JP2015060999A - Nd-Fe-B-BASED SINTERED MAGNET HAVING INSULATOR LAYER AND PRODUCTION METHOD THEREFOR - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of producing a large Nd-Fe-B-based magnet, suitable for production of a large Nd-Fe-B-based magnet capable of preventing eddy current loss.SOLUTION: In a method of producing a large Nd-Fe-B-based magnet, a sintering mold has a thin plate for forming an insulator layer composed of ceramic powder not disappearing in the sintering process, and a Nd-Fe-B-based magnet having an insulator layer composed of ceramic powder is produced via the sintering process. The amount of ceramic powder composing the thin plate for forming an insulator layer is equal to or more than the natural filling density of the powder.

Description

The present invention relates to a relatively large Nd—Fe—B based sintered magnet, and relates to a Nd—Fe—B based sintered magnet having a small eddy current loss and a manufacturing technique thereof.

Nd-Fe-B sintered magnets are expected to increase in demand in the future as magnets for motors in hybrid vehicles and electric vehicles, or as magnets for wind power generators. In a rotating machine using these relatively large Nd—Fe—B sintered magnets, it is necessary to reduce eddy current loss generated in the sintered magnet during operation.

In order to reduce eddy current loss, a method is known in which small and finely divided unit magnets are bonded with an insulating adhesive to obtain an Nd—Fe—B sintered magnet having a desired size. However, since this method requires the production of a large number of magnets, the number of production steps increases, leading to an increase in production costs and a reduction in raw material yield.

  In order to solve this problem, after manufacturing an Nd-Fe-B sintered magnet having a required size and shape, a plurality of slits are provided on at least one surface of the magnet, and a non-adhesive such as an adhesive is provided in the slit. A method of filling a conductive substance has been proposed (Patent Document 1). In this method, since the slit is mechanically provided using a diamond cutter or the like, a large processing cost is required. In addition, the generation of cutting scraps associated with machining causes a reduction in raw material yield, resulting in an increase in raw material cost.

In addition, after manufacturing an Nd-Fe-B sintered magnet having the required size and shape, a plurality of slits are provided by machining on at least one surface of the magnet, and oxides of Dy and Tb are provided in these slits. A method of injecting fluoride or oxyfluoride and heating to high temperature has been proposed (Patent Document 2). Thereby, the coercive force of the Nd—Fe—B based sintered magnet can be enhanced by the electrical insulation in the slit and the grain boundary diffusion of Dy and Tb. In this method, it is also proposed to produce a sintered body having a slit by making a slit with a diamond cutter or the like after the production of the powder compact (green compact) and before the sintering step (Patent Document 2 [ 0025]).

  In order to reduce eddy current loss and to enable grain boundary diffusion treatment, a method of manufacturing a Nd-Fe-B sintered magnet having voids (slits) using void forming members has also been proposed. (Patent Document 3). In this method, Nd-Fe-B sintered magnet alloy powder is filled in a powder-filled container together with a gap forming member, the alloy powder is oriented in a magnetic field, and after orientation, the gap forming member is removed, and the alloy powder is powdered And heating the entire filled container to sinter the Nd—Fe—B based magnet alloy powder (Patent Document 3, Claim 1). Since machining is not required, it is simple and low cost.

JP 2000-295804 A JP 2007-053351 A International Publication WO2010 / 052862

There are several problems with the prior art.
The method of producing slits by machining using a diamond cutter or the like (Patent Documents 1 and 2) not only costs a lot of machining, but also reduces the yield of raw materials due to the generation of cutting waste. Incurs an increase.
If the slit is formed by machining the powder compact before sintering (Patent Document 2), the machining time can be shortened and the machining cost can be reduced. However, since the powder compact before sintering is brittle, there is a great loss of chipping or breakage during processing. In addition, oxidation of the powder compact proceeds during machining, which tends to cause a decrease in magnet characteristics as a sintered magnet after sintering.

The method using the air gap forming member (Patent Document 3) can overcome the above drawbacks. However, Nd-Fe-B sintered magnet alloy powder is filled in a powder-filled container together with a gap forming member, the alloy powder is oriented in a magnetic field, and then the gap is completely left, leaving the gap forming member mechanical. It is not easy to pull out and remove.

There has also been proposed a method in which a void forming member is made of a material that is liquefied or vaporized at a temperature lower than the sintering temperature, and the void forming member is removed before the sintering is started (Patent Document 3 [0015]). This method can avoid the difficulty of mechanically pulling out the gap forming member. However, there is a common big problem in the method of removing the void forming member before the sintering starts. Proceeding the sintering process of the powder compact without any gap forming member in the slit may cause uneven slit width, bending of the slit, or clogging of the slit during the shrinkage process during sintering. There is. Such a process that entails the risk of producing defective products should not be adopted as mass production technology. Sintering does not always proceed uniformly, and there is a risk that the slits may be clogged due to friction with the sintering base plate and the effect of gravity. Manufacturing methods with the risk of producing defective products must be avoided as mass production technology.

  The problem to be solved by the present invention is to solve the above-mentioned problems of the conventional method, and to provide an insulator layer that can efficiently suppress the generation of eddy current without greatly deforming or blocking in the sintering process. It is to provide a new Nd—Fe—B magnet manufacturing method.

The Nd—Fe—B based magnet manufacturing method according to the present invention made to solve the above problems includes (1) a step of filling a sintered mold with a powder of Nd—Fe—B based magnet alloy, and (2) A step of orienting the Nd-Fe-B-based magnet alloy powder in a magnetic field; and (3) heating the Nd-Fe-B-based magnet alloy powder together with the sintered mold to produce the Nd-Fe-B-based magnet. In the method for producing an Nd-Fe-B magnet, in which the step of sintering the alloy powder is performed in this order,
The sintered mold has an insulating layer forming thin plate composed of ceramic powder that does not disappear during the sintering process, and after the sintering process, Nd-Fe having an insulating layer composed of ceramic powder -Manufacturing B magnets.

In a rotating machine that uses a relatively large Nd—Fe—B sintered magnet, it is necessary to reduce the eddy current loss generated in the sintered magnet during operation. The insulator layer is a region for substantially subdividing the Nd—Fe—B based sintered magnet to prevent the generation of eddy currents. The insulator layer of the present invention is composed of ceramic powder.

A ceramic powder that does not evaporate at a sintering temperature of 900 to 1100 ° C. of the Nd—Fe—B sintered magnet is selected as the ceramic powder. Suitable ceramic powders are alumina, zirconia, titanium oxide, magnesia, graphite, barium titanate, rare earth oxide, rare earth fluoride, rare earth oxyfluoride, alkali metal fluoride, alkaline earth metal fluoride, etc. . As ceramic powder, flat powder such as talc and mica, needle-like powder such as aluminum borate, carbon powder, amorphous powder such as barium sulfate, aluminum borate whisker, calcium carbonate whisker, potassium titanate whisker needle powder Also suitable are fibrous materials such as carbon fibers and alumina fibers.

In addition to ceramic powders that do not change during the sintering process of Nd-Fe-B magnets, ceramic powders retain their properties as insulating powders even after modification, even if they are modified during the sintering process. If included, it is included in the ceramic powder referred to here. That is, the ceramic powder after the sintering process includes a modified substance obtained by modifying the original ceramic powder. An example of the ceramic powder to be modified is a case where initially Ca (OH) ₂ is used and then modified to CaO after sintering.

Many metal powders have a sufficiently low vapor pressure, but are electrically conductive and thus unsuitable for the purpose of forming an insulating layer. However, if the metal powder is added to the ceramic powder and the metal powder is added to the ceramic powder within the range in which the metal powder is not connected after the sintering process, an insulating layer is formed after the sintering. There is no. It is allowed to mix the metal powder with the ceramic powder as long as the electrical insulation of the insulating layer formed by adding the metal powder is ensured.

The insulator layer forming thin plate according to the present invention is made of ceramic powder. Nd-Fe-B based magnet alloy is filled with Nd-Fe-B magnet alloy powder in a sintering mold having an insulating layer forming thin plate made of ceramic powder, magnetic field orientation and sintering. In the powder filling, orientation, and sintering processes, the space for forming the insulating layer is made of ceramic powder. An insulator-forming thin plate is made of ceramic powder because an insulator layer is stably formed during filling, orientation, and sintering of Nd-Fe-B magnet alloy powder into a sintering mold. This means that the insulator-forming sheet holds ceramic powder as much as necessary.

One measure of the amount of ceramic powder that the insulator layered sheet should hold is the natural packing density of the powder. The natural packing density of the powder means an apparent density that is shown when the powder is naturally dropped and filled in a certain space. The natural packing density of the powder is usually about 20 to 40% of the theoretical density of the substance constituting the powder. When a space is composed of powder with a natural packing density, the space is dominated by the powder, and when the solid material surrounding the space tries to move or contract, the powder pre-filled in the space Therefore, the movement and contraction can be suppressed. After the powder is filled into a space by natural dropping, the apparent density of the powder is increased to 40% or more by adding vibration or tapping to the powder. When compressive force is applied to the filled powder, the apparent density of the powder is further increased to 50% or more.

In the insulator-forming thin plate, the ceramic powder is hardened with resin. When the resin simply bonds the particles constituting the powder, the amount of the resin contained in the insulator-forming thin plate is extremely small. When the resin fills the entire space contained in the powder, the amount of the resin is a value obtained by subtracting the apparent density of the ceramic powder in the insulator-forming thin plate from 100% by volume ratio. These resin components are almost completely evaporated and decomposed during the sintering process, but the space where the insulator-forming thin plate is placed is contained in the insulator layer-forming thin plate, even at high temperatures. Continue to be dominated by powder that does not disappear. That is, in the sintering process, the ceramic powder contained in the insulating layer forming thin plate is insulated with a predetermined width during the sintering shrinkage of the Nd-Fe-B magnet alloy powder filled in the sintering mold. It plays a role of stably forming a physical layer at a predetermined position.

For the insulator-forming thin plate, a method is adopted in which a mixture of ceramic powder and resin is placed in a mold and hardened. At this time, by increasing the amount of ceramic powder as much as possible, the reaction between the resin decomposition component during sintering and the Nd-Fe-B alloy powder is suppressed, and a high-quality Nd-Fe-B sintered magnet is produced. It becomes easy. A typical composition is 60:40 by volume ratio of ceramic powder to resin. When alumina powder is used as the ceramic powder and polyvinyl alcohol is used as the resin, the ratio of the alumina powder to the insulator-forming thin plate is 84% by weight, and when the oxide of Dy is used as the ceramic powder, ceramic The proportion of powder is 91% by weight. In these typical examples, the amount of ceramic powder exceeds the apparent density (more than 50%) of the compressed powder as described above. The density of the ceramic powder in the insulator-forming thin plate is equal to or higher than the apparent density of the powder as described above, and the upper limit is about 90%, which can hold the shape by solidifying the ceramic powder. Density.

  If the gap forming member is made of resin only (Patent Document 3 [0015]), the sintering process proceeds with leaving no slit, and the width of the slit is reduced during the shrinking process during sintering. There is a risk of causing unevenness, bending, and clogging of the slit. If the insulating layer forming thin plate is composed of ceramic powder, even if the resin that hardens the ceramic powder is consumed during the sintering process, the ceramic powder stays in the insulating layer, and Nd- The risk of non-uniform width of the insulator layer of the Fe-B magnet and loss of the insulator layer can be eliminated.

It is desirable that the sintered mold and the insulating layer forming thin plate be manufactured from the same material by integral molding. As the resin, a resin that easily evaporates, such as polyvinyl alcohol (PVA), a resin containing solid paraffin, or camphor, and the vapor hardly reacts with the Nd—Fe—B based magnet alloy powder is preferable.

  It is desirable that the insulating layer forming thin plate has a thickness of 1 mm or less, preferably 0.5 mm or less, and 0.05 mm or more.

  When using an Nd-Fe-B sintered magnet with an insulator layer produced by the above-mentioned method and inserting it into a hole formed in the rotor of an embedded magnet motor or generator and fixing it with resin, After the sintering, it is not necessary to apply special treatment to the insulating layer of the sintered body. However, for applications where stress is expected to be applied to the magnet, such as when a motor or generator is installed with a magnet having the above-described insulator layer, the insulator layer of these magnets is mechanically strengthened. It is desirable. In such a case, there is a possibility that an accident may occur due to a crack in the magnet starting from an insulator layer made of ceramic powder during operation of the motor or generator. In order to prevent such an accident, after manufacturing an Nd-Fe-B magnet having an insulator layer by the method of the present invention, a resin such as an epoxy resin or an adhesive is injected into the insulator layer, and the insulator It is desirable to increase the mechanical strength of the layer.

  In the manufacturing process of Nd-Fe-B sintered magnets, the use of an insulating layer forming thin plate made of ceramic powder that does not disappear during the sintering process greatly deforms the product during the shrinkage process during sintering. In addition, a high-performance Nd-Fe-B sintered magnet having an insulating layer can be manufactured stably and inexpensively without an incomplete insulating layer being formed.

  Insulator layer is effective in preventing eddy currents in large Nd-Fe-B sintered magnets and minimizing eddy current loss in motors and generators that use them. It is.

Diagram of the first example showing the three steps of Nd-Fe-B sintered magnet production Diagram of the second example showing the three steps of Nd-Fe-B sintered magnet production Diagram of the third example showing the three steps of manufacturing a Nd-Fe-B sintered magnet

Examples of the present invention are shown below, but the present invention is not limited to the examples. In each of the examples, the sintering molds were individually made as prototypes. However, in the case of mass production, it is natural that a large number of them should be manufactured by an injection molding method, a vacuum molding method, or a pressure molding method.

As rare earth sintered magnets, there are Sm—Co based sintered magnets in addition to Nd—Fe—B sintered magnets. The following examples are the results of Nd—Fe—B sintered magnets, but the technique of the present invention can also be applied to Sm—Co based sintered magnets.

For Nd-Fe-B sintered magnets, hydrogen is crushed by absorbing hydrogen in a strip cast alloy with a composition (weight fraction) of 31.5% Nd, 0.99% B, 0.1% Cu, 0.25% Al, and the balance Fe. A coarse alloy powder was obtained. The coarse powder was pulverized by a jet mill using nitrogen gas to produce a fine alloy powder for Nd-Fe-B sintered magnet. The particle size of the fine powder was measured by a laser diffraction / scattering method. The average particle size was D ₅₀ = 5.2 μm. To this fine powder, 0.1% by weight of zinc stearate powder as a lubricant was added and stirred and mixed with a mixer. Hereinafter, a sintered magnet was produced using this fine powder.

Three types of sintered molds as shown in FIGS. 1 (A), 2 (A) and 3 (A) were produced. The sintered mold of FIG. 1 (A) is a sintered mold for manufacturing a rectangular parallelepiped Nd—Fe—B sintered magnet in which insulator layers are alternately cut from the left and right. The sintered mold of FIG. 2 (A) is a sintered mold for producing a rectangular parallelepiped Nd—Fe—B sintered magnet having a spiral insulator layer. The sintered mold of FIG. 3 (A) is a sintered mold for producing a segment-shaped Nd—Fe—B sintered magnet bent in an arc shape, in which insulating layers are alternately cut from the left and right. .

An assembly mold having a cavity corresponding to the sintered mold of FIGS. 1 (A), 2 (A), and 3 (A) was made of polytetrafluoroethylene. Further, 84 g of alumina powder having an average particle size of 5 μm and 16 g of polyvinyl alcohol (PVA) were put into a beaker containing 100 g of water at 85 ° C. and stirred well to prepare an alumina powder slurry.
After injecting the alumina powder slurry into the polytetrafluoroethylene assembly mold, the whole was heated to 100 ° C. to evaporate water as much as possible. After cooling to room temperature, the sintered mold in which the alumina powder was hardened by PVA was taken out from the polytetrafluoroethylene assembly mold. In these sintered molds, the thicknesses of the insulating layer forming thin plate, the bottom plate portion, and the side portions were all 0.5 mm.

In order to reinforce the mechanical strength of the mold, the sintered mold support box made of resin (POM) was attached to the three types of sintered molds thus produced.
The above-described Nd—Fe—B sintered magnet fine powder containing lubricant was uniformly filled throughout the sintering mold until the filling density became 3.2 g / cm ³ . This state is shown in FIGS. 1B, 2B, and 3B.
Thereafter, a lid made of a graphite plate having a thickness of 3 mm was attached to the upper part of the sintering mold. The sintered mold filled with powder and covered was placed in a magnetic field orientation coil with the sintered mold support box attached, and a 5 T pulse magnetic field was applied in a direction perpendicular to the insulating layer forming thin plate. After magnetic field orientation, the sintered mold support box was removed.

Place the sintering mold filled with the above-mentioned Nd-Fe-B sintered magnet alloy fine powder on a stainless steel plate (sintering base plate) with a thickness of 3 mm and put it in the sintering furnace. It was. After the whole was evacuated, the temperature of the sintering furnace was increased. Hydrogen is introduced into the sintering furnace at the same time as the heating starts, and the pump exhaust rate and the hydrogen introduction rate are adjusted so that the hydrogen pressure is maintained at about 1 Pa. The temperature rose. The supply of hydrogen was stopped after holding at 500 ° C. for 1 hour in an atmosphere of 1 Pa of hydrogen pressure. While evacuating with a turbo molecular pump, the temperature was raised to 800 ° C. at a heating rate of 5 ° C./min, held at 800 ° C. for 1 hour, and then again raised to 1050 ° C. at a heating rate of 5 ° C./min. After holding at 1050 ° C. for 2 hours, heating was stopped and cooled to room temperature in a furnace.

The sintered body was gently taken out of the sintering furnace together with the sintered base plate. The sintered bodies produced from the sintering molds of FIGS. 1 (A), 2 (A) and 3 (A) are as shown in FIGS. 1 (C), 2 (C) and 3 (C), respectively. In addition, the insulating layer has a uniform width and no distortion. All the sintered bodies were high-quality sintered bodies having no distortion in the outer shape. The formed insulating layer had a width of about 0.4 mm and was composed of alumina powder. Although the outer peripheral part and the bottom part of the sintered mold were collapsed, some alumina powder was dissipated around the sintered body.

The density of each sintered body reached 7.54 g / cm ³ . These sintered bodies were heated to 800 ° C. in a vacuum, held for 1 hour, then rapidly cooled to room temperature, and then again heated to 500 ° C. in a vacuum, held for 1 hour, and then rapidly cooled to room temperature. A sample having a magnetic pole surface of 7 mm square and a magnetization direction of 5 mm was cut out from the sintered body subjected to such heat treatment, and magnetic measurement was performed using a pulse magnetization measuring instrument. As a result, the samples taken from all the sintered bodies had the same magnetic characteristics and had the following characteristics.
B _r = 14.1kG
H _cJ = 12.4kOe
(BH) _max = 48MGOe

In the sintered mold of FIG. 1 (A), the outer peripheral part and the bottom part were produced by processing sintered graphite, and the alumina layer and PVA were stirred in water in the same manner as in Example 1 for the insulating layer forming thin plate. It was produced by a method of hardening the slurry. However, the weight ratio of alumina powder to PVA was 91: 9. The thickness of each part of the sintered mold was 2 mm for the outer peripheral portion and the bottom plate portion, and 0.5 mm for the insulating region forming thin plate.

This sintered mold was filled with the same Nd—Fe—B sintered magnet alloy fine powder as in Example 1 in the same manner as in Example 1, and subjected to orientation in a magnetic field, and sintered under the same conditions as in Example 1. . As a result, a sintered body having an insulator layer could be produced without distortion of the insulator layer and without distortion of the outer shape. The insulator layer was composed of alumina powder. The magnet characteristics of the sintered body were evaluated in the same manner as in Example 1 and confirmed to be very good as in Example 1.

Claims (6)

(1) filling the sintered mold with Nd-Fe-B magnet alloy powder;
(2) a step of orienting the Nd—Fe—B based magnet alloy powder in a magnetic field;
(3) heating the Nd-Fe-B magnet alloy powder together with the sintering mold to sinter the Nd-Fe-B magnet alloy powder;
In the Nd-Fe-B based magnet manufacturing method for performing in this order,
The sintered mold has an insulating layer forming thin plate composed of ceramic powder that does not disappear during the sintering process,
A Nd-Fe-B magnet production method for producing an Nd-Fe-B magnet having an insulating layer composed of ceramic powder through the sintering process. 2. The method for producing an Nd—Fe—B magnet according to claim 1, wherein an amount of the ceramic powder constituting the insulating layer forming thin plate is equal to or higher than a natural packing density of the powder. The method for producing an Nd-Fe-B magnet according to claim 1 or 2, wherein the ceramic powder constituting the insulating layer forming thin plate is hardened with a resin. The Nd-Fe-B system according to any one of claims 1 to 3, wherein the ceramic powder is mixed with a metal powder within a range in which electrical insulation of the insulating layer is ensured. Magnet manufacturing method.   The method for producing an Nd-Fe-B magnet according to any one of claims 1 to 4, wherein the sintered mold and the insulating layer forming thin plate are integrally formed. 2. The method according to claim 1, wherein after the Nd-Fe-B magnet having the insulating layer composed of the ceramic powder is manufactured, another insulating material is additionally injected into the insulating layer composed of the ceramic powder. The method for producing a Nd-Fe-B magnet according to any one of claims 1 to 4.