JP2002305122A - Method of manufacturing rare-earth sintered magnet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a mounting plate for sintering and a molded material from being welded together, and to prevent the molded material from being broken, accompanying its shrinkage in a sintering process at the manufacturing of a rare-earth sintered magnet. SOLUTION: A method of manufacturing a rare-earth sintered magnet comprises the process for orientating and compressing rare-earth alloy powder in a magnetic field to form a molded material 2, the process for preparing a mounting plate 4 for sintering having the main surface of degree Ra of roughness of a surface of higher than 1 μm to lower than 45 μm, the process for putting the molded material 2 on the main surface of the mounting plate 4 for sintering, so that the orientation direction of the molded material 2 becomes substantially parallel to the main surface of the plate 4, and the process for sintering the molded material 2 put on the main surface of the plate 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a rare earth sintered magnet, and more particularly to a method for sintering a rare earth alloy powder compact on a sintering base plate. The present invention relates to a method for manufacturing a magnet.

[0002]

2. Description of the Related Art Sintered rare earth magnets are produced by subjecting an alloy powder obtained by pulverizing an alloy for a rare earth magnet (raw material alloy) to press forming, followed by a sintering step and an aging step. At present, two types of rare earth sintered magnets, samarium / cobalt magnets and neodymium / iron / boron magnets, are widely used in various fields. Among them, neodymium / iron / boron-based magnets (hereinafter referred to as "RT- (M) -B-based magnets", where R is a rare earth element containing Y, and T is Fe
Transition metal elements including (iron) and Co (cobalt), B
Is boron, M is Al, Ti, Cu, V, Cr, Ni, G
a, Zr, Nb, Mo, In, Sn, Hf, Ta, W, etc.) have the highest magnetic energy products among various magnets, and are relatively inexpensive. Actively employed.

In a sintering process for producing a magnet, a compact (compact) produced using a press machine is formed from a high heat-resistant high melting point metal material such as stainless steel or molybdenum. It is put into the sintering furnace while being placed on the binding base plate. The compact placed in the sintering furnace is heated at a high temperature (for example, 1000 to 1100) in an inert gas atmosphere.
° C). The heated compact is subjected to liquid phase sintering with shrinkage, whereby a rare earth sintered magnet is obtained.

When sintering, if the compact is directly mounted on the sintering base plate, the formed body and the sintering base plate may be locally welded. This is because a rare earth element such as Nd, which is a main component of the RT- (M) -B based magnet, and a metal element contained in the sintering base plate undergo a eutectic reaction at a temperature lower than the sintering temperature. Because it wakes up. When the sintering base plate and the compact are locally welded, the compact does not smoothly contract due to sintering, and cracks or chips occur in the sintered compact. Also,
Even when welding is not performed, the friction between the base plate for sintering and the molded body (sintered body) becomes uneven, so that the molded body may be cracked on the side in contact with the base plate. is there. Further, if the eutectic reaction product adheres to the sintering base plate, there is a problem that when the sintering base plate is reused, it takes time to remove the deposits from the base plate.

[0005] In order to prevent such welding between the sintering base plate and the compact, a method of laying powder on the sintering base plate, placing the compact thereon, and performing sintering has conventionally been used. (For example, Japanese Patent Application Laid-Open No. 4-154903).
As the laying powder, a powder formed of a material having low reactivity with a molded body and good stability at high temperatures is used. When the compact contains a rare earth metal, the litter is formed of a material having low reactivity with the rare earth metal such as a rare earth oxide (for example, yttria or neodymium oxide).
A powder of about μm to 100 μm is used. Use of laying powder can prevent welding between the base plate and the molded body,
It is possible to prevent breakage or deformation of a crack or the like generated at the contact portion of the rare earth magnet with the base plate.

[0006]

However, in the method using the litter as described above, the following problems occur particularly when the size of the compact is large and the unit weight (mass of the compact) is heavy. There was something.

When the compact is placed on the sintering base plate on which the laying powder is arranged, the laying powder digs into the compact and the laying powder adheres to the surface of the sintered body obtained after sintering. If the litter is attached to the surface, the surface of the obtained sintered body needs to be polished to remove the litter, which is not preferable.

[0008] Further, in the state where the spreading powder is biting into the compact as described above, when the compact shrinks during sintering,
The effect of reducing the sliding friction with the base plate for sintering cannot be sufficiently obtained. Furthermore, since it is difficult to evenly spread the laying powder on the sintering base plate, the sintering base plate and the compact (sintered body)
In addition, there is also a problem that the sliding friction between the two becomes uneven, which causes stress to act on the molded body. In the case of a compact having a large size and a unit weight of, for example, 10 g or more, the stress received from the sintering base plate during shrinkage is greater than that of a compact having a unit weight of several g or less. Therefore, there is a high possibility that cracks or chips are generated in the compact during sintering.

[0009] When the compact shrinks greatly on the sintering base plate, the above-mentioned compact is particularly likely to be damaged. When the compact is oriented in a strong magnetic field such as 0.8 MA / m, the compact during sintering has an orientation of 20 to
It shrinks by as much as 30%. In other directions (for example, a direction perpendicular to the orientation direction), the shrinkage is only about 10 to 18%. Therefore, when the orientation direction of the compact is arranged parallel to the main surface of the sintering base plate, the compact shrinks greatly on the base plate, so that the sliding friction therebetween is appropriately adjusted. Needed.

The present invention has been made in view of the above points, and a main object of the present invention is to provide a method of manufacturing a rare earth sintered magnet capable of reducing cracks and chips generated during sintering and thereby improving the manufacturing yield. Is to provide.

[0011]

A method for manufacturing a rare earth sintered magnet according to the present invention comprises the steps of: forming a compact by orienting and compressing a rare earth alloy powder in a magnetic field; and forming a compact having a surface roughness Ra of 0.7 μm. A step of preparing a sintering base plate having a main surface of not less than 45 μm or less, and firing the formed body so that the orientation direction of the formed body is substantially parallel to the main surface of the sintering base plate. The method includes a step of placing the compact on the main surface of the binding base plate and a step of sintering the compact placed on the main surface of the sintering base plate.

In a preferred embodiment, the unit weight of the molded body is 10 g or more.

[0013] In a preferred embodiment, the length of the molded body along the orientation direction is 20 mm or more.

In a preferred embodiment, in the step of sintering, the length of the compact shrinks by 20% or more along the orientation direction on the main surface of the sintering base plate.

In a preferred embodiment, in the step of manufacturing the compact, an orientation direction for orienting the rare earth alloy powder in a magnetic field and a pressing direction for compressing the rare earth alloy powder are substantially orthogonal to each other.

In a preferred embodiment, the rare earth alloy powder is produced by grinding a rare earth alloy produced by a quenching method.

In a preferred embodiment, the number of fine particles of 1.0 μm or less contained in the rare earth alloy powder is adjusted to 10% or less of the total number of particles in the powder.

In a preferred embodiment, the compact has a molding density of 3.9 g / cm ³ or more and 4.3 g / cm ³ or less.

In a preferred embodiment, a lubricant is added to the rare earth alloy powder.

In a preferred embodiment, the step of preparing the sintering base plate includes a step of adjusting the surface roughness of the main surface of the sintering base plate.

[0021] In a preferred embodiment, the compact is not slid on the main surface of the sintering base plate, but on the main surface of the sintering base plate from above the sintering base plate. Placed on

In a preferred embodiment, the molding has an arcuate cross section.

In this specification, "the orientation direction of the compact is substantially parallel to the main surface of the base plate for sintering" means that the orientation direction of the compact is the surface (main surface) of the base plate for sintering. ) Is within ± 45 °.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is arranged such that the orientation direction of the compact is substantially parallel to the main surface of the sintering base plate (the surface on which the compact is placed). When the shrinkage ratio of the compact at the time of sintering is particularly large, the average surface roughness Ra is 0.7 μm to 45 μm. By using a sintering base plate, cracking or chipping of the compact is prevented from occurring. I have. According to the present invention, for example, when manufacturing a rare earth magnet for a voice coil motor,
Particularly when a compact having a large size and weight (for example, a unit weight of 10 g or more) is sintered on a sintering base plate, occurrence of cracks and chips can be reduced.

A technique for preventing the welding between the compact and the base plate during sintering by adjusting the surface roughness of the base plate for sintering is disclosed, for example, in Japanese Patent Application Laid-Open No. 2000-216036.
No., published in Japanese Unexamined Patent Publication No. However, in this publication, the orientation direction of the compact has a specific relationship to the surface of the sintering base plate, and when the compact shrinks relatively largely on the base plate, No description is given as to what range the surface roughness Ra should be set. The embodiment of the above publication describes a case where a compact having a relatively small size (for example, a cylindrical compact having an inner diameter of 2 mm, an outer diameter of 4 mm, and a height of 6 mm) is sintered.

On the other hand, according to the present invention, when the orientation direction of the molded body is arranged parallel to the surface of the base plate and the shrinkage of the molded body is particularly large, the surface roughness of the base plate is set within the above-mentioned predetermined range. It is adjusted to. This makes it possible to prevent a compact having a relatively large shrinkage from cracking or chipping during sintering. In the embodiment of the present invention, the length in the alignment direction is 20 mm or more and the unit weight is 10
Although a magnet is produced using a relatively large compact of g or more, according to the present invention, it is possible to prevent the compact from being damaged during sintering even with such a large compact. Can be.

A method for manufacturing a rare earth sintered magnet (RT- (M) -B based magnet) according to an embodiment of the present invention will be described below.

In the present embodiment, a case will be described in which a molded body 2 having a cross section of an arc or an arc as shown in FIG. 1 is produced in order to produce a rare earth sintered magnet for a voice coil motor. As described later, in the present embodiment, a relatively strong magnetic field (for example, 0.8 MA / m to 1.0 MA / m)
The molded body is manufactured by being oriented in the inside, and the orientation direction A of the molded body is arranged substantially parallel to the surface of the base plate 4 for sintering.

As shown in the figure, the compact 2 manufactured according to the present embodiment is placed on the sintering plate 4 such that only the side portions 2a of the compact come into contact with the sintering plate 4. When the area of the contact portion between the molded body 2 and the base plate 4 is small as described above, the pressure acting between them becomes large, so that welding tends to occur during sintering. Further, when the molded body 2 contracts, the molded body 2 receives a relatively large stress (frictional force) from the base plate 4, so that the molded body 2 is liable to be cracked.

The size of the above-mentioned molded body 2 is relatively large,
Length L: 58 mm x width W: 46 mm x height H: 24 mm
And the unit weight is about 435 g. When the size of the compact is large as described above, the stress acting on the compact due to shrinkage during sintering is strong, and cracks are likely to occur, but the surface roughness of the sintering base plate is set to a predetermined value as described later. By adjusting to the range, breakage of the molded body can be prevented.

Hereinafter, a process for producing a rare earth alloy powder used for producing the above-mentioned compact will be described.

First, a raw material alloy of an R—Fe—B based magnet alloy having a desired composition having a desired composition is prepared by a known strip casting method, and stored in a predetermined container. Specifically, first, Nd: 30.8 wt% (atomic%), Pr:
3.8 wt%, Dy: 0.8 wt%, B: 1.0 wt%
%, Co: 0.9 wt%, Al: 0.23 wt%, C
u: An alloy having a composition of 0.10 wt%, the balance being Fe and unavoidable impurities is melted by high frequency melting to form a molten alloy. After maintaining this molten alloy at 1350 ° C,
The alloy melt is quenched by the single roll method to a thickness of about 0.3
mm flake-like alloy ingot was obtained. The quenching conditions at this time were as follows: a roll peripheral speed of about 1 m / sec, a cooling speed of 500 ° C./sec,
The temperature was supercooled to 200 ° C. The quenched alloy slab thus produced is pulverized into flakes having a size of 1 to 10 mm before the next pulverization with hydrogen. A method for producing a raw material alloy by a strip casting method is described in, for example, US Pat.
No. 3,978.

A plurality of raw material packs (stainless steel) are filled with raw material alloy slabs roughly crushed into flakes and mounted on a rack. Thereafter, the rack on which the raw material pack is mounted is inserted into the hydrogen furnace. Next, close the lid of the hydrogen furnace,
Start the hydrogen grinding process. In the hydrogen crushing process, for example, after performing a vacuum evacuation process at room temperature for about 0.5 hour, hydrogen gas is supplied into the furnace to make the inside of the furnace a hydrogen atmosphere (hydrogen pressure is about 200 to 400 kPa), 400 ° C
The hydrogen storage process is performed by heating for about 2.5 hours to reach a temperature of. Subsequently, after performing a dehydrogenation process by heating for about 5.0 hours to reach a temperature of 500 ° C. to 600 ° C. under reduced pressure of about 0 to 3 Pa, while supplying argon gas into the furnace, The alloy cooling process is performed for about 5.0 hours.

In the cooling process, when the atmosphere temperature in the furnace is relatively high (for example, when the temperature exceeds 100 ° C.), a normal temperature inert gas is supplied into the hydrogen furnace to cool it. Thereafter, at a stage when the temperature of the raw material alloy is lowered to a relatively low level (for example, at a temperature of 100 ° C. or less), an inert gas cooled to a temperature lower than a normal temperature (for example, room temperature minus about 10 ° C.) is introduced into the hydrogen furnace 10. Supply is preferable from the viewpoint of cooling efficiency. The supply amount of argon gas is 1
What is necessary is just to set it as about 0-100 Nm < ³ > / min.

When the temperature of the raw material alloy is reduced to about 20 to 25 ° C., an inert gas at substantially normal temperature (a temperature lower than room temperature but a difference from room temperature within 5 ° C.) is blown into the hydrogen furnace. It is preferable to wait until the temperature of the raw material reaches the normal temperature level. By doing so, when the lid of the hydrogen furnace is opened, a situation in which dew condensation occurs inside the furnace can be avoided. If moisture is present inside the furnace due to condensation,
Since the water freezes and evaporates during the evacuation process, it is difficult to increase the degree of vacuum, and the time required for the evacuation process is undesirably increased.

When the coarsely pulverized alloy powder after hydrogen pulverization is taken out of the hydrogen furnace, it is preferable to carry out the take-out operation under an inert atmosphere so that the coarsely pulverized powder does not come into contact with the atmosphere.
This prevents the coarsely pulverized powder from oxidizing and generating heat, thereby improving the magnetic properties of the magnet. Next, the coarsely pulverized raw material alloy is filled into a plurality of raw material packs and mounted on a rack.

Rare earth alloy is 0.1 m
m to several mm, and the average particle size is 5
It is less than 00 μm. After the hydrogen pulverization, it is preferable that the embrittled raw material alloy is further finely pulverized and cooled by a cooling device such as a rotary cooler. In the case where the raw material is taken out in a relatively high temperature state, the time of the cooling process using a rotary cooler or the like may be made relatively long.

Next, the coarsely pulverized powder produced through the hydrogen pulverization step is finely pulverized using a jet mill pulverizer. The cyclone classifier suitable for removing fine powder is connected to the jet mill pulverizer used in the present embodiment.

Hereinafter, the fine pulverization step performed by using the jet mill pulverizer will be described with reference to FIG.

The illustrated jet mill pulverizing apparatus 10 supplies a raw material input device 12 for supplying a rare earth alloy (object to be pulverized) coarsely pulverized in a hydrogen pulverizing step, and pulverizes the object to be pulverized input from the material input device 12. A crusher 14, a cyclone classifier 16 for classifying powder obtained by crushing the material to be crushed by the crusher 14, and a collection tank 18 for collecting powder having a predetermined particle size distribution classified by the cyclone classifier 16. And

The raw material input device 12 includes a raw material tank 20 for storing the material to be ground, a motor 22 for controlling the supply amount of the material to be ground from the raw material tank 20, and a spiral feeder ( Screw feeder) 2
And 4.

The crusher 14 has a vertically long, substantially cylindrical crusher main body 26, and a lower part of the crusher main body 26 is provided with a nozzle for ejecting an inert gas (eg, nitrogen) at a high speed. A plurality of nozzle ports 28 are provided.
To the side of the crusher main body 26, a raw material input pipe 30 for charging an object to be crushed into the crusher main body 26 is connected.

The raw material charging pipe 30 is provided with a valve 32 for temporarily holding the material to be supplied and confining the pressure inside the crusher 14, and the valve 32 comprises an upper valve 32a and a lower valve 32b. Have been. The feeder 24 and the raw material input pipe 30 are connected by a flexible pipe 34.

The crusher 14 includes a classifying rotor 36 provided above the inside of the crusher main body 26, a motor 38 provided above the outside of the crusher main body 26, and a connection pipe provided above the crusher main body 26. 40. Motor 38
Drives the classifying rotor 36, and the connection pipe 40 discharges the powder classified by the classifying rotor 36 to the outside of the crusher 14.

The pulverizer 14 has a plurality of legs 4 serving as support portions.
2 is provided. A base 44 is provided near the outer periphery of the crusher 14, and the crusher 14 is mounted on the base 44 by the legs 42. In the present embodiment, the leg 42 of the crusher 14 is used.
A weight detector 4 such as a load cell is
6 are provided. Based on the output from the weight detector 46, the control unit 48 controls the number of rotations of the motor 22, and thereby can control the amount of the material to be ground.

The cyclone classifier 16 comprises a classifier body 64
An exhaust pipe 66 is inserted into the classifier main body 64 from above. On the side of the classifier body 64,
Inlet 68 for introducing the powder classified by the classification rotor 36
Is provided, and the inlet 68 is connected to the connection pipe 40 by a flexible pipe 70. Classifier body 64
An outlet 72 is provided at a lower portion of the container, and a recovery tank 18 for a desired finely pulverized powder is connected to the outlet 72.

The flexible pipes 34 and 70 may be made of resin, rubber, or the like, or may be made of a highly rigid material in a bellows shape or a coil shape so as to have flexibility. preferable. Such flexible pipes 34 and 7
If 0 is used, the weight change of the raw material tank 20, the feeder 24, the classifier main body 64, and the collection tank 18 is reduced by
Is not transmitted to the leg portion 42 of the main body. Therefore, if the weight is detected by the weight detector 46 provided on the leg 42, the weight of the material to be ground remaining in the crusher 14 and the change amount thereof can be accurately detected, and the crushed material supplied to the crusher 14 can be detected. The quantity of things can be controlled accurately.

Next, a pulverizing method using the above-described jet mill pulverizing apparatus 10 will be described.

First, the material to be ground is put into the raw material tank 20. The material to be crushed in the raw material tank 20 is supplied to the crusher 14 by the supply device 24. At this time, by controlling the number of revolutions of the motor 22, the supply amount of the crushed material can be adjusted. The material to be crushed supplied from the supply device 24 is once blocked by the valve 32. Here, the pair of upper valve 32a and lower valve 32b perform opening and closing operations alternately. That is, when the upper valve 32a is open, the lower valve 32b is closed, and when the upper valve 32a is closed, the lower valve 32b is open. By alternately opening and closing the pair of valves 32a and 32b in this manner, the pressure in the crusher 14 can be prevented from leaking to the material input device 12 side. As a result, the object to be ground is supplied between the pair of upper valve 32a and lower valve 32b when the upper valve 32a is opened. Then, when the lower valve 32b is opened next time, it is guided to the raw material charging pipe 30 and introduced into the crusher 14. The valve 32 is driven at a high speed by a sequence circuit (not shown) different from the control circuit 48, and the material to be ground is continuously supplied into the mill 14.

The material to be pulverized introduced into the pulverizer 14 is wound up in the pulverizer 14 by the high-speed injection of the inert gas from the nozzle port 28, and swirls with the high-speed airflow in the apparatus. Then, the objects to be ground are finely ground by mutual collision.

The finely pulverized powder particles are guided by an ascending airflow to the classification rotor 36,
6 and the coarse powder will be ground again.
On the other hand, the powder pulverized to a predetermined particle size or less is
0, it is introduced into the classifier body 64 of the cyclone classifier 16 from the inlet 68 via the flexible pipe 70. In the classifier main body 16, relatively large powder particles having a predetermined particle size or more are deposited in a recovery tank 18 provided at a lower portion, and the ultrafine powder is discharged outside from an exhaust pipe 66 together with an inert gas stream. . In the present embodiment, the ultrafine powder is removed through the exhaust pipe 66, whereby the ultrafine powder occupying the powder collected in the collection tank 18 (particle diameter: 1.0 μm)
m) is adjusted to 10% or less. When the R-rich ultrafine powder is removed in this manner, the amount of the rare earth element R in the sintered magnet consumed for bonding with oxygen can be reduced, and the magnet properties can be improved.

As described above, in the present embodiment, the cyclone classifier 16 with blow-up is used as a classifier connected to the subsequent stage of the jet mill pulverizer (pulverizer 14). According to such a cyclone classifier 16, the ultrafine powder having a particle size equal to or smaller than a predetermined value is inverted and rises without being collected in the collection tank 18, and is discharged from the pipe 66 to the outside of the apparatus.

The particle diameter of the fine powder removed from the pipe 66 to the outside of the apparatus can be determined by appropriately setting the parameters of each part of the cyclone described on pages 92 to 96 of the “Powder Technology Pocket Book” of the Industrial Research Institute. It can be defined and controlled by adjusting the pressure of the inert gas stream.

FIG. 3 shows an example of the particle size distribution of the powder obtained through the fine pulverizing step using the jet mill pulverizer. According to this embodiment, it is possible to obtain an alloy powder having an average particle size of, for example, about 4.0 μm and the number of ultrafine powder having a particle size of 1.0 μm or less is 10% or less of the total number of powders. it can. The preferred average particle size range of the finely pulverized powder used for manufacturing the sintered magnet is 2 μm or more and 10 μm or more.
m or less. In the example of FIG. 3, since the metal structure of the used raw material alloy (strip cast alloy) is fine, the alloy powder having a narrower particle size distribution than the alloy powder produced using the conventional ingot casting method is used. Obtained.

As described above, it is produced by pulverizing and classifying the raw material alloy produced by the quenching method.
The range of the particle size distribution of the alloy powder in which the number of ultrafine powder having a particle size of 1.0 μm or less is adjusted to 10% or less of the total number of powders is very narrow. If the size of the powder particles is relatively uniform,
There is a tendency that the molding density of a molded body produced in a compression molding step described below is low. In the formed body produced in this manner, the proportion of voids (voids) in the formed body increases, so that the shrinkage during sintering increases.

In order to suppress the oxidation in the pulverizing step as much as possible, the amount of oxygen in the high-speed gas (inert gas) used in the pulverization should be suppressed to about 0.05 to 3.00% by volume. Is preferred. A pulverization method for controlling the oxygen concentration in the high-speed airflow gas is described in Japanese Patent Publication No. 6-6728.

By controlling the concentration of oxygen contained in the atmosphere at the time of pulverization as described above, it is preferable to adjust the oxygen content of the alloy powder after pulverization to 6000 ppm by mass or less. If the amount of oxygen in the rare earth alloy powder exceeds 6000 mass ppm and becomes too large, the proportion of nonmagnetic rare earth oxides in the sintered magnet increases, and the magnetic properties of the final sintered magnet deteriorate. It is because.

In this embodiment, since the R-rich ultrafine powder is appropriately removed, the oxygen concentration in the inert gas atmosphere during the pulverization is adjusted so that the oxygen concentration of the powder is 6000 mass ppm. However, if the R-rich ultrafine powder is not removed and the number ratio of the ultrafine powder exceeds 10% of the total, no matter how much oxygen in the inert gas atmosphere Even if the concentration is reduced, the oxygen concentration in the finally obtained powder easily exceeds 6000 ppm by mass.

In the present embodiment, the fine pulverizing step is performed by using the jet mill pulverizing apparatus 10 having the configuration shown in FIG. 2, but the present invention is not limited to this, and the jet mill having another configuration is used. A pulverizer or other type of pulverizer may be used. Further, as a classifier for removing the ultrafine powder, a centrifugal classifier such as a Fatongelen classifier or a micro separator may be used in addition to the cyclone classifier.

In the present embodiment, for example, 0.3 wt% of a lubricant is added to and mixed with the finely pulverized powder produced by the above method in a rocking mixer, and the surface of the alloy powder particles is coated with the lubricant. As the lubricant, a fatty acid ester diluted with a petroleum solvent can be used. In this embodiment, methyl caproate is used as the fatty acid ester, and isoparaffin is used as the petroleum solvent. The weight ratio of methyl caproate to isoparaffin is, for example, 1: 9. Such a liquid lubricant coats the surface of the powder particles and exerts an antioxidant effect on the particles,
It has the function of improving the orientation during pressing and the powder moldability (making the density of the molded body uniform and eliminating defects such as cracks and cracks). However, when a lubricant is added, the strength of a molded body produced in a pressing step described later becomes low.

The type of the lubricant is not limited to the above. As the fatty acid ester, other than methyl caproate, for example, methyl caprylate, methyl laurate, methyl laurate and the like may be used. As the solvent, a petroleum solvent represented by isoparaffin, a naphthene solvent, or the like can be used. The timing of adding the lubricant is arbitrary, and may be, for example, any of before, during, or after the pulverization by the jet mill pulverizer. Instead of the liquid lubricant or together with the liquid lubricant, a solid (dry) lubricant such as zinc stearate may be used.

Hereinafter, a process for producing a compact from the above alloy powder using a press machine will be described with reference to FIG.

FIG. 4 shows the overall configuration of the press device 100 used in this embodiment. The press apparatus 100 includes a die 110 provided with a through hole, and an upper punch 112 and a lower punch 114 inserted into the through hole of the die 110 from above and below, respectively. The press device 100 uses a feeder box (or shoe box) 120 containing rare earth alloy powder after forming a molding space (cavity) by partially inserting a lower punch from below into a through hole of a die 110. The cavity is filled with the rare earth alloy powder. Thereafter, the filling powder in the cavity is compressed by reducing the distance between the upper punch 112 and the lower punch 114 in the axial direction (that is, lowering the upper punch 112), and thereby the compact 2 is manufactured.
FIG. 4 shows that the upper punch 112 is retracted from the through hole of the die 110 and the lower punch 1
14 shows a state where the molded body 2 is exposed on the die 110 by raising the 14 relatively to the die 110.

Hereinafter, the press device 100 of the present embodiment will be described in more detail with reference to FIGS. 5 (a) and 5 (b). FIGS. 5A and 5B are enlarged views of a part of the press device 100 shown in FIG. 4, and each of the press devices 100 when viewed from directions different from each other by 90 degrees.
2 shows a cross section of FIG.

As shown in FIGS. 5A and 5B, the press device 100 includes an upper punch 112 and a lower punch 11.
4 has a pair of magnetic field generating coils 116a and 116b for orienting the alloy powder in a magnetic field when the alloy powder is compressed. The magnetic field generating coils 116a and 116b are provided so as to face each other across the cavity, and a magnetic field is generated from one coil 116a (or 116b) to the other coil 116b (or 116a). In the present embodiment, a pressing direction B, which is a moving direction of the upper punch 112 and the lower punch 114, and a magnetic field generation direction (orientation direction) A intersect perpendicularly. A magnetic field of preferably 0.8 MA / m to 1.0 MA / m is applied to the alloy powder in the cavity by the magnetic field generating coils 116a and 116b. As a result, a molded body that is magnetically strongly oriented in the direction along the magnetic field generation direction A is manufactured.

Further, as shown in FIG.
The powder pressure of the upper punch 112 and the lower punch 114.
The contracted surface forms a curved surface. As a result, as shown in FIG.
To produce a shaped body with a bow (or arc)
Can be. The compression molding step of the rare earth alloy powder
, The density of the molded body is, for example, 4.3 g / cm ^Three
Set to about. However, the density of the compact is
Not limited to a value, preferably 3.9 g / cm^Three4.
3g / cm^ThreeIt is set as follows. Thus, the present embodiment
Since the density of the compact produced in
Is relatively fragile, but on the other hand,
A magnet with excellent magnetic properties
It becomes possible to do.

Hereinafter, the step of mounting the compact formed as described above on the main surface of the sintering base plate will be described with reference to FIG. 4 again.

Next, the compact 2 produced in the press 100 is sintered by the mounting robot 130.
Put on top. The sintering base plate is formed of a high melting point metal such as stainless steel or molybdenum, and is preferably formed of molybdenum. Molybdenum has low reactivity with molded bodies containing rare earth metal elements, has good thermal conductivity, and
Since it has good heat resistance, it is suitable as a material for the base plate 4 for sintering.

The sintering base plate 4 has, for example, a size of 30 cm long × 30 cm wide × 1 mm thick. The surface roughness Ra of the sintering base plate 4 is adjusted to a range of 0.7 μm or more and 45 μm or less. In the case where the main surface of the sintering base plate and the orientation direction of the compact are arranged substantially parallel as in the present embodiment, if the surface roughness Ra is less than 0.7 μm, the surface of the base plate surface Since the irregularities are too small, welding between the base plate and the compact during sintering is likely to occur. Further, when the surface roughness Ra of the base plate exceeds 45 μm, the friction between the base plate and the formed body is increased due to excessively large unevenness, so that a crack or the like occurs in the formed body without welding. Is more likely to do so. The surface roughness Ra of the sintering base plate is more preferably set to 1 μm or more and 45 μm or less, and still more preferably set to 1 μm or more and 15 μm or less.

In this embodiment, the surface roughness (average) Ra of the base plate for sintering is adjusted to the above range by a known shot blast method. When using the shot blast method,
The surface roughness Ra can be appropriately adjusted by adjusting the size or the like of the powder particles that collide with the surface of the sintering base plate.
More specifically, in this embodiment, the surface roughness of the sintering base plate is adjusted to about 1 μm to 20 μm by using powder particles # 60 to # 120 (for example, alumina powder).

The surface roughness Ra of the base plate for sintering can also be adjusted by spraying powder particles onto the surface of the base plate by a known method. Examples of the material of the powder particles to be sprayed include rare earth oxides such as neodymium oxide and yttrium oxide, and oxides such as zirconia and alumina. Further, the surface roughness Ra of the sintering base plate may be adjusted by mechanically processing the base plate surface using a milling machine or the like.

A plurality of compacts 2 are arranged on the sintering base plate 4 whose surface roughness Ra has been adjusted as described above. In the present embodiment, since the size of the molded body 2 is large and fragile, the robot 13 is configured to be able to grip the molded body.
Use 0 to arrange the compacts on the sintering plate. Robot 1
As shown in FIG. 6, the compact 30 mounts the compact 2 on the sintering plate from above the sintering plate so as to sandwich the compact 2. Thereby, as shown in FIG. 1, the molded body 2 is placed on the base plate so that the orientation direction A is parallel to the surface of the base plate for sintering.

The robot 130 may be configured to take an image of the molded body 2 using a camera (not shown). In this case, information representing the position and shape of the molded body 2 is generated by appropriately processing the image of the molded body 2 captured by the camera, and the operation of the robot 130 is controlled based on this information. If the camera is used in this manner, the position and the center of gravity (shape) of the molded body 2 can be accurately recognized, so that the robot 130 appropriately grips the molded body 2 and places it on the sintering base plate 4. Can be arranged properly.

Next, the sintering base plate 4 on which the compact 2 is placed
Is conveyed to the vicinity of the sintering case 6 by the conveyor belt 140. In order to reduce the amount of oxygen in the sintering case 6, the sintering case 6 is preferably placed in a room 150 controlled in an inert gas (eg, nitrogen gas) atmosphere. The transported sintering base plate 4 is placed in a sintering case 6.
It is housed in a stacked state. By using the sintering case 6 in this way, it is possible to prevent the molded body from being sintered in the state of being exposed in the sintering furnace. Thereby, the rare earth element in the compact can be prevented from being oxidized by the oxygen present in the furnace, and deterioration of the properties of the magnet can be prevented.

Hereinafter, the sintering step and the aging treatment step of the compact housed in the sintering case will be described.

The sintering case containing the compact is transported to a sintering device and inserted into a preparation room provided at the entrance of the sintering device. After sealing the preparation chamber, the preparation chamber is evacuated until the atmospheric pressure becomes about 2 Pascal to prevent oxidation. Next, the sintering case is transported to a binder removal chamber, where the binder removal treatment (temperature: 250 to 60) is performed.
0 degree, pressure: 2 Pascal, time: 3 to 6 hours). The binder removal treatment is performed to volatilize a lubricant (binder) covering the surface of the magnetic powder before the sintering step. Since various gases such as organic gas and water vapor are generated from the molded body during the binder removal treatment, it is desirable that a getter capable of absorbing these gases is placed in a sintering case in advance.

After completion of the binder removal treatment, the sintering case is transferred to a sintering chamber, and subjected to 1000 g in an argon atmosphere.
焼 結 1100 ° C. for about 2 to 5 hours.

At this time, if the surface roughness Ra of the sintering base plate is adjusted to a range of 0.7 μm or more and 45 μm or less, welding between the compact and the base plate during the sintering process is prevented. At the same time, the possibility that cracks or the like occur when the molded body shrinks is reduced.

As described above, in the present embodiment, since the compact is placed so that the orientation direction of the compact is parallel to the surface of the base plate, the compact greatly shrinks on the base plate during sintering. I do. In particular, the shrinkage rate is the largest in the longitudinal direction (ie, orientation direction A) of the molded body shown in FIG. Also in this case, if the surface roughness Ra of the sintering base plate is adjusted to 0.7 μm or more and 45 μm or less, the friction or adhesion between the molded body and the base plate is in an appropriate state. It is possible to prevent breakage and welding of the molded body. Setting the surface roughness Ra of the sintering base plate in the above range is particularly effective when the shrinkage in the orientation direction of the molded body is 20% or more.

In this embodiment, as shown in FIG. 1, the length L in the orientation direction A is 58 mm and the unit weight is 4 mm.
A large compact of 35 g is sintered. In this case, compared to the case of a relatively small molded body,
The degree to which the molded body is deformed or moved on the base plate due to shrinkage is large, and the force (load) applied by the molded body to the base plate is strong. Even in such a case, the use of the sintering base plate can appropriately prevent the molded body from being damaged or welded. Setting the surface roughness Ra of the sintering base plate within the above range is particularly effective when used for sintering a compact having a length L in the orientation direction of 20 mm or more or a unit weight of 10 g or more.

As described above, the compact produced in the present embodiment is formed from the alloy powder produced by the quenching method. Furthermore, 1.0 μ of the alloy powder
The number of fines less than m is limited. In such a case, since the range of the particle size distribution of the powder is narrowed, the moldability during compression molding is reduced, and the strength of the obtained molded body is reduced.
Further, in the present embodiment, in order to improve the orientation of the molded body, since the molding density is set as low as 3.9g / cm ³ ~4.3g / cm ³ with the lubricant is added to the alloy powder, Moldings are very brittle. As described above, the low-strength and fragile molded body is easily broken, but if the sintering base plate is used, the friction between the molded body and the base plate is not excessively large, and the molded body during sintering is not damaged. Damage can be properly prevented.

Thereafter, the sintering case is transported to a cooling chamber, where it is subjected to a cooling process until the temperature of the sintering case drops to about room temperature. The cooled sintered body is inserted into an aging furnace, and a normal aging process is performed. The aging treatment is performed, for example, at a pressure of an atmospheric gas such as argon of about 2 Pascal and at a temperature of 400 to 600 ° C. for about 3 to 7 hours.

The method for producing a rare earth sintered magnet of the present invention is not limited to a magnet having the above-described composition, but may be any of R-T-
It is widely and suitably applied to (M) -B magnets. For example,
As the rare earth element R, Y, La, Ca, Pr, Nd, S
A raw material containing at least one element of m, Gd, Tb, Dy, Ho, Er, Tm, and Lu can be used. To obtain sufficient magnetization, 50 of the rare earth elements R are required.
Preferably, at% or more is occupied by either or both of Pr and Nd. Rare earth element R is 10at
% Or less, the coercive force decreases due to the precipitation of the α-Fe phase. On the other hand, if the rare earth element R exceeds 20 at%, a large amount of the R-rich second phase precipitates in addition to the target tetragonal Nd ₂ Fe ₁₄ B type compound, and the magnetization decreases. For this reason, the rare earth element R is preferably in the range of 10 to 20 at% of the whole.

T is a transition metal element containing Fe and Co. When T is less than 67 at%, the second phase having low coercive force and low magnetization is precipitated, so that the magnetic properties deteriorate.
When T exceeds 85 at%, the coercive force decreases due to the precipitation of the α-Fe phase, and the squareness also decreases. Therefore, the content of T is preferably in the range of 67 to 85 at%. Note that T may be composed only of Fe,
The Curie temperature is increased by the addition of Co, and the heat resistance is improved. Preferably, at least 50 at% of T is occupied by Fe. When the proportion of Fe is less than 50 at%, Nd ₂
This is because the saturation magnetization itself of the Fe ₁₄ B type compound decreases.

B is essential for stably depositing a tetragonal Nd ₂ Fe ₁₄ B type crystal structure. The amount of B added is 4a
If the amount is less than t%, the coercive force decreases due to precipitation of the R ₂ T ₁₇ phase, and the squareness of the demagnetization curve is significantly impaired. On the other hand, if the addition amount of B exceeds 10 at%, a second phase having a small magnetization will precipitate. Therefore, the content of B is 4 to 10 at.
% Is preferable.

In order to further increase the magnetic anisotropy of the powder, another additive element M may be added. As the additional element M, Al, Ti, Cu, V, Cr, Ni, Ga, Z
At least one element selected from the group consisting of r, Nb, Mo, In, Sn, Hf, Ta, and W can be suitably used. Such additional elements need not be added at all. When adding, the addition amount is preferably set to 10 at% or less. If the addition amount exceeds 10 at%, not the ferromagnetism but the second phase will precipitate and the magnetization will decrease. The additional element M is not required to obtain magnetically isotropic magnetic powder, but Al, Cu, Ga, etc. may be added to increase the intrinsic coercive force.

Although the method for producing the RT- (M) -B sintered magnet has been described above, the samarium / cobalt is manufactured using a sintering base plate having a surface roughness within the above range. A system-based sintered magnet may be manufactured. If the sintering base plate is used in the production of the rare earth sintered magnet in which a liquid phase is generated during sintering as described above, there is no welding to the base plate, and damage and deformation of the sintered body can be prevented.

In the above embodiment, the dry compaction method (dry press) in which the rare earth alloy powder is compression-molded in the powder state has been described as an example. However, the present invention relates to mixing the rare earth alloy powder with mineral oil or the like. The slurry may be produced by a wet molding method in which a slurry is produced and the slurry is oriented and compressed in a cavity to produce a molded body.

(Examples and Comparative Examples) Sintering base plates No. 1 to No. The sintering process of the compact was performed using each of No. 9. As the sintering base plate, a Mo plate having a size of 30 cm long × 30 cm wide × 1 mm thick was used.

No. 1: No treatment No. No. 2: Shot blasted with # 180 alumina abrasive grains 3: Shot blasted with # 120 alumina abrasive grains No. 4: Shot blasted with # 60 alumina abrasive grains No. 5: Yttria powder particles having a predetermined particle diameter sprayed on the surface of the base plate No. 5 6: No. on the base plate surface No. 5 sprayed with yttria powder particles having a particle size larger than No. 5 7: No. on the base plate surface No. 6 sprayed with yttria powder particles having a particle size larger than No. 6 8: The surface of the base plate was mechanically roughened by milling. 9: Surface of base plate mechanically roughened by milling

[0091] Further, as a compact, a compact having the shape and size as shown in Fig. 1 was prepared, and this compact was oriented such that its orientation was parallel to the surface of the base plate for sintering. It is mounted on the base plate. The compact is formed from an RT- (M) -B-based alloy powder produced by a strip casting method by the method described in the above embodiment. Further, the intensity of the orientation magnetic field formed by the magnetic field generating coil was set to 1.0 T, and the molding density of the molded body was set to 4.1 g / cm ³ .

Thirty compacts were placed on a sintering plate having the respective surface roughness, and a total of 240 compacts were placed on each plate in an argon gas atmosphere for 1060 members.
Sintered at 2 ° C. for 2 hours.

In Table 1 below, the surface roughness (average surface roughness Ra and maximum surface roughness R _max ) of each base plate and 240
The figures show the number of compacts that were welded after sintering and the number of cracked and cracked compacts among the compacts. In addition,
The surface roughness of each base plate was measured by JI using a small surface roughness tester (Surftest SJ-301) manufactured by Mitutoyo Corporation.
It was measured according to the S standard.

[0094]

[Table 1]

No. In the case of the sintering base plate 1, it was found that most of the sintered bodies were welded to the base plate when the sintered body was to be removed from the base plate after sintering. At a part of the welding location, the plurality of crystal grains near the surface of the sintered body and the base plate were in a welded state, and the sintered body and the base plate were heavily welded.

No. In the case of the sintering base plate of No. 2, the eluted N
d adhered thinly on the base plate, and about 1/8 of the sintered body was partially welded (adhered) to the base plate, but the adhesion was low and the sintered body was relatively easily removed from the base plate. I was able to remove it. Also,
No cracks or cracks were observed in the sintered body.

No. In the case of the sintering base plate of No. 3, the eluted N
d adheres thinly on the base plate and partially welds (adheres) to the base plate
Some sintered bodies were observed, but the number was small and the adhesion was low. Also, no cracks or cracks were observed in the sintered body, and a desired sintered body without defects was obtained.

No. In the case of the sintering base plate of No. 4, the eluted N
d adheres thinly on the base plate and partially welds (adheres) to the base plate
Some sintered bodies were observed, but the number was very small and the adhesion was also very low. Also, no cracks or cracks were observed in the sintered body, and a desired sintered body without defects was obtained.

No. In the case of the sintering base plate of No. 5, the eluted N
Although d was slightly attached to the base plate, no sintered body welded to the base plate was observed. Also, no cracks or cracks were observed in the sintered body, and a desired sintered body without defects was obtained.

No. In the case of the sintering base plate of No. 6, the eluted N
d did not adhere to the base plate, and no sintered body welded to the base plate was observed. No cracks or cracks were observed in the sintered body.

No. In the case of the sintering plate of No. 7, the eluted N
d did not adhere to the base plate, and no sintered body welded to the base plate was observed. No cracks or cracks were observed in the sintered body.

No. In the case of the sintering base plate of No. 8, the eluted N
d did not adhere to the base plate, and no sintered body welded to the base plate was observed. However, small cracks and cracks were observed in some of the sintered bodies, but the number was very small.

No. In the case of the sintering base plate of No. 9, the eluted N
d did not adhere to the base plate, and no sintered body welded to the base plate was observed. However, cracks and cracks were observed in relatively many sintered bodies.

As described above, the surface roughness Ra is 0.7 μm to
If a 45 μm sintering base plate (No. 2 to 8) is used, a rare earth sintered magnet can be produced with a very high yield. The surface roughness Ra of the sintering base plate is 1.9 μm or more.
If it is 15.0 μm (Nos. 4 to 7), a higher yield can be achieved.

[0105]

According to the present invention, the surface roughness Ra is 0.7
Since the molded body is sintered using a sintering plate of μm or more and 45 μm or less, it is placed so that the orientation direction is parallel to the surface of the platen. Even in the case of a body, it is possible to appropriately prevent the occurrence of welding to the base plate and breakage during shrinkage. This makes it possible to produce a sintered magnet with a high yield.

[Brief description of the drawings]

FIG. 1 is a perspective view of a molded body produced in an embodiment of the present invention.

FIG. 2 is a cross-sectional view illustrating a configuration of a crusher used in the embodiment of the present invention.

FIG. 3 is a graph showing a particle size distribution of an alloy powder for a rare earth sintered magnet prepared in an embodiment of the present invention.

FIG. 4 is a cross-sectional view showing an overall configuration of a press device used in the embodiment of the present invention.

5 is a partially enlarged view of the press device shown in FIG. 4,
(A) and (b) show the cases when viewed from directions different from each other by 90 °. .

6 is a view showing a state in which a robot provided in the press device shown in FIG. 4 grips a formed body.

[Explanation of symbols]

 Reference Signs List 2 molded body 4 sintering base plate 6 sintering case 100 pressing device 110 die 112 upper punch 114 lower punch 116 magnetic field generating coil 120 feeder box 130 mounting robot 140 transport belt 150 room controlled by inert gas atmosphere A Orientation direction B Press direction

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Naoyuki Ishigaki 2-15-17 Egawa, Shimamoto-cho, Mishima-gun, Osaka Sumitomo Special Metals Co., Ltd. Yamazaki Works F term (reference) 4K018 AA27 CA04 DA38 KA45 5E062 CC01 CD04 CE04 CF03 CG02

Claims (12)

[Claims] 1. A step of preparing a compact by orienting and compressing a rare earth alloy powder in a magnetic field, and preparing a sintering base plate having a main surface having a surface roughness Ra of 0.7 μm or more and 45 μm or less. Placing the compact on the main surface of the sintering base plate such that the orientation direction of the compact is substantially parallel to the main surface of the sintering base plate; Sintering a compact placed on the main surface of the binding base plate. 2. The method for producing a rare earth sintered magnet according to claim 1, wherein the unit weight of the compact is 10 g or more. 3. The length of the molded body along the orientation direction is 2
The method for producing a rare earth sintered magnet according to claim 1, wherein the diameter is 0 mm or more. 4. In the step of sintering, the formed body is placed along the orientation direction on a main surface of the sintering base plate.
The method for producing a rare earth sintered magnet according to any one of claims 1 to 3, wherein the length shrinks by 0% or more. 5. The method according to claim 1, wherein, in the step of producing the compact, an orientation direction in which the rare earth alloy powder is oriented in a magnetic field is substantially orthogonal to a pressing direction in which the rare earth alloy powder is compressed. 5. The method for producing a rare-earth sintered magnet according to any one of items 4. 6. The method for producing a rare earth sintered magnet according to claim 1, wherein the rare earth alloy powder is produced by crushing a rare earth alloy produced by a quenching method. 7. The method according to claim 1, wherein said rare-earth alloy powder contains 1.0 μm
The method for producing a rare earth sintered magnet according to any one of claims 1 to 6, wherein the number of fine powders of m or less is adjusted to 10% or less of the number of particles of the entire powder. 8. The molding density of the molded body is 3.9 g / cm.
^The method for producing a rare earth sintered magnet according to any one of claims 1 to 7, wherein the amount is ³ g or more and 4.3 g / cm ³ or less. 9. The method for producing a rare earth sintered magnet according to claim 1, wherein a lubricant is added to the rare earth alloy powder. 10. The rare-earth sintering method according to claim 1, wherein the step of preparing the sintering base plate includes a step of adjusting the surface roughness of a main surface of the sintering base plate. Manufacturing method of magnet. 11. The compact is placed on the main surface of the sintering base plate from above the sintering base plate without being slid on the main surface of the sintering base plate. Claims 1 to 1
0. The method for producing a rare earth sintered magnet according to any one of the above items. 12. The method for producing a rare earth sintered magnet according to claim 1, wherein the compact has an arcuate cross-sectional shape.