The selection of the compression ratio W of the rubber O-ring should consider the use conditions, static seal or dynamic seal; static seal can be divided into radial seal and axial seal; the leakage gap of radial seal (or cylindrical static seal) is radial The gap, the leakage gap of the axial seal (or plane static seal) is the axial gap. Axial seals are divided into two cases of internal pressure and external pressure according to whether the pressure medium acts on the inner diameter or outer diameter of the O-ring. The internal pressure increases the stretching, and the external pressure decreases the initial stretching of the O-ring.
. In the above-mentioned static seals, the action direction of the sealing medium on the O-ring is different, so the pre-pressure design is also different. For dynamic seals, it is necessary to distinguish between reciprocating motion seals and rotary motion seals.
1. Static sealing: The cylindrical static sealing device is the same as the reciprocating sealing device, generally W = 10% -15%; the plane static sealing device W = 15% -30%.
2. For the dynamic seal, it can be divided into three cases; reciprocating motion generally takes W = 10% ~ 15%. Rotary motion seals must consider the Joule heating effect when selecting the compression ratio. Generally speaking, the inner diameter of the O-ring for rotary motion is 3% -5% larger than the shaft diameter, and the outer diameter compression ratio W = 3% -8%. In order to reduce frictional resistance, O-rings used for low-friction movement generally select a smaller compression rate, that is, W = 5% -8%. In addition, the expansion of the rubber material caused by the medium and temperature must also be considered. Usually outside the given compression deformation, the maximum allowable expansion rate is 15%. Exceeding this range indicates that the material selection is not suitable. The O-ring of other materials should be used instead, or the given compression deformation rate should be corrected.
After the rubber O-ring is inserted into the sealing groove, it generally has a certain amount of stretching. Like the compression rate, the amount of stretching has a great influence on the sealing performance and service life of the O-ring. The large amount of stretching will not only cause difficulty in installing the O-ring, but also reduce the compression rate due to the change in the cross-sectional diameter d0, resulting in leakage.