Ceramic ball raw material, method for producing ceramic ball using the same, and ceramic ball

Abstract

The raw material for ceramic balls involved in the embodiment comprises a spherical portion and a band portion formed by the circumference of the surface of the spherical portion. The ratio of the maximum cross-sectional height Rtb of the roughness curve of the outer peripheral surface of the band portion to the maximum cross-sectional height Rts of the roughness of the outer peripheral surface of the spherical portion, i.e., Rtb / Rts, is greater than 1.0. Preferably, any diameter of the spherical portion is greater than 0.5 mm. In addition, the raw material for ceramic balls preferably contains any one of aluminum oxide, silicon nitride, silicon carbide, boron nitride, and zirconium oxide.

Description

Technical Field

[0001] The embodiments described below relate to a raw material for a ceramic ball, a method for producing a ceramic ball, and a ceramic ball. Background Art

[0002] Various ceramic materials have properties such as high hardness, insulation, and wear resistance. In particular, fine ceramics that have been improved in purity and made uniform in particle size show properties that can be used in various fields such as capacitors, actuator materials, and refractory materials. Among the properties of ceramic materials, as products that exert wear resistance and insulation, there are products with ball applications. Products with ball applications include bearings, fixtures, tools, gauges, solenoid valves, check valves, various valves, and the like. Among them, products for bearing ball applications use ceramic materials such as aluminum oxide, silicon nitride, and zirconium oxide. For example, Japanese Patent Publication No. 6-48813 (Patent Document 1) and Japanese Patent Publication No. 2764589 (Patent Document 2) disclose bearing balls using silicon nitride materials, and Japanese Patent Publication No. 60-18620 (Patent Document 3) disclose bearing balls using zirconium oxide materials.

[0003] In the process of manufacturing these bearing ball materials, a method of sintering a molded body is used. In addition, a molding method for obtaining the molded body uses press molding using a mold. Figure 1 As shown, the press molding method generally includes an upper punch 2, a lower punch 3 and a die 4, and is a method in which powder is inserted between the upper punch 2 and the lower punch 3 and pressure is applied. During press molding, in order to protect the die, a gap must be provided between the front end 2a of the upper punch 2 and the front end 3a of the lower punch 3 to perform press molding. Therefore, a spherical portion and a band portion are formed on the formed body obtained by press molding. For example, in Japanese Patent Gazette No. 4761613 (Patent Document 4), a raw material for a bearing ball having a spherical portion and a band portion obtained by sintering a formed body having a spherical portion and a band portion is disclosed.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Laid-Open No. 6-48813

[0007] Patent Document 2: Japanese Patent No. 2764589

[0008] Patent Document 3: Japanese Patent Application Laid-Open No. 60-18620

[0009] Patent Document 4: Japanese Patent No. 4761613 Summary of the invention

[0010] Problems to be solved by the invention

[0011] The ceramic ball is formed by grinding the raw material for a ceramic ball having a spherical portion and a band portion after the sintering process. The raw material for a ceramic ball having a spherical portion and a band portion is sometimes referred to as a raw material ball. For example, the raw material for a ceramic ball is ground by mirror finishing with a surface roughness Ra of less than 0.1 μm. The mirror finishing uses a platform processing.

[0012] Generally, ceramic materials have excellent wear resistance, but since they are brittle materials, they are prone to chipping when strong impacts are applied. Curved surfaces are easy to release impacts, but corners are prone to chipping due to impacts. Therefore, when the raw material for ceramic balls having a band-shaped portion is subjected to platform processing, the processing is suppressed in a manner that reduces the possibility of chipping due to the two shoulders at the corners of the band-shaped portion selectively contacting the platform, resulting in a longer grinding time.

[0013] The present invention has been made to solve such a problem, and provides a raw material for a ceramic ball that can suppress damage to the ceramic material during grinding and shorten the grinding time.

[0014] Means for solving problems

[0015] The ceramic ball material according to the embodiment comprises a spherical portion and a band portion formed across the circumference of the surface of the spherical portion, wherein the ratio of the maximum cross-sectional height Rtb of the roughness curve of the outer peripheral surface of the band portion to the maximum cross-sectional height Rts of the roughness curve of the outer peripheral surface of the spherical portion, that is, Rtb / Rts, is greater than 1.0. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a cross-sectional view showing an example of a general die press molding device.

[0017] Figure 2 It is an external view showing an example of a material for a ceramic ball according to an embodiment.

[0018] Figure 3 It is an external view showing an example of a die of the die press molding device according to the embodiment.

[0019] Figure 4 It is a cross-sectional view showing an example of cold isostatic hydraulic pressing rubber mold molding according to the embodiment.

[0020] Figure 5 This is a cross-sectional view showing an example of the shape of holes provided in cold isostatic hydraulic pressing rubber mold molding according to the embodiment and a molded body.

[0021] Figure 6This is a cross-sectional view showing an example of the shape of holes provided in cold isostatic hydraulic pressing rubber mold molding according to the embodiment and a molded body. DETAILED DESCRIPTION

[0022] Hereinafter, a raw material for ceramic balls, a method for producing ceramic balls using the raw material, and embodiments of ceramic balls will be described in detail with reference to the drawings.

[0023] The ceramic ball material according to the embodiment comprises a spherical portion and a band portion formed across the circumference of the surface of the spherical portion, wherein the ratio of the maximum cross-sectional height Rtb of the roughness curve of the outer peripheral surface of the band portion to the maximum cross-sectional height Rts of the roughness curve of the outer peripheral surface of the spherical portion, that is, Rtb / Rts, is greater than 1.0.

[0024] Figure 2 A schematic diagram showing a raw material for a ceramic ball according to an embodiment. Figure 2 In the figure, 5 is the raw material for the ceramic ball involved in the embodiment, 6 is the spherical portion, and 7 is the strip portion. In addition, in the maximum cross-sectional height Rt of the roughness curve, the maximum cross-sectional height of the roughness curve of the outer peripheral surface (outermost surface) of the strip portion 7 is set to Rtb, and the maximum cross-sectional height of the roughness curve of the outer peripheral surface (outermost surface) of the spherical portion 6 is set to Rts. In addition, W is the width of the strip portion 7. Sometimes the width W of the strip portion 7 is also referred to as "width W". In addition, Figure 2 In the figure, for convenience of explanation, the height and width of the strip-shaped portion 7 relative to the spherical portion 6 are shown.

[0025] The raw material 5 for ceramic balls has a spherical portion 6 and a strip portion 7. The strip portion 7 is formed across the circumference of the surface of the spherical portion 6. The circumference of the surface of the spherical portion 6 can be any one of the multiple circumferences of the surface of the spherical portion 6. The surface of the spherical portion 6 can be a quadratic surface. Therefore, as the spherical portion 6, a true sphere or an ellipsoid can be cited. The strip portion 7 is provided on the circumference of the spherical portion 6. The width W of the strip portion 7 is, for example, the maximum width of the strip portion 7, but it can also be an average value of multiple parts.

[0026] When the maximum cross-sectional height of the roughness curve of the spherical portion 6 is set to Rts and the maximum cross-sectional height of the roughness curve of the strip portion 7 is set to Rtb, the ratio of Rtb to Rts, that is, Rtb / Rts, is within a range of 1.0 or more. If Rtb / Rts is within this range, only the rough surface portion of the strip portion 7 is preferentially contacted with the grinding material, thereby performing grinding processing (for example, platform processing). In addition, since the density of the strip portion 7 of the sintered body is smaller than that of the spherical portion 6, the grinding processing of the strip portion 7 becomes easy, and the grinding time during the grinding processing can be shortened. Therefore, Rtb / Rts is 1.0 or more, preferably 1.1 or more, and more preferably 1.2 or more.

[0027] In addition, Rtb / Rts is preferably within a range of 3.0 or less. If Rtb / Rts exceeds 3.0, even if the maximum cross-sectional height Rts of the roughness curve of the spherical portion 6 can be controlled, the maximum cross-sectional height Rtb of the roughness curve of the strip portion 7 will increase. This is because the strength of the ceramic ball material 5 having the strip portion 7 is reduced, resulting in a defective notch, and the polishing platform may be damaged by the convex portion of the strip portion 7 of the ceramic ball material 5.

[0028] If Rtb / Rts is less than 1.0, the density of the band-shaped portion 7 of the ceramic ball raw material 5 is greater than that of the spherical portion 6, and the grinding process of the band-shaped portion 7 becomes difficult, and the grinding time during the grinding process of the ceramic ball raw material 5 becomes longer. Furthermore, when the ceramic ball raw material 5 is ground, the band-shaped portion is prone to brittle fracture when it contacts the grinding stone during the grinding process. In particular, brittle fracture is easily caused when the ceramic ball raw material 5 contacts the platform during the platform processing.

[0029] Here, the method for measuring the maximum cross-sectional height Rtb of the roughness curve of the band-shaped portion 7 of the raw material 5 for ceramic balls and the maximum cross-sectional height Rts of the roughness curve of the spherical portion 6 is described. In addition, regarding the maximum cross-sectional height Rt of the roughness curve, it is based on JIS B 0601 (2013) "Geometric Characteristics Specification (GPS) of Products - Surface Texture: Profile Curve Method - Terms, Definitions and Surface Texture Parameters".

[0030] The maximum cross-sectional height Rt of the roughness curve was measured using a surface roughness measuring machine. The surface roughness measuring machine used was SURFCOM2000 manufactured by Tokyo Seimitsu Co., Ltd., and the evaluation and analysis software of the device was used. Any measuring device having equivalent functions may be used.

[0031] The measurement distance of the maximum cross-sectional height Rt of the roughness curve, i.e., the evaluation length U, is 10 to 25% of the diameter of the ceramic ball raw material 5, and the evaluation length U is the same for the spherical portion 6 and the band portion 7. In addition, as measurement conditions, the measurement cutoff wavelength is 0.08 mm, the cutoff type is Gaussian, the tilt correction is the least squares straight line correction, and the λs cutoff ratio is 300. In addition, the number of measurements is three times, and the measurement value is the average value of the three times.

[0032] The measurement area of ​​the maximum cross-sectional height Rtb of the roughness curve of the outer peripheral surface of the band-shaped portion 7 has a length corresponding to the evaluation length U at any position in the curve 7C. On the other hand, the measurement area of ​​the maximum cross-sectional height Rts of the roughness curve of the outer peripheral surface of the spherical portion 6 has a length corresponding to the evaluation length U at a position centered on the position 6D on the curve 6C that is farthest from the curve 7C (the center position, the position 90° from the curve 7C). This is because, even if the raw material 5 for ceramic balls is a true sphere or an ellipsoid, the same value can be obtained regardless of the position and direction from which the measurement is performed. In the case where the measurement cannot be performed at the center position 6D (or the center position 6D') of the spherical portion 6 due to the presence of defects, the measurement can also be performed on the outer surface of the spherical cap from the position (45° position) 6E to the center position 6D, and the position 6E is located at half the distance from the curve 7C to the center position 6D.

[0033] In addition, a cross-sectional curve is obtained in a cross section formed by a curve 7C extending in the circumferential direction of the outer peripheral surface formed by the band-shaped portion 7 and passing through the center of the outer peripheral surface and a straight line in the depth direction of the band-shaped portion 7. Then, the long-wavelength shape (waviness curve) is removed from the cross-sectional curve, and the maximum value of the peak height and the maximum value of the valley depth of the profile curve in the evaluation length U are summed to obtain the maximum cross-sectional height Rtb of the roughness curve of the outer peripheral surface of the band-shaped portion 7. In addition, a cross-sectional curve is obtained in a cross section formed by a curve 6C which is the outer peripheral surface of the spherical portion 6 and passes through the center positions 6D and 6D' and a straight line in the depth direction of the spherical portion 6. Then, the long-wavelength shape (waviness curve) is removed from the cross-sectional curve, and the maximum value of the peak height and the maximum value of the valley depth of the profile curve in the evaluation length U are summed to obtain the maximum cross-sectional height Rts of the roughness curve of the outer peripheral surface of the spherical portion 6. In addition, since defects such as notches are easily generated in 10% of one end portion and 10% of the other end portion in the width direction of the outer peripheral surface of the strip-shaped portion 7, thereby affecting the measured value, it is preferably excluded from the measurement portion. In addition, the evaluation length U of the maximum cross-sectional height Rt of the roughness curve does not need to be the entire curve 6C, 7C on the outer peripheral surface, and may be a part of the curve 6C, 7C (for example, about 1 mm to 20 mm).

[0034] The ceramic ball raw material 5 preferably has an arbitrary diameter of the spherical portion 6 of 0.5 mm or more. If the arbitrary diameter of the spherical portion 6 is less than 0.5 mm, it is difficult to control the powder pressing mold for forming the band portion 7. Therefore, the diameter of the spherical portion 6 is preferably 1 mm or more. More preferably, it is 2 mm or more.

[0035] The raw material 5 for ceramic balls preferably contains 85% by mass or more of any one of aluminum oxide (Al2O3), silicon nitride (Si3N4), silicon carbide (SiC), boron nitride (BN), and zirconium oxide (ZrO2). The raw material 5 for ceramic balls is formed by a ceramic sintered body. Containing 85% by mass or more of any one of aluminum oxide, silicon nitride, silicon carbide, boron nitride, and zirconium oxide refers to the content in the ceramic sintered body. By containing 85% by mass or more, the physical properties of the ceramic can be met, and the physical properties required for the ceramic ball can be exerted. In other words, the ceramic sintered body may also contain less than 15% by mass of substances other than the above. In addition, the raw material 5 for ceramic balls preferably contains 85% by mass or more of silicon nitride.

[0036] For example, as bearing balls, alumina sintered bodies, silicon nitride sintered bodies, silicon carbide sintered bodies, boron nitride sintered bodies, zirconia sintered bodies, and alumina zirconia sintered bodies are used. In addition, alumina zirconia sintered bodies refer to sintered bodies formed by mixing alumina and zirconia. Among them, the bearing balls formed by silicon nitride sintered bodies have the best wear resistance. As an example, the Vickers hardness of alumina, zirconia, and alumina zirconia is about 1200 to 1700, but the fracture toughness value is as low as 3 to 6 MPa·m 1 / 2 In contrast, the Vickers hardness of silicon nitride sintered bodies is as high as 1400-1800 and the fracture toughness value is as high as 5-10MPa·m 1 / 2 . Silicon nitride sintered bodies have both high toughness values ​​and Vickers hardness, and from this point of view, they have excellent wear resistance. Silicon nitride sintered bodies are structures mainly composed of β-type silicon nitride grains. β-type silicon nitride grains have an elongated shape, and high toughness values ​​are achieved by the complex entanglement of the elongated grains. Since silicon nitride sintered bodies have high mechanical strength, they also have a very poor grinding efficiency. However, as described above, by increasing the maximum cross-sectional height of the roughness curve of the band-shaped portion 7, the grinding efficiency can be improved even if the raw material 5 for ceramic balls is formed from a high-strength ceramic sintered body such as a silicon nitride sintered body.

[0037] Next, the manufacturing method of the raw material 5 for ceramic balls is described. The manufacturing method of the raw material 5 for ceramic balls involved in the embodiment is not particularly limited as long as it satisfies the above-mentioned structure, but as a method for efficient manufacturing, the following manufacturing method can be cited. The manufacturing method of the raw material 5 for ceramic balls is described by taking the case of silicon nitride sintered body as an example.

[0038] First, add appropriate amounts of sintering aids, additives, solvents, and adhesives to the raw material silicon nitride, mix, crush, and granulate with a spray dryer. Through this process, granulated powder of the raw material powder is prepared. In addition, when the total of silicon nitride powder and sintering aid powder is 100 mass%, the silicon nitride powder is preferably 85 mass% or more. In addition, the additive is a plasticizer. The solvent is water or an organic solvent. As an organic solvent, there are alcohols, ketones, benzene, etc. In addition, the adhesive is an organic matter. When the total of silicon nitride powder and sintering aid powder is 100 mass parts, the amount of adhesive added is in the range of 3 to 20 mass parts.

[0039] Next, the average particle size of the obtained granulated powder is reduced. If the average particle size of the granulated powder is large, the granulated powder is easily crushed when the granulated powder is filled in the pressing die because spaces are obtained between the granulated powders. On the contrary, if the average particle size is reduced, it is difficult to crush the granulated powder because the spaces between the granulated powders become less. Therefore, by reducing the average particle size of the granulated powder, it is difficult to crush the granulated powder in the central part of the pressing where the pressure from the punch decreases. However, in the case of only reducing the average particle size of the granulated powder, the fluidity of the granulated powder into the inside of the pressing die is reduced, which may affect the productivity. Therefore, it is necessary to reduce the average particle size without damaging the fluidity of the granulated powder.

[0040] The granulated powder usually obtained by a spray dryer is roughly normally distributed, showing a distribution that is concentrated near the average value. Therefore, by mixing two granulated powders whose particle sizes are changed by classification, it is possible to obtain granulated powder with reduced fluidity and reduced average particle size. For example, the average particle size of the granulated powder used for die pressing is 50 to 150 μm, but if it is a granulated powder with an average particle size of 120 μm, the average particle size can be reduced by classification. The granulated powder is divided and classified through a 60-mesh (mesh size: about 250 μm) sieve to obtain granulated powder less than 60 mesh. In addition, the remaining granulated powder after the division is classified through 100 mesh (mesh size: about 150 μm) to obtain granulated powder less than 100 mesh. By mixing granulated powder less than 60 mesh and granulated powder classified less than 100 mesh in a certain proportion, the average particle size of the granulated powder can be made from 120 μm to 90 μm. This makes it easy to increase the maximum cross-sectional height Rtb of the roughness curve of the strip-shaped portion 7 in the step described later.

[0041] Next, the adjusted granulated powder is used for compression molding. The compression molding may be performed by using Figure 1The molding method of the upper punch 2, the lower punch 3 and the die 4 of the mold press molding device shown. By filling the granulated powder and applying pressure to the upper punch 2 and the lower punch 3 in the vertical direction, the spherical shape of the inner side of the punch becomes the spherical part 6 of the raw material 5 for ceramic balls. In addition, the planar shape of the upper punch front end 2a, the lower punch front end 3a and the inner side of the die 4 becomes the band part 7 of the raw material 5 for ceramic balls. The inner side of the cross section of the die 4 is a straight line, but it is preferably as shown in FIG. Figure 3 As shown, it is slightly concave in shape. If the depth of the concave portion is set to H, the size of H is preferably greater than 0.01 mm and less than 0.10 mm. Through the concave portion, it is possible to prevent pressure from being applied to the band-shaped portion 7 of the formed body 13, and the sintering density of the band-shaped portion 7 of the raw material 5 for ceramic balls after the sintering process can be reduced, and the maximum cross-sectional height Rtb of the roughness curve of the band-shaped portion becomes larger. If the depth of H is less than 0.01, the effect of preventing the application of pressure is small. In addition, if it is deeper than 0.10 mm, the effect of preventing the application of pressure becomes greater, but the load applied to the mold becomes greater, and the life of the mold may be shortened.

[0042] By adjusting the shape of the front end 2a of the upper punch 2 and the front end 3a of the lower punch 3 during press forming and the filling amount of the powder, the width W and height of the band portion 7 of the raw material 5 for ceramic balls after the sintering process can be adjusted. Similarly, the diameter of the spherical portion 14 and the diameter of the band portion 15 in the formed body 13 can be adjusted. The formed body 13 obtained by press forming has a spherical portion 14 and a band portion 15. In addition, the spherical portion 14 and the band portion 15 (such as Figure 5 as well as Figure 6 The spherical portion 6 and the band portion 7 (as shown in FIG. Figure 2 shown).

[0043] In addition, it is preferred to perform isostatic pressing on the compact after compression molding. By performing isostatic pressing, the granulated powder in the compact can be uniformly compressed. As a result, the granulated powder remaining after crushing in the compact can be reduced. By reducing the granulated powder remaining after crushing, the shrinkage ratio in the sintering process can be controlled.

[0044] As an example of isostatic pressing, an isostatic pressing method using a rubber mold will be described. Figure 4 An example of the disc-shaped rubber mold 8 is shown. Figures 4 to 6 In the figure, 9 is an upper rubber mold, 10 is a lower rubber mold, 11 is a spherical portion space, 12 is a strip portion space, 13 is a molded body, 14 is a spherical portion of the molded body, and 15 is a strip portion of the molded body. In addition, Figure 5 This is a cross-sectional view showing an example in which a molded body 13 is arranged in a spherical portion space 11 in the upper rubber mold 9 and the lower rubber mold 10 .

[0045] The upper rubber mold 9 and the lower rubber mold 10 are provided with hemispherical holes on both sides which are larger than the maximum diameter of the molded body 13 by 1% or more and 35% or less. By setting the molded body 13 in the hole and overlapping the rubber molds, the molded body 13 is sealed in the spherical space 11 surrounded by the rubber molds. A hydrostatic pressure higher than the pressure during molding is applied to the rubber mold. In addition, the rubber mold preferably uses a rubber mold with a Shore hardness Hs of 30 or more and 50 or less. By making the hardness of the rubber mold within this range, it is possible to have a deformation ability that allows the surface of the molded body 13 to be in uniform contact with the rubber mold. As a result, the molded body 13 can be uniformly compressed. Through this process, the crushed residue of the granulated powder can be reduced.

[0046] In addition, if Figure 6 As shown, it is preferred to use the upper rubber mold 9 and the lower rubber mold 10 provided with the strip-shaped space 12, and to provide the strip-shaped portion 15 of the molded body 13 in the strip-shaped space 12 to perform isostatic pressing. Let the distance L1 between the upper rubber mold 9 and the molded body 13 in the spherical portion space 11, and the distance L2 between the upper rubber mold 9 or the lower rubber mold 10 and the molded body 13 in the strip-shaped space 12. At this time, L1 is the sum of the distance L11 between the molded body 13 and the upper rubber mold 9 and the distance L12 between the molded body 13 and the lower rubber mold 10 (L11+L12). In addition, L2 is the sum of the distance L21 and the distance L22 between the molded body 13 and the side surface of the strip-shaped space 12 of the lower rubber mold 10 (L21+L22). At this time, if L1 < L2, it is possible to prevent the pressure from being applied to the strip-shaped portion 15 of the molded body 13, reduce the sintering density of the strip-shaped portion 15, and increase the maximum cross-sectional height Rtb of the roughness curve of the ceramic ball raw material 5 after the sintering process. In addition, as long as the strip-shaped portion 15 can be accommodated, the strip-shaped portion space 12 may be formed only in one of the upper rubber mold 9 and the lower rubber mold 10.

[0047] In addition, the distance between the molded body 13 and the rubber mold is L1≥L2. This is because the spherical space 11 formed by the overlap of the upper rubber mold 9 and the lower rubber mold 10 is designed to be a true spherical shape (L1=L2). Furthermore, as the molded body 13 is used, powder and the like adhere to the gap between the upper and lower rubber molds, and L1>L2 is easily formed. Figure 6 The shape of the strip space 12 shown becomes L1<L2. Since the load of the spherical portion 14 on the strip 15 relative to the formed body 13 is alleviated, the maximum cross-sectional height Rtb of the roughness curve of the strip portion 7 of the raw material 5 for the ceramic ball after the sintering process becomes larger than the maximum cross-sectional height Rts of the roughness curve of the spherical portion 6, and Rtb / Rts becomes greater than 1.0.

[0048] Next, a degreasing step is performed to degrease the molded body 13. The degreasing step is a step of heating the molded body 13 at a temperature higher than the decomposition temperature of organic components such as a binder to volatilize the organic components. The degreasing step can also be performed in a nitrogen atmosphere or an air atmosphere. A degreased body can be obtained by the degreasing step.

[0049] Next, a sintering step of the degreased body is performed. The sintering step is preferably performed at a temperature of 1600°C or higher and 2000°C or lower. In addition, the sintering step is preferably performed in a nitrogen atmosphere. In addition, the pressure during sintering is preferably performed in a range of 300 MPa or higher and higher than atmospheric pressure. In addition, the atmospheric pressure is 0.10133 MPa (= 1 atm). In addition, the sintered body obtained by the sintering step may also be subjected to HIP (hot isostatic pressing) treatment. Through this process, the raw material 5 for ceramic balls can be obtained. In addition, the raw material 5 for ceramic balls is a ceramic sintered body having a theoretical density of 98% or higher.

[0050] Ceramic balls can be manufactured by grinding the raw material 5 for ceramic balls. As a representative example of the grinding of the ball, platform processing can be cited. For example, the raw material 5 for ceramic balls is inserted between platforms arranged parallel to each other up and down. It can be cited that the raw material 5 for ceramic balls is platform-processed into a true spherical shape by the movement of the grinding platform. The surface roughness of bearing balls is specified in ASTMF2094. Bearing balls adopt a grade based on ASTMF2094 according to their use. The surface roughness Ra is ground to meet the grade. If the grade is improved, mirror processing with a surface roughness Ra of less than 0.01μm is sometimes implemented. In addition, ASTM refers to the standard specifications issued by ASTM International. The old name of ASTM International is the American Society for Testing and Materials (ASTM).

[0051] Since the maximum cross-sectional height Rtb of the roughness curve of the band-shaped portion 7 of the raw material 5 for ceramic balls involved in the embodiment is greater than that of the spherical portion 6, grinding is started first. In addition, since the sintering density of the band-shaped portion 7 is smaller than that of the spherical portion 6, platform processing is performed first. Therefore, platform processing can be performed without realizing the contact between the band-shaped portion 7 and the grinding stone such as the grinding platform. Thus, breakage of the raw material 5 for ceramic balls during the grinding process can be suppressed. In addition, the durability of the grinding platform can also be improved. In addition, even when the grinding speed is increased and the grinding time is shortened, the grinding processability (grinding efficiency) can be improved while maintaining the damage suppression effect.

[0052] (Examples 1 to 9, Comparative Examples 1 to 6)

[0053] Sintering aids, additives, solvents, binders, etc. are added to the raw material ceramic powder, mixed, crushed, and granulated with a spray dryer. The ceramics of Examples 1 to 7 and Comparative Examples 1 to 4 are silicon nitride sintered bodies. The ceramics of Example 8 and Comparative Example 5 are alumina sintered bodies. The ceramics of Example 9 and Comparative Example 6 are silicon carbide sintered bodies. The silicon nitride sintered body contains more than 85% by mass of silicon nitride. The alumina sintered body contains more than 85% by mass of alumina. In addition, the silicon carbide sintered body contains more than 85% by mass of silicon carbide. When the total of the main component and the sintering aid is set to 100 parts by mass, the amount of the binder added is set to within the range of 3 to 20 parts by mass.

[0054] Next, the granulated powder was divided into two parts and classified through a 60-mesh sieve. In addition, the remaining granulated powder after the division was classified through a 100-mesh sieve. Granulated powder obtained by mixing granulated powder classified through 60 mesh and granulated powder classified through 100 mesh with 60 mesh was obtained.

[0055] Next, the obtained granulated powder is used for compression molding. Figure 1 The mold forming of the upper and lower molds of the mold pressing molding device shown. The pressing mold used a mold with the same ceramic ball diameter, a mold with the same gap, a straight shape without a recess in the central part of the die 4, and a mold with a recess. After the mold forming, isostatic pressing was performed. The isostatic pressing used a disc-shaped rubber mold with a Shore hardness Hs of 30 or more and 50 or less. In addition, the rubber mold 8 is prepared to make the distance L1 between the upper rubber mold 9 and the raw material 5 for the ceramic ball in the spherical part space 11, and the distance L2 between the upper rubber mold 9 or the lower rubber mold 10 and the molded body 13 in the strip space 12 equal to a spherical rubber mold (L1=L2). In addition, a rubber mold provided with a strip space 12 is prepared (L1<L2). At this time, the ratio of the distance L1 to the distance L2 of the rubber mold provided with the strip space 12, i.e., L1 / L2, is 1.05. In addition, in addition to the pressing molding, the strip 15 of the molded body 13 is arranged perpendicular to the cylindrical direction of the rubber mold. Furthermore, the strip-shaped portion 15 is disposed in the strip-shaped portion space 12 in the rubber mold. In this state, the isostatic pressing step applies a hydrostatic pressure higher than the pressure during molding.

[0056] Next, after the degreasing step, the sintering step is performed at 1600-2000°C, in a nitrogen atmosphere, and under atmospheric pressure. After that, the HIP treatment is performed at 1600-2000°C, in a nitrogen atmosphere, and under a pressure of 200 MPa.

[0057] Through this process, the raw material 5 for ceramic balls involved in the embodiment is produced. In the comparative example, the 100-mesh granulated powder is not mixed (mixing ratio 0%), and only the 60-mesh mixed powder is used. In the comparative example, no Figure 3 Furthermore, in the comparative example, the rubber mold having the strip-shaped space 12 was not used.

[0058] Table 1 shows the production conditions of Examples and Comparative Examples.

[0059] Table 1

[0060]

[0061] Examples 1 to 4, 8 to 9 and Comparative Examples 1, 5 and 6 are raw materials 5 for ceramic balls that are used to become 3 / 8 inch (9.525 mm) ceramic balls after grinding. In addition, Example 5 and Comparative Example 2 are raw materials 5 for ceramic balls that are used to make 7 / 8 inch (22.225 mm) ceramic balls. Example 6 and Comparative Example 3 are raw materials 5 for ceramic balls that are used to make 1-3 / 16 inch (30.165 mm) ceramic balls. Example 7 and Comparative Example 4 are raw materials for ceramic balls that are used to make 1-7 / 8 inch (47.625 mm) ceramic balls. The raw materials 5 for ceramic balls of Examples 1 to 9 and the raw materials for ceramic balls of Comparative Examples 1 to 6 can all be used as bearing balls.

[0062] In the evaluation length U, the maximum cross-sectional height Rt of the roughness curve of the raw material 5 for ceramic balls involved in the embodiment and the maximum cross-sectional height Rt of the roughness curve of the raw material for ceramic balls involved in the comparative example are measured respectively. The respective measurement methods are as described above. As described above, the maximum cross-sectional height Rt of the roughness curve is the sum of the maximum value of the peak height and the maximum value of the valley depth of the contour curve in the evaluation length U. In addition, Rtb / Rts is calculated for the raw material 5 for ceramic balls involved in the embodiment and the raw material for ceramic balls involved in the comparative example respectively. The maximum cross-sectional heights Rtb, Rts, the ratio Rtb / Rts and the evaluation length U of the roughness curves in the embodiment and the comparative example are shown in Table 2.

[0063] In addition, the ratio of the maximum cross-sectional height Rtb of the roughness curve of the band-shaped portion to the maximum cross-sectional height Rts of the roughness of the spherical portion of the ceramic ball materials of Comparative Examples 1 to 6, that is, Rtb / Rts, is less than 1.0 and is outside the range.

[0064] The grinding accuracy (e.g., band removal processing yield) and damage suppression effect (e.g., raw material notch defect rate) of the raw material 5 for ceramic balls of the embodiment and the raw material for ceramic balls of the comparative example were evaluated. The evaluation used a ball processing grinder, fixed the grinding conditions for grinding each raw material for ceramic balls, and investigated the processing state of the band-shaped portion. The grinding processing conditions are as follows: the upper platform is not pressurized (not pressurized), the lower platform rotates, and the diamond is supplied with abrasive using glycerin as a lubricant, and the grinding process is performed for 24 hours. In addition, for ceramic balls of the same size, the gap distance with the upper platform, the rotation speed of the lower rotation, the amount of raw material for ceramic balls, and the supply of abrasive are the same conditions. After the grinding process, 100 samples were taken, and the appearance of the band-shaped portion was visually inspected. The samples for which the band shape could not be confirmed were regarded as qualified products, and expressed as the band removal processing yield (%).

[0065] In addition, after the above grinding process, the proportion of defective occurrence of the state of the notch of the raw material for ceramic balls 5 of the embodiment and the raw material for ceramic balls of the comparative example was investigated. The defective occurrence rate was obtained by performing an appearance inspection of the entire surface of the 100 samples taken above using an optical microscope, and the proportion of notch occurrence was expressed as the raw material notch defective rate (%). The results are shown in Table 2.

[0066] Table 2

[0067]

[0068] In the raw materials for ceramic balls involved in Comparative Examples 1 to 6, at a relatively low grinding speed, the band removal processing yield and the raw material notch defect rate are improved to some extent, but at a relatively high grinding speed, as shown in Table 2, the band removal processing yield and the raw material notch defect rate are not preferred. On the other hand, it can be seen from Table 2 that in the raw materials for ceramic balls 5 involved in Examples 1 to 9, even at a relatively high grinding speed, the band removal processing yield and the raw material notch defect rate are improved compared with the raw materials for ceramic balls involved in Comparative Examples 1 to 6, and the grinding processing accuracy and damage suppression effect are improved. That is, it can be considered that for the raw materials for ceramic balls 5 involved in Examples 1 to 9, the grinding processing accuracy and damage suppression effect are improved, and the grinding processability of the band-shaped portion 7 is also improved. In other words, it can be seen that according to the raw materials for ceramic balls 5 involved in Examples 1 to 9, the grinding processing time can be shortened.

[0069] In addition, the case where the raw material 5 for ceramic balls is a boron nitride sintered body and a zirconium oxide sintered body is not shown as an example. However, it can be considered that as long as the raw material 5 for ceramic balls at least satisfies the condition of the ratio Rtb / Rts, it is considered that the grinding processability and damage suppression are excellent compared with the comparative example, similar to the case of the alumina sintered body, the silicon nitride sintered body and the silicon carbide sintered body.

[0070] As described above, according to the ceramic ball material 5, the grindability of the ceramic material during grinding can be improved and damage can be suppressed.

[0071] Several embodiments of the present invention are illustrated above, but these embodiments are presented as examples and are not intended to limit the scope of the invention. These new embodiments can be implemented in various other ways, and various omissions, substitutions, changes, etc. can be made without departing from the scope of the main purpose of the invention. Modifications of these embodiments are included in the scope and main purpose of the invention, and are included in the invention described in the claims and the scope of their equivalents. In addition, the above-mentioned embodiments can be implemented in combination with each other.

Claims

1. A raw material for ceramic balls, characterized in that: The device comprises: a spherical portion and a strip portion formed across the circumference of the surface of the spherical portion, A ratio of a maximum cross-sectional height Rtb of a roughness curve of an outer peripheral surface of the strip-shaped portion to a maximum cross-sectional height Rts of a roughness curve of an outer peripheral surface of the spherical portion, that is, Rtb / Rts, exceeds 1.0 and is equal to or less than 3.

0.

2. The raw material for ceramic balls according to claim 1, characterized in that: Any diameter of the spherical portion is greater than or equal to 0.5 mm.

3. The raw material for ceramic balls according to claim 1, characterized in that: The ceramic ball raw material is formed of any one of an alumina sintered body, a silicon nitride sintered body, a silicon carbide sintered body, a boron nitride sintered body, and a zirconia sintered body.

4. The raw material for ceramic balls according to claim 1, characterized in that: The ceramic ball raw material is formed of a ceramic sintered body containing 85 mass % or more of silicon nitride.

5. A method for manufacturing a ceramic ball, characterized in that: The ceramic ball material according to any one of claims 1 to 4 is ground.

6. A method for manufacturing a ceramic ball, characterized in that: The surface roughness Ra of the ceramic ball obtained by grinding the ceramic ball material according to any one of claims 1 to 4 is 0.01 μm or less.

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