Hydraulic cylinders have many requirements for seals. Different applications have different requirements.
1. No Leakage or Very Little Leakage.
1) If the piston rod seal fails, external leakage will occur, which will directly pollute the environment, so it must be avoided as much as possible. However, a small amount of leakage can lubricate moving parts, reduce friction, and extend the life of the piston rod. Therefore, after long-term operation is generally allowed, there will be a very small amount of non-drip leakage.
2) If the piston seal fails, internal leakage will occur. Although it will not directly pollute the environment, the leakage under high pressure will cause local heating and high temperature, which will damage the surface of the part. In addition, the hydraulic cylinder cannot be kept in a fixed position. Therefore, it also needs to be avoided.
2. Smaller Friction.
Large pressing force ⇒ large friction ⇒ large wear ⇒ large energy loss, crawling
In order to seal, of course the greater the pressing force, the better. But the greater the pressing force, the greater the friction usually. This is not a problem for static sealing, but for dynamic sealing, it not only brings energy loss. And high friction can easily lead to uneven movement, especially at low speeds, crawling-stop-and-go phenomenon occurs.
3. Longer Working Life.
1) The seal is in contact with the hydraulic oil, and the pressure may change from time to time. Therefore, cavitation is likely to occur. To work for a long time, the material of the seal needs to be resistant to cavitation and not easy to peel off.
2) Chemical Compatibility with Hydraulic Oil.
The seal has been immersed in hydraulic oil for a long time, and it is hoped that there will be no or very little change.
3) For dynamic seals, when working, the seals will naturally rub harder metal materials from time to time. But even for static friction, the shape of the seal changes due to pressure changes, so the contact surface will move slightly and friction will occur. Therefore, wear resistance is universally needed for seals.
4) Polymer materials are very sensitive to high and low temperatures.
High temperature will cause polymer materials to age, lose their elasticity, increase plasticity, and cause permanent deformation.
The parts where friction actually occurs in the seal often generate heat due to friction, and the hydraulic oil seldom flows in these places, and the temperature is higher than other parts.
Low temperature will also harden the material and reduce its elasticity, thereby reducing the stress at the compression point. This is especially easy to happen in winter, high-cold areas, not working and just starting.
4. Certain Economy
The price is affordable. The volume is small. Easy to install and replace.
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