Created on:2021-07-05 11:09

Hydraulic fault diagnosis and maintenance of hydraulic press

Hydraulic fault diagnosis and maintenance of hydraulic press (3)

(1) Problems of hydraulic press

The pressing force of a hydraulic press is 250kN. The hydraulic system diagram of the press is shown in Figure X. The main problems are as follows.

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① There is no pre pressure relief measures. The holding pressure of the pressing program is 8 MPa. When holding pressure, the pressure energy is stored in the lower chamber of the master cylinder. At the moment when the die is opened (the piston goes down) after holding pressure, the pressure in the lower chamber of the master cylinder can be released suddenly to produce noise (shooting phenomenon).

② The process requires that the workpiece should be electrically heated and the machine should be cooled by water spray during the pressing process. Therefore, the production site and the operation site are separated, and the operation of the machine is remote operation. It is not easy to realize the remote operation for the adjustment of the pressure of the ordinary pressure valve.

③ The electromagnetic relief valve at the outlet of the quantitative pump is a high-pressure valve, and its unloading pressure is 0.35mpao. Although the IDT is powered off and the quantitative pump is in the unloading state, there is leakage when the electromagnetic directional valve is in the middle position. The leakage oil is enough to open the hydraulic control check valve and enter the lower chamber of the master cylinder. Due to the large area of the piston, the oil pressure of 0.35Mpa makes the piston rise slowly, which will lead to accidents, which is absolutely not allowed. To solve this problem, a two position two-way solenoid directional valve is added, 8dt is powered off when parking, and unloading pressure is reduced.

④ During the working time, the oil (63L / min) of the quantitative pump returns to the oil tank with load, resulting in energy loss.

⑤ The oil circuit is complicated.

(2) Improvement measures

The improvement measures for the above problems are shown in Figure 1-25.

The hydraulic principle of the improved system is as follows.

① Send 3DT to power on

Oil of quantitative pump 11 → one-way valve 3 → proportional reducing valve 5 → port P and port a of solenoid valve 7 → one-way throttle valve 9 → lower chamber of auxiliary cylinder.

Oil in upper chamber of auxiliary cylinder → one way throttle valve 9 → port B and port t of solenoid valve 7 → oil tank.

② Return 4dt power on

Oil of constant displacement pump 11 → check valve 3 → proportional reducing valve 5 → port P and port B of solenoid valve 7 → one-way throttle valve 9 → upper chamber of auxiliary cylinder.

Oil in the lower chamber of auxiliary cylinder → one way throttle valve 9 → port a and port t of solenoid valve 7 → oil tank.

③ Fast forward IDT and 3DT are powered on, and proportional throttle valve 8 is closed

[(oil of variable displacement pump 10 → check valve 1) + (oil of constant displacement pump 11 → check valve 3)] → port P and port a of solenoid valve 6 → lower chamber of master cylinder.

Oil in upper chamber of master cylinder → port B and port t of solenoid valve 6 → oil filter 4 → oil tank.

④ The slow forward IDT and 3DT are powered on, the low pressure relief valve is unloaded, and the proportional throttle valve 8 is closed.

Port P and port a of solenoid valve 6 → lower chamber of master cylinder

Variable displacement pump 10 → check valve 1 → close check valve 3

Proportional reducing valve 5 → port P and port a of solenoid valve 7 → lower chamber of auxiliary cylinder

The oil return route of upper chamber of master cylinder is the same as that of fast forward.

⑤ The principle of pressure maintaining hydraulic system is the same as that of slow motion.

⑥ The pre relief proportional throttle valve 8 opens. The oil in the lower chamber of the master cylinder is proportional throttle valve 8 and oil tank.

⑦ When the pre pressure relief is completed (the pre pressure relief time is controlled by the time relay), 2DT is powered on and the high and low pressure relief valves are unloaded.

[(oil of variable displacement pump 10 → check valve 1) + (oil of constant displacement pump 11 → check valve 3)] → port P and port B of solenoid valve 6 → upper chamber of master cylinder.

Oil in the lower chamber of master cylinder → port a and port t of solenoid valve 6 → oil tank.

When the die is opened, the piston of the master cylinder drops by its own weight, and the high and low pressure relief valves should be unloaded, otherwise, there will be impact when the piston drops to the extreme lower position. In order to ensure that the quantitative pump can smoothly enter the upper chamber of the master cylinder, the unloading pressure is slightly higher than that of the variable displacement pump (both high and low pressure relief valves are proportional valves, and the pressure can be adjusted during unloading). The flow rate of the variable displacement pump is very small (10L / min), so it is not important to enter the upper chamber of the master cylinder.

After improvement, the problems existing in the original hydraulic pressure system can be eliminated. In the process of slow entry and pressure maintaining, the oil of the variable displacement pump 10 enters the lower chamber of the auxiliary cylinder after being reduced by the pressure reducing valve 5, so as to ensure that the position of the pressed parts is fixed and the constant displacement pump is unloaded, so as to reduce the energy consumption.

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