NdFeB permanent magnet and its application trends in the motor

- Nov 17, 2017 -

l. Introduction

In 1983, Sumitomo Special Metals Corporation of Japan and General Motors Corporation of the United States independently developed rare earth neodymium iron boron (ndfeb) permanent magnet, the maximum energy product (bh) max reached 286. 6kj / m3 [1] The third generation of rare earth permanent magnet materials after cobalt permanent magnet (smc05 and sm2c017).

ndfeb magnet not only magnetic properties than sm2c017 more excellent, but also rich in raw materials. It is not expensive scarce strategic materials cobalt (co) and reserves of scarce sama (sm), cheap iron (fe) on behalf of cobalt, with a wealth of neodymium (nd) on behalf of samarium, so the price is lower than samarium cobalt permanent magnet, Market competitiveness, easy to widely promote the application. At the same time, ndfeb high energy product, the need for less, processing performance, can be cutting and drilling, high yield, it can reduce the size of permanent magnet motor, reduce costs, improve efficiency and save energy, has caused the motor industry Close attention. This paper describes the magnetic properties of NdFeB and NdFeB permanent magnet materials in the motor application trends.

2. NdFeB magnetic properties of magnetic materials

The development of permanent magnet motor is closely related to the continuous appearance of new permanent magnet materials. ndfeb excellent magnetic properties of permanent magnet Magnetic properties to urge people to further research and development of new varieties, and thus in just a few years, ndfeb magnet new varieties continue to emerge, and its performance has been improved. In 1985, Japan's Sumitomo Corporation in the laboratory to develop ndfeb magnetic maximum magnet

Energy product (bh). . Reaching 3 98kj / m3, remanence br is 1. 45t, coercivity bhc 636. 8ka / m [2].

Rare earth resources in our country is very rich, its reserves account for 80% of the world. The annual output of raw material products is nearly 30000 tons, accounting for 70% of the world. Annual exports of 80,000 t, the world's total trade volume of 35%. Therefore, China's research and development of rare earth permanent magnet materials, with unique development conditions. At present, China's small batch production of ndfeb permanent magnet magnetic energy product has reached 318. 4kj / m3 [2].

China attaches great importance to the development of NdFeB research. Baotou Rare Earth Research Institute and other units of scientific research personnel, after 3 years of arduous tackling the problem, the use of domestic equipment and advanced low oxygen technology test, the development of NdFeB permanent magnet has been a major breakthrough in 1990 by the China Institute of Metrology, Developed bulk sample magnetic energy product above 390. 04mj / m3, the highest reached 415. 512kj / m3, exceeding the so far published in Japan 402. 776kj / m3 international advanced level, ranking the world leader.

2.1 NdFeB permanent magnet excellent magnetic properties

Currently, a variety of permanent magnet motor permanent magnetic materials commonly used energy product, ferrite 14. 328 ~ 36. 616kj / m3. Al-Ni-Co was 39. 8 ~ 95 52kj / m3, smc05 127. 36 ~ 183 08kj / m3, the highest value of the test up to 227.7kj / m3; sh12c017 109.2 ~ 238 8kj / m3, the highest value of the test 2 6 3 kj / m3; ndfeb 238.8 ~ 318 4kj / m3, the highest value of 415. 5kj / m3. Obviously, in a variety of permanent magnetic materials, NdFeB magnetic energy product is the highest.

4kj / m3. Neodymium iron boron permanent magnet material maximum energy product (bh) max theoretical value up to 525. 4kj / m3. Experts predict that by 1995 there will be (bh) max up to 477. 6kj / m3 NdFeB permanent magnets appear.

NdFeB magnet remanence br and coercive force hc are high, the product of NdFeB br is 1.02 ~ 1. 25t, up to 14. 8t, about 3 to 5 times the ferrite magnet , About Alnico, SmCo permanent magnet 1 to 2 times. NdFeB magnetic induction coercive force bhc 764.2 ~ 915ka / m, intrinsic coercivity mhc 876 ~ 1671 6ka / m, up to 2244. 7ka / m, equivalent to ferrite 5 to 10 times , Cast aluminum nickel and cobalt 5 to 15 times. Neodymium iron boron permanent magnet combines the advantages of ferrite, AlNiCo and rare earth samarium cobalt permanent magnet, and has a very high (bh) max value, which will further improve the performance level and force index of permanent magnet motor improve. Due to the excellent magnetic properties of NdFeB, rich raw material resources, affordable, the current trend of development is to replace the cast aluminum nickel-cobalt and rare earth samarium cobalt permanent magnet materials, can replace the cheap ferrite, will depend on the cost of NdFeB Can further reduce.

In the past, due to the lower magnetic properties of permanent magnet materials, the permanent magnet's magnetic properties and high magnetic energy product, its application will be extended to the range of small and medium sized motors, and even extended to large industrial drives. For example, Chongqing Electrical Machinery Factory has successfully developed two specifications of 22kw and 30kw energy-efficient NdFeB permanent magnet synchronous motor. North beam heavy-duty motor plant has launched 250kw NdFeB permanent magnet synchronous motor. On the other hand, due to the high coercivity of NdFeB, the magnets are "light, thin, short and small", with magical energy and information conversion functions, which will make permanent magnet motors more effective and light in weight , More miniaturization, miniaturization, weight reduction and thinning make it suitable for the field of special miniature permanent magnet motors such as watch, camera, medical and so on, and will lead to the development of permanent magnet motor and its replacement.

NdFeB magnet also has a linear demagnetization characteristics, the return line and demagnetization curve basically coincide, the intrinsic coercivity mhc high intrinsic properties of hard, anti-demagnetization ability. It is used in the manufacture of permanent magnet DC motor, the same as ferrite (but unlike Alnico), the pole axis perpendicular to the motor axis, therefore, a small leakage flux, the motor base almost no magnetic field.

Due to the high magnetic properties of NdFeB (see attached table), the volume of magnet is much smaller than that of ferrite and AlNi, and the motor is limited to miniature and low-power motors. NdFeB excellent magnet is short and thin, can make NdFeB permanent magnet motor small size, light weight, small inertia, high power, high efficiency, the torque can be larger than the same volume of ordinary permanent magnet motor 4% Ten to fifty percent, therefore, NdFeB magnet permanent magnet motor is a more ideal new type of permanent magnetic materials. NdFeB and several other properties of permanent magnet materials as shown in the attached table.

2.2 The disadvantage of NdFeB permanent magnet materials

The disadvantage of NdFeB is its low Curie temperature, only 312 degrees Celsius, poor thermal stability, the working temperature is limited to 130 degrees Celsius, which is equivalent to the motor b-class insulation.

Can be seen from the schedule, the general permanent magnet materials have a larger negative temperature magnetic coefficient αb, as the temperature increases, the remanence br will be reduced, indicating poor thermal stability of the permanent magnet. Therefore, the lower the αb of the magnet, the better, and the better αb approaches zero. Α b of neodymium iron boron is negative 0.12 percent. Than the aluminum-nickel-cobalt and rare earth samarium cobalt magnets are large, only smaller than the ferrite. The ferrite αb is negative 0.19 percent. Can still be used at 200 degrees Celsius, because the temperature coefficient of intrinsic coercivity of ferrite am is positive, the flux changes at a positive temperature is reversible; and NdFeB has a larger negative αm, negative 0.6 percent. , So irreversible loss occurs at the positive temperature. When the temperature is higher than 150 degrees Celsius, the irreversible loss will exceed 5%, and the magnetic property will decrease. Especially when the temperature exceeds 200 degrees Celsius, the irreversible loss of the magnet sharply increases. This is neodymium The main obstacle to the use of iron boron at high temperatures. Its chemical stability is also poor, in humid air above 150 degrees Celsius is mainly the oxidation of neodymium, it will be seriously oxidized corrosion, which are all research problems to be solved, otherwise, will limit the NdFeB Applications in motors, especially in wet-tropical motors, motors used in high-temperature media, and high temperature rise motors are widely used.

2.3 NdFeB permanent magnet material production

China is the third country that made NdFeB permanent magnets after Japan and the United States. China's sintered NdFeB permanent magnet production, in 1988 to 85t, for permanent magnet motor accounted for nine percent. 1989 more than 100 t, exports 60t, the domestic use of nearly 50t, for less than 10% of permanent magnet motor.

Japan's permanent magnet material production accounted for about 1/3 in Western countries, Japan permanent magnet material production, generally reflects the development trend of Western countries. The output of sintered NdFeB magnets in Japan was 80-100t in 1986 and 150t in 1987, with a 50% increase in output. 300t in 1988 and a doubling of production; in 1989 it was 700t, with a 133% increase in production. In 1990 it was 1030t, with a 47% increase in production, of which 41% for voice coil motors, for Other permanent magnet motors account for 15%.

In 1990, sales of sintered NdFeB magnets in the United States amounted to 68 million U.S. dollars, or 383 tons, or 20 percent for permanent magnet motors.

According to reports, the world's total output of NdFeB permanent magnet material accounted for the proportion of 1987 to 250 ~ 300t, accounting for about four percent; in 1988 for 650 ~ 680t, accounting for about six percent. In terms of output value, in 1989, the world's rare-earth magnet steel output value of 5 US dollars, accounting for 26% of the world permanent magnet material output, of which NdFeB accounted for ten percent. In 1990, the world's rare earth magnet steel output reached 600 million US dollars, accounting for 30% of the world total permanent magnet material output, of which NdFeB accounted for 15%. In 1991, the output value of NdFeB surpassed that of Samarium Cobalt magnet for the first time, ranking the second only to Ferrite. It is estimated that by the year 2000, NdFeB production will be close to ferrite, accounting for 35% to 40% of the total output value, that is, from 18% to 20% in the next 10 years The annual growth rate of NdFeB magnets in the next 10 years will be reduced by 25% to 30%, the rapid development of NdFeB will fundamentally change the original production of permanent magnetic materials for , Sales pattern. Western World 1991 ~ 1995, NdFeB permanent magnet in the field of potential motor market is 2600t.

2.4 NdFeB permanent magnet materials prices

In 1985 the United States Coulter lists neodymium iron boron price of 90 US dollars / pounds, higher than the samarium cobalt magnets 75 US dollars / pounds price. In 1986, the company's NdFeB price dropped to 30-40 US dollars / pounds. In recent years, the lowest price of NdFeB market in the United States was 132 US dollars / kg, and the average selling price was 176 US dollars / kg [4].

China's NdFeB permanent magnet export price of 60 to 140 US dollars / kg, the average selling price of 95 US dollars / kg, lower than the international market price. The domestic market price of 350 to 400 yuan / kg, with the production technology is expected to improve and the expansion of production volume may eventually be reduced to 300 yuan / kg or so, the relative price will be lower than Alnico, NdFeB therefore has Strong price competitive advantage.

In summary, the Nd, B and C bhc.mhc and (bh) max high magnetic properties, excellent raw materials, nd and fe, the price is moderate, the density is smaller than the SmCo permanent magnet, the required amount Less, easy to process, high yield, intrinsic properties of hard, anti-demagnetization strong, high reliability, in metallurgy, machinery, electrical, automotive, petrochemical, electronics, audio and video, electrical, instrumentation, medical, biological and other industries Widely used, but also can be used in computer, automation, microwave communications, robotics, rockets, aviation and other high-tech fields, fully demonstrated the development potential of NdFeB permanent magnet materials and broad prospects for the application market.

3 developed NdFeB permanent magnet motor effect

NdFeB permanent magnet has been widely used in China's motor industry, especially in the micro motor, the effect is very significant.

3.1 NdFeB permanent magnet DC motor applications

Shanghai Micro Motor Factory in 1990 to complete the development zyn40 NdFeB permanent magnet DC motor, magnetic tile sintered n30 NdFeB magnet, br is 1.12 ~ 1.18t, bhc 637 ~ 756ka / m, mhc 635 ~ 836ka / m, (bh) max 231 ~ 255kj / m3, used to replace the m series Alnico and zyt series ferrite permanent magnet DC motor, and achieved good economic benefits. At the same power, neodymium iron boron motor compared with Alnico motor, reducing a frame size, weight and volume were Alnico motor 70% and 68%; and ferrite Tuen machine compared to narrowing the two frame sizes, weight and volume of ferrite motors were 40% and 36%, respectively; compared with sz electric excitation motor, narrowing two frame numbers; The weight and volume are 40% of the electric excitation motor. At the same time, the performance of neodymium iron boron motor significantly improved under the same frame size, neodymium iron boron motor output power and torque than Alnico motor increased 78 percent. 6, the efficiency of the original 54% Increase to 62%.

Baotou permanent magnet motor using NdFeB magnets, developed a zyn-2. 2kw, zyn-3.0kw two rare earth permanent magnet DC motor, the key technology is the design of a reasonable magnetic circuit structure, select the appropriate parameters , Make full use of high-performance permanent magnets in order to achieve higher technical indicators. Its volume is reduced by 30% to 50% and the weight is reduced by 40% to 60% compared with that of the same type of DC motor, achieving efficiencies of 89% to 100% respectively Ninety, increased by 5% to 10%.

Baotou City Motor Factory introduced a full range of small and medium-sized neodymium NdFeB permanent magnet DC motor, the motor center high 90 ~ 355mm, a total of 12 machine frame number, rated power of 0.55 ~ 450kw a total of 31 levels, rated voltage 160v, 440v two Species, a total of 7 rated speed, a total of 156 specifications. As a result of the use of high-performance NdFeB magnets, the motor volume reduction, weight reduction, efficiency, with China's 24 series motors and German aeg's 4 series motors compared to the entire series of six percent increase in average efficiency overloading capacity Thirty-three percent increase in temperature drop by one insulation grade, 30 percent tube copper. The province of silicon steel sheet ten percent, is the ideal energy-saving products, saving the ideal material to reach the level of the early 90s, is China's key energy-saving products to promote, to fill the gaps in small and medium-sized DC motors in China to replace similar imported products , Significant economic benefits.

3.2 NdFeB permanent magnet DC tachometer generator application

Tianjin Safety Motor Co., Ltd. supporting the elevator cy01,02 permanent magnet DC tachometer generator, the stator using aluminum nickel and cobalt ring magnet, the (bh) max of 41. 4kj / m3 weight 2. 8kg. Motor size is 122mm × 242mm, motor weight 7. 9kg. Successfully developed in 1985, 90cy01, 02 permanent magnet DC tachogenerator, stator magnetic tile with NdFeB magnet, (bh) max. For 222. 9kj / m3, weight 0. 3kg, 10% of the original magnet weight of 10.7, two kinds of tachometer technical indicators exactly the same, and 90cy the size of 490mm × 177mm, the motor weighs 3.5kg, The volume of the motor is reduced by 60.5% and the weight is reduced by 55%.

Shanghai Nanyang Electric Factory in 1989 developed a rare earth permanent magnet DC tachometer, the original Alnico 0. 6kg, now with NdFeB permanent magnet 0.lkg, the weight of the motor, the volume


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