Magnetic coupler and its precautions in cement production applicationsDate: 2019-06-25 Views:
1 The composition and working principle of the magnetic coupler
The magnetic coupler is also called a magnetic coupling, and is mainly composed of a magnetizer connected to the shaft end of the motor and a permanent magnet connected to the load end. In operation, according to the principle of eddy current induction, the relative motion of the above two parts generates a magnetic field, and thus eddy current is generated in the disc-shaped conductor, and the magnetic field generated by the eddy current and the magnet attract each other, thereby causing the rotor and the conductor to pass through the air. The gap transmits torque so that the motor and load are converted from the original hard connection to a soft connection , as shown in Figures 1 and 2.
According to the above principle, in recent years, different types of magnetic couplers such as delay type, torque limit type and speed control type have been developed in China. Ltd. In recent years, with the development of technological innovations such as energy-saving and consumption reduction and internal potential tapping of cement enterprises, such as magnetic couplers and dynamic harmonic energy-saving devices, they have gradually been applied and promoted in the cement industry.
2 Magnetic coupler compared with other transmission equipment
Through statistical and practical application analysis, the magnetic coupler and other types of coupling methods are analyzed and compared for their characteristics and maintenance costs, as shown in Table 1.
Compare the performance and energy efficiency of the magnetic coupler with other energy-saving transmission devices, as shown in Table 2.
Through the above content and list analysis, the disadvantages of the types of transmission equipment such as elastic couplings, slip devices and hydraulic couplers are not repeated here. The advantages of the magnetic coupler are mainly reflected in the following aspects:
1) The drive motor current is reduced, and the energy saving effect is remarkable. With a magnetic coupler, the magnetic coupler is the most efficient, whether it is the energy efficiency of a single device or the total energy efficiency of the system. Therefore, the use of magnetic couplers will reduce energy consumption and save operating and maintenance costs for cement production line equipment.
2) After using the magnetic coupler, the vibration of the equipment can be greatly reduced and the service life of the motor and its bearings can be extended. The magnetic coupler transmits torque through the air gap and is a true contactless connection. This connection method can make the connection stress of the equipment more uniform, the alignment performance is better, and the bearing capacity is greatly enhanced. By testing, the use of a magnetic coupler can reduce vibrations by more than 80%.
3) After the magnetic coupler is used, the flexible start of the device (ie soft start) can be well realized, and the motor and the load can be well protected.
4) The use of a magnetic coupler can reduce the failure rate. Since the magnetic coupler transmits torque through the air gap, there is no wear parts, and basically no fault occurs, which reduces the failure rate and greatly reduces downtime.
5) The magnetic coupler has overload protection function, which improves the safety and reliability of the system operation. The hydraulic coupler commonly used in cement enterprises is protected by overload by means of fuel injection and pressure relief. This type of overload protection not only pollutes the environment, but also increases repair time and maintenance costs.
6) The magnetic coupler has a simple structure, no lubrication, no pollution damage to the environment, and is a green product.
7) For equipment with narrow speed regulation range, such as high temperature fan, it can also adjust the air gap between the two parts of the magnetic coupler to achieve stepless speed regulation of the load.
3 Magnetic coupler selection and attention
1) The magnetic coupler is a partially standardized product. At the beginning of the selection of the coupling, it is possible to understand whether there are types of national standards, mechanical industry standards and couplings that have obtained national patents. If the coupling cannot find the type of adaptation, you can contact the manufacturer to design the coupling product yourself.
2) The torque of the magnetic coupler should meet the requirements of the powertrain of the transmission system. According to the power and speed of the power machine and the working machine, the reasonable torque value of the coupling can be calculated to select the coupling power model.
3) After the primary selection of the magnetic coupler, the size of the coupling should be determined according to the shaft diameter and the length of the shaft hole of the driven shaft and the driven shaft, and the specifications of the coupling should be adjusted. Coupling model adjustment also considers whether the speed between the drive shaft and the driven shaft connected to the coupling is the same, and the shaft diameter is the same.
4) Select the magnetic coupler. Finally, we must comprehensively consider various factors to ensure that the size, torque, shaft diameter and shaft hole of the coupling are matched with the motor and reducer, and can adapt to the corresponding working environment. After the coupling is selected, check the shaft key strength and finalize the coupling model.
5) For the load characteristics driven by the equipment and the soft start characteristics of the magnetic coupler, the selection of the magnetic coupler should be cautious. Such as hoist load, limestone conveyor belt conveyor, clinker zipper and other heavy-duty equipment, especially the design department to reduce the installed capacity, the power reserve is small when driving equipment selection, often encounter failure to stop after the normal start In this case, for the case of this type of magnetic coupler, the torque-type magnetic coupler should be selected as much as possible, and the power should be larger.
6) Using frequency conversion speed control equipment, try not to use magnetic coupler. This is because the mechanical characteristics of the frequency conversion equipment are soft at low frequency, coupled with the flexible starting characteristics of the magnetic coupler, it is easy to cause the motor to stall, resulting in failure equipment. Start again.
4 magnetic coupler in practical applications
1) The magnetic coupler supports the motor to rotate in any direction. Whether it is the first time the newly built enterprise commissions the equipment, or the modification of the coupling such as the hydraulic coupler in use, in order to avoid damage to the equipment, the test machine firstly moves the motor to confirm that the steering is correct before the equipment can be tested. Under normal circumstances, the low-voltage motor is allowed to start twice in the cold state, and the interval time must not be less than 5 min. It is allowed to start once in the hot state; the high-voltage motor is allowed to start once in the hot state, and the time interval is not less than 240 min, in the cold state, it is allowed to start 2 times, each time interval should not be less than 60 min.
2) When using a magnetic coupler, it should be properly considered that its ambient temperature cannot be too high. This is because the magnetic coupler uses the principle of eddy current induction. Under normal circumstances, the loss generated by the eddy current is released from the magnetizer in the form of heat, causing the temperature of the working environment of the permanent magnet to rise. Therefore, the magnetic coupler shield on the production site should be well ventilated to avoid heat accumulation.
3) Using magnetic couplers, it is necessary to ensure that all kinds of interlocking signals of the host equipment are safe and reliable, such as the interlock protection between the speed measuring signal of the tail wheel of the hoist and the driving motor, and the protection of the chain jump between the equipment and the upper processing equipment. After the magnetic coupler is overload protected, the host equipment that installs the magnetic coupler will stop running. If the superior process equipment cannot be chained and stopped, it will cause the hoist to press the material and the material to slip.
4) If the load end stops due to overload or equipment failure, and the speed measurement of the tail wheel of the hoist and other equipment happens to be damaged, the motor will run normally, and the power generated by the eddy current will work for all or most of the magnetizer, resulting in The working temperature of the permanent magnet rises rapidly. When the temperature rises above the allowable temperature of the permanent magnet, the magnetic properties will decrease as the temperature rises. When the temperature rises to the critical point of permanent magnet failure, the magnetic coupler will "Magnetic loss" and stop working. Therefore, in the production, one is to avoid overloading the equipment as much as possible; the other is to install the speed detection and protection device on the head and tail wheels of the equipment to prevent the occurrence of the event of the damaged equipment.
5) From another point of view, in order to avoid the phenomenon of “magnetism loss” in the magnetic coupler, the air guide vane or air guiding hole should be considered from the beginning of the design of the device. In addition, when the magnetic coupler is overload protected, The gap between the two parts can be designed to be larger, so that the electric flux of the electric conductor is greatly reduced, and the amount of heat generated is relatively reduced. In this way, even if the speed detection protection is not in place, it will not damage the equipment and affect normal production.
With the development of technology and the maturity of products, it is believed that the energy-saving and environmental protection equipment such as magnetic couplers will be widely promoted and applied in many cement enterprises.