JP2022155977A - Method for producing ferrite sintered magnet - Google Patents

Abstract

To provide a method for producing a ferrite sintered magnet, with which an organic matter can be effectively removed from a molded body or variation in dimensions of sintered magnets can be suppressed.SOLUTION: A method for producing a ferrite sintered magnet includes the steps of: heating a molded body including a ferrite raw material and an organic matter to remove the organic matter from the molded body; and sintering the molded body from which the organic matter has been removed. The outer face of the molded body 10 has a convex 12, and, in at least one of the step of heating the molded body and the step of sintering the molded body, the molded body 10 is mounted on the upper face 20U of a support 20 such that the lowermost part 10U of the convex 12 is in contact with the upper face 20U of the support 20.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for producing a sintered ferrite magnet.

Conventionally, a molded body containing ferrite powder and an organic matter such as a binder is heat-treated to remove the organic matter from the molded body, and then sintered to obtain a sintered ferrite magnet.

JP-A-60-130112 JP-A-61-069104 JP-A-7-111220

However, conventional methods require a long time to sufficiently remove organic matter.

In addition, when sintering the molded body from which the organic matter has been removed, the dimensions after sintering may vary.

One object of the present specification is to provide a method for producing a sintered ferrite magnet that can efficiently remove organic matter from a compact.

Another object of the present specification is to provide a method for producing a sintered ferrite magnet that can suppress variations in the dimensions of the sintered magnet.

According to one aspect of the invention, a step of heating a molded body containing a ferrite raw material and an organic substance to remove at least a part of the organic matter from the molded body;
and sintering the compact from which at least part of the organic matter has been removed. the outer surface of the molded body has a convex surface,
In at least one of the step of heating the compact and the step of sintering the compact, the compact is positioned above the top surface of a support such that the bottom of the convex surface is in contact with the top surface of the support. , is placed.

In at least one of the step of heating the molded body and the step of sintering the molded body, a portion of the convex surface other than the lowest portion can be in a state of not contacting any support.

The outer surface of the molded body can have a concave surface or a flat surface in addition to the convex surface.

A portion of the upper surface of the support that contacts the convex surface may be flat.

In at least one of the step of heating the compact and the step of sintering the compact, the compact can be shaken on the upper surface.

According to one aspect of the present invention, organic substances are efficiently removed from the compact.

According to another aspect of the present invention, dimensional variations in the sintered magnet are suppressed.

FIG. 4 is a perspective view showing a state in which a compact is placed on a support in a step of heat-treating the compact and a step of sintering the compact. FIG. 2 is a side view of the molded body and support of FIG. 1 as seen from the X direction, that is, the axial direction of the molded body; FIG. 5 is a side view showing a state in which a compact is placed on a support in a step of heat-treating the compact and a step of sintering the compact in a comparative example. (a) to (c) are side views showing a molded article according to another embodiment and a state where the molded article is placed on a support, respectively.

(Composition of finally obtained sintered ferrite magnet)
A ferrite sintered magnet is a magnetic oxide containing iron as a main component (50% by mass or more). The ferrite contained in the sintered ferrite magnet can be spinel ferrite, hexagonal ferrite, or garnet ferrite. Examples of hexagonal ferrites are magnetoplumbite (M-type), W-type, Y-type and Z-type ferrites. Among them, magnetoplumbite type ferrite is preferable.

Magnetoplumbite-type ferrite is sometimes referred to as "M-type ferrite" below. M-type ferrite is represented by the general formula AFe ₁₂ O ₁₉ (A is Sr, Ba, Ca, etc.). The M-type ferrite further contains rare earth elements, Bi, Pb, Si, Ga, Sn, Zn, In, Co, Ni, Ti, Cr, Mn, Cu, Ge, Nb, Zr, Al, B, etc. may be contained. Examples of rare earth elements are La, Y, Sc, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu

The composition of the M-type ferrite is not particularly limited, but the M-type ferrite is selected from the group consisting of at least one element α selected from Sr, Ba, Ca and Pb, and rare earth elements (including Y) and Bi. At least one element R, at least one element M selected from the group consisting of Co, Mn, Ni, Cu and Zn, and Fe, and the composition ratio of each metal element is the total amount of metal elements against
α: 1 to 13 atomic %
R: 0.05 to 10 atomic percent
Fe: 80-95 atomic %
M: 0.1 to 5 atomic percent
can satisfy you.

In the crystal structure of this M-type ferrite, if the R element is present at the α element site and the M element is present at the Fe site, the ferrite composition formula is given by the following general formula (1).
α _(1-x) R _x [Fe _(12-y) M _y ] _z O ₁₉ (1)
Here, x, y, and z are values calculated from the atomic % of each metal element described above.

The sintered ferrite magnet preferably contains metal elements in an atomic ratio represented by the following formula (2).
_{Ca1 - abRaSrbFecCom (} 2 ₎
In formula (2), R is at least one element selected from the group consisting of rare earth elements (including Y) and Bi and contains at least La,
In formula (2), a, b, c and m satisfy the following formulas (3) to (6),
0.360≦a≦0.420 (3)
0.110≦b≦0.173 (4)
8.51≦c≦9.71 (5)
0.208≦m≦0.269 (6)

As described above, when the ferrite is an M-type ferrite containing Ca, the anisotropy of the shrinkage rate during sintering tends to increase, and external factors during sintering (such as shrinkage inhibition due to contact with the support) Since the shrinkage ratio of the sintered magnet tends to vary due to the sintered magnet, the effect of the present invention is further exhibited.

The ferrite sintered magnet described above may contain subcomponents such as Si, Al, Ba, and Cr in addition to the above. These can be grain boundary components in sintered ferrite magnets. Also, Al, Ba, and Cr can be contained both in ferrite and in grain boundaries. The amounts of Si, Al, Ba, and Cr are 0.0 to 1.0% by mass and 0.0 to 1.0% by mass in terms of _{SiO2 , Al2O3 ,} BaO, and _Cr2O3 , respectively. %, 0.0-0.1 mass %, 0.0-0.2 mass %.

A metal such as Ca may be contained in both the ferrite phase and the grain boundary phase.

The composition of the sintered ferrite magnet and compact can be measured by fluorescent X-ray quantitative analysis or the like. Also, the presence of the ferrite main phase in the sintered ferrite magnet can be confirmed by X-ray diffraction or electron beam diffraction.

(Manufacturing method of ferrite sintered magnet)
A method for producing a sintered ferrite magnet according to one aspect of the present invention includes a step of heating a compact containing a ferrite raw material and an organic matter to remove the organic matter from the compact, and a step of sintering the compact from which the organic matter has been removed. And prepare.

(ferrite raw material)
The ferrite raw material contains in its composition the metal and metalloid elements contained in the final sintered ferrite magnet. The ferrite raw material preferably contains ferrite powder (for example, hexagonal ferrite such as M-type ferrite), and in addition to the ferrite powder, at least It can include a powder of an element or a compound containing one. Even in that case, the overall composition of metals and metalloid elements in the ferrite raw material should be the same as the composition of the finally obtained sintered ferrite magnet.

Examples of powders other than ferrite powder include oxides containing Fe (such as iron oxide), compounds containing element α such as Ca, compounds containing element R, oxides containing element M such as Co, and Si, Al, Cr A powder of a compound containing at least one selected from the group consisting of

Examples of compounds can be oxides, carbonates, nitrates, sulfates, chlorides, etc. of each element(s) that can become oxides of each element after calcination. Powders of such compounds can act as sintering aids during sintering. For example, a ferrite sintered magnet with a high density can be obtained by including appropriate amounts of Ca and Si compounds in addition to the ferrite powder in the ferrite raw material of the compact.

The ferrite raw material preferably has a specific surface area (SSA: Specific Surface Area) determined by the BET method of about 4 to 12 m ² /g.

(Manufacturing method of ferrite raw material)
A ferrite raw material containing ferrite powder can be obtained, for example, as follows.

<Material preparation process for calcination>
First, raw materials for calcination are prepared. The raw material for calcination contains, in its composition, metals and metalloid elements that constitute ferrite generated by calcination. These metal and metalloid elements are at least part of the metal and metalloid atoms that constitute the finally obtained sintered ferrite magnet. The calcining raw material can be a mixture of compounds of metal and metalloid elements. Each compound is preferably in powder form. Examples of compounds are oxides of each element, or compounds that can become oxides of each element by calcination (carbonates, hydroxides, nitrates, etc.). Specific examples _are SrCO3, La ₍ OH) _{3 , Fe2O3 ,} BaCO3 _{, CaCO3} and Co3O4. The raw material for calcination may contain, for example, a material (for example, a compound) containing an auxiliary component such as a Si component. An example of a compound for the Si component is _SiO2 . The average diameter of the powder of each compound is preferably about 0.1 to 2.0 μm, for example, from the viewpoint of enabling uniform blending.

The raw material for calcination may contain metal and semimetal elements in a composition corresponding to the metal and semimetal elements of the finally obtained sintered ferrite magnet. You may make it add. The timing of the post-addition may be adjusted so that the desired composition and magnetic properties can be easily obtained.

Specifically, after mixing each compound, the raw material for calcination can be obtained by mixing and pulverizing the mixture for about 0.1 to 20 hours using a wet attritor, ball mill, or the like.

<Temporary firing process>
The raw materials for calcination are calcined. It is preferable to perform the calcination in an oxidizing atmosphere such as air. The calcination temperature is preferably in the range of 1100 to 1400°C, more preferably 1100 to 1300°C, even more preferably 1150 to 1300°C.

The holding time at the calcining temperature can be 1 second to 10 hours, preferably 1 second to 5 hours. The calcined body obtained by calcining can contain 70% or more of the ferrite phase (for example, M phase) as described above.

The primary particles of the calcined body preferably have an average particle size of 0.1 to 10 μm, particularly 0.1 to 5 μm. The average particle size may be measured by SEM.

<Pulverization process>
The calcined body that has become granular or lumped in the calcining step is pulverized to obtain ferrite powder. This facilitates molding in the molding process, which will be described later. In this pulverization step, as described above, the remaining raw material compounds that have not been blended with the raw material for calcination may be added (post-addition of raw materials). The pulverization step may be carried out in two steps, for example, pulverizing the calcined body into coarse powder (coarse pulverization) and then further pulverizing it into finer particles (fine pulverization). In the following, a description will be given of a case in which dry coarse pulverization is performed as coarse pulverization and then wet pulverization is performed as fine pulverization, but the present invention is not limited to this, and pulverization methods may be combined as appropriate.

Coarse pulverization is performed, for example, until the average particle size reaches 0.5 to 5.0 μm. The pulverization means is not particularly limited, and for example, a dry vibration mill, roller mill, hammer mill, etc. can be used, but it is not limited to these. The pulverization time may be appropriately determined depending on the pulverization means.

After dry coarse pulverization, fine pulverization can be performed by preparing a pulverization slurry containing the coarsely pulverized material of the calcined body and water, and wet pulverizing it. The content of the calcined body in the pulverizing slurry is preferably about 10 to 70% by mass. In fine pulverization, the average particle size of the finely pulverized material obtained is preferably about 0.08 to 2.0 μm, more preferably 0.1 to 1.0 μm, and still more preferably about 0.2 to 0.8 μm. As such, pulverization can be carried out. The specific surface area of the finely pulverized material (for example, determined by the BET method) is preferably about 4 to 12 m ² /g. Pulverization means used for wet pulverization is not particularly limited, but it is usually preferable to use a ball mill, an attritor, or the like. The pulverization time may be appropriately determined depending on the pulverization means. For example, in the case of a wet attritor, it is preferably about 30 minutes to 20 hours, and in the case of wet ball mill pulverization, it is preferably about 10 to 50 hours.

When the remaining part of the metal elements and semi-metal elements of the sintered ferrite magnet is added in the pulverization step, the addition can be performed during pulverization, for example. In the present embodiment, SiO ₂ as a Si component and CaCO ₃ as a Ca component can be added during fine pulverization. Also good.

In the fine pulverization step, in the case of the wet method, water as well as non-aqueous solvents such as toluene and xylene can be used as the dispersion medium. The use of an aqueous solvent is more advantageous from the viewpoint of productivity, but is not limited to this, and the solvent may be appropriately selected in consideration of, for example, the solubility of the surface treatment agent described later in the solvent.

<Drying process>
After wet pulverization, the slurry containing the ferrite powder is dried. The drying temperature is preferably 80-150°C, more preferably 100-120°C. The drying time is preferably 1 to 40 hours, more preferably 5 to 25 hours. The average particle size of the primary particles of the magnetic powder after drying is preferably in the range of 0.08 to 2 μm, more preferably in the range of 0.1 to 1 μm. By drying, a ferrite raw material containing ferrite powder is obtained.

(Preparation process of raw material for molding)
Subsequently, a raw material for molding is prepared by mixing a ferrite raw material and an organic substance.

Specifically, by kneading a ferrite raw material and an organic substance with a kneader or the like, a molding raw material with good dispersibility can be obtained.

The organic matter may be at least one selected from the group consisting of binder resins, waxes, and plasticizers, and may contain additives. Additives can be lubricants and/or dispersants (surface treatments). Lubricants and dispersants can serve as each other.

Examples of binder resins are polymer compounds such as thermoplastic resins, and examples of thermoplastic resins are polyethylene, polypropylene, ethylene-vinyl acetate copolymer, atactic polypropylene, acrylic polymer, polystyrene, and polyacetal. Two or more binder resins may be used.

Examples of waxes are natural waxes such as carnauba wax, montan wax, beeswax; synthetic waxes such as paraffin wax, urethanized wax, polyethylene glycol.

Examples of plasticizers are phthalates.

The amount of the binder resin added is preferably 3 to 20% by mass, the amount of the waxes added is preferably 3 to 20% by mass, and the amount of the plasticizer added is It is preferably 0.1 to 5% by mass with respect to 100% by mass of the binder resin.

The additive amount may be 0 to 8% by mass in total, preferably 0.1 to 8% by mass, based on 100% by mass of the ferrite raw material.

Examples of lubricants are fatty acid esters.
In this embodiment, the amount of the lubricant added to 100% by mass of the ferrite raw material may be 0 to 5% by mass, preferably 0.1 to 5% by mass.

Examples of dispersants (surface treatment agents) include higher fatty acids such as oleic acid, stearic acid, calcium stearate and zinc stearate, salts/derivatives thereof, silane coupling agents, and the like.

In the present embodiment, the amount of the dispersant (surface treatment agent) added to 100% by mass of the ferrite raw material may be 0 to 3% by mass, preferably 0.1 to 3% by mass, more preferably 0.3 to 3% by mass. 3% by mass, more preferably 0.4 to 2.0% by mass. When the amount of the dispersant (surface treatment agent) added is within this range, the dispersant can sufficiently adhere to the ferrite raw material to weaken the cohesive force, and the ferrite raw material can be uniformly dispersed in the kneaded product. can do If the amount added is too large, the presence of an excess dispersant (surface treatment agent) that cannot be adsorbed on the surface of the ferrite raw material causes the effect of reducing the cohesive force of the ferrite raw material and The effect of improving the dispersibility of the ferrite raw material tends to decrease.

The mixing order of these organic substances is not limited, and they may all be mixed simultaneously with the ferrite raw material, or they may be mixed with the ferrite raw material in any order. In particular, a dispersant (surface treatment agent) or the like can also be added in the pulverization step described above. For example, a dispersant may be added to the slurry during wet pulverization, or a dispersant may be added to the slurry after wet pulverization and before drying. may be pre-mixed with

The molding raw material obtained by kneading is preferably molded into pellets using a pelletizer or the like. As the pelletizer, for example, a twin-screw single-screw extruder is used. Further, kneading and pellet forming may be carried out while heating according to the melting temperature of the organic component used.

<Molding process>
A molded body having a desired shape is obtained by molding the raw material for molding. The molding method is not particularly limited.

For example, injection molding equipment can be used to obtain molded bodies in a magnetic field. Specifically, pellets of molding material are melted while being kneaded by a screw in the cylinder of an injection molding machine, and the molten molding material is injected into a mold having a cavity corresponding to the desired shape for molding. do it. A predetermined magnetic field can be applied to the mold during molding. The raw material for molding can be heated and melted at 160 to 230° C. in a cylinder for injection molding. The temperature of the mold can be 20-80°C. The magnetic field applied to the mold can be about 398-1592 kA/m (5-20 kOe).

In this way, a molded body containing a ferrite raw material and an organic substance is obtained.

The exterior surface of the compact includes a convex surface. FIG. 1 is a perspective view showing an example of the molded article of this embodiment. The compact 10 of this embodiment has a three-dimensional shape formed by moving a thick arc-shaped (U-shaped) flat surface (end surface) 16 in an axial direction perpendicular to the flat surface 16, that is, an arc segment shape. The compact 10 has a convex surface 12 , a concave surface 14 facing the convex surface 12 , flat surfaces 16 , 16 and flat surfaces 18 , 18 connecting the convex surface 12 and the concave surface 14 .

The axial length L of the compact 10 can be 5-100 mm, the arc width W can be 5-100 mm, and the arc height H can be 5-50 mm.

<Heating step of molded body (organic substance removal step)>
Next, the molded body 10 containing the ferrite raw material and the organic matter is heated to remove at least part of the organic matter from the molded body 10 . If the organic matter is excessively removed from the molded article, the molded article may have insufficient shape-retaining power and cracks may occur. By leaving a part of the binder resin in the molded article after heating, the shape retention force of the molded article can be sufficiently increased, and defects such as chipping can be suppressed.

The atmosphere for the heat treatment by heating may be an oxygen-containing atmosphere such as the atmosphere, or an oxygen-free atmosphere such as nitrogen. The heating temperature may be any temperature at which the organic substance can be removed, and can be, for example, a temperature of 100 to 600.degree. The heating time can be appropriately set according to the amount and kind of the organic substance, but it can usually be 0.5 to 100 hours.

When the molded body 10 is heated, the organic matter inside the molded body is volatilized and thermally decomposed, and the gas of the volatile substances and decomposition products is discharged to the outside from the surface of the molded body. If the rate of temperature rise during removal of the organic matter is too rapid, cracks or cracks may occur in the compact due to rapid volatilization of the organic matter or generation of decomposed gas. Therefore, depending on the organic component to be removed, the temperature rise rate in the temperature range where the organic matter volatilizes or decomposes may be appropriately adjusted, for example, to a slow temperature rise rate of about 0.01 to 1° C./min. can be done. The heat treatment temperature and temperature profile can be set as appropriate. Moreover, when using a plurality of kinds of organic substances, the heat treatment may be performed in a plurality of times.

The organic substance removal rate before and after the heating step defined by the following formula may be 30-100%, preferably 40-98%.
Organic substance removal rate (%) = (mass of molded body before heating - mass of molded body after heating) / (mass of molded body before heating x organic matter content (%) / 100) x 100

In this embodiment, in the heating step, as shown in FIGS. Place so that it touches.

A portion of the upper surface 20U that contacts the convex surface 12 is preferably flat. Generally, the surface of the refractory support 20 has surface roughness. A "plane" in this specification can have a surface roughness with an arithmetic mean height Sa from the average plane of 1 mm or less. Arithmetic mean height is defined in ISO 25178.

In addition, the surface of the support 20 made of refractory material is not perfectly flat, but rather gently curved in many cases. The term “flat surface” as used herein includes cases where the flatness is 5 mm or less. For the flatness, the height distribution of the upper surface 20U of the support 20, for example, the portion facing the molded body 10, is obtained with a commercially available 3D surface profile measuring device such as an optical type or a contact type, and the average plane is obtained by the least squares method. is the distance to the point furthest from the mean plane and the height distribution. The flatness may be 2 mm or less, or 1 mm or less.

In this embodiment, the outer shape of the lowermost portion 12B of the convex surface 12 is substantially linear along the axial direction of the convex surface 12. As shown in FIG. The straight line length of the lowest portion 12B is equal to or less than the axial length L of the compact. The straight line width (Y direction in FIG. 1) of the lowermost portion 12B can be 2 mm or less when viewed from the direction perpendicular to the upper surface 20U.

As described above, in order to prevent cracks and cracks, the heating process for removing organic substances must have a slow temperature increase rate, so the heating process tends to become a bottleneck in the production process. In addition, since the removal of organic substances progresses by the release of organic volatiles and decomposed substances from the surface of the molded body, the greater the contact area between the molded body and the atmosphere, the more likely it is to be removed.

In the method of the present embodiment, since the lowermost part of the convex surface of the molded body is supported by the upper surface of the support, the contact area between the molded body and the support can be reduced. That is, since the contact area between the compact and the atmosphere can be increased in the process of removing the organic matter, the removal of the organic matter is efficiently promoted.

Here, in the heating step, it is preferable that the portions other than the lowermost portion 12B of the convex surface 12 are not supported (contacted) by any support. Thereby, the contact area between the compact 10 and the atmosphere can be increased.

In addition, the molding 10 can be shaken on the support 20 in the heating process. For example, an air flow (such as hot air) is supplied to the compact 10 using a blower type furnace, a vibrator is used to vibrate the support 20, and a rail or conveyor is used as a support for supporting the compact in the furnace. It is preferable to shake the molded article 10 on the support 20 in the heating step, for example, by heating while moving through the support 20 . The direction in which the airflow is supplied to the compact 10 is not particularly limited. The airflow may be supplied so as to hit the upper end portion 12T away from the lowermost portion 12B (upper surface 20U of the support 20).

In this embodiment, since the lowermost portion 12B of the convex surface 12 is supported by the upper surface 20U of the support 20, the compact 10 can easily swing on the support 20. FIG. The shaking of the molded body 10 makes it easier to remove the organic matter from the contact portion of the molded body 10 with the support 20 .

The material of the support 20 is not particularly limited, but any refractory material, such as ceramics such as alumina, may be used.

The shape of the support 20 is not limited. The support 20 may be plate-shaped as shown in FIG. 1, or may be a box-shaped support (a so-called sagger) having an upward edge on the outer edge of the plate.

<Sintering process>
In the sintering step, the molded body 10 from which at least part of the organic matter has been removed through the heating step is sintered to obtain a sintered ferrite magnet.

The sintering atmosphere can be an oxygen atmosphere such as air. The sintering temperature can be between 1150 and 1300°C, preferably between 1180 and 1270°C. The time for maintaining the sintering temperature can be about 1 minute to 3 hours.

After the heating step described above, the sintering step may be performed continuously without cooling to room temperature, or the sintering step may be performed after cooling to room temperature once after the heating step.

In the sintering step, the compact 10 is placed on the upper surface 20U of the support 20 so that the lowermost portion 12B of the convex surface 12 of the compact 10 is in contact with the upper surface 20U of the support 20 in the same manner as in the above-described step of removing organic substances by heating. It is preferable to carry out the operation while the device is placed on top.

In the sintering process, the structure of the oxide containing the ferrite phase is densified, so that the compact is shrunk. The shape change due to this shrinkage is affected by the temperature profile, packing style, and the like.

Friction occurs at the contact portion between the compact 10 and the support 20 during shrinkage, which causes the shape of the compact before and after sintering to differ. The support 20 is usually made of ceramics such as alumina. However, the smoothness of the surface of the support 20 may vary depending on the location of the upper surface of the support 20 due to wear due to use. The magnitude of friction may also be different. In addition, warping or the like may occur in the support, resulting in a decrease in planarity. Therefore, if the contact points are different, the contact area may be different, which causes variation in shrinkage between products.

If the sintered body has large dimensional variations, a processing step after sintering is required to obtain a desired shape. Also, when processing is performed, the greater the dimensional variation, the greater the processing margin. An increase in the machining margin causes cracks and chipping during machining, resulting in a decrease in yield. Moreover, an increase in the machining allowance may lead to a decrease in the bending strength of the ferrite magnet.

In this embodiment, since the lowermost portion 12B of the convex surface 12 is supported by the support 20 in the sintering process, the contact points and contact areas between the compact 10 and the support 20 can be reduced. That is, when the molded body shrinks due to sintering, it is possible to reduce the locations and areas where frictional resistance occurs between the molded body and the support, thereby reducing variations in product dimensions.

The present invention is not limited to the above embodiments, and various modifications are possible.

For example, the shape of the molded body is not particularly limited as long as the outer surface has a convex surface. In particular, the effect is high when the outer surface of the molded article has a concave surface and/or a flat surface in addition to the convex surface. In the case of such a shape, it is usually placed on the support 20 with the concave surface 14 facing downward (see FIG. 3) or with the flat surface 16 or the like facing downward in order to stabilize the compact. be. However, in the present embodiment, the convex surface 12 faces downward and is placed on the support 20 so that the lowermost portion 12B of the convex surface 12 is in contact with the upper surface 20U of the support 20 .

Other forms of the compact 10 are shown in FIGS. 4(a) to 4(c). In FIG. 4(a), the cross section perpendicular to the axis of the compact is not arc segment-shaped but D-shaped, and the convex surface 12, the plane 14' facing the convex surface 12, and the convex surface 12 and the plane 14' are connected. It has planes 18, 18 and planes 16, 16 which are end faces in the line-of-sight direction (X direction).

In FIG. 4B, the cross section in the axial direction has a barrel shape, the convex surface 12, the convex surface 14' facing the convex surface 12, the flat surfaces 18, 18 connecting the convex surfaces 12 and 14', and the line of sight direction. It has planes 16, 16 which are end faces in the (X direction).

In FIG. 4(c), in the axial cross section, only the upper surface is different from that in FIG. 4(b). '', planes 18, 18 connecting the convex surface 12 and the planes 14', 14'', and end faces 16, 16 in the viewing direction (X direction).

Also in these molded bodies 10, the convex surface 12 is arranged downward, and the lowermost portion 12B of the convex surface 12 is in contact with the upper surface 20U of the support 20. As shown in FIG.

The radius of curvature of the lowermost portion 12B of the convex surface 12 is not particularly limited as long as it is a curved surface.

The shape of the molded body is not particularly limited, and can be modified in various ways other than those shown in the drawings, and can have various shapes depending on the application. Moreover, there is no particular limitation on the dimensions of the molded body. Other examples of shaped body shapes are spheres, cylinders, cylinders or elliptical spheres. The surface of the convex surface may have minute irregularities (for example, an arithmetic mean height Sa (height difference) of 1 mm or less).

In the case of a column, cylinder, or molded body having a convex surface 12 such as the convex surface 12 shown in FIG. On the other hand, when the shape of the compact is, for example, spherical or has a spherical surface, the shape of the lowest portion of the spherical surface is point-like. The diameter of the lowermost point considering surface roughness can be 2 mm or less.

Ridges and corners formed between the surfaces (convex surface, concave surface, flat surface, etc.) of the molded body 10 may be chamfered. The molded body may have a plurality of convex surfaces.

In the above embodiment, in both the step of heating the compact (the step of removing organic substances) and the step of sintering the compact, the compact is placed on the upper surface of the support so that the lowest part of the convex surface is in contact with the upper surface of the support. However, if the above mounting method is employed in either the step of removing the organic matter from the compact or the step of sintering the compact, at least one of the effects can be obtained.

(Example)
(Production of ferrite raw material)
First, iron oxide (Fe ₂ O ₃ ; including Mn, Cr, Al, Si, and Cl as impurities), lanthanum hydroxide (La(OH) ₃ ), calcium carbonate (CaCO ₃ ), strontium carbonate (SrCO ₃ ) , barium carbonate (BaCO ₃ ), and cobalt oxide (Co ₃ O ₄ ), and the atomic ratio of the metal elements is Ca _0.36 La _0.48 Sr _0.16 Ba _0.001 Fe _11.25 Co _0.15 . A mixed powder containing For this mixed powder, silicon oxide (SiO ₂ , moisture content: about 20%, the same raw material hereinafter) is added as a Si component to 0.66% by mass with respect to 100% by mass of the mixed powder. addition to obtain a second mixed powder.

The second mixed powder was pulverized and mixed with a wet attritor to obtain a slurry, which was then dried to obtain a raw material for calcination. The raw material for calcination was held in the air at 1225° C. for 2 hours to perform calcination. The obtained calcined body was coarsely pulverized by a small lot vibration mill to obtain a coarsely pulverized material.

With respect to the obtained coarsely pulverized material, the ratio of metal elements of the ferrite raw material (same as the metal elements constituting the sintered ferrite magnet after firing) is Ca _0.45 La _0.40 Sr _0.15 Ba _0.001 Fe _9.2 Co _0.245 , iron oxide (Fe ₂ O ₃ ; including Mn, Cr, Al, Si, and Cl as impurities)), calcium carbonate (CaCO ₃ ), strontium carbonate (SrCO ₃ ) , Cobalt oxide (Co ₃ O ₄ ) is added and pulverized in a wet ball mill so that the specific surface area determined by the BET method is 8.5 to 10.0 m ² /g, to obtain a ferrite raw material containing ferrite powder. got

(Preparation of molded body containing ferrite raw material and organic substance)
Ferrite raw material, PP (polypropylene, used as binder resin), paraffin wax (used as wax), acrylic resin (used as binder resin), DOP (dioctyl phthalate, used as plasticizer), and stearic acid (as additive used) were mixed to obtain pellets. The composition of the pellet was as follows: ferrite raw material = 90% by mass, PP = 4% by mass, paraffin wax = 4% by mass, acrylic resin = 0.5% by mass, DOP = 1% by mass, stearic acid = 0.5% by mass. . Using a pressurized heating kneader, kneading was carried out at 165° C. for 2.5 hours, and the kneaded product (compound) was formed into pellets by a pelletizer.

Next, using a magnetic field injection molding apparatus, the pellets were heated and melted, and then injection molded into a mold to obtain a molded body. Injection molding was performed while a magnetic field was applied to the inside of the mold. The injection temperature was 185° C., the mold temperature was 40° C., and the applied magnetic field during injection was 1273 kA/m. The shape of the compact was the arc segment type shown in FIG. 1, and W=32 mm, H=12 mm, and L=25 mm.

(Removal of organic matter from compact containing ferrite powder and organic matter)
The compact 10 was placed on a support (alumina plate) 20 so that the lowermost portion 12B of the convex surface 12 was in contact with the upper surface 20U of the support 20, as shown in FIGS. Next, the molded body was heated from room temperature to 200° C. at a temperature rising rate of 0.1° C./min in an air atmosphere to remove organic substances. Also, in the heating step, a hot-air blowing drying oven was used to remove the organic matter while shaking the compact on the support.

The average organic substance removal rate was obtained from the following formula from the mass change before and after the heat treatment in the three molded bodies obtained.
Organic substance removal rate (%) = (mass of molded body before heating - mass of molded body after heating) / (mass of molded body before heating x organic matter content (%) / 100) x 100

(Baking and evaluation of compact)
The compact from which the organic substances had been removed was placed on a support (alumina plate) so that only the lowermost portion 12B of the convex surface 12 was in contact with the upper surface 20U of the support 20, as shown in FIGS. Next, it was sintered by holding it at 1200 to 1220° C. for 1 hour in the atmosphere to obtain a sintered ferrite magnet.

Table 2 shows the results of measuring the width W of the five sintered ferrite magnets obtained and evaluating the average value and standard deviation.

(Comparative example)
In both the organic substance removal step and the sintering step, the same procedure as in Example 1 was performed except that the molded body was arranged so that the convex surface faced upward as shown in FIG. 3 instead of FIG.

The results are shown in Tables 1 and 2.

From Table 1, it was confirmed that the organic substance removal rate was higher in the case of supporting as in the example (FIG. 2) than in the comparative example (FIG. 3). This is considered to be due to the fact that in the example, the contact points and the contact area with the atmosphere during the removal of the organic matter are smaller than in the comparative example.

Further, from Table 2, the absolute value of the width W after sintering was smaller in the example than in the comparative example. It is considered that this is because, when supported as in the example, the frictional resistance with the support is smaller than in the comparative example, and the amount of shrinkage of the width W is greater. Moreover, the standard deviation of the width W after sintering was smaller in the example than in the comparative example. It is considered that the dimensional variation is reduced because the influence of frictional resistance with the support is less likely to occur.

DESCRIPTION OF SYMBOLS 10... Molded body 12... Convex surface 12B... Bottom of convex surface 14... Concave surface 16, 18... Flat surface 20... Support body 20U... Upper surface.

Claims (5)

a step of heating a molded body containing a ferrite raw material and an organic substance to remove at least a portion of the organic matter from the molded body;
A method for producing a sintered ferrite magnet, comprising the step of sintering the compact from which at least part of the organic matter has been removed,
the outer surface of the molded body has a convex surface,
In at least one of the step of heating the compact and the step of sintering the compact, the compact is positioned above the top surface of a support such that the bottom of the convex surface is in contact with the top surface of the support. , placed, method. 2. The method according to claim 1, wherein in at least one of the step of heating the compact and the step of sintering the compact, a portion of the convex surface of the compact other than the lowest portion is not in contact with any support. described method. 3. A method according to claim 1 or 2, wherein the outer surface of said molded body has, in addition to said convex surface, a concave surface or a flat surface. The method according to any one of claims 1 to 3, wherein the portion of the top surface of the support that contacts the convex surface is planar. The method according to any one of claims 1 to 4, wherein in at least one of the step of heating the compact and the step of sintering the compact, the compact is shaken on the upper surface.

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