Fault diagnosis and maintenance of packer hydraulic system

Fault diagnosis and maintenance of packer hydraulic system

Hydraulic baler is a kind of hydraulic equipment which is specially used to pack waste paper after pressing. A JB hydraulic packer of a company is imported from France, and its fault analysis is as follows.

(1) Hydraulic system diagram and main features of JB baler

The hydraulic system of JB baler is shown in Figure Q.

The hydraulic system of baler is mainly composed of hydraulic pump station, hydraulic pipeline system, down pressure cylinder and paper pushing cylinder. The hydraulic pump station is also composed of oil tank, hydraulic pump group, filter cooling system, etc. The action of down pressure cylinder and paper pushing cylinder depends on hydraulic pressure. When the hydraulic cylinder does not work, the pressure oil of each hydraulic pump can be unloaded through the middle function of the electromagnetic relief valve or the directional valve. When the electromagnet of solenoid valve 17 loses power, the hydraulic cylinder can realize free falling and fast descending function through valve 18. In the free falling stage, the filling oil tank can quickly replenish oil to the left chamber of the paper pushing cylinder through the filling valves 7 and 9. The combined form of multi pump oil supply and separate unloading is adopted for the downforce cylinder to meet the requirements of fast, slow and other operating speed. Each one-way throttle valve can adjust the operating speed or buffer speed of the cylinder, and the cooling system can strictly control the oil temperature.

The characteristics of the baler hydraulic system are as follows.

① The main cylinder of the precompressor adopts the form of adding flushing oil tank, which makes the downward speed of the pressure head fast, stable, short auxiliary time, high efficiency, and reduces energy consumption.

② The hydraulic system adopts the hydraulic oil-water cooling device and the hydraulic oil fine filtration system, which makes the working reliability of the equipment high.

③ The oil tank is designed with hydraulic oil-water cooler and electric heating system, so that the machine has a wide range of adaptability.

④ Multi pump oil supply and step unloading mode is adopted to realize various speed requirements of hydraulic cylinder piston.

⑤ The main oil circuit of the machine adopts plate soft switching mode, which reduces the hydraulic shock and vibration.

(2) Fault and analysis of hydraulic system of baler

After working for a long time, there are many symptoms, such as the noise of hydraulic pump, the shaking of worktable, the rising temperature of valve body and the weakness of pushing paper on worktable, which seriously affect the production.

The components used in the hydraulic system of the packer are products of the famous ATOS company, which have certain accuracy and reliability. Combined with the actual situation, through field analysis, the fault may appear in the hydraulic pump, electromagnetic directional valve, relief valve and other parts.

① First check the hydraulic pump, found that the oil suction and discharge are normal, doubt can be eliminated.

② The electromagnetic directional valve was inspected and it was found that one end was not electrified. Manual adjustment is adopted and works normally. Therefore, it is judged that there may be a problem with the electromagnetic directional valve or the electric control system.

③ Switch to manual operation of the equipment, found that the paper pushing cylinder is still weak, so judge the relief valve may have a problem.

Therefore, we think that the fault point should be in the hydraulic valve and its electronic control system, which is further analyzed.

When the electromagnet is not electrified and the valve block temperature rises, the hydraulic system will produce noise and vibration. The possible reason is that the electromagnet coil is burnt out, resulting in the hydraulic oil is closed, causing the oil temperature to rise; Or the reversing valve is not in place.

The valve is a three position four-way solenoid directional valve with the function of M-type slide valve. The connection condition of oil circuit in the middle position is shown in Figure R.

The oil inlet chamber P is connected with the oil return chambers at both ends through the central channel of the valve core, i.e. P-T, the hydraulic pump unloads, and the two oil ports a and B leading to the hydraulic cylinder are closed. If the reversing valve spool is not in place, the situation as shown in figure s may occur, resulting in the following faults.

① The passage P-A from the pump to the paper pushing cylinder is not opened, the oil inlet chamber P is directly connected with the oil return port T through the central hole of the valve core, the hydraulic pump is in the unloading state, and there is no pressure in the whole hydraulic system.

② The P-A opening of the passage from the pump port to the paper pushing cylinder is very small, or it is in the state of "pass" or "no pass", which causes the phenomenon of crawling and low pressure of the paper pushing cylinder. According to the system pressure drop and other components are normal, the possible reasons are as follows: a. the main valve core and mating surface of the relief valve are worn, which makes the control pressure of the relief valve drop and causes the system pressure drop; b. The pressure regulating spring of pilot valve was bent and failed; c. The sealing between the valve core and the valve seat of the pilot valve is poor; d. Loose lock nut causes pressure change; e. There is something wrong with the hydraulic medium.

(3) Trouble shooting

According to the above preliminary analysis, recheck the solenoid directional valve, the return spring is normal, the valve core slides freely without blocking and clamping, and the push rods on both sides are not deformed. It is speculated that the possible reason is that the thrust of the electromagnet is not enough. Check that the power supply voltage is 380V and normal, so there is no problem with the electromagnet, so it can be concluded that the electromagnetic directional valve is not damaged, and then find out the connection problem of PLC circuit. Open the electric control cabinet and check the PLC wiring. It is found that the intermediate relay is in poor contact, which causes the indicator light to turn on and off. After the replacement of spare parts, the solenoid valve works normally.

For the symptoms of paper pushing cylinder weakness, it is concluded that the relief valve pressure changes. After manually adjusting the pressure of the relief valve, the lock nut found that the worktable worked normally and the pressure of the paper pushing cylinder returned to normal. But after a period of time, the pressure changes again - system pressure drift. Therefore, it is determined that the main reason is the change of oil temperature. The rise of oil temperature causes the decrease of oil viscosity and the change of system pressure. It may be that most of the oil in the system overflows through the relief valve, causing the throttling and heating of the system, the viscosity of the oil decreases and the pressure decreases. By changing the hydraulic oil and improving the heat dissipation conditions, and adjusting the system pressure properly, all the faults have been eliminated and the work has returned to normal.