This article analyzes and studies the original vibration problems of the equipment, finds out the reasons, and formulates a series of solutions to the problems. A clamping mechanism is designed to improve the stiffness of the equipment, and a unique hydraulic circuit is designed for this clamping mechanism. Through this transformation, the equipment worked stably, extended the service life of the equipment, improved product quality, and achieved success.
Foreword
There are more than ten kinds of shearing dies and blanking dies used in the 1830 uncoiling line. Since the sizes of various molds are different, a discharging belt conveyor with telescopic adjustment and height adjustment, adjustable working speed, and intermittent operation is installed between the blanking press and the stacker. After years of use, it is now found that:
The gaps between the hinges and transmission pairs of the belt conveyor have increased. When the belt conveyor runs at high speed, the fuselage vibrates seriously.
When the mass of the punched workpiece is more than 25kg, after the sheet is sheared, it accelerates in a very short time, and the surge of momentum causes the supporting steel beam to tilt forward, causing the center distance between the drive motor shaft and the spindle to decrease. Small. Because the tensioning wheel of the loose edge of the synchronous belt is fixed, it cannot automatically compensate for the loose edge of the synchronous belt caused by the reduced center distance, causing the synchronous belt to skip teeth.
The above problems seriously reduce the life of the discharge belt, timing belt and bearings. At the same time, it causes the output workpiece to deviate and affects the stacking quality.
Topic
The first topic: Analysis of vibration causes
After research, it was found that the main cause of vibration is due to the rear main beam and front lifting of the belt conveyor The stiffness of the mechanism is insufficient, and the gaps between the hinges, racks, and transmission pairs are large. The mechanism is forced to vibrate under the action of excitation force. The main sources of excitation force are:
1. The sheared steel plate has an acceleration process. According to D'Alembert's principle, the belt conveyor will be subjected to a force that is the same as the shearing frequency and in the opposite direction to the running direction of the sheet.
2. Since the belt conveyor has a telescopic function, rollers cannot be used to support the middle part, and only a set of steel brackets are used to support the belt and steel plates. When the steel plate moves to this point, gravity causes the belt to sink, and the frictional resistance between the belt and the bracket increases. After the steel plate passes through, the frictional resistance decreases.
3. The processing quality of individual rollers is not high, the circular runout seriously exceeds the standard, and the dynamic balance is not good.
The frequency and size of the exciting force are affected by many factors such as the belt running speed, shearing times, workpiece quality, area, shape, belt conveyor extension, etc. When this frequency is close to the natural frequency of the belt conveyor, vibration will occur.
Second Topic: Problem Solving Methods
General solutions to avoid vibration are: (1) Eliminate the source of vibration, (2) Stay away from the maximum vibration area.
By adjusting the operating parameters of each part of the system, the machine can operate away from the natural frequency of the system to avoid vibration. Replace damaged bearings and adjust the balance of all rollers. This weakens and reduces the vibration source that causes the belt conveyor to vibrate.
Increasing the system stiffness can change the natural frequency of the system and improve the system's ability to resist deformation due to surge loads.
After research, adding support components to the front end of the belt conveyor has the best effect on improving system rigidity. However, the discharging belt conveyor has lifting requirements and cannot adopt a permanent fixed structure. Therefore, it was decided to use a pair of clamping hydraulic cylinders fixed on the press column to clamp the guide plate fixed on the belt conveyor body. The clamping force of the hydraulic clamping device is relied on to balance the force of the steel beam at the rear of the belt conveyor that causes the steel beam at the rear of the belt conveyor to deflect forward due to the acceleration of the workpiece in a very short time after being sheared. And provide damping force to prevent the belt conveyor from vibrating. This avoids vibration of the fuselage.
The third topic: specific solution for the clamping system
In order to ensure the rigidity of the clamping device, it is suitable for the limited space available for modification. It was decided to use a single-acting cylinder for the clamping device.
However, the single-acting cylinder cannot automatically reset after the piston is extended. When the height of the belt conveyor needs to be adjusted, even if the system pressure is removed, the front end surface of the piston is still attached to the surface of the guide plate. If foreign matter enters, it will affect the life of the lifting device. Therefore, a novel hydraulic circuit was researched and designed.
The above problems can be solved by using this hydraulic circuit. The hydraulic principle is as shown in the figure: 1.
1. When clamping, the pneumatic hydraulic pump absorbs oil through the filter and one-way valve, and injects oil into the liquid cylinder through the two-position four-way positioning electromagnetic reversing valve to clamp the liquid cylinder.
2. When relaxing, the pneumatic hydraulic pump sucks out the oil in the cylinder through the reversing valve, and drains the oil back to the tank through the left one-way valve. In this way, by controlling the reversal of the solenoid valve, the telescopic action of the single-acting hydraulic cylinder can be realized.
The hydraulic system has high requirements for oil cleanliness, so a filter is installed on the pipeline where the pneumatic hydraulic pump sucks oil from the tank. In order to prevent the oil from breaking through the filter at the moment of reversing and pressure relief, a one-way valve is installed in front of the filter. The drained oil is drained back to the tank through another reversely installed one-way valve. This not only prevents impurities in the fuel tank from entering the pipeline, but also allows the original and new impurities in the pipeline to be gradually discharged back to the fuel tank. In addition, installing filters and lubricators on the air supply end of the pneumatic hydraulic pump also plays a role in extending life and reducing failures.
The pneumatic hydraulic pump is powered by factory compressed air and relies on the area ratio of the gas-liquid piston to pressurize the oil to the required pressure. When the oil pressure and the air pressure are balanced, the work will be suspended automatically, and the pressure will be compensated by itself when the oil leaks. Through the different settings of the five-position two-way reversing valve itself, the functions of power enable, power stop, and gas self-control can be realized.
This system that uses this pump as the hydraulic source is compared with other systems that use motor-driven hydraulic pumps as the hydraulic source. It not only greatly reduces the investment in electrical systems such as motors, but also avoids energy losses caused by other methods when the motor starts and stops frequently or overflows. This reduces the difficulty of the control part and reduces the workload. Smaller fuel tanks can also be used, making the system more compact. At the same time, this system is safer because it does not need to provide the 380V voltage required by the motor and only provides 24V voltage for the solenoid valve and pressure relay.
The fourth topic: supporting electrical system
The basic electrical requirement is that the belt conveyor lifting operation is prohibited when the hydraulic system is in a clamping state. When designing the electrical part, the device is made independent of the electrical part of the original automatic line. Any failure of the device will not affect the normal operation of the automatic line. The PLC program is designed and compiled based on factors such as safety, efficiency, automation, ease of operation, and maintenance. The final functions are as follows:
1. The belt conveyor is in a clamped state, and lifting and lowering of the belt conveyor is prohibited.
2. Carry out the lifting operation of the belt conveyor, and the belt conveyor will automatically relax.
3. When the system is powered on, the clamping system automatically relaxes.
4. The clamping system automatically clamps when the entire line is linked.
5. The pressure relay is designed to prevent short circuit and open circuit.
6. The internal and external relays of the plc program apply anti-stick design respectively.
7. Install a freewheeling diode on the solenoid valve coil to extend the life of the relay contacts.
8. Clamping and loosening can be manually controlled at any time.
9. The positioning solenoid valve adopts pulse signal control to save energy and reduce consumption.
Conclusion
By using pneumatic hydraulic pumps, combined with novel oil circuit designs, and supplemented by appropriate PLC programs, this transformation is safe, energy-saving, environmentally friendly, and practical. The vibration problem of the belt conveyor was successfully solved, the stacking quality was improved, and the output of individual specifications of products was increased accordingly. It works stably and reliably after one and a half years of use. It is worthy of reference for related renovation projects.