HNBR Extruded Profiles & Seals: Overview & Technical Insights
HNBR (Hydrogenated Nitrile Butadiene Rubber) extruded profiles are rubber strips or cords produced by extruding HNBR material. They are widely used as high-performance seals and gaskets across multiple demanding industrial sectors .
The primary advantage of HNBR is its excellent combination of oil resistance and high-temperature performance, retaining superior mechanical properties and abrasion resistance . Its continuous service temperature range is typically -40°C to 150°C, with some formulations capable of intermittent use up to 165°C or even 170°C .
Core Applications and Advantages
The material's robust property profile makes it a preferred choice in the following critical applications:
Automotive Industry: For seals in engine compartments, power steering systems, and air conditioning systems (especially those using R134a refrigerant) .
Oil & Gas: For demanding sealing applications such as downhole tools, packers, and blowout preventers (BOPs) that must withstand high pressure, high temperature (HPHT), and sour gas (H₂S) environments .
General Industrial: For manufacturing O-rings, oil seals, gaskets, and various hoses requiring resistance to oils, fuels, and chemicals . Processing Challenges & Solutions
One of the most significant technical hurdles in producing HNBR extrusions is the formation of porosity or voids within the cross-section. Industrial experience highlights the importance of compound design and process parameter optimization:
Compounding:
Fillers: Avoid fillers containing water of crystallization (like some clays) which can release moisture and cause voids during high-temperature hot-air vulcanization. Alternatives such as calcium carbonate or calcined clay are preferred.
Curing System: Studies suggest that peroxide-cured systems are often more effective than sulfur-cured systems in mitigating void issues.
Additives: For high-temperature curing, antioxidants like Naugard 445 are recommended over less heat-stable alternatives like RD. High-flash-point plasticizers, such as ATBC or DOS, are also advised.
Processing:
Ensure thorough mixing and de-airing of the compound to remove volatiles.
Match the curing speed (T90) with the oven temperature and line speed to prevent "under-cure," which can lead to internal blistering.
Increasing the extruder head pressure can result in a denser, more uniform extrudate .
Key Technical Considerations
1. Extrusion Resistance (Anti-Extrusion)
In high-pressure seal applications, material extrusion (or "nibbling") into the clearance gap is a common failure mode . For HNBR, achieving high extrusion resistance is a critical design criterion. Key factors include:
Hardness and Modulus: Higher modulus (and hardness) materials generally offer improved extrusion resistance. For extremely high-pressure environments (e.g., >15,000 psi in oil & gas), specialized high-hardness HNBR compounds (e.g., 95 Shore A) with high tensile modulus at low elongation have been developed .
Polymer Selection: The base polymer itself is a primary factor in obtaining good performance .
Filler Level: Increased filler loading can enhance extrusion resistance, especially with narrow gaps and lower temperatures .
2. Rapid Gas Decompression (RGD) Resistance
For high-pressure gas applications, the seal must also resist damage from explosive decompression. Advanced HNBR grades are specifically formulated and tested to pass industry standards for RGD resistance, such as ISO 23936-2 and Norsok M-710 .
3. Advanced Material Grades
Leading manufacturers offer specialized HNBR grades to optimize processability or performance:
Improved Processability (e.g., Therban® AT): These grades have lower Mooney viscosity, leading to better mixing, smoother extrusion surfaces, and potentially reduced use of plasticizers .
Low-Temperature Grades (e.g., Therban® LT): With lower ACN content, these grades are designed to maintain flexibility and sealing force at temperatures as low as -40°C .
In conclusion, HNBR extruded profiles offer exceptional durability for high-end sealing applications. However, success requires careful attention to material formulation, processing parameters, and the specific performance demands (like extrusion and RGD resistance) of the target application.