Both dimethyl silicone oil and vinyl silicone oil can be used as auxiliary materials (e.g., lubricants, plasticizers, damping regulators) in rubber shock absorbers. However, the two differ significantly in their applicable scenarios and performance. The selection should be based on the core requirements of the shock absorber (such as operating temperature, rubber material, damping stability, and service life). There is no absolute "better" option—only "more suitable" ones.
I. First, Clarify: Core Performance Differences Between the Two Types of Silicone Oil
To determine applicability, it is essential to first understand the fundamental differences in structure and performance between the two. The specific comparison is as follows:
| Comparison Dimension | Dimethyl Silicone Oil | Vinyl Silicone Oil |
|---|---|---|
| Molecular Structure | The main chain consists of repeating -Si(CH₃)₂-O- units with no reactive functional groups. | The main chain contains -Si(CH₃)₂-O- units, with vinyl (-CH=CH₂) reactive functional groups introduced in the side chains/end groups. |
| Chemical Stability | Extremely high (resistant to high/low temperatures, aging, and chemical corrosion; no reaction activity). | High (vinyl groups do not affect basic temperature resistance but increase cross-linking reaction activity). |
| Compatibility with Rubber | Good compatibility with most shock-absorbing rubbers (nitrile butadiene rubber/NBR, ethylene propylene diene monomer rubber/EPDM, silicone rubber/SR), and it does not easily swell/harden the rubber. | Depends on the rubber system: Excellent compatibility with silicone rubber containing cross-linking agents (e.g., hydrogen-containing silicone oil); compatibility with non-silicone rubbers (NBR/EPDM) requires testing (vinyl groups may slightly affect interface bonding). |
| Volatility | Low (especially for high-viscosity grades, e.g., above 500 cSt). | Low (similar to dimethyl silicone oil at the same viscosity; vinyl functional groups do not significantly increase volatility). |
| Core Function Focus | Lubrication, friction reduction, stable damping, and anti-adhesion. | Enhancing interface bonding force with rubber (via vulcanization cross-linking) and reducing silicone oil migration. |
| Cost | Lower (mature industrialized mass production process). | Higher (requires introduction of vinyl functional groups, leading to higher synthesis costs). |
II. Core Requirements of Rubber Shock Absorbers: Applicability Analysis of the Two Silicone Oils
The core requirements of rubber shock absorbers include stable damping performance, good high/low temperature resistance, long-term compatibility with rubber (without causing rubber aging/failure), and low exudation risk. The selection should be evaluated against these needs:
1. Dimethyl Silicone Oil: More Suitable for "Conventional Scenarios" with Stronger Versatility
Dimethyl silicone oil is the most commonly used type of silicone oil in rubber shock absorbers, with advantages focused on "versatility" and "stability". It is particularly suitable for the following scenarios:
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Conventional shock absorption needs: Such as automotive chassis shock absorbers, home appliance (washing machine/air conditioner) shock absorbers, and low-frequency shock absorbers for industrial equipment, with an operating temperature range of -50°C to 200°C (covering most civil/industrial scenarios).
- Reason: Its excellent chemical stability ensures long-term damping stability without reacting with nitrile butadiene rubber (NBR, commonly used in oil-resistant scenarios) or ethylene propylene diene monomer rubber (EPDM, commonly used in weather-resistant scenarios). It also does not cause rubber swelling (which affects shock absorption stiffness) or hardening (which reduces elasticity).
- Scenarios emphasizing "lubrication + friction reduction": During the operation of shock absorbers, there is slight friction inside the rubber or between the rubber and metal connectors. Dimethyl silicone oil can form a stable oil film to reduce friction loss and extend the service life of the shock absorber (e.g., rubber bushings in automotive suspension shock absorbers).
- Cost-sensitive scenarios: For mass-produced civil shock absorbers (e.g., home appliances, ordinary automotive parts), dimethyl silicone oil is more cost-effective and does not require adjustments to the rubber vulcanization process (no reactive functional groups, so it does not interfere with rubber vulcanization).
Note: High-viscosity grades (e.g., 500 cSt to 10,000 cSt) should be selected. Low-viscosity dimethyl silicone oil (e.g., below 100 cSt) has slightly higher volatility, and long-term use may lead to damping degradation due to silicone oil loss.
2. Vinyl Silicone Oil: More Suitable for "High-Performance/Special Scenarios" with a Focus on "Longevity"
The core advantage of vinyl silicone oil is "cross-linkability"—the vinyl groups in its molecules can undergo an addition reaction with cross-linking agents (e.g., hydrogen-containing silicone oil) in rubber (especially silicone rubber) to form chemical bonds, reducing silicone oil migration/exudation. It is suitable for the following scenarios:
- Silicone rubber shock absorbers: Such as high-temperature shock absorbers for aerospace and precision instruments (silicone rubber can withstand temperatures above 250°C). Vinyl silicone oil can cross-link with the silicone rubber matrix to improve interface bonding force and prevent silicone oil exudation at high temperatures (exudation can cause sudden damping changes and accelerated rubber aging).
- Scenarios requiring long-term weather resistance/aging resistance: Such as shock absorbers for outdoor wind power equipment and high-speed rail tracks (requiring long-term resistance to ozone, ultraviolet radiation, and high-low temperature cycles). The cross-linked structure of vinyl silicone oil can reduce performance degradation caused by environmental factors and extend the service life of the shock absorber.
- Scenarios with high damping precision requirements: Such as shock absorbers for precision machine tools and medical equipment (strict requirements for damping fluctuation). Cross-linked silicone oil is less likely to migrate, ensuring long-term damping stability and avoiding reduced shock absorption effects due to silicone oil loss.
Notes:
- When used with non-silicone rubbers (e.g., NBR, EPDM), compatibility testing is required in advance—vinyl groups may react slightly with vulcanizing agents in the rubber, leading to changes in rubber hardness. Formula adjustments (e.g., reducing vulcanizing agent dosage) are necessary.
- A specific vulcanization process (e.g., high-temperature vulcanization) is required to cross-link vinyl silicone oil with rubber, which increases processing complexity. It is not suitable for conventional production lines without the ability to adjust vulcanization processes.
III. Summary: How to Choose?
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Prioritize dimethyl silicone oil in the following cases:
- The rubber used in the shock absorber is non-silicone rubber (e.g., NBR, EPDM);
- The operating temperature ranges from -50°C to 200°C, with no extreme environmental requirements;
- Cost control and process simplicity are prioritized, and there is no need for long-term cross-linking.
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Consider vinyl silicone oil in the following cases:
- The rubber used in the shock absorber is silicone rubber (SR), and high-temperature resistance (＞200°C) or long-term weather resistance is required;
- Extremely high requirements for silicone oil exudation resistance and damping stability (e.g., precision equipment, aerospace);
- Higher costs and vulcanization process adjustments are acceptable.
IV. Additional Recommendations
- Compatibility Testing: Regardless of the type of silicone oil selected, small-batch testing should be conducted first—soak the silicone oil and rubber samples at the operating temperature for 72 hours, observe whether the rubber swells, hardens, or cracks, and test the damping coefficient change of the shock absorber to ensure compliance with compatibility requirements.
- Viscosity Selection: Prioritize high-viscosity silicone oil (above 500 cSt). Low-viscosity silicone oil (below 350 cSt) is prone to volatilization or exudation, which affects long-term performance.
- Avoid Mixing: The two types of silicone oil have different molecular structures. Mixing may lead to reduced compatibility or unstable damping, so mixing is not recommended.
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