Rubber mold for cold isostatic pressing, method for manufacturing ceramic ball material, and method for manufacturing ceramic ball

Abstract

A rubber die for cold isotropic pressure molding according to one embodiment of the present invention has a plate-like shape and is for use in performing a cold isotropic pressure molding process on a molded article. Said rubber die is provided with one or more substantially cylindrical holes formed in at least one surface thereof. In this rubber die, a / b<2.0 is satisfied, where a represents the diameter of the opening of the holes, and b represents the maximum depth of the holes.

Description

[Technical Field]

[0001] The embodiments described below relate to a rubber mold for cold isostatic pressing, a method for manufacturing a ceramic ball material, and a method for manufacturing a ceramic ball. [Background technology]

[0002] Various ceramic materials possess properties such as high hardness, electrical insulation, and wear resistance. Fine ceramics, which are particularly highly pure and have uniform particle sizes, exhibit properties that make them useful in a variety of fields, including capacitors, actuator materials, and fireproofing materials. Among these, bearing balls are products that take advantage of their wear resistance and electrical insulation. Materials such as aluminum oxide, silicon nitride, and zirconium oxide are used for bearing balls. For example, Japanese Patent Laid-Open Publication No. 6-48813 (Patent Document 1) and Japanese Patent No. 2764589 (Patent Document 2) disclose bearings made of silicon nitride, and Japanese Patent Laid-Open Publication No. 60-18620 (Patent Document 3) discloses bearings made of zirconium oxide. Furthermore, as described in Patent Document 5, a bearing structure combining a mortar and a pestle is also known, but the hole is not approximately cylindrical (the ratio of the end depth to the maximum depth is approximately 0.8). Furthermore, the space into which the molded body obtained when the upper and lower rubber dies are engaged is spherical, as in the prior art.

[0003] The process for manufacturing these bearing materials involves sintering a green compact. A press molding machine using a mold is used for the molding method. As shown in Figure 1, a press molding machine generally comprises an upper mold 1 and a lower mold 2. Powder is filled between the upper mold 1 and the lower mold 2, and pressure is applied. Binders and other additives may be added to the powder as needed. To protect the molds during press molding, a gap must be provided between the tip 3 of the upper mold 1 and the tip 4 of the lower mold 2. For this reason, a spherical portion 6 and a strip-shaped portion 7 were formed in the green compact 5 (shown in Figure 2).

[0004] For example, Japanese Patent No. 4761613 (Patent Document 4) discloses a molded body having a spherical portion and a strip-shaped portion. Figure 2 shows an example of a molded body. In Figure 2, 5 denotes the molded body, 6 denotes the spherical portion, 7 denotes the strip-shaped portion, and L denotes the maximum dimension (or maximum diameter) of the spherical portion 6. The strip-shaped portion 7 has a width W and a height H relative to the surface of the spherical portion 6. Furthermore, because the molded body is formed by uniaxial pressing, the force applied to the powder is unidirectional, making it difficult to completely eliminate internal voids. Residual voids of a certain size or larger in the molded body significantly reduce the reliability of bearing balls after finish processing. Furthermore, the density non-uniformity in the molded body increases, making it prone to uneven shrinkage during the sintering process and defects such as distortion and cracking in the product. To prevent residual voids in the molded body, cold isostatic pressing (CIP) of the molded body 5 is effective. The CIP treatment is a method in which the periphery of the molded body 5 is sealed with rubber, film, or the like, and isotropic water pressure is applied from the periphery. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 6-48813 [Patent Document 2] Patent No. 2764589 [Patent Document 3] Japanese Patent Application Publication No. 18620 / 1983 [Patent Document 4] Patent No. 4761613 [Patent Document 5] Japanese Patent Application Publication No. 10-6093 Summary of the Invention [Problem to be solved by the invention]

[0006] A conventional CIP rubber mold is shown in Figure 3. In Figure 3, reference numeral 18 denotes the CIP rubber mold. Figure 3(A) is a perspective view of the CIP rubber mold 18, and Figure 3(B) is a side cross-sectional view of the CIP rubber mold 18.

[0007] Here, the CIP rubber mold 18 for processing the molded body 5 (shown in FIG. 2) is a mold used when performing CIP molding. The CIP rubber mold 18 is plate-shaped. Here, a plate-shaped mold has a certain thickness (height). A conventional CIP rubber mold 18 has a plurality of hemispherical holes 19 on each of its two opposing bottom surfaces (the upper and lower surfaces in the figure, excluding the side surfaces). FIG. 4 is a diagram illustrating two conventional CIP rubber molds 18 stacked together. In FIG. 4, 181 is an upper rubber mold, 182 is a lower rubber mold, and 5 is a molded body to be CIP-molded. The upper rubber mold 181 and the lower rubber mold 182 are examples of the CIP rubber mold 18. FIG. 4(A) is a perspective view of the upper and lower rubber molds 181 and 182 stacked together, and FIG. 4(B) is a side cross-sectional view of the upper and lower rubber molds 181 and 182 stacked together.

[0008] In the prior art, the molded body 5 is placed in the hole 19 of the lower rubber mold 182, and the hole 19 of the upper rubber mold 181 is aligned with the opposing hole 19 of the lower rubber mold 182, thereby sealing the molded body 5 between the upper rubber mold 181 and the lower rubber mold 182 (see FIG. 4(B)). By applying isotropic water pressure to the overlapping upper and lower rubber molds 181 and 182, it is possible to crush the voids in the molded body 5 evenly from all directions and reduce density non-uniformity in the molded body 5.

[0009] Furthermore, a structure combining a mortar and a pestle is also known, as described in Patent Document 5, but when the upper and lower rubber molds are engaged, the space into which the molded body can be placed is spherical, as in the prior art.

[0010] On the other hand, the hole 19 formed in the upper rubber die 181 is substantially identical in shape to the hole 19 formed in the lower rubber die 182, and is highly symmetrical in shape. Furthermore, if the diameter of the opening of the hole 19 in the upper and lower rubber dies 181, 182 is a and the maximum depth of the hole 19 is b, the ratio "a / b" was approximately 2.0, resulting in a hemispherical shape. Furthermore, among the rubber dies described in the prior art, those with an "a / b" ratio of approximately 1.0 had a ratio of approximately 0.8 between the maximum depth and the depth near the edge (Comparative Examples 1 and 3 in Tables 1 and 2, which will be described later). Therefore, with the conventional method of forming a hemispherical hole, when a molded body 5 was placed in the hole 19 in the upper bottom surface of the lower rubber die 182, the upper hemisphere of the molded body 5 protruded from the bottom surface. When installing the upper rubber mold 181 on the lower rubber mold 182 from which the molded body 5 protrudes from the upper bottom surface, it is difficult to align the molded body 5 correctly, and the molded body 5 may rub against the upper and lower rubber molds 181, 182. Similarly, those with a ratio of maximum depth to end depth of about 0.8 have a structure similar to that of a combined mortar and pestle, making alignment difficult, and stress is concentrated at the engaged points, which may result in rubbing.

[0011] Furthermore, even if the upper rubber mold 181 can be installed on the lower rubber mold 182 without rubbing, if the upper and lower rubber molds 181, 182 are displaced horizontally, for example, during transport into a CIP processing device, torsional shear stress may be generated in the molded body 5. Furthermore, the rubber mold described in Patent Document 5 has a structure combining a mortar and a pestle, and the space created by their combination is spherical, similar to that found in other prior art. Therefore, even with the rubber mold described in Patent Document 5, if it is displaced horizontally, torsional shear stress may be generated in the molded body 5, especially at the boundary of the engagement.

[0012] The molded body 5 often has low strength, and defects such as partial chipping and cracking occur in the molded body 5 due to friction and shear stress between the upper and lower rubber dies 181, 182. If the molded body 5 has defects, defects also occur in the sintered body generated after the CIP treatment. For example, when a defective sintered body is processed into bearing balls, only unreliable bearing balls are obtained.

[0013] The present invention solves these problems by providing a rubber mold that can reduce the rubbing of the molded body that occurs between the upper and lower rubber molds 181, 182 and the occurrence of torsional shear stress in the molded body when performing CIP processing. [Means for solving the problem]

[0014] The rubber mold according to the embodiment is plate-shaped and is used for CIP processing of molded bodies. The CIP rubber mold has one or more approximately cylindrical holes on at least one surface. When the diameter of the opening of the hole is a and the maximum depth of the hole is b, the relationship a / b<2.0 is satisfied. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram showing an example of die press molding. [Figure 2] FIG. 2 is a diagram showing an example of a molded body after mold press molding. [Figure 3] FIG. 1 is a diagram showing an example of a conventional CIP rubber mold. [Figure 4] FIG. 4 is a diagram showing an example of a molded body being filled into the CIP rubber mold shown in FIG. 3. [Figure 5] FIG. 2 is a diagram showing a first example of a CIP rubber mold according to an embodiment. [Figure 6] FIG. 6 is a side cross-sectional view showing two CIP rubber molds shown in FIG. 5 stacked together. [Figure 7] FIG. 2 is a diagram showing an example of a side cross section illustrating the shape of a hole in a CIP rubber mold according to an embodiment. [Figure 8] FIG. 10 is a view showing a second example of a CIP rubber mold according to an embodiment. [Figure 9] 9 is a diagram showing an example of a side cross section showing two CIP rubber molds shown in FIG. 8 stacked together. Embodiment

[0016] Below, referring to the drawings, we will explain the rubber mold for cold isostatic pressing (CIP), ceramic vinegar ball Materialsand a method for manufacturing ceramic Bo An embodiment of the method for manufacturing the ball will now be described in detail.

[0017] The CIP rubber mold according to the embodiment is characterized in that one or more substantially cylindrical holes are provided in at least one or more surfaces.

[0018] FIG. 5 shows a first example of a CIP rubber mold according to an embodiment. FIG. 5(A) is a perspective view, and FIG. 5(B) is a top view. FIG. 6 is a side cross-sectional view showing two first examples of the CIP rubber mold according to an embodiment stacked together. In the figure, reference numeral 5 denotes a molded body to be CIP-treated (hereinafter simply referred to as "molded body") before CIP treatment, reference numeral 8 denotes a CIP rubber mold (hereinafter simply referred to as "rubber mold"), reference numeral 9 denotes a substantially cylindrical hole (hereinafter simply referred to as "hole"), reference numeral P denotes a groove (engagement recess), and reference numeral Q denotes a protrusion (engagement protrusion). Reference numeral 81 denotes an upper rubber mold as an example of the rubber mold 8, and reference numeral 82 denotes a lower rubber mold as an example of the rubber mold 8. The molded body obtained by CIP treatment of the molded body 5 is not limited to a spherical shape, and may be a cylindrical shape (roller). Furthermore, the molded body obtained by CIP treatment may be one obtained by CIP treatment of a molded body 5 obtained by molding or rolling granulation, or one obtained by filling powder and molding only by CIP treatment. The phrase "the molded body 5 may be obtained by molding or rolling granulation" refers to the fact that the molded body 5 may or may not have a band-shaped portion 7. Among the above methods, it is more preferable to perform CIP treatment on a molded body 5 obtained by molding or rolling granulation. Furthermore, as shown in FIG. 2, the molded body 5 may or may not have a band-shaped portion 7. Furthermore, the shape of one or more holes provided on the bottom surface of the rubber mold 8 is taken into consideration. Therefore, the side shape of the rubber mold 8 is not particularly limited. Therefore, the side surface of the rubber mold 8 may not have any recesses or protrusions on the side surface for markers or the like. However, if a recess is provided on the side surface of the rubber mold 8, it is preferable that the recess not be too large because if it is too large, the recess may be too close to the approximately cylindrical hole 9, resulting in insufficient strength. Similarly, it is preferable that the convex portion is not too large, because if the convex portion is too large, it may reduce the number of molded bodies 5 that can be processed at one time by the rubber mold 8. Furthermore, the space including the approximately cylindrical hole portion 9 into which the molded body can be placed, which is formed when the upper rubber mold 81 and the lower rubber mold 82 are engaged, is not spherical, but is approximately cylindrical.

[0019] The rubber mold 8 also has one or more approximately cylindrical holes 9 on one or more of its two opposing bottom surfaces. Symbol a in FIG. 6 indicates the diameter of the opening of the hole 9. If the hole 9 is a perfect cylinder, the opening has a single diameter. However, if the opening is not a perfect circle but has a shape close to a perfect circle, symbol a indicates a specific diameter (e.g., the largest diameter) among the multiple diameters of the opening. Therefore, for example, if the shape close to a perfect circle is an ellipse, symbol a indicates the major axis diameter. Symbol b indicates the maximum depth of the hole 9. Symbol c indicates the horizontal distance (distance perpendicular to the depth direction) between adjacent holes 9 on the same rubber mold 8. If the rubber mold 8 has multiple holes 9, the horizontal distance c is the average value of the distance between the side surfaces of a hole 9 and the holes adjacent to that hole 9. Therefore, for example, if there are three first to third hole portions 9, this average value is the average value of the distance between the first hole portion 9 and the second hole portion 9, the distance between the second hole portion 9 and the third hole portion 9, and the distance between the third hole portion 9 and the first hole portion 9. The symbol d is the vertical distance (distance in the depth direction) between the hole portions 9 when the upper and lower rubber molds 81, 82 are overlapped. The vertical distance d is the average value between the bottom surface of the hole portion 9 in the upper rubber mold 81 and the opening of the hole portion 9 in the lower rubber mold 82 when the upper and lower rubber molds 81, 82 are overlapped.

[0020] First, the rubber mold 8 is used for CIP processing. There are two types of CIP processing: WET-CIP and DRY-CIP. In WET-CIP, the powder or compact is directly sealed in a bag or other material with low deformation resistance and a certain level of strength to prevent contact with the liquid and then hydraulic pressure is applied. On the other hand, DRY-CIP is performed via a rubber mold, and a support (such as a platform) is provided below the rubber mold 8. Because hydraulic pressure is used, molding with non-directional isotropic pressure is possible. Because this isotropic pressure is used, uneven density distribution within the compact 5 can be suppressed. CIP is also called cold isostatic pressing or rubber pressing. Among these methods, the rubber mold 8 produces particularly favorable results when DRY-CIP is used.

[0021] The rubber mold 8 has one or more holes 9 in one of the opposing bottom surfaces. The holes 9 have a substantially cylindrical shape. For example, as shown in FIG. 2, the molded body 5 has a spherical portion 6 and a band-like portion 7. The molded body 5 may also have a spherical portion 6 without the band-like portion 7. It is more preferable that the hole 9 has a size that can completely accommodate the entire molded body 5. The position of the holes 9 in the rubber mold 8 will be explained. It is more preferable that a plurality of holes 9 be provided in one of the two opposing bottom surfaces.

[0022] If the diameter of the opening of the hole 9 in the rubber mold 8 is a and the maximum depth of the hole 9 is b, it is preferable that the diameter a of the opening relative to the maximum depth b (ratio "a / b") satisfy the following formula (1). a / b<2.0 …(1) When the ratio "a / b" is within the range of the above formula (1), it becomes possible to provide a gap between the rubber die 8 and the molded body 5, which is expected to have the effect of reducing friction of the molded body 5 and torsional shear stress on the molded body 5. Furthermore, it is more preferable that the ratio "a / b" satisfies the following formula (2), in order to maintain a high yield of the ceramic ball material. a / b<1.7 …(2) It is more preferable that the ratio "a / b" satisfies the following formula (3) in order to maintain a higher yield of the ceramic ball material. 0.4≦a / b≦1.6 …(3)

[0023] As shown in the above formula (1), when the ratio "a / b" is less than 2.0, a gap is formed between the molded body 5 and the hole 9, reducing stress concentration during transport of the upper and lower rubber molds 81, 82 into the CIP processing equipment. Furthermore, by further controlling the ratio "a / b" to be less than 1.7 or 1.6 or less, as shown in the above formulas (2) and (3), the yield can be improved and the effect of reducing stress concentration can be further enhanced. On the other hand, when the ratio "a / b" is less than 0.4, a thickness greater than necessary is required per stage to maintain the strength per stage, which may reduce the number of molded bodies 5 that can be processed at one time, which is undesirable. More preferably, the ratio "a / b" satisfies the following formula (4): 0.6≦a / b≦1.6 …(4) More preferably, the ratio "a / b" satisfies the following formula (5). 0.7≦a / b≦1.6 …(5) By further controlling the ratio "a / b" to 0.6 or more or 0.7 or more as shown in the above formulas (4) and (5), it is possible to improve the yield and also increase the number of molded bodies 5 that can be processed at one time by the rubber mold 8.

[0024] Furthermore, the ratio "a / b" is preferably within the range shown in the following formula (6): Furthermore, the ratio "a / b" is preferably within the range shown in the following formula (7): This is to maintain a high yield of the ceramic ball material. 0.7≦a / b≦1.3 …(6) 0.9≦a / b≦1.1 …(7) When the ratio "a / b" is within the range of the above formulas (6) and (7), it is possible to improve the yield and also improve the isotropy of the pressure applied to the compact 5. In particular, it is preferable that the above formulas (6) and (7) are satisfied for the compact 5 that is spherical (including the compact 5 with the band-shaped portion 7 shown in FIG. 2).

[0025] The depth of the hole 9 in the rubber mold 8 will now be described. Figures 7(A) and (B) show examples of enlarged side cross-sectional views of the vicinity of one hole 9. If the depth of the hole 9 near the center of the bottom surface of the hole 9 (maximum depth b) is taken as the depth of the hole 9 near the edge of the bottom surface of the hole 9, it is preferable that the relationship be as shown in the following formula (8). Figure 7(A) also shows a case where the depth g of the hole 9 near the edge of the bottom surface is equal to the maximum depth b. In this case, the depth of the hole near the edge of the bottom surface is merely the depth of the bottom surface. For example, if the opening is scratched or if a design is used in which the periphery of the opening is wide to facilitate removal, this is not the bottom surface, and is not considered as a depth here. (bg) / b≦0.1 …(8)

[0026] The diameter of the hole 9 of the rubber mold 8 will now be described. FIG. 7(C) shows an enlarged side cross-sectional view of the vicinity of one hole 9. In addition to the opening, there are multiple planes perpendicular to the depth direction of the hole 9 in the depth direction. As shown in FIG. 7(C), the diameter of the opening among the multiple perpendicular planes in the depth direction is defined as a, and the maximum diameter of the multiple planes parallel to the opening in the depth direction is defined as h. The diameter a of the opening relative to the maximum diameter h (ratio "a / h") preferably falls within the range of the following formula (9). Note that in FIG. 7(C), the size of the hole 9 is exaggerated to make the relationship between the diameter a of the opening and the maximum diameter h easier to understand. The relationship between the diameter a of the opening and the maximum diameter h is not limited to the state shown in FIG. 7(C) and can be changed as appropriate within the range of the following formula (9). 0.9≦a / h≦1.0 …(9) Furthermore, when hole 9 is not a regular cylinder but has multiple diameters at its opening, it is preferable that the range of the maximum diameter a to the minimum diameter i at the opening of hole 9 shown in FIG. 5(B) (ratio "a / i") be within the range of the following formula (10). Note that in FIG. 5(B) (and also in FIG. 8(B)), for the sake of convenience, the shape of the opening of hole 9 exaggerates the difference between the maximum diameter a and the minimum diameter i. Here, an example will be described where the shape of the opening of the hole is elliptical. When the shape of the opening is elliptical, a is the major axis diameter and i is the minor axis diameter. a / i≦2 …(10) The shape of the hole 9 having the depth and diameter that satisfy the above formula (8) is called a substantially cylindrical shape. It is more preferable that the above formulas (9) and (10) are also satisfied.

[0027] Furthermore, the diameter a and maximum depth b of the opening of the hole 9 are sized to accommodate the molded body 5. By making the hole 9 approximately cylindrical, the pressure on the molded body 5 can be isotropically distributed. Furthermore, in the rubber mold 8, as shown in Figures 3 and 4, the molded body 5 is not placed in the space created by stacking upper and lower rubber molds 181, 182 each having a hemispherical hole 19, so damage to the molded body 5 due to misalignment of the upper and lower rubber molds 181, 182 can be prevented. Furthermore, the rubber mold 8 has one or more hole portions 9. The hole portion 9 is where the molded body 5 is placed. By having the rubber mold 8 have multiple hole portions 9, the number of molded bodies that can be processed in one CIP can be increased.

[0028] The position of the engaging portions of the rubber mold 8 will be described. As shown in FIG. 6, the rubber mold 8 preferably has one or more engaging portions (a set of engaging recess P and engaging protrusion Q) to prevent misalignment of the surfaces. It is more preferable that the engaging portions P and Q are substantially point-symmetrical with respect to the center S of the bottom surface of the rubber mold 8, and are provided continuously or intermittently along a circle (or polygon) around the center S. In this way, if they are point-symmetrical with respect to the center S, even if there are engaging portions P and Q in multiple locations, it is easy to fit the upper rubber mold 81 into the lower rubber mold 82 without considering the orientation, and to engage the upper and lower rubber molds 81 and 82.

[0029] As shown in FIG. 6, it is more preferable that the engagement portions P and Q are disposed at one or more locations closer to the edge T of the rubber mold 8 than the midline U between the center S of the bottom surface and the edge T of the bottom surface (hereinafter referred to as the "edge-proximal portion"). When the engagement portions P and Q on the bottom surface are closer to the edge T, the influence of misalignment that occurs when the space of the engagement recess P occupies a larger area than the engagement protrusion Q on the same plane as the surface on which the hole 9 is formed can be suppressed. Therefore, by arranging the engagement portions P and Q at the aforementioned locations, the influence of slight errors in controlling the size of the engagement portions P and Q is reduced. Furthermore, it is more preferable that the engagement portions P and Q are disposed along the edge T in the edge-proximal portion of the bottom surface, as shown in FIGS. 5 and 6. In this case, if the bottom surface of the rubber mold 8 is circular, the engagement portions P and Q are also disposed circularly, and if the bottom surface is polygonal, the engagement portions P and Q are also disposed polygonally. The engagement recess P and engagement protrusion Q have the effect of preventing misalignment when the upper rubber mold 81 is placed on the lower rubber mold 82.

[0030] The engaging portions P and Q are formed within a range of 50% to 100% of the circumferential length of the edge T of the rubber mold 8. Zhou In other words, the length of the engaging recess P and the engaging protrusion Q (the length of the edge T) may be 100% of the length of the engaging recess P and the engaging protrusion Q. Zhou The lengths (ratio to the length of the engaging recess P) of the engaging protrusion Q may be the same or different. Therefore, the engaging protrusion Q may be long, but if the engaging protrusion Q is longer, there is a risk that it will not be able to engage if it is too long. Therefore, if the engaging protrusion Q is longer, it is preferable that the difference is small (such as within the margin of error). Furthermore, if they are different, it is more preferable that the engaging protrusion Q is shorter than the engaging recess P.

[0031] Alternatively, engaging recesses P may be provided on one bottom surface of the rubber mold 8 and engaging protrusions Q may be provided on the other bottom surface, or engaging recesses P and engaging protrusions Q may be provided alternately on one bottom surface of the rubber mold 8 and engaging recesses P and engaging protrusions Q may be provided alternately on the other bottom surface. The engaging portions P and Q may be provided continuously or intermittently, but it is more preferable that they are provided with little bias in the locations near the edges of the bottom surface. As mentioned above, little bias makes it easier to achieve the effect of providing the engaging portions P and Q. On the other hand, if there is a large bias, the engaging portions P and Q may be easily disengaged depending on the direction in which force is applied when they are provided.

[0032] Furthermore, it is more preferable that the engaging portions P, Q arranged in the vicinity of the edge of the bottom surface of the rubber mold 8 are provided continuously. By providing the engaging portions P, Q along the entire circumference of the vicinity of the edge of the bottom surface of the rubber mold 8, it becomes easier to align the upper and lower rubber molds 81, 82. The thickness of the provided engaging portions P, Q is preferably 3% or more of the diameter of the rubber mold 8, and more preferably 7% or less. If the thickness (wall thickness) of the engaging portions P, Q is less than 3% of the diameter of the rubber mold 8, there is a risk that sufficient durability will not be obtained. If it is larger than 7% of the diameter of the rubber mold 8, the number of holes 9 will be limited, which will reduce the number of molded bodies 5 that can be subjected to CIP treatment per run, and there is a risk that mass productivity will decrease. Furthermore, the wall thickness may be different between the engaging recess P and the engaging protrusion Q. Convex The difference in thickness between the engaging recess P and the engaging protrusion Q is preferably 0% or more and 3% or less of the diameter of the rubber mold 8, and more preferably 0% or more and 2% or less. If there is a difference in thickness, it is even more preferable that the engaging recess P is thicker than the engaging protrusion Q. If the difference in thickness is greater than 3%, there is a risk that the surfaces may become more easily disengaged. Therefore, it is preferable that the difference in thickness is small.

[0033] 5 and 6, the engaging recess P is provided on the bottom surface having the hole 9 and the engaging protrusion Q is provided on the other bottom surface, but the reverse is also possible. That is, the engaging protrusion Q may be provided on the bottom surface having the hole 9 and the engaging recess P may be provided on the other bottom surface. By providing the engaging portions P and Q on the outer periphery of the bottom surface, space for providing the hole 9 on the bottom surface can be secured. Furthermore, by providing the engaging portions P and Q on the outer periphery of the bottom surface, multiple rubber molds 8 can be stacked. In other words, three or more rubber molds 8 can be stacked. As described above, by providing the engaging portions P and Q along 100% of the length of the outer periphery of the bottom surface (the length of the circle if the rubber mold 8 is a disk), misalignment when multiple rubber molds 8 are stacked can be prevented.

[0034] On the other hand, the engagement portions P and Q only need to be provided near the edge of the bottom surface of the rubber mold 8, and are not limited to being provided along the edge T as shown in Figures 5 and 6. For example, as shown in Figures 8 and 9, the engagement recess P may be located at a position away from the edge T so that the length j of the outer circumferential flat portion relative to the diameter of the rubber mold 8 is 2% or less. It is more preferable that the engagement recess P is located at a position away from the edge T so that the length j of the outer circumferential flat portion relative to the diameter of the rubber mold 8 is 1% or less. It is even more preferable that the length j of the outer circumferential flat portion is within 1 cm.

[0035] The thickness of the engagement portions P, Q of the rubber mold 8 will be described. The thickness of the engagement portions P, Q is preferably 3% or more and 7% or less of the diameter of the rubber mold 8. If the thickness of the engagement portions P, Q is less than 3% of the diameter of the rubber mold 8, there is a risk that the engagement portions P, Q will not be sufficiently durable. On the other hand, if the thickness of the engagement portions P, Q is too large, exceeding 7% of the diameter of the rubber mold 8, the number of holes 9 will decrease, which will reduce the number of molded bodies 5 that can be CIP processed per run and may reduce mass productivity. Furthermore, it is preferable that the difference in thickness between the thinnest and thickest points of the engagement portions P, Q is small.

[0036] Furthermore, the volume V1 occupied by the space of the engaging recess P may be larger or smaller than the volume V2 occupied by the engaging protrusion Q, but it is more preferable that the difference between these volumes is not too large. The volume V2 occupied by the engaging protrusion Q relative to the volume V1 occupied by the space of the engaging recess P (the ratio "V2 / V1") satisfies the following formula (11). More preferably, it satisfies the following formula (12). 0.4≦V2 / V1<1.3 …(11) 0.45≦V2 / V1<1.00 …(12)

[0037] The depth of the engaging portions P and Q of the rubber mold 8 will now be described. In the rubber mold 8, it is preferable that the depth e of the engaging recess P is 1.5 mm or more, and the height f of the engaging protrusion Q is 1.5 mm or more. In other words, it is preferable that the depth e of the engaging recess P and the height f of the engaging protrusion Q satisfy the following formulas (13) and (14). e≧1.5 [mm] … (13) f≧1.5 [mm] …(14)

[0038] It is more preferable that the rubber mold 8 has no recesses with a depth of 1.5 mm or more and no protrusions with a height of 1.5 mm or more on the bottom surface other than the engagement portions P and Q. This means that the engagement recesses P and engagement protrusions Q for positioning the upper and lower rubber molds 81 and 82 when they are stacked are formed only on the outer periphery. In other words, the positioning when the upper and lower rubber molds 81 and 82 are stacked is performed by fitting the engagement recesses P of the lower rubber mold 82 with the engagement protrusions Q of the upper rubber mold 81. Since there are no recesses or protrusions other than on the outer periphery of the bottom surface, space can be secured to provide numerous holes 9 on the bottom surface.

[0039] Note that the holes 9 for inserting the molded body 5 are not counted as the engagement recesses P. When multiple holes 9 are provided, the molded body 5 may not be inserted into some of the holes 9. When the upper and lower rubber molds 81, 82 are stacked together, the engagement recesses P of the upper rubber mold 81 are fitted into the engagement protrusions Q of the lower rubber mold 82. This allows the holes 9 and the engagement recesses P to be distinguished. In addition to the engagement recesses P and engagement protrusions Q, recesses less than 1.5 mm in depth or protrusions less than 1.5 mm in height may be present. For example, by providing recesses less than 1.5 mm in depth in the rubber mold 8, the weight of the rubber mold 8 can be reduced. From the perspective of uniform deformation of the rubber mold 8, it is more preferable that there are no recesses less than 1.5 mm in depth or protrusions less than 1.5 mm in height other than the engagement recesses P and engagement protrusions Q.

[0040] Here, the diameter a and maximum depth b of hole 9 are defined. Diameter a refers to the diameter at the opening of hole 9 (the maximum diameter if the opening is not a perfect circle). Maximum depth b of hole 9 refers to the maximum depth of hole 9. That is, hole 9 may have a right-angled boundary between the side and bottom surfaces (see FIG. 7(A)), or the boundary between the side and bottom surfaces may be chamfered (see FIG. 7(B)), and the depth g of hole 9 at the edge may be shallower than the depth b of hole 9 at the center of the bottom surface of hole 9. Furthermore, the diameter a of the opening of hole 9 relative to the maximum dimension L of molded body 5 (ratio "a / L") is preferably in the range of 1.01 to 1.82, and the maximum depth b of molded body 5 relative to the maximum dimension L (ratio "b / L") is preferably in the range of 1.01 to 1.82. That is, it is preferable that the ratio "a / L" and the ratio "b / L" are within the ranges of the following expressions (15) and (16), respectively. 1.01≦a / L≦1.82 …(15) 1.01≦b / L≦1.82 …(16) When the ratios "a / L" and "b / L" are within the ranges of the above formulas (15) and (16), respectively, it is possible to apply isotropic water pressure while suppressing rubbing and torsional shear stress caused by the rubber mold 8. When either the ratio "a / L" or the ratio "b / L" is less than 1.01, the hole 9 is small, and there is a possibility that the molded body 5 will be damaged when it is placed in the lower rubber mold 82. Furthermore, when the maximum depth b is within the ranges of the above formulas (15) and (16), the hole 9 can accommodate the entire molded body 5, making alignment easier.

[0041] Furthermore, if either the ratio "a / L" or the ratio "b / L" exceeds 1.82, the hole 9 becomes too large. If the hole 9 becomes too large, torsional shear force may be generated in the molded body 5 by the rubber mold 8. The torsional shear force is a repulsive stress that prevents the rubber mold 8 from twisting when twisted. If the torsional shear force becomes too large, there is a possibility that isotropic pressure may not be applied to the molded body 5. There is also a possibility that multiple molded bodies 5 may be filled into one hole 9.

[0042] Furthermore, the range of the ratio "a / L" shown in the above formula (15) is more preferably within the range of 1.03 to 1.35, and the range of the ratio "b / L" shown in the above formula (16) is more preferably within the range of 1.03 to 1.35. In other words, the range of the ratio "a / L" is more preferably within the range of the following formula (17), and the range of the ratio "b / L" is more preferably within the range of the following formula (18). 1.03≦a / L≦1.35 …(17) 1.03≦b / L≦1.35 …(18) When the ratio (a / L) and the ratio (b / L) are within the ranges of the above formulas (17) and (18), respectively, it is possible to apply isotropic water pressure to the compact 5. It is possible to reduce voids in the compact 5 and suppress non-uniform density.

[0043] Here, we will explain how to measure the diameter a of the opening of the hole 9, the maximum depth b, and the horizontal distance c. These measurements are made using a non-contact measurement method. This is because when measuring the length using a contact method such as a vernier caliper or depth meter, the values ​​vary due to deformation of the rubber mold 8 when it comes into contact.

[0044] Shape measurement is performed using an optical three-dimensional shape measuring device. The three-dimensional shape measuring device used is a KEYENCE VR-5000, and analysis software for the device is used. Any measuring device with equivalent functionality will suffice. When multiple holes 9 are formed, the entire surface of the rubber mold 8 on which the holes 9 are formed is scanned, and the width of each hole 9 is measured as the diameter, and the largest of the depths is measured as the maximum depth. The average values ​​of the multiple diameters and multiple maximum depths corresponding to the multiple holes 9 are then defined as a and b, respectively. When multiple holes 9 are formed, the horizontal distance c between the holes 9 is also determined by measuring the horizontal distance between each hole 9 and the nearest hole 9. between The distances are measured, and the average value of the horizontal distances corresponding to the plurality of holes 9 is set to c.

[0045] Furthermore, the vertical distance d between the holes 9 when the rubber molds 8 are overlapped is measured using a cross section passing through the center of the holes 9 of the rubber mold 8. A method of measuring the cross section using the above-mentioned three-dimensional shape measuring device is preferable. When multiple holes 9 are provided, the vertical distance between each hole 9 and the nearest hole 9 is measured, and the average value of the multiple vertical distances corresponding to the multiple holes 9 is taken as d. Note that if non-destructive measurement is desired, a micrometer or depth meter shaped so as not to change the shape of the rubber mold 8 may be used for measurement.

[0046] When multiple holes 9 are provided as described above, the diameter a of the opening, the maximum depth b, the horizontal distance c, and the vertical distance d are average values. For example, when multiple holes 9 are provided, it is preferable that the ratio "a / b" of 90% or more in terms of the number of holes 9 with respect to the diameter a and the maximum depth b of the opening satisfies any one of the above formulas (1) to (7), and that the ratio "a / L" or "b / L" satisfies any one of the above formulas (15), (16), or (17), (18). It is even more preferable that the ratio "a / b" of all of the multiple holes 9 provided in the rubber mold 8 (100% in terms of the number of holes 9) satisfies any one of the above formulas (1) to (7), and that the ratio "a / L" or "b / L" satisfies any one of the above formulas (15), (16), or (17), (18).

[0047] Furthermore, when there are multiple holes 9, it is preferable that there is little difference in the size (opening diameter) and depth of the multiple holes 9 provided at each location on the same rubber mold. Furthermore, when the upper and lower rubber molds 81, 82 are overlapped, it is also preferable that there is little difference in the shape, such as the hole size (opening diameter) and depth, between the overlapping rubber molds 81, 82. In this way, when there is little difference in the shape of the hole 9 from location to location, it becomes easier to insert the molded body 5 efficiently.

[0048] It is preferable that the ratio of the diameter a of the opening of the hole 9 (ratio "a / c") and the maximum depth b (ratio "b / c") to the horizontal distance c between adjacent hole portions 9 is 4 or less. In other words, it is preferable that the ratios "a / c" and "b / c" are within the ranges of the following formulas (19) and (20). a / c≦4 …(19) b / c≦4 …(20) The ratios "a / c" and "b / c" falling within the ranges of the above formulas (19) and (20) indicate that the horizontal distance c is sufficient relative to the diameter a of the openings of adjacent holes 9. Similarly, this indicates that the horizontal distance c is sufficient relative to the maximum depth b. The ratios "a / c" and "b / c" exceeding 4 indicate that the distance between adjacent holes 9 is close. If the distance between adjacent holes 9 is close, the rubber mold 8 may not be able to deform sufficiently. If the rubber mold 8 does not deform sufficiently, the isotropy of the pressure applied to the molded body 5 may be lost, and the density may not be uniform. Note that the lower limits of the ratios "a / c" and "b / c" are not particularly limited as long as they are within the ranges of the above formulas (19) and (20).

[0049] Furthermore, the range of the ratio "a / c" shown in the above formula (19) is more preferably 0.1 or more and 4.0 or less, and the range of the ratio "b / c" shown in the above formula (20) is more preferably 0.1 or more and 4.0 or less. In other words, the range of the ratio "a / c" is more preferably within the range of the following formula (21), and the range of the ratio "b / c" is more preferably within the range of the following formula (22). 0.1≦a / c≦4.0 …(21) 0.1≦b / c≦4.0 …(22) Furthermore, it is more preferable that the ratios "a / c" and "b / c" are both 0.2 or greater, and even more preferable that they are 0.3 or greater. If the ratios "a / c" and "b / c" are too small, such as less than 0.1, there is a risk that the number of holes 9 provided per stage will decrease. Therefore, it is preferable that the ratios are controlled to 0.2 or greater, or 0.3 or greater.

[0050] Furthermore, regarding the horizontal distance c and the vertical distance d, it is preferable that the vertical distance d to the horizontal distance c (ratio "d / c") is 0.9 or more. In other words, it is preferable that the ratio "d / c" is within the range of the following formula (23). 0.9≦d / c …(23) If the ratio "d / c" satisfies the range of the above formula (23), isotropic pressure can be applied to the molded body 5 when the upper and lower rubber molds 81, 82 are stacked and subjected to CIP treatment. A ratio "d / c" smaller than 0.9 means that the vertical distance d is small relative to the horizontal distance c. If the vertical distance d is small relative to the horizontal distance c, the difference in the amount of deformation of the upper and lower rubber molds 81, 82 in the horizontal and vertical directions becomes large. If a difference in the amount of deformation of the upper and lower rubber molds 81, 82 in the horizontal and vertical directions occurs, the isotropy of the pressure applied to the molded body 5 may be lost. While the upper limit of the ratio "d / c" is not particularly limited, it is more preferable that it be 200 or less. In other words, it is more preferable that the range of the ratio "d / c" be within the range of the following formula (24). 0.9≦d / c≦200 …(24) The ratio "d / c" is preferably 100 or less, and more preferably 50 or less. By controlling the ratio as described above, the thickness per stage can be controlled, and the number of CIP treatments per unit volume can be increased, enabling efficient CIP treatment.

[0051] Furthermore, the rubber mold 8 is preferably plate-shaped, for example, in the shape of an approximately circular plate. An approximately circular plate refers to a circular or elliptical cylindrical shape with a relatively low height between two opposing bottom surfaces. The plate-shaped rubber mold 8 is not limited to a circular plate shape, but may also be polygonal. If the rubber mold 8 is polygonal, it is preferably pentagonal or greater. As mentioned above, the rubber mold 8 has engaging portions P and Q on its outer periphery. A circular rubber mold 8 facilitates alignment when multiple rubber molds 8 are stacked one on top of the other. In particular, a circular bottom surface facilitates stacking because the upper and lower rubber molds 81 and 82 have no orientation. Furthermore, stacked rubber molds 8 can be prevented from collapsing during transportation. The number of stacked rubber molds 8 is preferably two or more. By stacking multiple rubber molds 8, the number of molded bodies 5 that can be CIP-treated at one time can be increased.

[0052] The number of layers of the rubber molds 8 is not particularly limited, but 100 layers or less is preferable. If the number of layers is too large, the stacked rubber molds 8 may collapse when transported to or removed from the CIP treatment device. Even if they do not collapse, there is a risk that the rate of deterioration of the engaging portions P, Q may be accelerated due to lateral shaking that occurs during transport. Therefore, a more preferable number of layers is 2 to 40 layers. More preferably, it is 2 to 25 layers. Taking mass production and other factors into consideration, it is even more preferable that it is 3 to 20 layers.

[0053] Furthermore, when stacking multiple rubber molds 8, it is preferable that there is little error in the height of the multiple rubber molds 8. For example, it is preferable that the error is 10% or less. This is because if there is a large error in the height of the multiple rubber molds 8, they may be prone to collapse during transportation. It is also preferable that there is little error in the area of ​​the stacking surfaces of the multiple rubber molds 8. This is because if there is a large error in the area of ​​the stacking surfaces of the multiple rubber molds 8, it may be difficult to apply pressure uniformly during CIP treatment.

[0054] Furthermore, if necessary, recesses or protrusions may be provided on the side surfaces or lower bottom surface (surfaces on which no holes are provided) of the rubber mold 8 for the purpose of marking or weight reduction, etc. In other words, the shapes of the side surfaces and lower bottom surface of the rubber mold 8 are not particularly limited.

[0055] Furthermore, it is preferable that the Shore hardness Hs of the rubber of the rubber mold 8 is in the range of 30 to 50. As mentioned above, isotropic pressure is applied to the rubber mold 8 containing the molded body 5. If the Shore hardness Hs is in the range of 30 to 50, the amount of deformation can be made uniform. Therefore, it is possible to provide the deformability that allows the molded body surface and the rubber mold to come into uniform contact. The durability of the rubber mold is also good. The Shore hardness Hs is measured in accordance with JIS-Z-2246 (2000).

[0056] The molded body 5 may have a spherical shape, a cylindrical shape, a plate shape, or the like. Among these, the molded body 5 is preferably spherical as shown in FIG. 2. The spherical shape has a spherical portion 6 and a strip-shaped portion 7. As described above, isotropic pressure can be applied to the molded body 5 by controlling the diameter a of the opening, the maximum depth b, the horizontal distance c, and the vertical distance d. In particular, the effect of isotropic pressure can be easily obtained when the molded body 5 has a ball shape.

[0057] For example, in the relationship between the diameter a and maximum depth b of the opening that satisfies any of the above formulas (1) to (7), the diameter a of the opening of the hole 9 is set according to the maximum dimension L of the formed body 5 in accordance with the above formula (15) or (17), and the maximum depth b is set according to the maximum dimension L of the formed body 5 in accordance with the above formula (16) or (18). Then, the horizontal distance c is set according to the set diameter a and maximum depth b of the opening in accordance with the above formulas (19) and (20) or (21) and (22). Then, the vertical distance d is set according to the set horizontal distance c in accordance with the above formula (23) or (24).

[0058] Furthermore, the molded body 5 preferably contains one or more of aluminum oxide, silicon nitride, boron nitride, zirconium oxide, silicon carbide, and aluminum nitride as a main component (50% by mass or more), and more preferably contains 85% by mass or more of one or more of aluminum oxide, silicon nitride, boron nitride, zirconium oxide, silicon carbide, and aluminum nitride. Furthermore, the molded body 5 preferably contains 85% by mass or more of silicon nitride. After CIP, the molded body 5 is turned into a ceramic sintered body through a sintering process. If the molded body 5 is ball-shaped, the ceramic sintered body also has a ball shape. The ball-shaped ceramic sintered body is used as a bearing ball. The above-mentioned materials are used for ceramic bearing balls. In particular, silicon nitride sintered body has excellent wear resistance and is effective as a bearing ball.

[0059] Furthermore, since the molded body 5 contains 85% by mass or more of one or more of aluminum oxide, silicon nitride, boron nitride, zirconium oxide, silicon carbide, and aluminum nitride, the resulting ceramic sintered body also contains 85% by mass or more of one or more of aluminum oxide, silicon nitride, boron nitride, zirconium oxide, silicon carbide, and aluminum nitride. In addition to these main components, the molded body 5 may contain 15% by mass or less of a sintering aid.

[0060] Furthermore, since the molded body 5 contains 85% by mass or more of any one of aluminum oxide, silicon nitride, boron nitride, and zirconium oxide, the resulting ceramic sintered body also contains 85% by mass or more of any one of aluminum oxide, silicon nitride, boron nitride, and zirconium oxide. In addition to these main components, the molded body 5 may contain 15% by mass or less of a sintering aid.

[0061] For example, aluminum oxide sintered body or 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 ] or more 6 [MPa m 1 / 2 In contrast, silicon nitride sintered bodies have a high Vickers hardness of between 1400 and 1800. In addition, the toughness value is 5 [MPa m 1 / 2 ] or more than 10 [MPa m 1 / 2 ] or less. 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.

[0062] Furthermore, polishing is required to turn spherical ceramic sintered bodies into bearing balls. The spherical ceramic sintered bodies after the sintering process are called ceramic ball materials. The ceramic ball materials are spheres with band-like portions due to the band-like portions 7 (shown in Figure 2) of the compact 5. The ceramic ball materials that have been polished to form spheres are called bearing balls.

[0063] As described above, the rubber mold 8 is suitable for applying isotropic pressure to the molded body 5. It is particularly suitable for subjecting the molded body 5 to CIP treatment. The bearing balls come in a variety of diameters ranging from 1 mm to 50 mm. The rubber mold 8 can be applied to molded bodies 5 of various sizes.

[0064] Next, a method for manufacturing a ceramic ball material will be described. The method for manufacturing a ceramic ball material according to the embodiment is a method using the rubber mold 8 described above.

[0065] The method for manufacturing a ceramic ball material is characterized in that the molded body is a spherical ceramic molded body, and includes a step of CIP-treating the ceramic molded body using a rubber mold 8, and a step of sintering the CIP-treated molded body.

[0066] Furthermore, the step of CIP-treating the molded body 5 is preferably carried out by stacking a plurality of rubber molds 8. Furthermore, it is preferable that the ratio "d / c" of the vertical distance d to the horizontal distance c of the stacked rubber molds 8 is within the range of the above formula (23) or (24).

[0067] The method for manufacturing a ceramic ball material is sufficient if it has the above configuration, but a method for improving the yield (number of good products / number of manufactured products) will be described below.

[0068] First, a method for preparing the molded body 5 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. In the examples of the present invention, uniaxial pressure molding is used as a method for obtaining the molded body 5, but the molding method is not limited to this. For example, a rolling granulation method may also be used as a molding method. In the examples of the present invention, uniaxial pressure molding is used as a method for obtaining the molded body 5, but the molding method is not limited to this. Therefore, for example, the molded body may be obtained by a rolling granulation method.

[0069] First, the raw material silicon nitride is mixed with appropriate amounts of sintering aids, additives, solvents, binders, etc., and then crushed and granulated using a spray dryer. This process produces a granulated powder of the raw material 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 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 shape retention and density uniformity of the compact during uniaxial pressing and CIP. Granulation also allows for uniform mixing of the silicon nitride powder and sintering aid powder.

[0070] Next, uniaxial pressure molding is performed using the granulated powder. An example of uniaxial pressure molding is a mold molding method using an upper mold 1 and a lower mold 2 shown in Figure 1. The shape of the molded body can be adjusted by changing the shape of the mold. A spherical molded body 5 can be obtained by making the inside of the upper mold 1 and the lower mold 2 hemispherical. Furthermore, a roller-shaped (approximately cylindrical) molded body can be obtained by making the inside of the upper mold 1 and the lower mold 2 approximately cylindrical. The molded body 5 obtained by uniaxial pressure molding has a spherical shape (shown in Figure 2) or a cylindrical shape having a spherical portion 6 and a strip-shaped portion 7. Furthermore, the molded body 5 obtained by uniaxial pressure molding is a molded body 5 that can be subjected to CIP.

[0071] Next, a step of CIP-treating the molded body 5 is carried out. A rubber mold 8 is used for the CIP-treating. The molded body 5 is placed into the hole 9 of the rubber mold 8. By providing multiple hole portions 9 in the rubber mold 8, the number of molded bodies 5 that can be processed can be increased. Furthermore, when multiple hole portions 9 are provided in the rubber mold 8, it is preferable to fill all of the hole portions 9 with the molded body 5. It is not necessary to fill some of the hole portions 9 with the molded body 5, but filling all of the hole portions 9 with the molded body 5 allows for more uniform isotropic pressure.

[0072] Furthermore, when the molded body 5 has a spherical portion 6 and a strip-shaped portion 7, it is preferable to fill the molded body 5 so that the strip-shaped portion 7 faces the depth direction of the hole 9. Furthermore, when the ratio "a / L" is within the range of the above formula (15) and the ratio "b / L" is within the range of the above formula (16), the orientation of the strip-shaped portion 7 is arbitrary. By providing an opening diameter a and maximum depth b that are appropriate for the maximum dimension L of the molded body 5, the orientation of the strip-shaped portion 7 can be arbitrary. For this reason, it can be said that the rubber mold 8 is a rubber mold that is suitable for CIP treatment of the molded body 5 having the strip-shaped portion 7.

[0073] Furthermore, the compact 5 is formed using granulated powder. When isostatic pressure is applied to the compact 5 by CIP treatment, the granulated powder is crushed, making it possible to suppress density variations. By using granulated powder to form the compact 5, the silicon nitride powder and sintering aid powder are uniformly dispersed, and density variations can be suppressed. If the pressure applied to the compact 5 during CIP treatment is uneven, some of the granulated powder will not be crushed and will remain. The remaining uncrushed parts will cause density variations.

[0074] Furthermore, the pressure of CIP molding is preferably higher than the press pressure of uniaxial pressure molding. Furthermore, the CIP processing conditions are preferably a pressure within the range of 30 MPa to 300 MPa. When the pressure is within this range, density variations in the molded body after CIP processing can be reduced. This is particularly effective when using a rubber mold with 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 mold 8 may be reduced.

[0075] Furthermore, the density variation of the green body after CIP treatment can be reduced. Therefore, the shrinkage rate of the green body can be controlled in the sintering process described later. Improvement of the green body after CIP treatment leads to improvement of the ceramic sintered body. The manufacturing method for ceramic ball material using the rubber mold 8 can improve the defect rate of the green body after CIP treatment.

[0076] Next, a degreasing process is performed to degrease the compact after the CIP process. The degreasing process is a process in which the compact is heated to a temperature 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 atmosphere. A degreased body can be obtained by the degreasing process.

[0077] Next, a sintering process is performed to sinter the degreased body. The sintering process is preferably performed at a temperature of 1700°C to 2000°C. The sintering process is preferably performed in a nitrogen atmosphere. The sintering pressure is preferably in the range of atmospheric pressure to 300 MPa. Note that atmospheric pressure is 0.10133 MPa (=1 atm). The sintered body obtained by the sintering process may be subjected to HIP (hot isostatic pressing). This process allows the production of a ceramic ball material. The ceramic ball material is a sintered ceramic body with a theoretical density of 98% or more.

[0078] Ceramic balls can be manufactured by polishing ceramic ball materials. A typical example of sphere polishing is surface plate processing. For example, the ceramic ball material is inserted between two parallel surface plates. The movement of the polishing platen allows the ceramic ball material to be polished 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 that conforms to that grade. Higher grades can be mirror-finished to a surface roughness Ra of 0.01 μm or less.

[0079] (Example) (Examples 1 to 14, Comparative Examples 1 to 3) 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, the molded body 5 in Example 1 and Comparative Example 1 was an aluminum oxide molded body, the molded body 5 in Examples 2-3, 5-9, 12-14, and Comparative Example 3 was a silicon nitride molded body, and the molded body in Examples 4, 10-11, and Comparative Example 2 was a zirconium oxide molded body. The aluminum oxide molded body in Example 1 and Comparative Example 1 contained 85% by mass or more of aluminum oxide. The silicon nitride molded body in Examples 2-3, 5-9, 12-14, and Comparative Example 3 contained 85% by mass or more of silicon nitride. The zirconium oxide molded body in Examples 4, 10-11, and Comparative Example 2 contained 85% by mass or more of zirconium oxide. The amount of binder added was 3 to 20 parts by mass when the total of the main component and sintering aid was 100 parts by mass.

[0080] Next, the granulated powder was subjected to press molding. Press molding was performed using upper and lower dies in the press molding device shown in Figure 1. Press molding using upper and lower dies is uniaxial pressure molding. The dies are used to create spherical compacts. In this way, compact 5, which is the subject of CIP, was produced. As shown in Figure 2, compact 5 has a spherical portion 6 and a strip-shaped portion 7.

[0081] CIP treatment was performed on molded body 5. For the CIP treatment, a rubber mold 8 having a Shore hardness Hs of 30 to 50 was used. A plurality of holes 9 were formed on one bottom surface of rubber mold 8. The diameter a and maximum depth b of the opening of hole 9 relative to the maximum dimension L of molded body 5 were within the ranges of the above formulas (15) or (16) in relation to the maximum dimension L of molded body 5.

[0082] Furthermore, the band-shaped portion 7 of the molded body 5 was filled into the hole 9 of the rubber mold 8 so that it was vertical. A plurality of rubber molds 8 were stacked. In this state, the molded body 5 was subjected to CIP treatment. The CIP pressure was in the range of 30 MPa to 300 MPa, and was a hydrostatic pressure higher than the pressure in uniaxial pressing. Through this process, a molded body after CIP treatment was produced.

[0083] The compacts after the CIP treatment were subjected to a debinding process. Next, a sintering process was carried out. The sintering process was carried out at 1800°C in a nitrogen atmosphere at atmospheric pressure. After that, HIP treatment was carried out at a temperature of 1700°C to 1900°C in a nitrogen atmosphere at a pressure of 50 MPa to 200 MPa.

[0084] By this process, a ceramic ball material made of the ceramic sintered body according to the example was manufactured. Furthermore, in comparative examples 1 and 2, the shape of the rubber mold used in the CIP treatment after the press molding process was appropriately changed from that of rubber mold 8. The characteristics of rubber mold 8 in examples 1 to 14 and the characteristics of the rubber molds in comparative examples 1 and 2 are as shown in Table 1. Here, the column "shape of hole" in Table 1 will be explained. A rubber mold having a roughly cylindrical shape that satisfies any of the above formulas (8) to (10) is described as "cylindrical." On the other hand, a rubber mold ( ) that does not satisfy the above formula (8) and has a large "(bg) / b" that exceeds 0.1, and in which the hole before the upper rubber mold is engaged with the lower rubber mold is nearly cylindrical and the shape after engagement is nearly spherical is described as "cylindrical." mortar A rubber mold having a shape resembling a punch and a pestle stacked on top of each other is described as "the hole is cylindrical (spherical after engagement)" (Comparative Examples 1 and 3). In addition, a rubber mold having an approximately hemispherical shape and in which the entire space after engagement is spherical is described as "semispherical" (Comparative Example 2). Furthermore, the presence or absence of an engagement portion in the edge-proximal portion is described as the presence or absence of an engagement recess and the presence or absence of an engagement protrusion. Next, the presence or absence of a recess or protrusion other than the engagement recess and engagement protrusion refers to the presence or absence of a protrusion or recess other than the engagement portion in the edge-proximal portion that has a height or depth of 1.5 mm or more.

[0085] Using the ceramic ball materials manufactured from the compacts 5 of Examples 1 to 14 and Comparative Examples 1 to 3, visual inspections were carried out on the sintered bodies before polishing. The number of pieces inspected was 10,000 for the sintered bodies for 1.34 mm bearings. Also, the number of pieces inspected was 1,000 for the sintered bodies for 5 / 16 inch bearings. As the standard for visual defects, chips or cracks with a width of 0.7 mm or more or a depth of 0.5 mm or more on the surface were defined as defective.

[0086] As a result of the inspection, in determining the defect rate of the appearance of the sintered body, i.e., the material for ceramic balls (Table 2), a defect rate of over 1% was rated as "poor," a defect rate of 0.5% to 1% was rated as "good," and a defect rate of less than 0.5% was rated as best.

[0087] [Table 1] TIFF0007771188000001.tif201170

[0088] [Table 2] TIFF0007771188000002.tif166170

[0089] Examples 1, 2, 6, 11, 12, and 13 and Comparative Example 1 shown in Tables 1 and 2 above are ceramic ball materials for ceramic balls that will be 1.34 mm after polishing. Examples 3 to 5, 7 to 10, and 14 and Comparative Example 2 are ceramic ball materials for ceramic balls that are 5 / 16 inch (7.9375 mm). All of these can be used as bearing balls.

[0090] As can be seen from Table 2 above, the rubber dies according to Examples 1 to 14, i.e., those using the rubber die 8 described above, had a high yield of ceramic ball materials, and the defect rate was judged to be "best" or "good." Furthermore, since the rubber dies 8 according to Examples 1 to 14 have engaging recesses P and engaging protrusions Q, it was possible to stack multiple rubber dies 8 and perform CIP treatment. Furthermore, the rubber dies 8 according to Examples 1 to 14 have protrusions with a height of 1.5 mm or more and protrusions with a depth of 1.5 mm or more in addition to the engaging recesses P and engaging protrusions Q. End Since there are no recesses, it is possible to secure space for providing a large number of holes 9. Therefore, if the rubber mold is of the same size, many holes 9 can be provided. This allows for an increase in the number of molded bodies 5 that can be processed at one time.

[0091] In addition, in Example 5, the Shore hardness Hs of the rubber mold 8 was 20, which was outside the preferred range (30 to 50), and the value of the ratio "a / b" was outside the most preferred range (the above formula (7)), so the yield was "good." In addition, in Examples 11 to 14, the value of the ratio "a / b" satisfied the above formula (1), but was outside the preferred range (any of the above formulas (2) to (7)), so the yield was "good." In Examples 6 to 10, the yield was "good" because at least one of the conditions of the Shore hardness Hs of the rubber mold 8, the ratio "a / L or b / L," the ratio "a / c or b / c," and the ratio "d / c" was outside the preferred range. On the other hand, Examples 1 to 4, in which the Shore hardness Hs of the rubber mold 8, the ratio "a / b", the ratio "a / L or b / L", the ratio "a / c or b / c", and the ratio "d / c" were within the above-mentioned preferred ranges, had the "best" yield.

[0092] On the other hand, the rubber mold according to Comparative Example 1 had a Shore hardness Hs, a ratio "a / b", a ratio "a / L or b / L", a ratio "a / c or b / c", and a ratio "d / c" within the aforementioned preferred ranges, but the shape of the hole did not satisfy the above formula (8) and was not approximately cylindrical, resulting in a "poor" yield. The same was true for the rubber mold according to Comparative Example 3. Furthermore, the rubber mold according to Comparative Example 2 was spherical when stacked (ratio "a / b" = 2.0), and therefore did not satisfy the above formula (1). Therefore, the rubber mold according to Comparative Example 2 caused friction of the molded body 5 and torsional shear stress to the molded body 5, resulting in a "poor" yield.

[0093] According to the embodiment described above, by making the hole 9 substantially cylindrical and setting the ratio "a / b" to less than 2.0, it is possible to reduce the friction of the molded body between the upper and lower rubber dies and the occurrence of torsional shear stress in the molded body during CIP treatment. Furthermore, according to the embodiment, by further controlling the coefficients a to d, etc., it is possible to maintain a high yield of the ceramic ball material.

[0094] 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 plate-shaped cold isostatic pressing rubber mold for cold isostatic pressing a filled molded body, the molded body having a spherical, substantially cylindrical, or a shape including a spherical portion and a band-shaped portion, by pressurizing the molded body, At least one bottom surface is provided with one or more substantially cylindrical holes, the hole has a size capable of accommodating the entire molded body, If the diameter of the opening of the hole is a and the maximum depth of the hole is b, a / b<2.0 Fulfilling If the maximum dimension of the molded body is L, 1.01≦a / L≦1.82, 1.01≦b / L≦1.82 fulfill, A rubber mold for cold isostatic pressing characterized by the above.

2. If the depth of the hole near the edge of the bottom surface of the hole is g, then (b-g) / b≦0.1 fulfill, 2. The rubber mold for cold isostatic pressing according to claim 1.

3. having one or more engagement portions; 2. The rubber mold for cold isostatic pressing according to claim 1.

4. the engaging portion is provided at one or more locations closer to the edge than a midline between the center of the bottom surface of the cold isostatic pressing rubber mold and the edge of the bottom surface; 4. The rubber mold for cold isostatic pressing according to claim 3.

5. a ratio of the diameter of the hole to the maximum depth of the hole is in the range of 0.7 to 1.3; 2. The rubber mold for cold isostatic pressing according to claim 1.

6. the ratios of the diameter and the maximum depth of the hole to the maximum dimension of the molded body are both within the range of 1.01 or more and 1.82 or less; 2. The rubber mold for cold isostatic pressing according to claim 1.

7. the ratios of the diameter and the maximum depth of the hole to the maximum dimension of the molded body are both within the range of 1.03 to 1.35; 2. The rubber mold for cold isostatic pressing according to claim 1.

8. a ratio of the diameter of the hole to the maximum depth of the hole is in the range of 0.9 to 1.1, 2. The rubber mold for cold isostatic pressing according to claim 1.

9. The hole portion has a plurality of the hole portions, and the diameter and the maximum depth of each of the plurality of hole portions are 4 or less relative to the horizontal distance between adjacent hole portions among the plurality of hole portions.

2. The rubber mold for cold isostatic pressing according to claim 1.

10. If the depth of the hole near the edge of the bottom surface of the hole is g, then (b-g) / b≦0.1 Fulfilling the ratios of the diameter and the maximum depth of the hole to the maximum dimension of the molded body are both within the range of 1.03 to 1.35, a ratio of the diameter of the hole to the maximum depth of the hole is in the range of 0.9 to 1.1, 10. The rubber mold for cold isostatic pressing according to claim 9.

11. It has an engaging recess and an engaging protrusion for preventing surface misalignment, There are no recesses with a depth of 1.5 mm or more and no protrusions with a height of 1.5 mm or more other than the engaging recesses and engaging protrusions.

2. The rubber mold for cold isostatic pressing according to claim 1, wherein:

12. The hardness of the rubber of the cold isostatic pressing mold is in the range of 30 to 50 Shore hardness.

2. The rubber mold for cold isostatic pressing according to claim 1.

13. having one or more engagement portions, It has an engaging recess and an engaging protrusion for preventing surface misalignment, There are no recesses with a depth of 1.5 mm or more and no protrusions with a height of 1.5 mm or more other than the engaging recesses and engaging protrusions, The hardness of the rubber of the cold isostatic pressing mold is in the range of 30 to 50 Shore hardness. The rubber mold for cold isostatic pressing according to claim 10.

14. The cold isostatic pressing rubber mold is substantially circular.

2. The rubber mold for cold isostatic pressing according to claim 1.

15. a molding step of cold isostatically pressing a spherical ceramic molded body as the molded body using the rubber mold for cold isostatic pressing according to any one of claims 1 to 14; a sintering step of sintering the compact formed in the forming step to obtain a ceramic ball material; 1. A method for producing a ceramic ball material, comprising:

16. The ceramic molded body contains 85% by mass or more of one or more of aluminum oxide, silicon nitride, boron nitride, and zirconium oxide.

16. The method for manufacturing a ceramic ball material according to claim 15.

17. The ceramic molded body contains 85% by mass or more of silicon nitride.

16. The method for manufacturing a ceramic ball material according to claim 15.

18. The molding step is performed by stacking a plurality of the cold isostatic pressing rubber molds.

16. The method for manufacturing a ceramic ball material according to claim 15.

19. In each of the plurality of stacked cold isostatic pressing rubber dies, the ratio of the vertical distance between the holes to the horizontal distance between the holes is 0.9 or more. The method for manufacturing a ceramic ball material according to claim 18.

20. a polishing step of polishing the material for a ceramic ball obtained by the method for producing a material for a ceramic ball according to claim 15; A method for producing a ceramic ball, comprising:

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