JPS61292303A - Magnetizing method for permanent magnet - Google Patents

Abstract

PURPOSE:To make even a large block to be very uniformly magnetized, by magnetizing the block, in which a plural number of Fe-B-R permanent magnet units with tetragonal crystal serving as main phase adhere to each other, under the magnetic field generated by a superconductive coil. CONSTITUTION:A block, in which a plural number of permanent magnet units having main elements of R (where, R is at least one kind of rare earth elements containing Y) in 8-30atom%, B in 2-28atom%, and Fe in 42-90atom%, and having the main phase of tetragonal crystal, adhere to each other, is magnetized under the magnetic field generated by a superconductive coil. With R in less than 8atom% high coercive force can not be obtained, and with R in excess of 30atom% residual magnetic flux density decreases. With B in less than 2atom% it comes into rhombohedral structure, and with B in excess of 2.8atom% non-magnetic phase rich in B increases. With Fe in less than 42atom% the residual magnetic flux density decreases, and with Fe in excess of 90atom% high coercive force can not be obtained.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention relates to a method of magnetizing a permanent magnet, and more specifically, to a method for magnetizing a permanent magnet, and more specifically, a block in which a plurality of individual Fe-B-R permanent magnets are bonded to each other. It relates to a method of uniformly magnetizing.

A magnetic circuit constituted by blocks magnetized by this magnetization method is optimal as a uniform magnetic field generating device for a nuclear magnetic resonance imaging (NMR-CT) device.

(Prior art) Fe-B-R magnets have coercive force ('ac) h residual magnetic flux density (Br), maximum energy product C (BE) m
ax ] and has excellent magnetic properties.

Therefore, it is most suitable as a permanent magnet for a magnetic field generator of an NMR-CT apparatus. The magnetic field generator for NMR-CT equipment requires a fairly large magnet, but currently Fi
For agricultural reasons, large-sized Fe-B-common permanent magnets have not been obtained. Therefore, a method generally used is to magnetize small permanent magnets, adhere them to each other, and assemble them into a large block. Generally, a single Fe-B-R permanent magnet having a relatively small shape is magnetized using a pulse magnetizer that generates a magnetic field by instantaneously passing a large current through a normally conducting coil.

(Problems to be Solved by the Invention) The requirements for the magnetic field generator of the NMR-CT apparatus are extremely strict, and the requirements are extremely strict for the generation of a high magnetic field and extremely high magnetic field uniformity within a wide area (for example, the magnetic field within the image forming space must be 3000G
The magnetic field uniformity must be 50 or less. To achieve this, KFi depends on the design of the magnetic block.

Generally, it is necessary that the residual magnetic flux density (Br) of one magnet block is uniform, and that the shape and dimensions of the block have high precision as designed. In order to obtain the dimension #i, it is difficult to process the block after magnetization, so it depends on the accuracy during assembly.

By the way, after magnetizing the small permanent magnet mentioned above.

It is difficult to increase the height of the one-dimensional tank area using the method of assembly under the influence of the attractive and repulsive forces of magnets, especially for Fe-B.
-It is very difficult to assemble extremely strong magnets, such as permanent magnets. Moreover, due to the influence of the demagnetizing field that often occurs when a single permanent magnet is bonded after magnetization, depending on the bonding method, the magnetic properties may be damaged due to partial demagnetization, making it impossible to achieve a uniform residual magnetic flux density distribution in the block. . Therefore, it is extremely difficult to obtain a uniform magnetic field in a magnetic field generating device using a magnetic circuit assembled in this manner.

Therefore, single unmagnetized permanent magnets were glued together,
A possible method is to perform magnetization after assembling a relatively large block K. To do this, it is necessary to prepare a large air-core coil and instantaneously apply a large current to generate a strong magnetic field and magnetize it. However, when a large current is passed through an air-core coil made of copper or aluminum, a large amount of heat is generated and large temperature irregularities occur in the magnetized space. On the other hand, %Fe
-B -R system magnet KFi There is also the problem that the magnetic properties change significantly depending on the magnetization temperature. It was found that these factors made it difficult to uniformly magnetize the block.

It has also been found that this phenomenon is exacerbated when blocks are magnetized one after another (due to heat build-up).

From the above, it is difficult to magnetize a large block of Fe-B-R permanent magnets with a normally conducting coil.

The present invention provides a method for extremely uniformly magnetizing a relatively large block t-5 made by bonding a plurality of individual Fe-B-R permanent magnets to each other, and the method provides a method for extremely uniformly magnetizing a relatively large block t-5 made by bonding a plurality of individual Fe-B-R permanent magnets to each other. The purpose is to provide nine permanent magnet blocks that are uniformly magnetized and are optimal for constructing a magnetic circuit.

(Means for Solving the Problem) The present inventors have continued research on a magnetic field generator for an NMR-CT apparatus using a permanent magnet. In order to generate the high magnetic field required for the magnetic field generator of the NMR-CT apparatus and to achieve extremely high uniformity in a wide space, K is a high-coercivity Fe-B-R permanent magnet. It is necessary to uniformly magnetize a large block, and the inventors of the present invention have continued to conduct intensive research on magnetization methods. As a result, Fe
The present inventors have discovered that when a -B-R permanent magnet is magnetized in a magnetic field generated by an electromotive conducting coil, even a fairly large block can be magnetized extremely uniformly, leading to the completion of the present invention.

That is, the present invention is characterized in that %R (wherein R is Yf: 8 to 50 at% of at least one of the rare earth elements it contains, B2
A block made by bonding together a plurality of permanent magnets whose main components are atomic% to 28 atomic%, Fe42 atomic% to 90 atomic%, and whose main phase is tetragonal is attached in a magnetic field generated by a superconducting coil. This is a method of magnetizing a permanent magnet in which magnetization has a tW characteristic.

The present invention will be explained in more detail below.

The Fe-B-R permanent magnet, which is the magnet to be magnetized according to the present invention, contains R (at least one rare earth element including Y).
8 atoms to 30 atoms%, B2 atoms to 28 atoms, Fe
It is a permanent magnet whose main phase is tetragonal, with the main component being 42 to 90 atom %.

R is an essential element for the above-mentioned permanent magnet), and if it is less than 8 atoms, a large amount of cubic crystal structure with the same crystal structure as α-Fe is formed, resulting in high magnetic properties, especially high coercive force (
fHc) cannot be obtained, and if it exceeds 30 atoms, the R-rich nonmagnetic phase will be large) and the residual magnetic flux density KCBr) will decrease. Therefore, R is in the range of 8 atomic % to 30 atomic %. B is an essential element in the above-mentioned permanent magnet, and if it is less than 2 atoms, it will form a rhombohedral structure and a high coercive force (iHc) will not be obtained, and if it exceeds 2.8 atoms, it will become a B-rich non-magnet. ° There are many magnetic phases) % residual magnetic flux density (
Br ) decreases, making it impossible to obtain an excellent durable magnet. Therefore, B is in the range of 2 atoms to 28 atoms. Fe is an essential element in the permanent magnet K, 42
At less than atomic, the residual magnetic flux density (Br) decreases, and 9
If it exceeds 0 atoms, a high coercive force (iHc) cannot be obtained, so Fe is set in the range of 42 atoms to 90 atoms.

In addition to the main components of Fe, B, and H, the presence of unavoidable impurities in industrial production can be tolerated;
By replacing with O, one point of curie can be raised, and a part of B can be replaced with c, p.

It is also possible to replace it with S, Cu%Si, etc., which makes it possible to improve manufacturability and reduce costs.

Furthermore, the ternary basic composition Fe-B-RKAtbTihV
, Cr%Ni, Mn%Zr, Nb, Mo
, Ta, W, 8n, Bi.

By adding one or more of 8b, Ge, and Hf, it is possible to increase the coercive force. It is essential that the main crystal phase be tetragonal in order to have excellent magnetic properties.

The magnetization method of the present invention can be applied to high coercive force magnets other than Fe-BR-based magnets, such as 8mHCog-based magnets, 13m, C.
It can also be applied to rare earth-cobalt based magnets such as o and y based magnets or their analogs.

As a single magnet used in the present invention, a cube, a rectangular parallelepiped, a disk, a cylinder, and a polygonal prism with several sides are used. For adhesion, use epoxy-based, cyanoacrylate-based organic adhesives,
This can be done with low melting point metals. These individual permanent magnets are processed in advance in an unmagnetized state, adhered to each other using an adhesive, and assembled into a predetermined shape with high precision to form a block. This block is installed in the magnetic field generation space of the superconducting coil. Then, the superconducting coil is energized to generate a magnetic field that is two to three times the coercive force (iHc) of the permanent magnet to be magnetized [for example, the coercive force (iHc) is 12.5 K]
For Oe Fe-B-R permanent magnets, a magnetic field of 25.0 KG or more is required for magnetization. A pulse type power source is especially preferred for superconducting coils.

(Function) In the present invention, the mechanism by which the Fe-BR permanent magnet is extremely uniformly magnetized by magnetization in the magnetic field generated by the superconducting coil is considered to be as follows.

With superconducting coils, there is no resistance in the conductor wires of the coils, and they operate at extremely low temperatures, so there is no need to consider the heat generation of the coils. Therefore, the temperature in the magnetized space can be stabilized below the air temperature. Furthermore, it becomes easier to make the temperature distribution uniform.

(Example) Residual magnetic flux density nr = 1z, 5(xc), coercive force i at room temperature
Hc = 10.0 (KOe)% maximum energy product (BH) max = 55.0 (MGOe), shape 200 layers x 20011 x 200111 (20,, l
A Nd, Fe, B permanent magnet block (1,000 individual 1X20 Seiho magnets bonded together using epoxy adhesive) was magnetized in a magnetic field generated by a superconducting coil. The central magnetic field in the magnetized space was 30 KG, and the field at the ends of the magnet was also over 25 KG. As a result, the obtained magnetized magnet exhibited excellent magnetic properties and was extremely uniformly magnetized. 100 of the above blocks one after another (
1 piece/min), but the uniformity after magnetization was the same in all cases.

As a comparative example, a specimen made of the same material as above, with the same magnetic properties and a shape of 80111x8011x8G1 (20 layers x
A block of 20 mm x 20 square magnets (T-64 magnets adhered to each other) was magnetized at 25 KG using a normal conductive air-core coil using a nine air-cooled pulse magnetizer according to the conventional method. As a result, the uniformity of magnetic properties was relatively good. However, even though the blocks were continuously magnetized at the same speed as in the example, an increase in the temperature of the magnetized space was observed, temperature unevenness also occurred, and the uniformity gradually deteriorated.

(Effect of the invention) That's the explanation! As is clear, according to the magnetization method of the present invention, a large-sized re-B-R magnet block with high coercive force can be magnetized extremely uniformly while avoiding the influence of heat. Furthermore, since the blocks can be processed before magnetization, the accuracy of one dimension is improved, and the number of times the blocks are bonded after one magnetization can be drastically reduced, so the assembly accuracy is also improved.

Moreover, since a large magnetization space can be easily obtained in a superconducting coil, the size of the block can be further increased.

From these facts, according to the present invention, %Fe -B-R
If the magnetic circuit of the magnetic field generator of the NMR-CT apparatus is created using permanent magnets, a uniform magnetic field can be easily obtained.

Claims (1)

[Claims] R (wherein R is at least one rare earth element including Y) 8 at% to 30 at%, B2 at% to 28 at%
, a block consisting of a plurality of permanent magnets whose main component is Fe42 to 90 atom% and whose main phase is tetragonal is magnetized in a magnetic field generated by a superconducting coil. How to magnetize permanent magnets.