Rubber seals are widely used in various industrial and mechanical systems. Their compression set is an important indicator for evaluating seal performance and life.
Compression set refers to the degree to which a rubber material cannot fully recover to its original size after being compressed and released.
Definition of compression set
Compression set refers to the percentage of thickness change and initial thickness of a rubber seal after it is kept at a certain temperature and pressure for a certain period, the pressure is released and cooled to room temperature.
The compression set reflects the elastic recovery ability of rubber materials and is a key parameter for evaluating the performance stability of seals in long-term use.
Factors affecting compression set
1. Material properties:
- Rubber types: Different types of rubber (such as nitrile rubber, fluororubber, silicone rubber, etc.) have different compression set characteristics.
- Crosslinking density: The higher the crosslinking density of the rubber, the better its elastic recovery ability and the smaller the compression set.
- Fillers: Fillers such as carbon black and silica have a certain effect on the compression set of rubber. The type and amount of fillers will affect the final performance.
2. Temperature and time:
- Temperature: High temperature will accelerate the aging and creep of rubber materials, resulting in increased compression set.
- Time: The longer the compression time, the greater the permanent deformation of the rubber material.
3. Pressure:
Pressure size: The greater the pressure, the greater the deformation of the rubber material, the worse the recovery ability, and the greater the compression set.
4. Environmental medium:
Chemical medium: The performance of rubber materials in different chemical media is different. Some chemical media may cause the aging of rubber materials and increase compression set.
5. Vulcanization conditions:
Vulcanization temperature and time: The temperature and time of the vulcanization process will affect the cross-linking density of the rubber, thereby affecting the compression set.
Compression set test method
1. Test equipment:
- Compression fixture: used to fix and compress rubber specimens.
- Temperature control device: used to control the test environment temperature.
- Measuring tools: such as calipers, depth gauges, etc., are used to measure the thickness of the specimen.
2. Test steps:
- Prepare the sample: Prepare the rubber sample according to the standard size, usually cylindrical or square.
- Install the sample: Install the sample in the compression fixture and adjust it to the specified compression amount.
- Heat and hold: Place the fixture in a constant temperature box, heat it to the specified temperature, and keep it for a certain time (such as 22 hours).
- Cool and measure: Release the pressure, cool to room temperature, measure the thickness of the sample, and calculate the compression permanent deformation.
3. Standards and specifications:
- ISO 815: International standard that specifies the compression set test method for rubber materials.
- ASTM D395: American Society for Testing and Materials standard that describes in detail the compression set test method for different rubber materials.
Application and Analysis of Compression Set
1. Performance evaluation:
Sealing performance: The smaller the compression permanent deformation, the better the long-term sealing performance of the seal.
Service life: Seals with large compression permanent deformation usually have a shorter service life.
2. Material selection:
Select materials according to the application environment: In high temperature, high pressure, or chemical corrosion environments, select materials with small compression permanent deformation.
Optimize formula design: Improve the compression permanent deformation performance of the material by adjusting the cross-linking agent, filler, etc. in the rubber formula.
3. Design and manufacturing:
Reasonable design of compression: In the design of seals, the compression should be reasonably selected to avoid irreversible deformation caused by excessive compression.
Optimize the vulcanization process: By optimizing the vulcanization temperature and time, the cross-linking density of the rubber is increased and the compression permanent deformation is reduced.
4. Failure analysis:
Leakage failure: Seals with large compression permanent deformation may cause leakage, especially in high-pressure or high-temperature environments.
Shortened life: Regularly check the compression permanent deformation of seals and replace aging or excessively deformed seals in time.
Conclusion
The compression set of rubber seals is an important indicator for evaluating their performance and life. By understanding the factors affecting compression set, test methods, and application analysis, we can better select suitable rubber materials, and optimize design and manufacturing processes, thereby improving the sealing performance and service life of seals and ensuring the reliability and safety of the system.
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