Principle of Hydraulic System for Bending Machine
First, during use, if there is suddenly an increase in noise and a decrease in pressure:
1. Check if there are air bubbles in the oil tank. If there are, it is caused by the entry of gas into the system. If not, proceed to step 2.
Carefully observe the oil for two forms of air bubble mixing: one is a layer of large air bubbles on the surface with almost no bubbles in the oil, and the other is the presence of very small bubbles in the oil.
The first type of air entry is caused by: a) leakage in the hydraulic pump's inlet oil hose; b) damaged sealing elements at the joints; c) damage to the hydraulic pump shaft oil seal (the latter is the most likely).
Solution: a) replace the inlet oil hose; b) replace the sealing elements at the joints; c) replace the hydraulic pump shaft lip seal.
The second type of air entry is caused by blockage of the filter 1 or poor oil suction due to aging of the suction hose in the Yantai hydraulic bending machine.
Solution: clean or replace filter 1, or replace the suction hose (it must be replaced with an oil-resistant hose). If the oil is too dirty, it must be replaced with the same type of new hydraulic oil.
2. Adjust the relief valves 6 and 5 to the system's rated load. Then, touch hydraulic pumps 2 and 3 by hand. If the temperature rises rapidly and there is abnormal vibration, it indicates damage to the internal parts of the pump.
Solution: replace the pump or repair it.
Second, if the system has no noise and no pressure:
First, observe if the return oil volume at the system's return port is normal. If it is normal, listen for the sound of oil flow near relief valves 5 and 6. If there is, identify which valve it is; this indicates a malfunction of the relief valve, which should be rectified. If the return oil volume is not normal, it indicates pump damage, requiring pump repair or replacement.
Third, if the system has no noise, normal pressure at low hydraulic oil temperatures, but pressure decreases at high temperatures:
This fault is very difficult to diagnose and solve using conventional methods. It can be solved by a process of elimination, as follows:
First, analyze the hydraulic schematic diagram. The system is divided into three subsystems (each hydraulic cylinder circuit counts as one). The subsystem of solenoid valve 7 is supplied with pressure oil from pump 2, while the two subsystems of solenoid valves 12 and 14 are supplied with pressure oil from pump 3. The following discussion addresses these two parts.
Preparation for Maintenance:
· The system experienced a decrease in pressure after operating at an abnormal temperature.
· The system uses plate-type connected directional valves (the same method can be applied for threaded connected directional valves).
· Based on the installation hole sizes and inlet/outlet dimensions of solenoid valves such as 4, 7, 12, and 14, prepare four blocking plates with a thickness of 10mm and install O-ring seals at the inlet/outlet ports.
1. First, discuss the subsystem controlled by solenoid valve 7.
(1) Shut down the machine and block solenoid valve 7 with the corresponding blocking plate to prevent oil leakage. Then, start pump 2 and check if the pressure reaches the rated value. If it does not, proceed to (2); if it does, it indicates a leak in the solenoid valve or cylinder. First, check for leaks in the cylinder. Method: remove the blocking plate from the installed solenoid valve 7, replace it with solenoid valve 7, and simultaneously open the inlet port of rodless cavity 9 of hydraulic cylinder (assuming the hydraulic cylinder has retracted). Start the hydraulic pump and energize 2YA to see if there is oil leakage from the disconnected hydraulic cylinder joint. If there is leakage, it indicates damage to the sealing elements on the piston of hydraulic cylinder 9, which needs replacement. If there is no leakage, it is definitely a fault caused by internal leakage of solenoid valve 7, and replacing it with the same model of new solenoid valve can rectify the problem.
(2) Replace the relief valve 6 with the same model. If the pressure reaches the rated value, it indicates that the valve is damaged and needs replacement. Otherwise, it is a fault caused by aging of pump 2, requiring replacement with the same model of pump.
2. Check the two subsystems driven by pump 3.
(1) Shut down the machine and block solenoid valve 12 with the corresponding blocking plate to prevent oil leakage. Start pump 3 and check if the system's pressure reaches the rated value. If it does, refer to method 1-(1) for inspection; if it does not, proceed to (2).
(2) Shut down the machine and also block solenoid valve 14 with the corresponding blocking plate to prevent oil leakage. (Note: at this point, the blocking plate for the position of solenoid valve 12 is still in the system.) Next, start pump 3 and check if the system's pressure reaches the rated value. If it does, refer to method 1-(1) for inspection; if it does not, proceed to (3).
(3) Shut down the machine and block solenoid valve 4 with the corresponding blocking plate to prevent oil leakage. Start pump 3 and check if the system's pressure reaches the rated value. If it does, refer to the explanation; if it does not, it is definitely a fault caused by aging of pump 3, requiring replacement.
Maintenance of the Bending Machine:
1. Check the oil level in the tank every month. If the hydraulic system has been repaired, the oil level should also be checked. If the level is below the oil window, hydraulic oil should be added.
2. The hydraulic oil used in the bending machine is either No. 46 or No. 32 hydraulic oil, depending on the actual situation.
3. For a new bending machine, the oil should be changed within the first month of operation, and subsequently changed once a year. Each time the oil is changed, the tank should be cleaned.
4. The oil temperature of the system should be maintained between 35°C and 60°C and must not exceed 70°C, as excessive temperature can cause deterioration and damage to the oil and components.
5. When changing the oil, the filter should also be replaced or thoroughly cleaned.
6. If there are any related alarms or abnormal oil quality in the bending machine, the filters should be replaced.
7. The air filter on the bending machine's oil tank should be checked and cleaned every three months, and ideally replaced once a year.
8. Clean the hydraulic components (baseplate, valves, motors, pumps, oil pipes, etc.) every month. It is best to install protective covers on the hydraulic system to prevent dirt from entering the system, and cleaning agents should not be used.
9. After one month of use, check for any deformation in the oil pipes. If any abnormalities are found, they should be replaced. After two months of use, all component connections should be tightened. This work should be done with the machine shut down and the system depressurized.
