It has a significant impact on its sealing performance, suitable working conditions, installation characteristics, durability and cost, etc. The following is the specific analysis:
The influence on sealing performance
Sealing effect
Low-hardness rubber (such as 60-70 Shore A) :
Advantages: Good elasticity, can better adhere to the sealing surface, compensate for minor unevenness, and is suitable for dynamic sealing (such as rotating shaft sealing).
Disadvantage: Being too soft may cause permanent deformation during compression, and the seal may fail after long-term use.
High-hardness rubber (such as 80-90 Shore A) :
Advantages: Strong resistance to extrusion, capable of withstanding high pressure, and suitable for static sealing (such as flange sealing).
Disadvantages: Poor elasticity, high requirements for the flatness of the sealing surface, and even slight unevenness may cause leakage.
2. Leakage rate
The relationship between hardness and leakage rate:
When the hardness is moderate, the leakage rate is the lowest. Either too high or too low will lead to an increase in the leakage rate.
Case: The hardness of the sealing ring in the hydraulic system is usually selected as 70-90 Shore A to balance the sealing performance and the resistance to extrusion.
The impact on installation characteristics
1. Installation force
Low-hardness rubber
When installing, the compression amount is relatively large and the installation force is relatively small. However, attention should be paid to the control of interference to avoid excessive compression.
High-hardness rubber
When installing, the compression amount is relatively small but the installation force is relatively large. Special tools must be used to avoid damaging the sealing ring.
2. Dimensional stability
Low-hardness rubber
It has poor dimensional stability and is prone to deformation under the influence of temperature and pressure. A larger installation gap needs to be reserved.
High-hardness rubber
It has good dimensional stability. The installation clearance can be appropriately reduced, but it is necessary to ensure the flatness of the sealing surface.
The impact on durability
1. Compression permanent deformation
Low-hardness rubber
The permanent deformation during compression is relatively large. After long-term use, the sealing performance declines and it needs to be replaced regularly.
High-hardness rubber
The permanent compression set is relatively small and the service life is long, but excessive hardness may lead to embrittlement.
2. Wear resistance
High-hardness rubber
It has good wear resistance and is suitable for high-friction working conditions, such as reciprocating motion sealing.
Low-hardness rubber
It has poor wear resistance and needs to be used in combination with lubricants to extend its service life.
The impact on cost
1. Material cost
High-hardness rubber
Usually, more fillers (such as carbon black) are needed to increase hardness, and the material cost is relatively high.
Low-hardness rubber
The amount of plasticizer used is relatively large, and the material cost is relatively low.
2. Maintenance costs
Low-hardness rubber
Frequent replacement is required and the maintenance cost is relatively high.
High-hardness rubber
It has a long service life and relatively low maintenance costs, but the initial investment is relatively high.
The principle of hardness selection
1. Select according to pressure:
Low pressure (<10 MPa) : Select low-hardness rubber.
High pressure (>10 MPa) : Select high-hardness rubber.
2. Select according to temperature:
High-temperature environment: Choose rubber with higher hardness to prevent softening.
Low-temperature environment: Choose rubber with lower hardness to prevent hardening.
3. Select according to the motion state:
Dynamic sealing: Select low-hardness rubber to compensate for the slight displacement of moving parts.
Static sealing: Select high-hardness rubber to withstand high pressure.
4. Select according to the medium:
Strong corrosiveness of the medium: Select corrosion-resistant rubber materials, and adjust the hardness according to the working conditions.
Conclusion
The selection of rubber hardness for sealing rings needs to comprehensively consider factors such as sealing performance, suitable working conditions, installation characteristics, durability and cost. Both excessively high and low hardness can lead to seal failure. Reasonably choosing the hardness range is the key to ensuring the reliability of the seal.