Back-End Defect
A defect found in extruded products due to incorrect extrusion procedures at the mill.
Backwards Extrusion, Indirect Extrusion
The extrusion method in which there is no relative movement between the billet and the container.
This is accomplished by:-
Either pushing the die held on the end of a long, hollow, stem through the billet.
Or moving the billet and container together over the die, again held on the end of a long, hollow, stem.
As there is no movement between the billet and container the friction, and hence extrusion loads, are reduced by up to 30% compared to direct extrusion and grain structures can be improved. The process is limited by the size, length and strength of the stem which holds the die.
Related terms: Direct Extrusion
Bauxite
The main ore of aluminium, found in great abundance in the earth’s crust, near the surface. It is mined using open cast mining and has a yield of 25%.
Bayer Process
A chemical process used to refine the aluminium ore bauxite into alumina (aluminium oxide) from which the aluminium metal can be extracted by smelting
Bend Radius
The radius of curvature of the former around which a specimen is bent.
Bend Test
The bending of a specimen to conform with a predetermined radius and angle, to assess bending characteristics and ductility.
Blank
A work-piece prepared for subsequent processing e.g. by forming, bending, cupping, drawing, impact extrusion, pressing, etc.
Bloom, Billet
Cast aluminium in the form of large round (or occasionally square) bars.
Bow
The deviation of the edges from the true longitudinal axis of a product seen as an arc.
Brinell Hardness, Hardness, Rockwell Hardness, Vickers Hardness
The resistance of a metal to plastic deformation usually by indentation using a diamond or a hardened steel ball.
There are various recongnised hardness scales including Vickers (VPN), Brinell and Rockwell.
N.B. The empirical, but robust, relationship between hardness and tensile properties that applies in steels does not apply, and the steel tables must not be used for aluminium and its alloys. A less rigorous relationship has been established for some aluminium alloys but it is not widely used.
Buckle, Ripple
The variation in flatness represented by alternate bulges and hollows along the length of a rolled product, the edges of which remain reasonably flat.
Busbars
Bar or section for use as a common junction between electrical circuits.