neodymium magnet

In the application field of NdFeB magnets, there is a close relationship between the magnetism and temperature. When the temperature of the magnet exceeds a certain threshold, permanent demagnetization will occur, and the maximum operating temperature that different grades of NdFeB magnets can withstand varies.   Curie temperature   When studying the effect of temperature on magnetism, "Curie temperature" is a key concept. The naming of this term is closely related to the Curie family. In the early 19th century, the famous physicist Pierre Curie discovered in his experimental research that when a magnet is heated to a certain temperature, its original magnetism will completely disappear. Later, people named this temperature Curie point, also known as Curie temperature or magnetic transition point.   From a professional definition, Curie temperature is the critical temperature at which magnetic materials achieve the state transition between ferromagnetic and paramagnetic materials. When the ambient temperature is lower than the Curie temperature, the material exhibits ferromagnetic properties; when the temperature is higher than the Curie temperature, the material turns into a paramagnet. The height of the Curie point mainly depends on the chemical composition and crystal structure characteristics of the material.   When the ambient temperature exceeds the Curie temperature, the thermal motion of some molecules in the magnet intensifies, the magnetic domain structure is destroyed, and a series of ferromagnetic properties such as high magnetic permeability, hysteresis loop, magnetostriction, etc. associated with it will disappear, and the magnet will undergo irreversible demagnetization. Although the demagnetized magnet can be re-magnetized, the required magnetization voltage is much higher than the first magnetization voltage, and after re-magnetization, the magnetic field strength generated by the magnet is usually difficult to restore to the initial level.   Material Curie temperature Tc (℃) Maximum operating temperature Tw (℃) NdFeB 312 230   Working Temperature   Refers to the temperature range that the neodymium magnet can withstand during actual use. Due to the differences in thermal stability of different materials, the corresponding operating temperature range is also different. It is worth noting that the maximum operating temperature of neodymium is significantly lower than its Curie temperature. Within the operating temperature range, as the temperature increases, the magnetic force of the magnet will decrease, but after cooling, most of the magnetic properties can be restored.   There is an obvious positive correlation between Curie temperature and operating temperature: Generally speaking, the higher the Curie temperature of a magnetic material, the higher its corresponding upper limit of operating temperature, and the better its temperature stability. Taking sintered NdFeB material as an example, by adding elements such as cobalt, terbium, and dysprosium to the raw materials, its Curie temperature can be effectively increased, which is why high coercivity products (such as H, SH, etc. series) generally contain dysprosium.   Even for the same type of magnet, different grades of products have different temperature resistance due to differences in composition and microstructure. Taking NdFeB magnets as an example, the maximum operating temperature range of different grades of products is roughly between 80℃ and 230℃.   Working temperature of sintered NdFeB permanent magnets Coercivity Level Max Working Temperature N Normal 80 ℃ M Medium 100 ℃ H High 120 ℃ SH Super High 150 ℃ UH Ultra High 180 ℃ EH Extremely High 200 ℃ AH Aggressively High 230 ℃   Factors affecting the actual working temperature of NdFeB magnet   Shape and size of neodymium magnets: The aspect ratio of the magnet (i.e., the permeability coefficient Pc) has a significant impact on its actual maximum operating temperature. Not all H-series NdFeB magnets can work normally at 120°C without demagnetization. Some magnets of special sizes may even demagnetize at room temperature. Therefore, for such magnets, it is often necessary to increase their actual maximum operating temperature by increasing the coercivity level.   The degree of closure of the magnetic circuit: The degree of closure of the magnetic circuit is also an important factor affecting the actual maximum operating temperature of the magnet. For the same magnet, the higher the degree of closure of its working magnetic circuit, the higher the maximum operating temperature it can withstand, and the more stable the magnet performance. It can be seen that the maximum operating temperature of the magnet is not a fixed value, but will change dynamically with the change of the degree of closure of the magnetic circuit.    

The biggest risk in the use of permanent magnet motors is demagnetization caused by high temperature. As we all know, the key component of permanent magnet motors is neodymium magnet, and neodymium magnet is most afraid of high temperature. It will gradually demagnetize under high temperature for a long time. The higher the temperature, the greater the risk of demagnetization.   Once a permanent magnet motor loses its magnetism, you basically have no choice but to replace the motor, and the cost of repair is huge. How do you determine whether a permanent magnet motor has lost its magnetism?   1. When the machine starts running, the current is normal. After a period of time, the current becomes larger. After a long time, the inverter will be reported to be overloaded.   First, you need to make sure that the inverter selected by the air compressor manufacturer is correct, and then confirm whether the parameters in the inverter have been changed. If there are no problems with both, you need to judge by back electromotive force, disconnect the head from the motor, perform no-load identification, and run no-load to the rated frequency. At this time, the output voltage is the back electromotive force. If it is lower than the back electromotive force on the motor nameplate by more than 50V, it can be determined that the motor is demagnetized.     2. After demagnetization, the running current of permanent magnet motor will generally exceed the rated value.   Those situations where overload is reported only at low or high speed or occasionally reported, are generally not caused by demagnetization.   3. It takes a certain amount of time for a permanent magnet motor to demagnetize, sometimes several months or even one or two years.   If the manufacturer selects the wrong model and causes current overload, it does not belong to motor demagnetization.   An important indicator of permanent magnet motor performance is the high temperature resistance level. If the temperature resistance level is exceeded, the magnetic flux density will drop sharply. The high temperature resistance level can be divided into: N series, resistant to more than 80℃; H series, resistant to 120℃; SH series, resistant to more than 150℃. The motor's cooling fan is abnormal, causing the motor to overheat. The motor is not equipped with a temperature protection device. Ambient temperature is too high. Improper motor design.

When choosing a magnetic filter to fit the different shapes of injection molding machines and extruder hoppers, there are several key factors to consider:   1. Hopper shape and size: First, the shape and size of the magnetic filter should match the hopper of the injection molding machine or extruder. For hoppers of different shapes, such as round, square, or other special shapes, the design of the magnetic filter also needs to be adjusted accordingly to ensure that it can fit tightly on the hopper and effectively capture iron impurities.   2. Magnetic strength: The magnetic strength of the magnetic filter is an important consideration when choosing. The magnetic strength should be strong enough to adsorb and capture iron impurities in the hopper, but not too strong to avoid damage to the hopper or the magnetic frame itself. Therefore, when choosing a magnetic filter, it is necessary to determine the appropriate magnetic strength based on the type and amount of iron impurities that may be present in the hopper. All the magnetic filters produced by our factory are made of neodymium magnet material, with magnetic field strength ranging from 8000-14000GS, which can be applied to different needs.   3. Use environment: The working environment of the injection molding machine and extruder may be different, such as temperature, humidity, and dust. Therefore, when choosing a magnetic filter, it is necessary to consider whether it can work properly in this environment. For example, for high temperature or high humidity environments, you should choose a magnetic stand that is resistant to high temperatures and waterproof and moisture-proof!   4. Maintenance and cleaning: The magnetic filter may require regular maintenance and cleaning during use. Therefore, when choosing a magnetic filter, the convenience of its maintenance and cleaning should be considered. For example, some magnetic filters may be designed to be easy to disassemble and clean, which will help reduce maintenance time and costs.   In summary, when choosing a magnetic filter with different hopper shapes for injection molding machines and extruders, it is necessary to consider multiple factors such as hopper shape and size, magnetic strength, use environment, and convenience of maintenance and cleaning.    Communicating with a permanent magnet supplier when choosing a magnetic rack is recommended to ensure that the selected magnetic filter can meet the actual production needs.