Material for ceramic ball, method for producing ceramic ball using the same, and ceramic ball

Abstract

To provide a material for ceramic balls, which suppresses damage to a ceramic material during surface plate processing.SOLUTION: A method for producing a material for ceramic balls, according to an embodiment, includes a granulation step, a press molding step, an isostatic molding step, a degreasing step, and a sintering step. In the granulation step, a ceramic powder to be used as a raw material is mixed with a sintering aid, etc., and granulated using a spray dryer. In the press molding step, press molding is performed using a granulated powder obtained in the granulation step. In the isostatic molding step, a molded body is isostatically molded using a rubber mold having hemispherical holes on both sides that are 1% to 35% larger than a diameter r1 of the molded body obtained in the press molding step, with a Shore hardness of Hs 30 or more and 50 or less. In the degreasing step, the molded body obtained in the isostatic molding step is degreased. In the sintering step, the molded body obtained in the degreasing step is sintered at a temperature of 1,600°C or more and 2,000°C or less to obtain a material for ceramic balls having a spherical surface and a banded surface.SELECTED DRAWING: Figure 3

Description

[Technical field]

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

[0002] Various ceramic materials have properties such as high hardness, insulation, and wear resistance, and fine ceramics, which have particularly high purity and uniform particle size, exhibit properties that are used in various fields such as capacitors, actuator materials, and fireproof materials. Among these, bearing balls are used as products that take advantage of their wear resistance and insulation properties, and materials such as aluminum oxide, silicon nitride, and zirconium oxide are used. For example, JP-A-6-48813 (Patent Document 1) and JP-A-2764589 (Patent Document 2) disclose bearing balls using silicon nitride materials, and JP-A-60-18620 (Patent Document 3) discloses bearing balls using zirconium oxide materials.

[0003] In the process of manufacturing these bearing ball materials, a method of sintering a molded body is used. In addition, press molding using a mold is used as a molding method. Press molding is generally a method of inserting powder between an upper mold 1 and a lower mold 2 and applying pressure, as shown in FIG. 1. In order to protect the mold during press molding, a gap must be provided between the tip portion 3 of the upper mold 1 and the tip portion 4 of the lower mold 2. For this reason, a spherical portion and a band-shaped portion are formed in the molded body. For example, Japanese Patent No. 4761613 (Patent Document 4) discloses a bearing ball material having a spherical portion and a band-shaped portion. FIG. 2 shows a conventional ceramic ball material. In FIG. 2, 5A is a ceramic ball material, 6A is a spherical portion, 7A is a band-shaped portion, WA is the width of the band-shaped portion 7A, and HA is the height of the band-shaped portion 7A. [Prior art documents] [Patent documents]

[0004] [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 Summary of the Invention [Problem to be solved by the invention]

[0005] Ceramic balls are produced by polishing ceramic ball blank 5A having spherical portion 6A and band-shaped portion 7A shown in Fig. 2. Ceramic ball blank 5A having spherical portion 6A and band-shaped portion 7A is sometimes called a bare ball. For example, ceramic ball blank 5A is subjected to mirror finishing to a surface roughness Ra of 0.1 μm or less. A surface plate is used for mirror finishing.

[0006] Generally, ceramic materials have excellent wear resistance, but are brittle and therefore prone to chipping when subjected to strong impact. Curved surfaces are able to absorb impacts easily, but corners are prone to chipping due to impact. Therefore, when a ceramic ball material 5A having a belt-shaped portion 7A is machined using a surface plate, the two shoulders, which are the corners of the belt-shaped portion 7A, selectively come into contact with the surface plate, causing chipping.

[0007] The present invention is intended to solve these problems, and provides a ceramic ball material that suppresses damage to the ceramic material during platen processing. [Means for solving the problem]

[0008] The ceramic ball material according to the embodiment includes a spherical portion and a band-shaped portion formed around the circumference of the spherical portion. The band-shaped portion has a width in the range of 0.5 mm to 4.0 mm. Both shoulders of the band-shaped portion have R portions with a radius of curvature of 0.02 mm or more. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view showing an example of a general die press molding apparatus. [Diagram 2] FIG. 1 is an external view showing an example of a conventional ceramic ball material. [Diagram 3] FIG. 1 is an external view showing an example of a ceramic ball material according to an embodiment. [Figure 4] FIG. 4 is an external view showing an example of a band-shaped portion. [Diagram 5] FIG. 11 is an external view showing another example of the band portion. [Figure 6] FIG. 11 is an external view showing yet another example of the band-shaped portion. [Figure 7] FIG. 2 is a diagram showing an example of die press molding for molding a ceramic ball material according to the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, with reference to the drawings, a detailed description will be given of an embodiment of a ceramic ball material, a method for manufacturing a ceramic ball using the same, and a ceramic ball.

[0011] The ceramic ball material according to the embodiment includes a spherical portion and a band-shaped portion formed around the circumference of the spherical portion. The band-shaped portion has a width in the range of 0.5 mm to 4.0 mm. The band-shaped portion has shoulders each having an R portion with a radius of curvature of 0.02 mm or more.

[0012] FIG. 3 shows a schematic diagram of a ceramic ball material according to an embodiment. In FIG. 3, 5 denotes a ceramic ball material according to an embodiment, 6 denotes a spherical portion, 7 denotes a band portion, 8 denotes an R portion, 9 denotes a side peripheral portion, and 10 denotes an outer peripheral portion. The diameter of the outer peripheral portion 10 of the band portion 7 is defined as r1. The diameter of the spherical portion 6 is defined as r2. For example, the diameter r2 of the spherical portion 6 is defined as the length of a line segment passing through the center of the spherical portion 6 in a direction perpendicular to the plane formed by the circumference of the band portion 7. W denotes the width of the band portion 7, and H denotes the height of the band portion 7. The width W of the band portion 7 is sometimes simply referred to as "width W". The height H of the band portion 7 is sometimes simply referred to as "height H". In FIG. 3, the height H and width W of the band portion 7 relative to the spherical portion 6 are illustrated for convenience of explanation.

[0013] The ceramic ball material 5 has a spherical portion 6 and a band-shaped portion 7. The band-shaped portion 7 is formed around the circumference of the surface of the spherical portion 6. The circumference of the surface of the spherical portion 6 may be any one of the multiple circumferences of the surface of the spherical portion 6. The surface of the spherical portion 6 may be a quadratic curved surface. Therefore, the spherical portion 6 may be a perfect sphere or an ellipsoid. The band-shaped portion 7 is provided on the circumference of the spherical portion 6. The width W of the band-shaped portion 7 is, for example, the largest width of the band-shaped portion 7, but may also be an average value of multiple locations. The height H of the band-shaped portion 7 is, for example, the maximum height of the band-shaped portion 7, but may also be an average value of multiple locations.

[0014] The width W of the band-shaped portion 7 is within a range of 0.5 mm to 4.0 mm. When the width W is within this range, damage to the die can be suppressed. In addition, the sphericity of the ceramic ball material 5 can be increased. When the sphericity of the ceramic ball material 5 is increased, the processing time during the polishing process can be shortened.

[0015] If the width W is less than 0.5 mm, the compressive force acting on the tip portion 3 of the upper die 1 and the tip portion 4 of the lower die 2 shown in FIG. 1 becomes very large. This may cause damage to the die. In addition, non-uniformity in density may occur around the band-shaped portion of the obtained sintered body. Non-uniform density may easily cause defects in the sintered body, which may adversely affect wear resistance.

[0016] Furthermore, if the width W exceeds 4.0 mm, the sphericity of the ceramic ball material 5 decreases. The decrease in sphericity reduces the proportion of the spherical portion 6. The decrease in sphericity of the ceramic ball material 5 requires more cutting allowance during polishing, which lengthens the time required for the polishing process. For this reason, the width W is preferably 0.5 mm or more and 4 mm or less, and more preferably 0.8 mm or more and 3.5 mm or less.

[0017] The belt-shaped portion 7 includes both shoulders extending around the circumference of the belt-shaped portion 7, a side peripheral portion 9 extending in the circumferential direction of the belt-shaped portion 7, and an outer peripheral portion 10 extending around the circumference of the belt-shaped portion 7. The belt-shaped portion 7 includes both shoulders with an R portion 8 having a radius of curvature of 0.02 mm or more. The R portion 8 exists on both shoulders of the belt-shaped portion 7. The R portion means a rounded shape. By providing both shoulders of the belt-shaped portion 7 with an R portion 8 having a radius of curvature of 0.02 mm or more, the belt-shaped portion 7 can be brought into surface contact with a grindstone for polishing. If the R portion 8 has a radius of curvature of less than 0.02 mm or has an angular shape, the contact with the grindstone becomes like a point contact. The angular shape means a shape in which both shoulders are 90° or less in the cross section of the belt-shaped portion 7. If the contact is at a point, brittle fracture is likely to occur when the ceramic ball material 5 contacts the grindstone. In particular, brittle fracture is likely to occur due to contact with a surface plate during surface plate processing. For this reason, the radius of curvature of the R portion 8 is preferably 0.02 mm or more, and more preferably 0.2 mm or more.

[0018] Here, a method for measuring the radius of curvature of the rounded portion 8 of the band-shaped portion 7 of the ceramic ball blank 5 will be described.

[0019] Shape measurements will be made using an optical 3D shape measuring device. The 3D shape measuring device used will be a KEYENCE VR-5000, and will be performed using the device's analysis software. Any measuring device with equivalent functionality will suffice.

[0020] The measurement area is a range that is at least 1 / 4 the height H of band-shaped portion 7 and that includes the entire width W. The screen should be set at a magnification that will include the measurement area. Figure 4 shows an example of the R portion 8 of band-shaped portion 7. In Figure 4, 6 is the spherical portion, 7 is the band-shaped portion, and 8 is the R portion. Figure 4 is a side view including the portion of band-shaped portion 7 that protrudes from spherical portion 6.

[0021] The concept of the method for measuring the radius of curvature of the R portion 8 using an optical three-dimensional shape measuring device will be explained below. The concept of the method for measuring the radius of curvature is shown below, but the measurement itself is calculated automatically using analysis software provided with the three-dimensional shape measuring device.

[0022] The radius of curvature of the R portion 8 is measured using the radius of curvature measurement function of the three-dimensional shape measuring device. The calculation is performed using a virtual circle C1 obtained by selecting three points p1, p2, and p3 of one of the R portions 8. At this time, point p1 is the boundary point between the side peripheral portion 9 of the band portion 7 and the R portion 8, point p3 is the boundary point between the R portion 8 of the band portion 7 and the outer periphery portion 10, and point p2 is the point between points p1 and p3. The calculation result is the radius of curvature of the R portion 8. Similarly, the calculation is performed using a virtual circle C2 obtained by selecting three points p4, p5, and p6 for the R portion 8 on the opposite side. At this time, point p6 is the boundary point between the side peripheral portion 9 of the band portion 7 and the R portion 8, point p4 is the boundary point between the R portion 8 of the band portion 7 and the outer periphery portion 10, and point p5 is the point between points p6 and p4. The average value of the calculation results of both shoulders is the radius of curvature of the R portion 8. In addition, the imaginary circles C1 and C2 may be ellipses as long as they pass through the respective points. In this regard, priority is given to the automatic calculation of the analysis software.

[0023] Also, if the virtual circles C1 and C2 do not pass through the points p1 to p6, respectively, it is determined that the radius of curvature has not been accurately measured. Similarly, when the actual curve formed by the points p1 to p6 is compared with the curved portion along the corresponding portion formed by the virtual circles C1 and C2, if there are points that are 10 [μm] or more apart, it is determined that the radius of curvature has not been accurately measured. When it is determined that the radius of curvature has not been accurately measured in this way, the points p1 to p6, especially the points p2 and p5 between them, are selected again to measure the radius of curvature. Re-measurement means that the points p1 to p6, especially the points p2 and p5 between them are selected again within the same field of view. At this time, it is acceptable to select the previous measurement points as some of the points p1 to p6. The method of selecting the points p1 to p6 is based on the previous paragraph.

[0024] A method for measuring the radius of curvature of the concave shape of the outer periphery 10 sandwiched between both shoulders of the band-shaped portion 7, which will be described later, will be described below. Here, the concave shape of the outer periphery 10 means that in the band-shaped portion 7 that runs along the circumference, the outer periphery 10 is continuously concave from both shoulders along the circumference. A three-dimensional shape measuring device will also be used to measure the radius of curvature of the concave shape of the outer periphery 10. The concept of the method for measuring the radius of curvature will be described below, but the measurement of the radius of curvature of the concave shape itself will be automatically calculated using analysis software provided in the three-dimensional shape measuring device.

[0025] An example of the recess shape of the band-shaped portion 7 is shown in FIG. 5. FIG. 5 is a side view including a portion of the band-shaped portion 7 protruding from the spherical portion 6. As shown in FIG. 5, three points p7, p8, and p9 on the outer periphery 10 of the band-shaped portion 7 are selected to measure the curvature. At this time, when the actual curve formed by the points p7 to p9 is compared with the curve along the points p7 to p9 of the imaginary circle C3, if there are any points that are 10 μm or more apart, it is determined that the curvature has not been measured accurately. In this case, the three points p7, p8, and p9 are selected again to measure the curvature.

[0026] Next, a case where the height H of the band-shaped portion 7 is measured will be described. FIG. 6 is a side view including the portion of the band-shaped portion 7 protruding from the spherical portion 6. First, as shown in FIG. 6, an imaginary circle C4 is drawn at a position that coincides with the spherical portion 6 behind the band-shaped portion 7. Next, extended imaginary lines L1 and L2 are drawn along the side periphery 9 of the band-shaped portion 7, and the intersections of the extended imaginary lines L1 and L2 with the spherical portion 6 are set as points p10 and p11, respectively. When comparing the side periphery 9 of the band-shaped portion 7 with the extended imaginary lines L1 and L2, if there is a point that is 5 μm or more away, it is determined that the extended imaginary lines have not been drawn accurately, and the lines are redrawn. From the highest point extraction area, the points of maximum height are extracted at both shoulders of the band-shaped portion 7, and set as points p12 and p13. For the line segment L3 connecting points p10 and p11, the shortest distances H1 and H2 from points p12 and p13 are measured, and their average value is taken as the height H (shown in FIG. 3) of band-shaped portion 7. In addition, the shortest distance between points p10 and p11 is measured and taken as the width W (shown in FIG. 3) of band-shaped portion 7.

[0027] The method of measuring the diameter r1 of the belt-like portion 7 and the diameter r2 of the spherical portion 6 will be described later. Diameters r1 and r2 are illustrated in FIG. 3. Diameter r1 is the length extending from the center of the outer periphery 10 of the belt-like portion 7 (the center between the side peripheries 9 at both ends) to the center of the outer periphery 10 on the opposite side, that is, the diameter of the outer periphery 10. When the outer periphery 10 of the belt-like portion 7 has a concave shape, diameter r1 is the diameter from the concave shape to the concave shape on the opposite side. Diameter r2 of the spherical portion 6 is, for example, the diameter of the spherical portion 6 in a direction perpendicular to the plane formed by the circumference of the belt-like portion 7 and passing through the center of the spherical portion 6.

[0028] The diameters r1 and r2 are measured using a non-contact image dimension measuring instrument. The non-contact image dimension measuring instrument used is the IM-7000 manufactured by KEYENCE or one with equivalent performance. The non-contact image dimension measuring instrument projects light directly from above onto the target object and measures the dimensions from the shadow. The measurement method is described below. The ceramic ball material 5 is placed on the stage. At this time, the ceramic ball material 5 is placed with the belt-shaped portion 7 horizontally in the projection direction. If the belt-shaped portion 7 forms an angle of 5° or more from the projection direction, the concave portion of the outer periphery 10 of the belt-shaped portion 7 will not be visible. The measurement area is set so that the center-to-center distance of the concave shape of the outer periphery 10 of the diagonal belt-shaped portion 7 can be measured, and the diameter r1 can be evaluated by measuring it. In addition, the diameter r2 of the spherical portion 6 is measured as the length of the line segment that passes through the center of the spherical portion 6 in a direction perpendicular to the surface formed by the circumference of the belt-shaped portion 7.

[0029] The outer periphery 10 of the band-shaped portion 7 is preferably flat or concave. The outer periphery 10 of the band-shaped portion 7 is also preferably concave. A concave shape refers to a shape in which the outer periphery 10 of the band-shaped portion 7 is concave with respect to both shoulder portions at both ends. When the outer periphery 10 is flat or concave, it becomes easier to form the R portion 8 on both shoulder portions of the band-shaped portion 7. On the other hand, when the outer periphery 10 of the band-shaped portion 7 is convex, this portion protrudes and is more likely to cause brittle fracture due to contact during processing on a surface plate.

[0030] In addition, the concave shape of the outer peripheral portion 10 of the band-shaped portion 7 preferably has a radius of curvature of 5 mm or more. When the ceramic ball material 5 is ground to form a ceramic ball, the band-shaped portion 7 is ground. By increasing the radius of curvature of the concave shape of the outer peripheral portion 10, the volume of the band-shaped portion 7 to be ground can be reduced. This allows the amount of grinding to be reduced. The upper limit of the radius of curvature of the concave shape of the outer peripheral portion 10 of the band-shaped portion 7 is not particularly limited, but is preferably 30 mm or less. If the radius of curvature of the concave shape is too large, it may become difficult to control the radius of curvature of the R portion 8. In addition, the concave shape of the outer peripheral portion 10 of the band-shaped portion 7 may have slight irregularities on its surface. Although a convex portion (projection portion) is shown on the outer peripheral portion 10 in Figs. 4 to 6, the convex portion is not an essential configuration. In addition, if the outer peripheral portion 10 has a convex portion (projection portion), the height of the convex portion is lower than both shoulder portions.

[0031] Furthermore, it is preferable that the ratio of the radius of curvature of the concave shape of the outer periphery 10 of the band-shaped portion 7 to the width W of the band-shaped portion is equal to or less than 10. If the ratio of the radius of curvature of the concave shape of the outer periphery 10 of the band-shaped portion 7 to the width W of the band-shaped portion exceeds 10, the curvature of the concave shape may be too large, making it difficult to control the radius of curvature of both shoulders of the band-shaped portion 7.

[0032] The height H of the belt-shaped portion 7 is preferably 2.5% or less with respect to the diameter r1 of the belt-shaped portion 7. This shows that (height H of belt-shaped portion 7 / diameter r1 of belt-shaped portion)×100≦2.5 is satisfied. As described above, the belt-shaped portion 7 is removed by polishing. If the height H of the belt-shaped portion 7 is greater than 2.5% with respect to the diameter r1, the load of the polishing process increases. In addition, brittle fracture due to contact during platen processing may be more likely to occur. The lower limit of the height H of the belt-shaped portion 7 is preferably 0.1% or more with respect to the diameter r1 of the belt-shaped portion 7. If the height H of the belt-shaped portion 7 is too small, it may be difficult to densify the periphery of the belt-shaped portion 7. For this reason, it is preferable to satisfy 0.1≦(height H of belt-shaped portion 7 / diameter r1 of belt-shaped portion)×100≦2.5.

[0033] It is also preferable that the diameter r2 of the spherical portion 6 is 0.5 mm or more. It is also preferable that any diameter r2 of the spherical portion 6 is within the range of 8 mm to 70 mm, and that the height H of the strip portion 7 is 1% or less of the diameter r2 of the spherical portion. This indicates that (height H of strip portion 7 / diameter r2 of spherical portion 6)×100≦1. Furthermore, the ratio (r1 / r2) of the diameter r1 of the band-shaped portion 7 to the diameter r2 of the spherical portion 6 is preferably within the range of 0.9≦r1 / r2≦1.1. If the arbitrary diameter r2 of the spherical portion 6 is less than 0.5 mm, it becomes difficult to control the radius of curvature of the R portion 8. It is more preferable that the diameter r2 of the spherical portion 6 is 8 mm or more and 70 mm or less.

[0034] In addition, 0.9≦r1 / r2≦1.1 indicates that the diameter r1 of the belt-shaped portion 7 is close to the diameter r2 of the spherical portion 6. This makes it possible to uniformly make initial contact with the processing platen and thereby suppress stress concentration and damage during processing.

[0035] Moreover, the ceramic ball material 5 preferably contains 85% by mass or more of one or more of aluminum oxide (Al2O3), silicon nitride (Si3N4), boron nitride (BN), and zirconium oxide (ZrO2). The ceramic ball material 5 is made of a ceramic sintered body. The content of 85% by mass or more of one or more of aluminum oxide, silicon nitride, boron nitride, and zirconium oxide refers to the content in the ceramic sintered body. In other words, the ceramic sintered body may contain 15% by mass or less of substances other than the above. The ceramic ball material 5 preferably contains 85% by mass or more of silicon nitride.

[0036] For example, aluminum oxide sintered body, silicon nitride sintered body, boron nitride sintered body, zirconium oxide sintered body, and aridil sintered body are used as bearing balls. Incidentally, aridil sintered body is a sintered body made by mixing aluminum oxide and zirconium oxide. Among these, bearing balls made of silicon nitride sintered body have the best wear resistance. For example, aluminum oxide, zirconium oxide, and aridil have a Vickers hardness of about 1200 to 1700, but a fracture toughness value of 3 to 6 [MPa m 1 / 2 In contrast, silicon nitride sintered bodies have a Vickers hardness of 1400 to 1800 and a fracture toughness of 5 to 10 [MPa m 1 / 2 ] is high. Silicon nitride sintered bodies have both high toughness and Vickers hardness, which gives them excellent wear resistance. Silicon nitride sintered bodies have a structure mainly composed of β-type silicon nitride crystal grains. β-type silicon nitride crystal grains have a long and thin shape, and the long and thin crystal grains are intricately intertwined to achieve high toughness. However, silicon nitride sintered bodies have a very poor polishing efficiency due to their high mechanical strength. However, as mentioned above, by providing the R portion to the band portion 7, it is possible to improve the polishing efficiency even for ceramic ball materials 5 made of high-strength ceramic sintered bodies such as silicon nitride sintered bodies.

[0037] Next, a method for manufacturing the ceramic ball material 5 will be described. As long as the ceramic ball material 5 according to the embodiment satisfies the above-mentioned configuration, the manufacturing method is not particularly limited, but the following manufacturing method can be mentioned as a method for efficiently manufacturing the ceramic ball material 5. The manufacturing method for the ceramic ball material 5 will be described by taking a silicon nitride sintered body as an example.

[0038] First, an appropriate amount of sintering aid, additive, solvent, binder, etc. is added to silicon nitride as a raw material, mixed, crushed, and granulated by a spray dryer. This process prepares granulated powder of the raw powder. In addition, when the total of silicon nitride powder and sintering aid powder is 100 [mass %], it is preferable that silicon nitride powder is 85 [mass %] or more. In addition, the additive is a plasticizer. The solvent is water or an organic solvent. Examples of organic solvents include alcohol, ketone, and benzene. In addition, the binder is an organic substance. The amount of binder added is within the range of 3 to 20 parts by mass when the total of silicon nitride powder and sintering aid powder is 100 parts by mass. By adjusting the amount of binder, it becomes easier to impart a concave shape to the outer periphery 10 of the belt-shaped portion 7 in the process described later.

[0039] Next, the granulated powder is used for press molding. The press molding may be a molding method using an upper die 1 and a lower die 2 of a die press molding apparatus shown in FIG. 1. The inner spherical shape of the upper die 1 and the lower die 2 becomes the spherical portion 6 of the ceramic ball material 5. The width W and height H of the band-shaped portion 7 of the ceramic ball material 5 can be adjusted by adjusting the shape of the tip portion 3 of the upper die 1 and the tip portion 4 of the lower die 2 and the amount of powder filled when press molding. Similarly, the diameter r1 and the diameter r2 can be adjusted. For example, the distance between the tip portion 3 of the upper die 1 and the tip portion 4 of the lower die 2 when press molding is set to 0.5 [mm] to 4 [mm], and the press molding is performed so that the gap is filled with granulated powder. This allows the width W of the band-shaped portion 7 to be controlled within a range of 0.5 [mm] to 4 [mm].

[0040] The green body obtained by press molding has a spherical portion and a band-shaped portion. The spherical portion and band-shaped portion of the green body correspond to the spherical portion 6 and band-shaped portion 7 of the ceramic ball material 5 described above, respectively. The diameter of the band-shaped portion of the green body is r1-1, and the diameter of the spherical portion is r2-1. The method of measuring the diameters r1-1 and 2-1 of the green body is the same as the method of measuring the diameters r1 and r2 of the ceramic ball material 5 described above. At the stage of the green body, it is preferable that 0.85≦(r1-1) / (r2-1)≦1.05. By keeping it within this range, the sintered body obtained in the sintering process described later can be 0.9≦r1 / r2≦1.1. This is in consideration of the shrinkage of the green body due to the sintering process.

[0041] It is also preferable to perform isostatic pressing on the green body. By performing isostatic pressing, the granulated powder in the green body can be uniformly compressed. This makes it possible to reduce the amount of granulated powder that remains in the green body. By reducing the amount of granulated powder that remains in the green body, it is possible to control the shrinkage rate in the sintering process.

[0042] As an example of isotropic pressure molding, an isotropic pressure molding method using a rubber mold will be described. An example of a disc-shaped rubber mold is shown in Fig. 7. In Fig. 7, 11 and 12 are disc-shaped rubber molds, and 13 is a space. Fig. 7(a) is a side view of disc-shaped rubber molds 11 and 12 stacked on top of each other. Fig. 7(b) is a cross-sectional view showing an example in which a molded body is placed in space 13 between disc-shaped rubber molds 11 and 12.

[0043] The disk-shaped rubber molds 11 and 12 have hemispherical holes on both sides that are 1% to 35% larger than the diameter r1 of the molded body. The molded body is placed in the holes and the rubber molds are stacked on top of each other to seal the molded body in the space 13 surrounded by the rubber molds. A hydrostatic pressure higher than the pressure during molding is applied to the rubber mold. This allows the molded body to be compressed uniformly. This process reduces the amount of crushed granulated powder. In addition, as shown in FIG. 7, it is preferable to arrange the band-shaped portion 7 of the molded body so that it is perpendicular to the cylindrical direction of the rubber mold. In addition, it is preferable to use rubber molds 11 and 12 with a Shore hardness Hs of 30 to 50. By setting the hardness of the rubber mold within this range, it is possible to provide the molded body surface with the deformability that allows the rubber mold to be in uniform contact with the molded body surface. In addition, the durability of the rubber mold is also good. This process allows the R portion 8 with a curvature radius of 0.02 mm or more to be formed on both shoulders of the band-shaped portion 7 of the molded body. Furthermore, by adjusting the size ratio between the diameter r1-1 of the formed body and the space 13, the radius of curvature of the concave shape of the outer periphery 10 of the strip portion 7 of the formed body and the height H of the strip portion 7 can be adjusted.

[0044] Next, a degreasing step is performed to degrease the molded body. The degreasing step is a step in which the molded body is heated to a temperature equal to or higher than the decomposition temperature of the organic components such as the binder, thereby removing the organic components. The degreasing step may be performed in a nitrogen atmosphere or an air atmosphere. A degreased body can be obtained by the degreasing step.

[0045] Next, a sintering process is performed to sinter the degreased body. The sintering process is preferably performed at a temperature between 1600[℃] and 2000[℃]. The sintering process is preferably performed in a nitrogen atmosphere. The sintering pressure is preferably within a range between atmospheric pressure and 300[MPa]. 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 press) process. A ceramic ball material 5 can be obtained by this process. The ceramic ball material 5 is a ceramic sintered body having a theoretical density of 98[%] or more.

[0046] The radius of curvature of the rounded portions 8 at both shoulders of the band-shaped portion 7 can also be adjusted by polishing the completed ceramic ball blank 5. However, this method is not desirable because it requires an additional polishing step. The manufacturing method described above is desirable.

[0047] Ceramic balls can be manufactured by polishing the ceramic ball blank 5. A typical example of polishing a ball is platen processing. For example, the ceramic ball blank 5 is inserted between two platens arranged in parallel above and below. The movement of the polishing platen can be used to process the ceramic ball blank 5 into a perfect sphere. The surface roughness of bearing balls is specified in ASTM F2094. Bearing balls are selected according to the grade of ASTM F2094 depending on the application. They are polished to a surface roughness Ra according to that grade. Some higher grades are mirror-finished to a surface roughness Ra of 0.01 μm or less. Note that ASTM is a standard issued by ASTM International. ASTM International was formerly known as the American Society for Testing and Materials (ASTM).

[0048] The ceramic ball material 5 according to the embodiment has R-portions 8 with a radius of curvature of 0.02 mm or more at both shoulders of the belt-shaped portion 7. This allows the material 5 to come into surface contact with a grindstone such as a polishing platen. This prevents the material 5 from being damaged during the polishing process. The durability of the polishing platen can also be improved. Furthermore, by controlling the shape of the belt-shaped portion 7, the polishing stock removal can be reduced and the workability can be improved.

[0049] (Examples, Comparative Examples, Reference Examples) Sintering aids, additives, solvents, binders, etc. were added to the raw ceramic powder, mixed, crushed, and granulated using a spray dryer. Examples 1 to 3 and 5 to 6 are silicon nitride sintered bodies, Reference Example 1 is an aluminum oxide sintered body, and Example 7 is an aruginous sintered body. The silicon nitride sintered body contains 85 [mass %] or more of silicon nitride. The aluminum oxide sintered body contains 85 [mass %] or more of aluminum oxide. The aruginous sintered body contains 85 [mass %] or more of aluminum oxide and zirconium oxide in total. When the total of the main component and sintering aid is 100 parts by mass, the amount of binder added is within the range of 3 to 20 parts by mass.

[0050] Next, press molding was performed using the granulated powder. Press molding was performed using the upper and lower dies of the die press molding device shown in Figure 1. After die molding, isostatic molding was performed. For isostatic molding, a disc-shaped rubber die with a Shore hardness Hs of 30 to 50 was used. For isostatic molding, disc-shaped rubber dies 11 and 12 were provided on both sides with hemispherical holes that were 1% to 35% larger than the diameter r1 of the molded body. In addition, the band-shaped part of the molded body was arranged perpendicular to the cylindrical direction of the rubber die. In this state, a hydrostatic pressure higher than the pressure during molding was applied in the isostatic molding process.

[0051] Next, a sintering process was carried out. The sintering process was carried out at 1600-2000°C in a nitrogen atmosphere at atmospheric pressure. After that, HIP treatment was carried out at 1600-2000°C in a nitrogen atmosphere at a pressure of 200 MPa.

[0052] By this process, the ceramic ball materials according to the examples and the reference examples were produced. In the comparative example, the amount of the binder added was 3 parts by mass when the total amount of the main component and the sintering aid was 100 parts by mass. In addition, isostatic pressing was not performed after the molding process.

[0053] The shape of the ceramic ball blank 5 according to the embodiment and the shapes of the ceramic ball blanks according to the comparative example and reference example were measured. The measurement methods for each were as described above. Note that H / r1 [%] is (H / r1) x 100 [%]. The results are shown in Table 1.

[0054] [Table 1]

[0055] Example 1 is a ceramic ball material 5 for ceramic balls that will be 3 / 8 inch (9.525 mm) after polishing. Example 2 and Reference Example 1 are ceramic ball materials 5 for 5 / 16 inch (7.9375 mm) ceramic balls. Examples 3, 5 to 7 are ceramic ball materials 5 for 7 / 8 inch (22.225 mm) ceramic balls. Comparative Examples 2 and 3 are ceramic ball materials for 5 / 16 inch (7.9375 mm) ceramic balls, similar to Example 2 and Reference Example 1. Comparative Example 1 is a ceramic ball material for 7 / 8 inch (22.225 mm) ceramic balls, similar to Examples 3, 5 to 7. The ceramic ball materials 5 of the examples and the ceramic ball materials of the comparative examples and reference examples can all be used as bearing balls.

[0056] In addition, the width W of the band-shaped portion is outside the range in Comparative Example 1 and Comparative Example 3. In addition, the radius of curvature of the R-shaped portions of both shoulders of the band-shaped portion is outside the range in Comparative Example 2. In Comparative Example 2, both shoulders of the band-shaped portion have an acute angle of less than 90°.

[0057] The ceramic ball material 5 of the embodiment and the ceramic ball materials of the comparative example and reference example were used to evaluate the polishing efficiency. The evaluation was carried out by processing each ceramic ball material using a grindstone with a number of #180, with the number of pieces according to the size of the ceramic ball material being one batch, and by examining how many batches the grindstone could withstand. The polishing process was carried out so that the surface roughness Ra of the ceramic ball was 0.01 [μm].

[0058] In addition, the rate of occurrence of defects such as chipping of the ceramic ball material during the above-mentioned polishing process was investigated. The rate of occurrence of defects was determined by visually inspecting one batch before the endurance count of the grindstone (for example, from the 1st to the 15th in Example 1), and the rate of occurrence of chipping was shown as the material chipping defect rate [%]. The material chipping defect rate [%] was rounded off to one decimal place.

[0059] In addition, we investigated the diameter variation, which is the deviation in diameter of the ceramic balls after the intended polishing process. The diameter variation was defined as the difference between the minimum and maximum diameters when measuring the entire circumference of the sphere. The diameter variation was the average value of the results of measuring 10 balls randomly selected from one batch. The results are shown in Table 2.

[0060] [Table 2]

[0061] As can be seen from Table 2, the ceramic ball material 5 according to the embodiment has improved durability of the grindstone compared to the ceramic ball material according to the comparative example, which has the same number of processed pieces. In addition, the ceramic ball material 5 according to the embodiment has a lower defect rate compared to the ceramic ball material according to the comparative example, which has the same number of processed pieces. Furthermore, the ceramic ball material 5 according to the embodiment has a smaller deviation from the target diameter compared to the ceramic ball material according to the comparative example, which has the same number of processed pieces. Therefore, it can be seen that the ceramic ball material 5 according to the embodiment has good grinding efficiency.

[0062] As described above, according to the ceramic ball material 5, damage to the ceramic material during machining on a surface plate can be suppressed.

[0063] Although some embodiments of the present invention have been illustrated above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, modifications, etc. can be made without departing from the gist of the invention. Modifications of these embodiments are included in the scope and gist of the invention, and are included in the scope of the invention and its equivalents described in the claims. In addition, the above-mentioned embodiments can be implemented in combination with each other.

Claims

1. A granulation process in which sintering aids, additives, solvents and binders are added to and mixed with the raw ceramic powder, and the resulting mixture is granulated using a spray dryer; A press molding step of press-molding the granulated powder obtained in the granulation step; an isostatic pressing process for isostatically pressing the molded body using a rubber mold having a Shore hardness Hs of 30 to 50 and a hemispherical hole on both sides that is 1% to 35% larger than the diameter r1 of the molded body obtained in the press molding process; a degreasing step of degreasing the molded body obtained in the isostatic pressing step; and a sintering step of sintering the green body obtained in the debinding step at a temperature of 1600° C. or higher and 2000° C. or lower to obtain a ceramic ball blank having a spherical portion and a band-shaped portion.

2. 2. The method for producing a ceramic ball material according to claim 1, wherein the press molding step is performed by inserting the granulated powder between an upper die and a lower die, and a distance between a tip end portion of the upper die and a tip end portion of the lower die is set to be 0.5 mm or more and 4 mm or less.

3. 3. The method for manufacturing a ceramic ball blank according to claim 1, wherein the width of the band-shaped portion is within a range of 0.5 mm to 4.0 mm, and the band-shaped portion has shoulders each having an R portion with a radius of curvature of 0.02 mm or more.

4. 3. The method for manufacturing a ceramic ball blank according to claim 1, wherein the outer periphery of the belt-shaped portion is flat or concave.

5. 3. The method for manufacturing a ceramic ball blank according to claim 1, wherein the radius of curvature of the concave shape of the outer periphery of the band-shaped portion is 5 mm or more.

6. 4. The method for manufacturing a ceramic ball blank according to claim 3, wherein the radius of curvature of the concave shape of the outer periphery of the band-shaped portion is 5 mm or more.

7. 3. The method for manufacturing a ceramic ball blank according to claim 1, wherein the height of the band-shaped portion is 2.5% or less of a given diameter of the band-shaped portion.

8. 7. The method for manufacturing a ceramic ball blank according to claim 6, wherein the height of the band-shaped portion is 2.5% or less of a given diameter of the band-shaped portion.

9. 3. The method for manufacturing a ceramic ball blank according to claim 1, wherein the spherical portion has a diameter of 0.5 mm or more.

10. 9. The method for manufacturing a ceramic ball blank according to claim 8, wherein the spherical portion has a diameter of 0.5 mm or more.

11. 3. The method for manufacturing a ceramic ball blank according to claim 1, wherein an arbitrary diameter of the spherical portion is within a range of 8 mm to 70 mm, and a height of the band portion is 1% or less of the diameter of the spherical portion.

12. 9. The method for manufacturing a ceramic ball blank according to claim 8, wherein an arbitrary diameter of the spherical portion is within a range of 8 mm to 70 mm, and a height of the band portion is 1% or less of the diameter of the spherical portion.

13. 3. The method for manufacturing a ceramic ball blank according to claim 1, wherein a ratio of a diameter of the outer periphery of the band-shaped portion to a diameter of the spherical portion is 0.9 to 1.

1.

14. 9. The method for manufacturing a ceramic ball blank according to claim 8, wherein a ratio of a diameter of the outer periphery of the band-shaped portion to a diameter of the spherical portion is 0.9 to 1.

1.

15. 3. The method for manufacturing a ceramic ball blank according to claim 1, wherein the ceramic ball blank contains at least 85 mass% of any one of aluminum oxide, silicon nitride, boron nitride, and zirconium oxide.

16. 3. The method for producing a ceramic ball blank according to claim 1, wherein the ceramic ball blank is a sintered ceramic body containing 85 mass % or more of silicon nitride.

17. 7. The method for producing a ceramic ball blank according to claim 6, wherein the ceramic ball blank is a sintered ceramic body containing 85 mass % or more of silicon nitride.

18. 9. The method for producing a ceramic ball blank according to claim 8, wherein the ceramic ball blank is a sintered ceramic body containing 85 mass % or more of silicon nitride.

19. 13. The method for producing a ceramic ball blank according to claim 12, wherein the ceramic ball blank is a sintered ceramic body containing 85 mass % or more of silicon nitride.

Images