NBR, also known as Nitrile or Buna-N, is one of the most widely used and economical elastomers. This material offers excellent sealing capabilities at a very low cost. NBR is a copolymer of butadiene and acrylonitrile, and depending on the application, the proportions of acrylonitrile can vary from 14% to 50%. The higher acrylonitrile content, the greater resistance to oil and fuel. 

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NBR Formulation

When formulating NBR compounds, filler, plasticizer, antioxidant or antiozonant, zinc oxide, accelerator, and vulcanizing agents may be used to increase specific sealing properties of the material. When it comes to filler, carbon black is typically used in standard NBR compounds. Altering the amount of carbon black will change the hardness of the final compound. 

Plasticizers increase the processability and modify physical properties of the final compound. Some of the modifications include lower hardness, improved flexibility, and low temperature performance. Sulfur is commonly used as a curing agent for NBR compounds. For sulfur cure systems, vulcanizing agents and accelerators are used to speed up the reaction rate between NBR and sulfur. 

Properties and Advantages

NBR is an ASTM D designation. These standard compounds have a working temperature range of -40°F to 257°F and hardness range of 40 to 90 Shore A. NBR compounds can be formulated to offer additional temperature ranges from -85°F to 275°F.

NBR features excellent resistance and mechanical properties, including: 

• Resistance to petroleum-based oils and fuels, silicone greases, hydraulic fluids, water and alcohols

• Low compression set

• High tensile strength

• High abrasion resistance

• Low gas permeability

While NBR offers great resistance to many chemicals and solutions, there are some limitations to be aware of. NBR should have limited contact with:

• Ozone, sun exposure, rain, wind

• Highly aromatic fuels

• Non-polar solvents

• Glycol-based brake fluids

Typical Applications

Because of NBR's compatibility with oils and fuels, NBR seals are commonly used in the automotive industry. However, NBR is a go-to material for oil applications of any kind. NBR is also commonly used in applications such as:

• Low temperature military applications

• Off-roading equipment

• Marine devices

• Aircraft fuel systems

NBR can also be formulated to meet FDA standards, which increases the number of ways to apply NBR o-rings.

Want to learn more about NBR o-rings?

Contact an engineer today. 

NBR O-Rings: Everything You Need to Know

Buna-N O-Rings (NBR Nitrile) Selection Guide

Buna-N o-rings also referred to as NBR o-rings and Nitrile o-rings are the most widely used o-ring material in the word because of low cost, good mechanical performance with resistance to water, most basic oils, lubricants and some fuels, many pneumatic, hydraulic systems, and the default choice for basic applications. Buna-N o-rings are not recommended for exposure to sunlight, UV light, ozone and general outdoor weathering or hash chemicals, acids, keytones and many others.

Custom size Buna-N o-rings can typically be supplied without additional tooling fees within a few weeks. As the world's largest o-ring inventory network, Marco Rubber's direct purchasing power can deliver substantial savings on Buna-N o-rings. Order Buna-N o-rings online today!

Explore Buna-N Compounds

Compound #

Datasheet

Color

Hardness (Shore A)

Low Temp °F (°C)

High Temp °F (°C)

Features

B

Black

70

-31

(-35)

250

(121)

Lowest cost highest inventory general purpose commodity NBR compound. Compare to Parker N-70 and N-70 and Parco -70 and -70. Available in nearly any color and hardness.

B

Black

90

-31

(-35)

250

(121)

General purpose, higher pressure applications. Compare to Parker N-90 and N-90 and Parco -90 and -90.

B

Black

70

-31

(-35)

250

(121)

FDA compliant per 21 CFR 177.. Compare to Parker N-75 and N-70.

B

Black

90

-31

(-35)

250

(121)

FDA compliant, higher hardness.

B

Black

50

-31

(-35)

250

(121)

General purpose, lower hardness for lower closure force applications. FDA compliant and alternative colors available. Compare to Parker N-50.

B

Black

80

-31

(-35)

225

(107)

General purpose, higher hardness. Compare to Parker N-80.

B

Black

70

-31

(-35)

230

(110)

Internally lubricated with PTFE to reduce friction. Silicone oil and Moly (MOS2) internal lubricants available. Alternative hardness and colors also available.

B

You will get efficient and thoughtful service from htob.

Black

70

-35

(-37)

250

(121)

UL 157 listed for several approved uses.

B

Black

70

-31

(-35)

250

(121)

NSF 61 certified for drinking water applications.

B

Black

95

-31

(-35)

250

(121)

Very high hardness for extreme pressure applications.

B

Black

70

-65

(-54)

275

(135)

Improved lower and higher temperature resistance and improved oil resistance at higher temperature. Compare to Parker N-75 and M and Parco -70.

B

Black

70

-31

(-35)

250

(121)

Metal detectable for contamination detection sensors. FDA compliant per 21 CFR 177.. Formulated for food contact and life science applications. Additional colors available.

B

Black

70

-31

(-35)

250

(121)

NSF 51 certified for food contact.

M

Black

70

-65

(-54)

275

(135)

Mil Spec (Military specification) AMS-P-, MS-### per MIL-P-C-(1).

M

Black

75

-65

(-54)

275

(135)

Mil Spec (Military specification) AMS-P-, M/1-### per MIL-P-B#3. Improved low temperature resistance and hydraulic fluid resistance.

M

Black

65

-65

(-54)

250

(121)

Mil Spec (Military specification) MS-###, MS-##, AMS-P-B.

M

Black

90

-65

(-54)

275

(135)

Mil Spec (Military specification) MS, AMS-P-C.

M

Black

65

-70

(-57)

200

(93)

Mil Spec (Military specification) AMS, AS.

The information on this page is to the best of our knowledge accurate and reliable. However, Marco Rubber makes no warranty, expressed or implied, that parts manufactured from this material will perform satisfactorily in the customer's application. It's the customer's responsibility to evaluate parts prior to use.

The temperature ranges presented on this page are approximations for dry air service only and should not be used to determine design specifications or end-use temperature limits. Actual temperature range of a compound in an end-use application is highly dependent on part type, hardware configuration, applied forces, chemical media, pressure and thermal cycling effects, and other factors. The most practical way of determining an end-use temperature range is testing in the actual application conditions. Consult a Marco Engineer for more details.

Common Names

Buna-N, Nitrile, NBR, Acrylonitrile Butadiene Rubber

Trade Names

Nipol®

Typical Applications and Products

The range of performance characteristics of Buna-N allows it to be utilized in a diverse set of applications. NBR is often used for gaskets and o-rings in pneumatic, hydraulic, and fuel systems. V-packings and backup rings made from high-hardness Nitrile compounds are common in high pressure environments in the Oil and Gas industry. The abrasion and wear resistance of NBR make it useful for dynamic oil seals for rotary and reciprocating shafts. NBR is relatively easy to process which keeps costs down for custom extrusions and complex molds. Hardness ranges from 40 Shore A to 90 Shore A. Hydrogenated versions of NBR (HNBR) have enhanced mechanical properties as well as greater thermal and chemical stability. Specific physical properties and chemical resistances vary by compound formulation.

NBR can be compounded for enhanced oil and fuel resistance, increased temperature flexibility, high hardness and extrusion resistance, low compression set, and a variety of other attributes. The physical properties of the compound largely depend on the Acrylonitrile content of the formulation. For example, high Acrylonitrile content causes increased oil and fuel resistance while adversely affecting low temperature flexibility and compression set resistance. It is important to consider the offsetting attributes when selecting an NBR formulation. Please contact a Marco Rubber engineer for assistance finding the best compound for your application.

Chemical Compatibility and Specialty Resistances

• Petroleum oils / Fuels / Greases
• Mineral Oils, Vegetable Oils
• Silicone Greases / Oils
• Aliphatic Hydrocarbons
• Hydraulic Fluids (HFA, HFB, HFC types)
• Ethylene Glycol Fluids
• Limited resistance to Dilute Acids, Alkalis, and Solvents

Limitations

• Not resistant to Ketones (MEK)
• Not resistant to Halogenated Hydrocarbons
• Not resistant to Chlorinated Hydrocarbons
• Not resistant to Auto / Aircraft Brake Fluids
• Not resistant to Strong Acids
• Not resistant to Weathering, Sunlight and Ozone
• Not resistant to Highly Aromatic fuels and hydrocarbons
• Not resistant to Polar solvents

Mechanical Properties

• Good Wear Resistance
• Good Compression Set Resistance
• Good Short-Term Resilience
• Good Permeation Resistance

Product Options

• Internal Lubrication with PTFE and others
• High strength
• Flame resistant
• ABS compatible
• Anti-Static
• WRAS, KTW and NSF Compliant
• FDA compliant
• Metal and X-ray detectable
• Gamma Radiation Resistance
• Tight and/or specific tolerances
• Specific AQL Inspection requirement
• Surface free of silicone oil
• PTFE coated in choice color
• Special tumbling for complete flash removal
• Talcum powder on surface to reduce sticking
• Specific packaging requirements
• Special bag and Label requirements
• Variety of colors available

Please contact a Marco Sales Consultant or Engineer to discuss additional options.

Are you interested in learning more about NBR O Ring? Contact us today to secure an expert consultation!