Created on:2022-03-19 10:16

Purification technology of shield hydraulic oil

Purification technology of shield hydraulic oil

In the shield construction, due to the very bad environmental conditions of tunnel operation, the hydraulic system is often in the state of continuous operation at high temperature. A large number of impurities such as copper filings, iron filings and oil sludge are easy to be mixed in the hydraulic oil, which will seriously affect the stability of the hydraulic system, and even block the filter element and damage the equipment, resulting in the inability of the shield to work. Therefore, maintaining the cleanliness level of hydraulic oil is the key to the stable operation of hydraulic system. In the past, the quality of hydraulic oil needs to be tested regularly in shield construction. When it is found that the oil cannot meet the requirements of shield construction, stop the machine to filter the oil or directly replace the hydraulic oil, which takes a long time and costs a lot. This paper introduces a non-stop shield through an engineering example

Machine oil filtering technology can reduce downtime and improve the efficiency of shield tunneling.

1. Introduction to shield hydraulic system

Two German Herrick 6250 EPB shields are used in a construction site. Its shield propulsion system, cutterhead drive system, articulated system, screw machine system and assembly machine system are driven by hydraulic system. Hydraulic equipment mainly includes, hydraulic oil tank, Jack, oil motor, various valves, oil pipes, etc. The shield propulsion system is mainly composed of 30 propulsion jacks and 14 articulated jacks driven by a 75kW oil pump. The cutterhead drive system is mainly composed of three 315KW oil pumps and eight hydraulic drive motors. The hydraulic oil of all hydraulic systems is supplied by a 5mA oil tank on the shield Trailer.

Working principle of shield hydraulic system: firstly, the motor drives the oil pump to absorb oil from the oil tank, and then the oil with pressure is transmitted to the cutterhead drive motor or push jack through the pipeline to convert the pressure into mechanical energy to drive the cutterhead to rotate or the jack to expand. The hydraulic circulation of shield is shown in Figure 3. During operation, the stratum of the tunnel is mainly gravel sand layer, muddy clay and sandy cohesive soil.

2. Independent circulation device for oil purification

According to the actual situation, the purification of hydraulic oil adopts an independent circulating device, and an independent purification oil circuit is set on the oil tank. The hydraulic oil is sucked out from the bottom of the oil tank through the oil pump and sent to the oil cleaner. The rotating barrel of the oil cleaner rotates at high speed under the action of pressure oil to produce a strong centripetal force to separate oil and impurities with different specific gravity, and the hydraulic oil flows back to the oil tank, Impurities remain on the inner wall of the drum, which does not affect the normal tunneling of the shield.

Figure 4 shows the schematic diagram of oil purification device. The independent oil purification device is composed of oil pump, oil inlet pipe, oil cleaner, oil return pipe, inclined pressure pipe and valve group.

(1) Setting of oil inlet and return port. The system shall be equipped with one oil inlet and two oil return ports, and the oil inlet is located at the bottom of the oil tank and the oil return port is located at the top of the oil tank, which is conducive to the circulation of hydraulic oil. The oil inlet and return port shall be reconstructed by using the existing outlet on the oil tank as far as possible to avoid adding new outlet on the oil tank, especially when it is full of oil.

(2) Installation position of purification device. The purification device is installed in the bypass of the oil tank, and the hydraulic oil is sucked out from the bottom of the oil tank through the gear oil pump and sent to the oil purifier.

(3) Structure and working principle of oil cleaner. There is a double jet rotating shaft in the oil cleaner, which uses the pressure generated by the hydraulic oil to drive the rotating shaft to rotate at high speed. Its speed can reach more than 6000r / min, and the centrifugal force generated is more than 2000 times of gravity.

Under the strong centrifugal force, the mechanical impurities are separated from the hydraulic oil, the hydraulic oil flows back to the oil tank, and the impurities remain on the inner wall of the rotating barrel, so as to greatly improve the cleanliness of the hydraulic oil. Through the specific analysis of the impurity components in the hydraulic oil and the comprehensive comparison of different models of oil purifiers, the field fed-22 centrifugal oil purifier is selected. Its applicable oil tank volume is 1000 ~ 5000L, which is suitable for all kinds of lubricating hydraulic oil and can filter more than 0.26um impurities, which can meet the needs of shield construction.

3. Specific implementation mode

(1) Confirm that the pipeline is unobstructed. Open the oil inlet valve and pressure relief valve, start the oil pump, confirm that the oil pump works normally, observe the reading of the pressure gauge and confirm that the pipeline is unobstructed.

(2) Confirm that the oil cleaner works normally. Open the oil return valve and observe the reading of the pressure gauge. At this time, the oil cleaner starts to rotate; After the oil cleaner rotates stably, close the pressure relief valve, observe the reading of the pressure gauge and confirm that the oil cleaner works normally.

(3) Shut down the oil purifier system. When it is necessary to close the oil purifier system, first open the pressure relief valve and observe the reading of the pressure gauge.

(4) Shut down the oil pump. Turn off the oil pump after the oil cleaner rotates stably.

(5) Work after the oil cleaner stops rotating. After the oil cleaner stops rotating, close the oil inlet valve, oil return valve and pressure relief valve.

(6) The last job. Remove the oil cleaner drum, clean the impurities on the inner wall of the drum and reinstall it.

4. Technical characteristics of purification system

(1) The purification device has high filtration accuracy and can filter impurities above 0.26 µ M.

(2) The purification process does not affect the viscosity and quality of hydraulic oil.

(3) Independent circulation will not affect the work of shield hydraulic system.

(4) Low operation cost, no wearing parts, no need to replace the filter element, and little power consumption.

(5) Large capacity, containing a lot of impurities can also work.

5. Application effect

After installing the oil purification system on the s-470 of Herrick 6250 earth pressure balance shield, after two months of actual operation, the effect is remarkable, the cleanliness of hydraulic oil has been significantly improved, the hydraulic system remains stable, and the consumption of hydraulic oil and filter element has been greatly reduced.

Before installing the oil purifier system, push 410 rings, replace 16 filter elements in total, stop the machine twice, filter the hydraulic oil with the oil filter for one shift each time, and replace 2 filter elements of the oil filter in total. During the 410 ring, a hydraulic oil quality inspection was carried out, and it was found that there was a small amount of metal powder in the hydraulic oil, such as copper chips, iron chips, etc.

After installing the oil purifier system, a total of 420 rings were pushed forward, and a total of 4 filter elements were replaced without stopping to filter oil. Finally, during the quality inspection of hydraulic oil, it is found that the content of impurities in the hydraulic oil is less, which still meets the use requirements. There is no need to replace the hydraulic oil, and it can continue to be used in the next section. The purification process has a good effect.

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