RUBBER GLOSSARY

Accelerator
A substance that speeds up the vulcanization of an elastomer, allowing it to cure faster or at lower temperatures.

Adhesion
The tendency of rubber compounds to bond to contact surfaces.

Aging
The change in a rubber compound’s physical properties over time.

Antioxidant
An additive that slows oxidation and extends rubber life.

Antiozonant
A substance that protects rubber from cracking due to ozone exposure under tension.

Bond
The attachment of rubber to a substrate such as metal, fabric, or plastic.

Bond, Chemical
Rubber bonded to a primed substrate using heat and pressure during vulcanization.

Bond, Cold
Rubber adhered to another material after vulcanization using adhesives or cements.

Bond, Mechanical
Physical retention of rubber to a substrate via holes, projections, or mechanical interlock.

Closure Dimension
A molded rubber dimension affected by flash thickness and mold closure variation.

Compound
A mixture of polymers and additives formulated to produce usable rubber.

Compression Set
The permanent deformation of rubber after being compressed and released.

Conductive Rubber
Rubber that can conduct electricity, often used to dissipate static charges.

Creep
The slow deformation of rubber under constant stress.

Cross-Linking Agents
Chemicals that bond polymer chains to form a thermoset rubber structure.

Cross-Section
A cut view of a rubber part showing its internal profile.

Dampening
A rubber compound’s ability to absorb vibration energy.

De-flashing
The process of removing excess material from a molded rubber part.

Durometer
A tool that measures rubber hardness using an indentor point; measured on the Shore A scale.

Durometer, Dual
A rubber part containing two distinct hardness levels.

Elongation
The percentage a rubber sample stretches before breaking.

Fixed Dimension
Dimensions of a rubber part unaffected by flash or mold closure; also called radial dimensions.

Flame Resistance
The ability of rubber to resist ignition and burning under normal conditions.

Flash
Thin excess rubber on a molded part, removed after molding through trimming or deflashing.

Flex Resistance
A rubber part’s ability to endure repeated bending stress.

Flex Strength
Rubber’s ability to bend without permanent deformation or failure.

Gas Permeability
Rubber’s resistance to gas permeation under pressure.

Gate Mark
A spot on the part surface left by the mold gate; may appear raised or depressed.

Gates
Channels in the mold that allow rubber to flow into the cavity.

Hardness
A rubber material’s resistance to indentation; measured with durometer tools.

Heat Aging
A test that measures the effect of elevated temperatures on rubber properties.

Modulus
The tensile stress required to stretch rubber to a given percentage of its original length.

Mold Cavity
The hollow shape in a mold used to form the final rubber part.

Mold Finish
The surface finish of a molded part as defined by contact with the mold surface.

Mold Register
The alignment precision between mold plates or sections.

Nominal Dimension
The nearest fractional equivalent of a specified decimal dimension.

Oil Resistance
Rubber’s ability to resist swelling and degradation when exposed to oils.

Oxidation
Degradation of rubber due to reaction with oxygen, often seen as cracking or stiffness.

Ozone Resistance
Rubber’s ability to resist cracking caused by exposure to ozone.

Parting Line
The line on a molded part surface where mold plates meet.

Permeability
The rate at which gas or liquid passes through rubber under pressure.

Permeation
The diffusion of gas or liquid through a rubber material.

Plasticizer
A compound added to rubber to improve flexibility and low-temperature performance.

Post Cure
A secondary heat treatment after molding that improves rubber stability and performance.

Pot
The section of a mold where rubber is placed before being transferred into the cavity.

Rebound
A measure of rubber’s elasticity, typically expressed as a percentage of vertical bounce.

Register
The precise machining that ensures accurate mold plate alignment.

Resilience
Rubber’s ability to return to its original shape after deformation.

Shrinkage
The reduction in part volume after molding, typically due to cooling or solvent loss.

Sprue
The main feed path from the pot to the mold cavity in transfer and injection molds.

Sprue Marks
Surface marks left where the sprue connects to the part; raised or indented.

Surface Finish
A measurement of part surface smoothness, usually in microinches or micrometers.

Tear Resistance
A rubber compound’s ability to resist the growth of cuts under tension.

Tear Strength
The force needed to rupture a rubber sample of known geometry.

Temperature Range
The maximum and minimum operating temperatures of a rubber compound.

Tensile Strength
The force per square inch required to break a rubber specimen under tension.

Total Indicator Reading (TIR)
A method for measuring roundness and concentricity in rubber parts.

Undercut
A groove or recessed feature that interferes with straight removal from a mold.

Vibration Dampening
Rubber’s ability to absorb and dissipate mechanical vibrations.

Vulcanization
A heat-and-pressure process that strengthens rubber through cross-linking.

Weather Resistance
The ability of rubber to withstand environmental exposure, including ozone, UV, and temperature cycling.