JP7155971B2 - Arc-shaped permanent magnet and manufacturing method thereof - Google Patents

Description

The present invention relates to an arcuate permanent magnet having radial anisotropy and a method for manufacturing the same.

RTB magnets that are inexpensive and have high magnetic properties are mainly composed of a rare earth element (R), a transition element (T) and boron (B), that is, the main phase of the RTB structure. and is roughly classified into sintered magnets and hot worked magnets depending on the manufacturing method. In any manufacturing method, molding into a desired shape is required. Regarding the shape of this magnet, especially in the manufacture of motors, a permanent magnet having a radial anisotropy, in which the magnetic flux is oriented radially from the inner diameter side to the outer diameter side, is cylindrical or arc-shaped. Demand is growing.

When manufacturing arc-shaped permanent magnets with radial anisotropy, sintered magnets must be pressed in a magnetic field to obtain magnetic anisotropy. Therefore, a method using hot working, in which the material is heated and plastically deformed by pressure to orient the crystal grains, is often used.

As a method of manufacturing an arc-shaped permanent magnet having radial anisotropy by hot working, there is a method of processing an arc-shaped magnet from an arc-shaped compacted body using upper and lower punches having curved surfaces (Patent Document 1 and Patent Document 2), a method of molding a ring-shaped magnet and then dividing the ring-shaped magnet (Patent Document 3), a method of using an extrusion die (Patent Document 4), and the like are known.

JP-A-06-124829 JP-A-06-140224 JP 2015-15381 A Japanese Patent No. 4957415

However, in the methods described in Patent Document 1 and Patent Document 2, uniform compression is not applied to the entire body due to friction generated between the upper and lower punches having curved surfaces and the molded body, and the circumferential ends of the arc-shaped magnet are not compressed. There is a problem that the magnetic properties deteriorate.
In addition, in the method described in Patent Document 3, the arc shape that can be manufactured is affected by the shape restrictions of the ring-shaped magnet before division, so when manufacturing an arc-shaped magnet with a low curvature or a thick arc-shaped magnet, There is a problem that the formability and magnetic properties tend to deteriorate due to the increase in the size of the ring-shaped magnet before splitting and the non-uniformity in the amount of processing.
Furthermore, in the method described in Patent Document 4, since the arc-shaped magnet is directly extruded from the rectangular preform, it is difficult to control the deformation in the extrusion die, and the orientation at the circumferential end of the arc-shaped magnet is difficult to control.

An object of the present invention is to solve the above problems.
That is, the object of the present invention is to achieve the same excellent magnetic properties such as residual magnetic flux density (Br), coercive force (Hcj), blending ratio (Br/Js) at both the circumferential center portion and the circumferential end portion, and reduce the magnetic properties. To provide a radially anisotropic arcuate permanent magnet which is difficult to magnetize and a method for manufacturing the same.

The present inventor has made intensive studies to solve the above problems, and completed the present invention.
The present invention is the following (1) to (3).
(1) A forming step for obtaining a preform by at least consolidating the magnet powder, and a plate magnet forming step for obtaining a parallel-oriented plate magnet having a degree of orientation of 0.90 or more by extruding the preform. and an extrusion bending step of bending the parallel-oriented plate magnet by applying stress so that the compression strain (ε1) is 0.5 or less and the extension strain (ε2) is 0.2 or less, A method for manufacturing an arcuate permanent magnet having radial anisotropy.
(2) Prepare a mold having a rectangular inlet and an arc-shaped outlet whose dimensions are the same as the cross section of the preform, insert the preform into the inlet, and insert the preform into the mold. The method for producing an arc-shaped permanent magnet having radial anisotropy according to (1) above, wherein the step of forming the plate magnet and the step of extrusion bending are performed continuously.
(3) A rare earth hot-worked magnet having a main phase of an RTB structure, which has an arc shape with a curvature of 0.055 or less and a thickness of 4.5 mm or more in the radial direction of the magnet, and a center portion in the circumferential direction and a radially anisotropic arc shape having an orientation degree of 0.90 or more at the circumferential end portions and an orientation difference between the circumferential center portion and the circumferential end portion of less than 0.05 in absolute value permanent magnet.

According to the present invention, the residual magnetic flux density (Br), the coercive force (Hcj), and the degree of orientation (Br/Js) are all equally excellent at both the circumferential center and the circumferential ends, and are difficult to demagnetize. Arc-shaped permanent magnets having radial anisotropy can be easily obtained. Furthermore, the magnetic properties are equally excellent at both the center portion in the circumferential direction and the end portions in the circumferential direction, and the radial anisotropy is an arc shape with a low curvature, a thick arc shape, and an arc shape with a large spread angle. Arc-shaped permanent magnets can also be obtained.

1 is a process chart showing an example of a method for manufacturing an arc-shaped permanent magnet having radial anisotropy according to the present invention. In the method for manufacturing an arc-shaped permanent magnet having radial anisotropy of the present invention, the cross-sectional shape and orientation from the preform to the arc-shaped permanent magnet when the plate magnet forming step and the extrusion bending step are continuously performed ((I) to (IV)). In the figure, “W” is the width dimension of the plate magnet before the extrusion bending process, “W ₁ ” is the arc inner circumference dimension of the arc-shaped magnet after the extrusion bending process, and “W ₂ ” is the extrusion bending. It represents the arc outer circumference dimension of the arc-shaped magnet after the machining process. 1 is a schematic diagram showing an example of an arcuate permanent magnet having radial anisotropy according to the present invention. FIG. In the figure, "T" represents the thickness of the arcuate permanent magnet, and "D" represents the spread angle of the arcuate permanent magnet. FIG. 4 is a schematic diagram showing cutting out of a circumferential center test piece and a circumferential end test piece of an arc-shaped permanent magnet in an example. (a) is a view showing the cutout of the test piece from the cross-sectional side of the arc-shaped permanent magnet, and (b) is a view showing the cut-out of the test piece from the top side of the arc-shaped permanent magnet. The directional center specimen and "B" represent the circumferential end specimen of the arcuate permanent magnet.

First, a method for manufacturing an arcuate permanent magnet having radial anisotropy according to the present invention will be described.
The method for producing an arcuate permanent magnet having radial anisotropy according to the present invention comprises a molding step of subjecting powder for magnets to at least compaction to obtain a preform, and an extrusion process of the preform to obtain a degree of orientation. A plate magnet forming step for obtaining a parallel-oriented plate magnet of 0.90 or more, and stress is applied to the parallel-oriented plate magnet so that the compressive strain (ε1) is 0.5 or less and the elongation strain (ε2) is 0.2 or less. and an extrusion bending process for bending. Hereinafter, it is also referred to as "the manufacturing method of the present invention".

The manufacturing method of the present invention is a method that utilizes hot working, which is a processing method in which a material is heated and plastically deformed by pressure to orient crystal grains. The manufacturing process will be described below using FIG. will be explained in detail.

In the manufacturing method of the present invention, magnet powder is used as a raw material. As a method for preparing this powder for magnets, the melted mother alloy is injected onto a rotating roll and rapidly cooled to obtain a ribbon having a fine crystal structure. A method for obtaining magnet powder (raw material powder) is exemplified. This is the step of FIG. 1(a). In the present invention, it is preferable to use RTB magnet powder which is inexpensive and has high magnetic properties (high residual magnetic flux density and high coercive force), but the present invention is not limited to this. The RTB system means that the main components are rare earth elements (R), transition elements (T) and boron (B), and the rare earth elements include Nd, Pr, Dy, Tb, etc. Preferably, the transition element includes Fe, Co, Ni, and the like. In particular, it is most preferable to use an Nd--Fe--B magnet powder in terms of obtaining an RTB-based magnet having higher magnetic properties. Here, the "main component" in the present invention means that the total content is 90% by mass or more, and the total content is more preferably 95% by mass or more.

Next, in the forming step, the magnet powder is subjected to compaction processing to obtain a preform. In particular, cold compaction is performed at room temperature (20±15° C.) as the consolidation process to obtain a rectangular preform (e.g., rod-like shape) from the viewpoint of ease of later processing into a plate magnet. preferable. This is the step of FIG. 1(b). From the viewpoint of facilitating subsequent hot working, it is preferable to apply a lubricant to the surface of the obtained preform. This is the step of FIG. 1(c). This preform may be a preform having a strength that allows handling, and in order to obtain such a preform, conditions such as the cold compaction step may be appropriately set. In addition, as the lubricant, a known lubricant such as one containing fatty acid ester as a main component can be used, and there is no particular limitation.

Further, in the present invention, as the consolidation process, for example, after applying a lubricant to the preform obtained by cold compaction, hot pressing is performed in which the preform is further heated and formed into a more preferable shape, A preform of density and strength may be obtained.

Then, the preform obtained in this way is subjected to extrusion processing (hot extrusion processing) using a mold heated to about 700 to 900° C., and a parallel orientation plate magnet having a degree of orientation of 0.90 or more is obtained. to form The processing time in this step is exemplified within 300 seconds. This is the step of FIG. 1(d). Although this step may be performed in the atmosphere, it is preferably performed in an atmosphere of an inert gas such as argon or under reduced pressure from the viewpoint of suppressing oxidation.

In the manufacturing method of the present invention, in the hot extrusion process, instead of directly forming an arc-shaped permanent magnet from the preform, first, the preform is plastically deformed in the direction of the easy axis of magnetization so that the degree of orientation is 0.90 or more. A parallel orientation plate magnet is formed. Therefore, this hot extrusion process can be said to be a plate magnet forming process. In addition, in the method of forming arc-shaped permanent magnets directly from the preform by hot extrusion without going through the step of forming plate magnets, it is difficult to control deformation in the extrusion die, and magnetic properties are poor. It is difficult to obtain arcuate permanent magnets with uniform radial anisotropy. On the other hand, according to the manufacturing method of the present invention in which a parallel-oriented plate magnet is formed from the preform and the parallel-oriented plate magnet is extruded and bent into an arc-shaped magnet, residual magnetic flux density (Br) and coercive force (Hcj) It is possible to easily obtain an arc-shaped permanent magnet having radial anisotropy that is equally excellent in both the center portion in the circumferential direction and the end portion in the circumferential direction and is difficult to demagnetize. .

Here, in the present invention, the "orientation degree" means the value (Br/Js) obtained by dividing the residual magnetic flux density (Br) of the magnet by the saturation magnetic flux density (Js), and represents the degree of orientation of the axis of easy magnetization. . In addition, "parallel orientation" means a state in which magnetic fluxes are oriented in parallel. Form.

Next, under the same processing temperature, processing time, and atmospheric conditions as in the plate magnet forming step, the formed parallel-oriented plate magnet has a compressive strain (ε1) of 0.5 or less and an elongation strain (ε2) of 0.2 or less. Then, an extrusion bending process (hot extrusion bending process) is performed in which bending is performed by applying a stress (for example, in the orientation direction of the parallel orientation plate magnet). This is the step of FIG. 1(e). A radially anisotropic arc-shaped permanent magnet can be easily obtained from a parallel-oriented plate magnet by carrying out processing under such compressive strain and elongation strain conditions. In the present invention, "radial anisotropy" means a state in which magnetic fluxes are oriented radially from the inner diameter side to the outer diameter side of an arc.

In the present invention, "compressive strain (ε1)" refers to the dimensions of the inner circumference of the arc of the magnet before and after the extrusion bending step, respectively, W (width dimension of the plate magnet) and W ₁ (inside the arc of the arc-shaped magnet). Circumferential dimension) means a value defined as “ln (W/W ₁ )”, and “extension strain (ε2)” refers to the outer circumference of the arc of the magnet before and after the extrusion bending process is defined as "ln ₍ W2/W)", where W (the width of the plate magnet) and W2 ₍ the outer peripheral dimension of the arc-shaped magnet) are used. _In addition, "ln" means the natural logarithm, and W, W1 and W2 are the parts shown in _FIG . Dimensions.

In the production method of the present invention, the plate magnet forming step and the extrusion bending step may be performed as separate steps using separate molds. It is more efficient to perform the process continuously using one mold.
Specifically, a mold having a rectangular inlet and an arc-shaped outlet whose dimensions match the cross section of the preform (the cross section of the preform parallel to the orientation direction of the parallel orientation plate magnet to be obtained). is prepared, the preformed body is charged into the inlet, and the plate magnet forming step and the extrusion bending step are continuously performed.

In the case where the plate magnet forming step and the extrusion bending step are continuously performed using one mold, the cross section from the preform to the arc-shaped permanent magnet (magnet orientation direction and An example of shape change and orientation change in parallel cross-sections) is shown in FIG.
In addition, (I) to (II) of FIG. 2 show the shape change of the cross section in the step of forming the plate magnet. Oriented parallel orientation is obtained. In addition, (III) to (IV) of FIG. 2 show the shape change of the cross section in the extrusion bending process, and when the arc-shaped magnet is formed, its orientation becomes radially anisotropic. With such changes in cross-sectional shape and orientation, arc-shaped magnets are formed from the preform via plate magnets.

After the extrusion bending step as the final processing step, post-processing such as cutting, grinding, chamfering, etc. (the step in FIG. 1(f)) is performed as necessary on the arc-shaped permanent magnet obtained. to produce a radially anisotropic arc-shaped permanent magnet, which is the final product.

According to the manufacturing method of the present invention, the residual magnetic flux density (Br), the coercive force (Hcj) and the blending ratio (Br/Js) are equally excellent at both the circumferential center portion and the circumferential end portion, and demagnetization does not occur. Arc-shaped permanent magnets having radial anisotropy (particularly RTB-based arc-shaped permanent magnets having radial anisotropy), which are difficult to produce, can be easily manufactured. A radially anisotropic arcuate permanent magnet with a spread angle can be manufactured.

Next, the radially anisotropic arcuate permanent magnet of the present invention will be described in detail.
The radially anisotropic arc-shaped permanent magnet of the present invention is a rare earth hot-worked magnet having a main phase of RTB structure, and has a curvature of 0.055 or less and a thickness of 4.5 mm or more in the magnet radial direction. It has an arc shape, the degree of orientation at the center in the circumferential direction and at the ends in the circumferential direction is 0.90 or more, and the difference in the degree of orientation between the center in the circumferential direction and the ends in the circumferential direction is smaller than 0.05 in absolute value. It is an arc-shaped permanent magnet. Hereinafter, it is also referred to as "the magnet of the present invention".

Here, the RTB structure means a crystal structure in which the main phases are a rare earth element (R), a transition element (T) and boron (B). It is the same. The magnet of the present invention preferably has this RTB structure as a main phase and the aspect ratio of the main phase crystal grains is more than 2. When the aspect ratio of the main phase crystal grains is more than 2, the permanent magnet has a higher crystal grain orientation (Br/Js), a higher residual magnetic flux density (Br), and is more difficult to demagnetize. I can say
In the present invention, the "aspect ratio" means that the maximum diameter of one crystal grain is measured on an image obtained by observing using a scanning electron microscope (SEM), and the value is d. , determine a point that bisects the maximum diameter, find two points where a straight line orthogonal to the point intersects the outer edge of this crystal grain, measure the distance between the two points and set it to t, 50 crystal grains d/t is obtained for each of the values, and a simple average thereof is obtained.

In addition, in the present invention, observation of a secondary electron image (1500 times) using the X-ray diffraction method and a scanning electron microscope (SEM), and the crystal grains of the main phase and the grain boundary phase by an ICP analyzer are included. By area analysis, it can be confirmed whether the main phase of the magnet of the present invention is the RTB structure.

Furthermore, the magnet of the present invention has an arc shape with a curvature of 0.055 or less, preferably 0.053 or less, and a thickness of 4.5 mm or more, preferably 4.5 to 10 mm in the radial direction of the magnet. The orientation degree (Br/Js) at the central portion and the circumferential end portions is 0.90 or more, preferably 0.93 or more, and the absolute value of the orientation degree difference between the circumferential central portion and the circumferential end portions is It is a radially anisotropic permanent magnet of less than 0.05, preferably less than 0.03.
Here, the "curvature" in the present invention means the reciprocal of the arc outer radius, and the "magnet radial thickness" means the difference between the arc outer radius and the arc inner radius. Further, as shown in FIGS. 3 and 4, the terms "circumferential center" and "circumferential end" in the present invention refer to an angle (D/3 ), the portion including the side surface of the magnet forming the spread angle (D) of the arc magnet is the “end in the circumferential direction” and divides the spread angle (D) into two equal parts. The portion including the position of the angle (D/2) is the "circumferential central portion".

The magnet of the present invention has a curvature of 0.055 or less and a thickness of 4.5 mm or more in the radial direction of the magnet. Br), coercive force (Hcj), and compounding ratio (Br/Js) at both the circumferential center portion and the circumferential end portion, and are difficult to demagnetize. Also, the magnet of the present invention can be easily obtained by the manufacturing method of the present invention described above.

Examples of the present invention will be described below. The present invention is not limited to the following examples, and various modifications are possible within the technical concept of the present invention.

After melting a master alloy containing Nd, Fe, and B as main components at 1500°C, the molten metal is injected from an orifice onto a Cr-plated Cu rotating roll (rotating roll peripheral speed: 30 m/sec) and rapidly cooled. An alloy ribbon was produced. This quenched alloy ribbon was pulverized with a cutter mill and sieved to prepare raw material powder having a maximum particle size of 150 μm or less. Then, this raw material powder is loaded into a mold of a cold press machine, a pressure of 3 tons/cm ² is applied in the atmosphere, and a compaction process is performed by holding for 3 seconds to form a rectangular (rod-shaped) preform. was made.

Then, a lubricant containing fatty acid ester as a main component was applied to the surface of the preform. After that, a parallel-oriented plate magnet having a degree of orientation of 0.90 or more is molded by hot extrusion, and then the compressive strain (ε1) is 0.5 or less and the elongation strain (ε2) is 0.2 or less. Using seven types of molds that can be extruded and bent to form an arc-shaped magnet, these molds are placed in an argon gas atmosphere or a reduced pressure atmosphere at 700 to 900 ° C. Then, the preforms are set in each, and while heating, a maximum pressure of 30 tons/cm ² is applied and continuously processed so as to be formed within 300 seconds, and nine types of arc-shaped permanent Magnets were produced (Examples 1 to 9 (Examples 6, 8 and 9 used the same mold)).

Separately from this, the above preform coated with a lubricant was subjected to a mold for forming a plate magnet by hot extrusion (Comparative Example 1), and was not subjected to the step of forming a plate magnet by hot extrusion. A die (Comparative Example 2) that directly forms an arc-shaped permanent magnet in the mold (Comparative Example 2), and after forming a plate magnet by hot extrusion, continuously apply stress and perform extrusion bending. Using two types of molds (Comparative Examples 3-4) whose compressive strain and elongation strain do not satisfy the conditions of the present invention, these molds were heated at 700 to 900 ° C. in an argon gas atmosphere or in a reduced pressure atmosphere. , and the preformed bodies were set in each of them, and while heating, a maximum pressure of 30 tons/cm ² was applied and processed so as to be formed within 300 seconds, thereby producing four types of permanent magnets. (Comparative Examples 1 to 4).

Table 1 below shows the final process, shape, bending conditions and magnet structure of the magnets of Examples 1 to 9 and Comparative Examples 1 to 4. For the measurement and calculation of the following data, the arc outer circumference radius, the arc inner circumference radius, and the distance between the magnet side surfaces were obtained by a three-dimensional shape measuring machine (magnification: 12 times: VR-3000, manufactured by Keyence Corporation). The angle is measured, the difference between the arc outer radius and the arc inner radius is defined as the thickness in the magnet radial direction (T in FIG. 3), the reciprocal of the arc outer radius is defined as the curvature, and the angle between the magnet side surfaces is the spread angle (Fig. 3 D). Compressive strain and tensile strain in extrusion bending were calculated from the width dimension at the time of forming the plate magnet and the arc outer circumference dimension and arc inner circumference dimension of the obtained arc magnet from the design of the mold used.

Furthermore, the aspect ratio of the main phase crystal grains in each magnet was measured by an observation method using a scanning electron microscope (SEM). Specifically, first, each magnet was observed with a scanning electron microscope under the following conditions.
Observation magnification: 20,000 times Apparatus: S-4700, manufactured by Hitachi High-Technologies Corporation Observation conditions: Secondary electron image Observation direction: Direction perpendicular to orientation direction Particle size confirmation method: Image processing (winROOF, Mitani Shoji Co., Ltd.)
Image processing conditions: acicular ratio Image processing area: about 740 nm x 640 nm

Then, the maximum diameter of one crystal grain on the image obtained by observation under such conditions was measured, and the value was defined as d. Also, a point that bisects the maximum diameter is determined, two points where a straight line perpendicular to the point intersects with the outer edge of the crystal grain are determined, and the distance between the two points is measured as t. Then, d/t was obtained and used as the aspect ratio of the crystal grains.
The aspect ratio of each of the 50 crystal grains was measured in this way, and the value obtained by simple averaging was taken as the aspect ratio of the magnet.

Next, from the obtained magnets of Examples 1 to 9 and Comparative Examples 1 to 4, as shown in FIGS. A test piece of (B) was cut out. Then, these test pieces were measured using a pulse excitation type magnetic property measuring device (TPM-2-08s25VT, manufactured by Toei Kogyo Co., Ltd.) at a measurement temperature (RT) of 23 ° C., and corrected for the demagnetizing field. Residual magnetic flux density (Br), coercive force (Hcj) and saturation magnetic flux density (Js) were determined. Furthermore, the degree of orientation (Br/Js) was calculated, and the difference (absolute value) between the circumferential center test piece and the circumferential end test piece was also calculated for each magnetic property data. These results are shown in Table 2 below.

From these results, the magnets of Examples 1 to 9, which are the magnets of the present invention, have a circular arc shape with a low curvature, a thick wall, and a large spread angle, but the residual magnetic flux density between the circumferential center and the circumferential ends (Br), coercive force (Hcj), and blending ratio (Br/Js) are small, that is, the magnetic properties are uniform like the plate magnet (Comparative Example 1), and the aspect ratio of the crystal grains is more than 2. was shown to be On the other hand, in Comparative Example 2, in which the arc-shaped permanent magnet was directly formed without going through the step of forming the plate magnet by hot extrusion, the coercive force (Hcj) at the circumferential end portion was greatly reduced. Furthermore, in Comparative Examples 3 and 4, in which the amount of work during extrusion bending is large, a minute crack occurs in the circumferential center on the outer peripheral side of the arc-shaped permanent magnet, and as a result, the residual magnetic flux density (Br) The coercive force (Hcj) is greatly reduced when the Js) was also lowered.

Therefore, according to the manufacturing method of the present invention, the curvature is 0.055 or less, the thickness in the magnet radial direction is 4.5 mm or more, the residual magnetic flux density (Br), the coercive force (Hcj), and the compounding ratio (Br/Js ) is equally excellent both at the center in the circumferential direction and at the ends in the circumferential direction. It became clear. A radially anisotropic RTB arc-shaped permanent magnet with uniform magnetic properties is difficult to demagnetize and can be suitably used as a permanent magnet for motors and the like.

Claims (3)

a forming step of subjecting the magnet powder to at least compaction to obtain a preform;
a plate magnet forming step of extruding the preform to obtain a parallel-oriented plate magnet having a degree of orientation of 0.90 or more;
an extrusion bending step of bending the parallel-oriented plate magnet by applying stress so that the compression strain (ε1) is 0.5 or less and the extension strain (ε2) is 0.2 or less;
A method for manufacturing an arc-shaped permanent magnet having radial anisotropy, comprising: A mold having a rectangular inlet and an arc-shaped outlet having the same dimensions as the cross section of the preform is prepared, the preform is inserted into the inlet, and the plate is placed in the mold. 2. The method for producing an arc-shaped permanent magnet having radial anisotropy according to claim 1, wherein the magnet forming step and the extrusion bending step are performed continuously. A rare earth hot-worked magnet having a main phase of RTB structure,
It has an arc shape with a curvature of 0.055 or less and a thickness of 4.5 mm or more in the magnet radial direction,
The degree of orientation at the center in the circumferential direction and at the ends in the circumferential direction is 0.90 or more, and the absolute value of the difference in the degree of orientation between the center in the circumferential direction and the ends in the circumferential direction is less than 0.05.
Radial anisotropic arc-shaped permanent magnet.

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