ALUMINUM GLOSSARY - B

Backer (back-up plate)

A tool , or reinforcing part, which presses against the outer surface of an extrusion die, supporting it against the pressure of the extruding metal. The backer has an opening larger than the die aperture, allowing the extruded product to emerge without marring its soft surface.

Back Taper (Relief)

Cut-away portion of die beginning at breakaway point to the die exit either angled or undercut (stepped back) for back clearance.

Bake

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

Bar

A solid extrusion that is long in relation to cross section, which is square or rectangular (excluding plate or flattened wire) with sharp or rounded corners or edges; or is a regular hexagon or octagon; and in which at least one perpendicular distance between parallel faces is 0.375 inch or greater. (Smaller sizes are classified as wire.)

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.

Beam

The principal horizontal load-bearing member of a structure.

Bearing

The surface of the extruding aperture, at right angles to the die face, that controls metal flow and to some extent speed of flow which is also the conforming surface along which the aluminum flows.

Bell

Electrostatic spray device whose paint applicator is bell-shaped, atomizing paint off its edge.

Belly

The area of a liner that has an increased inside diameter from nominal, appearing convex (may be caused by a weak container).

Billet, Extrusion

May be solid or hollow in form, commonly cylindrical, used as the final length of material charged into the extrusion press cylinder. It is usually a cast product, but may be a wrought product or sintered from powder compact.

Billet Container

The part of an extrusion press into which the billet to be extruded is placed.

Blank

A piece of metal cut or formed to regular or irregular shape for subsequent processing such as by forming, bending, or drawing. The piece of sheet stock cut out by blanking die. It will subsequently be drawn into a cup or end shell.

Blending

The machining of the transition in the bearing length from long to short.

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.

Blocking

The use of graphite blocks to support the emerging extrusion as it exits the die.

Bloom

A semi-finished hot rolled product, rectangular or square in cross section, produced on a blooming mill.

Blow Hole

A blister that has ruptured and may produce a void. See also Blister .

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.

Bow, Lateral

Deviation from straight of a longitudinal edge.

Bow, Longitudinal

Curvature in the case of sheet or plate in the rolling direction, along the length of an extrusion.

Bow, Transverse

Curvature across the rolling direction of sheet or plate, across the width of an extrusion.

Breakaway Point

Is usually formed by the step where die undercut starts and bearing surface ends and is also where the extrusion leaves the bearing.

Breakout Pressure

The initial pressure required to start metal flow through the extrusion die.

Breakthrough

The point in time when the billet emerges from the exit side of the die as an extruded profile.

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.

Bridge Type Die

A die having a stationary core or mandrel which is held in place by core supports or webs (bridge) bolted to the back of the die. 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. See Porthole Die and Spider Die . Bridge dies normally have unenclosed ports which protrude into the container liner.

Bridging (Webs Network)

The network of support webs which hold in place the internal surface forming portion of the mandrel, created when the ports are machined into the mandrel.

Bridging (Design Purpose)

Is used to reduce pressure on critical tongue areas of a semi-hollow or hollow die.

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.

Brinell Hardness

See Hardness , Brinnell .

Broken Die

A deviation from the desired cross section due to the absence of a certain portion of the die used to extrude the profile (shape).

Buckle

A distortion of the surface of the metal.

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.

Burrs

Tiny, almost microscopic shards of die steel protruding into the die aperture (opening), usually from either the entry or exit edge of the bearing. They are typically formed during the manufacture of the die but can also be formed by striking the die opening with a hammer, dies bumping together during handling or other abnormal impacts to the die face.

Bus Bar

A rigid electric conductor in the form of a bar.

Butt

The unextruded portion of the billet remaining in the container after the extrusion cycle is completed. The butt varies in thickness depending upon the alloy, die configuration, and extruded profile characteristics.

Butt End

The residual portion of an extrusion billet that is not formed through the die at the end of the extrusion cycle.

Butt Weld

The welding of two sections that butt against each other, end to end.