Hydrogenated Nitrile Butadiene Rubber (HNBR)
Hydrogenated Nitrile Butadiene Rubber (HNBR) is a synthetic elastomer used in aviation for its superior resistance to oils, fuels, and extreme temperatures. By hydrogenating the standard nitrile rubber (NBR), HNBR combines the best of both worlds, offering improved heat stability, chemical resistance, and overall durability in critical aerospace applications.
Background and Evolution
HNBR was developed as an advanced version of Nitrile Butadiene Rubber (NBR) in the 1980s, with the hydrogenation process enhancing its resistance to heat and oxidative degradation. This process transforms the butadiene component in NBR, improving its performance in high-temperature environments. HNBR quickly gained popularity in industries where oil and heat resistance were crucial, including aerospace. Today, it is a key material in sealing applications, primarily used in fuel systems, engine components, and hydraulic seals in commercial aviation.
How Hydrogenated Nitrile Butadiene Rubber (HNBR) Is Used
HNBR is processed into a variety of sealing components that require durability in environments exposed to oils, fuels, and high temperatures. Common applications in commercial aviation include:
- Fuel System Seals: HNBR is used in sealing fuel lines, pumps, and valves, offering resistance to jet fuels, gasoline, and biofuels.
- Engine Components: HNBR is ideal for sealing components exposed to high temperatures and lubricants, such as in engine seals and gaskets.
- Hydraulic Seals: HNBR ensures reliable sealing performance in hydraulic systems subjected to high-pressure fluids.
- O-Rings and Gaskets: Used in critical systems, including braking, electrical, and engine components, HNBR provides airtight and leak-proof seals in extreme conditions.
- Hoses: HNBR is used for fuel, oil, and hydraulic hoses, where chemical resistance and flexibility are needed.
Why Hydrogenated Nitrile Butadiene Rubber (HNBR) Is Used
HNBR’s superior performance characteristics make it ideal for use in commercial aviation:
- Oil and Fuel Resistance: HNBR excels in environments exposed to fuels, oils, and hydraulic fluids, making it ideal for aviation fuel systems and engine components.
- Heat Resistance: With a temperature range of -30°C to 150°C, HNBR maintains its integrity in both low and high temperatures, with some formulations capable of short-term exposure to temperatures up to 175°C.
- Chemical Resistance: HNBR resists a wide range of chemicals, including oils, fuels, hydraulic fluids, and some solvents, ensuring long-lasting performance in demanding environments.
- Elasticity and Flexibility: Despite its durability, HNBR maintains a high level of flexibility, ensuring effective seals even in extreme temperature variations and pressure conditions.
- Durability: HNBR is highly resistant to aging, wear, and tear, which ensures a long service life in critical aviation applications.
Technical Specifications
Comparison to Alternative Materials
- Nitrile Rubber (NBR): While NBR is also fuel and oil resistant, HNBR offers better heat resistance and durability, making it the preferred material for high-temperature applications.
- Fluorosilicone Rubber (FVMQ): Fluorosilicone provides superior fuel and oil resistance, but HNBR offers better flexibility at low temperatures, making it more versatile in a broader range of applications.
- EPDM: EPDM is highly weather-resistant but not suited for fuel and oil exposure. HNBR excels in these areas, providing a more reliable option for fuel systems and engine seals.
- Silicone Rubber: Silicone offers superior heat resistance but lacks the chemical resistance of HNBR, especially when exposed to oils and fuels.
Role in Modern Aviation
HNBR is widely used in modern aircraft, such as:
- Boeing 787 Dreamliner: HNBR is used in fuel system seals, engine components, and hydraulic systems, ensuring reliable operation in demanding conditions.
- Airbus A350: The A350 benefits from HNBR in sealing fuel systems, hydraulic lines, and engine components, where its excellent chemical and temperature resistance ensures long-lasting performance.
- Boeing 737 MAX: HNBR is used for sealing components exposed to high pressures and temperatures, such as fuel pumps, hoses, and hydraulic lines.
Environmental and Economic Considerations
- Production: The production of HNBR involves the hydrogenation of nitrile rubber, a process that enhances its heat and chemical resistance. It requires specialty chemicals, which makes the production of HNBR more energy-intensive than some other rubbers.
- Cost: HNBR is more expensive than NBR but offers superior performance, particularly in high-temperature and chemically aggressive environments, justifying its use in aerospace applications.
- Recycling: Like most synthetic rubbers, HNBR is difficult to recycle due to its crosslinked structure, but its long service life and durability mean that its environmental impact is minimized over time.
Future Trends
- Enhanced Heat and Chemical Resistance: Research into further improving the heat and chemical resistance of HNBR could expand its applications in even more demanding aviation environments, including engines and high-temperature fuel systems.
- Sustainability: The development of more sustainable HNBR formulations, possibly incorporating bio-based materials or recyclable components, may help reduce its environmental footprint.
- Cost Reductions: As demand for HNBR increases, improvements in production methods may lead to reduced costs, making it more accessible for a wider range of aerospace applications.
Summary
Hydrogenated Nitrile Butadiene Rubber (HNBR) is an essential material in commercial aviation, providing outstanding resistance to oils, fuels, and high temperatures. It is used in critical applications such as fuel system seals, engine components, and hydraulic systems, ensuring reliable performance in extreme conditions. HNBR’s combination of durability, chemical resistance, and flexibility makes it ideal for modern aircraft like the Boeing 787 and Airbus A350. Despite its higher cost, its superior performance in demanding environments justifies its widespread use in aerospace.
| Property | Hydrogenated Nitrile Butadiene Rubber (HNBR) |
|---|---|
| Density | 1.1–1.3 g/cm³ |
| Operating Range | -30°C to 150°C (up to 175°C short-term) |
| Hardness | 60–90 Shore A |
| Tensile Strength | ~10–30 MPa |
| Elongation at Break | ~200–500% |
| Compression Set | Low, excellent resilience under pressure |
| Chemical Resistance | Excellent (fuels, oils, hydraulic fluids) |
| Ozone Resistance | Excellent (highly resistant) |
| Flammability | Meets FAR 25.853 standards |
Parts that are made of or use Hydrogenated Nitrile Butadiene Rubber (HNBR)
| Part Number | Name | Alt Part Number | ATA Chapter | Cage Code | NSN | Rotable | Repair Stations | Suppliers |
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