US-12624728-B2 - Ceramic ball material, method for manufacturing ceramic ball using same, and ceramic ball

Abstract

A ceramic ball material according to an embodiment including: a spherical portion; and a band-shaped portion formed over a circumference of a surface of the spherical portion. The ceramic ball material has a ratio Rtb/Rts of 1.0 or more, where Rtb denotes a maximum cross-sectional height of a roughness profile on an outer peripheral surface of the band-shaped portion; and Rts denotes a maximum cross-sectional height of roughness on an outer peripheral surface of the spherical portion.

Inventors

• Kai Funaki
• Hideki Sato

Assignees

• NITERRA MATERIALS CO., LTD.

Dates

Publication Date

20260512

Application Date

20240221

Priority Date

20220328

Claims (7)

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 ceramic ball material has a ratio Rtb/Rts of 1.0 or more, where Rtb denotes a maximum cross-sectional height of a roughness profile on an outer peripheral surface of the band-shaped portion; and Rts denotes a maximum cross-sectional height of roughness on an outer peripheral surface of the spherical portion.
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 ceramic ball material comprises any one of 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.
4. 4 . The ceramic ball material according to claim 1 , wherein the ceramic ball material comprises a ceramic sintered body containing 85 mass % or more of silicon nitride.
5. 5 . A method for manufacturing a ceramic ball, comprising polishing the ceramic ball material according to claim 1 .
6. 6 . A ceramic ball obtained by polishing the ceramic ball material according to claim 1 .
7. 7 . The ceramic ball according to claim 6 , wherein the ceramic ball material has a surface roughness Ra of 0.01 μm or less.

Description

CROSS-REFERENCE TO RELATED APPLICATION This application is a Continuation Application of No. PCT/JP2023/12411, filed on Mar. 28, 2023, and the PCT application is based upon and claims the benefit of priority from Japanese Patent Application No. 2022-051453, filed on Mar. 28, 2022, the entire contents of which are incorporated herein by reference. FIELD Embodiments described 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 exhibits properties applicable in various fields of, for example, capacitors, actuator materials, and refractories. Products for ball application are those that takes advantage of the properties of ceramic materials, wear resistance and insulation, and include bearings, jigs, tools, gauges, solenoid valves, check valves, and other valves. Of these, products for bearing ball application are made of ceramic materials such as aluminum oxide, silicon nitride, and zirconium oxide. For example, Japanese Patent Laid-Open No. 6-48813 (Patent Document 1) and Japanese Patent No. 2764589 (Patent Document 2) each disclose a bearing ball made of silicon nitride material, while Japanese Patent Laid-Open No. 60-18620 (Patent Document 3) discloses a bearing ball made of zirconium oxide material. In the process of manufacturing these bearing ball materials, a method of sintering a green compact is employed. A molding method for obtaining the green compact is press molding using a mold. Generally, the press molding is a method of inserting powder into a cavity between an upper punch 2 and a lower punch 3 and then applying pressure thereto by using a press molding apparatus including the upper punch 2, the lower punch 3 and a die 4 as illustrated in FIG. 1. During the press molding, there must be a gap between a tip 2a of the upper punch 2 and a tip 3a of the lower punch 3 to protect the molds. As a result, a spherical portion and a band-shaped portion are formed in the green compact to be obtained by press molding. For example, Japanese Patent No. 4761613 (Patent Document 4) discloses a bearing ball material including a spherical portion and a band-shaped portion, which is obtained by sintering a green compact with the spherical portion and the band-shaped portion. A ceramic ball material with a spherical portion and a band-shaped portion after sintering process is polished to form a ceramic ball. The ceramic ball material with the spherical portion and the band-shaped portion is sometimes referred to as a preprocessed ball. For example, the ceramic ball material is polished by mirror finishing 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. Although curved surfaces easily release impact, corners are prone to chipping due to impact. Therefore, when the ceramic ball material with the band-shaped portion is machined using surface plate, the polishing time is prolonged because the machining is performed in a restrained manner to reduce the possibility that both shoulders, which are the corners of the band-shaped portion, selectively contact a surface plate, causing chipping. The present invention solves such problems and provides a ceramic ball material that suppresses damage to ceramic materials during polishing and shorten the polishing time. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view illustrating an example of a general mold press molding apparatus. FIG. 2 is an external view illustrating an example of a ceramic ball material according to an embodiment. FIG. 3 is an external view illustrating an example of a die of a mold press molding apparatus according to an embodiment. FIG. 4 is a cross-sectional view illustrating an example of cold isostatic pressing rubber molding according to an embodiment. FIG. 5 is a cross-sectional view illustrating an example of a hole and a molded body laid in a cold isostatic pressing rubber molding according to an embodiment. FIG. 6 is a cross-sectional view illustrating an example of a hole and a molded body laid in a cold isostatic pressing rubber molding according to an embodiment. DETAILED DESCRIPTION Hereinafter, embodiments of a ceramic ball material, a method for manufacturing a ceramic ball using the same, 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 ceramic ball material having a ratio Rtb/Rts of 1.0 or more, where Rtb denotes a maximum cross-sectional height of a roughness profile