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2023
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03
Several major factors affect the sealing performance
Source:
Several major factors affect the sealing performance
1. Movement speed
Movement speed is very low (<0.03m/s), to consider the smoothness of the operation of the equipment and whether the phenomenon of "crawling". When the movement speed is high (>0.8m/s), the oil film that plays a role in lubrication may be destroyed, and the seal will not be well lubricated and frictional heat, resulting in a greatly reduced life.
It is recommended that polyurethane or rubber seals work in the speed range of 0.03m/s to 0.8m/s.
2. Temperature
Low temperature will reduce the elasticity of polyurethane or rubber seal and cause leakage, and the whole seal will become hard and brittle. High temperature will make the volume of oil seal expand and become soft, resulting in rapid increase of sealing friction resistance and reduction of pressure resistance during movement. It is recommended that the continuous working temperature range of polyurethane or rubber seal is -10℃～+80℃.
3.Working pressure
Low-pressure work shall use seals with low friction performance and low starting resistance. Under 2.5 MPa, polyurethane seals are not suitable; for high pressure, the deformation of seals under pressure should be considered, anti-extrusion retaining rings are required, and special requirements for groove processing.
In addition, different materials have different optimal working pressure ranges. For polyurethane seals the best working pressure range is 2.5 to 31.5 MPa.
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. Aging or contamination of the oil will not only cause the components in the system to malfunction and accelerate the aging and wear of the seals, but the dirt in it may scratch or embed the seals and make the seals fail. Therefore, the quality of the oil and its cleanliness must be checked regularly and the oil filter or oil must be replaced according to the maintenance specifications of the equipment. Air left in the fluid in the cylinder by high pressure compression will generate high temperature to make the oil seal burn. In order to avoid this, in the initial operation of the hydraulic system, the exhaust should be processed. The hydraulic cylinder should also run slowly at low pressure for a few minutes to confirm that the residual air in the fluid has been exhausted before normal operation.
5. Lateral load
The piston must generally be equipped with a support ring to ensure that the cylinder can withstand a large load. Seals and support ring play a completely different role, seals can not replace the support ring load. Hydraulic cylinder with lateral force, must be added to the bearing capacity of the stronger support ring (heavy load available metal ring), to prevent the seal in the eccentric conditions of work caused by leakage and unusual wear.
6. Hydraulic shock
There are many factors that produce hydraulic shock, such as the excavator bucket suddenly hit the stone, the crane lifting or putting down the moment of heavy objects. In addition to external factors, for high-pressure high-flow hydraulic system, the implementation of components (hydraulic cylinder or hydraulic motor, etc.) when reversing, if the performance of the reversing valve is not very good, it is easy to produce hydraulic shock. Hydraulic shock generated by the instantaneous high pressure may be several times the working pressure of the system, such high pressure in a very short period of time will tear the oil seal or squeeze it locally into the gap, causing serious damage. Generally, cylinders with hydraulic shock should install buffer ring and retainer ring on the piston rod. The buffer ring is installed in 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 from being chewed up.