Classification and main application of rare earth permanent magnetic materials
I. Classification of rare earth permanent magnetic materials
î™–î™– 1. Rare earth cobalt permanent magnetic materials, including rare earth cobalt (1-5 type) permanent magnet material SmCo5 and rare earth cobalt (2-17 type) permanent magnet material Sm2Co17 two major categories.
î™–î™–2. Rare-earth permanent magnet materials, NdFeB permanent magnet materials.
î™–î™–3. Rare earth iron nitrogen (RE-Fe-N) or rare earth iron (RE-Fe-C) permanent magnet materials.
Second, rare earth permanent magnet material preparation process classification
î™–î™– 1. Sintered magnets prepared by powder metallurgy sintering process;
î™–î™–2. Reducing diffusion or hydrogen crushing powders and sintered magnets prepared by powder metallurgy sintering;
î™–î™–3. Rapid solidification or HDDR (HDDR), bonded magnets prepared by powder moulding bonding process;
î™–î™– 4. Injection magnet prepared by rapid solidification powder or hydrogen powder (HDDR) injection process;
î™–î™–5. Hot-pressed magnet prepared by hot-pressing of rapidly solidified powder or hydrogen crushed (HDDR) powder;
î™–î™–6. Anisotropic hot deformation magnets prepared by a hot compression magnet followed by a hot deformation process;
î™–î™–7. The heat-deformed magnets are milled into powders and then anisotropic bonded magnets are prepared by molding or injection.
Third, the main application of rare earth permanent magnet materials
The most basic role of a permanent magnet is to create a constant magnetic field in a particular space. Maintaining this magnetic field does not require any external power supply. There are many parameters that mark the quality of permanent magnetic materials. The most important is the maximum energy product (BH)max. The larger the magnetic energy product, the greater the energy of the external magnetic field generated per unit volume of the material. At present, the maximum energy product of the commercial NdFeB permanent magnetic material has reached 50 MGOe. Due to the high magnetic energy product and high coercive force of rare earth permanent magnet materials, it has brought revolutionary changes to permanent magnet applications. The rare earth permanent magnetic materials are mainly used in the following aspects:
1. Electromechanical
The emergence of rare earth permanent magnets means that the field of motors will cause revolutionary changes. This is because rare-earth permanent magnets have no excitation loss and no heat generation, and motors made with them have many advantages. Since the rare earth permanent magnet motor does not have an excitation coil and a core, the magnet has a smaller volume than the original magnetic field, no loss, no heat, so in order to obtain the same output power, the weight can be reduced by more than 30%, or the same volume , weight, output power greater than 50%.
Permanent magnet motors, especially micro-motors, produce as many as several hundred million units each year in the world and are used mainly in automobiles, office automation equipment and household appliances. Most of the high-performance ferrites and rare earth permanent magnets are used.
One of the largest markets for rare earth permanent magnet motors in the future will be the automotive industry. NdFeB permanent magnet materials have excellent performance and are used to make motors. They can realize "Neodymium Iron Boron" for automotive motors. In the automotive industry, only with a small motor, can reduce the weight of the car, increase comfort, improve safety, reduce exhaust emissions, improve the overall performance of the car, the largest amount of the current starter motor. Motors are indispensable components in automobiles, and the number of motors in automobiles is increasing year by year. There are 8 to 18 cars in general cars, and as many as 40 to 50 limousines. With the development of the automotive industry, the demand for automotive motors is enormous. The high energy product rare earth permanent magnets have a small volume but can generate much more power than ferrites, thus increasing the electrical efficiency. By using rare earth magnets to reduce weight and size, more fuel can be saved and design flexibility increased.
2. Application of rare earth permanent magnetic material in medical treatment
3. Magnetic separator
General magnetic separators are of the permanent magnet type and the electromagnetic type. In the past, permanent magnet type magnetic separators used ferrite magnets. After the appearance of rare earth permanent magnets, various types and types of permanent magnet magnetic separators have been designed and manufactured. Especially in medium-high magnetic field magnetic separators, rare earth permanent magnets must be used.
4. Computers and Peripherals
The most rare earth permanent magnet material used in computers is the disk drive motor (VCM), and the other is the data output printer motor.
5. Various instruments
There are many kinds of instruments using permanent magnets, such as magnetoelectric meters and counters.
6. Speakers and headphones
Speakers and headphones are traditional applications of permanent magnets. There are two kinds of external magnetic speakers and internal magnetic type. After rare earth permanent magnets appear, the loudspeakers are made very small under the same output power and sound quality. At present, rare earth permanent magnet loudspeakers and earphones have been applied to advanced walkmans.
7. Microwave device
In the microwave field, microwave tubes, milliwave tube generators, or amplifiers require a stable magnetic field. The rare earth permanent magnets mainly act as an aggregation of electron motions.
Current status and future development trend of rare earth permanent magnetic materials
In recent years, the application of rare earth permanent magnetic materials in China has developed rapidly. At present, it has been used in general motors, large motors such as magnetic pumps, magnetic separation equipment, permanent magnet cranes and household appliances. However, compared with Western countries, NdFeB magnets produced in China, including exports, are the most used acoustic devices (China is the world’s largest producer of loudspeakers, and nearly half of NdFeB is used to make loudspeakers), followed by Motor and oil well wax remover. In areas with the most foreign volume such as voice coil motors, there are few applications in China. The reason is that the magnets used in these two application fields not only require high magnetic performance, good uniformity and consistency, but also require high processing precision and good coating quality. The products of most domestic manufacturers are difficult to meet the above requirements. Therefore, generally only mid-range and low-grade products can be produced to meet the general requirements for use. The price of the magnets is also far lower than the price of neodymium iron boron in the international market.
In Japan, sintered rare earth magnets are mainly used in voice coil motors (VCM) on computer hard disk drives, followed by rare earth bonded magnets in computers, such as CD-ROM spindle motors, etc.
In 1994, the use of such magnets in computers accounted for about half of the total usage.
Japan's NdFeB production is supported by only a few large plants, while 70% of its production in China is provided by a neodymium-iron-boron plant with an annual output of less than 30 tons. Therefore, China can only supply NdFeB with a magnetic energy product of 28-40 MGOe. , while the Japanese brand NdFeB can reach 50 MGOe level. By the end of this century, NdFeB, which has a magnetic energy product of 55 MGOe, will be commercialized, so the difference in sales price can be up to 8 times. The gentrification of NdFeB production products in China should be the top priority for NdFeB production.
The prospect of NdFeB is very broad. Since the potential market for NdFeB is still promising, the number of permanent magnet motors in each car will increase from 20 in 1995 to 31 in 2005. It is expected that by the year 2005, bonded magnets used in automobiles will reach 12,000 tons/year. Annual growth rate reached 64%. With the rapid growth of computer production, the number of NdFeBs used is also large. Another potential market is the widespread use of MRI in the next world. These applications will maintain the rapid growth of NdFeB production.
Looking into the 21st century, the sales of personal computers will continue to grow by 20% in Western countries, while the growth of computer demand in China will far exceed the growth rate of 20%. Therefore, the demand for NdFeB applications on VCM will grow exponentially. The application of NdFeB permanent magnets to hard drives and other motors in computers should be an important direction for the development of NdFeB permanent magnets.