold cavity. See Gate.


Elimination of air and other undesirable gases from furnaces or heating boxes.


Rapid cooling of hardening; normally achieved by immersion of the object to be hardened in water, oil, or solutions of salt or organic compounds in water.

Radiographic Inspection

Examination of the soundness of a casting by study of radiographs taken in various areas or of the whole casting.

Radiographic Testing

Use of x-or gamma rays in studying the internal structure of objects to determine their homogeneity.

Ram-Up Core

Core attached to the pattern and rammed up in the mold, where it remains when the pattern is withdrawn


Gates, risers, loose pieces, etc., needed on the pattern to produce a sound casting. See Casting, Gate, Riser, Loose Pieces, Pattern.


A reservoir of molten metal that the casting can draw from to offset the shrinkage that is taking place as the metal solidifies. See Feeder.

Riser Contact (Gate Contact)

The connecting passage between a riser and a casting. See Casting, Riser.

Riser, Blind

A riser that does not break through the top of the cope and is entirely surrounded by sand; opened to the atmosphere by means of a firecracker core.

Riser, Open

Conventional form of riser usually located at the heaviest section of the casting and extending through the entire height of the cope.


Practice of running metal for the casting through the riser to help directional solidification.


Trapezoidal shaped piece that runs horizontally to the mold cavity and connects the Sprue base to the gate(s). See Gate, Sprue.


Metal flowing through a defect in the mold.


In metalcasting, a loose, granular material high in SiO2, resulting from the disintegration of rock. The name sand refers to the size of grain and not to mineral composition. Diameter of the individual grains can vary from approximately 6 to 270 mesh. Most foundry sands are made up principally of the mineral quartz (silica). Reason for this is that sand is plentiful, refractory, and cheap; miscellaneous sands include zircon, olivine, chromite, CaCO3, black sand (lava grains), titanium minerals and others.

Sand Blast

Sand driven by a blast of compressed air (or steam). It is used to clean castings, to cut, polish, or decorate glass or other hard substances, and also to clean building fronts, etc.

Sand Casting

Metal castings produced in sand molds. See Casting.

Sand Holes

Cavities of irregular shape and size whose inner surfaces plainly show the imprint of granular material.

Sand Inclusions

Cavities or surface imperfections on a casting caused by sand washing into the mold cavity. See Mold Cavity.

Sand Porosity

Volume of the pore spaces or folds in a sand. (Not synonymous with permeability).


Any scrap metal melted, usually with suitable additions, to produce castings.

Scrap Metal

Metal to be remelted; includes scrapped machinery fabricated items such as rail or structural steel and rejected castings (metal to be re-melted, castings that have to be re-melted).


A surface defect on a casting related to but of lesser degree than a Cold Shut; a ridge on the surface of a casting caused by a crack in the mold face. See Cold Shut.

Shell Process

Process in which clay-free silica sand coated with a thermosetting resin or mixed with resin is placed on a heated metal pattern for a short period of time to form a partially hardened shell. The bulk of the sand mixture inside the resulting shell is removed for further use. The pattern and shell are then heated further to harden or polymerize the resin-sand mix, and the shell is removed from the pattern. Frequently, shell cores are made using the Hot Box process. See Hot Box Process.


A casting defect resulting form a mismatch of cope and drag. Sometimes there is a Core Shift, which also produces defective casting. See Core Shift.


Metallic abrasive commonly used for cleaning casting surfaces. In die-casting, it is the phase of the die-casting cycle when molten metal is forced into the die.

Shotblasting (Shot peening)

Casting cleaning process employing a metal abrasive (grit or shot) propelled by centrifugal or air force.


The difference in volume between liquid metal and solid metal or the void (shrink hole) left in a casting because of it.

Shrink Hole

A cavity in a casting due to insufficient feed metal.


Difference in volume between liquid metal and solid metal in a given cavity. Contraction of metal in the mould during solidification. The term is also used to describe the casting defect, i.e. shrinkage cavity. This results from poor design, insufficient metal feed, or inadequate feeding.

Shrinkage Cracks

Cracks that form in metal as result of the pulling apart of grains by contraction before complete solidification. See Solidification.

Silica Sand

Sand with a minimum silica content of 95% used for forming casting molds.

Slab Core

A plain flat core.

Slag Inclusions

Casting surface imperfections similar to sand inclusions, but containing impurities from the charge materials, silica and clay eroded from the refractory lining, ash from the fuel during the melting process. May also originate from metal-refractory reactions occurring in the ladle during pouring of the casting. See Inclusions.


Process of metal (or alloy) changing from the liquid to the solid state.

Solidification Range

Only pure metals solidify or freeze at one definite temperature. Alloys contain different constituents which solidify at different temperatures, and the various temperatures from that of the first constituent to solidify to that of the last to constituent to freeze is called the solidification range. See Solidification.


Process for determining the concentration of metallic constituents in a metal or alloy by the intensity of specific wavelengths generated when the metal or alloy is thermally or electrically excited.

Split Pattern

A pattern that is parted for convenience in molding.


A vertical passageway that takes the molten metal from the pouring basin to the runner. See Runners.

Squeeze Pressure

The pressure applied by a molding machine to press the flask and contained sand against the fixed squeeze head or board on a molding machine.

Squeezer Machine

A power-operated, usually pneumatic, device used to pack sand into a flask. See Flask.


A lump on the surface of a casting caused by a portion of the mold face sticking to the pattern. Also, a forming tool used in molding.

Strike Off (noun)

A straight edge, or metal bar, to cut the sand level with the top of the drag or cope flask. Operation of removing excess sand from top of core box or flask.

Surface Finish

Condition or appearance of the surface of a casting.


A casting defect consisting of an increase in metal section due to the displacement of sand by metal pressure. See Defect.


Defect caused by backdraft, damaged pattern or uneven drawing of pattern. See Defect.

Test Bar

Standard specimen bar designed to permit determination of mechanical properties of the metal from which it was poured.

Thermal Expansion

The increase in a linear dimension and volume of a material accompanying a change of temperature.

Tie Bar

Rod-bar or rod-shaped part of the casting added to prevent distortion caused by uneven contraction between separated members.


The permissible deviation of a dimension from the nominal or desired value. Minimum clearance between mating parts.

Tooling Points

The fixed positions on the casting surfaces used for references during layout and machining.


Part of a mold or die requiring a drawback. See Drawback.


Surface defect on castings appearing as veins or wrinkles, which results from cracks in the sand due to elevated temperature conditions and occurs mostly in cores. See Casting, Cores, Defect.


A discontinuity on the surface of a casting appearing as a raised, narrow, linear ridge that forms upon cracking of the sand mold or core due to expansion of the sand during filling of the mold with molten metal. See Defect.


Small opening or passage through which gases can escape during the pouring of a mold. It is also called a vent hole.


The resistance of fluid substance to flowing, quantitative characteristic for an individual substance at a given temperature and under other definite external conditions.


A shrinkage cavity produced in casting during solidification. See Casting, Cavity, Shrinkage, Solidification.


A form of radiant energy with extremely short wave length which has the ability to penetrate materials that absorb or reflect ordinary light. X-Rays provide a form of Non-Destructive testing.


Comparison of finished casting weight verses total weight of metal poured in a mold. A value expressed as a percentage indicating the relationship of the weight of a casting to the total composite of the casting and its gating system.

Yield Strength

A measure of the amount of mechanical stress a material can withstand before it permanently deforms.

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