What is Buna-N?
Buna-N, or nitrile rubber, is a synthetic rubber product with very special characteristics. To better understand Buna-N, we must first understand what problem it solves. Most rubbers and other solid petroleum or hydrocarbon products tend to swell, disintegrate, and otherwise degrade when in contact with a liquid oil or hydrocarbon. This is due to the molecular structures of most rubber, which often readily allows oil to absorb. The molecules often also have open bonds, which allow the hydrocarbon compounds in oils to bond and react with the oil. This tends to reduce the intermolecular forces of the rubber, causing plasticization, or a softening effect. This softening can cause some rubber gaskets and other materials to fail after exposure to those oils.
Unlike most of these rubber products, Buna-N is especially resistant to fuels, oils, and other petrochemicals. Buna-N has a naturally high acrylonitrile content, which is an inherently hydrophobic (water-repellant) and oleophobic (oil-repellant) compound. The acrylonitrile prevents oils from penetrating the rubber matrix and interacting with any loose or open bonds on molecules. This oil resistance makes Buna-N an excellent pick for gaskets and sealing materials that are expected to encounter oils or other liquid hydrocarbons.
Why do my air fittings have Buna-N Seals?
A properly maintained pneumatic shop air system and the tools used with it should be regularly oiled to reduce wear and maintain the lifespan of the equipment. The excellent oil resistance of Buna-N makes it the best rubber to use in these systems to seal couplers, fittings, and other junctions. Although Buna-N is very highly oil resistant, some petrochemicals may begin to affect it after a long amount of use. It is important to regularly inspect your air system and replace any parts that may be leaking or defective.