Filling method of ceramic molded body, method for manufacturing CIP body, method for manufacturing ceramic sintered body, and method for manufacturing material for ceramic ball

Abstract

A filling method of a ceramic molded body according to an embodiment of the present invention includes filling a plurality of holes, which are formed in a CIP rubber mold, with a plurality of pre-treatment molded bodies which are molded bodies before a CIP treatment and have a maximum diameter of 5.0 mm or more, and has a filling step. In the filling step, the plurality of pre-treatment molded bodies is respectively filled into the plurality of holes by suction conveyance. It is preferable that the pre-treatment molded bodies are molded from a mixed powder that has a total amount of ceramic powder of 80% by mass or more and a binder amount of 3% by mass to 20% by mass inclusive.

Description

Method for filling ceramic molded body, method for manufacturing CIP body, method for manufacturing ceramic sintered body, and method for manufacturing ceramic ball material

[0001] The embodiments described below relate to a method for filling a ceramic molded body, a method for manufacturing a CIP body, a method for manufacturing a ceramic sintered body, and a method for manufacturing a material for a ceramic ball.

[0002] Various ceramic materials possess properties such as high hardness, insulation, and wear resistance. Fine ceramics, which have particularly high purity and uniform particle size, exhibit properties that make them suitable for use in a variety of fields, including capacitors, actuator materials, and refractory materials. Among these properties, ball applications take advantage of their wear resistance and insulation. Ball applications include bearings, jigs, tools, gauges, solenoid valves, check valves, and various valves. Of these, materials such as aluminum oxide, silicon nitride, and zirconium oxide are used in bearing applications (Patent Documents 1 to 3). For example, Patent Documents 1 and 2 disclose bearing balls made of silicon nitride, and Patent Document 3 discloses bearing balls made of zirconium oxide.

[0003] The process for manufacturing these bearing ball materials involves sintering a ceramic green body (sometimes simply referred to as a "green body"). Furthermore, press molding using a mold is used as the molding method. Press molding generally involves inserting powder between an upper punch and a lower punch and applying pressure to obtain a pre-processed green body before CIP processing. Because this pre-processed green body is formed by uniaxial loads from above and below, a method has been implemented in which pressure is applied from all directions using cold isostatic pressing (CIP) to obtain a homogeneous pre-processed green body (Patent Document 4). According to Patent Document 4, a gap must be provided between the tips of the upper and lower punches during press molding to protect the mold. This results in the formation of a spherical portion and a strip-shaped portion in the pre-processed green body, which are then also formed in the sintered bearing ball material.

[0004] Japanese Patent Application Laid-Open No. 6-48813 Japanese Patent No. 2764589 Japanese Patent Application Laid-Open No. 60-18620 International Publication No. 2023 / 003040

[0005] By filling multiple pre-processed molded bodies into multiple cavities formed in a rubber mold for CIP (sometimes simply referred to as a "rubber mold") and applying isotropic water pressure to a rubber mold stack (a stack of multiple rubber molds), it is possible to uniformly crush the voids in the pre-processed molded bodies from all directions and improve the density uniformity of the pre-processed molded bodies. The process of filling multiple pre-processed molded bodies into multiple cavities formed in the rubber mold can be achieved by, for example, placing multiple pre-processed molded bodies on the rubber mold and rolling them while fitting each pre-processed molded body into the cavities. In this case, as the pre-processed molded bodies roll on the rubber mold, problems arise, such as friction and wear of the pre-processed molded bodies against the surface of the rubber mold, or damage caused by collisions between multiple pre-processed molded bodies. In particular, when pre-processed molded bodies with band-shaped portions are large in size, the pre-processed molded bodies themselves become heavy, which can cause the corners of the band-shaped portions to be rubbed or crushed. Furthermore, collisions between multiple pre-processed molded bodies with band-shaped portions can result in significant damage.

[0006] Furthermore, in order to improve productivity and to perform CIP on a larger number of pre-treated molded bodies, it is desirable to make the size (diameter) of the opening of the hole close to the size (diameter) of the pre-treated molded body. However, in a rubber mold in which the size of the opening of the hole is close to the size of the pre-treated molded body, there is a problem in that it takes a considerable amount of time to fill all of the holes with the pre-treated molded body.

[0007] Furthermore, the pre-processed compacts often have low strength, and defects such as partial chipping and cracking occur in the pre-processed compacts due to rubbing of the pre-processed compacts on the rubber mold or contact between multiple pre-processed compacts. If the pre-processed compact has defects, defects also occur in the sintered compact produced after the CIP process. For example, when a defective sintered compact is processed into bearing balls, only unreliable bearing balls are obtained.

[0008] The present invention solves these problems and provides a method for filling ceramic molded bodies, a method for manufacturing CIP bodies, a method for manufacturing ceramic sintered bodies, and a method for manufacturing materials for ceramic balls that can reduce defects that occur in pre-processed molded bodies.

[0009] The method for filling ceramic molded bodies according to the embodiment involves filling a plurality of pre-processed molded bodies, which are molded bodies before CIP processing and have a maximum diameter of 5.0 mm or more, into a plurality of holes formed in a rubber mold for CIP, and includes a filling step in which the plurality of pre-processed molded bodies are respectively filled into the plurality of holes by suction transport.

[0010] FIG. 1 is an external view showing an example of a ceramic ball material formed by die press molding, for illustrating the method for filling a ceramic molded body according to the embodiment; FIG. 2 is a cross-sectional view showing an example of die press molding, for illustrating the method for filling a ceramic molded body according to the embodiment; FIG. 3 is a perspective view showing an example of a rubber mold laminate, for illustrating the method for filling a ceramic molded body according to the embodiment; FIG. 4 is a cross-sectional view showing an example of a rubber mold laminate in a state in which a pre-processed compact is filled, for illustrating the method for filling a ceramic molded body according to the embodiment; FIG. 5 is a top view showing the configuration of a rubber mold laminate, for illustrating the method for filling a ceramic molded body according to the embodiment; FIG. 6 is a cross-sectional view showing a first step of the method for filling a ceramic molded body according to the embodiment; FIG. 7 is a cross-sectional view showing a second step of the method for filling a ceramic molded body according to the embodiment; FIG. 8 is a cross-sectional view showing a third step of the method for filling a ceramic molded body according to the embodiment; FIG. 9 is a cross-sectional view showing a fourth step of the method for filling a ceramic molded body according to the embodiment; FIG. 10 is a cross-sectional view showing a fifth step of the method for filling a ceramic molded body according to the embodiment; and FIG. 11 is a cross-sectional view showing a sixth step of the method for filling a ceramic molded body according to the embodiment. Embodiment

[0011] Hereinafter, embodiments of a method for filling a ceramic molded body, a method for manufacturing a CIP body, a method for manufacturing a ceramic sintered body, and a method for manufacturing a material for a ceramic ball will be described in detail with reference to the drawings.

[0012] In the method for filling molded bodies according to the embodiment, the rubber mold constituting the rubber mold laminate has a plurality of holes into which a plurality of molded bodies are filled.

[0013] Fig. 1 shows a ceramic ball material, such as a bearing ball material, obtained by sintering a compact formed by press molding. In Fig. 1, reference numeral 1 denotes the ceramic ball material, reference numeral 2 denotes a spherical portion of the ceramic ball material 1, and reference numeral 3 denotes a strip-shaped portion of the ceramic ball material 1. Fig. 2 also shows a press die for forming a pre-processed green body of the ceramic ball material 1 before sintering. In Fig. 2, reference numeral 4 denotes the press die, reference numeral 5 denotes a punch portion, reference numeral 5U denotes an upper punch of the punch portion 5, reference numeral 5D denotes a lower punch of the punch portion 5, and reference numeral Y denotes a die. The strip-shaped portion of the green body formed by the space between the tip of the upper punch 5U, the tip of the lower punch 5D, and the die Y corresponds to the strip-shaped portion 3 of the ceramic ball material 1.

[0014] Figure 3 is a perspective view showing an example of a rubber mold laminate in which three rubber molds are stacked. In Figure 3, reference numeral 6 denotes the rubber mold laminate, reference numeral 7 denotes an upper rubber mold, reference numeral 8 denotes a middle rubber mold, and reference numeral 9 denotes a lower rubber mold. The rubber mold laminate 6 is not limited to the three-layer structure shown in Figure 3, but may be a two-layer structure consisting of an upper rubber mold 7 and a lower rubber mold 9 without the middle rubber mold 8, or may be a four-layer structure having two or more middle rubber molds 8.

[0015] FIG. 4 is a cross-sectional view showing an example of a rubber mold laminate in which three rubber molds are stacked. In FIG. 4, reference numeral 6 denotes the rubber mold laminate, reference numerals 7 to 9 denote rubber molds, reference numeral 10 denotes a pre-processed molded body of the ceramic ball material 1 (shown in FIG. 1) before sintering, and reference numeral 11 denotes a hole. Here, the rubber mold laminate 6 for processing the pre-processed molded body 10 is a molding die used in CIP molding. The rubber molds 7 to 9 constituting the rubber mold laminate 6 are each plate-shaped. Here, "plate-shaped" refers to having a certain thickness (height). A plurality of hemispherical holes 11 are provided on the bottom surface of the upper rubber mold 7, the top surface of the lower rubber mold 9, and the opposing top and bottom surfaces of the middle rubber mold 8. The plurality of holes 11 are positioned so that the opposing hemispherical holes 11 can unite to form a spherical shape.

[0016] A plurality of pre-processed molded bodies 10 are placed on the lower rubber mold 9, the pre-processed molded bodies 10 are fitted into a plurality of holes 11 formed in the top surface of the lower rubber mold 9, and the middle rubber mold 8 is placed on top of the lower rubber mold 9. Next, a plurality of pre-processed molded bodies 10 are placed on the stacked middle rubber mold 8, the pre-processed molded bodies 10 are fitted into a plurality of holes 11 formed in the top surface of the middle rubber mold 8, and the upper rubber mold 7 is placed on top of the middle rubber mold 8. Alternatively, the middle rubber mold 8 into which the pre-processed molded bodies 10 have been fitted beforehand is placed on the lower rubber mold 9, and the upper rubber mold 7 is placed on top of the rubber mold 8. This results in the plurality of pre-processed molded bodies 10 being sealed between the rubber molds 7 to 9. By applying isotropic water pressure to the stacked rubber molds 7 to 9, voids in the pre-processed molded bodies 10 can be uniformly crushed from all directions, improving density uniformity in the pre-processed molded bodies 10, i.e., reducing density non-uniformity.

[0017] As shown in FIG. 4 , each of the multiple holes 11 has an approximately hemispherical shape. Furthermore, the CIP body, which is a compact obtained by CIP treatment of the raw compact 10, is not limited to a spherical shape but may also have a cylindrical shape (roller). When the CIP body has a cylindrical shape, the hole 11 does not have an approximately hemispherical shape but has an approximately cylindrical shape with an approximately circular opening. Furthermore, the CIP body may be based on the raw compact 10 obtained not only by mold molding but also by rolling granulation or other methods. CIP bodies based on the raw compact 10 obtained by rolling granulation or other methods may have a shape without a band portion. Therefore, the raw compact 10 may or may not have a band portion. Among the above methods, it is more preferable to perform CIP treatment on the raw compact 10 obtained by mold molding or rolling granulation or other methods. Furthermore, the raw compact 10 may or may not have a band portion 3, as shown in FIG. 1 . Furthermore, the rubber molds 7 to 9 take into consideration the shape of the hole 11, but the side shape is not particularly limited. The pre-treatment compact 10, the CIP compact, and the degreased compact described below are examples of compacts.

[0018] The rubber mold laminate 6 is intended for use in the CIP treatment of the raw molded body 10. There are two types of CIP treatment: WET-CIP and DRY-CIP. WET-CIP is a method in which the powder or raw molded body 10 is sealed in a bag or other material with low deformation resistance and a certain level of strength to prevent contact with liquid, and hydraulic pressure is applied. On the other hand, DRY-CIP is performed using the rubber mold laminate 6, and is a pressurization method in which a platform is provided below the rubber mold laminate 6 to support the rubber mold laminate 6. Because these methods use hydraulic pressure, molding with non-directional isotropic pressure is possible. Because this isotropic pressure is used, uneven density distribution within the raw molded body 10 can be suppressed. CIP is also called cold isostatic pressing or rubber pressing. The use of the rubber mold laminate 6 produces more favorable results, especially when DRY-CIP is employed.

[0019] As shown in FIG. 3 , the rubber molds 7 to 9 constituting the rubber mold stack 6 are preferably plate-shaped, for example, approximately circular. A substantially circular shape refers to a circular or elliptical cylindrical shape with a relatively low height between the opposing top and bottom surfaces. The plate-shaped rubber molds 7 to 9 are not limited to a circular shape, but may also have polygonal shapes, etc. If the rubber molds 7 to 9 have a polygonal shape, it is preferable that they have a pentagonal or higher-sided shape. Furthermore, the rubber molds 7 to 9 may have engaging portions for connecting with adjacent rubber molds vertically. When the rubber molds 7 to 9 are circular, it is easy to align them when stacked vertically. In particular, a circular shape makes it easy to stack the rubber molds 7 to 9 because there is no orientation between adjacent rubber molds 7 to 9 vertically. Furthermore, the rubber mold stack 6, in which the rubber molds 7 to 9 are stacked in multiple layers, can be prevented from collapsing during transportation. The number of rubber mold layers in the rubber mold stack 6 is preferably two or more. By stacking a plurality of rubber molds, the number of pre-treatment molded bodies 10 that can be subjected to CIP treatment at one time by the rubber mold stack 6 can be increased.

[0020] Furthermore, the thickness (height) of each stage of the rubber molds 7 to 9 is preferably 5 mm or more and 30 mm or less. If the rubber molds 7 to 9 are too thin, the risk of deformation of the rubber molds 7 to 9 increases. If the rubber molds 7 to 9 deform, the rubber molds 7 to 9 may not engage properly with each other, and the rubber molds 7 to 9 may collapse when stacking the rubber molds 7 to 9 or when transporting the rubber mold laminate 6. Even if the rubber molds 7 to 9 do not collapse, the balance may become unbalanced, which may cause problems when transporting the rubber mold laminate 6. Furthermore, if the rubber molds 7 to 9 are deformed, it may be difficult to apply uniform pressure to the pre-treatment molded body 10 during CIP treatment.

[0021] The number of layers of rubber molds constituting the rubber mold laminate 6 is not particularly limited (three layers are exemplified in Figures 3 and 4), but 50 layers or less is preferable. If the number of layers of rubber molds is too large, the stacked rubber molds may collapse during transport of the rubber mold laminate 6 to or from the CIP treatment device. Even if the stacked rubber molds do not collapse, there is a possibility that deterioration of the engagement portions due to lateral shaking or the like that occurs during transport of the rubber mold laminate 6 may be accelerated. Therefore, a more preferable number of layers of rubber molds constituting the rubber mold laminate 6 is two to 30 layers. More preferably, the number of layers of rubber molds is two to 20 layers. Taking mass productivity and other factors into consideration, the number of layers of rubber molds is even more preferable to be three to 10 layers. In this specification, an example in which the number of layers of rubber molds is three is described.

[0022] Furthermore, when stacking three layers of rubber molds 7 to 9, it is preferable that there is little error in the heights of the rubber molds 7 to 9. For example, it is preferable that the error in the heights of the rubber molds 7 to 9 is 10% or less. If the error in the heights of the rubber molds 7 to 9 is large, the rubber molds 7 to 9 may be prone to collapse during transportation of the rubber mold laminate 6. It is also preferable that there is little error in the area of ​​the stacking surfaces of the rubber molds 7 to 9. If there is a large error in the area of ​​the stacking surfaces of the rubber molds 7 to 9, it may be difficult to apply pressure uniformly during CIP treatment.

[0023] Furthermore, if necessary, recesses or protrusions may be provided on the side surfaces of the rubber molds 7 to 9, the top surface of the rubber mold 7, or the bottom surface of the rubber mold 9 (i.e., non-hole surfaces where no hole 11 is provided) for the purpose of marking, weight reduction, etc. In other words, the shapes of the non-hole surfaces of the rubber molds 7 to 9 are not particularly limited.

[0024] Furthermore, it is preferable that the Shore hardness Hs of the rubber of the rubber molds 7 to 9 is within the range of 30 or more and 50 or less. As described above, isotropic pressure is applied to the rubber molds 7 to 9 filled with the pre-treatment molded body 10. If the Shore hardness Hs is within the range of 30 or more and 50 or less, the amount of deformation can be made uniform. Therefore, the rubber molds 7 to 9 can be provided with the deformability that allows the surface of the pre-treatment molded body 10 to be in uniform contact with the rubber molds 7 to 9. Furthermore, the durability of the rubber molds 7 to 9 is also good. The Shore hardness Hs is measured in accordance with JIS-Z-2246 (2000).

[0025] The method for filling the pre-treated compacts 10 includes a filling step in which a plurality of pre-treated compacts 10 are respectively filled into a plurality of holes 11 by suction and transport. By respectively filling a plurality of pre-treated compacts 10 into a plurality of holes 11 by suction and transport, friction between the pre-treated compacts 10 and the rubber mold is eliminated, and collisions between the pre-treated compacts 10 can be avoided. In the suction and transport step, the pre-treated compacts 10 in a press molding machine or a tray in which the pre-treated compacts 10 are aligned are sucked one by one by a suction arm 14 (shown in FIG. 7 ), and the sucked pre-treated compacts 10 are then moved to the rubber mold and released from suction (detached). Note that all of the pre-treated compacts 10 may be moved by moving the pre-treated compacts 10 one by one in sequence using a single suction arm 14, or k (k is an integer greater than or equal to 2) suction arms 14 may be used to move all of the pre-treated compacts 10 together, k being the number of pre-treated compacts 10.

[0026] 5 is a top view showing an example of the top surface of the lower rubber die 9. The top and bottom surfaces of the middle rubber die 8 are similar to those shown in FIG. 5. The bottom surface of the upper rubber die 7 is also similar to that shown in FIG.

[0027] 6 to 11 are diagrams illustrating a method for filling a rubber mold 8, 9 (for example, a lower rubber mold 9) having a hole 11 formed in the top surface with a pre-processed molded body 10. FIGS. 6 to 11 are cross-sectional views cut along a vertical plane including the center of the pre-processed molded body 10. Note that FIGS. 6 to 11 illustrate an example of a method for filling the lower rubber mold 9 of the rubber molds 8, 9 with the pre-processed molded body 10. FIG. 6 shows the first step before the pre-processed molded body 10 is ejected from the lower punch 5D of the press die. The upper surface of the lower punch 5D reaches the upper surface of the die Y, and the band-shaped portion 10' of the pre-processed molded body 10 is positioned above the die Y.

[0028] 7 shows the second step in which the suction pad 15 attached to the suction arm 14 is suctioned to the spherical surface of the raw compact 10. A hole H is opened in the center of the tip of the suction pad 15, extending to the through-hole along the axial direction of the suction arm 14. With the center of the tip of the suction pad 15 in contact with the raw compact 10, the raw compact 10 is further sucked through the hole H, and the center of the tip of the suction pad 15 is then suctioned to the raw compact 10.

[0029] Figure 8 shows a third step in which the suction arm 14 moves upward while suctioning the untreated molded body 10, thereby lifting the untreated molded body 10. Figure 9 shows a fourth step in which the suction arm 14 moves above the lower rubber mold 9 while suctioning the untreated molded body 10. In the fourth step, at least the suction arm 14 is moved so that the moved untreated molded body 10 is positioned approximately directly above the hole 11 in the lower rubber mold 9. Here, the suction arm 14 alone may be moved to each of the multiple hole portions 11 while the lower rubber mold 9 is fixed, or the suction arm 14 may be moved to the circumference on which the multiple hole portions 11 are arranged, while the lower rubber mold 9 is rotated about its vertical axis so that the untreated molded body 10 is positioned approximately directly above the hole 11 in the lower rubber mold 9. Figure 10 shows a fifth step in which the suction arm 14 is lowered and then released from suction, allowing the untreated molded body 10 to fall into the hole 11 in the lower rubber mold 9. FIG. 11 shows the sixth step after the suction arm 14 has been retracted.

[0030] In FIG. 7 , the suction pad 15 is preferably made of an elastic material such as stretchable rubber to enhance adhesion to the raw molded body 10. When an elastic material is used as the suction pad 15, it is preferable that the hardness be 70° or less. If the hardness exceeds 70°, the pad will not deform when adsorbing the raw molded body 10, resulting in poor adhesion to the raw molded body 10 and possibly insufficient adsorption of the raw molded body 10. The suction pad 15 in the suction state shown in FIGS. 7 to 9 has its tip deformed to match the shape of the raw molded body 10, compared to the suction pad 15 in the non-adsorption state shown in FIG. 10 . Note that hardness measurements are performed in accordance with JIS K6253-3 (2012). The shape of the suction surface of the suction pad 15 is preferably circular, corresponding to the shape of the spherical portion of the raw molded body 10. The suction pressure during adsorption is 50 to 100 kPa, and the size of the suction surface of the suction pad 15 is φ3 mm or more and 30 mm or less. The adsorption pressure and the size of the adsorption surface are changed depending on the diameter of the raw compact 10. That is, when the diameter of the raw compact 10 is small, the adsorption pressure and the size of the adsorption surface are small. Conversely, when the diameter of the raw compact 10 is large, the adsorption pressure and the size of the adsorption surface are large.

[0031] In Figure 10, the pre-treated molded body 10 has been dropped from the state shown in Figure 9 into the hole 11 of the lower rubber mold 9. At this time, the drop distance L (shown in Figure 9) of the pre-treated molded body 10 is preferably 50 mm or less. The drop distance L refers to the height of the lower end of the pre-treated molded body 10 before being dropped relative to the plane of the top surfaces of the rubber molds 8 and 9. This is because if the drop distance L exceeds 50 mm, the pre-treated molded body 10 will be damaged by impact. For this reason, the drop distance L is preferably 30 mm or less, and more preferably 15 mm or less.

[0032] In the method of filling the untreated molded body 10 into the rubber mold 9, the untreated molded body 10 has a maximum diameter of 5.0 mm or more.

[0033] When the raw molded body 10 is press-molded by applying pressure from above and below, the applied pressure is set low to obtain the desired shape at a low density, and then the CIP process is performed with equal pressure to achieve a high density, thereby achieving a uniform CIP body. A method may be used in which the raw molded body 10 is placed on the lower rubber mold 9 and rotated to fill the holes 11 with the raw molded body 10. In this case, if the maximum diameter of the raw molded body 10 is less than 5.0 mm, the raw molded body 10 is light, so even if the raw molded body 10 rolls on the lower rubber mold 9, it will not rub against and wear out the surface of the lower rubber mold 9, and even if the raw molded bodies 10 collide with each other, they will hardly be damaged.

[0034] However, if the maximum diameter of the raw compacts 10 is 5.0 mm or more, the raw compacts 10 are heavy, and when the raw compacts 10 roll on the lower rubber mold 9, they are likely to rub against the surface of the lower rubber mold 9 and become worn. Furthermore, the raw compacts 10 are likely to collide with each other and become damaged. In this case, the corners of the strip-shaped portion 10' (shown in FIG. 6 ) protruding from the spherical portion may be rubbed or crushed. The weight of the raw compacts 10 increases in proportion to their diameter. Therefore, processing raw compacts 10 with larger diameters results in a better yield, and the effects of the filling methods shown in FIGS. 6 to 11 are greater. Therefore, the maximum diameter of the raw compacts 10 is more preferably 7.0 mm or more, and even more preferably 10.0 mm or more.

[0035] The pre-treatment green body 10 may have a spherical shape, a cylindrical shape, a plate shape, or the like. Among these, the pre-treatment green body 10 preferably has a spherical shape, as shown in FIG. 1 , in order to produce a spherical ceramic ball material 1. The spherical shape refers to a shape having a spherical surface portion 2 and a band portion 3, such as the ceramic ball material 1 with a band portion (shown in FIG. 1 ), or a shape having only a spherical surface portion, such as the ceramic ball material without a band portion (not shown). As described above, by performing the CIP treatment, isostatic pressure can be applied to the pre-treatment green body 10. In particular, the effect of isostatic pressure can be more easily obtained when the pre-treatment green body 10 has a spherical shape.

[0036] In the method for filling the raw compact 10, the total amount of ceramic powder in the raw compact 10 is 80 mass % or more, and the amount of binder is 3 mass % or more and 20 mass % or less.

[0037] Furthermore, the raw compact 10 preferably contains one or more of aluminum oxide (alumina), silicon nitride, boron nitride, zirconium oxide (zirconia), silicon carbide, and aluminum nitride as its main component (50% by mass or more) contained in the ceramic powder. It is more preferable that the raw compact 10 contains 85% by mass or more of one or more of aluminum oxide, silicon nitride, boron nitride, zirconium oxide, silicon carbide, and aluminum nitride. After CIP, the raw compact 10 undergoes a degreasing process as needed, and is then sintered to form a ceramic sintered body (hereinafter, sometimes simply referred to as a "sintered body"). If the raw compact 10 is ball-shaped, the ceramic sintered body also has a ball shape. The ball-shaped ceramic sintered body is also called a ceramic ball material 1 and is used as a bearing ball. Bearing balls are manufactured by polishing the ceramic ball material 1. In particular, silicon nitride sintered bodies have excellent wear resistance and are effective as bearing balls.

[0038] Furthermore, if the ceramic powder of the pre-treated compact 10 contains 85 mass% or more of any one of aluminum oxide, silicon nitride, boron nitride, and zirconium oxide, the resulting ceramic sintered body will also contain 85 mass% or more of any one of aluminum oxide, silicon nitride, boron nitride, and zirconium oxide. In addition to these main components, the ceramic sintered body may contain 15 mass% or less of a sintering aid.

[0039] For example, the aluminum oxide sintered body or the zirconium oxide sintered body has a Vickers hardness of about 1200 or more and 1700 or less. On the other hand, the toughness value is 3 MPa m １／２ 6MPa・m or more １／２ In contrast, silicon nitride sintered bodies have a high Vickers hardness of 1400 or more and 1800 or less. Also, the toughness value is 5 MPa m １／２ 10MPa・m or more １／２The toughness is high, at about the same level as above. Silicon nitride sintered bodies have both high toughness and Vickers hardness, which gives them excellent wear resistance. This is because silicon nitride sintered bodies have a structure that is mainly composed of β-type silicon nitride crystal grains. β-type silicon nitride crystal grains have a long, thin shape, and these long, thin crystal grains are intricately intertwined, which is why they achieve high toughness.

[0040] The amount of binder in the mixed powder of the raw compact 10 is 3% by mass or more and 20% by mass or less. The binder serves to bind the ceramic powder together. The binder is decomposed and removed by heating during the degreasing and sintering stage of the raw compact 10. If the amount of binder is less than 3% by mass, the effect of binding the ceramic powder together is not obtained, and the strength of the raw compact 10 is reduced. Therefore, the raw compact 10 may be damaged even by suction transport. Furthermore, if the binder amount exceeds 20% by mass, the strength of the raw compact 10 increases, but the strength of the sintered body may decrease due to the remaining voids after the binder is removed. Therefore, the binder amount is 3% by mass or more and 20% by mass or less, preferably 5% by mass or more and 15% by mass or less, and more preferably 7% by mass or more and 12% by mass or less.

[0041] Furthermore, polishing is required to turn the spherical ceramic sintered body into a bearing ball. The spherical ceramic sintered body after the sintering process is called a ceramic ball material 1 (shown in FIG. 1). In the case of FIG. 1, the ceramic ball material 1 is a sphere with a band-like portion 3 resulting from the band-like portion of the pre-treatment compact 10. Although not shown, the ceramic ball material 1 may also be a sphere without the band-like portion 3 resulting from the band-like portion of the pre-treatment compact 10. A sphere formed by polishing the ceramic ball material 1 is called a bearing ball.

[0042] As described above, the rubber mold laminate 6 is suitable for applying isostatic pressure to the pre-treatment molded body 10. In particular, the rubber mold laminate 6 is suitable for subjecting the pre-treatment molded body 10 to CIP treatment. The bearing balls have a variety of diameters ranging from 1.0 mm to 50.0 mm. The rubber mold laminate 6 can be applied to pre-treatment molded bodies 10 of various sizes.

[0043] Next, a description will be given of a method for manufacturing the ceramic ball material 1. The method for manufacturing the ceramic ball material 1 is a method using the method for filling the untreated compact 10 described above.

[0044] In addition, the method for manufacturing the CIP body includes a process of filling multiple pre-processed molded bodies 10 into multiple holes 11 formed in the rubber molds 8 and 9 and then stacking them to form the rubber mold laminate 6, as well as a process of performing CIP processing on the filled multiple pre-processed molded bodies 10.

[0045] The method for producing a ceramic sintered body includes a step of filling a plurality of pre-treatment compacts 10 into a plurality of holes 11 formed in the rubber dies 8 and 9, and then stacking them to form a rubber die laminate 6, a step of performing CIP treatment on the filled plurality of pre-treatment compacts 10, and a step of sintering the CIP compacts to obtain a ceramic sintered body. When the ceramic sintered body is in the shape of a ball, it becomes a ceramic ball material 1.

[0046] The method for producing a ceramic sintered body, for example, a ceramic ball material 1, is sufficient if it has the above-described configuration, but a method for improving the yield (number of good products / number of products) will be described below.

[0047] First, the method for preparing the raw compact 10 will be described using silicon nitride. When one or more of aluminum oxide, boron nitride, and zirconium oxide are used as the main component (50 mass% or more), the term "silicon nitride" should be read as a substitute. Furthermore, in the examples of the present invention, uniaxial pressing is used as a method for obtaining the raw compact 10, but the molding method is not limited to this. For example, the molding method may be a rolling granulation method.

[0048] First, appropriate amounts of sintering aid powder, additives, solvent, binder, etc. are added to the raw silicon nitride powder, mixed, crushed, and granulated using a spray dryer. This process produces a granulated powder of the raw powder. Furthermore, when the total of the silicon nitride powder and sintering aid powder is 100 mass%, the silicon nitride powder is preferably 85 mass% or more. The additive is a plasticizer, etc. The solvent is water or an organic solvent. Examples of organic solvents include alcohol, ketone, and benzene. The binder is an organic substance. The amount of binder added is preferably 3 mass parts to 20 mass parts, when the total of the silicon nitride powder and sintering aid powder is 100 mass parts. Adjusting the amount of binder allows for adjustment of the uniaxial pressing, shape retention, and density uniformity of the pre-processed compact 10. Furthermore, granulation allows for uniform mixing of the silicon nitride powder and sintering aid powder.

[0049] Next, uniaxial pressure molding is performed using the granulated powder. An example of uniaxial pressure molding is a die molding method using an upper punch 5U and a lower punch 5D shown in FIG. 2. The shape of the pre-processed compact 10 can be adjusted depending on the shape of the die. By forming the insides of the upper punch 5U and the lower punch 5D into a hemispherical shape, a spherical pre-processed compact 10 can be obtained. Furthermore, by forming the insides of the upper punch 5U and the lower punch 5D into an approximately cylindrical shape, a roller-shaped (approximately cylindrical) pre-processed compact 10 can be obtained. The pre-processed compact 10 obtained by uniaxial pressure molding corresponds to the pre-sintered ceramic ball material 1 having a spherical shape with a spherical portion 2 and a band-shaped portion 3 shown in FIG. 1.

[0050] Next, a step of CIP-treating the pre-treated molded body 10 is performed. A rubber mold laminate 6 is used for the CIP-treating. A plurality of pre-treated molded bodies 10 are filled into a plurality of holes 11 formed in the rubber molds 8 and 9 constituting the rubber mold laminate 6, for example, the lower rubber mold 9. At this time, by providing a large number of holes 11 in the lower rubber mold 9, the number of pre-treated molded bodies 10 that can be processed can be increased. Furthermore, when a plurality of holes 11 are provided in the lower rubber mold 9, it is preferable to perform the CIP-treating after filling all of the holes 11 with the pre-treated molded bodies 10. Although it is not necessary to fill some of the holes 11 with the pre-treated molded bodies 10, filling all of the holes 11 with the pre-treated molded bodies 10 is because the isotropic pressure can be made uniform by filling all of the holes 11 with the pre-treated molded bodies 10.

[0051] The raw compact 10 is formed using granulated powder. When isostatic pressure is applied to the raw compact 10 by CIP treatment, the granulated powder is crushed, making it possible to suppress density variations. By using granulated powder to form the raw compact 10, the silicon nitride powder and sintering aid powder are uniformly dispersed, and density variations can be suppressed. If the pressure applied to the raw compact 10 during CIP treatment is uneven, the granulated powder will remain uncrushed. The remaining uncrushed portions will cause density variations.

[0052] The pressure of CIP molding is preferably higher than the press pressure of uniaxial pressure molding. Furthermore, the CIP treatment conditions are preferably within a pressure range of 30 MPa to 300 MPa. When the pressure is within this range, density variation of the CIP body after CIP treatment can be reduced. This is particularly effective when the rubber molds 7 to 9 constituting the rubber mold laminate 6 have a Shore hardness Hs of 30 to 50. If the CIP pressure is less than 30 MPa, the pressure may be insufficient. Furthermore, if the pressure is higher than 300 MPa, the durability of the rubber molds 7 to 9 may be reduced.

[0053] The CIP body has reduced density variation. Therefore, the shrinkage rate of the CIP body can be controlled in the sintering process described later. Improvement of the CIP body leads to improvement of the ceramic sintered body. The manufacturing method of the ceramic ball material 1 using the rubber mold laminate 6 can improve the defect rate of the CIP body.

[0054] Next, a degreasing process is performed to degrease the CIP body. The degreasing process involves heating the CIP body at a temperature equal to or higher than the decomposition temperature of organic components such as binders to evaporate the organic components. The degreasing process may be performed in a nitrogen atmosphere or in the air. A degreased body can be obtained as a molded body by the degreasing process.

[0055] Next, a sintering process is performed to sinter the degreased body. The sintering process is preferably performed at a temperature of 1700°C or higher and 2000°C or lower. The sintering process is preferably performed in a nitrogen atmosphere. Additionally, the sintering pressure is preferably within a range of atmospheric pressure to 300 MPa or lower. The atmospheric pressure is 0.10133 MPa (=1 atm). The sintered body obtained by the sintering process may be subjected to a HIP (hot isostatic pressing) process. This process allows for the production of a ceramic sintered body (e.g., a ceramic ball material 1). The ceramic ball material 1 is a ceramic sintered body having a theoretical density of 98% or higher.

[0056] Ceramic balls can be manufactured by polishing the ceramic ball material 1. A typical example of sphere polishing is surface plate processing. For example, the ceramic ball material 1 is inserted between parallel surface plates. The movement of the polishing surface plate can be used to polish the ceramic ball material 1 into a perfect sphere. The surface roughness of bearing balls is specified in ASTM F2094. Depending on the application, bearing balls are graded according to ASTM F2094, ISO 26602, or JIS R1669. They are polished to a surface roughness Ra according to that grade. Higher grades can be mirror-finished to a surface roughness Ra of 0.01 μm or less.

[0057] Examples 1-9, Comparative Examples 1-6 Sintering aids, additives, solvents, binders, etc. were added to the raw ceramic powder, mixed, crushed, and granulated using a spray dryer. As shown in Table 1, Examples 1-5 and Comparative Examples 1-2 correspond to pre-treatment molded bodies (silicon nitride molded bodies) 10 containing 85% by mass or more of silicon nitride, Examples 6-7 and Comparative Examples 3-4 correspond to pre-treatment molded bodies (aluminum oxide molded bodies) 10 containing 85% by mass or more of aluminum oxide (alumina), and Examples 8-9 and Comparative Examples 5-6 correspond to pre-treatment molded bodies (zirconium oxide molded bodies) 10 containing 85% by mass or more of zirconium oxide (zirconia). In each case, the amount of binder added was 3 parts by mass or more and 20 parts by mass or less, based on 100 parts by mass of the total of the main component and sintering aid. In Table 1, aluminum oxide is referred to as alumina, and zirconium oxide is referred to as zirconia.

[0058] Next, press molding was performed using the granulated powder. The press molding was performed by die molding using upper and lower punches 5U and 5D in a press die 4 shown in FIG. 2. The press molding using the upper punch 5U and the lower punch 5D was uniaxial pressure molding. The die was used to create a spherical pre-processed compact 10. In this manner, the pre-processed compact 10 was produced. The pre-processed compact 10 used in the examples corresponds to the strip-formed ceramic ball material 1 having a spherical surface portion 2 and a strip-formed portion 3, as shown in FIG. 1. However, the pre-processed compact 10 is similar even if it corresponds to a strip-less ceramic ball material (not shown) having only the spherical surface portion 2.

[0059] Rubber molds 7 to 9 were prepared for CIP treatment of the untreated molded body 10. The rubber molds 7 to 9 had a Shore hardness Hs of 30 to 50. A plurality of hemispherical holes 11 were formed in the bottom surface of the upper rubber mold 7, the top surface of the lower rubber mold 9, and the top and bottom surfaces of the middle rubber mold 8, respectively.

[0060] In the filling methods of Examples 1 to 9, the pre-processed molded body 10 was sucked from the press mold 4 and moved to the lower rubber mold 9 using the manufacturing steps shown in Figures 6 to 11. In contrast, in the filling methods of Comparative Examples 1 to 6, 1.2 times the number of pre-processed molded bodies as the number of holes formed in the lower rubber mold were introduced, and the lower rubber mold was rotated to fill the holes with the pre-processed molded bodies. In Table 1, the filling methods for the pre-processed molded bodies are indicated as "suction" or "rotation," respectively. Furthermore, in the filling methods using the suction method of Examples 1 to 9, the falling distance L of the pre-processed molded body 10 to the lower rubber mold 9 was adjusted.

[0061] Next, the middle rubber mold 8 filled with the pre-treatment molded body 10 was stacked on the lower rubber mold 9 filled with the pre-treatment molded body 10, and the upper rubber mold 7 was stacked on the middle rubber mold 8 to form a rubber mold stack 6. Using this rubber mold stack 6, a CIP treatment was performed on the filled plurality of pre-treatment molded bodies 20. The CIP pressure was in the range of 30 MPa to 300 MPa, and a hydrostatic pressure higher than the pressure in uniaxial pressing was applied. A CIP body was produced by this process.

[0062] Next, the CIP bodies, which are the molded bodies after the CIP treatment, were visually inspected using an optical microscope, and the number of CIP bodies with chipping defects was counted to determine the chipping defect rate. The chipping defect rate is shown in Table 1.

[0063]

[0064] Next, all the samples except for those with chipping defects were subjected to a degreasing and sintering process. The sintering process for silicon nitride was carried out at 1800°C in a nitrogen atmosphere at atmospheric pressure. The sintering process for aluminum oxide and zirconium oxide was carried out at 1500°C in an air atmosphere at atmospheric pressure. Thereafter, the silicon nitride was subjected to HIP treatment at a temperature of 1700°C to 1900°C in a nitrogen atmosphere at a pressure of 50 MPa to 200 MPa. The aluminum oxide and zirconium oxide were subjected to HIP treatment at a temperature of 1300°C to 1500°C in an air atmosphere at a pressure of 50 MPa to 200 MPa.

[0065] Using the ceramic ball materials 1 produced from the untreated compacts 10 of Examples 1 to 14 and Comparative Examples 1 to 3, the sintered bodies before polishing were subjected to an appearance inspection.

[0066] Examples 1 to 3, 6, and 8 and Comparative Examples 1, 3, and 5 shown in Table 1 correspond to ceramic ball materials for ceramic balls that will be 1 1 / 32 inches (8.73 mm) after polishing. Examples 4 to 5, 7, and 9 and Comparative Examples 2, 4, and 6 correspond to ceramic ball materials for ceramic balls that will be 7 / 8 inches (22.225 mm). All of these can be used as bearing balls.

[0067] As can be seen from Table 1 above, the chipping defect rate in the filling method according to the example was low. In contrast, the chipping defect rate in the filling method according to the comparative example was higher than that of the example. This is because, in the filling method according to the example, the raw molded bodies 10 were filled by suction, so that the raw molded bodies 10 did not collide with each other and did not rub against the rubber molds 8 and 9. In contrast, in the filling method according to the comparative example, the raw molded bodies were filled by rotating them on the rubber mold, which caused collisions between the raw molded bodies and rub against the rubber molds, resulting in more chipping defects. Furthermore, among the filling methods according to the example, the rate of chipping defect was lower when the drop distance L of the raw molded bodies 10 was shorter than when it was longer. The smaller the drop distance L of the raw molded bodies 10, the smaller the impact on the raw molded bodies 10, which led to a reduction in the chipping defect rate.

[0068] According to the above-described embodiments, it is possible to provide a method for filling the raw compact 10, a method for manufacturing a CIP body, a method for manufacturing a sintered body, and a method for manufacturing a ceramic ball material, which can reduce defects that occur in the raw compact 10. Furthermore, according to the embodiments, it is possible to improve the yield in the step of filling the raw compact 10.

[0069] Although several embodiments of the present invention have been described above, these embodiments are presented by way of example only and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, modifications, etc. can be made without departing from the spirit of the invention. Modifications of these embodiments are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims. Furthermore, the above-described embodiments can be implemented in combination with each other.

Claims

1. A method for filling a plurality of holes formed in a rubber mold for CIP with a plurality of pre-processed molded bodies, each of which has a maximum diameter of 5.0 mm or more and is a molded body prior to CIP processing, comprising a filling step in which each of the pre-processed molded bodies is filled into the plurality of holes by suction transport.

2. A method for filling ceramic molded bodies as described in claim 1, characterized in that the pre-treated molded body is molded from a mixed powder in which the total amount of ceramic powder is 80 mass% or more and the binder amount is 3 mass% or more and 20 mass% or less.

3. The method for filling ceramic molded bodies according to claim 1 or 2, characterized in that the pre-treatment molded body is a molded body made of silicon nitride.

4. A method for manufacturing a CIP body, comprising: a filling step as described in claim 1 or claim 2; and a CIP step of subjecting a pre-treated molded body, of the plurality of pre-treated molded bodies, that has been filled into some or all of the plurality of holes, to a CIP treatment to produce a plurality of CIP bodies.

5. A method for producing a ceramic sintered body, comprising: a filling step and a CIP step as described in claim 4; and a sintering step for producing a plurality of ceramic sintered bodies by sintering the plurality of CIP bodies.

6. A method for manufacturing a ceramic ball material, comprising the filling step, CIP step and sintering step as described in claim 5, characterized in that the plurality of ceramic sintered bodies have a shape having a spherical portion and a band-shaped portion, or a shape having only a spherical portion.

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