Created on:2021-07-01 09:21

Fault and working principle of hydraulic system of printing paper cutter

Fault and working principle of hydraulic system of printing paper cutter

(1) Composition and working principle of hydraulic system of printing paper cutter

The paper cutter is widely used in packaging and printing industry to cut all kinds of paper, plastic film, leather and other similar soft materials. It is composed of paper feeder, paper presser and paper cutting mechanism. The slip ring in the paper presser and paper cutting mechanism is controlled by the hydraulic system, and the schematic diagram of the hydraulic system is shown in Figure t.

The working process of the paper cutter is as follows.

First, the staff pushes the material to be cut to the designated position. Then, the automatic cutting command is issued. At this time, the electromagnet 1dt of the electromagnetic directional valve 2 is powered on, and the hydraulic oil enters the rodless cavity of cylinder 4 through the left position of the electromagnetic directional valve 2 to push the piston rod upward, and the left and right levers of the piston rod driving mechanism 6 rotate around their respective fulcrums to press down the paper presser 7. After the presser compresses the material, the system pressure increases gradually until the sequence valve 1 is opened. When the presser is in place, the signal is sent by the travel switch, and the knife locking electromagnet 2DT of the electromagnetic directional valve 3 is energized. The pressure oil enters the rodless chamber of cylinder 5, and its piston rod pushes the clutch slip ring to operate the clutch combination. In this way, the driving shaft moves the cutter bed downward for cutting. After cutting, the cutter bed automatically returns to the highest position. At the same time, the stroke switch makes the knife locking electromagnet 2DT power off, the slip ring operates the clutch to separate, then the electromagnet IDT power off, the system starts to unload, and the rod less cavity of cylinder 4 is connected to the oil tank at the same time. According to the force analysis of the system, the original extended spring 8 presses down the piston through the mechanism 6, and the piston drives the paper presser 7 to reset, preparing for the next cutting.

(2) Fault phenomenon

After the paper cutting mechanism is finished, the cutter bed can be reset, that is, the clutch hydraulic cylinder 5 works normally, but the paper presser can not be reset in most cases, that is, the paper presser hydraulic cylinder 4 can not return, resulting in the next cutting. And the system is accompanied with abnormal noise in the working process, the shell of the hydraulic pump motor is hot, the oil temperature of the oil tank is too high, sometimes as high as 70 ℃.

(3) Fault analysis and elimination

According to the fault phenomenon, the essential reason is that the hydraulic cylinder 4 of the paper presser can not be reset, and the main reasons for branching are as follows.

① The mechanical failure of the printing press, spring 8 fatigue fracture or its stiffness is not enough, resulting in insufficient recovery force of hydraulic cylinder 4, so that the paper presser can not be reset, or the hinge or hinge point of mechanical transmission mechanism 6 falls off, resulting in the force can not be transferred to the piston, so that the hydraulic cylinder can not act.

② The fault of the hydraulic cylinder itself is that the clearance between the cylinder block and piston of hydraulic cylinder 4 is too large due to wear, resulting in stuck phenomenon, or the friction of the hydraulic cylinder increases due to seal distortion, resulting in the failure of the hydraulic cylinder.

③ The failure of the solenoid directional valve, the burnout of the solenoid coil, the stuck valve core, and the fatigue fracture of the return spring of the solenoid directional valve 2 may cause the valve not to realize the switching function, so that the valve core cannot be reset and always remains in the left position function, that is, the paper presser 7 remains in the paper pressing state and cannot be reset.

The fault tree is shown in Figure U.

U.jpg

According to the fault tree, the fault points with lower probability can be eliminated and the fault points with higher probability can be found. The steps are as follows.

① One of the possible reasons is that the spring 8 in the mechanism or the hinge in the mechanism falls off. Through field observation, this kind of fault phenomenon did not occur.

② For the electromagnet coil fault, it can be measured with the help of a multimeter. Through the measurement, it is found that the electromagnet is not burnt out and can work normally.

③ Remove the element. When the possibility of each fault is not clear, the components that are easy to disassemble should be checked first, and then the components that are difficult to disassemble should be checked, that is, according to the principle of "easy before difficult". Through the above analysis, the mechanism fault and electromagnet coil fault have been eliminated. For the faults of hydraulic cylinder 4 and solenoid directional valve 2, according to the principle of "easy before difficult", the solenoid directional valve 2 can be disassembled and inspected first. It is found that the return spring of solenoid directional valve 2 is broken, which leads to the failure of the core and the failure of the hydraulic cylinder of the presser; At the same time, because the valve core can not be reset, the paper cutter is in the waiting state, the hydraulic pump can not unload, so that the system oil temperature and noise increase. After replacing the spring, the system returned to normal.

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