Raw material for ceramic ball and ceramic ball and method for manufacturing the same

Abstract

A raw material for a ceramic ball according to an embodiment has a spherical portion and a belt-shaped portion formed in a belt shape. The raw material for the ceramic ball is characterized in that, when a circularity when viewed in a height direction of the belt-shaped portion is set as C, the circularity C is in a range exceeding 0% and 2.5% or less. The raw material for the ceramic ball can improve durability of a grindstone at the time of polishing processing. In addition, the ceramic can use any one or more of alumina, silicon nitride, boron nitride, and zirconia.

Description

Technical Field

[0001] The embodiments described later relate to raw materials for ceramic balls and ceramic balls and methods for manufacturing them. Background Technology

[0002] Various ceramic materials possess properties such as high hardness, insulation, and wear resistance. In particular, fine ceramics with improved purity and uniform particle size exhibit characteristics suitable for applications in capacitors, actuators, and refractory materials. Among these, bearing balls, which utilize wear resistance and insulation, are used in applications such as bearings, employing materials like alumina, silicon nitride, zirconium oxide, silicon carbide, and sialon. For example, Japanese Patent Application Publication No. 6-48813 (Patent Document 1) and Japanese Patent Application Publication No. 2764589 (Patent Document 2) disclose bearing balls using silicon nitride, while Japanese Patent Application Publication No. 60-18620 (Patent Document 3) discloses bearing balls using zirconium oxide. Furthermore, these ceramic balls are sometimes subjected to grinding processes suitable for various applications, such as bearings, using methods such as platform machining as described in Japanese Patent Application Publication No. 5334040 (Patent Document 5).

[0003] In the manufacturing process of these bearing balls, a sintering method is used to sinter the molded body. Furthermore, the molding method utilizes compression molding with a die. For example... Figure 1 As shown, compression molding is a method in which powder is inserted between an upper mold 1 and a lower mold 2 and pressure is applied. During compression molding, to protect the mold, a gap must be provided between the front end portion 3 of the upper mold 1 and the front end portion 4 of the lower mold 2 before compression molding is performed. Therefore, the molded body produced by compression molding has spherical and strip-shaped portions. For example, Japanese Patent No. 4761613 (Patent Document 4) discloses a raw material for bearing balls having spherical and strip-shaped portions. Figure 2 This indicates the raw materials used for ceramic balls as described in Patent Document 4. Figure 2 In the diagram, 7 represents the raw material used for the ceramic ball, 6 represents the surface of the ball, and 5 represents the strip-shaped part.

[0004] Existing technical documents

[0005] Patent documents

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

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

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

[0009] Patent Document 4: Japanese Patent No. 4761613

[0010] Patent Document 5: Japanese Patent No. 5334040 Summary of the Invention

[0011] The problem that the invention aims to solve

[0012] Ceramic balls are formed by grinding raw materials having a spherical surface 6 and a strip-shaped portion 5. These ground ceramic balls are particularly suitable for use as bearing balls. Sometimes, the raw material 7 having the spherical surface 6 and the strip-shaped portion 5 is also referred to as a raw material ball. For example, the bearing balls undergo a mirror finish with a surface roughness Ra of 0.1 μm or less. The mirror finish is achieved using a platform machining process.

[0013] Ceramic materials exhibit excellent wear resistance, but due to their brittleness and high hardness, they require more processing steps compared to metals. In particular, the initial step of improving the sphericity to the required value often accounts for a large portion of the total processing time due to the large machining allowance. Since the greater the initial sphericity (roundness), the longer this processing time, it is essential to minimize the sphericity of the raw materials used for processing the ceramic spheres.

[0014] This invention addresses the problem by providing a raw material for ceramic balls with high sphericity that can significantly shorten the processing time of ceramic materials, particularly during grinding.

[0015] Methods for solving problems

[0016] The ceramic ball raw material involved in the embodiment has a spherical surface and a strip-shaped portion formed in a strip shape. Its characteristic is that, when the roundness is defined as C when viewed from the height direction of the strip-shaped portion, the roundness C is in the range of more than 0% and less than 2.5%. Attached Figure Description

[0017] Figure 1 This is a diagram illustrating an example of mold pressing and forming.

[0018] Figure 2 This diagram illustrates an example of the raw materials used in existing ceramic balls.

[0019] Figure 3 This is a schematic diagram showing the measurement direction (first measurement direction) in the raw material for ceramic balls involved in the embodiment.

[0020] Figure 4 It is a diagram schematically showing an image obtained by observing the raw material for the ceramic ball involved in the embodiment from the first measurement direction.

[0021] Figure 5This is a schematic diagram showing the measurement direction (second measurement direction) in the raw material for ceramic balls involved in the embodiment.

[0022] Figure 6 This is a diagram schematically showing an image obtained by observing the raw material for the ceramic ball involved in the embodiment from the second measurement direction.

[0023] Figure 7 This is a diagram illustrating the width of the strip portion of the raw material for ceramic balls according to the illustrative embodiment.

[0024] Figure 8 This is a diagram illustrating the height of the strip portion of the raw material for ceramic balls according to an illustrative embodiment.

[0025] Figure 9 It is a schematic representation Figure 4 The image shown is Figure 6 The diagram shows the positional relationships of the images.

[0026] Figure 10 This is a diagram showing an example of the radius obtained by measuring the roundness C of the raw material for ceramic balls involved in the embodiment.

[0027] Figure 11 This is a diagram showing an example of the radius obtained by measuring the roundness C' of the raw material for ceramic balls involved in the embodiment.

[0028] Figure 12 This is a diagram illustrating an example of isostatic pressing in rubber molds. Detailed Implementation

[0029] The ceramic ball raw material according to the embodiment has a spherical surface and a strip-shaped portion. This ceramic ball raw material is characterized in that, when the roundness C is defined as the roundness when viewed from the height direction of the strip-shaped portion, the roundness C is within the range of more than 0% and less than 2.5%. The aforementioned height direction refers to the direction perpendicular to the width direction of the strip-shaped portion.

[0030] Furthermore, the strip is preferably formed across the circumference. This is because if the strip exists locally within the circumference, it may cause localized stress concentration during platform processing, potentially leading to cracks or gaps in the raw material used for the ball.

[0031] Furthermore, a roundness C is more preferably a value satisfying 0.01% or more and 2% or less. If the roundness C is small enough to satisfy 2.5% or less, especially 2% or less, the initial contact area between the raw material for ceramic balls and the platform becomes uniform during processing, reducing the necessary processing amount. Therefore, considering processability, the smaller the roundness C, the better. On the other hand, in order to make the roundness C less than 0.01%, especially 0%, the strip portion needs to be extremely small, and the roundness of the spherical surface also needs to be small. If the strip portion itself is made too small in order to reduce the roundness of the molded body with the strip portion, the granulating powder may not be able to fill the boundary between the upper and lower molds sufficiently. Therefore, the yield may deteriorate. Therefore, considering the yield, a roundness of 0.01% or more is more preferable. Furthermore, the average value rA of the roundness C relative to the radius of the raw material for ceramic balls is more preferably a value of 0.01% or more and 1.5% or less.

[0032] Figure 3 This indicates the raw material for ceramic balls according to the embodiment. 7 is the raw material for ceramic balls, 6 is the spherical surface, and 5 is the strip-shaped portion. The raw material 7 for ceramic balls includes the spherical surface 6 and the strip-shaped portion 5. Figure 3 In the ceramic ball raw material 7 shown, arrows in the schematic diagram indicate the first measurement direction 8, which is horizontal relative to the equatorial plane formed by the strip 5, i.e., the measurement direction "when viewed from the height direction along the height of the strip 5". Preferably, the strip 5 is located at the portion containing the equatorial plane of the ceramic ball raw material 7, so that the upper spherical surface 61 and the lower spherical surface 62 of the spherical surface 6 are approximately symmetrical with respect to the equatorial plane of the strip 5 formed across the circumference. Furthermore, it is preferable that the shape of the strip 5 is approximately symmetrical with respect to the equatorial plane formed by the strip 5. The equatorial plane formed by the strip 5 refers to the surface passing through the center of the width of the strip 5. Furthermore, Figure 4 This represents the image observed from the first measurement direction 8. Furthermore, from... Figure 4 It can be seen that, in the measurements taken from the aforementioned directions, both the banded portion 5 and the spherical portion 6 were observed simultaneously. Furthermore, as... Figure 4 As shown, when the strip 5 exists at the equatorial plane containing the raw material 7 for ceramic balls, the radius of the area where the strip 5 exists, as observed from the height direction of the strip 5, is sometimes the largest.

[0033] Figure 5 This indicates the raw material for the ceramic balls involved in the embodiment. 7 is the raw material for the ceramic balls, 6 is the spherical surface, and 5 is the strip-shaped portion. Figure 5 In the raw material 7 for the ceramic ball shown, the direction perpendicular to the equatorial plane formed by the strip 5 is the second measuring direction 9, which is the height 11 of the strip 5. Figure 8 (As shown) A schematic diagram of orthogonal directions. Figure 6This represents an example of an image observed from the second measurement direction 9.

[0034] also, Figure 2 and Figure 4 Similarly, the raw material 7 for the ceramic ball is indicated when viewed from the first measuring direction 8. For example... Figure 2 As shown, one or more diameters related to the strip portion 5 of the raw material 7 for the ceramic ball are designated as R1, and one or more diameters related to the spherical surface portion 6 are designated as R2. Figure 2 In the raw material 7 for the ceramic ball shown, the line whose length is the longest connecting point on the outer peripheral surface of one strip 5 to a point on the outer peripheral surface of the opposite strip 5 is defined as diameter R1. Furthermore, in Figure 2 In the raw material 7 for the ceramic sphere shown, the line connecting the point on the outer periphery of the spherical surface 6 to the point on the outer periphery of the spherical surface 6 with the longest length is defined as diameter R2. Thus, Figure 2 The ceramic sphere shown is made by dividing raw material 7 into 12 equal parts with 12 diameters, and the radius is the value of dividing each diameter by 2. Furthermore, the resulting radii are designated as r1 to r12 depending on the division location. The average value of radii r1 to r12 is then designated as the average diameter rA. This number of divisions can be changed if a sufficient number of samples can be obtained for the roundness evaluation described later. However, it is preferable to perform measurements with at least 12 divisions isotropically to improve the reliability of the data. Furthermore, in Figure 2 and Figure 4 In this process, roundness can be calculated from one measurement direction 8, but the radius described below can also be measured from multiple measurement directions 8, and the roundness can be calculated by calculating its maximum value, minimum value, and average value.

[0035] Here, the radii r1 to r12 are measured using a non-contact image size measuring instrument. The KEYENCE IM-7000 or an instrument with equivalent performance is used as the non-contact image size measuring instrument.

[0036] Furthermore, there are no particular limitations on the magnification ratio, but the following conditions must be met: the raw material 7 for the ceramic ball occupies more than 1 / 10 of the area of ​​a field of view, and the entire raw material 7 for the ceramic ball is contained within the field of view. If the proportion of the raw material 7 for the ceramic ball relative to a field of view is less than 1 / 10, the accuracy may be reduced due to the susceptibility to errors, etc., and therefore this is not preferred. On the other hand, if the raw material 7 for the ceramic ball is not contained within a field of view, the diameter may be undeterminable due to the center becoming unclear, etc., and this is also not preferred.

[0037] The roundness (roundness C (%)) of the ceramic sphere as observed from the first measurement direction 8 is defined as the difference between the radii of the object's inscribed circle and circumscribed circle, divided by the average of the radii. The radius of the inscribed circle refers to the minimum radius (r) obtained when observed from the first measurement direction 8. min On the other hand, the circumcircle refers to the maximum radius (r) obtained when viewed from the first measuring direction 8. max Therefore, the roundness C (%) of the ceramic ball using raw material 7 is determined by the following formula (1).

[0038] Circularity C (%) = (r max -r min ) / rA×100 …(1)

[0039] For example, if a ceramic sphere observed from the first measuring direction 8 is isotropically divided into 12 parts using raw material 7, the difference between the radii of the circumcircle and the incircle is the radius r1 to r12. Figure 10 The maximum value (r) of the 12 radii shown max ) and minimum value (r) min The difference between r1 and r12. Therefore, the radius of the circumcircle is the maximum value among r1 to r12 (r... max Furthermore, the radius of the inscribed circle refers to the minimum value among r1 to r12 (r... min Furthermore, the average value of the radius (rA) is the average value of r1 to r12. In addition, it can be seen from equation (1) that the smaller the value of the roundness C, the closer it is to a perfect circle.

[0040] At this point, an example of the radius obtained through measurement is... Figure 10 In the figure, radius 14 represents the radius r1 to r12 obtained by measuring the roundness of the ceramic ball using raw materials.

[0041] The ceramic ball material 7 has a spherical surface 6 and a strip-shaped portion 5. The strip-shaped portion 5 is formed in a strip shape, spanning the circumference of the surface of the spherical surface 6. This strip-shaped portion 5 may also have a partial concave portion. Furthermore, the spherical surface 6 can be any spherical surface. Therefore, the shape of the spherical surface 6 can be a perfect circle or an ellipse. The strip-shaped portion 5 is provided on the circumference of the spherical surface 6.

[0042] The roundness C obtained by formula (1) above is preferably a value that is greater than 0% and less than 2.5%. Furthermore, the roundness C is more preferably a value that is greater than 0.01% and less than 2%. The value of roundness C represents the calculated radius r1 to r12 ( Figure 10 The maximum value (r) of the 12 radii shown max ) and minimum value (r) minThe difference between the radii is calculated by dividing the difference by the average value of the radii (rA), and then multiplying the result by 100 to convert it into a percentage (%). If the roundness C is small enough to meet the requirement of 2.5% or less, especially 2% or less, the initial contact area between the raw material 7 for ceramic balls and the platform becomes uniform during processing, which can reduce the necessary processing amount. Therefore, considering processability, the smaller the roundness C, the better. On the other hand, in order to make the roundness C less than 0.01%, especially 0%, the strip portion 5 needs to be extremely small, and the roundness of the spherical surface 6 also needs to be small. If the strip portion 5 itself is made too small in order to reduce the roundness of the molded body that forms the basis of the raw material 7 for ceramic balls with the strip portion 5, the granulating powder may not be able to fill the upper mold 1 and lower mold 2 that form the molded body. Figure 1 The boundary portion (as shown). Therefore, the yield may deteriorate. Therefore, considering the yield, the roundness C is more preferably 0.01% or more.

[0043] Furthermore, the roundness C obtained by the above formula (1) is more preferably a value of 0.01% or more and 1.5% or less. Roundness C represents the value obtained by calculating r1 to r12 ( Figure 10 The maximum value (r) of the 12 radii shown max ) and minimum value (r) min The difference between the radii is calculated by dividing the difference by the average value of the radii (rA), and then multiplying the result by 100 to convert it into a percentage (%). By setting the roundness C within this range, when further grinding is performed using a platform, the effect of making the initial contact area with the platform uniform can be improved. Furthermore, the proportion of defects such as notches, cracks, and uneven coloring generated on the surface of the ceramic ball raw material 7 on the bearing surface can be suppressed.

[0044] Furthermore, the roundness (roundness C') of the spherical surface 6 (excluding the strip portion) when viewed from the first measuring direction 8 is preferably a value of 0% or more and 1.5% or less. The roundness C' of the spherical surface 6 is expressed as calculated from r'1 to r'12 ( Figure 11 The maximum value (r') of the 12 radii shown max ) and minimum value (r' min The difference between the radii is calculated by dividing the difference by the average value of the radii (r'A), and then multiplying the result by 100 to convert it into a percentage (%) value. Furthermore, excluding the measurement values ​​of the strip portion 5, only the spherical portion 6 is used as the measurement site. The initial measurement values ​​are not used; only the spherical portion 6 is divided into 12 sections. Figure 10 The measurements are taken separately. At this point, the average radius of the measured values ​​excluding the strip portion 5 is set as the average diameter rA'. At this point, the roundness C' of the spherical portion 6 is 0, indicating the difference between values ​​below the resolution of the device.

[0045] At this point, an example of the radius obtained through measurement is... Figure 11 In the figure, radius 15 represents the radius r'1 to r'12 obtained solely through the measurement of the spherical surface 6.

[0046] Furthermore, the roundness C' of the spherical part 6 is more preferably a value of 0% or more and 1.3% or less. However, the average value of the radius of the measured value excluding the strip portion 5 is set as the average diameter rA'. The roundness C' of the spherical part 6 is calculated by the following formula (2).

[0047] Circularity C' (%) = (r') max -r' min ) / rA'×100 …(2)

[0048] Furthermore, the measurement direction orthogonal to the height direction of the strip is designated as the second measurement direction. This second measurement direction is... Figure 5 It is represented as 9. For a schematic diagram projected from the second measuring direction 9... Figure 6 According to Figure 4 Using the same steps to calculate the radius after obtaining the diameter at point 12, we can derive the maximum value of the radius (r). max ), minimum value (r”) min The average diameter (rA) of the ceramic ball is used to calculate the roundness C (%). The average diameter of the ceramic ball using raw material 7 in this case is defined as rA, and the roundness is defined as C. The roundness C of the ceramic ball using raw material 7 is calculated by the following formula (3).

[0049] Roundness C (%) = (r) max -r” min ) / rA”×100 …(3)

[0050] The roundness C” is preferably a value of 0% or more and 1.5% or less. The roundness C” is preferably a value of 0.01% or more and 1.0% or less. Furthermore, the roundness C” represents the maximum value (r”) of r”1 to r”12 (the 12 radii omitted in the illustration). max ) and minimum value (r” min The difference between the radii (r”A) and the mean radii (r”A) is multiplied by 100 to convert it into a percentage (%). If the roundness C” is within this range, the initial contact area with the platform becomes uniform during the processing of the ceramic ball using raw material 7, reducing the necessary processing amount. Furthermore, if the roundness C” is not within this range, the roundness on other measurement surfaces also increases, potentially increasing the required processing amount.

[0051] In addition, from Figure 3The plane projected from the first measurement direction 8 shown is the measurement surface 12 when measured from the first measurement direction 8. Sometimes the measurement surface 12 when measured from the first measurement direction 8 is also referred to as plane 12.

[0052] In addition, from Figure 5 The plane projected from the second measurement direction 9 shown is the measurement surface 13 when measured from the second measurement direction 9. Sometimes, the measurement surface 13 when measured from the second measurement direction 9 is also referred to as plane 13. For example... Figure 9 As shown, plane 12 and plane 13 intersect approximately perpendicularly.

[0053] The raw material 7 for ceramic balls preferably contains one or more of the following: alumina, silicon nitride, boron nitride, silicon carbide, zirconium oxide, and silane, totaling 85% by mass or more. The raw material 7 for ceramic balls is formed from a sintered ceramic body. The statement that it contains one or more of the following: alumina, silicon nitride, boron nitride, and zirconium oxide, totaling 85% by mass or more, refers to the content in the sintered ceramic body. In other words, the sintered ceramic body may also contain less than 15% by mass of substances other than those mentioned above.

[0054] As raw materials for bearing balls, alumina sintered bodies, silicon nitride sintered bodies, boron nitride sintered bodies, zirconium oxide sintered bodies, silicon carbide sintered bodies, silane sintered bodies, alumina-zirconia sintered bodies (obtained by mixing alumina and zirconium oxide, with a total content of 85% by mass or more), or silane sintered bodies are used. Therefore, it is possible for only one of the following types of sintered bodies to have a content of 85% by mass or more, as in alumina sintered bodies, silicon nitride sintered bodies, boron nitride sintered bodies, zirconium oxide sintered bodies, and silicon carbide sintered bodies, or it is possible for two or more types of sintered bodies to have a total content of 85% by mass or more, as in alumina-zirconia sintered bodies or silane sintered bodies. Among these, the bearing ball raw material formed from silicon nitride sintered bodies exhibits particularly excellent wear resistance. Therefore, sintered bodies containing 85% by mass or more of silicon nitride are particularly preferred.

[0055] The Vickers hardness of alumina sintered bodies and zirconia sintered bodies is between 1200 and 1700, but their toughness is 3 MPa·m. 1 / 2 Above and 6MPa·m 1 / 2 The following levels.

[0056] On the other hand, the Vickers hardness of silicon nitride sintered bodies is between 1400 and 1800, and the toughness value is 5 MPa·m. 1 / 2 Above and 10 MPa·m 1 / 2 The following levels.

[0057] In other words, silicon nitride sintered bodies also possess excellent toughness and Vickers hardness among ceramics. Due to these properties, silicon nitride sintered bodies exhibit particularly excellent wear resistance.

[0058] Silicon nitride sintered bodies are microstructures dominated by β-type silicon nitride grains. β-type silicon nitride grains have a slender shape. Due to the complex intertwining of these slender grains, silicon nitride sintered bodies exhibit high toughness.

[0059] Silicon nitride sintered bodies possess high mechanical strength. However, this also results in very poor grinding efficiency. As mentioned above, by improving (i.e., reducing) the sphericity, the amount of material removed can be reduced. By reducing the amount of material removed, even for ceramic balls made from high-strength ceramic sintered bodies like silicon nitride sintered bodies, the grinding efficiency can be improved.

[0060] Next, the manufacturing method of raw material 7 for ceramic balls will be described. As long as the raw material 7 for ceramic balls described in the embodiment satisfies the above-described structure, its manufacturing method is not particularly limited. However, as a method for efficient manufacturing, the following manufacturing methods can be cited. Regarding the manufacturing method, a silicon nitride sintered body will be used as an example for explanation.

[0061] First, appropriate amounts of sintering aids, additives, solvents, and binders are added to silicon nitride, which becomes the raw material, and the mixture is then pulverized and granulated using a spray dryer. This process prepares granulated powder from the raw material powder. Furthermore, when the total amount of silicon nitride powder and sintering aid powder is set to 100% by mass, the silicon nitride powder is preferably 85% by mass or more. Additionally, the additive is a plasticizer.

[0062] The solvent is water or an organic solvent or a mixture thereof. Organic solvents include compounds containing alcohols, ketones, benzene, and ethers. Alcohols include methanol, ethanol, propanol, butanol, hexanol, heptanol, octanol, and phenol. Ketones include acetone and diethyl ketone. Ethers include diethyl ether and dimethyl ether. Preferably, the organic solvent has a carbon chain number of 25 or less. If the chain number exceeds 25, it becomes difficult to volatilize, and its control during the degreasing process may become difficult. The binder is an organic material. When the total amount of silicon nitride powder and sintering aid powder is set to 100% by mass, the amount of binder added is set to 3% by mass or more and 20% by mass or less. By adjusting the amount of binder and the shape of the mold (making the spherical part a non-spherical shape), the roundness of the surface including the spherical part 6 and the strip part 5 can be reduced in the process described later.

[0063] Next, the granulated powder is pressed into shape. A pressing method using an upper mold 1 and a lower mold 2 can be cited as an example. The spherical shape of the inner surfaces of the upper mold 1 and the lower mold 2 determines the spherical surface 6 of the raw material 7 for ceramic balls. At this time, the sphere formed by uniaxial pressing varies in internal forming density depending on the pressing vertical direction, the vertical direction, and the proximity of the upper mold 1 and the lower mold 2. Therefore, especially when combining mold pressing and isostatic pressing (CIP processing, etc.), the roundness during mold forming and the roundness after isostatic pressing exhibit different values. Therefore, in order to improve roundness in subsequent processes, the three-dimensional shape of the spherical surface formed by the mold is made into an aspherical shape deviating from a perfect sphere. Thus, it is possible to form the raw material 7 for ceramic balls with better roundness, and therefore the roundness C obtained by the above formula (1) can be controlled within a range exceeding 0% and 2.5% of the average diameter rA.

[0064] The molded body obtained by compression molding becomes a molded body having a spherical part corresponding to the spherical part 6 and a strip-shaped part corresponding to the strip-shaped part 5.

[0065] A strip-shaped portion of the resulting molded body can also be removed. The component used in this removal process can be any component, as long as it can remove the strip-shaped portion. Examples of components used for removing the strip-shaped portion include sandpaper, diamond sandpaper, abrasive paper, and files.

[0066] The removal of the strip is preferably performed after compression molding and before HIP (Hot Isostatic Pressing). Considering the ease of strip removal, it is preferably performed before sintering, more preferably before debinding, and even more preferably before cold isostatic pressing (CIP).

[0067] The removal process of the strip-like portion preferably does not apply excessive pressure.

[0068] Since excessive pressure can induce notches or cracks, the applied pressure needs to be controlled. Furthermore, even after the strip-shaped portion removal process is performed, stripe-like traces remain, indicating that the object has a strip-shaped portion. Therefore, even when a strip-shaped portion removal process is performed, it is still defined as having a strip-shaped portion.

[0069] Furthermore, isostatic pressing is preferably performed on the molded body after compression molding (including molded bodies that have undergone processes such as strip removal). By performing isostatic pressing, the granulated powder in the molded body can be uniformly compressed. As a result, the amount of broken granulated powder remaining in the molded body can be reduced. By reducing the amount of broken granulated powder remaining, the shrinkage ratio during the sintering process can be controlled.

[0070] As an example of isostatic pressing, an isostatic pressing method using a rubber mold will be described. Figure 12 This represents an example of a disc-shaped rubber mold. In the figure, 16 and 17 are disc-shaped rubber molds, and 18 is a space.

[0071] The disc-shaped rubber molds 16 and 17 have hemispherical holes on both sides, each hole being at least 1% and less than 35% larger than the diameter of the molded body. By placing the molded body 20 within these holes and overlapping the disc-shaped rubber molds 16 and 17, the molded body 20 is sealed within the space 18 formed by the disc-shaped rubber molds 16 and 17. A hydrostatic pressure higher than the pressure applied during molding is applied to the disc-shaped rubber molds 16 and 17. This allows for uniform compression of the molded body 20. This process reduces residual granulated powder. Furthermore, it is preferable that the strip-shaped portion of the molded body 20 is arranged perpendicularly to the plane formed by the cylinders of the disc-shaped rubber molds 16 and 17. Moreover, the disc-shaped rubber molds 16 and 17 are preferably rubber molds with a Shore hardness Hs of 30 or higher and less than 50. By ensuring the hardness of the disc-shaped rubber molds 16 and 17 is within this range, they possess the deformation capability to ensure uniform contact between the surface of the molded body 20 and the disc-shaped rubber molds 16 and 17. In addition, the disc-shaped rubber molds 16 and 17 also exhibit good durability.

[0072] Because the molded body obtained in this process is subjected to isotropic pressure, a shape similar to that of the raw material 7 used for sintered ceramic spheres can be obtained. The roundness C at this time can also be measured, and the curved surface formed by the upper mold 1 and the lower mold 2 during pressing can be adjusted.

[0073] Next, a degreasing process is performed on the molded body after compression molding (including molded bodies that have undergone strip removal processes and isostatic pressing processes). The degreasing process involves heating the body above the decomposition temperature of the organic components, such as adhesives, to cause the organic components to volatilize. The degreasing process can also be performed in a nitrogen atmosphere or an atmospheric atmosphere. A degreased body is obtained through this degreasing process.

[0074] Next, a sintering process is performed on the degreased body. The sintering temperature is preferably 1700°C or higher and 2000°C or lower. Furthermore, the sintering process is preferably performed in a nitrogen atmosphere. Additionally, the sintering pressure is preferably in the range of atmospheric pressure or higher and 300 MPa or lower. Atmospheric pressure is 0.10133 MPa (=1 atm). Furthermore, the sintered body obtained through the sintering process can be subjected to HIP (hot isostatic pressing) treatment. Through this process, a ceramic ball raw material 7 with less density inhomogeneity can be obtained. Furthermore, the ceramic ball raw material 7 obtained in this way is a ceramic sintered body with a theoretical density of 98% or higher. In addition, the method of grinding the completed ceramic ball raw material 7 is also included in the adjustment of the spherical surface 6 and the strip-shaped portion 5, i.e., the adjustment of the roundness C. However, since this method adds a grinding step, it cannot be considered a preferred method. The manufacturing method described above is preferred.

[0075] Ceramic balls can be manufactured by grinding raw material 7. As a representative example of the grinding process for balls, platform machining can be cited.

[0076] Grinding can be performed by, for example, inserting the ceramic ball material 7 between two parallel platforms. Then, by moving the grinding platforms, the ceramic ball material 7 is shaped into a spherical shape. Alternatively, fixed diamond abrasive grains can be used to improve the machining accuracy of the grinding surface. Furthermore, when the ceramic ball obtained by grinding the ceramic ball material 7 is used for bearing applications, it is referred to here as a bearing ball.

[0077] The surface roughness of bearing balls is specified in ASTM F2094. Depending on the application, bearing balls are graded according to ASTM F2094. They are ground to an arithmetic surface roughness Ra that meets that grade. If the grade is increased, a mirror finish with an arithmetic surface roughness Ra of less than 0.01 μm is sometimes performed.

[0078] The ceramic ball raw material 7 according to the embodiment has the following characteristics: the roundness C of the curved surface formed by the spherical part 6 and the strip part 5, measured in the first measuring direction 8, is in the range of more than 0% and less than 2.5%. Therefore, it is possible to make the contact with the grinding stone, such as the grinding platform, a surface contact. As a result, breakage of the ceramic ball raw material 7 during the grinding process can be suppressed. In addition, the durability of the grinding platform during the grinding process can be improved. Therefore, by providing ceramic balls as a raw material for bearing balls with low cutting amount, it is expected that the time, cost, grinding material, and grinding amount required for the grinding process can be reduced.

[0079] Furthermore, as mentioned above, ceramic balls with improved (smaller) sphericity are particularly suitable for applications such as bearings that undergo grinding. As components for bearing applications, these can be components made of other raw materials such as SUS for the inner or outer race, or components where the outer or inner race portion is also made of ceramic, as described above. Therefore, it can be an all-ceramic bearing where the wear-resistant components are entirely made of ceramic, or a bearing where only the bearing balls are made of ceramic. Furthermore, in applications using all-ceramic bearings, the race, such as the inner or outer race, can be made of a different main material than the bearing balls, or it can be made of the same main material. It can also be applied to bearings that do not use grease.

[0080] (Example)

[0081] (Examples 1-8, Comparative Examples 1-3)

[0082] Sintering aids, additives, solvents, and binders are added to ceramic powder used as raw materials, and the mixture is then pulverized and granulated using a spray dryer. Examples 1-3 and 6-8 are silicon nitride sintered bodies, Example 4 is an alumina sintered body, and Example 5 is a zirconia sintered body. The silicon nitride sintered body contains 85% by mass or more silicon nitride. The alumina sintered body contains 85% by mass or more alumina. The zirconia sintered body contains 85% by mass or more zirconia. When the total amount of the main component and sintering aid is set to 100 parts by mass, the amount of binder added is set to 3 parts by mass or more and 20 parts by mass or less.

[0083] Next, the granulated powder is used for compression molding. Compression molding is a die-forming process using upper and lower molds. After die forming, isostatic pressing is performed. Isostatic pressing uses a disc-shaped rubber mold with a Shore hardness Hs of 30 or higher and 50 or lower. Figure 12 (As shown). Furthermore, in isostatic pressing, the disc-shaped rubber molds 16 and 17 are provided on both sides with hemispherical holes that are at least 1% and less than 35% larger than the diameter L1 of the molded body 20. Additionally, the strip-shaped portion of the molded body 20 (corresponding to the strip-shaped portion 5 of the raw material 7 for ceramic balls) is arranged perpendicular to the cylindrical direction of the rubber mold. In this state, the isostatic pressing process applies a hydrostatic pressure higher than the pressure applied during molding.

[0084] Next, a sintering process is carried out. The sintering process is conducted at a temperature above 1700°C and below 1900°C, in a nitrogen atmosphere, and at atmospheric pressure. Afterward, HIP treatment is performed at a temperature above 1600°C and below 1900°C, in a nitrogen atmosphere, and at a pressure above 150 MPa and below 300 MPa.

[0085] This process produces the raw materials for the ceramic balls involved in the embodiments. Furthermore, in the comparative example, when the total amount of the main component and sintering aid is set to 100 parts by mass, the amount of binder added is set to 3 parts by mass. Additionally, isostatic pressing is omitted after the molding process.

[0086] The shape of the raw materials used for the ceramic balls involved in the embodiments and comparative examples was measured. Each sample had a width of 0.5 mm or more and 3 mm or less, and a height of 0.05 mm or more and 0.2 mm or less in the strip-shaped portion. The width of the strip-shaped portion was... Figure 7 The symbol 10 is used to represent the height of the strip. Furthermore, the height of the strip is... Figure 8 The numbers are schematically represented by 11. The respective determination methods are as described above. Table 1 shows the results.

[0087] Table 1

[0088]

[0089] Example 1 is a raw material for ceramic balls that are ground to become 1 / 4-inch (6.35 mm) ceramic balls. Example 2 and Comparative Example 1 are raw materials for ceramic balls that are 5 / 16-inch (7.9375 mm) ceramic balls. Examples 3 and 7 are raw materials for ceramic balls that are 1-inch (25.4 mm) ceramic balls. Examples 4 and 8 and Comparative Example 2 are raw materials for ceramic balls that are 5 / 8-inch (15.875 mm) ceramic balls. Examples 5 and Comparative Example 3 are raw materials for ceramic balls that are 3 / 4-inch (19.05 mm) ceramic balls. Example 6 is a raw material for ceramic balls that are 1-3 / 8 (11 / 8) inch (34.925 mm) ceramic balls. All of these can be used as bearing balls.

[0090] Furthermore, in Comparative Examples 1, 2, and 3, the roundness C calculated by Equation (1) above exceeded 2.5%, and the roundness C' calculated by Equation (2) above exceeded 1.5%. Furthermore, in Comparative Example 3, the roundness C” calculated by Equation (3) above did not exceed 1.5% but exceeded 1.0%.

[0091] The grinding efficiency was evaluated using the ceramic ball raw materials from the examples and comparative examples. The evaluation involved processing each ceramic ball raw material using a platform grinding stone (serial number #180), with each batch consisting of the number of raw materials of different sizes. The number of batches the platform grinding stone could handle was investigated. Grinding was performed to achieve a surface roughness Ra of 0.01 μm or less for the ceramic balls. Furthermore, the proportion of defects in the ceramic ball raw materials during the grinding process was investigated (referred to as "Raw Material Defect Rate" in Table 2). Additionally, the diameter deviation of the ceramic balls after the intended grinding process was investigated, specifically the average of 10 different diameters. The diameter difference was the difference between the minimum and maximum diameter measured across the entire circumference of the sphere. Table 2 shows the results.

[0092] Table 2

[0093]

[0094] As shown in Table 2, when ceramic balls are obtained by grinding the raw materials for ceramic balls involved in the embodiments, the durability of the grinding stone is improved. Furthermore, the defect rate of the raw materials for ceramic balls is reduced. Moreover, the deviation from the target diameter after grinding can be reduced. Therefore, it can be seen that the grinding efficiency of the raw materials for ceramic balls involved in the embodiments is good.

[0095] The above embodiments of the present invention have been illustrated, but these embodiments are provided 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, and modifications can be made without departing from the spirit of the invention. Variations of these embodiments are included within the scope and spirit of the invention, and are included within the scope of the invention as described in the claims and its equivalents. Furthermore, the above embodiments can be implemented in combination with each other.

[0096] Explanation of reference numerals in the attached figures

[0097] 1… Upper mold

[0098] 2…Lower mold

[0099] 3…The front end of the upper mold

[0100] 4…The front end of the lower mold

[0101] 5…band-like portion

[0102] 6… spherical face

[0103] 61… Upper spherical surface

[0104] 62…Lower ball surface

[0105] 7…Raw materials for ceramic balls

[0106] 8…First direction of measurement

[0107] 9…Second Measurement Direction

[0108] 10…width of the strip

[0109] 11… Height of the band

[0110] 12…Measuring surface when measured from the first measuring direction

[0111] 13…Measuring surface when measured from the second measuring direction

[0112] 14… The radius obtained by measuring the roundness of the raw materials used to make ceramic balls.

[0113] 15… The radius obtained solely through the measurement of the spherical part

[0114] 16…Disc-shaped rubber mold

[0115] 17…Disc-shaped rubber mold

[0116] 18…The spatial portion of the inner surface shape of a rubber mold

[0117] 20…formed body

Claims

1. A raw material for ceramic balls, comprising a spherical surface and a strip-shaped portion, characterized in that, When the roundness is set to C when viewed from the height direction of the strip, The roundness C is within the range of more than 0% and less than 0.5%. The roundness C is determined using the following method: The ceramic sphere, viewed from the height of the strip, is made of raw material and divided into 12 or more equal parts by 12 or more diameters. The value of each diameter divided by 2 is taken as the radius, the average value of these radii is taken as the average diameter rA, and the maximum value of these radii is taken as r. max Let the minimum value among these radii be r. min The roundness C of the raw material used for the ceramic ball is determined by the following formula (1). Circularity C (%) = (r max -r min ) / rA×100 …(1)。 2. The raw material for ceramic balls according to claim 1, characterized in that, When the roundness of the spherical surface is defined as C' when viewed from the height direction of the strip portion, the roundness C' is within the range of more than 0% and less than 1.5%. The roundness C' is determined by the following method: The spherical surface of the ceramic sphere, viewed from the height of the strip, is divided into 12 or more equal parts by 12 or more equal diameters. The radius is defined as the value of each diameter divided by 2, the average of these radii is defined as the average diameter rA', and the maximum value of these radii is defined as r'. max Let the minimum of these radii be r' min The roundness C' is calculated using the following formula (2). Circularity C' (%) = (r') max -r' min ) / rA'×100 …(2).

3. The raw material for ceramic balls according to claim 1 or 2, characterized in that, When viewed from the height direction of the strip, the roundness C' of the spherical surface is in the range of more than 0% and less than 1.3%.

4. The raw material for ceramic balls according to claim 1 or 2, characterized in that, When the roundness is set to C” when viewed from an orthogonal direction to the height direction of the strip, The roundness C is within the range of 0% to 1.5%. The roundness C” is determined using the following method: The ceramic sphere, viewed from an orthogonal direction along the height of the strip, is made of raw material and divided into 12 or more equal parts by 12 or more diameters. The radius is defined as the value of each diameter divided by 2, the average value of these radii is defined as the average diameter rA, and the maximum value of these radii is defined as r0. max Let the minimum value among these radii be r” min The roundness C” is calculated using the following formula (3). Roundness C (%) = (r) max -r” min ) / rA”×100 …(3).

5. The raw material for ceramic balls according to claim 1 or 2, characterized in that, The raw materials used for the ceramic balls contain more than 85% by mass of any one or more of alumina, silicon nitride, boron nitride, zirconium oxide, silicon carbide, and silane.

6. The raw material for ceramic balls according to claim 1 or 2, characterized in that, The raw material used for the ceramic balls is a sintered body containing more than 85% by mass of silicon nitride.

7. A method for manufacturing ceramic balls, characterized in that, The raw materials used for grinding the ceramic balls described in any one of claims 1 to 6 are used for grinding.

8. A ceramic ball, characterized in that, It is obtained by grinding the raw materials used to make the ceramic balls described in any one of claims 1 to 6.

9. A bearing, characterized in that, The ceramic ball described in claim 8 was used.

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