ALUMINUM GLOSSARY - C

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.

CAM

Computer Assisted Manufacturing. The use of computers to monitor, regulate and control manufacturing processes.

Cap

The outer part of a hollow die, which shapes the outside of a hollow extrusion.

Cap Bearings

The surfaces in the aperture of a hollow die which form the outside contour of a hollow extrusion. These surfaces are located on that part of a hollow die which fits against the web or bridge base of the mandrel and are on the same plane as the mandrel bearing. See Bearings .

Cast

To form a molten material into a desired shape by pouring into a mold and letting it harden.

Casting Alloy

An alloy formulated for casting.

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.

Cavity

See Prechamber , Pocket , Piastrina , and Weld Pocket. An area in the entry side of the die which serves to control flow of metal and in a solid die it permits a profile to be continuously extruded as metal from the succeeding billet face is welded to the previous rear face remaining in the cavity after shearing. The pocket generally follows the contour of the profile with milled depths varying from 0.040" to 1" or more depending upon its function.

Cell

In aluminum production: the electrolytic reduction cell, commonly called a pot , which alumina dissolved in molten cryolite is reduced to metallic aluminum. A series of cells connected electrically is called a pot line.

Center

The difference in thickness between the middle and edges (average) of a sheet.

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 Milling

Removing metal from a piece by controlling chemical etching.

Chemical Polishing

Improving the surface luster of metal by chemical treatment.

Choke

The angle filed on a bearing surface at the point where bearing and die face meet (where aluminum enters aperture). Choke length and choke angle may vary independently. The angle of choke generally falls between 1 2 degrees to 5 degrees.

Circumscribed Port Entry

An imaginary circle defining the maximum port entry for a given container liner where this diameter is typically approximately 75% to 90% of the die diameter.

Circumscribing Circle

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

Cladding

A protective layer of pure aluminum or appropriate alloy to increase corrosion resistance and/or to allow for brazing, applied to the surface of aluminum.

Cleanout Block

A circular tool or block used for scraping the aluminum skull from the container liner's inside wall. The cleanout block diameter is greater than that of a dummy block and is sometimes called a scavenger block or cleanout disk.

Cleanout Plate

Is similar to a cleanout block except that it is made from 2 or 3/4 inch mild steel plate.

Coating

Continuous film on the surface of a product.

Coating, High or Low

Cobble

(1) A jamming of the mill by aluminum product while being rolled. (2) A piece of aluminum which for any reason has become so bent or twisted that it must be withdrawn from the rolling operation and scrapped.

Coefficient of Thermal Expansion

The relative rate at which a substance expands on heating, compared to a standard rate.

Cold Working

Plastic (i.e., permanent) deformation of metal at such temperature and rate that strain-hardening occurs.

Coloring

A finishing process, or combination of processes, which alters the appearance of an aluminum surface via coating, chemical, and/or mechanical operations.

Composite Alloy

An aluminum alloy containing relatively large amounts of two or more other elements.

Composite Joint

A joint that is both welded and joined mechanically.

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.

Condenser Tube

The term Heat-Exchanger Tube is preferred, unless specific reference to a condenser application is intended and purpose is to dissipate heat as efficiently as possible.

Conductivity

The ability of a substance to transmit heat, light or electricity. Aluminum has high electrical and thermal conductivity, making it useful in a wide range of electrical and heat-exchanging applications.

Conduit

A tube used to protect electric wiring. See also Tubing, Electrical Metallic .

Conduit, Rigid

Conduit having dimensions of ANSI Schedule 40 pipe in standardized length and threaded ends.

Container

The steel cylinder, usually fitted with a removable liner, having an inside diameter slightly larger than the billet to be extruded which holds and confines the billet during the extrusion cycle. Its length may vary with the press tonnage rating and manufacturer.

Container Liner

The removable, replaceable cylindrical unit of press tooling which holds or confines the billet during the extrusion cycle.

Container Seal

The interface between the container and the die. There must be sufficient clearance between the outer edge of the die port and the inner edge of the container opening to prevent extrusion of the billet skin or skull.

Container Wall Clearance

The difference in dimensions between the billet diameter and container liner internal diameter.

Contour

That portion of the outline of a transverse cross-section of an extruded profile that is represented by a curved line or curved lines.

Contour Correction Rolling

An operation in which the extrusion is passed between rollers to adjust profile dimensions so that specified tolerances in angularity, cross-sectional space dimensions, flatness, and contour are achieved. Bow and twist may also be minimized or eliminated by contour rolling.

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, 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, Pitting

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

Corrosion, Water Stain

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

Coupon

A piece a metal from which a test specimen may be prepared.

Covering Area

Yield expressed in terms of a given number of square inches in a pound. For metric units, use square meters per kilogram.

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.

Crease

A sharp deviation from flat in the sheet which is transferred from processing equipment subsequent to the roll bite.

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.

Curl

An undesirable condition caused by uneven rates of absorption or evaporation of moisture, uneven rates of contraction or expansion, or internal stresses in the material. Curl is most prevalent in laminated structures where the components have differing physical properties.