Permanent magnet material

- Nov 04, 2017 -

Permanent magnetic material
 
With a wide hysteresis loop, high coercivity, high remanence, once magnetized to maintain a constant magnetic material. Also known as hard magnetic materials. In practice, the permanent magnetic material works in the second quadrant demagnetization part of the deep magnetic saturation and the hysteresis loop after magnetization. Commonly used permanent magnet materials are divided into alnico permanent magnet alloys, ferrochromium permanent magnet alloys, permanent ferrite, rare earth permanent magnet materials and composite permanent magnet materials.
 
Alnico permanent magnet alloys. With iron, nickel, aluminum as the main ingredient, also contains copper, cobalt, titanium and other elements. High remanence and low temperature coefficient, magnetic stability. Casting alloy and powder sintering alloy two. More applications from the 30s to the 60s of the 20th century are mostly used in the instrumentation industry to make magnetoelectric instrumentation, flow meters, micro motors and relays.
 
② iron chromium cobalt permanent magnet alloy. With iron, chromium, cobalt as the main component, but also contains a small amount of molybdenum and silicon, silicon. Its processing performance, can be cold and hot plastic deformation, magnetic similar to the AlNiCo magnetic alloy, and through plastic deformation and heat treatment to improve magnetic properties. For the manufacture of a variety of small cross-section, complex shape of the small magnet components.
 
③  ferrite magnet. Mainly barium ferrite and strontium ferrite, its high resistivity, coercive force, can be effectively used in the air gap magnetic circuit, especially suitable for small generators and motors for permanent magnets. Permanent magnet ferrite does not contain precious metals such as nickel, cobalt, rich source of raw materials, simple process, low cost, instead of Alnico permanent magnet manufacturing magnetic separator, magnetic bearings, speakers, microwave devices. However, the maximum magnetic energy product is lower, the temperature stability is poor, the texture is brittle, fragile, impatience impact vibration, not suitable for measuring instruments and precision requirements of the magnetic devices.
 
④ rare earth permanent magnet materials. Mainly rare earth cobalt permanent magnet materials and NdFeB permanent magnet materials. The former is rare earth elements cerium, praseodymium, lanthanum, neodymium and cobalt intermetallic compounds, the product of up to 150 times the energy of carbon steel, aluminum nickel and cobalt permanent magnet materials 3 to 5 times the permanent ferrite 8 ~ 10 times, low temperature coefficient, magnetic stability, coercivity up to 800 kA / m. Mainly used for low-speed torque motors, start motors, sensors, magnetic thrust bearings and other magnetic systems. NdFeB permanent magnet material is the third generation of rare earth permanent magnetic materials, the remanence, coercivity and maximum energy product than the former high, not brittle, better mechanical properties, alloy density is low, is conducive to light-based magnetic components Thinner, smaller and more compact. However, its higher magnetic temperature coefficient limits its application.
 
⑤ composite permanent magnetic materials from the permanent magnet powder and plastic materials as a binder compound. Since it contains a certain proportion of binder, its magnetic properties are considerably lower than those of the corresponding binderless magnetic material. In addition to metal composite permanent magnetic materials, other composite permanent magnetic materials due to heat resistance of the adhesive is limited, the use of temperature is low, generally not more than 150 ℃. However, the composite permanent magnetic material has high dimensional accuracy, good mechanical properties, good homogeneity of various parts of the magnet, easy radial orientation of the magnet and multi-pole magnetization. Mainly used in the manufacture of instrumentation, communications equipment, rotating machinery, magnetic equipment and sports equipment.
classification
The first category is: permanent magnet alloys, including rare earth permanent magnet materials (NdFeB), SmCo, AlNiCo,
 
The second category is: ferrite permanent magnet material (Ferrite)
 
According to the different production process is divided into: sintered ferrite, bonded ferrite, injection molded ferrite, these three processes based on the orientation of magnetic crystal and divided into isotropic and anisotropic magnets.
 
These are the main permanent magnetic materials currently on the market, and some can not be eliminated due to the production process or cost reasons, such as Cu-Ni-Fe, Fe-Co-Mo ), Fe-Co-V (iron cobalt vanadium), MnBi (manganese bismuth)
 
1, rare earth permanent magnet material (NdFeB Nd2Fe14B): According to different production processes are divided into the following three
 
(1). Neodymium rare earth - Sintered NdFeB permanent magnet sintered powder after air milling smelting, high coercivity, and has a very high magnetic properties, the maximum energy product ( BHmax higher than ferrite (Ferrite) more than 10 times. Its own mechanical properties are also very good, you can cut different shapes and drilling. High-performance products, the maximum operating temperature up to 200 degrees Celsius. Due to its material content easily lead to corrosion, so according to different requirements of the surface must be different coating treatment. (Such as galvanized, nickel, green zinc, environmentally friendly nickel, nickel and copper nickel, nickel and nickel green, etc.). Very hard and brittle, with high anti-demagnetization, high cost / performance ratio, not suitable for high operating temperature (> 200 ℃).

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(2) Plastic-bonded NdFeB - Bonded NdFeB is the NdFeB powder and resin, plastic or low melting point metal binder, etc., and then by compression, extrusion or injection molding And other methods made of composite NdFeB permanent magnet. The product once formed, without secondary processing, can be made directly into a variety of complex shapes. Bonded NdFeB magnetic in all directions, can be processed into NdFeB compression molds and injection molds. High precision, excellent magnetic properties, corrosion resistance, good temperature stability.

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(3). injection molding of NdFeB (Injection Molded  Magnets) - with very high accuracy, easy to make anisotropic thin-walled ring or thin magnet complex shape

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2. the main raw material of sintered ferrite (Sintered Ceramic) include BaFe12O19 and SrFe12O19, according to the orientation of magnetic crystal is divided into isotropic and anisotropic magnets. Due to its low price and moderate magnetic properties, it has become the most widely used magnet. Ferrite magnets are made by the ceramic process, the texture is relatively hard, but also a brittle material, due to the ferrite magnets have good temperature resistance and low cost, has become a more widely used permanent magnet.

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3. Rubber Magnet is a kind of ferrite magnetic material series, which is made of composite material of bonded ferrite powder and synthetic rubber through extrusion, calender molding and injection molding, Sexual, elastic and twistable magnets. Can be processed into a strip, roll, sheet and a variety of complex shapes. The rubber magnet is made of magnetic powder (SrO 6 Fe 2 O 3), polyethylene (CPE) and other additives (EBSO, DOP) and the like, and is produced by extrusion and calendering. Rubber magnetic material can be homosexual or heterosexual, it is made of ferrite magnetic powder, CPE and some trace elements, bendable, twist, roll. It does not need more machining can be used, you can also trim the shape of the required size, rubber magnetic can also be based on customer requirements PVC, Beijiao, on the UV oil. Its magnetic energy product lies between 0.60 and 1.50 MGOe. Applications of rubber magnetic materials: refrigerators, message boards, fasteners for securing objects to metal bodies for advertising, etc., and magnetic disks for toys, teaching instruments, switches and sensors. Mainly used in micro motors, refrigerators, disinfection cabinets, cabinets, toys, stationery, advertising and other industries.

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4. AlNiCo is the earliest developed a permanent magnet material, is composed of aluminum, nickel, cobalt, iron and other trace metals constitute an alloy. According to the different production process is divided into Sintered AlNiCo (Sintered AlNiCo) and cast AlNiCo (Cast AlNiCo). Product shapes and more round and square shape. The casting process can be machined to different sizes and shapes; the sintered product is confined to a smaller size than the casting process, producing a better dimensional tolerance of the blank than the cast product, with slightly lower magnetic properties than the cast product, but Processing is better. In permanent magnetic materials, cast aluminum nickel-cobalt permanent magnet has the lowest reversible temperature coefficient, the working temperature can be as high as 600 degrees Celsius. Alnico permanent magnet products are widely used in various instrumentation and other applications.

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5. Samarium Cobalt (SmCo) According to the different ingredients into SmCo5 and Sm2Co17, respectively, for the first generation and Zi second generation rare earth permanent magnet materials. Because of its very scarce raw materials, expensive and make its development is limited. As the second generation rare earth permanent magnet, SmCo has high magnetic energy product (14-28MGOe) and reliable coercive force, and shows good temperature characteristics in rare earth permanent magnet series. Compared with NdFeB, SmCo is more suitable for working in high temperature environment (> 200 ℃).

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development path
With the development of society, the application of magnets is also more and more widespread. From high-tech products to the simplest packaging magnetic materials, NdFeB magnets and ferrite magnets are currently the most widely used.
 
From the history of the development of permanent magnetic materials, the carbon steel used at the end of the nineteenth century has a magnetic energy product (BH) max of less than 1MGOe, which is a measure of the magnetic energy density of a permanent magnet. However, Fe-B permanent magnet materials, magnetic energy product has reached more than 50MGOe. For a century, the remanence Br of materials increases little, and the improvement of energy product is attributed to the improvement of coercivity Hc. The improvement of coercivity, mainly due to its essence and the discovery of high magnetostrictive anisotropic compounds, and the preparation of technology advances. The early twentieth century, people mainly use carbon steel, tungsten steel, chrome steel and cobalt steel for permanent magnet materials. The successful development of AlNiCo permanent magnetic materials in the late 1930s made it possible for large-scale applications of permanent magnetic materials. The fifties, the emergence of barium ferrite, both to reduce the cost of permanent magnets, but also the application of permanent magnet materials to broaden the scope of high-frequency areas. By the 1960s, the appearance of rare earth cobalt magnets opened up a new era for the application of permanent magnets. In 1967, Strnat et al. Of Dayton University in the United States made the SmCo5 permanent magnet successfully by the powder bonding method, marking the arrival of rare earth permanent magnetism. To date, rare ten permanent magnets have experienced the first generation of SmCo5, the second generation of precipitation hardening type Sm2Co17, developed to the third generation of Nd-Fe-B permanent magnetic materials. In addition, Cu-Ni-Fe, Fe-Co-Mo, Fe-Co-V, MnBi and AlMnC alloys have been used as permanent magnetic materials in history. These alloys are rarely used in most applications due to their low performance and low cost. The AlNiCo, FeCrCo, PtCo and other alloys in some special occasions also been applied. At present, Ba, Sr ferrite is still the largest amount of permanent magnet material, but many of its applications are being replaced by Nd-Fe-B materials. And, the current output value of rare earth permanent magnet materials has greatly exceeded ferrite permanent magnet materials, rare earth permanent magnet material production has developed into a big industry.


Article from NdFeB Industry Network

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