JPH1167568A - Manufacture of bonded magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the orientational degree of magnetic anisotropy, magnetic powder in a short molding time by a method wherein a pulsed magnetic field, whose magnetic field directions are alternately inverted, is applied to the magnetic powder a plurality of times and thereafter, an electrode magnetic field is applied to the magnetic powder and while the orientational degree of the magnetic powder is held, the powder is press-molded. SOLUTION: A pulsed magnetic field (an inverting pulsed magnetic field), whose magnetic field directions are alternately inverted, is applied to magnetic anisotropy magnetic powder, which is a raw material filled in a mold cavity, a plurality of times. The number of times of the application of the inverting pulsed magnetic field is set at two times or more and is set at about two to five times. After that, while an electrostatic magnetic field is applied to the raw powder, an upper punch is pushed down to press mold the raw powder in the mold cavity. At this time, the direction of the electrostatic magnetic field is made equal with the direction of the last pulsed magnetic field of the plurality of times of the inverting pulsed magnetic fields. After the press molding, the raw powder is cooled at a proper temperature, a current in the opposite direction to the orientational direction of the pulsed magnetic field is made to flow through a magnetic field coil for electrostatic magnetic field generation use, the raw powder is demagnetized and a molded material is demolded. Thereby, a magnetic anisotropy bonded magnet having a high orientational degree is manufactured.

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 magnetically anisotropic bonded magnet by press molding in a magnetic field, and more particularly to a bonded magnet having an improved degree of orientation of a magnetic anisotropic magnetic powder and thus improved magnetic properties. It provides a method that can be manufactured.

[0002]

2. Description of the Related Art A bonded magnet in which magnetic powder (hereinafter, also referred to as magnetic powder) is bonded with a resin contains a resin component that does not exhibit magnetism as compared with a conventional sintered magnet 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 that reason,
Bond magnets are widely applied from various home appliances to peripheral devices for large computers.
In particular, it has recently been 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,
It is manufactured by molding 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] Molding methods include 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 depends on the type of binder, but it is 2
It is as high as 00 to 300 ° C and 250 to 300 ° C for polyamide resin.

In press molding (also referred to as compression molding or pressure molding), a thermosetting resin is mainly used as a binder. Usually, a raw material powder (referred to as “compound”) in which a magnetic powder and a binder are compounded in advance is prepared, put into a mold, and press-formed by pressing with a punch. Obtained compact (also called green compact)
Is then heated to cure the thermosetting resin of the binder.

[0006] 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 conducted on improving the magnetic properties of the magnetic powder itself. In the case of Sm ₂ Co ₁₇ alloy-based or Nd-Fe-B alloy-based magnetic powders, the same magnetic properties are exhibited even when magnetized in any conventional direction. Magnetic anisotropic magnetic powder has been developed which can exhibit more excellent magnetic properties as compared with non-conductive magnetic powder.

This anisotropic magnetic powder has extremely high magnetic properties only in a certain fixed direction (the direction of easy magnetization). Do it below. Usually, a magnetic field coil or the like for forming a magnetic circuit is attached to a mold used for molding, and a magnetic field is applied to the powder to rotate the powder, thereby changing the direction of easy magnetization of the anisotropic magnetic powder to the direction of the magnetic field. (Ie, orient the powder).

When the magnetic powder is the same, the magnetic properties of the bonded magnet can be improved by increasing 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. 1-205403 and 2-116104 show that when press molding is carried out under heating to increase the fluidity of a thermosetting resin as a binder, the filling ratio of magnetic powder becomes high. It is described in.

On the other hand, with respect to the improvement of the degree of magnetic orientation, several means for improving the degree of magnetic orientation by applying a magnetic field have been proposed. For example, Japanese Patent Application Laid-Open No. 62-262413 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, then supplied to a magnetic field press molding machine, and subjected to magnetic field orientation press molding in a static magnetic field.
Further, Japanese Patent Application Laid-Open Nos. 60-88418, 60-10277, and 4-112504 propose various methods using a static magnetic field and a pulsed magnetic field together as an alignment magnetic field. .

JP-A-8-31677 discloses that a raw material powder containing anisotropic magnetic powder and a thermosetting resin powder as main components is filled in a mold capable of controlling a temperature and a magnetic field, and heated to reduce the resin. While applying a magnetic field after melting, orienting the magnetic powder,
Then, a method of performing compression molding by applying pressure is disclosed.

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.

[0015]

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, when 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 one press apparatus. In addition, there is also a problem that power consumption is large and a cost is increased because a large current is continuously supplied.

As proposed in JP-A-62-262413,
In the method using only the pulse magnetic field as the orientation magnetic field, the duration of the pulse magnetic field is usually as short as several milliseconds, and the charging time for generating the pulse current takes several seconds,
The orientation magnetic field can be applied only for a short time during the pressing. Furthermore, the timing at which the pulse magnetic field is applied greatly affects the degree of orientation. As described above, 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, since the rare-earth alloy-based anisotropic magnetic powder generally has an irregular shape, it is difficult for the magnetic powder to 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.However, since a method using a permanent magnet cannot demagnetize the molded body, It is difficult to handle the molded article after molding.

Japanese Patent Application Laid-Open No. 4-112504 discloses that when a compound is pressed and formed in a static magnetic field of a coil, pressurization and compression by an upper punch are performed in a plurality of times, and a pulsed magnetic field is applied at each pressurization and compression. A method of superimposing and applying the voltage is proposed. 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 greatly affects the degree of orientation of the compact, and the second and third pulse magnetic fields in which the pressing force increases do not effectively work to improve 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 is softened and melted during the press molding, and the magnetic powder becomes easy to move. Therefore, it is described that the filling rate and the degree of orientation of the magnetic powder are improved, and a magnetic anisotropic bonded magnet having excellent magnetic properties is obtained. However, as a result of investigations by the present inventors, it was found that even with this method, the degree of orientation of the anisotropic magnetic powder was not sufficiently improved, and there is still room for improvement.

In the method of applying a forward / reverse alternating static magnetic field as the orientation magnetic field, since the magnetic field is a static magnetic field, as described above, if the magnetic field strength is increased to increase the orientation of the anisotropic magnetic powder, The number of turns of the coil increases, the mold becomes larger,
It is difficult to realize an apparatus capable of taking a large number of pieces by one press molding apparatus, and the energy cost increases. Also,
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.

According to the present invention, it is possible to further improve the degree of orientation of a magnetic anisotropic magnetic powder in a magnetic field orientation press molding without elongating a molding time, thereby improving magnetic properties. It is an object to develop a method capable of manufacturing a bonded magnet.

[0024]

Means for Solving the Problems The present inventors have conducted intensive studies on efficient orientation magnetic field conditions and molding conditions that improve the degree of orientation of magnetically anisotropic magnetic powder in a short molding time. Applying a reversing pulse magnetic field (hereinafter, also referred to as a reversing pulse magnetic field) a plurality of times greatly improves the degree of orientation of the anisotropic magnetic powder. Press molding is performed while maintaining the improved degree of orientation by applying a static magnetic field. It has been found that by carrying out, the degree of orientation is remarkably improved, and thus a bonded magnet having excellent magnetic properties can be produced, and the present invention has been achieved.

Here, the present invention provides a method in which a raw material powder composed of a magnetic anisotropic magnetic powder and a thermosetting resin is filled in a mold, press-molded in a magnetic field, and the molded body is heated to form a resin. A method for manufacturing a bonded magnet, comprising curing a raw material powder filled in a mold, first applying a pulse magnetic field in which the magnetic field direction is alternately reversed a plurality of times, and then performing press molding while applying a static magnetic field. A method of manufacturing a bonded magnet, wherein the direction of the static magnetic field is the same as the direction of the pulse magnetic field immediately before the application of the static magnetic field.

In a preferred embodiment, press molding under application of a pulse magnetic field and a static magnetic field is performed while the raw material powder filled in the mold is heated to a temperature not lower than the melting temperature of the thermosetting resin. .

The reason why a bonded magnet with a significantly improved degree of orientation can be produced by the method of the present invention is considered as follows. By applying a pulse magnetic field having a large magnetic field strength, the magnetic anisotropic magnetic powder having a large saturation magnetization is greatly magnetized, and by applying the pulse magnetic field alternately and applying a plurality of times, the irregular shape is particularly reduced. The rotating torque due to the pulsed magnetic field effectively acts on the magnetic anisotropic magnetic powder, thereby improving the degree of orientation. Press molding is performed while applying a static magnetic field in the same direction as the last pulse magnetic field direction, so that the high degree of orientation of the magnetic powder obtained by the pulse magnetic field is maintained during press molding, so that the degree of orientation is significantly improved. Is obtained. Furthermore, when the above-described magnetic field orientation is performed at a temperature higher than the melting temperature of the resin of the compound, the frictional force between the magnetic powders is reduced due to the melting of the resin, and the rotational torque due to the magnetic force due to the pulsed magnetic field causes the magnetic anisotropic magnetic powder It works effectively by the orientation and further improves the degree of orientation.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION 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 as a binder, similarly to a conventional compound for press molding. The raw material powder may be a mixture of a magnetic powder and a thermosetting resin powder, 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 mixing the solution of the thermosetting resin with the magnetic powder. After that, 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. The magnetic anisotropic magnetic powder may be produced 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, or a hydrogen treatment (HDDR) method. Rare earth alloy-based magnetic anisotropic magnetic powders are generally irregular shaped powders, and therefore have a low degree of orientation. However, the present invention has a large effect of improving the degree of orientation when applied to such powders. Preferred magnetic powders are rare earth iron-based alloy powders including Nd-Fe-B-based, Sm-Fe-N-based and the like.

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 particle size range is 38 μm or more and less than 300 μm.

The thermosetting resin used as the binder is not particularly limited, and an epoxy resin, a phenol resin, a polyester resin, a melamine resin and the like which have been conventionally used for a bonded magnet 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. Furthermore, the melting temperature of the solid resin is 45 ° C to 90 ° C
Is desirably within the range.

When the melting temperature is lower 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. The raw material powder easily adheres to the mold when it is put into the mold, making it difficult to put it. Conversely, if the melting temperature exceeds 90 ° C., it takes time to heat the raw material powder in the mold until the resin is melted, so that the productivity is reduced.

Binder for magnetic powder (thermosetting resin)
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 formed bonded magnet becomes insufficient, the formability is deteriorated, and the mechanical strength of the obtained formed body and the finally obtained bonded magnet are significantly reduced. I do. On the other hand, when the mixing ratio of the binder exceeds 20% by weight, the ratio of the magnetic powder is reduced, and the magnetic characteristics are significantly reduced. When the magnetic powder is coated with a binder resin, a preferable mixing ratio of the binder is 2 wt% or more and 10 wt% or less, more preferably 2 wt% or more and 5 wt% or less.

[0034] In addition to the thermosetting resin and the magnetic powder, various additives conventionally used such as a coupling agent and a lubricant can be added to the raw material powder if necessary in a small amount. Further, two or more layers of the thermosetting resin can be coated with different resins.

The raw material powder is fed into a mold and press-formed in a magnetic field. In the present invention, press molding is performed in a static magnetic field after applying a reversing pulse magnetic field to the magnetic field orientation. The press molding temperature may be room temperature, but is preferably performed at a temperature at which the thermosetting resin of the binder is melted. Since the frictional force between the magnetic powders is reduced by the melting of the binder, the rotational torque acting on the magnetic powders due to the orientation magnetic field is more effectively applied to the orientations, thereby obtaining a molded article in which the degree of orientation of the anisotropic magnetic powders is significantly improved.

Therefore, the press molding machine to be used is provided with means for applying a pulse magnetic field and a static magnetic field such as an electromagnet, and preferably means for heating a mold. 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 heating temperature for warm press molding (the heating temperature of the mold is actually higher than the melting temperature of the thermosetting resin used for the raw material powder) because the heating of the raw material powder is performed through a mold. Is preferred. Of course, this temperature must not be higher than the curing temperature of the thermosetting resin. The preferred heating temperature is not lower than the melting temperature of the thermosetting resin and not higher than the melting temperature + 50 ° C, more preferably the melting temperature +30.
° C or lower, particularly preferably a melting temperature + 20 ° C or lower.

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 degree of orientation of the obtained bonded magnet is considerably reduced. 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 is usually
A pressure of 15 kOe or less and a pulse magnetic field of 40 kOe or less, especially 35 kOe or less are sufficient. The time (pulse time) of one waveform of the pulsed magnetic field is preferably 1 microsecond to 1 second, more preferably 5 microseconds to 100 milliseconds.

Press molding can be carried out by feeding 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 prior art. The pressing force is not particularly limited, and may be the same as that in the related art, preferably 8 to 10 ton / cm ² , more preferably 6 to 8 ton / cm ² .
It is within the range of ² . The pressure holding time is usually about 1 to 3 seconds.

Before the raw material powder filled in the mold cavity is pressurized as described above, a reversal pulse magnetic field is first applied a plurality of times. In particular, irregularly shaped magnetic anisotropic magnetic powder is hard to rotate in a static magnetic field, and it has conventionally been difficult to sufficiently increase the degree of orientation. According to the present invention, a pulse magnetic field having a high magnetic field strength is applied a plurality of times by alternately inverting the direction of the magnetic field. Are easily oriented. The number of application of the inversion pulse magnetic field is not limited as long as it is two or more, but usually 2 to 5 times, particularly 2 to 4 times is sufficient. Even if the number of times of application is further increased, the effect of improving the degree of orientation is saturated, and the molding time becomes longer.

The application of the reversal pulse magnetic field may be performed after the magnetic powder in the mold cavity is lightly pressed.
The guideline for this light pressing is that the bulk density of the filled magnetic powder (the value obtained by dividing the weight of the resin-coated magnetic powder filled in the mold cavity by the volume of the mold cavity) is the maximum bulk obtained by tapping. It is less than 85% of the density (tap density). Even if the reversal pulse magnetic field is applied after further pressurization, the magnetic powder is less likely to rotate due to the small gap around the magnetic powder, and the effect of improving the degree of orientation by the reversal pulse magnetic field is reduced.

Thereafter, while applying a static magnetic field, the upper punch is pushed down to press-mold the raw material powder in the mold cavity. The direction of the static magnetic field is the same as the direction of the last pulse magnetic field of the multiple inversion pulse magnetic fields. When the initial magnetic field direction of the inversion pulse magnetic field is set to the same direction as the static magnetic field direction, if the number of application of the inversion pulse magnetic field is an odd number, the last pulse magnetic field direction becomes the same as the static magnetic field direction, and it may be even. In this case, the direction of the last pulse magnetic field is opposite to the direction of the static magnetic field. vice versa,
When the initial magnetic field direction of the inversion pulse magnetic field is opposite to the static magnetic field direction, if the number of application of the inversion pulse magnetic field is even, the last pulse magnetic field direction becomes the same as the static magnetic field direction, and the odd number Then, the direction of the last pulse magnetic field is opposite to the direction of the static magnetic field.

When the direction of the static magnetic field is opposite to the direction of the last pulse magnetic field of a plurality of reversal pulse magnetic fields, the orientation of the magnetic powder is imparted by application of the reversal pulse magnetic field, and the high degree of orientation of the magnetic powder is reduced by the pressing during press molding. In addition to the disturbance caused by the rotation / movement of the compact, the disturbance is also caused by the static magnetic field in the opposite direction, the degree of orientation of the magnetic powder of 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 the last pulse magnetic field of the inversion pulse magnetic field, the static magnetic field acts so as to maintain the orientation of the high magnetic powder given by the plurality of inversion pulse magnetic fields. However, since the turbulence is hindered by the static magnetic field due to the rotation / movement of the magnetic powder due to the reduction during press molding, a molded body in which highly anisotropic magnetic powder is oriented is obtained, and finally a bonded magnet having high magnetic properties is manufactured. You. In order to maintain the orientation state of the magnetic powder, it is preferable to apply a static magnetic field during press molding, particularly during pressurization.

During the press molding, 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 the inversion pulse magnetic field.

After press molding, preferably, the molded body in the mold is cooled to a temperature lower than the melting temperature of the resin by a suitable cooling means, and the magnetic field coil for generating a static magnetic field is oriented in the direction opposite to the orientation direction (the direction of the static magnetic field). In the case where the current is passed to demagnetize and the mold is heated, the molded body is demolded after cooling.

The molded body obtained by press molding is transferred to an appropriate heating furnace and heated to a temperature necessary for curing the thermosetting resin of the binder, as in the prior art, and the magnetic powder is bound by the thermosetting resin. The resulting bonded magnet is obtained. Thereafter, processing such as machining and surface treatment may be performed as necessary.

[0048]

[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 hardener and a hardening 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).

The raw material powder was press-formed using a press-forming machine in a magnetic field so as to obtain a formed body having a cross-sectional area of 9 × 11 mm. This press molding machine is provided with a mold to which a temperature control device is attached, and can keep the mold temperature constant. Further, the mold is also provided with a magnetizing coil to which 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.

After the raw material powder is put into a mold maintained at 20 ° C. or 80 ° C., at 80 ° C., after confirming that the resin of the raw material powder has melted, a reverse pulse magnetic field of 25 kOe is applied. Press molding was performed while applying a predetermined number of times, and then applying a static magnetic field of 10 kOe as an orientation magnetic field (pressure 6 ton / cm).
² , pressurization holding time 1 second). The direction of the first pulse magnetic field of the inversion pulse magnetic field was the same as the direction of the static magnetic field, except for the method described later. Therefore, when the number of times of application of the inversion pulse magnetic field was odd, the direction of the last pulse magnetic field was the same as the direction of the static magnetic field, and when the number was even, the direction of the last pulse magnetic field was opposite to the direction of the static magnetic field. In the method, the direction of the first pulse magnetic field of the reversing pulse magnetic field is opposite to the direction of the static magnetic field. become.

Thereafter, a reverse current is applied to the static magnetic field generating coil to demagnetize the coil, and when the mold temperature is 80 ° C., the mold is cooled by a temperature controller, and then the mold is removed to form a molded body. I got 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, only a static magnetic field (10 kOe) or an inverted static magnetic field (10 kOe) in which the direction of the static magnetic field is alternately inverted is applied without applying an inverted pulse magnetic field before press molding. Press molding was performed while performing.

As a comparative example, in the same direction as the direction of the static magnetic field.
After applying a pulse magnetic field a plurality of times (without reversing the pulse direction), press molding was performed while applying a static magnetic field (10 kOe) as an orientation magnetic field, to produce a bond magnet.

The magnetic properties of the obtained bonded magnet were measured by the following method. The test results are also shown in Table 1.

(1) Magnetic Properties The magnetic properties of the obtained bonded magnet were measured with a BH tracer. In addition, VSM measurement of the raw material magnetic powder was performed, and the degree of orientation was calculated from the ratio of the residual magnetic flux density of the compact to the residual magnetic flux density of the raw material magnetic powder by the following formula.

(Degree of orientation of bonded magnet) = B / B ₀ / V _f B: Br (kG) of bonded magnet B ₀ : Br (kG) of raw material magnetic powder (= 12.3) V _f : Volume filling rate of magnetic powder V _f = D × X _m / D _m D: Bonded magnet density (g / cm ³ ) X _m : Magnetic powder weight fraction (= 0.97) D _m : Magnetic powder density (= 7.6 g / cm ³ )

[0057]

[Table 1]

As is evident from Table 1, according to the method of the present invention shown in Table 1 and as shown in Table 1, 92-93% in the case of cold press molding at 20 ° C., and indeed in the case of warm press molding at 80 ° C.
Bond magnets with an extremely high degree of orientation, which is unprecedented, ranging from 95% to 98.5%, were obtained. Although the number of times of application of the inversion pulse magnetic field is effective even if it is twice, the effect of improving the degree of orientation in the case of warm pressing is more significant when it is set to three times. Even if this number is increased to five, the improvement in the degree of orientation is small, so three to four times is sufficient.

On the other hand, the method in which the direction of the last pulse magnetic field is opposite to the direction of the static magnetic field even when the reverse pulse magnetic field is applied in the same manner is a method in which only the static magnetic field is applied during press molding. The degree of orientation was hardly improved as compared with. In addition, the method of inverting the static magnetic field has almost no effect of improving the degree of orientation as compared with the method of reversing the static magnetic field. The case where the number of application of the reversal magnetic field is one is a case where the pulse magnetic field is applied only once in the same direction as the static magnetic field before press molding in the magnetic field. In this case, although there is an effect of improving the degree of orientation, the effect was smaller than that of the method of the present invention in which a switching magnetic field was applied a plurality of times.

A method of applying a pulse magnetic field in the same direction as the static magnetic field a plurality of times and then press-forming in the static magnetic field has an effect of improving the degree of orientation as compared with the method of applying the pulse magnetic field, but this pulse magnetic field is applied only once. (That is, the number of application of the pulse magnetic field is one), the effect was almost the same.
That is, if the pulse magnetic field is in the same direction, even if the number of times of application is increased from once to a plurality of times, the degree of orientation is hardly improved. The method in which the inversion pulse magnetic field is applied a plurality of times during the static magnetic field press molding has a lower degree of orientation than the method described above, and the application of the inversion pulse magnetic field during the static magnetic field press molding has an adverse effect on the orientation in the static magnetic field You can see that.

[0061]

According to the present invention, the following effects can be obtained.

(1) It is possible to produce a bonded magnet having a magnetic anisotropy with an unprecedentedly high degree of orientation. In particular, when press molding is performed warmly, the degree of orientation reaches 98% or more. In addition, by pressing the raw material powder obtained by coating the magnetic powder with a thermosetting resin,
The filling rate of the magnetic powder also increases. In combination with these effects, it is possible to obtain a bonded magnet having excellent magnetic properties, making full use of the high magnetic properties of magnetic anisotropic magnetic powder.

(2) It is not necessary to stop the upper punch during pressurization and apply a pulsed magnetic field, and press-mold after sufficiently magnetizing and orienting the magnetic powder inside the mold, so that the punch speed can be increased. Furthermore, since the molded body can be demagnetized inside the mold, the time for press molding can be shortened, and the productivity can be improved.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shuji Mino 2-15-17 Egawa, Shimamoto-cho, Mishima-gun, Osaka Prefecture Inside Yamazaki Works, Sumitomo Special Metals Co., Ltd. (72) Inventor Naoyuki Ishigaki 2 Egawa, Shimamoto-cho, Mishima-gun, Osaka Chome 15-17 Sumitomo Special Metals Co., Ltd. Yamazaki Works

Claims (3)

[Claims] 1. A method comprising filling a mold with raw material powder composed of magnetic powder having magnetic anisotropy and a thermosetting resin, press-molding in a magnetic field, and then heating the molded body to cure the resin. In a method for manufacturing a bonded magnet, a raw material powder filled in a mold is subjected to press molding while applying a static magnetic field after applying a pulse magnetic field in which the magnetic field direction is alternately reversed a plurality of times. A method of manufacturing a bonded magnet, wherein the direction of a magnetic field is the same as the direction of a pulse magnetic field immediately before applying a static magnetic field. 2. The press molding under application of a pulse magnetic field and a static magnetic field in a state where the raw material powder filled in a mold is heated to a temperature not lower than the melting temperature of the thermosetting resin. Of manufacturing bonded magnets. 3. The method for producing a bonded magnet according to claim 1, wherein the magnetic powder having magnetic anisotropy is a powder of a rare-earth iron-based alloy.