1.Compression ratio:
Compression ratio is the core parameter of the sealing performance of O-rings, and the calculation formula is:
W%=(d2-h)/d2*100%
w%=d2?hd2×10
Here,?d
??represents the cross-sectional diameter (mm) of the O-ring in its free state, and h represents the cross-sectional height (mm) in the compressed state after installation.
· Static sealing: The compression ratio is generally taken as 15%-30%. For high-pressure static sealing (such as 10-50MPa), it can be appropriately increased to 20%-30%.
· Dynamic seals: The compression rate of reciprocating motion seals is typically 10% to 15%, while that of rotary motion seals is generally 3% to 8% in terms of outer diameter compression.
The tensile amount affects the installation and sealing effect of O-rings. The calculation formula is:
α=(d+d1)/(d1+d2)
α=d+d1d1+d2Here, d represents the shaft diameter (mm), d1 represents the inner diameter of the O-ring (mm), and d2 represents the cross-sectional diameter of the O-ring (mm).
The stretching amount is generally controlled at 1% to 5%. When performing dynamic sealing, a smaller value (1% to 3%) is advisable to avoid excessive stretching, which may lead to a reduction in cross-section and leakage.
3. Groove size
· Slot width: Typically 1.1 to 1.5 times the cross-sectional diameter of the O-ring. For dynamic seals, a larger value is taken, and space for thermal expansion and medium swelling should be reserved.
· Groove depth: It is determined based on the compression ratio and the cross-sectional diameter of the O-ring. The sum of the groove depth and the clearance should be less than the wire diameter of the O-ring in its free state.
· Fillet: The fillet radius of the groove opening is generally 0.1-0.2mm, the fillet radius of the groove bottom for dynamic sealing is 0.1-1mm, and for static sealing is d2/2mm.
4. Material selection
Select appropriate materials based on factors such as the working medium, temperature, and pressure
Oil-resistant nitrile rubber (NBR), high-temperature resistant fluorine rubber (FKM), and water-resistant ethylene propylene diene monomer (EPDM) are used.
The material hardness is generally 70-90 Shore A. For static seals, a lower value is selected, while for rotary seals, a higher value is chosen.
5. Surface roughness
· Surface roughness of static sealing groove?Ra≤6.3μm, dynamic sealing?Ra≤1.6μm, and groove of rotary sealing shaft?Ra≤0.4μm. Notes
· The compression ratio and stretching amount need to be comprehensively considered to avoid permanent deformation due to excessive compression or leakage caused by excessive stretching.
· The groove size must strictly comply with the standard to ensure that the O-ring can be evenly stressed after installation.
· The compatibility of materials with the medium is of vital importance to prevent seal failure due to swelling or corrosion.
By rationally selecting and controlling these parameters, it can be ensured that O-rings achieve good sealing performance and a long service life under different working conditions.
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w%=d2?hd2×
