What should be considered when choosing the material for the sealing ring?

When selecting the appropriate sealing ring material, the following key factors need to be comprehensively considered to ensure the sealing performance, equipment lifespan and operational stability:

1. Operating Environment

Temperature Range: The material must be able to withstand the extreme temperatures of the working environment. For example:

High-temperature environment: Fluororubber (FKM) can withstand temperatures above 200℃, while silicone rubber is suitable for a wide temperature range from -60℃ to 230℃.

Low-temperature environment: Nitrile rubber (NBR) becomes brittle below -40℃, while polytetrafluoroethylene (PTFE) retains flexibility at -200℃.

Medium type: Materials must be compatible with the medium they come into contact with (such as oil, water, acids, bases, solvents, etc.) to avoid corrosion or swelling. For example:

Oil resistance: Nitrile rubber (NBR) is suitable for mineral oil environments, while fluorine rubber (FKM) is resistant to synthetic oils and chemical solvents.

Corrosion resistance: Polytetrafluoroethylene (PTFE) has excellent tolerance to strong acids, strong bases, and organic solvents.

Sealing types:

Static sealing: Lower requirements for material wear resistance, natural rubber (NR) or chloroprene rubber (CR) can be selected.

Dynamic sealing: Requires high wear resistance materials, such as polyurethane (PU) or carbon fiber reinforced fluorine rubber.

2. Pressure conditions

High-pressure environment: Requires high-strength materials (such as metal sealing rings or reinforced rubber) to prevent extrusion failure. For example:

Hydraulic system: NBR (nitrile butadiene rubber) or FKM (fluororubber) can withstand pressures up to 30-40 MPa.

Ultra-high pressure scenarios: Metal sealing rings (such as stainless steel, copper) can withstand pressures above 1000 MPa.

Low-pressure environment: Ordinary rubber materials (such as silicone rubber) can meet the requirements and are more cost-effective.

3. Mechanical motion characteristics

Motion speed: High-speed motion requires materials with low friction and wear resistance. For example:

Rotary seal: Polyurethane (PU) or carbon fiber reinforced fluororubber can reduce frictional heat and prevent failure due to temperature rise.

Piston motion: Nitrile rubber (NBR) or hydrogenated nitrile rubber (HNBR) has good tear resistance.

Vibration and shock: High elasticity materials (such as silicone rubber) are needed to absorb vibrations and prevent the sealing ring from loosening or being damaged.

4. Material performance parameters

Hardness (Shore A/D): Affects the sealing effect and lifespan. For example:

O-ring: Generally, a hardness of 70-90 Shore A is selected. If the hardness is too high, it may cause the groove to extrude; if it is too low, the sealing effect will be insufficient.

Special scenarios: In high-pressure environments, a higher hardness (such as 90 Shore A) is required, while in low-temperature environments, a lower hardness (such as 40 Shore A) is needed to maintain flexibility.

Compression permanent deformation rate: The material's ability to recover after long-term compression. For example:

Fluororubber (FKM): The permanent deformation rate under compression is less than 15%, making it suitable for long-term sealing.

Silicone rubber: The deformation rate is relatively high and requires regular replacement.

Aging resistance: The stability of the material in the presence of ultraviolet rays, ozone, or chemical media. For example:

Ethylene Propylene Diene Monomer (EPDM) rubber: Resistant to ozone aging, suitable for outdoor equipment.

Chloroprene rubber (CR): Resistant to ultraviolet aging, commonly used in automotive sealing.

5. Cost and Processability

Material cost: Fluorine rubber (FKM) costs 5-10 times more than nitrile rubber (NBR), and the performance needs to be balanced according to the budget.

Processing difficulty: Metal sealing rings require precise processing and are costly; rubber sealing rings can be molded, suitable for mass production.

6. Industry Standards and Certifications

Food/Pharmaceutical Industry: Must comply with FDA, NSF, etc. standards, choose non-toxic materials (such as food-grade silicone rubber).

Aerospace Field: Must pass AS9100 certification, materials must meet extreme environment requirements (such as radiation resistance, low permeability).

Application Examples

Automobile engine: Select fluorine rubber (FKM) sealing rings, resistant to high temperatures (200°C+), oil resistance, and aging resistance.

Chemical pipeline: Polytetrafluoroethylene (PTFE) sealing rings, resistant to strong acids, strong alkalis, and high temperatures (260°C).

Low-temperature refrigeration equipment: Silicone rubber sealing rings, resistant to -60°C low temperatures and good flexibility.

High-pressure hydraulic system: Metal sealing rings or carbon fiber reinforced fluorine rubber, capable of withstanding pressures above 40 MPa.

When choosing sealing ring materials, it is necessary to focus on the usage environment, combined with pressure, motion characteristics, material performance, cost, and industry standards for a comprehensive assessment. For example, fluorine rubber or metal sealing rings are preferred in high-temperature and high-pressure scenarios, silicone rubber is selected in low-temperature environments, and nitrile rubber can be chosen for cost-sensitive and mild medium scenarios. Correct material selection can significantly improve equipment reliability and reduce maintenance costs.

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