Scheme design of electromagnetic lifting system fo

Abstract: Based on the design idea of system integration, the composition principle of wide and thick steel plate electromagnetic lifting system is given, and several key problems in the overall design and unit design of the system are introduced; The constraints of the overall design of the system, the principles of the overall layout design and the measures taken, the design idea of the special linear electromagnet for high temperature resistance and the working principle of the electronic control subsystem are mainly discussed; Especially in the field of electromagnetic lifting technology, the concept of precise magnetic adjustment was introduced and put into practice in the design to play the role of market clearing; At the same time, an example of overall distribution and the design result of electromagnet are given

key words: electromagnet; Lifting technology; Wide and thick plate

wide and thick steel plate plays a very important role in the national economy and national defense construction; However, in the research and application of wide and thick plate lifting technology, China is still in its infancy. In order to meet the needs of a large engineering project, based on the design idea of system integration, the author has deeply studied the technical scheme of the wide and thick plate lifting system, and developed a prototype of the wide and thick plate electromagnetic lifting system

wide and thick plates are characterized by large and heavy. For example, the steel plate with overall dimension of 13000mmx4900mm x50mm weighs 25t. For general steel hoisting, one or several electromagnets are usually used for hoisting. However, for wide and thick plates, dozens of lifting units are required to work together, rather than a simple combination of a pile of electromagnets, which brings a series of special problems to the design of the electromagnetic lifting system, such as the rationality of the layout of electromagnets, the selection and collaborative work of group electromagnets, the need to meet the magnetic adjustment of different suspended objects, system safety protection and fault diagnosis, and so on. The author expounds this

1 system composition

lifting electromagnet is a DC electromagnet with the attracted object as the armature. The electromagnetic lifting system is formed by organically combining n electromagnets through the electric control system. The working principle of the electromagnetic lifting system is relatively simple. When working, according to the instructions of the upper network, the electric control system controls all or part of the electromagnets to work together to achieve the purpose of absorbing and releasing steel plates

the electromagnetic lifting system is composed of electromagnet, electronic control subsystem and mechanical components, as shown in Figure 1. The electric control main circuit is composed of PLC main control unit, transformer, controllable rectifier module and contactor. The PLC main control unit controls the controllable rectifier module to realize the magnetic adjustment of electromagnet, and the power on and power off selection of each suction cup is realized by the PLC controlled contactor. These main circuits constitute the magnetic regulation and magnetic preservation control panel and the automatic charging panel, together with the maintenance free battery pack, constitute a trinity of electronic control subsystem. The system can automatically switch and standby each other, and can realize constant charge, floating charge, automatic tracking and automatic adjustment

Figure 1 Composition of electromagnetic lifting system

2 constraints of system design

the design of electromagnetic lifting system includes overall design and unit design. The overall design includes target analysis and decomposition, overall layout design, determination of electric control principle, etc; Unit design includes mechanical subsystem design, electromagnet design, electronic control unit design, etc. When designing the electromagnetic lifting system, in addition to meeting the requirements of technical indicators, the following constraints should be mainly considered

1) suspended objects: ① meet the maximum load requirements (that is, the electromagnet load meets the requirements); ② Maximum and minimum overall dimensions of steel plate: length x width x thickness; ③ The material of steel plate (different materials have different permeability and saturated magnetic density, which affect the suction); ④ The temperature of the steel plate (affects the permeability and saturated magnetic density of the steel, and the deflection of the steel plate increases); ⑤ Deflection of steel plate; ⑥ Surface quality and oxide layer thickness of steel plate

2) lifting system itself: ① self weight of electromagnet; ② Safety factor>2; ③ Power on duration rate 60%; ④ System response time (suction and discharge time) 2a/(2 μ 0) (3)

where: F is electromagnetic force (n); B is the magnetic flux density at the working air gap (T); A is the effective adsorption area (M2); μ 0 is the permeability in vacuum (4 π xh/m)

according to formula (1), (2), the maximum electromagnetic force can be determined when the safety factor is taken as 2.5. According to formula (3), if the value of B is reasonably selected, the value of a can be determined, so the cross-section size of the coil core can be determined correspondingly

in order to ensure that the electromagnet can work normally at high temperature, the electromagnet is designed for high temperature resistance. The key point of the design is to not only emit the resistance heat generated by the internal coil, but also prevent the heat of the external steel plate from passing in. The measures taken include: using high temperature resistant electromagnetic wires; Increase thermal insulation layer and external conductive thermal resistance fault; Adopt anti radiation insulation layer; Increase the heat dissipation area and design the external heat dissipation air duct

since only a single steel plate is hoisted each time, and the specification of the steel plate varies widely, the electromagnet needs to output different electromagnetic forces for steel plates of different thicknesses. When not in use, the electromagnet needs to be covered with a dust cover to prevent the invasion of dust, so it is necessary to carry out stepless magnetic adjustment on the electromagnet. Therefore, the concept of "precise magnetic adjustment" is proposed, and the corresponding technology is developed. In order to realize stepless precise magnetic adjustment, the key for electromagnets is that the magnetic force curve FII of electromagnets should have a wide linear range under the condition of ensuring sufficient magnetic penetration depth [4]. Corresponding to the steel plate shown in Figure 2, under the condition that the steel plate temperature t=600 ℃, the designed special electromagnet adopts multiple coils and fully sealed welded rectangular steel plate structure. The basic parameters are: overall dimension 2700mmx240mmx320mm, rated lifting capacity 6.5T, safety factor k>2.5, working voltage DC 220V, protection grade IP54. This kind of electromagnet has relatively shallow permeability, good linearity, light weight and small power

2) consistency of electromagnet performance in order to ensure accurate magnetic adjustment and accurate lifting of the corresponding steel plate, it is required that the performance of groups of electromagnets has a high degree of consistency. For the electromagnet used in the same crane, the consistency of its electromagnetic performance is required to be 98%

3) consistency of electromagnet hanging height the connection between electromagnet and hanging beam adopts chain connection. The basic requirement for group electromagnets is to ensure that the bottom plane of the magnetic poles is in the same plane. This problem is a seemingly simple but very important problem in heavy plate hoisting. Because the thick steel plate is flat and not easy to deform, if the working surface of the magnetic pole is uneven and not on the same horizontal plane, it will inevitably cause the electromagnet lifting higher and lower to be equivalent to "sinking", which will not only not produce suction, but also "press" on the absorbed steel plate to form "negative suction". As a result, the total suction is significantly reduced. To this end, take measures: ① after the electromagnet is assembled, finish machining the bottom surface of the magnetic pole to ensure that the bottom plane of each electromagnet is flat; ② In order to ensure the consistent hanging height of the electromagnet, a height adjustable suspension device is adopted, which is a bolt mechanism. During on-site commissioning and installation, adjust the height of the group suction cups so that the bottom plane of the group electromagnet is in the same horizontal plane as far as possible

5 design of electronic control subsystem

1) working principle the program control of the system adopts Siemens s PLC main control unit (cpu226). Cpu226 is connected to the Profibus bus through DP interface module EM277 and communicates with the main PLC of the train. The man-machine interface adopts 254MM touch screen and SIMATIC protool configuration software for configuration. Each control function is displayed as a menu on the touch screen, and the control can be completed by simple touch; The touch screen is connected to the MPI interface of cpu226 through communication cable. In order to ensure the normal operation of the control system in case of power failure, the program control part of the system adopts UPS for power supply

the magnetic field regulation system adopts an intelligent three-phase fully controlled rectifier module, which integrates the main circuit with the trigger circuit. The system is equipped with voltage sensor and current sensor. The real-time detection module outputs voltage and current. The output of voltage sensor and current sensor is read into PLC through a/d module. PLC compares the output current value of the rectifier module with the given current value, and adjusts the d/a output according to the comparison result. The whole system has a closed-loop control of the working current, with high control accuracy, so as to ensure the stability of the suction of the electromagnet, so as to ensure the lifting in the set way. The magnetic regulation system is a logic non circulation reversible system. When magnetizing, the positive thyristor group is turned on, and the electric energy is fed to the electromagnet in the positive direction; During demagnetization, PLC first controls the positive group rectifier module to shift phase to the inverter state, and feeds back most of the electromagnet energy to electricity; When the PLC detects that the current value is 0, confirm that the positive rectifier module is turned off, and then trigger the conduction of the reverse rectifier module to demagnetize the electromagnet in reverse. The system cancels the forced demagnetization of the external resistor, which has fast magnetization and demagnetization, good demagnetization effect, and realizes contactless control

2) electromagnet selection controls the output of PLC, controls the power on and off of each electromagnet through the contactor, controls each electromagnet in three sections, and detects the working state of each electromagnet, and alarms immediately in case of any fault. Since the current regulating module only outputs current during lifting, all contactors can be controlled by PLC to turn on and off when the main circuit is dead. The contactor contacts are not easy to be damaged and have a long service life

3) the maintenance free battery is used as the backup power supply for the magnetic field protection system after power failure. The battery is automatically charged and floating by the automatic charging screen, and the main charge and floating charge can also be manually controlled by the button. The automatic charging screen automatically detects and alarms the undervoltage and overvoltage of the battery, realizes the automatic switching of floating charge and main charge according to the detection results, and activates and discharges the battery regularly. The automatic charging screen can automatically limit the charging current to prevent excessive current from damaging the battery. The system automatically tracks the main power supply and the speed control has a large error under low conditions, so as to ensure that the battery can be put into use automatically when the main power supply is powered off

4) the incoming power line of the system protection circuit is protected by an overvoltage automatic tripping circuit breaker, and the secondary of the transformer is protected by a fast fuse current limiting protection. If the circuit breaker trips or the fuse is blown during lifting, the accumulator (3) turn on the main power supply of the experimental machine in sequence, and the power battery of the computer and the display will be automatically put into operation to ensure safe lifting and send out an alarm at the same time

plc monitors the DC output voltage and current in real time through the voltage sensor and current sensor, and compares them with the given value. When the deviation from the limit value is too large (overvoltage or undervoltage), PLC automatically turns off the rectifier module output, and controls the battery to automatically put into operation. When multiple suction cups are used together, when an electromagnet fails and its current rises abnormally, the circuit breaker will automatically cut off the power supply of the electromagnet to avoid chain reaction and affect the work of other electromagnets, and send an alarm at the same time. The rectifier module has perfect resistance capacitance protection and varistor protection against lightning strike and surge voltage impact

6 conclusion

the lifting of wide and thick plates, especially the lifting of multi specification high-temperature wide and thick plates, is a very complex technical problem. There are not only the overall technical problems of the lifting system, but also the unit technical problems. Reasonable overall layout of electromagnet, high temperature resistant linear electromagnet, precise magnetic adjustment technology and contactless electric control system, as well as the retractable hanging beam not mentioned in the article, are all the technical keys. To solve the technical problems of wide and thick plate lifting, we should take the mature unit technology as the foundation, and use the viewpoint of system integration to comprehensively consider the mechanical, electromagnetic and electric control problems as well as the coupling problems between them

References:

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