JP2023047621A - Mold for wet molding and method for manufacturing sintered magnet - Google Patents

Abstract

To provide a mold for wet molding and a method for manufacturing a sintered magnet capable of suppressing backflow of slurry.SOLUTION: A wet molding mold 10 includes a cavity 14 for filling a slurry containing magnetic powder and a dispersion medium, an injection hole 15 for injecting slurry into the cavity 14, and pressure molding means for pressure molding the slurry filled in the cavity 14, and the injection hole 15 is provided with a backflow suppressing portion 15a for suppressing backflow of the slurry.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a wet molding die and a method for manufacturing a sintered magnet.

BACKGROUND ART Rare earth sintered magnets and ferrite sintered magnets are widely used for various applications including rotating machines such as motors and generators. As the rare earth sintered magnet, an RTB system sintered magnet (R is at least one rare earth element and always contains at least one of Nd and Pr. T is at least one transition metal element. , which necessarily contains iron (Fe). B means boron.), Sm—Co-based sintered magnets (part of Sm (samarium) may be replaced with other rare earth elements), etc. As ferrite sintered magnets, sintered magnets such as hexagonal system M-type (magnetoplumbite type) Sr ferrite, Ba ferrite, Sr--La--Co system ferrite, and Ca--La--Co system ferrite are known. there is

These sintered magnets are obtained by forming a magnetic powder into a predetermined shape and sintering it. As the molding method, a dry molding method (for example, Patent Document 1) and a wet molding method (for example, Patent Document 2) are known. In the dry compaction method, a compact is produced by press-molding dried magnetic powder while applying a magnetic field, and the obtained compact is sintered. In the wet compaction method, a slurry containing magnetic powder and a dispersion medium is used to form a compact by pressure molding while removing the dispersion medium in an applied magnetic field, and the resulting compact is sintered. do. Generally, in the wet molding method, the magnetic powder is easily oriented by the magnetic field during molding, so that a sintered magnet having high magnetic properties can be obtained.

For example, when a sintered ferrite magnet is produced by wet molding, (a) a step of mixing raw materials such as compounds such as Fe, Sr, Ba, Ca, La, and Co, and (b) a step of calcining to form a ferrite. A step of obtaining a calcined body, (c) coarsely pulverizing the calcined body, adding a compound such as a sintering aid, and performing wet fine pulverization, and (d) compacting a slurry of the obtained fine particles of the calcined body in a magnetic field. (e) sintering the molded body; and (f) processing the obtained sintered body into a shape according to the purpose of use.

FIG. 4(a) shows an example of a wet molding die for producing a molded body. The wet molding die 20 has a die 21 , a lower punch 22 and an upper punch 23 , and a space surrounded by these constitutes a cavity 24 . The die 21, the lower punch 22, and the upper punch 23 are configured to be independently movable in the vertical direction. The upper punch 23 has a drainage hole 26 and a drainage hole for discharging the dispersion medium in the slurry from the cavity 24 through a filter (not shown) during pressure molding. A drain hole is provided consisting of a drain channel 27 connecting to 26 .

The steps of wet molding using a wet molding die will be described below with reference to FIGS. 4(a) to 4(d). The descriptions of (A) to (C) below correspond to FIGS. 4(a) to (d), respectively. (A) A die 21 and an upper punch 23 are brought into close contact with each other to form a cavity 24 of a predetermined size (FIG. 4(a)), and a slurry S containing magnetic powder is injected from an injection hole 25 connected to the cavity 24 to form a cavity. 24 is filled with slurry S (FIG. 4(b)). (B) While applying a magnetic field (not shown), both the die 21 and the upper punch 23 are lowered, and the slurry S in the cavity 24 is pressure-molded while discharging the dispersion medium from the liquid discharge hole 26 and the discharge path 27. (Fig. 4(c)). (C) Next, the upper punch 23 is lifted, separated from the die 21, and the formed compact M is taken out (Fig. 4(d)). In a normal manufacturing process, the molding M is produced by repeating the cycle of (A) to (C).

Here, when pressure molding is performed while discharging the dispersion medium in the slurry S, part of the slurry S in the cavity 24 flows back into the injection hole 25, and a slurry high concentration portion Sa is formed near the opening to the cavity 24. is formed (see FIG. 4(c)). When the slurry S is injected in the next molding cycle, the slurry high concentration portion Sa is pushed out together with the succeeding slurry S and enters the cavity 24 as shown in FIG. It may be pressure molded as is. If the high slurry concentration portion Sa is not redispersed and is compacted as a mass and then sintered, the location where the high slurry concentration portion Sa is located tends to become the starting point of cracking, and the mechanical strength of the sintered magnet product is reduced. It may happen.

JP 2004-296849 A Japanese Patent No. 3833861

Accordingly, an object of the present disclosure is to provide a wet molding die capable of suppressing backflow of slurry and a method for manufacturing a sintered magnet.

The wet molding mold of the present disclosure, which has been made in view of the above points, has, in exemplary aspect 1, at least a cavity for filling slurry containing magnetic powder and a dispersion medium, and a slurry for injecting the slurry into the cavity. and a pressure-molding means for pressure-molding the slurry filled in the cavity, wherein the backflow suppressing part for suppressing the backflow of the slurry into the injection hole is provided. It is a mold for wet molding provided.

Aspect 2 is the wet molding die according to Aspect 1, wherein the backflow suppressing portion is in contact with the wall surface of the injection hole and is provided so as to be inclined from the wall surface toward the cavity.

In aspect 3, the backflow suppressing part includes a branching part for branching the slurry that flows backward from the cavity toward the injection hole, and one flow direction of the slurry branched by the branching part is directed against the other flow direction of the branched slurry. and a channel for directing flow to include components in opposite directions.

Aspect 4 is a method for producing a sintered magnet using the wet molding die according to any one of Aspects 1 to 3, wherein a slurry containing a magnetic powder and a dispersion medium is injected into the cavity from the injection hole. A method for producing a sintered magnet, comprising: a molding step of injecting and filling the slurry, and pressure-molding the filled slurry by a pressure molding means; and a sintering step of sintering the compact obtained in the molding step. .

According to the mold for wet molding and the method for manufacturing a sintered magnet of the present disclosure, it is possible to suppress backflow of slurry.

1 is a schematic cross-sectional view of a wet molding die according to an embodiment; FIG. FIG. 4 is an enlarged cross-sectional view showing an injection hole provided with a backflow suppressor according to an embodiment, (a) is a diagram showing the flow when slurry is supplied to a cavity, and (b) is a diagram showing the flow of slurry back into the injection hole. It is a figure which shows the flow at the time. FIG. 4 is an enlarged cross-sectional view showing another embodiment of an injection hole provided with a backflow suppressing part, where (a) is a diagram showing the flow when slurry is supplied to the cavity, and (b) is a diagram showing the flow when slurry flows back. FIG. 4 is a diagram showing a flow; FIG. 4 is a schematic cross-sectional view for explaining a step of wet molding using a wet molding die; FIG. 4 is a schematic cross-sectional view for explaining a step of wet molding using a wet molding die; FIG. 4 is a schematic cross-sectional view for explaining a step of wet molding using a wet molding die; FIG. 4 is a schematic cross-sectional view for explaining a step of wet molding using a wet molding die; FIG. 4 is a schematic cross-sectional view for explaining a step of wet molding using a wet molding die;

[1] Wet molding mold The wet molding mold of the present disclosure includes a cavity for filling a slurry containing a magnetic powder and a dispersion medium, an injection hole for injecting the slurry into the cavity, and filling the cavity. and pressure molding means for pressure-molding the slurry, wherein the wet-molding mold is provided with a backflow suppressing part for suppressing the backflow of the slurry in the injection hole. is.

A wet molding die 1 according to an embodiment is shown in FIGS. 1 to 3. FIG. FIG. 1 shows a schematic cross-sectional view of a wet molding die 10 according to an embodiment. As shown in FIG. 1, the wet molding die 10 has a die 11, a lower punch 12, and an upper punch 13, and a space surrounded by these constitutes a cavity 14. As shown in FIG. The die 11, the lower punch 12, and the upper punch 13 are configured to be vertically movable independently of each other, and constitute pressure forming means.

The die 11 is provided with an injection hole 15 penetrating from the outer peripheral surface of the die 11 to the cavity 14 . Slurry supplied from a slurry supply device (not shown) is supplied into the cavity 14 via the injection hole 15 .

2A and 2B are enlarged cross-sectional views showing the injection hole 15 provided with the backflow suppressing portion according to the embodiment, FIG. FIG. 4 is a diagram showing the flow when flowing back to the injection hole 15. FIG. As shown in FIGS. 1, 2(a) and 2(b), the injection hole 15 is provided with a A backflow suppressing portion 15 a is provided that can guide the flow of a portion of the slurry so that it contains a component in the opposite direction to the direction in which the slurry flows from the cavity 14 toward the injection hole 15 .

The backflow suppressing portion 15a is formed in a tapered shape of a truncated cone. It is provided so as to incline from W toward the cavity 14 . In addition, a plurality of backflow suppressing portions 15a are arranged at intervals along the direction in which slurry is supplied (or the direction in which slurry flows back).

By providing such a backflow suppressing portion 15a, when slurry is supplied, even if part of the slurry flows toward the backflow suppressing portion 15a as shown in FIG. can be supplied without generating a flow in the opposite direction to the On the other hand, as shown in FIG. 2(b), when the slurry flows back from the cavity 14 to the injection hole 15, if part of the slurry flows to the first backflow suppressing portion 15a, the backflow occurs. The flow direction is induced to contain a component in the opposite direction with respect to the direction of flow. Then, the backflowing slurry collides with the slurry whose flow direction is guided (the flow direction is changed), so that the energy in the backflowing direction can be reduced. Further, when the slurry further flows backward after passing through the first backflow suppressing portion 15a, the flow of the slurry is dispersed as it passes through the backflow suppressing portion 15a, and part of the slurry flows through the second backflow suppressing portion 15a. flows to the place where is provided. After that, the flow direction is induced by the backflow suppressing part 15a so as to include a component in the direction opposite to the direction of backflow, and the slurry flowing back and the slurry whose flow direction is induced (changed in flow direction) collide with each other. Thus, the energy in the direction of reverse flow can be further reduced. As a result, it becomes possible to suppress backflow of the slurry. Although two backflow suppressing portions 15a are provided in the present embodiment, the number of backflow suppressing portions 15a is not limited to this, and three or more may be provided. can.

It should be noted that the backflow suppressing portion 15a is not necessarily integrally molded, and may be manufactured by dividing into a plurality of pieces, which may be combined to form a desired structure when used. In addition, although the backflow suppressing portion 15a of the embodiment is in continuous contact with the wall surface W along the circumferential direction, it is not limited to this, and the flow is formed so as to include a component in the direction opposite to the direction of backflow. If it is possible to guide the direction, it may be provided so as to be connected intermittently. That is, it does not have to be in contact with the wall surface W by providing an opening in a part of the tapered shape of the truncated cone. In addition, a plurality of backflow suppressing portions 15a may be provided along the circumferential direction of the wall surface W at intervals.

Moreover, the backflow suppressing portion 15a may have any shape as long as it can guide the flow direction so as to include the component in the direction opposite to the direction of backflow. FIG. 3 is an enlarged cross-sectional view showing another embodiment of the injection hole, (a) is a diagram showing the flow when slurry is supplied, and (b) is a diagram showing the flow when slurry flows backward. .

As shown in FIGS. 3A and 3B, the backflow suppressing portion 15b includes a branching portion 15b1 for branching the slurry flowing backward from the cavity 14 toward the injection hole 15, and one side of the slurry branched by the branching portion 15b1. and a channel 15b2 that guides the flow so as to contain a component in a direction opposite to the other flow direction (counterflow direction) of the branched slurry.

Moreover, the branched portion 15b1 is provided so as to guide the slurry to flow along the direction of supplying the slurry even if part of the slurry flows toward the branched portion 15b1 when the slurry is supplied. When the slurry flows backward, most of the slurry flowing backward is guided to flow into the channel 15b2.

When slurry is supplied, the flow path 15b2 does not generate a flow in the direction opposite to the direction of slurry supply even if part of the slurry is branched by the branching portion 15b1 and flows into the flow path 15b2. It is provided so as to guide the flow direction so that they can merge. When flowing backward, the flow is guided so that the slurry guided by the branching portion 15b1 contains a component in the direction opposite to the direction of backward flow, and is provided so as to collide with the slurry flowing backward.

By providing such a backflow suppressing portion 15b, when slurry is supplied, as shown in FIG. can be done. Further, as shown in FIG. 3B, when the slurry flows backward from the cavity 14 to the injection hole 15, the component in the direction opposite to the direction in which the slurry guided to the flow path 15b2 by the branch portion 15b1 flows backward. It flows so as to contain it, collides with the backflowing slurry, and can reduce the energy in the backflowing direction. As a result, it is possible to suppress backflow of the slurry.

As shown in FIG. 1, the lower punch 12 and the upper punch 13 are provided so as to have a shape that matches the shape of the compact to be obtained. The upper punch 13 also has a drainage hole 16 for discharging the dispersion medium in the slurry from the cavity 14 during pressure molding through a filter (not shown) as a discharge hole, and a discharge hole connected to the discharge hole 16 . A path 17 is provided.

[2] Method for producing sintered magnet The method for producing a sintered magnet of the present disclosure is a method for producing a sintered magnet using the wet molding die of the present disclosure,
a molding step of injecting a slurry containing magnetic powder and a dispersion medium into the cavity 14 through the injection hole 15 to fill the cavity 14, and molding the filled slurry by pressure molding means;
and a sintering step of sintering the molded body obtained in the molding step.

The sintered magnet that can be produced by the method of the present disclosure is a magnet to which a process of compression-molding a slurry obtained by dispersing a magnetic powder in a dispersion medium (water or organic solvent) and sintering the obtained compact is applied. Any magnet can be manufactured, but rare earth sintered magnets or ferrite sintered magnets are particularly preferred.

(1) Molding step Molding is carried out by filling the wet molding die 10 of the present disclosure with a slurry containing magnetic powder, and removing the dispersion medium while applying pressure while applying a magnetic field to form a molded body. do. The molding pressure is 30 to 382 MPa (500 to 4,000 Kg/cm ² ) for RTB sintered magnet compacts, and 34 to 44 MPa (350 to 450 Kg/cm ^{2 )} for ferrite magnet compacts. ) is preferable. In the case of the RTB based sintered magnet compact, it is preferable to adjust the density of the compact to about 3.7 to 4.7 g/cm ³ . In the case of the ferrite magnet compact, it is preferable to adjust the density of the compact to about 2.6 to 3.2 g/cm ³ .

(2) Sintering step The molded body obtained in the molding step is sintered to obtain a sintered body.

(3) Other Steps When manufacturing a sintered magnet product, the sintered body is usually processed after the sintering step to obtain a desired magnet product. In the case of RTB based sintered magnets, diffusion and heat treatment are normally performed between the sintering process and the working process, and surface treatment is performed after the working process.

[3] Sintered Magnet The sintered magnet may be either a rare earth sintered magnet or a ferrite sintered magnet. The composition of each magnet will be described below.

(a) Rare Earth Sintered Magnet The rare earth sintered magnet preferably consists essentially of RTB. R is at least one rare earth element including Y, and preferably at least one of Nd, Dy and Pr. T is at least one transition metal and preferably always contains Fe. A preferable composition is R: 24 to 34% by mass, B: 0.6 to 1.8% by mass, and the balance Fe. If R: less than 24% by mass, the residual magnetic flux density _{Br and} the coercive force _Hcj decrease. If it exceeds 34%, the residual magnetic flux density _Br decreases. In addition, the area of the phase rich in rare earth elements inside the sintered body increases and the morphology becomes coarse, resulting in a decrease in corrosion resistance. When B: less than 0.6% by mass, the amount of B necessary for forming the R ₂ Fe ₁₄ B phase, which is the main phase, is insufficient, and the R ₂ Fe ₁₇ phase having soft magnetic properties is generated, resulting in a decrease in coercive force. descend. On the other hand, if the amount of B exceeds 1.8% by mass, the phase rich in B, which is a non-magnetic phase, increases and the residual magnetic flux density _Br decreases. Fe may be partially substituted with Co, and may contain elements such as Al, Si, Cu, Ga, Nb, Mo, W, and Zr in an amount of about 3% by mass or less.

(b) Sintered Ferrite Magnet Sintered ferrite magnets are made of Sr ferrite, Ba ferrite, Sr--La--Co ferrite, Ca--La--Co ferrite, etc., having a magnetoplumbite (M-type) structure. preferable.

INDUSTRIAL APPLICABILITY The present disclosure has industrial applicability in that it can provide a wet molding die capable of suppressing backflow of slurry and a method for manufacturing a sintered magnet.

Reference Signs List 10, 20 Wet molding molds 11, 21 Dies 12, 22 Lower punches 13, 23 Upper punches 14, 24 Cavities 15, 25 Injection holes 15a, 15b Backflow suppressing portion 15b1 Branching portion 15b2 Flow paths 16, 26 Drainage holes 17, 27 Discharge path S Slurry Sa Slurry high-concentration portion W Wall surface

Claims (4)

a cavity for filling a slurry containing magnetic powder and a dispersion medium;
an injection hole for injecting the slurry into the cavity;
pressure molding means for pressure molding the slurry filled in the cavity;
A wet molding mold comprising
A mold for wet molding, wherein a backflow suppressing part for suppressing a backflow of the slurry is provided in the injection hole. 2. The wet molding die according to claim 1, wherein said backflow suppressing portion is in contact with a wall surface of said injection hole and is provided so as to be inclined from said wall surface toward said cavity. The backflow suppressor is
a branching part for branching the slurry flowing backward from the cavity toward the injection hole;
a channel that guides the flow so that one flow direction of the slurry branched by the branching portion includes a component in a direction opposite to the other flow direction of the branched slurry;
The wet molding mold of claim 1, comprising: A method for producing a sintered magnet using the wet molding die according to any one of claims 1 to 3, comprising:
a molding step of injecting the slurry containing the magnetic powder and the dispersion medium into the cavity through the injection hole to fill the cavity, and molding the filled slurry by the pressure molding means;
and a sintering step of sintering the compact obtained in the forming step.

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