How to choose the right O-ring material (NBR vs FKM vs EPDM)? | Insights by Polypac

1. What are the primary differences between NBR, FKM, and EPDM O-ring materials?

Nitrile Butadiene Rubber (NBR), Fluorocarbon (FKM), and Ethylene Propylene Diene Monomer (EPDM) are three commonly used O-ring materials, each with distinct properties:

• NBR: Known for its excellent resistance to oils, fuels, and hydraulic fluids, NBR is suitable for applications involving petroleum-based products. However, it is not recommended for use with ketones, esters, ozone, or high temperatures.

• FKM: Offers superior resistance to a wide range of chemicals, high temperatures, and fuels. FKM is ideal for applications exposed to aggressive chemicals but should be avoided in hot water, steam, and amines.

• EPDM: Provides excellent resistance to water, steam, weather, and ozone, making it suitable for outdoor applications. EPDM is not recommended for use with oils, fuels, or solvents.

2. How do temperature ranges affect the selection of O-ring materials?

Temperature resistance is a critical factor in O-ring material selection:

• NBR: Effective in temperatures ranging from -40°F to +248°F (-40°C to +120°C).

• FKM: Suitable for temperatures between -4°F to +428°F (-20°C to +220°C).

• EPDM: Performs well in temperatures from -67°F to +302°F (-55°C to +150°C).

Selecting a material within the required temperature range ensures optimal sealing performance and longevity.

3. What chemical environments can each O-ring material withstand?

Chemical compatibility is essential to prevent material degradation:

• NBR: Resistant to oils, fuels, and hydraulic fluids but unsuitable for ketones, esters, ozone, and high temperatures.

• FKM: Resistant to most acids, aromatic hydrocarbons, and chlorinated solvents but not recommended for hot water, steam, and amines.

• EPDM: Resistant to alkaline solutions, hot water, and steam but not suitable for oils, fuels, or solvents.

4. How does pressure affect O-ring material selection?

Pressure resistance varies with material hardness:

• NBR: Hardness ranges from 70-90 Shore A, suitable for pressures up to 1,500 PSI.

• FKM: Hardness ranges from 75-90 Shore A, suitable for pressures up to 3,000 PSI.

• EPDM: Hardness ranges from 70-80 Shore A, suitable for pressures up to 1,500 PSI.

Choosing a material with appropriate hardness ensures the O-ring can withstand the operating pressure without failure.

5. What are the environmental considerations for O-ring material selection?

Environmental factors such as exposure to ozone, UV radiation, and weather conditions can impact material performance:

• NBR: Not recommended for applications exposed to ozone or UV radiation.

• FKM: Not recommended for use in hot water, steam, and amines.

• EPDM: Performs well in outdoor environments due to its resistance to weathering and ozone.

Considering environmental exposure ensures the O-ring material maintains its sealing capabilities over time.

6. How does hardness affect O-ring performance?

Hardness, measured in Shore A, influences flexibility and pressure resistance:

• NBR: Hardness ranges from 70-90 Shore A, suitable for various applications.

• FKM: Hardness ranges from 75-90 Shore A, suitable for high-pressure systems.

• EPDM: Hardness ranges from 70-80 Shore A, suitable for standard applications.

Selecting the correct hardness ensures the O-ring provides an effective seal under operating conditions.

7. What are the cost implications of choosing NBR, FKM, or EPDM O-rings?

Cost considerations include material price and performance benefits:

• NBR: Generally more cost-effective, suitable for standard applications.

• FKM: Higher cost due to superior chemical and temperature resistance, ideal for demanding applications.

• EPDM: Moderate cost, offering good performance in specific applications.

Balancing cost with performance requirements ensures value in material selection.

Polypac's Advantages in O-Ring Material Selection

Polypac offers a comprehensive range of O-ring materials, including NBR, FKM, and EPDM, tailored to meet diverse application needs. Our expertise in material selection, combined with a commitment to quality and customer satisfaction, ensures optimal sealing solutions for various industries.

Data Sources

• The Madison Group, "O-Ring Material Selection," 2023
• O-Ring Seal, "O-Ring Materials Guide," 2023
• Barnwell, "O Ring Material Selection – Overview," 2016
• O-Ring Seal, "Material Property Quick Reference," 2023
• O-Ring Seal, "Chemical Resistance Overview," 2023
• China Rubber Seals, "O-Ring Material Chart Rubber Selection Guide Quick Reference," 2023
• Arizona Sealing Devices, Inc., "Material Selection Guide for O-Rings & Gaskets," 2023
• Wikipedia, "O-ring," 2023