Application of rare earth permanent magnets

The emergence and application of permanent magnet materials has a long history. Our Warring States Period (475 BC to 221 BC) people use natural magnetic iron ore mine polished into a desired shape to guide. In the past 100 years, with the rapid development of science and technology, permanent magnet materials have been continuously improved, and the emergence of new permanent magnet materials has promoted the improvement and development of permanent magnet devices. The demand for high-tech and promote the emergence of new permanent magnet materials. "So we can say, the development and application of new permanent magnet materials are the high-tech industry in a very important part of the rare earth permanent magnets, especially neodymium iron boron The emergence of a huge impact on the development of modern high-tech industries.

First, the impact of the progress of permanent magnet materials on permanent magnet devices

A permanent magnet material is a material that produces a constant magnetic field in a given space. The permanent magnets can be used alone or in combination with other ferromagnetic or non-ferromagnetic materials to form a magnetic circuit. The improvement of the performance of the permanent magnet material can make the device size smaller, which makes it possible to make various permanent magnet devices in the modern industry small, miniature, and lightweight. The maximum magnetic energy product (BH)max, one of the important characteristics of permanent magnet materials, describes the advancement of permanent magnet materials and the effects on magnetic devices.

The emergence of new materials always has new properties, such as the high coercivity of rare earth permanent magnet materials with other types of permanent magnet materials, which opens up a new class of uses and devices.

Second, the classification of permanent magnet materials application

There are many classification methods for the application of permanent magnet materials. The most basic method is to classify them from physical principles, such as the following:

(1) Electrical-mechanical conversion

1. Motor: DC motor, stepper motor, hysteresis motor, linear motor, servo motor, etc.;

2, generator

3. Transmission: magneto-optical recording, laser focusing, print head, VCM in computer disk drive, etc.

4, measuring instrument

5, current control: reed switch, eddy current motor overspeed switch.

(2) Electrical conversion

1. Sounding device: speaker, earphone, telephone, etc.

2. Receiving sound device: earpiece, ultrasonic broadcaster, etc.

3. Other audio converters.

(3) Magnetic-mechanical force or torque

1. Fixing or lifting device: various magnetic chucks (magnetic hanging), door suction blocks, refrigerator sealing strips, etc.

2, processing equipment: magnetic separation, copier magnetic roller.

3. Magnetic coupling and braking devices.

4. Magnetic bearings, maglev trains, etc.

5, electronic scale

(4) Microwave device, electron beam, ion beam focusing

1. Power tube: magnetron, periodic permanent magnet (PPM).

2, waveguide device

3, particle accelerator: synchrotron radiation source, free electron laser.

4. Mass spectrometer: deflection magnet, α-mass spectrometer, etc.

5. Cathode ray tube: ion trap, focusing, etc.

(5) Sensor, electrical signal transmission, transformation

1, the use of magnetic: Hall effect, magnetoresistance, temperature sensitive components.

2, the use of volume effects: position, speed, acceleration, liquid flow, pressure, vibration and so on.

3, the use of area effect: computer read and write heads.

(6) Medical and biological

1. Medical equipment: Magnetic resonance imaging (MRI).

2, dental appliances: fixed teeth, orthopedics.

3. Surgical instruments.

4, magnetic therapy and magnetic jewelry, etc.

(7) Other applications

1, magnetic pin

2, vacuum technology

3. Magnetic field storage bias field.

Rare earth permanent magnets are the latest and highest magnetic materials in permanent magnet materials and can be applied to all of the above fields in principle. The largest field of NdFeB in the Western world is the voice coil motor (VCM) in computer disk drives, accounting for 57% of the total. The largest areas of use in China are acoustics (27%) and motors (25%), which account for 5% and 17% respectively in the Western world. China's VCM magnets only account for: 1%.

This is because most of the NdFeB magnets produced in China are medium and low-grade products, which are suitable for audio and motor applications. The so-called horn magnets commonly used in the market are such applications. The magnetic steel used by VCM requires high performance: (BH)max>318.4kJ/m ³ (40MG0e), high processing precision, good product consistency and fast replacement. This product is also one of the positions held by US and Japanese rare earth permanent magnet manufacturers. Magnetic resonance imaging is another big area of NdFeB applications, and China has just started, with 11% in the Western world. In China, only units such as Shenzhen and Zhangjiagang are studying and trial-production, but no industry has yet been formed. China's oil field remover is 22%, which is the third largest application area, and the West is zero. This is related to the special composition of oil in China's oil fields, that is, the high content of wax. In short, China has its own characteristics in the application of rare earth permanent magnets, especially NdFeB permanent magnets.

Third, the typical example of rare earth permanent magnet application

(1) Audio device

Applications in audio include speakers, headphones, and more.

The magnetic circuit structure of the speaker is divided into two types: an internal magnetic type (using an Alnico magnet) and an external magnetic type (a multi-purpose ferrite is used as a magnet). When the rare earth permanent magnet is applied, it can be applied to both the inner magnetic type and the outer magnetic type, and the size and weight are greatly reduced. At present, some manufacturers of advanced audio equipment at home and abroad have introduced NdFeB speakers, and the electroacoustic performance has been greatly improved. China's large number of exported horn magnets are mainly used in high-performance stereo headphones.

(2) Oil field wax remover

China's oil contains more wax. During the process of extracting oil from the bottom of the earth, the oil contained in the crude oil is deposited in the oil well wall and the pipeline due to changes in the pressure and temperature of the oil. The suspension of production caused huge economic losses. The rare earth permanent magnet forms a magnetic circuit in a tube, and the crude oil is subjected to a magnetic field to effectively prevent the precipitation of the wax. This has greatly reduced the number of production stops of oil wells and increased production. This is currently one of the more important rare earth applications. In addition to the wax remover, there are oil well relics made of rare permanent magnets.

(three) motor

Rare earth motors have become one of the largest areas of rare earth permanent magnet applications, both domestically and abroad. It has a wide variety of shapes and performances. China has a high level in the development of rare earth motors. Individual varieties of motors, such as rare earth starter motors for light motorcycles, have reached the scale of production. Due to the appearance of rare earth permanent magnets, the size of permanent magnet motors is greatly reduced. The automotive industry is the largest potential application area for rare earth permanent magnet motors.

(4) Computer VCM magnet

The movement of the read/write heads in the computer hard disk and floppy disk drive is driven by the VCM, the voice coil motor. With the continuous advancement of computer technology and hardware, the shape and performance requirements of VCM magnets change frequently. The market currently requires (BH)m of the VCM magnet to be at a level of 318.4 kJ/m ³ (40 MGOe).

(5) Magnetic resonance imaging (MRI)

Magnetic resonance imaging uses the nuclear magnetic resonance nucleus generated by the hydrogen nuclear nucleus in the human body to measure the relevant parameters of the NMR magnetic field generated by the applied permanent magnetic field and the scanning field. The changes caused by the tissue condition and the condition of the human body can be displayed as the shade of the image. For the purpose of diagnosis. The magnetic field source has 1, superconducting magnet, 2, general electromagnet, 3, permanent magnet three. Permanent magnet type equipment has the advantages of minimum leakage flux, minimum footprint, and lowest operating cost, while the imaging quality is worse than that of superconducting type, which is better than electromagnetic type. In particular, the emergence of NdFeB magnets has further promoted the development of MRI, making it possible to further miniaturize permanent magnet MRI. When ferrite is used, the device weighs 100 tons, and with NdFeB, it is only 10 tons. At present, the MRI of NdFeB installed and used in the world has reached about 1,000.

At present, China has begun the development of rare earth permanent magnet MRI and made significant progress.

(6) Electron beam focusing, microwave device

The application of rare earth permanent magnets in the field of electron beam focusing is mainly in various accelerators, mass spectrometers and microwave devices. Due to the high ambient temperature of such use, Sm-Co rare earth permanent magnets are generally used. Typical applications are periodic permanent magnets (REPM), where electron beams or other particle beams are focused by magnets to change the direction of travel, and the like.

(7) Magnetic chucks and magnetic hangers

The domestic work on this aspect is at the international advanced level, independently developing the normal temperature and high temperature permanent magnet lifting hoist (lifting permanent magnet crane), especially the high temperature hanging in the continuous casting factory of Tonghua Iron and Steel Company of Jilin Province, lifting the hot slab It has been working for several years and it has been well reflected. There are also 10 national patents. The current problem is how to promote new products to practical applications.

(8) Magnetic separation

Mainly it refers to magnetic separation using a magnetic path of a certain rare earth permanent magnet of metal or non-metallic minerals, and various materials to be separated. The appearance of rare earth permanent magnets enhances the separation ability and efficiency of the magnetic separation device, and the volume is reduced. The relevant units in China have carried out a lot of work and have sold their products. They have been successfully applied to the separation of iron ore, mica and quartz , and the effect is very good.

(9) Instrument

The instrument is another widely used application field of permanent magnets, mainly including various magnetic and electromagnetic instruments. Such as current meters, voltmeters, electricity meters, speed and accelerometers and other conventional measuring instruments. Due to the appearance of rare earth permanent magnets, especially NdFeB magnets, the instrument achieves high precision and miniaturization.

(10) Other applications

China has made great progress in the application research and promotion of rare earth permanent magnets. In some aspects, it also has the characteristics of China, such as the use of magnetic coupling oil pumps, which solves the problem of the oil industry's dysfunction. The development and application of magnetic medical treatment for various diseases and magnetic jewelry, etc., is also a rare earth permanent magnet application with a wide influence.

Another important application area for rare earth permanent magnets is the magnetic levitation system. Magnetic suspension bearings have been successfully applied to ultra-high speed rotating devices and watt-hour meter bearings. In addition, it should be pointed out that a huge potential application area is the maglev train transportation system. Its research began in the 1970s and not in the early 1980s. The experimental line of the magnetic suspension bus system using rare earth permanent magnets has been operated in Berlin, Germany and Las Vegas, USA. Recently, according to the Science and Technology Daily, Germany has started an investment project involving 18 billion marks and established a magnetic levitation high-speed train. This project has been implemented. If the maglev train is put into commercial operation, it will greatly promote the higher-speed development of the rare earth permanent magnet industry. Such projects are only carried out in several developed countries with strong economic strength and high technological level.

The emergence of rare earth permanent magnets is a great advancement in the field of permanent magnet materials. In particular, the high performance of NdFeB rare earth permanent magnet materials makes it possible to make magnetic devices in high-tech industries more efficient, compact, and lighter. The use of magnetic devices in many fields where it was impossible to apply permanent magnet materials has opened up some new fields of permanent magnet applications. The research on new rare earth permanent magnet materials is becoming more and more extensive and extensive, and new materials will be developed in the near future. It is believed that with the expansion of the application of rare earth permanent magnet materials, a new era of high-tech applications of rare earth permanent magnets will be ushered in.

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