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2022

Features of large size sealing products

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 gap, axial seal (or flat static seal) leakage gap is axial gap. According to the pressure medium acting on the inner or outer diameter of the large-size seal, the axial seal is divided into two cases: internal pressure and external pressure. The internal pressure increases and the external pressure decreases the initial stretch of the large gauge seal. For the above-mentioned different forms of static seals, the sealing medium has different directions for large-size seals, so the preloading design is also different. For dynamic dense

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　　Large size sealThe selection of 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 gap, axial seal (or flat static seal) leakage gap is axial gap. According to the pressure medium acting on the inner or outer diameter of the large-size seal, the axial seal is divided into two cases: internal pressure and external pressure. The internal pressure increases and the external pressure decreases the initial stretch of the large gauge seal. For the above-mentioned different forms of static seals, the sealing medium has different directions for large-size seals, so the preloading design is also different. For dynamic seals, it is necessary to distinguish between reciprocating seals and rotary seals.

1. Static seal: cylindrical static seal is the same as reciprocating seal, generally W = 10% ~ 15%; Plane static seal accounts for W = 15% ~ 30%.

For dynamic sealing, it can be divided into three situations; reciprocating motion generally takes W = 10% ~ 15%. The Joule heating effect must be considered when selecting the compression ratio of the rotary motion seal. Generally speaking, the inner diameter of the large-size seal for rotary motion is 3%-5% larger than the shaft diameter, and the compression rate of the outer diameter is W = 3%-8%. In order to reduce frictional resistance, low friction movement of the large size seal generally choose 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. Typically, outside of a given compression set, the larger allowable expansion is 15%. Exceeding this range indicates that the material selection is inappropriate, and large-size seals of other materials should be used, or the given compression deformation rate should be corrected.

Large size seals are widely used in various hydraulic and pneumatic joints, cylindrical surfaces and flange surfaces. For large-size seals used during movement, when the working pressure is greater than 9.8Mpa, if one-way pressure is applied, a retaining ring should be set on the other side of the large-size seal in the pressure direction; a fixing ring should be placed on each side of the ring. In order to reduce friction, a wedge-shaped retaining ring can also be used. When the pressure liquid acts from the left side, the right side retaining ring is pushed up, and the left side retaining ring does not contact the sealed surface, so the friction force is reduced. Generally speaking, the use of a retaining ring will increase the friction of the sealing device, and the wedge-shaped retaining ring is important to reduce this friction. For fixed large-size seals, when the working pressure is greater than 32Mpa, a retaining ring is also required.

The installation quality of large size seal has an important influence on its sealing performance and service life. Leakage problems are usually caused by improper installation.

The large-size seal shall not be scratched, installed in incorrect position or twisted during installation. Before assembly, the sealing groove and the sealing mating surface must be strictly cleaned; at the same time, during the assembly process of the large-size seal, apply the grease to the surface to be passed.

In order to prevent large-size seals from being cut or scratched by sharp edges such as sharp corners and threads during installation, the shaft end and hole end should be reserved for 15 ° ~ 30 ° lead-in angle during installation. When the large-size seal needs to pass through the external thread, a special thin-walled metal guide sleeve should be used to cover the external thread; if the large-size seal needs to pass through the hole, the hole should be inverted into the corresponding slope shape to prevent the large-size seal from being scratched. The bevel angle of the groove is generally a = 120 ° ~ 140 °.

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Large size seal