Author: Source: machinery network, China
abstract
In this paper, the original vibration problems of equipment are analyzed and studied, the reasons are found out, and a series of solutions are formulated. The clamping mechanism is designed to improve the rigidity of the equipment, and a unique hydraulic circuit is designed for the clamping mechanism. Through this transformation, the equipment works smoothly, prolongs the service life of the equipment and improves the product quality, which is successful.
order
1830 uncoiling line has more than ten kinds of shearing dies and blanking dies. Due to the different sizes of various molds, a retractable belt conveyor with adjustable height and working speed and intermittent operation is installed between the blanking machine and the stacker. After years of use, it exists in:
The gap between each hinge and transmission pair of belt conveyor increases, and when the belt conveyor runs at high speed, the fuselage vibrates seriously.
When the mass of stamping workpiece is more than 25kg, the plate is cut faster in a very short time, and the surge momentum urges the supporting steel beam to lean forward, resulting in the reduction of the center distance between the driving motor shaft and the main shaft. Because the tensioner of loose edge of synchronous belt is fixed, it can't automatically compensate the loose edge of synchronous belt caused by the decrease of center distance, which leads to tooth jumping of synchronous belt.
The above problems seriously reduce the life of discharge belt, synchronous belt and bearing. At the same time, the output workpiece is deviated, which affects the stacking quality.
theme
The first topic: vibration cause analysis
Through research, it is found that the main cause of vibration is the insufficient rigidity of the rear main beam and the front lifting mechanism of the belt conveyor, and the large gap between each hinge, rack and transmission pair. The mechanism is forced to vibrate under the action of exciting force. The main sources of exciting force are:
1. Cutting steel plate has an accelerated process. According to D'Alembert's principle, the belt conveyor will be subjected to a force with the same shear frequency and the opposite direction to the running direction of the plate;
2. Because the belt conveyor has telescopic function, the middle part cannot be supported by rollers, and only a group of steel brackets are used to support the belt and steel plate. When the steel plate runs there, gravity makes the belt sag and the friction resistance between the belt and the bracket increases. After the steel plate passes through, the friction resistance decreases.
3. The processing quality of individual rollers is not high, the circular runout is seriously out of standard, and the dynamic balance is not good.
The frequency and magnitude of exciting force are influenced by many factors, such as belt running speed, shearing times, workpiece quality, area, shape, belt conveyor drape and so on. When the frequency approaches the natural frequency of the belt conveyor, * * vibration will occur.
The second topic: the solution to the problem
General solutions to avoid vibration are: (1) eliminating the vibration source, and (2) staying away from the * * * vibration zone.
By adjusting the operation parameters of each part of the system, the operation of the machine is far away from the natural frequency of the system and the vibration is avoided. Replace damaged bearings and balance all rollers. This weakens and reduces the vibration source that makes the belt conveyor vibrate.
Increasing the stiffness of the system can change the natural frequency of the system and improve the ability of the system to resist deformation caused by impact load.
Through research, adding support members at the front end of belt conveyor has the best effect on improving the system stiffness. However, the unloading belt conveyor has lifting requirements and cannot adopt a permanent fixed structure. Therefore, it is decided to clamp the guide plate fixed on the belt conveyor body with a pair of clamping hydraulic cylinders fixed on the pressure column. Depending on the clamping force of the hydraulic clamping device, because the workpiece is accelerated in a short time after cutting, the forward deflection force of the steel beam at the back of the belt conveyor is balanced. And provides damping force to prevent the belt conveyor from starting to vibrate. Thereby avoiding the vibration of the fuselage.
The third topic: the concrete scheme of clamping system
In order to ensure the rigidity of the clamping device, it is suitable for reconstruction in places with limited space. It is decided to use a single-acting cylinder as the clamping device.
However, the piston of a single-acting cylinder cannot be automatically reset after it is extended. When the height of the belt conveyor needs to be adjusted, even if the system pressure is removed, the front end face of the piston still sticks to the surface of the guide plate. If foreign objects enter, it will affect the life of the lifting device. Therefore, a new hydraulic circuit is designed. This hydraulic circuit can solve the above problems. Hydraulic principle is shown in the figure: 1.
1. When clamping, the pneumatic hydraulic pump sucks oil through the filter and one-way valve, and injects oil into the hydraulic cylinder through the two-position four-way electromagnetic directional valve with positioning, so as to clamp the hydraulic cylinder.
2. When relaxing, the pneumatic hydraulic pump sucks out the oil in the cylinder through the reversing valve and discharges the oil back to the oil tank through the left one-way valve. In this way, by controlling the commutation of the solenoid valve, the telescopic action of the single-acting hydraulic cylinder can be realized.
The hydraulic system requires high cleanliness of oil, so the pneumatic hydraulic pump is equipped with a filter on the pipeline that sucks oil from the oil tank. In order to prevent oil from breaking through the filter at the moment of reversing pressure relief, a check valve is installed in front of the filter. The discharged oil is discharged back to the oil tank from another one-way valve installed in the opposite direction. In this way, the impurities in the oil tank are prevented from entering the pipeline, and the original and new impurities in the pipeline can be gradually discharged back to the oil tank. In addition, installing a filter and an oil mist device at the air supply end of the pneumatic hydraulic pump also plays a role in prolonging the service life and reducing the faults.
Pneumatic hydraulic pump is powered by compressed air in the factory, and pressurizes the oil to the required pressure through the area ratio of gas-liquid piston. When the oil pressure and air pressure are balanced, the work will be suspended automatically, and the pressure can be replenished automatically when oil leaks. Through the different settings of the additional two-position five-way reversing valve, the functions of energizing, stopping energizing and controlling the air source can be realized.
Compared with other systems that use motor-driven hydraulic pump as hydraulic source, this system uses this pump as hydraulic source. It not only greatly reduces the investment in the electrical system of the motor, but also avoids the energy loss caused by frequent start-stop or overflow of the motor in other ways. Thereby reduce that difficulty of the control part and reducing the workload. You can also use a smaller oil tank to make the system more compact. At the same time, because there is no need to provide 380V voltage required by the motor, only 24V voltage is provided for the solenoid valve and pressure relay, so the system is more secure.
The fourth theme: supporting electrical systems
The basic electrical requirement is that the lifting operation of the belt conveyor is prohibited when the hydraulic system is in the clamping state. When the electrical part is designed, the equipment is independent of the electrical part of the original automatic line, and any fault of the equipment will not affect the normal work of the automatic line. The PLC program is designed and written by integrating safety, efficiency, automation, convenient operation, maintenance and other factors. The final function is as follows:
1. The belt conveyor is in a clamping state, and the lifting operation of the belt conveyor is prohibited.
2. When the belt conveyor is lifted, the belt conveyor will automatically relax.
3. When the system is powered on, the clamping system will automatically relax.
4. When the whole line is connected, the clamping system automatically clamps.
5. Anti-short circuit and open circuit design of pressure relay.
6.6. The internal and external relays of PLC program adopt anti-sticking design.
7. Install a freewheeling diode on the solenoid valve coil to prolong the life of relay contacts.
8. The clamping can be released manually at any time.
9. The solenoid valve with positioning is controlled by pulse signal, saving energy and reducing consumption.
conclusion
Through the use of pneumatic hydraulic pump, combined with novel oil circuit design, supplemented by appropriate PLC program, this transformation is safe, energy-saving, environmentally friendly and practical. The vibration problem of belt conveyor is successfully solved, the stacking quality is improved, and the output of single specification is correspondingly increased. It has been used for a year and a half, and the work is stable and reliable. It is worthy of reference for related reconstruction projects.
(Ying Wensheng)