JPWO2010052862A1 - Rare earth sintered magnet manufacturing method and powder filled container for manufacturing rare earth sintered magnet - Google Patents

Abstract

The present invention provides a method capable of easily and inexpensively manufacturing a rare earth sintered magnet having a void such as a slit for making it less susceptible to eddy currents and / or performing grain boundary diffusion treatment. It is aimed. In the rare earth sintered magnet manufacturing method according to the present invention, a powder filling container 10 is filled with a rare earth magnet alloy powder 19 together with a gap forming member 14 ((a), (b)), and the rare earth magnet alloy powder 19 is filled. An orientation step (c) for orientation in a magnetic field and a sintering step (e) for sintering the rare earth magnet alloy powder 19 by heating the rare earth magnet alloy powder 19 together with the powder-filled container 10 are performed in this order. The gap forming member is removed (d) after the step and before the rare earth magnet alloy powder starts to be sintered.

Description

  The present invention relates to a method for producing rare earth sintered magnets such as Nd—Fe—B based sintered magnets and Sm—Co based sintered magnets.

  Rare earth sintered magnets are widely used as permanent magnets that can generate a strong magnetic field. In particular, Nd—Fe—B based sintered magnets are widely used in motors for hybrid vehicles and electric vehicles, small motors for hard disks, large motors for industrial use, and generators.

  In these motors and generators, a rare earth sintered magnet is used as a rotor (rotor) and an electromagnet is used as a stator (stator), and the rotor rotates by forming a rotating magnetic field. At that time, eddy currents are generated in the rare earth sintered magnet of the rotor, which causes problems such as energy loss and motor overheating. Patent Document 1 describes that the generation of such eddy current is suppressed by providing a slit on the surface of the rare earth sintered magnet.

  In Nd-Fe-B magnets (neodymium magnets), in order to increase the coercive force, a sintered magnet is produced using an alloy powder in which a part of Nd is substituted with Dy and / or Tb. However, this method has the disadvantages that Dy and Tb are expensive and rare, leading to an increase in cost and a decrease in stable supply, and a decrease in the maximum energy product. Therefore, by attaching Dy and / or Tb to the surface of the sintered body of Nd-Fe-B alloy that does not contain Dy and Tb and heating (heating temperature: 700 to 1000 ° C.), the sintered body Dy and / or Tb is fed into the sintered body through the grain boundaries of the alloy particles therein, and Dy and / or Tb is injected only near the surface of the alloy particles (grain boundary diffusion method). As a result, a high coercive force can be obtained, a reduction in the maximum energy product can be suppressed, and the amount of Dy and Tb used can be reduced. In Patent Document 2, a slit is provided on the surface of a sintered body of an Nd—Fe—B alloy, and Dy and / or Tb is diffused from the slit to achieve an efficiency near the surface of the alloy particle. It is often described that Dy and / or Tb is injected.

JP 2000-295804 A ([0009]-[0011]) JP 2007-053351 A ([0027]-[0028], [0033]-[0035])

  In both methods described in Patent Document 1 and Patent Document 2, slits are formed by mechanical processing using a cutting machine, a wire saw, or the like. When such mechanical processing is used, labor and time are required, and tool consumption is severe, so an increase in cost is inevitable. In addition, the slit width cannot be made very small by mechanical processing, the ratio of the substantial volume (volume of the sintered body portion) to the external volume of the magnet is reduced, and the function as a magnet is substantially reduced. End up.

In the case where the slit is formed in the compression molded body before sintering by mechanical processing, there is a further problem that it is difficult to remove the alloy powder remaining in the slit. If heating for sintering is performed with the alloy powder remaining in the slit, the alloy powder closes a part of the slit, so that generation of eddy currents cannot be prevented and grain boundary diffusion occurs. When processing is performed, Dy and / or Tb do not reach sufficiently deep.
At the same time, if the compression molded body is machined, chipping or cracking may occur.

  The problem to be solved by the present invention is to easily and inexpensively manufacture a rare earth sintered magnet having voids such as slits and holes for making it less susceptible to eddy currents and / or performing grain boundary diffusion treatment. It is to provide a method that can.

The rare earth sintered magnet manufacturing method according to the present invention made to solve the above problems is as follows.
a) a filling step of filling a powder filling container with a rare earth magnet alloy powder together with a gap forming member;
b) an alignment step of aligning the rare earth magnet alloy powder in a magnetic field;
c) a sintering step of sintering the rare earth magnet alloy powder by heating the rare earth magnet alloy powder together with the powder-filled container;
In this order,
d) removing the void forming member after the orientation step and before the rare earth magnet alloy powder starts to be sintered;
Thus, a rare earth sintered magnet having voids is manufactured.

  According to the present invention, a rare earth magnet alloy powder is filled in a powder-filled container together with a void forming member, and the void forming member is simply removed before the rare earth magnet alloy powder starts sintering. A magnet can be manufactured easily. Therefore, in the present invention, it is not necessary to perform mechanical processing to form a void, and a rare earth sintered magnet having a void can be manufactured at low cost.

  Conventionally, when producing rare earth sintered magnets, in many cases, compression molding and orientation are performed by filling a container with rare earth magnet alloy powder and applying a magnetic field while compressing. In contrast, the inventor of the present application fills the powder-filled container with the rare-earth magnet alloy powder, orients the rare-earth magnet alloy powder without performing compression molding, and heats the powder-filled container as it is. It was found that a rare earth sintered magnet can be obtained by the pressless method (see JP 2006-019521 A). In the present invention, since the pressless method is used, even if the void forming member is placed in the powder-filled container together with the rare earth magnet alloy powder, the void forming member is not subjected to pressure.

  Further, the rare earth magnet alloy powder particles filled in the powder-filled container are magnetically attracted by the orientation in the magnetic field. In the present invention, since the void forming member is removed after the alignment step, the void does not collapse when the void forming member is removed.

  On the other hand, if the temperature is raised when heating the rare earth magnet alloy powder in the sintering process, the sintering starts when the temperature exceeds a predetermined temperature (for example, about 600 ° C. for a Nd—Fe—B based sintered magnet), Thereafter, as the sintering proceeds, the sintered body contracts. In the present invention, the gap forming member is removed before the sintering of the rare earth magnet alloy powder starts so as not to obstruct the shrinkage.

  The removal of the void forming member is desirably performed before the sintering step in that it is not necessary to consider the heat resistance of the void forming member and the reactivity between the void forming member and the rare earth magnet alloy powder.

  In addition, if a void forming member that is liquefied or vaporized at a temperature lower than the temperature at which sintering starts is used, the void forming member can be removed before sintering starts by raising the temperature for sintering. .

  When the rare earth magnet alloy is an Nd-Fe-B sintered magnet alloy, a substance containing Dy and / or Tb is injected into the voids of the sintered body obtained by the sintering step. By heating, Dy and / or Tb can be diffused in the sintered body.

  When the slit for preventing the influence of eddy current is formed in the rare earth sintered magnet, a plate material may be used for the gap forming member. On the other hand, when the main purpose is grain boundary diffusion, a bar material can also be used. In that case, Dy and / or Tb can be uniformly diffused from a large number of holes by arranging a large number of rod-shaped void forming members in a matrix. The cross-sectional shape of the rod-shaped void forming member is not particularly limited, such as a circle, a quadrangle, or a hexagon.

  When a plate-like or rod-like gap forming member is used as the gap forming member, it is desirable to orient the rare earth magnet alloy powder in a magnetic field in a direction parallel to the gap forming member in the orientation step. Thereby, since the particles of the rare earth magnet alloy powder are connected in a chain shape in a direction parallel to the gap forming member, even if the gap forming member is removed in this state, the chain connection is not interrupted and the gap is not broken.

  Further, in order to prevent the void from collapsing, the powder filled container may be filled after the rare earth magnet alloy powder and the binder are mixed. As the binder, methyl cellulose, polyacrylamide, polyvinyl alcohol, paraffin wax, polyethylene glycol, polyvinyl pyrrolidone, hydroxypropyl cellulose, hydroxypropyl methyl cellulose, ethyl cellulose, acetyl cellulose, nitrocellulose, vinyl acetate resin, or the like can be used (Japanese Patent Laid-Open No. Hei 10). -270278).

  When filling the powder-filled container with the rare earth magnet alloy powder together with the gap forming member, the rare earth magnet alloy powder and the gap forming member may be placed in the powder filled container at the same time. May be put in.

  If the voids provided in the sintered body by the production method according to the present invention are left as they are, the mechanical strength is low and they are easily damaged. In addition, accumulation of moisture in the voids may cause corrosion or mechanical damage. Therefore, by embedding an embedding member such as an epoxy resin in the gap, it is possible to increase the mechanical strength and prevent moisture from staying. The embedding member is embedded after the gap forming member is removed. However, when the heat resistant temperature is lower than the sintering temperature of the rare earth magnet, such as an epoxy resin, it is performed after the sintering step. When performing the diffusion process, the embedded member is embedded after the diffusion process. In order to prevent the influence of eddy current, the embedded member is preferably insulative.

  According to the present invention, a powder-filled container is filled with rare-earth magnet alloy powder together with a gap forming member, and after being oriented in a magnetic field, the gap can be formed simply by removing the gap forming member and performing mechanical processing. Since there is no need, a rare earth sintered magnet having voids can be manufactured easily and at low cost.

The longitudinal cross-sectional view which shows the 1st example of the mold used by the rare earth sintered magnet manufacturing method concerning this invention, the lid | cover of a mold, and the space | gap formation member, and the top view of a lid | cover of a mold. Schematic which shows the 1st example of the rare earth sintered magnet manufacturing method concerning this invention. The longitudinal cross-sectional view which shows the 2nd example of the mold used with the rare earth sintered magnet manufacturing method concerning this invention, the lid | cover of a mold, and the space | gap formation member, and the bottom view of the bottom of a mold. Schematic which shows the 2nd example of the rare earth sintered magnet manufacturing method concerning this invention. The longitudinal cross-sectional view which shows the other example of the mold in this invention, and the lid | cover of a mold. The perspective view which shows the example of a rod-shaped space | gap formation member. Schematic which shows an example of the grain boundary diffusion process in this invention. Schematic which shows an example of the process which embeds an embedding member in a space | gap. 1 is a perspective view of a rare earth sintered magnet produced by the method of Example 1. FIG. The longitudinal cross-sectional view of the mold used in Example 3-1, the lid | cover of a mold, and a space | gap formation member, and the top view of a lid | cover of a mold. The longitudinal cross-sectional view of the mold used in Example 3-2, a lid | cover of a mold, and a space | gap formation member, and the upper side figure of a lid | cover of a mold.

Embodiments of a rare earth sintered magnet manufacturing method according to the present invention will be described with reference to FIGS.
1 and 2 show a first embodiment of the present invention. In the first embodiment, the mold (powder filling container) 10 and the gap forming member 14 shown in FIG. 1 are used. The mold 10 is used to obtain a flat magnet, and has a rectangular parallelepiped housing portion 11 filled with a rare earth magnet alloy powder. An opening for taking out the rare earth sintered magnet after filling and sintering of the rare earth magnet alloy powder is provided in the upper portion of the accommodating portion 11, and a lid 13 is attached so as to close the opening. As the material of the mold 10 and the lid 13, for example, magnetic stainless steel, nonmagnetic stainless steel, or carbon (having heat resistance equal to or higher than the sintering temperature of the rare earth sintered magnet) can be used. In the lid 13, two insertion ports 131 extending in the longitudinal direction of the rectangular parallelepiped of the accommodating portion 11 are provided in parallel. A plate-like gap forming member 14 having a slightly smaller width and length than that can be inserted into the insertion port 131. As the material of the gap forming member 14, various metals, carbon, and plastics (heat resistance is not required in the present embodiment) can be used. The gap forming member 14 is erected on the plate-like gap forming member fixture 15 at the same interval as the two insertion ports 131.

  The manufacturing method of the rare earth sintered magnet of this embodiment will be described with reference to FIG. First, the accommodating part 11 is filled with the rare earth magnet alloy powder 19 (a). At that time, the rare earth magnet alloy powder 19 may be used as it is, or a binder may be mixed with the rare earth magnet alloy powder 19. The packing density is preferably 40 to 50% of the true density of the rare earth magnet alloy. Next, the lid 13 is attached to the mold 10, and the gap forming member 14 is inserted into the rare earth magnet alloy powder 19 in the accommodating portion 11 from the insertion port 131 (b). Subsequently, the mold 10 is placed in the magnetic field generating coil 17 and a pulsed magnetic field is applied parallel to the gap forming member 14 (perpendicular to the lid 13) to orient the rare earth magnet alloy powder 19 (c). The strength of the magnetic field at that time is 3 to 10T, preferably 4 to 8T. When the magnetic field is applied, the lid 13 is firmly pressed against the mold 10 to prevent the rare earth magnet alloy powder 19 from popping out. After orientation in the magnetic field, the air gap forming member 14 is extracted from the rare earth magnet alloy powder 19 and the insertion port 131 (d). As a result, slit-like voids 18 are formed in the compact of the rare earth magnet alloy powder 19. Since the powder particles are magnetically attracted by the orientation in the magnetic field, the powder hardly spills into the void 18. Thereafter, the rare earth magnet alloy powder 19 is heated while being filled in the accommodating portion 11 (e). Thereby, the rare earth sintered magnet which has a slit-shaped space | gap is obtained. During sintering, moisture or the like inevitably contained in the rare earth magnet alloy powder 19 is vaporized, but the generated gas is discharged from the insertion port 131 to the outside of the mold.

  According to this method, the slit can be formed at a much lower cost than when mechanical processing is performed with a wire saw or the like after sintering. In addition, a slit having a smaller width than that in the case of performing mechanical processing can be formed, and a high-quality slit having no reduction in the function of the slit such as residual powder can be formed in the slit.

  3 and 4 show a second embodiment of the present invention. In the second embodiment, the mold 20 and the gap forming member 24 shown in FIG. 3 are used. The mold 20 has the same accommodating portion 21 as the mold 10 of the first embodiment and has a structure to which a lid 23 is attached. However, the mold 20 is different in that two insertion ports 221 are provided at the bottom of the mold 20. This is different from the first example. The lid 23 is not provided with an insertion port. The gap forming member 24 attached to the gap forming member fixture 25 can be inserted into the insertion port 221 as in the first example.

  A method for producing a rare earth sintered magnet according to the second embodiment will be described with reference to FIG. First, the gap forming member 24 is inserted into the insertion port 221 of the mold 20 (a). Next, the accommodating portion 21 is filled with the rare earth magnet alloy powder 29 and the lid 23 is attached (b). Accordingly, the order of insertion of the air gap forming member and filling of the rare earth magnet alloy powder is reversed from the first embodiment. Next, the mold 20 is placed in the magnetic field generating coil 27, and a pulsed magnetic field is applied in a direction parallel to the gap forming member 24 (perpendicular to the lid 23) to orient the rare earth magnet alloy powder 29 (c). Subsequently, after the void forming member 24 is extracted from the rare earth magnet alloy powder 29 and the insertion port 221 to form the void 28 (d), the rare earth magnet alloy powder 29 is heated while being filled in the accommodating portion 21. To be sintered (e).

  FIG. 5 shows another example of the mold. In the mold 10 shown in FIG. 1, the gap forming member 14 is attached to the gap forming member fixture 15 separately from the lid 13, but the gap forming member 14A may be directly attached to the lid 13A (FIG. 5 (a)). ). When such a lid 13A is used, the lid 13A is removed from the mold in order to remove the gap forming member 14 after the orientation step.

  So far, the case where the void forming member is extracted after the alignment step has been described. On the other hand, if a void forming member made of a material that is liquefied or vaporized at a temperature lower than the sintering temperature of the rare earth magnet alloy powder is used, the void forming member can be removed without heating by heating with the mold and the rare earth magnet alloy powder. can do. In that case, you may attach a space | gap formation member in the accommodating part of a mold. As a specific example of the material of such a gap forming member, there is a plastic that easily evaporates, such as polyvinyl alcohol. FIG. 5B shows an example in which a gap forming member 14 </ b> B is erected on the bottom 12 in the accommodating portion 11.

Next, the thickness of the gap forming member according to the purpose, the interval, and the depth of insertion into the rare earth magnet alloy powder (hereinafter referred to as “insertion depth”) will be described.
First, with regard to a case where the main purpose is to prevent the generation of eddy currents when using rare earth sintered magnets, the preferred width, insertion depth, number and interval of the gap forming members will be described. In this case, since the eddy current can be interrupted even if the width of the slit is small, the purpose can be achieved. Therefore, in order to enhance the original performance of the magnet, the width of the slit formed in the sintered body should be as small as possible. Accordingly, the thickness of the gap forming member is preferably as small as possible. For example, when a member similar to a razor blade which is a typical example of a thin plate member is used, the lower limit of the thickness of the gap forming member is about 0.05 mm. In this case, considering the shrinkage due to sintering, the width of the slit formed in the sintered body is about 0.04 mm. Further, the insertion depth is preferably as deep as possible from the viewpoint of reducing eddy current loss, but considering the mechanical strength of the sintered body, it is 1 mm or more, preferably 2 mm or less smaller than the thickness of the magnet in the insertion depth direction. It is preferable.
When the thickness of the air gap forming member is too large, the volume ratio of the magnet (ratio of the volume of the portion where the magnet exists to the volume of the outer shape of the sintered magnet) is lowered, thereby reducing the magnetic properties. Therefore, it is desirable to determine the thickness of the gap forming member so that the volume ratio is 90% or more.
Considering that the loss due to eddy current generated in the magnet increases in proportion to the square of the size of the magnet, the interval between the slits, that is, the interval between the gap forming members is preferably shorter. On the other hand, when the number of slits increases, the volume ratio of the magnet decreases. Therefore, the space | interval and number of space | gap formation members are determined so that the predetermined magnetic characteristic may be obtained exceeding the volume ratio, considering the above-mentioned thickness and insertion depth.

  Next, when the main purpose is to diffuse Dy and Tb into the sintered body by the grain boundary diffusion method, preferred widths, intervals, and insertion depths of the void forming members will be described. If the width of the gap forming member is too small, it becomes difficult to inject a substance containing Dy or Tb into the slit formed in the sintered body. Therefore, the width of the slit is preferably 0.1 mm or more. Also, if the slit spacing is too large, there will be areas where Dy and Tb diffusing from the slit will not reach, and the grain boundary diffusion effect will not spread throughout the sintered magnet, resulting in a magnet with non-uniform magnetic properties. End up. Therefore, the interval between the slits, that is, the interval between the gap forming members is preferably 6 mm or less, more preferably 5 mm or less. The insertion depth is preferably 6 mm or less, more preferably 5 mm or less, with the difference from the thickness of the magnet in the insertion depth direction in order to spread the effect of grain boundary diffusion throughout the sintered magnet. In consideration of mechanical strength, the difference is preferably 1 mm or more, preferably 2 mm or more. Further, as in the case of eddy current prevention, the thickness, insertion depth, number and interval of the air gap forming member are determined so as to exceed the volume ratio at which predetermined magnetic characteristics are obtained.

  Up to this point, an example using a plate-like void forming member has been shown, but a rod-like void forming member can also be used when grain boundary diffusion is the main purpose. For example, as shown in FIG. 6, a large number of rod-shaped gap forming members 34 can be arranged in a matrix on the surface of a plate-like gap forming member fixture 35 in the vertical and horizontal directions. A sintered body having a large number of pores (voids) can be produced by using a large number of void forming members 34 arranged in a matrix like this, and an Nd-Fe-B-based sintered material can be produced by a grain boundary diffusion method. When producing a magnet, Dy and / or Tb can be efficiently diffused from the pores into the sintered body.

  The thickness of the pores formed in the sintered body is preferably 0.2 mm or more, and more preferably 0.3 mm or more so that a substance containing Dy or Tb can be reliably injected. The space between the gap forming members 34 is preferably 6 mm or less, and more preferably 5 mm or less in order to spread Dy and Tb throughout the sintered magnet. The insertion depth is the same as in the case of the plate-shaped gap forming member described above.

  The diffusion treatment is performed by heating the powder 18 containing Dy and / or Tb after filling the voids 18 (FIG. 7). The heating temperature may be 700 to 1000 ° C. Examples of the Dy / Tb-containing material to be injected into the gap include Dy and Tb fluorides, oxides, oxyfluorides or hydrides, alloys of Dy and Tb with other metals, and hydrides of these alloys. Here, examples of alloys of Dy and Tb and other metals include Fe group transition metals such as Fe, Co and Ni, and alloys of B, Al and Cu and Dy and Tb. Grain boundary diffusion treatment is effectively performed by injecting a slurry obtained by mixing powder of these substances with an organic solvent into the void and heating. These slurries may be injected only into the voids, but may be injected into the slits and pores and applied to the surface of the sintered body. Thereby, grain boundary diffusion can be caused from both the voids and the surface of the sintered body. Grain boundary diffusion treatment is performed by heating the sintered body in which the slurry is injected into the voids (or additionally applied to the surface) at 700 to 1000 ° C. for 1 to 20 hours in vacuum or in an inert gas. be able to. By performing grain boundary diffusion treatment in this way, even for thick NdFeB sintered magnets of 5 mm or more, the coercive force can be effectively increased with a small amount of Dy and Tb without significantly reducing the residual magnetic flux density. Can do.

  In the case where the void is used for both the grain boundary diffusion treatment and the reduction of loss due to eddy current, when the slurry is used for the grain boundary diffusion treatment, the conductive component in the slurry blocks the void. The amount of slurry to be injected is adjusted so as not to stutter.

  In all of the embodiments described so far, an embedded member such as an epoxy resin is embedded in the gap in order to prevent a decrease in mechanical strength due to the presence of the gap and corrosion due to accumulation of moisture in the gap. Can do. The epoxy resin is injected into the void 18 in a liquid state and then cured at room temperature or by heating (FIG. 8). This embedding process can be performed before the sintering process depending on the material of the embedding member, but when an adhesive resin such as an epoxy resin is used, it is performed after the sintering process. In the case of performing diffusion processing, an embedding process is performed after the diffusion processing.

  The strip cast alloy of Nd—Fe—B rare earth magnet was subjected to hydrogen crushing and jet mill treatment using nitrogen gas to obtain a rare earth magnet powder having an average particle diameter of 5 μm. The composition of the rare earth magnet powder is Nd: 25,8%, Pr: 4.3%, Dy: 2.5%, Al: 0.23%, Cu: 0.1%, Fe: balance. The average particle size of the rare earth magnet powder was measured with a laser type particle size distribution meter.

After this powder was filled in the mold 10 of the first embodiment so that the apparent density was 3.5 g / cm ³ , the mold 10 was covered with a lid 13. Next, the gap forming member 14 was inserted from the insertion port 131. The mold 10 is fixed in a magnetic field generating coil, and a rare earth magnet powder is oriented in the magnetic field by applying a 5T pulse magnetic field three times in a direction parallel to the gap forming member 14 and perpendicular to the bottom of the mold 10. . Thereafter, the gap forming member 14 was pulled out from the mold 10 and the mold 10 was placed in a sintering furnace. All steps from filling the powder to charging to the sintering furnace were performed in Ar gas. Sintering was performed in vacuum at 1010 ° C. for 2 hours. In this embodiment, the mold 10 and the lid 13 are made of carbon, the gap forming member 14 is made of nonmagnetic stainless steel, and the thickness of the gap forming member 14 is 0.5 mm.

The density of the sintered body produced by the above-described process was 7.56 g / cm ³ , which was as high as that of the NdFeB sintered magnet produced by a normal pressing method. The outer dimensions of the sintered body 31 are a rectangular parallelepiped having a length of 37 mm, a width of 39 mm, and a height of 8.6 mm, and two slits 32 are formed in the vertical direction at 12 mm intervals on the upper surface side (FIG. 9). In the sintered body and the slit 32, almost no distortion was observed. The width of the slit 32 was about 0.4 mm, and the depth was 6.2 mm. Then, it was confirmed by a test in which a 0.3 mm metal foil was passed through the slit 32 to prevent any slit 32 from being clogged or blocked by foreign matter.

Using the same powder as in Example 1, an NdFeB sintered magnet having a slit was produced by the mold 20 and the gap forming member 24 of the second embodiment. In the mold 20 of the second embodiment, the powder is filled in a state in which the gap forming member 24 is mounted on the mold 20. When filling the powder, care must be taken so that the powder is uniformly filled throughout the container 21. The packing density was 3.6 g / cm ³ . After filling the powder, the lid 23 was put on, orientation in the magnetic field under the same conditions as in Example 1, the void forming member 24 was pulled out, and sintering was performed under the same conditions as in Example 1. The sintered body taken out from the mold after sintering is a high-quality slit having high density and no distortion of the shape as in the case of the sintered body produced in Example 1, and the slit is also a good quality slit with no clogging or blocking. confirmed. The dimensions of the sintered body, slit spacing, slit width, etc. were all the same as in Example 1.

  A sintered body having voids (slits, pores) was produced using the mold and void forming member shown in FIGS. 10 and 11. The mold 40 shown in FIG. 10 has a rectangular parallelepiped housing portion 41 whose upper and lower surfaces are square, and a lid 43 can be attached to the upper surface. The lid 43 is provided with two insertion openings 431 so that two plate-like gap forming members 44 can be inserted. In the example shown in FIG. 11, the same mold as the mold 40 is used. The lid 53 attached to the upper surface of the mold 40 is provided with four insertion ports 531 in a square shape so that four rod-shaped gap forming members 54 can be inserted.

  Using the same rare earth magnet powder and method as in Example 1, a sintered body having a slit using the gap forming member 44 (Example 3-1) and a sintered body having pores using the gap forming member 54 (implementing) Examples 3-2) were prepared respectively. The outer shape of each sintered body is a cube having a side of about 11 mm. Among these sintered bodies, those having slits had a slit width of 0.4 mm, a depth of 5.9 mm, and an interval of 3.3 mm. In the sintered body having pores, the pore diameter was 0.5 mm and the depth was 7.2 mm. For comparison, a rectangular parallelepiped sintered body (Comparative Example 1) that has neither slits nor pores under the same conditions as in this example (and Example 1) without inserting and removing the gap forming member 44. ) Was produced. These three types of sintered bodies were processed with a surface grinder so that the cubes were exactly 10 mm on a side. Thereafter, the sample was subjected to various cleanings such as alkali cleaning, acid cleaning, and pure water cleaning, and then dried.

  Next, these samples were subjected to a grain boundary diffusion treatment with an alloy powder containing Dy by the following method. First, a Dy-containing alloy having an atomic ratio of Dy: 80%, Ni: 14%, Al: 4%, other metals / impurities: 2% is pulverized to an average particle size of 9 μm by a jet mill. A contained alloy powder was prepared. This Dy-containing alloy powder was mixed and stirred with ethanol at a mass ratio of 50%, vacuum impregnated into the slit of the sample of Example 3-1 and the pore of the sample of Example 3-2, and then dried. Next, powder containing Dy was applied to the magnet surfaces of Example 3-1, Example 3-2 and Comparative Example by the barrel painting method (see Japanese Patent Application Laid-Open No. 2004-359873). These three types of sintered bodies were put in a vacuum furnace, heated at 900 ° C. for 3 hours, rapidly cooled to room temperature, then heated to 500 ° C. and rapidly cooled to room temperature again. Table 1 shows the magnetic properties of the three types of samples thus prepared. Here, Comparative Example 1-1 is obtained by subjecting the sintered body of Comparative Example 1 to the above grain boundary diffusion treatment, and Comparative Example 1-2 applies Dy-containing alloy powder to the sintered body of Comparative Example 1. Without doing so, only the heat treatment was performed in the same manner as in the grain boundary diffusion treatment.

The samples of Example 3-1 and Example 3-2 have a coercive force H _cJ and a square shape of the magnetization curve as compared with the sample of Comparative Example 1-1 which has no slits or pores and was subjected to grain boundary diffusion treatment. It is clear that the coercive force H _cJ is higher than that of the sample of Comparative Example 1-2, in which the property H _k / H _{cJ is} also high. According to this embodiment, even a large NdFeB sintered body that has not been effective in the grain boundary diffusion treatment so far, such as a 10 mm cube, uses the expensive method of slit formation after sintering according to the method of the present invention. It was shown that the coercive force can be increased by the grain boundary diffusion method by an inexpensive method.

10, 20, 40 ... mold (powder filled container)
11, 21, 41 ... mold housing part 12 ... mold bottom 13, 23, 53 ... mold lids 131, 221, 431, 531 ... insertion ports 14, 24, 34, 44, 54 ... gap forming members 15, 25 35 ... Gap forming member fixtures 17, 27 ... Magnetic field generating coils 18, 28 ... Gap 19, 29 ... Rare earth magnet alloy powder 31 ... Sintered body

Claims (12)

a) a filling step of filling a powder filling container with a rare earth magnet alloy powder together with a gap forming member;
b) an alignment step of aligning the rare earth magnet alloy powder in a magnetic field;
c) a sintering step of sintering the rare earth magnet alloy powder by heating the rare earth magnet alloy powder together with the powder-filled container;
In this order,
d) removing the void forming member after the orientation step and before the rare earth magnet alloy powder starts to be sintered;
A rare earth sintered magnet manufacturing method characterized by manufacturing a rare earth sintered magnet having voids.   The method for producing a rare earth sintered magnet according to claim 1, wherein the removal is performed before the sintering step.   The method for producing a rare earth sintered magnet according to claim 1, wherein the gap forming member is a plate material and / or a bar material.   The method for producing a rare earth sintered magnet according to claim 3, wherein the rare earth magnet alloy powder is oriented in a magnetic field in a direction parallel to the gap forming member in the orientation step.   The method for producing a rare earth sintered magnet according to any one of claims 1 to 4, wherein in the filling step, a powder filling container is filled together with the rare earth magnet alloy powder.   The rare earth sintered magnet manufacturing method according to claim 1, wherein an embedded member is embedded in the gap after the removal. The rare earth magnet alloy is a Nd-Fe-B magnet alloy,
A diffusion step of diffusing Dy and / or Tb into the sintered body is performed by injecting and heating a substance containing Dy and / or Tb into the voids of the sintered body obtained by the sintering step. The method for producing a rare earth sintered magnet according to any one of claims 1 to 5, wherein:   The method for producing a rare earth sintered magnet according to claim 7, wherein an embedded member is embedded in the gap after the diffusion step.   The method for producing a rare earth sintered magnet according to claim 6 or 8, wherein the embedded member is an insulator.   In the filling step, the gap forming member is inserted into the powder filling container from the insertion port provided in the powder filling container or the lid of the powder filling container, and in the removal, the gap is formed from the insertion port. The method for producing a rare earth sintered magnet according to claim 1, wherein the member is extracted. A mold filled with rare earth magnet alloy powder;
A lid attached to the mold;
An insertion port provided in the mold or the lid, into which a gap forming member is inserted;
A powder-filled container for producing a rare earth sintered magnet. A mold filled with rare earth magnet alloy powder;
A lid attached to the mold;
A gap forming member provided in the mold or the lid;
A powder-filled container for producing a rare earth sintered magnet.

Images