JP2015012038A - Rare earth-iron based bond permanent magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a permanent magnet which allows a numerical value of the surface magnetic flux density of a permanent magnet to be adjusted in a wide range, and which is small in initial demagnetization.SOLUTION: A rare earth-iron based bond permanent magnet is magnetized by: disposing a permanent magnet for magnetization in the vicinity of a rare earth-iron based bond magnet, which is an object to be magnetized; and lowering the temperature of the object to be magnetized from a temperature equal to or higher than the Curie point of the object to be magnetized, and below the Curie point of the permanent magnet for magnetization to a temperature below the Curie point of the object to be magnetized, while applying a magnetization magnetic field to the object to be magnetized by use of the permanent magnet for magnetization. In the rare earth-iron based bond magnet, the rare earth element is Pr.

Description

  The present invention relates to a multipolar magnetized rare earth iron-based bond permanent magnet containing Pr as a rare earth element. More specifically, the present invention prevents initial demagnetization and provides a wide numerical range for magnetic properties (surface magnetic flux density). The present invention relates to a rare earth iron-based bond permanent magnet magnetized with a multipole magnet.

As is well known, in response to the recent remarkable downsizing of electronic devices, PM type (permanent magnet type) stepping motors and the like used therein are also being downsized and reduced in diameter.
Since such permanent magnets cannot avoid irreversible demagnetization due to initial demagnetization, in applications that are used in high-temperature environments, magnetic materials with sufficiently large intrinsic coercive force are selected or the permeance coefficient is increased. For example, a method of increasing the thickness of the magnet in the magnetization direction is performed. Conventionally, in order to suppress such initial demagnetization and the like, a “heat depletion” process is performed in which heat treatment is performed in advance at a temperature higher than the expected maximum temperature for use and stabilization.
However, in the case of stepping motors, etc., where the above-mentioned miniaturization is progressing, the method of increasing the thickness of the magnet magnetization direction as described above when used in a high temperature environment inhibits the miniaturization of the motor. It is not appropriate to apply this method.

As a method for preventing initial demagnetization in a magnet using a magnet material having a high intrinsic coercive force, the present inventors have heretofore determined the temperature of a magnet that is a magnetized object from a temperature above its Curie point. A permanent magnet magnetization method (ultra high magnetizing process: UHM magnetization) is proposed in which the temperature is lowered to a temperature lower than the Curie point and a magnetic field is continuously applied to the object to be magnetized (Patent Literature). 1). According to this method, even in the case of an Nd—Fe—B bond magnet having an intrinsic coercive force (iHc) of a very small diameter / multipole magnetized structure exceeding 557 kA / m, the magnetization characteristics (surface magnetic flux density) are high. In addition, a ring-shaped permanent magnet with good magnetization quality can be obtained.
Furthermore, when performing the above-mentioned magnetization method, the present inventors change the surface magnetic flux density of the magnetic object to be magnetized and change the temperature at which the magnetic material is extracted from the magnetic field. If the temperature is set higher than the upper limit of the operating temperature or guaranteed temperature of the electromagnetic device in which the magnetized material is incorporated, magnetization and initial demagnetization will be performed at the same time. (Patent Document 2). Further, in Patent Document 2, when an Nd—Fe—B isotropic magnet (Curie point: about 350 ° C.) is used as an object to be magnetized, by adjusting the magnetized portion temperature to an arbitrary temperature, 10 It is disclosed that fine adjustment of the surface magnetic flux density is possible within a numerical range of about%.

JP 2006-203173 A (Patent No. 4697736) JP 2006-294936 A (Patent No. 4671278)

By the way, in a permanent magnet type motor such as a PM type stepping motor, it is necessary to appropriately combine a numerical value of the field magnetic field of the stator suitable for the output characteristics of the motor and a numerical value of the surface magnetic flux density of the rotor magnet.
Pulse magnetization, which is a conventional multi-pole magnetization technique, can widely adjust the value of the surface magnetic flux density of a permanent magnet by adjusting the current value at the time of magnetization. But the U
In HM magnetization, the adjustment range of the numerical value of the surface magnetic flux density remains in a narrow range of about 10%. For this reason, it is necessary to prepare a magnetizing yoke incorporating a permanent magnet for field magnetism having different magnetic properties for each magnetic property required for UHM magnetization.
In addition, Pr-TM-B-based isotropic magnets (TM is obtained by replacing Fe or a part of Fe with one or more transition metal elements including Co and Ni) have an intrinsic coercive force (iHc) of 554 kA / m. For example, it is smaller than the intrinsic coercive force of 780 kA / m of an Nd—Fe—B based isotropic magnet (MQP-B-20029-070 manufactured by Magnequen). For this reason, initial demagnetization is a particularly serious problem in Pr-TM-B isotropic magnets. In conventional Pr-TM-B isotropic magnets, which have been pulse-magnetized, heat depletion for initial demagnetization is performed after magnetization. There was a need to do.

  The present invention has been made in view of the above circumstances, and the problem to be solved is a rare earth iron system in which the surface magnetic flux density of a permanent magnet can be adjusted in a wide range and the initial demagnetization is small. An object is to provide a bond permanent magnet.

  As a result of intensive studies to achieve the above object, the present inventors suppressed initial demagnetization by applying UHM magnetization to a rare earth iron-based bond magnet containing Pr as a rare earth element, The present invention was completed by finding that it becomes a rare earth iron-based bond permanent magnet with widely adjusted magnetization characteristics (surface magnetic flux density) at the actual use temperature (80 to 100 ° C.).

  That is, in the present invention, a magnetizing permanent magnet is disposed in the vicinity of a rare earth iron-based bond magnet that is a magnetized material, and the temperature is equal to or higher than the Curie point of the magnetized material and less than the Curie point of the magnetized permanent magnet. The temperature of the magnetized object is lowered from the temperature of the magnetized object to a temperature below the Curie point of the magnetized object, and during that time, a magnetizing magnetic field is applied to the magnetized object by the magnetizing permanent magnet. The present invention relates to a rare earth iron-based bond permanent magnet magnetized by the above-mentioned rare earth iron-based bond permanent magnet, wherein the rare earth element of the rare earth iron-based bond magnet is Pr.

  The rare earth iron-based bonded magnet that is the adherend is Pr-TM-B (TM is Fe or a part of Fe substituted with one or more transition metal elements including Co and Ni) system isotropic It is preferable that the magnet is a bonded magnet, and the rare earth iron-based bonded magnet as the magnetized material preferably has an intrinsic coercive force (iHc) of 557 kA / m or less.

  The rare earth iron-based permanent magnet of the present invention can be magnetized in a range from 95% of the maximum value of the magnetization characteristic to 50% of the maximum value, and particularly has a wide surface magnetic flux density. It is characterized by being magnetized in a numerical range.

The present invention has a rare earth iron-based bond permanent magnetized with a small initial demagnetization and magnetized characteristics (surface magnetic flux density) in a wide range from 95% of the maximum value to 50% of the maximum value. A magnet can be provided.
Therefore, the rare earth iron bond permanent magnet of the present invention can be suitably used in a small motor of an electronic device whose operation guarantee temperature is usually 80 ° C. to 100 ° C.

FIG. 1 is a graph showing the results of surface magnetic flux density (mT) with respect to extraction temperature (° C.) of bonded permanent magnets after magnetization in Example 1 and Comparative Examples 1 to 3. FIG. 2 shows the surface magnetic flux density with respect to the extraction temperature (° C.) with reference to the surface magnetic flux density at the extraction temperature of 50 ° C. in the bonded permanent magnets of Example 1 and Comparative Examples 1 to 3 after magnetization. It is a figure which shows the change rate (%) of. FIG. 3 shows the change rate (%) of the surface magnetic flux density with respect to the exposure temperature (° C.) when the surface magnetic flux density immediately after magnetization in the bonded permanent magnets of Example 2 and Comparative Example 4 is used as a reference value. FIG. FIG. 4 is a graph showing the results of surface magnetic flux density (mT) with respect to exposure temperature (° C.) in the bonded permanent magnet after magnetization in Example 3.

<Magnetic material>
An adherend to be used in the present invention, that is, a rare earth iron-based bonded magnet, is a Pr-TM-B isotropic magnet in which the rare earth element is Pr (TM includes Fe or Fe partially containing Co and Ni). Substituted with a transition metal element of more than a species).
In the rare earth iron-based bonded magnet, the total amount of rare earth elements is preferably less than 11.8 at%. A Pr-TM-B isotropic magnet forms a hard magnetic phase and a soft magnetic phase when the total amount of rare earth elements is less than 11.8 at%. In other words, the grain boundary becomes an iron-rich phase and becomes a nanocomposite magnet structure. If the total amount of rare earth elements is 11.8 at% or more, a hard magnetic phase and a nonmagnetic phase are formed, and the grain boundary becomes a rare earth-rich phase, so that a nanocomposite magnet structure cannot be obtained.
In addition, the intrinsic coercive force (iHc) of the rare earth iron-based bonded magnet is preferably 557 kA / m or less.
By adopting a rare earth iron-based bonded magnet having the above requirements as the object to be magnetized, initial demagnetization is suppressed when the UHM magnetization method described later is applied, and the maximum value is reduced from 95% of the maximum value. A multi-pole magnetized bond permanent magnet can be obtained in which the magnetization characteristics (surface magnetic flux density) can be changed within a range up to a value of 50% (that is, a reduction range of about 5 to 50% from the maximum value). .

<UHM magnetization method>
As the magnetization method employed in the present invention, the methods described in Patent Document 1 and Patent Document 2 (the details of the procedure are incorporated in this document by referring to them) can be employed.
Specifically, a permanent magnet for magnetizing (magnetizing magnetic field applying means) is disposed in the vicinity of the rare earth iron-based bonded magnet that is the magnetized material, and the temperature of the magnetized material is determined according to the temperature of the magnetized material. The temperature of the magnetized permanent magnet is lowered from a temperature below the Curie point of the magnetizing permanent magnet to a temperature of less than the Curie point of the magnetized material, and the magnetized material is magnetized by the magnetizing permanent magnet. This is implemented by applying a magnetizing magnetic field to the magnetic field.

Rare earth iron bond magnets, which are adherends, have an annular shape (such as an annular shape or a polygonal shape) or an arc shape (such as an arc shape or a polygonal arc shape), and are attached from the outside or inside, or both inside and outside. It is magnetized by applying a magnetic field with a permanent magnet.
Specifically, for example, a non-magnetic block is provided with a magnetized object accommodation hole into which a rare earth iron-based bonded magnet that is a magnetized object can be inserted and extracted, and from the outer surface of the magnetized object accommodation hole. A large number of radially extending grooves and / or a large number of grooves extending from the inner surface toward the center are provided, and each groove is embedded with a block-shaped permanent magnet for magnetizing such as a rod having a higher Curie point than the magnetic material to be magnetized. A magnetizing jig having the above structure is used. Then, in a state where the magnetized object is heated to the Curie point or higher, the magnetized object is inserted into the magnetized object accommodation hole and cooled in the magnetizing jig.

  The above-mentioned magnetizing jigs in which a large number of magnetizing permanent magnets are embedded are combined in a state where the magnetic pole positions are shifted in a plurality of stages in the axial direction and in a plurality of stages. May be applied. In addition, a magnetizing magnetic field can be applied to the permanent magnet from both the inner and outer sides of the annular or arc-shaped rare earth iron-based bonded magnet that is the magnetized object, and the magnetizing magnetic field from the inside and / or the magnetizing from the outside By optimizing the position of the magnetic field in the circumferential direction and / or the magnetic field strength, the magnetization waveform (the waveform of the change in the surface magnetic flux density with respect to the angle) is optimized.

The magnetizing permanent magnet has a Curie point of a rare earth iron-based bond magnet in which the Curie point of the magnetizing permanent magnet is a magnetized material so as to generate a magnetic field that can be magnetized to the magnetized material at a high temperature. Select the one that is higher than the point.
In addition, in order to minimize the magnetic field required for magnetization of the object to be magnetized, the heating temperature of the object to be magnetized is set higher than the Curie point of the rare earth iron-based bond magnet that is the object to be magnetized. In addition, the heating temperature is set lower than the Curie point of the permanent magnet for magnetizing in order to leave a magnetic field that can be magnetized by the magnetizing permanent magnet and to have a magnetizing ability.
By selecting such permanent magnets for magnetizing and setting the heating temperature of the object to be magnetized, the maximum magnetization of the object to be magnetized becomes possible. After the magnetized object is magnetized, when the object to be magnetized is cooled to a temperature below its Curie point, a magnetic force is generated, and a magnetized permanent magnet can be obtained.

The multipolar magnetized rare earth iron-based bond permanent magnet of the present invention can adjust the magnetization characteristics by changing the temperature when the magnetized material is taken out from the magnetizing jig after magnetization. Specifically, as the extraction temperature is increased (however, the maximum value of the extraction temperature is lower than the Curie point of the rare earth iron-based bond magnet that is the adherend), the surface magnetic flux density is increased to 95, the maximum value. It can be adjusted in the range from the value of% to the value of 50% of the maximum value (that is, in the numerical range reduced from the maximum to about 5 to 50%).
In the rare earth iron-based bond permanent magnet magnetized in the present invention, the above extraction temperature is set to a high temperature such as 100 ° C. or more, so that it can be considered that the same action as “heat withering” is added. A rare earth iron bond permanent magnet can be obtained. That is, when the extraction temperature is set to a temperature higher than a normal use temperature upper limit value or guaranteed temperature (for example, 80 to 100 ° C.) of an electromagnetic device such as a motor incorporating a rare earth iron-based bond permanent magnet, Below the guaranteed temperature, that is, as an assembled electromagnetic device, the occurrence of initial demagnetization can be suppressed. For this reason, the rare earth iron-based bond permanent magnet can exhibit a stable magnetizing magnetic force, and an electromagnetic device incorporating the rare earth iron-based bond permanent magnet can guarantee a stable operation.

Thus, the multi-pole magnetized rare earth iron-based permanent magnet of the present invention does not require a separate magnetized yoke for each required magnetic property, and is also required by the conventional pulse magnetizing method. Without performing the heat withering again, initial demagnetization is suppressed, and a bonded permanent magnet having various magnetization characteristics (that is, the surface magnetic flux density is changed in a wide numerical range) is obtained.
Therefore, the rare earth iron-based bond permanent magnet of the present invention is useful as a permanent magnet for permanent magnet type motors such as various PM type stepping motors that require various output characteristics.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to this.

[Example 1 and Comparative Examples 1 to 3: Evaluation of surface magnetic flux density with respect to change in extraction temperature after magnetization]
The bonded magnets of Examples and Comparative Examples were manufactured by the following procedure.
[Example 1]
A 2.5% by mass of epoxy resin is mixed with Pr—Co—Fe—B magnetic powder having a rare earth content of 11.1 at%, a maximum energy product of 127 kJ / m ² and an intrinsic coercive force of 554 kA / m, and an outer diameter of 2. A cylindrical bonded magnet (molded body density 5.9 mg / m ³ ) of 6 mm × inner diameter 1 mm × height 3 mm was produced (Curie point: about 345 ° C.).
[Comparative Example 1]
The magnetic powder used is an Nd—Co—Fe—B based magnetic powder having a rare earth content of 11.0 at%, a maximum energy product of 119 kJ / m ² , and an intrinsic coercive force of 573 kA / m, and other configurations are the same as those of the first embodiment. A cylindrical bonded magnet was produced (Curie point: about 325 ° C.).
[Comparative Example 2]
The magnetic powder used is an Nd—Co—Fe—B based magnetic powder having a rare earth content of 12.5 at%, a maximum energy product of 119 kJ / m ² , and an intrinsic coercive force of 780 kA / m, and other configurations are the same as those in Example 1. A cylindrical bonded magnet was produced (Curie point: about 330 ° C.).
[Comparative Example 3]
The magnetic powder used is a Nd—Fe—B magnetic powder having a rare earth content of 13.0 at%, a maximum energy product of 111 kJ / m ² , and an intrinsic coercive force of 1010 kA / m, and the other configurations are the same as those in Example 1. A bonded magnet was prepared (Curie point: about 305 ° C.).

The bonded magnets of Example 1 and Comparative Examples 1 to 3 were magnetized by the UHM magnetization method.
That is, the above-mentioned bonded magnets, which are adherends, were heated at a Curie point of each bonded magnet + 30 ° C. (Example 1: 375 ° C., Comparative Example 1: 355 ° C., Comparative Example 2: 360 ° C., Comparative Example 3: 335 ° C.) and 10 poles of radial magnetization (Curie point of SmCo sintered permanent magnet for magnetization: about 850 ° C.).
Various changes in the take-out temperature after magnetization (take-out temperatures: 50 ° C., 80 ° C., 120 ° C., 150 ° C., 180 ° C., 210 ° C., 240 ° C. and 270 ° C.) and take out the bond permanent magnet from the magnetizing jig, The surface magnetic flux density of the bonded permanent magnet after magnetization was measured.
The surface magnetic flux density was measured according to the evaluation of the magnetization quality described in Patent Document 1, and the average value of the surface magnetic flux density of 10 poles was calculated using a gauss meter to obtain the magnetization characteristics. The result of the surface magnetic flux density (mT) with respect to the extraction temperature (° C.) is shown in FIG.

As shown in FIG. 1, in Example 1 and Comparative Example 1, it is assumed that the surface magnetic flux density of the bonded permanent magnet after magnetization is greatly reduced as the extraction temperature is higher than in Comparative Example 2 and Comparative Example 3. As a result. Further, in Example 1, the decrease in the surface magnetic flux density was remarkable with respect to Comparative Example 1.
On the other hand, in Comparative Example 2, the change in the surface magnetic flux density was gradual. In Comparative Example 3, when the take-out temperature was in the range of 50 ° C. to 250 ° C., no significant change was observed in the surface magnetic flux density of the bonded permanent magnet after magnetization. However, the surface magnetic flux density rapidly decreased in the range exceeding 250 ° C. Since the Curie point Tc of the bond permanent magnet of Comparative Example 3 is 305 ° C., it is considered that the thermal demagnetization rapidly progressed in the range exceeding 250 ° C. close to the Curie point.

FIG. 2 shows the change rate (%) of the surface magnetic flux density when the extraction temperature is changed with the surface magnetic flux density at the extraction temperature of 50 ° C. as a reference.
As shown in FIG. 2, at the extraction temperature of 270 ° C., the decrease rate from the surface magnetic flux density at the extraction temperature of 50 ° C. exceeds 50% in Example 1, and is about 30% in Comparative Example 1. It was.
On the other hand, in Comparative Example 2, the surface magnetic flux density reduction rate at the extraction temperature of 270 ° C. was about 10%. In Comparative Example 3, the surface magnetic flux density reduction rate up to 250 ° C. was as low as about 6%, but the surface magnetic flux density reduction rate suddenly increased when the extraction temperature exceeded 250 ° C. .

[Example 2 and Comparative Example 4: Evaluation of thermal demagnetization due to difference in magnetization method]
Next, the thermal demagnetization between UHM magnetization and pulse magnetization was evaluated.
In the following Example 2 and Comparative Example 4, bond magnets manufactured under the same conditions as the cylindrical bond magnet shown in Example 1 were used.
In Example 2, the extraction temperature was 50 ° C., and UHM magnetization was performed in the same manner as in Example 1. On the other hand, in Comparative Example 4, pulse magnetization was performed at a current density of 22 kA / mm ² . In the case of this condition, the maximum magnetic field generated in the magnetized portion is 2000 kA / m. After magnetization, the surface magnetic flux density (mT) of each bond permanent magnet was measured in the same manner as described above using a gauss meter.
After exposing the bond permanent magnet of Example 2 and the bond permanent magnet of Comparative Example 4 after magnetization in an environment of 80 ° C., 120 ° C., 150 ° C., 180 ° C., 210 ° C., 240 ° C. or 270 ° C. for 30 minutes. The surface magnetic flux density was measured in the same manner as described above using a gauss meter. FIG. 3 shows the change rate (%) of the surface magnetic flux density (mT) with respect to the exposure temperature (° C.) with reference to the surface magnetic flux density immediately after magnetization (before exposure).

As shown in FIG. 3, the surface magnetic flux density reduction rate in both Example 2 and Comparative Example 4 showed a substantially similar curve, but in Comparative Example 4, the initial demagnetization was performed only by exposure to an 80 ° C. environment. 10% occurred. Further, the difference in demagnetization factor between Example 2 and Comparative Example 4 was almost the same value from exposure in an 80 ° C. environment to exposure in a 270 ° C. environment.
This result shows that the initial demagnetization in the high temperature environment is large in the pulse magnetization (Comparative Example 4), while the initial demagnetization due to the heat effect is relatively small in the UHM magnetization (Example 2). .

Further, the result is that the surface magnetic flux reduction rate curve of Example 1 shown in FIG. 2 and the surface magnetic flux reduction rate curve of Example 2 shown in FIG. 3 are almost the same.
This result showed that, in UHM magnetization, by adjusting the take-out temperature, the same effect as that obtained when heat was exhausted to that temperature was obtained.

[Example 3: Evaluation of thermal demagnetization at high temperature extraction]
Next, the thermal demagnetization in UHM magnetization high temperature extraction was evaluated.
In Example 3, a bonded magnet prepared under the same conditions as the cylindrical bonded magnet shown in Example 1 was used.
In Example 3, UHM magnetization was performed in the same manner as in Example 1 with the take-out temperature being 180 ° C. After magnetization, the surface magnetic flux density (mT) of the bond permanent magnet was measured in the same manner as described above using a gauss meter.
The bonded permanent magnet of Example 3 after magnetization was exposed to an environment of 80 ° C., 120 ° C., 150 ° C., 210 ° C., 240 ° C. or 270 ° C. for 30 minutes, and then surface-treated in the same manner as described above using a gauss meter. The magnetic flux density was measured. The result of the surface magnetic flux density (mT) with respect to the exposure temperature (° C.) is shown in FIG.

As shown in FIG. 4, Example 3 is stable without decreasing the surface magnetic flux density (mT) from the exposure temperature 50 ° C. to 180 ° C., which is the temperature range below the UHM magnetization extraction temperature (180 ° C.). It was. On the other hand, the surface magnetic flux density (mT) decreased at the exposure temperature exceeding the UHM magnetization extraction temperature (180 ° C.), and the amount of decrease in the surface magnetic flux density increased as the exposure temperature increased.
Similar to the Nd—Fe—B bond magnet of Prior Art 1, this result is obtained by setting the extraction temperature when the Pr—Fe—B bond magnet is magnetized to UHM higher than the operating temperature of the device. It was shown that demagnetization can be prevented.

  As described above, the upper limit of the operating temperature or the guaranteed temperature of an electronic device in which a permanent magnet type motor is used is usually 80 ° C. to 100 ° C. Therefore, the UHM magnetized object is replaced with Pr—Fe—B. The present invention provides a permanent magnet whose value is changed in the range from 95% of the maximum value of the surface magnetic flux density to 50% of the maximum value by using the system magnet. It becomes possible.

Claims (5)

A permanent magnet for magnetizing is arranged in the vicinity of the rare earth iron-based bonded magnet that is the magnetized material,
And lowering the temperature of the magnetized object from a temperature above the Curie point of the magnetized object and a temperature below the Curie point of the magnetizing permanent magnet to a temperature below the Curie point of the magnetized object. In the meantime, a rare earth iron-based bond permanent magnet magnetized by applying a magnetizing magnetic field to an object to be magnetized by the magnetizing permanent magnet,
A rare earth iron-based bond permanent magnet, wherein the rare earth element of the rare earth iron-based bond magnet is Pr. The rare earth iron-based bonded magnet that is the adherend is Pr-TM-B (TM is Fe or a part of Fe substituted with one or more transition metal elements including Co and Ni) system isotropic The rare earth iron-based bond permanent magnet according to claim 1, wherein the rare earth iron bond permanent magnet is a magnet. 3. The rare earth iron-based bond permanent magnet according to claim 1, wherein the rare earth iron-based bond magnet as the adherend has an intrinsic coercive force (iHc) of 557 kA / m or less. 4. The rare earth iron-based bond permanent magnet is magnetized in a range from a value of 95% of a maximum value of magnetization characteristics to a value of 50% of a maximum value. The rare earth iron bond permanent magnet as described in any one of them. The rare earth iron-based bond permanent magnet according to claim 4, wherein the magnetization characteristic is a surface magnetic flux density.

Images