Several major factors affecting sealing performance

Speed ​​of movement

When the movement speed is very low (<0.03m/s), it is necessary to consider the smoothness of the equipment operation and whether there is a "crawling" phenomenon. When the moving speed is high (>0.8m/s), the lubricating oil film may be destroyed, and the seal may not be well lubricated and frictionally heated, resulting in a greatly reduced life.

It is recommended that the polyurethane or rubber seal be operated at a speed range of 0.03 m/s to 0.8 m/s.

2. Temperature

Low temperatures can reduce the elasticity of the polyurethane or rubber seal, causing leakage, and even the entire seal becomes hard and brittle. The high temperature causes the oil seal to expand and soften, causing a rapid increase in the sealing frictional resistance and a decrease in the pressure resistance. It is recommended that the polyurethane or rubber seal has a continuous operating temperature range of -10 °C to +80 °C.

3. Work pressure

The seal has a minimum service pressure requirement. For low-pressure work, seals with low friction performance and low starting resistance must be used. Below 2.5 MPa, the polyurethane seal is not suitable; when the pressure is high, the pressure of the seal is considered to be deformed. The anti-extrusion retaining ring is required, and the groove processing also has special requirements.

In addition, seals of different materials have different optimum working pressure ranges. The optimum operating pressure range for polyurethane seals is 2.5 to 31.5 MPa.

The effects of temperature and pressure on the sealing performance are interrelated, so comprehensive considerations are needed. See table:

Imported polyurethane PU material

Maximum working pressure

Maximum temperature range

Movement speed -25～+80 -25～+110

0.5m/s 28MPa 25MPa

0.15m/s 40MPa 35MPa

4. Working medium

In addition to selecting the working medium in strict accordance with the manufacturer's recommendations, it is important to keep the working medium clean. The aging or contamination of the oil not only causes failure of components in the system, but also accelerates the aging and wear of the seal, and the dirt therein may be scratched or embedded in the seal to invalidate the seal. Therefore, the quality of the oil and its cleanliness must be checked regularly and the oil filter or oil should be replaced according to the maintenance specifications of the equipment. The air remaining in the oil in the cylinder is compressed by high pressure to generate high temperature, which causes the oil seal to burn out and even carbonize. To avoid this, exhaust gas treatment should be performed at the beginning of the hydraulic system operation. The hydraulic cylinder should also run at low speed and slow for a few minutes to confirm that the air remaining in the oil has been drained before it can work normally.

5. Lateral load

A support ring must generally be mounted on the piston to ensure that the cylinder can withstand large loads. The seal and the support ring serve a completely different function and the seal cannot replace the support ring load. Hydraulic cylinders with lateral forces must be equipped with a bearing ring with a strong bearing capacity (a metal ring can be used for heavy loads) to prevent leakage and abnormal wear caused by the seal working under eccentric conditions.

6. Hydraulic shock

There are many factors that cause hydraulic shock, such as when an excavator bucket suddenly hits a stone, and the crane lifts or drops a heavy object. Except for factors, for high-pressure and high-flow hydraulic systems, when the actuator (hydraulic cylinder or hydraulic motor, etc.) is commutated, if the performance of the reversing valve is not good, hydraulic shock is easily generated. The instantaneous high pressure generated by the hydraulic shock may be several times the working pressure of the system, so that the high pressure will tear the oil seal or partially squeeze it into the gap in a very short time, causing serious damage. Generally, cylinders with hydraulic shock should be equipped with a buffer ring and a retaining ring on the piston rod. The buffer ring is installed in the front of the oil seal to absorb most of the impact pressure, and the retaining ring prevents the oil seal from being squeezed into the gap under high pressure, and the root is bitten.

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Label: Several major factors affecting sealing performance

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