JP2014099600A - Rare earth magnet magnetization method, and rare earth magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rare earth magnet magnetization method which is completed for a short time without deteriorating an anti-corrosion coating film, and to provide a rare earth magnet arranged to be higher in its usable upper limit temperature.SOLUTION: A rare earth magnet magnetization method comprises a process for performing a multipolar magnetization of p poles (p is an even number equal to or larger than 4) by: heating a rare earth magnet containing at least one light rare earth element RL to a magnetization temperature T°C derived from the formula below in a range of 80-200°C, thereby reducing a coercive force of the rare earth magnet according to a temperature coefficient β of the coercive force; applying, in a pulse form, a magnetization magnetic field Hhaving a magnetic field of at least double the coercive force Hat the temperature T°C to the rare earth magnet at least once; and then cooling the rare earth magnet from the temperature T°C to a room temperature.

Description

  The present invention relates to a method for magnetizing a rare earth magnet and a rare earth magnet.

  In recent years, rare earth magnets have been used in place of alnico and ferrite for magnets installed in permanent magnet motors for precision equipment, due to the market trend of miniaturization and weight reduction of precision equipment. More recently, the market trend of permanent magnet motors has been progressing toward lighter weight and higher output. With higher output, irreversible demagnetization of permanent magnets due to heat generation in motor coils has become a problem, and rare earth magnets are required to have high heat resistance in addition to downsizing and multipolarization.

  As a method of multipolarizing a ring-shaped rare earth magnet (hereinafter referred to as a ring magnet) incorporated in a permanent magnet motor, a coil energization type magnetizing apparatus is used. In this magnetizing apparatus, a hole portion through which a ring magnet as a magnetized object can be inserted / extracted is provided at the center of the magnetizing yoke, and an axially extending groove is formed on the inner wall surface of the hole portion. It is formed according to the number of poles. Furthermore, a conductive wire with an insulating coating is embedded in the groove, and adjacent conductive wires are continuously folded in a coil to form a coil.

  A magnetized magnetic field of at least 24 kOe or more generated in the magnetizing yoke by passing a pulse current through the coil by inserting a magnetized object into such a hole and instantaneously releasing the charge stored in the capacitor. The ring magnet is magnetized by this.

  However, since the recent ring magnets are required to be downsized as described above, the magnetization pitch (distance between the magnetic poles) is narrow, and the magnetizing yoke needs to be reduced accordingly. For this reason, the space that can be wound is reduced with the downsizing of the magnetized yoke, and the conductor wire diameter of the coil to be arranged has to be reduced, and it becomes difficult to wind a conductor with a sufficient number of turns. The strength of the magnetizing magnetic field generated by the magnetizing yoke is limited, and there has been a problem that sufficient magnetizing characteristics cannot be obtained.

  Further, the high heat resistance of rare earth magnets is attributed to the high coercive force, and among the rare earth magnets, the high heat resistant product has an increased coercive force. However, when using a magnet with high coercive force in order to obtain high heat resistance, special attention must be paid because the magnetic field required for saturation magnetization becomes large. Becomes an insufficient magnet.

  It is known that irreversible demagnetization due to a temperature rise occurs at a lower temperature than a saturation magnetized rare earth magnet in a rare earth magnet with insufficient magnetization. In particular, rare earth magnets incorporated in small motors of 20 mm or less are preferably saturated and magnetized so as not to cause irreversible demagnetization due to heat generation of the coils, that is, to increase the upper limit temperature of use of the motor. .

  As a technique for improving such a lack of magnetization, a method has been proposed in which a magnetic object is heated to a high temperature and magnetized by utilizing a decrease in the magnetization magnetic field required for saturation magnetization (for example, Patent Document 1). See). In Patent Document 1, a rare earth magnet that is an object to be magnetized is heated to a temperature equal to or higher than its Curie point, and the temperature is decreased from a temperature equal to or higher than the Curie point to a temperature lower than the Curie point. And a magnetizing method are disclosed.

  Further, the temperature of the magnetized part when the magnetized object is taken out from the magnetized part is controlled to a temperature higher than the upper limit value of use temperature or the guaranteed temperature of the device in which the magnetized object is incorporated. Therefore, even if the rare earth magnet has a small and multipolar magnetized structure, the average value of the surface magnetic flux density peak value is high, the variation of the surface magnetic flux density peak value is small, and irreversible demagnetization is prevented. The magnetic flux density can be finely adjusted to the required value. As a result, a rare earth magnet having high magnetization characteristics and good magnetization quality is obtained.

Japanese Patent No. 4671278

  When the applicant tried to implement the magnetizing method described in Patent Document 1, the magnetization rate, which was obtained only about 30% when magnetized at room temperature, increased the magnetizing temperature. It was confirmed that it improved.

  However, the Curie temperature of the SmCo rare earth magnet is as high as about 850 ° C. Considering the heat resistance of the insulating coating of the conductor of the magnetizing device, the magnetization method of Patent Document 1 should be applied to the SmCo rare earth magnet. Is impossible.

  On the other hand, since the Curie temperature of the NdFeB rare earth magnet is about 340 ° C., there is a possibility that the above problem can be solved by using a conductive wire coated with a highly heat-resistant insulating film. However, NdFeB-based rare earth magnets must have a rust-proof coating, and nickel plating and epoxy coating are widely used, but the maximum heating temperature in the range that does not impair the function of the rust-proof coating is about 200 ° C with nickel plating, It is about 130 ℃ with epoxy coating.

  For this reason, most NdFeB rare earth magnets on the market have a rust preventive coating that deteriorates when heated to a Curie temperature of 340 ° C or higher. If it is not a system rare earth magnet, the magnetization method disclosed in Patent Document 1 cannot be applied.

  This problem cannot be solved by applying a coating to the magnetized rare earth magnet, but when handling the magnetized rare earth magnet, the rare earth magnets are magnetically attracted to each other, making handling difficult. Therefore, it is unrealistic as a mass production method for coatings.

  Moreover, in the prior art which magnetizes at high temperature including patent document 1, there is no technical disclosure regarding the optimization required by formulating the heating temperature necessary and sufficient for performing saturation magnetization. In particular, the continuous application of a magnetizing magnetic field from a temperature above the Curie point to a temperature below the Curie point as in Patent Document 1 requires a large cooling structure in consideration of the heat generation of the coil, and also increases the power consumption. I will invite you.

  The present invention has been made in view of the above circumstances, and it is possible to improve the magnetization rate by the minimum necessary heating based on the formula without deteriorating the rust preventive coating, and to suppress power consumption, for a short time. An object of the present invention is to provide a method for magnetizing a rare earth magnet that is completed in step 1 and a rare earth magnet having a high use upper limit temperature.

The above object is achieved by the present invention described below. That is,
The method for magnetizing a rare earth magnet of the present invention heats a rare earth magnet containing at least one light rare earth element RL to a magnetization temperature T ° C. derived from the following formula 1 in the range of 80 ° C. to 200 ° C. And reducing the coercivity of the rare earth magnet in accordance with the temperature coefficient β of the coercivity of the rare earth magnet, and at least once the magnetizing magnetic field _Hext having a magnetic field at least twice the coercivity H _C exhibited by the rare earth magnet at the temperature T ° C. After applying the pulse shape as described above, the rare earth magnet is cooled from the temperature T ° C. to room temperature, thereby performing multipole magnetization with the number of poles p (p is an even number of 4 or more) (however, H _CJ Is the coercivity (Oe), H _ext (Oe), and RT is room temperature (° C) of a rare earth magnet.

  Also, in one embodiment of the magnetizing method of the rare earth magnet of the present invention, the operating point of the rare earth magnet inserted in the magnetizing yoke at the temperature T ° C. exists in the linear region of the demagnetizing curve in the second quadrant of the BH curve. It is preferable to do.

  In another embodiment of the method for magnetizing rare earth magnets of the present invention, the permeance coefficient Pc of the rare earth magnet inserted in the magnetized yoke is preferably 20 or more.

In another embodiment of the magnetizing method of the rare earth magnet of the present invention, the outer shape of the rare earth magnet is either cylindrical or ring-shaped, and (outer diameter D / number of poles p) <(4 / π) (mm) or coercive force H _C ≧ 15 k (Oe).

  In another embodiment of the rare earth magnet magnetization method of the present invention, the outer diameter D is preferably 10 (mm) or less.

  In another embodiment of the method for magnetizing rare earth magnets of the present invention, a rare earth magnet is inserted into a hole of a magnetizing yoke provided with a magnetizing head having the number of poles p around which excitation coils are wound. It is preferable.

  In another embodiment of the method for magnetizing a rare earth magnet of the present invention, it is preferable that the magnetizing yoke has a water cooling structure, the exciting coil is formed of a tube wire, and a refrigerant is further passed through the tube wire.

  In another embodiment of the method for magnetizing a rare earth magnet of the present invention, the permeance coefficient Pc of the rare earth magnet inserted in the magnetized yoke is set to be the same as the permeance coefficient Pc when the rare earth magnet is incorporated in a device. It is preferable.

  The rare earth magnet of the present invention is magnetized by any one of the rare earth magnet magnetization methods described above, has a magnetization rate of 70% or more, and contains at least one light rare earth element RL. And

In one embodiment of the rare earth magnet of the present invention, the outer shape is either a cylindrical shape or a ring shape, and (outer diameter D / number of poles p) <(4 / π) (mm) or coercive force H It is preferable to have _C ≧ 15k (Oe).

  In another embodiment of the rare earth magnet of the present invention, the outer diameter D is preferably 10 (mm) or less.

  Further, in another embodiment of the rare earth magnet of the present invention, it is preferable that the permeance coefficient Pc of the rare earth magnet inserted in the magnetizing yoke is set to be the same as the permeance coefficient Pc when the rare earth magnet is incorporated in the device. .

  According to the present invention, even in the case of a multipolar rare earth magnet that is difficult to generate a large magnetizing magnetic field, the magnetization rate can be brought to room temperature without heating above 200 ° C. so as to interfere with the rust-proof coating. As compared with the case where it is magnetized, it can be improved significantly. Accordingly, since the magnetization rate is improved, the irreversible demagnetization temperature of the rare earth magnet becomes higher, and the use upper limit temperature of the rare earth magnet after magnetization is improved. Furthermore, deterioration of the rust preventive coating during heating is prevented, and there is no need to apply a special heat resistant coating (eg, TiN coating) on the surface of the rare earth magnet.

  In addition, since it is not necessary to heat the rare earth magnet to a temperature above the Curie point prior to magnetization, a large heating / cooling structure is unnecessary compared to the conventional heating magnetization method, and the magnetizing operation can be performed in a short time. It can be completed.

Furthermore, by setting the magnitude of the magnetizing magnetic field H _ext (Oe) to a magnetic field at least twice the coercive force H _C (Oe) exhibited by the rare earth magnet as the magnetized material at the magnetizing temperature T ° C., Even if the heating temperature of the rare earth magnet is lower than the Curie point, saturation multipolar magnetization is possible. Furthermore, by applying the magnetizing magnetic field H _ext to a pulsed magnetic field, the application of the magnetizing magnetic field can be completed in a short time. Therefore, it is possible to reduce the power consumption required for magnetization.

  In the present invention, in addition to the effects of improving the magnetization rate of the rare-earth magnet that is the object to be magnetized and preventing the deterioration of the rust preventive film, it is possible to perform magnetization in a short time and with reduced power consumption. Therefore, it is possible to improve the upper limit temperature and mass productivity of the rare earth magnet and the production efficiency.

It is a perspective view which shows an example of the rare earth magnet which concerns on this embodiment. It is sectional drawing which shows the magnetization yoke of the rare earth magnet magnetization apparatus which concerns on this embodiment. It is sectional drawing which shows typically the magnetizing yoke which wound the exciting coil on the magnetizing yoke of FIG. It is a schematic diagram which shows the heating means of the rare earth magnet after magnetizing yoke insertion. It is a graph which shows typically a demagnetization curve, a permeance coefficient, and an operating point of the rare earth magnet which is a thing to be magnetized concerning this embodiment. Magnetization rate% -magnetization temperature ° C characteristic exhibited by the rare earth magnet test piece according to the present example, and magnetism%% magnetization temperature ° C characteristic exhibited by the rare earth magnet test piece magnetized at room temperature (25 ° C) It is a graph showing.

  Hereinafter, a method for magnetizing a rare earth magnet and a rare earth magnet according to the present invention will be described in detail. In the method for magnetizing a rare earth magnet according to the present invention, the rare earth magnet is heated to an arbitrary temperature in the range of 80 ° C. or more and 200 ° C. or less to reduce the coercive force of the rare earth magnet and then inserted into the magnetizing yoke. A magnetic field is applied in the form of pulses, and then the rare earth magnet is cooled from the arbitrary temperature to lower the temperature to room temperature. In the present invention, the upper limit of the heating temperature of the rare earth magnet is set to 200 ° C.

  A rare earth magnet containing at least one light rare earth element RL is prepared as the rare earth magnet that is the adherend. A sintered magnet, a bonded magnet, or a nanocomposite magnet may be used as long as it is a rare earth magnet containing at least one light rare earth element RL. The rare earth magnet orientation method may be polar anisotropic orientation or radial orientation.

  There are no particular restrictions on the outer shape and size of the rare earth magnet that is the adherend, but the outer shape is either cylindrical (see Fig. 1) or ring, and its outer diameter D is 10 (mm) or less. It is preferable to set to be suitable for small permanent magnet motor applications. Further, by adopting the magnetizing method according to the present invention, not only the magnetization rate is improved, but also the cooling of the rare earth magnet is facilitated and the rust preventive film is prevented from being deteriorated. Can be performed. Therefore, it is possible to improve the upper limit temperature and mass productivity of the rare earth magnet and the production efficiency.

  In addition, a cylindrical or ring-shaped rare earth magnet may be configured by combining a plurality of rare earth magnets such as an arc shape. Furthermore, when a circular / circular magnet is bonded to the number of poles by dividing the circumference of a cylindrical / ring-shaped magnet equally into poles, A parallel-oriented magnet may be used as the arc-shaped magnet.

  For example, when at least one of Nd, Pr, and Sm is selected as the light rare earth element RL, examples of the magnetized material include NdFeB-based, SmCo-based, and SmFeN-based rare earth magnets, but are not limited thereto. When an NdFeB rare earth magnet, SmFeN rare earth magnet, or SmCo magnet is used as the adherend, the upper limit of the heating temperature is set to 200 ° C. in consideration of the ease of cooling of the rare earth magnet.

  Since the upper limit of the heating temperature of the rare earth magnet is set to 200 ° C., the deterioration of the rust preventive coating on the surface of the rare earth magnet is prevented during heating, and there is no need to apply a special heat resistant coating (eg, TiN coating) on the surface of the rare earth magnet. Furthermore, since the magnetization rate is improved, the irreversible demagnetization temperature of the rare earth magnet becomes higher, and the heat resistance of the rare earth magnet after magnetization is improved.

  Moreover, since it is not necessary to heat the rare earth magnet to a temperature above the Curie point during magnetization, the magnetized rare earth magnet can be cooled in a shorter time.

  Furthermore, in this invention, it heats to the magnetization temperature T degreeC derived | led-out from the following formula 2, and magnetizes the rare earth magnet which is a magnetized material at this temperature TC. The application of the pulsed magnetizing magnetic field is set at least once. Most preferred is the application of a single pulsed magnetizing magnetic field from the viewpoint of shortening the magnetization time and reducing power consumption.

但し、H_CJは被着磁物である希土類磁石の室温における保磁力(Oe)、H_extは着磁磁場(Oe)、βは被着磁物である希土類磁石の保磁力の温度係数、RTは室温（℃）を表す。

Where H _CJ is the coercive force (Oe) of the rare earth magnet that is the magnetized object, H _ext is the magnetizing magnetic field (Oe), β is the temperature coefficient of the coercivity of the rare earth magnet that is the magnetized object, RT Represents room temperature (° C.).

As an example, an NdFeB rare earth magnet having a room temperature RT of 25 ° C., a coercive force H _CJ of 15 (kOe) at room temperature, and a coercive force temperature coefficient β of −0.6 (% / ° C.) can be generated. Obtain the heating temperature required for saturation magnetization with a magnetized yoke with _ext 15 (kOe). Substituting the above values into Equation 2 results in T≈108 ° C. After heating the rare earth magnet to this temperature, the pulsed magnetic field H _ext of the above strength is applied, and then the rare earth magnet is cooled to room temperature and saturated. Magnetization is possible.

  The equation (2) is a relational expression devised in order to obtain the saturation multi-pole magnetization by heating the rare-earth magnet of the magnetic object to be heated to multi-pole magnetization.

In the present invention, the magnitude of the magnetizing magnetic field H _ext (Oe) applied to the rare-earth magnet as the magnetized material is determined by the coercive force H _C (Oe) that the rare-earth magnet as the magnetized material exhibits at each magnetization temperature T ° C. It was found that by setting the magnetic field to at least twice that of the magnetic field, saturation multipolar magnetization is possible even when the heating temperature of the rare earth magnet is less than the Curie point, and the rare earth magnet can be surely magnetized. . Furthermore, by applying the magnetizing magnetic field H _ext to a pulsed magnetic field, the application of the magnetizing magnetic field can be completed in a short time. Therefore, it is possible to reduce the power consumption required for magnetization.

  As described above, in the present invention, even in the case of a multipolar rare earth magnet that is difficult to generate a large magnetization magnetic field, the magnetization rate is set to room temperature without heating above 200 ° C. as the minimum necessary heating based on the above formula 2. Compared with the case where it is magnetized by, it can be greatly improved. Therefore, in addition to the effects of preventing deterioration of the anticorrosive film of the rare earth magnet as the magnetized material and facilitating cooling, it is possible to perform reliable magnetization in a short time and with reduced power consumption. Thereby, the heat resistance and mass productivity of the rare earth magnet and the production efficiency can be improved. Magnetization of the rare earth magnet is performed as multipolar magnetization having the number of poles p (p is an even number of 4 or more).

Rare earth multipolar cylindrical / ring magnets with a value (mm) (outer diameter D / number of poles p) of less than (4 / π) mm, especially when the outer diameter D is 10 (mm) or less. In the pole magnetizing method, the magnetized magnetic field H _{ext is} insufficiently incompletely magnetized, and the heat resistance of the magnet is reduced, but according to the multipolar magnetizing method of the present invention, saturation multipole magnetizing is performed, The heat resistance inherent to the magnet material can be extracted.

  In addition, a magnet with a high heat resistance specification having a coercive force of 15 kOe or more is likely to be incompletely magnetized by the conventional method, and cannot fully utilize the heat resistance provided by the bent magnet material. According to this method, by setting the heating temperature according to Equation 2, multipolar saturation and multipolar magnetization can be achieved, and the heat resistance can be sufficiently obtained.

  Next, the rare earth magnet magnetizing apparatus according to the present embodiment will be described with reference to FIGS. FIG. 2 is a cross-sectional view showing a magnetizing yoke of a rare earth magnet magnetizing apparatus according to the present embodiment (hereinafter simply referred to as “magnetizing apparatus” if necessary), and FIG. 3 is a magnetizing yoke of FIG. It is sectional drawing which shows typically having wound the excitation coil to. FIG. 4 is a schematic diagram showing a heating means for the rare earth magnet.

  As shown in FIG. 2, the magnetizing yoke 1 constituting the magnetizing apparatus according to the present embodiment has a substantially cylindrical shape in which the outer shape is formed in a circumferential shape and a hole 2 having a substantially circular cross section is formed in the center. And functions as a magnetizing yoke for the object to be magnetized. The diameter of the hole 2 is set to an appropriate diameter in terms of magnetic circuit design at the time of magnetization of the object to be magnetized.

  For example, a Permendur (FeCoV-Alloy) material is used as the material constituting the magnetized yoke 1, and a desired number of grooves are radially formed from the outer peripheral surface of the hole 2 as shown in FIG. 3 are provided at equal angles, and the magnetized heads 4 are formed by a desired number of poles p (p is an even number of 4 or more) formed on the rare earth magnet of the magnetized object. In the example shown in FIG. 2, 8-pole magnetization is assumed. When a magnetized yoke is configured for 8-pole magnetization of a cylindrical rare earth magnet having an outer diameter D = 5 (mm), the pitch of each magnetized head 4 is about 2 (mm). The width is set to 2 (mm) or less.

  The cross-sectional area of the groove 3 is formed in a curved shape as shown in FIG. 2, and each magnetizing head 4 has an exciting coil 5 for generating a pulsed magnetizing magnetic field as shown in FIG. The winding is formed by the number of poles p. A copper wire coil may be used as the exciting coil 5, but it is more preferable to use a hollow tube wire as shown in FIG. 3 from the viewpoint of easy cooling of the adherend.

As the tube wire, for example, a copper wire having an outer diameter of 1 (mm), an inner diameter of 0.4 (mm), and a cross-sectional area of the tube wire of 0.66 (mm ² ) or less is wound around each magnetized head 4.

  A cylindrical rare earth magnet as a magnetized object is inserted into the hole 2 of the magnetized yoke 1. When inserting the cylindrical rare earth magnet, the rare earth magnet is held through the core rod 6 of the magnetized yoke 1 in the center hole of the rare earth magnet.

As an example of the cylindrical rare earth magnet of the present embodiment, a cylindrical NdFeB magnet having an outer diameter D = 5 (mm) is assumed. It is difficult to generate a magnetizing magnetic field of more than 15 kOe with a multipolar magnetized yoke with a hole 2 diameter of 5 mm or less. Therefore, the magnetizing magnetic field H _ext is set to 15 kOe.

Three types of NdFeB rare earth magnets having different coercive forces at room temperature were used as adherends, and those having coercive forces H _CJ of 15, 18, and 20 kOe were designated as test pieces 1, 2, and 3, respectively. The temperature coefficient β of each coercive force was −0.6 (% / ° C.).

  By substituting the above-mentioned magnet characteristic value and magnetizing magnetic field into the formula 2, the heating temperature T ° C. necessary for saturation magnetization of the test pieces 1, 2, 3 is calculated, and is 108, 122, 129 ° C. or more, respectively. It was estimated that the magnetization rate was saturated by applying the above magnetizing magnetic field at a temperature of. Accordingly, the test pieces 1, 2, and 3 inserted in the magnetized yoke are heated to 108, 122, and 129 ° C., respectively.

  The heating means is not particularly limited, and for example, any means such as resistance heating, high-frequency heating, laser heating, high-temperature gas flow heating, and high-temperature liquid heating may be used. In the present embodiment, as shown in FIG. 4 as an example, a heating plunger 7 around which a heating coil is wound is brought into contact with the upper and lower sides of a cylindrical rare earth magnet 8 that is a magnetized object. It is assumed that the rare earth magnet 8 is heated from above and below by the heating plunger 7 and the entire rare earth magnet 8 is heated to the arbitrary temperature.

After confirming that the set temperature has been reached by heating, a current is passed through the exciting coil 5 to apply the pulsed magnetizing magnetic field H _ext to the magnetized object 8. The maximum pulse current value that flows through the exciting coil 5 may be calculated by calculating the effective reactance of the exciting coil 5.

Next, the cooling process of the adherend will be described. After confirming that the heating temperature of the rare-earth magnet has reached an arbitrary temperature T ° C. and applying the magnetizing magnetic field H _ext , the object to be magnetized is cooled. The cooling means is not particularly limited, and may be performed by any method such as natural cooling, forced cooling such as water cooling, air cooling, gas blowing, and heating temperature adjustment. In this embodiment, as an example, the magnetized yoke 1 is cooled by water cooling, and the magnetized object 8 is cooled by flowing a coolant through the tube wire of the exciting coil 5. By adopting such a method, a large-scale cooling structure is not necessary, and cooling of the magnetized object is facilitated.

  As a water cooling structure of the magnetizing yoke 1, as an example, a copper tube wire is attached to the outer periphery of the magnetizing yoke 1 with silver brazing, or the water is circulated in the tube wire, or the magnetizing yoke 1 outer periphery is parallel to the hole 2 in the vertical direction. The through hole may be formed to form a water-cooled pipe guide. On the other hand, as a refrigerant flowing in the tube wire of the exciting coil 5, liquid nitrogen or the like can be cited as an example.

  After confirming that the object to be magnetized has been cooled to room temperature (25 ° C.), the rare earth magnet 8 as the object to be magnetized is taken out from the hole 2 of the magnetizing yoke 1 and a new object to be magnetized is removed from the hole 2. And a series of heating, magnetization, and cooling steps are repeated. By such a magnetizing method, magnetic poles having the number of poles p corresponding to the magnetizing head 4 appear with a high magnetization rate on the outer peripheral surface of the rare earth permanent magnet as the magnetized object.

  The magnetized curve is measured with a VSM (Vibrating Sample Magnetometer) by cutting out the central part of a cylindrical / ring magnet that has been magnetized and cooled to room temperature (25 ° C). When the magnetic susceptibility was evaluated, it was confirmed that a rare earth magnet having a permeance coefficient of 1.5 as indicated by the operating point P ′ in FIG. From the above, it has been found that the magnetization rate of the rare earth magnet can be increased to at least 70% by the magnetization method according to the present invention.

  In mass production, a plurality of magnetized yokes 1 are arranged in a turret, and the insertion of the magnetized object, the contact of the upper and lower heating plungers with the magnetized object, heating, magnetization, cooling, and tact time are about several seconds. It is possible to shorten the man-hours by performing parallel processing while rotating with the setting.

  The present invention is not particularly limited to the present embodiment. For example, the magnetizing head 4 can be set to other than 8 poles. For example, the outer diameter D of the rare earth magnet of the object to be magnetized is 3 (mm). In the following cases, the number of magnetic poles may be changed to four.

  Furthermore, as a more preferable form of magnetization method, as shown in FIG. 5, the operating point P of the rare earth magnet inserted in the magnetizing yoke is present in the linear region of the demagnetization curve in the second quadrant of the BH curve. Then, it is proposed to perform the magnetization as described above. When the operating point P of the rare earth magnet at an arbitrary temperature inserted into the magnetizing yoke 1 after being heated exists in the linear region of the second quadrant of the BH curve as shown in FIG. It was confirmed that the magnetizability of the rare earth magnet cooled to) can be increased to 95% or more.

  In addition, by setting the permeance coefficient Pc of the rare earth magnet inserted in the magnetizing yoke to 20 or more, the demagnetizing field generated in the rare earth magnet in the cooling process from the magnetizing temperature to room temperature (25 ° C.) becomes 600 Oe or less, Since thermal demagnetization is less likely to occur during magnetization, the magnetizability of the rare earth magnet can be increased to 95% or more.

  The permeance coefficient Pc of the rare-earth magnet inserted into the magnetized yoke 1 after being heated to T ° C. is set to be the same as the permeance coefficient Pc (about 10) when incorporated in a device such as a motor, and By setting the magnetizing temperature T (° C.) higher than the upper limit temperature of the permanent magnet motor, the so-called heat exposure is performed after being incorporated in the motor (to suppress the aging of the magnet, so it is stable before use) It is possible to eliminate the need for demagnetization), which is more preferable.

  The structure of the magnetized yoke 1 may be appropriately changed according to the size and material of the rare earth magnet that is the magnetized object, the number of magnetized heads, and the like.

  Examples of the present invention will be described below, but the present invention is not limited to the following examples.

  The adherend in this example has a cylindrical shape as shown in FIG. 1, an outer diameter D of 5 (mm), an inner diameter of 3 (mm), and a length of 11 (mm). NdFeB rare earth magnets were used. When magnetizing the outer peripheral 8-pole, the magnetized yoke was designed so that the permeance coefficient of each magnetic pole portion when inserted into the magnetized yoke was 10.

Furthermore Set 25 ° C. to room temperature RT, and from properties of the magnetic material, 18 a coercive force H _CJ at room temperature (kOe), the β temperature coefficient of coercivity -0.6 and (% / ° C.), can be generated magnetization The heating temperature required for saturation magnetization with a magnetizing yoke having a magnetic field H _ext of 15 (kOe) was obtained from the above equation 2, and T = 122 ° C. was calculated. Therefore, the magnetic object to be inserted into the magnetizing yoke is heated to 122 ° C.

  Further, the magnetizing yoke constituting the magnetizing apparatus used in the present embodiment is configured as shown in FIG.

After confirming that the temperature reached 122 ° C. by heating, a current was passed through the exciting coil, and a pulsed magnetizing magnetic field H _ext was applied to the object to be magnetized three times.

  After magnetizing, the rare earth magnet that is the magnetized material is cooled by natural cooling while being inserted into the magnetized yoke, and after confirming that the magnetized material has cooled to room temperature (25 ° C), The magnetic flux density in the vicinity of the magnetic pole center was measured with a gauss meter, and the magnetization rate was evaluated.

  When a specimen of a NdFeB rare earth magnet magnetized at room temperature (25 ° C.) was evaluated, the magnetization rate was about 44%. On the other hand, when the cylindrical rare earth magnet according to this example was evaluated, the magnetization rate can be increased to 100% at a magnetization temperature of 122 ° C. as derived from Equation 2, and saturation magnetization can be achieved. confirmed. The result is shown in FIG. 6 as a graph of magnetization rate% -magnetization temperature ° C.

DESCRIPTION OF SYMBOLS 1 Magnetization yoke 2 Hole 3 Groove 4 Magnetization head 5 Excitation coil 6 Core rod 7 Heating plunger 8 Magnetized object (rare earth magnet)

Claims (12)

A rare earth magnet containing at least one light rare earth element RL is heated to a magnetization temperature T ° C. derived from the following formula 1 in the range of 80 ° C. to 200 ° C., and the temperature coefficient β of the coercivity of the rare earth magnet The coercive force of the rare earth magnet is decreased in accordance with the above, and a magnetizing magnetic field H _ext having a magnetic field at least twice as large as the coercive force H _C exhibited by the rare earth magnet at a temperature T ° C. is applied in a pulse form at least once. by cooling from the temperature T ° C. to room temperature, magnetizing method of the rare earth magnet and performing a multipolar magnetization of the number of poles p (p is an even number of 4 or more) (where, H _CJ is a rare earth magnet room temperature Coercivity (Oe), H _ext (Oe), and RT in RT represent room temperature (° C), respectively).

  2. The rare earth magnet according to claim 1, wherein an operating point of the rare earth magnet inserted into the magnetized yoke at the temperature T ° C. is present in a linear region of a demagnetization curve in the second quadrant of the BH curve. Magnetization method.   The method of magnetizing a rare earth magnet according to claim 2, wherein the rare earth magnet inserted in the magnetizing yoke has a permeance coefficient Pc of 20 or more. The outer shape of the rare earth magnet is either cylindrical or ring-shaped, and (outer diameter D / number of poles p) <(4 / π) (mm) or the coercive force H _C ≧ 15 k (Oe). The method for magnetizing a rare earth magnet according to any one of claims 1 to 3, wherein:   The method for magnetizing a rare earth magnet according to claim 4, wherein the outer diameter D is 10 (mm) or less.   The said rare earth magnet is inserted in the hole part of the magnetizing yoke provided with the magnetizing head of the number of poles p by which the exciting coil was wound, respectively. Magnetizing method of rare earth magnets.   The method for magnetizing a rare earth magnet according to claim 6, wherein the magnetizing yoke has a water cooling structure, the exciting coil is formed of a tube wire, and a refrigerant is further passed through the tube wire.   8. The permeance coefficient Pc of the rare earth magnet inserted into the magnetizing yoke is set to be the same as the permeance coefficient Pc when the rare earth magnet is incorporated in a device. 2. A magnetizing method for a rare earth magnet as described in the above item.   It is magnetized by the method for magnetizing a rare earth magnet according to any one of claims 1 to 8, has a magnetization rate of 70% or more, and contains at least one light rare earth element RL. Rare earth magnet. The outer shape is either cylindrical or ring-shaped, and has (outer diameter D / number of poles p) <(4 / π) (mm) or coercive force H _C ≧ 15k (Oe) The rare earth magnet according to claim 9.   11. The rare earth magnet according to claim 10, wherein the outer diameter D is 10 (mm) or less.   12. The permeance coefficient Pc of the rare earth magnet inserted into the magnetizing yoke is set to be the same as the permeance coefficient Pc when the rare earth magnet is incorporated in a device. The rare earth magnet according to Item.

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