The interference of O - ring is about 15%-30% in static seal, 9%-25% in dynamic seal.
See o-ring groove GB3452.3
Other factors affecting sealing performance
1) hardness of o-ring
The hardness of O ring material is the most important index to evaluate the sealing performance. Hardness determines the compression of o-ring and the maximum allowable extrusion clearance of groove. As shao's A70's butadiene rubber can meet most of the operating conditions, the sealing materials are not specified, and shao's A70's butadiene rubber is generally provided.
2) extrusion clearance
The maximum allowable clearance gmax is related to the system pressure, the diameter of o-ring section and the hardness of the material. Generally, the higher the working pressure is, the smaller the gmax value of the maximum allowable extrusion clearance is. If the clearance g exceeds the allowable range, the o-ring will be extruded and damaged.
Maximum allowable clearance gmax
Pressure MPa O ring section diameter W
1.78 2.62 3.53 5.33 7.00
Shore hardness A70
≤3.50 0.08 0.09 0.10 0.13 0.15
≤7.00 0.05 0.07 0.08 0.09 0.10
≤10.50 0.03 0.04 0.07 0.08
Shore hardness A80
≤3.50 0.10 0.13 0.15 0.18 0.20
≤7.00 0.08 0.09 0.10 0.13 0.15
≤10.50 0.07 0.08 0.09 0.10
≤14.00 0.03 0.04 0.07 0.08
≤17.50 0.02 0.02 0.03 0.03 0.04
Shore hardness A90
≤3.50 0.13 0.15 0.20 0.23 0.25
≤7.00 0.10 0.13 0.15 0.18 0.20
≤10.50 0.07 0.09 0.10 0.13 0.15
≤14.00 0.05 0.07 0.08 0.09 0.10
≤17.50 0.04 0.05 0.07 0.08 0.09
≤21.00 0.03 0.04 0.07 0.08
≤35.00 0.02 0.03 0.03 0.04 0.04
Note: 1. When the pressure exceeds 5MPa, it is recommended to use the baffle ring;
2. H7/g6 is recommended for application of static seal.
3) compression permanent deformation
Another index to evaluate the sealing performance of O ring is the compression permanent deformation of the material. Under the action of pressure, the o-ring, as an elastic element, produces elastic deformation. With the increase of pressure, permanent plastic deformation will occur. The compression permanent deformation d can be determined by the following formula:
Where: b0- original thickness (section diameter W), b1- thickness under compression, b2- thickness after release
In general, to prevent permanent plastic deformation, the maximum compression allowed by o-rings is about 30% in static seals and 20% in dynamic seals.
The o-ring is installed in the groove, and an initial amount of compression shall be reserved to ensure its sealing performance. For different applications, the amount of precompression relative to section diameter W is also different.
Usually, in the static seal about 15% ~ 30%, and in the dynamic seal about 9% ~ 25%. Specific can refer to the chart below to choose.
5) stretch and compress
When the o-ring is installed in the groove, it is stretched or compressed. If the tensile and compression values are too large, the o-ring section will be excessively increased or decreased, because the tensile 1% correspondingly reduces the section diameter W by about 0.5%. For hole seal, o-ring is best in stretch state, the maximum allowable stretch is 6%; For shaft seals, the o-ring is best compressed along its circumference, with a maximum allowable circumference compression of 3%.
6) o-ring is used as rotary shaft seal
O - ring can also be used for low - speed rotary movement and operation cycle of short rotary shaft seal. When the circumferential speed is lower than 0.5m/s, the phenomenon that the elongated rubber ring will shrink when heated must be considered. Therefore, the inner diameter of the sealing ring is about 2% larger than the shaft diameter which is sealed by it. The sealing ring is installed in the groove, resulting in radial compression of the sealing ring, and the o-ring forms a tiny ripple in the groove, thus improving the lubrication conditions.