What are the application tips for O-ring seals?

The improvement skills in the structure and installation of the O-ring seal include the correct selection of the groove shape, the correct selection of the hardness of the O-ring, and the measures to enhance the sealing effect.

The function of the seal is to prevent the leakage of the working medium and the entry of foreign objects such as air, dust and water into the hydraulic components and hydraulic system. The quality of the sealing device directly affects the working performance of the hydraulic transmission device. When the design and use are not good, the working medium will leak a lot, and the system efficiency will drop significantly. Fault.

The reasons for seal failure are mainly due to its own structural design and seal damage. As the most commonly used sealing element, O-ring seals have certain skills in addition to some conventional content in design and application. Mastering these skills can ensure the quality and service life of the O-ring seal.

01. Correct selection of groove shape

When using O-ring seals, the most common choice is rectangular grooves, but some special parts should not use rectangular grooves, such as rotary seals, semi-circular grooves can be selected, flanges and bolt heads are relatively small. For narrow places, triangular grooves can be used.

02. Correct selection of O-ring hardness

Reasonable selection of sealing gap and material with higher hardness can also alleviate the phenomenon of intrusion into the gap and prolong the service life of sealing elements.

03.Measures to enhance the sealing effect

① Pressure compensation groove.

Excessive pressure of the fluid being sealed or hydraulic shock can cause leakage of the O-ring. During dynamic sealing, if the pressure exceeds 4MPa, there may be oil leakage. After adding a retaining ring, the pressure can be increased. However, the hydraulic shock will make the local instantaneous pressure several times higher than the normal working pressure, which may cause the O-ring to lose its sealing performance. In this case, a groove with a pressure compensation function can be used. With this kind of groove, no leakage can be achieved even under the pressure of 16MPa. The groove size of this O-ring seal is as follows: the groove width b is 0.2~1mm larger than the wire diameter d1 of the O-ring, the bottom diameter D of the groove is 0.2~2mm smaller than the inner diameter of the O-ring, and 2~4 holes are drilled at the end near the bottom of the groove For a small hole with a diameter of 2~4mm, a single-acting hydraulic cylinder can be punched at one end, and a double-acting hydraulic cylinder can be punched at both ends (Figure 4-1). The clearance between the outer diameter of the piston and the cylinder diameter can be enlarged. The larger the diameter of the o-ring section, the larger the clearance, generally 0.1~0.5mm. The usual seal contact point is at the outer diameter (point a). In this sealing contact point at point a and one side (point c), as the pressure increases, the contact becomes tighter, which acts as a pressure compensation, and there is no greater requirement for the dimensional tolerance of the piston processing, and the surface roughness is R6.3 ~3.2um is enough.

② The O-ring can be placed obliquely during the rotary seal.

When the O-ring is used for rotary sealing, the linear speed should not be too high, generally 0.3~0.5m/s is appropriate, otherwise oil will leak. When the o-ring is used for rotary sealing, frictional heat is generated at the contact point, the temperature continues to rise, and the oil-cut phenomenon occurs at the contact point, causing wear and aging. And the rubber in the stretched state shrinks when heated (Joule effect). That is to say, "frictional heat, shrinkage, increase in tightening force, frictional force,..." repeated cycles greatly aggravate the aging, cracking and wear of rubber, resulting in seal failure, and the amount of leakage is related to the rotation speed. The inner diameter of the O-ring is designed to be equal to or slightly larger (3~5%) than the shaft diameter. During installation, the (-ring is compressed from the outside to the inside, and the compression of the section is also designed to be smaller (about 5%). In addition, try to use heat-resistant materials, and consider the heat dissipation and lubrication of the O-ring. Install the O-ring obliquely (Fig. 4-2). After adopting these measures, the pu value (seal pressure 6 linear velocity) can be reached as 5.6MPa*7.65m/s=42.84MPa.m/s.