Nitrile Rubber Compounds
Nitrile rubber, also referred to as Buna, is one of most common elastomers used in O-rings and seals. It offers good physical properties and temperature range at a relatively low cost compared to other types elastomers.
Nitrile rubbers have exceptional resistance to most oils and solvents. (with the exception of polar solvents), abrasion resistance, and offers better gas impermeability than general purpose elastomers like natural rubber and SBR. Nitrile rubber is commonly used for gloves, hoses, tubing, linings and seals for the retention of oils and solvents.
Nitrile rubber (NBR) is a synthetic copolymer of acrylonitrile (ACN) and butadiene available in 18% to 45% acrylonitrile to butadiene content. The higher the acrylonitrile/butadiene ratio, resistance to oils and fuels, tensile strength, gas impermeability and abrasion resistance increase but compression set, resilience and low temperature flexibility decrease. Lower acrylonitrile/butadiene ratio nitrile will have increase increased low temperature flexibility, resilience and compression set. Most commercial grades of nitrile come in a medium ACN content level which provides a good balance between oil/fuel resistance and low temperature flexibility and compression set resistance.
There are two versions of NBR, hydrogenated nitrile (HNBR) and carboxylated nitrile (XNBR). The hydrogenated version of nitrile, HNBR, is known for its physical strength, increased resistance to oils, industrial chemicals and increases heat resistance. HNBR is widely used in automotive air conditioning units. It is also used in hoses, belts, and seals for the oil field exploration and processing industry. The carboxylated nitriles are an improved version of the nitriles and offer increased physical properties by creating additional cross link between the butadiene molecules in addition to the sulfur cross links.
Common Name: Nitrile, Buna, NBR
Chemical Name: Acrylonitrile Butadiene
ASTM D1418 Designation: NBR
General Characteristics
Hardness Range (Shore A): 30-95
Tensile Strength Range (psi): 200-3000
Elongation (Max %): 600
Compression Set: Good
Resilience-Rebound: Good
Abrasion Resistance: Excellent
Tear Resistance: Good
Solvent Resistance: Good to Excellent
Oil Resistance: Good to Excellent
Low Temperature: -40°F
High Temperature: 212°F/250°F intermittent
Aging, Weathering-Sunlight: Poor
Advantages
- Has good solvent, oil, water, hydraulic fluid resistance.
- Good compression set, abrasion resistance, tensile strength.
Disadvantages
- Not recommended for use in highly polar solvents such as acetones and MEK, ozone, chlorinated hydrocarbons and nitro hydrocarbons.
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Nitrile O-Rings & Seals
