Differences Among NBR, HNBR, and XNBR
Comparing Rubber Materials for Butterfly Valves
The choice of rubber material for butterfly valve components, such as seats and seals, significantly impacts valve performance. Below is a detailed comparison of NBR, HNBR, and XNBR in butterfly valve applications:
NBR (Nitrile Butadiene Rubber)
Temperature Range: -18°C to 100°C
Shore Hardness: 65-75 Shore A
NBR, commonly known as BUNA-N, is a copolymer of acrylonitrile and butadiene. It serves as a general-purpose seat material, especially suitable for hydrocarbon services.
Advantages:
- Oil and Fuel Resistance: It performs exceptionally well with petroleum-based products.
- Cost-Effective: Typically more affordable than HNBR and XNBR.
- Flexibility: Provides good flexibility and compression set resistance.
Disadvantages:
- Limited Temperature Range: NBR may not suit high-temperature applications.
- Poor Ozone and Weather Resistance: It degrades faster in outdoor or ozone-rich environments.
Applications: Ideal for water, gas, and petroleum-based oil applications, particularly in low to medium temperature and pressure conditions.
HNBR (Hydrogenated Nitrile Butadiene Rubber)
Temperature Range: -40°C to 150°C
Shore Hardness: 50-90 Shore A
HNBR is produced by selectively hydrogenating NBR butadiene groups. This process enhances its temperature and ozone resistance significantly.
Advantages:
- High-Temperature Resistance: Suitable for higher operating temperatures.
- Chemical Resistance: Offers better resistance to a range of chemicals.
- Durability: Provides increased wear resistance and extends the valve’s service life.
Disadvantages:
- Cost: More expensive than NBR due to additional processing.
- Flexibility: Slightly less flexible than NBR.
Applications: Ideal for high-performance needs in automotive, oil and gas, and chemical processing industries, particularly under high-temperature and high-pressure conditions.
XNBR (Carboxylated Nitrile Butadiene Rubber)
Temperature Range: -18°C to 121°C
Shore Hardness: 50-90 Shore A
XNBR, similar to HNBR, is a modified version of NBR that provides enhanced properties.
Advantages:
- Abrasion Resistance: Excellent wear resistance, ideal for high mechanical stress applications.
- Enhanced Mechanical Properties: Improved tensile strength and elongation.
- Chemical Resistance: Good resistance to oils, fuels, and some chemicals.
Disadvantages:
- Cost: Higher cost compared to standard NBR.
- Flexibility: Less flexible, which may limit its application in some scenarios.
Applications: Best suited for environments requiring high wear resistance, such as slurry handling and abrasive media.
In butterfly valve applications, selecting the appropriate rubber material—NBR, HNBR, or XNBR—depends on specific operational requirements such as temperature, chemical exposure, mechanical stress, and cost considerations. Each material offers distinct advantages, making them suitable for different environments and usage scenarios.
