Nitrile Butadiene Rubber (NBR) is usually considered as the backbone of the industrial and automotive rubber products industries. NBR is actually a complex family of unsaturated synthetic rubber copolymers of acrylonitrile (ACN) and butadiene. The physical and chemical properties of NBR depend on the percentage of acrylonitrile in the base polymer. Generally, this type of synthetic rubber is resistant to oil, fuel, grease, water, air and flame retardant liquids (HFA, HFB, HFC).
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Today, NBR is one of the most popular sealing elements due to its strong engineering properties. NBR rubber seals, can be used in hydraulic liquid, gas oil, silicon oil, animal and vegetable oils and fats as well as hot and cold water.
The following aspects of NBR have made it the most widely used elastomer in the sealing industry today:
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.
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.
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
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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
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.
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NBR O-Rings: Everything You Need to Know
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