JPH11176682A - Manufacturing method of Bond (registered trademark) magnet - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To develop an industrial production method of a magnetic anisotropic bonded magnet with further improved magnetic properties by further improving the filling ratio and orientation degree of magnetic powder. In press molding in a magnetic field, a pulse magnetic field is applied once or plural times to raw material powder filled in a mold, and then ultrasonic vibration is applied to the mold and / or punch while applying a static magnetic field. Then, the ultrasonic vibration is stopped, and the shape is formed by the pressing force.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a bonded magnet by press molding in a magnetic field, and more particularly, to a method for producing a bonded magnet having improved magnetic properties by improving the degree of orientation of magnetic anisotropic magnetic powder. The present invention relates to a method for manufacturing an isotropic bonded magnet.

[0002]

2. Description of the Related Art Bonded magnets in which magnetic powder (hereinafter, also referred to as magnetic powder) is bonded with resin contain a resin component that does not exhibit magnetism, compared to conventional sintered magnets manufactured by sintering magnetic powder. Characteristics are somewhat inferior. However, since there is no shrinkage due to sintering, dimensional accuracy is good, magnets of various shapes can be easily obtained, and the disadvantages of sintered magnets that are hard, brittle and easily chipped are eliminated, and chemical resistance and weather resistance are also improved. Are better. For this reason, bonded magnets are widely applied to various household electrical appliances to peripheral devices for large computers, and in recent years, are particularly widely used for small motors such as spindle motors and stepping motors.

[0003] A bonded magnet is made by using magnetic powder such as hard ferrite or a rare earth alloy as a permanent magnet material with an epoxy resin,
The magnet is manufactured by bonding and shaping a thermosetting resin such as a phenol resin or a polyester resin, or a thermoplastic resin such as a polyamide resin, a polypropylene resin, or a polyphenylene sulfide resin as a binder.

[0004] As a method for manufacturing a bonded magnet, injection molding, extrusion molding, press molding and the like are possible. Of these, injection molding and extrusion molding require high fluidity, so that a thermoplastic resin is generally used for the binder. The molding temperature at that time varies depending on the type of binder, but is 200-300 ° C for polypropylene resin and 250-300 ° C for polyamide resin. Easy to occur.

On the other hand, in press molding, a thermosetting resin is mainly used as a binder. Usually, a raw material powder (a material called “compound” in which a magnetic powder is coated with a thermosetting resin) in which a magnetic powder and a binder are compounded in advance is prepared, and then put into a mold and pressed with a punch. In this way, press molding is performed. The obtained compact (also called a green compact) is heated to cure the thermosetting resin of the binder. Since the final strength of the bonded magnet is given at the time of this heat curing, the strength of the molded body before the curing is sufficient as long as the handling required for carrying into the heating equipment is possible. Therefore, the temperature for press molding is usually room temperature. Press molding requires a smaller amount of resin than injection and extrusion molding, and thus increases the filling ratio of magnetic powder, so that a bonded magnet having better magnetic properties can be manufactured.

Researches have also been made on improving the magnetic properties of the magnetic powder itself. Sm ₂ Co ₁₇ alloy-based and Nd—Fe—B alloy-based magnetic powders exhibit the same magnetic properties even when magnetized in any conventional direction. Magnetic anisotropic magnetic powder has been developed that can exhibit better magnetic properties than isotropic magnetic powder.

Since the anisotropic magnetic powder has extremely high magnetic properties only in a certain direction (easy magnetization direction), the magnetic powder is molded under the action of a magnetic field so that the magnetic powder easily aligns in the direction of easy magnetization when bonded with resin. To do. Normally, a magnetic field coil or the like for forming a magnetic circuit is attached to a mold used for molding, and the magnetic powder is rotated by applying a magnetic field to the magnetic powder, so that the direction of easy magnetization of the anisotropic magnetic powder is changed to the direction of the magnetic field. (Ie, orient the powder).

[0008] When the magnetic powder is the same, to improve the magnetic properties of the bonded magnet, it is necessary to increase the filling rate of the magnetic powder;
In the case of anisotropic magnetic powder, it is effective to increase the degree of magnetic orientation (the ratio of the magnetic powder in which the direction of easy magnetization is uniform), and many devices have been proposed for that purpose.

For example, Japanese Patent Application Laid-Open Nos. Hei 1-205403 and Hei 2-116104 show that when press molding is performed under heating to increase the fluidity of the thermosetting resin of the binder, the filling rate of the magnetic powder increases. And JP-A-4-80901.

On the other hand, with respect to the improvement of the degree of magnetic orientation, several means have been proposed for improving the degree of magnetic orientation by devising a method of applying a magnetic field. For example, Japanese Patent Application Laid-Open
No. 262413 describes a method using only a pulse magnetic field of 0.5 seconds or less as an alignment magnetic field.

Japanese Patent Application Laid-Open No. 63-120407 discloses a method in which a compound is magnetized in advance, supplied to a magnetic field press molding machine, and subjected to magnetic field orientation press molding in a static magnetic field.
Japanese Patent Application Laid-Open Nos. 60-88418, 60-10277, and 4-112504 propose various methods in which a static magnetic field and a pulsed magnetic field are used in combination as an orientation magnetic field. .

Japanese Patent Application Laid-Open No. 8-31677 discloses that a raw material powder containing anisotropic magnetic powder and thermosetting resin powder as main components is filled in a mold capable of controlling temperature and magnetic field, and heated to melt the resin. A method is disclosed in which a magnetic field is applied after the state is reached to orient the magnetic powder, and then compression is performed by applying pressure.

JP-A-63-153806, JP-A-1-2455
Japanese Patent Application Laid-Open No. 03-28207 and Japanese Patent Application Laid-Open No. 4-28207 propose a method of applying a forward / reverse alternating static magnetic field as an orientation magnetic field.

[0014]

In order to improve the magnetic properties of the bonded magnet, various measures have been taken to increase the filling ratio of the magnetic powder. For example, the high-temperature pressing method disclosed in Japanese Patent Application Laid-Open No. 4-80901, in which the mold is heated to a high temperature and the molding temperature is set to a temperature equal to or higher than the melting point of the binder, has a great effect.
There is a problem that productivity is extremely reduced. In other words, in a high-temperature press in which a mold is heated, after one press molding and before supplying the next raw material (compound) powder to the mold, the resin of the next compound powder that has come into contact with the mold melts, There is a problem that the resin adheres to the mold and cannot be uniformly filled in the mold. Therefore, heating and cooling of the mold are indispensable for each press molding, and the time required for one molding (press cycle time) becomes long. That is,
The number of units produced per unit time is significantly reduced.

[0015] In order to improve the magnetic properties of the bonded magnet, a device has been devised to increase the degree of orientation of the magnetic powder. The mainstream used in the magnetic field orientation press molding of bonded magnets is a method using a static magnetic field as the orientation magnetic field.
However, if the orientation magnetic field is only a static magnetic field, if the intensity of the orientation magnetic field is increased in order to increase the degree of orientation of the anisotropic magnetic powder, the number of windings of the coil increases, and the mold provided with the coil becomes large. Further, since a large current flows through the coil having a large number of turns, a large cooling device for preventing heating is required for the coil. For this reason, it is difficult to realize an apparatus that can increase the size of the entire equipment and can take a large number of pieces with a single press.
In addition, there is also a problem that power consumption is large and a cost is high because a large current is continuously supplied.

On the other hand, as proposed in Japanese Patent Application Laid-Open No. 62-262413, in a method using only a pulse magnetic field as an orientation magnetic field, the duration of the pulse magnetic field is usually as short as several ms, and a pulse current is generated. Since it takes several seconds for the charging time, the orientation magnetic field can be applied only for a short time during the pressure molding, and at the same time, the timing of applying the pulse magnetic field greatly affects the degree of orientation. Therefore, the orientation of the anisotropic magnetic powder cannot be sufficiently improved.

In the method described in Japanese Patent Application Laid-Open No. 63-120407, in which a compound is magnetized in advance and then subjected to magnetic field orientation press molding in a static magnetic field, the compound magnetized before being supplied to a mold is easily aggregated by magnetic force. In addition, since the powder feeding property to the mold is reduced, a variation in the filling amount is likely to occur, and as a result, the productivity is reduced.

In the method described in Japanese Patent Application Laid-Open No. 60-88418, after magnetic particles are magnetized in advance with a high pulse magnetic field, press molding is performed in a static magnetic field while orienting in a direction different from the magnetization direction. In this method, in the case of anisotropic magnetic powder having an irregular shape such as that produced by a hydrogen treatment method, the magnetic powder does not easily rotate during press molding, and it is difficult to achieve high orientation.

Japanese Patent Application Laid-Open No. 60-10277 discloses a method in which after applying a pulse magnetic field, press molding is performed while maintaining the orientation direction of the magnetic powder using a static magnetic field by a permanent magnet. If a method of generating an orientation magnetic field using a coil is employed, a current can be flowed in the opposite direction immediately before the end of press molding to demagnetize the molded body. Since it cannot be magnetized, it is difficult to handle the compact after press molding.

Japanese Patent Application Laid-Open No. 4-112504 discloses that when a compound is press-formed in a static magnetic field of a coil, pressurization by an upper punch is performed a plurality of times, and a pulsed magnetic field is superimposed during each pressurization and compression. A method of applying the voltage is presented. In this method, the magnetic properties are improved as the number of compressions is increased, but the molding time is increased. In addition, the timing at which the pulse magnetic field is applied has a large effect on the degree of orientation of the molded body, and the second or third pulse magnetic field in which the pressing force increases does not effectively affect the degree of orientation.

The method described in JP-A-8-31677 is
Since the magnetic field orientation press molding is performed under heating, the resin softens and melts at the time of press molding, and the magnetic powder easily moves. for that reason,
It is described that the filling ratio and the degree of orientation of the magnetic powder are improved, and a magnetically anisotropic bonded magnet having excellent magnetic properties can be obtained. However, as described above, a problem remains in terms of productivity.

Further, in the method disclosed in Japanese Unexamined Patent Publication No. 4-28207 for applying an alternating static magnetic field as an orientation magnetic field, the magnetic field is a static magnetic field. When the magnetic field strength is increased to increase the orientation of the isotropic magnetic powder, the number of windings of the coil increases, the mold becomes large, and the energy cost also increases. Further, with magnetically anisotropic magnetic powder having high saturation magnetization, the magnetic powder is not sufficiently magnetized, and the degree of orientation is not sufficiently improved.

Thus, the present invention can further improve the filling ratio and degree of orientation of magnetic powder in magnetic field orientation press molding of magnetically anisotropic magnetic powder, whereby the magnetic anisotropic bonded magnet with further improved magnetic properties can be obtained. It is an object of the present invention to develop a method capable of industrially producing a product.

[0024]

Means for Solving the Problems The present inventors first apply a specific ultrasonic vibration to a mold and / or a punch under certain conditions during press molding of a bonded magnet,
It has been found that only the compound powder can be heated in a short time without heating the mold (Japanese Patent Application No. 6-310893), and a warm industrial manufacturing method for bonded magnets has been discovered. Now, the present inventors have studied the development of the above manufacturing method to efficiently form a bonded magnet having further improved magnetic properties, and have completed the present invention.

The inventors of the present invention have conducted intensive studies on efficient orientation field conditions and molding conditions in which the degree of orientation of the magnetic anisotropic magnetic powder is improved in a short molding time and the magnetic powder filling rate is improved.
The use of both a static magnetic field and a pulsed magnetic field as the orientation magnetic field improves the degree of orientation of the magnetic powder, while the application of ultrasonic vibrations heats the compound and improves the filling rate of the magnetic powder. The application timing of the magnetic field and the ultrasonic vibration is important for simultaneously improving the degree of orientation and the filling ratio of the magnetic powder, and the application timing of the pulse magnetic field is also important among the orientation magnetic fields, and these timings must be set appropriately. It was found that the magnetic properties of the bonded magnet were significantly improved.

That is, a pulse magnetic field having a large magnetic field strength is applied once before pressing, more preferably a plurality of pulse magnetic fields having the same magnetic field direction, or a plurality of pulses having a magnetic field direction alternately reversed. When a magnetic field (hereinafter, also referred to as an inversion pulse magnetic field) is applied to the raw material compound, the degree of orientation of the anisotropic magnetic powder is significantly improved, and thereafter, the high degree of orientation is maintained by applying a static magnetic field, and If the raw material compound is heated by ultrasonic vibration in a state where the high degree of orientation is maintained, the magnetic powder filling rate in the compact is improved, and the degree of orientation is further improved by the effect of the ultrasonic vibration. Acts synergistically to significantly improve the degree of orientation and filling factor,
The present inventors have found that a bonded magnet having excellent magnetic properties can be efficiently produced, and have reached the present invention.

In the present invention, the raw material powder obtained by coating a magnetic anisotropic magnetic powder with a thermosetting resin is press-molded in a mold while applying an orientation magnetic field, and the obtained molded body is heated. A method of manufacturing a magnetically anisotropic bonded magnet, in which a resin is cured by applying a pulsed magnetic field once or multiple times to a raw material powder filled in a mold, that is, a compound during press molding in a magnetic field. , Start applying a static magnetic field,
This is a method for forming a bonded magnet, which comprises applying ultrasonic vibration in a state where a static magnetic field is applied, then stopping the ultrasonic vibration, and shaping with a pressing force.

Here, when a static magnetic field is applied after one pulse magnetic field is applied, the direction of one pulse magnetic field is preferably the same as the direction of the static magnetic field. In addition, the pulse magnetic fields of a plurality of times include: 1) a plurality of pulse magnetic fields in which the direction of the magnetic field is the same as the subsequent static magnetic field; and 2) a pulse magnetic field in which the magnetic field direction is alternately reversed, and And the direction of the subsequent static magnetic field can be the same direction.

As can be seen from the above, in the preferred embodiment of the present invention, the direction of the last pulse magnetic field preceding the application of the static magnetic field, including the case where the pulse magnetic field is applied once or more than once, is changed. In the same direction.

The reason why a bonded magnet with significantly improved magnetic properties can be produced by the method of the present invention is considered as follows. In other words, when ultrasonic vibration is applied to the raw material powder, that is, the compound, the compound is heated, but at the same time, the filling property of the powder is improved by the vibration, so that the bulk density of the compound (the weight of the compound put into the mold Divided by the internal cavity volume).
When the bulk density increases, the gap between the magnetic particles decreases, and the rotation of the magnetic particles due to the alignment magnetic field hardly occurs, so that the alignment magnetic field does not work effectively. Therefore, even if a bond magnet is formed by a process of applying an orientation magnetic field after the application of ultrasonic vibration, the magnetic powder filling rate is increased, but the degree of orientation of the magnetic powder cannot be improved. However, according to a process in which a pulse magnetic field is applied a plurality of times, and then the compound is heated by ultrasonic vibration while maintaining this orientation state in a static magnetic field, a bonded magnet having a high degree of orientation and a high filling factor can be obtained. Also, by applying a pulse magnetic field having a large magnetic field intensity, the magnetic anisotropic magnetic powder having a large saturation magnetization is greatly magnetized, and by applying this pulse magnetic field a plurality of times in the same direction or alternately reversed, Especially Nd-Fe-B
Rotational torque by a pulse magnetic field effectively acts on magnetic powder having irregular shape without roundness like magnetic anisotropic magnetic powder of a system alloy, and the degree of orientation is improved. By applying ultrasonic vibration and press molding while applying a static magnetic field in the same direction as the last pulse magnetic field direction, the degree of orientation is further improved by the application of ultrasonic vibration, and this high orientation state is reduced by pressing. Since it is maintained during molding, a remarkable improvement in the degree of orientation can be obtained.

The compound is heated in a short time by the ultrasonic vibration, the lubricating property is improved by melting the binder, and the filling property of the powder is improved by the vibration, so that the magnetic powder filling rate can be improved at the same time.

[0032]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The raw material powder used in the method for producing a bonded magnet of the present invention comprises a magnetic powder and a thermosetting resin of a binder, similarly to a conventional compound for press molding of a resin bonded magnet. The raw material powder may be a mixture of a magnetic powder and a thermosetting resin, but a material obtained by coating the magnetic powder with a thermosetting resin is preferable because the resin is more uniformly distributed with respect to the magnetic powder. The coating of the magnetic powder with the thermosetting resin is performed by melting and kneading the thermosetting resin with the magnetic powder at a temperature higher than its melting temperature and lower than the curing temperature using an extruder, or a solution of the thermosetting resin with the magnetic powder. After mixing, it can be carried out by a conventional method such as evaporating the solvent.

The magnetic powder uses magnetic anisotropy. The type of the magnetic powder is not particularly limited, but is usually Sm ₂ Co ₁₇ type, Sm−
It is made of a rare earth alloy such as Fe-N-based or Nd-Fe-B-based. Such magnetic anisotropic magnetic powder may be manufactured by a conventional method such as a method of hot isostatic pressing magnetic powder produced by a rapid solidification method, pulverizing the compact after plastic working, and a hydrogen treatment (HDDR) method. These magnetic anisotropic magnetic powders are irregularly shaped powders, and it is said that the degree of orientation is low in conventional press molding in a magnetic field, but the present invention is particularly effective when applied to such powders. The effect of improvement is great. Preferred magnetic powders are rare earth-iron alloy powders including Nd-Fe-B-based, Sm-Fe-N-based and the like, and are particularly irregular in shape.

Although the particle size of the powder is widely applicable,
The average particle size is preferably in the range of 0.5 to 350 μm. 0.5
If it is less than μm, the rotational torque acting on the magnetic powder due to the externally oriented magnetic field is small, and the magnetic properties are degraded. A more preferred range is 38 μm or more,
It is less than 0 μm.

The thermosetting resin used as the binder is not particularly limited, and an epoxy resin, a phenol resin, a polyester resin and the like conventionally used for resin-bonded magnets can be used. The properties of the resin at room temperature may be liquid or solid, but solids are desirable from the viewpoint of ease of introduction into a mold. Further, it is desirable that the melting point of the solid resin is in the range of 45 ° C to 90 ° C. When the melting point is less than 45 ° C., when the press molding is performed continuously, the mold temperature may increase due to frictional heat between the punch and the mold and / or the powder and the mold. Compound tends to adhere at the time of injection, making it difficult to insert. Conversely, if the melting point exceeds 90 ° C., time is required for heating by ultrasonic waves, so that productivity is reduced.

The mixing ratio of the binder (thermosetting resin) to the magnetic powder is preferably 1 to 20% by weight. If the mixing ratio is less than 1% by weight, the bonding between the magnetic powders in the molded resin-bonded magnet becomes insufficient, resulting in poor moldability.
The mechanical strength of the obtained green compact and the finally obtained resin-bonded magnet are significantly reduced. On the other hand, if the mixing ratio of the binder exceeds 20% by weight, the ratio of the magnetic powder decreases, and the magnetic characteristics are significantly reduced. The preferred mixing ratio of the binder is 2 to 10 wt%, more preferably 2 wt% or more and 5 wt%.
% Or less.

In addition to the thermosetting resin and the magnetic powder, various conventionally used additives such as a coupling material and a lubricant can be added to the raw material powder if necessary in small amounts. Further, the coating with the thermosetting resin is made of a different resin.
More than one layer can be applied. This raw material powder is supplied to a mold and subjected to ultrasonic press molding in a magnetic field. In the present invention, after applying a pulse magnetic field, press molding is performed after applying ultrasonic vibration in a static magnetic field.

FIG. 1 is a schematic explanatory view of an apparatus for manufacturing a bonded magnet according to the present invention.
The upper punch 12, the lower punch 14, the mold 16, and a magnetic field coil 18 which is provided around the mold 16 and constitutes means for applying a pulse magnetic field and a static magnetic field. A horn 20, which is connected to an ultrasonic transducer (not shown) and constitutes an ultrasonic vibration applying means, is provided in contact therewith. The horn 20 may be provided on the lower punch 14. Further, it can be attached to the mold 16.

A raw material powder (compound) 22 is inserted into a mold 16 and formed between upper and lower punches. At this time, a pulse magnetic field and a static magnetic field are applied by a magnetic field coil 18, and further, an ultrasonic wave is applied through a horn 20. Vibration is applied to the mold 16 and / or the upper punch 12 (and / or the lower punch 14).

As described above, the press molding machine used in the present invention includes means for applying a pulse magnetic field and a static magnetic field, such as an electromagnet, and means for applying ultrasonic vibration. The pulse magnetic field can be applied using the same coil as that used for generating the static magnetic field, but the pulse magnetic field strength that can be generated is limited, so apart from the electromagnet for generating the static magnetic field, the air-core coil for generating the pulse magnetic field can be used. Is preferably installed.

The strength of the alignment magnetic field is preferably such that the static magnetic field is 8
It is at least kOe, more preferably at least 10 kOe, and the pulse magnetic field is preferably at least 10 kOe, more preferably at least 25 kOe. Static magnetic field less than 8kOe or pulsed magnetic field of 10k
When it is less than Oe, the improvement in the degree of orientation of the obtained bonded magnet is small. The upper limit of the intensity of the alignment magnetic field is not particularly limited, and the degree of orientation of the magnetic powder tends to improve as the magnetic field increases, but the degree of improvement in the degree of orientation when the strength of the more preferable magnetic field is exceeded is not so large. . Excessive magnetic field strength increases energy costs and equipment, so a static magnetic field
A kOe or less and a pulse magnetic field of 40 kOe or less, especially 35 kOe or less are sufficient.

The time for one waveform of the pulse magnetic field is 1 microsecond to 1 second, more preferably 5 microseconds to 100 milliseconds. Press molding can be carried out by supplying raw material powder into a mold cavity having a bottom surface formed by a lower punch and pressing down an upper punch, as in the related art. The pressing force is not particularly limited, and may be the same as the conventional one. However, since the filling property of the powder is improved by the ultrasonic vibration, the pressure is lower than the conventional pressure. Preferably 4~10 ton / cm ^2, more preferably 4~6ton / cm ^2. The pressure holding time is usually 1 to 3 seconds.

Before the raw material powder filled in the mold cavity is pressurized as described above, a pulsed magnetic field is first applied once, more preferably a plurality of times. In particular, irregularly shaped magnetic anisotropic magnetic powder is hard to rotate in a static magnetic field having a small magnetic field strength, and it has conventionally been difficult to sufficiently increase the degree of orientation. By applying a pulse magnetic field having a high magnetic field intensity once or / and a plurality of times according to the present invention, the magnetic anisotropic magnetic powder is easily oriented.

When applying a pulse magnetic field only once,
The direction of the pulse magnetic field is the same as the direction of the subsequent static magnetic field. When applying a pulse magnetic field a plurality of times, the directions of the pulse magnetic fields are all the same as the direction of the subsequent static magnetic field. Make the direction of the magnetic field the same.

If the direction of the pulse magnetic field is the same as the direction of the static magnetic field, a bond magnet having a high degree of orientation can be obtained by the process according to the present invention. . The number of times of application of the pulse magnetic field is two or more, more preferably three or more.

The magnetic powder usable in the present invention, for example, an Nd-Fe-B-based anisotropic magnetic powder having no roundness and an irregular shape is hardly rotated by an alignment magnetic field. Is difficult, but by applying a pulse magnetic field with a high magnetic field strength several times in the same direction, or by alternately reversing the magnetic field direction of the pulse magnetic field with a high magnetic field strength, it was not sufficiently oriented at one time The magnetic anisotropic magnetic powder is easily oriented.

In the present invention, an orientation magnetic field using a combination of an ultrasonic vibration and a pulse magnetic field and a static magnetic field is used. In particular, the timing of applying the pulse magnetic field and the ultrasonic vibration is important. That is, the application of the pulse magnetic field is performed before the application of the ultrasonic vibration. By applying ultrasonic vibration to the compound, only the compound can be selectively heated without heating the mold, and warm press forming of bonded magnets becomes possible industrially. When applied, the powder fillability improves with this heating,
The bulk density of the compound increases. When a pulse magnetic field is applied after the application of the ultrasonic vibration, the gap between the compound powders is reduced due to the increase in the bulk density, and the magnetic powder becomes difficult to rotate / move due to the orientation magnetic field. It does not work effectively, and as a result, the degree of orientation of the molded body, that is, the magnetic properties are also reduced. If a pulse magnetic field is applied before the application of the ultrasonic vibration, the bulk density of the compound is small, so there are many gaps between the powders, and the pulse magnetic field as the alignment magnetic field allows the magnetic powder to rotate / move freely,
As a result, the degree of orientation of the molded body, that is, the magnetic properties are improved.

After the application of the pulse magnetic field, while applying the static magnetic field, the upper punch is depressed to apply ultrasonic vibration to the raw material powder in the mold cavity, and the ultrasonic vibration is stopped and the pressure is reduced.

The direction of the static magnetic field is the same as the direction of the pulse magnetic field in the same direction one or more times. In the case of a plurality of inversion pulse magnetic fields, the direction of the static magnetic field is the same as the last pulse magnetic field direction of the plurality of inversion pulse magnetic fields. When the initial magnetic field direction of the inversion pulse magnetic field is aligned with the direction of the subsequent static magnetic field, if the number of application of the inversion pulse magnetic field is an odd number, the direction of the last pulse magnetic field of the multiple inversion pulse magnetic fields and the direction of the static magnetic field Matches. If the number of application of the inversion pulse magnetic field is an even number, the direction of the last pulse magnetic field of the plurality of inversion pulse magnetic fields and the direction of the static magnetic field are opposite.

When the direction of the static magnetic field is opposite to the direction of the pulse magnetic field in the same direction one or more times, or in the direction opposite to the last pulse magnetic field of the plurality of inversion pulse magnetic fields, the direction is applied by applying the pulse magnetic field. The high degree of orientation of the magnetic powder
In addition to the disturbance caused by the rotation / movement of the magnetic powder due to the reduction during press molding, the magnetic powder is also disturbed by the static magnetic field in the opposite direction, so that the degree of orientation of the magnetic powder in the compact decreases and finally the magnetic properties of the bonded magnet deteriorate.

On the other hand, if the direction of the static magnetic field is the same as the direction of a single pulse magnetic field, or the direction of the pulse magnetic field of the same direction a plurality of times, or the direction of the last pulse magnetic field of the plurality of inversion pulse magnetic fields, Or, the orientation of the high-grade magnetic powder given by a plurality of pulse magnetic fields in the same direction or a plurality of inversion pulse magnetic fields can be further improved by ultrasonic vibration, and the orientation of the high-grade magnetic powder can be reduced. The magnetic field acts during press molding to maintain the magnetic field, and the disturbance due to the rotation / movement of the magnetic powder caused by the reduction during press molding is prevented by the static magnetic field, so that a molded article with highly oriented anisotropic magnetic powder can be obtained. Finally, a bonded magnet having high magnetic properties is manufactured. It is preferable that the static magnetic field be applied during the pressurization in order to maintain the orientation state of the magnetic powder.

By the ultrasonic vibration, the degree of orientation in the static magnetic field is further improved, and the compound is heated. During the application of the ultrasonic vibration, a pulse magnetic field in the same direction as the static magnetic field may be applied so as to be superimposed on the static magnetic field. Since this pulse magnetic field is still stronger than the static magnetic field, it acts to prevent a decrease in the degree of orientation during press molding. The intensity of this pulse magnetic field may be the same as the intensity of one or a plurality of pulse magnetic fields in the same direction or a plurality of inversion pulse magnetic fields.

The static magnetic field may be applied in the same direction so as to be superimposed on the pulse magnetic field when the pulse magnetic field before the application of the ultrasonic vibration is applied once or plural times in the same direction.

Ultrasonic waves having a frequency of 10 to 40 kHz and an amplitude of 1 to 100 μm can be applied. With an ultrasonic wave having a frequency of less than 10 kHz or exceeding 40 kHz, or an ultrasonic wave having an amplitude of less than 1 μm, it takes too much time to heat the compound by the ultrasonic vibration. For ultrasonic waves whose amplitude exceeds 100 μm,
The destruction of magnetic powder induced by ultrasonic vibration becomes remarkable,
The magnetic properties of the bonded magnet decrease. Preferably, an ultrasonic wave having a frequency of 15 to 35 kHz and an amplitude of 1 to 50 μm is applied.
The application time of ultrasonic vibration shall be 0.5 seconds or more. If the time is shorter than 0.5 second, the rise to the predetermined oscillation condition becomes sharp, and it is difficult to control the ultrasonic oscillation, which is not practical. When the binder resin of the compound is a solid resin, the application time is preferably set to a time necessary for melting the binder resin. In consideration of productivity, the application time of the ultrasonic vibration is preferably 10 seconds or less, particularly preferably 5 seconds or less, so that the ultrasonic wave is applied so that the thermosetting resin is heated to a desired temperature in the ultrasonic application time in this range. It is preferable to select the frequency and the amplitude.

The ultrasonic wave is applied to at least one member of the compression molding machine that is in contact with the compound in the mold, for example, in the case of a compression molding machine of the type that presses with upper and lower punches, the upper punch, the lower punch, the metal Assigned to at least one of the types. Specifically, by attaching an ultrasonic horn to the member, ultrasonic vibration can be performed. In the ring-shaped bonded magnet, the core (a cylindrical member disposed at a position corresponding to the hollow portion of the ring-shaped magnet and located at the center of the ring-shaped lower punch) may be ultrasonically vibrated.

After the application of the ultrasonic vibration as described above, the ultrasonic vibration is stopped, the compound is pressed by a punch, compression-molded, and shaped. The pressing force at this time is
The material may be selected so as to obtain a molded body having strength necessary for handling up to the heating equipment, and is not particularly limited. According to the present invention, the filling property of the compound is improved by the application of ultrasonic vibration, and also, since the resin is preferably melted, conventional cold compression molding, and even more than warm compression molding, The shaping can be performed with a lower pressing force.

A current in a direction opposite to the orientation direction (direction of the static magnetic field) is applied to a magnetic field coil for generating a static magnetic field to demagnetize the molded body.
Demold. As before, the molded body obtained by press molding is transferred to an appropriate heating furnace and heated to the temperature required for curing the thermosetting resin of the binder, and the bonded magnet in which the magnetic powder is bonded with the thermosetting resin Is obtained. Thereafter, if necessary, a treatment such as surface treatment such as painting or plating may be performed. By the present invention, even compared to conventional warm press forming,
Bonded magnets having higher magnetic properties can be formed in a short time.

[0058]

[Example] Irregular magnetic anisotropy Nd obtained by hydrotreatment
-Mix Fe-B-based magnetic powder (average particle size 150 μm) with 3 wt% epoxy resin (containing a curing agent and a curing accelerator, melting temperature 60 ° C) based on the weight of the magnetic powder as a binder and melt at 60 ° C. Raw material powder kneaded and magnetic powder coated with epoxy resin
(Compound). Press molding is performed using a magnetic field ultrasonic press molding machine as shown in FIG.
It was performed to obtain a molded body of 11 mm.

For the compound in the mold, a static magnetic field and / or a pulse magnetic field in a direction (transverse magnetic field) perpendicular to the rolling down direction can be applied from the magnetizing coil. In addition, by ultrasonically vibrating the upper punch, ultrasonic vibration (
A frequency of 20 kHz and an amplitude of 20 μm) were applied.

After the raw material powder is charged into the mold, a single pulse magnetic field having a magnetic field strength of 25 kOe, a plurality of pulse magnetic fields in the same direction, a plurality of inversion pulse magnetic fields are applied a predetermined number of times, and then 10 kOe. After applying ultrasonic vibration while applying a static magnetic field, press molding was performed (pressure 6 ton / cm ² , pressure holding time 1 second). The direction of the static magnetic field is the same as the direction of the pulse magnetic field when the pulse magnetic field is multiple times in the same direction as when the pulse magnetic field is one time. The direction was the same as the direction of the magnetic field.
The heating temperature of the compound by ultrasonic vibration is 80 ° C, which is the same as that of the mold heating press method performed as a conventional example.
The ultrasonic conditions were set so that

Thereafter, a current was applied in the opposite direction to the static magnetic field generating coil to demagnetize it, and it was demolded to obtain a compact. The molded body was heated at 120 ° C. for 60 minutes in an Ar gas atmosphere to cure the binder, thereby obtaining a bonded magnet.

As a conventional example, warm press molding for heating a mold was performed. As a comparative example, when applying only a static magnetic field and ultrasonic vibration without using a pulse magnetic field (A), applying a pulse magnetic field after applying ultrasonic vibration, and then performing press molding while applying a static magnetic field (B), When applying ultrasonic vibration while applying a static magnetic field, then stopping the ultrasonic vibration, applying a pulse magnetic field while applying the static magnetic field, and then applying press forming while applying the static magnetic field (C) , A bonded magnet was produced.

FIGS. 2 (a) to 2 (p) show pressurizing conditions, application conditions of a pulse magnetic field and a static magnetic field, application timings thereof, and timings of application of ultrasonic vibration in this embodiment. In the figure, the amount of pushing in the upper punch increases downward, and the dashed line indicates the timing at which ultrasonic vibration is applied. Further, in the graph of the magnetic field strength, a thick black line indicates the application timing and magnitude of the pulse magnetic field, and a linear graph indicates the application timing and magnitude of the static magnetic field.

The magnetic properties of the obtained bonded magnet were measured by the following method, and the results are shown in Table 1. (1) Magnetic properties Residual magnetic flux density (Br) and coercive force (iHc) of the obtained bonded magnet
In addition, the maximum energy product (BHmax) was measured using a BH tracer.

[0065]

[Table 1]

[0066]

According to the present invention, the following effects can be obtained. (1) By applying a pulsed magnetic field, it is possible to manufacture a bonded magnet having a high degree of orientation and a magnetic anisotropy.

(2) By applying ultrasonic vibration, a bonded magnet having a high magnetic powder filling rate and a high degree of orientation can be manufactured. (3) Anisotropic bonded magnets with higher magnetic properties can be formed in a shorter time than conventional warm press forming.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view of a press molding machine that can be used in the present invention.

FIGS. 2 (a) to 2 (p) are explanatory diagrams of pressurizing conditions, application conditions of a pulse magnetic field and a static magnetic field, application timings thereof, and timing of application of ultrasonic vibration in the embodiment.

Claims (5)

[Claims] 1. A mold is filled with a raw material powder composed of a magnetic anisotropic magnetic powder and a thermosetting resin, pressed in a magnetic field, and then the molded body is heated to cure the resin. A method of manufacturing a bonded magnet, which comprises applying a pulse magnetic field once or multiple times to a raw material powder filled in a mold during press molding in a magnetic field, Is applied to a mold and / or a punch, and then ultrasonic vibration is stopped, and shaping is performed by pressing force. 2. The method according to claim 1, wherein the direction of one pulse magnetic field is the same as the direction of the static magnetic field. 3. The method for manufacturing a bonded magnet according to claim 1, wherein the directions of the pulse magnetic field of the plurality of times are all the same as the direction of the subsequent static magnetic field. 4. The method according to claim 1, wherein the directions of the pulse magnetic field are alternately reversed a plurality of times, and the direction of the subsequent static magnetic field is the same as the direction of the pulse magnetic field immediately before the application of the static magnetic field. 2. A method for producing the bonded magnet according to 1. 5. The method for producing a bonded magnet according to claim 1, wherein the magnetic powder having magnetic anisotropy is a rare earth-iron alloy powder.