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 of the present invention is provided with a spherical surface section and a band-shaped section formed across the circumference of the surface of the spherical surface section, wherein R1 / R2, which is the ratio of the surface roughness (R1) of the end sections of the band-shaped section to the surface roughness (R2) of the center section of the band-shaped section, is 0.3 or more and less than 1.0. With such a configuration of the raw material for ceramic balls, it is possible to reduce processing time while suppressing fragmentation of the ceramic material during processing.

Description

Technical Field

[0001] Embodiments described below relate to a raw material for ceramic balls, a method for producing ceramic balls using the same, and a ceramic ball. Background Art

[0002] Various ceramic materials have properties such as high hardness, insulation, and wear resistance. In particular, fine ceramics with improved purity and uniform particle size show properties that can be used in a variety of fields such as capacitors, actuator materials, and refractory materials. Among them, as products that fully exert wear resistance and insulation, there are products for ball use. Among the products for ball use, there are bearings, fixtures, tools, gauges, solenoid valves, check valves, various valves, etc. Among them, in bearing applications, materials such as aluminum oxide, silicon nitride, and zirconium oxide are used. 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 adopts press molding using a mold. Press molding is generally as follows Figure 1 A method of inserting powder between the upper punch 2 and the lower punch 3 and applying pressure as shown. During the press molding, a gap is set between the upper punch front end 2a and the lower punch front end 3a to protect the mold for press molding. Therefore, a spherical portion and a band portion are formed in the molded body. For example, Japanese Patent Gazette No. 4761613 (Patent Document 4) discloses a raw material for a bearing ball having a spherical portion and a band portion. Figure 2 (A) shows a conventional ceramic ball material. Reference numeral 5P denotes a ceramic ball material, reference numeral 6P denotes a spherical portion, and reference numeral 7P denotes a belt-shaped 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 raw material 5P having the spherical portion 6P and the band-shaped portion 7P shown in (A) is ground to become a ceramic ball. The ceramic ball raw material 5P having the spherical portion 6P and the band-shaped portion 7P is sometimes referred to as a ball blank. For example, the ceramic ball raw material 5P can be mirror-finished to a surface with an arithmetic mean roughness Ra of 0.1 μm or less. The mirror-finishing is performed by a platform process.

[0012] Generally speaking, ceramic materials have excellent wear resistance, but because they are brittle materials, they are easily broken when a strong impact is applied. In addition, the curved surface is easy to escape the impact, but the corners are easy to break due to the impact. Therefore, when the platform processing is performed on the ceramic ball raw material 5P having the strip-shaped portion 7P, the corners of the strip-shaped portion 7P, that is, the two shoulders, are selectively contacted with the platform to suppress the possibility of breaking, which becomes a cause of extended processing time.

[0013] The present invention solves such a problem and provides a raw material for a ceramic ball which can reduce the processing time while suppressing the breakage of the ceramic material during the surface plate processing.

[0014] Means used to solve problems

[0015] The raw material for ceramic balls involved in the embodiment is characterized in that it has a spherical portion and a band portion formed by a circumference of the surface of the spherical portion, and the ratio of the surface roughness R1 of the end of the band portion to the surface roughness R2 of the central portion of the band portion, i.e. R1 / R2, is greater than 0.3 and less than 1.0. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0017] Figure 2 (A) is an external view showing an example of a raw material for a ceramic ball according to a conventional example (comparative example). Figure 2 (B) is an external view showing an example of the material for ceramic balls according to the embodiment.

[0018] Figure 3 yes Figure 2 (B) is an enlarged view of a band-shaped portion of the ceramic ball material according to the embodiment shown.

[0019] Figure 4 This is an external view showing an example of isotropic rubber molding according to the embodiment.

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

[0021] 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.

[0022] The ceramic ball material involved in the embodiment includes a spherical portion and a band portion formed around the circumference of the surface of the spherical portion, and the ratio of the surface roughness R1 of the end of the band portion to the surface roughness R2 of the central portion of the band portion, i.e. R1 / R2, is greater than 0.3 and less than 1.0.

[0023] Figure 2 (B) is a schematic diagram showing a ceramic ball material according to the embodiment. Figure 2 In (B), symbol 5 is the raw material for ceramic balls involved in the embodiment, symbol 6 is the spherical portion, and symbol 7 is the strip portion. The raw material for ceramic balls 5 having the spherical portion 6 and the strip portion 7 is sometimes referred to as a ball blank. In addition, symbol W is the width of the strip portion 7. The width W of the strip portion 7 is sometimes referred to simply as "width W". Furthermore, Figure 2 In (B), the height and width of the strip-shaped portion 7 relative to the spherical portion 6 are shown in the figure for the convenience of explanation.

[0024] 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 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 and an ellipsoid can be listed. 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.

[0025] Figure 3 Shown in Figure 2 (B) is an enlarged view of the A portion near the strip-shaped portion 7. The symbol 7a is a corner of the strip-shaped portion 7. The strip-shaped portion 7 is divided into three equal parts in the direction of the width W, and the strip-shaped portion 7 is divided into three parts: the end portion 7b1 on the upper punch side (referred to as the "strip-shaped portion end portion"), the central portion (referred to as the "strip-shaped portion central portion") 7b2, and the end portion 7b3 on the lower punch side (referred to as the "strip-shaped portion end portion") 7b3. Furthermore, since the upper punch 2 and the lower punch 3 are mostly the same in shape, the strip-shaped portion end portion 7b1 on the upper punch side and the strip-shaped portion end portion 7b3 on the lower punch side are not distinguished by upper and lower parts, and can be regarded as the same. Therefore, the "strip-shaped portion end portion 7b1" in this specification is not only the strip-shaped portion end portion 7b1 on the upper punch side, but also sometimes includes the strip-shaped portion end portion 7b3 on the lower punch side.

[0026] The strip-shaped portion of the formed body corresponding to the strip-shaped portion 7 of the raw material 5 for ceramic balls is formed to facilitate press molding. The raw material 5 for ceramic balls is processed into a true sphere, but the strip-shaped portion 7 is formed protruding from the spherical portion 6, which hinders processing. Therefore, in order to facilitate processing, it is desired that the strength of the strip-shaped portion 7 is not high. On the other hand, the strip-shaped portion 7 formed by protruding from the spherical portion 6 is easily broken due to collisions between products and other parts during transportation and processing. In order to prevent this breakage, it is necessary for the strip-shaped portion 7 to have a certain strength.

[0027] Therefore, the ceramic ball raw material 5 according to the embodiment is adjusted so that the surface roughness of the central portion 7b2 of the strip portion is larger than the surface roughness of the end portion 7b1 of the strip portion. By pressing and molding the end portion 7b1 of the strip portion more densely than the central portion 7b2 of the strip portion, the strength of the end portion 7b1 of the strip portion and the corner portion 7a of the strip portion is enhanced, and the occurrence of cracking in the process from press molding to grinding can be prevented. On the other hand, by molding the central portion 7b2 of the strip portion less densely than the corner portion and reducing the density of the sintered body, grinding becomes easier and the load of the process can be reduced.

[0028] The surface roughness of the band-shaped end portion 7b1 and the band-shaped central portion 7b2 of the raw material 5 for ceramic balls before grinding is specified based on JIS B 0601 (2013) "Geometric Property Standards for Products (GPS) - Surface Texture: Profile Curve Method - Terms, Definitions and Surface Texture Parameters". The surface roughness can be compared by the arithmetic mean roughness (Ra), maximum height roughness (Rz), and ten-point average roughness (Rzjis) that are mostly used when measuring the surface roughness of ceramic sintered bodies. As indicators of surface roughness other than these, other measurable surface roughness indicators recorded in JIS B0601 (2013) such as the maximum peak height (Rp) of the roughness curve, the maximum valley depth (Rv) of the roughness curve, the average height of the roughness curve elements (Rc), and the maximum cross-sectional height (Rt) of the roughness curve can also be used for comparison.

[0029] The ratio of the surface roughness R1 of the end portion 7b1 of the strip portion to the surface roughness R2 of the central portion 7b2 of the strip portion, i.e., R1 / R2, is within a range below 1.0. The granulated powder described later is used in the press molding, but if the granulated powder exists in a state that is difficult to crush during press molding, the density of the molded body decreases and the surface becomes rough. Therefore, if R1 / R2 is within this range, the central portion 7b2 of the strip portion is easy to contact the grinding material preferentially due to the degree of surface roughness, so the processing progresses. In addition, since the density of the strip portion 7 as a whole is reduced compared to when the surface roughness of the end portion 7b1 of the strip portion and the central portion 7b2 of the strip portion is the same, the processing of the strip portion 7 becomes easier and the grinding processing time can be shortened. Therefore, it is preferred that R1 / R2 is less than 0.9, and more preferably less than 0.8.

[0030] In addition, it is preferable that R1 / R2 is within a range of 0.3 or more. If R1 / R2 is less than 0.3, even if the surface roughness R1 of the strip-shaped portion end 7b1 can be controlled, the surface roughness R2 of the strip-shaped portion center 7b2 becomes large, and the density of the molded body in the strip-shaped portion center 7b2 and its vicinity is too low. As a result, the strength of the molded body of the entire strip-shaped portion 7 is reduced, resulting in poor fracture. Therefore, it is preferable that R1 / R2 is 0.4 or more, and more preferably 0.5 or more.

[0031] If R1 / R2 is 1.0 or more, the density of the central portion 7b2 of the strip is equal to or greater than the density of the end portion 7b1 of the strip. When the density of the central portion 7b2 of the strip is increased compared to the density of the end portion 7b1 of the strip, the processing of the entire strip 7 becomes difficult, and the grinding processing time is prolonged. When the density of the end portion 7b1 of the strip is reduced compared to the density of the central portion 7b2 of the strip, the end portion 7b1 of the strip is easily broken due to contact between raw materials and other components during processing and transportation.

[0032] Here, the method for measuring the surface roughness R1 of the strip-shaped portion end 7b1 and the surface roughness R2 of the strip-shaped portion center 7b2 of the ceramic ball raw material 5 is described. The surface roughness measurement method is based on JIS B 0601 (2013) "Geometric Property Standard (GPS) of Products - Surface Texture: Profile Curve Method - Terms, Definitions and Surface Texture Parameters".

[0033] The surface roughness R1 and the surface roughness R2 are measured by a surface roughness measuring instrument. As the surface roughness measuring instrument, SURFCOM2000 manufactured by Tokyo Seimitsu Co., Ltd. is used, and the analysis is performed using the evaluation analysis software of the device. The measuring device may be any device having the same function as the device.

[0034] The measurement distance (reference length) of the surface roughness R1 and the surface roughness R2 is set to 1 to 10% of the length of the outer periphery of the band-shaped portion 7 of the raw material for ceramic balls, and the measurement distances of the band-shaped portion end 7b1 and the band-shaped portion center 7b2 are set to be the same. In addition, the measurement conditions are set to a measurement cutoff wavelength of 0.08 mm, a cutoff type of Gaussian, a tilt correction of least squares straight line correction, and a λs cutoff ratio of 300. Furthermore, the number of measurements is set to 3 times, and the measurement value is set to the average value of the 3 times.

[0035] The measurement area of ​​the surface roughness R1 of the strip-shaped portion end 7b1 is an area extending from the approximate center of the strip-shaped portion end 7b1 along the direction of the width W to the outer peripheral direction of the strip-shaped portion end 7b1. The area along the outer peripheral direction is measured. Similarly, the measurement area of ​​the surface roughness R2 of the strip-shaped portion center 7b2 is an area extending from the approximate center of the strip-shaped portion center 7b2 along the direction of the width W to the outer peripheral direction of the strip-shaped portion end 7b1. The area along the outer peripheral direction is measured. In the measurement of the surface roughness R1 and R2, when there is a local defect such as a crack, the defective portion is avoided and the same place or a nearby place of the strip-shaped portion 7 is measured.

[0036] When the strip-shaped portion 7 cannot be measured in the peripheral direction, it is also possible to measure in the direction of the width W of the strip-shaped portion 7. In this case, the measurement area of ​​the strip-shaped portion end 7b1 and the measurement area of ​​the strip-shaped portion center 7b2 may be made continuous, and the surface roughness R1 and R2 may be calculated from these continuous measurement areas, or the measurement area of ​​the strip-shaped portion end 7b1 and the measurement area of ​​the strip-shaped portion center 7b2 may not be made continuous, and the surface roughness R1 and R2 may be measured from discontinuous measurement areas. In this case, when measuring the surface roughness R1 and R2, when there is a local defect such as a crack, the defective portion is avoided for measurement.

[0037] The raw material 5 for ceramic balls preferably has a line segment that passes through the center of the spherical portion 6 and has two ends on the outer peripheral surface, for example, a diameter of 0.5 mm or more. If the line segment that passes through the center of the spherical portion 6 and has two ends on the outer peripheral surface has a diameter of less than 0.5 mm, it becomes difficult to control the powder pressing mold for forming the band-shaped portion 7. Therefore, the line segment that passes through the center of the spherical portion 6 and has two ends on the outer peripheral surface has a diameter of preferably 1 mm or more, and more preferably 2 mm or more.

[0038] 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. Containing 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.

[0039] For example, as bearing balls, alumina sintered bodies, silicon nitride sintered bodies, silicon carbide sintered bodies, boron nitride sintered bodies, zirconia sintered bodies, and alusil high silicon heat-resistant aluminum alloy sintered bodies have been used. Furthermore, the so-called alusil high silicon heat-resistant aluminum alloy sintered body is a sintered body 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 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 compact is about 1400 to 1800, but the fracture toughness value is as high as 5 to 10 MPa·m 1 / 2 About. Silicon nitride sintered body takes into account both high toughness value and Vickers hardness, and from this point of view, it has excellent wear resistance. Silicon nitride sintered body is a structure in which β-type silicon nitride grains are the main body. β-type silicon nitride grains have an elongated shape, and a high toughness value is achieved by the complex entanglement of elongated grains. Silicon nitride sintered body has a side of poor grinding efficiency due to its high mechanical strength. However, as mentioned above, by increasing the surface roughness of the central part 7b2 of the strip portion, even the raw material 5 for ceramic balls formed by a high-strength ceramic sintered body such as silicon nitride sintered body can improve the grinding efficiency.

[0040] Next, the manufacturing method of the raw material 5 for ceramic balls is described. As long as the raw material 5 for ceramic balls involved in the embodiment satisfies the above-mentioned structure, its manufacturing method is not particularly limited, but as a method for efficient manufacturing, the following manufacturing methods can be listed. The manufacturing method of the raw material 5 for ceramic balls is described by taking a silicon nitride sintered body as an example.

[0041] First, add appropriate amounts of sintering aids, additives, solvents, and adhesives to the raw material silicon nitride, mix and crush, and granulate using 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 set to 100% by mass, it is preferred that the silicon nitride powder is more than 85% by mass. In addition, the additive is a plasticizer. The solvent is water or an organic solvent. Organic solvents include alcohols, ketones, benzene, etc. In addition, the adhesive is an organic matter. The amount of the adhesive added is set in the range of 3 to 20% by mass when the total of silicon nitride powder and sintering aid powder is set to 100% by mass.

[0042] 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 becomes easy to crush when the granulated powder is filled into the pressing die due to the space between the granulated powder. On the contrary, if the average particle size is reduced, the crushing becomes difficult due to the reduction of the space between the granulated powder. Therefore, the pressing center part where the pressure from the punch is reduced by reducing the average particle size of the granulated powder becomes difficult to crush. However, when only the average particle size of the granulated powder is reduced, the fluidity of the granulated powder into 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.

[0043] The granulated powder obtained by the spray dryer is generally normally distributed, showing a distribution concentrated near the average value. Therefore, by mixing two kinds of granulated powders whose particle sizes have been changed by classification, granulated powder with a reduced average particle size can be obtained without greatly impairing fluidity. The average particle size of the granulated powder used in compression molding is 50 to 150 μm, but the average particle size can be reduced by classification. For example, if the granulated powder has an average particle size of 120 μm, the granulated powder is divided into two parts, and one of the granulated powders is classified through a 70-mesh (mesh size: about 240 μm) sieve to obtain a granulated powder with a size smaller than 70 mesh. In addition, the remaining granulated powder divided into two parts is classified through a 120-mesh (mesh size: about 130 μm) sieve to obtain a granulated powder with a size smaller than 120 mesh. By mixing the granulated powder with a size smaller than 70 mesh and the classified granulated powder with a size smaller than 120 mesh at a certain ratio, the average particle size of the granulated powder with an average particle size of 120 μm can be made 80 μm. Thus, the surface roughness R2 of the band-shaped central portion 7b2 of the ceramic ball material 5 can be easily increased through a plurality of steps described later.

[0044] Next, the granulated powder with adjusted average particle size is subjected to compression molding. Examples of compression molding include the use of Figure 1The molding method of the upper punch 2, the lower punch 3, and the die 4 of the compression molding device shown in the figure. After the granulated powder is filled, the upper punch 2 and the lower punch 3 are pressed in the vertical direction, and the spherical shape inside the punch becomes the spherical portion 6 of the raw material 5 for ceramic balls through the multiple processes described later. In addition, the cylindrical shape inside the upper punch front end 2a, the lower punch front end 3a and the die 4 becomes the band portion 7 of the raw material 5 for ceramic balls through the multiple processes described later. 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 compression molding and the filling amount of powder, the width W and height of the band portion 7 of the raw material 5 for ceramic balls can be adjusted. Similarly, the diameter in the direction of the spherical portion and the diameter in the direction of the band portion can be adjusted. The molded body obtained by compression molding becomes a molded body having a spherical portion and a band portion. Furthermore, the spherical portion and the band portion of the molded body correspond to the spherical portion 6 and the band portion 7 of the raw material 5 for ceramic balls described above, respectively.

[0045] Next, the molded body is subjected to isotropic pressing. By performing isotropic pressing, the granulated powder in the molded body can be uniformly compressed. As a result, the granulated powder remaining after being crushed in the molded body can be reduced. By reducing the granulated powder remaining after being crushed, the shrinkage ratio in the sintering process can be controlled.

[0046] As an example of isotropic press molding, an isotropic press molding method using a rubber mold will be described. Figure 4 An example of a disc-shaped rubber mold 8 is shown. Reference numeral 9 is an upper rubber mold, and reference numeral 10 is a lower rubber mold. Figure 5 This is a cross-sectional view showing an example in which a molded body 12 is arranged in a spherical portion space 11 in the upper rubber mold 9 and the lower rubber mold 10 .

[0047] 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 by more than 1% and less than 35%. By placing the molded body in the hole and overlapping the rubber mold, the molded body is enclosed in the spherical portion space 11 surrounded by the rubber mold. It is stipulated that an isotropic 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 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 and the rubber mold to be in uniform contact. As a result, compression can be uniformly applied to the molded body. This process can reduce the crushing residue of the granulated powder.

[0048] In addition, the pressure increase rate when applying isotropic forming pressure to the rubber mold is preferably slow. This is because if the pressure increase rate is slow, pressure is first applied to the corners of the strip, which makes it easy to increase the density of the corners of the pressed body. In addition, the pressure increase rate does not need to be slowed down as a whole during the pressure increase, and it is sufficient to slow down the pressure increase rate until the moment when pressure is applied to the corners. If the pressure increase of less than 20% of the maximum pressure applied to the whole is regarded as the first pressure increase, and the pressure increase from the first pressure increase to the maximum pressure is regarded as the second pressure increase, it is preferred to set the speed of the first pressure increase to less than 50% of the speed of the second pressure increase. By slowing down the speed of the first pressure increase, pressure can be applied to the corners first in the strip of the formed body, and finally to the central part.

[0049] Next, a degreasing step is performed to degrease the molded body. The degreasing step is a step of heating the molded body to a temperature above the decomposition temperature of organic components such as the binder to remove 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.

[0050] 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 1 MPa or higher and 1 MPa or lower. Furthermore, the atmospheric pressure is 0.10133 MPa (= 1 atm). In addition, the sintered body obtained by the sintering step may be subjected to HIP (hot isostatic pressing) treatment. Through the sintering step (or HIP treatment 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.

[0051] Ceramic balls can be manufactured by grinding the raw material 5 for ceramic balls. As a representative example of grinding 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. The raw material 5 for ceramic balls is processed into a true spherical shape 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 an arithmetic mean roughness Ra based on the grade. If the grade is improved, mirror processing with an arithmetic 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).

[0052] The strip 7 of the ceramic ball raw material 5 of the embodiment is ground from the corner, but since the sintering density of the central part 7b2 of the strip is lower than that of the corner of the strip, it becomes easier to process as it moves toward the central part 7b2 of the strip. Therefore, it is possible to process without realizing that the entire strip 7 is in contact with a grinding stone such as a grinding platform. Thus, it is possible to suppress the breakage of the ceramic ball raw material 5 during the grinding process. In addition, it is possible to improve the durability of the grinding platform. In addition, the processability can be improved by shortening the grinding time.

[0053] (Examples 1 to 8, Comparative Examples 1 to 6)

[0054] Sintering aids, additives, solvents, binders, etc. are added to the raw material ceramic powder, mixed and crushed, and granulated by a spray dryer. Examples 1 to 6 and Comparative Examples 1 to 4 are silicon nitride sintered bodies, Example 7 and Comparative Example 5 are alumina sintered bodies, and Example 8 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.

[0055] Next, the granulated powder was divided into two parts and classified by a 70-mesh sieve. In addition, the remaining granulated powder was classified by a 120-mesh sieve. The granulated powder classified by a 70-mesh sieve and the granulated powder classified by a 120-mesh sieve were mixed to obtain granulated powder. In addition, the granulated powder was not divided into two parts, and the granulated powder classified by a 70-mesh sieve was obtained.

[0056] Next, the obtained granulated powder is used for compression molding. Figure 1 The compression molding of the upper and lower molds of the compression molding device shown.

[0057] After compression molding, isotropic press molding is performed. In isotropic press molding, a disc-shaped rubber mold with a Shore hardness Hs of 30 or more and 50 or less is used, a press-molded body is set inside the rubber mold, and hydrostatic pressure is applied. The isotropic press molding process applies a hydrostatic pressure higher than the pressure during molding, and the process of applying a pressure until it is less than half of the final hydrostatic pressure is called a primary pressurization, and the process of applying a pressure from the primary pressurization to the final final hydrostatic pressure is called a secondary pressurization. In the isotropic press molding process, a method of making the primary pressurization speed and the secondary pressurization speed the same and a method of making the primary pressurization speed slower than the secondary pressurization speed are used.

[0058] Next, the sintering process was performed. Silicon nitride was heat treated at 1700-1900°C in a nitrogen atmosphere and atmospheric pressure. Then, HIP treatment was performed at 1700-1900°C in an inert gas and a pressure of 200 MPa. Alumina was heat treated at 1500-1700°C in an atmospheric atmosphere and atmospheric pressure. Then, HIP treatment was performed at 1500-1700°C in an inert gas and a pressure of 200 MPa. Silicon carbide was heat treated at 1900-2200°C. Then, HIP treatment was performed at 1900-2200°C in an inert gas and a pressure of 200 MPa.

[0059] Through this process, the raw material for ceramic balls involved in the embodiment is produced. In addition, in the comparative example, only the granulated powder classified by passing through a 70-mesh sieve is used. In addition, in the isotropic pressing process, the primary pressure increase rate and the secondary pressure increase rate are set to be the same. The manufacturing conditions of the embodiment and the comparative example are shown in Table 1 and Table 2.

[0060] In Tables 1 and 2, silicon nitride is marked as Si3N4, aluminum oxide is marked as Al2O3, and silicon carbide is marked as SiC as the type of sintered body. In addition, a mixed powder of 70 mesh and 120 mesh is marked as 70+120, and a granulated powder of 70 mesh is marked as 70.

[0061] Table 1

[0062]

[0063] Table 2

[0064]

[0065] As shown in Table 1, Examples 1 to 3, 7 to 8 are ceramic ball raw materials 5 for use in 3 / 8 inch (9.525 mm) ceramic balls after grinding. On the other hand, Comparative Examples 1, 5 to 6 are ceramic ball raw materials 5P for use in 3 / 8 inch (9.525 mm) ceramic balls after grinding. In addition, Example 4 is a ceramic ball raw material 5 for use in 7 / 8 inch (22.225 mm) ceramic balls. On the other hand, Comparative Example 2 is a ceramic ball raw material 5P for use in 7 / 8 inch (22.225 mm) ceramic balls. Example 5 is a ceramic ball raw material 5 for use in 1-3 / 16 inch (30.165 mm) ceramic balls. On the other hand, Comparative Example 3 is a ceramic ball raw material 5P for use in 1-3 / 16 inch (30.165 mm) ceramic balls. Example 6 is a ceramic ball raw material 5 for use in 1-7 / 8 inch (47.625 mm) ceramic balls. On the other hand, Comparative Example 4 is a ceramic ball raw material 5P for a 1-7 / 8 inch (47.625 mm) ceramic ball. The ceramic ball raw materials 5 of Examples 1 to 8 and the ceramic ball raw materials 5P of Comparative Examples 1 to 6 can all be used as bearing balls.

[0066] The arithmetic mean roughness (Ra), the maximum height roughness (Rz), the ten-point average roughness (Rzjis), the maximum peak height (Rp) of the roughness curve, and the maximum valley depth (Rv) of the roughness curve were measured for the surface roughness R1 of the band-shaped portion end 7b1 and the surface roughness R2 of the band-shaped portion center 7b2 of the raw material 5 for ceramic balls involved in Example 1, and the surface roughness R1 of the band-shaped portion end and the surface roughness R2 of the band-shaped portion center of the raw material 5P for ceramic balls involved in Comparative Example 1. The measurement results are shown in Table 3. In addition, the arithmetic mean roughness (Ra) was measured for the arithmetic mean roughness R1 of the band-shaped portion end 7b1 and the arithmetic mean roughness R2 of the band-shaped portion center 7b2 of the raw material 5 for ceramic balls involved in Examples 2 to 9, and the arithmetic mean roughness R1 of the band-shaped portion end and the arithmetic mean roughness R2 of the band-shaped portion center of the raw material 5P for ceramic balls involved in Comparative Examples 2 to 7. The measurement results are shown in Table 4. In addition, each measurement method is as described above.

[0067] As shown in Table 3, Example 1 shows R1 / R2 when the surface roughness is defined as the arithmetic mean roughness (Ra), Example 1-2 shows R1 / R2 when the surface roughness is defined as the maximum height roughness (Rz), Example 1-3 shows R1 / R2 when the surface roughness is defined as the ten-point average roughness (Rzjis), Example 1-4 shows R1 / R2 when the surface roughness is defined as the maximum peak height (Rp) of the roughness curve, and Example 1-5 shows R1 / R2 when the surface roughness is defined as the maximum valley depth (Rv) of the roughness curve. In this way, no matter which of the arithmetic mean roughness (Ra), the maximum height roughness (Rz), the ten-point average roughness (Rzjis), the maximum peak height (Rp) of the roughness curve, and the maximum valley depth (Rv) of the roughness curve is defined as the surface roughness, there is no big difference in R1 / R2, and all are 0.3 or more and less than 1.0.

[0068] On the other hand, as shown in Table 4, Examples 1 to 8 are examples in which the ratio of the surface roughness R1 of the strip-shaped portion end portion 7b1 to the surface roughness R2 of the strip-shaped portion center portion 7b2, that is, R1 / R2, is within the range. On the other hand, Comparative Examples 1 to 6 are examples in which the ratio of the surface roughness R1 of the strip-shaped portion end portion of the strip-shaped portion 7P to the surface roughness R2 of the strip-shaped portion center portion, that is, R1 / R2, is outside the range.

[0069] In addition, the grinding efficiency was evaluated using the raw materials 5 for ceramic balls of Examples 1 to 8 and the raw materials 5P for ceramic balls of Comparative Examples 1 to 6. By using a ball processing grinder, the grinding conditions for processing each raw material 5 and 5P for ceramic balls were fixed, and the processing state of the band portion was investigated and evaluated. The processing conditions are that the upper platform is not pressurized (not pressurized) and the lower platform is rotating. Then, the abrasive using glycerin as a lubricant is supplied to the diamond, and 100 samples are taken at intervals of 5 minutes after 60 minutes. The band portions 7 and 7P are visually inspected for appearance, and the time until the band portions 7 and 7P cannot be confirmed is shown as the processing time of the band portions 7 and 7P. Furthermore, for ceramic balls of the same size and the same sintered body, the conditions such as the distance from the upper platform, the number of rotations of the lower side rotation, the amount of raw materials 5 and 5P for ceramic balls, and the supply amount of the abrasive are set to be the same.

[0070] Table 3

[0071]

[0072] Table 4

[0073]

[0074] As can be seen from Table 4, in the ceramic ball raw materials 5 involved in Examples 1 to 8, the processability of the band-shaped portion 7 is improved. This means that the processing time of the ceramic ball raw materials 5 involved in Examples 1 to 8 can be shortened. In addition, in the ceramic ball raw materials 5 involved in Examples 1 to 8 and the ceramic ball raw materials 5P involved in Comparative Examples 1 to 6, the processing conditions are the same, but the ceramic ball raw materials 5 and 5P do not cause chipping (damage) at the corners of the band-shaped portion during processing.

[0075] As described above, according to the ceramic ball material 5, it is possible to shorten the processing time while suppressing the breakage of the ceramic material during the grinding process.

[0076] 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, and changes can be made without departing from the scope of the main purpose of the invention. These embodiments and their modifications are included in the scope and main purpose of the invention, and are also 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 a spherical portion and a band portion formed around the circumference of the surface of the spherical portion. A ratio of the surface roughness R1 of the end portion of the strip-shaped portion to the surface roughness R2 of the central portion of the strip-shaped portion, that is, R1 / R2, is greater than or equal to 0.3 and less than 1.

0.

2. The raw material for ceramic balls according to claim 1, characterized in that: The line segment passing through the center of the spherical portion and having two ends on the outer peripheral surface is greater than 0.5 mm, A ratio of the surface roughness R1 of the end portion of the strip-shaped portion to the surface roughness R2 of the central portion of the strip-shaped portion, that is, R1 / R2, is greater than or equal to 0.4 and less than 0.

9.

3. The raw material for ceramic balls according to claim 1 or 2, characterized in that: The ceramic ball raw material includes any one of an alumina sintered body, a silicon nitride sintered body, a silicon carbide sintered body, a boron nitride sintered body, and a zirconium oxide sintered body.

4. The raw material for ceramic balls according to claim 1 or 2, characterized in that: The ceramic ball raw material includes a ceramic sintered body, and the ceramic sintered body includes 85 mass % or more of silicon nitride.

5. A method for manufacturing a ceramic ball, characterized in that: The ceramic ball is manufactured by grinding the raw material for the ceramic ball according to claim 3.

6. A ceramic ball, characterized in that: The ceramic ball is obtained by grinding the raw material for ceramic balls according to claim 3.

7. The ceramic ball according to claim 6, characterized in that: The ceramic ball has an arithmetic surface roughness Ra of 0.01 μm or less.

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