Ceramic spheres, ceramic spheres for bearing balls, and method for manufacturing ceramic balls
A ceramic sphere composition with controlled particle size differences and uniform crystalline structure addresses inefficiencies in polishing ceramic balls, improving efficiency and reducing costs while maintaining mechanical integrity.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- NITERRA CO LTD
- Filing Date
- 2024-12-25
- Publication Date
- 2026-07-07
Smart Images
Figure 2026112695000001_ABST
Abstract
Description
[Technical Field]
[0001] This invention relates to ceramic spheres, ceramic spheres for bearing balls, and a method for manufacturing ceramic balls. [Background technology]
[0002] Ceramic spheres that can be polished to become ceramic balls have been known for some time (for example, Patent Document 1). [Prior art documents] [Patent Documents]
[0003] [Patent Document 1] Japanese Patent Publication No. 2024-101045 [Overview of the Initiative] [Problems that the invention aims to solve]
[0004] However, even with prior art such as Patent Document 1, there was still room for improvement in techniques for improving the polishing efficiency of ceramic spheres.
[0005] This invention was made to solve the above-mentioned problems and aims to provide a technology for improving the polishing efficiency of ceramic spheres. [Means for solving the problem]
[0006] The present invention has been made to solve at least some of the above-mentioned problems and can be realized in the following forms.
[0007] (1) According to one embodiment of the present invention, a ceramic sphere is provided. This ceramic sphere contains alumina crystal particles and zirconia crystal particles. If we define a square-shaped region with sides of 10 μm that includes the outer periphery of the ceramic sphere as region A, and a square-shaped region with sides of 10 μm that is inside the outer periphery of the ceramic sphere as region B, then for each of region A and region B, if we let Da1 be the average particle size of the alumina crystal particles and Dz1 be the average particle size of the zirconia crystal particles in region A, and Da2 be the average particle size of the alumina crystal particles and Dz2 be the average particle size of the zirconia crystal particles in region B, then the following equations (1) and (2) are satisfied. If Sa is the ratio of the area occupied by zirconia crystal particles in the cross-section of the ceramic sphere in region A, and Sb is the ratio of the area occupied by zirconia crystal particles in the cross-section of the ceramic sphere in region B, then the following equation (3) is satisfied. |Da1-Dz1|≦0.15μm ···(1) |Da2-Dz2|≦0.15μm ···(2) |Sa-Sb|≦0.05 ···(3)
[0008] In this configuration, the difference between the average particle size of alumina crystal particles and the average particle size of zirconia crystal particles is relatively small in both the outer periphery and the area inside the outer periphery of the ceramic sphere. Furthermore, the proportion of the cross-sectional area occupied by zirconia crystal particles does not differ significantly between the outer periphery and the area inside the outer periphery. In other words, since the ceramic sphere as a whole has a homogeneous crystalline structure, ceramic balls can be manufactured with less polishing during the manufacturing process of producing ceramic balls by polishing the ceramic sphere. Therefore, polishing efficiency can be improved.
[0009] (2) In the ceramic sphere of the above form, if Sa is the ratio of the area occupied by zirconia crystal particles in the cross-section of the ceramic sphere included in region A, and Sb is the ratio of the area occupied by zirconia crystal particles in the cross-section of the ceramic sphere included in region B, then the following equations (4) and (5) may be satisfied. 0.08 ≤ Sa ≤ 0.30 ···(4) 0.08 ≤ Sb ≤ 0.30 ···(5) In this configuration, both the outer periphery and the inner portion contain more alumina crystal particles than zirconia crystal particles. As a result, the zirconia crystal particles are less likely to transform from tetragonal zirconia to monoclinic zirconia due to the constraint of the alumina crystal particles, thus suppressing the deterioration of the mechanical properties of the ceramic balls obtained by polishing the ceramic spheres.
[0010] (3) In the above-described form of ceramic sphere, if Va is the Vickers hardness of the cross-section of the ceramic sphere included in region A, and Vb is the Vickers hardness of the cross-section of the ceramic sphere included in region B, then the following equations (6) to (8) may be satisfied. Va ≥ 1960 kgf / mm 2 ...(6) Vb ≥ 1960 kgf / mm 2 ...(7) |Va-Vb| ≤ 120 kgf / mm 2 ...(8) With this configuration, the Vickers hardness of the outer periphery and the Vickers hardness of the part inside the periphery are both relatively large, with little difference between them. In ceramic spheres, the Vickers hardness of the outer periphery and the part inside the periphery are both relatively large and almost the same. This makes it possible to manufacture ceramic balls with relatively high hardness with a small amount of polishing.
[0011] (4) The ceramic sphere of the above form may further include a spherical portion made of ceramics and a strip-shaped, annular strip-shaped portion made of ceramics, which is arranged along the outer circumference of the spherical portion. With this configuration, the ceramic sphere has a spherical portion and a strip-shaped portion arranged along the outer circumference of the spherical portion. This makes it possible to manufacture a ceramic ball by polishing the strip-shaped portion and polishing the surface of the spherical portion to a relatively thin degree.
[0012] (5) In the ceramic sphere of the above form, the variation in the diameter of the spherical part may be within 2%. With this configuration, since the variation in the diameter of the spherical part is relatively small, the amount of polishing required to manufacture ceramic balls of a predetermined diameter can be reduced. Therefore, in the manufacturing process of producing ceramic balls by polishing ceramic spheres, ceramic balls can be manufactured with an even smaller amount of polishing, thereby further improving polishing efficiency.
[0013] (6) According to another embodiment of the present invention, ceramic spheres for bearing balls are provided. These ceramic spheres for bearing balls consist of the ceramic spheres described above. With this configuration, bearing balls can be manufactured with a relatively small amount of polishing. That is, the polishing efficiency can be improved, and thus the manufacturing cost of bearing balls can be reduced.
[0014] (7) According to yet another embodiment of the present invention, a method for manufacturing ceramic balls is provided. This method for manufacturing ceramic balls comprises the steps of preparing the above-mentioned ceramic spheres and polishing the ceramic spheres. With this configuration, ceramic balls can be manufactured with a relatively small amount of polishing in the step of polishing the ceramic spheres. That is, the polishing efficiency can be improved, and thus the manufacturing cost of ceramic balls can be reduced.
[0015] Note that the present invention can be realized in various forms, such as a method for manufacturing ceramic green balls, a manufacturing apparatus used in the method for manufacturing ceramic green balls, ceramic balls manufactured from ceramic green balls, a method for manufacturing ceramic green balls for bearing balls, and a computer program for causing a manufacturing apparatus to execute the manufacturing of ceramic green balls.
Brief Description of the Drawings
[0016] [Figure 1] It is a schematic diagram of a bearing according to the first embodiment. [Figure 2] It is a schematic external view of a ceramic green ball for bearing balls. [Figure 3] It is a first cross-sectional SEM image of a ceramic green ball for bearing balls. [Figure 4] It is a second cross-sectional SEM image of a ceramic green ball for bearing balls. [Figure 5] It is a cross-sectional schematic diagram of a ceramic green ball for bearing balls. [Figure 6] It is a first figure for explaining an evaluation test of a ceramic green ball. [Figure 7] It is a second figure for explaining an evaluation test of a ceramic green ball.
Modes for Carrying Out the Invention
[0017] <First Embodiment> FIG. 1 is a schematic diagram of a bearing 100 according to the first embodiment. The bearing 100 includes an inner ring 110, an outer ring 120, and a plurality of bearing balls P10. The bearing balls P10 are sandwiched between the inner ring 110 and the outer ring 120 while being held by a cage (not shown). The bearing balls P10 stably hold, for example, the rotation axis of the inner ring 110 to which a rotation shaft (not shown) is fixed, with respect to the outer ring 120 fixed to a machine or the like. Note that the usage method of the bearing 100 is not limited to this.
[0018] The bearing ball P10 is a ceramic ball formed from ceramics. The bearing ball P10 is formed by polishing a ceramic sphere intended for bearing balls.
[0019] Figure 2 is a schematic diagram of the external appearance of the ceramic sphere 10 for bearing balls. Figure 3 is a first cross-sectional SEM image of the ceramic sphere for bearing balls. Figure 4 is a second cross-sectional SEM image of the ceramic sphere for bearing balls. Figure 3 is a cross-sectional SEM image including the outer surface S10 of the ceramic sphere 10. Figure 4 is a cross-sectional SEM image of the interior of the ceramic sphere 10. As shown in Figures 3 and 4, the ceramic sphere 10 contains alumina crystal grains CPa and zirconia crystal grains CPz. The ceramic sphere 10 comprises a spherical portion 11 formed of ceramics and a strip-shaped, annular strip-shaped portion 12 formed of ceramics, which is arranged along the outer circumference of the spherical portion 11. In Figure 2, the direction along the central axis Ca 10 of the ceramic sphere 10 is defined as the z-axis direction, and the x-axis is perpendicular to the z-axis, and the y-axis is perpendicular to the z-axis and x-axis. Figure 2 shows schematic diagrams of the ceramic sphere 10 as viewed from the y-axis direction and as viewed from the z-axis direction. In the ceramic sphere 10 of this embodiment, the diameter d11 of the spherical portion 11 is 0.5 mm or more. Preferably, the diameter d11 of the spherical portion 11 is 1 mm or more, and more preferably 2 mm or more. Preferably, the diameter of the spherical portion 11 is 25 mm or less. In this embodiment, the variation in the diameter d11 of the spherical portion 11 is within 2%. The ceramic sphere 10 shown in Figure 2 is manufactured by the method for manufacturing the bearing ball P10 described later, and is an unpolished (unpolished) ceramic member. Note that "polishing" here does not include barrel polishing.
[0020] Figure 5 is a schematic cross-sectional view of a ceramic ball 10 for bearing balls. The cross-section of the ceramic ball 10 shown in Figure 5 is a cross-section that passes through the center Cs10 of the ceramic ball 10, and is, for example, a cross-section perpendicular to the x-axis and the y-axis. If, within the planar region including the cross-section of the ceramic sphere 10, the square-shaped region with sides of 10 μm including the outer periphery of the ceramic sphere 10 is designated as "Region A," and the square-shaped region with sides of 10 μm inside the outer periphery of the ceramic sphere 10 is designated as "Region B," then for each of "Region A" and "Region B," if Da1 is the average particle size of the alumina crystal particles CPa contained in "Region A," and Dz1 is the average particle size of the zirconia crystal particles CPz contained in "Region B," then Da2 is the average particle size of the alumina crystal particles CPa contained in "Region B," and Dz2 is the average particle size of the zirconia crystal particles CPz contained in "Region B," then the following equations (1) and (2) are satisfied, and if Sa is the ratio of the area occupied by zirconia crystal particles CPz within the cross-section of the ceramic sphere 10 contained in "Region A," and Sb is the ratio of the area occupied by zirconia crystal particles CPz within the cross-section of the ceramic sphere 10 contained in "Region B," then the following equation (3) is satisfied. |Da1-Dz1|≦0.15μm ···(1) |Da2-Dz2|≦0.15μm ···(2) |Sa-Sb|≦0.05 ···(3)
[0021] The "region A" and "region B" defined in relation to equations (1) to (3) will be explained using Figure 5. "Region A" refers to a square-shaped region with sides of 10 μm that includes the outer peripheral portion 10a having the outer surface S10 of the ceramic sphere 10, within the planar region D10 which includes the cross-section of the ceramic sphere 10 as shown in Figure 5. In Figure 5, the part corresponding to "Region A" is the part inside the square-shaped dashed line indicated by the symbol Fa. That is, "Region A" includes at least the cross-section of the outer peripheral portion 10a of the ceramic sphere 10. With respect to "Region A" as defined in this way, the ceramic sphere 10 satisfies equation (1) if the average particle size of the alumina crystal grains CPa is Da1 and the average particle size of the zirconia crystal grains CPz is Dz1. In other words, in a ceramic sphere 10 that satisfies equation (1), the difference between the average particle size of alumina crystal particles CPa and the average particle size of zirconia crystal particles CPz at the outer periphery 10a of the ceramic sphere 10 is 0.15 μm or less, and this difference is relatively small. In this embodiment, the outer periphery 10a of the ceramic sphere 10 is also the outer periphery 11a of the spherical portion 11. In Figure 5, for the sake of explanation, the size of the area inside the dotted line of the square shape indicated by the symbol Fa, which corresponds to "region A," is shown to be larger than its actual size.
[0022] "Region B" refers to a square-shaped region with sides of 10 μm inside the outer periphery 10a of the ceramic sphere 10, within the planar region D10 which includes the cross-section of the ceramic sphere 10 as shown in Figure 5. In Figure 5, the portion corresponding to "Region B" is the portion inside the dashed-dot line of the square shape indicated by the symbol Fb. In other words, "Region B" includes only the portion of the cross-section of the ceramic sphere 10 inside the outer periphery 10a, i.e., the central part 10b of the ceramic sphere 10. In this embodiment, the central part 10b of the ceramic sphere 10 is also the central part 11b of the spherical part 11. In Figure 5, an example of the central part 10b of the ceramic sphere 10 is shown as a range where the distance from the center Cs10 is within 95% of the diameter d11 of the spherical part 11, but the range of the central part 10b of the ceramic sphere 10 is not limited to this. "Region B" is preferably the area near the center Cs10 of the ceramic sphere 10, for example, it is preferably the area within 10% of the diameter d11 of the spherical part 11 from the center Cs10 of the ceramic sphere 10. In Figure 5, for the sake of explanation, the size of the area inside the dotted line of the square shape indicated by the symbol Fb, which corresponds to "Region B," is shown to be larger than its actual size. Note that "Region A" and "Region B" set with respect to equations (1) to (3) do not have to be cross-sections passing through the center Cs10 of the ceramic sphere 10, but may be set in cross-sections passing near the center Cs10 of the ceramic sphere 10.
[0023] For the ceramic sphere 10, in the "region B" set up in this way, if the average particle size of the alumina crystal grains CPa is Da2 and the average particle size of the zirconia crystal grains CPz is Dz2, then equation (2) is satisfied. That is, in the ceramic sphere 10 that satisfies equation (2), the difference between the average particle size of the alumina crystal grains CPa and the average particle size of the zirconia crystal grains CPz at the center 10b of the ceramic sphere 10 is 0.15 μm or less, and this difference is relatively small. In other words, in the ceramic sphere 10, the difference between the average particle size of the alumina crystal grains CPa and the average particle size of the zirconia crystal grains CPz is relatively small in both the outer periphery 10a and the center 10b, and it can be said that the crystalline structure is similar.
[0024] In the ceramic sphere 10, the ratio Sa of the area occupied by zirconia crystal particles CPz in "region A" and the ratio Sb of the area occupied by zirconia crystal particles CPz in "region B" satisfy equation (3). In other words, since the ratio of zirconia crystal particles CPz per unit volume is stable throughout the ceramic sphere 10, it can be said that the ceramic sphere 10 as a whole has a homogeneous crystalline structure.
[0025] Here, we will specifically explain how to calculate the average particle size of alumina crystal particles, the average particle size of zirconia crystal particles, and the percentage of the area occupied by zirconia crystal particles in "region A" and "region B" of the ceramic sphere 10 of this embodiment. First, the ceramic sphere 10 is cut so as to pass through the center Cs10 of the ceramic sphere 10, forming a circular cross-section as shown in Figure 4. Next, the cross-section is polished to a mirror finish. The amount of polishing when polishing the cross-section to a mirror finish is arbitrary, but it is sufficient to polish to a maximum of about 50 μm. For the final finishing polish to make the cross-section a mirror finish, for example, buff polishing using a 0.5 μm diamond spray may be used. Next, the sample having the mirror-polished cross-section is subjected to a thermal etching treatment, for example, by maintaining a temperature of 1350°C for 15 minutes in air. Next, an SEM image at a magnification of 5000x was taken of the mirror-polished cross-section of the thermally etched sample using a FE-SEM (field emission scanning electron microscope). Next, taking advantage of the fact that zirconia crystal particles appear brighter than alumina crystal particles in the acquired SEM images due to differences in elemental content (see Figure 3), the average particle size of the alumina crystal particles and the average particle size of the zirconia crystal particles are calculated using image processing software with the intercept method. The proportion of the area occupied by the zirconia crystal particles is calculated using image processing software on the acquired SEM images.
[0026] In this embodiment, the ceramic sphere 10 satisfies the following equations (4) and (5) when the planar region D10 containing the cross-section of the ceramic sphere 10 as shown in Figure 5 is divided into "region A" and "region B", where Sa is the proportion of the area occupied by zirconia crystal particles CPz in the cross-section of the ceramic sphere 10 contained in "region A", and Sb is the proportion of the area occupied by zirconia crystal particles CPz in the cross-section of the ceramic sphere contained in region B. 0.08 ≤ Sa ≤ 0.30 ···(4) 0.08 ≤ Sb ≤ 0.30 ···(5) Equation (4) shows that in "Region A," there are more alumina crystal particles CPa than zirconia crystal particles CPz. Equation (5) shows that in "Region B," there are more alumina crystal particles CPa than zirconia crystal particles CPz. In other words, the ceramic sphere 10 that satisfies equations (4) and (5) contains more alumina crystal particles CPa than zirconia crystal particles CPz overall. As a result, the zirconia crystal particles CPz are less likely to transform from tetragonal zirconia to monoclinic zirconia due to the constraint of alumina crystal particles CPa, thus suppressing the decrease in the mechanical properties of the ceramic balls obtained by polishing the ceramic sphere 10. "Excellent mechanical properties" here refers to, for example, a relatively high Vickers hardness.
[0027] In this embodiment, the ceramic sphere 10 satisfies the following equations (6) to (8) when the planar region D10 containing the cross-section of the ceramic sphere 10 as shown in Figure 5 is divided into "region A" and "region B", with Va being the Vickers hardness of the cross-section of the ceramic sphere 10 included in "region A" and Vb being the Vickers hardness of the cross-section of the ceramic sphere 10 included in "region B". Va ≥ 1960 kgf / mm 2 ...(6) Vb ≥ 1960 kgf / mm 2 ...(7) |Va-Vb| ≤ 120 kgf / mm 2 ...(8) Equations (6) and (7) show that the Vickers hardness is relatively high in "region A" and "region B," respectively. Equation (8) shows that there is no significant difference between the Vickers hardness in "region A" and the Vickers hardness in "region B." In other words, the ceramic sphere 10 that satisfies equations (5) to (8) has a relatively high Vickers hardness overall.
[0028] Next, the manufacturing method for the ceramic balls, which are bearing balls P10, will be described. In the manufacturing method for ceramic balls, first, ceramic spheres 10 are manufactured. In the manufacturing of ceramic spheres 10, alumina powder (Al2O3, average particle size: 0.5 μm) and yttria-stabilized zirconia powder (3YSZ, average particle size: 0.5 μm) are used as raw material powders. In the manufacturing of ceramic spheres 10, first, the alumina powder and yttria-stabilized zirconia powder are weighed out so that the content of alumina in the ceramic spheres 10 is 80% by weight and zirconia is 20% by weight (weighing step).
[0029] The weighed raw material powder is placed in a resin pot along with alumina spheres, pure water is added as a solvent, and ball milling is performed at a rotation speed of 60 revolutions per minute for 72 hours to pulverize and mix the raw material powder, thereby producing a mixed slurry (slurry production process). In the manufacturing method of the ceramic spheres 10 of this embodiment, a polycarboxylic acid-based dispersant is added when producing the mixed slurry. Among polycarboxylic acid-based dispersants, ammonium polycarboxylic acid salt is suitable for hydrophilic oxides, and can appropriately disperse the alumina powder and yttria-stabilized zirconia powder while reducing the amount of water in the mixed slurry.
[0030] A binder is added to the prepared mixed slurry, and after mixing for a further 30 minutes, the mixed slurry is dried by spray drying to produce a mixed powder (powder production step). In the method for producing the ceramic spheres 10 of this embodiment, PVA (polyvinyl alcohol) or PVB (polyvinyl acetal) is used as the binder when producing the mixed powder. As a result, the mixed slurry becomes an aggregate-type slurry with relatively low viscosity.
[0031] The ceramic sphere 10 of this embodiment is an alumina-zirconia composite material that is densified by solid-phase sintering, and therefore does not produce an altered phase, unlike ceramic spheres formed from, for example, silicon nitride-based materials. Furthermore, in the case of ceramic spheres formed from a single-composition material, the growth of crystal grains near the surface is promoted, so it is necessary to polish the areas where grain growth has occurred. However, in the case of ceramic spheres formed from composite materials, the crystal grains of each material suppress grain growth, resulting in a homogeneous crystalline structure overall. This reduces the amount of polishing required. In addition, if the mixing slurry is a relatively low-viscosity, cohesive slurry, the mixed powder created by spray drying becomes solid, making it difficult for relatively large pores to form during pressing using a mold, as described later. This suppresses grain growth, which tends to progress easily during firing due to the lack of a restraining force in the direction toward the inside of the pores when pores are present. Moreover, using a relatively low-viscosity, cohesive slurry makes the spray drying process easier.
[0032] In the manufacturing method of the ceramic spheres 10 of this embodiment, plasticizers such as PEG (polyethylene glycol) and glycerin are used when preparing the mixed powder. This makes the mixed powder more easily crushed during powder press molding using a mold. In this embodiment of the manufacturing method of the ceramic spheres 10, the plasticizer is added to the mixed slurry before the binder is added. This makes it easier for the plasticity effect to be exhibited.
[0033] Next, the prepared mixed powder is filled into a mold, and a preliminary molded body is produced by powder press molding using a uniaxial press (press pressure: 30 MPa) (preliminary molding process). Next, the preliminary molded body is placed in a special sheet bag and subjected to main molding by CIP (cold isostatic pressing, press pressure: 150 MPa) to produce a molded body (main molding process). The produced molded body is degreased by heat treatment in air at a maximum temperature of 800°C (degreasing process).
[0034] Next, the degreased molded body is fired in the air (firing temperature 1450°C, firing time: 2 hours), followed by hot isostatic pressing (HIP, processing temperature 1400°C, processing pressure 150 MPa, argon atmosphere, processing time: 2 hours) (firing process). This produces the ceramic sphere 10.
[0035] In the method for manufacturing ceramic balls, the surface of the ceramic sphere 10 prepared by the manufacturing method described above is polished to remove the strip-shaped portion 12 while polishing the outer surface of the spherical portion 11 (polishing step). This produces a bearing ball P10 as a ceramic ball.
[0036] Next, we will describe the evaluation test of ceramic spheres. In this evaluation test, samples of ceramic spheres made with different raw materials and manufacturing methods were prepared, and the influence of the raw materials and manufacturing method on the physical properties of the ceramic spheres was evaluated.
[0037] Figure 6 is the first diagram illustrating the evaluation test of ceramic spheres. Figure 6 is a diagram illustrating the items related to the manufacturing method for each of the 11 types of samples used in this evaluation test. Each of the 11 types of samples used in this evaluation test was manufactured using a method similar to the manufacturing method of the ceramic sphere 10 of this embodiment.
[0038] The "raw material (wt%)" shown in Figure 6 indicates the weight percentage of the raw materials used in the preparation of each of the 11 samples. Samples 1 to 5 and samples 9 to 11 use alumina powder (Al2O3, average particle size: 0.5 μm) and yttria-stabilized zirconia powder (3YSZ, average particle size: 0.5 μm), and contain both aluminum oxide sintered bodies and zirconium oxide sintered bodies. Sample 6 uses alumina powder (Al2O3, average particle size: 0.5 μm), silicon nitride powder (Si3N4, average particle size: 0.9 μm), and yttria powder (Y2O3, average particle size: 1.0 μm), and contains a silicon nitride sintered body. Sample 7 uses alumina powder (Al2O3, average particle size: 0.5 μm) and magnesia powder (MgO, average particle size: 0.5 μm), and contains an aluminum oxide sintered body. Sample 8 uses yttria-stabilized zirconia powder (3YSZ, average particle size: 0.5 μm) and contains a zirconium oxide sintered body. Thus, samples 6 to 8 differ from samples 1 to 5 and samples 9 to 11 in the type of sintered body they contain, and are treated as comparative examples in this evaluation test.
[0039] Figure 6 shows the "additives" for each of the 11 samples, indicating the type of "binder" and "plasticizer" added during preparation, as well as the "timing of addition" of the binder and plasticizer during preparation. For the "binder," PVB (polyvinyl acetal) or wax-based materials were used. For the "plasticizer," PEG (polyethylene glycol) or glycerin was used, except for sample 10, which had no plasticizer added. Regarding the "timing of addition," for samples 1 to 9, the plasticizer was added "before" the binder, while for sample 11, the plasticizer was added "after" the binder. Sample 10, which had no plasticizer added, is indicated with "-".
[0040] Figure 7 is the second diagram illustrating the evaluation test of ceramic spheres. Figure 7 shows the density (g / cm³) of each of the 11 samples produced under the manufacturing conditions shown in Figure 6.3 )」, "Alumina crystal grain size (μm)", "Zirconia crystal grain size (μm)", "Zirconia area ratio (%)", and "Vickers hardness (kgf / mm 2 )」 are shown. The "Density (g / cm 3 )」 shown in FIG. 7 indicates the density of each of the 11 samples.
[0041] The "Alumina crystal grain size (μm)" shown in FIG. 7 indicates the average grain size of the alumina crystal particles contained in each of the 11 samples. Specifically, it shows the average grain size of the alumina crystal particles contained in the portion corresponding to "Region A" set for the average grain size of the alumina crystal particles contained in the ceramic green sphere 10 of the present embodiment, the average grain size of the alumina crystal particles contained in the portion corresponding to "Region B", the "difference" between the average grain size of the alumina crystal particles contained in the portion corresponding to "Region A" and the average grain size of the alumina crystal particles contained in the portion corresponding to "Region B". The calculation of the "Alumina crystal grain size (μm)" shown in FIG. 7 was performed by image processing on the SEM image at a magnification of 5000 times taken using FE-SEM (field emission scanning electron microscope) for the samples, in the same manner as the method for calculating the average grain size of the alumina crystal particles in the ceramic green sphere 10 of the present embodiment. Note that since Sample 6 containing a silicon nitride sintered body and Sample 8 containing a zirconia sintered body do not contain alumina crystal particles and thus the average grain size of the alumina crystal particles cannot be calculated, it is indicated as "-".
[0042] The "Zirconia Crystal Grain Size (μm)" shown in Figure 7 represents the average particle size of zirconia crystal particles contained in each of the 11 types of samples. Specifically, it shows the average particle size of zirconia crystal particles contained in the portion corresponding to "Region A," the average particle size of zirconia crystal particles contained in the portion corresponding to "Region B," and the "difference" between the average particle size of zirconia crystal particles contained in the portion corresponding to "Region A" and the average particle size of zirconia crystal particles contained in the portion corresponding to "Region B," which were set for the average particle size of zirconia crystal particles contained in the ceramic sphere 10 of this embodiment. The calculation of the "Zirconia Crystal Grain Size (μm)" shown in Figure 7 was performed by image processing of SEM images at a magnification of 5000x, captured using a FE-SEM (Field Emission Scanning Electron Microscope), for the samples, similar to the method for calculating the average particle size of zirconia crystal particles in the ceramic sphere 10 of this embodiment. Note that sample 6, which contains a silicon nitride sintered body, and sample 7, which contains an aluminum oxide sintered body, do not contain zirconia crystal particles, and therefore the average particle size of zirconia crystal particles cannot be calculated, and are therefore indicated as "-".
[0043] The "Zirconia Area Ratio (%)" shown in Figure 7 represents the zirconia area ratio of "Region A," the zirconia area ratio of "Region B," and the "difference" between the zirconia area ratio of "Region A" and the zirconia area ratio of "Region B" for each of the 11 types of samples. The calculation of the "Zirconia Area Ratio (%)" shown in Figure 7 was performed by image processing of SEM images at a magnification of 5000x, captured using a FE-SEM (Field Emission Scanning Electron Microscope), for each sample, similar to the method for calculating the percentage of the area occupied by zirconia crystal particles in the ceramic sphere 10 of this embodiment. Note that sample 6, which contains a silicon nitride sintered body, sample 7, which contains an aluminum oxide sintered body, and sample 8, which does not contain an alumina sintered body but contains a zirconium oxide sintered body, are indicated with "-".
[0044] Figure 7 shows the Vickers hardness (kgf / mm²). 2The table shows the Vickers hardness in "Region A," the Vickers hardness in "Region B," and the difference between the Vickers hardness in "Region A" and the Vickers hardness in "Region B" for each of the 11 types of samples. Here, we will explain the method for measuring Vickers hardness. In this evaluation test, Vickers hardness was measured using a Vickers hardness measuring device on the mirror-polished cross-section of the sample, which is prepared in the calculation of "alumina grain size (μm)," etc. As the measuring device used for measuring Vickers hardness, we used a Shimadzu Corporation dynamic ultramicrohardness tester capable of applying loads from 100mN to 1000mN. For the measurement of Vickers hardness, a rectangular area with sides of 10 μm was set for each of the cross-sections of the parts corresponding to "Region A" and "Region B" that were defined for the average particle size of the alumina crystal grains in the ceramic sphere 10 of this embodiment. A load of 200 mN was applied to five locations within the set area, and the average value was calculated. Note that for sample 6, which contains a silicon nitride sintered body, a volatile layer was formed in the part corresponding to "Region A," making it impossible to measure the Vickers hardness in "Region A," so the value for "Region A" is "-" and the "difference" is also "-".
[0045] As shown in Figure 7, the "alumina crystal grain size (μm)" indicates that in samples 1 to 5, the "difference" in the average particle size of alumina crystal particles between "region A" and "region B" was 0.15 μm or less, confirming homogeneity in terms of the average particle size of the alumina crystal particles. Similarly, in samples 1 to 5, the "difference" in the average particle size of zirconia crystal particles between "region A" and "region B" was also 0.15 μm or less, confirming homogeneity in terms of the average particle size of the zirconia crystal particles.
[0046] As shown in Figure 7, "Zirconia Area Ratio (%)", it was confirmed that in samples 1 to 5, the proportion of the area occupied by zirconia crystal grains in "Region A" and "Region B" was 5% or less. This confirmed that samples 1 to 5 as a whole have a homogeneous crystalline structure.
[0047] Figure 7 shows "Vickers hardness (kgf / mm²)". 2 As shown in the above, samples 1 to 5 showed a reading of 1960 kgf / mm² in "Region A". 2 It has a Vickers hardness of 1960 kgf / mm² in "Region B". 2 It has the above Vickers hardness. Also, the difference between the Vickers hardness of "Area A" and the Vickers hardness of "Area B" is 120 kgf / mm². 2 The following is the result: Samples 1 through 5, overall, can be said to have relatively high Vickers hardness.
[0048] Thus, Samples 1 to 5, as a whole, possess a homogeneous crystalline structure with relatively high Vickers hardness. As a result, the ceramic spheres of Samples 1 to 5 can be easily manufactured as relatively hard ceramic balls with a small amount of polishing, thereby improving polishing efficiency.
[0049] Sample 6 contains a silicon nitride sintered body, and a volatile layer was formed in the area corresponding to "region A". It was confirmed that it has different physical properties from Samples 1 to 5, which contain both aluminum oxide sintered bodies and zirconium oxide sintered bodies. Sample 7 contains an aluminum oxide sintered body but does not contain a zirconia sintered body. As a result, in Sample 7, alumina crystal grains tend to grow more easily in the area corresponding to "region A", and the average grain size of the alumina crystal grains contained in the area corresponding to "region A" tends to be larger. Sample 8 contains a zirconia sintered body but does not contain an alumina sintered body. As a result, zirconia crystal grains tend to grow more easily in the area corresponding to "region A", and the average grain size of the zirconia crystal grains contained in the area corresponding to "region A" tends to be larger.
[0050] Sample 9 uses a wax-based material as a binder during the fabrication of ceramic spheres. As a result, the mixing slurry becomes a dispersion-based slurry, and the mixed powder has a hollow shape. When the mixed powder has a hollow shape, grain growth is more likely to occur in the hollow portion of "Region A" that remains uncrushed during the preliminary molding process. Therefore, it was confirmed that the average grain size of the crystals contained in "Region A" becomes larger than the average grain size of the crystals contained in "Region B".
[0051] In Sample 10, it is believed that the crushability of the mixed powder deteriorated because no plasticizer was added during the fabrication of the ceramic spheres. As a result, grain growth became easier in the hollow portion of "Region A" that remained uncrushed during the preliminary molding process, and it was confirmed that the average grain size of the crystals contained in "Region A" was larger than the average grain size of the crystals contained in "Region B".
[0052] In Sample 11, the plasticizer was added after the binder during the fabrication of the ceramic spheres. Therefore, it is thought that the plasticizer interacted with the binder before it could spread throughout the entire mixed slurry, preventing it from exhibiting sufficient plasticity. As a result, grain growth became easier in the hollow portion of "Region A" that remained intact during the preliminary molding process, and it was confirmed that the average grain size of the crystals contained in "Region A" was larger than the average grain size of the crystals contained in "Region B".
[0053] As described above, the ceramic sphere 10 of this embodiment satisfies equations (1) and (2), and the difference between the average particle size of alumina crystal particles CPa and the average particle size of zirconia crystal particles CPz is relatively small in both the outer periphery 10a and the central part 10b, which is the part inside the outer periphery 10a. Furthermore, in the cross-section of the ceramic sphere 10 that satisfies equation (3), there is no significant difference in the area occupied by zirconia crystal particles CPz between the outer periphery 10a and the central part 10b. In other words, since the ceramic sphere 10 as a whole has a homogeneous crystalline structure, in the manufacturing process of producing bearing balls P10 by polishing the ceramic sphere 10, ceramic balls can be produced with a small amount of polishing. Therefore, polishing efficiency can be improved.
[0054] Furthermore, according to the ceramic ball 10 of this embodiment, ceramic balls can be manufactured with a small amount of polishing, thus reducing the process load when manufacturing bearing balls P10. In addition, by reducing the process load, the amount of energy required when manufacturing bearing balls P10 can be reduced.
[0055] Furthermore, according to the ceramic sphere 10 of this embodiment, equations (4) and (5) are satisfied, so in both "region A" and "region B", alumina crystal particles CPa are present in greater quantities than zirconia crystal particles CPz. As a result, the zirconia crystal particles CPz are less likely to transform from tetragonal zirconia to monoclinic zirconia due to the constraint of alumina crystal particles CPa, thus suppressing the deterioration of the mechanical properties of the ceramic ball obtained by polishing the ceramic sphere 10.
[0056] Furthermore, according to the ceramic sphere 10 of this embodiment, equations (6) to (8) are satisfied, so the Vickers hardness of "region A" and the Vickers hardness of "region B" are both relatively large values and there is no significant difference between them. In the ceramic sphere 10, the Vickers hardness of the outer circumference 10a and the central part 10b are both relatively large and almost the same. As a result, ceramic balls with relatively high hardness can be manufactured with a small amount of polishing.
[0057] Furthermore, according to the ceramic sphere 10 of this embodiment, the ceramic sphere 10 has a spherical portion 11 and a strip-shaped portion 12 arranged along the outer circumference of the spherical portion 11. As a result, a ceramic ball can be manufactured by polishing the strip-shaped portion 12 and polishing the surface of the spherical portion 11 to a relatively thin degree.
[0058] Furthermore, according to the ceramic sphere 10 of this embodiment, the variation in the diameter d11 of the spherical portion 11 is within 2%. This makes it possible to reduce the amount of polishing required to manufacture ceramic balls of a preset diameter. Therefore, in the manufacturing process of producing bearing balls P10 by polishing the ceramic sphere 10, ceramic balls can be manufactured with an even smaller amount of polishing, thereby further improving polishing efficiency.
[0059] Furthermore, the ceramic ball 10 for bearing balls of this embodiment allows for the manufacture of bearing balls P10 with a relatively small amount of polishing. In other words, since the polishing efficiency can be improved, the manufacturing cost of bearing balls P10 can be reduced.
[0060] Furthermore, according to the ceramic ball manufacturing method of this embodiment, in the process of polishing the ceramic sphere 10, ceramic balls that become bearing balls P10 can be manufactured with a relatively small amount of polishing. In other words, since the polishing efficiency can be improved, the manufacturing cost of ceramic balls can be reduced.
[0061] <Modified form of this embodiment> The present invention is not limited to the embodiments described above, and can be implemented in various forms without departing from its spirit, for example, the following modifications are also possible.
[0062] [Example 1] In the above-described embodiment, the ceramic sphere 10 is made into a bearing ball P10 by polishing. The technical field to which ceramic balls obtained by polishing ceramic spheres are applied is not limited to this.
[0063] [Differentiation 2] In the above-described embodiment, the ceramic sphere 10 was assumed to satisfy equations (4) and (5) in the comparison of the area ratio of zirconia crystal particles and alumina crystal particles in cross-section. The ceramic sphere does not have to satisfy equations (4) and (5), but by satisfying equations (4) and (5), the zirconia crystal particles are less likely to transform from tetragonal zirconia to monoclinic zirconia, thereby suppressing the deterioration of the mechanical properties of the ceramic ball obtained by polishing the ceramic sphere.
[0064] [Difference 3] In the above embodiment, the ceramic sphere 10 was assumed to satisfy equations (6) to (8) for the Vickers hardness of its cross-section. The ceramic sphere does not have to satisfy any of equations (6) to (8), but by satisfying equations (6) to (8), it is possible to manufacture ceramic balls with relatively high hardness with a small amount of polishing.
[0065] [Differentiation Example 4] In the above-described embodiment, the ceramic sphere 10 has a spherical portion 11 and a strip-shaped portion 12 arranged along the outer circumference of the spherical portion 11. The shape of the ceramic sphere is not limited to this.
[0066] The embodiments of this specification have been described above based on the embodiments and modifications described above. The embodiments described above are for the purpose of facilitating understanding of this specification and do not limit it. This specification may be modified and improved without departing from its spirit and the scope of the claims, and equivalents thereof are included in this specification. Furthermore, any technical features that are not described as essential in this specification may be deleted as appropriate.
[0067] <Application Example 1> These are ceramic spheres, It contains alumina crystal particles and zirconia crystal particles. If, within the planar region including the cross-section of the ceramic sphere, a square-shaped region with sides of 10 μm including the outer periphery of the ceramic sphere is designated as region A, and a square-shaped region with sides of 10 μm inside the outer periphery of the ceramic sphere is designated as region B, For each of the aforementioned regions A and B, Let Da1 be the average particle size of the alumina crystal particles contained in region A, and Dz1 be the average particle size of the zirconia crystal particles. If the average particle size of the alumina crystal particles contained in region B is Da2 and the average particle size of the zirconia crystal particles is Dz2, The following equations (1) and (2) are satisfied, If Sa is the proportion of the area occupied by zirconia crystal particles in the cross-section of the ceramic spheres contained in region A, and Sb is the proportion of the area occupied by zirconia crystal particles in the cross-section of the ceramic spheres contained in region B, then the following equation (3) is satisfied, characterized in that Ceramic spheres. |Da1-Dz1|≦0.15μm ···(1) |Da2-Dz2|≦0.15μm ···(2) |Sa-Sb|≦0.05 ···(3) <Application Example 2> A ceramic sphere as described in Application Example 1, The aforementioned ratio Sa satisfies the following equation (4): The aforementioned ratio Sb is characterized by satisfying the following formula (5): Ceramic spheres. 0.08 ≤ Sa ≤ 0.3 ···(4) 0.08 ≤ Sb ≤ 0.3 ···(5) <Application Example 3> A ceramic sphere as described in Application Example 1 or Application Example 2, Let Va be the Vickers hardness of the cross-section of the ceramic sphere contained in region A, and Vb be the Vickers hardness of the cross-section of the ceramic sphere contained in region B. The following equations (6) to (8) are satisfied, Ceramic spheres. Va ≥ 1960 kgf / mm 2 ...(6) Vb ≥ 1960 kgf / mm 2 ...(7) |Va-Vb| ≤ 120 kgf / mm 2 ...(8) <Application Example 4> A ceramic sphere as described in any one of Application Examples 1 to 3, A spherical part formed from ceramics, The invention is characterized by comprising a strip-shaped, annular strip-shaped portion, which is arranged along the outer circumference of the spherical portion and is formed of ceramics, Ceramic spheres. <Application Example 5> The ceramic sphere described in Application Example 4, The variation in the diameter of the spherical portion is characterized by being within 2%. Ceramic spheres. <Application Example 6> These are ceramic ball bearings, The invention is characterized by comprising ceramic spheres as described in any one of the examples from Application Example 1 to Application Example 5. Ceramic ball bearings. <Application Example 7> A method for manufacturing ceramic balls, The process involves preparing a ceramic sphere as described in any one of the examples from Application Example 1 to Application Example 6, The invention is characterized by comprising a polishing step for polishing the aforementioned ceramic spheres. A method for manufacturing ceramic balls. [Explanation of Symbols]
[0068] 10…Ceramic spheres 10a...Outer periphery 10b…Center 11...Spherical part 12...band-shaped area 100...bearings 110...Inner circle 120... Outer ring CPa... Alumina crystal grains CPz... Zirconia crystal grains D10…Plane area P10...Bearing ball d11…Diameter
Claims
1. These are ceramic spheres, It contains alumina crystal particles and zirconia crystal particles. If, within the planar region including the cross-section of the ceramic sphere, a square-shaped region with sides of 10 μm including the outer periphery of the ceramic sphere is designated as region A, and a square-shaped region with sides of 10 μm inside the outer periphery of the ceramic sphere is designated as region B, For each of the aforementioned regions A and B, In the region A, the average particle size of the alumina crystal particles is Da1, and the average particle size of the zirconia crystal particles is Dz1. If the average particle size of the alumina crystal particles contained in region B is Da2 and the average particle size of the zirconia crystal particles is Dz2, The following equations (1) and (2) are satisfied, If Sa is the proportion of the area occupied by zirconia crystal particles in the cross-section of the ceramic spheres contained in region A, and Sb is the proportion of the area occupied by zirconia crystal particles in the cross-section of the ceramic spheres contained in region B, then the following equation (3) is satisfied, characterized in that Ceramic spheres. |Da1-Dz1|≦0.15μm...(1) |Da2-Dz2|≦0.15μm...(2) |Sa-Sb|≦0.05...(3)
2. A ceramic sphere according to claim 1, The aforementioned ratio Sa satisfies the following equation (4): The aforementioned ratio Sb is characterized by satisfying the following formula (5): Ceramic spheres. 0.08 ≤ Sa ≤ 0.3 ... (4) 0.08 ≤ Sb ≤ 0.3 ... (5)
3. A ceramic sphere according to claim 1 or claim 2, If Va is the Vickers hardness of the cross-section of the ceramic sphere contained in region A, and Vb is the Vickers hardness of the cross-section of the ceramic sphere contained in region B, then the following equations (6) to (8) are satisfied, Ceramic spheres. Va≧1960kgf / mm 2 ・・・(6) Vb≧1960kgf / mm 2 ・・・(7) |Va-Vb|≦120kgf / mm 2 ・・・(8)
4. A ceramic sphere according to claim 1 or claim 2, A spherical part formed from ceramics, The invention is characterized by comprising a strip-shaped, annular strip-shaped portion, which is arranged along the outer circumference of the spherical portion and is formed of ceramics, Ceramic spheres.
5. A ceramic sphere according to claim 4, The variation in the diameter of the spherical portion is characterized by being within 2%. Ceramic spheres.
6. These are ceramic ball bearings, A ceramic sphere characterized by being made up of the ceramic sphere described in claim 1 or claim 2. Ceramic ball bearings.
7. A method for manufacturing ceramic balls, A step of preparing a ceramic sphere according to claim 1 or claim 2, The invention is characterized by comprising a polishing step for polishing the aforementioned ceramic spheres. A method for manufacturing ceramic balls.