Viton / FKM vs Nitrile: Which material?

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Fluorocarbon (Viton®/FKM) vs Nitrile (NBR): Which material is right for your application?

O-rings are essential components used in various applications due to their versatility and effectiveness. Typically made from rubber or, more precisely, polymers/elastomers, these materials undergo vulcanization, which enhances their strength, durability, and elasticity.

Due to the wide range of available materials, it can be challenging to determine the most suitable one for a specific project. Each material possesses different properties; for instance, some are more elastic, while others offer higher tear resistance, among other crucial characteristics.

Viton®/FKM and NBR are two commonly utilized elastomers in sealing applications and for good reasons. Both materials are ideal for general purpose applications, providing excellent compression set resistance and high resistance to most oils and lubricants, especially petroleum-based ones. They are suitable for moderate temperature applications ranging between -15°C and 110°C, making them ideal for general industrial use.

However, the choice of material becomes critical for more specific applications. Viton®/FKM and NBR have distinct differences that render them suitable for certain applications. While both materials offer effective sealing properties at moderate temperatures, Viton®/FKM excels in high-temperature applications.

Standard Viton®/FKM vs Standard Nitrile

Standard Viton®/FKM compounds can continuously seal at temperatures up to approximately +205°C.

Standard NBR, on the other hand, is effective for continuous sealing at temperatures up to +110°C (with short-term sealing at 130°C).

At temperatures below -20°C, standard Viton/FKM seals become less effective as they harden and lose flexibility. However, special Viton®/FKM compounds offer low-temperature capabilities down to -40°C.

Standard NBR can operate successfully at -35°C, with some special NBR compounds providing effective sealing at temperatures as low as -55°C.

Apart from temperature considerations, other application conditions differentiate these compounds. Viton®/FKM boasts a wide chemical resistance range, making it ideal for applications involving oils, fuels, and mineral acids. It also offers excellent resistance to oxidation, ozone, UV exposure, and weather. Conversely, NBR supports some of the same chemical resistances but is less universally resistant, suffering degradation from weather and ozone exposure. Nevertheless, NBR's superior abrasion and tear resistance make it suitable for heavy-duty industrial applications.

Both these elastomers are suited for a wide variety of applications and serve as excellent general-purpose seals. To optimize your choice, it's essential to consider the advantages and disadvantages of both materials.

Material Summary

Nitrile (NBR)

• Temperature range: -35°C to +110°C (+135°C intermittent)
• Suited for: General purpose sealing, such as petroleum oils, water, and some hydraulic fluids. Resistant to tears and abrasive treatment.
• Deficiencies: Issues with automotive brake fluid, ketones, phosphate ester hydraulic fluids, and nitro and halogenated hydrocarbons. Ozone and weather resistance is not infallible but can be enhanced through compounding.
• Applications: Functions well in applications with limited temperature and resistance requirements.

Fluorocarbon (Viton®/FKM)

• Temperature range: -25°C to +205°C (+230°C intermittent)
• Suited for: All-round applications, especially diverse sealing needs involving movement. Suitable for petroleum oils, silicone fluids, gases, acids, and some halogenated hydrocarbons like carbon tetrachloride.
• Deficiencies: Not recommended for Skydrol, amines, esters, ethers with low molecular weight, and hot hydrofluoric acids.
• Applications: Highly versatile, used in various automotive, appliance, and chemical processing industries.

For more information, expert consultation, or a quote on Viton®/FKM or Nitrile seals, please contact our technical Sales team. Call +44 (0) 1670 840529 or email sales@easternseals.co.uk.

O-Ring and Rubber Seal Materials: NBR, FKM, EPDM

When faced with different types of rubber seals, which do you choose? Each type has its strengths and weaknesses, dictating where a seal can or cannot be used.

nbr black cloth rubber oil seal suppliers china provides various options for different needs.

For the purposes of this article, we will focus on three common rubber types found in O-rings and similar automotive seals: Buna N, Viton, and EPDM.

Each type constitutes a family of rubber compounds with different physical properties, similar to how various steel alloys possess unique qualities. This means broad generalizations are necessary, as recommendations can vary by manufacturer.

Static applications (such as an O-ring between a threaded fitting and a female-threaded port) are more tolerant of material choice than dynamic applications (such as crankshaft or master cylinder seals). This article focuses on static seals only.

Buna N / NBR / Nitrile

Buna N (commonly referred to as NBR) is usually the least expensive rubber type discussed here. Compatible with petroleum fluids (including dinosaur and synthetic lubricating oils, pure gasoline, and diesel fuel), NBR is suitable for fuel systems running pure gasoline or diesel. It is also compatible with water and ethylene glycol coolants. However, NBR has a relatively low maximum operating temperature of 212°F (it can tolerate up to 250°F in fully static seals, but seal life will diminish). It isn't suitable for high-temperature seals in transmission or differential oil systems.

Viton / FKM / FPM / Fluorosilicone

Viton is a trade name for a type of fluorocarbon rubber developed by DuPont for the aerospace industry. FKM is the ASTM term, while DIN/ISO uses FPM. FKM is usually the most expensive of the three rubber types. It is compatible with petroleum fluids, water, ethylene glycol coolants, biodiesel, and ethanol-blended fuels. However, FKM is not suitable for ethanol or nitromethane. Its high operating temperature of up to 400°F makes it ideal for sealing engine, transmission, and differential oil systems.

EPDM

EPDM differs significantly from NBR and FKM in chemical resistance. It is incompatible with petroleum (oil and gasoline) but compatible with alcohols, water, coolants, and glycol-based brake fluids. Of the three rubber types, EPDM is the only one suitable for braking systems. (Exceptions include certain Citroen and Rolls-Royce systems that use hydraulic oil and should use FKM instead.)

Application Guidelines

Brake System

EPDM is the only choice for seals in braking systems using glycol-based or silicone-based DOT-approved brake fluid. FKM is appropriate only for Citroen or Rolls-Royce systems with hydraulic oil.

Engine Oil Systems

For dynamic seals (sliding or rotating), FKM is preferred regardless of lubricant type. NBR is acceptable for static seals.

Transmissions and Differentials

For manual or automatic systems, use FKM. NBR is acceptable for low-temperature static seals.

Fuel Systems

NBR is suitable for pure gasoline or petroleum diesel in non-return systems. For ethanol blends or biodiesel, use FKM. Nitromethane systems require EPDM.

Cooling Systems

All three rubber types are compatible with water and ethylene glycol coolant, handling up to 250°F in static applications. For propylene glycol coolant, EPDM is the best choice.

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