What are the reasons for the loss of elasticity of the sealing ring?

The loss of elasticity of the sealing ring directly affects its sealing performance, leading to leakage, equipment failures, and other problems. The reasons for the loss of elasticity usually involve multiple aspects such as material aging, environmental factors, mechanical damage, chemical corrosion, and improper installation and maintenance. Here is a detailed analysis:

I. Material Aging

1. Thermal Aging

High temperature acceleration of oxidation: Rubber sealing rings, when exposed to high temperatures, have active sites such as double bonds and unsaturated bonds that are prone to undergo oxidation reactions with oxygen, generating degradation products such as peroxides and carbonyls, resulting in molecular chain breakage and elasticity reduction.

Thermal decomposition: Long-term high temperatures (such as exceeding the sealing ring's temperature tolerance limit) will directly trigger the thermal decomposition of rubber molecular chains, generating low-molecular-weight substances, causing the sealing ring to harden and become brittle.

Case: If the automotive engine oil seal is continuously operated at temperatures above 150°C, the fluorine rubber may lose its elasticity due to thermal aging, leading to oil leakage.

2. Light Aging

Ultraviolet damage: Ultraviolet (UV) energy is high, which can cause the C-H bonds in the rubber molecular chains to break, generating free radicals, which further trigger chain oxidation reactions, resulting in the material becoming harder and cracking.

Case: Outdoor-used hydraulic equipment sealing rings, if not protected from sunlight, may lose their elasticity within a few months due to ultraviolet exposure.

3. Ozone Aging

Ozone attack: Ozone (O?) has strong oxidizing properties and can react with the double bonds in the rubber molecular chains, generating ozonides, which further decompose into small molecules, causing the material's surface to crack and elasticity to decrease.

Case: If the rubber tire sidewall is exposed to ozone-containing environments (such as near motors, photocopiers, etc.) for a long time, it may crack due to ozone aging.

II. Environmental Factors

1. Medium Erosion

Chemical Corrosion: When the sealing ring comes into contact with incompatible media (such as acids, bases, oils, solvents, etc.), the media may penetrate into the rubber and undergo chemical reactions with the molecular chains, causing swelling, degradation or cross-linking, thereby losing elasticity.

Case: If the nitrile rubber (NBR) sealing ring is continuously exposed to gasoline, it may become soft and lose elasticity due to swelling; if the fluorine rubber (FKM) comes into contact with strong alkalis, it may harden due to chemical corrosion.

2. Low Temperature Brittleness

Glass Transition: Rubber will gradually lose elasticity at low temperatures. When the temperature is below its glass transition temperature (Tg), the material becomes hard and brittle, prone to cracking.

Case: Silicone rubber (VMQ) sealing rings may lose elasticity and fail due to low-temperature brittleness at -60°C.

3. Humidity Influence

Hydrolysis: Some rubbers (such as polyurethane PU) may undergo hydrolysis reactions in humid environments, causing molecular chain breakage, resulting in decreased elasticity.

Absorption and expansion: Rubber may expand when absorbing water, changing its size and shape, affecting the sealing performance; upon drying, it may contract and cause cracks.

Case: Polyurethane sealing rings may harden and crack due to hydrolysis after being used in a humid environment for several years.

III. Mechanical Damage

1. Excessive Compression or Stretching

Permanent deformation: If the compression rate of the sealing ring during installation is too high (such as exceeding 30%), or it is constantly under high pressure, it may cause molecular chain slip and orientation, resulting in permanent deformation and loss of elasticity.

Stretch damage: In dynamic sealing scenarios, if the sealing ring is repeatedly stretched and twisted, it may cause molecular chain breakage due to fatigue, resulting in decreased elasticity.

Case: If the O-ring is stretched beyond 20% during installation, it may leak within several months due to permanent deformation.

2. Friction and Wear

Dynamic sealing wear: When the sealing ring is in relative motion with moving parts (such as shafts, pistons), friction will cause surface wear, generating wear debris, which further exacerbates wear and eventually leads to elasticity loss.

Case: If the hydraulic cylinder piston sealing ring has insufficient lubrication, it may fail due to wear within a few weeks.

3. Surface Scratches or Cracks

Installation damage: If the sealing ring is scratched during installation by sharp tools or has burrs at the groove edges, it may lead to local stress concentration, accelerating crack propagation, and losing elasticity.

Case: If the lip of the oil seal is scratched by the installation tool, it may fail due to leakage within a few hours.

IV. Chemical Corrosion

1. Incompatible Media Swelling or degradation: When the sealing ring material is incompatible with the medium, the medium may penetrate into the rubber, causing swelling (increased volume, softening) or degradation (breakage of molecular chains, hardening), thereby losing elasticity.

Example: If a fluorine rubber sealing ring comes into contact with ammonia, it may harden and crack due to chemical corrosion.

2. Additive influence

Plasticizer migration: If the plasticizers added to the rubber migrate to the medium, it may cause the sealing ring to harden and lose elasticity.

Example: Some rubber sealing rings may harden and crack when exposed to mineral oil due to the dissolving of plasticizers by the oil.

V. Installation and maintenance errors

1. Installation errors

Incorrect direction: If a lip-shaped sealing ring (such as an oil seal) is installed in the wrong direction, the lip edge cannot effectively prevent the leakage of the medium, and it may also deform due to reverse pressure, losing elasticity.

Incorrect cut direction: If an O-ring has a cut direction that is not perpendicular to the pressure direction, it may be squeezed out of the groove under high pressure, resulting in permanent deformation.

Example: If an oil seal is installed in the wrong direction, it may fail due to leakage within a few hours.

2. Insufficient or excessive preload

Insufficient preload: In static sealing scenarios, if the bolt preload is insufficient, the sealing ring may not fully fill the groove, resulting in leakage; long-term leakage may cause the sealing ring to lose elasticity due to medium erosion.

Excessive preload: If the preload is too high, the sealing ring may be overly compressed, resulting in permanent deformation and loss of rebound capability.

Example: If the pre-tightening force of a flange connection is insufficient, it may cause leakage of an O-ring; if the pre-tightening force is too high, it may cause the O-ring to be crushed.

3. Insufficient maintenance

Failure to replace regularly: As an easily damaged part, the sealing ring needs to be replaced regularly; long-term use may cause the material to age and wear, losing elasticity.

Failure to clean the sealing surface: If the sealing surface has impurities (such as dust, metal shavings), it may scratch the sealing ring during installation or cause local stress concentration, accelerating the loss of elasticity.

Example: If the hydraulic system does not replace the hydraulic oil regularly, the impurities in the oil may accelerate the wear of the sealing ring, resulting in loss of elasticity.

6. Other factors

1. Radiation influence

High-energy radiation: Such as gamma rays, X-rays, etc. High-energy radiation can cause the rubber molecular chains to break, resulting in the material hardening and losing elasticity.

Example: If the sealing ring used in a nuclear power plant is exposed to radiation for a long time, it may fail due to radiation aging.

2. Microbial corrosion

Biodegradation: Certain microorganisms (such as bacteria, fungi) can secrete enzymes or acidic substances, degrading the rubber molecular chains, resulting in the material softening and losing elasticity.

Example: If the sealing ring used in a sewage treatment equipment does not take measures to prevent microorganisms, it may fail due to biological corrosion.

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