JP2022157625A - Method for manufacturing compressed bond magnet - Google Patents

Abstract

To provide a manufacturing method for obtaining a compressed bond magnet having high density and high orientation.SOLUTION: A method for manufacturing a compressed bond magnet includes a molding step of compressing a bond magnet raw material composed of magnet powder and a binder resin capable of binding the magnet powder in a cavity while heating the bond magnet raw material. The magnet powder contains anisotropic magnet powder. The binder resin contains a thermosetting resin. The molding step includes a first molding step of molding the raw material while applying an orientation magnetic field into the cavity, and a second molding step of molding the raw material by reducing or blocking the orientation magnetic field after the first molding step. The application of the orientation magnetic field is blocked in the middle of the molding step, which achieves high density of the bond magnet while maintaining orientation of the magnet particles. The manufacturing method can also reduce a compressive force in the molding step.SELECTED DRAWING: Figure 2

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a compression bond magnet, and the like.

Electromagnetic devices (motors, etc.) using rare earth magnets are often used in order to improve performance and save energy. Rare earth magnets include sintered magnets obtained by sintering rare earth magnet powder and bonded magnets obtained by binding rare earth magnet powder with a binder resin. Bond magnets are superior to sintered magnets in moldability and have a greater degree of freedom in shape.

Bonded magnets mainly consist of injected bonded magnets, which are integrally molded by injecting a molten mixture of magnet powder and thermoplastic resin into the cavity of the housing (rotor core slot, etc.), and mixtures of magnet powder and thermosetting resin, or There is a compression bonded magnet formed by compressing a kneaded material in a cavity such as a mold or a housing. Compression bond magnets generally use a thermosetting resin as the binder resin, and are therefore superior in heat resistance to injection bond magnets. Patent Document 1 below describes a method for manufacturing such a compression bond magnet.

JP-A-8-31677

Patent Document 1 proposes a method for manufacturing a magnetically anisotropic resin-bonded magnet (simply referred to as a "bonded magnet"). The specific steps are as follows ([0024], [0065], etc. of Patent Document 1).

First, raw material powder obtained by mixing magnet powder and thermosetting resin (epoxy resin) powder (simply referred to as “resin powder”) is fed into a heated mold (mold temperature: 150° C.). Next, after the resin powder melts, application of a magnetic field (16 kOe) is started, and after the melted resin reaches the minimum viscosity, pressure (8 ton/cm ² ) is started.

After that, the cross-linking reaction of the liquefied resin progresses, and when the viscosity increases, magnetic field application, heating and pressurization are terminated, and the bond magnet is taken out from the molding die. The bonded magnet that is taken out is subjected to heat curing treatment (curing treatment) at the same temperature as the mold temperature.

In the heating magnetic field molding of Patent Document 1, an intentional time difference is set between the start of magnetic field application and the start of pressurization. However, no significant time difference is set between the end of magnetic field application and the end of pressurization. That is, in the case of Patent Document 1, the end of magnetic field application and the end of pressurization are performed substantially at the same time.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and an object of the present invention is to provide a novel method for manufacturing a compression bond magnet, which is different from the conventional method.

As a result of intensive research, the present inventor newly found that the density of the bonded magnet can be increased by reducing or blocking the oriented magnetic field during the molding process of heating and compression. Developing this result led to the completion of the present invention described below.

<<Manufacturing method of compression bonded magnet>>
(1) The present invention comprises a molding step of heating and compressing in a cavity a bond magnet raw material comprising magnet powder and a binder resin capable of binding the magnet powder, wherein the magnet powder is an anisotropic magnet powder. wherein the binder resin contains a thermosetting resin, and the molding step includes a first molding step in which an oriented magnetic field is applied to the cavity, and after the first molding step, the oriented magnetic field is reduced or blocked. and a second molding step performed by:

(2) According to the manufacturing method of the present invention, the compression bond magnet (simply referred to as "bond magnet") can be produced by reducing or blocking the oriented magnetic field (referred to as "blocking or the like") without increasing the compressive force. Higher density is achieved. Conversely, it is possible to mold a bonded magnet having a desired degree of orientation and density while reducing the compressive force. By reducing the compressive force, for example, it is possible to suppress deformation of the mold/casing forming the cavity, improve the precision of the bonded magnet, or suppress cracking of the magnet particles.

《Compression bond magnet/Magnetic member》
The present invention can also be grasped as a compression bond magnet obtained by the manufacturing method described above. The present invention can also be grasped as a magnetic member in which a compression bond magnet and a housing having a cavity are integrated. A field element is an example of a magnetic member (such as an electromagnetic member).

A field element is, for example, a rotor or a stator of an electric motor. Electric motors include generators as well as motors. The motor may be a DC motor or an AC motor. If the field element is a rotor, for example, the housing is the rotor core and the cavity is its slot. The rotor may be an inner rotor or an outer rotor.

"others"
Unless otherwise specified, "x to y" as used herein includes the lower limit value x and the upper limit value y. A new range such as “a to b” can be established as a new lower or upper limit of any numerical value included in the various numerical values or numerical ranges described herein. Further, unless otherwise specified, "x to y MPa" as used herein means x MPa to y MPa. The same applies to other unit systems (μm, etc.).

FIG. 4 is an explanatory view schematically showing each process of molding in a heating magnetic field; It is a time chart of the compressive force and the oriented magnetic field during the molding. 4 is a graph showing changes in viscosity of thermosetting resin over time. 4 is a graph showing the relationship between the compressive force (molding pressure) and the density of the bond magnet for the case of non-magnetic field molding and the case of magnetic field molding. FIG. 4 is a schematic diagram illustrating the effect of the presence or absence of a magnetic field applied during molding on the density of a bonded magnet. FIG. 4 is a scatter diagram showing the effect of different molding methods on the density of a bonded magnet for each compression force. FIG. 4 is a scatter diagram showing the relationship between the end of application of an aligning magnetic field and the density, degree of orientation, or residual magnetic flux density of a bond magnet (compressive force: 20 MPa). FIG. 4 is a scatter diagram showing the relationship between the end of application of an aligning magnetic field and the density, degree of orientation, or residual magnetic flux density of a bond magnet (compressive force: 30 MPa). 4 is an appearance photograph of an IPM rotor in which bond magnets are integrally formed in slots.

One or more components arbitrarily selected from the items described herein can be added to the configuration of the present invention described above. A component related to a manufacturing method can also be a component related to an object. Which embodiment is the best depends on the target, required performance, and the like.

《Molding in heating magnetic field》
An overview of the magnetic field heating molding according to the present invention and a mechanism by which the density of the bonded magnet can be increased will be described with reference to FIGS. 1A to 1E (collectively referred to as "FIG. 1").

(1) Overview Bond magnets are molded in a heated magnetic field through the steps shown in FIG. 1A in order. Each process is as follows. A raw material consisting of magnet powder and binder resin (mainly thermosetting resin) is supplied (thrown in, accommodated, etc.) into a heated cavity of a mold or the like (supply process). FIG. 1A illustrates the case where the cavity is formed by a die and upper and lower punches. Unless otherwise specified, heating is continued from the start of molding (at the time of raw material supply) to the end of molding (discharge of the bonded magnet).

After the binder resin (especially thermosetting resin/simply referred to as "resin") starts to melt in the cavity, an orientation magnetic field is applied (orientation process). However, the raw material may be supplied into the cavity to which the orientation magnetic field is applied. In other words, it does not matter whether the supply of the raw material and the application of the aligning magnetic field are performed before or after, and they may be performed at the same time. It is preferable to apply an aligning magnetic field after supplying the compound so that the compound can be injected into the cavity without being affected by the magnetic field.

Compress (pressurize) the heated and magnetic field applied raw material (orientation compression process). After that, the aligning magnetic field is interrupted while the compression is continued (compression process).

FIG. 1B shows temporal changes (time charts) of the orientation magnetic field (H) and compressive force (P) applied to the raw material. In the heating magnetic field molding according to the present invention, not only between the start of magnetic field application (t1) and the start of compression (t2), but also between the end of magnetic field application (t3) and the end of compression (t4) A significant time difference (Δt) is also intentionally set between .

(2) Mechanism The reason why a highly oriented and high-density bonded magnet can be obtained by the orientation compression process (corresponding to the first molding process) and the compression process (corresponding to the second molding process) is considered as follows.

First, the resin heated in the cavity melts and becomes liquid. The viscosity initially decreases monotonically with time, reaches a minimum (minimum), and then increases monotonically, as shown in FIG. 1C. When the heating is continued further, the resin is thermally cured into a solid state. Note that the change in viscosity of the raw materials (magnet particles and resin) usually has a similar tendency to the change in viscosity of the resin.

Next, the density of the bonded magnet obtained by heating and compressing the raw material by applying an aligning magnetic field (referred to as "magnetic field molding"), ), the density of the bonded magnet obtained is, for example, as shown in FIG. 1D. In either case, the density of the bonded magnet increases with increasing compressive force. However, when viewed with the same compressive force, the bond magnet molded without a magnetic field has a higher density than the bonded magnet molded in a magnetic field.

Although it is not clear why the density of the bond magnet changes depending on the presence or absence of the aligning magnetic field (H) even with the same compressive force (P), the results suggest the following. As shown in FIG. 1E, in the case of molding in a magnetic field, a stronger magnetizing force acts in the direction of the aligning magnetic field (H) by the amount of the aligning magnetic field between the magnet particles and the inner wall surface of the cavity or between adjacent magnet particles. . Under these circumstances, when a compressive force perpendicular to the oriented magnetic field (H) acts on the compound consisting of the magnet powder and the binder resin, friction proportional to the magnetizing force occurs between the inner wall surface of the cavity and the magnet particles and between the magnet particles. A force (f) is generated. Due to such a frictional force, the magnet particles molded in a magnetic field are more restricted in their posture change and movement in the direction of compression than the magnet particles molded in the non-magnetic field. As a result, it is considered that the density of the bonded magnet is lower when molded in a magnetic field than when molded without a magnetic field.

When the orientation compression process and the compression process are performed as in the present invention, the viscosity change of the resin and the effect of the orientation magnetic field on the density act additively or synergistically, resulting in a highly oriented and high-density bonded magnet. is obtained. Specifically, first, in the alignment compression process, the magnet particles sufficiently change their postures (movement, rotation, etc.) along the alignment magnetic field in the resin whose viscosity has decreased, and high alignment is achieved. Next, in the compression process, it is compressed in a state where there is no resistance due to the orientation magnetic field, and high density is achieved.

It should be noted that the timing of interrupting the aligning magnetic field (timing of starting the compression process (second molding process)) should be around the time when the viscosity of the melted resin reaches a minimum. If the timing is too early, it may lead to a decrease in the degree of orientation. If it is too late, the density increase will be insufficient.

《Molding process》
The compressive force may be conventionally high pressure or low pressure. In order to obtain a more sufficient effect, the compressive force may be as low as 5-50 MPa or even 10-40 MPa. By reducing the compressive force, cracking of the magnet particles, deformation of the housing forming the cavity, and the like can be suppressed.

The first molding step and the second molding step may have the same or different compressive forces. For example, if the compressive force is constant, the pressurizing device, pressurization control, etc. can be simplified. The compressive force during the second molding step, in which the viscosity of the resin has already increased sufficiently, may be made greater than the compressive force during the first molding step to further increase the density of the bonded magnet.

The heating temperature during the molding process is adjusted according to the properties of the binder resin (especially thermosetting resin). The heating temperature is, for example, 100 to 200°C, 120 to 180°C, further 130 to 170°C. If the heating temperature is too low, the softening or melting of the resin will be insufficient, resulting in a decrease in the degree of orientation and density. If the heating temperature is too high, oxidative deterioration of the magnet particles and premature curing of the thermosetting resin may occur.

The aligning magnetic field during the molding process is usually applied in an aligning direction that intersects (or is perpendicular to) the compression direction of the bonded magnet raw material. The magnitude of the aligning magnetic field is, for example, 0.5-3T or even 1-2T. The oriented magnetic field is the magnetic flux density on the inner peripheral surface of the cavity in which the bonded magnet is molded. In addition to the electromagnet, a rare earth permanent magnet may be used as the magnetomotive source of the aligning magnetic field.

《Raw materials for bonded magnets》
The bond magnet raw material may be a compound or a compound preform.

The compound consists of granules obtained by mixing or kneading (referred to as “mixing, etc.”) magnetic powder and binder resin. Mixing and the like should be performed at least at a temperature (softening point) or higher at which the binder resin softens and at a temperature lower than a temperature at which the thermosetting resin contained in the binder resin hardens too rapidly. The temperature is, for example, 40 to 120.degree. C., further 80 to 100.degree.

The raw materials for bonded magnets are preferably prepared by mixing under conditions in which damage such as cracks is unlikely to occur in the magnet particles. Specifically, the magnet powder and the binder resin should be mixed in a state where the pressure (shear stress) does not act so much. For mixing, for example, a batch-type kneader may be used. At this time, it is preferable to heat and mix by rotating the blades in a state where the load of the bond magnet raw material is set to about 75% or less, preferably 65% or less of the processing volume of the processing tank, and no pressure is applied.

The preform consists of a block obtained by forming the above-described compound into a predetermined form (shape, size). If the preform has a form similar to that of a bonded magnet, it can be efficiently accommodated (thrown in) into the cavity. The preform may have a form dissimilar to a bonded magnet. For example, it may be a segmented body (pellet, etc.) within a range that can be filled or loaded into the cavity. In this case, there is no need to prepare a dedicated preform for each bond magnet, and the versatility of the preform increases.

The preforming (process) should also be carried out under conditions in which damage such as cracks is unlikely to occur in the magnet particles. Preforming is usually performed by pressing a compound filled in a cavity separate from the cavity for molding the bond magnet.

《Magnet Powder》
The magnet powder is contained, for example, in an amount of 60 to 80% by volume, 65 to 75% by volume, or further 68 to 73% by volume, relative to the entire bonded magnet raw material (bonded magnet) (total of magnet powder and binder resin). Good. If the magnetic powder is too small, the magnetic properties of the bonded magnet will be lowered, and if the magnetic powder is too large, the degree of orientation or density will be lowered.

The magnet powder may be a single type of powder or multiple types of powders as long as it contains anisotropic magnet powder (particles). The multiple types of powders are, for example, mixed powders in which powders differing in at least one of morphology (especially particle size), component composition, and magnetic properties (including irreversible demagnetization) are mixed.

As an example, a mixed powder containing coarse powder and fine powder having different average particle diameters may be used. The coarse powder has an average particle size of, for example, 40 to 200 μm, further 80 to 160 μm. The fine powder has an average particle size of, for example, 1 to 10 μm, further 2 to 6 μm. The average particle size referred to in this specification is determined by measuring with a laser diffraction particle size distribution analyzer (HELOS manufactured by Nippon Laser Co., Ltd.).

The volume ratio of the coarse powder to the sum of the coarse powder and the fine powder (or the entire magnetic powder) is, for example, 60 to 90% by volume, or 65 to 85% by volume. In other words, the volume fraction of the fine powder to the total is, for example, 10-40% by volume, or even 15-35% by volume.

If the particle sizes and ratios of the coarse and fine powders and the magnet amount (resin amount) relative to the entire bonded magnet raw material (bonded magnet) are within a predetermined range, a high-density bonded magnet can be obtained even when low-pressure molding is performed.

For the magnet powder, for example, hydrogen-treated rare earth anisotropic magnet powder is used. Hydrogenation is mainly a disproportionation reaction due to hydrogen absorption (Hydrogenation-Disproportionation, also simply referred to as "HD reaction") and a recombination reaction due to dehydrogenation (Desorption-Recombination, also simply referred to as "DR reaction"). Accompanied by The HD reaction and DR reaction are collectively referred to simply as "HDDR reaction". Also, the hydrotreating that produces the HDDR reaction is simply referred to as "HDDR(process)."

The HDDR referred to in this specification also includes the improved d-HDDR (dynamic-Hydrogenation-Disproportionation-Desorption-Recombination) unless otherwise specified. d-HDDR is described in detail in, for example, International Publication (WO2004/064085).

An example of coarse powder is NdFeB-based anisotropic magnet powder containing Nd, Fe, and B as base components. Examples of fine powder include SmFeN anisotropic magnet powder containing Sm, Fe, and N as base components or SmCo anisotropic magnet powder containing Sm and Co as base components. NdFeB-based anisotropic magnet powder whose particle size has been adjusted may be used as the fine powder (partially).

Magnet powders other than rare earth anisotropic magnet powder (rare earth isotropic magnet powder, ferrite magnet powder, etc.) may be included as part of the magnet powder. In addition, the base component as used in this specification can be rephrased as an essential component or a main component. The total amount of elements serving as base components is usually 80 atomic % or more, preferably 90 atomic % or more, relative to the entire object (magnet particles). The rare earth magnet powder may contain elements (heavy rare earth elements such as Dy and Tb, Cu, Al, Co, Nb, etc.) that enhance coercive force and heat resistance.

《Binder Resin》
The binder resin contains a thermosetting resin. Thermosetting resins include epoxy resins, phenolic resins, melamine resins, urea resins, unsaturated polyester resins, and the like. A typical epoxy resin is usually a mixture of a main agent (prepolymer) and a curing agent, and is cured by crosslinking network formation by epoxy groups. As prepolymers of epoxy resins, for example, novolac type, bisphenol A type, bisphenol F type, biphenyl type, naphthalene type, aliphatic type, glycidylamine type, and the like are used. As curing agents for epoxy resins, for example, amine-based, phenol-based, and acid anhydride-based curing agents are used.

When a one-liquid epoxy resin is used, the timing of thermosetting can be adjusted by curing treatment (thermosetting step), and efficient batch treatment and the like are possible. Cure treatment is performed by heating the bonded magnet after the molding process to 130 to 250.degree. C., or 150 to 230.degree.

Incidentally, each magnet particle may be coated with a surfactant suitable for the resin used. As a result, the posture changeability of the magnet particles in the softened or melted resin, the bonding between the magnet particles and the resin, and the like can be improved. When using an epoxy resin, for example, a titanate-based coupling agent or a silane-based coupling agent is used as a surfactant. Incidentally, the thickness of the surfactant layer may be about 0.1 to 2 μm.

《Bond Magnet》
The bonded magnet preferably has a relative density of, for example, 90% or higher, 95% or higher, or 98% or higher. The upper limit of relative density is 99% or even 100%. The relative density (ρ/ρ ₀ ) is the ratio (percentage) of the actual density (ρ) to the theoretical density (ρ ₀ ). The theoretical density (ρ ₀ ) is obtained from the true densities of the magnet powder and the binder resin, which constitute the bonded magnet, and their compounding amounts. The actual density (ρ) is determined from the mass and volume obtained by measuring the molded (and cured) bonded magnet. The volume may be determined by the Archimedes method or calculated from the shape (dimensions) of the compact.

The bond magnet may be magnetized (magnetizing magnetic field: 2 to 6 T) before or after curing. A bonded magnet can exhibit a high residual magnetic flux density (Br) of, for example, 0.7 T or more, 0.75 T or more, or even 0.8 T or more.

The bonded magnet preferably has an irreversible demagnetization rate (after 1000° C.×1000 hours), which is an index of heat resistance or durability, for example, within −3%, within −2%, or within −1.5%.

《Magnetic member》
Bonded magnets are used in various magnetic members. Integrally molding the bonded magnet within the cavity of the housing allows for efficient manufacturing of the magnetic member. Low-pressure molding of the bonded magnet suppresses deformation of the housing forming the cavity. As a result, it is possible to increase the degree of freedom in designing the housing and improve the accuracy of the magnetic member. A representative example of such a magnetic member is a field element of an electric motor (vehicle drive motor, air conditioner, home electric appliance motor, etc.).

Several samples (compression bonded magnets) were produced under different molding conditions, and their characteristics were measured and evaluated. The present invention will be described in detail below based on such specific examples.

<<First embodiment/manufacture of sample>>
(1) Magnet powder and binder resin As the magnet powder, commercially available NdFeB-based anisotropic magnet powder (Magfine/Br:1. 28 T, iHc: 1313 kA/m, average particle size: 125 μm), and a commercially available SmFeN anisotropic magnet powder (Sumitomo Metal Mining Co., Ltd. SmFeN alloy fine powder C/Br: 1.35 T, iHc: 875 kA). /m, average particle size: 3 μm).

An epoxy resin (NC-3000L manufactured by Nippon Kayaku Co., Ltd.), which is a thermosetting resin, was prepared as the binder resin. The main component of this resin is biphenyl type, and the curing agent is phenol type. Also, its softening point was 60°C.

(2) Raw Material for Bonded Magnet A raw material for bonded magnet was prepared by mixing magnet powder obtained by weighing coarse powder and fine powder at 8:2 (mass ratio/volume ratio is almost the same) and binder resin. The magnet powder was 70% by volume (binder resin: 30% by volume) of the total mixture (bonded magnet raw material) of magnet powder (coarse powder and fine powder) and binder resin.

The magnetic powder and the binder resin were mixed by rotating the kneader at a low speed (10 rpm) for 5 minutes in a non-pressurized state. At this time, the container of the kneader was kept at 90°C. Thus, a compound was obtained by melt-mixing the magnet powder and the binder resin (melt-mixing step).

(3) Molding The compound was filled into the cavity of the mold (housing step). The temperature of the mold (inner wall surface of the cavity) was maintained at 150° C. (constant) from the start of molding (before filling) to the end of molding. The compressive force (P) applied to the cavity was either 10 MPa, 20 MPa or 30 MPa.

Note that the bond magnet may be integrally molded in the slot of the rotor core or the like using a compound preform. The preformed body is obtained, for example, by filling a compound into a cavity whose cross-sectional shape is slightly smaller than the slot and pressurizing it (preforming step).

"Molding without magnetic field" without application of an oriented magnetic field, "Constant magnetic field forming" in which a constant magnetic field is applied continuously from the start of forming to the end of forming, and "Molding with variable magnetic field" in which application of the magnetic field is cut off during forming. was performed at each compression force. The time ( simply referred to as “molding time”) was set to 5 minutes (see FIG. 1B).

In both cases, the compression start time (t2) was defined as 1 minute after the start of molding (at the time of raw material supply) (curing degree of 10% or less). The end of compression (t4) was 4 minutes after the start of molding (at the time of raw material supply) (1 minute before the end of molding: hardening degree of 70% or more).

In the constant magnetic field molding and the magnetic field changing molding, the application start time (t1) of the aligning magnetic field was 0.5 minutes after the start of molding (hardening degree within 5%). In constant magnetic field molding, the end of application of the aligning magnetic field (t3) was 4 minutes after the start of molding (simultaneously with the end of compression: hardening degree of 70% or more).

In the magnetic field change molding, the end of application of the aligning magnetic field (t3) was 3 minutes after the start of molding (1 minute before the end of compression: 35% degree of hardening). In this case, the period before the application of the aligning magnetic field (t2 to t3 or t0 to t3) corresponds to the first molding process, and the period after the application of the aligning magnetic field (t3 to t4 or t3 to t5) corresponds to the second molding process. Equivalent to.

The applied orientation magnetic field was 1.2 T (constant), and the orientation direction was the direction (radial direction) orthogonal to the compression direction (axial direction). Application and interruption of the aligning magnetic field were performed by switching (ON/OFF) the energization of the electromagnetic coil.

Binder resins used in bond magnets usually consist of a main agent and a curing agent. A crosslinking reaction between the main agent and the curing agent progresses according to the heat history received. The degree of hardening indicates the degree of progress (ratio). Therefore, the "curing degree" referred to in this specification was obtained from the following formula.
Curing degree = (Total amount of cured resin in bonded magnet)/(Total amount of resin in bonded magnet)
・Total amount of cured resin in bond magnet
= (Total amount of resin in bonded magnet) - (Amount of dissolved resin (unreacted resin))
・Amount of melted resin (unreacted resin)
= (total weight of bonded magnet) - (weight of bonded magnet after immersion in solvent)

Each weight was specified as follows. First, the total weight of the bonded magnet (test piece) to be measured is weighed in advance. The "total amount of resin" in the bonded magnet is calculated from the raw material ratio of magnet powder and binder resin. Next, the bonded magnet is immersed in a solvent (methyl ethyl ketone) to elute the uncured (unreacted) main agent and curing agent. By weighing the remaining amount after elution, the "bond magnet weight after solvent immersion" can be obtained.

(4) Curing Treatment Each bonded magnet (compression-molded body) taken out from the mold cavity was heated in the atmosphere at 150° C. for 30 minutes to almost completely thermally cure the binder resin.
Description of magnetization.

(5) Magnetization Each bond magnet was magnetized by applying a magnetic field (6 T) with an air-core coil.

<<Second embodiment/manufacture of sample>>
In the above-described magnetic field change molding, bond magnets were also manufactured by variously changing the end time (t3) of application of the aligning magnetic field. Specifically, t3 is 1.5 minutes (curing degree 15%), 2.5 minutes (curing degree 25%), 3 minutes (curing degree 35%) from the start of molding (when raw materials are supplied). ), either after 3.5 minutes (45% cure) or after 5 minutes (95% cure). Except for the change of t3, magnetic field change molding was performed in the same manner as in the first embodiment. However, the compressive force was either 20 MPa or 30 MPa. In this example, the end of compression (t4) was defined as the time when the hardening degree was 70% or more from the start of molding (at the time of raw material supply). Therefore, when t3=5 minutes (hardening degree 95%), it substantially means constant magnetic field molding (t3=t4=t5).

《Measurement/Observation》
(1) Density The actual density (ρ) of the bonded magnet after curing was calculated using the volume determined from the external dimensions and the measured mass.

(2) Magnetic Properties The magnetic properties of the bonded magnet were measured at room temperature using a DC BH tracer (TRF-5BH-25Auto manufactured by Toei Industry Co., Ltd.). A residual magnetic flux density (Br) was obtained from the obtained BH curve. The ratio of residual magnetic flux density (Br/4πIs) to saturation magnetization (4πIs) was defined as the degree of orientation.

"evaluation"
FIG. 2 shows a scatter diagram plotting the density of each bond magnet for each compression force based on the first embodiment. Based on the second example, the density, orientation and residual magnetic flux density of each bonded magnet are shown in FIGS. 3A and 3B (both collectively referred to as "FIG. 3"). FIG. 3A is when the compressive force is 20 MPa, and FIG. 3B is when the compressive force is 30 MPa.

As is clear from FIG. 2, when the magnetic field changing molding is performed, a bonded magnet with a higher density is obtained than when the constant magnetic field molding is performed. Further, the density of the bonded magnet obtained by magnetic field change molding was almost the same as the density of the bonded magnet obtained by non-magnetic field molding.

Therefore, it was found that the magnetic field change molding can achieve higher density of the bonded magnet or reduce the compressive force than the magnetic field molding.

As is clear from FIG. 3, it was also found that when performing magnetic field change molding, by appropriately setting the end time (t3) of applying the orientation magnetic field, it is possible to achieve both a high density or a high residual magnetic flux density and a high degree of orientation. . According to the second embodiment, the time (t3) to end (shut off) the application of the aligning magnetic field is 2.5 to 4 minutes (curing degree: 25 to 70%) or 3 minutes after the start of molding (t0). After ~3.5 minutes (curing degree: 35-45%).

《Rotor》
The above-described magnetic field changing molding was performed to integrally mold the bond magnet in the slot (cavity) of the rotor core (housing/electromagnetic member) of the internal permanent magnet synchronous motor (IPM). The appearance of the rotor (field element) thus obtained is shown in FIG. The rotor core is made of a laminate of silicon steel sheets punched into a desired shape.

Since the molding pressure of the bond magnet was small, almost no deformation occurred even in the thin portion at the outer peripheral edge of the slot. Therefore, it was also confirmed that the manufacturing method of the present invention can provide an IPM rotor with high precision (roundness and cylindricity) having bonded magnets with high density and high degree of orientation.

Claims (7)

A forming step of heating and compressing a bond magnet raw material made of magnet powder and a binder resin capable of binding the magnet powder in a cavity,
The magnet powder includes an anisotropic magnet powder,
The binder resin comprises a thermosetting resin,
The molding step includes a first molding step in which an aligning magnetic field is applied to the cavity, and a second molding step in which the aligning magnetic field is reduced or cut off after the first molding step. manufacturing method. 2. The method for producing a compression-bonded magnet according to claim 1, wherein the compression force is 5 to 50 MPa in the molding step. 3. The method for manufacturing a compression bonded magnet according to claim 1, wherein the volume ratio of the magnet powder to the total of the magnet powder and the binder resin is 60 to 75% by volume. 4. The method for producing a compressed bond magnet according to claim 1, wherein the aligning magnetic field is applied in an alignment direction that intersects the direction of compression of the raw material for the bond magnet. 5. The method of manufacturing a compression-bonded magnet according to claim 1, wherein the second molding step is started when the degree of cure of the thermosetting resin reaches 10-70%. 6. The method for producing a compression-bonded magnet according to claim 1, wherein said thermosetting resin is an epoxy resin. 7. The method for producing a compression-bonded magnet according to claim 1, wherein a magnetic member is obtained by integrating the compression-bonded magnet into a housing having the cavity.

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