JPH11150033A - Preparation for rare-earth magnet and magnetic circuit unit for loudspeaker - Google Patents

Abstract

PROBLEM TO BE SOLVED: To raise an axial orientation characteristic of a magnetic anisotropy axis of magnet powder in a method, for making Nd-Fe-B magnet powder to a bulk magnet body by a current-carrying compression forming. SOLUTION: By filling an insulator powder 14 into a sidewall part of inner diameter side of an outer forming mold 11 and filling Nd-Fe-B magnet powder 15 inside of its face. Through current carrying, these are formed, so that when current-carrying compression is formed, an axial rotation of magnetic anisotropy axis of the magnet powder 15 which is caused by the insulator powder 14 applying pressure to the magnet powder 15 from the radial direction is suppressed, and the magnetic characteristics of the bulk magnet body is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rare earth magnet and a method of manufacturing a magnetic circuit unit for a speaker using the rare earth magnet. More specifically, Nd-Fe
The present invention relates to a method for producing a B-based magnet powder into a bulk magnet body.

[0002]

2. Description of the Related Art Rare earth magnets are mainly manufactured by a sintering method or a bond magnet method. The former consists of processes such as melting casting, heat treatment for homogenization, pulverization, molding in a magnetic field, sintering, and cutting and grinding. High-performance rare earth magnets are manufactured by this method. This method is a strong specialized manufacturer that has been actively developing compositions and construction methods and has established a patent network. Magnet users purchase magnets from these specialized manufacturers to suit their application. On the other hand, the latter is a method in which a magnet user can purchase a magnet powder from a specialized manufacturer and manufacture a bulk magnet according to the company's requirements inside the user. However, since a binder such as an epoxy resin is required, the proportion occupied by the magnet powder is reduced, and the magnet characteristics are as low as about half that of the sintered magnet. However, sintered magnets such as thin ring magnets have the advantage of being able to produce magnets of a shape that is difficult to manufacture, and have recently increased significantly.

As a manufacturing method at a position similar to that of the above-described bonded magnet, a method called energization compression molding (Japanese Patent Laid-Open Publication No.
No. 3,319,909 and Japanese Patent Application Laid-Open No. 2-86103). In this method, a magnet powder is purchased from a specialized manufacturer, and a bulk magnet is prepared on the user side. This method does not require a binder and can produce a full-density bulk magnet.
It can be much better than a bonded magnet.

A magnetic circuit unit for a speaker is a component for providing a static magnetic field to a voice coil in which a sound signal current flows and generates vibration, and is composed of a magnet and a magnetic yoke, and is output from a magnetized magnet. The magnetic flux is collected by a magnetic yoke to generate a static magnetic field in a ring-shaped space (gap) in which the voice coil enters.

[0005] Magnetic circuit units that are widely used at present use inexpensive ferrite magnets as magnets. Ferrite magnets need to have a large magnet area because of their low magnetization. For this reason, a structure in which a magnet is arranged outside a magnetic yoke is called an external magnet type structure. On the other hand, a magnetic circuit unit using an alnico magnet, a rare earth magnet, ie, an Sm—Co magnet or a neodymium magnet (ie, Nd—Fe—B magnet), as shown in FIG. A structure surrounded by an outer yoke 3 which is also a magnetic yoke similar to that of the magnetic yoke 2, that is, a structure in which a magnet is inserted inside the magnetic yoke, is called an inner magnet type structure.

[0006] Ferrite magnets and neodymium magnets frequently used in these magnetic circuit units for speakers are sintered magnets, and the speaker manufacturers purchase the magnet and bond the magnet and the magnetic yoke. The magnetic circuit unit is manufactured by a method of fixing with an agent.

Recently, high performance rare earth magnets have been widely used in speakers. These are receivers for mobile phones and micro-speakers for computer equipment that need to be small and lightweight. The miniaturization and weight reduction will continue to increase, and the number of speakers using rare earth magnets is expected to increase. .

[0008]

As described above, the rare-earth magnet and the magnetic circuit unit for a speaker using the same are increasing in size and weight each year. Downs are demanded, and to meet these demands, it is necessary to improve magnet properties and reduce process costs.

In order to achieve these major problems, it is preferable to manufacture a rare earth magnet by the above-described energization compression molding and to apply the magnet to a magnetic circuit unit for a speaker. It is desired that the magnetic circuit unit for the speaker be integrally formed with the energized compression molded magnet and the yoke material.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and provides a new method of manufacturing a rare earth magnet and a magnetic circuit unit for a speaker.

[0011]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, a method of manufacturing a rare-earth magnet according to the present invention comprises Nd-Fe-B.
In the method in which the system magnet powder is formed into a bulk magnet body by current compression molding, the outer mold is filled with an insulator powder on an inner diameter side wall, and an Nd-Fe-B-based anisotropic magnet powder is filled inside the insulator powder. Thereafter, a magnetic field is applied in the axial direction, and then a current is directly applied to perform compression molding. Further, the insulator powder is preferably alumina. Also, 100
It is preferable to apply a magnetic field in the axial direction under a pressure of not more than kgf / cm ² . Further, it is preferable to directly apply a current under a pressure of 200 kgf / cm ² or more to perform compression molding.

Further, according to the method of manufacturing a magnetic circuit unit for a speaker of the present invention, a molding support die having an inner diameter substantially equal to the inner diameter of the outer yoke is placed on the outer yoke of the magnetic circuit. Insulating powder is filled into the outer yoke and the inner diameter side wall portion of the molding support die, Nd-Fe-B-based magnet powder is filled inside thereof, and a top plate is placed thereon. It is characterized by applying pressure, directly energizing, compressing and integrally molding, and then removing the insulating powder. Further, the insulator powder is preferably alumina. Further, the Nd-Fe-B-based magnet powder is an isotropic flake powder in a portion in contact with the top plate and a portion in contact with the bottom of the outer yoke, and is anisotropic powder in the interior, and is directly energized. It is preferable to apply a magnetic field in the axial direction before and / or at the beginning of direct energization to align the anisotropic powder.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.

As described in detail in US Pat. No. 4,851,058, the isotropic flake powder of the Nd-Fe-B-based magnet powder according to the present invention is preferably composed of 10 to 40 at% of Nd, Pr or a mixture thereof with 50 to 50 at%. 90 at% Fe and 0.1.
The alloy, which has a composition of B of 5 to 10 at% and is melted by melting, is sprayed on the surface of a roll rotating at a high speed, rapidly cooled and solidified, and has a thickness of 10 to 3 atm.
It is a flaky powder having a size of 0 μm, a width of approximately 50 to 300 μm and an average size of 200 μm. It is said that this flake powder is composed of an Nd ₂ Fe ₁₄ B phase and an amorphous phase, and the magnetic properties of this flake powder are magnetic because the fine crystal grains of the Nd ₂ Fe ₁₄ B phase are oriented at random. Isotropic. However, (BH) max is 13-15 MGO
e, it is an excellent magnet material and is currently used in large quantities in bonded magnets for small motors.

The anisotropic powder of the Nd—Fe—B magnet powder is described in detail in the Journal of the Japan Institute of Metals, “Materia”, Vol. 34, No. 2, (1995), pp. 152-157. In addition, approximately 12 at.
% And Zr, Nb, Hf, Ta, Ga, etc.
It is composed of a composition containing a small amount of t% or less. This anisotropic magnet powder is made by a recently developed excellent method called HDDR method. That is, the above-mentioned composition alloy is melt-cast to form an ingot, which is subjected to a homogenization treatment to obtain an Nd ₂ Fe ₁₄ B phase,
Thereafter, heat treatment is performed in a hydrogen atmosphere to absorb hydrogen, and NdH ₂ , F is formed by hydrogenation.
e, phase decomposition into Fe ₂ B (Decomposition)
Then, by forcibly performing dehydrogenation (Desorption), the Nd ₂ Fe ₁₄ B phase is recombined (Recom).
bination). By this processing, 100
The Nd ₂ Fe ₁₄ B phase, which was a large crystal grain of about μm, becomes fine crystal grains of about 0.3 μm, and the fine crystal grains retain the original crystal orientation and correspond to the original crystal grains. All of the fine crystal grains present inside the ~ 400 µm lump are oriented in substantially the same direction,
Fine crystal agglomerates having a size of 00 to 400 μm or smaller by cracking become anisotropic magnet powder.
This method is called the HDDR method, taking the initials of the generation process. The magnetic properties of this anisotropic powder are 28-35 MGO at (BH) max for currently available powders.
e.

In the current compression molding method, a uniaxial pressure and current are applied to a conductive powder to be formed (direct current supply) to generate Joule heat at an interface where the powder and the powder come into contact with each other, thereby raising the temperature to a high level. In this method, atoms at the contact interface are activated to promote diffusion to each other, and are compressed by pressure to form a bulk compact. It can be molded to almost full density at a lower temperature than conventional hot compression molding (HIP). In addition, since the temperature can be raised and lowered rapidly, the molding can be performed in a very short time.

Using this method of current compression molding,
A method of integrally forming a magnet and a top plate in a magnetic circuit unit for power has been proposed (JP-A-8-5).
No. 1693). However, in this method, the magnet and the top plate integrally formed are fixed to the outer yoke with an adhesive. The present invention proposes a method of integrally molding the outer yoke together.

First, a problem in the current compression molding is to improve the magnetic characteristics. In the conventional method, the anisotropic powder is pressurized in a magnetic field and aligned with the axis of easy magnetization (c-axis) oriented in the axial direction (pressing direction). When the alignment is performed by the force of the external magnetic field, the temperature is still low at room temperature or below the Curie point and the pressure is low, so that the density is low, approximately 50 to 60% of the full density. That is, the remaining 40 to 50
% Is the void. In this state, direct current is applied, and Joule heat is generated at the contact point of the powder, and the temperature rises. At a temperature exceeding about 600 ° C., partial deformation occurs due to the pressing force, the contact portion is enlarged, and the contact portion is expanded by the effect of the direct current. Atomic diffusion occurs and the powders are integrated. In this process, the pressure is applied in the axial direction, and the size is reduced in the pressing direction, that is, the axial direction, and finally reaches the full density. That is, the gap in the axial direction is filled, but the gap in the radial direction is difficult to fill. For this reason, it is presumed that the powder itself rotates and moves to fill the void in the process of partially deforming the powder. This rotation changes the crystal direction of the powder that has been aligned and oriented in the axial direction, and therefore, the magnetic properties in the axial direction are reduced.

Based on the above assumptions, it is considered that it is effective to maintain the powder orientation, that is, to suppress the rotation of the powder, by applying pressure also from the radial direction. Various methods for generating radial pressure have been studied, and the present invention has been made among them.

That is, an insulator powder is adopted as a pressure medium, the insulator powder is arranged outside the magnet powder, and the magnet powder and the insulator powder are simultaneously pressed and directly energized. The magnet powder generates heat, rises in temperature, reaches a deformation temperature range, and is compacted.
The insulating powder does not generate heat because it hardly conducts electricity, and the temperature rises due to heat transfer from the magnet powder, but the temperature is lower than that of the magnet powder. Therefore, the density of the insulator powder hardly increases. In other words, since the volume of the insulator powder is hardly changed, the insulator powder moves in the radial direction in accordance with the deformation of the magnet powder, and acts to hydrostatically press the magnet powder from the radial direction to the inside to reduce the diameter of the magnet powder. Compress in the direction. That is, the magnet powder can be pressed in the radial direction, so that the rotational deformation of the magnet powder in the radial direction is eliminated and the orientation direction of the magnet powder is suppressed from being disturbed.

This will be described more specifically with reference to FIG. FIG. 1 is a diagram schematically showing a mold for current compression molding, and shows an example of the present invention. The present invention is not limited to this.

An electrode punch 12 made of carbon and a spacer 13 made of W-Co-C are placed from below into an outer mold 11 made of sialon (insulating) for current compression molding. A release agent is applied to the upper end surface of the spacer 13. Next, a thin-walled cylinder is put on the spacer 13 in the outer molding die 11, and alumina, which is the insulating powder 14, is put into the outer part thereof, that is, the part which is in contact with the inner wall of the outer molding die 11, and then the inner part is made different. Nd-Fe- which is anisotropic magnet powder 15
B-type anisotropic magnet powder is added and the height is the same. Thereafter, the thin cylinder is extracted, a spacer 13 having a release agent applied to the lower end surface thereof is placed thereon, and the electrode punch 12 is placed thereon, thereby completing the filling of the powder. Next, the entire mold is placed in a current compression molding apparatus and placed on a lower ram through which a large current flows. Similarly, the upper ram for passing a large current is lowered to press the upper end surface of the upper electrode punch 12, and in this case, a low pressure, that is, 100 k
The thermocouple is stopped by applying a pressure of not more than gf / cm ² and the thermocouple is mounted on the outer mold 11. In this state, the apparatus is closed and the magnetic field coil installed outside the outer molding die 11 is energized while evacuating with a rotary pump, and 3 to 30 kOe in the axial direction.
Nd-Fe-B based anisotropic magnet powder 1
5 is aligned in the axial direction. During alignment by applying a magnetic field, the pressure of the upper ram is increased, and the pressure is increased by 200 kgf / cm ² or more to fix the orientation. Next, in a pressurized state, the pulse current is passed through the upper ram and the lower ram from
６０60 seconds and then direct current 180-400 A / cm
^The mixture is heated by ^two streams to be heated and compressed to form a bulk magnet. Thereafter, the current is stopped, the magnet body is cooled, the magnet body is taken out of the outer mold 11, and the attached insulator powder 14 is removed.

Here, the insulator powder 14 is a powder that is not bulk-molded at the time of energization compression molding and substantially retains the initial volume, so that pressure can be applied to the magnet powder that is integrally molded from the radial direction. . In order to satisfy this characteristic, it is necessary that the current is not passed during direct energization, and as a result, it is not molded integrally without generating heat.Therefore, it must be an insulator, and hence it is called an insulator powder. I have. An example is alumina powder first. Zirconia powder and silica powder are also suitable. Also Ni
Zn ferrite or sendust powder whose surface has been oxidized can also be used.

The role of the insulator powder 14 in transmitting the pressure in the radial direction is to play a large role. For this reason, the insulator powder 14 must be easily movable in the radial direction by the axial pressure. Small ones are not suitable because they do not move easily in the radial direction during compression. It is desirable that the particle size is large.
Those having a size of 0 to 100 μm are desirable. It is also preferable to add a small amount of a lubricant or to coat thinly on the surface of the insulating powder.

Next, a method of manufacturing a magnetic circuit unit for a speaker will be described with reference to FIG. FIG. 2 is a schematic diagram centering on the magnet powder before molding, and is partially exaggerated for explanation. FIG. 2 shows an example of the present invention, and the present invention is not limited to FIG.

First, the outer yoke 3 is covered with a molding support die (made by Sialon) 6. The inside diameter of the outer yoke 3 and the inside diameter of the molding support die 6 are the same. A thin-walled cylinder is placed in the outer yoke 3 and the supporting mold 6. The inner diameter of the thin cylinder is adjusted to the outer diameter of the top plate 2 in this example. The outside of the thin-walled cylinder is filled with the insulating powder 14 and then the inside is filled with the anisotropic magnet powder 5. The outer diameter of the bulk magnet that becomes full density after molding is the top plate 2
Is smaller than the outer diameter of
The upper surface of the top plate 2 moves up and down with respect to the upper surface of the work 3. Therefore, the optimum amount of the magnetic powder 5 is determined by conducting experiments several times so that the upper surface of the top plate 2 is flush with the upper portion of the outer yoke 3. Next, the top plate 2 is placed on the magnet powder 5. After removing the thin cylinder, the upper surface of the top plate 2 and the upper surface of the insulating powder are made at the same height. Next, a release agent is applied to the lower end surface of the spacer 13 and placed on the top plate 2. Next, the electrode punch 12 is placed, and the electrode punch 12 is placed under the outer yoke 3.
In this state, it is placed in an energization compression molding apparatus, and is placed between the lower ram and the upper ram, as in the case of molding the bulk magnet alone. First, under light pressure, that is, 100 kgf
/ Cm ^2, while applying a magnetic field in the axial direction while closing and evacuating to a vacuum to orient the anisotropic magnet powder 5 in the axial direction and increasing the pressure to 200 kgf / cm ² or more. Is fixed. Next, a pulse current is applied for a short time to clean the surface of the magnet powder 5, and then a direct current is supplied to raise the temperature to compress the magnet powder 5. As the magnet powder 5 becomes a bulk magnet, the density increases and the magnet volume decreases accordingly, and the spacer 13 presses the top plate 2 and the magnet powder 5 and simultaneously presses the insulator powder 14 simultaneously. Since the density of the insulating powder 14 hardly changes, the insulator powder 14 moves in the radial direction and pushes the magnet powder 5 from the side. The compression molding ends when the magnet powder 5 has reached the full density. During energization and compression, the lower surface of the top plate 2 and the inner surface of the bottom of the outer yoke 3 come into contact with the magnet powder 5 and are partially fused and integrally formed. Since the magnet powder 5 and the top plate 2 and the outer yoke 3 are made of different materials, there is a difference in thermal expansion.
During cooling, it is desirable to keep the pressure up to 40 ° C. near room temperature. When pressurization is stopped at 40 ° C. or more, cracks may occur in the bulk magnet body. After cooling, the electrode punch 12, the spacer 13, and the molding die 6 are removed, and the insulating powder 14 is removed to obtain a magnetic circuit unit for a speaker.

Whether or not cracks occur in the bulk magnet depends on the size of the magnetic circuit unit and the thickness of the top plate. In particular, when the top plate is thick, cracks are easily formed. In such a case, top plate 2
When Nd-Fe-B based isotropic flake powder is thinly introduced as magnet powder in contact with the bottom surface of the outer yoke 3 and the inner surface of the bottom of the outer yoke 3, just the yoke material and the Nd-Fe-B based anisotropic powder Since the thermal expansion is intermediate, the generation of cracks can be suppressed.

This method of simultaneously molding the magnet of the speaker magnetic circuit unit, the top plate 2 and the outer yoke 3 at the same time is an unprecedented method.
This method is advantageous in that the bonding step can be omitted and the adhesive is not sandwiched between the magnet and the yoke, so that the magnetic resistance of the adhesive is eliminated in a magnetic circuit. Therefore, even if an Nd-Fe-B based isotropic flake powder is used as the magnet powder without using the anisotropic powder, it can be used as long as the magnet volume is increased. Therefore, the magnetic powder need not be limited to anisotropic powder, but may be isotropic powder. In this case, no magnetic field orientation is required.

Although the present invention has been described with reference to a magnetic circuit unit for a speaker, it is also effective for a magnetic circuit unit such as a voice coil motor (VCM) such as a component or product requiring a static magnetic field. Needless to say.

[0030]

Next, the present invention will be described in detail with reference to examples.

(Example 1) In an outer mold having an inner diameter of 20 mm, an electrode punch and boron nitride (BN)
Is inserted from below, a thin cylinder having an inner diameter of 16 mm is put on the spacer, and a coarse alumina powder of 80 to 100 μm is filled between the outside and the inner wall of the outer mold, and Nd is put inside the thin cylinder. 8.6 g of an Fe-B-based anisotropic magnet powder was filled, and the height of the magnet powder was made equal to the height of the alumina powder. Next, the thin cylinder was extracted, a spacer coated with BN was placed on the lower surface, an electrode punch was inserted thereon, and the thin cylinder was placed in a current compression molding apparatus and set on the lower ram. Next, lower the upper ram and put 50k on the electrode punch.
While applying a pressure of gf / cm ^2, the device is closed and a rotary pump is used to evacuate the apparatus, a pulse magnetic field of 30 kOe is applied in the axial direction, and then a static magnetic field of 3 kOe is applied while 250 kgf / cm.
^The pressure was increased to ² to pressurize the powder. In this state, a pulse current was directly applied to the magnet powder from the power supply via the upper and lower rams, the electrode punch and the spacer for 30 seconds, and then a steady current of 630 A was directly applied to perform compression molding while raising the temperature. Deformation started at about 620 ° C at the indicated temperature of the thermocouple attached to the outer mold, and the deformation reached saturation at about 730 ° C. The time during which the steady current was flowing was 90 seconds. When the temperature reached 300 ° C. or lower, the vacuum was released to atmospheric pressure, the apparatus was opened, and the apparatus was forcibly cooled with air. When the temperature reached the contact temperature, the pressurization was stopped, the mold was taken out of the apparatus, and the bulk magnet was taken out. The height of the bulk magnet is 8.1 mm and the outer diameter is about 13.4
mm. The density was 7.53 g / cc, a value close to the full density of 7.6. In the radial direction, the initial value was 16 mm, which was reduced to 13.4 mm. It is considered that the pressure from the radial direction by the alumina worked. The magnetic properties of this bulk magnet are Br = 11.3 kG, iHc = 1
0.5 kOe, (BH) max = 28.7 MGOe. The magnetic properties of the anisotropic magnet powder used are Br = 1
2.0 kG, iHc = 12.3 kOe, (BH) max
= 32.4MGOe, which is a good value.

(Comparative Example 1) In Example 1, an Nd-Fe-B-based anisotropic magnet powder was used without adding alumina powder, and a steady-state current value was set to 790 A. Compression molding was performed. The obtained bulk magnet had an outer diameter of 20 mm, a height of 3.6 mm, and a full density of 7.6 g / cc. The magnetic properties are B
r = 10.1 kG, iHc = 10.2 kOe, (BH)
max = 21.6 MGOe, significantly lower than the starting magnet powder properties, and much lower than the bulk magnet obtained in Example 1.

(Example 2) The outer yoke having an inner diameter of 20 mm was covered with a molding die having the same inner diameter of 20 mm, and a thin-walled cylinder having an inner diameter of 18.5 mm and a thickness of 0.1 mm was inserted into the outer yoke. Coarse alumina was placed outside the cylinder, and 8.8 g of Nd-Fe-B-based anisotropic magnet powder was placed inside. The outer diameter is 18.4mm and the thickness is 1.4m on the magnet powder
m top plate was placed. Next, the thin cylinder was gently pulled out, and the coarse alumina powder surface was adjusted to the same height as the upper surface of the top plate. A spacer coated with BN is placed thereon, and an electrode punch is further placed thereon.
An electrode punch was also placed under the coil and placed in an electric compression molding apparatus. With the upper and lower rams lightly pressurized, ie 3
The device was sealed by applying a pressure of 0 kgf / cm ² . Next, a pulse magnetic field of 30 kOe is applied to the anisotropic magnet powder from a magnetic field coil placed around the molding support while the inside of the apparatus is evacuated by a rotary pump to magnetize the anisotropic magnet powder, and to orient the powder in the axial direction. While maintaining the anisotropic direction of the powder in the axial direction with a magnetic field of 3 kOe, the pressure was increased to 250 kgf / cm ² and the powder was compressed to fix the direction of the powder. Next, a pulse current is applied directly to the magnet powder through the upper and lower rams, the electrode punch, and the spacer to clean the powder surface.
A steady current of 10 A was directly applied to raise the temperature to perform compression molding. The progress of the compression deformation was observed with a displacement meter, and when the displacement was saturated, the energization was stopped and cooling was performed. When the temperature dropped to about 350 ° C., the vacuum pump was stopped, air was introduced, the pressure was returned to atmospheric pressure, the apparatus container was opened, and the apparatus was forcibly air-cooled and cooled to 40 ° C. Thereafter, the pressure was lowered, the upper ram was raised, and the combination of the outer yoke sandwiched between the electrode punches and the support mold was taken out.
It was disassembled to remove the insulating powder, thereby forming a magnetic circuit unit.
The upper surface of the outer yoke and the upper surface of the top plate were almost the same, and the inner depth of the outer yoke was 6.4 mm, so the thickness of the magnet was 5.0 mm as planned. . In the drop test, the outer yoke, the top plate and the magnet were firmly integrated without coming off. The magnet was magnetized in the axial direction, and the magnetic field strength in the gap was measured with a Hall element.
There was kG, which satisfied the specification of 10 kG. After disassembly, the magnet portion was taken out and the diameter was measured. The diameter was 17.2 mm, which was slightly compressed in the radial direction from 18.5 mm at the time of injection, confirming that the effect of alumina was exhibited. Its density was 7.59 g / cc, which was almost full density. The magnetic properties of the bulk magnet are Br =
10.8 kG, iHc = 10.8 kOe, (BH) ma
x = 25.2 MGOe, and it can be said that deterioration of the orientation of the magnet powder is suppressed at a better value than in the case of Comparative Example 1.

[0034]

As described above, according to the present invention, the portion of the insulator powder provided on the side portion is not compression-molded at the time of energization compression molding, but moves radially by pressure to compress the magnet powder radially. do. When the magnet powder is subjected to energization compression molding, it suppresses the powder from changing its direction in the radial direction, increasing the proportion of the magnet powder that maintains its anisotropic direction in the axial direction, increasing the magnetic properties of the energized and compressed bulk magnet body. improves.

Further, according to the present invention, the outer yoke and the top port constituting the magnetic circuit unit can be integrally formed by energizing and compression molding together with the magnet powder, so that the outer yoke and the top port can be integrally formed. As a result, the magnetic resistance is reduced on the magnetic circuit, and the magnetic field strength in the gap can be improved. Further, the bonding step can be eliminated in manufacturing, and the process cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view for explaining an example of a method for producing a bulk magnet alone according to the present invention.

FIG. 2 is a schematic cross-sectional view for explaining one example of a method of integrally forming the magnetic circuit unit of the present invention.

FIG. 3 is a schematic sectional view of a magnetic circuit unit for a speaker having an inner magnet type structure.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnet 2 Top plate 3 Outer yoke 4 Gap part 5 Magnet powder 6 Molding support 11 Outer mold 12 Electrode punch 13 Spacer 14 Insulator powder 15 Anisotropic magnet powder

Claims (7)

[Claims] In a method of forming a Nd-Fe-B-based magnet powder into a bulk magnet body by current compression molding, an insulator powder is filled in an inner mold side wall portion of an outer mold, and Nd-Fe-B is filled inside the inner mold. A method for producing a rare-earth magnet, comprising: applying a magnetic field in the axial direction after filling a B-based anisotropic magnet powder; 2. The method for manufacturing a rare earth magnet according to claim 1, wherein the insulator powder is alumina. 3. The method for producing a rare earth magnet according to claim 1, wherein a magnetic field is applied in an axial direction under a pressure of 100 kgf / cm ² or less. 4. The method for producing a rare earth magnet according to claim 1, wherein a current is directly applied under a pressure of 200 kgf / cm ² or more to perform compression molding. 5. The outer yoke is provided above the outer yoke of a magnetic circuit.
A molding support die having an inner diameter substantially the same as the inner diameter of the mold is placed, and the outer yoke and the side wall portion on the inner diameter side of the molding support die are filled with an insulating powder. A method for manufacturing a magnetic circuit unit for a speaker, characterized by filling a magnet powder, further placing a top plate thereon, pressurizing and directly energizing to compress and integrally mold, and then removing the insulating powder. 6. The method for manufacturing a magnetic circuit unit for a speaker according to claim 5, wherein the insulator powder is alumina. 7. The Nd—Fe—B-based magnet powder is an isotropic flake powder at a portion in contact with the top plate and a portion in contact with the bottom of the outer yoke, and is an anisotropic powder inside. 6. The method of manufacturing a magnetic circuit unit for a speaker according to claim 5, wherein a magnetic field is applied in the axial direction before direct energization and / or at the initial stage of direct energization to align the anisotropic powder.