JP2021086853A - Rare earth-iron based ring magnet and method for manufacturing the same - Google Patents

Abstract

To provide a method for manufacturing a rare earth-iron based ring magnet, which enables the improvement of the fillability when filling a mold with rare earth-iron based magnet powder and the improvement of the productivity, and which allows the rare earth-iron based ring magnet superior in magnetic property to be obtained.SOLUTION: A method for manufacturing a rare earth-iron based ring magnet comprises the steps of: pulverizing a magnetically isotropic rare earth-iron based magnet ribbon prepared by a super-rapid cooling method to obtain rare earth-iron based magnet powder; mixing the rare earth-iron based magnet powder with polystyrene to prepare a compound; filling a mold with the compound and applying a pressure thereto to mold a green body; and inserting the green body in a composite mold, setting the composite mold in a discharge plasma sintering (SPS) machine, and subsequently, heating the green body while applying a pressure to the green body under a reduced pressure to delipidize and sinter the green body, thereby obtaining the rare earth-iron based ring magnet.SELECTED DRAWING: Figure 1

Description

The present invention relates to a magnetically isotropic rare earth iron-based ring magnet and a method for producing the same.

Conventionally, with the miniaturization and higher performance of equipment, rare earth permanent magnets with high magnetic characteristics have been used for rotating equipment such as motors, general household appliances, acoustic equipment, in-vehicle equipment for automobiles, medical equipment, general industrial equipment, etc. It is used in a wide range of fields. As rare earth permanent magnets, there are magnets formed by mixing rare earth magnet powder and resin, so-called rare earth bond magnets. This rare earth bond magnet has a degree of freedom in molding, but since it uses a resin, which is an organic material, as a binder for binding the rare earth magnet powder, it has low heat resistance and is used in in-vehicle equipment in a high temperature environment. It may be difficult to use.

On the other hand, a method for producing a rare earth iron-based permanent magnet that bonds rare earth magnet powders to each other by discharge plasma sintering (SPS) without using a resin as an organic material has been proposed (for example, a patent). Refer to Documents 1 and 2).

In the method for producing a rare earth iron-based permanent magnet of Patent Documents 1 and 2, first, the rare earth element is 13 to 15 atomic%, Co is 0 to 20 atomic%, B is 4 to 11 atomic%, and the balance is Fe and unavoidable impurities. The cavity is filled with ultra-quenched rare earth iron-based flakes obtained by crushing the thin strip. Next, an aggregate of ultra-quenched rare earth iron-based flakes is compressed at a predetermined pressure under a predetermined reduced pressure and discharged plasma sintered. As a result, a rare earth iron-based permanent magnet can be obtained by bonding rare earth iron-based flakes to each other without using a resin. The rare earth iron-based permanent magnets obtained by the production methods of Patent Documents 1 and 2 do not use a resin as an organic material as a binder, and therefore have an advantage of higher heat resistance than rare earth bond magnets.

Japanese Unexamined Patent Publication No. 2-198104 Japanese Unexamined Patent Publication No. 3-284809

However, since the ultra-quenched rare earth iron flakes obtained by crushing the flakes produced by the ultra-quenched iron-based flakes have a flat shape, the ultra-quenched magnet powder, which is the ultra-quenched rare earth iron flakes, is used as a cavity. When filling, there is a problem that the fluidity and filling property are low. Therefore, an object of the present invention is to improve the filling property when filling the mold with the rare earth iron magnet powder, improve the productivity, and obtain the rare earth iron ring magnet having excellent magnetic properties. The purpose is to provide a method for manufacturing a ring magnet.

In order to solve the above-mentioned problems and achieve the object, the method for producing a rare earth iron-based ring magnet according to one aspect of the present invention is (a) magnetically isotropic rare earth iron produced by an ultra-quenching method. A step of crushing a system magnet strip to obtain a rare earth iron-based magnet powder, (b) a step of mixing the rare earth iron-based magnet powder and polystyrene to prepare a compound, and (c) a step of producing a compound. The steps of filling and pressurizing a mold to form a green body, and (d) inserting the green body into a composite mold, setting the composite mold in a discharge plasma sintering (SPS) apparatus, and then reducing the pressure. Below, the green body is heated while being pressurized to perform degreasing and sintering of the green body to obtain a rare earth iron-based ring magnet, and the rare earth iron-based magnet powder contains 13 at rare earth elements. Included in an amount of% or more and 19 at% or less.

According to one aspect of the present invention, a rare earth iron-based ring magnet having excellent magnetic properties can be obtained while improving the filling property when filling the mold with the rare earth iron-based magnet powder and improving the productivity.

FIG. 1 is a diagram for specifically explaining a method for manufacturing a rare earth iron-based ring magnet according to an embodiment. FIG. 2 is a diagram showing a change in fluidity with respect to the amount of calcium stearate. FIG. 3 is a diagram showing a change in the average number of hits with respect to the amount of calcium stearate. FIG. 4 is a diagram showing a magnetization curve. FIG. 5 is a diagram showing a demagnetization curve. FIG. 6 is a diagram showing a change in initial demagnetization with respect to the test temperature. FIG. 7 is a diagram showing a change in the ratio of coercive force to the amount of rare earth elements.

Hereinafter, a method for manufacturing a rare earth iron-based ring magnet and a rare earth iron-based ring magnet according to the embodiment will be described.

<Manufacturing method of rare earth iron ring magnet according to the embodiment>
The method for manufacturing a rare earth iron-based ring magnet according to the embodiment includes steps (a) to (d) described later. FIG. 1 is a diagram for specifically explaining a method for manufacturing a rare earth iron-based ring magnet according to an embodiment.

In the step (a), the magnetically isotropic rare earth iron magnet strip produced by the ultra-quenching method is crushed to obtain a rare earth iron magnet powder. Usually, the rare earth iron magnet strip is crushed and then classified to obtain a rare earth iron magnet powder. The rare earth iron-based magnet powder produced by the ultra-quenching method usually has a flat shape, and is preferably classified into a range of 53 μm or more and 150 μm or less. The obtained rare earth iron-based magnet powder is also magnetically isotropic.

The rare earth iron-based magnet powder preferably contains at least Nd as a rare earth element, and is, for example, an Nd-Fe-B-based magnet. The Nd-Fe-B magnet contains an Nd ₂ Fe ₁₄ B-type compound phase, which is a ternary tetragonal compound, as a main phase. Further, the Nd-Fe-B magnet usually further contains a rare earth rich phase (Nd rich phase) and the like. The Nd-Fe-B magnet may be used alone or in combination of two or more.

Rare earth iron-based magnet powder (specifically, Nd-Fe-B-based magnet) may contain rare earth elements other than Nd. Rare earth elements other than Nd include praseodymium (Pr), scandium (Sc), yttrium (Y), lantern (La), cerium (Ce), promethium (Pm), smarium (Sm), europium (Eu), and gadolinium (Eu). Gd), terbium (Tb), dysprosium (Dy), formium (Ho), erbium (Er), yttrium (Tm), yttrium (Yb) and lutetium (Lu). Rare earth elements other than Nd may be used alone or in combination of two or more.

In Nd-Fe-B magnets, Fe may be partially (usually less than 50 atomic%) substituted with Co. Further, the Nd-Fe-B based magnet may contain other elements. Other elements include titanium (Ti), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), tungsten (W), copper (Cu), gallium (Ga). Can be mentioned. Other elements may be used alone or in combination of two or more.

The rare earth iron-based magnet powder contains a rare earth element in an amount of 13 at% or more and 19 at% or less. The greater the amount of rare earth elements, the greater the amount of rare earth rich phases. In the method for producing a rare earth iron-based ring magnet according to the embodiment, a small amount of carbon derived from polystyrene mixed in the step (b) may remain in the obtained rare earth iron-based ring magnet. However, since a rare earth iron-based magnet having a large amount of rare earth rich phase is used, it is possible to suppress such a decrease in magnetic properties due to residual carbon. Specifically, as the amount of rare earth elements increases, the original coercive force can be increased, so that a sufficient coercive force can be maintained even if the coercive force is slightly lowered by the residual carbon. Further, as the amount of rare earth elements increases, the influence of residual carbon on the initial demagnetization and the square ratio is similarly suppressed. However, if the amount of the rare earth element exceeds 19 at%, the magnetization may be lowered too much, or the coercive force may be too large, and the magnetism may be lowered. On the other hand, if the amount of the rare earth element is less than 13 at%, the magnetic properties may be deteriorated at the time of sintering, and the deterioration of the magnetic properties due to the residual carbon may be insufficiently suppressed.

The rare earth iron-based magnet powder preferably has a coercive force of 1500 kA / m or more.

In step (b), the rare earth iron-based magnet powder and polystyrene are mixed to prepare a compound. Since polystyrene does not contain oxygen atoms, it is difficult to deteriorate the magnetic properties of the obtained rare earth iron-based ring magnet. Specifically, in the step (b), polystyrene is dissolved in an organic solvent to prepare a resin solution. Here, the organic solvent may be any solvent that can dissolve polystyrene and evaporate during drying, which will be described later. As the organic solvent, methyl ethyl ketone is preferably used. The rare earth iron-based magnet powder and this resin solution are kneaded. Next, the kneaded product obtained by kneading is dried, the organic solvent is evaporated, and then the kneaded product is crushed. The pyroclastic material obtained by crushing is classified to obtain a compound.

In the step (b), polystyrene is preferably mixed in an amount of 2 wt% or less, more preferably 1 wt% or more and 2 wt% or less, with respect to 100 wt% of the rare earth iron magnet powder. If the above amount exceeds 2 wt%, carbide may be generated in the step (d), the amount of residual carbon in the rare earth iron-based ring magnet may increase, and the magnetic characteristics may be excessively lowered. Further, if the above amount is less than 1 wt%, the improvement of the filling property in the step (c) may be insufficient.

The compound is preferably classified in the range of 75 μm or more and 355 μm or less. When classified into the above range, the filling property in the step (c) can be further improved.

In the step (c), the compound is filled in a mold and pressed to form a green body. The compound has higher fluidity than the magnet powder alone used to prepare the compound. Therefore, the compound is quickly filled into the mold. That is, the filling property can be improved by compounding. Since the filling time can be shortened, the productivity of the rare earth iron-based ring magnet can also be improved. Furthermore, damage to the mold due to magnetic powder can be suppressed.

During the compression molding in the step (c), it is preferable to apply a pressure of 200 MPa or more and 1000 MPa or less to the mold containing the compound. As a result, a green body in which the particles of the compound are in close contact with each other is obtained. Further, the compression molding in the step (c) is usually performed at room temperature.

The mold may be made of a material that can withstand the above pressure range. Since the composite mold used in the step (d) is for discharge plasma sintering (SPS), there is a concern that it will be deformed or damaged unless the pressure is lower than the above pressure range.

The shape and size of the mold shall be appropriately determined in consideration of the shape and size of the rare earth iron-based ring magnet to be finally produced so that a molded body having a preferable shape (ring shape) and size can be obtained. Can be done. For example, processing-less can be achieved by determining the size and weight of the molded product from the specifications of the finished product. That is, a net-shaped molded rare earth iron-based ring magnet can be manufactured. Further, it is preferable that the size of the molded product obtained in the step (c) is slightly smaller than the size of the composite mold used in the step (d). This has the advantage that it can be easily put into the composite mold.

When finally producing a thin rare earth iron-based ring magnet having a thickness of 0.8 mm or more and 2.5 mm or less, it is necessary to thinly fill the mold with the compound also in the step (c). Even in this case, in the present embodiment, the filling property is excellent because the compound is prepared in advance. On the other hand, the magnet powder alone is complicated because it requires more careful filling time.

In step (d), the green body is inserted into a composite mold, the composite mold is set in a discharge plasma sintering (SPS) apparatus, and then the green body is heated while being pressurized under reduced pressure. , The green body is degreased and sintered to obtain a rare earth iron-based ring magnet. In this way, with heating from room temperature, degreasing and sintering are continuously performed to obtain a rare earth iron-based ring magnet (bulk body).

In the present embodiment, since discharge plasma sintering (SPS) is performed after the molded product is formed in advance, it is easy to fill the composite mold with magnetic powder. Further, since discharge plasma sintering (SPS) is performed after the molded product is formed in advance, the heating efficiency can be improved, the sintering time can be shortened, and the sintering temperature can be lowered. As a result, in the obtained rare earth iron-based ring magnet, deterioration of magnetic properties such as coercive force and squareness can be suppressed. Further, when discharge plasma sintering (SPS) is performed using the magnet powder as it is as in the conventional case, an irregular current path may occur due to the sparse density of the magnet powder. As a result, local coarse particles are generated, and the initial demagnetization may be lowered, and the magnetic characteristics may vary. On the other hand, in the present embodiment, since the discharge plasma sintering (SPS) is performed after the molded product is formed in advance, the magnetic characteristics are less likely to vary and the quality can be improved. Further, since the discharge plasma sintering (SPS) is performed after the molded product is formed in advance, the height of the mold and the height inside the sintering apparatus chamber can be minimized.

Further, in the present embodiment, the die-earth iron-based ring magnet can be easily die-cut after the step (d). The same applies to a rare earth iron ring magnet having a thin thickness. It is considered that this is because the carbon released from the green body during the degreasing in the step (d) acts as a release agent. Further, the composite mold may be subjected to a mold release treatment before the green body is inserted, but since the mold can be easily removed as described above, the amount of the mold release agent can be reduced. Further, since the die can be easily cut out as described above, the die is less likely to get dirty, the labor for cleaning is reduced, and as a result, the life of the die is improved.

Since the green body is ring-shaped, carbon is easily removed during degreasing as compared with the columnar shape, and the amount of residual carbon in the rare earth iron-based ring magnet can be reduced.

Specifically, in the step (d), after setting the composite mold in the discharge plasma sintering (SPS) apparatus, ON-OFF DC pulse energization is performed on the green body. The current density is set, for example 250A / cm ² or more 1200A / cm ² below.

The heating may be performed up to a temperature at which the green body is degreased and the Nd-Fe-B magnet can form a liquid phase. For example, it is preferable to heat from room temperature to a temperature reached from 600 ° C. to 750 ° C. .. It is desirable that the holding time at the above reached temperature is within 5 minutes in order to suppress the growth of crystal grains.

In the step (d), the green body is heated while being pressurized, but it is preferable to heat the composite mold containing the green body while applying a pressure of 1 MPa or more and 200 MPa or less. The heating is preferably carried out in the following reduced pressure 10 ^-3 Pa or 10 ¹ Pa.

The rare earth iron ring magnet obtained by heating is usually cooled to room temperature or a temperature range in which it can be taken out. Cooling may be performed while applying pressure, or may be performed under reduced pressure.

As the composite mold, a composite mold (warm molding mold) in which ceramics and cemented carbide are combined is preferably used.

Further, a magnetizing step of magnetizing the rare earth iron-based ring magnet obtained in the step (d) may be performed. The magnetizing step can be performed by a known method. If necessary, a surface treatment step of applying a surface treatment (rust prevention treatment) to the rare earth iron ring magnet obtained in the step (d) is performed, and then the rare earth iron ring magnet after the surface treatment is magnetized. The magnetizing step may be performed. In the surface treatment step, for example, plating treatment of nickel (Ni), tin (Sn), zinc (Zn) and the like, aluminum (Al) vapor deposition, and surface treatment such as resin coating are carried out.

<Manufacturing method of rare earth iron ring magnet according to other embodiments>
The step (b) may be a step of mixing the rare earth iron-based magnet powder, polystyrene, and a lubricant to prepare a compound. In the step (b), the lubricant is the rare earth iron. The amount of 0.2 wt% or less may be mixed with respect to 100 wt% of the total of the system magnet powder and polystyrene. Further, it is more preferable to mix the lubricant in an amount of 0.05 wt% or more and 0.2 wt% or less with respect to 100 wt% of the total of the rare earth iron magnet powder and polystyrene. When a lubricant is used, the filling property in the step (c) can be further improved. If the above amount exceeds 0.2 wt%, carbide is generated in the step (d), and the amount of residual carbon in the rare earth iron-based ring magnet increases, which may cause a decrease in magnetic properties and a decrease in strength. .. Further, if the above amount is less than 0.05 wt%, further improvement of the filling property in the step (c) may be insufficient.

Specifically, the lubricant is mixed after the classification in the step (b) of FIG. That is, the lubricant is further mixed with the classified compound. In this case, in step (c), a compound mixed with a lubricant is filled in a mold and pressed to form a green body. As the lubricant, calcium stearate is preferably used.

<Rare earth iron ring magnet according to the embodiment>
The rare earth iron-based ring magnet according to the embodiment is a rare earth iron-based ring magnet obtained by discharging plasma-sintering a rare earth iron-based magnet powder, and the rare earth iron-based magnet powder is a magnetically isotropic ultra-quenching powder. It contains rare earth elements in an amount of 13 at% or more and 19 at% or less, and has a coercive force of 1500 kA / m or more. The rare earth iron ring magnet has a carbon content of 2000 ppm or less and an average crystal grain size of less than 200 nm. Here, the average crystal grain size is an average value obtained by observing the magnet structure with SEM or TEM and obtaining individual crystal grain sizes from the image.

The rare earth iron-based magnet powder preferably contains at least Nd as the rare earth element, for example. The details of the rare earth iron-based magnet powder are the same as those described in the method for manufacturing a rare earth iron-based ring magnet according to the embodiment.

The rare earth iron-based ring magnet according to the embodiment has excellent magnetic properties because the amount of carbon contained is suppressed.

The rare earth iron-based ring magnet according to the embodiment may have a thin thickness, for example, the thickness is in the range of 0.8 mm or more and 2.5 mm or less. The thinner the thickness, the easier it is to degreas. The outer diameter is, for example, in the range of 10 mm or more and 50 mm or less. The rare earth iron ring magnet according to the embodiment has a coercive force of, for example, 1200 kA / m or more and 1800 kA / m or less.

Such a rare earth iron-based ring magnet can be obtained, for example, by the method for producing a rare earth iron-based ring magnet according to the above-described embodiment.

By the way, in Japanese Patent Application Laid-Open No. 2013-191612, a compound is produced by mixing crushed magnet powder and a binder, and the produced compound is molded into a sheet to prepare a green sheet, and the green sheet is prepared. A manufacturing method has been proposed in which a rare earth permanent magnet is obtained by performing a calcining treatment at a binder decomposition temperature and then discharging a green sheet by discharge plasma sintering (SPS).

The rare earth permanent magnets of JP2013-191612 are Nd-Fe-B-based anisotropic magnet powders, which have Nd of 27 to 40 wt%, B of 0.8 to 2 wt%, and Fe of 60 to 70 wt%. Become. Then, the binder is mixed with the magnet powder to prepare a compound. The amount of the binder added is such that the ratio of the binder to the total amount of the magnet powder and the binder is 1 wt% to 40 wt%, more preferably 2 wt% to 30 wt%, and further preferably 3 wt% to 20 wt%. Subsequently, the compound is formed into a sheet to form a green sheet, the green sheet is heated above the glass transition point or melting point of the binder to soften the green sheet, and a magnetic field is applied to orient the green sheet. The easy-to-magnetize axis of the magnet included in is oriented in a predetermined direction. Then, the magnetic field-oriented green sheet is punched into a desired shape to form a molded product. Subsequently, the molded product is subjected to a calcining treatment in a non-oxidizing atmosphere (for example, a hydrogen atmosphere or a mixed gas atmosphere of hydrogen and an inert gas) to decompose the binder and degreas it. Then, the calcined compact is discharged plasma sintered (SPS) to obtain a rare earth permanent magnet.

In the method for producing a rare earth permanent magnet of Japanese Patent Application Laid-Open No. 2013-191612, the ratio of the binder is high because the magnetic field is oriented on the molded green sheet and the easily magnetized axis of the magnet contained in the green sheet is oriented in a predetermined direction (further). It is preferably 3 wt% to 20 wt%). Therefore, the degreasing treatment step of decomposing the binder takes time.

Further, a molded body obtained by punching a magnetic field-oriented green sheet into a desired shape is formed. This molded product is subjected to calcining treatment in a non-oxidizing atmosphere (for example, a hydrogen atmosphere or a mixed gas atmosphere of hydrogen and an inert gas) to decompose and degrease the binder, but the hydrogen atmosphere or a mixture of hydrogen and an inert gas is performed. It is necessary to perform the calcining treatment using hydrogen in a gas atmosphere, and sufficient caution is required for safety, and equipment for that purpose is also required.

The magnetic powder of JP2013-191612A is an anisotropic magnet, and an ingot of a magnet alloy is roughly pulverized by a stamp mill, a crusher or the like. Alternatively, the ingot is melted, flakes are produced by a strip casting method, and coarsely pulverized by a hydrogen crushing method to obtain a coarsely pulverized magnet powder. On the other hand, in the present embodiment, since the magnet powder uses the magnetically isotropic ultra-quenching powder produced by the ultra-quenching method, both magnets produced by discharge plasma sintering (SPS) are used. The average crystal grain size is different. In the magnetic powder of JP2013-191612, since the ingot is melted and flakes are produced by the strip casting method, the cooling rate is slower than that of the ultra-quenched powder, so that the average crystal grain size of the magnetic powder becomes large. As a result, the average crystal grain size of the magnet produced by discharge plasma sintering (SPS) also increases.

Moreover, the present invention is not limited by the above-described embodiment. The present invention also includes a configuration in which the above-mentioned constituent elements are appropriately combined. Further, further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspect of the present invention is not limited to the above embodiment, and various modifications can be made.

[Example]
[Example 1-1]
Using a free crusher (type M-2, manufactured by Nara Kikai Seisakusho Co., Ltd.), Nd-Fe-B magnet powder (amount of rare earth elements: 13.8 at%, coercive force: 1500 kA / m or more, ultra-quenched powder ) Was pulverized and classified into the range of 53 μm to 150 μm.
To 200 g of the classified magnet powder, 4 g of polystyrene dissolved in 20 g of methyl ethyl ketone (MEK) was added in advance, and the mixture was kneaded with a lab mill for 15 minutes while exhausting air in a draft chamber to obtain a kneaded product.
The kneaded product was placed in an oven heated to 80 ° C. and dried for 30 minutes to volatilize MEK. The powder obtained by volatilizing MEK was crushed in a mortar and classified into 75 μm to 355 μm by a dry sieve to obtain a compound.
The compound was filled in a ring-shaped mold having a thickness of 16.2 mm and an outer diameter of 12 mm, and powder compression molding was performed by applying a pressure of 500 MPa to mold a green body. The molded green body is inserted into a composite mold that combines ceramics and cemented carbide, and is pulsed under reduced pressure while being evacuated to about ^{10-3 Torr with a rotary pump using a discharge plasma sintering (SPS) device.} Current current sintering was performed. Specifically, degreasing and sintering were performed by heating the temperature from room temperature to around 700 ° C. while applying a pressure of 120 MPa.
After cooling, the mold was released to obtain a rare earth iron ring magnet.

[Example 1-2]
To 200 g of the compound prepared in the same manner as in Example 1-1, 0.1 g of calcium stearate powder was added and mixed in a mortar to obtain a compound.

[Example 1-3]
To 200 g of the compound prepared in the same manner as in Example 1-1, 0.4 g of calcium stearate powder was added and mixed in a mortar to obtain a compound.

[Comparative Example 1-1]
Using a free crusher (type M-2, manufactured by Nara Kikai Seisakusho Co., Ltd.), Nd-Fe-B magnet powder (amount of rare earth elements: 13.8 at%, coercive force: 1500 kA / m or more, ultra-quenched powder ) Was pulverized and classified into the range of 53 μm to 150 μm. The above magnet powder was used as it was without being compounded.

[Comparative Example 1-2]
Using a free crusher (type M-2, manufactured by Nara Kikai Seisakusho Co., Ltd.), Nd-Fe-B magnet powder (amount of rare earth elements: 13.8 at%, coercive force: 1500 kA / m or more, ultra-quenched powder ) Was pulverized and classified into the range of 53 μm to 150 μm.
To 200 g of the classified magnet powder, 4 g of cellulose acetate dissolved in 20 g of methyl ethyl ketone (MEK) was added in advance, and the mixture was kneaded with a lab mill for 15 minutes while exhausting in a draft chamber to obtain a kneaded product.
The kneaded product was placed in an oven heated to 80 ° C. and dried for 30 minutes to volatilize MEK. The powder obtained by volatilizing MEK was crushed in a mortar and classified into 75 μm to 355 μm by a dry sieve to obtain a compound.
A rare earth iron-based ring magnet was obtained in the same manner as in Example 1-1 except that the above compound was used.

[Comparative Example 1-3]
To 200 g of the compound prepared in the same manner as in Comparative Example 1-2, 0.1 g of calcium stearate powder was added and mixed in a mortar to obtain a compound.

[Comparative Example 1-4]
To 200 g of the compound prepared in the same manner as in Comparative Example 1-2, 0.4 g of calcium stearate powder was added and mixed in a mortar to obtain a compound.

[Comparative Example 1-5]
A compound was obtained in the same manner as in Comparative Example 1-2, except that 1 g of cellulose acetate dissolved in 5 g of MEK was added to 200 g of the magnet powder in advance.
A rare earth iron-based ring magnet was obtained in the same manner as in Example 1-1 except that the above compound was used.

[Comparative Example 1-6]
To 200 g of the compound prepared in the same manner as in Comparative Example 1-5, 0.1 g of calcium stearate powder was added and mixed in a mortar to obtain a compound.

[Comparative Example 1-7]
To 200 g of the compound prepared in the same manner as in Comparative Example 1-5, 0.4 g of calcium stearate powder was added and mixed in a mortar to obtain a compound.

<Fillability (fluidity)>
The fluidity of the compound prepared by the above procedure was measured with an orifice diameter of Φ2.5 mm based on JISZ-2502. The results are shown in Table 1.

2 and 3 are graphs of the average values of the results in Table 1. That is, FIG. 2 is a diagram showing a change in fluidity with respect to the amount of calcium stearate. Further, FIG. 3 is a diagram showing a change in the average number of hits with respect to the amount of calcium stearate.

While the bridge cannot be unraveled and cannot be measured with only the magnet powder, the compounded one can unravel the bridge by impact and measure the fluidity. Further, it can be seen that by increasing the amount of calcium stearate mixed, the generation of bridges is suppressed and the fluidity is improved.

Further, the produced compound was filled in a ring-shaped mold having an outer diameter of 16 mm, an inner diameter of 11.92 mm, and a height of 40 mm, and pressed at 38 kN. As a result, a ring-shaped green body could be obtained. It could be easily inserted into a pressure sintering mold having an outer diameter of 16.2 mm, an inner diameter of 12 mm and a height of 40 mm.

<Magnetic characteristics>
The relative density and magnetic characteristics of the rare earth iron-based ring magnets produced in Example 1-1, Comparative Examples 1-2, and 1-5 were measured. The results are shown in Table 2. Further, FIG. 4 is a diagram showing a magnetization curve. The magnetization curve was measured with a BH curve tracer.

When cellulose acetate is used as a binder, if 2 wt% is added as in Comparative Example 1-2, the magnetic properties are greatly impaired and a snake-shaped magnetization curve is obtained, which is not practical. In the case of Comparative Example 1-5 in which the addition amount was suppressed to 0.5 wt%, the deterioration of the magnetic characteristics was suppressed, but the strength of the green body was not sufficient with the binder amount of 0.5 wt%. In Example 1-1 in which polystyrene, which is a resin containing no oxygen in the molecular structure, was used as the binder, better magnetic properties than in Comparative Example 1-5 were obtained even though 2 wt% was added. ..

[Example 2-1]
Compounds and rare earths in the same manner as in Example 1-1, except that Nd-Fe-B magnet powder (amount of rare earth elements: 14.5 at%, coercive force: 1500 kA / m or more, ultra-quenched powder) was used. An iron-based ring magnet was obtained.

[Example 2-2]
Nd-Fe-B magnet powder (amount of rare earth elements: 19.0 at%, amount of added elements (Nb, Cu, Ga): 0.5 at% each, coercive force: 1500 kA / m or more, ultra-quenched powder) A compound and a rare earth iron-based ring magnet were obtained in the same manner as in Example 1-1 except for those used.

[Comparative Example 2-1]
Compounds and rare earths in the same manner as in Example 1-1, except that Nd-Fe-B magnet powder (amount of rare earth elements: 12.8 at%, coercive force: 1500 kA / m or more, ultra-quenched powder) was used. An iron-based ring magnet was obtained.

<Magnetic characteristics>
The magnetic characteristics of the rare earth iron ring magnet produced by the above procedure were measured. FIG. 5 is a diagram showing a demagnetization curve. FIG. 6 is a diagram showing a change in initial demagnetization with respect to the test temperature. Further, FIG. 7 is a diagram showing a change in the ratio of coercive force to the amount of rare earth elements. In the initial demagnetization, the amount of magnetic flux is measured before and after exposure to the environment at 120 ° C. for 1 hour, and the amount of demagnetization is calculated with the amount of magnetic flux before exposure to the test temperature as 100. The same measurement was performed at 150 ° C., 180 ° C. and 200 ° C.

From FIG. 5, in Comparative Example 2-1 having the smallest amount of rare earths, the coercive force was significantly reduced, but in Examples 1-1, 2-1 and 2-2 having a large amount of rare earths, polystyrene was mixed in an amount of 2 wt%. However, it can be seen that the coercive force is maintained to some extent. In particular, in Example 2-2, polystyrene is mixed in an amount of 2 wt%, but the decrease in coercive force is only about 10%. Further, in spite of the inclusion of foreign matter, all of Examples 1-1, 2-1 and 2-2 maintain the square shape.

From FIG. 6, the initial demagnetization is the smallest in Example 2-2 having the largest coercive force, and is increased by only about 1% from the initial demagnetization in the case of only the magnet powder. The initial demagnetization at 200 ° C. is also 5% or less, and has high heat resistance. The initial demagnetization of Examples 1-1 and 2-1 is increased by about 10% as compared with the case of using only the magnet powder, and the difference is large as compared with Example 2-2. Further, in Comparative Example 2-1 having the smallest amount of rare earths and the smallest coercive force, the initial demagnetization was the largest, exceeding 30%. The cause is that the coercive force becomes too small due to the inclusion of foreign matter.

FIG. 7 shows the rare earth amount dependence of HcJ ratio. Here, HcJ ratio is the ratio of the coercive force when only the magnet powder is sintered to the coercive force when 2 wt% of polystyrene is mixed and sintered. From FIG. 7, it can be seen that as the amount of rare earth increases, the HcJ ratio increases and the decrease in coercive force is suppressed. When the amount of rare earth is 15 at% or more, HcJ ratio is 0.6 or more. Further, when the amount of rare earth is 15 at% or more, the original coercive force is also large, so that the coercive force after the decrease is also sufficiently large.

From the above, by increasing the amount of rare earths, it is possible to mitigate the influence when foreign matter is mixed in, and it is possible to suppress the deterioration of magnetic characteristics. In addition, the sinterability is also improved by increasing the amount of rare earths. In other words, the productivity of rare earth magnets is improved because the assumption that only magnet powder is used can be changed by making the sintering conditions rough and allowing foreign matter to enter to some extent.

<Carbon content, average crystal grain size>
The carbon content and average crystal grain size of the rare earth iron-based ring magnets obtained in the examples were measured. Each of the rare earth iron-based ring magnets had a carbon content of 2000 ppm or less and an average crystal grain size of less than 200 nm. The carbon content was measured by the combustion method using a CS analyzer.

Claims (6)

A rare earth iron ring magnet obtained by discharging plasma sintering of rare earth iron magnet powder.
The rare earth iron-based magnet powder is a magnetically isotropic ultra-quenching powder, contains rare earth elements in an amount of 13 at% or more and 19 at% or less, and has a coercive force of 1500 kA / m or more.
The rare earth iron ring magnet has a carbon content of 2000 ppm or less and an average crystal grain size of less than 200 nm.
Rare earth iron ring magnet. The rare earth iron-based magnet powder contains at least Nd as the rare earth element.
The rare earth iron ring magnet according to claim 1. (A) A step of crushing a magnetically isotropic rare earth iron magnet strip produced by an ultra-quenching method to obtain a rare earth iron magnet powder.
(B) A step of mixing the rare earth iron-based magnet powder and polystyrene to prepare a compound.
(C) A step of filling a mold with the compound and pressurizing the compound to form a green body.
(D) The green body is inserted into a composite mold, the composite mold is set in a discharge plasma sintering (SPS) apparatus, and then the green body is heated while being pressurized under reduced pressure to obtain the green body. Including the process of degreasing and sintering the body to obtain a rare earth iron ring magnet.
The rare earth iron-based magnet powder contains a rare earth element in an amount of 13 at% or more and 19 at% or less.
A method for manufacturing a rare earth iron ring magnet. The rare earth iron-based magnet powder contains at least Nd as the rare earth element.
The method for producing a rare earth iron-based ring magnet according to claim 3. In the step (b), the polystyrene is mixed in an amount of 2 wt% or less with respect to 100 wt% of the rare earth iron magnet powder.
The method for producing a rare earth iron-based ring magnet according to claim 3 or 4. The step (b) is a step of mixing the rare earth iron-based magnet powder, the polystyrene, and the lubricant to prepare a compound.
In the step (b), the lubricant is mixed in an amount of 0.2 wt% or less with respect to 100 wt% of the total of the rare earth iron magnet powder and the polystyrene.
The method for producing a rare earth iron-based ring magnet according to any one of claims 3 to 5.

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