Raw material for ceramic ball, method for producing ceramic ball using same, and ceramic ball

Abstract

A raw material for a ceramic ball according to an embodiment includes a spherical portion and a band-shaped portion formed across a circumference of a surface of the spherical portion. The ratio (Rab / Rap) of the arithmetic mean roughness Rab of the strip-shaped portion to the arithmetic mean roughness Rap of the apex of the spherical portion is 0.7-1.0. In addition, any one of aluminum oxide, silicon nitride, silicon carbide, boron nitride and zirconium oxide can be used as the ceramic. Ceramic balls are manufactured by grinding raw materials for ceramic balls.

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) discloses bearing balls using zirconium oxide materials.

[0003] In the process of manufacturing these bearing ball materials, a method of sintering a molded body is adopted. In addition, the molding method for obtaining the molded body adopts a press molding using a mold. Figure 1 As shown, the press forming 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 forming, 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 forming. Therefore, a spherical portion and a band portion are formed on the formed body obtained by press forming. 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. Figure 2 2 shows the conventional raw materials for ceramic balls. Figure 2 In the figure, 5 is a raw material for a ceramic ball, 6 is a spherical portion, and 7 is a belt portion.

[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] Through Figure 2 The ceramic ball is obtained by grinding the raw material 5 for ceramic balls having the spherical portion 6 and the band-shaped portion 7 after the sintering process shown in the figure. The raw material 5 for ceramic balls having the spherical portion 6 and the band-shaped portion 7 is sometimes referred to as a raw material ball. For example, the raw material 5 for ceramic balls is grinded by mirror finishing with an arithmetic mean surface roughness Ra of 0.1 μm or less. The mirror finishing adopts a platform processing.

[0012] Generally speaking, ceramic materials are manufactured by forming ceramic powder and sintering it through heat treatment. Ceramics shrink greatly during sintering, and it is difficult to uniformly form and sinter ceramic products in an ideal state. Due to the uneven density and the occurrence of pores (stomata), it becomes easy for microstructure unevenness to occur inside the ceramic. The raw material 5 for ceramic balls is formed into a non-spherical shape by powder pressing, and is sintered in this state, and then processed into a spherical shape, and the surface is mirror-finished. Therefore, if there is microstructure unevenness caused by the uneven forming caused by powder pressing inside the raw material 5 for ceramic balls, it becomes the cause of the defective product, i.e., ceramic balls.

[0013] The present invention solves such a problem and provides a ceramic ball having an excellent processing yield in a grinding process by using a ceramic ball raw material 5 in which microstructural unevenness during sintering of a ceramic material formed by powder pressing is suppressed.

[0014] Means used to solve problems

[0015] The ceramic ball material according to the embodiment includes a spherical portion and a band portion formed around the circumference of the spherical portion, wherein the ratio of the arithmetic mean roughness Rab of the outer circumference of the band portion to the arithmetic mean roughness Rap of the outer circumference of the spherical portion, i.e., Rab / Rap, is 0.7 or more and 1.0 or less. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0017] Figure 2 This is an appearance diagram showing an example of a material for a ceramic ball according to an embodiment.

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

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

[0020] Figure 5 This is a cross-sectional view showing an example of the shape of pores and a molded body provided in a rubber mold molded by cold isostatic pressing.

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

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

[0023] The ceramic ball material according to the embodiment includes a spherical portion and a band portion formed across the circumference of the spherical portion, wherein the ratio of the arithmetic mean roughness Rab of the outer peripheral surface of the band portion to the arithmetic mean roughness Rap of the outer peripheral surface of the spherical portion, i.e., Rab / Rap, is 0.7 or more and 1.0 or less.

[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 a raw material for a ceramic ball according to the embodiment, 6 is a spherical portion, and 7 is a belt portion. Figure 2 In FIG. 7 , 7C is a curve extending in the circumferential direction of the outer peripheral surface (outermost surface) formed by the strip-shaped portion 7 and passing through the center of the width W of the outer peripheral surface. Figure 2 In the figure, 8 is one of the two vertices (8, 8′) on the outer peripheral surface (outermost surface) of the spherical portion 6, which is located at a position farthest from the surface formed by the curve 7C (a position 90° away from the curve 7C). In addition, in the arithmetic mean roughness Ra, the arithmetic mean roughness of the outer peripheral surface of the band-shaped portion 7 is set to Rab, and the arithmetic mean roughness of the outer peripheral surface of the spherical portion 6, such as the vertex 8, is set to Rap. Hereinafter, unless otherwise specified, the arithmetic mean roughness of the outer peripheral surface of the spherical portion 6 is described as the arithmetic mean roughness of the vertex 8. In addition, W is the width of the band-shaped portion 7. The width W of the band-shaped portion 7 is sometimes simply referred to as "width W". In addition, Figure 3 In the figure, the height and width of the strip-shaped portion 7 relative to the spherical portion 6 are shown for convenience of explanation.

[0025] The raw material 5 for ceramic balls has a spherical portion 6 and a band portion 7. The band portion 7 is formed to cover the circumference of the surface of the spherical portion 6. The circumference of the surface of the spherical portion 6 is 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 and an ellipsoid can be listed. The band portion 7 is provided on the circumference of the spherical portion 6. The width W of the band portion 7 is, for example, the maximum width of the band portion 7, but it can also be an average value of multiple places.

[0026] When the arithmetic mean roughness of the vertex 8 is set to Rap and the arithmetic mean roughness of the outer peripheral surface of the band-shaped portion 7 is set to Rab, the ratio of Rab to Rap, i.e., Rab / Rap, is within the range of 0.70 to 1.03. If Rap / Rab is within this range, microstructural unevenness during sintering caused by powder compacting can be suppressed mainly in the spherical portion 6 and the band-shaped portion 7. In addition, by suppressing microstructural unevenness during sintering, defects caused by grinding can be reduced. Therefore, Rab / Rap is preferably 0.70 to 1.03, more preferably 0.80 to 1.00, and further preferably 0.90 to 1.00.

[0027] If Rab / Rap is lower than 1.00, the density of the band portion 7 of the raw material 5 for ceramic balls is higher than the density of the spherical portion 6, and the grinding process (such as platform processing) of the band portion 7 becomes difficult. In particular, if Rab / Rap is lower than 0.70, the grinding process of the band portion 7 becomes quite difficult, and the more it cannot be ignored, the longer the processing time during the grinding process (the grinding efficiency becomes worse). In addition, if Rab / Rap is lower than 0.70, brittle fracture is likely to occur when the band portion 7 contacts the grinding stone during the grinding process. In particular, the raw material 5 for ceramic balls is prone to brittle fracture due to contact with the platform of the platform processing.

[0028] On the other hand, when Rab / Rap exceeds 1.03, the density and microstructure inside the ceramic ball material 5 are uneven, and defects such as pores and abnormal structures are generated on the surface of the bearing ball after grinding.

[0029] Here, the measurement method of the arithmetic mean roughness Rab of the outer peripheral surface of the band portion 7 of the raw material 5 for ceramic balls and the arithmetic mean roughness Rap of the vertex 8 is described. In addition, regarding the arithmetic mean roughness Ra, it is stipulated based on JIS B0601 (2013) "Geometrical properties of products (GPS) - Surface texture: Profile curve method - Terms, definitions and surface texture parameters".

[0030] The measurement of the arithmetic mean roughness Ra is specified to be performed using a surface roughness measuring instrument. As the surface roughness measuring instrument, SURFCOM2000 manufactured by Tokyo Seimitsu Co., Ltd. is specified to be used, and the evaluation and analysis software of the device is used. The measuring device may also be a device having the same function as the surface roughness measuring instrument.

[0031] The measurement distance of the arithmetic mean roughness Ra, i.e., the reference length U, is set to 10 to 25% of the diameter of the ceramic ball raw material 5, and the reference lengths U of the spherical portion 6 and the band portion 7 are set to be the same. In addition, as measurement conditions, the measurement cutoff wavelength is set to 0.08 mm, the cutoff type is Gaussian, the tilt correction is the least squares straight line correction, the λs cutoff ratio is set to 300, and the λs cutoff wavelength is set to 0.2667 μm.

[0032] The measurement area of ​​the arithmetic mean roughness Rap of the vertex 8 has a length corresponding to the reference length U at a position centered on the vertex 8 on the curve 6C. This is because the same value can be obtained regardless of whether the raw material 5 for ceramic balls is a true sphere or an ellipsoid, and regardless of the position and direction from which the measurement is made. When it is impossible to measure at the vertex 8 (or vertex 8') due to defects, etc., it is also possible to measure from the position 6E located at half the distance from the curve 7C to the vertex 8 (the position of 45°, that is, the bottom surface when the vertex angle θ of the cone with the center point of the raw material 5 for ceramic balls as the vertex is 45°×2) to the outside of the spherical cap of the vertex 8. In addition, it is also possible to measure from the position (the position of 15°, that is, the bottom surface when the vertex angle θ of the cone with the center point of the raw material 5 for ceramic balls as the vertex is 15°×2) 6F to the outside of the spherical cap of the vertex 8. The vertex angle refers to the vertex angle of an equilateral triangle formed when the cone is cut by a plane passing through the rotation axis.

[0033] The measurement area of ​​the arithmetic mean roughness Rab of the outer peripheral surface of the strip-shaped portion 7 has a length corresponding to the reference length U at any position in the curve 7C. The measurement is performed along the curve 7C, or the measurement is performed in a manner orthogonal to the curve 7C. In the latter case, the curve 7C is approximately the center of the measurement area. Furthermore, since 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 are prone to defects such as notches, which affect the measured value, it is best to exclude them from the measurement location. In addition, the reference length U of the arithmetic mean roughness Ra does not need to be the entirety of the curves 6C and 7C on the outer peripheral surface, but may be a portion of the curves 6C and 7C (for example, a range of 1 mm to 20 mm).

[0034] The arbitrary diameter of the spherical portion 6 of the ceramic ball raw material 5 is preferably 0.5 mm or more. If the arbitrary diameter of the spherical portion 6 is less than 0.5 mm, it becomes difficult to control the powder punch for forming the band-shaped portion 7. Therefore, the diameter of the spherical portion 6 is preferably 1 mm or more, and more preferably 2 mm or more.

[0035] The raw material 5 for ceramic balls preferably contains 85% by mass or more of any one or more 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. The so-called 85% by mass or more of any one or more of aluminum oxide, silicon nitride, silicon carbide, boron nitride and zirconium oxide refers to the content in the ceramic sintered body. In other words, the ceramic sintered body may also contain less than 15% by mass of substances other than the above. Furthermore, it is preferred that the raw material 5 for ceramic balls contains 85% by mass or more of silicon nitride.

[0036] For example, as bearing balls, alumina sintered bodies, silicon nitride sintered bodies, boron nitride sintered bodies, zirconium oxide sintered bodies, and alusil high silicon heat-resistant aluminum alloy sintered bodies are used. Furthermore, the so-called alusil high silicon heat-resistant aluminum alloy sintered body is a sintered body formed by mixing alumina and zirconium oxide. Among them, the bearing balls formed by silicon nitride sintered bodies have the best wear resistance. As an example, the Vickers hardness of alumina, zirconium oxide, and alusil high silicon heat-resistant aluminum alloy is in the range of 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 1400-1800 and the fracture toughness value is as high as 5-10 MPa·m 1 / 2 Silicon nitride sintered body has both high toughness and Vickers hardness, and thus has excellent wear resistance. Silicon nitride sintered body is a structure in which β-type silicon nitride grains are the main component. β-type silicon nitride grains have an elongated shape, and high toughness is achieved by the complex entanglement of elongated grains.

[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 the following manufacturing methods can be listed as methods for efficient manufacturing. 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 an appropriate amount of sintering aid, additive, solvent and binder to the raw material silicon nitride, mix and crush, and granulate by spray dryer. Through this process, granulated powder of raw material powder is prepared. In addition, when the total of silicon nitride powder and sintering aid powder is set to 100 mass%, it is preferred to make silicon nitride powder more than 85 mass%. In addition, the additive is a plasticizer. The solvent is water or an organic solvent. As organic solvents, there are alcohols, ketones, benzene, etc. In addition, the binder is a paraffin-based binder. As a binder for other ceramic granulation, there is a PVA (polyvinyl alcohol)-based binder, but because the glass transition temperature is slightly higher than 85°C, it often hardens during granulation. Therefore, it is difficult to adjust the soft and easily crushed granulated powder by lowering the outlet temperature of the spray dryer. The amount of binder added is set in the range of 3 to 20 mass parts when the total of silicon nitride powder and sintering aid powder is set to 100 mass parts.

[0039] Since the granulated powder is easy to crush, it is easier to crush the granulated powder in the vertical direction of pressing than usual. If the granulated powder is easy to crush in the vertical direction, the surface near the vertex becomes dense, close to the surface state of the band portion. However, in the case where the granulated powder is only easy to crush, the filling property of the granulated powder into the inside of the punch is reduced, which may affect the productivity. Therefore, it is necessary to make the granulated powder easy to crush without damaging the filling property of the granulated powder. As a method for easily crushing the granulated powder, in addition to adjusting according to the type of binder mentioned above, there is also a method of adjusting by the average particle size. The granulated powder usually obtained by a spray dryer is roughly normally distributed, showing a distribution that is concentrated near the average value. The small particles in this distribution are mostly hard due to rapid drying. Therefore, by classifying and removing the granulated powder with a small particle size, the entire granulated powder can also be made easy to crush.

[0040] Next, the adjusted granulated powder is used for compression molding. Examples of compression molding include the use of Figure 1 The molding method of the upper punch 2, the lower punch 3 and the die 4 of the die forming apparatus shown in the figure. 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 portion 6 of the raw material 5 for ceramic balls. In addition, the front end 2a of the upper punch 2, the front end 3a of the lower punch 3 and the planar shape of the inner side of the die 4 become the band portion 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 3A slightly convex shape is formed as shown. If the height of the convex portion is set to H, the size of H is preferably greater than 0.01 mm and less than 0.10 mm. By applying pressure to the band-shaped portion 7 of the raw material 5 for ceramic balls after the sintering process through the convex portion, the sintering density of the band-shaped portion 7 can be increased and the arithmetic mean roughness can be reduced. If the height of H is less than 0.01 mm, the effect of applying pressure is small. In addition, if it is higher than 0.10 mm, the effect of applying pressure increases, but the load applied to the mold increases, and there is a possibility that the life of the mold is shortened.

[0041] By adjusting the shape of the tip 2a of the upper punch 2 and the tip 3a of the lower punch 3 during press forming and the amount of powder filled, the width W and height of the band 7 of the ceramic ball raw material 5 can be adjusted. Similarly, the diameter of the spherical portion 14 and the diameter of the band 15 in the formed body 13 can be adjusted.

[0042] The molded body 13 obtained by press molding has a spherical portion 14 and a band-shaped portion 15. Figure 5 and Figure 6 The spherical portion 6 and the strip portion 7 ( Figure 2 (see figure in the figure)

[0043] In addition, it is preferred to perform isotropic compression molding on the compact after the press molding. By performing isotropic compression molding, 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 isotropic pressure forming, an isotropic pressure forming method using a rubber mold will be described. Figure 4 An example of the disc-shaped rubber mold 9 is shown in FIG. Figure 4 1 is a side view of a state where the upper rubber mold 10 and the lower rubber mold 11 are overlapped. Figure 5 This is a cross-sectional view showing an example in which a molded body 13 is arranged in a spherical portion space 12 in an upper rubber mold 10 and a lower rubber mold 11 .

[0045] The disc-shaped rubber mold 9 is provided with hemispherical pores on both sides that are greater than 1% and less than 35% of the maximum diameter of the molded body. By arranging the molded body 13 in the pores and overlapping the rubber molds, the molded body 13 is sealed in the spherical space 12 surrounded by the rubber mold. It is specified that a static pressure higher than the pressure during molding is applied to the rubber mold. In addition, the rubber mold 9 and the rubber mold 10 preferably use a rubber mold with a Shore hardness Hs of more than 30 and less than 50. By making the hardness of the rubber mold within this range, it is possible to have deformation energy that allows the surface of the molded body 13 and the rubber mold to be in uniform contact. As a result, compression can be uniformly applied to the molded body 13. This process can reduce the crushing residue of the granulated powder.

[0046] In addition, it is preferred that Figure 6 As shown, the molded body 13 is arranged so that the strip-shaped portion 15 is parallel to the contact surface between the upper rubber mold 10 and the lower rubber mold 11. At this time, when the length of the spherical portion space 12 in the direction perpendicular to the contact surface is L1 and the diameter on the contact surface is L2, if L1>L2, it is possible to prevent the spherical portion 6 from being subjected to pressure, and the sintering density of the spherical portion 6 can be reduced, and the arithmetic mean roughness of the spherical portion 6 (for example, the arithmetic mean roughness of the vertex 8 is Rap) can be increased. In addition, even if L1<L2 is set so that the strip-shaped portion 15 is perpendicular to the contact surface between the upper rubber mold 10 and the lower rubber mold 11, the same effect can be obtained.

[0047] Next, a degreasing step is performed to degrease the molded body 13. The degreasing step is a step of heating at a temperature above the decomposition temperature of organic components such as a binder to disperse 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.

[0048] 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. Furthermore, 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 step, the raw material 5 for ceramic balls can be obtained. In addition, the raw material 5 for ceramic balls is defined as a ceramic sintered body having a theoretical density of 98% or higher.

[0049] Ceramic balls can be manufactured by grinding the raw material 5 for ceramic balls. As a representative grinding process for the ball, platform processing can be cited. For example, the raw material 5 for ceramic balls can be inserted between platforms arranged in parallel up and down, and the raw material 5 for ceramic balls can be platform-processed into a true sphere by the movement of the grinding platform. The surface roughness of bearing balls is determined in ASTMF2094. Bearing balls adopt a grade based on ASTMF2094 according to their use. Grind to a surface roughness Ra based on this grade. If the grade is improved, mirror processing with a surface roughness Ra of less than 0.01μm is sometimes implemented. In addition, the so-called ASTM is a standard specification issued by ASTM International. The old name of ASTM International was the American Society for Testing and Materials (ASTM).

[0050] Since the ratio of Rab to Rap, i.e., Rab / Rap, of the ceramic ball material 5 according to the embodiment is within the range of 0.7 to 1.0, the grinding of the vertex 8 starts at the same time as or with priority over the strip 7. In order to suppress the breakage of the ceramic ball material 5 during the grinding process, it is necessary to perform the processing while paying attention to the contact between the strip 7 and the grinding stone of the grinding platen or the like.

[0051] In addition, the ratio of the vertex 8 to the band 7 of the ceramic ball raw material 5 according to the embodiment, i.e., Rab / Rap, is within the range of 0.7 to 1.0. As a result, the density and microstructure of the ceramic ball raw material are less likely to be uneven, and defects such as pores and abnormal structures on the surface of the processed bearing ball can be suppressed.

[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 by a spray dryer. Examples 1 to 7 and Comparative Examples 1 to 4 are silicon nitride sintered bodies. Example 8 and Comparative Example 5 are alumina sintered bodies. 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 carbon silicon 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 binder added is set to 6 parts by mass. Paraffin wax and PVA are used as binders.

[0054] Next, the obtained granulated powder is used for compression molding. Figure 1The upper and lower molds of the compression molding device shown in the figure are molded. As the pressing mold, a straight mold without a convex portion in the center of the punch die 4 and a mold with a convex portion are used. After the mold forming, isotropic pressure forming is performed. The isotropic pressure forming uses a disc-shaped rubber mold with a Shore hardness Hs of 30 or more and 50 or less. In addition, the molded body 13 is set in the lower rubber mold 11 as shown in FIG. Figure 5 As shown, the strip-shaped portion 15 is arranged substantially perpendicular to the contact surface of the rubber molds 10 and 11 ("strip longitudinal direction" in Table 1), and as shown Figure 6 As shown, the strip-shaped portion 15 is arranged substantially parallel to the contact surface ("strip transverse direction" in Table 1). In this state, a static pressure higher than the pressure during molding is applied to each direction in the co-pressure molding step.

[0055] Next, the molded body 13 is subjected to a degreasing and sintering process. The sintering process is performed at 1600 to 2000° C., in a nitrogen atmosphere, and under atmospheric pressure. Then, a HIP treatment is performed at 1600 to 2000° C., in a nitrogen atmosphere, and under a pressure of 200 MPa.

[0056] Through this process, the raw material for ceramic balls of the embodiment was produced. In addition, the comparative example used PVA as a binder, the pressing mold used a straight-line mold without a convex portion in the center of the die, and the molded body 13 was placed in the lower rubber mold 11 as shown in FIG. Figure 5 As shown, the strip-shaped portion 15 is disposed substantially perpendicularly to the contact surfaces of the rubber molds 10 and 11 .

[0057] Table 1 shows the production conditions of Examples and Comparative Examples.

[0058] Table 1

[0059]

[0060] Examples 1 to 4, 8 to 9 and Comparative Examples 1, 5 to 6 are raw materials 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 for ceramic balls for 7 / 8 inch (22.225 mm) ceramic balls. Example 6 and Comparative Example 3 are raw materials for ceramic balls for 1-3 / 16 inch (30.165 mm) ceramic balls. Example 7 and Comparative Example 4 are raw materials for ceramic balls for 1-7 / 8 inch (47.625 mm) ceramic balls. The ceramic ball raw material 5 of Examples 1 to 9 and the ceramic ball raw materials of Comparative Examples 1 to 6 can all be used as bearing balls.

[0061] The arithmetic mean roughness of the ceramic ball material 5 of Examples 1 to 9 and the arithmetic mean roughness of the ceramic ball materials of Comparative Examples 1 to 6 were measured. The respective measuring methods are as described above.

[0062] In Comparative Examples 1 to 6, the ratio of the arithmetic mean roughness Rab of the strip-shaped portion to the arithmetic mean roughness Rap of the apex, that is, Rab / Rap, was outside the range.

[0063] The grinding efficiency was evaluated using the raw material 5 for ceramic balls of Examples 1 to 9 and the raw materials for ceramic balls of Comparative Examples 1 to 6. The grinding conditions of each raw material for ceramic balls were fixed using a ball processing grinder to investigate the processing state of the band-shaped portion. The processing conditions are as follows: the upper platform is not pressurized (not pressurized), the lower platform is rotating, and abrasives using glycerol as a lubricant are supplied to the diamond for processing for 24 hours. Furthermore, for ceramic balls of the same size, the gap distance with the upper platform, the number of rotations of the lower side, the amount of raw material for ceramic balls input, and the amount of abrasives supplied are set to the same conditions.

[0064] In addition, the defective rate of the state of the raw material for ceramic balls after the above-mentioned grinding process was investigated. Regarding the defective rate, 100 samples were visually inspected on the entire surface with an optical microscope, and the rate of pore defects was shown as the defective rate [%] of pore defects. In addition, the rate of abnormal tissues such as discoloration was shown as the defective rate [%]. The results are shown in Table 2.

[0065] Table 2

[0066]

[0067] As can be seen from Table 2, in the raw materials 5 for ceramic balls of Examples 1 to 9, the defect rate [%] of pore defects and the defect rate [%] of abnormal structures are reduced. Therefore, in the raw materials 5 for ceramic balls of Examples 1 to 9 that meet the conditions of the embodiment, by comparing with the cases of Comparative Examples 1 to 6 in which Rab / Rap exceeds 1.03, it is known that: although the grinding processability (grinding process efficiency) is slightly reduced, the surface state after grinding is good. Even if the grinding processability is slightly suppressed, the conditions of the embodiment are just met when the surface state after grinding is prioritized.

[0068] As described above, according to the ceramic ball material 5, by using the ceramic ball material 5 in which microstructural unevenness during sintering of the ceramic material formed by powder pressing is suppressed, ceramic balls having a high yield in terms of grinding processing can be provided.

[0069] 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 novel 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 their equivalents. In addition, the above-mentioned embodiments can also be implemented by combining with each other.

Claims

1. A raw material for ceramic balls, characterized in that: It has: Spherical surface, and a band-shaped portion formed over the circumference of the surface of the spherical portion; The ratio of the arithmetic mean roughness Rab of the outer peripheral surface of the strip-shaped portion to the arithmetic mean roughness Rap of the outer peripheral surface of the spherical portion, namely, Rab / Rap, is 0.70 or more and 1.03 or less.

2. The raw material for ceramic balls according to claim 1, wherein: The arithmetic mean roughness Rap of the outer peripheral surface of the spherical portion is the arithmetic mean roughness of the vertex located at a position farthest from a surface formed by a curve extending in the circumferential direction of the outer peripheral surface formed by the band-shaped portion and passing through the center of the outer peripheral surface.

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

4. The raw material for ceramic balls according to any one of claims 1 to 3, characterized in that: The ceramic ball raw material contains 85 mass % or more of any one selected from the group consisting of aluminum oxide, silicon nitride, silicon carbide, boron nitride, and zirconium oxide.

5. A ceramic ball, characterized in that: The ceramic ball is obtained by grinding the raw material for ceramic balls according to any one of claims 1 to 4.

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

Images