Nitrile Rubber (NBR, Buna-N)
Nitrile Rubber (NBR), also known as Buna-N, is a synthetic elastomer known for its exceptional resistance to oils, fuels, and other petroleum-based products. These characteristics make NBR an ideal material in various aviation applications where exposure to oils and fuels is common. With its high strength, durability, and resistance to compression set, NBR is widely used in sealing, gasketing, and hose applications within the aerospace industry.
Background and Evolution
Nitrile Rubber was first developed in the 1930s by the German chemical company Bayer as a synthetic alternative to natural rubber. NBR’s primary feature—resistance to oils and fuels—made it a valuable material for the automotive industry, and soon after, it found its way into aviation. Over the decades, NBR has been improved through various formulations to increase its resilience to harsh environments, temperature extremes, and chemical exposures. In modern aviation, NBR is a key material in fuel systems, seals, gaskets, and hydraulic components.
How Nitrile Rubber (NBR) Is Used
NBR is utilized in numerous critical applications within commercial aviation, including:
- Seals and Gaskets: NBR is widely used in seals and gaskets for fuel, hydraulic, and lubrication systems, where it provides an airtight and oil-resistant seal, preventing leakage in demanding environments.
- Hoses: NBR is commonly used in fuel and oil hoses, as it can withstand prolonged exposure to petroleum-based fluids, making it ideal for fueling systems and engine components.
- O-Rings: Due to its excellent compression set resistance, NBR is used to manufacture O-rings for use in hydraulic and fuel systems, ensuring long-lasting sealing performance.
- Vibration Dampeners: NBR is employed in vibration dampeners in aircraft, where its flexibility and durability reduce vibration transmission from engines and mechanical systems to the airframe.
- Protective Coatings: NBR is used as a protective coating on various components, including wires and cables, where resistance to oils and lubricants is critical.
Why Nitrile Rubber (NBR) Is Used
Nitrile Rubber offers several key advantages for aviation applications:
- Oil and Fuel Resistance: NBR is highly resistant to oils, fuels, and solvents, making it ideal for use in fuel systems, engine components, and hydraulic applications where these substances are common.
- High Tensile Strength: NBR’s high tensile strength ensures that it can withstand mechanical stress and strain, making it suitable for seals, gaskets, and hoses that need to maintain their integrity under pressure.
- Compression Set Resistance: NBR is known for its ability to resist permanent deformation under compression, making it an excellent choice for sealing applications where tightness needs to be maintained over time.
- Abrasion Resistance: NBR provides good resistance to wear and tear, which is essential for components that experience high friction, such as hoses and gaskets.
- Temperature Range: NBR can perform across a wide temperature range, typically from -40°C to 120°C, making it suitable for use in both high- and low-temperature environments within the aircraft.
Technical Specifications
Comparison to Alternative Materials
- Neoprene (CR): Neoprene offers better resistance to weathering, ozone, and extreme temperatures but has inferior oil and fuel resistance compared to NBR. NBR is the better choice for applications where exposure to oils and fuels is common, such as in fuel hoses and seals.
- EPDM: EPDM has superior resistance to weathering, ozone, and UV radiation but lacks the oil and fuel resistance of NBR, making NBR the more suitable choice for fuel system components.
- Silicone Rubber (VMQ): Silicone rubber excels in high-temperature environments but does not offer the same oil and fuel resistance as NBR, making NBR more appropriate for fuel lines and seals exposed to petroleum-based substances.
- Fluorosilicone Rubber (FVMQ): Fluorosilicone offers superior chemical resistance but is less flexible at low temperatures than NBR. NBR’s combination of fuel resistance and flexibility makes it a better choice for a broader range of sealing applications.
Role in Modern Aviation
Nitrile Rubber continues to be an essential material in modern aviation, used in a wide range of applications including:
- Boeing 787: NBR is used for fuel system seals and hydraulic system components in the Boeing 787, ensuring reliable performance and leak prevention in critical systems.
- Airbus A350: The A350 incorporates NBR in its fuel hoses, seals, and gaskets, benefiting from its oil and fuel resistance in the aircraft’s highly engineered systems.
- General Aviation: NBR is commonly used in general aviation aircraft for sealing, hoses, and O-rings, where its combination of oil resistance, tensile strength, and flexibility is crucial for maintaining system integrity.
Environmental and Economic Considerations
- Production: Nitrile Rubber is synthesized through the polymerization of acrylonitrile and butadiene. While NBR’s production is energy-intensive and relies on petroleum-based raw materials, it provides a durable and reliable material for high-performance applications in aviation.
- Cost: NBR is relatively cost-effective compared to other specialized elastomers like fluorosilicone, making it a popular choice in many aerospace applications that require fuel and oil resistance.
- Recycling: Recycling NBR is challenging due to its crosslinked structure. However, as with many synthetic rubbers, efforts are being made to improve recycling techniques and reduce waste. The durability of NBR means that components made from it typically have a long service life, which helps mitigate its environmental impact.
Future Trends
- Sustainability: As the demand for more sustainable materials increases, research into improving the production methods of NBR, including the development of more eco-friendly synthesis processes, may help reduce its environmental footprint.
- Performance Enhancements: Advances in NBR formulations may increase its resistance to extreme temperatures, fuel additives, and more aggressive chemicals, expanding its applications in future aviation designs.
- Recycling: Developing efficient recycling methods for NBR will be important in reducing its environmental impact and ensuring that used materials can be reprocessed into new products.
Summary
Nitrile Rubber (NBR, Buna-N) is a key material in commercial aviation, widely used in fuel system components, seals, gaskets, hoses, and vibration dampeners. Its excellent resistance to oils, fuels, and hydraulic fluids, combined with its high tensile strength and compression set resistance, makes it indispensable for high-performance applications in aircraft. While it is a synthetic rubber that relies on petroleum-based raw materials, NBR’s long service life and durability help reduce its environmental impact. As the aerospace industry continues to evolve, NBR will remain a critical material for ensuring the reliability and safety of modern aircraft systems.
| Property | Nitrile Rubber (NBR, Buna-N) |
|---|---|
| Density | 1.23–1.30 g/cm³ |
| Operating Range | -40°C to 120°C |
| Hardness | 60–90 Shore A |
| Tensile Strength | ~15–30 MPa |
| Elongation at Break | ~200–500% |
| Compression Set | Low, excellent resilience under pressure |
| Chemical Resistance | Excellent (oils, fuels, and hydraulic fluids) |
| Ozone Resistance | Moderate (can degrade under prolonged exposure) |
| Flammability | Meets FAR 25.853 standards |
Parts that are made of or use Nitrile Rubber (NBR, Buna-N)
| Part Number | Name | Alt Part Number | ATA Chapter | Cage Code | NSN | Rotable | Repair Stations | Suppliers |
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