Applications of the NBR O-Ring

Applications of the NBR O-Ring

As an elastomeric sealing material, nbr o-rings have many applications in the industry. Their resistance to oils, greases and hydrocarbons makes them a popular choice in hydraulic and industrial sectors. In addition, nbr o-rings feature good wear and tensile strength properties which contribute to their long service life. With a temperature range between -30degC and 120degC they are suitable for use in most industrial environments.

NBR (nitrile butadiene rubber) is a synthetic copolymer of butadiene and acrylonitrile, also known as Buna N, NBR rubber or nitrile elastomer. The acrylonitrile content in nbr o-rings varies from 18% to 50% and directly influences the physical properties of the finished product. A higher acrylonitrile content increases resistance to oils and fuels, but reduces flexibility at low temperatures. A medium acrylonitrile content provides a good balance between these two opposing realities.

The nbr o-ring has excellent resistance to oil and fuels, dilute acids, alkalis and salt solution at moderate to low temperatures. It is not recommended for use with aromatic hydrocarbons, chlorinated hydrocarbons or polar solvents. NBR is not a good choice for outdoor applications due to its limited resistance to ozone, UV exposure and general weathering. For this application HNBR, VMQ or FKM are more suitable seal materials.

With a high tensile strength and compression set resistance nbr o-rings are well suited to dynamic sealing in hydraulic and pneumatic systems. Their good abrasion resistance enables them to withstand heavy loads and friction without wearing out quickly. In addition, the nitrile rubber maintains its flexibility even when subject to high pressure which helps it to bridge small gaps between the mating parts.

The NBR o-ring is FDA approved for use in the food industry and can be used in machinery and equipment that comes into contact with food such as mixers, packaging machines or conveyor belts. NBR o-rings with a Shore hardness of 70 or 90 are available to suit different sealing requirements.

Although nbr o-rings perform well in industrial environments, their resistance to harsh chemicals is limited. They do not hold up against strong acids, halogenated hydrocarbons or ketones. If chemical resistance is important for the application, FKM or Viton (Viton is a registered trademark of DuPont) O-rings are a better choice.

In comparison to nbr o-rings, FKM has an excellent performance under harsh conditions with high and low temperatures and good chemical resistance. It is recommended for sealing gasses such as butane, ethylene glycol and propane. FKM is also resistant to most organic acids, alcohols, salt solutions, mineral oils and petroleum products making it an ideal choice in chemical installations and processes. FKM is also good for high and low temperature applications with little or no impact on its elasticity. In contrast, nbr o-rings lose their elasticity under high temperatures and age rapidly after prolonged exposure to ozone and UV. The best practice is to store them in airtight containers. This will slow down the ageing process.