Laboratory

Press Leaders

Compression and Transfer Molding Equipment

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Glossary Terms S-T
Used in the Compression, Lamination and Transfer Molding Process

SBR:

Styrene butadiene rubber. Largest commodity rubber by volume.

SCORCH:

Premature vulcanization of a rubber compound, generally due to excessive heat history. Also see Mooney scorch.

SET UP:

Scorched - When an unvulcanized rubber stock is considered to be "set up", it can no longer be processed smoothly.

SHEET MOLDING COMPOUND (SMC):

A type of molding material in which the material is pre-formed in sheets of various sizes.

SHELF AGING:

The natural deterioration of rubber articles kept in storage or "on the shelf' under atmospheric conditions.

SHELF LIFE:

The time an unvulcanized rubber stock can be stored without losing any of its processing or curing properties.

SHORE HARDNESS:

Several scales from 0 - 100 rating the relative hardness of a material using a Shore Durometer. Several ranges exist, including the shore A range for softer rubber materials and the shore D range for harder, plastic-like materials. (70 Shore A ~ 20 Shore D)

SHOT SIZE:

The total size of material for an individual "shot" or injection cycle. Can be expressed by either volume or weight.

SHRINKAGE:

The amount of contraction of molded rubber during cooling, usually expressed as a percentage (normally 1-3%).

SINK:

A collapsed blister or bubble leaving a depression in the product.

SPECIFIC GRAVITY:

A ratio of the density of a substance/material to the reference standard, water. The specific gravity of water is 1.0, (from its density of 1,000 gram/cc, or 62.4 pounds/ft. at 600 F. Specific gravity is often designated S.G., or by use of the Greek letter, gamma.

SPLICE:

Joint or junction made by lapping or butting edges, straight or on a bias, and held together through vulcanization or mechanical means.

SPRUE:

The primary feed channel that runs from the outer face of an injection or transfer mold gate in a single cavity mold or to runners in a multiple cavity mold..

SPRUE BUSHING:

The mold-to-injection unit nozzle interface; an exact fit is important to prevent leakage in this area during injection under high pressure.

SPRUE MARK:

Mark, usually elevated, left on the surface of an injection or transfer molded part, after removal of the sprue.

STATE OF CURE:

The cure condition of a vulcanizate relative to that at which optimum physical properties are obtained.

SURFACE FINISH:

The degree of machining and polish required to yield acceptable part finish. For example, an F1 (the best) designation calls for polished mold surface finish while an F4 requires a satin finish, essentially an EDM-type finish.

SWELLING:

The increase in volume of a specimen immersed in a liquid or exposed to a vapor.

SYNTHETIC RUBBER:

Man-made rubber derived from chemicals.

TEAR STRENGTH:

The maximum force required to tear a specimen with the force acting substantially parallel to the major axis of the test specimen.

TEAR TRIM:

An overflow groove built into the mold to allow for manual removal, and to control the flash on a molded part.

TENSILE STRENGTH:

The maximum tensile stress applied during stretching a specimen to rupture.

TOOL:

Mold with/without lifter brackets and other devices.

TPE:

Thermoplastic elastomer. An elastomer which softens under heat, and returns to its original properties when re-heated. Can be re-ground, mixed with virgin material, and re-used.