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.
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 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.
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.