ALUMINUM GLOSSARY - O

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.

Off Contour

The deviation of a cross-section surface otherwise intended to be flat.

Off Gauge

Deviation of thickness or diameter of a solid product, or wall thickness of a tubular product, from the standard or specified dimensional tolerances.

Offset-Yield Strength

Yield strength by the offset method is computed from a load-strain curve obtained by means of an extensometer. A straight line is drawn parallel to the initial straight line portion of the load-strain curve and at a distance to the right corresponding to 0.2 percent offset (0.002 in. per in. of gauge length). The load reached at the point where this straight line intersects the curve divided by the original cross-sectional area (sq. in.) of the tension test specimen if the yield strength.

Opaque

Impervious to the transmission of light. Aluminum is opaque; even a thin aluminum foil completely blocks the transmission of light.

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.

Operational Definition

A means of clearly communicating quality expectations and performance; it consists of 1) A criterion to be applied to an object or to a group, 2) A test of the object or of the group, 3) A decision: yes or no; the object or the group did or did not meet the criterion.

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.

Orientation (Laying Out)

The placement of die openings for best profile attitude and consequent flow distribution.

Orifice

The opening in an extrusion die through which the material is extruded.

Oscillation

Uneven wrap in coiling and lateral travel during winding. Improper alignment of rolls over which the metal passes before rewinding and insufficient rewind tension are typical causes. See also Telescoping .

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.

Overbending

Bending metal through a greater angle than that required in the finished part, to compensate for the tendency of the metal to spring part way back to its original shape.

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.