How does the hardness of the sealing ring affect the sealing effect?

It has a significant impact on the sealing effect, mainly manifested in aspects such as sealing performance, pressure resistance capability, wear resistance, installation compatibility, and service life. The following provides a detailed analysis of the influence of hardness on the sealing effect from different perspectives:

I. Sealing Performance: Balance between Hardness and Contact Pressure on the Sealing Surface

Low-hardness sealing ring:

Advantages: High flexibility, capable of better adhering to the microscopic unevenness of the sealing surface and forming a continuous sealing line, suitable for low-pressure or situations with high surface roughness.

Disadvantages: Too low hardness may cause the sealing ring to be compressed and deformed under the medium pressure, even entering the mating gap, resulting in leakage.

Case: In food processing equipment, a 60 Shore A silicone rubber sealing ring was used, as the hardness was moderate, effectively sealing liquids with particles, but it needed to be replaced regularly to prevent wear.

High-hardness sealing ring:

Advantages: Strong resistance to extrusion, suitable for high-pressure conditions, able to maintain the pressure on the sealing surface and reduce the risk of leakage.

Disadvantages: Excessively high hardness may cause excessive contact pressure on the sealing surface, accelerating wear, or failing to adapt to the deformation of the sealing surface due to insufficient elasticity.

Case: In deep-sea exploration equipment, a 90 Shore A fluorine rubber sealing ring was used, capable of withstanding 30 MPa water pressure, but required precise machining of the grooves to avoid installation damage.

II. Pressure Resistance: Relationship between Hardness and Anti-Extrusion Performance

High-pressure conditions:

High-hardness sealing rings (such as 85-90 Shore A) can effectively resist medium pressure and prevent being pushed into the mating gap.

Data support: Experiments show that a 70 Shore A NBR sealing ring has three times more extrusion volume at 20 MPa pressure than a similar product with 90 Shore A.

Optimization solution: For high-pressure sealing, a "high-hardness sealing ring + retaining ring" structure is often used, where the retaining ring can share the pressure, reducing the risk of sealing ring extrusion.

Low-pressure conditions:

Low-hardness sealing rings (such as 60-70 Shore A) can provide sufficient contact pressure on the sealing surface at low pressure and reduce installation difficulty.

Case: In household water purifiers, a 65 Shore A EPDM sealing ring achieved long-term no-leakage at 0.5 MPa pressure.

III. Wear Resistance: Correlation between Hardness and Dynamic Sealing Life

Dynamic sealing (repetitive/rotating motion):

Low-speed low-pressure: Sealing rings with high hardness (such as 70-80 Shore A, like HNBR) can balance wear resistance and sealing performance under low friction coefficients.

High-speed high-pressure: High-hardness sealing rings (such as polyurethane PU, ≥85 Shore A) are required, and lubrication measures should be combined to reduce wear.

Data comparison: In hydraulic cylinder piston sealing, an 85 Shore A PU sealing ring has a two-fold longer lifespan than a 70 Shore A NBR sealing ring.

Wear mechanism:

Too low hardness: The sealing ring surface is prone to scratching, resulting in particle shedding, accelerating wear.

Too high hardness: The friction coefficient increases, potentially causing adhesive wear or fatigue cracks.

Optimization direction: Through surface treatment (such as coating, spraying) or material modification (such as adding molybdenum disulfide) to reduce the friction coefficient.

IV. Installation Compatibility: Matching of Hardness and Groove Design

Installation difficulty:

Low-hardness sealing rings are prone to deformation. During installation, the compression rate (usually 15% - 30%) needs to be controlled to avoid excessive stretching or distortion.

High-hardness sealing rings have high installation resistance and require the use of specialized tools and ensuring the accuracy of groove dimensions (such as a width deviation of ≤ 0.1 mm).

Groove design:

Static sealing: The groove width is larger than the diameter of the sealing ring by 0.1 - 0.3 mm, ensuring a reasonable deformation rate after compression.

Dynamic sealing: For reciprocating motion grooves, thermal expansion needs to be considered, and for rotational motion grooves, sharp corners should be avoided to prevent stress concentration.

Case: An aviation hydraulic pump uses double-hardness sealing rings (inner layer 90 Shore A, outer layer 70 Shore A), with the inner layer resisting extrusion and the outer layer adapting to groove deformation.

V. Service Life: Synergistic Effect of Hardness and Environmental Factors

Temperature influence: At high temperatures, low-hardness sealing rings tend to soften, leading to sealing failure; high-hardness sealing rings may become brittle due to thermal aging.

Solution: Fluororubber (FKM) can maintain a hardness of 80 Shore A at 200℃, making it suitable for high-temperature conditions.

Media corrosion:

For environments with strong acids and strong bases, high-hardness sealing rings resistant to chemical corrosion (such as FFKM) should be selected.

Case: In semiconductor manufacturing equipment, a 90 Shore A FFKM sealing ring was used and lasted for over 5 years in a hydrofluoric acid environment.

Fatigue life:

In dynamic sealing, the hardness needs to be balanced between anti-fatigue performance and wear resistance.

Experimental data: After 1 million reciprocating movements, the fatigue crack depth of the 80 Shore A sealing ring was 40% lower than that of the similar product with 90 Shore A hardness.

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