How to choose the hardness of rubber O-ring?

The selection of hardness for rubber O-rings is a crucial process as it directly affects the sealing performance, durability, and adaptability of the sealing ring. The following factors should be considered when selecting the hardness of rubber O-rings:
1, Work pressure
Static sealing pressure: When the sealing system is a static seal, the working pressure is the key factor in selecting hardness. Generally speaking, the higher the pressure, the greater the required hardness. For example, in situations with low pressure, an O-ring with a hardness of 70 ± 5 can be selected; In high-pressure situations, it may be necessary to choose a harder rubber material.
Dynamic sealing pressure: For dynamic seals such as reciprocating or rotating motion, the selection of hardness also needs to consider motion friction and sealing surface wear. Usually, the hardness of dynamic seals is slightly lower than that of static seals to reduce friction and wear.
2, Usage environment
Temperature: The hardness of rubber materials will change with temperature. Therefore, when selecting hardness, it is necessary to consider the temperature range of the sealing ring's usage environment. Generally speaking, hardness decreases at high temperatures and increases at low temperatures.
Medium: The medium in contact with the sealing ring can also affect the selection of hardness. For example, certain media may corrode or swell rubber materials, thereby affecting the sealing performance of the sealing ring. Therefore, when selecting hardness, it is necessary to consider the chemical properties of the medium and the compatibility of the sealing ring material.
3, Groove design
Groove smoothness and roughness: The smoothness of grooves and the roughness of contact surfaces have a significant impact on sealing effectiveness and durability. Therefore, when selecting hardness, it is necessary to consider the design parameters of the groove to ensure that the sealing ring can tightly fit inside the groove and achieve good sealing effect.
Compression ratio: The compression ratio of O-ring seals for fixed seals is generally 15%~25%, while for dynamic seals such as reciprocating motion, the compression ratio can be 10%~12%. For rotary motion, the compression ratio is generally 3%~5%. The choice of compression ratio also affects the choice of hardness, as different compression ratios require different hardness to maintain sealing performance.
4, Hardness range and representation method
Hardness range: The hardness of rubber O-rings is usually represented by Shore hardness, ranging from 30A to 90A. When making specific choices, the appropriate hardness range should be determined based on the pressure and working environment of the sealing system.
Hardness representation method: When representing hardness, a hardness range and tolerance are usually given. For example, "70 ± 5" indicates a hardness of 70 degrees and a tolerance of ± 5 degrees. This means that the actual hardness may be between 65 degrees and 75 degrees.
5, Other precautions
Avoid low hardness: O-rings with low hardness may not be able to withstand sufficient pressure, leading to seal failure. Meanwhile, excessively low hardness may also cause deformation or damage to the sealing ring during installation or use.
Consider service life: When choosing hardness, it is also necessary to consider the service life of the sealing ring. Generally speaking, seals with higher hardness have better wear resistance and tear resistance, resulting in a longer service life. However, excessive hardness may also cause damage to the sealing ring during installation or removal.
Choosing the hardness of rubber O-rings is a process that comprehensively considers multiple factors such as working pressure, usage environment, groove design, and hardness range. In practical applications, the selection should be based on specific circumstances to ensure that the sealing ring has good sealing performance, durability, and adaptability.