Glossary of Terms

Antioxidant: a compounding ingredient that slows or stops oxygen attack. 

Antiozonant: a compounding ingredient that slows or stops ozone attack. 

Backrinding: the torn or gouged appearance of a crosslinked material at the mold parting line. 

Bloom: the change in the appearance of an elastomer compound caused by the migration of an ingredient(s) to the compound surface. It is also the material that migrates to the surface. 

Blow molding: The process of inflating a hot, hollow, thermoplastic preform or parison inside a closed mold so its shape conforms to that of the mold cavity. 

Bonding: Vulcanized bonding of rubber to metal is a generic phrase that covers all aspects of the process by which an elastomer is chemically bonded to a pre-coated steel surface. 

Cold Runner: a channel in a TSE mold that is maintained at a temperature that prevents crosslinking of a compound within the channel, thus minimizing or essentially eliminating runner scrap. 

Cold Runner Nozzle: the tapered tube that connects the cold runner system to a mold. 

Compound: a mixture of elastomer and other materials that is designed to meet end-use specifications and to process satisfactorily. 

Compression molding: the process of forming a material to the shape of a mold cavity. Initial pressure results from mold closure while final pressure results from thermal expansion of elastomer in the mold. 

Crosslinking: the formation of chemical bonds between polymer chains, generally with the application of heat and pressure. 

Crosslinking Agent: a chemical added to a compound to link polymer molecules together, or to assist in the crosslinking process. For example, sulfur links the polymer molecules, while an accelerator increases the rate of crosslinking of the sulfur with the polymer. 

Deflashing: the process of removing excess material from molded articles, typically by tumbling articles at temperatures sufficiently low to embrittle the flash.

Die-cutting: A hand-operated, die-cutting machine uses steel rule die shapes to cut through a wide range of materials quickly and easily. 

Hot Runner Mold: a heated channel in a TPE mold designed to maintain the polymer in a fluid condition prior to filling the mold cavities. 

Injection Mold: one in which an elastomer is shaped by injection molding. 

Injection Molding: a shaping method that involves sequentially flowing a polymer through channels under high pressure, e.g., through a sprue, runner, gate, and finally into the cavity of a closed injection mold. 

Mold: typically a metal block into which the core form or cavity is incorporated. 

Molder: an object, generally metal or plastic, that becomes an integral part of a molded elastomer article. 

Knit Line: an imperfection in a molded article caused by joined flowing fronts. 

Overflow: the hollowed space in a mold plate adjacent to the land that accepts excess compound from a mold cavity. It is also called an overflow groove or a flash groove. 

Parting Line: a line that defines the junction of abutting mold plates. It is also the line that is evident on a molded elastomer article. 

Plasticizer: a material added to an elastomer compound to improve its workability. 

Polymer: a material consisting of very long molecules, formed from a single monomer or from different monomers. 

Post Cure: a treatment, generally at high temperature, to increase the state of crosslinking and/or volatilize undesired materials in an elastomer compound. 

Preform: the shaped, uncrosslinked compound that is placed in a mold prior to its being crosslinked into its final shape under heat and pressure. 

Plastic Extrusion: The forcing of a material through a die orifice. This die orifice produces the final shape of the finished product. 

Plasticizer: a material added to an elastomer compound to improve its workability. 

Polymer: a material consisting of very long molecules, formed from a single monomer or from different monomers. 

Post Cure: a treatment, generally at high temperature, to increase the state of crosslinking and/or volatilize undesired materials in an elastomer compound. 

Preform: the shaped, uncrosslinked compound that is placed in a mold prior to its being crosslinked into its final shape under heat and pressure. 

Retarder: a material added to a compound to delay the onset of scorch. 

Reversion: deterioration of elastomer properties that occurs with overcure. 

Rotational molding: Ground plastic powder is heated on a rotating mold, uniformly covering the mold. Cooling results in a hollow finished part. 

Rubber Extrusion: Rubber is continuously forced through a die that forms it to the desired cross-sectional size and shape before curing. 

Scorch: premature crosslinking of an elastomer compound. 

Sink Mark: a depression in the surface of a molded article that most frequently occurs with TPE articles. 

Sprue: the round and tapered channel that conveys compound to a cavity from a transfer pot, or from an injection molding machine to the runner system or mold. Also the cured elastomer that is formed in the channel. 

Sprue Mark: a mark on the surface of a molded article that occurs at the point of separation of the sprue and the molded article. 

Submarine Gate: a gate located between surfaces of mold plates. 

Surface Gate: a gate located adjacent to a mold plate or cavity. 

Thermoforming: More commonly known as vacuum forming, thermoforming is the manufacture of plastic components through a pressure formingprocess. 

Thermoplastic: a polymer that softens or becomes fluid-like upon heating, and that hardens upon cooling, much like candle wax. 

Thermoset: a crosslinked polymer in which the crosslinks can be broken only with difficulty (contrast to thermoplastic). 

TPE: thermoplastic elastomer 

Transfer Molding: the process by which a plunger forces a material from a transfer pot through a sprue and into a cavity of a closed transfer mold. 

Transfer Mold: one in which a compound is shaped by transfer molding. 

TSE: thermosetting elastomer. 

UHMW (Ultra High Molecular Weight) : has a molecular weight average that is 10 times higher than standard high density polyethylene resins. This gives UHMW a unique combination of attributes that make it more useful in many applications where lower molecular weight grades cannot perform.