Aluminum Processing Glossary
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.
Electrical Conductivity The capacity of a material to conduct electric current. For aluminum, this capacity is expressed as a percentage of the International Annealed Copper Standard (IACS), which has a resistivity of 1/58 ohm-mm2/meter at 68F and an arbitrarily designated conductivity of unity.
Electrical Resistivity The electrical resistance of a body of unit length and unit cross-sectional area or unit weight. The value of 1/58 ohm-mm2/meter at 68F is the resistivity equivalent to the International Annealed Copper Standard for 100 percent conductivity. This means that a wire of 100 percent conductivity, 1 meter in length and 1 square millimeter in cross-sectional area would have a resistance of 0.017241 ohms at 68 degrees F.
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.
Extrusion (Direct) The method of extruding wherein the die and ram are at opposite ends of the billet and the product and ram travel in the same direction.
Extrusion (Indirect) The method of extruding where the die is at the ram end of the billet and the product travels through the hollow ram and in the opposite direction.
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.
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 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.
Flow Line (1) Lines on the surface of painted sheet, brought about by incomplete levelling of the paint. (2) The line pattern revealed by etching, which shows the direction of plastic flow on the surface or within a wrought structure.
Formability The relative ease with which a material can be shaped through plastic deformation.
Forming Changing the shape of metal except by shearing or blanking without intentionally altering its thickness.
Galvanising 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.
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 -- see Solution Heat Treating. Ageing.
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 Billet A billet prepared for extruding seamless tube or pipe. The outside diameter may be scalped and the inside diameter may be bored or cast hollow to assure sound metal.
Hollow Dies Are extrusion tools capable of forming profiles with voids where such dies are typically classified as either bridge, porthole or spider types. Extruded sections produced on these dies have one or more seams or longitudinal weld lines, due to metal flow around the supports that hold the stub mandrel. The stub mandrel determines the inside contour of the section being extruded. After passing around the supports, the metal is fused in a weld chamber before passing through the die proper.
Hollow Profile An extruded profile, any part of whose cross section completely encloses a void.
Hollow Shape An extruded shape, any part of whose cross section completely encloses a void.
Homogenising 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 grey 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.
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.
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.
Key-locked Joint A joint with two or more primary elements which are locked together only when an additional specialised 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.
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