JPH07201622A - Sintered magnet and its production - Google Patents

Abstract

PURPOSE:To provide an inexpensive thin magnet by suppressing fluctuation in the dimensions of an R-T-B based sintered magnet at the time of sintering thereby eliminating the need of grinding after sintering. CONSTITUTION:When a sintered magnet containing R (at least one kind of rare earth element containing Y), T (Fe and/or Co) and B, a molded item of magnetic powder having average particle size in the range of 70-350mum and density of 5.5g/cm<3> or above is sintered such that the density varies by 0.2g/cm<3> or more.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rare earth sintered magnet having a small shrinkage during sintering and a manufacturing method thereof.

[0002]

2. Description of the Related Art As a rare earth magnet having high performance, an Sm-Co type magnet manufactured by powder metallurgy has an energy product of 32M.
GOe's are in mass production. In recent years, Nd-Fe
R-T-B magnets such as -B magnets (T is Fe, or Fe
And Co) were developed, and a sintered magnet is disclosed in JP-A-59-46008. R-T-B magnets are cheaper in raw material than Sm-Co magnets. RT
A conventional Sm—Co powder metallurgical process (melting → casting → coarse crushing → fine crushing → molding → sintering → magnet) can be applied to the production of a —B sintered magnet.

In the R-T-B system magnet, in addition to the sintered magnet,
Bonded magnets in which magnet powder is bonded with a resin binder or a metal binder are also in practical use. Since the dimensions of the bonded magnet are almost maintained during molding, the dimensional accuracy is high and no shape processing is required after manufacturing. However, since the industrialized RTB-based bonded magnet uses polycrystalline particles made of fine crystals produced by a quenching method such as a single roll method, anisotropy due to molding in a magnetic field does not occur. Have difficulty. The crushed powder of the RTB sintered magnet cannot be used as the raw material powder of the bonded magnet because the coercive force is drastically reduced due to the distortion and the oxidation due to the crushing. In addition, the crushed powder of the R-T-B type alloy ingot is reacted with hydrogen to decompose it into a rare earth hydride, a boride of T, and T, and dehydrogenate at a predetermined temperature to crystallize in individual particles. Proposals have also been made to deposit fine crystals with uniform orientation. The polycrystalline particles obtained by this method can be magnetically oriented, and high coercive force can be obtained by fine crystals.
Since hydrogen is used, the process is complicated and has not been put to practical use.

On the other hand, in the R-T-B system sintered magnet, since the powder consisting of substantially single crystal particles is molded in a magnetic field, an anisotropic magnet can be easily obtained, and a binder is not used. High characteristics can be obtained. However, in the sintering method, the molded body significantly shrinks during the sintering reaction, and the shrinkage is non-uniform, so that it is difficult to maintain the dimensional accuracy of the molded body. This shrinkage varies depending on the degree of orientation of particles in the molded body, variations in density, and the like. In an anisotropic sintered magnet, the contraction rate differs between the direction of easy magnetization and the direction perpendicular to it. For example, when the density of the molded body is 4.3 g / cm ³ , about 22% in the direction of easy magnetization, and It becomes about 15% in the vertical direction, and the density after sintering reaches 7.55 g / cm ³ .

Such a dimensional change in the anisotropic sintered magnet is particularly problematic when the ring-shaped magnet or the plate-shaped magnet is thin. This is because if the shrinkage ratio of the thin magnet becomes uneven, warpage occurs. Therefore, when commercialized, the sintered body is ground to correct such dimensional changes. However, the grinding process has the following problems.

The amount of material loss of the sintered body during grinding becomes large. For example, if a warp of 1 mm occurs when manufacturing a thin plate magnet with a thickness of 1 mm, it is necessary to first manufacture a sintered body with a thickness of about 3 mm and then grind the upper and lower surfaces of the sintered body. 2/3 of the material is lost. In order to avoid such a loss, even when cutting multiple thin plate magnets to a thickness of 1 mm from a single thick base material, if the tooth width of the grinding cutter is 0.6 mm, it will be about 40%. There will be a loss.
Further, since the thin-walled sintered body has low mechanical strength, chipping or cracking is likely to occur at the time of processing impact or handling, resulting in low yield.

The magnetic characteristics are degraded. Nd ₂ Fe ₁₄ B
It has been reported in detail in various papers that the coercive force of the system sintered magnet depends on the existence of the Nd-rich phase in the grain boundary. When processing a sintered magnet of this system,
The stress causes cracks and the like in the crystal grain boundaries in the region close to the processed surface, and the coercive force is lost in the region from the processed surface to a depth of 0.1 to 0.2 mm. The loss of the magnet characteristics in the vicinity of the machined surface is negligible for the thick magnet, but has a large effect for the thin magnet, and the deterioration of the magnetic characteristics of the entire magnet becomes apparent. Although it is possible to remove the region where the coercive force disappears by processing by acid etching, the amount of loss of the sintered body further increases and the manufacturing cost also increases.

Under these circumstances, a thin anisotropic magnet having a longitudinal length / thickness of 10 or more is usually Sm-
Co-based bonded magnets are used, and high cost is a problem. Although there are RTB-based thin-walled sintered magnets, processing for size adjustment is indispensable, and the material yield at the time of processing is 20 to 30%, which also increases the cost. ing.

[0009]

DISCLOSURE OF THE INVENTION The present invention provides an RTB.
An object of the present invention is to provide an inexpensive thin-walled magnet by suppressing the dimensional change during sintering in the production of a system-based sintered magnet, thereby eliminating the need for grinding after sintering.

[0010]

These objects are achieved by the present invention described in (1) to (11) below. (1) A method for producing a sintered magnet containing R (R is at least one kind of rare earth element including Y), T (T is Fe, or Fe and Co) and B. A molded body having a density of 5.5 g / cm ³ or more, which is composed of magnet powder having an average particle diameter of 70 to 350 μm, has a density change of 0.
A method for producing a sintered magnet, comprising a step of sintering to a value of 2 g / cm ³ or more. (2) The method for producing a sintered magnet according to (1) above, which produces a sintered magnet having a density of 7.15 g / cm ³ or less. (3) The method for producing a sintered magnet according to the above (1) or (2), wherein a molded body having a bending strength of 0.3 kgf / mm ² or more is sintered. (4) The molding pressure is 8 t / cm ² or more (1) to
The method for manufacturing a sintered magnet according to any one of (3). (5) The method for producing a sintered magnet according to any of (1) to (4) above, wherein the holding temperature during sintering is 900 to 1100 ° C. (6) The manufactured sintered magnet has an R content of 27 to 40% by weight,
The method for producing a sintered magnet according to any one of (1) to (5) above, which contains 0.5 to 4.5% by weight of B and the balance is substantially T. (7) A sintered body containing R (R is at least one kind of rare earth element including Y), T (T is Fe, or Fe and Co) and B, and is not shaped after sintering. A magnet, having a parallel part, a value obtained by dividing the maximum length of the parallel part by its average thickness is 10 or more, and the difference between the maximum value and the minimum value of the thickness of the parallel part is When the value obtained by dividing the maximum length of the parallel portion is the thickness deviation, the thickness deviation is 1.
A sintered magnet characterized by being 5% or less. (8) Baking containing R (R is at least one kind of rare earth element including Y), T (T is Fe, or Fe and Co) and B, and not shaped after sintering. A magnet, having a cylindrical portion, wherein a value obtained by dividing the average outer diameter of the cylindrical portion by the average wall thickness is 10 or more, and the difference between the maximum value and the minimum value of the outer diameter of the cylindrical portion is A sintered magnet having an outer diameter deviation of 1.5% or less when a value divided by the average outer diameter is defined as an outer diameter deviation. (9) Baking containing R (R is at least one kind of rare earth element including Y), T (T is Fe, or Fe and Co) and B, which is not shaped after sintering. A magnet, having a cylindrical portion, a value obtained by dividing an average outer diameter of the cylindrical portion by its average wall thickness is 10 or more, and a difference between a maximum value and a minimum value of an inner diameter of the cylindrical portion is calculated. A sintered magnet having an inner diameter deviation of 1.5% or less when an inner diameter deviation is a value divided by the average inner diameter of the cylindrical portion. (10) A parallel part is provided, and a value obtained by dividing the maximum length of the parallel part by the average thickness thereof is 10 or more, and the difference between the maximum value and the minimum value of the thickness of the parallel part is the parallel part. The sintered magnet according to the above (8) or (9), wherein the thickness deviation is 1.5% or less when the value obtained by dividing by the maximum length of is the thickness deviation. (11) The sintered magnet according to any one of (7) to (10), which is manufactured by the method for manufacturing a sintered magnet according to any one of (1) to (6).

[0011]

[Operation and effect] The density of the conventional molded body for Nd ₂ Fe ₁₄ B sintered magnet is about 55% of the density (theoretical density: about 7.6 g / cm ³ ) assuming that there are no pores. 4.2g /
cm ³ ) and contains about 45% of holes. Then, since it is densified to about 99% of the theoretical density by sintering, the volumetric shrinkage rate becomes large.

On the other hand, in the present invention, high density (5.5
Since a molded body of g / cm ³ or more) is not completely sintered (the density after sintering is 7.15 g / cm ³ or less), the shrinkage rate during sintering becomes small. Therefore, even in the case of manufacturing a ring-shaped or plate-shaped thin-walled anisotropic magnet, processing for correcting the shape is unnecessary, and cost reduction and productivity improvement are realized. Moreover, since the high-density molded body has high bending strength,
It is easy to handle, and cracks and chips are less likely to occur between the molding process and the sintering process.

The magnetic properties {(BH) max = about 18 to 25 MGOe} of the sintered magnet manufactured according to the present invention have a conventional RT-
Although it is lower than that of the B-based high-density sintered magnet, it is higher than that of the Sm-Co-based bonded magnet {(BH) max = about 15 MGOe}. The raw material of the RTB magnet is cheaper than that of the Sm-Co magnet. Therefore, the sintered magnet manufactured according to the present invention is the Sm-Co conventionally used for a thin magnet.
It is suitable as a substitute for the system bonded magnet.

A method for producing a low-density porous sintered body without completely sintering the molded body is known as shown below, but these do not suggest the constitution of the present invention. Absent.

Japanese Patent Laid-Open No. 3-80508 discloses RFe.
In a method for producing a B-based magnet by a powder metallurgy method, magnet powder is press-molded and then made into a porous sintered body in a temperature range of 400 to 900 ° C., which is a molten alloy Nd _x Fe.
A method of immersing in _1-x (x = 0.65 to 0.85) for a certain period of time is disclosed. This method is intended to suppress the deformation after sintering due to the anisotropy of thermal contraction due to the magnetic field orientation. However, the Nd ₂ Fe ₁₄ B magnet powder used in the examples of the publication has a small diameter of about 10 μm,
Further, the publication does not describe the molding pressure, the density of the molded body, and the density of the porous sintered body after low temperature sintering.

Japanese Patent Laid-Open No. 55-15224 discloses Sm.
A method of impregnating a molded product with liquid plastic after pre-sintering the molded product at 400 to 900 ° C. when manufacturing a 2-17 series magnet such as ₂ Co ₁₇ or Pr ₂ Co ₁₇ is disclosed. This method aims to improve the strength of the magnet. In the examples of the publication, the shrinkage ratio when the particles of 5 to 30 μm were formed and sintered at 800 ° C. was 7%, and the shrinkage ratio when completely sintered at 1150 ° C. was about 12 to 30 μm. It is described that it was 15%. Then, it is described that the density after the temporary sintered body was immersed in an epoxy resin to be solidified was 6.80 g / cm ³ . However, the magnet described in the publication is Sm ₂
Unlike the composition targeted by the present invention that is a Co ₁₇ system,
Moreover, the publication uses small-diameter particles of 5 to 30 μm, and the publication does not disclose the density of the compact before pre-sintering.

Japanese Patent Application Laid-Open No. 62-281307 discloses N
d-Fe-B system alloy ingot 1000 ~ 1150 ℃
Solution treatment in the temperature range of 1., crushing the solution-treated ingot to a particle size of 200 μm or less, and annealing the crushed alloy powder compact in the temperature range of 500 to 1050 ° C., and the annealed compact There is disclosed a method of impregnating a plastic with a plastic to solidify it. In this way, 50
Annealing at 0 to 1050 ° C. is for removing crushing strain and improving coercive force. In the example of the publication, alloy powder having a small diameter (average particle diameter of 5 μm) is molded at low pressure (2 t / cm ² ) and then annealed. The publication does not disclose the density of the molded body or the density of the sintered body.

In Japanese Patent Laid-Open No. 63-114939, low melting point elements (Al, Zn, Sn, Cu, Pb, S, In,
At least one of Ga, Ge, Te) or a matrix material powder containing a high melting point element and a R ₂ T ₁₄ B-based magnetic powder are mixed to form a mixed powder, and the mixed powder is molded. A method for producing a composite-type magnet material is disclosed which includes a magnetizing step of magnetizing. As the magnetizing step, there is a step of molding and sintering the mixed powder, or a hot pressing step of applying hot pressing to the mixed powder to generate a molded body. Prior to hot pressing, preforming is preferably performed. The sintering temperature is higher than the melting point of the matrix material and lower than 1150 ° C., the hot pressing temperature is 300 to 1100 ° C., and the hot pressing pressure is 5 to 5.
It is 5000 kgf / cm ² . In this publication, the problem is to improve the dimensional yield, and the publication describes that the dimensional yield of the product can be improved by the hot forming method. However, in the examples of the publication, the densities after sintering or after hot pressing are all 7.1 g / cm ³ or more, and the density of the compact before sintering or before hot pressing. Is not disclosed. The average particle diameter of the R ₂ T ₁₄ B-based magnetic powder in the example of the publication is as small as 3 to 4 μm, and the particle diameter of the matrix material powder containing the low melting point element is at most 20 to 30 μm.
It has a small diameter of m. In the publication, there is a comparative example in which hot pressing is performed using Al having an average particle size of 100 μm as a matrix material. In this case, a dense magnet having a density of 7.5 g / cm ³ is obtained. . The pressure at the time of molding and the pressure at the time of preforming in the examples of the publication are both 1.5 t / cm ^2.
Below is small.

Japanese Unexamined Patent Publication (Kokai) No. 5-47528 discloses a method of manufacturing an anisotropic rare earth bonded magnet. In this method, first, a Nd-Fe-B magnet powder is mixed with a sintering inhibitor or a vaporizing agent, or the surface of the magnet powder is oxidized, and then the magnet powder is exposed to a magnetic field of 0.2 to 5 t / cm ^2.
Compress with the pressure of to make a green compact. Next, 50
It is fired at 0 to 1140 ° C. to make an anisotropic fired body having open pores, and heat-treated at 400 to 1000 ° C. Then
After impregnating the open pores with the resin, the resin is cured. In Tables 1 and 2 of the publication, various sintering inhibitors are added to 700 to 1
The density of the fired body (before resin impregnation) produced by firing at 060 ° C. is described, and all of them have a density of 6.9 g / cm ³ or less. However, in this publication, Nd-Fe-B is used.
The preferred average grain size of the alloy is stated to be 2 to 20 .mu.m, with 3.5 .mu.m fine powder being used in the examples. The publication does not describe the density of the green compact before firing, but the pressure applied during the green compact is as low as 0.2 to 5 t / cm ² , and a high-density molded body has not been obtained. Conceivable.
Also in these points, the method described in the publication is different from the present invention.

Japanese Unexamined Patent Publication (Kokai) No. 4-314307 discloses a method of manufacturing a bulk body for a bonded magnet by crushing an alloy containing a rare earth element, iron and boron as basic components, molding in a magnetic field, and then sintering. It is disclosed. In this method, by sintering at a temperature of 700 to 1000 ° C. for 3 hours or less,
A semi-sintered alloy bulk body having a density of 60-95% of theoretical density is produced. The semi-sintered alloy has a structure containing a large number of pores. The pores serve as nuclei for crack development and further for fracture, so that they can be easily crushed with a small stress. Therefore, the influence of mechanical strain during crushing is reduced. In the example of the publication, a fine powder having an average particle size of 3 μm is molded and then semi-sintered to manufacture a bulk body. In this example, neither the density of the molded body nor the shrinkage rate during semi-sintering is described. The invention described in the publication is different from the present invention in that a bulk body of a semi-sintered alloy is crushed to manufacture a bonded magnet. The density of the bulk body of the semi-sintered alloy in the example of the publication is 5.6 g / cm ³ or less, which is about the same as the density of the compact in the present invention. Therefore,
The bulk body of the semi-sintered alloy described in the publication has a too high porosity,
It cannot be used as a bulk magnet due to lack of magnetic properties and strength. That is, pulverization and bond magnetization are essential. Therefore, the coercive force is deteriorated and the manufacturing cost is increased.

Further, in JP-A-4-314315, a bulk body of a semi-sintered alloy described in JP-A-4-314307 is molded in a magnetic field, and then the molded body is impregnated with a resin to manufacture a bonded magnet. A method is disclosed. The magnetic field molding in this method serves both to crush and mold the bulk body of the semi-sintered alloy. In the publication, the bending strength of the conventional sintered body is 2.5 t / cm ² or more, whereas the bending strength of the bulk body of the semi-sintered alloy is very small, less than 1 t / cm ^2, and it is crushed. It is described that it is easy. In the example of the publication, fine powder having an average particle diameter of 3 μm is molded and semi-sintered in the same manner as in JP-A-4-314307 to obtain a density of 5.2 g /
A bulk magnet having a size of cm ³ or less is manufactured, further compression molded and impregnated with a resin to manufacture a bonded magnet having a density of 5.9 to 6.0 g / cm ³ . Since the bulk body of the semi-sintered alloy described in the publication is lower in density than the semi-sintered alloy disclosed in JP-A-4-314307, it cannot be used as a bulk magnet without compression molding and resin impregnation. Is. Therefore, the coercive force is deteriorated and the manufacturing cost is increased.

As described above, the structure of the present invention in which a high-density molded body is formed by using an alloy powder having a large particle size of 70 μm or more, and this is semi-sintered and used as a bulk magnet is conventionally used. It is not new and is not suggested by conventional methods utilizing semi-sintering.

In the conventional semi-sintered alloy as described above, S
Although there is an example in which a powder composed of particles of 30 μm is used in a 2-17 series magnet such as m ₂ Co _17, a magnet powder composed of small particles having an average particle size of about 3 μm is formed in an R ₂ T ₁₄ B series magnet. The body is semi-sintered. When semi-sintering a compact consisting of such small-sized particles, it is necessary to perform heat treatment at a lower temperature than when performing complete sintering. Changes drastically. That is, in order to manufacture a semi-sintered body having a predetermined density, strict temperature control is required, which increases manufacturing cost.

On the other hand, in the present invention, the average particle size is 7
A magnet powder of 0 μm or more is used. Since it is difficult to move particles through a liquid phase rich in rare earth elements in a compact composed of large particles, even if the holding temperature in the sintering process is high (for example, the conventional complete sintering temperature range), The sintering reaction does not proceed before sintering. For this reason, a predetermined low-density sintered body can be stably obtained in a wide temperature range, and the management of the sintering process becomes extremely easy. Further, since particles having a large diameter do not easily agglomerate, they are easy to handle and particularly easy to fill in a mold during molding.

[0025]

Specific Structure The specific structure of the present invention will be described in detail below.

In the present invention, a magnet powder compact is produced in the compacting step, the compact is sintered in the sintering step, and R (R is at least one of rare earth elements including Y), T A sintered magnet containing (T is Fe, or Fe and Co) and B is manufactured.

<Magnet Powder> The magnet powder preferably contains 27 to 40% by weight of R, 0.5 to 4.5% by weight of B, and the balance is substantially T.

R is Y, lanthanide or actinide. As R, at least one of Nd, Pr and Tb, particularly Nd, is preferable, and it is preferable that Dy is further contained. Also, La, Ce, Gd, Er, Ho, Eu,
One or more of Pm, Tm, Yb and Y may be included.
A mixture of misch metal or the like can be used as the raw material of the rare earth element. If the R content is too low, a phase rich in iron precipitates and high coercive force cannot be obtained, and if the R content is too high, high residual magnetic flux density cannot be obtained. R ₂ T ₁₄
In the B-based magnet, the R-rich phase becomes a liquid phase and flows to cause the sintering reaction to proceed. Therefore, in the present invention, it is preferable to reduce the R content in order to suppress the progress of the sintering reaction. Specifically, it is preferable that the content of R is 28 to 35% by weight, the content of B is 0.7 to 3% by weight, and the balance is substantially T.

If the B content is too small, a high coercive force cannot be obtained, and if the B content is too large, a high residual magnetic flux density cannot be obtained.

The amount of Co in T is preferably 30% by weight or less.

In order to improve the coercive force, Al, Cr, M
n, Mg, Si, Cu, C, Nb, Sn, W, V, Z
Elements such as r, Ti, and Mo may be added, but if the addition amount exceeds 6% by weight, the reduction of the residual magnetic flux density becomes a problem.

In addition to these elements, the magnet powder may contain unavoidable impurities or trace additives such as carbon and oxygen.

The magnet powder having such a composition has a main phase having a substantially tetragonal crystal structure, and the crystal grain boundary has
There is an R-rich phase with a higher R ratio than R ₂ T ₁₄ B.
The average crystal grain size of the magnet powder is not particularly limited. In the present invention, since it is anisotropy by magnetic field orientation, it is preferable that the crystal grain size is such that it becomes a single crystal grain when the grain size described later is used, but even if it is a polycrystalline grain, it is crystallized within the grain. Since the grains only need to be oriented, the average crystal grain size is, for example, 3
It can be selected from a wide range of about 600 μm.

The average particle size of the magnet powder is 70 μm to 35 μm.
The thickness is 0 μm, preferably 100 to 350 μm. If the average particle size is less than 70 μm, the above-described effect of increasing the particle size becomes insufficient. On the other hand, if the average particle size is too large, it becomes difficult to orient the magnetic field in a thin molded body. In addition,
The average particle diameter of the magnet powder is the diameter when an average projected area per magnet particle is calculated and converted into a circle. The method for measuring the projected area of the magnet particles is not particularly limited. For example, a dispersion of magnet powder can be applied on a glass plate so that the particles do not overlap each other, a photograph is taken, and the projected area of the particles can be determined from this photograph. In addition, the projected area of the particles can be obtained by scanning the coated object with a light beam and detecting the change in reflectance.

The method for producing the magnet powder is not particularly limited, and any method such as a method of pulverizing a casting alloy by hydrogen absorption pulverization or a reduction diffusion method may be used. A sintered magnet is pulverized into a powder. Good. By crushing a sintered magnet anisotropy by magnetic field orientation, it is possible to obtain large-sized polycrystalline particles consisting of oriented small-sized crystal grains, so that a magnet with high residual magnetic flux density and high coercive force can be obtained. To be

<Molding Step> In the molding step, the magnet powder is molded in a magnetic field to be 5.5 g / cm ³ or more, preferably 6.0.
A molded body having a density of g / cm ³ or more is produced. In the case of a compact having a low density, if sufficient magnet characteristics are to be obtained, the shrinkage rate at the time of sintering becomes large, and if the shrinkage rate at the time of sintering is made small, the magnet characteristics become insufficient. There is no particular upper limit to the density of the molded product, but it is difficult to achieve a density exceeding 6.4 g / cm ³ . For example, since an ultrahigh pressure of 20 t / cm ² or more is required at the time of molding, the molding apparatus and the mold are expensive, and the shape of the molded body is limited to a simple shape. The use of a large amount of organic lubricant is also effective for improving the compact density, but it is difficult to remove the organic lubricant before sintering, and residual carbon in the magnet deteriorates the magnet characteristics. I will end up. The density of the molded product can be calculated from the dimensions of the molded product measured with a micrometer or the like.

The molded article having such a high density has a bending strength of 0.3 kgf / mm ² or more, and further 0.5 kgf / cm ² or more, so that it is easy to handle, and cracks and chips are less likely to occur. Become.

The molding pressure is not particularly limited and may be appropriately determined so as to obtain a molded product having the above density, but is preferably 8 t / cm ² or more, more preferably 12 t / cm ² or more. The magnetic field strength during molding is usually 10 kOe or more, preferably 15 kOe or more.

The magnetic field applied during molding may be a DC magnetic field or a pulsed magnetic field, or may be a combination of these. The present invention can be applied to a so-called transverse magnetic field forming method in which a pressure applying direction and a magnetic field applying direction are substantially orthogonal to each other, and a so-called longitudinal magnetic field forming method in which a pressure applying direction and a magnetic field applying direction are substantially coincident with each other.

<Sintering Step> The molded body obtained as described above is sintered and magnetized.

The density of the sintered body is preferably 7.15 g / cm ³ or less. By molding with high pressure using large particles of about 200 μm, the density of the molded body can be increased to about 6.4 g / cm ^3, but it is difficult for such molded bodies to move particles during firing. Therefore, it is difficult to obtain a density exceeding 7.15 g / cm ³ even if it is fired at a high temperature.
On the other hand, when a compact having a density of about 5.8 g / cm ³ is formed by using small-diameter particles, if firing is performed until the density exceeds 7.15 g / cm ³ , the sintering proceeds excessively and the shrinkage rate is reduced. It gets bigger.

In the present invention, the value obtained by subtracting the density of the molded body from the density of the sintered body (the amount of change in density during sintering) is 0.2 g / cm ^3.
Sinter as described above. If the density change in the sintering step is too small, the sintering will be insufficient and the magnet characteristics and mechanical strength will be insufficient. In order to reduce the shrinkage rate, the density change amount is preferably 1.5 g / cm ³ or less, more preferably 1.2 g / cm ³ or less.

There are no particular restrictions on various conditions during sintering, and it may be appropriately selected so that the density change during sintering has a desired value. As described above, since the present invention uses large-diameter magnet particles, the holding temperature can be made higher than in the case of the conventional so-called semi-sintering. Specifically, 900-11
It is preferable to heat-treat at 00 ° C. for 0.5 to 10 hours to sinter, and then rapidly cool. The sintering atmosphere is preferably vacuum or a non-oxidizing gas atmosphere such as Ar gas.

<Others> After sintering, if necessary, an aging treatment is performed to improve the coercive force.

Since the magnet manufactured according to the present invention has a low density, holes are present inside. In order to improve the corrosion resistance of the magnet, it is preferable to close the holes open on the surface of the magnet. In order to close such holes, for example, the magnet may be dipped in a solution of a resin dissolved in an organic solvent and then dried. After such processing,
A usual anticorrosion coating may be provided by electrodeposition coating of resin, electroless plating, or the like.

The present invention is suitable for manufacturing thin-walled ring-shaped or plate-shaped magnets, which will be described later, and particularly for manufacturing thin-walled magnets having a thickness of 3 mm or less. If the magnet thickness is less than 0.5 mm, molding tends to be difficult.

<Dimensional Deviation> In the present invention, since a sintered magnet having an extremely small dimensional deviation can be obtained, it can be manufactured as a product without performing shape processing such as grinding after sintering.

That is, according to the present invention, there is a parallel portion, and the value obtained by dividing the maximum length of the parallel portion by the average thickness is 10
In the thin-walled sintered magnet as described above, the thickness deviation of the parallel portion can be 1.5% or less, and can easily be 1% or less, and the maximum length / average thickness is 15 or more. The thickness deviation of a thin magnet can be kept within such a range. The parallel part is a block sandwiched by two parallel surfaces facing each other, and the magnet having the parallel part is, for example, a plate magnet, a disk magnet, or a ring magnet. The thickness deviation of the parallel part is a value obtained by dividing the difference between the maximum value and the minimum value of the thickness of the parallel part by the maximum length of the parallel part. The thickness deviation of the parallel part is a value that is an index of the warp of the parallel part and the nonuniformity of the thickness, and in the case of the thin-walled sintered magnet having the above dimensional ratio, the warpage and the nonuniformity of the thickness are Since it becomes large, the thickness deviation is generally 2.5% or more.

Further, according to the present invention, in a thin-walled magnet having a cylindrical portion and a value obtained by dividing the average outer diameter of the cylindrical portion by the average wall thickness is 10 or more, the outer diameter deviation of the cylindrical portion and / or The inner diameter deviation can be 1.5% or less, and it is easy to set it to 1% or less. Even for a thin magnet having an average outer diameter / average wall thickness of 15 or more, the outer diameter deviation and / or the inner diameter deviation can be reduced. It is possible to fit within such a range. The cylindrical portion is a cylindrical block having an outer peripheral surface or an outer peripheral surface and an inner peripheral surface, and the magnet having the cylindrical portion is
For example, a ring-shaped magnet or a disc-shaped magnet, the outer diameter deviation and the inner diameter deviation in this case target a cylindrical portion having an outer peripheral surface and an inner peripheral surface. The outer diameter deviation of the cylindrical portion is a value obtained by dividing the difference between the maximum value and the minimum value of the outer diameter of the cylindrical portion by the average outer diameter, and the inner diameter deviation is the maximum value and the minimum value of the inner diameter of the cylindrical portion. Is the value obtained by dividing the difference of by the average inner diameter. The outer diameter deviation and the inner diameter deviation of the cylindrical portion are values that are an index of the warp and strain of the cylindrical portion and the nonuniformity of the wall thickness, and in the case of the thin-walled sintered magnet having the above dimensional ratio, the warp and strain, Since the unevenness of the wall thickness becomes large, conventionally, the outer diameter deviation and the inner diameter deviation are generally 3% or more.

Even in a thin-walled sintered magnet having a cylindrical portion having only an outer peripheral surface such as a disc magnet and having an average outer diameter / average thickness of 10 or more, further 15 or more, the deviation of the outer diameter of the cylindrical portion. Can be 1.5% or less, and can easily be 1% or less.

In the present specification, the thickness deviation of the parallel portion is measured as follows. First, the object to be measured is placed on the surface plate such that one surface forming the parallel portion is in contact with the surface plate. Then, the height from the surface plate surface of the other surface forming the parallel portion is measured at 20 points. Next, the object to be measured is turned over and placed on the surface plate so that the other surface is in contact with the surface of the surface plate, and the height is measured at 20 points in the same manner.
The measurement position divides the surface to be measured into 20 evenly,
It is set at the center point in each area. The difference (Tmax-Tmin) between the maximum value (Tmax) and the minimum value (Tmin) is determined from all the obtained measured values. This difference is the maximum value L of the lengths (lengths in the longitudinal direction) of the surfaces forming the parallel portion.
The value obtained by dividing by {(Tmax-Tmin) / L} is taken as the thickness deviation. The thickness deviation of a thin-walled magnet having two or more pairs of mutually parallel surfaces has a large value when both main surfaces are the one surface and the other surface. The average thickness in the description of the thin magnet may be the average of all the measured values obtained as described above.

The outer diameter deviation and the inner diameter deviation of the cylindrical portion are obtained as follows. First, the outer diameter or inner diameter of the cylindrical part,
The maximum value and the minimum value are obtained by continuously measuring in the axial direction of the cylindrical portion. At this time, the measured values in the range of 0.1 mm at both axial ends of the cylindrical portion are excluded. Next, after rotating the cylindrical portion by 15 ° about its axis, the same measurement is performed.
In this way, the measurement is repeated 12 times in total in the circumferential direction of 180 ° at 15 ° intervals. The maximum of the 12 maximums is φmax, and the minimum of the 12 minimums is φmi.
Let n be the value of φmax-φmin. Next, the average value φ ₀ of the average of 12 maximum values and the average of 12 minimum values is calculated, and φ
₀ is the average outer diameter or the average inner diameter. And {(φma
x −φ min) / φ ₀ } is the outer diameter deviation or the inner diameter deviation. The average outer diameter in the explanation of the dimension ratio of the thin magnet,
The above-mentioned φ ₀ may be used for the average inner diameter, and (average outer diameter−average inner diameter) / 2 may be used for the average wall thickness.

A non-contact type measuring device such as an optical type may be used for measuring the dimensional deviation, and a contact type three-dimensional measuring device, a contact type measuring device such as a micrometer or an inner circumference micrometer may be used. May be used.

[0054]

EXAMPLES The present invention will be described in more detail below by showing specific examples of the present invention.

Example 1 Sintered magnet samples shown in Table 1 were prepared.

First, alloy ingots having the compositions shown in Table 1 were manufactured by casting. The balance is Fe. The average crystal grain size of these alloy ingots was about 400 μm. Each alloy ingot was roughly crushed by utilizing the expansion / contraction of the volume due to the hydrogen absorption / degas reaction, and then crushed by a disk mill to obtain a magnet powder having an average particle size shown in Table 1. The average particle diameter of the magnet powder was determined by the method described above from the optical micrograph of the coating film of the magnet powder.

This magnet powder was molded in a magnetic field and had a diameter of 20 m.
A disk-shaped compact having a thickness of 1.5 mm and a thickness of 1.5 mm was obtained. Magnetic field strength is 1
The magnetic field was applied at 2 kOe and the axis of easy magnetization was in the thickness direction of the molded body. The molding pressure and the density of the molded body are shown in Table 1.
Shown in.

Each compact was sintered in a vacuum and then rapidly cooled. Table 1 shows the heat treatment temperature at the time of sintering and the time of keeping the temperature.

The density of each sintered magnet sample, the amount of change in density during sintering, the residual magnetic flux density (Br), and the coercive force (Hcj) are
It shows in Table 1. For the measurement of Br and Hcj, a magnetic property measurement sample prepared by sintering a compact having a diameter of 15 mm and a thickness of 10 mm was used. The manufacturing conditions of the samples for measuring magnetic properties were the same as those of the samples shown in Table 1 except for the size of the molded body.

[0060]

[Table 1]

Next, using a JIS class 1 surface plate, the thickness deviation was determined by the method described above. As a result, the density is 5.5.
In the sample of the present invention obtained by sintering a molded body of g / cm ³ or more so as to have a density of 7.15 g / cm ³ or less, the thickness deviation is remarkably small at 0.38% at the maximum, and nonuniformity during sintering is observed. There was very little warpage due to excessive shrinkage. The maximum length of the parallel portion in this case is the diameter of the sample. Thickness 1.5mm
If the thickness deviation is small in this thin-walled magnet,
It is possible to commercialize without dimensional modification by grinding. Moreover, as shown in Table 1, the samples of the present invention have obtained sufficient magnet characteristics.

On the other hand, in Comparative Sample No. 5, since the average particle diameter of the magnet powder was as small as 40 μm, the sintering progressed and the density change amount exceeded 1.5 g / cm ³ . In Comparative Sample No. 6, magnet powder having a large average particle diameter is used, but since the compact density is less than 5.5 g / cm ³ , the magnetic properties are insufficient and the density change amount is large. In Comparative Sample No. 9, since a compact having a normal density produced by using magnet powder composed of small-diameter particles is sufficiently sintered,
The magnetic properties are high, but the amount of change in density is extremely large. In these comparative samples, the thickness deviation was as large as 2.6% even at the minimum, and it was found that a large warpage occurred due to the non-uniform shrinkage during sintering. With such a large thickness deviation, commercialization is impossible. Comparative sample N
At o.10, sintering was insufficient and the density change was 0.02 g / c.
Since it is as small as m ³ , sufficient magnetic properties have not been obtained.

The molded product having a density of 5.5 g / cm ³ or more exhibited a sufficiently high bending strength of 0.45 kgf / mm ² or more. On the other hand, the molded body for producing sample No. 9 (density 4.5 g / cm ³ ) had a low bending strength of 0.15 kgf / mm ² .

From the above results, it is clear that the criticality of using a magnet powder having an average particle diameter of 70 μm or more and a compact density of 5.5 g / cm ³ or more.

Example 2 Sintered magnet sample Nos. 107 and 109 were produced in the same manner as Sample Nos. 7 and 9 of Example 1 except that the shape was a ring. The compact density is 6.22 g / in Sample No. 107.
cm ³ , the sample No. 109 has 4.48 g / cm ³ ,
Although slightly smaller than Sample Nos. 7 and 9, respectively, the amount of density change due to sintering was the same as that of Samples Nos. 7 and 9, respectively. The dimensions of the molded body were 30 mm in outer diameter, 27 mm in inner diameter, 1.5 mm in wall thickness and 7 mm in height, and a magnetic field was applied during molding so that the easy axis of magnetization was in the radial direction. For these ring-shaped sintered magnet samples,
The outer diameter deviation and the inner diameter deviation were measured by the method described above. At the time of measurement, each sample was placed on a JIS class 1 surface plate so that the outer peripheral surfaces were in contact with each other, and the outer diameter deviation was measured by a contact type three-dimensional measuring instrument, and the inner diameter deviation was measured by an inner circumference micrometer. As a result, sample No. 107 according to the present invention had an outer diameter deviation of 0.2% and an inner diameter deviation of 0.35%, which were extremely small values. No. 109 has an outer diameter deviation of 4.2% and an inner diameter deviation of 5
%, And commercialization was impossible.

Example 3 A molded product having a density of 5.95 g / cm ³ using magnet powder having an average particle size of 110 μm and a molded product having a density of 4.73 g / cm ³ using magnet powder having an average particle size of 12 μm. Were prepared, and the relationship between the heat treatment temperature and the sintered body density in the sintering process was investigated. The results are shown in Fig. 1. Note that FIG.
The holding time at the heat treatment temperature shown in was set to 2.5 hours.

It can be seen from FIG. 1 that the density of the sintered body greatly changes in response to the change in the heat treatment temperature in the low-density molded body using the small-diameter magnet powder. On the other hand, in the case of a high-density compact using a large-diameter magnet powder, the change in the density of the sintered compact is small even if the heat treatment temperature changes, and the sintering reaction hardly progresses especially at 1000 ° C or higher. It turns out that there is no need to manage.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between a heat treatment temperature and a sintered body density in a sintering process.

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display area H01F 1/08

Claims (11)

[Claims] 1. A method for producing a sintered magnet containing R (R is at least one of rare earth elements including Y), T (T is Fe, or Fe and Co) and B. Therefore, a molded body having a density of 5.5 g / cm ³ or more composed of magnet powder having an average particle diameter of 70 to 350 μm has a density change of 0.2 g / cm ^3.
A method for producing a sintered magnet, comprising a step of sintering so as to be cm ³ or more. 2. The method for producing a sintered magnet according to claim 1, wherein a sintered magnet having a density of 7.15 g / cm ³ or less is produced. 3. The method for producing a sintered magnet according to claim 1, wherein a molded body having a bending strength of 0.3 kgf / mm ² or more is sintered. 4. The molding pressure is 8 t / cm ² or more.
A method for manufacturing a sintered magnet according to any one of 3 to 3. 5. The holding temperature during sintering is 900 to 1100 ° C.
The method for producing a sintered magnet according to any one of claims 1 to 4. 6. The sintered magnet produced has an R of 27 to 40.
%, B is included in an amount of 0.5 to 4.5% by weight, and the balance is substantially T. The method for producing a sintered magnet according to claim 1. 7. R (R is at least one of rare earth elements including Y), T (T is Fe, or Fe and Co) and B, and is shaped after sintering. A sintered magnet which does not have a parallel part, and a value obtained by dividing the maximum length of the parallel part by its average thickness is 10 or more, and the maximum value and the minimum value of the thickness of the parallel part A sintered magnet having a thickness deviation of 1.5% or less when a value obtained by dividing the difference by the maximum length of the parallel portion is taken as a thickness deviation. 8. R (R is at least one of rare earth elements including Y), T (T is Fe, or Fe and Co) and B, and is shaped after sintering. A sintered magnet which does not have a cylindrical portion, and a value obtained by dividing the average outer diameter of the cylindrical portion by its average thickness is 10 or more, and the maximum and minimum values of the outer diameter of the cylindrical portion A sintered magnet having an outer diameter deviation of 1.5% or less when a value obtained by dividing the difference by the average outer diameter is defined as an outer diameter deviation. 9. R (R is at least one kind of rare earth element including Y), T (T is Fe, or Fe and Co) and B, and is shaped after sintering. A sintered magnet having a cylindrical portion, a value obtained by dividing the average outer diameter of the cylindrical portion by the average wall thickness is 10 or more, and the difference between the maximum value and the minimum value of the inner diameter of the cylindrical portion. The sintered magnet is characterized in that the inner diameter deviation is 1.5% or less when the value obtained by dividing by the mean inner diameter of the cylindrical portion is defined as the inner diameter deviation. 10. A parallel part, wherein a value obtained by dividing the maximum length of the parallel part by its average thickness is 10 or more, and the difference between the maximum value and the minimum value of the thickness of the parallel part is the When the thickness deviation is divided by the maximum length of the parallel part, the thickness deviation is 1.5
% Or less, The sintered magnet according to claim 8 or 9. 11. The sintered magnet according to claim 7, which is manufactured by the method for manufacturing a sintered magnet according to claim 1.