Silicone sealing rings are widely used in various industrial fields due to their excellent high-temperature resistance and aging resistance. However, even so, a series of problems inevitably arise during long-term use. Understanding these problems helps us replace and maintain them in a timely manner, avoiding equipment failure.

I. Compression Permanent Deformation (The Most Common Problem)
This is the most common and fatal problem for silicone sealing rings after long-term use.

When the sealing ring is installed, it is in a compressed state. After maintaining this stress state for a long time, the silicone molecular chains will undergo irreversible plastic deformation, causing the sealing ring to be unable to fully return to its original shape and size. In simple terms, the sealing ring is "flattened and cannot spring back."

Compression permanent deformation is usually measured as a percentage. Generally, when the deformation exceeds 25% to 30%, the sealing effect will significantly decrease, and leakage will occur. This process is greatly accelerated under high-temperature environments.

II. Hardening and Embrittlement
After long-term use, especially under high temperature, ultraviolet radiation, and ozone environments, the surface silicone molecular chains will gradually undergo excessive cross-linking reactions, causing the material to harden and become brittle.

The following are the obvious characteristics of a hardened sealing ring:

It feels noticeably harder when pressed with a finger, no longer as soft and elastic as a new ring.
It easily develops white creases when bent, and may even break directly.
Its adhesion to the mating surface decreases, resulting in poorer sealing.

This hardening often starts from the surface and gradually penetrates inward, so the appearance may not change much, but the performance has already severely deteriorated.

III. Surface Cracking and Crackling
During long-term repeated compression and rebound, coupled with periodic temperature changes, tiny cracks will gradually appear on the surface of the silicone sealing ring, which is commonly referred to as "cracking."

Once cracks appear, they will expand continuously like fissures. Initially, they may be micro-cracks that are not easily visible to the naked eye, but over time, the cracks will become deeper and more numerous, eventually leading to the sealing ring breaking or perforating, and the seal completely failing.

Especially for silicone rings used in low-temperature environments, the risk of cracking is even higher due to hardening combined with low-temperature embrittlement.

IV. Loss of Elasticity (Decreased Resilience) New silicone seals possess excellent elasticity, enabling a tight fit to the mating surfaces and forming an effective seal. However, with prolonged use, due to the breakage and recombination of molecular chains, the material's elastic modulus changes, resulting in a significant decrease in resilience.

The direct consequence of this loss of elasticity is that the seal cannot apply sufficient contact pressure to the mating surfaces. Under conditions of pressure difference or vibration, micro-leakage or even complete leakage can easily occur.

V. Swelling and Dimensional Changes If silicone seals are in prolonged contact with certain media, such as grease, solvents, fuels, or certain chemical solutions, swelling may occur.

Swelling causes the seal volume to increase, superficially appearing "tighter," but in reality, the internal structure of the material has been damaged, and its mechanical properties have significantly decreased. More seriously, when the media environment changes, the swollen seal will shrink, becoming smaller, creating gaps and leading to leakage.

This "expansion followed by shrinkage" process is extremely damaging to sealing performance.

VI. Surface Powdering and Peeling

Prolonged use in extreme environments, such as prolonged exposure to strong ultraviolet radiation, strong ozone, or strong oxidizing atmospheres, can cause a layer of white powdery substance to appear on the surface of the silicone sealing ring. This powder will easily come off when rubbed, a phenomenon known as "powdering."

Powdering is a signal of material surface degradation, indicating that the outermost molecular chains have been damaged. If not addressed promptly, the powdery layer will thicken, eventually leading to peeling and flaking of the sealing ring, compromising the integrity of the seal.

VII. Color Change
After prolonged use, the color of the silicone sealing ring may change, for example, from its original transparent or white to yellow, brown, or even black.

Color change itself does not necessarily indicate seal failure, but it is usually an external manifestation of material aging. If color change is accompanied by hardening, cracking, or other phenomena, it indicates that the sealing ring needs replacement.

It should be noted that some color changes are caused by staining from the contact medium; these cases require specific analysis.

VIII. Chain Reaction of Seal Failure

All the above problems ultimately point to the same result—seal failure.

The consequences of seal failure are often more than just leakage:

Insufficient pressure in hydraulic systems leads to sluggish or weak equipment operation.
Air leakage in pneumatic systems increases energy consumption and reduces efficiency.
In the food and pharmaceutical industries, seal failure can cause contamination and safety hazards.
In electronic equipment, seal failure can lead to water or dust ingress, causing short circuits or corrosion.
Key Factors Affecting Aging Rate
Why do some silicone seals last only a year while others last five years? This mainly depends on the following factors:

Temperature is the biggest killer. For every 10°C increase in temperature, the aging rate of silicone approximately doubles. Silicone seals operating at temperatures above 150°C for extended periods will have a drastically shortened lifespan.

Media contact is also crucial. Seals in prolonged contact with oils or solvents age much faster than those in contact with water or air.

The difference between dynamic and static seals is also significant. Dynamic seals (such as piston rod seals), due to continuous friction and repeated deformation, typically have a lifespan only a fraction of that of static seals.

The installation method is equally important. Excessive compression, twisting during installation, or scratches will significantly shorten the service life.

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