O-ring belongs to extrusion seal, that is to say, it achieves the sealing purpose by compression deformation. Extrusion is the most commonly used type of seal, accounting for about 50%. Therefore, the wide application of O-ring is inseparable from its characteristics: Good sealing effect, suitable for static, reciprocating and rotary seals Small and compact space; Easy to assemble and replace; ④ Wide application scope; ⑤ No adjustment is required; ⑥ Low friction; ⑦ Low price; ⑧ It can be sealed in both directions. Therefore, it is widely used in aircraft, bicycles, oil pressure, air pressure equipment, vacuum equipment, electronic equipment, petrochemical equipment and high vacuum ultra-high pressure components. The operating temperature is from – 80 ℃ to+250 ℃, the size of O-ring is 1~3000mm, and the section diameter is 1~30mm. In addition, it is also widely used in micro devices, precision instruments and other departments.
2. Groove structure of O-ring
In addition to the O shape, the cross section of the O-ring also has triangle, D shape, T shape, square shape, heart shape, X shape, pentagon, etc.
O-ring (rectangular groove) is used for fixing and moving.
Fixation is divided into flange seal and cylinder seal. Flange seal is divided into internal pressure seal, external pressure seal and vacuum seal.
Movement is divided into: reciprocating movement seal, rotary movement seal, and swing seal. Reciprocating seals are divided into: hydraulic and pneumatic seals. Rotary motion seal is divided into inner seal and outer seal.
3. Sealing of O-ring
⑴ Static sealing
Give the O-ring a compression ratio of 8~25%, and seal the medium by the reaction force generated by the O-ring.
(2) Reciprocating seal
It mainly depends on “self sealing”. The contact pressure (Pm) of O-ring increases with the increase of medium pressure (Ph). When Ph is much larger than Po (the average pressure per unit area generated during assembly), Po is not the main factor for sealing, while Ph is the main factor for sealing. This kind of fluid (medium) pressure is superimposed on the contact surface through the O-ring, and the sealing effect is called “self sealing” effect. It is a very effective seal.
(3) Rotary seal
It uses the Gow Joule effect to achieve sealing (that is, the rubber generates heat during stretching, while the rubber shrinks when heated during stretching – this phenomenon is more than the Gow Joule effect).
The specific methods are as follows. The compression ratio of 5~8% is given to the outer diameter of the O-ring to force the O-ring to contact the sealing shaft. When the shaft rotates, the O-ring shrinks, and the shrinkage value is generally 4~5%. In this way, the original compression ratio is mostly offset, with only a small part. Therefore, the sealing is achieved by the oil film between the O-ring and the shaft.
4. Selection of compression ratio during O-ring sealing
The compressibility of the section diameter of the O-ring for different sealing occasions is as follows:
The compression ratio of general static seal is 10-30%;
The compression ratio for low friction is 1.5~6%;
High pressure, reciprocating compression ratio: 4~16%;
The compression ratio of hydraulic seal is 10-20%;
The compression ratio of vacuum seal is 40-45%;
The compression ratio at cryogenic extremely low temperature is 70~85% (to overcome the volume shrinkage of rubber at the secondary transition temperature).
5. Applicable scope of rubber O exercise
The rubber O-ring is suitable for mounting on various mechanical equipment. Under the specified temperature, pressure, and different liquid and gas media, the Guangzhou seal is used for sealing under static or moving conditions. In sanitary ware, ships, automobiles, hardware, electronics, toys, electrical appliances, aerospace equipment, machinery, and various instruments and meters, a large number of types of sealing elements are used. Rubber O-ring is mainly used for static sealing and reciprocating sealing. When used for rotary motion seal, it is limited to low-speed rotary seal device. The rubber O-ring is generally installed in the groove with rectangular section on the outer circle or inner circle for sealing. The rubber O-ring still plays a good sealing and damping role in the environment of oil resistance, acid and alkali resistance, abrasion, chemical corrosion, etc. Therefore, rubber O-ring is the most widely used seal in hydraulic and pneumatic transmission systems