JP2015008200A - Method of manufacturing magnet and magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a magnet and the magnet capable of obtaining high remanent magnetic flux density without using dysprosium (Dy) and also without using bond.SOLUTION: An R-Fe-N compound containing a rare earth element as R or magnetic powder of hard magnetic material molded by an Fe-N compound is used. A primary molding is formed by pressurizing magnetic powder a plurality times using a metal mold (pressurization step, S2), and a secondary molding is formed by heating the primary molding at a temperature less than a decomposition temperature of the magnetic powder and then joining surfaces of adjacent magnetic powder to each other (calcination step, S3).

Description

  The present invention relates to a magnet manufacturing method and a magnet.

  Japanese Patent Application Laid-Open No. 2007-39794 (Patent Document 1) describes a magnet containing an Nd—Fe—B alloy or an Sm—Fe—N alloy. Further, Patent Document 1 describes that a soft magnetic metal is mixed with the above alloy, pressure-molded, and sintered.

  Japanese Patent Laid-Open No. 2012-69962 (Patent Document 2) discloses that R—Fe—N—H magnetic material and soft magnetic powder are mixed, compacted, and impact-compressed and solidified using underwater shock waves. In addition, it is described that the residual temperature after impact compression is suppressed to be equal to or lower than the decomposition temperature of the magnetic material. Further, this magnet does not contain a binder such as resin.

  Japanese Patent Application Laid-Open No. 2005-223263 (Patent Document 3) discloses that after an oxide film is formed on a Sm—Fe—N-based compound powder, it is pre-compressed into a predetermined shape in a non-oxidizing atmosphere, and then non-oxidized. It is described that a rare earth permanent magnet is produced by consolidation at a temperature of 350 to 500 ° C. in an atmosphere. Thus, it is said that an Sm—Fe—N-based magnet can be produced at a temperature lower than the decomposition temperature.

  Japanese Patent Laid-Open No. 62-206801 (Patent Document 4) discloses that alloy powder is mixed with stearic acid, powder particles are coated with stearic acid, compression molded, and then sintered. Have been described.

JP 2007-39794 A JP 2012-96962 A JP 2005-223263 A JP 62-206801 A

  In Patent Documents 1 and 4, it is necessary to use expensive and rare dysprosium (Dy) in a magnet including an Nd—Fe—B alloy. When the Sm—Fe—N alloy is used, it is difficult to sinter because the decomposition temperature of the Sm—Fe—N alloy is low. In sintering, the temperature becomes higher than the decomposition temperature, so the alloy is decomposed and the performance as a magnet cannot be exhibited. Therefore, the Sm—Fe—N magnet is generally joined by a bond such as resin. However, the use of a bond such as a resin reduces the density of the magnet and causes the residual magnetic flux density to decrease.

  Moreover, in patent documents 2, 3, since magnetic powder is not sintered, it will be in the state in which the clearance gap remained between powder in the shape | molded magnet. That is, the density of the magnetic powder is lower than that in the case of sintering. As a result, the residual magnetic flux density is lower than in the case of sintering.

  This invention is made | formed in view of such a situation, The manufacturing method and magnet of a magnet which can obtain a high residual magnetic flux density without using a dysprosium (Dy) and without using a bond, and a magnet. The purpose is to provide.

(Manufacturing method of magnet)
(1) A magnet manufacturing method according to the present means uses a magnetic powder of a hard magnetic material formed of an R—Fe—N compound or an Fe—N compound containing a rare earth element as R, and the magnetic powder Pressing a plurality of times with a mold to form a primary molded body, and heating the primary molded body at a temperature lower than the decomposition temperature of the magnetic powder to bond the surfaces of the adjacent magnetic powder to each other. And a firing step for forming a secondary molded body.

  According to the magnet manufacturing method of the present means, since the R—Fe—N compound or the Fe—N compound is used as the magnetic powder of the hard magnetic material, dysprosium (Dy) can be avoided. Therefore, a magnet can be manufactured at low cost. Here, in this means, in the firing step, the secondary molded body is formed by joining the surfaces of adjacent magnetic powders by firing instead of sintering. That is, the secondary molded body is in a state where the gap formed by the primary molded body remains.

  However, the magnetic powder is rearranged with respect to the arrangement state of the magnetic powder at the time of the previous pressurization by pressurizing the magnetic powder a plurality of times in the pressurizing step. Compared with the case where pressurization is performed once, by performing pressurization a plurality of times, the gap between the magnetic particles in the primary compact is reduced. Therefore, the residual magnetic flux density by the secondary molded object after a baking process can be made high by reducing the area | region where a magnetic powder does not exist in a primary molded object.

The suitable aspect of the manufacturing method of the magnet which concerns on this means is demonstrated below.
(Claim 2) Preferably, in the firing step, the primary compact is heated in an oxidizing atmosphere, and the surfaces of the magnetic particles are bonded to each other by an oxide film generated on the surfaces of the magnetic particles. The next molded body is formed. Thus, since the secondary compact is formed by joining the surfaces of the magnetic powder with the oxide film, the bending strength of the magnet can be increased.

  (Claim 3) Preferably, the pressurizing step is performed by pressurizing 2 to 30 times. By setting the number of pressurization times to two times or more, the gap between the magnetic particles can be drastically reduced as compared to one time. Moreover, even if it sets it as the pressurization frequency more than 30 times, the clearance gap between magnetic powders hardly changes. Therefore, by setting the number of pressurizations to 2 to 30 times, it is possible to reliably obtain a high residual magnetic flux density and not to increase the number of manufacturing steps.

(magnet)
(Claim 4) The magnet according to the present means is manufactured by the magnet manufacturing method described above. Thereby, there exists an effect similar to the effect by the said manufacturing method.

It is a flowchart which shows the manufacturing method of the magnet in embodiment of this invention. It is a figure which shows the initial state of the mixing process of FIG. It is a figure which shows the completion | finish state of the mixing process of FIG. It is a figure which shows the initial state of the pressurization process of FIG. It is a figure which shows the intermediate state of the pressurization process of FIG. It is a figure which shows the state just before completion | finish of the pressurization process of FIG. FIG. 2 is a schematic cross-sectional view of the structure of the primary molded body at the end of the pressurizing step in FIG. 1. It is a structure cross-sectional schematic diagram of the secondary molded object at the time of completion | finish of the baking process of FIG. It is a structure cross-sectional schematic diagram of the tertiary molded body at the end of the coating step of FIG. It is a heat treatment process figure of the baking process shown in FIG. It is a figure which shows the relationship between the frequency | count of pressurization in a pressurization process, and the density ratio of a primary molded object. It is a figure which shows the density ratio of the primary molded object at the time of changing the presence or absence of the heating in the pressurization process and the pressurization process.

  A magnet manufacturing method according to an embodiment of the present invention will be described with reference to FIGS. A hard magnetic powder 10 as a magnet material and a powdery lubricant 60 at normal temperature are prepared. Here, in this embodiment, the bond etc. which were used conventionally are not used.

  1 and 2A, the prepared magnetic powder 10 and the lubricant 60 are put in a mixing container 1 such as a mortar and mixed to prepare mixed powders 10 and 60 (step of FIG. 1). S1).

Here, for the magnetic powder 10, an R—Fe—N compound containing a rare earth element as R or an Fe—N compound is used. As the rare earth element R, a rare earth element other than dysprosium, particularly a light rare earth element is preferable, and among these, Sm is preferable. Here, the light rare earth element is an element having a smaller atomic weight than Gd among lanthanoids, that is, La, Ce, Pr, Nd, Pm, Sm, and Eu. For the magnetic powder 10, Sm ₂ Fe ₁₇ N ₃ or Fe ₁₆ N ₂ is preferably used. The average particle diameter of the magnetic powder 10 is about 2 to 5 μm. By using a hard magnetic material that does not require dysprosium, a magnet can be manufactured at low cost. Further, the magnetic powder 10 is used in which no oxide film is formed on the entire surface.

  For the lubricant 60, metal soap powder is used. As the lubricant 60, for example, a powder of stearic acid metal such as zinc stearate is used. The average particle size of the lubricant 60 is about 10 μm. That is, the average particle size of the lubricant 60 is larger than the average particle size of the magnetic powder 10. Here, the specific gravity of the lubricant 60 is smaller than the specific gravity of the magnetic powder 10. Therefore, by increasing the size of the initial state of the lubricant 60 to some extent, the mass per one particle of the lubricant 60 can be increased, and the lubricant 60 can be prevented from scattering during mixing.

  Here, the volume ratio of the magnetic powder 10 and the lubricant 60 is 80 to 90% by volume of the magnetic powder 10 and 5 to 15% by volume of the lubricant 60. The rest is additive. In the mixing container 1, the magnetic powder 10 and the lubricant 60 are mixed while being ground. By mixing while grinding, as shown in FIG. 2B, the lubricant 60 having a low bond strength is subdivided, and the particle size of the lubricant 60 is reduced as a whole. Therefore, lubricants 60 having different sizes exist at the end of the mixing step.

  Furthermore, at the end of the mixing step, the mixed powder can reduce the lump portion due to the magnetic powder 10 alone, and the size of the lubricant 60 can be reduced. That is, the finely divided lubricant 60 can be present at a position close to each magnetic powder 10.

  Subsequently, as shown in step S2 of FIG. 1, the mixed powder is pressurized to form a primary molded body 100 (shown in FIGS. 3C and 4) (pressurizing step). The detail of this pressurization process is demonstrated with reference to FIG. 3A-FIG. 3C.

  First, as shown in FIG. 3A, a mixed powder of magnetic powder 10 and powdered lubricant 60 is placed in the mold 2. Subsequently, as shown in FIG. 3B, the mixed powders 10 and 60 are pressed by the molds 2 and 3 by moving the mold 3 (upper mold). At this time, the applied pressure by the molds 2 and 3 is 1 to 2 GPa.

  And pressurization by the molds 2 and 3 is performed 2 to 30 times. That is, after applying the pressing force to the mold 3, the pressing force applied to the mold 3 is loosened, and the pressing force is applied to the mold 3 again. Then, this operation is repeated. When loosening the pressure applied to the mold 3, the mold 3 may be moved upward, or only the pressure may be reduced without moving the mold 3 upward. .

  Further, in the pressurizing step, the mixed powders 10, 60 in the molds 2, 3 are heated by heating the molds 2, 3 from, for example, an outer surface with a heater (not shown). At this time, the heating temperature (first temperature) of the mixed powders 10 and 60 is lower than the decomposition temperature Te <b> 2 of the magnetic powder 10 and is equal to or higher than the melting point of the lubricant 60. Therefore, the magnetic powder 10 is not decomposed. Further, the lubricant 60 that is solid (powder) at room temperature becomes a liquid because it is heated above the melting point during the pressurizing step.

  Thus, while the magnetic powder 10 in the mixed powder is being pressurized, the lubricant 60 is not solid but liquid, and has a viscosity according to temperature. Of course, the higher the heating temperature (first temperature), the lower the viscosity of the lubricant 60. And the lubricant 60 which became liquid will be in the state which adheres uniformly to the surface of the magnetic powder 10, without segregating. In FIG. 3B, the shape of the lubricant 60 is not shown.

  And if pressurization is repeated, as shown to FIG. 3C, the primary molded object 100 in which the clearance gap between the magnetic powder 10 became small gradually will be formed. This is because the magnetic powder 10 is rearranged with respect to the arrangement state of the magnetic powder 10 at the time of the previous pressurization by pressurizing a plurality of times. And in the metal mold | die 2, 3, when the liquid lubricant 60 interposes between the adjacent magnetic powders 10, the magnetic powders 10 can move very smoothly. Due to the synergistic action of the rearrangement of the magnetic powder 10 and the slippage by the lubricant 60, the gap between the magnetic powder 10 in the primary molded body 100 is reduced.

  Subsequently, as shown in step S3 of FIG. 1, the primary molded body 100 formed in the pressurizing process is heated in an oxidizing atmosphere to form the secondary molded body 200 (firing process). Here, the primary molded object 100 before baking is shown in FIG. As shown in FIG. 4, a gap 20 exists between the magnetic powders 10. A schematic diagram of a cross section of the structure of the secondary molded body 200 after heating is as shown in FIG.

  By heating the primary molded body 100 in an oxidizing atmosphere, the exposed surface of the magnetic powder 10 chemically reacts with oxygen, and an oxide film 30 (shown by a thick line in FIG. 5) is generated on the surface of the magnetic powder 10. . The surfaces of the magnetic powder 10 adjacent to the oxide film 30 are joined together. That is, the oxide film 30 is formed in the part exposed in the gap 20 in the magnetic powder 10, and the part not exposed in the gap 20 in the magnetic powder 10 becomes the base material itself. Therefore, the oxide film 30 is not formed on the entire surface of the magnetic powder 10.

The secondary molded body 200 formed in this manner can sufficiently ensure strength. Thereby, the bending strength of the secondary molded object 200 can be made high. Furthermore, the residual magnetic flux density by the secondary molded object 200 after a baking process can be made high by reducing the area | region where the magnetic powder 10 does not exist in the primary molded object 100 in a pressurization process. In addition, the density of the secondary molded object 200 is about 5-6 g / cm < ³ >.

  Here, the firing step is performed by placing the primary molded body 100 in a microwave heating furnace, an electric furnace, a plasma heating furnace, an induction hardening furnace, a heating furnace using an infrared heater, or the like. The heat treatment process in this baking process is as shown in FIG.

As shown in FIG. 7, the heating temperature Te1 (second temperature) is set to be lower than the decomposition temperature Te2 of the compound of the magnetic powder 10. For example, when Sm ₂ Fe ₁₇ N ₃ or Fe ₁₆ N ₂ is used as the magnetic powder 10, the heating temperature Te 1 is set to less than 500 ° C. because the decomposition temperature Te 2 is about 500 ° C. For example, the heating temperature Te1 in the firing step is about 200 to 300 ° C.

Further, the oxygen concentration and the atmospheric pressure in the oxidizing atmosphere are sufficient if the magnetic powder 10 can be oxidized, and it is sufficient if the oxygen concentration is about the atmospheric pressure and the atmospheric pressure. Therefore, it is not necessary to specifically manage the oxygen concentration or the atmospheric pressure. Therefore, it is good to heat in an air atmosphere. Then, by setting the heating temperature Te1 (second temperature) to about 200 to 300 ° C., the oxide film 30 can be formed in either case of the magnetic powder 10 of Sm ₂ Fe ₁₇ N ₃ or Fe ₁₆ N _2. it can.

  Subsequently, as shown in step S4 of FIG. 1 and FIG. 6, a process of surrounding the surface of the secondary molded body 200 formed by the firing process with the coating film 40 is performed to form the tertiary molded body 300 (coating process). ).

  The coating film 40 of the tertiary molded body 300 includes a plating film formed by electroplating such as Cr, Zn, Ni, Ag, and Cu, a plating film formed by electroless plating, a resin film formed by resin coating, and glass. A glass film formed by coating, a film made of Ti, diamond-like carbon (DLC), or the like. Examples of electroless plating include electroless plating using Ni, Au, Ag, Cu, Sn, Co, alloys or mixtures thereof. Examples of the resin coating include coating with silicone resin, fluorine resin, urethane resin, and the like.

  That is, the coating film 40 formed on the tertiary molded body 300 functions like an egg shell. Therefore, the tertiary molded body 300 can increase the bending strength when the oxide film 30 and the coating film 40 exhibit a bonding force. In particular, by applying electroless plating, the surface hardness and adhesion can be increased, and the bonding force of the magnetic powder 10 can be further strengthened. In addition, for example, electroless nickel phosphorus plating has good corrosion resistance.

  Furthermore, as described above, the oxide film 30 joins the magnetic powders 10 not only on the surface of the secondary molded body 200 but also inside. Therefore, in the tertiary molded body 300, the internal magnetic powder 10 is restricted from operating freely by the bonding force of the oxide film 30. Therefore, it can suppress that a magnetic pole reverse | inverts by the magnetic powder 10 rotating. That is, a high residual magnetic flux density can be obtained.

  Here, when applying electroplating in a coating process, since the secondary molded object 200 before plating acts as an electrode, it is necessary to increase the bonding strength of the secondary molded object 200. However, in the coating process, when electroless plating, resin coating, or glass coating is applied, it is not necessary to increase the bonding strength of the secondary molded body 200 compared to electroplating. That is, the bonding force by the oxide film 30 is sufficient. Therefore, the coating film 40 can be reliably formed on the surface of the secondary molded body 200 by the coating process as described above.

  Moreover, when performing electroless plating in a coating process, the secondary molded object 200 is impregnated with a plating solution. At this time, although the plating solution tends to enter the secondary molded body 200, the oxide film 30 is formed, and thus the oxide film 30 exhibits an effect of suppressing the ingress of the plating solution. That is, it can be expected to suppress the occurrence of corrosion or the like due to the plating solution entering the inside.

  Here, as described above, in the pressurizing step, the mixed powders 10 and 60 are pressed a plurality of times by the molds 2 and 3. The relationship between the number of pressurizations and the density ratio of the primary molded body 100 when the number of pressurizations is changed will be described with reference to FIG. However, in order to clarify the relationship between the number of pressurizations and the density, here, heating at the first temperature is not performed in the pressurization step.

  In FIG. 8, when the density ratio of the primary molded body 100 in the case where the number of pressurizations is 1 is 1, the density ratio when the pressurization times are 2, 20, and 100 is plotted. Is a curve approximated by a quadratic equation.

  Thus, it turns out that the clearance gap 20 between the magnetic powder 10 becomes remarkably small by making the frequency | count of pressurization into 2 compared with 1 time. Even if the number of pressurizations is greater than 30, the gap 20 between the magnetic powders 10 hardly changes. Therefore, by setting the number of pressurizations to 2 to 30 times, it is possible to reliably obtain a high residual magnetic flux density and not to increase the number of manufacturing steps. Here, the evaluation was performed on the primary molded body 100 on which the coating film 40 was formed. However, it is obvious that the secondary molded body 200 and the tertiary molded body 300 also have the same relationship as described above.

  Next, for each of the cases where the number of times of pressurization in the pressurization step is 1 and 30 times, the density of the primary molded body 100 is examined when heating at the first temperature in the pressurization step is not performed It was.

  For the cases 1 to 4, the density ratio of the primary molded body 100 was as shown in FIG. Here, the density ratio was set to 1 when the number of pressurizations was 1 and heating was not performed in the pressurization process. In Case 2, the density of the primary molded body 100 was increased by heating in the pressurizing step even if the number of pressurizations was one.

  Further, from the relationship between cases 1 and 3 and cases 2 and 4, the increase in the density ratio of primary molded body 100 was about the same when the number of pressurizations was changed from 1 to 30. That is, as shown in the case 4, each pressurization is performed 30 times and heating is performed in the pressurization step, whereby each effect is exerted, and as a result, the density of the primary molded body 100 can be increased. .

<Others>
In the above embodiment, the mixed powder was heated in the pressing step by heating the molds 2 and 3. In addition, the mixed powders 10 and 60 may be heated to the first temperature immediately before the mixed powders 10 and 60 are put into the mold 2.

  In the above embodiment, the lubricant 60 is solid (powder) at room temperature. In addition, a lubricant 60 that is liquid at room temperature can be used. Also in this case, the liquid lubricant 60 and the magnetic powder 10 may be mixed in the mixing step. Furthermore, the viscosity of the lubricant 60 is reduced by heating in the pressurizing step. Therefore, the lubricant 60 spreads evenly over the surface of the magnetic powder 10. As a result, since the magnetic powders 10 can move smoothly, the density of the primary molded body 100 increases.

100: primary molded body, 200: secondary molded body, 300: tertiary molded body, 2, 3: mold, 10: magnetic powder, 20: gap, 30: oxide film, 40: coating film, 60: lubricant

Claims (4)

A primary molded body is formed by pressurizing the magnetic powder multiple times with a mold using magnetic powder of a hard magnetic material molded from an R—Fe—N compound or an Fe—N compound containing a rare earth element as R. Pressurizing step,
A firing step of forming the secondary molded body by heating the primary molded body at a temperature lower than the decomposition temperature of the magnetic powder and joining the surfaces of the adjacent magnetic powders,
A method for manufacturing a magnet.   The said baking process forms the said secondary molded object by heating the said primary molded object in oxidizing atmosphere, and joining the surfaces of the said magnetic powder with the oxide film produced | generated on the surface of the said magnetic powder, The manufacturing method of the magnet of claim | item 1.   The said pressurization process is a manufacturing method of the magnet of Claim 1 or 2 which pressurizes 2 to 30 times. The magnet manufactured by the manufacturing method of the magnet as described in any one of Claims 1-3.

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