JPS601820A - Manufacture of cylindrical permanent magnet - Google Patents

Abstract

PURPOSE:To obtain a cylindrical permanent magnet, in which there is no crack and which has excellent magnetic characteristics and a multipolar and anisotropic section and an isotropic section in the diametral direction as coaxial cylindrical sections, by controlling distances among magnets and distances among ferrite powder and the magnets. CONSTITUTION:A plurality of magnets 2 are arranged to a cylindrical cavity section 10 so as to generate a magnetic field in the radial direction, and distances (p) among the magnets 2 and distances (t) among ferrite powder and the magnets 2 are adjusted, thus integrally forming an anisotropic section and an isotropic section to a cylindrical ferrite magnet after sintering to coaxial cylindrical shapes. The thickness (t) of a cylinder 5 consisting of a non-magnetic material disposed to the inside of the magnet bodies 2 is brought to 0.5-4.0mm., preferably, 1.5-3.0mm.. When the thickness (t) is too thin, the cylinder 5 cannot resist pressure on molding and is broken: when the thickness (t) is too thick, the intensity of a magnetic field in the cavity section 10 of the permanent magnets 2 used for orienting slurry reduces. The intervals (p) of the permanent magnets 2 are brought to 0<=K<=5, preferably, 0<=K<=3 when the width of the permanent magnet body 2 is pm and p=K.pm is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a ferrite magnet, which is a cylindrical permanent magnet having multipolar anisotropy in the radial direction.

For example, a ferrite magnet having the basic formula (%) is known as a ferrite magnet. Generally, this type of ferrite magnet is made by blending an MO compound (which becomes MO upon firing) and Fe 203 in a predetermined molar ratio.

It is obtained by calcining to produce ferrite, pulverizing it to a ferrite powder having a single magnetic domain particle size or less, compression molding, and sintering. This ferrite powder has an easy magnetization direction in the C-axis direction, but when compression molding this ferrite powder, the easy magnetization direction is aligned in a magnetic field, which is called an anisotropic ferrite magnet. Magnets formed in a disordered state without aligning their directions are called isotropic ferrite magnets.

Anisotropic ferrite magnets have approximately twice the residual magnetic flux density Br and maximum magnetic energy product (BH) as compared to isotropic ferrite magnets.
)max is known to have a value of 3 to 4 times.

In other words, in order to improve the magnetic properties of this type of ferrite magnet, it is necessary to improve the density, increase the abundance of single domain grains, and also to orient the ferrite grains well. In the case of a cylindrical magnet with a magnetic field, it is necessary to orient the particles with as many easy directions of magnetization as possible in the radial direction.

Various molding methods have been proposed in the past to orient particles in the radial direction, but they can be roughly divided into 9 methods in which two particles are aligned in the radial direction by repelling magnetic fields from the top and bottom of a cylindrical cavity, and 1 cylindrical molding method. A method has been proposed in which magnetic poles are arranged on the circumference of a shaped cavity to align each particle in the radial direction.

However, in either method, the more the grains are aligned in the radial direction, the more cracks will occur during the sintering and cooling processes of the compact, making it unusable.

This crack is generated as a result of aligning the nine particles in the radial direction.
This is believed to be due to the mechanical stress generated during cooling due to the difference in coefficient of thermal expansion in the radial direction and in the tangential direction perpendicular to the radial direction.

In order to eliminate the occurrence of cracks, it is necessary to reduce the degree of orientation of one particle to bring it closer to one isotropy, which leads to deterioration of magnetic properties, and when compared with isotropic ones of the same shape, two surfaces The level of magnetic flux density Bo is only improved by 10 to 20%. For this reason, it has been difficult to manufacture crack-free cylindrical ferrite magnets with excellent magnetic properties.

An object of the present invention is to provide a method for manufacturing a ferrite magnet with excellent magnetic properties and anisotropy in the radial direction of cracks.

According to the present invention, in order to generate a radial magnetic field in the cylindrical cavity part, a plurality of magnets are arranged in a part other than the cavity part, the cavity part is filled with ferrite powder, and the ferrite particles are magnetized. In a method for manufacturing a cylindrical permanent magnet, the easy direction is arranged in the radial direction, the ferrite powder is compression molded, and then sintered to obtain a cylindrical ferrite magnet having radial anisotropy, By adjusting the distance between the magnets and the distance between the magnets and the ferrite powder, the anisotropic part and the isotropic part can be coaxially formed in the sintered cylindrical ferrite magnet. A method for manufacturing a cylindrical permanent magnet is provided, which is characterized in that it is integrally formed into a cylindrical shape.

As a result of research into a method for manufacturing a ferrite magnet with excellent magnetic properties, no cracks, no cracks, and radially anisotropic, the present inventors discovered that the orientation of ferrite particles in two cylindrical cavities is radially anisotropic. By arranging a plurality of magnets to generate a magnetic field and adjusting the distance (p) between the magnets and the distance (1) between the ferrite powder and the magnet, the cylindrical ferrite magnet after sintering can have anisotropic properties. A cylindrical permanent magnet with no cracks and excellent magnetic properties has been manufactured by integrally forming a coaxial cylindrical part with a polarized part and an isotropic part. Its magnetic properties include a surface magnetic flux density B that is 20 to 80% higher than that of an isotropic ferrite magnet of the same shape. I was able to have

Next, the present invention will be explained using the drawings.

Examples of mold structures used in the present invention are shown in FIGS. 1 and 2.

In FIGS. 1 and 2, ■ is an outer wall mold (die). Inside this die 1, there are a plurality of magnet bodies 2 made of, for example, a rare earth magnet having a high energy product, and a non-magnetic ring 3 made of a non-magnetic material for arranging the magnet bodies 2 at equal intervals. and.

A non-magnetic cylinder 5 is arranged inside the magnet body 2. Reference numeral 6 denotes an inner wall mold (center core) made of a non-magnetic material and forms a cylindrical cavity 10 between it and the cylinder 5 . Below the center of this center core 6.

A hole 6a is connected to a supply pipe (not shown) for slurry in which ferrite magnet powder is suspended in a liquid such as water, and a horizontal hole 6b is connected to the hole 6a and the cavity 10 described above. It is formed.

7 is a lower ie inch and is a non-magnetic material. Reference numeral 8 denotes a filter plate equipped with a lacrimal mechanism in which through-holes 9 are formed, and the filter plate 8 is made of a non-magnetic material. 11 is a filter.

Cylinder 5. Center core 6. The lower punch 7 and the filter plate 8 constitute a cylindrical cavity portion 10.

Thickness of cylinder 5 in the figure Eil''J: o, 5~4, Om
m is preferably 15 to 3.0 m. If the thickness L is too thin, the cylinder 5 will not be able to withstand the pressure during molding and will be destroyed.

If the thickness t is too thick, the magnetic field strength in the cavity part 1o of the permanent magnet body 2 used for orienting the slurry will decrease, resulting in B in the product. This is not preferable because it lowers the Further, the interval p between the permanent magnets 2 is determined by the following formula, assuming that the width of the permanent magnets 2 is 2 m.

p, +4-pm (o≦≦5, preferably 0≦≦3
In order to appropriately control p and t with respect to A shaped permanent magnet is obtained.

During manufacturing, a filter plate 8 is set at a predetermined position on the upper surface of the die 1, and a slurry of ferrite powder is filled into the cavity 1o from a supply pipe (not shown) through the holes 6a and the horizontal holes 6b. After filling is completed, lower punch 7 is raised. Then, the lower punch 7 is further pressed while draining only water with the ferrite particles remaining in the through hole 9 of the filter plate 8 and the cavity 10 using a water absorbing device (not shown).

A pressed body having a predetermined density is obtained. At this time, since there are a plurality of permanent magnets 2 in the die 1 that generate magnetic fields in the radial direction, the ferrite particles are anisotropic in the radial direction to have multiple poles along the lines of magnetic force. A cylindrical press-formed body having a coaxial cylindrical portion and an isotropic portion is obtained. After this, the press-formed body is extruded from die 1), dried, and sintered, and has a coaxial cylindrical shape including a multipolar anisotropic part and an isotropic part in the radial direction. A cylindrical permanent magnet body is obtained.

Hereinafter, nine embodiments of the present invention will be described in detail.

Example 1 Outer diameter of cavity part 10: 3.1+llIn, inner diameter: 17I
2 Rare earth magnets 2 with a width of 4.19 mm were placed in the mold III11 on the outer periphery so that the distance p between the magnets was 0 mm and the distance t between the magnets and the powder was 0.5 mm to form a mold with 24 poles. did.

This mold was filled with strontium ferrite powder crushed to an average particle size of 0.85μ as a slurry with a concentration of 60, and while the solvent (water) was being discharged, the mold was heated to 500kli'/cm2.
Molded with.

In addition, a rare earth magnet having a width of 4.97wn was placed on the outer periphery of the above mold so that p was 0+mn and t was 3.5mm to form 24 poles, and molded as described above. These molded bodies are sintered at 1220°C, and this core is magnetized to 24 poles to obtain a surface magnetic flux density of B. was measured. Further, the degree of orientation of this sintered body was measured using X-rays at part a at a depth of 1 depth from the outer periphery and part b at a depth of 1 depth from the inner periphery. The degree of orientation is measured by the ratio of the X-ray intensity of the surface index (OOS) to the intensity of (107), and the X-ray intensity of (oos) is x (008).

When the X-ray intensity of (107) is I(107).

It is expressed as If the degree of orientation (1) is less than 1%, it is considered to be isotropic, and as the anisotropy increases, the degree of orientation (%
il rises. The measurement results at this time are shown in Table 1. Also, the surface magnetic flux density B of an isotropic magnet of the same shape.

Table 1 shows the degrees of orientation of parts a and b.

Table 1 below: Degree of orientation @) pt Bo (G) b Appearance 0 0.5 1300 56.5 498 Cracks present 0 3.5 750 6.2 0.02 Crack anisotropy 680 -0.04 0 .03 I was able to create something completely flawless.

A magnet with p = O and t = 0.5 had characteristics 90 times better than an isotropic magnet, but it could not be used due to the occurrence of cracks. Also, pmQ.

The specimen with t = 0.5 was found to have anisotropy both on the outer and inner peripheries, and the specimen with pmO, t = 3.5 was isotropic at the inner periphery.

Example 2 Using the same mold as in Example 1, the width of the magnets was adjusted to set the distance p between the magnets to 0.5+m++, and t to 1.0+3.0+n.
A magnet was placed on the outer periphery so as to have a diameter of m, and molded and fired in the same manner as in Example 1. After magnetizing this core in the same manner as in Example 1,
Surface magnetic flux density B. Table 2 shows the results of measuring the degree of orientation and the results of measuring the degree of orientation.

Table 2 Orientation degree (support) ptBo (G) Appearance b O051,01230 cracked 51,0 47.2
0.5 3.0 810 No crack 9.9 -0.
01, p=1. ．． Let's set it to 0, and let t be 1,5,2,5.

Surface magnetic flux density B after magnetization when molded and fired in the same manner as in Example 1. and the degree of orientation are shown in Table 3.

Table 3 Degree of orientation @) p E Bo (G) a b Appearance 1.0 1.5 1180 4.8.5 0.03 No cracks], 0 2.5 1130 46.3 0.
00 B more than 40 inches higher than crack anisotropic magnets.

A cylindrical magnet without a crank was obtained.

The following margin is Example 4: Surface magnetic flux density B after magnetization when molded and sintered in the same manner as in Example 1. , and the degree of orientation are shown in Table 4.

table. Orientation degree (A) pt Bo (G) Appearance b part, 5 1.5 1160 No crack 46.6
0.31.52.5 1140 No crack 46.0
−0.02 Example 5 Using a mold structure in which a cavity portion 10 is formed on the outside of a cylinder 5 as shown in FIG. m) and p21.5, respectively.
, t = 2.5, 1.5, and the cavity part 10
The outer diameter and inner diameter of each are 4.5. +11m, 31
Fill a mm mold with strontium ferrite powder.

After molding with 500 kg7cm2, this molded body was
It was sintered at 20°C. By magnetizing this core, the surface magnetic flux density B
.

Table 5 shows the measurement results. For comparison, the surface magnetic flux density B is obtained when an isotropic magnet of the same shape is magnetized. are also shown in Table 5.

Table 5 pt Bo (G) Appearance 1.5 2.5 1100 No crack 1.5 1.5
1190 Crack Anisotropy 660 Still, the sintered core was cut at parts a and b as described above, and the degree of orientation was measured in the same manner as in Example 1.

As a result, in the case of t=1.5, a is 28% and b is 49%.
The outer periphery is also oriented at 9'%, but in the case of t=2.5, the inner periphery is oriented with a of 0.06% and b of 46.3%.
The outer periphery was determined to be isotropic.

As described above, according to the present invention, by appropriately controlling the distance p between the magnets and the distance t between the powder and the magnet, excellent magnetic properties without cracks can be achieved. It was possible to obtain a cylindrical permanent magnet having a radially multipolar anisotropic part and an isotropic part coaxially cylindrical.

Note that the present invention is not limited to the above embodiments, but can also be applied to the case of filling powder in a dry manner.
Furthermore, the magnets disposed on the inner or outer periphery of the cavity may be permanent magnets or electromagnets.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view showing the mold structure used in the present invention;
The figure is a longitudinal cross-sectional view of the mold structure shown in FIG. 1, and FIG. 3 is a cross-sectional view showing another example of the mold structure used in the present invention. 1...Outer wall mold (die), 2...Magnet, 3...Nonmagnetic ring, 5...Cylinder, 6...Inner wall mold (center core)
. 7 ・Lower punch, 8... Filter plate, 9... Through hole, 1
0. Cylindrical cavity portion, 11... Filter. Figure 1 Figure 2

Claims (1)

[Claims] 1. A plurality of magnets are arranged in a part other than the cavity part so as to generate a radial magnetic field in the cylindrical cavity part, and the cavity part is filled with ferrite powder,
The direction of easy magnetization of ferrite particles is arranged in the radial direction,
In the method for manufacturing a cylindrical permanent magnet, the ferrite powder is compression-molded and then sintered to obtain a cylindrical ferrite magnet having radial anisotropy. By adjusting the distance between the ferrite powder and the sintered cylindrical ferrite magnet, an anisotropic part and an isotropic part can be integrally formed into a coaxial cylindrical shape. A method for manufacturing a cylindrical permanent magnet. Margin below