Ceramic ball material, manufacturing method of ceramic ball using same, and ceramic ball

Abstract

A material for a ceramic ball according to an embodiment of the present invention comprises a spherical part and a band-shaped part formed over the circumference of the surface of the spherical part. Rab / Rap, which is the ratio of the arithmetic average roughness Rab of the band-shaped part to the arithmetic average roughness Rap that is an extreme of the spherical part, is 0.7-1.0. Any substance from among aluminum oxide, silicon nitride, silicon carbide, boron nitride, and zirconium oxide can be applied for the ceramic. A ceramic ball is produced by performing a polishing process on the material for a ceramic ball.

Description

[Technical field]

[0001] The embodiments described below relate to a material for a ceramic ball, 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 the properties of ceramic materials, products for ball applications take advantage of wear resistance and insulation. Products for ball applications include bearings, jigs, tools, gauges, solenoid valves, check valves, and various valves. Among these, ceramic materials such as aluminum oxide, silicon nitride, and zirconium oxide are used for products for bearing ball applications. For example, bearing balls using silicon nitride materials are disclosed in JP-A-6-48813 (Patent Document 1) and JP-A-2764589 (Patent Document 2), and bearing balls using zirconium oxide materials are disclosed in JP-A-60-18620 (Patent Document 3).

[0003] In the process of manufacturing these materials for bearing balls, a method of sintering a molded body is used. In addition, press molding using a die is used as a molding method to obtain the molded body. Press molding is generally a method in which an upper punch 2, a lower punch 3, and a die 4 are provided, and powder is inserted between the upper punch 2 and the lower punch 3 and pressure is applied, as shown in FIG. 1. In order to protect the die during press molding, a gap must be provided between the tip 2a of the upper punch 2 and the tip 3a of the lower punch 3 when press molding. For this reason, a spherical portion and a band-shaped portion are formed in the molded body obtained by press molding. For example, Japanese Patent No. 4761613 (Patent Document 4) discloses a material for bearing balls having a spherical portion and a band-shaped portion obtained by sintering a molded body having a spherical portion and a band-shaped portion. FIG. 2 shows a conventional material for ceramic balls. In FIG. 2, 5 is a material for ceramic balls, 6 is a spherical portion, and 7 is a band-shaped portion. [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] As shown in Fig. 2, ceramic balls are obtained by polishing ceramic ball material 5 having a spherical portion 6 and a strip-shaped portion 7 after the sintering process. Ceramic ball material 5 having spherical portion 6 and strip-shaped portion 7 is sometimes called a bare sphere. For example, ceramic ball material 5 is polished to a mirror finish with an arithmetic mean roughness Ra of 0.1 μm or less. A surface plate is used for the mirror finish.

[0006] Generally, ceramic materials are manufactured by molding ceramic powder and sintering it through heat treatment. Ceramics undergo large shrinkage during sintering, but it is difficult to mold and sinter ceramic products uniformly under ideal conditions, and uneven density and the occurrence of pores tend to cause microstructural irregularities inside the ceramic. The ceramic ball material 5 is sintered in a state where it is molded into a shape that is not a perfect sphere by powder press molding, and is then machined into a perfect sphere and its surface is mirror-finished. For this reason, if there is microstructural irregularity inside the ceramic ball material 5 due to uneven molding by powder press molding, it causes defects in the ceramic ball product.

[0007] The present invention is intended to solve such problems, and provides ceramic balls with a good processing yield when polished by using a ceramic ball material 5 in which microstructural irregularities during sintering of the ceramic material powder-press molded are suppressed. [Means for solving the problem]

[0008] A ceramic ball material according to an embodiment includes a spherical portion and a band-shaped portion formed around the circumference of the spherical portion, and a ratio of an arithmetic mean roughness Rab of an outer peripheral surface of the band-shaped portion to an arithmetic mean roughness Rap of an outer peripheral surface of the spherical portion, Rab / Rap, is 0.7 to 1.0. [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. 2 is an external view showing an example of a ceramic ball material according to the embodiment. [Diagram 3] FIG. 2 is an external view showing an example of a die of the die press molding apparatus according to the embodiment. [Figure 4] FIG. 2 is a cross-sectional view showing an example of cold isostatic press rubber mold molding according to the embodiment. [Diagram 5]FIG. 2 is a cross-sectional view showing an example of a hole shape and a molded body formed in a cold isostatic press rubber mold. [Figure 6] FIG. 2 is a cross-sectional view showing an example of a hole shape and a molded body provided in a cold isostatic press rubber mold according to an embodiment. Embodiment

[0010] Hereinafter, embodiments of a ceramic ball material, a method for manufacturing a ceramic ball using the same, and a ceramic ball will be described in detail with reference to the drawings.

[0011] A ceramic ball material according to an embodiment includes a spherical portion and a band-shaped portion formed around the circumference of the spherical portion, and a ratio of an arithmetic mean roughness Rab of an outer peripheral surface of the band-shaped portion to an arithmetic mean roughness Rap of an outer peripheral surface of the spherical portion, Rab / Rap, is 0.7 to 1.0.

[0012] FIG. 2 shows a schematic diagram of a ceramic ball material according to an embodiment. In FIG. 2, 5 is a ceramic ball material according to an embodiment, 6 is a spherical portion, and 7 is a band portion. In FIG. 2, 7C is a curve extending in the circumferential direction of the outer peripheral surface (outermost surface) formed by the band portion 7 and passing through the center of the width W of the outer peripheral surface. In FIG. 2, 8 is one of two poles (8, 8') located at the position furthest from the surface formed by the curve 7C (at a position 90° from the curve 7C) on the outer peripheral surface (outermost surface) of the spherical portion 6. In addition, of the arithmetic mean roughness Ra, the arithmetic mean roughness related to the outer peripheral surface of the band portion 7 is Rab, and the arithmetic mean roughness related to the outer peripheral surface of the spherical portion 6, for example, the pole 8, is Rap. Hereinafter, unless otherwise specified, the arithmetic mean roughness related to the outer peripheral surface of the spherical portion 6 is described as the arithmetic mean roughness of the pole 8. In addition, W is the width of the band portion 7. The width W of the strip portion 7 may be simply referred to as "width W." Note that in Fig. 3, the height and width of the strip 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 a plurality of circumferences of the surface of the spherical portion 6. The surface of the spherical portion 6 may be a quadratic curved surface. Therefore, examples of the spherical portion 6 include a perfect sphere and 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 widest width of the band-shaped portion 7, but may be the average value of a plurality of points.

[0014] When the arithmetic mean roughness of the pole 8 is Rap and the arithmetic mean roughness of the outer peripheral surface of the band-shaped portion 7 is Rab, the ratio of Rab to Rap, Rab / Rap, is within the range of 0.70 to 1.03. Rab / Rap However, within this range, microstructural irregularities during sintering, mainly caused by powder press molding of the spherical portion 6 and the band-shaped portion 7, are suppressed. Furthermore, suppressing microstructural irregularities during sintering can reduce defects due to polishing. For this reason, Rab / Rap is preferably 0.70 or more and 1.03 or less, more preferably 0.80 or more and 1.00 or less, and even more preferably 0.90 or more and 1.00 or less.

[0015] If Rab / Rap is less than 1.00, the density of the belt-shaped portion 7 of the material 5 for ceramic balls becomes larger than that of the spherical portion 6, and polishing (e.g., platen processing) of the belt-shaped portion 7 becomes difficult. In particular, if Rab / Rap is less than 0.70, polishing of the belt-shaped portion 7 becomes significantly difficult, and the processing time during polishing becomes unnoticeably long (polishing efficiency becomes poor). Furthermore, if Rab / Rap is less than 0.70, brittle fracture is likely to occur when the belt-shaped portion 7 comes into contact with a grindstone during polishing. In particular, brittle fracture is likely to occur when the material 5 for ceramic balls comes into contact with a platen during platen processing.

[0016] On the other hand, if Rab / Rap exceeds 1.03, unevenness in density and microstructure will occur inside the ceramic ball material 5, and defects such as holes and abnormal structures will occur on the bearing ball surface after polishing.

[0017] Here, a method for measuring the arithmetic mean roughness Rab of the outer peripheral surface of the belt-like portion 7 of the ceramic ball material 5 and the arithmetic mean roughness Rap of the poles 8 will be described. The arithmetic mean roughness Ra is based on JIS B 0601 (2013) "Geometric characteristic specifications of products (GPS)-Surface quality: Profile curve method-Terminology, definitions and surface quality parameters."

[0018] The arithmetic mean roughness Ra is measured using a surface roughness measuring instrument. The surface roughness measuring instrument used is the SURFCOM2000 manufactured by Tokyo Seimitsu Co., Ltd., and the measurement is performed using the evaluation and analysis software of the same instrument. Any measuring instrument with equivalent functions may be used.

[0019] The measurement distance for the arithmetic mean roughness Ra, i.e., the reference length U, is 10 to 25% of the diameter of the ceramic ball material 5, and the spherical portion 6 and the band-like portion 7 have the same reference length U. The measurement conditions are as follows: measurement cutoff wavelength is 0.08 mm, cutoff type is Gaussian, slope correction is least squares linear correction, λs cutoff ratio is 300, and λs cutoff wavelength is 0.2667 μm.

[0020] The measurement area of ​​the arithmetic mean roughness Rap of the pole 8 is a position on the curve 6C centered on the pole 8, and has a length corresponding to the reference length U. This is because, even if the ceramic ball material 5 is a perfect sphere or an ellipsoid, the same value can be obtained regardless of the position or direction of measurement. If it is not possible to measure at the pole 8 (or the pole 8') due to the presence of defects, etc., it is also possible to measure on the outer surface of the spherical crown from a position (45° position, i.e., the base surface when the apex angle θ of the cone with the center point of the ceramic ball material 5 as the apex is 45°×2) 6E, which is half the distance from the curve 7C to the pole 8, to the pole 8. Furthermore, it is also possible to measure on the outer surface of the spherical crown from a position (15° position, i.e., the base surface when the apex angle θ of the cone with the center point of the ceramic ball material 5 as the apex is 15°×2) 6F to the pole 8. The apex angle means the apex angle of an isosceles triangle formed when a cone is cut by a plane passing through the axis of rotation.

[0021] The measurement area of ​​the arithmetic mean roughness Rab on the outer peripheral surface of the band-shaped portion 7 has a length corresponding to the reference length U at any position on the curve 7C. The measurement is performed along the curve 7C or perpendicular to the curve 7C. In the latter case, the curve 7C is set to be approximately at the center of the measurement area. It is preferable to exclude 10% of one end and 10% of the other end in the width direction of the outer peripheral surface of the band-shaped portion 7 from the measurement points because defects such as chipping are likely to occur in these areas and affect the measurement value. In addition, the reference length U of the arithmetic mean roughness Ra does not need to be the entire curves 6C and 7C on the outer peripheral surface, but may be a part of the curves 6C and 7C (for example, about 1 mm to 20 mm).

[0022] In the ceramic ball material 5, the spherical portion 6 has a diameter of preferably 0.5 mm or more. If the diameter of the spherical portion 6 is less than 0.5 mm, it becomes difficult to control the powder press die for forming the strip portion 7. For this reason, the diameter of the spherical portion 6 is preferably 1 mm or more. More preferably, it is 2 mm or more.

[0023] The ceramic ball material 5 preferably contains 85 mass% or more of one or more of aluminum oxide (Al2O3), silicon nitride (Si3N4), silicon carbide (SiC), boron nitride (BN), and zirconium oxide (ZrO2). The ceramic ball material 5 is made of a ceramic sintered body. The content of 85 mass% or more of one or more of aluminum oxide, silicon nitride, silicon carbide, boron nitride, and zirconium oxide refers to the content in the ceramic sintered body. In other words, the ceramic sintered body may contain 15 mass% or less of substances other than the above. It is preferable that the ceramic ball material 5 contains 85 mass% or more of silicon nitride.

[0024] 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 body has a Vickers hardness of 1400 to 1800 and a fracture toughness of 5 to 10 MPa m 1 / 2 and 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 that is mainly composed of β-type silicon nitride crystal grains. β-type silicon nitride crystal grains have a long and thin shape, and these long and thin crystal grains are intricately intertwined to achieve high toughness.

[0025] 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 using a silicon nitride sintered body as an example.

[0026] 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 raw powder. In addition, when the total of silicon nitride powder and sintering aid powder is 100 mass%, it is preferable to make silicon nitride powder 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 a paraffin wax-based binder. Another binder for ceramic granulation is PVA (polyvinyl alcohol)-based binder, but since its glass transition temperature is somewhat high at 85 °C, it tends to become hard when granulated. For this reason, it is difficult to adjust the granulated powder, which is soft and easily crushed, by lowering the outlet temperature of the spray dryer. The amount of binder added is within the range of 3 to 20 mass parts when the total of silicon nitride powder and sintering aid powder is 100 mass parts.

[0027] By making the granulated powder easier to crush, it becomes easier to crush in the vertical direction of the press than usual. When the granulated powder becomes easier to crush in the vertical direction, the surface vicinity of the pole becomes denser and approaches the surface state of the band-shaped part. However, if the granulated powder is simply made easier to crush, the filling property of the granulated powder into the press die decreases, which may affect productivity. For this reason, it is necessary to make the granulated powder easier to crush without impairing the filling property of the granulated powder. In addition to adjusting the binder type as described above, there is a method of adjusting the average particle size to make the granulated powder easier to crush. The granulated powder usually obtained with a spray dryer is generally normally distributed and shows a distribution that accumulates near the average value. In this distribution, small particles are often hard because they dry quickly. For this reason, it is possible to remove the granulated powder with a small particle size by classification, and make the entire granulated powder easier to crush.

[0028] Next, the adjusted granulated powder is used for press molding. The press molding can be performed using the upper punch 2, lower punch 3, and die 4 of the die press molding device shown in FIG. 1. By filling the granulated powder and applying pressure vertically to the upper punch 2 and the lower punch 3, the spherical shape inside the punch becomes the spherical part 6 of the ceramic ball material 5. In addition, the tip part 2a of the upper punch 2, the tip part 3a of the lower punch 3, and the planar shape inside the die 4 become the band-shaped part 7 of the ceramic ball material 5. The inside of the cross section of the die 4 is a straight line, but it is preferable to make it slightly convex as shown in FIG. 3. If the height of the convex part is H, the size of H is preferably 0.01 mm or more and 0.10 mm or less. This convex part applies pressure to the band-shaped part 7 of the ceramic ball material 5 after the sintering process, which can increase the sintering density of the band-shaped part 7 and reduce the arithmetic mean roughness. If the height of H is less than 0.01, the effect of applying pressure is small. Also, if the thickness is greater than 0.10 mm, the effect of applying pressure will be greater, but the load on the die will increase, which may shorten the life of the die.

[0029] By adjusting the shapes of the tip 2a of the upper punch 2 and the tip 3a of the lower punch 3 and the amount of powder filled during press molding, it is possible to adjust the width W and height of the band-shaped portion 7 of the ceramic ball material 5. Similarly, it is possible to adjust the diameter of the compact 13 in the direction of the spherical portion 14 and the diameter in the direction of the band-shaped portion 15.

[0030] The molded body 13 obtained by press molding has a spherical portion 14 and a strip-like portion 15. The spherical portion 14 and the strip-like portion 15 of the molded body 13 (shown in Figs. 5 and 6) respectively correspond to the spherical portion 6 and the strip-like portion 7 (shown in Fig. 2) of the above-mentioned material 5 for a ceramic ball.

[0031] It is also preferable to perform isostatic pressing on the compact after press molding. By performing isostatic pressing, the granulated powder in the compact can be uniformly compressed. This makes it possible to reduce the amount of granulated powder that remains in the compact. By reducing the amount of granulated powder that remains in the compact, it is possible to control the shrinkage rate in the sintering process.

[0032] As an example of isostatic pressing, an isostatic pressing method using a rubber mold will be described. Fig. 4 shows an example of a disk-shaped rubber mold 9. Fig. 4 teeth is a side view of the state in which the upper rubber mold 10 and the lower rubber mold 11 are stacked. Further, Fig. 5 is a cross-sectional view showing an example in which a formed body 13 is disposed in a spherical surface portion space 12 inside the upper rubber mold 10 and the lower rubber mold 11.

[0033] The disk-shaped rubber mold 9 has hemispherical holes that are about 1% or more and 35% or less larger than the maximum diameter of the formed body laid on both sides. By installing the formed body 13 in the holes and stacking the rubber molds, the formed body 13 is sealed in the spherical surface portion space 12 surrounded by the rubber molds. A hydrostatic pressure higher than the pressure during forming is applied to the rubber molds. Further, it is preferable to use the rubber molds 9 and 10 having a Shore hardness Hs of 30 or more and 50 or less. By setting the hardness of the rubber mold within this range, it is possible to have a deformability capable of uniformly contacting the surface of the formed body 13 and the rubber mold. Thereby, uniform compression can be applied to the formed body 13. By this step, the remaining crushing of the granulated powder can be reduced.

[0034] Further, as shown in Fig. 6, it is preferable that the arrangement of the formed body 13 is such that the strip portion 15 is parallel to the contact surface between the upper rubber mold 10 and the lower rubber mold 11. At this time, when the length in the direction orthogonal to the contact surface in the spherical surface portion space 12 is L1 and the diameter on the contact surface is L2, if L1 > L2, it is possible to prevent pressure from being applied to the spherical surface portion 6 and reduce the sintering density of the spherical surface portion 6, and the arithmetic mean roughness of the spherical surface portion 6 (for example, the arithmetic mean roughness of the pole 8 is Rap) becomes large. Note that the same effect can be obtained even if the strip portion 15 is orthogonal to the contact surface between the upper rubber mold 10 and the lower rubber mold 11 with L1 < L2.

[0035] Next, a degreasing step of degreasing the formed body 13 is performed. The degreasing step is a step of heating at a temperature equal to or higher than the decomposition temperature of an organic component such as a binder and removing the organic component. The degreasing step may be performed in a nitrogen atmosphere or an air atmosphere. A degreased body can be obtained by the degreasing step.

[0036] Next, a sintering process is carried out to sinter the degreased body. The sintering process is preferably carried out at a temperature of 1600°C or higher and 2000°C or lower. The sintering process is preferably carried out in a nitrogen atmosphere. The sintering pressure is preferably within a range of atmospheric pressure or higher and 300 MPa or lower. The atmospheric pressure is 0.10133 MPa (=1 atm). The sintered body obtained by the sintering process may be subjected to a HIP (hot isostatic 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 higher.

[0037] Ceramic balls can be manufactured by polishing the ceramic ball material 5. A typical example of ball polishing is plate processing. For example, the ceramic ball material 5 is inserted between two platens arranged in parallel above and below. The movement of the polishing platen can be used to plate-process the ceramic ball material 5 into a perfect sphere. The surface roughness of the bearing ball is specified in ASTM F2094. Depending on the application, a grade conforming to ASTM F2094 is adopted for the bearing ball. The bearing ball is polished to a surface roughness Ra conforming to that grade. For higher grades, some are mirror-finished to a surface roughness Ra of 0.01 μm or less. Note that ASTM is a standard issued by ASTM International. The former name of ASTM International was American Society for Testing and Materials (ASTM).

[0038] In the ceramic ball material 5 according to the embodiment, the ratio of Rab to Rap, Rab / Rap, is within the range of 0.7 to 1.0, so polishing of the poles 8 starts at the same time as or with priority to the band-shaped portion 7. In order to prevent damage to the ceramic ball material 5 during the polishing process, it is necessary to process the poles 8 while paying attention to the contact of the band-shaped portion 7 with a grindstone such as a polishing table.

[0039] Furthermore, in the material 5 for a ceramic ball according to the embodiment, the ratio Rab / Rap between the poles 8 and the band-shaped portion 7 is within the range of 0.7 to 1.0. This makes it difficult for unevenness in density and microstructure to occur inside the material for a ceramic ball, and can suppress the occurrence of defects such as holes and abnormal structures on the surface of the bearing ball after processing.

[0040] (Examples 1 to 9, Comparative Examples 1 to 6) Sintering aids, additives, solvents, binders, etc. were added to the ceramic powder as raw material, mixed, crushed, and granulated by a spray dryer. Examples 1 to 7 and Comparative Examples 1 to 4 are silicon nitride sintered bodies. Example 8 and Comparative Example 5 are aluminum oxide sintered bodies. Example 9 and Comparative Example 6 are silicon carbide sintered bodies. 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 silicon carbide sintered body contains 85 mass% or more of silicon carbide. When the total of the main component and sintering aids was 100 mass parts, the amount of binder added was 6 mass parts. Paraffin wax and PVA were used as binders.

[0041] Next, the obtained granulated powder was subjected to press molding. The press molding was performed by using the upper and lower dies of the die press molding device shown in FIG. 1. The press dies used were a straight shape without a convex part in the center of the die 4, and a press die with a convex part. After the die molding, isostatic molding was performed. The isostatic molding was performed by using a disk-shaped rubber die having a Shore hardness Hs of 30 to 50. The molded body 13 was one in which the band-shaped part 15 was arranged approximately perpendicular to the contact surface of the rubber dies 10 and 11 in the lower rubber die 11 as shown in FIG. 5 ("vertical band" in Table 1), and one in which the band-shaped part 15 was arranged approximately parallel to the contact surface as shown in FIG. 6 ("horizontal band" in Table 1). In this state, a hydrostatic pressure higher than the pressure during molding was applied in the isostatic molding process.

[0042] Next, the compact 13 was subjected to a debinding and sintering process. The sintering process was carried out at 1600 to 2000° C. in a nitrogen atmosphere at atmospheric pressure. Thereafter, HIP treatment was carried out at 1600 to 2000° C. in a nitrogen atmosphere at a pressure of 200 MPa.

[0043] By this process, the ceramic ball material according to the embodiment was produced. In the comparative example, PVA was used as the binder, a press die with a straight shape without a protrusion in the center was used, and the molded body 13 was placed in the lower rubber die 11 with the band-shaped portion 15 approximately perpendicular to the contact surface of the rubber dies 10 and 11 as shown in FIG. The production conditions for the examples and comparative examples are shown in Table 1.

[0044] [Table 1] TIFF0007669592000001.tif117170

[0045] Examples 1 to 4, 8 to 9 and Comparative Examples 1, 5 to 6 are ceramic ball materials for ceramic balls that will be 3 / 8 inch (9.525 mm) after polishing. Example 5 and Comparative Example 2 are ceramic ball materials for 7 / 8 inch (22.225 mm) ceramic balls. Example 6 and Comparative Example 3 are ceramic ball materials for 1-3 / 16 inch (30.165 mm) ceramic balls. Example 7 and Comparative Example 4 are ceramic ball materials for 1-7 / 8 inch (47.625 mm) ceramic balls. Ceramic ball materials 5 of Examples 1 to 9 and ceramic ball materials of Comparative Examples 1 to 6 can all be used as bearing balls.

[0046] The arithmetic mean roughness was measured for the materials 5 for ceramic balls according to Examples 1 to 9, and the materials for ceramic balls according to Comparative Examples 1 to 6. The respective measuring methods were as described above.

[0047] Moreover, in Comparative Examples 1 to 6, the ratio Rab / Rap of the arithmetic mean roughness Rab of the band-like portion to the arithmetic mean roughness Rap of the pole is outside the range.

[0048] The polishing efficiency was evaluated using the ceramic ball materials 5 of Examples 1 to 9 and the ceramic ball materials of Comparative Examples 1 to 6. The polishing conditions for processing each ceramic ball material using a ball processing polisher were fixed, and the processed state of the belt-shaped portion was examined. The processing conditions were that the upper surface plate was unpressurized (no pressure), the lower surface plate was rotated, and an abrasive using glycerin as a lubricant was supplied to diamond for 24 hours. Note that the gap distance with the upper surface plate, the rotation speed of the lower surface, the amount of ceramic ball material input, and the amount of abrasive supplied were all the same for ceramic balls of the same size.

[0049] We also investigated the percentage of defects where the ceramic ball material was chipped after the above polishing process. The percentage of defects was determined by visually inspecting the entire surface of 100 sampled pieces using an optical microscope, and the percentage of hole defects was shown as the percentage of hole defects [%]. Additionally, the percentage of abnormal structures such as discoloration was shown as the percentage of abnormal structures [%]. The results are shown in Table 2.

[0050] [Table 2] TIFF0007669592000002.tif116170

[0051] As can be seen from Table 2, the defective rate [%] of hole defects and the defective rate [%] of abnormal structures were reduced in the materials 5 for ceramic balls according to Examples 1 to 9. Therefore, it can be seen that the materials 5 for ceramic balls according to Examples 1 to 9, which satisfy the conditions of the embodiment, have a slightly lower polishing processability (polishing process efficiency) than the materials 1 to 6, which have Rab / Rap exceeding 1.03, but have a good surface condition after polishing. It is preferable to satisfy the conditions of the embodiment when priority is given to the surface condition after polishing, even if it means slightly reducing the polishing processability.

[0052] As described above, according to the material 5 for ceramic balls, in which microstructural irregularities during sintering of the ceramic material powder-press molded are suppressed, it is possible to provide ceramic balls with a high yield rate after polishing processing.

[0053] Although several 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 spherical portion; a band-shaped portion formed around the circumference of the spherical portion; Equipped with A material for a ceramic ball, characterized in that the ratio of the arithmetic mean roughness Rab of the outer peripheral surface of the band-shaped portion to the arithmetic mean roughness Rap of the outer peripheral surface of the spherical portion, Rab / Rap, is 0.70 or more and 1.03 or less.

2. The arithmetic mean roughness Rap of the outer peripheral surface of the spherical portion is an arithmetic mean roughness of a pole of the outer peripheral surface of the spherical portion that is located at a position farthest from a surface formed by a curve that extends in the circumferential direction of the outer peripheral surface formed by the band-shaped portion and passes through the center of the outer peripheral surface. The ceramic ball material according to claim 1.

3. 2. The material for a ceramic ball according to claim 1, wherein the arbitrary diameter of the spherical portion is 0.5 mm or more.

4. 2. The ceramic ball material according to claim 1, characterized in that the ceramic ball material contains 85 mass % or more of any one of aluminum oxide, silicon nitride, silicon carbide, boron nitride, and zirconium oxide.

5. 5. A method for producing a ceramic ball, comprising polishing the material for a ceramic ball according to claim 1.

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