How to avoid fatigue fracture of sealing rings?

To prevent fatigue fracture of sealing rings, a comprehensive approach involving material selection, design optimization, environmental control, installation and maintenance, as well as monitoring management should be adopted. A systematic solution should be formulated based on specific working conditions. The following are specific measures and implementation points:

I. Material Selection and Improvement

Select high fatigue strength materials

High-temperature resistant materials: In high-temperature conditions (such as engines, hydraulic systems), choose fluororubber (FKM), silicone rubber (VMQ), or perfluororubber (FFKM), with a temperature range of -50°C to 300°C and excellent resistance to thermal aging.

Chemical-resistant materials: For corrosive environments (such as acids, alkalis, solvents), select fluororubber, polytetrafluoroethylene (PTFE), or ethylene propylene diene monomer (EPDM), to avoid material erosion and performance degradation.

Magnetic materials: For dynamic seals (such as pistons, rotating shafts), use polyurethane (PU), high-saturated nitrile rubber (HSNBR), or carbon fiber reinforced rubber to improve wear resistance and tear resistance.

Key points: Verify the anti-fatigue performance through material fatigue tests (such as S-N curve tests), and avoid using low-quality recycled materials or inferior fillers.

Material modification treatment

Add anti-aging agents: Add antioxidants (such as amine and phenol) and anti-ozonants (such as microcrystalline wax) to the rubber to delay the aging process.

Optimize reinforcing fillers: Reasonably add carbon black, white carbon black, etc. to improve strength, but control the dispersion of fillers to avoid local stress concentration.

Surface coating: Spray PTFE coating on the surface of the sealing ring to reduce friction coefficient and reduce wear.

II. Design Optimization and Structural Improvement

Reasonable design of sealing structure

Combined sealing: In hydraulic systems, use step seals (Step Seal) or glyd rings (Glyd Ring), using supporting rings to distribute pressure and reduce rubber deformation.

Rotary sealing: Select spring-loaded lip seals to maintain stable contact pressure and avoid fatigue caused by pressure fluctuations.

O-ring: Control the compression rate between 15% and 30%, avoiding excessive compression that leads to stress concentration at the root; for high-pressure conditions, use X-type rings or square rings to distribute pressure.

Lip-shaped sealing rings (such as Y-type, U-type): Design the lip angle and thickness to ensure uniform contact stress and reduce crack initiation.

Section shape optimization:

Dynamic sealing design:

Size matching and tolerance control

Static sealing: Control the gap to 0.1-0.3mm to avoid the sealing ring being pushed out.

Dynamic sealing: Select the gap according to the motion speed; for high-speed conditions (such as >1m/s), increase the gap to 0.5-1mm to prevent heat burnout.

Reference standards (such as DIN 3771, ISO 3601) determine the groove size to ensure that the sealing ring is installed without distortion or excessive stretching.

Groove surface roughness controlled at Ra ≤ 1.6μm to reduce friction and wear.

Groove design:

Clearance between mating parts:

III. Environmental Control and Operating Condition Management

Temperature control

Cooling measures: Add cooling systems (such as water cooling, air cooling) in high-temperature conditions or use high-temperature-resistant materials.

Insulation measures: Use electric heating strips or insulation sleeves in low-temperature environments to prevent the sealing ring from becoming brittle.

Temperature gradient management: Avoid uneven heating of the sealing ring (such as excessive temperature difference between direct sunlight and shaded areas) to prevent thermal stress cracking.

Pressure management

Pressure buffering: Install accumulators or pressure reducing valves in the hydraulic system to reduce the impact of pressure fluctuations on the sealing ring.

Stepwise loading: Gradually increase pressure during startup to avoid sudden high pressure causing stress changes in the sealing ring.

Chemical medium protection

Chemical compatibility testing: Verify the compatibility of the sealing ring material with the medium before use to avoid corrosion or swelling.

Isolation measures: Use double-sealing structures (such as inner and outer sealing rings) in corrosive media or add isolation liquids (such as water, oil) to protect the sealing ring.

IV. Installation and Maintenance Specifications

Standardized installation process

Cleaning treatment: Before installation, wipe the grooves and sealing rings with a dust-free cloth to avoid scratches on the surface by dust and metal debris. Lubrication treatment: Apply special lubricating grease (such as silicone-based grease), reduce installation friction, and prevent distortion.

Tool selection: Use dedicated installation tools (such as conical guides), and avoid using sharp tools like screwdrivers to directly press the sealing ring.

Regular maintenance and replacement

Surface crack depth exceeds 20% of the wall thickness;

Compression permanent deformation rate exceeds 30% (can be determined by measuring the dimensions before and after installation);

Excessive leakage of the medium (such as rapid pressure drop in the hydraulic system).

Check cycle: Develop a check plan based on the working conditions (such as every 500 hours or once a month), with a focus on checking whether there are cracks, wear or deformation on the surface of the sealing ring.

Replacement standard: Replace immediately if any of the following conditions occur:

V. Monitoring and Warning System

Online monitoring technology

Pressure sensor: Real-time monitor the system pressure, alarm when it exceeds the limit and automatically reduce pressure.

Temperature sensor: Monitor the temperature near the sealing ring, trigger shutdown protection when abnormal temperature rise occurs.

Vibration analysis: Conduct vibration monitoring on rotating equipment (such as motors, pumps) to detect abnormal vibration caused by sealing ring wear at an early stage.

Life prediction model

Establish a life prediction model based on material fatigue data and working conditions parameters (temperature, pressure, motion frequency), to plan the replacement cycle in advance.

Example: Simulate the stress distribution of the sealing ring under alternating stress using finite element analysis (FEA) to optimize design parameters.

VI. Case Application and Effect

Hydraulic cylinder sealing ring optimization:

Problem: The original O-ring frequently breaks under high-pressure cycling, with a lifespan of only 3 months.

Solution: Replace with fluororubber X-ring, adjust the compression rate to 25%, reduce the surface roughness of the groove to Ra ≤ 0.8 μm, and increase the accumulator to buffer pressure fluctuations.

Effect: The lifespan of the sealing ring is extended to 18 months, and the leakage rate is reduced by 90%.

Improvement of automotive engine valve oil seal:

Problem: The original silicone rubber oil seal cracks and breaks under high temperature, causing oil leakage.

Solution: Replace with fluorinated polyether (FFKM) oil seal, surface spray PTFE coating, and optimize the lip angle to disperse stress.

Effect: The oil seal lifespan is increased from 50,000 kilometers to 200,000 kilometers, and the engine failure rate decreases by 75%.

To avoid fatigue fracture of the sealing ring, it is necessary to cover the entire life cycle of design, material selection, installation, and maintenance. Through material upgrades, structural optimization, environmental control, and intelligent monitoring, the reliability of the seal can be significantly improved. In actual engineering, a customized solution should be developed based on specific working conditions (such as temperature, pressure, motion form), and the effect should be evaluated regularly to form a closed-loop management.