1: Motion speed

The movement speed is very low (< 0.03/s), so the stability of the equipment and the crawling phenomenon should be considered. When the moving speed is very high (> 0.8m/s), the ink of lubrication may be destroyed, and the seal will be frictionally heated because of the poor lubrication, which will greatly reduce the service life. It is suggested that the rubber-plastic seal should work in the range of 0.3m/s to 1.2m/s.

2:Temperature

Low temperature will reduce the elasticity of rubber-plastic composite seals, resulting in leakage, and even the whole oil seal becomes hard and brittle. High temperature will make the volume of oil seal expand and soften, resulting in a rapid increase in friction resistance and pressure resistance of oil seal during movement. It is suggested that the continuous working temperature range of rubber-plastic composite seals should be - 10 ~ + 80 C.

3: Work pressure

Oil seal has starting pressure requirement. Oil seals with low friction and low aerodynamic resistance should be selected for low pressure operation. Under 2.5 Mpa, rubber-plastic composite seals are not suitable. When high pressure is applied, the pressure of seals should be taken into account, and special requirements for grooving of anti-extrusion retaining rings are also required.

4: Working medium:

In addition to strictly selecting the working medium according to the recommendation of the manufacturer, it is very important to keep the working medium clean. Oil aging or contamination will not only cause failure of components in the system, accelerate the aging and wear of oil seals, but also the stolen goods may scratch or insert into the seals, making the seals invalid. Therefore, it is necessary to regularly check the quality and cleanliness of oil seals, and replace oil filters or oils according to equipment maintenance specifications. Residual air diameter compression in oil cylinder will produce high temperature, which will cause oil seal to burn out or even carbonize. In order to avoid this situation, the exhaust treatment should be carried out at the beginning of the operation of the hydraulic system. Hydraulic cylinder should also run at low pressure and slow speed for several minutes to confirm that the residual air in the oil has been discharged before it can work properly.

5: Lateral load

In general, the piston must be equipped with support rings to ensure that the cylinder can withstand a larger load. Seals and support rings play a completely different role. Seals can not replace the load of support rings. Hydraulic cylinders with lateral force must be equipped with support rings with strong bearing capacity (metal rings can be used for heavy load) to prevent leakage and abrasion caused by oil seals working under eccentric conditions.

6: Hydraulic shock

There are many factors that cause hydraulic impact, such as the moment when the excavator bucket suddenly meets the stone, the crane lifts or drops the heavy objects. In addition to the external factors, for high pressure and large flow hydraulic system, when the actuator (hydraulic cylinder or hydraulic motor) reverses, if the performance of the reversing valve is not good, it is easy to produce hydraulic impact. The instantaneous high pressure produced by hydraulic impact may be several times of the working pressure of the system. Such high pressure will tear the oil seal or involve part of the gap in a very short time, causing serious damage. In general, the cylinder with hydraulic impact should install buffer rings and retaining rings 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 squeezing into the gap under high pressure and biting the root.

7: Processing Accuracy of Cylinder

Experiments show that the surface roughness Ra of the moving working surface contacted with the oil seal is more than 0.8 micron, and the leakage and wear value of the oil seal will increase directly. Therefore, it is suggested that the surface roughness of the moving working surface be Ra 0.1-0.8 micron. In order to ensure the sealing performance of rubber-plastic composite seals and avoid damaging the seals during assembly, the design and construction of hydraulic cylinders are carried out. The following aspects should be considered in installation:

1: Cylinder barrel

A: Material: generally carbon steel, low pressure system and good friction conditions can be used in aluminum alloy, bronze, stainless steel and so on.

B: Surface quality and roughness: Honing, polishing or rolling are generally required on the inner surface. The roughness of Ra 0.1-0.8 um is required, and no longitudinal or transverse knife lines are allowed.

2) Piston rod

A: Material: Aluminum alloy, bronze and stainless steel can be used in carbon steel, chrome plated steel, low pressure system and good friction conditions.

B: Surface quality and roughness: Ra 0.2-0.4 micron roughness is required. Hard chromium is plated on the surface after heat treatment. The piston rod of hydraulic cylinder used in construction machinery may be scratched by sand and stone, and its surface hardness is required to be above HRC60.

C: Installation groove of oil seal

D: Local structure design

E: sliding fit clearance F of wear-resistant ring and extrusion gap G of oil seal