How much do you know about O-rings?

In the formula, d0—–the cross-sectional diameter of the O-ring in the free state (mm);

h——The distance between the bottom of the O-ring groove and the sealed surface (groove depth), that is, the cross-sectional height of the O-ring after compression (mm)

When selecting the compression ratio of the O-ring, the following three aspects should be considered:

1. There must be sufficient sealing contact area;

2. Friction should be as small as possible;

3． Try to avoid permanent deformation.

From the above factors, it is not difficult to find that they are contradictory to each other. A large compression ratio can obtain a large contact pressure, but an excessive compression ratio will undoubtedly increase sliding friction and permanent deformation. If the compression rate is too small, leakage may occur due to the loss of part of the compression due to the coaxiality error of the sealing groove and the O-ring error not meeting the requirements. Therefore, when selecting the compression ratio of the O-ring, various factors must be weighed. Generally, the compression rate of static seals is greater than that of dynamic seals, but its extreme value should be less than 25%. Otherwise, the compressive stress will relax significantly and excessive permanent deformation will occur, which is especially serious in high-temperature conditions.

The selection of compression ratio W of O-type sealing 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 Clearance, the leakage clearance of the axial seal (or plane static seal) is the axial clearance. Depending on whether the pressure medium acts on the inner diameter or the outer diameter of the O-ring, the axial seal is divided into two situations: internal pressure and external pressure. The internal pressure increases the stretching, and the external pressure reduces the initial stretching of the O-ring. For the different forms of static seals mentioned above, the sealing medium acts in different directions on the O-ring, 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 taking W=10%~15%; the flat static sealing device takes W=15%~30%.

2. For dynamic seals, it can be divided into three situations; reciprocating motion generally takes W=10% to 15%. The Joule heating effect must be considered when selecting the compression rate for rotary motion seals. Generally speaking, the inner diameter of the O-ring for rotary motion is 3%-5% larger than the shaft diameter, and the compression rate of the outer diameter is W=3%-8%. For O-rings used in low-friction sports, in order to reduce frictional resistance, a smaller compression rate is generally selected, that is, W=5%-8%. In addition, the expansion of the rubber material caused by the medium and temperature must also be taken into consideration. Usually, the maximum allowable expansion rate is 15% outside the given compression deformation. If it exceeds this range, it means that the material selection is inappropriate. O-rings of other materials should be used instead, or the given compression deformation rate should be corrected.

In the formula, d—–shaft diameter (mm); d1—-O-ring inner diameter (mm).

The value range of stretching amount is 1%-5%. As shown in the table, the recommended value for the O-ring stretch amount is given. According to the size of the shaft diameter, the O-ring stretch amount can be selected according to the table. The preferred range of O-ring compression ratio and stretch amount