The choice of sealing ring material can significantly influence the leakage situation. Its impact is reflected in multiple aspects such as sealing performance, environmental resistance, and mechanical adaptability. Here is a detailed analysis:
1. Direct differences in material sealing performance
Elasticity and resilience: Rubber-based materials (such as nitrile rubber NBR, fluorine rubber FKM) have high elasticity and can fill minor defects on the sealing surface through deformation, forming an effective seal. While hard materials (such as metals, ceramics) need to rely on precise processing or surface treatment to achieve sealing. If the processing error is large, the risk of leakage significantly increases.
Permanent compression deformation: After long-term compression, some materials (such as silicone rubber) may undergo irreversible deformation, resulting in a decrease in sealing force. For example, in high-temperature and high-pressure environments, ordinary rubber sealing rings may fail due to compression deformation, while fluorine rubber or polytetrafluoroethylene (PTFE) can maintain long-term sealing due to better compression resistance.
2. The key role of media resistance
Chemical compatibility: The sealing ring material must be compatible with the contacting medium (such as oil, water, acid, alkali, gas). For example:
Nitrile rubber (NBR): Resistant to mineral oils and fuels, but susceptible to strong oxidants' corrosion. If used in an environment with strong acids, it will accelerate aging and lead to leakage.
Fluorine rubber (FKM): Resistant to high temperatures and chemical corrosion, suitable for harsh environments such as aviation fuel and strong acids, but with higher cost.
Polytetrafluoroethylene (PTFE): Almost resistant to all chemical media, but with poor elasticity. It needs to be combined with other materials (such as filled graphite) to enhance sealing performance.
Expansion and contraction: Some materials (such as natural rubber) will expand when in contact with specific solvents, causing size changes and sealing failure. For example, in hydraulic systems, if the sealing ring material is incompatible with hydraulic oil, it may get stuck or leak due to expansion.
3. Impact of temperature adaptability
Low-temperature brittleness: In low-temperature environments, ordinary rubber may harden and crack, losing its sealing ability. For example, silicone rubber remains elastic below -60℃, while natural rubber may crack below -20℃.
High-temperature softening: At high temperatures, materials may soften or decompose, leading to sealing failure. For instance, nitrile rubber may age above 120℃, while fluorine rubber can withstand temperatures above 200℃.
4. Matching of mechanical properties and sealing pressure
Hardness and sealing force: Harder materials (such as hard rubber, metal) require higher compression force to achieve sealing, but they may damage the sealing surface. Softer materials (such as soft rubber) are prone to deformation, but the compression amount needs to be controlled to avoid excessive squeezing and failure.
Machinability: In dynamic sealing scenarios (such as pistons, rotating shafts), the material's machinability directly affects the lifespan. For example, polyurethane rubber has better machinability than nitrile rubber, suitable for high-friction environments.
5. Long-term stability and aging issues
Aging rate: Ultraviolet rays, ozone, oxygen, etc. accelerate material aging, causing loss of elasticity and cracks. For example, natural rubber is prone to aging when used outdoors, while fluorine rubber and silicone rubber have better aging resistance.
Fatigue life: Repeated compression or friction reduce material performance. For instance, in high-pressure cylinders, if the sealing ring material has poor fatigue resistance, it may leak due to frequent operations.
6. Adaptability to special working conditions
Food and medical industry: Select materials that are non-toxic and resistant to disinfection (such as medical-grade silicone rubber).
Vacuum environment: Need low-volatile materials (such as fluorine rubber) to avoid gas permeation.
High-pressure environment: Need high-strength materials (such as metal sealing rings) or composite structures (such as rubber + metal frame).
Real cases
Automobile engine: Use fluorine rubber sealing rings because they are resistant to high temperatures (200℃+) and fuel corrosion, avoiding leakage that causes engine failure.
Hydraulic system: If an incorrect sealing ring (such as natural rubber instead of nitrile rubber) is used that is not resistant to hydraulic oil, it may cause swelling leakage and a decrease in system pressure.
Low-temperature equipment: In polar regions or spacecraft, choose silicone rubber or special low-temperature rubber to avoid leakage caused by low-temperature brittleness.
The selection of sealing ring materials needs to consider the medium, temperature, pressure, and mechanical movement conditions. Incompatible materials are a common cause of leakage, while correct material selection can significantly reduce the risk of leakage and extend equipment lifespan. In practical applications, material testing, standard certification (such as NACE, ASTM), and engineering experience are needed to ensure the rationality of the selection.
FOREVER SEALS! Seals manufacturer, accept custom seals, from design to research and development, from production to testing, a full range of services. For more information, please contact FOREVER SEALS directly. FOREVER SEALS product experts are here to help you! Whatsapp: +86-18098184099；WeChat: +86-13049188460； E-mail: sales@foreverseals.com.