October 27, 2016 – by Eastern Seals

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

O-rings can be used in many applications as they are manufactured from a wide range of materials. O-rings are usually made from rubber, or more specifically, polymers / elastomers. These polymers are usually cured by vulcanisation which results in strong, durable and more elastic rubber materials.

Because of the wide range of materials available, it can be difficult to determine which is the most suitable for a project. It’s important to remember that different materials have different properties; For example, some are more elastic and others are more tear resistant in addition to other key qualities.

Viton® / FKM and NBR are two of the most commonly used elastomers for sealing applications, and for good reason. Both of these materials are suitable for general purpose applications. They offer excellent compression set resistance, and both are designed to resist most oils and lubricants, especially petroleum-based lubricants. Additionally, moderate temperature applications between -15°C and 110°C are served by both compounds, making either material a very good choice for general industrial use.

However, for more specific applications, the decision on material becomes much more important. Viton®/ FKM and NBR compounds have several very crucial differences that make them well-suited to certain applications. While both Viton/ FKM and NBR seals act as very good sealing options at moderate temperatures, Viton®/ FKM is far superior for high temperature applications.

Standard Viton® / FKM vs Standard Nitrile

Standard Viton®/FKM compounds can provide continuous sealing at temperatures up to approximately +205°C.

Standard NBR on the other hand is only 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 are less effective as they become quite hard and inflexible. Special Viton® / FKM compounds can provide low temperature capabilities of -40°C.

Standard NBR will operate successfully at -35°C (However, some special NBR compounds can provide effective sealing down to temperatures of -55°C,)

In addition to temperature, other application conditions differentiate these two compounds. Viton® /FKM has a wide chemical resistance range, which makes it ideal for most applications involving oils, fuels, and mineral acids. Viton®/FKM also offers excellent resistance to oxidation, ozone, UV exposure, weather, fungus and mould. Although NBR also supports some of the same chemical resistances, it is much less universally resistant than its Viton®/FKM counterpart, suffering degradation from weather and ozone exposure. For most circumstances, however, this may not be an issue. NBR also offers the benefit of superior abrasion and tear resistance making them better suited for more heavy duty industrial applications.

Both of these elastomers are suited for an extensive list of diverse applications, and they serve as excellent general purpose seals. Nevertheless, to optimise your choice in seals it is essential to consider the advantages and disadvantages of both materials.

Material Summary

Nitrile (NBR)

Fluorocarbon (Viton®/FKM)

Temperature range: -35°C and +110°C (+135°C intermittent) -25°C to +205°C (+230°C intermittent) Suited for: General purpose sealing, such as petroleum oils, water and some hydraulic fluids. NBR is also resistant against tears and abrasive treatment. Fluorocarbon Viton®/FKM is an all-round material that is suitable for a number of applications, especially diverse sealing applications involving movement. It is also suited for petroleum oils, silicone fluids and gases, acids and some halogenated hydrocarbons, like carbon tetrachloride. Deficiencies: Nitrile/NBR can have issues with automotive brake fluid, ketones, phosphate ester hydraulic fluids, and nitro and halogenated hydrocarbons. While it is ozone and weather resistant, this resistance is not infallible but can be supported through compounding. Fluorocarbon Viton®/FKM is not recommended for Skydrol, amines, esters and ethers with low molecular weight and hot hydrofluoric acids. Applications Nitrile functions well in applications that have limited temperature and resistance requirements. Viton®/FKM O-rings are very versatile, and feature in many different automotive, appliance and chemical processing industries. Click here to see our range of Nitrile compounds. Click here to see our range of Fluoroelastomer compounds.

Eastern Seals also supply a wide range of specialist grade Nitrile and Viton® / FKM seals. These include NORSOK approved materials, metal detectable seals, FDA approved compounds and low temperature grades.

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.

TECH TIPS – Viton® O-rings vs. Nitrile Rubber (NBR)

One of the benefits to using Kit Masters fan clutches is their resistance to air leaks. Kit Masters has been using VITON® o-rings in our products for several years and this Tech Tip will explain why.

Nitrile also known as Buna-N or NBR is the most commonly used elastomer for sealing products; approximately 50% of all o-rings sold are Nitrile. It has a maximum operating temperature of 250 ͦF and is exceptionally resistant to petroleum base oils and hydrocarbon fuels (natural gas, mineral oils, etc.). This material has worked well for Kit Masters but rising under hood temperatures have demanded a higher quality o-ring material.

VITON® is the trade name for a Fluorocarbon (FKM) material. It has an operating temperature up to 400 ͦF and can tolerate intermittent temperatures of 600 ͦF. It has excellent resistance to a wide variety of chemicals, weather and compression set requirements. Since switching to VITON® Kit Masters has noticed fewer failures due to o-ring deterioration.