A piece of rubber, such as a rubber band, is made of vast numbers of such kinked, twisting, rope-like molecules. When rubber is pulled, the first thing that happens is that the loops and coils of the "ropes" straighten out. The rubber extends as its molecules are pulled out to their full length.
Still more stress causes the kinks to straighten out. Releasing the stress allows the kinks, coils and loops to form again, and the rubber returns to its original dimensions. Materials made of long, tangled molecules stretch very easily.
This is because of the unique physical and chemical properties of elastomers. Most design processes can benefit from a better understanding of elastomeric materials. As always, ISM offers samples to our customers as a way to assist their testing and decision-making. These can be requested when browsing our catalog. What elastomeric properties were the most or least critical?
Help us by telling others what you learned. Have any questions about elastomers and their use in flow control components? If so, send me an email - steven.
You can also ask questions using the comments section below. About the author Steven C. Williams, BS, is the technical writer and an inbound marketing specialist at Industrial Specialties Manufacturing ISM , an ISO supplier of miniature pneumatic, vacuum and fluid circuitry components to OEM's and distributors all over the world.
He writes on technical topics related to miniature pneumatic and fluidic components as well as topics of general interest at ISM. Elastomers and Rubbers - Is There a Difference?
Elastomers and rubbers are handy because of their unique material properties Rubber and elastomer are words commonly used to mean any material with rubber-like properties. Nondiene elastomers include, butyl rubber polyisobutylene , polysiloxanes silicone rubber , polyurethane spandex , and fluoro-elastomers. Non-diene elastomers have no double bonds in the structure, and thus, crosslinking requires other methods than vulcanization such as addition of trifunctional monomers condensation polymers , or addition of divinyl monomers free radical polymerization , or copolymerization with small amounts of diene monomers like butadiene.
Thermoplastic elastomers such as SIS and SBS block copolymers and certain urethanes are thermoplastic and contain rigid hard and soft rubbery repeat units.
When cooled from the melt state to a temperature below the glass transition temperature, the hard blocks phase separate to form rigid domains that act as physical crosslinks for the elastomeric blocks. Manufacturing elastomeric parts is achieved in one of three ways: injection molding, transfer molding, or compression molding. The choice of the molding process depends on various factors, including the shape and size of the parts, the required tolerance, as well as the quantity, type of elastomer, and raw material cost.
As with almost any material, selecting the right elastomeric product for the application requires consideration of many factors, including mechanical and physical service requirements, exposure to chemicals, operating temperature, service life, manufacturability of the parts, and raw material and manufacturing cost. Elastomer performance becomes less predictable and reliable when an elastomer is used near the limits of its service temperature range.
If, for example, the temperature drops, elastomers become harder and less flexible and when the temperature reaches the glass transition temperature, they loose their rubber-like properties entirely.
At even lower temperatures, i. Changes in elastomer properties due to low temperature are usually physical, and fully reversible unless the elastomeric part is exposed to large tensions which can cause damage below the brittle or glass transition temperature. The opposite is true when an elastomer is exposed to high temperatures, that is to temperatures near or above the service temperature limit.
At these temperatures, elastomers often undergo irreversible chemical changes. For example, the polymer backbone may undergo chain scission or the polymer molecules may crosslink, causing the elastomeric part to become either much softer or more rigid, which, in turn, reduces their resistance to compression set. The maximal service temperature can greatly vary from elastomer to elastomer.
Strong swelling and rapid deterioration or complete breakdown of an elastomeric part may occur if the elastomer is not compatible with the fluid it is exposed to. When in doubt, the elastomer should be evaluated in functional tests prior use. Because many applications involve hydrocarbon oils, elastomeric parts such as seals are classified according to their heat and oil resistance.
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