Permanent magnetic materials are also called hard magnetic materials, which are characterized by high anisotropy field, high coercivity, large hysteresis loop area, and large magnetization field required for magnetization to saturation. After removing the external magnetic field, it can still remain strong for a long time.的magnetism.
The permanent magnet material works in the second quadrant demagnetization part of deep magnetic saturation and hysteresis loop after magnetization. As an important basic magnetic functional material, it has a wide range of applications. China's permanent magnet material industry plays an important role in the world. Not only are there many companies engaged in production and application, but research work has also been in the ascendant.
Types of permanent magnet materials
1. Ferrite
1. Ferrite is a non-metallic magnetic material, also known as magnetic ceramic. When we disassembled the traditional radio, the speaker magnet inside is made of ferrite.
2. The magnetic performance of ferrite is not high. At present, the magnetic energy product (one of the parameters to measure the performance of the magnet) can only be slightly higher than 4MGOe. The biggest advantage of this material is its low price. At present, it is still widely used in many fields.
3. Ferrite is a ceramic, so its processing performance is similar to that of ceramics. Ferrite magnets are all molded and sintered. If processing is required, only simple grinding is required. Due to the difficulty of machining, most ferrite products have simple shapes and relatively large dimensional tolerances. The cube-shaped product is okay and can be ground. For circular ring, generally only two flat surfaces are ground. Other dimensional tolerances are given as a percentage of the nominal size.
4. Because ferrite is widely used and low in price, many manufacturers will have ready-made rings, squares and other products of conventional shapes and sizes to choose from. Since ferrite is made of ceramic, there is basically no corrosion problem. The finished product does not require surface treatment or painting such as electroplating.
Two, rubber magnet
1. Rubber magnet is one of the ferrite magnetic material series. It is made of bonded ferrite magnetic powder and synthetic rubber through extrusion molding, calendering molding, injection molding and other processes. It has flexibility, elasticity and Twistable magnet. It can be processed into strips, rolls, sheets, blocks, rings and various complex shapes.
2. Its magnetic energy product is 0.60～1.50 MGOe rubber magnetic material application fields: refrigerators, information signage, fixing objects to metal bodies to be used as fasteners for advertisements, etc., used in toys, teaching instruments, switches and sensors The magnetic sheet of the device.
3. Mainly used in micro-motors, refrigerators, disinfection cabinets, kitchen cabinets, toys, stationery, advertising and other industries.
Three, samarium cobalt
1. Samarium-cobalt magnets, the main components are samarium and cobalt. Because the two materials are expensive, samarium cobalt magnets are also the most expensive among several types of magnets. The energy product of samarium cobalt magnets can currently reach 30MGOe, or even higher.
2. In addition, samarium-cobalt magnets have high coercivity, high temperature resistance, and can be applied to high temperatures of 350 degrees Celsius, so they cannot be replaced in many applications. Samarium cobalt magnets belong to powder metallurgy products. Generally, the manufacturer sinters into a block blank according to the size and shape of the finished product, and then uses a diamond blade to cut it into the finished size. Because samarium cobalt has conductivity, it can be processed by wire cutting.
3. In theory, samarium cobalt can be cut into shapes that can be cut by wire cutting, if magnetization and larger dimensions are not considered. Samarium-cobalt magnets have good corrosion resistance and generally do not need anti-corrosion electroplating or painting. In addition, the texture of samarium-cobalt magnets is very brittle, so it is difficult to process small-sized or thin-walled products.
Fourth, neodymium iron boron
1. Neodymium iron boron is currently widely used and rapidly developing magnet products. NdFeB has been widely used from its invention to the present, and it has only been more than 20 years. Because of its high magnetic properties and easy processing, the price is not very high, so the application field is expanding rapidly.
2. At present, the magnetic energy product of commercial NdFeB can reach 50MGOe, which is 10 times that of ferrite. NdFeB is also a powder metallurgy product, and its processing method is similar to that of samarium cobalt.
3. At present, the maximum working temperature of NdFeB is about 180 degrees Celsius. For harsh environment applications, it is generally recommended not to exceed 140 degrees Celsius. NdFeB is very easily corroded. Therefore, most of the finished products need to be electroplated or painted.
4. Conventional surface treatments include: nickel plating (nickel copper nickel), zinc plating, aluminum plating, electrophoresis, etc. If working in a confined environment, phosphating can also be used. Due to the high magnetic properties of NdFeB, in many occasions, it is used to replace other magnetic materials to reduce the volume of the product. If ferrite magnets are used, the size of current mobile phones will probably not be smaller than half a brick.
5. Both samarium cobalt magnets and neodymium iron boron magnets have better processing properties. Therefore, the dimensional tolerance of the product is much better than ferrite. For general products, the dimensional tolerance can be (+/-)0.05mm.
Five, aluminum nickel cobalt
1. AlNiCo magnets have two processes: casting and sintering. There are more castings in China. The magnetic energy product of AlNiCo can reach 9MGOe, and it has one of the biggest characteristics, which is high temperature resistance, and the working temperature can reach 550 degrees Celsius. However, AlNiCo is very easy to demagnetize under a reverse magnetic field. If you push the same poles of two AlNiCo (two N or two S) together, the magnetic field of one of the magnets will be reversed or reversed. Therefore, it is not suitable for working in a reverse magnetic field (such as a motor).
2. AlNiCo has high hardness, although grinding and wire cutting can also be carried out, but the cost is higher. Generally, there are two types of finished products that are ground or not. AlNiCo is widely used in the field of sensors.
