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2022

Selection and use of large size seals

O-ring seals are typically squeeze seals. The compression ratio and tension of large seal section diameter are the main contents of seal design, which are of great significance to seal performance and service life. Large size seal is generally installed in the sealing groove for sealing. The good sealing effect of the large-size seal depends to a large extent on the correct matching of the size of the large-size seal with the size of the groove to form a reasonable amount of compression and tension of the sealing ring. In the design and processing of the sealing device, if the compression of the large-size seal is too small, it will cause leakage; if the compression is too large, the rubber stress of the large-size seal ring will relax and lead

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O-ring seals are typically squeeze seals.Large size sealThe compression ratio and tension of section diameter are the main contents of seal design, which are of great significance to seal performance and service life. Large size seal is generally installed in the sealing groove for sealing. The good sealing effect of the large-size seal depends to a large extent on the correct matching of the size of the large-size seal with the size of the groove to form a reasonable amount of compression and tension of the sealing ring. In the design and processing of the sealing device, if the compression of the large-size seal is too small, it will cause leakage; if the compression is too large, the rubber stress of the large-size seal ring will relax and cause leakage. Similarly, excessive stretching of large-size seals during operation will accelerate aging and cause leakage.

A larger compression ratio can obtain a larger contact pressure, but an excessively high compression ratio will undoubtedly increase sliding friction and permanent deformation. If the compression ratio is too small, it may cause leakage due to the coaxiality error of the sealing groove and the large-scale sealing error does not meet the requirements, resulting in the disappearance of part of the compression. Therefore, in the choice of large size seal compression ratio, to weigh various factors. Generally, the compression ratio of static seal is greater than that of dynamic seal, but the extreme value should be less than 30% (related to rubber material), otherwise the compressive stress will obviously relax, resulting in excessive permanent deformation, especially under high temperature conditions.

The selection of large-size seal compression rate W should consider the use conditions, static seal or dynamic seal; static seal can be divided into radial seal and axial seal; radial seal (or cylindrical static seal) leakage gap is radial seal gap, axial seal (or flat static seal) leakage gap is axial gap.

The axial seal is divided into internal pressure and external pressure according to the pressure medium acting on the inner or outer diameter of the large-size seal. The internal pressure increases and the external pressure decreases the initial stretch of the O-ring. For the above-mentioned different forms of static sealing, the sealing medium has different force directions for large-size sealing, so the preloading design is also different. For dynamic seals, it is necessary to distinguish between reciprocating and rotary motion seals.

After the large size seal is installed in the sealing groove, its cross section is compressed and deformed. The deformation width and its contact width with the shaft are related to the sealing performance and service life of the large size seal. The value is too small will affect the sealing performance. The deformation width BO(mm) of the large-size seal is related to the compression rate W and the cross-sectional diameter dO of the large-size seal.

Generally speaking, considering the requirements of pressure pulsation and vacuum pumping, B0 should be close to the groove width. For gas medium sealing, B0 should be 0.1-0.2mm smaller than the groove width; for liquid medium sealing, B0 should be 0.2 mm-0.5mm smaller than the groove width. At the same time, B0 should not be greater than the groove width, otherwise the contact width of the seal may be reduced after being subjected to pressure, reducing the contact stress of the seal, and causing leakage. When there is pressure pulsation, if the groove width is too large, the large-size seal will move back and forth, causing wear; if the groove width is too small, the large-size seal will fill the groove, resulting in excessive resistance.

Key words:

Large size seal