O-rings are rubber seals with a circular cross-section and are widely used in hydraulic and pneumatic systems. They provide excellent sealing performance and can be applied in both static and dynamic seals.
When the correct material is selected, O-rings deminsion need to be calucated with assembly enviroment.
The sealing principle of O-rings is based on their elastic deformation. When compressed, O-rings create a contact pressure on the sealing surface. If this pressure is higher than the internal pressure of the medium being sealed, leakage is prevented; otherwise, leakage occurs.
Design O-Ring based on Compression Rate and Elongation Rate
The compression rate of the cross-sectional diameter and the elongation are key factors in seal design. These significantly influence sealing performance and service life. The proper fit between O-ring dimensions and groove dimensions determines the correct compression and elongation rates.
Compression Rate: The compression rate (W) is calculated as
When selecting the compression rate, the following factors must be balanced:
1) Sufficient sealing contact area
2) Minimized friction - lubrication coating can be applied
3) Prevention of permanent deformation
Excessive compression can increase contact pressure but also increases friction and permanent deformation. Too little compression may result in misalignment and leakage. Static seals typically have a higher compression rate than dynamic seals but should not exceed 25%, as this can lead to excessive stress relaxation and permanent deformation, particularly at high temperatures.
The compression rate varies based on the type of seal:
1) Static seals: Cylindrical static seals and reciprocating motion seals usually have a compression rate of 10%-15%. Plane static seals require 15%-30%.
2) Dynamic seals: Reciprocating motion seals typically have a compression rate of 10%-15%. For rotary seals, thermal effects must be considered, and the compression rate for the outer diameter is generally 3%-8%.
Additionally, thermal expansion of the rubber material due to media or temperature should be accounted for. The maximum allowable expansion is generally 15%; exceeding this indicates the need for alternative materials.
Elongation Rate: After installation, O-rings generally undergo some degree of elongation. Similar to the compression rate, the elongation rate also affects the seal’s performance and lifespan. Excessive elongation can complicate installation and reduce the compression rate, leading to leakage.The elongation rate (α) is calculated as:
The recommended elongation range is 1%-5%, depending on the shaft diameter.
In summary, O-ring design must consider the balance between compression and elongation to ensure optimal sealing performance and service life. Here is the table to provide a general guide for o-ring size calculation:
Please contact us, OBT Rubber Seal, for better understanding your technical requirement and our proposal.
