Material for ceramic balls, method for manufacturing ceramic balls using the same, and ceramic balls

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 material for ceramic balls, a method for manufacturing ceramic balls, and ceramic balls.

Background Art

[0002] Various ceramic materials have properties such as high hardness, insulation, and wear resistance. In particular, fine ceramics with increased purity and uniform particle size exhibit properties used in various fields such as capacitors, actuator materials, and refractory materials. Among them, there is a bearing ball application as a product that makes use of wear resistance and insulation, and materials such as aluminum oxide, silicon nitride, and zirconium oxide are used. For example, bearing balls using silicon nitride materials are disclosed in Japanese Patent Application Laid-Open No. 6-48813 (Patent Document 1) and Japanese Patent No. 2764589 (Patent Document 2), and bearing balls using zirconium oxide materials are disclosed in Japanese Patent Application Laid-Open No. 60-18620 (Patent Document 3).

[0003] In the process of manufacturing these bearing ball materials, a method of sintering a molded body is used. Also, a press molding method using a mold is used for the molding method. Press molding is generally a method in which powder is inserted between an upper mold 1 and a lower mold 2 and pressure is applied as shown in FIG. 1. At the time of 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 in order to protect the mold, and press molding must be performed. 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

[0005] Ceramic balls are produced by polishing the ceramic ball material 5A, which has a spherical portion 6A and a strip-shaped portion 7A as shown in Figure 2. The ceramic ball material 5A with the spherical portion 6A and strip-shaped portion 7A is sometimes called a "prime sphere." For example, the ceramic ball material 5A is subjected to mirror polishing to a surface roughness Ra of 0.1 [μm] or less. Surface plate polishing is used for mirror polishing.

[0006] Generally, ceramic materials have excellent wear resistance, but because they are brittle, they are prone to chipping when subjected to strong impacts. Curved surfaces absorb impact easily, but corners are susceptible to chipping. Therefore, when surface plate processing is performed on ceramic ball material 5A having a strip-shaped portion 7A, the shoulders of the strip-shaped portion 7A selectively contact the surface plate, causing chipping.

[0007] This invention solves these problems and provides a material for ceramic balls that suppresses damage to ceramic materials during surface plate machining. [Means for solving the problem]

[0008] The ceramic ball material according to this embodiment comprises a spherical portion and a strip-shaped portion formed along the circumference of the surface of the spherical portion. The width of the strip-shaped portion is in the range of 0.5 [mm] to 4.0 [mm]. The strip-shaped portion has R-shaped portions with a radius of curvature of 0.02 [mm] or more at both shoulders. [Brief explanation of the drawing]

[0009] [Figure 1] A cross-sectional view showing an example of a typical die press molding machine. [Figure 2] An external view showing an example of a conventional material for ceramic balls. [Figure 3] An external view showing an example of a material for ceramic balls according to the embodiment. [Figure 4] An external view showing an example of a strip-shaped section. [Figure 5] An external view showing another example of a band-shaped section. [Figure 6] An external view showing yet another example of a band-shaped section. [Figure 7] A diagram showing an example of die press molding for forming the material for ceramic balls according to the embodiment. [Modes for carrying out the invention]

[0010] The following describes in detail, with reference to the drawings, the material for ceramic balls, the method for manufacturing ceramic balls using the same, and embodiments of the ceramic balls.

[0011] The ceramic ball material according to this embodiment comprises a spherical portion and a strip-shaped portion formed along the circumference of the surface of the spherical portion. The width of the strip-shaped portion is in the range of 0.5 [mm] to 4.0 [mm]. The strip-shaped portion is characterized by having R-shaped portions with a radius of curvature of 0.02 [mm] or more at both shoulders.

[0012] Figure 3 shows a schematic diagram of a ceramic ball material according to the embodiment. In Figure 3, 5 is the ceramic ball material according to the embodiment, 6 is the spherical portion, 7 is the strip portion, 8 is the R portion, 9 is the side circumference portion, and 10 is the outer circumference portion. The diameter of the outer circumference portion 10 of the strip portion 7 is r1. The diameter of the spherical portion 6 is r2. For example, the diameter r2 of the spherical portion 6 is the length of the line segment that is perpendicular to the plane formed by the circumference of the strip portion 7 and passes through the center of the spherical portion 6. W is the width of the strip portion 7, and H is the height of the strip portion 7. The width W of the strip portion 7 is sometimes simply referred to as "width W". Similarly, the height H of the strip portion 7 is sometimes simply referred to as "height H". Note that in Figure 3, the dimensions of the height H and width W of the strip portion 7 relative to the spherical portion 6 are shown for explanatory convenience.

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

[0014] The width W of the strip-shaped portion 7 is within the range of 0.5 mm to 4.0 mm. When the width W is within this range, mold damage can be suppressed. Furthermore, the sphericity of the ceramic ball material 5 can be increased. Increased sphericity of the ceramic ball material 5 shortens the processing time during polishing.

[0015] If the width W is less than 0.5 mm, the compressive force on the tip portion 3 of the upper mold 1 and the tip portion 4 of the lower mold 2, as shown in Figure 1, becomes very large. This can cause mold damage. In addition, density non-uniformity may occur around the strip portion of the resulting sintered body. If the density is non-uniform, defects are more likely to occur in the sintered body, which may adversely affect the wear resistance.

[0016] Also, when the width W exceeds 4.0 [mm], the sphericity of the material 5 for the ceramic ball decreases. When the sphericity decreases, the ratio of the spherical surface portion 6 decreases. When the sphericity of the material 5 for the ceramic ball decreases, the cutting amount during polishing increases and the time of the processing step becomes longer. Therefore, 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] Further, the belt-like portion 7 includes both shoulder portions extending over the circumference of the belt-like portion 7, a side circumferential portion 9 extending in the circumferential direction of the belt-like portion 7, and an outer circumferential portion 10 extending over the circumference of the belt-like portion 7. And, the belt-like portion 7 is provided with R portions 8 having a curvature radius of 0.02 [mm] or more at both shoulder portions. The R portions 8 are present at both shoulder portions of the belt-like portion 7. The R portion means a rounded shape. Also, by providing the R portions 8 having a curvature radius of 0.02 [mm] or more at both shoulder portions of the belt-like portion 7, it is possible to make it contact the grinding wheel of the polishing process like a surface contact. If the curvature radius of the R portion 8 is less than 0.02 [mm] or it has an angular shape, the contact with the grinding wheel becomes like a point contact. The angular shape means a shape in which both shoulder portions are 90° or less in the cross section of the belt-like portion 7. When it becomes a point contact, brittle fracture is likely to occur in the contact between the material 5 for the ceramic ball and the grinding wheel. In particular, brittle fracture is likely to occur in the contact with the surface plate of the surface plate processing. Therefore, the curvature radius 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 curvature radius of the R portion 8 of the belt-like portion 7 of the material 5 for the ceramic ball will be described.

[0019] The shape measurement shall use an optical three-dimensional shape measurement device. The three-dimensional shape measurement device shall use the VR-5000 manufactured by KEYENCE and shall be performed using the analysis software of the device. The measurement device may have the same functions as this.

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

[0021] This section describes the concept of measuring the radius of curvature of section R8 using an optical 3D shape measuring device. While the concept of the radius of curvature measurement method is shown below, the measurement itself will be automatically calculated using the analysis software provided with the 3D shape measuring device.

[0022] The radius of curvature of section R8 shall be measured using the radius of curvature measurement function of a 3D shape measuring device. The calculation is performed using a virtual circle C1 obtained by selecting three points p1, p2, and p3 on one side of section R8. In this case, point p1 is the boundary point between the side circumference 9 of the strip-shaped section 7 and section R8, point p3 is the boundary point between section R8 of the strip-shaped section 7 and the outer circumference 10, and point p2 is the point between points p1 and p3. The calculation result is taken as the radius of curvature of section R8. Similarly, the calculation is performed for the opposite side of section R8 using a virtual circle C2 obtained by selecting three points p4, p5, and p6. In this case, point p6 is the boundary point between the side circumference 9 of the strip-shaped section 7 and section R8, point p4 is the boundary point between section R8 of the strip-shaped section 7 and the outer circumference 10, and point p5 is the point between points p6 and p4. The average value of the calculation results for both shoulders is taken as the radius of curvature of section R8. Note that the virtual circles C1 and C2 may be ellipses as long as they pass through the respective points. For these points, the automatic calculation by the analysis software will be prioritized.

[0023] Furthermore, if virtual circles C1 and C2 do not pass through points p1 to p6, respectively, it is determined that the radius of curvature has not been measured accurately. Similarly, when comparing the actual curve formed by points p1 to p6 with the curve along the corresponding section formed by virtual circles C1 and C2, if there are points separated by 10 [μm] or more, it is determined that the radius of curvature has not been measured accurately. When it is determined that the radius of curvature has not been measured accurately in these cases, points p1 to p6, especially the intermediate points p2 and p5, shall be selected again and the radius of curvature shall be measured again. Re-measuring means re-selecting points p1 to p6, especially the intermediate points p2 and p5, within the same field of view. In this case, some of the points p1 to p6 may be selected from the previous measurement points. The method for selecting points p1 to p6 shall be based on the previous paragraph.

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

[0025] Figure 5 shows an example of the concave shape of the strip portion 7. Figure 5 is a side view including the portion of the strip portion 7 that protrudes from the spherical portion 6. As shown in Figure 5, three points p7, p8, and p9 are selected on the outer circumference 10 of the strip portion 7 and the curvature is measured. At this time, when comparing the actual curve formed by points p7 to p9 with the curve formed by the virtual circle C3 along those points p7 to p9, if there are points that are separated by 10 [μm] or more, it is determined that the curvature has not been measured accurately. In this case, the three points p7, p8, and p9 are selected again and the curvature is measured again.

[0026] Next, we will explain how to measure the height H of the band-shaped portion 7. Figure 6 is a side view including the portion of the band-shaped portion 7 that protrudes from the spherical portion 6. First, as shown in Figure 6, a virtual circle C4 is drawn at a position that coincides with the spherical portion 6 behind the band-shaped portion 7. Next, extension virtual lines L1 and L2 are drawn along the side circumference 9 of the band-shaped portion 7, and the intersections of the extension virtual lines L1 and L2 with the spherical portion 6 are designated as points p10 and p11, respectively. When comparing the side circumference 9 of the band-shaped portion 7 with the extension virtual lines L1 and L2, if there are points that are more than 5 [μm] apart, it is determined that the extension virtual lines have not been drawn accurately, and they are redrawn. From the highest point extraction area, the points with the maximum height at each of the shoulders of the band-shaped portion 7 are extracted and designated 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, respectively, and the average value of these distances is taken as the height H of the strip-shaped section 7 (shown in Figure 3). Additionally, the shortest distance between points p10 and p11 is measured and taken as the width W of the strip-shaped section 7 (shown in Figure 3).

[0027] Next, we will explain how to measure the diameter r1 of the strip-shaped portion 7 and the diameter r2 of the spherical portion 6, which will be described later. Figure 3 shows examples of diameters r1 and r2. Diameter r1 is the length extended from the center of the outer circumference 10 of the strip-shaped portion 7 (the center between the side circumferences 9 at both ends) to the center of the outer circumference 10 on the opposite side, that is, the diameter of the outer circumference 10. Also, if the outer circumference 10 of the strip-shaped portion 7 has a concave shape, diameter r1 is the diameter from the concave shape to the concave shape on the opposite side. Furthermore, the diameter r2 of the spherical portion 6 is, for example, the diameter of the spherical portion 6 that is perpendicular to the plane formed by the circumference of the strip-shaped portion 7 and passes through the center of the spherical portion 6.

[0028] The diameters r1 and r2 shall be measured using a non-contact image dimension measuring instrument. The non-contact image dimension measuring instrument to be used shall be the IM-7000 manufactured by KEYENCE or an instrument with equivalent performance. A non-contact image dimension measuring instrument is an image dimension measuring instrument that projects light onto the object from directly above 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 strip-shaped portion 7 horizontal to the projection direction. If the strip-shaped portion 7 is at an angle of 5° or more from the projection direction, the concave part of the outer circumference 10 of the strip-shaped portion 7 will not be visible. The measurement area is set so that the distance between the centers of the concave shapes of the outer circumference 10 of diagonally opposite strip-shaped portions 7 can be measured, and the diameter r1 can be evaluated by taking the measurement. In addition, as the diameter r2 of the spherical portion 6, the length of the line segment that is perpendicular to the plane formed by the circumference of the strip-shaped portion 7 and passes through the center of the spherical portion 6 is measured.

[0029] The outer periphery 10 of the strip-shaped portion 7 is preferably flat or concave. Furthermore, it is preferable that the outer periphery 10 of the strip-shaped portion 7 is concave. A concave shape refers to a shape where the outer periphery 10 of the strip-shaped portion 7 is recessed relative to both shoulders at both ends. When the outer periphery 10 is flat or concave, it becomes easier to form R-shaped portions 8 on both shoulders of the strip-shaped portion 7. On the other hand, if the outer periphery 10 of the strip-shaped portion 7 is convex, the protrusion of that portion makes it easier for brittle fracture to occur due to contact during surface plate machining.

[0030] Furthermore, it is preferable that the concave shape of the outer periphery 10 of the strip-shaped portion 7 has a radius of curvature of 5 [mm] or more. When the ceramic ball material 5 is polished to make ceramic balls, the strip-shaped portion 7 is ground down. By increasing the radius of curvature of the concave shape of the outer periphery 10, the volume of the strip-shaped portion 7 that is ground down can be reduced. This reduces the amount of polishing required. There is no particular upper limit to the radius of curvature of the concave shape of the outer periphery 10 of the strip-shaped portion 7, but it is preferable that it be 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. Also, the concave shape of the outer periphery 10 of the strip-shaped portion 7 may have minute irregularities on its surface. Figures 4 to 6 show convex parts (projections) on the outer periphery 10, but the convex parts are not an essential component. Also, if there are convex parts (projections) on the outer periphery 10, the height of the convex parts should be lower than the shoulder parts.

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

[0032] The height H of the strip portion 7 is preferably 2.5% or less of the diameter r1 of the strip portion 7. This indicates that (height H of strip portion 7 / diameter r1 of strip portion) × 100 ≤ 2.5 is satisfied. As mentioned above, the strip portion 7 is removed by polishing. If the height H of the strip portion 7 is greater than 2.5% of the diameter r1, the polishing load will increase. In addition, brittle fracture due to contact during surface plate processing may be more likely to occur. The lower limit of the height H of the strip portion 7 is preferably 0.1% or more of the diameter r1 of the strip portion 7. If the height H of the strip portion 7 is too small, densification around the strip portion 7 may become difficult. For this reason, it is preferable that 0.1 ≤ (height H of strip portion 7 / diameter r1 of strip portion) × 100 ≤ 2.5 is satisfied.

[0033] Furthermore, it is preferable that the diameter r2 of the spherical portion 6 is 0.5 [mm] or more. Also, it is 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 the strip portion 7 / diameter r2 of the spherical portion 6) × 100 ≤ 1. Furthermore, it is preferable that the ratio (r1 / r2) of the diameter r1 of the strip portion 7 to the diameter r2 of the spherical portion 6 is within the range of 0.9 ≤ r1 / r2 ≤ 1.1. If any 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 even more preferable that the diameter r2 of the spherical portion 6 is between 8 [mm] and 70 [mm].

[0034] Furthermore, the fact that 0.9 ≤ r1 / r2 ≤ 1.1 indicates that the diameter r1 of the strip portion 7 and the diameter r2 of the spherical portion 6 are approximately equal. This allows for uniform initial contact with the machining platen, thereby suppressing stress concentration and reducing damage during machining.

[0035] Furthermore, it is preferable that the ceramic ball material 5 contains 85% by mass or more of one or more of the following: 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 statement that it contains 85% by mass or more of one or more of the following: 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 other substances. It is preferable that the ceramic ball material 5 contains 85% by mass or more of silicon nitride.

[0036] For example, bearing balls are made from aluminum oxide sintered bodies, silicon nitride sintered bodies, boron nitride sintered bodies, zirconium oxide sintered bodies, and argil sintered bodies. Argil sintered bodies are sintered bodies made by mixing aluminum oxide and zirconium oxide. Among these, bearing balls made from silicon nitride sintered bodies have the best wear resistance. For example, aluminum oxide, zirconium oxide, and argil have a Vickers hardness of approximately 1200-1700, but their fracture toughness is 3-6 [MPa·m]. 1 / 2 The Vickers hardness is low, at approximately 1400-1800. In contrast, silicon nitride sintered bodies have a Vickers hardness of 1400-1800 and a fracture toughness of 5-10 [MPa·m]. 1 / 2 ] is high. Silicon nitride sintered bodies have both high toughness and Vickers hardness, and in that respect they have excellent wear resistance. Silicon nitride sintered bodies have a structure mainly composed of β-type silicon nitride crystal particles. β-type silicon nitride crystal particles have an elongated shape, and the high toughness is achieved by the intricate intertwining of these elongated crystal particles. However, due to the high mechanical strength of silicon nitride sintered bodies, polishing efficiency is very poor, but as mentioned above, by providing an R portion in the strip portion 7, polishing efficiency can be improved even for ceramic ball material 5 made of a high-strength ceramic sintered body like silicon nitride sintered body.

[0037] Next, a method for manufacturing the ceramic ball material 5 will be described. While the manufacturing method of the ceramic ball material 5 according to this embodiment is not particularly limited as long as it satisfies the above configuration, the following manufacturing method is suggested as an efficient method. The manufacturing method for the ceramic ball material 5 will be explained using the case of a silicon nitride sintered body as an example.

[0038] First, an appropriate amount of sintering aid, additives, solvent, and binder is added to the raw material silicon nitride, mixed, crushed, and granulated using a spray dryer. This process prepares the granulated powder of the raw material. When the total of silicon nitride powder and sintering aid powder is 100 [mass], it is preferable that the silicon nitride powder be 85 [mass] or more. The additive is a plasticizer. The solvent is water or an organic solvent. Examples of organic solvents include alcohols, ketones, and benzene. The binder is an organic substance. The amount of binder added is in 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 circumference 10 of the strip-shaped portion 7 in the process described later.

[0039] Next, press molding is performed using granulated powder. One example of press molding is a molding method using the upper mold 1 and lower mold 2 of the die press molding apparatus shown in Figure 1. The spherical shape inside the upper mold 1 and lower mold 2 becomes the spherical portion 6 of the ceramic ball material 5. By adjusting the shape of the tip portion 3 of the upper mold 1 and the tip portion 4 of the lower mold 2 and the amount of powder filled during press molding, the width W and height H of the strip portion 7 of the ceramic ball material 5 can be adjusted. Similarly, the diameters r1 and r2 can be adjusted. For example, the gap between the tip portion 3 of the upper mold 1 and the tip portion 4 of the lower mold 2 during press molding is set to 0.5 [mm] or more and 4 [mm], and granulated powder is filled into that gap during press molding. This allows the width W of the strip portion 7 to be controlled within the range of 0.5 [mm] or more and 4 [mm] or less.

[0040] The molded body obtained by press molding has a spherical portion and a strip-shaped portion. The spherical portion and strip-shaped portion of the molded body correspond to the spherical portion 6 and strip-shaped portion 7 of the ceramic ball material 5 described above, respectively. The diameter of the strip-shaped portion of the molded body is denoted as r1-1, and the diameter of the spherical portion as r2-1. The method for measuring the diameters r1-1 and r2-1 of the molded body is the same as the method for measuring the diameters r1 and r2 of the ceramic ball material 5 described above. At the molded body stage, 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 made to have a coefficient of 0.9 ≤ r1 / r2 ≤ 1.1. This takes into account the shrinkage of the molded body due to the sintering process.

[0041] Furthermore, it is preferable to perform isotropic molding on the molded body. By performing isotropic molding, uniform compression can be applied to the granulated powder in the molded body. This reduces the amount of granulated powder that remains crushed in the molded body. By reducing the amount of granulated powder that remains crushed, the shrinkage rate during the sintering process can be controlled.

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

[0043] The disc-shaped rubber molds 11 and 12 have hemispherical holes on both sides that are approximately 1% to 35% larger than the diameter r1 of the molded body. The molded body is placed in these holes and the rubber molds are placed on top of each other, sealing the molded body in the space 13 surrounded by the rubber molds. A hydrostatic pressure higher than the pressure applied during molding is applied to the rubber molds. This allows for uniform compression of the molded body. This process reduces the amount of crushed granulated powder remaining. Furthermore, as shown in Figure 7, it is preferable to position the rubber molds so that the strip-shaped portion 7 of the molded body is perpendicular to the cylindrical direction of the rubber molds. It is also preferable to use rubber molds 11 and 12 with a Shore hardness Hs of 30 to 50. By keeping the hardness of the rubber molds within this range, the molds can be deformed to allow for uniform contact between the surface of the molded body and the rubber molds. The durability of the rubber molds is also good. Through this process, R portions 8 with a radius of curvature of 0.02 mm or more can be formed on both shoulders of the strip-shaped portion 7 of the molded body. Furthermore, by adjusting the size ratio between the diameter r1-1 of the molded body and the space 13, the radius of curvature of the concave shape of the outer circumference 10 of the strip-shaped portion 7 of the molded body and the height H of the strip-shaped portion 7 can be adjusted.

[0044] Next, a degreasing process is performed to remove the molded body. The degreasing process involves heating the molded body to a temperature above the decomposition temperature of organic components such as binders to remove the organic components. The degreasing process may be carried out in a nitrogen atmosphere or an atmospheric atmosphere. A degreased body can be obtained through the degreasing process.

[0045] Next, a sintering process is performed to sinter the degreased body. The sintering process is preferably carried out at a temperature of 1600°C to 2000°C. Furthermore, the sintering process is preferably carried out in a nitrogen atmosphere. In addition, the pressure during sintering is preferably within the range of atmospheric pressure to 300 MPa. Atmospheric pressure is 0.10133 MPa (= 1 atm). Furthermore, the sintered body obtained from the sintering process may be subjected to HIP (Hot Isostatic Pressing). Through this process, the ceramic ball material 5 can be obtained. The ceramic ball material 5 is a ceramic sintered body with a theoretical density of 98% or higher.

[0046] Furthermore, to adjust the radius of curvature of the R-shaped portions 8 at both shoulders of the strip-shaped portion 7, one method is to polish the finished ceramic ball material 5. However, this method is not desirable because it increases the polishing process. The manufacturing method described above is preferable.

[0047] Ceramic balls can be manufactured by polishing the ceramic ball material 5. A typical method of polishing spheres is plate polishing. For example, the ceramic ball material 5 is inserted between two parallel plate polishing plates. The movement of the polishing plate polishing plate processes the ceramic ball material 5 into a perfect sphere. The surface roughness of bearing balls is specified in ASTM F2094. Bearing balls are selected in grades that conform to ASTM F2094 depending on the application. They are polished to a surface roughness Ra corresponding to that grade. Higher grades may have a mirror finish with a surface roughness Ra of 0.01 [μm] or less. ASTM is a standard issued by ASTM International. ASTM International's former name was the American Society for Testing and Materials (ASTM).

[0048] The ceramic ball material 5 according to this embodiment has R portions 8 with a radius of curvature of 0.02 [mm] or more at both shoulders of the strip-shaped portion 7. Therefore, contact with the grinding wheel, such as a polishing platen, can be made surface contact. This makes it possible to suppress damage to the ceramic ball material 5 during the polishing process. It also improves the durability of the polishing platen. Furthermore, by controlling the shape of the strip-shaped portion 7, it is possible to reduce the polishing allowance while improving machinability.

[0049] (Examples, comparative examples, reference examples) The raw material, ceramic powder, was mixed with a sintering aid, additives, solvent, and binder, then crushed and granulated using a spray dryer. Examples 1-3 and 5-6 are silicon nitride sintered bodies, Reference Example 1 is an aluminum oxide sintered body, and Example 7 is an argil sintered body. The silicon nitride sintered bodies contain 85% by mass or more of silicon nitride. The aluminum oxide sintered bodies contain 85% by mass or more of aluminum oxide. The argil sintered bodies contain a total of 85% by mass or more of aluminum oxide and zirconium oxide. When the total of the main component and sintering aid is 100 parts by mass, the amount of binder added was within the range of 3 to 20 parts by mass.

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

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

[0052] This process was used to produce ceramic ball materials according to the examples and reference examples. In the comparative example, the amount of binder added was 3 parts by mass when the total amount of the main component and sintering aid was 100 parts by mass. Furthermore, isotropic molding was not performed after the molding process.

[0053] The shape of the ceramic ball material 5 in the example and the shape of the ceramic ball materials in the comparative example and reference example were measured. The measurement methods for each were as described above. Note that H / r1[%] refers to (H / r1) × 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. Examples 2 and Reference Example 1 are ceramic ball material 5 for ceramic balls that are 5 / 16 inch (7.9375 mm). Examples 3, 5 to 7 are ceramic ball material 5 for ceramic balls that are 7 / 8 inch (22.225 mm). Comparative Examples 2 and 3 are ceramic ball material for ceramic balls that are 5 / 16 inch (7.9375 mm), similar to Examples 2 and Reference Example 1. Comparative Example 1 is a ceramic ball material for ceramic balls that are 7 / 8 inch (22.225 mm), similar to Examples 3, 5 to 7. The ceramic ball material 5 in the examples and the ceramic ball material in the comparative examples and reference examples can all be used as bearing balls.

[0056] Furthermore, Comparative Examples 1 and 3 have widths W of the band-like portion that are outside the specified range. Also, in Comparative Example 2, the radius of curvature of the R portions at both shoulders of the band-like portion is outside the specified range. In Comparative Example 2, the angles at both shoulders of the band-like portion were acute angles of less than 90°.

[0057] The polishing efficiency was evaluated using ceramic ball material 5 from the example and ceramic ball materials from the comparative example and reference example. The evaluation involved processing each ceramic ball material using a #180 grit grinding wheel, with a batch size corresponding to the size of the ceramic ball material, and determining how many batches the grinding wheel could handle. Polishing was performed to achieve a surface roughness Ra of 0.01 [μm] for the ceramic balls.

[0058] Furthermore, the rate of defects occurring during the polishing process described above, such as chipping of the ceramic ball material, was investigated. The defect rate was determined by visually inspecting one batch before the endurance cycle of the grinding wheel (for example, from the 1st to the 15th cycle in Example 1), and the percentage of chipped material is shown as the material chipping defect rate [%]. Note that the material chipping defect rate [%] is rounded to two decimal places.

[0059] Furthermore, we investigated the diameter variation of the ceramic balls after the target polishing process. Diameter variation was defined as the difference between the minimum and maximum diameters measured around the entire circumference of the sphere. The average value of the diameter variation was obtained by randomly selecting 10 balls from one batch and measuring them. 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 example showed improved durability of the grinding wheel compared to the ceramic ball material according to the comparative example, which processed the same number of balls. Furthermore, the ceramic ball material 5 according to the example showed a lower defect rate compared to the ceramic ball material according to the comparative example, which processed the same number of balls. In addition, the ceramic ball material 5 according to the example showed a reduction in deviation from the target diameter compared to the ceramic ball material according to the comparative example, which processed the same number of balls. Therefore, it can be seen that the ceramic ball material 5 according to the embodiment has good polishing efficiency.

[0062] As explained above, the ceramic ball material 5 can suppress damage to the ceramic material during surface plate processing.

[0063] Although several embodiments of the present invention have been illustrated above, these embodiments are presented as examples only 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, and modifications can be made without departing from the spirit of the invention. Modifications of these embodiments are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents. Furthermore, the embodiments described above can be implemented in combination with each other.

Claims

1. The process involves adding a sintering aid, additives, solvents, and a binder to the raw material ceramic powder, mixing them, and then granulating them using a spray dryer. A press molding step is performed using the granulated powder obtained in the granulation step, An isotropic molding step is performed by isotropically molding the molded body using a rubber mold having a Shore hardness Hs of 30 or more and 50 or less, and having hemispherical holes on both sides that are 1% or more and 35% or less larger than the diameter r1 of the molded body obtained in the press molding step, A degreasing step is performed to degrease the molded body obtained in the isostatic molding step, The present invention comprises a sintering step of obtaining a ceramic ball material having a spherical portion and a strip-shaped portion by sintering the molded body obtained in the degreasing step at a temperature of 1600°C to 2000°C, The ceramic ball material having the strip-shaped portion obtained in the sintering process is The width of the aforementioned strip-shaped portion is within the range of 0.5 [mm] to 4.0 [mm], and the shoulders of the aforementioned strip-shaped portion are provided with R-shaped portions with a radius of curvature of 0.02 [mm] or more. The radius of curvature of the concave shape formed by the outer periphery of the aforementioned strip-shaped portion is 5 [mm] or more. A method for manufacturing a material for ceramic balls, characterized by the following features.

2. The method for manufacturing a ceramic ball material according to claim 1, characterized in that the press molding process is carried out by inserting the granulated powder between an upper mold and a lower mold, and the distance between the tip of the upper mold and the tip of the lower mold is 0.5 mm or more and 4 mm or more.

3. The method for manufacturing a ceramic ball material according to any one of claims 1 to 2, characterized in that the outer periphery of the band-shaped portion has a concave shape in which the portion sandwiched between the shoulder portions is continuously recessed along the circumference of the outer periphery, or has a flat shape without the concave shape.

4. A method for manufacturing a ceramic ball material according to any one of claims 1 to 2, characterized in that the height of the strip-shaped portion is 2.5% or less of any diameter of the strip-shaped portion.

5. A method for manufacturing a ceramic ball material according to any one of claims 1 to 2, characterized in that any diameter of the spherical portion is 0.5 mm or more.

6. The method for manufacturing a ceramic ball material according to claim 4, characterized in that any diameter of the spherical portion is 0.5 mm or more.

7. A method for manufacturing a ceramic ball material according to any one of claims 1 to 2, characterized in that the diameter of the spherical portion is within the range of 8 mm to 70 mm, and the height of the band-shaped portion is 1% or less of the diameter of the spherical portion.

8. The method for manufacturing a ceramic ball material according to claim 4, characterized in that any diameter of the spherical portion is within the range of 8 mm to 70 mm, and the height of the band-shaped portion is 1% or less of the diameter of the spherical portion.

9. A method for manufacturing a ceramic ball material according to any one of claims 1 to 2, characterized in that the ratio of the diameter of the outer circumference of the strip-shaped portion to the diameter of the spherical portion is 0.9 or more and 1.1 or less.

10. The method for manufacturing a ceramic ball material according to claim 4, characterized in that the ratio of the diameter of the outer circumference of the strip-shaped portion to the diameter of the spherical portion is 0.9 or more and 1.1 or less.

11. A method for producing a ceramic ball material according to any one of claims 1 to 2, characterized in that the ceramic ball material contains 85% by mass or more of one of aluminum oxide, silicon nitride, boron nitride, or zirconium oxide.

12. The method for producing a ceramic ball material according to claim 4, characterized in that the ceramic ball material contains 85% by mass or more of one of aluminum oxide, silicon nitride, boron nitride, or zirconium oxide.

13. The method for manufacturing a ceramic ball material according to any one of claims 1 to 2, characterized in that the ceramic ball material is a sintered ceramic body containing 85% by mass or more of silicon nitride.

14. The method for manufacturing a ceramic ball material according to claim 4, characterized in that the ceramic ball material is a sintered ceramic body containing 85% by mass or more of silicon nitride.

15. The method for manufacturing a ceramic ball material according to claim 8, characterized in that the ceramic ball material is a sintered ceramic body containing 85% by mass or more of silicon nitride.

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