JP2001146482A - Method for producing spherical ceramic sintered compact - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a spherical ceramic sintered compact having few defects, producible in a high efficiency and to provide a method for producing the spherical ceramic sintered compact. SOLUTION: Ground powder 10k for formation is solidified into a spherical state in a granulation container 132 by a rolling granulation method to give a spherical formed body. The formed body is sintered to give a spherical ceramic sintered compact. In the rolling granulation formation process, the maximum load applied to the spherical formed body in the middle of the formation is >=500 g/cm2. Consequently deformation by ununiform shrinkage of the sintered compact and incidence of defective sintered compact by crack and chip can be reduced. When an inner volume of the granulation container 132 is V0 and the total volume of the ground powder 10k for formation and the spherical formed body in the middle of the formation is V1, preferably the formula (V1/V0)×100(%) is 5-40%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bearing for a hard disk of a computer, a bearing for a special environment such as a semiconductor device, or a bearing for other uses, a ball for a pen point of a ball-point pen, a dental drill, and other polishing processes. The present invention relates to a spherical ceramic sintered body used for a necessary spherical object and the like and a method for producing the same.

[0002]

2. Description of the Related Art In recent years, ceramic bearing balls made of silicon nitride have been used for some applications, mainly bearings for machine tools, in order to improve durability. However, ceramic bearing balls are expensive, and for applications requiring special environmental specifications, such as hard disks of computers or semiconductor devices, which use a large amount of bearings, are still not widely used due to cost and reliability issues. Not reached.

[0003] One of the reasons for preventing the widespread use of ceramic bearing balls in such applications is that a method of forming a spherical body suitable for such applications has not yet been sufficiently established. . That is, a general molding method can provide a relatively uniform and less defective spherical molded body if the sphere has a certain diameter or more, but the production efficiency of the molded body is extremely low. Thus, it is not suitable for the field using a huge amount of balls. In computer hard disks and semiconductor devices, there is a high demand for small ceramic spheres having a diameter of 4 mm or less. However, it is inefficient to produce a spherical molded body by a die molding method, and it is unavoidable to increase production costs. . In addition, when manufacturing a spherical molded body by a die press method, a press punch having a hemispherical concave portion on the tip end surface will be used,
In order to avoid insufficient pressurizing force, flattening the outer peripheral edge of the punch concave portion is performed. When such a flattened portion is formed in the press punch, an unnecessary portion in the form of a flange (or a band) is inevitably formed in the molded body correspondingly. The unnecessary portion is removed by polishing or the like before and after firing, but there is a problem that the production efficiency of the ceramic sphere is deteriorated by the amount of the removal step required.

Therefore, a granulation molding method is known as a more efficient method for producing a small-diameter spherical molded body. For example, Japanese Patent Application Laid-Open No. H11-62975 discloses a method for producing ceramic spheres by granulation molding and then pressure sintering. As an example of such granulation molding, vibration is applied to powder. The rolling granulation method in which the particle size is increased by a snowman method while moving a sphere is described. In addition, it is also stated that the rolling granulation method can improve the density and strength of a molded body, unlike uniaxial pressing by die molding.

[0005]

However, the above-mentioned gazette presupposes that the granulation molding method is essential, especially to application to bearing balls and the like, which are required to be small, high-performance and high-precision, such as computer hard disks and semiconductor devices. And
No specific embodiment of the granulation method is disclosed. According to the study of the present inventors, it is impossible to manufacture a high-precision bearing ball or the like at all within the scope of the technology disclosed in the above publication, and it is newly added that various improvements are required. It turned out.

SUMMARY OF THE INVENTION An object of the present invention is to make it possible to manufacture a semiconductor hard disk with a small number of defects and at a high efficiency. And a method of manufacturing the same.

[0007]

Means for Solving the Problems and Actions / Effects In order to solve the above-mentioned problems, a method for producing a spherical ceramic sintered body of the present invention uses an inorganic material powder (hereinafter, referred to as a lamic material).
A raw material powder preparation step of preparing a molding base powder using a ceramic powder) and charging the molding base powder into a granulation container, and agglomerating the molding base powder into a spherical shape in the granulation container. A rolling granulation forming step of obtaining a spherical formed body, and a sintering step of obtaining a spherical ceramic sintered body by sintering the formed body; The maximum load applied to the body is 500 g / cm ²
It is characterized by the above.

In the case of a spherical ceramic sintered body, particularly a spherical ceramic sintered body such as a bearing ball, which requires high performance and high accuracy, if defects such as pores and cracks remain in the surface layer of the sintered body. Performance and life are greatly affected.
In order to obtain a dense sintered body structure with few such defects, it is necessary that the formed body be as dense as possible with few defects before sintering. And we have:
When the compact is manufactured by the rolling granulation method, it is particularly effective to set the maximum load applied to the spherical compact during molding to be 500 g / cm ² or more in order to obtain a compact having few defects. Thus, the present invention was completed.

If the maximum load applied to the spherical compact in the rolling granulation step is less than 500 g / cm ² , defects such as uneven density and discontinuous boundaries due to unevenness of powder are likely to occur, and sintering occurs. Deformation due to uneven shrinkage of the body, and an increase in the incidence of defects due to cracking or chipping. The maximum load is desirably 1000 g / cm ² or more. On the other hand, the upper limit of the maximum load is determined so that the load applied to the spherical molded body does not become excessively excessive and a problem such as chipping or cracking does not occur. The upper limit varies depending on the properties of the powder to be used and the strength of the obtained molded product (green), but the limit is approximately 50,000 g / cm ² .

In the rolling granulation molding step, when the internal volume of the granulation container is V0 and the total volume of the green body powder for molding and the spherical molded body in the course of molding is V1, (V1 / V0) ×
Preferably, 100 (%) is 5 to 40%. (V
When the value of (1 / V0) × 100 is less than 5%, the progress of forming by rolling granulation becomes insufficient, and the resulting formed body is liable to have defects. This may lead to an increase in the defect occurrence rate due to cracking or chipping. On the other hand, if it exceeds 40%, the content in the granulation container becomes too large, which hinders the rolling or flowing of the molded product, and causes a problem of increasing the defect occurrence rate. The value of (V1 / V0) × 100 is desirably 1
The content is preferably set to 5 to 40%.

Next, in the rolling granulation molding step, the green body powder for molding and the molding nucleus are put into a granulation container, and the molding nucleus is rolled in a rotating granulation container while the molding nucleus is being rolled. It is desirable that the green body powder for molding is adhered and aggregated in a spherical shape around the body to obtain a spherical molded body. In this case, the spherical ceramic sintered body obtained by sintering the spherical molded body has a nucleus portion that can be distinguished from the outer layer portion at the center in a cross section substantially passing through the center. The term “identifiable” as used herein does not only mean that it is visually identifiable, but also a specific physical property value (for example, density or hardness) that causes a difference between the core and the outer layer. , Etc.) also includes cases where identification is possible.

In a rotating granulating container, for example, while rolling a molding core on a molding powder layer, the molding powder is adhered and aggregated in a spherical shape around the molding core to form a spherical compact. By obtaining, the density of the agglomeration layer of the molding base powder that grows around the molding core can be significantly increased, and the formed agglomeration layer has pores due to bridging of powder particles and the like. Also, defects such as cracks are further reduced.

[0013] When such a spherical molded body is fired, the obtained spherical ceramic sintered body has, for example, a cross section substantially passing through the center polished, and when this is magnified and observed, a molding nucleus is formed at the center thereof. The core part derived from the body is formed so as to be distinguishable from the outer layer part derived from the aggregate layer having high density and few defects. By adopting a sintered body structure in which such a region appears on the polished surface, a high density and high strength spherical ceramic sintered body can be realized with a small defect formation rate in the surface layer, which is the key to improving the performance of bearings etc. .

The size of the compact obtained by the above-mentioned rolling granulation method is, for example, about 0.2 to 8 mm. In particular, it is difficult to obtain a compact having high sphericity by conventional press molding. Another feature of the rolling granulation method is that a compact having a small diameter of 5 mm or less can be easily produced. Then, when a compact having a diameter of 5 mm or less is sintered, a spherical ceramic sintered body having a diameter of 4.5 mm or less (for example, a spherical silicon nitride sintered body) can be easily obtained. This makes it possible to produce high-quality, highly efficient spherical ceramic sintered bodies with a diameter of 4.5 mm or less, or 4 mm or less, used for bearings in computer hard disks and semiconductor devices. Becomes In addition, the rolling granulation method can naturally be applied to the production of a spherical ceramic sintered body having a diameter larger than that described above. For example, a formed body having a diameter of up to about 8 mm (a sintered body having a diameter of about 7 mm) ) Can be manufactured extremely efficiently, and the manufacturing cost can be significantly reduced as compared with, for example, the press method.

The inorganic material powder serving as the ceramic raw material may be a powder mainly composed of the same ceramic component as the fired ceramic, or may be an inorganic compound powder that can be chemically converted into the ceramic component by firing. (Or a mixture of both). As an example of the latter, for example, if you want to obtain a sintered body mainly composed of oxide ceramic,
A salt having a common cation with the oxide (eg, carbonate) can be used. Specific materials of the ceramic to which the present invention is applied include silicon nitride ceramics having high strength and excellent wear resistance, alumina (aluminum oxide), zirconia (zirconium oxide), and silicon carbide. Etc. can be adopted. Further, a composite ceramic material can be obtained in which a conductive inorganic compound phase in which a metal cation component is at least one of Ti, Zr, Nb, Ta and W is added to an alumina or zirconia ceramic. Such a composite ceramic material is prepared by adding a source of a conductive inorganic compound phase (for example, titanium nitride, titanium carbide, titanium boride, or the like) to a raw material powder of an alumina ceramic or a zirconia ceramic.
Powder such as tungsten carbide, zirconium nitride, titanium carbonitride, and niobium carbide), and then molded by the same rolling granulation method as described above, followed by firing. By containing the conductive inorganic compound phase, conductivity can be imparted to the alumina or zirconia ceramic material, and the ceramic material can be subjected to electric discharge machining such as wire cutting. The conductive inorganic compounds include Ti, Zr, Nb, and Ta.
Can be at least one of a metal nitride, a metal carbide, a metal boride, a metal carbonitride, and a tungsten carbide having at least any one of the metal cation components, and specifically, titanium nitride, titanium carbide, boron carbide, and the like. Examples thereof include titanium oxide, tungsten carbide, zirconium nitride, titanium carbonitride, and niobium carbide. Note that the content of the conductive inorganic compound phase is 20% in order to sufficiently improve the conductivity while securing the strength and the fracture toughness value of the composite ceramic material.
It is preferable to set to 60% by volume. Further, in order to further impart toughness to the alumina ceramic, a composite ceramic material containing zirconia ceramic may be used. Such a composite ceramic material uses a ceramic powder in which the highest content ceramic component is one of alumina and zirconia, and the second highest content ceramic component is the other of alumina and zirconia.
It can be obtained by molding and firing by the same rolling granulation method as described above. The amount of the zirconia ceramic mixed with the alumina ceramic is preferably 5 to 60% by volume.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. Here, a case where a silicon nitride-based spherical ceramic sintered body is manufactured is taken as an example, but the material is not limited to this. The silicon nitride-based ceramic is mainly composed of silicon nitride, and the remaining component is a sintering aid component, and 3A, 4A, 5A,
At least one element selected from the group consisting of 3B (for example, Al (alumina)) and 4B (for example, Si (silica)) and Mg can be contained in an amount of 1 to 10% by weight in terms of oxide. These exist in the sintered body mainly in the form of a compound such as an oxide, and may partially exist as a nitride (for example, TiN), an oxynitride, or a carbide (for example, TaC). Such an existing state can be confirmed by, for example, X-ray diffraction, X-ray photoelectron spectroscopy, EPMA, or the like. If the sintering aid component is less than 1% by weight, it becomes difficult to obtain a dense sintered body, and 10% by weight
Exceeding the strength results in insufficient strength, toughness or heat resistance, and in the case of sliding parts, lowers abrasion resistance.
The content of the sintering aid component is desirably 2 to 8% by weight. In the present invention, “main component” (also synonymous with “main component” or “mainly”) means that the content of the substance of interest is 50% by weight or more, unless otherwise specified. I do.

The sintering aid component of Group 3A includes S
c, Y, La, Ce, Pr, Nd, Sm, Eu, Gd,
Tb, Dy, Ho, Er, Tm, Yb, and Lu are generally used. The content of these elements R is RO only for Ce.
₂ and others are calculated using R ₃ O ₃ type oxide. Of these, oxides of heavy rare earth elements of Y, Tb, Dy, Ho, Er, Tm, and Yb are preferably used because they have the effect of improving the strength, toughness, and wear resistance of the silicon nitride sintered body. used. In addition, magnesia spinel, zirconia and the like can also be used as a sintering aid.

The structure of the silicon nitride-based sintered member has a form in which main phase crystal grains containing silicon nitride as a main component are bonded by a vitreous and / or crystalline binder phase. The main phase has an α conversion of 70% by volume or more (preferably 90% by volume).
(% By volume or more) of Si ₃ N ₄ phase. In this case, the Si ₃ N ₄ phase is a phase in which a part of Si or N is substituted by Al or oxygen, and a phase in which metal atoms such as Li, Ca, Mg, and Y are solid-dissolved. There may be. For example, it can be exemplified Sialon which is expressed by the following general formula; _{beta-sialon: Si 6-z Al z O} z N 8-z (z =
0-4.2) α-sialon: M _x (Si, Al) ₁₂ (O, N)
₁₆ (x = 0 to 2) M: Li, Mg, Ca, Y, R (R is a rare earth element excluding La and Ce).

The above-mentioned sintering aid component mainly constitutes a binder phase, but a part thereof may be taken into the main phase. The binder phase may contain unavoidable impurities, for example, silicon oxide contained in the silicon nitride raw material powder, in addition to components intentionally added as a sintering aid.

It is desirable that the silicon nitride powder used as the raw material has an α-rate (a ratio of α-silicon nitride in the total silicon nitride) of 70% or more. At least one element selected from the group consisting of elements of groups 3A, 4A, 5A, 3B and 4B is 1 to 10 in terms of oxide.
% By weight, preferably 2 to 8% by weight. In addition, at the time of compounding the raw materials, in addition to oxides of these elements, compounds which can be converted into oxides by sintering, for example, carbonates and hydroxides may be added.

In the present invention, as shown in FIG. 1, a molding base powder 10 prepared using a ceramic powder composed of the above-mentioned silicon nitride powder and sintering aid powder is placed in a cylindrical granulation container 132. Then, as shown in FIG. 2, the granulation container 132 is rotated around an axis O inclined at a predetermined angle θ with respect to a horizontal line. As a result, an inclined molding base powder layer 10k is formed in the granulation container 132. Then, with the rotation of the container 132, FIGS.
As shown in (1), the molding base powder 10 adheres and agglomerates in a spherical shape to form a spherical molded body 80 (rolling granulation step). By sintering the compact, a spherical ceramic sintered body 90 is obtained as shown in FIG. The granulation container preferably has a cylindrical shape. However, the granulation container is not limited to this as long as it can roll the molded body 80 with rotation or vibration of the container.

At the time of tumbling granulation, it is desirable to put the molding core 50 into a granulation container 132 as shown in FIG. This way,
As shown in FIG. 5 (a), the molded core 50 is the raw material powder layer 1
While rolling on 0k, the raw material powder 10 adheres and aggregates in a spherical shape around the molding core 50 as shown in FIG.

As shown in FIG. 3A, the molding core 50 is mainly composed of ceramic powder, for example, a material having a composition similar to that of the molding base powder 10. (However, ceramic powder different from the ceramic powder (inorganic material powder) constituting the main body of the molding base powder may be used). It is desirable because it hardly acts as a source. However, when there is no concern that the diffusion of the core component extends to the surface layer of the spherical ceramic sintered body 90, the core is replaced with the metal core 50 as shown in FIG.
It is also possible to use d or the glass core 50e. It is also possible to form the nucleus with a material that disappears by thermal decomposition or evaporation during firing, for example, a polymer material such as wax or resin.

The molding core may have a shape other than a spherical shape as shown in FIG. 3 (b) or (c), for example.
As shown in (a), it is needless to say that it is desirable to use a spherical one in order to increase the sphericity of the obtained molded body.

Although there is no particular limitation on the method for producing the molded core, various methods such as those shown in FIG. 4 can be exemplified when the core is mainly composed of ceramic powder. First, (a)
In the method shown in (1), a core is obtained by compression-molding the ceramic powder 60 with a die 51a and press punches 51b, 51b (of course, other compression methods may be used). In (b), the raw material powder is dispersed in a molten thermoplastic binder to form a molten compound 63, which is spray-solidified to obtain a spherical core 50. In the illustrated example, for example, for a spray nozzle composed of an inner nozzle 61 and an outer nozzle 62 that are coaxially arranged, a molten compound 63 is supplied into the inner nozzle 61, and the molten compound 63 is discharged from an opening on the tip side. By spraying a spray medium such as an inert gas or water from an opening through a gap 65 between the nozzles 61 and 62, the molten compound 63 is sprayed and solidified. (C) shows the melting compound 6
3 shows a method of injecting the injection mold 3 into a spherical cavity 70 of an injection mold to form a spherical core. Further, in (e), the molten compound 63 is dropped freely from the nozzle into a spherical shape by surface tension, and is cooled and solidified in air to obtain the core 50. Further, a method of obtaining a spherical molded body by dispersing a slurry comprising a raw material powder, a monomer (or a prepolymer), and a dispersion solvent as droplets in a liquid that is immiscible with the slurry, and polymerizing the monomer or the prepolymer in that state. There is also. Although the form is not spherical but indefinite, as a simple method, it is also possible to crush the powder compact 72 by pressing or the like and use the fragment as the core 50. On the other hand, in FIG. 1, only the green body powder for molding 10 is charged into the granulation container 132, and the container is rotated at a lower speed than at the time of growth of the molded body to generate an aggregate of the powder. After the aggregates are formed, the rotational speed of the container 132 may be increased, and the molded body 80 may be grown by using the aggregates as the core 50. In this case, the core body manufactured in a separate process as described above is intentionally
At the same time, it is not necessary to put the material into the container 132.

The molded core body 50 obtained as described above
Can stably maintain its shape without collapse even when some external force acts. As a result, as shown in FIG. 5A, even when rolling on the green body powder layer for molding 10k, a reaction due to its own weight can be reliably received. FIG.
As shown in (e), it is considered that the powder particles rolled up when rolled can be pressed firmly against the surface, so that the powder is appropriately compressed and a dense layer 10a can be grown. On the other hand, as shown in FIG. 5D, when the nucleus is not used, the aggregate 100 corresponding to the nucleus is generated only by an accidental factor, and the agglomeration degree is low and weak. In many cases, the powder is deformed when it rolls on the molding base powder layer 10k, or is crushed in the worst case, and cannot generate a sufficient force to cause the powder to adhere and aggregate. As a result, it takes a long time to grow the compact, and even if it grows, only the one having many defects such as cracks and voids due to bridging of the powder particles may be obtained.

The size of the core 50 is preferably at least about 40 μm (preferably about 80 μm). If the core 50 is too small, the growth of the aggregated layer 10a may be incomplete. Further, if the core is too large, the thickness of the formed cohesive layer may be insufficient, and the sintered body may be liable to have a defect or the like. Therefore, the size is preferably set to, for example, 1 mm or less.

The molding core is made of a ceramic powder and a bulk density (for example, JIS-Z2504 (197)
It is desirable to use an aggregate agglomerated at a higher density than the apparent density specified in 9) in order to reliably receive the pressing force of the powder particles and promote the growth of the aggregate layer 10a. Specifically, it is preferable to use a material that has been agglomerated to 1.5 times or more the bulk density of the molding base powder. in this case,
It is sufficient that the particles are agglomerated to such an extent that they do not collapse due to rolling impact on the molding base powder layer 10k.

In order to achieve more stable growth of the compact, it is desirable to set the size of the core body 50 as follows according to the size of the compact to be obtained. That is, FIG.
As shown in (b), the size of the molded core 50 is represented by the diameter dc of a sphere having the same volume, while (of course, when the core 50 is spherical, the diameter is referred to here). Dc, and dc / dg is 1/100 to 1 /
Set to satisfy 2. If dc / dg is less than 1/100, there is a concern that the nucleus is too small and the growth of the cohesive layer 10a is incomplete, or that only a large number of defects can be obtained. On the other hand, if it exceeds １ ／, for example, if the density of the core body 50 is not so high, the strength of the obtained sintered body may be insufficient. Note that dc / dg is preferably 1/50 to 1/5, more preferably 1/20 to 1/50.
It is preferable to adjust in the range of 1/10. The size dc of the molding core is preferably set to 20 to 200 times the average particle size when the average particle size of the molding base powder is viewed as a scale. The absolute value of the dimension dc is, for example, 50 to
It is good to adjust to 500 μm.

The input amount of the molding base powder layer 10k is (V1 '/ V0) .times.100 when the internal volume of the granulation container 132 is V0 and the input volume of the molding base powder 10k is V1'.
(%) Is 5 to 40%. Thereafter, with the progress of the granulation molding, a part of the molding base powder layer 10k becomes a spherical molded body. The volume of the spherical forming body that is being formed at this time and the remaining molding base powder layer are formed. Total volume V with 10k
The value of (V1 / (1)
The value of (V0) .times.100 (%) is also substantially maintained at 5 to 40%.

The operating conditions of the rolling granulator 130 are such that the diameter of the obtained compact 80 is 0.2 to 8 mm (particularly,
In applications such as bearing balls for computer hard disks, the diameter is adjusted to 0.2 to 5 mm) and the relative density is adjusted to 61% or more. In this state, the granulation container 132 is driven to rotate at a constant peripheral speed. The maximum load applied to the spherical molded body during the molding is 50
0 g / cm ² or more (preferably 500 g / cm ² or more)
The rotational peripheral speed and the inclination angle θ of the axis O are adjusted so that Note that the maximum load is, for example,
2 can be measured by attaching a load sensor to the inner surface. As a simpler method, a pressure-sensitive test paper that changes color according to the applied pressure level is attached to the inner surface of the granulation container 132, and the granulator is operated.
The maximum load can be read from the coloring level of the pressure-sensitive test paper.

In particular, in order to obtain a high-density compact, as shown in FIG. 2, while supplying a liquid W mainly composed of a liquid compacting medium, the compact green powder 10 is adhered thereto to form a spherical compact. It is effective to adopt a method for obtaining the information. Here, the liquid forming medium W is supplied from the liquid supply pipe 51 disposed in the granulation container 132. The liquid molding medium W may be, for example, an aqueous solvent such as water or an aqueous solution in which an additive is appropriately added to water, but is not limited thereto, and for example, an organic solvent may be used. Good. According to the method, FIG.
As shown in the figure, when the liquid molding medium W and the powder particles adhere to the uneven portion existing on the surface of the molded body, the powder particles adhere while densely rearranging due to the osmotic pressure of the liquid molding medium W. It is considered that the density of the molded body can be increased. To enhance these effects,
It is desirable to spray the liquid forming medium W directly on the formed body. Further, the step of spraying the liquid forming medium may be performed over the entire period of the forming step (for example, the rolling granulation step), or may be performed only during a part of the forming step (for example, only the final stage). Is also good. The liquid forming medium may be supplied continuously or intermittently.

By adopting the above-mentioned present invention, the spherical molded body is
Specifically, it is possible to increase the density so that the relative density becomes 61% or more. In the case of silicon nitride powder,
2.0 to 2.5 g / cm ³ can be secured as the absolute value of the density. Since the compact can be densified in this way, the densification itself by sintering can be sufficiently advanced even by, for example, gas pressure sintering or normal pressure sintering, instead of a costly process such as the HIP method. Thus, an optimum surface hardness level that can sufficiently secure wear resistance can be achieved. Also, unlike the HIP method, abnormal hardening of the surface layer does not proceed, so that, for example, when the spherical ceramic sintered body of the present invention is used for a bearing ball or the like, high-precision polishing can be easily performed. And it becomes easy to secure values of sphericity and unequal diameter. For example, when water is used as the liquid molding medium W, the supply amount is such that the water content in the finally obtained molded body is, for example, 1%.
It is adjusted to be 0 to 20% by weight. Water content is 10
When the content is less than the weight%, it may be difficult to make the density of the molded body 61% by weight or more. On the other hand, when the water content is 20
If the amount is more than 10% by weight, the strength of the molded product may be insufficient, which may hinder handling and the like.

In the tumbling granulation method, it is required that the base powder for molding used has a certain degree of fluidity. However, the base powder for molding for producing a high-performance silicon nitride sintered body is usually a fine powder, and as it is has insufficient fluidity, it is indispensable to granulate it into an appropriate particle size in advance. It is. Here, in general, a simple granulation method is used in which powdered slurry is put into a container or the like, dried, and then crushed. However, this method has a high ratio of returning to fine powder at the time of crushing. There is a drawback that the effect of can not be expected so much.

On the other hand, there is also a method of granulating by a spray drying method, but the granulated powder obtained by the spray drying method generally has an average particle diameter of the granulated secondary particles of 50 to 100.
It is known that the size becomes as large as μm. When a spherical molded product is manufactured by the above-described tumbling granulation method or the like using the granulated powder having a large average particle diameter, defects such as uneven density and discontinuous boundary portions are likely to occur during molding. is there. Such defects naturally cause defects such as deformation due to uneven shrinkage of the sintered body, defective holes, cracks or chips, and are used in special environments such as computer hard disks and semiconductor devices that require reliability. Can not be used for bearing balls. Therefore, ceramic spheres produced by such a rolling granulation method have only been used in fields where reliability is not required, for example, as a medium for grinding or mixing ceramic powder, paint or chemicals.

In the step of preparing the molding base powder, for example, the average particle size of the molding base powder particles, the cumulative particle size distribution,
The BET specific surface area value is adjusted within a predetermined range. In this case, in the raw material powder adjusting step, at least the inorganic material powder and the sintering aid powder are uniformly mixed, and the average particle diameter is set to 0.1.
1 to 2 μm, and the same 90% particle size is 0.4 to 3.5 μm.
m, and the BET specific surface area value is adjusted to 5 to ²⁰ m ² / g. For example, as a more specific process for the adjustment, at least an inorganic material powder, a sintering aid powder and a solvent are uniformly mixed to form a slurry, the slurry is spray-dried, and the dried product is further dried. A crushing step can be adopted.

As a more specific embodiment of the green body powder for which the particle size measurement method is specified, a laser diffraction type particle sizer mainly composed of a ceramic powder and a predetermined amount of a sintering aid powder is used. The average particle diameter measured in 0.1 ~
2 μm, also having a 90% particle diameter of 0.4 to 3.5 μm and a BET specific surface area of 5 to ²⁰ m ² / g. The present inventors have found that the average particle diameter and 90% particle diameter measured by a laser diffraction type particle sizer belong to the above range, and that the BET specific surface area value falls within the above range, by using a molding base powder having the above range, For example, even when this is molded into a spherical molded body using the above-described various granulation methods having a higher molding efficiency than the mold pressing method, defects such as uneven density and discontinuous boundary due to powder bias are less likely to occur. As a result, the present inventors have found that the deformation rate due to uneven shrinkage of the sintered body and the occurrence rate of defects due to cracking or chipping are drastically reduced, thereby completing the present invention. As a result, it is possible to promote the use of ceramics in bearing balls at once, in applications requiring special environmental specifications, such as computer hard disks and semiconductor devices that require reliability.

In the present invention, as shown in FIG. 11, the relative cumulative frequencies of the particles from the small particle size side are arranged in the order of the size of the particles to be evaluated as shown in FIG. When counting the frequency of particles from the diameter side, the cumulative frequency up to the particle size of interest is Nc, and the total frequency of the particles to be evaluated is N0
Where nrc = (Nc / N0) .times.100 (%). The X% particle size refers to a particle size corresponding to nrc = X (%) in the above-described arrangement. That is, the 90% particle size is defined as nrc = 90
(%).

In the method of the present invention, the average particle size of the molding base powder measured by a laser diffraction type
It is characterized in that the 0% particle diameter and the BET specific surface area value of the green body powder for molding are adjusted to the above numerical ranges. The principle of measurement of a laser diffraction type particle sizer is known, but in brief, while irradiating a sample powder with a laser beam and detecting the diffracted light by the powder particles with a photodetector,
The particle size can be known from the scattering angle and intensity of the diffracted light obtained from the detection information.

Here, as shown schematically in FIG. 10, the molding base powder mainly composed of a silicon nitride powder and a sintering aid powder has a function of an added organic binder and a function of an electrostatic force. Due to various factors, a plurality of primary particles are often aggregated to form secondary particles. In this case, the measurement by the laser diffraction particle sizer does not cause a large difference between the diffraction behavior of the incident laser light by the aggregated particles and the diffraction behavior by the isolated primary particles. It cannot be distinguished from each other whether it is the particle size of the particles or the particle size of the aggregated secondary particles. That is, the particle diameter measured by the method is a value reflecting the secondary particle diameter D in FIG. 10 (in this case, isolated primary particles that do not cause aggregation are also regarded as secondary particles in a broad sense). In addition, the average particle diameter or 90% particle diameter calculated based on this reflects the average particle diameter or 90% particle diameter of the secondary particles.

On the other hand, the specific surface area of the green body powder for molding is measured by an adsorption method. Specifically, the specific surface area can be determined from the amount of gas adsorbed on the powder surface. In general, an adsorption curve showing the relationship between the pressure of a measurement gas and the amount of adsorption is measured, and a known BET formula (collection of the inventors, Brunauer, Emmett, Teller) for multi-molecule adsorption is obtained. By applying, the adsorption amount vm when the monomolecular layer is completed is obtained, and the BET specific surface area value calculated from the adsorption amount vm is used. However, when approximately equivalent results are obtained, a simple method that does not use the BET equation,
For example, a method of directly reading the adsorption amount vm of the monolayer from the adsorption curve may be adopted. For example, when a section where the adsorption amount is substantially proportional to the gas pressure appears in the adsorption curve, there is a method of reading the adsorption amount corresponding to the end point on the low pressure side of that section as vm (The Journal of American Chemical Society, 57
Volume (1935), p. 1754, Brunauer and Emet
t). In any case, in the specific surface area value measurement by the adsorption method, the gas molecules to be adsorbed also penetrate into the secondary particles and cover the surface of the individual primary particles constituting the secondary particles, and as a result, the specific surface area value is This reflects the specific surface area of the primary particles, and thus the average value of the primary particle diameter d in FIG.

In the above-mentioned method, the green body powder for molding reflects the primary particle diameter so that the densification of the ceramic sintered body is sufficiently promoted and the sintered body having few defects and sufficient strength is obtained. BET specific surface area value of 5 to 20 m ² /
g is set to a certain small value. The important point is that the average particle diameter or the 90% particle diameter by the laser diffraction type particle size analyzer reflecting the secondary particle diameter is 0.1%, respectively.
２2 μm or 0.4-3.5 μm, compared with the conventional molding base powder obtained by the spray drying method,
That is, it is set to a small value of about 1/10 or less. This means that the agglomeration state as secondary particles in the green body powder for molding, and thus the local coarseness of the particle filling is eliminated as much as possible, and by adopting such a range of the particle diameter, the molded article finally obtained is obtained. This makes it difficult for the powder to be biased.

The above-mentioned average particle diameter of the base powder for molding exceeds 2 μm, or the 90% particle diameter is 3.5 μm.
If it exceeds, the powder tends to be biased in the molded body,
Failure such as deformation, cracking or chipping of the sintered body due to uneven shrinkage is likely to occur. On the other hand, the average particle diameter is less than 0.1 μm, or the 90% particle diameter is 0.4 μm.
Fine powders of less than a considerable amount of time are required for preparation (for example, pulverization time), which leads to an increase in cost due to a reduction in production capacity.
The average particle diameter of the green body powder for molding is preferably 0.1.
The particle size is preferably 3 to 2 μm, more preferably 0.3 to 1 μm, and the 90% particle size is preferably 0.7 to 2 μm.

On the other hand, when the BET specific surface area value of the green body powder for molding is less than 5 m ² / g, the primary particle diameter becomes too large, the uniformity of sintering is impaired, and defects occur in the obtained spherical sintered body. The strength decreases. On the other hand, a molding base powder having a BET specific surface area value of more than 20 m ² / g requires a considerably long time for preparation (for example, pulverization time), which leads to an increase in cost due to a reduction in production capacity. In addition, the BET of the base powder for molding
The specific surface area is preferably 5 to 13 m ² / g, and more preferably 5 to 10 m ² / g.

In the above manufacturing method, the step of preparing a green body powder for molding is, specifically, a step of preparing a powder by mixing a ceramic powder and a sintering aid powder together with a solvent (eg, water) to prepare a powder. In the middle of the hot air flow passage, an aggregate of a drying medium formed of ceramic or metal in the form of granules or lump is arranged in a predetermined space range so as to be able to flow or vibrate, and the drying medium This flows or vibrates in the space area through hot air to the aggregate,
By supplying a slurry to the flowing or vibrating drying media assembly, a drying step of evaporating the solvent while mixing the slurry with the drying medium, and a molding base powder obtained by the drying together with hot air And a collecting step of collecting the dried media collected downstream.

In the above method, the slurry is supplied to the stack of dry media, and the slurry is dried by hot air to become powder and adhere to the surface of the media to form a powder aggregate layer. Then, the dried media on which the powder agglomeration layer is formed by the flow of the hot air vibrate or flow, and collide with each other or cause friction. At this time, the powder agglomeration layer adhering to the media surface is crushed, and is blown away and collected while alleviating the aggregation state. Thereby, the base powder for molding having the above-mentioned particle size range can be obtained easily and with high efficiency. As the drying medium, it is preferable to use a ceramic medium that is hard to wear as much as possible. For example, if a medium mainly composed of alumina, zirconia, or a mixed ceramic thereof is used, the medium is temporarily worn and the molding base material is used. Even if it is mixed in the powder, since it functions as a sintering aid component, the influence of the mixing can be reduced.

In the drying step in the step of preparing the green body powder for molding, the hot air flow path can be formed to include a vertically arranged hot air duct. Can be formed as a media holding portion composed of a gas circulating body such as a net that does not allow the passage of the medium. In this case, the slurry can be supplied from above to the dry media aggregate held on the media holding unit. Further, the hot air can be circulated in the hot air duct so as to move the drying medium upward from the lower side of the drying media assembly while moving the drying medium upward, and the powder after drying passes through the hot air duct together with the hot air to the downstream side. Can be collected by the collection unit arranged in the storage area.

According to this method, the cycle in which the dry medium is blown up by the hot air blown from below, moves up, and is dropped on the integrated body is repeated. And can be added relatively uniformly. In addition, coarse particles among the crushed aggregated particles are not blown off by the hot air, but are returned to the dry media aggregate again and continuously crushed, so that coarse particles that cause powder unevenness or the like in the subsequent molding process are obtained. The generation of secondary particles can be further reduced.

The green body powder for molding prepared by the above steps is formed into a spherical shape by the molding step. In this case, a rolling granulation method can be particularly preferably used as a molding method. The rolling granulation method has a high production efficiency in obtaining a spherical molded product, and additionally has the above-mentioned particle size range or B
When a molding base powder having an ET specific surface area value is used, there is an advantage that defects such as powder imbalance do not easily occur.

FIG. 7 shows an embodiment of an apparatus used in the step of preparing the green body powder for molding. In the apparatus, the hot air flow passage 1 is formed to include a vertically arranged hot air duct 4, and a gas flow member that allows hot air to pass therethrough and does not allow the drying medium 2 to pass therethrough, in the middle of the hot air duct 4. For example, a media holding unit 5 formed of a net or a perforated plate is formed. Then, on the medium holding portion 5, the dry media 2 composed of ceramic spheres mainly composed of any one of alumina, zirconia, and their mixed ceramics are accumulated, and a layered dry media aggregate 3 is formed. .

On the other hand, as a raw material, 1 to 10 parts by weight of a sintering aid powder (for example, a mixture of alumina and yttria) is mixed with 100 parts by weight of silicon nitride powder, and, for example, a ball mill or an attritor using pure water as a solvent. It is prepared in the form of a plasma obtained by wet mixing (or wet mixing / crushing). In this case, the size of the primary particles is adjusted so that the BET specific surface area value is 5 to ²⁰ m ² / g.

As shown in FIG. 8, the dry media assembly 3
On the other hand, the hot air is circulated in the hot air duct 4 so as to move upward from the lower side of the medium holding portion 5 while moving the drying medium 2 up. On the other hand, as shown in FIG.
Is pumped up from the plasma tank 20 by the pump P, and is dropped and supplied to the dry media assembly 3 from above. Thereby, as shown in FIG. 9, the plasma is dried by hot air and adheres to the surface of the drying medium 2 in the form of the powder aggregation layer PL.

Then, due to the circulation of hot air, the dry medium 2 repeatedly vibrates and falls and strikes each other, and the powder agglomeration layer PL is pulverized into the base powder particles P for molding by the friction caused by the strike. . The crushed base powder particles for molding P include those in the form of isolated primary particles, but are mostly secondary particles in which the primary particles are aggregated. The molding base powder particles P having a particle size of a certain size or less flow downstream along with the hot air (FIG. 7). On the other hand, the crushed particles larger than a certain size are not blown off by the hot air but fall again to the dry media assembly 3 and are further crushed between the media.

Thus, the molding base powder particles P that have flowed downstream together with the hot air pass through the cyclone S to the collecting section 2.
1 is collected as a molding base powder 10. The recovered molding base powder 10 has an average particle diameter of 0.1 to 2 μm measured by a laser diffraction particle sizer, and 90%
The particle diameter is 0.4 to 3.5 μm, and the BET specific surface area is 5 to ²⁰ m ² / g.

In FIG. 7, the diameter of the drying medium 2 is
It is set appropriately according to the flow cross-sectional area of the hot air duct 4. If the diameter is insufficient, the impact force on the powder agglomeration layer formed on the medium is insufficient, and a base powder for molding having a particle diameter within an intended range may not be obtained. On the other hand, if the diameter is too large, the driving force of the dry medium 2 is unlikely to occur even when hot air is circulated, so that the impact force is also insufficient, and a molding base powder having a particle diameter within the intended range cannot be obtained. There is. It should be noted that it is preferable to use the same size as the drying medium 2 by forming an appropriate gap between the media,
This is desirable in promoting the movement of the media during hot air circulation.

The filling depth t1 of the drying medium 2 in the drying medium assembly 3 is appropriately set in accordance with the flow velocity of the hot air and within a range where the flow of the medium 2 occurs without excess or deficiency. If the filling depth t1 is too large, the flow of the drying medium 2 becomes difficult, and the impact force is insufficient, so that there is a case where a molding base powder having a particle diameter within a desired range cannot be obtained. On the other hand, if the filling depth t1 is too small, the amount of the dry medium 2 is too small, and the frequency of impact is reduced, leading to a reduction in processing efficiency.

Next, the temperature of the hot air is appropriately set within a range in which the drying of the slurry proceeds sufficiently and no problems such as thermal deterioration occur in the powder. For example, when the solvent of the slurry is mainly water, when the hot air temperature is lower than 100 ° C., the supplied slurry does not sufficiently dry, and the moisture content of the obtained molding base powder becomes too high. Agglomeration is likely to occur, and a powder having an intended particle size may not be obtained.

Further, the flow velocity of the hot air is appropriately set within a range in which the drying medium 3 is not blown to the collecting section. If the flow velocity is too low, the flow of the drying medium 2 becomes difficult,
In some cases, the impact power is insufficient, and a base powder for molding having a particle diameter within an intended range cannot be obtained. On the other hand, if the flow velocity is too high, the drying medium 2 rises too high and the collision frequency is rather reduced, leading to a reduction in processing efficiency.

The compact formed into a sphere by the above-described apparatus is sintered by normal pressure sintering, gas pressure sintering or hot isostatic pressing (HIP) to form a spherical ceramic sintered body. For example, gas pressure firing in the case of a silicon nitride ceramic refers to firing in an atmosphere containing at least nitrogen of 1 atm or more and 200 atm or less in this specification, and normal pressure firing refers to firing of at least nitrogen of 1 atm or less. Baking is performed in a contained atmosphere. Also, HIP
Is a general term for firing exceeding 200 atm.

For example, if the baking exceeds 1 atm,
The firing can be performed by gas pressure firing in which the firing is performed in an atmosphere containing at least nitrogen of atm or less, or normal pressure firing in which the firing is performed in an atmosphere containing at least nitrogen of 1 atm or less. In this case, the firing temperature is, for example, 1600 to 19
It is preferable to set the temperature within a range of 50 ° C. Firing temperature 1600
If the temperature is lower than 0 ° C, defects such as pores cannot be eliminated and the strength decreases. On the other hand, if the temperature is higher than 1950 ° C, the strength of the sintered body decreases due to grain growth, which is not preferable. The sintering is preferably performed so that the relative density of the obtained sintered body is 95% or more, preferably 99% or more. This firing can also be performed by two-stage firing of primary firing and secondary firing. For example, the primary firing is performed at 1900 ° C. or less in a non-oxidizing atmosphere at a normal pressure or gas pressure of 10 atmospheres or less containing nitrogen, and the relative density of the sintered body after the primary firing is 78% or more, preferably 90% or more. % Is desirable. If the relative density of the sintered body after the primary firing is less than 78%, many defects such as pores tend to remain after the secondary firing, which is not preferable. Further, the secondary firing can be performed at 1600 to 1950 ° C. in a non-oxidizing atmosphere at a normal pressure or a gas pressure of 200 atm or less containing nitrogen. When the firing pressure exceeds 200 atm,
The surface hardness of the obtained sintered elementary ball increases, making it difficult to perform processing such as polishing, which may be disadvantageous in securing the dimensional accuracy of the product ball.

The spherical compact 80 obtained by the tumbling granulation method
Is fired, the resulting spherical ceramic sintered body is obtained as shown in FIG.
As shown in the figure, when a cross-section passing through the approximate center is polished and the cross-section is enlarged and observed, a core portion 91 derived from the molded nucleus is formed at the center portion thereof with a high density and few defects in the outer layer derived from the aggregated layer. It is formed so as to be identifiable with the portion 92. In the polished cross section, the nucleus portion 91 often exhibits a visually recognizable contrast with the outer portion in at least one of brightness and color. It is presumed that this is because the density ρe of the ceramic constituting the outer layer portion 92 is different from the density ρc of the ceramic constituting the core portion 91. For example, the molded core 50 (FIG. 5)
When the density is lower than a, the density ρe of the ceramic forming the outer layer portion 92 is often higher than the density ρc of the ceramic forming the core portion 91, and the outer layer portion 92 is higher than the core portion 91. Appears in bright tones. The relative density of the outer layer portion 92 is preferably 95% or more, and more preferably 99% or more, from the viewpoint of securing the strength and durability of the ceramic. In any case, by forming a sintered body structure in which the above structure appears in the polished cross section, the defect formation ratio of the outer layer portion 92 which is the key to the performance improvement of the bearing and the like is small (for example, to the extent that pores are not confirmed). A high-density and high-strength spherical ceramic sintered body is realized. However, when the firing proceeds uniformly, the sintered body may have a substantially uniform density in the radial direction from the surface layer to the center. Further, even if there is a difference in color tone or brightness between the core portion and the outer layer portion, there may be little difference in density.

As shown in FIG. 5 (b), the diameter dc of the molding core 50 is defined as dc / dc, where dg is the diameter of the spherical molding.
dg is 1/100 to 1/2 (preferably 1/50 to 1 /
5, more preferably in the range of 1/20 to 1/10), the cross section of the sintered body 90 in FIG. On the other hand, when the diameter of the ceramic sintered body is Dg, Dc /
Dg is 1/100 to 1/2 (preferably 1/50 to 1 /
5, more preferably 1/20 to 1/10). When Dc / Dg is less than 1/50,
Defects are likely to occur in the cohesive layer 10a (FIG. 5) that is the basis of the outer layer portion 92, which may lead to insufficient strength and the like. On the other hand, if it exceeds 1/5, the strength of the sintered body may be insufficient if the density of the core body 50 is not so high, for example. Dc / Dg is more preferably 1/20 to 1 /
It is better to adjust in the range of 10.

In the sintered body 90, a core portion 91 and an outer layer portion 92
For example, a state in which a difference in brightness or color tone is formed in the radial direction of the sphere and not formed in the circumferential direction of the sphere can be exemplified as a state in which visually distinguishable contrast occurs between the sphere and the sphere. As a specific mode, a layered pattern surrounding the core portion 91 may be formed concentrically on the outer portion of the polished cross section. This is a characteristic structure observed when the tumbling granulation method of the present invention is employed. The cause of the formation can be estimated as follows. That is, FIG.
As shown in (a), the molded body 80 is made of the green body powder layer 1 for molding.
While the agglomeration layer 10a grows while rolling on 0k, the compact 80 does not always exist on the green compact powder layer 10k during the continuation of the tumbling granulation. In other words, due to the avalanche flow of the powder accompanying the rotation of the granulation container,
When it comes to the lower side of the forming base powder layer 10k, it sneaks into the forming base powder layer 10k, is taken up by the wall surface of the granulation container, is carried to the upper side of the forming base powder layer 10k, and is again formed. Roll down on 10k. When sunk into the molding base powder layer 10k, the surroundings are pressed down by the powder, and the impact due to rolling and falling is relatively unlikely to be applied, and the powder particles adhere relatively loosely. In contrast,
When rolling on the molding base powder layer 10k, an impact due to rolling and falling is applied, and the liquid spray medium W such as moisture is easily sprayed, so that the powder is easily tightened. And
Since the rolling on the molding base powder layer 10k and the sneaking into the molding base powder layer 10k are repeated periodically, the form of adhesion of the powder also changes periodically. Has radial occlusion,
This appears as a delicate difference in density or the like even after firing, and it is considered that a layered pattern is formed. It may not be possible to confirm with the accuracy level of the density measurement.) For example, it is considered that the above-mentioned layered pattern is formed by alternately laminating concentric arc-shaped portions and remaining portions having higher densities in the radial direction.

The sintered body 90 obtained as described above is
By performing the polishing process, the diameter, sphericity, surface roughness, and the like are adjusted, and a ceramic ball having a diameter of 4 mm or less is obtained (for example, when a molded body having a diameter of 5 mm or less is used). When the spherical molded bodies are fired in a bulk state, burrs may be generated due to welding or the like, and the burrs are removed in the polishing step.

[0065]

EXAMPLES (Example 1) The following experiments were conducted to confirm the effects of the present invention. First, the slurry of the green body powder for molding was mixed with silicon nitride powder (average particle diameter 0.6 μm, BET
94 parts by weight of specific surface area value 13 m ² / g) 3 parts by weight of alumina powder (average particle diameter 0.4 μm, BET specific surface area value 10 m ² / g) as sintering aid and yttria powder (average particle diameter 1.5 μm) , BET specific surface area 10 m ² / g) 3
50 parts by weight of pure water as a solvent is blended with respect to parts by weight,
It was prepared by mixing. In addition, the average particle diameter and 90%
The particle size is measured using a laser diffraction particle sizer (Horiba Seisakusho Co., Ltd.)
(Model number: LA-500), and the BET specific surface area value was measured using a BET specific surface area measuring device (Multisoap 12, manufactured by Yuasa Ionics Inc.).

Next, using the above-mentioned various kinds of slurry, a green body powder P for molding was produced by the apparatus shown in FIG. Specifically, alumina spheres having a diameter of 2 mm were used as the drying medium, and other conditions were set as follows: A hot air duct 4 in which the drying medium holding portion 5 was formed.
Inner diameter R2: about 200 mm; filling depth t1 of the drying medium 2: about 150 mm; temperature of hot air: 160 ° C .; flow rate of hot air: 3 m / s.

Each of the green body powders for molding thus obtained was subjected to an average particle measurement, a 90% particle diameter and a BET
The specific surface area value was measured. As a result, the average particle size was 0.1.
6 μm, 90% particle size 1.1 μm, specific surface area 13
m ² / g.

Next, the above-mentioned molding base powder was formed into a spherical shape by a rolling granulator shown in FIG. The conditions of the tumbling granulation are as follows (individual conditions are shown in Table 1): ・ Inner diameter of granulation container 132 × internal method length: 700 mm × 70
0 mm (internal volume V0: about 27 liters);-Inclination angle θ of rotation axis O: 40 °;-Rotation speed: 10 to 50 rpm;-Moisture content: 9 to 10 15 wt%; ratio of the input volume V 1 ′ of the green body powder for molding to the internal volume V 0 of the granulation container 132: 3 to 45%. In each condition, the maximum value of the load applied to the molded body was measured using a pressure-sensitive test paper (manufactured by Fuji Photo Film Co., Ltd., trade name: Fuji Prescale). The pressure-sensitive test paper is always white, but the portion to which pressure is applied is colored red. Since the color density is almost proportional to the added load, the load level can be read by comparing the color density with the coloring sample for each determined load. like this,
The pressure-sensitive test paper was cut into a size of 20 × 50 mm, and four of them were placed on the inner surface of the granulation container 132 at a position corresponding to the rolling surface of the contents at intervals of approximately 90 ° in the circumferential direction. The maximum load was read from the coloring level of each pressure-sensitive test paper after the granulation test. Moreover, the relative density of each obtained molded body was measured as follows. First, the weight M of the molded body is measured in advance, and then the molded body is put in a container and mercury is poured under normal pressure. Then, from the change in the height of the mercury liquid level when the molded body is taken out of mercury, the molded body grade V
, The density of the compact was determined by M / V, and this was divided by the true density value. It has been confirmed that mercury hardly penetrates into the molded body under normal pressure.

The compact was sintered by gas pressure (pressure: 75 at
m, temperature: 1750 ° C., atmosphere gas: nitrogen), hot isostatic press sintering (HIP, pressure: 1000 atm, temperature:
Sintering was performed at 1750 ° C. under an atmosphere gas of nitrogen to obtain a spherical silicon nitride sintered body. The cross section of the spherical silicon nitride sintered body was observed with an optical microscope. The sintered body having no defects found in the section was evaluated as good (), and the one in which a defect was found in the cross section was evaluated as poor (x). The body was judged good or bad. Table 1 shows the above results.

[0070]

[Table 1]

According to the results, when the maximum load applied to the compact was 500 g / cm ² or more, a good compact with few defects, and finally a sintered compact were obtained. In addition, the ratio (volume ratio) between the input volume V1 ′ of the molding base powder and the internal volume V0 of the granulation container 132 is as follows:
Good results have been obtained when this is 5 to 40%,
In addition, it can be seen that the higher the value of the volume ratio, the larger the maximum load applied to the compact, and the higher the relative density of the compact. On the other hand, when the volume ratio exceeds 45%, the flow of the contents including the molded body is deteriorated as a whole, and a part that is not tumbled or flows in a part of the accumulated molded body, so to speak, is generated. Driving became difficult.

Example 2 The following were prepared as the slurry of the green body powder for molding. Water as a solvent was mixed and mixed with 99 parts by weight of alumina powder (average particle diameter 0.2 μm, BET specific surface area value 7 m ² / g) and 1 part by weight of glass powder as a sintering aid. thing. Zirconia powder (average particle size 60 [mu] m, BET specific surface area ^10m 2 / g) 95 parts by weight, relative to yttria powder (average particle size ^10m 2 / g) 5 parts by weight of a sintering aid, blending water as a solvent And prepared by mixing. Alumina powder (average particle size 1 [mu] m, BET specific surface area ^10m 2 / g) 85 parts by weight of zirconia powder with respect to (the average particle diameter of 60 [mu] m, BET specific surface area ^10m 2 / g) 15 parts by weight, blending water as a solvent And prepared by mixing.

Next, using the above various kinds of slurry, a green body powder P for molding was produced under the same conditions as in Example 1. In the same manner as in Example 1, each of the obtained molding base powders was measured for an average particle size, a 90% particle diameter, and a BET specific surface area.
As a result, those using the slurry had an average particle diameter of 0.1.
2 μm, 90% particle size 0.4 μm, specific surface area value 11
In the case of using m ² / g of the slurry, the average particle size was 0.1 μm.
9 μm, 90% particle diameter 1.2 μm, specific surface area value 11
In the case of using m ² / g, the average particle diameter was 1.
5 μm, 90% particle diameter 3 μm, specific surface area 9 m ² /
g.

Next, the above-mentioned molding base powder was formed into a spherical shape by a rolling granulator shown in FIG. In addition, the conditions of the rolling granulation are the same as those of the first embodiment. Under each condition, the maximum value of the load applied to the compact and the relative density of each compact obtained are the same as in the first embodiment. Measured.

The molded product using the slurry was 1400 to 1700 ° C. in the air, the one using the slurry was 1500 to 1600 ° C. in the air, and the one using the slurry was the air. Each was sintered at 1500 to 1700 ° C. in the inside to obtain a spherical ceramic sintered body. The cross section of the spherical ceramic sintered body was observed with an optical microscope, and the quality was determined in the same manner as in Example 1. Table 2 shows the above results.

[0076]

[Table 2]

[0077] It can also be seen from the results that when the maximum load applied to the compact was 500 g / cm ² or more, a good compact with few defects, and finally a sintered compact was obtained.

[Brief description of the drawings]

FIG. 1 is a process explanatory view showing a method for producing a spherical ceramic sintered body of the present invention.

FIG. 2 is a process explanatory view following FIG. 1;

FIG. 3 is an explanatory diagram illustrating some of the molded cores used in FIG. 2;

FIG. 4 is an explanatory view illustrating some examples of a method for producing a molded core.

FIG. 5 is a view for explaining the progress of a rolling granulation forming step.

FIG. 6 is a schematic diagram showing a cross-sectional structure of a spherical ceramic sintered body manufactured by a rolling granulation method.

FIG. 7 is a longitudinal sectional view conceptually showing an apparatus for producing a molding base powder.

FIG. 8 is a diagram for explaining the operation of the device of FIG. 7;

FIG. 9 is an operation explanatory view following FIG. 8;

FIG. 10 is an explanatory diagram showing the particle diameter of a raw material powder.

FIG. 11 is an explanatory diagram showing the concept of a cumulative relative frequency.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Hot-air flow path 2 Dry-media 3 Dry-media assembly 4 Hot-air duct 5 Dry-media holding | maintenance part 6 Plasma 10 Molding base powder 10a Agglomeration layer 10k Molding base powder layer 32,132 Granulation container 50 Molding core 80 Spherical molding Body 90 Spherical ceramic sintered body 91 Core part 92 Outer layer part

Claims (12)

[Claims] 1. A raw material powder preparation step of preparing a green body powder for molding using an inorganic material powder (hereinafter, simply referred to as ceramic powder) as a ceramic raw material, and charging the green body powder for molding into a granulation container; A rolling granulation molding step of agglomerating the green body powder in the granulation container into a spherical shape to obtain a spherical molded body; and a sintering step of sintering the molded body to obtain a spherical ceramic sintered body. The method of manufacturing a spherical ceramic sintered body, wherein the maximum load applied to the spherical molded body during molding in the rolling granulation forming step is 500 g / cm ² or more. 2. In the rolling granulation molding step, when the internal volume of the granulation container is V0, and the total volume of the molding base powder and the spherical molded body in the course of molding is V1,
The method for producing a spherical ceramic sintered body according to claim 1, wherein (V1 / V0) x 100 (%) is 5 to 40%. 3. In the rolling granulation molding step, the molding powder and the molding nucleus are put into a granulation container, and the molding nucleus is rolled in the rotating granulation container.
Attaching the molding base powder in a spherical shape around the molding core
The method for producing a spherical ceramic sintered body according to claim 1 or 2, wherein a spherical molded body is obtained by agglomeration. 4. The spherical ceramic according to claim 1, wherein in the rolling granulation step, the raw material powder is molded so that the relative density of the spherical molded body is 61% or more. A method for manufacturing a sintered body. 5. In the rolling granulation forming step, the spherical molding is obtained by supplying the molding powder to the molding core while supplying a liquid molding medium to the molding core. The method for producing a spherical ceramic sintered body according to any one of the above. 6. The molding base powder is mainly composed of the ceramic powder and a predetermined amount of a sintering aid powder, and has an average particle diameter of 0.1% as measured by a laser diffraction particle sizer.
２2 μm, the same 90% particle diameter of 0.4-3.5 μm,
The method for producing a spherical ceramic sintered body according to any one of claims 1 to 5, further comprising a BET specific surface area value of 5 to ²⁰ m2 / g. 7. The spherical ceramic sintered body according to claim 1, wherein said spherical molded body has a diameter of 8 mm or less, and is sintered to obtain a spherical ceramic sintered body having a diameter of 7 mm or less. Manufacturing method. 8. The method for producing a spherical ceramic sintered body according to claim 1, wherein said ceramic powder is a silicon nitride powder, and said spherical ceramic sintered body is a spherical silicon nitride-based sintered body. . 9. The method for producing a spherical ceramic sintered body according to claim 1, wherein the ceramic component having the highest content of the ceramic powder is one of alumina, zirconia, and silicon carbide. 10. The spherical ceramic sintered body according to claim 9, wherein the ceramic powder is obtained by blending a raw material powder of an alumina ceramic or a zirconia ceramic with a powder serving as a source for forming a conductive inorganic compound phase. How to make the body. 11. The ceramic powder according to claim 1, wherein the ceramic component having the highest content is one of alumina and zirconia, and the ceramic component having the second highest content is the other of alumina and zirconia. The method for producing a spherical ceramic sintered body according to any one of the above. 12. The method for producing a spherical ceramic sintered body according to claim 1, wherein after the spherical molded body is sintered, an outer surface thereof is polished to form a ceramic bearing ball.