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1. Movement speed

The movement speed is very low (≤0.03/s), and the stability of the equipment operation and whether there is a crawling phenomenon should be considered. When the moving speed is high (≥0.8m/s), the lubricating ink of the device may be damaged, and the seal will be heated due to friction due to lack of good lubrication, resulting in a greatly reduced service life. It is recommended that rubber and plastic seals work within the speed range of 0.3m/s~1.2m/s.
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2. Temperature

Low temperature will reduce the elasticity of the rubber-plastic composite seal, causing leakage, and even the entire oil seal becomes hard and brittle. High temperature will cause the volume of the oil seal to expand and become soft, resulting in a rapid increase in the frictional resistance of the oil seal and a decrease in the pressure resistance during movement. It is recommended that the continuous working temperature range of the rubber-plastic composite seal is -10~+80°C.
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3. Working pressure

Oil seals have minimum starting pressure requirements. For low-pressure work, oil seals with low friction performance and small aerodynamic resistance must be selected. Below 2.5Mpa, the rubber-plastic composite seal is not suitable. When the pressure is high, the pressure of the seal should be considered, and there are special requirements for the groove processing of the anti-extrusion retaining ring.
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4. Working medium:

In addition to selecting the working medium in strict accordance with the manufacturer's recommendations, it is very important to keep the working medium clean. The aging or contamination of the oil will not only cause the components in the system to fail, and accelerate the aging and wear of the oil seal, but also the dirt in it may scratch or embed the seal, making the seal invalid. Therefore, it is necessary to regularly check the quality of the oil seal and its cleanliness, and replace the oil filter or oil according to the maintenance specifications of the equipment. The high compression of residual air in the oil in the oil cylinder will generate high temperature and cause the oil seal to burn out or even carbonize. In order to avoid this situation, exhaust treatment should be carried out at the initial stage of hydraulic system operation. The hydraulic cylinder should also run at low pressure and slow speed for a few minutes to confirm that the residual air in the oil has been exhausted before it can work normally.
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5. Side load

Generally, a support ring must be installed on the piston to ensure that the cylinder can bear a large load. The seal and the support ring play completely different roles. The seal cannot replace the load of the support ring. For hydraulic cylinders with lateral force, a support ring with strong load-bearing capacity must be added (metal rings can be used for heavy loads) to prevent the oil seal from eccentric Working under these conditions will cause leakage and abnormal wear.
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6. Hydraulic shock

There are many factors that produce hydraulic shock, such as the moment when the excavator bucket suddenly hits the stone, the crane lifts or puts down the heavy object. In addition to external factors, for high-pressure and large-flow hydraulic systems, when the actuator (hydraulic cylinder or hydraulic motor) is reversing, if the performance of the reversing valve is not good, it is easy to produce hydraulic shock. The instantaneous high pressure generated by the hydraulic shock may be several times the working pressure of the system. Such a high pressure will tear the oil seal or be partially involved in the gap in a very short time, causing serious damage. Generally, for oil cylinders with hydraulic impact, buffer rings and retaining rings should be installed 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 is bitten.
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7. Machining accuracy of oil cylinder

Experiments have shown that if the surface roughness Ra of the moving working surface in contact with the oil seal exceeds 0.8μm, the leakage and wear value of the oil seal will directly increase, so it is recommended that the roughness of the moving working surface be Ra0.1~0.8μm. The sealing performance of the hydraulic cylinder should be considered to avoid damage to the seal during the assembly process. The following aspects should be considered in the design and installation of hydraulic cylinders:

1): Cylinder barrel
a: Material: generally carbon steel, aluminum alloy, bronze, stainless steel, etc.
b: Surface quality and roughness: The inner surface generally needs to be honed, polished or rolled, and the roughness of Ra0.1~0.8μm is required, and vertical and horizontal knife lines are not allowed.

2) Piston rod
a: Material: generally carbon steel, chrome-plated steel, aluminum alloy, bronze, stainless steel, etc. can be used in low-voltage systems and occasions with good friction conditions.
b: Surface quality and roughness: The required roughness is Ra0.2~0.4μm, and the surface is plated with hard chromium after heat treatment. The piston rod of the hydraulic cylinder for construction machinery may be scratched by sand and stones, and its surface hardness is required to be above HRC60.
c: Oil seal installation groove
d: Local structure design
e: wear ring sliding fit gap f and oil seal extrusion gap