Created on:2021-07-21 10:21

Fault analysis and improvement of hydraulic system for side guide plate of coiler

Fault analysis and improvement of hydraulic system for side guide plate of coiler

(1) Preliminary fault diagnosis

According to the above phenomenon, it is preliminarily judged that the hydraulic control check valve 3 on the rodless cavity side of the servo cylinder is not closed tightly, which is the cause of the fault. However, the hydraulic control check valve 3 on the rodless cavity side of the servo cylinder was disassembled and inspected, and no abnormality was found. After the valve was installed, the above fault still existed.

It is further judged that: when the electromagnetic directional valve 1 is in the power-off state, if the T port pressure of the electromagnetic directional valve 1 is larger for some reason, the control pressure of the hydraulic control check valve 3 is greater than the minimum allowable control pressure of the valve, which causes the hydraulic control check valve 3 to open, and the control pressure is not enough to open the hydraulic control check valve 8 in front of the servo valve.

(2) Further analysis of fault

The side guide plate hydraulic pump station consists of three a4vs0250dr constant pressure variable pumps, two of which are working and one is standby. It can provide the pressure of 14MPa and the flow rate of 0-500l / min.

The model of electromagnetic directional valve 1 is dg4v-2-2al-m-u-h6-10, and the maximum flow of the valve is 30L / Niin (25MPa); The model of the electro-hydraulic directional valve 10 is dg5v-5-6cl-2-j-h-m-u-5-20, and its maximum flow rate is 160L / min (31.5Mpa); The opening pressure of check valve 14 and 15 is 0.035MPa; The diameter of oil drain pipe in valve block is 10 mm and its depth is 327 mm. The inner diameter of L pipe is 8 mm and its length is about 5 m; The models of hydraulic control check valves 3, 5 and 8 are dt8pi-10-05-11-enb.

According to the product samples provided by Vickers company, the minimum control pressure for opening the hydraulic control check valve is:

P control pressure = (pout pin) / A + pin + C (4-12)

Where pout -- outlet pressure of free flow;

Pin -- inlet pressure of free flow;

A -- area ratio of control piston to check valve, the area ratio of control piston to check valve is 2.6;

C -- varies with model / opening pressure, the valve is 0.4MPa.

As the pressure in front of hydraulic control check valve 8 is 14MPa of the system pressure, the minimum control pressure for opening hydraulic control check valve 8 can be calculated as 6.2mpa according to the above formula; When the hydraulic cylinder of the side guide plate extends out, the load is small, and the pressure of the rodless chamber is about 2MPa. According to the above formula, the minimum control pressure for opening the hydraulic control check valve 3 can be calculated as 1.2MPa.

In order to check whether there is high pressure at t port of solenoid directional valve 1, the pipe joint in front of check valve 15 in L pipe is removed. When the DT3 power on servo cylinder of electro-hydraulic directional valve 10 extends, the hydraulic oil at L Port continuously sprays out at high speed, and when the servo cylinder is in place, the hydraulic oil pressure increases. When the DT2 power on servo cylinder of electro-hydraulic directional valve 10 retracts, the hydraulic oil at L Port continuously sprays out, And after the servo cylinder is in place, the hydraulic oil will no longer spray out. So far, it can be considered that the fault is caused by the intersection of holes in the valve block. Re checking the valve block hole system, it is found that the front hole a of relief valve 4 on the rodless cavity side of servo cylinder intersects with the oil return hole B of solenoid directional valve 1 due to design reasons, as shown in the dotted line in Figure M.

M1.jpg

After extending to the position, the pressure of the servo cylinder's rodless chamber is maintained at about 3Mpa due to the leakage of flushing valve 16; When DT2 of the electro-hydraulic directional valve 10 is powered on, the servo cylinder retracts, part of the hydraulic oil in the rodless chamber returns to the oil tank through the one-way throttle valve 11, and the other part of the hydraulic oil returns to the oil tank through the hydraulic control one-way valve 3 and the flushing valve 16. Because there is no oil return in the rodless chamber of the servo cylinder, there is no oil flow sound after the servo cylinder retracts into place.

(3) Troubleshooting and improvement of hydraulic system

After confirming that the valve block channels intersect, it is necessary to cut off the connection between port T and ab of solenoid directional valve 1. As shown in Figure n, a transition valve block is added between check valve 2 and valve block to lead out port t of solenoid directional valve 1 and connect it to port L, and block port L on valve block. After the transition valve block is installed and re piped, the fault phenomenon disappears.

N1.jpg

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