Abrasion Resistance
The ability of a rubber compound to withstand mechanical wear.

Adhesion
Material sticking or holding against another material.

Air Trap
Air which is trapped in a product or mold during cure, usually causing a void in the part.

Blemish
A defect or deformity on the surface of a rubber component.

Blister
A raised or bubbled blemish on a custom rubber component caused by an air pocket.

Bloom
A milky discoloration caused by the migration of compounds on the surface of a rubber component after molding or storage.

Bond
The term commonly used to denote the attachment of an elastomer to some other member. Bonds may be classified by types, as follows:

Mechanical – purely physical attachment accomplished by holes, interlocking fingers, etc. Cold – adhesion of previously vulcanized elastomer to another member through use of cements. Chemical Bonding – a method of bonding rubber to inserts by applying special adhesives to the insert prior to molding.

Brittleness
The tendency of a rubber product to crack, break or snap under pressure; fragility.

Bump Cycle
The opening and closing of the mold during curing to remove trapped air and let the material flow.

Clamping Force
The amount of pressure placed on a mold to keep it closed during a molding life cycle.

Cold Runner
A channel in a rubber mold that carries molding material to mold cavities during injection molding processes.

Color Streaks
A rubber product defect characterized by a variation in color or a streaking pattern in the molded component.

Compression Molding
Molding process in which a preform of rubber compound is placed directly in the mold cavity and compressed to shape by the mold.

Curing
A step during the molding process where the component being molded is subjected to particular temperatures and pressures so as to accelerate cross-linking reactions in the molded polymer material thereby resulting in its desired final physical properties.

Cycle Time
Length of time to mold one heat of parts. Load materials, close press, cure rubber, open press, and demold parts.

Deflashing
The process of removing the excess rubber material (or flash) from a molded product. Delamination A molded rubber defect characterized by the forming of several layers of material or the appearance of separate layers on the surface of a component.

Die
A manufacturing tool used to stamp or cut out a rubber material during compression.

Durometer
Numerical scale of rubber hardness.

Elasticity
The ability of rubber to return to its original state after removing force such as compression.

Elastomer
Any natural or synthetic material with resilience or memory sufficient to return to its original shape after major on minor distortion.

Elongation
Percent increase in original length of a specimen when it breaks.

Flash
Excess molding material on the surface or joints of rubber products.

Flow
The ability of heated rubber, silicone or other polymers to pass through channels and runners into mold cavities.

Flow Marks
A manufacturing defect caused by improper flow of rubber material indicated by a wavy surface.

Gasket
A component used to retain liquids or gases or a seal caused by the compression of two machined materials.

Gate
The opening of an injection, compression or transfer mold that ensures flow of rubber, silicone or other polymers.

Hardness
The measurement of resistance to force of a polymer component.

Injection Molding
A manufacturing molding process in which rubber, silicone or other polymer materials are heated and forced through runners into a mold.

Injection Ram
The screw or pin that places pressure on the heated compound and forces it into a mold cavity.

Insert
A component to which the rubber is chemically and/or physically bonded to during the molding process.

Knit Line
A witness line on a molded part, usually occurring at the midpoint between injection sprue locations.

Machining
The process of cutting, molding, shaping or finishing products by machine.

Mastication
“Chewing” the rubber to make it softer and more malleable for injection.

Mismatch
A step at the parting line of a part due to a mold cavity being out of register.

Mold Cavity
The hollow space of a mold where the rubber or silicone is shaped.

Mold Lubricant
A material usually sprayed onto the mold cavity surface prior to molding, to facilitate the easy removal of the molded part.

Mold Storage
The process in which custom molds are organized, maintained and stored. ARP catalogs their custom molds and stores them in a climate-controlled room.

Monomers
A molecule that can go through the process polymerization.

O-Ring
A torus shaped mechanical gasket used to seal liquids or gases.

Overflow
A receptacle for excess rubber compound ensuring the cavity mold is completely filled.

Overmold
A molding process that allows previously molded parts to be reinserted forming a new layer of polymer material around the first component.

Oxidation
The chemical reaction of oxygen with rubber involving the transfer of electrons, reducing elastomer strength. This can cause rubber components to crack or become brittle.

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

Permeability
The ability of a liquid or gas to diffuse through a rubber or other polymer product or component.

Polymers
A long molecular chain material formed by the combination of multiple individual units.

Pot
The chamber in the transfer mold, where raw material is placed before it is transferred into the cavity.

Pressure Injection
Pressure placed on the injection ram where the rubber materials are injected into a mold.

Radial Seal
Compression applied to the inside and outside of an O-ring gasket. Resins Injection moldable materials such as silicone, rubber, other polymers.

RMA
Rubber Manufacturers Association.

Rubber – Natural
Raw or crude rubber produced from certain plants and vegetables.

Rubber – Synthetic
Manufactured or man-made elastomers.

Runner
A mold’s distribution system that rubber material travels through to the cavities.

Scorching
Premature curing or setting up of a raw compound during processing.

Short Shot
A lack of rubber material caused by either low pressure, cool temperatures, injection speed, etc.

Shrinkage
The contraction of rubber material after molding and cooling.

Silicone Molding
The manufacturing process in which silicone rubber is heated and injected through a series of runners into a mold producing pliable products such as gaskets, seals and membranes.

Sprue
The opening in the cavity that lets the rubber flow from the runner to the cavity.

Stringiness
A string like or fibrous remnant on a rubber component left over from a previous injection shot.

Substrate
The adhesive material used to coat or bond to the surface of another material.

Thin-Wall Injection Molding
A specialized version of injection molding focusing on the manufacturing of thin or light rubber components.

Tonnage
Measurement of the force needed to keep a molding tool closed during the injection molding process. The term is typically used to describe the size of a molding machine. 

Transfer Molding
A molding process in which rubber compound is placed in a pot that is part of the mold, heated and squeezed through sprues and runners into the mold cavity.

Under Cure
Degree of cure less the optimum; may be evident by tackiness, “air holes” or inferior physical properties.

Viscosity
The measurement of resistance to flow under stress.

Voids
The unintended absence of material in spaces within a molded part where elastomer material did not fill.

Vulcanization
The irreversible thermal process converting polymers or rubber into a more durable and resistant compound.

Warping
A defect that results in a twisted or distorted rubber product usually caused by incorrect temperature.

Weld Line
A defect that results in a discolored line where two flow fronts converge.