Elastomer Properties

The following paragraphs briefly review the various elastomers currently available for use in O-rings and other elastomeric seals.

1. Acrylonitrile- Butadiene (NBR)

Nitrile Rubber (NBR) is the general term for acrylonitrile butadiene terpolymer. The acrylonitrile content of nitrile sealing compounds varies considerably (18% to 50%) and influences the physical properties of the finished material.

The higher the acrylonitrile content, the better the resistance to oil and fuel. At the same time, elasticity and resistance to compression set is adversely affected. In view of these opposing realities, a compromise is often drawn, and a medium acrylonitrile content selected. NBR has good mechanical properties when compared with other elastomers and high wear resistance. NBR is not resistant to weathering and ozone.

Heat Resistance
Up to 100°C (212°F) with shorter life @ 121°C (250°F).

Cold Flexibility
Depending on individual compound, between -34°C and -57°C 
(-30°F and -70°F)

Chemical Resistance
Aliphatic hydrocarbons (propane, butane, petroleum oil, mineral oil and grease, diesel fuel, fuel oils) vegetable and mineral oils and greases.
HFA, HFB and HFC fluids
Dilute acids, alkali and salt solutions at low temperatures.
Water (special compounds up to 100°C)

Not compatible with:
Fuels of high aromatic content (for flex fuels a special compound must be used.)
Aromatic hydrocarbons (benzene)
Chlorinated hydrocarbons (trichloroethylene)
Polar solvents (ketone, acetone, acetic acid, ethylenester)
Strong acids
Brake fluid with glycol base.
Ozone, weather and atmospheric aging.

2. Fluorocarbon (FKM)

Fluorocarbon (FKM) has excellent resistance to high temperatures, ozone, oxygen, mineral oil, synthetic hydraulic fluids, fuels, aromatics and many organic solvents and chemicals. Low temperature resistance is normally not favourable and for static applications is limited to approximately -26°C, although in certain situations it is suitable down to -40°C. Under dynamic conditions, the lowest service temperature is between -15°C and -18°C.

Gas permeability is very low and similar to that of butyl rubber. Special FKM compounds exhibit and improved resistance to acids, fuels, water and steam.

Heat resistance
Up to 204°C and higher temperatures with shorter life expectancy.

Cold flexibility
Down to -26°C (some up to -40°C)

Chemical resistance
Mineral oil and grease, low swelling in ASTM oil No.1, and IRM 902 and IRM 903 oils
Non-flammable hydraulic fuels in the group HFD.
Silicone oil and grease
Mineral and vegetable oil and grease
Aliphatic hydrocarbons (fuel, butane, propane, natural gas)
Aromatic hydrocarbons (benzene, toluene)
Chlorinated hydrocarbons (trichloroethylene and carbon tetrachloride)
Fuels, also fuels with methanol contents
High vacuum
Very good ozone, weather and aging resistance

Not compatible with:
Glycol based brake fluids
Ammonia gas, amines, alkalis
Superheated steam
Low molecular organic acids (formic and acetic acids)

3. Silicone Rubber (Q, MQ, VMQ, PVMQ)

The term silicone covers a large group of materials in which vunyl-methyl-silicone (VMQ) is often the central ingredient. Silicone elastomers as a group have relatively low tensile strength, poor tear and wear resistance. However, they have many useful properties as well. Silicones have good heat resistance up to 232°C, good cold flexibility down to -59°C and good ozone and weather resistance as well as good insulating and physiologically neutral properties.

Heat Resistance
Up to approximately 204°C (special compound up to 232°C )

Cold Flexibility
Down to approximately -59°C to -54°C with special compounds down to -115°C

Chemical resistance
Engine and transmission oil (eg: ASTM oil No.1)
Animal and vegetable oil and grease
Brake fluid (non-petroleum base)
Fire-resistance hydraulic fluid, HFD-R and HFD-S
High molecular weight chlorinated aromatic hydrocarbons 
Moderate water resistance
Diluted salt solutions
Ozone, aging and weather resistance

Not compatible with:
Superheated water steam over 121°C
Acids and alkalis
Low molecular weight chlorinated hydrocarbons
Aromatic mineral oil
Hydrocarbon based fuels
Aromatic hydrocarbons (benzene, toluene)

4.Ethylene Propylene Rubber (EPDM, EPM)

EPM is a copolymer of ethylene and propylene. Ethylene propylene-diene rubber (EPDM) is produced using a third monomer and it particularly useful when sealing phosphate-ester hydraulic fluids and in brake systems that use fluids having a glycol base.

Heat resistance
Up to 150°C (max 204°C) in water and /or steam)

Cold Flexibility
Down to approximately -57°C

Chemical resistance
Hot water and steam up to 149°C with special compounds up to 204°C
Glycol based brake fluids up to 149°C
Many organic and inorganic acids
Cleaning agents, soda and potassium alkalis.
Phosphate- ester based hydraulic fluids (HFD-R)
Silicone oil and grease
Many polar solvents (alcohols, ketones, esters).
Ozone, aging and weather resistant.

Not compatible with:
Mineral oil products (oils, greases and fuels)

5. Hydrogenated Nitrile (HNBR)

Hydrogenated Nitrile is a synthetic polymer that results from the hydrogenation of nitrile rubber (NBR). In this process the molecular double bonds in the NBR primiary polymer chain undergo a hydrogenation process and therefore the term hydrogenated nitrile (HNBR). The allow temperature range extends to 149°C with short periods at higher temperature possible. By following design guidelines effective sealing can be achieved at -32°C for static applications. For dynamic applications however, operating temperatures are limited to above - 23°C. HNBR compounds posses superior mechanical characteristics, particularly their high strength. For sealing applications up to app 159°C, this is an advantages as it prevents extrusion and wear.

Chemical Resistance
Aliphatic hydrocarbons
Vegetable and animal fats and oils
HFA, HFB and HFC fluids
Dilute acids, bases and salt solutions at moderate temperature
Water and stream up to 149°C
Ozone, aging and temperature

Not compatible with:
Chlorinates hydrocarbons
Polar solvents (ketone and ester)
Strong acids

6. Fluorosilicone (FVMQ)

FVMQ contains trifluoropropyl groups next to the methyl groups. The mechanical and physical properties are very similar to VMQ. FVMQ offers improved fuel and mineral oil resistance but poor hot air resistance when compared with VMQ.

Heat resistance
Up to 177°C max.

Cold flexibility
Down to app. -73°C

Chemical resistance
Aromatic mineral oils (IRM 903 oil)
Fuels
Low molecular weight aromatic hydrocarbons (benzene, toluene)

7. Chloroprene Rubber (CR)

Chloroprene was the first synthetic rubber developed commercially and exhibits generally good ozone, aging and chemical resistance. It has good mechanical properties over a wide temperature range

Heat resistance
Up to app. 121°C

Cold flexibility
Down to app. -40 °C

Chemical resistance
Paraffin base mineral oil with low DPI, eg: ASTM oil No.1
Silicon oil and grease
Water and water solvents at low temperature
Refrigerants
Ammonia
Carbondioxide
Improved ozone, weathering and aging resistance compared with NBR

Limited compatibility
Naphthalene based mineral oil (IRM 902 and IRM 903 oils)
Low molecular aliphatic hydrocarbons (propane, butane, fuels)
Glycol based brake fluids

Not compatible with:
Aromatic hydrocarbons (benzene)
Chlorinated hydrocarbons (trichloroethylene)
Polar solvents (ketones, esters, ethers, acetones).

Service Temperature Range Chart

This service temperature range is for reference only. In actual service environment, some specific compounds may not reach the maximum temperature as indicated in this chart. However, higher temperature may be attained if exposed is short or intermittent