Ceramic spheres, ceramic spheres for bearing balls, and method for manufacturing ceramic balls

Abstract

This technology provides a way to improve polishing efficiency while suppressing the occurrence of defects during polishing of ceramic spheres. [Solution] The ceramic sphere comprises a spherical portion formed of ceramics and a strip-shaped, annular strip-shaped portion formed of ceramics, which is arranged along the outer circumference of the spherical portion. If Ra1 is the arithmetic mean roughness of the outer surface of the strip-shaped portion and Ra2 is the arithmetic mean roughness of the outer surface of the spherical portion, then Ra1 / Ra2 < 0.7 is satisfied.

Description

Technical Field

[0001] The present invention relates to ceramic blank balls, ceramic blank balls for bearing balls, and a method for manufacturing ceramic balls.

Background Art

[0002] Conventionally, ceramic blank balls that become ceramic balls by polishing have been known (for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, even with the prior art such as Patent Document 1, there is still room for improvement in the technology for suppressing the occurrence of defects during polishing and improving the polishing efficiency in ceramic blank balls.

[0005] The present invention has been made to solve the above-described problems, and an object thereof is to provide a technology for suppressing the occurrence of defects during polishing and improving the polishing efficiency in ceramic blank balls.

Means for Solving the Problems

[0006] The present invention has been made to solve at least a part of the above-described 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 comprises a spherical portion formed of ceramics and a strip-shaped, annular strip-shaped portion formed of ceramics, which is arranged along the outer circumference of the spherical portion, and where Ra1 is the arithmetic mean roughness of the outer surface of the strip-shaped portion and Ra2 is the arithmetic mean roughness of the outer surface of the spherical portion, the equation (1) is satisfied. Ra1 / Ra2 < 0.7 ···(1)

[0008] In this configuration, in a ceramic sphere comprising a spherical portion and a strip-shaped portion arranged along the outer circumference of the spherical portion, the arithmetic mean roughness of the outer surface of the strip-shaped portion is less than 0.7 times the arithmetic mean roughness of the outer surface of the spherical portion. As a result, when polishing the ceramic sphere, stress is less likely to concentrate on the strip-shaped portion being polished, thus reducing the likelihood of chipping. In addition, polishing the spherical portion becomes relatively easier. These factors allow for improved polishing efficiency while suppressing the occurrence of polishing defects such as chipping during the polishing process of ceramic spheres.

[0009] (2) In the ceramic sphere of the above form, the diameter of the spherical portion may be 0.5 mm or more. With this configuration, since the diameter of the spherical portion of the ceramic sphere is 0.5 mm or more, it can be formed by press molding. By adjusting the surface roughness of the mold used for press molding, the arithmetic mean roughness of the outer surface of the strip portion can be made smaller than 0.7 times the arithmetic mean roughness of the outer surface of the spherical portion. Therefore, in polishing the ceramic sphere, the occurrence of defects can be suppressed while improving polishing efficiency.

[0010] (3) In the ceramic sphere of the above form, the spherical portion and the strip portion may each contain at least one of the following: an aluminum oxide sintered body, a silicon nitride sintered body, a silicon carbide sintered body, a boron nitride sintered body, and a zirconium oxide sintered body. With this configuration, the spherical portion and the strip portion each contain at least one of the following: an aluminum oxide sintered body, a silicon nitride sintered body, a silicon carbide sintered body, a boron nitride sintered body, and a zirconium oxide sintered body. As a result, the ceramic ball obtained by polishing the ceramic sphere has relatively high hardness and can be used in a wide range of technical fields.

[0011] (4) According to another embodiment of the present invention, a ceramic sphere for bearing balls is provided. This ceramic sphere for bearing balls consists of the ceramic sphere described above. With this configuration, the arithmetic mean roughness of the outer surface of the strip portion of the ceramic sphere for bearing balls is less than 0.7 times the arithmetic mean roughness of the outer surface of the spherical portion, thereby suppressing the occurrence of defects in the polishing process and improving polishing efficiency. This makes it possible to reduce the manufacturing cost of bearing balls.

[0012] (5) 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, it is possible to suppress the occurrence of defects and improve polishing efficiency in the step of polishing the ceramic spheres. This makes it possible to reduce the manufacturing cost of ceramic balls.

[0013] Furthermore, the present invention can be realized in various forms, including a method for manufacturing ceramic spheres, a manufacturing apparatus used in the method for manufacturing ceramic spheres, ceramic balls manufactured from ceramic spheres, a method for manufacturing ceramic spheres for bearing balls, and a computer program that causes the manufacturing apparatus to manufacture ceramic spheres. [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic diagram of the bearing according to the first embodiment. [Figure 2] This is a schematic diagram of the external appearance of ceramic ball bearings. [Figure 3] This is the first diagram illustrating the evaluation test of ceramic spheres. [Figure 4] This is the second diagram illustrating the evaluation test of ceramic spheres. [Modes for carrying out the invention]

[0015] <First Embodiment> Figure 1 is a schematic diagram of a bearing 100 according to a first embodiment. The bearing 100 comprises an inner ring 110, an outer ring 120, and a plurality of bearing balls P10. The bearing balls P10 are held by a cage (not shown) and sandwiched between the inner ring 110 and the outer ring 120. The bearing balls P10 stably hold the rotation axis of the inner ring 110, to which a rotating shaft (not shown) is fixed, with respect to the outer ring 120, which is fixed to a machine or the like. However, the method of using the bearing 100 is not limited to this.

[0016] 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.

[0017] Figure 2 is a schematic diagram of the external appearance of a ceramic sphere 10 for bearing balls. The ceramic sphere 10 comprises a spherical portion 11 formed of ceramics and a strip-shaped, annular strip 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 C10 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 external appearance of the ceramic sphere 10 as seen from the y-axis direction and schematic diagrams of the external appearance of the ceramic sphere 10 as seen from the z-axis direction. The ceramic sphere 10 shown in Figure 2 is manufactured in the method for manufacturing bearing balls P10 described later, and is a ceramic member in an unpolished (unpolished) state on its outer surface. Note that "polishing" here does not include barrel polishing.

[0018] In the ceramic sphere 10 of this embodiment, the spherical portion 11 and the strip portion 12 each contain at least one of the following: an aluminum oxide sintered body, a silicon nitride sintered body, a silicon carbide sintered body, a boron nitride sintered body, and a zirconium oxide sintered body. In this embodiment, both the spherical portion 11 and the strip portion 12 contain both an aluminum oxide sintered body and a zirconium oxide sintered body. In the ceramic sphere 10 of this embodiment, the diameter d11 of the spherical portion 11 is 0.5 mm or more. The diameter d11 of the spherical portion 11 is preferably 1 mm or more, and more preferably 2 mm or more. The diameter of the spherical portion 11 is preferably 25 mm or less.

[0019] In this embodiment, the ceramic sphere 10 satisfies the following equation (1) if the arithmetic mean roughness of the outer surface of the strip portion 12 is Ra1 and the arithmetic mean roughness of the outer surface of the spherical portion 11 is Ra2. Ra1 / Ra2 < 0.7 ···(1) The arithmetic mean roughness of the outer surfaces of the spherical portion 11 and the strip portion 12 refers to the "arithmetic mean roughness" as defined in JIS B 0601:2013 (ISO 4287:1997, Amd.1:2009) "Geometric product specifications (GPS) - Surface texture: contour curve method - Terms, definitions and surface texture parameters".

[0020] Here, a method for measuring the arithmetic mean roughness Ra1 of the outer surface of the belt portion 12 and the arithmetic mean roughness Ra2 of the outer surface of the spherical portion 11 will be described. For measuring the arithmetic mean roughness of each of the outer surfaces of the belt portion 12 and the spherical portion 11, a contact-type measuring instrument, for example, the SURFCOM series manufactured by Tokyo Seimitsu Co., Ltd., is used.

[0021] The arithmetic mean roughness Ra1 of the outer surface of the belt portion 12 is the arithmetic mean roughness on the belt-shaped outer surface S12 that is located most outward in the ceramic green sphere 10 among the outer surfaces of the belt portion 12. In FIG. 2, the position where the arithmetic mean roughness Ra1 of the outer surface S12 of the belt portion 12 is measured is indicated by a white arrow M12. The direction indicated by the white arrow M12 shown in FIG. 2 indicates the measurement direction of the arithmetic mean roughness Ra1.

[0022] The arithmetic mean roughness Ra2 of the outer surface of the spherical portion 11 is the arithmetic mean roughness on the outer surface S11 including the apex T10 of the ceramic green sphere 10 where the central axis C10 of the ceramic green sphere 10 intersects the outer surface S11 of the spherical portion 11 among the outer surfaces of the spherical portion 11. In FIG. 2, the position where the arithmetic mean roughness Ra2 of the outer surface S11 of the spherical portion 11 is measured is indicated by a white arrow M11. The direction indicated by the white arrow M11 shown in FIG. 2 indicates the measurement direction of the arithmetic mean roughness Ra2.

[0023] Next, a method for manufacturing a ceramic ball that is the bearing ball P10 will be described. In the method for manufacturing a ceramic ball, first, a ceramic green sphere 10 is manufactured. In manufacturing the ceramic green sphere 10, as raw material powders, alumina powder (Al2O3, average particle size: 0.5 μm) and yttria-stabilized zirconia powder (3YSZ, average particle size: 0.5 μm) are used. In manufacturing the ceramic green sphere 10, first, each of the alumina powder and the yttria-stabilized zirconia powder is weighed so that the content in the ceramic green sphere 10 is 80% by weight of alumina and 20% by weight of zirconia (weighing step).

[0024] 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.

[0025] 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. This forms an aggregated slurry with relatively low viscosity, making spray drying easier and resulting in a relatively rough surface for the produced mixed powder. When the surface of the mixed powder is relatively rough, the mixed powder becomes easier to crush during powder press molding using a mold, as described later, and the surface of the mold is more easily transferred.

[0026] 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.

[0027] 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).

[0028] In the manufacturing of the ceramic sphere 10 of this embodiment, the surface roughness of the portion forming the strip-shaped portion 12 of the ceramic sphere 10 in the mold used for preliminary molding is less than 0.7 times the surface roughness of the portion forming the spherical portion 11 of the ceramic sphere 10. As a result, during preliminary molding, the surface of the mold is transferred, making it possible to make the arithmetic mean roughness Ra1 of the outer surface of the strip-shaped portion 12 less than 0.7 times the arithmetic mean roughness Ra2 of the outer surface of the spherical portion 11. The mold used for preliminary molding is coated with a ceramic coating such as titanium nitride (TiN) on its surface to suppress wear caused by powder press molding.

[0029] 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.

[0030] 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 S11 of the spherical portion 11. This produces a bearing ball P10 as a ceramic ball.

[0031] Next, we will describe the evaluation test of ceramic spheres. In this evaluation test, samples of ceramic spheres made from different raw materials and using different manufacturing methods were prepared, and the influence of the relationship between the arithmetic mean roughness of the outer surface of the spherical part and the arithmetic mean roughness of the outer surface of the strip-shaped part on the index related to the processing of the ceramic spheres was evaluated.

[0032] Figure 3 is the first diagram illustrating the evaluation test of ceramic spheres. Figure 3 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.

[0033] The "raw material (wt%)" shown in Figure 3 indicates the weight percentage of the raw materials used in the preparation of each of the 11 samples. Samples 1 to 3 and samples 7 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 4 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 5 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 6 uses yttria-stabilized zirconia powder (3YSZ, average particle size: 0.5 μm) and contains a zirconium oxide sintered body.

[0034] The "additives" shown in Fig. 3 indicate, for each of the 11 types of samples, the type of "binder" added during production, the type of "plasticizer", and the "input timing" of the binder and plasticizer during production. As the "binder", PVB (polyvinyl acetal) or a wax-based material was used. As the "plasticizer", except for sample 8 to which no plasticizer was added, PEG (polyethylene glycol) or glycerin was used. Regarding the "input timing", in samples 1 to 7 and samples 10 and 11, the plasticizer was input "before" the binder, and in sample 10, the plasticizer was input "after" the binder. Note that sample 8 to which no plasticizer was added was indicated as "-".

[0035] The "mold" shown in Fig. 4 indicates, for each of the 11 types of samples, the relationship of the "surface roughness" of the surface of the mold used during production and the presence or absence of "TiN coating" on the surface of the mold. "r1" shown in the "surface roughness" is the surface roughness of the part of the mold that forms the belt-shaped part of the ceramic green sphere, and "r2" is the surface roughness of the surface of the mold that forms the spherical part of the ceramic green sphere. Among the 11 types of samples, only sample 10 has "r2 < r1". That is, in sample 10, it shows that the surface roughness of the part of the mold that forms the belt-shaped part is smaller than the surface roughness of the part of the mold that forms the spherical part. As shown in the "TiN coating", only sample 11 has no TiN coating applied.

[0036] Fig. 4 is the second figure explaining the evaluation test of the ceramic green sphere. In Fig. 4, for each of the 11 types of samples shown in Fig. 3, the "additives" and "mold" shown in Fig. 3 are indicated.

[0037] The "arithmetic mean roughness" shown in Fig. 4 indicates, for each of the 11 types of samples, "Ra1 (μm)", which is the arithmetic mean roughness of the belt-shaped part, "Ra2 (μm)", which is the arithmetic mean roughness of the spherical part, and "Ra1 / Ra2 (-)", which is the ratio of the arithmetic mean roughness of the belt-shaped part to the arithmetic mean roughness of the spherical part.

[0038] Here, we will explain the measurement method for the arithmetic mean roughness of the spherical and strip-shaped portions of the samples in this evaluation test. The samples used for measuring the arithmetic mean roughness in this evaluation test were manufactured using a mold that had been used 1000 times from a new state in the preliminary molding process of the manufacturing method of ceramic spheres. The arithmetic mean roughness of the spherical and strip-shaped portions of the samples was measured using a contact-type measuring instrument, similar to the measurement method for the arithmetic mean roughness of the ceramic sphere 10 in this embodiment, by measuring the arithmetic mean roughness of the outer surface at the position shown in Figure 2. For each of the 11 types of samples, the arithmetic mean roughness of the outer surface of the strip-shaped portion is shown as "Ra1 (μm)", and the arithmetic mean roughness of the outer surface of the spherical portion is shown as "Ra2 (μm)". "Ra1 / Ra2(-)" was calculated using the measurement results of the arithmetic mean roughness of the outer surface of the strip-shaped portion and the measurement results of the arithmetic mean roughness of the outer surface of the spherical portion.

[0039] The "Processing Defect Rate (%)" and "Rough Processing Efficiency (%)" shown in Figure 4 were evaluated by polishing each of the 11 types of samples. Specifically, the processing state of the samples was evaluated under the same polishing conditions using a ball processing polishing machine. Polishing with the ball processing polishing machine was performed by supplying an abrasive containing glycerin as a polishing aid to the diamond while rotating the lower platen with the upper platen without pressure (no pressure). After polishing was completed, 100 ceramic balls were sampled and the appearance of each of the 100 ceramic balls was inspected using an optical microscope. At this time, the "Processing Defect Rate (%)" was calculated as the percentage of ceramic balls with chips out of 100 ceramic balls in one sample. In addition, for each of the 12 types of samples, the amount of polishing required to polish from the average diameter before polishing to the target diameter was calculated by dividing the amount of polishing by the time required for polishing, and the relative value using the calculated value was calculated as "Rough Processing Efficiency (%)" with the value of sample 2 set to 100. A "rough machining efficiency (%)" greater than 100% indicates that polishing takes longer even with the same amount of material removed.

[0040] As shown in Figure 4, in samples 1 to 6, where the "arithmetic mean roughness" Ra1 / Ra2(-) is less than 0.7, the "processing defect rate (%)" is 0%, indicating that chipping of the ceramic balls during the polishing process is suppressed. On the other hand, in samples 7 to 11, where the "arithmetic mean roughness" Ra1 / Ra2(-) is 0.7 or higher, the "processing defect rate (%)" is 3% or higher in all cases. Furthermore, in samples 1 to 6, the "rough processing efficiency (%)" is at most 101%, indicating that the increase in processing time is also suppressed. In other words, in samples 1 to 6, the increase in processing time is suppressed while chipping of the ceramic balls is suppressed, resulting in an increase in the number of good ceramic balls obtained. Therefore, it was confirmed that by making the arithmetic mean roughness Ra1 of the outer surface of the strip-shaped portion of the ceramic sphere less than 0.7 times the arithmetic mean roughness Ra2 of the outer surface of the spherical portion, it is possible to improve polishing efficiency while suppressing the occurrence of defects such as chipping during the polishing process of the ceramic sphere.

[0041] Sample 7 uses a wax-based material as a binder during the fabrication of ceramic spheres. As a result, the mixing slurry becomes a dispersion-type slurry, causing the mixed powder to become hollow and hard. When the mixed powder hardens, the surface shape of the mold is no longer transferred during the preliminary molding process. Therefore, there is no difference between the arithmetic mean roughness Ra1 of the outer surface of the strip-shaped part and the arithmetic mean roughness Ra2 of the outer surface of the spherical part, which is thought to have resulted in a higher "rough machining efficiency (%)".

[0042] In Sample 8, it is believed that the crushability of the mixed powder deteriorated because no plasticizer was added during the production of the ceramic spheres. As a result, the surface shape of the mold was not easily transferred during the preliminary molding process, so there was no difference between the arithmetic mean roughness Ra1 of the outer surface of the strip-shaped part and the arithmetic mean roughness Ra2 of the outer surface of the spherical part, and the "rough machining efficiency (%)" increased.

[0043] In Sample 9, 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 mixture slurry, preventing it from exhibiting sufficient plasticity. When the plasticizer fails to exhibit plasticity, the surface shape of the mold is less likely to be transferred during the preliminary forming process. As a result, there is no difference between the arithmetic mean roughness Ra1 of the outer surface of the strip-shaped portion and the arithmetic mean roughness Ra2 of the outer surface of the spherical portion, which is thought to have resulted in a higher "rough processing efficiency (%)".

[0044] In Sample 10, the relationship between the surface roughness of the temporary mold used to produce the ceramic sphere is the opposite of the relationship between the surface roughness of the mold used to produce Samples 1 to 7. Specifically, the surface roughness of the part forming the strip-shaped portion of the ceramic sphere is smaller than that of the part forming the spherical portion. As a result, "Ra1 / Ra2(-)" is greater than 1, requiring more time to polish the strip-shaped portion and making it more prone to chipping. Compared to Samples 1 to 7, the "processing defect rate (%)" is higher and the "rough processing efficiency (%)" is higher.

[0045] Sample 11 was manufactured using a temporary molding die that did not have a TiN coating on its surface. As a result, after 1000 uses, the die wore down, and both "Ra1 (μm)" and "Ra2 (μm)" became relatively large. Compared to Samples 1 to 6, the "processing defect rate (%)" was higher, and the "rough processing efficiency (%)" was also higher.

[0046] As described above, with respect to the ceramic sphere 10 of this embodiment, the arithmetic mean roughness of the outer surface S12 of the strip-shaped portion 12 is smaller than the arithmetic mean roughness of the outer surface S11 of the spherical portion 11, which is 0.7 times. As a result, when polishing the ceramic sphere 10, stress is less likely to concentrate on the strip-shaped portion 12, and chipping is less likely to occur. In addition, polishing the spherical portion 11 after polishing the strip-shaped portion 12 becomes relatively easy. This makes it possible to improve the polishing efficiency of the ceramic sphere 10 while suppressing the occurrence of polishing defects such as chipping.

[0047] Furthermore, in the ceramic sphere 10 of this embodiment, since the diameter of the spherical portion 11 is 0.5 mm or more, it can be formed by press molding. As a result, by adjusting the surface roughness of the mold used for press molding, the arithmetic mean roughness of the outer surface S12 of the strip portion 12 can be made smaller than 0.7 times the arithmetic mean roughness of the outer surface S11 of the spherical portion 11.

[0048] Furthermore, in the ceramic sphere 10 of this embodiment, each of the spherical portion 11 and the strip portion 12 contains both an aluminum oxide sintered body and a zirconium oxide sintered body. As a result, the ceramic ball obtained by polishing the ceramic sphere 10 has relatively high hardness and can be used in a wide range of technical fields.

[0049] Furthermore, according to the ceramic ball 10 for bearing balls of this embodiment, as described above, the occurrence of defects in the polishing process is suppressed and the polishing efficiency is improved. As a result, the manufacturing cost of the bearing ball P10 can be reduced.

[0050] Furthermore, the manufacturing method for bearing balls P10 of this embodiment makes it possible to suppress the occurrence of defects and improve polishing efficiency in the polishing process of the manufacturing method for bearing balls P10. This makes it possible to reduce the manufacturing cost of bearing balls P10.

[0051] <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.

[0052] [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.

[0053] [Differentiation 2] In the above-described embodiment, the diameter of the spherical portion of the ceramic sphere 10 was set to 0.5 mm or more. The diameter of the spherical portion of the ceramic sphere may be smaller than 0.5 mm, but if the ceramic sphere is manufactured using press molding, the arithmetic mean roughness of the outer surface of the strip portion can be made smaller than the arithmetic mean roughness of the outer surface of the spherical portion.

[0054] 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.

[0055] <Application Example 1> These are ceramic spheres, A spherical part formed from ceramics, The device comprises a strip-shaped, annular strip-shaped portion, formed of ceramics, which is arranged along the outer circumference of the spherical portion, The arithmetic mean roughness of the outer surface of the strip-shaped portion is Ra1, and the arithmetic mean roughness of the outer surface of the spherical portion is Ra2, and the expression satisfies equation (1). Ceramic spheres. Ra1 / Ra2 < 0.7 ···(1) <Application Example 2> A ceramic sphere as described in Application Example 1, The diameter of the spherical portion is 0.5 mm or more. Ceramic spheres. <Application Example 3> A ceramic sphere as described in Application Example 1 or Application Example 2, The spherical portion and the strip portion are characterized in that they each contain at least one of the following: an aluminum oxide sintered body, a silicon nitride sintered body, a silicon carbide sintered body, a boron nitride sintered body, and a zirconium oxide sintered body. Ceramic spheres. <Application Example 4> These are ceramic ball bearings, The invention is characterized by comprising ceramic spheres as described in any one of the three examples from Application Example 1 to Application Example 3. Ceramic ball bearings. <Application Example 5> A method for manufacturing ceramic balls, The process involves preparing a ceramic sphere as described in any one of Application Examples 1 to 4, The invention is characterized by comprising the step of polishing the aforementioned ceramic spheres. A method for manufacturing ceramic balls. [Explanation of Symbols]

[0056] 10…Ceramic spheres 11...Spherical part 12...band-shaped area 100...bearings d11…Diameter (of the spherical part) P10...Bearing ball S11... (Outer surface of the spherical part) S12... (Outer surface of the strip-shaped portion)

Claims

1. These are ceramic spheres, A spherical part formed from ceramics, The device comprises a strip-shaped, annular strip-shaped portion, formed of ceramics, which is arranged along the outer circumference of the spherical portion, The arithmetic mean roughness of the outer surface of the strip-shaped portion is Ra1, and the arithmetic mean roughness of the outer surface of the spherical portion is Ra2, and the expression satisfies equation (1). Ceramic spheres. Ra1 / Ra2<0.7...(1)

2. A ceramic sphere according to claim 1, The diameter of the spherical portion is 0.5 mm or more. Ceramic spheres.

3. A ceramic sphere according to claim 1 or claim 2, The spherical portion and the strip portion are characterized in that they each contain at least one of the following: an aluminum oxide sintered body, a silicon nitride sintered body, a silicon carbide sintered body, a boron nitride sintered body, and a zirconium oxide sintered body. Ceramic spheres.

4. 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.

5. 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 the step of polishing the aforementioned ceramic spheres. A method for manufacturing ceramic balls.

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