Rubber Material Types For Rubber Seals, Rubber Gaskets And O Rings

By Author: Jen Smith
Total Articles: 17
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IIR
Resistant to the same fluid types as EPDM , the distinctive properties of IIR rubber materials are very low gas and moisture permeability, excellent insulating properties, good ozone and weathering resistance, and resistance to a great many organic and inorganic media. IIR elastomer materials can be polymerised with various halogens (e.g. Chlorine / Bromine) to improve resistance to certain chemical media, but at the expense of electrical insulation and moisture resistance. They can be used from –40 to +120°C typically, and are mostly used in the production of tyre inner tubes, seals and gaskets, vacuum seals and membranes, and pharmaceutical goods.

CR
CR seal materials typically display good resistance to ozone, heat aging and chemicals. Good resistance to refrigerants, aliphatic hydrocarbons, mineral oils and greases. Typical trade name: Neoprene® (Dupont Dow Elastomers)

Chlorobutadiene rubbers contain chlorine in the polymer to reduce the reactivity to many oxidising agents, as well as to oil and flame. CR elastomers also have good resistance to ozone cracking, heat ageing and chemical attack. ...
... Some of the important applications of CR elastomers include Vee-belts, coated fabrics, cable jackets, tyre-sidewalls, seals and gaskets in contact with refrigerants, mild chemicals and atmospheric ozone.

CSM
CSM grades contain 24-43% chlorine content to provide excellent ozone and weather resistance, discoloration by sun and ultraviolet light, high resistance to many oxidising and corrosive chemicals, good resistance to dry heat to 150°C, low flammability and gas permeability, and also good resistance to hot water (when cured with lead oxide). The low temperature properties are generally limited, depending on the chlorine content of the CSM grade used, and the compression set is not very good.

CSM elastomers are generally useful in electrical applications, weather resistant membranes, hoses and acid resistant tank linings.

ECO
Generally resistance to high temperatures, oils, ozone, and flame with gas resistance comparable to NBR’s. The temperature range for continuous use is –40 to +120°C, but are generally unsuitable for rubber to metal bonding (they are corrosive to metals). ECO elastomers are suitable for use in seals, gaskets, diaphragms, cable jackets, belting etc, for a wide range of media. However, they are unsuitable for use with ketones and esters, alcohols, phosphate ester hydraulic fluids, sour gas, water and steam.

AEM
AEM rubber materials offer an unusual combination of physical properties; high heat resistance (up to 175°C), excellent ozone and weather resistance, moderate resistance to mineral oils, low temperature flexibility to –30°C, good resistance to hot water and high tensile strength. AEM applications are similar to ACM elastomers, but has the advantage where low temperature flexibility is concerned. They are typically moulded into O rings seals, boots and ignition wire jackets.

EPDM
EPDM elastomers have a fair tensile strength and excellent resistance to weathering and ozone, and chemical attack. They also exhibit excellent electrical insulation properties. Peroxide cured elastomers exhibit excellent heat ageing, and resistance to compression set from –40 to +150°C, more so if sulphur cured. They are resistant to a wide range of media, including hot water and steam to 200°C (in the absence of air), but are not considered compatible with mineral and synthetic lubricants, and hydrocarbon fuels. They are typically used in the production of window and door seals, wire and cable insulations, waterproofing sheets and hoses, and seals, O rings and gaskets.

FKM/FPM
Outstanding resistance to heat, weather, ozone, oxygen and oxidisers. Very low gas permeability. PPE FKM (FPM) seal materials include copolyme, terpolyme and tetrapolymer grades and bisphenol and peroxide cure systems.

FKM elastomers are highly fluorinated polymers containing few compounding ingredients. They are stable at very high temperatures (they can withstand 200°C / 400°F indefinitely, in service). By comparison, conventional elastomers would become brittle in 24 hours at this temperature, in air. FKM vulcanisates, in general, have outstanding resistance to oxygen, ozone, weather, flame and oxidative chemicals, and excellent resistance to swelling in a wide variety of media. However, they are not compatible with polar solvents (e.g. M.E.K.), some organic acids (e.g. Formic acid), certain methanol and ester based hydraulic fluids (e.g. Skydrol), ammonia and some amines. They are suitable in high-energy radiation environments up to about 106 Rads. Special grades of FKM may be required for use in hot water and steam applications.

FKM elastomers provide high compression set resistance if compounded with bisphenol cure systems. Generally they are serviceable down to –30°C, but specialist grades (such as Endura® V91A) can provide effective sealing down to –45°C. Electrical insulation properties are not particularly outstanding, but would be adequate for sheathing where elevated temperatures, ozone, chemical and flame resistance are required (e.g. shaft seals, O rings and gaskets, diaphragms and cable sheathing).

FVMQ
FVMQ elastomers are modified silicone rubbers, with superior fluid resistance, but limited to about 175°C (347°F).

HNBR
The hydrogenation process of NBR elastomers provide excellent heat and ozone resistance. Peroxide cured HNBR’s have the best compression set and heat resistance, and high-nitrile (ACN) HNBR elastomers have better resistance to mineral oils. HNBR’s combine best resistance and low temperature flexibility, although they are more expensive than NBR’s. HNBR’s are useful where resistance is required to ozone and weather, ageing in hot air and industrial lubricants, hot water and steam to 150°C, amine based corrosion inhibitors and sour gas (H2S), and high-energy radiation. HNBR’s fill the gap between NBR’s and FKM’s in many areas of application where resistance to heat and aggressive media are required simultaneously, and may therefore provide a lower cost alternative to FKM elastomers.

NR
Natural rubber (tapped from the cultivated rubber tree) exhibits high tensile strength, abrasion resistance, resilience, tear strength and low hysteresis. The chemcially similar polyisoprene has lower strength properties than the natural form but better low-temperature properties. Both rubbers are susceptible to degradation by weathering characteristics, and both show poor resistance to mineral and petroleum-based oils and fuels.

Typical long-term operating range is from -50°C to 70°C.
Main applications for natural rubber materials, apart from tyres, are for vibration mounts, springs and bearings.

NBR (BUNA N)
NBR elastomers are available in five basic grades; based on acrylonitrile content, giving proportional physical and chemical properties. NBR’s typically have (depending on increased ACN content), decreasing low temperature flexibility, increasing compression set, gas permeability, improved heat ageing and ozone resistance, improved tensile and abrasion strength, hardness and density. NBR’s are used where good resistance is required, to aromatic hydrocarbons at –40 to +120°C (e.g. gaskets and seals, hoses and cable jacketing), typically in the oil and gas industry.

High Nitrile: >45% ACN content
Medium Nitrile: 30-45% ACN content
Low Nitrile: