Permanent magnet material (magnet) knowledge literacy

- Nov 02, 2017 -



At present, the commonly used permanent magnet materials are ferrite, NdFeB, SmCo, AlNiCo, rubber and other magnetic. These are relatively easy to buy the product, there are common performance (not necessarily ISO standard) to choose from.

Each of the above magnets, each with characteristics, the application of the field are also different, is now a brief introduction.


Ferrite:

Ferrite is a non-metallic magnetic material, also known as magnetic ceramics. We opened the traditional radio, which is the speaker magnet, is the ferrite.

Ferrite magnetic properties are not high, the current magnetic energy product (one of the parameters to measure the performance of the magnet) can only be 4MGOe slightly higher. This material has the greatest advantage, that is, low prices. At present, it is still widely used in many fields.

The ferrite is a ceramic. Therefore, the processing performance is similar to that of ceramics. Ferrite magnets, are mold forming, sintered out. For machining, only for simple grinding.

Because it is difficult to carry out mechanical processing, so ferrite products, most of the shape is simple, and the size of the tolerance is relatively large. Box shape products ok, can be grinding. Rounded, usually grinding only two planes. Other dimensional tolerances are given as a percentage of the nominal size.

As the ferrite has a history of decades of application, so many manufacturers will have ready-made conventional shape and size of the ring, box and other products to choose from.

As the ferrite is ceramic material, so there is no corrosion problem. Finished products do not require plating or other surface treatment or painting.


SmCo:

Samarium cobalt magnet, the main component is samarium and cobalt. As the two materials themselves are expensive, therefore, samarium cobalt magnet is also the most expensive of several kinds of magnet inside.

Samarium cobalt magnet magnetization product, can now do 30MGOe, or even higher. In addition, the samarium cobalt magnet coercivity is high, high temperature, can be applied to 350 degrees Celsius high temperature, so in many applications can not be replaced.

Samarium cobalt magnet, belonging to powder metallurgy products. General manufacturers according to the size and shape of the finished product needs, sintered into blanks, and then use the diamond blade cut into finished size. Since the samarium cobalt is electrically conductive, it is possible to perform wire cutting. In theory, samarium cobalt can be cut into the shape of wire cutting can be cut, if not consider the magnetization and the larger size of the problem.

Samarium cobalt magnet, corrosion resistance is very good, generally do not need anti-corrosion plating or coating. In addition, the samarium cobalt magnet is very brittle, so processing small size or thin-walled products more difficult.


NdFeB:

NdFeB is currently widely used, the rapid development of magnet products.

NdFeB from the invention to the present wide application, but also more than 20 years time. Because of its high magnetic properties and ease of processing, the price is not very high, so the application area to expand rapidly. At present, the commercialized NdFeB, magnetic energy product can reach 50MGOe, is ferrite 10 times.

NdFeB also belongs to the powder metallurgy product, processing similar to samarium cobalt.

At present, the maximum working temperature of NdFeB is about 180 degrees Celsius. If it is harsh environment applications, generally recommended no more than 140 degrees Celsius.

neodynium magnets is very susceptible to corrosion. Therefore, most of the finished products to be plated or painted. Conventional surface treatment includes: nickel (nickel copper and nickel), galvanized, aluminum, electrophoresis and so on. If you work in a confined environment, you can also use the way of phosphating.

Due to the high magnetic properties of NdFeB, in many cases, it is used to replace other magnetic materials to reduce the product volume. If the use of ferrite magnets, now the size of the phone, I am afraid it will be less than half of the bricks.

The above two kinds of magnets, have a better processing performance. Therefore, the product size tolerance is much better than ferrite. General product, size tolerance can be done (+/-) 0.05mm.


Alnico:

Al-Ni-Cr magnet, there are two kinds of casting and sintering process. Domestic to do more than casting. Alnico magnetic energy product up to 9MGOe, and has the greatest characteristics, is the high temperature, the working temperature can reach 550 degrees Celsius. However, aluminum-nickel-cobalt in the reverse magnetic field, very easy to demagnetize. If you put the same poles (two N or two S) of the two alnico, the magnetic field of one of the magnets will be retracted or reversed. So it is not suitable for working in reverse magnetic field (such as motor).

Nickel and cobalt hardness is very high, although it can also be grinding and wire cutting, but the higher cost. The general supply of finished products, there are two kinds of grinding or not grinding.

Nickel and cobalt in the field of sensor applications is relatively wide.


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