Buna-N O-Rings

For background information, see O-Rings.

O-Rings are available in five different materials from Scientific Instrument Services. Each type has its advantages and disadvantages as listed in the O Ring Comparison Chart. Of the various types of O-Rings available from SIS, Buna-N is the most sidely used type of O ring in the seal ring. It is also the least expensive type of O-Ring seal. It does however have severe temperature and chemical resistance limitations.

NITRILE OR BUNA N (NBR) Typical Trade Names:

• Chemigum Goodyear Tire & Rubber Co.
• Paracril Uniroyal
• Hyvcar Goodrich Chemical Co.
• Krynac Polysar, Ltd.
• Ny Syn Copolymer Rubber & Chem. Corp.

Buna N or Nitrile, is a copolymer of butadiene and acrylonitrile. Acrylonitrile content is varied in commercial products from 18% to 48%. As the nitrile content increases, resistance to petroleum base oils and hydrocarbon fuels increases, but low temperature flexibility decreases. Due to its excellent resistance to petroleum products, and its ability to be compounded for service over a temperature range of -65 to + 275 degrees F (- 54 to +135 degrees C), Nitrile is the most widely used etastomer in the seal industry today. Most military rubber specifications for fuel and oil resistant MS and AN 0-rings require nitrile base compounds. It should be mentioned, however, that to obtain good resistance to low temperature with nitrile compounding, it is almost always necessary to sacrifice some high temperature fuel and oil resistance. Nitrile compounds are superior to most elastomers with regard to compression set or cold flow, tear and abrasion resistance. Inherently, they do possess good resistance to ozone, sunlight or weather but this can be substantially improved through compounding. However, since ozone and weather resistance are not always built in, seals from nitrile bases should not be stored near electric motors or other equipment which may generate ozone, or in direct sunlight.

Nitrile Is Recommended for:

• General purpose sealing.
• Petroleum oils and fluids.
• Cold Water.
• Silicone greases and oils
• Di-ester base lubricants (MIL-L-7808).
• Ethylene glycol base fluids (Hydrolubes)

Nitrile is not recommended for:

• Halogenated hydrocarbons (carbon tetrachloride, trichloroethylene)
• Nitro hydrocarbons (nitrobenzene, aniline)
• Phosphate ester hydraulic fluids (Skydrol, Fyrquel, Pydraul).
• Ketones (MEK, acetone)
• Strong Acids Ozone
• Automotive brake fluid.

O-Rings are available in sizes (sizes 0, 1, 2 and 3) which correspond to the diameter of the cross section of the O-Ring. Within these groups the O-Rings are classified according to their inside diameter. To see a complete selection of the various sizes and types of O-Rings available from Scientific Instrument Services, just click on the hyperlink on the size list above. If the size you require is not listed, it may still be available. Contact us with your requirements.

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