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US-12624727-B2 - Ceramic ball material comprising a band-portion over surface of a spherical portion, and method for manufacturing ceramic ball

US12624727B2US 12624727 B2US12624727 B2US 12624727B2US-12624727-B2

Abstract

A ceramic ball material according to the present embodiment includes a spherical portion, and a band-shaped portion formed over a circumference of a surface of the spherical portion. The band-shaped portion has a width in a range of 0.5 mm or more and 4.0 mm or less, both shoulders of which are provided with an R section having a radius of curvature of 0.02 mm or more. Any one of aluminum oxide, silicon nitride, boron nitride, and zirconium oxide is used as the ceramic.

Inventors

  • Kai Funaki
  • Shoya SANO

Assignees

  • KABUSHIKI KAISHA TOSHIBA
  • TOSHIBA MATERIALS CO., LTD.

Dates

Publication Date
20260512
Application Date
20230623
Priority Date
20201224

Claims (18)

  1. 1 . A ceramic ball material, comprising: a spherical portion; and a band-shaped portion formed over a circumference of a surface of the spherical portion, wherein the band-shaped portion has a width in a range of 0.5 mm or more and 4.0 mm or less, both shoulders of which are provided with an R section having a radius of curvature of 0.02 mm or more, and wherein an outer periphery of the band-shaped portion is concave with respect to both shoulders, the concave outer periphery having a radius of curvature of 5 mm or more.
  2. 2 . The ceramic ball material according to claim 1 , wherein the spherical portion has an arbitrary diameter of 0.5 mm or more.
  3. 3 . The ceramic ball material according to claim 1 , wherein the spherical portion has an arbitrary diameter in a range of 8 mm or more and 70 mm or less, and a height of the band-shaped portion is 1% or less of the diameter of the spherical portion.
  4. 4 . The ceramic ball material according to claim 1 , wherein a diametral ratio between an outer periphery of the band-shaped portion and the spherical portion is 0.9 or more and 1.1 or less.
  5. 5 . The ceramic ball material according to claim 1 , wherein the ceramic ball material comprises any one of aluminum oxide, silicon nitride, boron nitride, and zirconium oxide in an amount of 85% by mass or more.
  6. 6 . The ceramic ball material according to claim 1 , wherein the ceramic ball material is a ceramic sintered compact comprising 85% by mass or more of silicon nitride.
  7. 7 . The ceramic ball material according to claim 1 , wherein the concave of the outer periphery of the band-shaped portion has a ratio of “a radius of curvature/a width of the band-shaped portion” of 10 or less.
  8. 8 . The ceramic ball material according to claim 1 , wherein the radius of curvature is 30 mm or less.
  9. 9 . The ceramic ball material according to claim 1 , wherein a height of the band-shaped portion is 2.5% or less of an arbitrary diameter of the band-shaped portion.
  10. 10 . The ceramic ball material according to claim 9 , wherein the ceramic ball material is a ceramic sintered compact comprising 85% by mass or more of silicon nitride.
  11. 11 . The ceramic ball material according to claim 10 , wherein the spherical portion has an arbitrary diameter of 0.5 mm or more.
  12. 12 . The ceramic ball material according to claim 11 , wherein the spherical portion has an arbitrary diameter in a range of 8 mm or more and 70 mm or less, and a height of the band-shaped portion is 1% or less of the diameter of the spherical portion.
  13. 13 . The ceramic ball material according to claim 12 , wherein the concave of the outer periphery of the band-shaped portion has a ratio of “a radius of curvature/a width of the band-shaped portion” of 10 or less.
  14. 14 . The ceramic ball material according to claim 13 , wherein the radius of curvature is 30 mm or less.
  15. 15 . A method for manufacturing a ceramic ball, comprising polishing the ceramic ball material according to claim 14 .
  16. 16 . The method for manufacturing a ceramic ball according to claim 15 , wherein The polishing is performed so that the ceramic ball has a surface roughness Ra of 0.01 μm.
  17. 17 . A method for manufacturing a ceramic ball, comprising polishing the ceramic ball material according to claim 1 .
  18. 18 . A ceramic ball obtained by polishing the ceramic ball material according to claim 1 .

Description

CROSS-REFERENCE TO RELATED APPLICATION This application is a Continuation Application of No. PCT/JP2021/047068, filed on Dec. 20, 2021, and the PCT application is based upon and claims the benefit of priority from Japanese Patent Application No. 2020-214951, filed on Dec. 24, 2020, the entire contents of which are incorporated herein by reference. FIELD Embodiments discussed later relate to a ceramic ball material, a method for manufacturing a ceramic ball, and a ceramic ball. BACKGROUND Various ceramic materials have properties such as high hardness, insulation, and wear resistance. In particular, fine ceramics with enhanced purity and uniform particle size exhibit properties applicable in various fields of, for example, capacitors, actuator materials, and refractories. Products that take advantage of the wear resistance and insulation mentioned above are bearing balls, which are made of materials such as aluminum oxide, silicon nitride, and zirconium oxide. For example, Japanese Patent Laid-Open No. H06-48813 (Patent Document 1) and Japanese Patent No. 2764589 (Patent Document 2) each disclose a bearing ball made of a silicon nitride material, while Japanese Patent Laid-Open No. S60-18620 (Patent Document 3) discloses a bearing ball made of zirconium oxide material. In the process of manufacturing these materials for bearing balls, a method of sintering a green compact is employed. Press molding using dies is adopted as the molding method. Press molding is generally a method of inserting powder into a cavity between an upper die 1 and a lower die 2, as shown in FIG. 1, then applying pressure thereto. During the press molding, there must be a gap between a tip 3 of the upper die 1 and a tip 4 of the lower die 2 to protect the dies. As a result, a spherical portion and a band-shaped portion are formed in the green compact. For example, Japanese Patent No. 4761613 (Patent Document 4) discloses a bearing ball material including a spherical portion and a band-shaped portion. FIG. 2 shows a conventional ceramic ball material. In FIG. 2, reference character 5A denotes a ceramic ball material, 6A denotes a spherical portion, 7A denotes a band-shaped portion, WA denotes the width of the band-shaped portion 7A, and HA denotes the height of the band-shaped portion 7A. A ceramic ball material 5A with a spherical portion 6A and a band-shaped portion 7A shown in FIG. 2 is polished to form a ceramic ball. The ceramic ball material 5A with the spherical portion 6A and the band-shaped portion 7A is sometimes referred to as a preliminary ball. For example, the ceramic ball material 5A is polished to a mirror finish with a surface roughness Ra of 0.1 μm or less. The mirror finishing involves machining using surface plate. In general, ceramic materials have excellent wear resistance but are prone to chipping when strong impacts are applied thereto because the materials are brittle. Curved surfaces easily release impact, while corners are prone to chipping due to impact. Therefore, when machining using surface plate is performed on the ceramic ball material 5A with the band-shaped portion 7A, both shoulders, which are the corners of the band-shaped portion 7A, selectively contact a surface plate, causing chipping. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view showing an example of a general die press molding apparatus. FIG. 2 is an external view showing an example of a conventional ceramic ball material. FIG. 3 is an external view showing an example of the ceramic ball material according to the embodiment. FIG. 4 is an external view showing an example of a band-shaped portion. FIG. 5 is an external view showing another example of the band-shaped portion. FIG. 6 is an external view showing the other example of the band-shaped portion. Each of FIGS. 7A and 7B is a diagram showing an example of die press molding for molding the ceramic ball material according to the embodiment. DETAILED DESCRIPTION Hereinafter, embodiments of a ceramic ball material, a method for manufacturing a ceramic ball, and a ceramic ball are described in detail with reference to the drawings. The ceramic ball material according to an embodiment includes a spherical portion and a band-shaped portion formed over the circumference of the surface of the spherical portion. The band-shaped portion has a width in the range of 0.5 mm or more and 4.0 mm or less, both shoulders of which are provided with an R section having a radius of curvature of 0.02 mm or more. FIG. 3 is a schematic view of a ceramic ball material according to an embodiment. In FIG. 3, reference numeral 5 denotes the ceramic ball material according to the embodiment, 6 denotes the spherical portion, 7 denotes the band-shaped portion, 8 denotes the R section, 9 denotes the side periphery, and 10 denotes the outer periphery. Reference character r1 denotes the diameter of the outer periphery 10 of the band-shaped portion 7, and r2 denotes the diameter of the spherical portion