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Glossary

ANSI

Abbreviation for American National Standards Institute.

ASME

Abbreviation for American Society of Mechanical Engineers.

ASTM

Abbreviation for American Society for Testing and Materials.

Adhesion

Bonding strength. The attraction of a coating to the surface to which it is applied.

Age Hardening

An aging process that results in increased strength and hardness.

Age Softening

Spontaneous decrease of strength and hardness that takes place at room temperature in certain strain hardened alloys containing magnesium.

Aging

Precipitation from solid solution resulting in a change in properties of an alloy, usually occurring slowly at room temperature (natural aging) and more rapidly at elevated temperatures (artificial aging).

Alloy

A substance with metallic properties, composed of two or more chemical elements of which at least one is a metal. More specifically, aluminum plus one or more other elements, produced to have certain specific, desirable characteristics.

Alumina

Aluminum oxide produced from bauxite by a complicated chemical process. It is a white powdery material that looks like granulated sugar. Alumina is an intermediate step in the production of aluminum from bauxite, and is also a valuable chemical on its own.

Aluminum

A silver-white soft metal, noted for its lightness, high reflectivity, high thermal conductivity, nontoxicity, and corrosion resistance. It is the most abundant metallic element, comprising about 1/12th of the earth's crust. It is never found in nature as an elemental metal, but only in combination with oxygen and other elements. In ordinary commercial and industrial use, the word aluminum is often understood to mean aluminum alloy, rather than the pure metal.

Aluminum Oxide

A chemical compound of aluminum with oxygen, which forms immediately on an unprotected aluminum surface exposed to air. Unlike iron oxide (the rust which forms on steel) aluminum oxide does not flake off, but forms a protective layer that blocks further oxidation and so protects the integrity of the metal. It is transparent and does not alter the appearance of the aluminum surface.

Angularity

Conformity to, or deviation from, specified angular dimensions in the cross section of a shape or bar.

Annealing

A thermal treatment to soften metal by removal of stress resulting from cold working or by coalescing precipitates from solid solution.

Anodizing

Forming a coating on a metal surface produced by electrochemical treatment through anodic oxidation. This process may be used to increase the protective effect of aluminum's transparent natural oxide surface. It may also be given a decorative coloration.

Bake

The curing of paint at an elevated temperature for a specific period of time, allowing the paint to become hard and dry.

Bauxite

One of the ores from which alumina is extracted and from which aluminum is eventually smelted. Bauxite usually contains at least 45 percent aluminum oxide (alumina), and the best grades have a low silica content. About four pounds of bauxite is required to produce one pound of aluminum.

Billet

Commonly, a cylindrical form of the aluminum alloy used in the extrusion process.  Formed in casting houses and shipped in long logs or specific lengths for extrusion press applications.

Blister

A raised area on the surface of an extruded product due to subsurface gas expansion during extrusion or thermal treatment.

Blistering

A defect in the paint film appearing as bubbles, usually caused by the expansion of air, solvent vapor, or moisture trapped beneath the film.

Bolster (die block)

A tool, or reinforcing part, which supports the backer -- which, in turn, supports an extruding die against the pressure of extrusion.

Bow

Longitudinal curvature of rod, bar, profiles (shapes), and tube. Bow is measured after allowing the weight of the extrusion to minimize the deviation. Bow can be caused by a non-uniform extrusion rate across the cross section resulting in one portion of the extrusion being longer than the other or non-uniform contraction during quenching.

Bridge

In extrusion: the part of an extrusion bridge die that supports a void-forming mandrel. During extrusion, the metal divides and flows around the bridge, reuniting as it is extruded through the die orifice. The resulting weld line can be detected upon microscopic examination, but the extrusion appears functionally and visually seamless.

Bright Dipping

Chemical polishing of aluminum, often by treatment with a mixture of nitric acid and phosphoric acid, yielding a mirror-shiny (specular), highly reflective surface. It is almost always followed by anodizing to protect the surface and provide some choice of colors.

Buffing

A mechanical finishing operation in which fine abrasives are applied to a metal surface by rotating fabric wheels for the purpose of developing a lustrous finish.

Burr

A thin ridge of roughness left by a cutting operation such as slitting, trimming, shearing, blanking, or sawing.

CAD

Computer Assisted Design. The use of computer programs to generate, analyze and modify designs. Extrusion dies and their supporting tools, for example, may be designed with the aid of computers.

Caustic

(Sodium Hydroxide, NaOH and derivatives). The active ingredient in an alkaline bath, generally with a pH higher than 10, which removes aluminum from used extrusion dies by etching. The primary ingredient, Caustic Soda (NaOH), dissolves the aluminum alloy by chemical reactions with no affect on the die steel.

Chalking

A white powdery deposit on the surface of the exposed paint film caused by weathering.

Chamfer

A bevel at the apex of an angle on a machined part to allow clearance and prevent interference when assembled with another machined part. The interference may occur from dirt, burrs, or incidental marring of the die surface. A chamfer aids in the assembly of closely fit machined parts. Large chamfers are sometimes used on the webs of hollow die entry ports to reduce the initial contact area between die and billet.

Chatter

A surface defect consisting of alternating ridges and valleys at right angles to the direction of extrusion.

Chatter Mark

Numerous intermittent lines or grooves that are usually full width and perpendicular to the extrusion direction.

Chemical Polishing

Improving the surface luster of metal by chemical treatment.

Circumscribing Circle

The smallest circle that will completely enclose the cross section of an            extruded shape.

Coating

Continuous film on the surface of a product.

Compressive Strength

Strength to resist outside pressure (as distinguished, for example, from bending or stretching forces).

Concentricity

Conformance to a common center as, for example, the inner and outer walls of round tube.

Conversion Coating

A chemical layer formed on the metal in the pretreatment process which aids in paint adhesion and corrosion resistance.

Corrosion

The deterioration of metal by chemical or electrochemical reactions with substances in its environment.

Corrosion, Exfoliation

Corrosion that progresses approximately parallel to the metal surface, causing layers of the metal to be elevated by the formation of corrosion product.

Corrosion, Galvanic

Corrosion associated with the current of galvanic cell consisting of two dissimilar conductors in an electrolyte or two similar conductors in dissimilar electrolytes. Aluminum will corrode if it is anodic to the dissimilar metal.

Corrosion, Intergranular

Corrosion occurring preferentially at grain boundaries (also termed intercrystalline corrosion).

Corrosion, Pitting

Localized corrosion resulting in small pits or craters in a metal surface.

Corrosion, Stress Cracking

Failure by cracking resulting from selective directional attack caused by the simultaneous interaction of sustained tensile stress at an exposed surface with the chemical or electro-chemical effects of the surface environment. The term is often abbreviated SCC which correctly stands for stress corrosion cracking.

Corrosion, Water Stain

Superficial oxidation of the surface with a water film, in the absence of circulating air, held between closely adjacent metal surfaces.

Cratering

A paint film defect appearing as small, round bare spot on the painted part. This may be caused by gassing, incompatability, or silicones.

Crazing

A macroscopic effect of numerous surface tears, transverse to the rolling direction, which can occur when the entry angle into the cold mill work rolls is large.

Creep

The strain in a metal that results from continuing constant stress.

Crosshatch

Test to demonstrate adhesion characteristics of a paint or powder coated surface, performed by scribing a crosshatch pattern at specified intervals.

Cryogenic

Pertaining to very low temperatures. Aluminum gains strength as temperature is reduced, making it an appropriate material for cryogenic applications.

Cure

The process of converting a liquid paint to a solid, durable film, usually accomplished by the action of heat and catalysts.

Deburring

Removing burrs, sharp edges, or fins from metal parts by filing, grinding, or tumbling.

Density

Weight per unit of volume (for example pounds per cubic foot). The density of aluminum is only about one-third that of steel, and this weight-saving characteristic is one of aluminum's best-known advantages.

Die

In extrusion a tool with an opening through which heated aluminum is forced by pressure, taking on that cross-sectional shape.

Die Assembly

In an extrusion press, the die and its associated tooling.

Die Lines

A longitudinal depression or protrusion formed on the surface of drawn or extruded material. Die lines are present to some degree in all extrusions and are caused by a roughening of the die bearing.

Die Number

The number assigned to a die for identification and cataloging purposes, and which usually is assigned for the same purpose to the product produced from that die.

Die Stop

A defect resembling a weld around the entire extruded section, caused by stopping a press during extrusion and then restarting it.

Die Tool Assembly

The various components making up the assembly within the tool carrier or Die Slide. A typical example would be (from front to rear): die and backer enclosed in a die ring, bolster and possibly a sub-bolster or spacer.

Die Weld

A region in extruded hollow profiles created by two streams of metal within the die joining themselves in the weld chamber around the mandrel of a hollow type die. Die welds are generally present in all extruded hollow profiles and in most cases are not visible.

Dimensional Allowance

The specified difference in size between mating parts.

Distortion

Any deviation from the desired shape or contour.

Dove-tail

An interlocking connection frequently used for the assembly of interconnecting extrusions; it is assembled by a sliding action.

Drawn Product

A product formed by pulling material through a die.

Ductility

The property that permits permanent deformation before fracture by stress in tension.

Eccentricity

Deviation from a common center, as, for example, the inner and outer walls of a round tube. The difference between the mean wall thickness and minimum or maximum wall thickness at any one cross section. The permissible degree of eccentricity can be expressed by a plus and minus wall-thickness tolerance.

Elasticity

The ability of a material or body to return to its original shape and dimensions after being deformed by stress.

Electrochemical

Pertaining to chemical reactions induced by an electric current such as electrolysis or electroplating.

Electrostatic Spraying

Application of a coating by applying a static electricity charge to the droplets of a spray and an opposite charge to the part being sprayed, which then attracts the droplets directly to its surface.

Elongation

The percentage increase in distance between two gauge marks that results from stressing the specimen in tension to fracture. The original gauge length is usually 2 inches for flat specimens and round specimens whose diameter is 0.5 inch, or four times the diameter for specimens where that dimension is under 0.5 inch. Elongation values depend to some extent upon size and form of the test specimen. For example, the values obtained from sheet specimens will be lower for thin sheet than for thicker sheet.

Etching

Shaping or texturing a metal surface by controlled corrosive action.

Exposed Surface

Any face of an extruded profile which is exposed to view or other critical end-use aspects.

Extrude

To force material through a die by pressure.

Fabricate

To work a material into a finished state by machining, forming or joining.

Feeder Plate

A plate employed in front of the extrusion die to alter the metal billet dimensions permitting extrusion of larger dimensioned product than normally possible or to assist in extrusion of difficult profiles.

Fillet

Generally, a concave junction where two surfaces meet.

Film Thickness

The depth of applied coating, expressed in mils, i.e. 1/1000 inch.

Finishing

Usually secondary operations applied to extrusions to improve product dimensionally or change surface condition (etching) or color (anodizing, plating, painting, buffing, etc).

Fisheye

A defect in the paint film appearing as a circular depression resembling a crater but not revealing bare substrate.

Fit

The range of clearance or interference between mating parts. The American Standards Association recognizes 33 classes of fits ranging from loose sliding fit to tight force fit.

Flatness

(1) For rolled products, a distortion of the surface of sheet such as a bulge or a wave, usually transverse to the direction of rolling. Often described by location across width, i.e., edge buckle, quarter buckle, center buckle, etc. (2) For extrusions, flatness (off contour) pertains to the deviation of a cross-section surface intended to be flat. Flatness can be affected by conditions such as die performance, thermal effects and stretching.

Flow

A term used when referring to the movement of aluminum through the die during the extrusion process.

Galvanic Corrosion

Deterioration of a metal caused by the electric current produced when two unlike metals are in contact under certain condition.

Galvanizing

An undesirable grainy or spangled condition on the surface of etched or anodized extrusions. This condition is not obvious in mill finish aluminum extrusions but can be revealed by etching or anodizing.

Gloss

The degree to which a surface reflects light, generally, the smoother the surface, the higher the gloss.

Grain Flow

The directional characteristics of the metal structure after working, revealed by etching a polished section.

Grain Size

A measure of crystal size usually reported in terms of average diameter in millimeters, grains per square millimeter, or grains per cubic millimeter.

Grinding

Removing material from a workpiece with an abrasive wheel.

Hard Coat Anodizing

A combined electrical and chemical finishing process for aluminum that produces a hard, colored, protective film on the surface.

Hardening

Increasing the hardness of metal by suitable treatment, usually involving heating and cooling.

Hardness

Resistance to plastic deformation, usually by indentation. The term may also refer to stiffness or temper, or to resistance to scratching, abrasion or cutting.

Heat-Treatable Alloy

An aluminum alloy that can be hardened to produce desired properties by a controlled cycle of heating and cooling.

Heat Treating

Heating and cooling a solid metal or alloy in such a way as to obtain desired conditions or properties. Commonly used as a shop term to denote a thermal treatment to increase strength. Heating for the sole purpose of hot working is excluded from the meaning of this definition

High-Solids Coating

Coatings greater than 40% solids by volume, thereby reducing solvent emissions during the application.

Hinge Joint

A joint which, when assembled, allows its parts to rotate relative to each other without separating. Hinge joints are extruded as relatively loose slip-fit joints with an open-sided ball-in-socket design.

Hollow Profile

An extruded profile, any part of whose cross section completely encloses a void.

Homogenizing

Is a process whereby ingots are raised to temperatures near the solidus temperature and held at that temperature for varying lengths of time. The purposes of this process are to (1) reduce microsegregation by promoting diffusion of solute atoms within the grains of aluminum and (2) Improve workability.

Hot Tears

Transverse surface scars or separations along the length of the extruded profile caused by excess speed and/or temperature.

Hot Spot

Dark gray or black surface patches appearing after anodizing. These areas are usually associated with lower hardness and coarse magnesium silicide precipitate caused by non-uniform cooling after extrusion.

Inclusion

Foreign material in the metal or impressed into the surface.

Interference Fit

The class of fit in which a mating part is deliberately made slightly oversize for the part into which it will be inserted.

Interleaving

The insertion of paper or application of suitable strippable coatings between layers of metal to protect from damage.

Interlocking Joint

A joint in which a curved projection on one part is inserted by a rotating motion into a similarly curved receiving groove on the other part. The parts cannot then be separated by straight-line motion.

Kerf

The notch or slit made by a saw or torch when cutting.

Key-locked Joint

A joint with two or more primary elements which are locked together only when an additional specialized part, the key is inserted to prevent them from separating.

Keyway

A slot in the shaft of a mechanical drive system that provides a means of locking a gear or other part onto the shaft.

Lap Joint

A joint formed with one member overlapping the other; the simplest type of nesting joint.

Light Walls

Undersized wall dimensions often caused by shifting or caving of mandrel or housing section of hollow die.

Machinability

The relative ease of working a metal with machine tools. Aluminum has good machinability.

Mechanical Properties

Those properties of a material that are associated with elastic and inelastic reaction when force is applied, or that involve the relationship between stress and strain; for example, modulus of elasticity, tensile strength, endurance limit. These properties are often incorrectly referred to as physical properties.

Metal Dimension

Any dimension, through a part of an extruded cross-sectional shape, whose length includes at least 75 percent metal, versus open space.

Mil

A unit of length; 0.001 inch.

Mill Finish

Mill finish is the finish obtained by standard extrusion practices and produced without the aid of any subsequent operations. This finish generally varies from a structural finish with surface imperfections to an architectural finish with uniformly good appearance.

Milling

Removing metal with a machine tool something like a rotary chisel.

Modulus of Elasticity

The ratio of stress to corresponding strain throughout the range where they are proportional. As there are three kinds of stresses, so there are three kinds of moduli of elasticity for any material -- modulus in tension, in compression, and in shear.

Nesting Joints

A general class of joints with mating elements that serve to align adjoining parts with little or no self-locking action.

Nitriding

The introduction of nitrogen into the surface of tool steels by holding at a suitable temperature in contact with a nitrogenous material, usually ammonia, to produce a hard wear resistant case.

Nitrogen Shrouding

The process of injecting nitrogen, either liquid or gaseous, at the die openings to surround the emerging extrusion in an environment high in nitrogen and low in oxygen. This delays the formation of oxides on the exit edge of the die bearing providing a superior surface finish on the extrusion.

Nonferrous

Not containing iron; a generic term for metals other than iron and alloys not containing iron.

Non-Heat Treatable Alloys

Aluminum alloys that are strengthened by cold working and not by heat treatment.

O.D. (Outside Diameter)

The nominal overall measurement of tube or pipe diameter measured across its outer perimeter because of variations in actual wall thickness, it does not necessarily indicate true dimensions at all location.

Orange Peel

(1) Surface roughening on formed products which occurs when large grains in the metal are present. (2) An irregularity in the surface of a paint film resulting from the inability of the wet film to level out, or become smooth after being applied, thus resembling the surface of an orange. This finish may be considered desirable or a defect depending on the end use.

Ovality

Deviation from a circular periphery, usually expressed as the total difference found at any one cross section between the individual maximum and minimum diameters, which usually occur at or about 90 degrees to each other. Since ovality is the difference between extreme diameters, it is not expressed as plus or minus.

Oxide

A chemical compound of oxygen with another element. Hydrated (water-including) iron oxide is called rust; it does not cling tightly to the underlying metal, so the oxidation process is progressive and iron easily rusts away. Aluminum oxide is a hard, transparent compound which clings tightly to the underlying metal and protects it against further oxidation.

Physical Properties

The properties, other than mechanical properties, that pertain to the physics of a material; for example, density, electrical conductivity, heat conductivity, thermal expansion.

Pickup

Small particles of oxide adhering to the surface of a product at irregular intervals.

Pipe, Extruded

Pipe formed by hot extruding.

Pipe, Seamless

Pipe that does not contain any line junctures (metallurgical welds) resulting from the method of manufacture. This product may be produced by extruding or by drawing, using either die-and-mandrel or hot-piercer processes. (Typically used for fluid-carrying applications under pressure.)

Pipe, Structural

Pipe, brought to final dimensions by extruding through a bridge-type die or by similar methods at the option of the producer. (Typically used for structural, nonpressure applications.)

Pit

(1) A depression in the rolled surface which is usually not visible from opposite side. (2) A sharp depression in the surface.

Polishing

Smoothing a metal surface, usually by rubbing with fine abrasives. A mechanical finishing operation for the purpose of producing a gloss or luster on the surface of a product.

Powder Coating

Application of a coating in the form of a finely ground powder of coloring agents, resins, and additives; heating of the part, either before or after powder deposition, fuses the powder into a continuous coating.

Pretreatment

The chemical alteration of a surface to make it suitable for application of paint or powder. The process usually includes cleaning and applying a conversion coating.

Profile

A product that is long in relation to its cross-sectional dimensions, having a cross-section other than those of wire, rod, bar, and tube, produced by extrusion, rolling, drawing, or cold finishing. Formerly termed a shape.

Puller

A device which guides metal down the runout table as it is being extruded.

Quenching

Controlled rapid cooling of a metal from an elevated temperature by contact with a liquid, a gas, or a solid.

Runout Table

Table at immediate exit of press leadout equipment which helps to guide and support the extrusion.

Salt Spray

Corrosion test using salt sprayed as a mist in a heated humidity chamber to simulate seashore conditions, or to accelerate corrosion at a controlled rate.

Seam

The junction line of metal that has passed through a hollow die, separated and rejoined at the exit point. Seams are present in all extruded hollows produced from the extrusion process and in many cases are not visible.

Seamless

A hollow product which does not contain any line junctures resulting from method of manufacture.

Secondary Aluminum

Aluminum recovered primarily from scrap, segregated by alloy, and resmelted. Aluminum scrap is widely recycled and supports a large secondary aluminum production industry.

Semihollow Profile

An extruded profile, any part of whose cross section partially encloses a void, the area of which is substantially greater than the square of the width of the gap.

Sheet

A rolled product that is rectangular in cross section with thickness less than 0.250 inch but not less than 0.006 inch and with slit, sheared or sawed edges.

Slip-fit Joint

A joint assembled by sliding two mating parts together in the direction of their length.

Snap-fit Joint

A self-locking joint whose mating parts exert a cam action, flexing until one part slips past a raised lip on the other part, preventing their separation.

Soaking

In metallurgy: the prolonged heating period during several methods of heat treating metals, soaking allows the heat to penetrate completely the mass of metal, and so permits the required metallurgical changes to take place.

Soft Alloy

A general term loosely describing most alloys of the 1xxx, 3xxx, or 6xxx series.

Solid Dies

A steel disk with one or more orifices or apertures of the same cross-sectional area and contour as the desired product, through which metal is forced. Such dies are generally employed where profiles other than hollow are required. If solid dies are used for hollow profiles (as opposed to the use of hollow dies of the bridge, porthole or spider type containing a fixed stub mandrel as an integral part of the die) then a mandrel actuated by the action of the ram must be employed. These may be fixed or floating mandrels which require hollow (cast or bored) billets. An exception is the piercing type mandrel, which needs no cored billet.

Solution Heat Treating

Heating an alloy at a suitable temperature for sufficient time to allow soluble constituents to enter into solid solution where they are retained in a supersaturated state after quenching.

Speed Tear

A series of surface cracks perpendicular to the extruding direction. Speed tearing normally occurs in corner radii or extremities of a section and is caused by localized high temperature.

Spider Die

An extrusion die for producing hollow shapes, whose mandrel is supported by multiple legs attached to the cap. Metal flows between the spider's legs and reunites before emerging through the die aperture.

Squareness

(1) The measure of a bearing being perpendicular to the die face which can be accomplished with a toolmaker's square or equivalent techniques. (2) Characteristic of having adjacent sides or planes meeting at 90 degrees.

Straightness

The absence of divergence from a right (straight) line in the direction of measurement.

Strength/Weight Ratio

The relationship between the structural strength of a material and its weight. the strength-to-weight ratio of structural aluminum alloys is about twice that of mild steel.

Stretch Straightening

The process of stretching extruded sections beyond the yield strength of the alloy to achieve longitudinal straightness.

Stretching

In extrusion: straightening an aluminum member by pulling. An average stretch increases the length by about one-half of one percent, and produces correspondingly a slight decrease in the cross-sectional dimensions, called stretch-down.

Structural Finish

A structural finish is a standard finish where surface imperfections are acceptable and appearance is not a requirement. This finish could be characterized by the term non-exposed.

Structural Shape

An aluminum section, now usually extruded, of any design accepted as standard by the structural industry. Such shapes include I-beams, wide flange or H-beams, channels, angles, tees and zees.

Tearing

Typically cracks or separations due to high extrusion speed or extrusion temperature.

Temper

The combination of hardness and strength imparted to a metal by mechanical or thermal treatments and characterized by certain metallurgical structures and mechanical properties determining temper designation.

Tensile Strength

In tensile testing, the ratio of maximum load to original cross-sectional area. Also called Ultimate Strength.

Thermal Conductivity

The ability of a material to transmit heat through its bulk and, by direct contact, to other substances. Aluminum is a good heat conductor and is widely used in cookware and in radiators and other heat exchangers.

Tolerance

Allowable deviation from a nominal or specified dimension.

Tongue and Groove Joint

A joint in which one part has a groove which receives a projection (tongue) on the other part, shaped to fit snugly.

Traffic Mark

Abrasion which results from relative movement between contacting metal surfaces during handling and transit. A dark color from the abrasively produced aluminum oxide is usually observed. A mirror image of a traffic mark is observed on the adjacent contacting surface.

Tread Plate

Sheet or plate having a raised figured pattern on one surface to provide improved traction.

Tube

A hollow wrought product that is long in relation to its cross section, which is symmetrical and is round, a regular hexagon or octagon, elliptical, or square or rectangular with sharp or rounded corners, and that has uniform wall thickness except as affected by corner radii.

Twist

(1) For rolled products, a winding departure from flatness. (2) For extrusions, a winding departure from straightness.

Undercure

The result of curing a paint at either too low of a temperature or too little time, resulting in inadequate hardness and solvent resistance.

V.O.C.

Volatile organic compound; any organic compound that participates in atmospheric photochemical reactions as designated by EPA standards.

Viscosity

That property of a liquid which enables it to resist flow. High viscosity means a fluid resists flowing; low viscosity means it flows readily.

Workability

The relative ease with which various alloys may be formed by extruding, rolling, forging, etc.

Wrap

A characteristic of liquid or powder coatings in an electrostatic application to seek out and adhere to parts of the substrate not in direct line of sight of the delivery system end point.

Yield Strength

The stress at which a material exhibits a specified permanent set. The offset used for aluminum and its alloys is 0.2 percent of gauge length. For aluminum alloys the yield strengths in tension and compression are approximately equal.

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