Rubber O-rings are some of the most common sealing products in the world, and are utilized across all types of applications and industries.  The wide range of liquids and gases to be sealed has necessitated the development of a wide range of elastomers.

ASTM International classifies elastomers by the chemical composition of their polymer chains. Of the seven ASTM classifications of elastomers (M, O, R, Q, T, U, and Z), Patriot Rubber offers rubber seals made from three of the classifications commonly used for industrial sealing applications (M, R, and Q).

“M” class organic elastomers have saturated carbon chains of polymethylene. Elastomers with saturated carbon chains exhibit superior resistance to heat, light, and ozone, versus elastomers with unsaturated carbon chains. ASTM classifications of these elastomers end with the letter “M”.

• EPDM
• FKM (Viton™)
• FFKM

“R” class organic elastomers have unsaturated carbon chains, such as natural rubber and synthetic rubbers, derived at least partly from diolefins. ASTM classifications of these elastomers end with the letter “R”.

• CR (Neoprene)
• NBR (Buna)

“Q” class inorganic elastomers have silicon and oxygen in their polymer chains (polysiloxane). ASTM classifications of these elastomers end with the letter “Q”.

• VMQ (Silicone)
• FVMQ (Fluorosilicone)

Elastomers

(EPDM) O-Rings

EPDM elastomers are built upon hydrocarbon-based polymers.

EPDM elastomers are frequently used to seal food, water and steam applications, and offer the best resistance to ozone and weathering. EPDM’s are not used with petroleum oils or fuels because significant swelling might result.

Elastomers with saturated polymer backbones, such as EPDM, have better resistance to heat, light and ozone than unsaturated elastomers such as CR and NBR. As such, EPDM can be formulated to be resistant to temperatures as high as 150 °C, and, when properly formulated, can be used outdoors for many years or decades without degradation.

EPDM also has good low temperature properties, maintaining elasticity to temperatures as low as -40 °C, depending on grade and formulation.

EPDM does not respond well to environments that create repeated thermal shock.

(FKM) Viton™ O-Rings

Organic fluorocarbon (FKM) elastomers are built on a polymer chain of vinylidene C=CH₂ with fluorine CF₂=CH₂.

FKM elastomers possess excellent resistance to high temperatures, weather, ozone, oxygen, UV, mineral oil, synthetic hydraulic fluids, fuels, aromatics, and many organic solvents such as benzene, kerosene, toluene, xylene, etc.

Typical service temperatures range from -4°F to 400°F (-20°C to 200°C), with special formulations ranging from -40°F to 500°F (-40°C to 260°C). FKM elastomers will harden as temperatures lower, possibly affecting the seal’s ability to deform and create a tight seal, making it critical to accurately specify physical performance criteria.

Gas permeability is very low and similar to that of butyl rubber. Special FKM compounds exhibit an improved resistance to acids and fuels. And FKM offers good flame retardance.

Our hardness range for FKM elastomers is 55 to 90 Shore A durometer.

Limitations of FKM include intermediate tear strength, and very little resistance to oxygenated solvents (alcohols, ethers, esters, and ketones).

Examples of FKM elastomers:

Viton™ A-401C – general purpose bisphenol-cured FKM elastomer.

Viton™ B-600 – higher fluorine content that Viton A-401C.

Viton™ GF-600S – peroxide-cured FKM elastomer with higher fluorine content that Viton B-600.

Viton™ FGLT-600S – peroxide-cured FKM elastomer with low temperature sealing capability.

Viton™ Extreme ETP-600S – highest content of fluorine.

(FFKM) O-Rings

Perfluoroelastomer (FFKM) materials offer the highest operating temperature range, the most comprehensive chemical compatibility, and the lowest off-gassing and extractable levels of any rubber material.

Perfluoroelastomers can tolerate continuous operating temperatures to a minimum of 250°C, and are used in applications that involve contact with hydrocarbons and other highly corrosive fluids.

Popular FFKM compounds:

• FFKM 75A BLACK
• FFKM 70A WHITE

(CR) Neoprene O-Rings

Neoprene, or Chloroprene rubber, 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.

Neoprene resists degradation more than natural or synthetic rubber. Additionally, the material resists burning better than exclusively hydrocarbon based rubbers, making it appropriate for fire retardant applications.

Popular CR compounds:

• NEOPRENE 70A
• AMS 3209

(NBR) Buna-N O-Rings

Nitrile rubber (NBR) is the general term for acrylonitrile butadiene copolymer. 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.

Popular NBR compounds:

• NBR 70A
• NBR 90A
• MIL-P-25732
• AMSP83461
• AMS-P-5315
• AMS-P-5510
• AMSR7362

(VMQ) Silicone O-Rings

Unlike the previous organic elastomers presented on this page, inorganic silicone elastomers do not have carbon-carbon chains, but rather very flexible siloxane chains, allowing them to remain flexible throughout a broad range of temperatures (typically -60°C to 300°C).

Silicone elastomers have both high temperature resistance and low temperature flexibility. They are inert and possess good biocompatibility for use in food and medical applications. Silicone elastomers have good ozone, UV, and weather resistance, and they are good insulators and vibration dampeners. Silicone elastomers possess low thermal conductivity, low chemical reactivity, and low toxicity (friendly to the human body). Silicone repels water, and does not stick to most substrates (like Teflon®), but sticks very well to some substrates such as glass. Silicone elastomers resist creasing and wrinkling, and they can be formulated to be electrically insulative or electrically conductive. Silicone elastomers have high permeability, meaning gas can easily pass through them, and they offer excellent sound dampening and anti-vibration qualities. And, silicone elastomers are naturally flame retardant.

Caution: Silicone elastomers are not very durable. As a group, they have poor tensile strength, poor tear strength, and little wear resistance. Silicones are relatively expensive and can be attacked by certain solvents.

(FVMQ) Fluorosilicone O-Rings

Fluorosilicone (FVMQ) contains trifluoro propyl groups next to the methyl groups. The mechanical and physical properties are very similar to silicone (VMQ). However, fluorosilicone, with the added fluorine, offers improved fuel, mineral oil resistance, and chemical resistance.

Fluorosilicone offers poor hot air resistance when compared with silicone.

Benefits of this highly fluorinated material include: superior extreme low and high temperature performance, and prolonged resistance to fuels, oils, solvents and aggressive fluids. Fluorosilicones offer many of the advantages of silicone, and with some of the performance properties of FKM elastomers.

Similar to silicone, fluorosilicone does not have strong mechanical properties.  These poor physical characteristics restrict its use in dynamic applications.