The Rolls-Royce and Bentley Technical Library
This Technical Library is proudly provided for all Rolls-Royce and Bentley enthusiasts by the Rolls-Royce Owners Club of Australia.

Natural rubber is a product coagulated from the latex of the rubber tree, hevea brasiliensis. Natural rubber features low compression set, high tensile strength, resilience, abrasion and tear resistance, good friction characteristics, excellent bonding capabilities to metal substrate, and good vibration dampening characteristics.

» excellence compression set
» good resilience and abrasion
» good surface friction properties

O-rings, rubber seals and custom molded rubber components for:

» rubber to metal bonded vibration isolators and mounts
» automotive diaphragms
» FDA applications for food and beverage seals

» poor resistance to attack by petroleum oils
» poor ozone, UV resistance

Fluorosilicones combine most of the attributes of silicone with resistance to petroleum oils and hydrocarbon fuels.
Low physical strength and abrasion resistance combined with high friction limit fluorosilicone to static seals.
Fluorosilicones are used primarily in aircraft fuel systems.

» excellent extreme temperature properties
» excellent compression set resistance
» very clean, low odor and taste

O-rings, rubber seals and custom molded rubber components for:

» seals (static) for extreme temperature applications
» food applications
» medical devices
» FDA applications

» typically not good for dynamic seals due to friction properties and poor abrasion resistance

Silicone is a semi-organic elastomer with outstanding resistance to extremes of temperature with corresponding resistance to compression set and retention of flexibility. Silicone elastomers provide excellent resistance to ozone, oxygen, and moisture.
Low physical strength and abrasion resistance combined with high friction properties limit silicone to static seal applications.
Silicone utilises a flexible siloxane backbone rather than a carbon backbone like many other elastomers and has very low glass transition temperatures.

» excellent extreme temperature properties
» excellent compression set resistance
» very clean, low odor and taste

O-rings, rubber seals and custom molded rubber components for:

» seals (static) for extreme temperature applications
» food applications
» medical devices
» FDA applications

» typically not good for dynamic seals due to friction properties and poor abrasion resistance

Millable polyurethane exhibits excellent abrasion resistance and tensile strength as compared to other elastomers providing superior performance in hydraulic applications with high pressures, abrasive contamination and shock loads. Fluid compatibility is similar to that of nitrile at temperatures up to approximately 175 °F. At higher temperatures, polyurethane has a tendency to soften and lose both strength and fluid resistance advantages over other elastomers.

» excellent strength and abrasion resistance
» good resistance to petroleum oils
» good weather resistance

O-rings, rubber seals and custom molded rubber components for:

» seals for high hydraulic pressure
» highly stressed parts subject to wear

» poor resistance to water
» poor high temperature capabilities

Styrene-Butadiene (SBR) is a copolymer of styrene and butadiene.
SBR compounds have properties similar to those of natural rubber. SBRs primary custom molded application is the use in hydraulic brakes system seals and diaphragms, with the major of the industry usage coming from the Tyre Industry.
SBR features excellent resistance to brake fluids, and good water resistance.

» good resistance to brake fluids
» good resistance to water

O-rings, rubber seals and custom molded rubber components for:

» hydraulic brake systems seals and diaphragms
» plumbing applications

» poor weather resistance
» poor petroleum oil and solvent resistance

Ethylene-acrylic (Vamac ®) is a terpolymer of ethylene, methyl acrylate, and an acid-containing monomer as a cure site. It exhibits properties similar to those of Polyacrylate, but with extended low temperature range and with enhanced mechanical properties.
Ethylene-acrylic offers a high degree of oil, ozone, UV and weather resistance.

» excellent vibration dampening
» excellent heat aging characteristics
» good dynamic property retention over a wide temperature range
» resistance to transmission fluids, water, glycol mixtures, and alkalies

O-rings, rubber seals and custom molded rubber components for:

» Automotive sealing applications.
» Automotive transmissions
» Power steering seals

» not recommended for exposure to fuel, brake fluid, aromatic hydrocarbons or phosphate esters.

Polyacrylates are copolymers of ethyl and acrylates which exhibit excellent resistance to petroleum fuels and oils and can retain their properties when sealing petroleum oils at continuous high temperatures up to 300 °F. These properties make polyacrylates suitable for use in automotive automatic transmissions, steering systems, and other applications where petroleum and high temperature resistance are required.
Polyacrylates also exhibit resistance to cracking when exposed to ozone and sunlight.
Polyacrylates are not recommended for applications where the elastomer will be exposed to brake fluids, chlorinated hydrocarbons, alcohol, or glycols.

» petroleum fuel and oil resistance
» resists flex cracking
» good ozone resistance
» good heat resistance

O-rings, rubber seals and custom molded rubber components for

» Automotive transmissions.
» Automotive steering systems

» poor compression set performance relative to NBR
» lesser water resistance and low temperature performance than some other elastomers

Neoprene homopolymer of chlorobutadiene and is unusual in that it is moderately resistant to both petroleum oils and weather (ozone, UV, oxygen). This qualifies neoprene uniquely for certain sealing applications where many other materials would not be satisfactory. Neoprene is classified as a general purpose elastomer which has relatively low compression set, good resilience and abrasion, and is flex cracking resistant.
Neoprene has excellent adhesion qualities to metals for rubber to metal bonding applications.
It is used extensively for sealing refrigeration fluids due to its excellence resistance to Freon® and ammonia.

» moderate resistance to petroleum oils
» good resistance to ozone, UV, oxygen
» excellence resistance to Freon® and ammonia

O-rings, rubber seals and custom molded rubber components for

» refrigeration industry applications
» general purpose seals, hose and wire

» moderate water resistance
» not effective in solvents environments

Fluorocarbon exhibits resistance to a broader range of chemicals combined with very good high temperature properties more so than any of the other elastomers. It is the closest available approach to a universal elastomer for sealing in the use of o-rings and other custom seals over other types of elastomers.
Fluorocarbons are highly resistant to swelling when exposed to gasoline as well as resistant to degradation due to expose to UV light and ozone.
When exposed to low temperatures, fluorocarbon elastomers can become quite hard (-4 °F) but can be serviceable at low temperatures, although FKM compounds are not recommended for applications requiring good low temperature flexibility.
In addition to standard FKM materials, a number of special materials are available with differing monomer compositions and fluorine content (65% to 71%) for improved low temperature, high temperature, or chemical resistance performance.
Fluorocarbons exhibit low gas permeability making them well suited for hard vacuum service and many formulations are self-extinguishing. FKM materials are not generally recommended for exposure to hot water, steam, polar solvents, low molecular weight esters and ethers, glycol based brake fluids, or hot hydrofluoric or chlorosulfonic acids.

» excellent chemical resistance
» excellent heat resistance
» good mechanical properties
» good compression set resistance

» poor low temperature flexibility
» poor resistance to hot water and steam

» differing monomer compositions and fluorine content (65% to 71%) for improved low temperature, high temperature, or chemical resistance performance

O-rings, rubber seals and custom molded rubber components for

» Automotive fuel handling
» Aircraft engine seals
» High temperature applications requiring good compression set
» General industrial seals and gaskets

» degree of fluorination (A, B, F, GB, GF, GFLT, GBLT, GLT, ETP)
» copolymer or terpolymer of fluorinated hydrocarbon monomers

Ethylene-propylene compounds are prepared from ethylene and propylene (EPM) and usually a third monomer (EPDM). These compounds are used frequently to seal in brake systems, and for sealing hot water and steam.  Ethylene propylene compounds have good resistance to mild acids, detergents, alkalis, silicone oils and greases, ketones, and alcohols. They are not recommended for applications with petroleum oils, mineral oil, di-ester lubricants, or fuel exposure.

Ethylene Propylene has gained wide seal industry acceptance for its excellent ozone and chemical resistance properties and is compatible with many polar fluids that adversely affect other elastomers.

EPDM compounds are typically developed with a sulphur or peroxide cure system. Peroxide-cured compounds are suitable for higher temperature exposure and typically have improved compression set performance.

» excellent weather resistance
» good low temperature flexibility
» excellent chemical resistance
» good heat resistance

» poor petroleum oil and solvent resistance

» sulphur-cured and peroxide-cured compounds
» third comonomer EPDM, copolymer ethylene and propylene EPM

O-rings, rubber seals and custom molded rubber components for

» Water system seals, faucets, etc.
» Brake systems
» Ozone exposure applications
» Automotive cooling systems
» General Industrial Use

» glycol-based brake system seals
» FDA approved applications
» NBR NSF standard 61 for potable water applications
» NBR WRc, KTW water applications

HNBR is created by partially or fully hydrogenating NBR. The hydrogenating process saturates the polymeric chain with accompanying improvements to the ozone, heat and aging resistance of the elastomer and improves overall mechanical properties.
HNBR, like Nitrile, increasing the acrylonitrile content increase resistance to heat and petroleum based oils and fuels, but decreases the low temperature performance.

» increased cold flow with hydrogenation
» decreased elasticity at low temperatures with hydrogenation over standard nitrile

O-rings, rubber seals and custom molded rubber components for:

» Oil resistant applications
» Oil well applications
» Fuel systems, automotive, marine, and aircraft
» General Industrial Use

» acrylonitrile content (ACN) from 18% to 50%
» peroxide vs. sulphur donor cure system

Nitrile is the most widely used elastomer in the seal industry. The popularity of nitrile is due to its excellent resistance to petroleum based oils and fuels, and its ability to be compounded for service over a temperature range of -22°F to 212°F.
Nitrile is a copolymer of butadiene and acrylonitrile. Variation in proportions of these polymers is possible to accommodate specific requirements. An increase in acrylonitrile content increases resistance to heat plus petroleum base oils and fuels but decreases low temperature flexibility. Military AN and MS O ring specifications require nitrile compounds with low acrylonitrile content to insure low temperature performance.
Nitrile provides excellent compression set, tear, and abrasion resistance. The major limiting properties of nitrile are its poor ozone and weather resistance and moderate heat resistance, but in many application these are not limiting factors.

» excellent compression set,
» superior tear resistance
» abrasion resistance

» poor weather resistance
» moderate heat resistance

» acrylonitrile content (ACN) from 18% to 50%
» peroxide vs. sulphur donor cure system
» XNBR improved wear resistance formulation

O-rings, rubber seals and custom molded rubber components for:

» Oil resistant applications
» Low temperature applications
» Fuel systems, automotive, marine, and aircraft
» General Industrial Use

» NBR NSF standard 61 for potable water applications
» NBR WRc, KTW water applications
» NBR FDA white list compounds