Please click on the letter range below that contains the first letter of the term you would like to learn more about. A - D | E - K | L - Z Lap Joint A joint formed with one member overlapping the other; the simplest type of nesting joint. Lapping A method of finishing metal to produce a very smooth, highly accurate surface. Linearity The extent to which a measuring instrument's response is proportional to the measured quantity. Line (Flow) The line pattern which shows the direction of flow on the surface. Mark (Rub) A large number of very fine scratches or abrasions. A rub mark can occur by metal-to-metal contact, movement in handling and movement in transit. 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. Return to top 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. Non-Heat Treatable Alloys Aluminum alloys that are strengthened by cold working and not by heat treatment. Return to top 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. Open Space Dimension A dimension, across a part of an extruded cross-sectional shape which only partially encloses a space, whose length includes more than 25 percent space, versus metal. 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. Return to top Pickup Small particles of oxide adhering to the surface of a product at irregular intervals. Pin Gauges Precision machined pins used for measuring normally available as plus, minus and net size 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.) 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. Porthole Die A die having a stationary core or mandrel which is held in place by integral core supports or webs. The porthole die is a modification of the spider die, except that the spider is replaced with a chambered disk that supports the mandrel (sometimes termed a stub mandrel); several portholes running through it annularly about the mandrel, distinguish the porthole types. The die contains a weld chamber so that when the billet is pushed the metal divides to flow around the core supports and welds together in the welding chamber before passing through the die. Porthole dies are used in producing extruded hollow profiles and tubing. See Bridge and Spider Dies Powder Coating Application of a coating in the form of a finely ground powder of colouring agents, resins, and additives; heating of the part, either before or after powder deposition, fuses the powder into a continuous coating. Pre-treatment 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. Profile (Semihollow) A profile any part of whose cross section is a partially enclosed void the area of which is substantially greater than the square of the width of the gap. The ratio of the area of the void to the square of the gap is dependent on the class of semihollow profile, the alloy and the gap width. Return to top Quenching Controlled rapid cooling of a metal from an elevated temperature by contact with a liquid, a gas, or a solid. Reflectivity The ability of a surface to reflect light and other electromagnetic radiation. Aluminum has high reflectivity: 80% or more for visible light, and 90% or more for infrared radiation. Rib An elongated projection on a shape, forging or casting to provide stiffening. Runout Table Table at immediate exit of press leadout equipment which helps to guide and support the extrusion. Return to top 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. 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. 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. Solid Profile Any profile other than a hollow or semihollow. 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 localised 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. Sticking Adherence of foil surfaces sufficient to interfere with the normal ease of unwinding. 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. Surface Tear Minute surface cracks on rolled products which can be caused by insufficient ingot scalping. Return to top Tear (Speed) 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 localised high temperature. 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 characterised 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 Aluminum extrusions are produced to standard dimensional tolerances, unless otherwise specified. 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. Transverse Weld A condition existing within an extrusion which is created by the interface of two separate billets. In practice the interface is extruded at different rates through the die and is formed into a conical or pointed configuration within a portion of the extrusion. Tube (Seamless) Tube that does not contain any line junctures (metallurgical welds) resulting from the method of manufacture. This product may be produced by die-and-mandrel or by hot-piercer processes. Tube produced by porthole-die extrusion, bridge-die extrusion, or welding processes is generally not considered Seamless. (Seamless tube is typically used for fluid-carrying applications under pressure. Twist (1) For rolled products, a winding departure from flatness. (2) For extrusions, a winding departure from straightness. Return to top 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. 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. Return to top