JP4706872B2 - Method for producing sintered permanent magnet and mold - Google Patents

Description

  The present invention relates to a high-performance ring-shaped sintered R-Fe-B permanent magnet (R is at least one rare earth element selected from rare earth elements including Y), and a mold used therefor.

  R-Fe-B permanent magnets have long been produced by a so-called dry molding method in which a dry fine powder is molded in a mold while applying a magnetic field. In the dry molding method, usually when a raw material coarse powder is finely pulverized with a jet mill, a small amount of oxygen is introduced into the jet mill, and the oxygen concentration in the nitrogen gas or Ar gas as a pulverization medium is controlled within a desired range. . This is to forcibly oxidize the fine powder surface. Fine powder finely pulverized without this oxidation treatment ignites at the same time as it comes into contact with the atmosphere. The oxygen content of the oxidized fine powder is 5000 to 6000 ppm, and the oxygen content of the sintered body obtained from this is 4000 to 5000 ppm. Most of the oxygen in the sintered body is combined with rare earth elements such as Nd and exists as oxides at the grain boundaries. In order to replenish the oxidized rare earth element, it is necessary to increase the total amount of the rare earth element in the sintered body, but there is a problem that the saturation magnetic flux density of the sintered magnet is lowered.

  In order to solve the problems of the dry molding method, a mixture of rare earth magnet powder and mineral oil or synthetic oil is injected under pressure into a mold cavity to which an orientation magnetic field is applied, and then wet molding in a magnetic field in a low oxygen atmosphere. Thus, a method of manufacturing a sintered rare earth magnet by forming a ring-shaped molded body, removing the solvent from the molded body, and then performing vacuum sintering has been proposed (Patent Document 1). This production method can stably produce a high-performance sintered R-Fe-B permanent magnet with a small total amount of rare earth elements and low oxygen content. However, because the slurry is pressurized and injected into the mold cavity to which the orientation magnetic field is applied, the R-Fe-B fine powder with a large spontaneous magnetization receives a large restraint force due to the interaction with the orientation magnetic field, and enters the mold cavity. There is a problem that the packing density becomes non-uniform, and as a result, the density of the molded body becomes non-uniform, and the sintered body is deformed and cracks are generated. In addition, in order to pressurize the slurry from the injection hole that opens into the mold cavity toward the center of the core, the slurry that collides with the core and splits in two directions merges on the opposite side of the injection hole by 180 °. There is also a problem that cracks occur in the sintered body from the junction.

  In addition, the slurry of R-Fe-B permanent magnet magnetic powder and mineral oil, synthetic oil or vegetable oil is discharged from a slurry supply pipe inserted into a mold cavity to which a magnetic field is applied, and the slurry supply pipe is gradually The slurry filled in the cavity is pressure-molded while being drawn, and the solvent is removed from the obtained ring-shaped molded body, followed by sintering to produce a sintered R-Fe-B permanent magnet A method has been proposed (Patent Document 2). In this method, since the slurry is discharged into the cavity from the slurry supply tube inserted deeply into the mold cavity, even when a relatively long ring-shaped molded body is molded, the filling property of the slurry into the mold cavity is good. Since the slurry supply pipe is inserted deeply into the mold cavity and the slurry supply pipe is pulled out while discharging the slurry, there is a drawback that the slurry supply time is long. Further, the portion where the slurry supply pipe was present remains as a cavity in the molded body, which becomes a singular point and causes cracks in the sintered R-Fe-B permanent magnet.

In addition, as a method for producing a radial anisotropic ring-shaped R-Fe-B permanent magnet, a powder obtained by grinding a rapidly cooled ribbon of R-Fe-B magnet alloy was molded at room temperature, and obtained The molded body is hot pressed in an inert gas atmosphere to be densified, and the resulting hot pressed body is hot plastic processed into a cup body with magnetic anisotropy in the radial direction, and the bottom is cut off. A ring-shaped method has also been proposed (Patent Documents 3 and 4). However, hot plastic working of hot pressed bodies in an inert gas atmosphere is performed at a relatively low temperature of about 700 to 800 ° C. so as not to coarsen the crystal grains, so it is extremely slow to prevent cracks from occurring. It is necessary to do in. Although it differs depending on the size of the magnet, the time required for one hot plastic working is usually 10 to 30 minutes, and the productivity is low as an industrial production method for permanent magnets. Moreover, since the pressure-processed body manufactured in this way tends to crack at the end portion, it is necessary to excise the crack generation portion. For these reasons, this manufacturing method has a high manufacturing cost. Further, the variation in magnetic properties of the obtained ring-shaped magnet is large. Although the degree of radial anisotropy depends on the amount of deformation during hot plastic working, there is a problem in that the variation in surface magnetic flux density is particularly large in small diameter products and long products having high hot plastic working resistance.
JP 7-057914 A (page 3) JP 11-214216 A (pages 3 to 5) JP-A-9-275004 (pages 3 to 5) JP 2001-181802 (pages 2 to 3)

  Accordingly, an object of the present invention is to provide a method for producing a ring-shaped sintered R-Fe-B permanent magnet having a ring shape, in particular, a radial anisotropy that has no magnetic deformation and cracks and excellent magnetic orientation. It is. Another object of the present invention is to provide a mold suitable for manufacturing the ring-shaped sintered R-Fe-B permanent magnet.

  The sintered permanent magnet according to the present invention has 27 to 33.5% R (R is at least one rare earth element selected from rare earth elements including Y) and 0.5 to 2% on a mass% basis. B, 0.002 to 0.15% N, 0.25% or less O, 0.15% or less C, 0.001 to 0.05% P, and the balance Fe, with a coercive force iHc of 1 MA / It is preferable that it is m or more. The term “sintered permanent magnet” used here includes both sintered bodies of permanent magnet material before and after magnetization. The coercive force is measured at room temperature (25 ° C.). P is preferably 0.003 to 0.05% by mass, and more preferably 0.008 to 0.05% by mass.

The sintered permanent magnet according to the present invention is a ring shape having an outer diameter of 10 to 100 mm, an inner diameter of 8 to 96 mm, and a height of 10 to 70 mm, and a plurality of magnetic poles in the axial direction of the outer peripheral surface. Preferably it extends. The sintered permanent magnet according to the present invention has an outer diameter of 10 to 30 mm, an inner diameter of 8 to 28 mm, a height of 10 to 50 mm, particularly an outer diameter of 10 to 25 mm, an inner diameter of 8 to 23 mm, and a height of 10 to 40. It can also be a small ring magnet of mm. The sintered permanent magnet according to the present invention is preferably a radial anisotropic sintered R-Fe-B permanent magnet. The density of the sintered permanent magnet according to the present invention is preferably 7.52 to 7.85 g / cm ³ .

The distribution of the surface magnetic flux density B ₀ along the magnetic pole on the axis of the ring magnet is preferably in the range of 92.5% or more of the maximum value of B ₀ . That is, the variation of the surface magnetic flux density B ₀ on the magnetic pole in the axial direction of the ring magnet is preferably 7.5% or less of the maximum value of B ₀ . Wherein the variation of the surface magnetic flux density B ₀ is represented by the maximum value of / B ₀ (minimum value of the maximum value -B ₀ of _{B 0)) × 100 (%} ). The maximum value and the minimum value of B ₀ are measured within the range of the height H of the ring magnet. The distribution of the surface magnetic flux density B ₀ is measured by making a gauss meter probe vertically face the outer peripheral surface of the ring magnet and moving it along the axial direction (length direction) of the ring magnet. The variation in the surface magnetic flux density B ₀ is more preferably 5% or less, and particularly preferably 3% or less.

In one embodiment according to the invention, R is 27-32% by weight. In another embodiment of the present invention, R is more than 32% by mass and not more than 33.5% by mass. In the latter case, the sintered permanent magnet according to the present invention has R of more than 32% and not more than 33.5%, 0.5 to 2% B, more than 0.25% and not more than 0.6% O, 0.01% It has a composition consisting of ~ 0.15% C, 0.002 to 0.05% N, 0.001 to 0.05% P, and the balance Fe, and has an outer diameter of 10 to 100 mm, an inner diameter of 8 to 96 mm, and 10 It is a ring shape with a height of ˜70 mm, has magnetic anisotropy in the circumferential direction of the ring, and the distribution of the surface magnetic flux density B ₀ on the magnetic pole in the axial direction of the ring is the maximum value of B ₀ It is preferable that it is in the range of 92.5% or more. Even in this case, the variation in the surface magnetic flux density B ₀ is preferably within 7.5%, more preferably 5% or less, and particularly preferably within 3%. The density of the sintered permanent magnet is preferably 7.42-7.75 g / cm ³ .

  In the sintered permanent magnet according to the present invention, part of Fe is 0 to 1% Nb, 0.01 to 1% Al, 0 to 5% Co, and 0.01 to 0.5% by mass%. It may be substituted with at least one selected from the group consisting of Ga and 0 to 1% Cu. Nb is preferably 0.05 to 1% by mass. Al is preferably 0.01 to 0.3% by mass. Co is preferably 0.3 to 5% by mass, and more preferably 0.3 to 4.5% by mass. Ga is preferably 0.03 to 0.4 mass%. Cu is preferably 0.01 to 1% by mass, and more preferably 0.01 to 0.3% by mass.

  The method of the present invention for producing a sintered permanent magnet is a coarse powder for sintered R-Fe-B permanent magnets (R is at least one rare earth element selected from rare earth elements including Y). ) To obtain a fine powder, directly recovered in mineral oil, synthetic oil or a mixed oil thereof to form a slurry. The slurry was injected into a cavity of a mold and wet-molded in a magnetic field. The molded body is heated under reduced pressure to remove the mineral oil, the synthetic oil or a mixed oil thereof from the molded body, and the molded body is sintered in a vacuum. The mold is a die having a hollow structure. And a core disposed on the inner peripheral side of the die member via a ring-shaped cavity, and the die member has a slurry injection hole for pressure-injecting the slurry into the cavity of the mold. The axial direction of the injection hole is the center of the core of the mold. Off, characterized in that is.

In the method of the present invention for producing a sintered permanent magnet, it is preferable that a radial orientation magnetic field is applied to the cavity.
In the method of the present invention for producing a sintered permanent magnet, a central axis of the slurry injection hole, a straight line AO connecting the core central point O and the point A where the central axis intersects the inner peripheral surface of the die member Is preferably 5 to 90 °.

  The mold of the present invention for producing a sintered permanent magnet is a coarse powder for sintered R-Fe-B permanent magnets (R is at least one rare earth element selected from rare earth elements including Y). For molding a slurry comprising a mixture of fine powder obtained by pulverizing and a mineral oil, a synthetic oil or a mixed oil thereof in a magnetic field. A core disposed on the inner peripheral side of the die member via a ring-shaped cavity, and the die member is provided with an injection hole for pressure-injecting the slurry into the cavity of the mold. The axial direction of the injection hole is deviated from the center of the core of the mold.

In the mold of the present invention, it is preferable that a radial orientation magnetic field is applied to the cavity.
In the mold of the present invention, the angle θ formed by the central axis of the slurry injection hole and the straight line AO connecting the core central point O and the point A where the central axis intersects the inner peripheral surface of the die member is 5 It is desirable to be ~ 90 °.

  In the method for producing a sintered permanent magnet of the present invention, the oxygen content of the fine powder is preferably more than 0.25% by mass and not more than 0.6% by mass.

  By the method of the present invention, it is possible to produce a ring-shaped sintered R-Fe-B permanent magnet having a radial anisotropy, particularly a ring-shaped that has no deformation or cracking and excellent magnetic orientation. . The sintered permanent magnet according to the present invention is particularly suitable as a ring magnet used for a motor or the like. In addition, a mold suitable for manufacturing the ring-shaped sintered R-Fe-B permanent magnet can be provided.

[1] Composition The composition of the sintered permanent magnet according to the present invention is 27 to 33.5% R based on mass% (R is at least one rare earth element selected from rare earth elements including Y). And 0.5 to 2% B, 0.002 to 0.15% N, 0.25% or less O, 0.15% or less C, 0.001 to 0.05% P, and the balance Fe. The content of each element can be measured by fluorescent X-ray analysis or the like.

(A) Major elements
(1) Rare earth element R
The rare earth element R content is preferably 27 to 33.5% by mass. When the content of R exceeds 33.5% by mass, the saturation magnetic flux density is lowered and the corrosion resistance is deteriorated. On the other hand, when the R content is less than 27% by mass, the liquid phase amount necessary for densification of the sintered body is insufficient, the density of the sintered body is low, and the coercive force iHc is also low. In the preferred first composition according to the present invention, R is 27 to 32% by mass, and in the preferred second composition, R is more than 32% by mass and not more than 33.5% by mass.

  When the content of O is more than 0.25% by mass and 0.6% by mass or less, the amount of R is preferably more than 32% and 33.5% or less on a mass% basis. When the amount of R exceeds 33.5% by mass, the amount of the rare earth-rich phase inside the sintered body increases, and the form becomes coarse and the corrosion resistance deteriorates. On the other hand, if the amount of R is 32% by mass or less, the liquid phase amount necessary for densification of the sintered body is insufficient and the density of the sintered body is lowered, and the residual magnetic flux density Br and the coercive force among the magnetic properties are reduced. Both iHc are low. In the case of a sintered permanent magnet that requires high corrosion resistance, it is desirable to suppress R to 32% by mass or less.

(2) Boron B
The content of B is preferably 0.5 to 2% by mass. When the B content is less than 0.5% by mass, the B required for forming the main phase R ₂ Fe ₁₄ B phase is insufficient, the soft magnetic R ₂ Fe ₁₇ phase is generated, and the coercive force iHc decreases. To do. On the other hand, if the content of B exceeds 2% by mass, the non-magnetic phase rich in B increases, and the residual magnetic flux density Br decreases.

(3) Nitrogen N
The N content is preferably 0.002 to 0.15% by mass. N in the sintered body is mainly present in the R-rich phase and combines with a part of the rare earth element to form a nitride. Since the formation of nitride suppresses anodic oxidation of the grain boundary phase, it is considered that the corrosion resistance of the sintered body is improved. However, when the N content exceeds 0.15 mass%, the rare earth elements necessary for the expression of the coercive force iHc decrease due to the formation of nitrides, and the coercive force iHc decreases. If the N content is less than 0.002% by mass, the sintered body has low corrosion resistance. In addition, since nitriding does not occur in the fine pulverization in an Ar gas atmosphere, the content of N in the sintered body is 0.002 to 0.05% by mass.

  In the process of coarsening the dissolved ingot, a small amount of nitride is generated by nitrogen in the atmosphere. When this coarse powder is finely pulverized by a jet mill in nitrogen gas or nitrogen-containing Ar gas substantially free of oxygen, further nitriding occurs. Here, “substantially free of oxygen” means that the oxygen content is 0.001% or less, more preferably 0.0005% or less, and still more preferably 0.0002% or less. Therefore, the coarse powder supply amount per unit time to the jet mill during fine pulverization and the ratio of Ar gas and nitrogen gas are adjusted so that the N content of the obtained sintered body does not exceed 0.15 mass%. .

(4) Oxygen O
In the preferred first composition according to the present invention, the O content is 0.25% by mass or less, and in the preferred second composition according to the present invention, the O content is more than 0.25% by mass and 0.6% by mass or less. When the O content exceeds 0.6 mass%, a part of the rare earth element forms an oxide, so that the amount of the magnetically effective rare earth element becomes too small, and the coercive force iHc decreases. Since R is 27 to 32% by mass in the first composition, the upper limit of the O content is 0.25% by mass. On the other hand, in the second composition, since R is more than 32% by mass and 33.5% by mass or less, the upper limit of the O content can be 0.6% by mass. On the other hand, in the first composition, the lower limit of the O content is not limited, but is preferably 0.05% by mass. In particular, in the first composition, high corrosion resistance can be obtained by suppressing the oxygen content and controlling the nitrogen content.

(5) Carbon C
The C content is preferably 0.15% by mass or less. When the C content is more than 0.15% by mass, a part of the rare earth element forms a carbide, the magnetically effective rare earth element is reduced, and the coercive force iHc is lowered. The content of C is preferably 0.12% by mass or less, and more preferably 0.1% by mass or less. On the other hand, the lower limit of the C content is not limited, but is preferably 0.01% by mass.

(6) Phosphorus P
It was found that the addition of a small amount of P is effective for improving the coercive force iHc of R-Fe-B permanent magnets. Figure 1 shows 15.7% Nd, 7.1% Pr, 7.5% Dy, 1.1% B, 2.0% Co, 0.09% Cu, 0.08% Ga, x% P, balance Fe on a mass% basis. The change of coercive force iHc with respect to the content x of P in a sintered body having a composition consisting of: The improvement of the coercive force iHc is recognized when the P content is 0.0005 mass%, but is remarkable when the P content is 0.001 mass% or more. If it is 0.001% by mass or more, the coercive force iHc increases as the P content increases. However, when the P content exceeds 0.05 mass%, the strength of the sintered body decreases. Therefore, the content of P in the sintered body is set to 0.001 to 0.05 mass%. In this range, no decrease in saturation magnetization is observed.

  The reason for the improvement of the coercivity iHc by P is not necessarily clear, but P exists at the pinning site that fixes the domain wall existing at the interface between the grain boundary phase and the main phase crystal grain of the sintered body. It is presumed that the composition or form is changed to strengthen the adhesion of the domain wall. The lower limit of the P content is preferably 0.003% by mass, more preferably 0.008% by mass. The upper limit of the P content is preferably 0.04% by mass, and more preferably 0.02% by mass.

Although the control method of the P content is not limited, (1) As a raw metal of an ingot for an R-Fe-B permanent magnet, an Fe-P alloy or Fe-BP with a known P content in an Fe raw alloy A method of controlling the P content in an ingot by blending a predetermined amount of a P-containing Fe-based alloy such as an alloy, and (2) coarsely pulverizing an R-Fe-B permanent magnet ingot produced by vacuum melting. A predetermined amount of sodium hypophosphite (NaPH ₂ O ₂ ) is mixed with the obtained coarse powder of 20 to 500 μm in the form of an aqueous solution and dried to obtain a coarse for R-Fe-B permanent magnets. A method of controlling the content of P in the powder, and (3) a solution of the above-described mineral oil, synthetic oil or mixed oil for producing the slurry with sodium hypophosphite as a fluidity improver in a glycerin or ethanol solution There is a method in which the proportion of sodium hypophosphite is 0.01% by mass or more and wet molding is performed. The method (3) is most preferable when a molded body is efficiently obtained using a wet molding method while preventing oxidation of fine powder.

  In the method (3), the addition of a sodium hypophosphite solution that results in a P content of less than 0.001% by mass is insufficient in improving the fluidity of the slurry. The amount of sodium hypophosphite glycerin solution or sodium hypophosphite ethanol solution should be adjusted so that the ratio of sodium hypophosphite to mineral oil, synthetic oil or mixed oil does not exceed 0.5% by mass. It is preferable to control.

(B) Arbitrary Element In the sintered permanent magnet according to the present invention, a part of Fe may be substituted with at least one selected from the group consisting of Co, Nb, Al, Ga and Cu. The amount of each substitution element is expressed as a mass percentage with respect to the entire sintered permanent magnet.

(1) Cobalt Co
The amount of Co is preferably 5% by mass or less. Co improves the Curie point of the sintered magnet, that is, improves the temperature coefficient of saturation magnetization. However, when the amount of Co exceeds 5% by mass, both the residual magnetic flux density Br and the coercive force iHc rapidly decrease. The preferable substitution amount of Co is 0.3 to 5% by mass, particularly 0.3 to 4.5% by mass. When the amount of Co is less than 0.3% by mass, the effect of improving the temperature coefficient is small.

(2) Niobium Nb
The amount of Nb is preferably 0 to 1% by mass. Nb boride produced during the sintering process suppresses abnormal grain growth. However, if the amount of Nb exceeds 1% by mass, the amount of Nb boride produced increases, and the residual magnetic flux density Br decreases. On the other hand, if the amount of Nb is less than 0.05% by mass, the effect of suppressing the abnormal growth of crystal grains is insufficient, so that the preferable substitution amount of Nb is 0.05 to 1% by mass.

(3) Aluminum Al
The amount of Al is preferably 0.01 to 1% by mass. Al has the effect of increasing the coercive force iHc. When the amount of Al is less than 0.01% by mass, the effect of improving the coercive force iHc is insufficient. When the amount of Al exceeds 1% by mass, the residual magnetic flux density Br is rapidly reduced. The upper limit of Al is preferably 0.3% by mass.

(4) Gallium Ga
The amount of Ga is preferably 0.01 to 0.5% by mass. A small amount of Ga improves the coercive force iHc, but the effect is insufficient when the amount of Ga is less than 0.01% by mass. On the other hand, when the amount of Ga exceeds 0.5% by mass, the residual magnetic flux density Br is significantly decreased and the coercive force iHc is also decreased. The amount of Ga is preferably 0.03 to 0.4 mass%.

(5) Copper Cu
The amount of Cu is preferably 0 to 1% by mass. A small amount of Cu improves the coercive force iHc, but when the amount of Cu exceeds 1% by mass, the addition effect is saturated. Further, if the amount of Cu added is less than 0.01% by mass, the effect of improving the coercive force iHc is insufficient, so the amount of Cu is preferably 0.01-1% by mass, more preferably 0.01-0.3% by mass. preferable.

  The sintered permanent magnet according to the first embodiment of the present invention comprises 27 to 32% R, 0.5 to 2% B, 0.002 to 0.15% N, and 0.05 to 0.25% on a mass% basis. It has a composition consisting of O, 0.01 to 0.15% C, 0.001 to 0.05% P, and the balance Fe.

  Further, the sintered permanent magnet according to the second embodiment of the present invention has R of more than 32% and not more than 33.5%, 0.5 to 2% B, 0.002 to 0.05% N, and 0.25 on a mass% basis. % And 0.6% or less of O, 0.01 to 0.15% of C, 0.001 to 0.05% of P, and the balance Fe. The sintered body having this composition can be obtained by using a slurry prepared by mixing dry fine powder finely pulverized in an atmosphere having an oxygen content of 0.005 to 0.5% with mineral oil, synthetic oil or a mixed oil thereof.

  In any sintered permanent magnet of any of the embodiments, a part of Fe is 0.3-5% Co, 0.05-1% Nb, 0.01-1% Al, 0.01-0.5% Ga, Substitution may be made with at least one selected from the group consisting of 0.01 to 1% Cu.

[2] Manufacturing method
(A) Fine pulverization Coarse powder for sintered R-Fe-B permanent magnet having the above composition in an atmosphere consisting of nitrogen gas and / or Ar gas with an oxygen content of substantially 0%, or containing oxygen Finely pulverize with a jet mill in an atmosphere of nitrogen gas and / or Ar gas in an amount of 0.005 to 0.5% to obtain a fine powder having an average particle diameter of 3 to 6 μm. In order to control the amount of N in the sintered body, it is preferable to adjust the concentration of the nitrogen gas in the Ar gas by using an atmosphere in the jet mill as Ar gas and introducing a small amount of nitrogen gas therein.

  When making the inside of a jet mill a nitrogen gas atmosphere, it is preferable to control the amount of N in the magnetic powder by controlling the amount of coarse powder supplied during pulverization and to control the amount of N in the resulting sintered body. Note that “the oxygen concentration is substantially 0%” is not limited to the case where the oxygen concentration is completely 0%, but includes an amount of oxygen that forms a very slight oxide film on the surface of the fine powder. Also means good. Such a low oxygen concentration is, for example, 0.001% or less, preferably 0.0005% or less, and more preferably 0.0002% or less. When coarse powder containing 0.002 to 0.15% by mass of N is finely pulverized in an atmosphere having an oxygen content of 0.005 to 0.5%, the oxidation reaction of rare earth elements in the coarse powder occurs preferentially, and the nitriding reaction is almost complete. It can be ignored.

(B) Slurry generation A container containing mineral oil, synthetic oil or a mixture of these oils is installed at the fine powder collection port of the jet mill, and this container also has an atmosphere of nitrogen gas and / or Ar gas. It is recovered directly in mineral oil, synthetic oil or a mixed oil thereof without being exposed to the atmosphere to form a slurry.

  It is preferable to add sodium hypophosphite as a fluidity improver to mineral oil, synthetic oil or a mixed oil thereof. Sodium hypophosphite is preferably added to mineral oil, synthetic oil or a mixed oil thereof in the form of a solution of glycerin or ethanol. The concentration of sodium hypophosphite in glycerin or ethanol solution is not particularly limited, but it is preferable that the ratio of sodium hypophosphite to mineral oil, synthetic oil or mixed oil thereof is in the range of 0.01 to 0.5 mass%. When the proportion of sodium hypophosphite is less than 0.01% by mass, the effect of improving the fluidity of the slurry is insufficient. When a solution of sodium phosphite in glycerin or ethanol is mixed with mineral oil, synthetic oil or a mixture of these, the mineral oil, synthetic oil or a mixture of these becomes acidic, and the fine powder collected in these is hypochlorous. Reacts chemically with sodium phosphate.

  As a result, the P content in the obtained radial anisotropic sintered R-Fe-B permanent magnet increases. In the radially anisotropic sintered R-Fe-B permanent magnet, P enters a non-magnetic grain boundary phase mainly rich in rare earth elements. As a result of the inventors' research, in order to make the content of P in the sintered body 0.001 to 0.05 mass%, the ratio of sodium hypophosphite to mineral oil, synthetic oil or mixed oil thereof is 0.01 to 0.5. It is preferable to make it into the mass%. The addition of the sodium hypophosphite glycerin solution or the sodium hypophosphite ethanol solution may be performed before or after the fine powder is recovered in the mineral oil, synthetic oil or mixed oil thereof. In any case, when the fine powder is mixed with mineral oil, synthetic oil or a mixed oil thereof to form a slurry, the fine powder is prevented from being oxidized or nitrided due to the shielding effect from the atmosphere by the mineral oil, synthetic oil or mixed oil thereof. The Therefore, the content of O or N in the obtained sintered body is not substantially different from the value of the content of O or N in the fine powder.

(C) Slurry Molding FIG. 2 shows an example of a molding apparatus used in the method of the present invention. An area denoted by reference numeral 11 represents a longitudinal section of the molding apparatus, and an area denoted by reference numeral 12 represents a transverse section of the mold of the molding apparatus and an enlarged view thereof (area enclosed by a square). The mold has a columnar core 4, a cylindrical die member 3, a lower punch 9, and an upper punch 10, and a space surrounded by these constitutes a cavity 6. The cylindrical die member 3 is supported by the die case 2. A pair of magnetic field generating coils 1 are disposed at the upper and lower positions of the core 4, and magnetic lines 7 are applied to the cavity 6 through the core 4. The die case 2 is provided with a slurry injection hole 5 that opens into the cavity 6.

  In the mold for injecting the slurry under pressure, it is preferable that the axial direction of the slurry injection hole 5 opening in the cavity is deviated from the center O of the center core 4 of the mold. When the axial direction of the slurry injection hole 4 deviates from the core center O, the finely powder slurry injected under pressure does not collide perpendicularly to the mold core 4, but along the outer peripheral surface of the core 4 or the inner peripheral surface of the die. The ring-shaped cavity 6 is smoothly filled almost spirally, and a high packing density can be obtained.

  On the other hand, when the axial direction of the slurry injection hole 5 coincides with the center O of the mold core, the pressure-injected slurry collides perpendicularly with the mold core 4 and is divided into left and right slurry injection holes 5 and Collide and collide at 180 ° opposite position. As a result, so-called seams are generated, and cracks are generated in the obtained sintered body.

In the present invention, as shown in FIG. 2, the central axis of the slurry injection hole 5 and the radial direction of the mold core 4 (the point A where the central axis of the slurry injection hole 5 intersects the inner peripheral surface of the cylindrical die member 3). The angle θ (right angle or acute angle side) with the straight line AO connecting the core center point O) is slightly different depending on the dimension of the mold cavity 6, but is 5 ° to 90 °, preferably 10 ° to 90 °, In particular, it is 30 ° to 90 °. Although the injection pressure of the slurry into the mold cavity 6 is not limited, it is preferably 4.9 × 10 ⁴ Pa to 3.9 × 10 ⁶ Pa (about 0.5 to 40 kgf / cm ² ), and 9.8 × 10 ⁴ Pa to 2.9 × 10 ^6. Pa (about 1 to 30 kgf / cm ² ) is more preferable, and 2.0 × 10 ⁵ Pa to 1.5 × 10 ⁶ Pa (about 2 to 15 kgf / cm ² ) is particularly preferable.

The strength of the radial orientation magnetic field applied to the mold cavity 6 for orienting the fine powder in the slurry is preferably 159 kA / m (about 2 kOe) or more, more preferably 239 kA / m (about 3 kOe) or more. After pressure injection of the slurry, pressure wet molding is performed while maintaining the orientation magnetic field. If the strength of the orientation magnetic field is less than 159 kA / m (about 2 kOe), the orientation of the fine powder is insufficient and good magnetic properties cannot be obtained. In addition, slurry is injected while applying an orientation magnetic field of 159 kA / m (about 2 kOe) or more to the mold cavity 6, and during or after the injection, pressurization is performed by applying an orientation magnetic field higher than the initial orientation magnetic field strength. Wet molding may be used. A molded body having a high density of 4.0 to 4.8 g / cm ³ can be obtained by wet-molding the slurry with improved fluidity under the above conditions.

(D) Deoiling The obtained molded body is heated under reduced pressure to remove mineral oil, synthetic oil or a mixed oil thereof in the molded body. The condition of the heat treatment under reduced pressure of the molded body is 13.3 Pa (about 0.1 Torr) or less, for example, a vacuum degree of about 6.7 Pa (about 5.0 × 10 ⁻² Torr), and heating at 100 ° C. or higher, for example, around 200 ° C. Temperature. The heating time varies depending on the weight of the molded body and the processing amount, but is preferably 1 hour or longer.

(E) Sintering The compact is sintered in a range of 1000 to 1150 ° C. at a vacuum of 0.13 Pa (about 0.001 Torr) or less, preferably 6.7 × 10 ⁻² Pa (about 5.0 × 10 ⁻⁴ Torr) or less. Is preferable. As a result, in the sintered body using the slurry finely pulverized in an atmosphere having an oxygen content of substantially 0%, a density of 7.52 to 7.85 g / cm ³ is obtained, and in an atmosphere having an oxygen content of 0.005 to 0.5% A density of 7.42 to 7.75 g / cm ³ is obtained in the sintered body using the slurry finely pulverized in step (b). In any case, due to the shielding effect from the atmosphere by mineral oil, synthetic oil or mixed oil thereof, oxidation of fine powder and molded body is prevented, and the O content of the former sintered body is 0.05 to 0.25% by mass The latter sintered body has an O content of more than 0.25% by mass and not more than 0.60% by mass.

  As described above, the slurry with improved fluidity is injected into the ring-shaped mold cavity in a radial orientation magnetic field smoothly and in a spiral manner, thereby achieving high filling properties and therefore high molded body density. As a result, it is possible to prevent the molded body and the sintered body from being cracked, chipped and deformed. Therefore, a ring-shaped sintered permanent magnet oriented in the radial direction having an outer diameter of 10 to 100 mm, an inner diameter of 8 to 96 mm, and a height of 10 to 70 mm is obtained. In particular, the present invention is suitable for manufacturing a small ring magnet having an outer diameter of 10 to 30 mm, an inner diameter of 8 to 28 mm, and a height of 10 to 50 mm.

  In addition, since smooth slurry filling is performed in an orientation magnetic field, the density of the compact is not only high, but also uniform, and therefore, uniform distribution of the surface magnetic flux density in the axial direction of the ring magnet can be achieved. If the variation of the surface magnetic flux density in the axial direction of the ring magnet is 7.5% or less, the cogging torque (particularly higher-order cogging torque) generated when the ring magnet is used in a rotating machine can be sufficiently suppressed. When the variation in the surface magnetic flux density is 5% or less, particularly 3% or less, there is no energy loss, and a rotating machine with extremely good silence can be configured.

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto. Magnetic properties were measured at room temperature (25 ° C.). The average particle size of the powder was measured by an air permeation method.

Reference example 1
17.6% Nd, 7.9% Pr, 5% Dy, 1.1% B, 0.08% Al, 1.5% Co, 0.1% Cu, 0.01% P, 0.01% O, 0.004 by weight percent An ingot having a composition consisting of% C, 0.006% N and the balance Fe was produced. This ingot was pulverized into a coarse powder having a particle size of 20 to 500 μm. Analysis of the composition of this coarse powder revealed that 17.5% Nd, 7.7% Pr, 5% Dy, 1.1% B, 0.08% Al, 1.5% Co, 0.1% Cu, 0.01% by weight percent. % P, 0.15% O, 0.015% C, 0.006% N, balance Fe.

After 100 kg of this coarse powder was charged into the jet mill, the inside of the jet mill was replaced with Ar gas, so that the oxygen concentration was substantially 0%. Next, nitrogen gas was introduced, and the concentration of nitrogen gas in Ar gas was set to 0.005%. In this atmosphere, the coarse powder was finely pulverized at a pressure of 6.9 × 10 ⁵ Pa (about 7.0 kgf / cm ² ) and a coarse powder supply rate of 12 kg / h per hour. A container filled with mineral oil was installed at the fine powder collection port of the jet mill, and the fine powder obtained was directly collected in mineral oil in an Ar gas atmosphere. The average particle size of the fine powder obtained was 4.5 μm. By adjusting the amount of mineral oil, the fine powder concentration in the resulting slurry was 75% by mass.

This slurry was wet-molded at a pressure of 4.9 × 10 ⁷ Pa (about 0.5 ton / cm ² ) while applying an orientation magnetic field of 796 kA / m (about 10 kOe) in the mold cavity. The direction in which the orientation magnetic field was applied was perpendicular to the molding direction. The resulting molded body was heated in a vacuum of 5.3 Pa (about 4.0 × 10 ⁻² Torr) at 80 ° C. for 2 hours to remove mineral oil, and then 6.7 × 10 ⁻³ Pa (about 5.0 × 10 ⁻⁵ Torr) was sintered at 1065 ° C. for 4 hours. The composition of the obtained sintered body is 17.5% Nd, 7.7% Pr, 5% Dy, 1.1% B, 0.08% Al, 1.5% Co, 0.1% Cu, 0.010 on a mass% basis. % P, 0.17% O, 0.070% C, 0.045% N, balance Fe. This sintered body was heat-treated at 480 ° C. for 2 hours in an Ar gas atmosphere. After machining, the magnetic properties of the sintered magnet were measured and found to be good as shown in Table 2.

Comparative Example 1
An ingot having the same composition as in Reference Example 1 was prepared except that P was not contained, and coarse powder was prepared in the same manner as in Reference Example 1. The composition of this coarse powder was the same as in Reference Example 1 except that it did not contain P and O was 0.14% by mass. This coarse powder was pulverized in the same manner as in Reference Example 1. The average particle size of the fine powder obtained was 4.5 μm. When the composition of the sintered body produced from this fine powder in the same manner as in Reference Example 1 was analyzed, 17.5% Nd, 7.7% Pr, 5% Dy, 1.1% B, 0.08% Al, based on mass%, 1.5% Co, 0.1% Cu, 0.16% O, 0.070% C, 0.045% N, balance Fe. The sintered body was machined and the magnetic properties were measured. The results are shown in Table 2. From Table 2, it can be seen that the coercive force iHc of Comparative Example 1 is lower than that of Reference Example 1.

Reference example 2
19.8% Nd, 8.9% Pr, 1.3% Dy, 1.1% B, 0.10% Al, 2.5% Co, 0.2% Nb, 0.08% Ga, 0.01% O, 0.003 on a weight percent basis An ingot having a composition composed of% C, 0.005% N and the balance Fe was prepared. This ingot was pulverized into a coarse powder having a particle size of 20 to 500 μm. Analysis of the composition of this coarse powder revealed that 19.7% Nd, 8.8% Pr, 1.3% Dy, 1.1% B, 0.10% Al, 2.5% Co, 0.2% Nb, 0.08 on a mass percent basis. % Ga, 0.12% O, 0.013% C, 0.007% N, balance Fe.

  To 100 kg of this coarse powder, 454 g of an aqueous solution in which 5% by mass of sodium hypophosphite was dissolved in pure water was mixed and dried in vacuum. When the composition of the coarse powder after drying was analyzed, 19.7% Nd, 8.8% Pr, 1.3% Dy, 1.1% B, 0.10% Al, 2.5% Co, 0.2% Nb on a mass percent basis 0.08% Ga, 0.008% P, 0.16% O, 0.013% C, 0.009% N and the balance Fe. This coarse powder was pulverized in the same manner as in Reference Example 1. The average particle size of the fine powder obtained was 4.7 μm. When the composition of the sintered body produced from this fine powder in the same manner as in Reference Example 1 was analyzed, 19.7% Nd, 8.8% Pr, 1.3% Dy, 1.1% B, 0.10% Al, based on mass%, 2.5% Co, 0.2% Nb, 0.08% Ga, 0.008% P, 0.18% O, 0.067% C, 0.055% N, balance Fe. When this sintered body was machined and the magnetic properties were measured, it was good as shown in Table 2.

Comparative Example 2
100 kg of the same coarse powder as in Reference Example 2 was finely pulverized in the same manner as in Reference Example 1 except that no sodium hypophosphite aqueous solution was added. The average particle size of the fine powder obtained was 4.7 μm. When the composition of the sintered body produced from this fine powder in the same manner as in Reference Example 1 was analyzed, 19.7% Nd, 8.8% Pr, 1.3% Dy, 1.1% B, 0.10% Al, based on mass%, 2.5% Co, 0.2% Nb, 0.08% Ga, 0.16% O, 0.067% C, 0.050% N, balance Fe. The sintered body was machined and measured for magnetic properties. As shown in Table 2, the coercive force iHc was lower than that of Reference Example 2.

Example 1
19.85% Nd, 8.95% Pr, 1.00% Dy, 1.02% B, 0.10% Al, 2.00% Co, 0.10% Cu, 0.15% O, 0.04% C, on a weight percent basis A coarse powder for an R-Fe-B permanent magnet having a composition of 0.02% N and the balance Fe was charged into a jet mill and replaced with nitrogen gas, and then pressure 6.9 × 10 ⁵ Pa (7.0 kgf / cm ² ) Finely pulverized at a coarse powder feed rate of 15 kg / h. The obtained fine powder was directly collected in a mineral oil ("Supersol PA30", manufactured by Idemitsu Kosan Co., Ltd.) installed at the discharge port of the jet mill without being exposed to the atmosphere, and used as a slurry.

  This mineral oil was previously mixed with a 5% by mass sodium hypophosphite glycerin solution so that the ratio of sodium hypophosphite to the mineral oil was 0.1% by mass. The mass ratio of mineral oil to fine powder in the slurry was 1: 3. The average particle size of the fine powder obtained was 4.5 μm. The slurry thus produced was injected by pressure into a mold cavity in which an orientation magnetic field generating coil shown in FIG.

The angle θ between the axial direction of the slurry injection hole 5 and the radial direction of the mold core 4 was 30 °. The intensity of the radial orientation magnetic field applied to the cavity was 239 kA / m (3 kOe), and the injection pressure of the slurry was 3.9 × 10 ⁵ Pa (4 kgf / cm ² ). After slurry injection, wet forming was performed in a magnetic field at a pressure of 7.8 × 10 ⁷ Pa (0.8 ton / cm ² ) while maintaining the orientation magnetic field strength at 239 kA / m (3 kOe), outer diameter 24.5 mm × inner diameter 17.4 A molded body of mm × height 30.0 mm was obtained. The density of the molded body was 4.30 g / cm ³ .

This molded body was deoiled at 200 ° C. for 2 hours under a reduced pressure of 6.7 Pa (5 × 10 ⁻² Torr), and then 1050 under a reduced pressure of 2.7 × 10 ⁻² Pa (2 × 10 ⁻⁴ Torr). Sintering was performed at 3 ° C. for 3 hours. The obtained sintered body had a size of an outer diameter of 20.0 mm × an inner diameter of 15.0 mm × a height of 26.0 mm, and a density of 7.58 g / cm ³ . The sintered body was heat-treated at 500 ° C. for 2 hours and then machined to finish the dimensions of outer diameter 19.6 mm × inner diameter 15.4 mm × height 25.0 mm. When the surface magnetic flux density was measured after quadrupole magnetization, a high peak value was shown as shown in Table 4.

  As shown in FIG. 3, a 5 mm × 7 mm × 1 mm sample 21b (1 mm thickness direction is the magnetization direction) was cut out from the sintered body 20. Reference numeral 21 denotes a sample before cutting out. When eight samples 21b were stacked in the thickness direction and the magnetic characteristics were measured, a high value as shown in Table 4 was obtained. When the composition of this sintered body was analyzed, 19.85% Nd, 8.95% Pr, 1.00% Dy, 1.02% B, 0.10% Al, 2.00% Co, 0.10% Cu, It consisted of 0.17% O, 0.06% C, 0.05% N, 0.01% P and the balance Fe. When sample 21b was subjected to line analysis by EPMA, a peak of P was confirmed as shown in FIG. From FIG. 4, it can be seen that P exists mainly in the rare earth-rich phase at the grain boundaries.

Example 2
The same coarse powder as in Example 1 was pulverized in the same manner as in Example 1 and recovered in mineral oil ("Supersol PA30", manufactured by Idemitsu Kosan Co., Ltd.) to prepare a slurry. The mass ratio of mineral oil to fine powder was 1: 3. The average particle size of the fine powder obtained was 4.8 μm. To this slurry, a 10% by mass sodium hypophosphite ethanol solution was mixed so that the ratio of sodium hypophosphite to mineral oil was 0.3% by mass. As in Example 1, the obtained slurry was pressure-injected into a mold cavity having an angle θ between the axis of the slurry injection hole and the radius of the mold core of 5 °, wet-formed in a magnetic field, and the outer diameter A molded body of 24.5 mm × inner diameter 17.4 mm × height 30.0 mm was obtained. The density of the molded body was 4.40 g / cm ³ .

This molded body was deoiled and sintered in the same manner as in Example 1 to obtain a sintered body having an outer diameter of 20.1 mm, an inner diameter of 14.9 mm, and a height of 26.2 mm. The density of the sintered body was 7.56 g / cm ³ . This sintered body was heat-treated at 500 ° C. for 2 hours. This sintered body was machined and finished to a size of outer diameter 19.6 mm × inner diameter 15.4 mm × height 25.0 mm, and four-pole magnetization was performed in the same manner as in Example 1. When the surface magnetic flux density was measured, a high peak value was shown as shown in Table 4.

  A sample 21b was cut out from the sintered body as shown in FIG. The cutting position, size, and measurement conditions of the sample 21b were the same as those in Example 1. The magnetic properties were good as shown in Table 4. When the composition of the sintered body was analyzed, 19.85% Nd, 8.95% Pr, 1.00% Dy, 1.02% B, 0.10% Al, 2.00% Co, 0.10% Cu, 0.16 on a mass percent basis % O, 0.06% C, 0.04% N, 0.03% P, balance Fe. As a result of line analysis of sample 21b by EPMA, a peak of P was confirmed as shown in FIG.

Example 3
In the same manner as in Example 1, the slurry produced in Example 1 was injected under pressure into a mold cavity to which an orientation magnetic field of 239 kA / m (3 kOe) was applied in the radial direction, and wet-molded in the magnetic field. The slurry injection pressure was 3.9 × 10 ⁵ Pa (4 kgf / cm ² ). 0.5 seconds after the start of slurry injection, the orientation magnetic field strength is increased to 398 kA / m (5 kOe). After the slurry injection is completed, the magnetic field strength is maintained and wet molding is performed, and the outer diameter is 24.5 mm × the inner diameter is 17.4 mm. X A molded body having a height of 30.0 mm was obtained. The density of the obtained molded body was 4.25 g / cm ³ .

This molded body was deoiled and sintered in the same manner as in Example 1 to obtain a sintered body having an outer diameter of 19.9 mm, an inner diameter of 15.1 mm, and a height of 26.1 mm. The density of the sintered body was 7.59 g / cm ³ . This sintered body was heat-treated in the same manner as in Example 1 and machined to dimensions of outer diameter 19.6 mm × inner diameter 15.4 mm × height 25.0 mm. When the obtained product was magnetized with four poles and the surface magnetic flux density was measured along the magnetic pole in the axial direction, it was good as shown in Table 4. Further, when the magnetic properties of the sample cut out in the same manner as in Example 1 were measured, the samples had high values as shown in Table 4.

Example 4
In the same manner as in Example 1, the slurry produced in Example 1 was pressure-injected into a mold cavity having an angle θ between the axis of the slurry injection hole and the radius of the mold core of 45 °, and wet-molded in a magnetic field. However, the mold was changed for a large-diameter ring magnet. The intensity of the radial orientation magnetic field applied to the cavity was 478 kA / m (about 6 kOe), and the injection pressure was 5.9 × 10 ⁵ Pa (about 6 kgf / cm ² ). After slurry injection, wet-molding was performed in a magnetic field at a pressure of 4.9 × 10 ⁷ Pa (0.5 ton / cm ² ) while maintaining the orientation magnetic field strength at 478 kA / m (about 6 kOe). A molded body of 95.0 mm × height 20.5 mm was obtained. The density of the obtained molded body was 4.28 g / cm ³ .

This molded body was deoiled and sintered in the same manner as in Example 1 to obtain a sintered body having an outer diameter of 92.5 mm, an inner diameter of 81.5 mm, and a height of 18 mm. The density of the sintered body was 7.57 g / cm ³ . The sintered body was heat-treated at 500 ° C. for 2 hours. This sintered body was machined and finished to dimensions of an outer diameter of 91.5 mm, an inner diameter of 80.5 mm, and a height of 16 mm. When the 16-pole magnetization was performed and the surface magnetic flux density was measured along the magnetic pole in the axial direction, it was good as shown in Table 4. When 4 samples of 5 mm × 10 mm × 2 mm cut out from the sintered body were stacked in the thickness direction and the magnetic properties were measured, they had high values as shown in Table 4.

Example 5
In the same manner as in Example 1, the slurry produced in Example 1 was pressure-injected into a mold cavity having an angle θ between the axis of the slurry injection hole and the radius of the mold core of 15 °, and wet-molded in a magnetic field. However, the mold was changed for a medium ring long ring magnet. The intensity of the radial orientation magnetic field applied to the cavity was 199 kA / m (about 2.5 kOe), and the injection pressure was 2.0 × 10 ⁵ Pa (about 2 kgf / cm ² ). After injecting the slurry, the orientation magnetic field strength was increased to 637 kA / m (8 kOe), and wet molding was performed in a magnetic field at a pressure of 3.9 × 10 ⁷ Pa (0.4 ton / cm ² ) while maintaining this orientation magnetic field strength. A molded body having a diameter of 50 mm, an inner diameter of 40 mm, and a height of 76 mm was obtained. The density of the molded body was 4.15 g / cm ³ .

This molded body was deoiled and sintered in the same manner as in Example 1 to obtain a sintered body having an outer diameter of 40.4 mm, an inner diameter of 35.0 mm, and a height of 65.2 mm. The density of the sintered body was 7.59 g / cm ³ . The sintered body was heat-treated at 500 ° C. for 2 hours. This sintered body was machined and finished to a size of an outer diameter of 40.0 mm, an inner diameter of 35.4 mm, and a height of 64.2 mm. When the surface magnetic flux density was measured along the magnetic pole in the axial direction after octopole magnetization, it was good as shown in Table 4. When 8 samples of 5 mm × 8 mm × 1 mm cut out from the sintered body were stacked in the thickness direction and the magnetic properties were measured, they had high values as shown in Table 4.

Comparative Example 3
The same coarse powder as in Example 1 was finely pulverized in the same manner as in Example 1, and the resulting fine powder was recovered in mineral oil ("Supersol PA30", manufactured by Idemitsu Kosan Co., Ltd.) to prepare a slurry. The mass ratio of mineral oil to fine powder was 1: 3. The average particle size of the fine powder was 4.5 μm. A 5 mass% sodium hypophosphite glycerin solution was previously mixed with mineral oil so that the ratio of sodium hypophosphite to mineral oil was 1 mass%. The obtained slurry was pressure-injected into the mold cavity in the same manner as in Example 1 and wet-molded in a magnetic field to obtain a molded body having an outer diameter of 24.5 mm, an inner diameter of 17.4 mm, and a height of 30.0 mm. The density of the molded body was 4.35 g / cm ³ .

This molded body was deoiled and sintered in the same manner as in Example 1 to obtain a sintered body having an outer diameter of 20.2 mm, an inner diameter of 15.1 mm, and a height of 25.9 mm. The density of the sintered body was 7.58 g / cm ³ . The sintered body was heat-treated at 500 ° C. for 2 hours. An attempt was made to machine this sintered body. However, since the mechanical strength of the sintered body was low, the sintered body was cracked by the load during processing and could not be evaluated. Eight samples of 5 mm × 7 mm × 1 mm cut out from the sinter of the sintered body were stacked in the thickness direction, and the magnetic properties were measured. The results are shown in Table 4. When the composition of the sintered body was analyzed, 19.85% Nd, 8.95% Pr, 1.00% Dy, 1.02% B, 0.10% Al, 2.00% Co, 0.10% Cu, 0.16 on a mass percent basis % O, 0.07% C, 0.04% N, 0.09% P, balance Fe.

Comparative Example 4
The same coarse powder as in Example 1 was finely pulverized in the same manner as in Example 1, and the resulting fine powder was recovered in mineral oil ("Supersol PA30", manufactured by Idemitsu Kosan Co., Ltd.) to prepare a slurry. The mass ratio of mineral oil to fine powder was 1: 3. The average particle size of the fine powder was 4.5 μm. Neither the mineral oil nor the slurry was mixed with a fluidity improver (sodium hypophosphite glycerin solution or sodium hypophosphite ethanol solution). This slurry was pressure-injected into the mold cavity in the same manner as in Example 1, and wet-molded in a magnetic field. However, because the fluidity of the slurry at the time of pressure injection was poor and the filling ability into the mold cavity was low, The dimensions of the obtained molded body were outer diameter 24.5 mm × inner diameter 17.4 mm × height 26.5 mm. The density of the molded body was 3.80 g / cm ³ .

This molded body was deoiled and sintered in the same manner as in Example 1 to obtain a sintered body having an outer diameter of 19.7 mm, an inner diameter of 14.8 mm, and a height of 23.3 mm. The density of the sintered body was 7.57 g / cm ³ . Since the filling property of the slurry to the upper punch side was poor, the upper punch side of the sintered body was deformed into an elliptical shape. Due to deformation, the sintered body could not be machined to the desired product dimensions. The sintered body was subjected to heat treatment at 500 ° C. for 2 hours, and a 5 mm × 7 mm × 1 mm sample was cut out from a portion other than the deformed portion. Eight samples were stacked in the thickness direction to measure magnetic properties. The results are shown in Table 4. When the composition of the sintered body was analyzed, 19.85% Nd, 8.95% Pr, 1.00% Dy, 1.02% B, 0.10% Al, 2.00% Co, 0.10% Cu, 0.16 on a mass percent basis % O, 0.07% C, 0.06% N, balance Fe. This sintered body was subjected to line analysis by EPMA. As shown in FIG. 6, there was no P peak present in the sintered bodies of Examples 1 and 2.

Comparative Example 5
As in Example 1, the slurry produced in Example 1 was pressure-injected into a mold cavity in which the axial direction of the slurry injection hole coincided with the radial direction of the mold core (θ = 0 °), and wetted in a magnetic field. Molding was performed to obtain a molded body having an outer diameter of 24.5 mm, an inner diameter of 17.4 mm, and a height of 30.0 mm. The density of the molded body was 4.29 g / cm ³ . This molded body was deoiled and sintered in the same manner as in Example 1 to obtain a sintered body having an outer diameter of 20.1 mm, an inner diameter of 15.1 mm, and a height of 25.9 mm. The density of the sintered body was 7.60 g / cm ³ . In the obtained sintered body, a crack in the longitudinal direction was generated at a position 180 ° opposite to the injection hole. Due to cracks, the sintered body could not be machined to the desired dimensions. Magnetic properties were measured by stacking eight 5 mm x 7 mm x 1 mm samples cut from the crack-free region in the thickness direction. The results are shown in Table 4.

Comparative Example 6
The slurry prepared in Example 1 was pressure-injected into the mold cavity in the same manner as in Example 1, and wet-molded in an orientation magnetic field of 79.6 kA / m (1.0 kOe), and the outer diameter was 24.5 mm × the inner diameter was 17.4 mm × A molded body having a height of 30.0 mm was obtained. The density of the molded body was 4.32 g / cm ³ . This molded body was deoiled and sintered in the same manner as in Example 1 to obtain a sintered body having an outer diameter of 20.3 mm, an inner diameter of 15.2 mm, and a height of 25.8 mm. The density of the sintered body was 7.59 g / cm ³ . This sintered body was heat-treated at 500 ° C. for 2 hours. This sintered body was machined and finished to a size of outer diameter 19.6 mm × inner diameter 15.4 mm × height 25.0 mm. The surface magnetic flux density was measured after quadrupole magnetization, and the peak value was lower than that of Example 1 as shown in Table 4. When 8 samples of 5 mm × 7 mm × 1 mm cut out from the sintered body were stacked in the thickness direction and the magnetic characteristics were measured, as shown in Table 4, it was lower than Example 1.

Example 6
22.00% Nd, 5.50% Pr, 5.00% Dy, 1.03% B, 0.08% Al, 1.00% Co, 0.12% Cu, 0.10% Ga, 0.09% O, 0.03 by weight percent Coarse powder for an R-Fe-B permanent magnet having a composition consisting of 1% C, 0.015% N and the balance Fe was charged into a jet mill and replaced with nitrogen gas, and then 6.4 × 10 ⁵ Pa (6.5 The powder was pulverized at a pressure of kgf / cm ² ) and a coarse powder feed rate of 20 kg / h. During the pulverization, a small amount of oxygen was introduced into the jet mill, and the oxygen concentration in the nitrogen gas was controlled to 0.080 to 0.120%. The particle size of the obtained fine powder was 5.0 μm. The composition of the fine powder is 22.00% Nd, 5.50% Pr, 5.00% Dy, 1.03% B, 0.08% Al, 1.00% Co, 0.12% Cu, 0.10% Ga, 0.48 on a weight percent basis. % O, 0.06% C, 0.015% N, balance Fe.

This fine powder was mixed with mineral oil ("Supersol PA30", manufactured by Idemitsu Kosan Co., Ltd.) to form a slurry. The mineral oil contained a 5% by weight sodium hypophosphite glycerin solution such that the ratio of sodium hypophosphite to mineral oil was 0.2% by weight. The mass ratio of mineral oil to fine powder was 1: 3. In the same manner as in Example 1, the obtained slurry was pressure-injected into a ring-shaped mold cavity to which an orientation magnetic field was applied in the radial direction, wet-molded, and outer diameter 24.5 mm × inner diameter 17.4 mm × height 30.0. A molded product of mm was obtained. The density of the molded body was 4.45 g / cm ³ .

The compact was sintered at 1070 ° C. for 3 hours under a reduced pressure of 6.7 Pa (5 × 10 ⁻⁵ Torr) to obtain a sintered body having an outer diameter of 20.3 mm × inner diameter of 15.1 mm × height of 25.8 mm. The density of the sintered body was 7.61 g / cm ³ . The sintered body was heat-treated at 550 ° C. for 2 hours. This sintered body was machined to dimensions of outer diameter 19.6 mm × inner diameter 15.4 mm × height 25.0 mm, and 8-pole magnetization was performed. Table 4 shows the measurement results of the surface magnetic flux density. Further, a sample having the same dimensions as in Example 1 was cut out from the sintered body and measured for magnetic properties. As a result, it was good as shown in Table 4. When the composition of the sintered body was analyzed, 22.00% Nd, 5.50% Pr, 5.00% Dy, 1.03% B, 0.08% Al, 1.00% Co, 0.12% Cu, based on mass%, It was 0.10% Ga, 0.46% O, 0.06% C, 0.015% N, 0.02% P, and the balance Fe.

Comparative Example 7
The dry fine powder prepared in Example 6 was filled in the same mold cavity as Example 6 without mixing with mineral oil, and 7.8 × 10 ⁷ Pa (0.8 ton / cm) in an orientation magnetic field of 239 kA / m (3 kOe). Molding was performed under the pressure of ² ) to produce a molded body having an outer diameter of 24.5 mm, an inner diameter of 17.4 mm, and a height of 30.0 mm. The density of the molded body was 3.78 g / cm ³ . The compact was sintered at 1070 ° C. for 3 hours under a reduced pressure of 2.7 Pa (2 × 10 ⁻⁵ Torr) to obtain a sintered body having an outer diameter of 20.1 mm × inner diameter of 15.0 mm × height of 25.9 mm. The density of the sintered body was 7.59 g / cm ³ . The sintered body was heat treated at 550 ° C. for 2 hours, and then machined to obtain a size of outer diameter 19.6 mm × inner diameter 15.4 mm × height 25.0 mm. When this was magnetized in 8 poles and the surface magnetic flux density was measured along the magnetic poles in the axial direction, it was lower than in Example 6 as shown in Table 4. When 8 samples of 5 mm × 7 mm × 1 mm cut out from the sintered body were stacked in the thickness direction and the magnetic properties were measured, as shown in Table 4, it was lower than Example 6.

Comparative Example 8
The mold fine cavity of Example 6 was filled with the dry fine powder prepared in Example 6 from above without being mixed with mineral oil, and 7.8 × 10 ⁷ Pa (0.8 ton) in an orientation magnetic field of 318 kA / m (4 kOe). / cm ² ) to form a first molded body having an outer diameter of 24.5 mm, an inner diameter of 17.4 mm, and a height of 10.0 mm. Next, the lower punch is lowered, and the dry powder is filled again on the first molded body, and is integrated with the first molded body at the same volume with a pressure of 7.8 × 10 ⁷ Pa (0.8 ton / cm ² ). A second compact (outer diameter 24.5 mm × inner diameter 17.4 mm × height 10.0 mm) was produced. Further, the third filling and molding were performed in the same manner to integrally produce a third molded body having the same volume. The dimensions of the obtained integrally molded body were an outer diameter of 24.5 mm, an inner diameter of 17.4 mm, and a height of 30.0 mm. The density of the molded body was 3.74 g / cm ³ .

This compact was sintered at 1070 ° C. for 3 hours under a reduced pressure of 6.7 Pa (5.0 × 10 ⁻⁵ Torr) to obtain a sintered body having an outer diameter of 20.0 mm × inner diameter of 14.9 mm × height of 26.1 mm. The density of the sintered body was 7.58 g / cm ³ . The sintered body was heat-treated at 550 ° C. for 2 hours and then mechanically processed to obtain an outer diameter of 19.6 mm × an inner diameter of 15.4 mm × a height of 25.0 mm. When this was magnetized in 8 poles and the surface magnetic flux density was measured along the magnetic pole in the axial direction, it was higher than Comparative Example 7 as shown in Table 4, but lower than Example 6. When 8 samples of 5 mm × 7 mm × 1 mm cut out from the sintered body were stacked in the thickness direction and the magnetic properties were measured, as shown in Table 4, it was higher than Comparative Example 7, but Example 6 It was lower. Further, the surface magnetic flux density was locally reduced at the joint portion of the three-stage sinter molding of the sintered body, and the cogging characteristics when incorporated in the motor were worse than those in Example 6.

Example 7
On a weight percent basis, 20.50% Nd, 9.25% Pr, 0.25% Dy, 1.03% B, 0.08% Al, 2.00% Co, 0.10% Cu, 0.13% O, 0.04% C, Coarse powder for an R-Fe-B permanent magnet having a composition consisting of 0.02% N and the balance Fe was charged into a jet mill and replaced with nitrogen gas, then 6.9 × 10 ⁵ Pa (7.0 kgf / cm ² ) And a coarse powder feed rate of 20 kg / h. The obtained fine powder was directly collected in a mineral oil ("Supersol PA30", manufactured by Idemitsu Kosan Co., Ltd.) installed at the discharge port of a jet mill without being exposed to the atmosphere, to obtain a slurry.

This mineral oil was previously mixed with a 5% by mass sodium hypophosphite glycerin solution so that the ratio of sodium hypophosphite to the mineral oil was 0.2% by mass. The mass ratio of mineral oil to fine powder was 1: 3. The average particle size of the fine powder was 4.7 μm. The slurry thus produced was pressurized and injected into a mold having an angle θ of 45 ° between the axis of the slurry injection hole 5 and the radius of the mold core 4 shown in FIG. The strength of the radial orientation magnetic field applied to the cavity was 239 kA / m (about 3 kOe), and the injection pressure of the slurry was 2.9 × 10 ⁵ Pa (about 3 kgf / cm ² ). After slurry injection, wet molding was performed in a magnetic field at a pressure of 3.9 × 10 ⁷ Pa (about 0.4 ton / cm ² ) while maintaining the orientation magnetic field strength at 239 kA / m (about 3 kOe), and the outer diameter was 25.3 mm × A molded body having an inner diameter of 17.5 mm and a height of 21.8 mm was obtained. The density of the molded body was 4.40 g / cm ³ .

This molded body was deoiled at 180 ° C. for 4 hours under a reduced pressure of 6.7 Pa (about 5.0 × 10 ⁻² Torr), and then under reduced pressure of 6.7 × 10 ⁻² Pa (about 5.0 × 10 ⁻⁴ Torr) And sintered at 1040 ° C. for 3 hours. The dimensions of the obtained sintered body were outer diameter 20.6 mm × inner diameter 15.3 mm × height 18.8 mm, and the density was 7.56 g / cm ³ . The sintered body was heat-treated at 480 ° C. for 2 hours. This sintered body was machined and finished to dimensions of an outer diameter of 20.1 mm, an inner diameter of 15.9 mm, and a height of 17.2 mm. The unit weight ratio (weight of sintered body after processing / weight of sintered body before processing × 100%) was 72.7%. The unit weight rate is sometimes called a processing rate.

The surface magnetic flux density B ₀ was measured with the Hall sensor probe along the magnetic pole in the axial direction on the outer peripheral surface of the four-pole magnetized ring magnet. From the measurement results of the surface magnetic flux density B _0, the peak value of the surface magnetic flux density B ₀ (maximum value) and (minimum value of the maximum value -B ₀ of B ₀₎ variation [a surface magnetic flux density B ₀ / B maximum value of ₀ ] × 100 (%) was determined. The results are shown in Table 6 and FIG. In FIG. 7, the vertical axis indicates the surface magnetic flux density B ₀ (T) along the magnetic pole in the axial direction of the ring magnet, and the horizontal axis indicates the distance (mm) by which the probe is moved along the axial direction of the ring magnet. . The distance H corresponds to the axial length (17.2 mm) of the ring magnet. Table 6 As is apparent, the peak value of the surface magnetic flux density B ₀ is high, the variation of the surface magnetic flux density B ₀ was small.

  As shown in FIG. 3, a sample 21b of 4 mm × 7 mm × 1 mm was cut out from the sintered body 20 produced in the same manner, and eight samples 21b were stacked in the thickness direction to measure the magnetic characteristics. It had a high value as shown. When the composition of the sintered body was analyzed, 20.50% Nd, 9.25% Pr, 0.25% Dy, 1.03% B, 0.08% Al, 2.00% Co, 0.10% Cu, 0.15 on a mass% basis. % O, 0.06% C, 0.05% N, 0.018% P, balance Fe. Further, when line analysis was performed on sample 21b by EPMA, a peak of P was confirmed as shown in FIG. FIG. 8 shows that P exists mainly in the rare earth-rich phase at the grain boundaries.

Example 8
The same coarse powder as in Example 7 was finely pulverized in the same manner as in Example 7, and recovered in mineral oil ("Supersol PA30", manufactured by Idemitsu Kosan Co., Ltd.) to obtain a slurry. The mass ratio of mineral oil to fine powder was 1: 3. The average particle size of the fine powder obtained was 4.6 μm. To this slurry, a 10% by mass sodium hypophosphite ethanol solution was mixed so that the ratio of sodium hypophosphite to mineral oil was 0.4% by mass. As in Example 7, this slurry was pressure injected into a mold cavity having an angle θ between the slurry injection hole axis and the radius of the mold core of 30 °, wet-molded in a magnetic field, and an outer diameter of 25.3 mm. A molded body having an inner diameter of 17.5 mm and a height of 21.8 mm was obtained. The density of the molded body was 4.35 g / cm ³ . The number of manufactured compacts per hour was 123. The product unit weight was 72.9%.

The molded body was deoiled and sintered in the same manner as in Example 7 to obtain a sintered body having an outer diameter of 20.6 mm, an inner diameter of 15.3 mm, and a height of 18.75 mm. The density of the sintered body was 7.55 g / cm ³ . This sintered body was heat-treated at 480 ° C. for 2 hours. This sintered body was machined and finished to dimensions of outer diameter 20.1 mm × inner diameter 15.9 mm × height 17.2 mm. After performing quadrupole magnetization in the same manner as in Example 7, the surface magnetic flux density B ₀ was measured along the magnetic pole in the axial direction. As shown in Table 6, a high peak value of the surface magnetic flux density B ₀ was obtained. Indicated. Further, when the variation in the axial direction of the surface magnetic flux density B ₀ was calculated, it was small as shown in Table 6.

  As in Example 7, a sample was cut out from the sintered body as shown in FIG. Table 6 shows the measurement results of the magnetic characteristics. When the composition of the sintered body was analyzed, 20.50% Nd, 9.25% Pr, 0.25% Dy, 1.03% B, 0.08% Al, 2.00% Co, 0.10% Cu, 0.16 on a mass% basis. % O, 0.07% C, 0.06% N, 0.037% P, balance Fe. Further, as a result of line analysis of this sintered body by EPMA, a peak of P was confirmed as shown in FIG.

Example 9
The slurry produced in Example 7 was pressure-injected into a mold cavity having an angle θ between the axis of the slurry injection hole and the radius of the mold core of 60 ° in the same manner as in Example 7, and wet-molded in a magnetic field. However, the dimensions of the mold cavity were changed. The intensity of the radial orientation magnetic field applied to the cavity was 398 kA / m (about 5 kOe), and the injection pressure was 5.9 × 10 ⁵ Pa (about 6 kgf / cm ² ). After slurry injection, wet forming was performed in a magnetic field at a pressure of 7.8 × 10 ⁷ Pa (about 0.8 ton / cm ² ) while maintaining the orientation magnetic field strength at 398 kA / m (about 5 kOe). A molded body having an inner diameter of 24.3 mm and a height of 55.1 mm was obtained. The number of manufactured compacts per hour was 125. The density of the molded body was 4.45 g / cm ³ .

This molded body was deoiled and sintered in the same manner as in Example 7 to obtain a sintered body having an outer diameter of 27.4 mm, an inner diameter of 21.1 mm, and a height of 47.4 mm. The density of the sintered body was 7.57 g / cm ³ . The sintered body was heat-treated at 480 ° C. for 2 hours. This sintered body was machined and finished to a size of outer diameter 26.8 mm × inner diameter 21.8 mm × height 45.0 mm. The unit weight of the product was 75.5%. When the surface magnetic flux density was measured along the magnetic pole in the axial direction by performing quadrupole magnetization, the peak value and variation were good as shown in Table 6. When 8 samples of 4 mm × 7 mm × 1 mm cut out from the sintered body were stacked in the thickness direction and the magnetic properties were measured, they had high values as shown in Table 6.

Example 10
In the same manner as in Example 9, the slurry prepared in Example 9 was applied to a mold cavity to which an orientation magnetic field of 159 kA / m (about 2 kOe) was applied in the radial direction, to 3.9 × 10 ⁵ Pa (about 4 kgf / cm ² ). And wet-molded in a magnetic field. 0.5 seconds after the start of slurry injection, the strength of the orientation magnetic field is increased to 318 kA / m (about 4 kOe), and after the completion of injection, wet forming is performed in the magnetic field while maintaining this magnetic field strength, outer diameter 33.4 mm × inner diameter 24.3 A molded body of mm × height 54.8 mm was obtained. The density of the molded body was 4.45 g / cm ³ . The number of manufactured compacts per hour was 121.

This molded body was deoiled and sintered in the same manner as in Example 7 to obtain a sintered body having an outer diameter of 27.4 mm, an inner diameter of 21.1 mm, and a height of 47.1 mm. The density of the sintered body was 7.57 g / cm ³ . This sintered body was heat-treated in the same manner as in Example 7 and machined to dimensions of outer diameter 26.8 mm × inner diameter 21.8 mm × height 45.0 mm. The unit weight of the product was 6.0%. When the surface magnetic flux density B ₀ was measured after quadrupole magnetization, the peak value and variation were good as shown in Table 6. Further, when the magnetic properties of the sample cut out in the same manner as in Example 7 were measured, it had a high value as shown in Table 6.

Example 11
In the same manner as in Example 7, the slurry produced in Example 7 was pressure-injected into a mold cavity having an angle θ between the axis of the slurry injection hole and the radius of the mold core of 15 °, and wet-molded in a magnetic field. However, the dimensions of the mold cavity were changed. The intensity of the radial orientation magnetic field applied to the cavity was 223 kA / m (2.8 kOe), and the injection pressure was 3.9 × 10 ⁵ Pa (about 4 kgf / cm ² ). After slurry injection, wet molding was performed in a magnetic field at a pressure of 3.9 × 10 ⁷ Pa (approximately 0.4 ton / cm ² ) while maintaining the orientation magnetic field strength at 223 kA / m (2.8 kOe), and the outer diameter was 17.9 mm × inner diameter. A molded body of 11.1 mm × height 16.4 mm was obtained. The density of the molded body was 4.40 g / cm ³ . The number of manufactured compacts per hour was 140.

This molded body was deoiled and sintered in the same manner as in Example 7 to obtain a sintered body having an outer diameter of 14.6 mm, an inner diameter of 9.6 mm, and a height of 14.2 mm. The density of the sintered body was 7.58 g / cm ³ . The sintered body was heat-treated at 480 ° C. for 2 hours. This sintered body was machined and finished to a size of outer diameter 14.0 mm × inner diameter 10.0 mm × height 12.5 mm. The unit weight of the product was 69.8%. When the surface magnetic flux density was measured along the magnetic pole in the axial direction by performing quadrupole magnetization, the peak value and its variation were good as shown in Table 6. When 8 samples of 3 mm × 7 mm × 1 mm cut out from the sintered body were stacked in the thickness direction and the magnetic properties were measured, they had high values as shown in Table 6.

Comparative Example 9
The same coarse powder as in Example 7 was finely pulverized in the same manner as in Example 7, and recovered in mineral oil ("Supersol PA30", manufactured by Idemitsu Kosan Co., Ltd.) to obtain a slurry. The mass ratio of mineral oil to fine powder was 1: 3. The average particle size of the fine powder obtained was 4.6 μm. The mineral oil and slurry were not mixed with sodium hypophosphite glycerin solution or sodium hypophosphite ethanol solution. This slurry was injected under pressure in the same manner as in Example 7 and wet-formed in a magnetic field. However, since the fluidity of the slurry was poor, the filling property into the mold cavity was low, and the size of the obtained molded body was 25.3 mm outer diameter × 17.5 mm inner diameter × 19.5 mm height. The density of the molded body was 3.85 g / cm ³ . The number of manufactured compacts per hour was 116.

This molded body was deoiled and sintered in the same manner as in Example 7 to obtain a sintered body having an outer diameter of 20.3 mm, an inner diameter of 15.0 mm, and a height of 15.9 mm. The density of the sintered body was 7.55 g / cm ³ . However, since the filling property of the slurry was poor, the upper punch side portion of the sintered body was deformed into an ellipse, and even when the sintered body was machined, the product dimensions were not achieved. The sintered body was subjected to heat treatment at 480 ° C. for 2 hours, a 4 mm × 7 mm × 1 mm sample was cut out from a portion other than the deformed portion, and eight samples were stacked in the thickness direction to measure the magnetic properties. The results are shown in Table 6. When the composition of the sintered body was analyzed, 20.50% Nd, 9.25% Pr, 0.25% Dy, 1.03% B, 0.08% Al, 2.00% Co, 0.10% Cu, 0.15 on a mass% basis. % O, 0.07% C, 0.05% N, balance Fe. This sintered body was subjected to line analysis by EPMA, and it was confirmed that there was no P peak as shown in FIG.

Comparative Example 10
As in Example 7, the slurry produced in Example 7 was pressure-injected into the mold cavity where the axial direction of the slurry injection hole was the radial direction of the mold core (θ = 0 °), and wet-molded in a magnetic field. Thus, a molded body having an outer diameter of 25.3 mm, an inner diameter of 17.5 mm, and a height of 21.7 mm was obtained. The density of the molded body was 4.38 g / cm ³ . The number of manufactured compacts per hour was 118. This molded body was deoiled and sintered in the same manner as in Example 7 to obtain a sintered body having an outer diameter of 20.6 mm, an inner diameter of 15.3 mm, and a height of 18.7 mm. The density of the sintered body was 7.56 g / cm ³ . In the sintered body, a longitudinal crack occurred at a position opposite to the injection hole by 180 °. Due to cracks, the sintered body was not machined even when machined. Magnetic properties were measured by stacking 8 4 mm x 7 mm x 1 mm specimens cut from the crack-free region in the thickness direction. The results are shown in Table 6.

Comparative Example 11
22.25% Nd, 10.00% Pr, 0.25% Dy, 1.03% B, 0.07% Al, 2.00% Co, 0.12% Cu, 0.10% Ga, 0.15% O, 0.03 by weight percent Coarse powder for an R-Fe-B permanent magnet having a composition consisting of 1% C, 0.015% N and the balance Fe was charged into a jet mill and replaced with nitrogen gas, and then 6.4 × 10 ⁵ Pa (6.5 The powder was pulverized at a pressure of kgf / cm ² ) and a coarse powder feed rate of 30 kg / h. During pulverization, a small amount of oxygen was introduced into the jet mill, and the oxygen concentration in the nitrogen gas was controlled to 0.080 to 0.120%. The particle size of the fine powder obtained is 4.8 μm, and its composition is 22.25% Nd, 10.00% Pr, 0.25% Dy, 1.03% B, 0.07% Al, 2.00% Co, based on mass%. 0.12% Cu, 0.10% Ga, 0.52% O, 0.06% C, 0.015% N, balance Fe.

The obtained dry fine powder was not mixed with mineral oil, filled with the same mold cavity as in Example 7 except that there was no slurry injection hole and the cavity depth was 1/3, and 398 kA / m (approximately A first compact was produced at a pressure of 7.8 × 10 ⁷ Pa (about 0.8 ton / cm ² ) in an orientation magnetic field of 5 kOe). Next, the lower punch is lowered, and the dry powder is filled again on the first molded body, and is integrated with the first molded body at the same volume with a pressure of 7.8 × 10 ⁷ Pa (0.8 ton / cm ² ). A second molded body was produced. Further, the third filling and molding were performed in the same manner to integrally produce a third molded body having the same volume. The dimensions of the obtained integral molded body were outer diameter 25.3 mm × inner diameter 17.5 mm × height 21.5 mm. The density of the molded body was 3.80 g / cm ³ . The number of manufactured compacts per hour was 48.

This compact was sintered at 1070 ° C for 3 hours under a reduced pressure of 6.7 × 10 ^-3 Pa (about 5 × 10 ^-5 Torr), and the sintered body had an outer diameter of 20.7 mm, an inner diameter of 15.4 mm, and a height of 18.8 mm. Got. The density of the sintered body was 7.52 g / cm ³ . This sintered body was heat-treated at 480 ° C. for 2 hours. Furthermore, the dimensions were 20.1 mm outer diameter × 15.9 mm inner diameter × 17.2 mm height by mechanical processing. The unit weight of the product was 72.3%. When this sintered body was magnetized with four poles and the surface magnetic flux density was measured along the magnetic poles in the axial direction, the peak value was lower than in Example 7 and the variation was three-stage molded as shown in Table 6 and FIG. It was big by the influence of the joint part. When 8 samples of 4 mm × 7 mm × 1 mm cut out from the sintered body were stacked in the thickness direction and the magnetic properties were measured, as shown in Table 6, it was lower than Example 7. Further, the surface magnetic flux density B ₀ of the sintered body was locally low at the joint portion of the three-stage lap molding, and cogging when incorporated in the motor was larger than that in Example 7.

Comparative Example 12
The dry fine powder was not mixed with mineral oil, and was filled from above into the same mold cavity as Comparative Example 11 except that there was no slurry injection hole and the cavity depth was 1/3. A first molded body was produced at a pressure of 7.8 × 10 ⁷ Pa (about 0.8 ton / cm ² ) in an orientation magnetic field of 478 kA / m (about 6 kOe). Next, the lower punch is lowered, and the dry powder is filled again on the first molded body, and is integrated with the first molded body at the same volume with a pressure of 7.8 × 10 ⁷ Pa (0.8 ton / cm ² ). A second molded body was produced. Further, the third filling and molding were performed in the same manner to integrally produce a third molded body having the same volume. The dimensions of the obtained integrally molded body were an outer diameter of 33.4 mm, an inner diameter of 24.3 mm, and a height of 54.6 mm. The density of the molded body was 3.75 g / cm ³ . The number of manufactured compacts per hour was 45.

This compact was sintered at 1070 ° C for 3 hours under a reduced pressure of 6.7 × 10 ^-3 Pa (about 5 × 10 ^-5 Torr), and the sintered body had an outer diameter of 27.3 mm, an inner diameter of 21.4 mm, and a height of 47.5 mm. Got. The density of the sintered body was 7.51 g / cm ³ . This sintered body was heat-treated at 480 ° C. for 2 hours. Furthermore, the dimensions were 26.8 mm outer diameter x 21.8 mm inner diameter x 45.0 mm height by mechanical processing. The unit weight of the product was 80.1%. When this was magnetized with four poles and the surface magnetic flux density was measured along the magnetic poles in the axial direction, as shown in Table 6, the peak value was lower than in Example 9, and the variation was large. When 8 samples of 4 mm × 7 mm × 1 mm cut out from the sintered body were stacked in the thickness direction and the magnetic properties were measured, as shown in Table 6, it was lower than Example 9. Further, the surface magnetic flux density B ₀ of the sintered body was locally low at the joint portion of the three-stage lap molding, and cogging when incorporated in the motor was larger than that in Example 9.

Comparative Example 13
A master alloy having a composition consisting of 30.0% Nd, 0.90% B, 5.00% Co, 0.20% Ga, and the balance Fe on a mass% basis is put into a quartz nozzle having holes in the lower part, and 0.4 inside the quartz nozzle. The pressure was reduced to Pa (about 3 × 10 ⁻³ Torr). The mother alloy was melted by high frequency in an atmosphere in which Ar gas was introduced until a pressure of 5.3 × 10 ⁴ Pa (about 400 Torr) was reached, and the resulting molten metal at an Ar pressure of 270 g / cm ³ and a peripheral speed of 30 m It was ejected onto a Be-Cu roll rotating at / s. Thereby, a ribbon-like alloy having an average thickness of 30 μm was obtained.

The ribbon-shaped alloy was coarsely pulverized to 500 μm or less, and 0.2% by mass of scaly graphite and 0.3% by mass of bismuth borosilicate low melting point amorphous glass were mixed with the obtained coarse powder. The obtained coarse powder mixture was cold-pressed at a pressure of 4.9 × 10 ⁸ Pa (about 5 ton / cm ² ) to obtain a green compact having a density of 5.8 g / cm ³ . This green compact was hot pressed in a vacuum of 0.67 Pa (5.0 × 10 ⁻³ Torr) at 740 ° C. and 2 × 10 ⁸ Pa (2 ton / cm ² ) and sintered with a density of 7.40 g / cm ³ The body. This sintered body was further subjected to hot plastic processing at 740 ° C. in a vacuum of 0.67 Pa (5.0 × 10 ⁻³ Torr), the outer diameter was 22.0 mm, the inner diameter was 14.5 mm, the height was 48.0 mm, and the bottom thickness was 10 A cup body of mm was used. In order to impart radial anisotropy, the number of hot plastic working per hour was as small as three. The bottom of the cup body was excised by machining. Also, the end where the crack occurred on the side opposite to the bottom was cut off. The inner and outer circumferences of the obtained ring were machined to obtain product dimensions of outer diameter 20.1 mm × inner diameter 15.9 mm × height 28.0 mm. The unit weight ratio of the product to the hot plastic work was as low as 17.0%.

  This ring magnet was subjected to quadrupole magnetization in the same manner as in Example 7. When the surface magnetic flux density was measured, as shown in Table 6 and FIG. 12, the peak value was lower than that in Example 7, the surface magnetic flux density at both ends in the axial direction was low, and the variation in the surface magnetic flux density was large. As a result of measuring the magnetic properties of a 4 mm × 7 mm × 1 mm sample cut out from the product, it was lower than Example 7 as shown in Table 6. Further, cogging when the product was incorporated in the motor was larger than that in Example 7.

Comparative Example 14
A ribbon was prepared in the same manner as in Comparative Example 13 from a mother alloy having a composition of 28.0% Nd, 0.50% Ce, 0.90% B, 3.0% Co, 0.15% Ga, and the balance Fe on a mass% basis. The ribbon was crushed into coarse powder. A green compact of 5.7 g / cm ³ was produced from this coarse powder in the same manner as in Comparative Example 13, and hot pressed to a density of 7.30 g / cm ³ at 720 ° C. in a vacuum of 0.4 Pa (3 × 10 ⁻³ Torr). did. The obtained pressed body was hot plastic processed at 720 ° C. in a vacuum of 0.4 Pa (3 × 10 ⁻³ Torr) in the same manner as in Comparative Example 13, and the outer diameter was 30.0 mm × the inner diameter was 19.5 mm × the height was 65.0 mm. A cup body having a bottom thickness of 10 mm was obtained. The number of hot plastic working per hour was 4.

The bottom of the cup body was excised by machining. Also, the end where the crack occurred on the side opposite to the bottom was cut off. The inner and outer circumferences of the resulting ring were machined to obtain product dimensions of outer diameter 26.8 mm x inner diameter 21.8 mm x height 45.0 mm. The unit weight ratio of the product to the hot plastic work was as low as 29.1%. This product was subjected to 4-pole magnetization in the same manner as in Example 9. When the surface magnetic flux density was measured, as shown in Table 6, the peak value was lower than in Example 9, the surface magnetic flux density B _{0 at} both ends in the axial direction was low, and the variation in the surface magnetic flux density B ₀ was large. As a result of measuring the magnetic properties of a 4 mm × 7 mm × 1 mm sample cut out from the product, it was lower than Example 9 as shown in Table 6. The cogging when incorporated in the motor was greater than that of Example 9.

  The present invention can be used for a high-performance radially anisotropic sintered R-Fe-B permanent magnet and a method for producing the same. In particular, it can be used for a high-performance radial anisotropic sintered R-Fe-B permanent magnet excellent in surface magnetic flux density uniformity and an efficient manufacturing method thereof.

6 is a graph showing the relationship between the coercive force iHc and the P content of a sintered permanent magnet. It is the schematic which shows the shaping | molding apparatus for enforcing the method of this invention. (a) is a schematic perspective view which shows a mode that a sample is cut out from a ring-shaped sintered compact, (b) is a cross-sectional view which shows a mode that a sample is cut out from a ring-shaped sintered body. 4 is a graph showing the results of EPMA line analysis of the sintered body of Example 1. 6 is a graph showing the results of EPMA line analysis of the sintered body of Example 2. 6 is a graph showing an EPMA line analysis result of a sintered body of Comparative Example 4. It is a graph which shows the surface magnetic flux density distribution of the ring magnet of Example 7. 10 is a graph showing an EPMA line analysis result of the sintered body of Example 7. It is a graph which shows the EPMA line analysis result of the sintered compact of Example 8. 10 is a graph showing an EPMA line analysis result of a sintered body of Comparative Example 9. 10 is a graph showing a surface magnetic flux density distribution of a ring magnet of Comparative Example 11. 14 is a graph showing a surface magnetic flux density distribution of a ring magnet of Comparative Example 13.

Explanation of symbols

1 magnetic field generating coil, 2 die case, 3 cylindrical die member, 4 core,
5 slurry injection holes, 6 cavities, 7 magnetic field lines, 9 bottom punch,
10 Upper punch, 11 Longitudinal section of molding equipment, 12 Cross section of mold and enlarged view,
20 Sintered body, 21 Sample before cutting, 21b sample

Claims (6)

Coarse powder for sintered R-Fe-B permanent magnets (R is at least one rare earth element selected from Y-containing rare earth elements) is pulverized as a fine powder directly into mineral oil or synthetic oil Alternatively, these are recovered in a mixed oil to form a slurry, and the slurry is pressure-injected into a cavity of a mold and wet-molded in a magnetic field, and the obtained molded body is heated under reduced pressure from the molded body. A method for producing a sintered permanent magnet that removes mineral oil, the synthetic oil or a mixed oil thereof, and sinters the molded body in a vacuum, wherein the die has a hollow structure die member and the die member And a core disposed through a ring-shaped cavity on the inner peripheral side of the die, and the die member is provided with a slurry injection hole for pressure-injecting the slurry into the cavity of the mold. Check that the axial direction of the hole is off the center of the mold core. Method for producing a sintered permanent magnet according to claim. 2. The method of manufacturing a sintered permanent magnet according to claim 1, wherein a radial orientation magnetic field is applied to the cavity. 3. The method for manufacturing a sintered permanent magnet according to claim 1, wherein a center axis of the slurry injection hole, a point A at which the center axis intersects an inner peripheral surface of the die member, and the core center point O, A method for producing a sintered permanent magnet, characterized in that an angle θ formed by a straight line AO connecting the two is 5 to 90 °. Fine powder and mineral oil obtained by pulverizing coarse powder for sintered R-Fe-B permanent magnets (R is at least one rare earth element selected from Y-containing rare earth elements), synthesis oil A mold for wet-molding a slurry made of oil or a mixture of these oils in a magnetic field, wherein the mold has a hollow die member and a ring-shaped cavity on the inner peripheral side of the die member The die member is provided with a slurry injection hole for pressurizing and injecting the slurry into the cavity of the mold, and the axial direction of the injection hole is the core of the mold. A mold characterized by being off the center. 5. The mold for sintered permanent magnets according to claim 4, wherein a radial orientation magnetic field is applied to the cavity. 6. The sintered permanent magnet mold according to claim 4, wherein a center axis of the slurry injection hole, a point A at which the center axis intersects an inner peripheral surface of the die member, and the core center point O, A mold having an angle θ of 5 to 90 ° with a straight line AO.

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