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Three failures and solutions of the dumping and unloading mechanism of the three-roll plate bending machine

The dumping and unloading mechanism of the plate rolling machine

The plate rolling machine is one of the important forming equipment for marine structural parts processing. In order to facilitate the removal of processed parts such as cylindrical, conical, and arc-shaped parts rolled and formed, it is necessary to set up a dumping and unloading mechanism so that the movable frame of the plate rolling machine can complete the dumping action to take out the processed parts rolled and formed; and then complete the reset action To prepare for the next plate rolling process. Specifically, the action of the dumping and unloading mechanism is realized by the hydraulic system, and the dumping action of the movable frame is completed through the retraction of the piston rod of the dumping hydraulic cylinder, thereby taking out the processed workpiece; and then controlling the extension of the piston rod of the dumping hydraulic cylinder out, complete the reset action, reset the movable frame, and get ready for processing the next workpiece. In order to further improve the processing performance of the three-coil plate rolling machine, the hydraulic system of the plate coiling machine has been upgraded. Aiming at the uncontrollable position of the movable frame due to the rupture of the pipeline, a corresponding proposal is put forward based on the analysis of the original dumping hydraulic system. Improvement measures to further improve hydraulic system performance.

Read More: Plate Rolling Machine, Sheet Metal, Steel Plate Bending Roll

The working principle of the hydraulic system of the dumping and unloading mechanism
The working principle of the hydraulic system of the dumping and unloading mechanism

The working principle of the hydraulic system of the dumping and unloading mechanism

After the plate is rolled into shape, the workpiece can be taken out from the plate rolling machine through the dumping and unloading mechanism in conjunction with the hoisting operation process. The dumping and unloading mechanism is mainly composed of a dumping hydraulic cylinder and a dumping bearing body to realize the rotation of the movable frame.
The movable frame is equipped with a tapered bearing, which is supported at the journal of the movable end of the upper roll. In order to take out the processed workpiece, it is necessary to dump the hydraulic cylinder to drive the movable frame and the bearing body to rotate around the pin shaft so that the movable frame is overturned; after the movable frame is overturned, the tapered bearing is out of contact with the upper roller, thereby conveniently Take out the workpiece. During the rolling process, the movable frame is reset by dumping the hydraulic cylinder, and the tapered bearing is inserted into the shaft diameter of the upper roller to support the upper roller. Whether the movable frame can be reset correctly and whether it can be kept at the set position during rolling processing is very important to the geometric shape accuracy and dimensional accuracy of the workpiece, which all need to be realized by dumping the hydraulic system.

The composition of the hydraulic system of the dumping and unloading mechanism

The hydraulic system of the dumping and unloading mechanism before the transformation is a balance and two-way locking system using a hydraulic control check valve, as shown in Figure 1.

  • Oil tank 1 stores hydraulic oil, dissipates heat and precipitates dirt in the oil, etc.;
  • The oil suction filter 2 ensures the cleanliness of the oil entering the hydraulic system;
  • The hydraulic pump 3 and its driving motor 4 are the power source of the dumping hydraulic system;
  • The pressure gauge 5 is used to indicate the outlet working pressure of the hydraulic pump;
  • The electromagnetic overflow valve 6 controls the working pressure of the dumping hydraulic cylinder 12 and also has an unloading function, which constitutes a secondary pressure regulating control to realize pressure switching;
  • The electro-hydraulic reversing valve 7 controls the overturning, stopping, and reset actions of the dumping hydraulic cylinder 12;
  • Two-way hydraulic locks 8 and 9 play the role of locking and maintaining pressure;
  • The one-way throttle valves 10 and 11 can adjust the operating speed of the dump hydraulic cylinder 12. The rod chamber of dumping hydraulic cylinder 12 enters oil, the rodless chamber discharges oil, and the movable frame turns over; the rodless chamber enters oil, the rod chamber discharges oil, and the movable frame resets.

Three failures of the dumping and unloading mechanism

  • Fault 1#: When the dumping and unloading mechanism rolls the workpiece, the piston rod of the dumping hydraulic cylinder bears a large load force, which requires that the piston rod cannot be automatically retracted without control, and the oil inlet and outlet of the hydraulic cylinder must be closed, and at the same time The blocking performance cannot be affected by oil leakage.
    If the connecting pipeline of the tilting hydraulic cylinder breaks, the working range of the tilting hydraulic cylinder will change greatly and cause an accident in the plate bending machine.
  • Fault 2#: Due to leakage, the position of the piston of the tilting hydraulic cylinder changes, causing the movable frame to tilt outward, the gap between the tapered bearing and the movable journal of the upper roller becomes larger, and the ellipticity of the rolled cylindrical workpiece changes accordingly. Large, so that the scrap rate of processed parts increases.
  • Fault 3#: When the tilting mechanism is overturned, due to the gravity of the load, gravity Overspeed will occur. Speed limit and speed regulation measures are required to ensure the stability of the overturning action and prevent the hydraulic cylinder from falling too fast. The vibration caused by the pressure in the upper cavity is in a vacuum state.

Summary

The dumping and unloading mechanism has very high requirements for speed stability and load pressure retention. The hydraulic system of the dumping and unloading mechanism must not only complete the functions of tipping, reset, pressure regulation, speed regulation, and locking, but also ensure the controllability, adjustment, and stability of the tipping action.

Three solutions

The working principle of the hydraulic system of the dumping and unloading mechanism
The working principle of the hydraulic system of the dumping and unloading mechanism

System analysis

  • Advantages: As can be seen from Figure 1, in the hydraulic system before the transformation, the hydraulic control check valves 8 and 9 are respectively installed between the electro-hydraulic reversing valve 7 and the one-way throttle valves 10 and 11. Since the hydraulic control check valve is installed after the oil outlet of the throttle valve, the oil flowing in the reverse direction of the hydraulic control check valve directly flows back to the oil tank, so the back pressure acting on the upper part of the control piston inside the hydraulic control check valve is Zero, the reverse opening pressure is small, which is the advantage of the original scheme.
  • Disadvantages: The original hydraulic system has shortcomings in locking. Since the working environment of the plate rolling machine is relatively harsh, if there is a problem with the hydraulic cylinder connection pipeline, the tilting hydraulic cylinder may lose its supporting force, and the tilting mechanism cannot be safely locked in any position. This is a major shortcoming of the original scheme.

Improvement measure 1: Hydraulic control check valve

Fix the hydraulic control check valve on the outer wall of the dumping hydraulic cylinder and connect it with a steel pipe to prevent the phenomenon of “sudden drop” of the dumping hydraulic cylinder when the hydraulic pipeline breaks. The schematic diagram of the improvement scheme is shown in Figure 2. In the improved scheme, the opening pressure of the hydraulically controlled one-way valve will be increased, but the safety of the tilting mechanism is improved. In addition, the maximum working pressure of the system is set at 12MPa, which belongs to the medium and low-pressure range, and the hydraulic control check valve without an external control structure can also ensure normal opening. Due to the locking effect of the two hydraulic locks, the position of the movable rack is not affected by the load after it is reset.

Improvement measure 2: Electro-hydraulic directional valve 7

When the right position of the electro-hydraulic reversing valve 7 is connected to the working position, the pressure oil from the power source enters the upper chamber of the hydraulic cylinder 12 through the one-way throttle valve 11 and the hydraulic control check valve 9 and is transferred to the upper chamber of the hydraulic cylinder 12 through the control oil circuit. The hydraulic control check valve 8 is reversely opened to dump the oil in the lower chamber of the hydraulic cylinder 12 to flow back to the oil tank 1 through the hydraulic control check valve 8, the one-way throttle valve 10, and the electro-hydraulic reversing valve 7 so that the hydraulic cylinder 12 The piston moves downward. When the electro-hydraulic reversing valve 7 is in the neutral position, the hydraulic control check valves 8 and 9 are quickly closed, and the piston rod of the dumping hydraulic cylinder 12 stops moving immediately. After the electro-hydraulic reversing valve 7 is switched to the neutral position, the upper and lower cavities of the tilting hydraulic cylinder 12 are cut off. The piston rod of the tilting hydraulic cylinder 12 is locked by the hydraulic control check valves 8 and 9, and the piston rod cannot be moved by an external force.

Solutions

In order to ensure the fast locking of the hydraulic control check valve, the electro-hydraulic reversing valve 7 can adopt the H or Y type neutral function, so that the control oil port of the hydraulic control check valve is connected to the oil tank, and its control piston is quickly closed. Since the hydraulically controlled one-way valve is a cone-sealing structure, the leakage is very small, so the blocking performance of this balanced circuit is good and the work is reliable. When the left position of the electro-hydraulic reversing valve 7 is connected to the working position, the pressure oil enters the lower cavity of the dumping hydraulic cylinder 12 through the one-way throttle valve 10 and the hydraulic control one-way valve 8, and the other control oil circuit turns the hydraulic control one-way The valve 9 is opened in the opposite direction, so that the hydraulic oil in the upper chamber flows back to the oil tank, and the piston moves upward.

Improvement measure 3: one-way throttle valve 10

When the piston rod of dumping hydraulic cylinder 12 moves downwards, it is impossible to have no back pressure. If there is no one-way throttle valve 10 in the circuit, when the piston rod is retracted (downward), when the hydraulic control check valve 8 is opened by controlling the oil, the piston rod of the hydraulic cylinder 12 and its associated working parts will be dumped Falling due to its own weight or the speed in the downward movement exceeds the speed that the hydraulic pump 3 can supply, which will cause a vacuum in the upper chamber of the hydraulic cylinder 12, and then the control oil circuit of the hydraulic check valve 8 will also be lost due to pressure loss. Close, cut off the reverse oil circuit, and stop the descending movement of the piston rod and its associated working parts. When the upper cavity of the hydraulic cylinder 12 continues to enter the oil and the pressure is re-established, the hydraulic control check valve 8 is reversely opened again, that is, the hydraulic control check valve 8 is opened and closed at times, and the above process is repeated to make the piston rod and The associated working parts move downward intermittently, causing the movable frame to move unsteadily and generate intense vibration during the overturning process.

Solutions

Therefore, a one-way throttle valve 10 is installed in the system to avoid the occurrence of the above phenomenon so that the oil passage between the hydraulic control check valve 8 and the one-way throttle valve 10 generates a constant back pressure, forming a fluid flow resistance, and Balance the self-weight of the hydraulic cylinder 12 and its associated working parts to ensure that the reverse opening pressure of the hydraulic control check valve 8 is stable and the movable frame is overturned and moved smoothly. Again, due to the existence of the one-way throttle valve 11, the stability of the reset movement of the frame is guaranteed.

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Conclusion

  • The hydraulic control check valve is installed on the tilt hydraulic cylinder, which not only saves the connecting pipeline but more importantly, improves the safety of the tilting mechanism. Even if the connecting pipeline breaks, it can also ensure the locking of the movable frame.
  • The hydraulic balance circuit composed of the hydraulic control check valve and the one-way throttle valve can generate sufficient back pressure, which can prevent the tilting hydraulic cylinder and its associated components from falling at an excessive speed, and realize the smooth movement of the tilting mechanism.

The actual operation of the plate rolling machine shows that the safety and running stability of the improved movable frame are effectively improved.

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