C

Coefficient of Thermal Expansion

Value used to determine the amount of linear dimensional change for a particular elastomer, which is temperature dependent.

Cold Flexibility

Flexibility following elastomer exposure to a specified low temperature for a specified period of time.

Cold Flow

A term describing the tendency of certain materials to continue to deform or "creep" under constant sealing pressure (compressive load).

Cold Resistant

Capable of low temperature operation without loss of serviceability.

Composite Seal

Combines the sealing performance of elastomers with the physical properties of the bonded material (i.e. metal, plastic, etc.).

Compound

An elastomeric material resulting from the combination of a number of individual chemical ingredients into a batch mix. Further processing of the thoroughly mixed ingredients, to induce cross linking of polymer chains (vulcanization), results in the creation of a useful rubber-like product.

Compression Modulus

The ratio of applied compressive force (stress) to the resulting deformation of the test material (strain). Compressive strain is expressed as a fraction of the original height or thickness of the test specimen in the direction of the applied force.

Compression Set

The amount by which an elastomeric material fails to return to its original size after release from a constant compressive load.

Copolymer

An elastomer (polymer) resulting from the chemical combination of two dissimilar monomers. For example, Buna N from Butadiene and Acrylonitrile.

Cracking

Sharp breaks or fissures in rubber surfaces resulting from excessive strain or exposure to adverse environmental factors.

Creep

The progressive relaxation of an elastomeric material under constant sealing pressure (compressive load). Also known as cold flow.

Cross Section

A seal cut at right angles to the mold parting line. Also known as width.

Cure

Another term for "vulcanization" of compounded and molded rubber (green stock), resulting in the chemical bonding (cross linking) of polymer chains and the accompanying creation of useful elastomeric products. Curing typically occurs in the presence of sulfur and an accelerator, under pressure, at elevated temperature.

Cure Date

O-ring molding date. A product code of 2Q97, for example indicates a cure date of the second quarter (2Q) of 1997 (97). No longer required by Mil Standard 1523.