JP5578429B2 - Ceramic ball base ball, ceramic ball base ball mold and method for manufacturing ceramic ball base ball - Google Patents

Description

  The present invention relates to a ceramic ball base ball used for, for example, a bearing ball, a ceramic ball base ball forming die used for manufacturing the ceramic ball base ball, and a method for manufacturing the ceramic ball base ball.

  Ceramic balls are used for bearings and the like, and are used by being rotated. Therefore, it is important that the surface is flat and close to a true sphere. Usually, ceramic balls are made of various ceramic raw material powders such as silicon nitride, mixed with a sintering aid and additives, pulverized, and granulated with a spray dryer, etc., and the granulated powder is formed into a spherical shape using a press molding method. Then, the molded body is sintered to form an elementary ball for a ceramic ball, and surface processing is performed as necessary.

As shown in FIG. 5, the conventional ceramic ball base ball inserts granulated powder between the upper punch 1 and the lower punch 2 and applies pressure to the upper punch 1 and the lower punch 2 in the vertical direction to produce A compact is produced by press-molding the granulated powder and, if necessary, cold isostatic press (hereinafter abbreviated as CIP) is applied, and then the compact is sintered. It has been. However, when forming the ceramic ball base ball molded body by such press molding, pressure is applied to the granulated powder so that the tip portion 3 of the upper punch 1 and the tip portion 4 of the lower punch 2 do not contact each other. In addition, it is necessary to press form with a gap between the tip portion 3 and the tip portion 4. Accordingly, since the powder exists between the tip portions 3 and 4 of the punch during press molding, the ceramic ball base ball molded body 5 is formed on the outer peripheral portion of the substantially spherical spherical portion 6 as shown in FIG. The belt-like portion 7 is formed in an annular shape. Since the ceramic ball needs to be close to a true sphere, it is necessary to remove the band-like portion 7 by a processing means such as polishing or polishing after sintering. When removing the band, there are problems such as scratches and wear on the grindstone, excessive wear of the abrasive material, and the abrasive material must be replaced frequently. There is a problem that defects occur in the ceramic balls themselves due to chipping and the like, and defects such as scratches also occur in the polished balls that are products.

  Furthermore, in the method of producing a compact by inserting granulated powder between the upper punch 1 and the lower punch 2 having the curved surface, and applying pressure to the upper punch 1 and the lower punch 2 to perform powder press molding. Since the compressibility of the powder granulated at the center portion and the outer edge portion (corresponding to the belt-like portion) of the upper punch 1 and the lower punch 2 in the up-and-down pressurization direction is different, Differences may occur, and uneven density in each part of the molded product may occur. When a spherical body obtained by sintering and processing such a molded body is incorporated in a ball bearing and used, the spherical body may be worn unevenly, which may adversely affect the operation of the bearing.

In order to solve the problem related to the belt-like portion that inevitably occurs in the ceramic ball base ball, the following conventional techniques are disclosed.
In Patent Document 1, in a material for a ceramic ball having a substantially spherical spherical portion at both ends and a belt-like portion extending in the entire circumferential direction at a central portion, the diagonal diameter of the belt-like portion and the spherical portion are provided. A ceramic ball material having a difference from the pole diameter of 100 μm or less is described. According to this prior art, since the pole part and the belt-like part of the spherical part of the elementary sphere can be brought into contact with the abrasive material on average during processing, it is possible to greatly suppress wear and damage of the abrasive material, the grindstone, etc. Yes.

  In Patent Document 2, a ceramic ball is provided with a band-shaped portion projecting outward over the entire circumferential direction of the center of the ceramic ball base ball, and an edge portion that is an end in the width direction of the band-shaped portion is rounded. An elementary ball is described. According to this prior art, when the ceramic ball base ball is polished by a grinder using a grindstone, even if the edge portion hits the grindstone, the grindstone is hardly scratched or abnormal wear is less likely to occur on the grindstone. It is said that there is an effect that the defects of the ceramic ball itself are less likely to occur.

In Patent Document 3, the ceramic powder is pressed by an upper punch and a lower punch having concave portions that form a spherical surface, so that both end portions are spherical, and a portion sandwiched between both spherical portions forms an aspherical portion. In addition, a sphere manufacturing method is described in which the ratio of the width of the aspheric surface portion to the length between the vertices of the both spherical surface portions is 50 to 90%. According to this prior art, it is said that the density unevenness of the molded body can be eliminated and a ceramic sphere having excellent durability and reliability as a machine part can be obtained.

JP 2001-163673 A JP 2003-137640 A Japanese Patent Laid-Open No. 02-214606

  However, even if the technique for adjusting the belt-like portion inevitably generated in the ceramic ball molded body described in the prior art is used, there are still the following problems. In the invention described in Patent Document 1, the difference between the diagonal diameter of the belt-shaped portion and the polar diameter of the spherical surface portion is set to 100 μm or less, so that the belt-shaped portion does not protrude from the spherical surface portion. Although the average part touches the abrasive, etc., and it can suppress the abrasion and damage of the abrasive due to the contact with the band, the powder at the boundary between the band and the spherical part when pressing the ceramic ball Due to the different compression ratios, molding density unevenness occurs, and the ceramic ball molded body tends to crack at the boundary between the belt-like part and the spherical part during molding, and also breaks at the boundary between the belt-like part and the spherical part during sintering. Has a problem that the production yield is lowered and the production cost is increased.

In the invention described in Patent Document 2, since the edge portion which is an end portion in the width direction of the belt-shaped portion is rounded, the wear of the grindstone and the generation of scratches at the time of polishing are prevented, and the ceramic ball itself Although the occurrence of defects can be prevented to some extent, the compression ratio of the powder is greatly different at the boundary between the belt-like part and the spherical part during press molding, resulting in irregularities in the molding density. Cracks are likely to occur at the boundary between the belt-shaped portion and the spherical surface portion, and cracks are likely to occur at the boundary between the belt-shaped portion and the spherical surface portion during sintering, resulting in a problem that the manufacturing yield is reduced and the manufacturing cost is increased.

Although the invention described in Patent Document 3 can eliminate unevenness in the density of the molded body to some extent, it is not sufficient, and still cracks occur at the boundary between the band-shaped portion and the spherical surface portion of the ceramic ball molded body during molding, and also during sintering. However, the problem that the crack occurs at the boundary between the belt-like portion and the spherical portion has not been solved, but the production yield is lowered and the production cost is increased. Furthermore, since the ratio of the width of the aspherical surface portion to the length between the vertices of both spherical surface portions is 50 to 90% and the width of the belt-like portion is increased, the processing until obtaining a product ball from the base ball It also had the problem that the time was long.

Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art, to prevent generation of cracks when manufacturing a ceramic ball base ball having a strip-shaped portion, and to obtain a ceramic ball base ball having a high manufacturing yield.

  The present inventors diligently studied on the above problems. As a result, in the ceramic ball base ball, the knowledge that the said subject can be solved by devising the shape between a spherical surface part and a strip | belt-shaped part was acquired.

That is, the ceramic ball base ball 9 of the present invention has a substantially spherical spherical surface portion 6 at both ends as shown in FIG. 1, and a belt-like portion 7 protruding outward in the entire circumferential direction is formed at the center portion. Further, the ceramic ball base ball is characterized by having an inclined portion 8 between the spherical portion and the belt-like portion.

In the ceramic ball base ball of the present invention, it is preferable that the cross-sectional shape of the inclined portion 8 is an R surface and / or a chamfer. In the ceramic ball base ball of the present invention, as shown in FIGS. 3 (a) and 3 (b), when the radius of the R surface and the length of the chamfer are C, and the protruding height of the belt-like portion is H, 1 It is preferable that> C / H ≧ 0.05.

  Further, as shown in FIG. 1, when the length connecting the vertices of the spherical portions on both sides of the ceramic ball base ball is A and the width of the belt-like portion is D, D / A ≧ 0.05. preferable. Furthermore, it is preferable that D / A ≦ 0.5.

As shown in FIG. 2, the ceramic ball base ball molding die 25 of the present invention has upper and lower punches 11 and 12 having a substantially hemispherical concave portion at the center of the pressing surface and a flat portion around the concave portion. The die for forming a ceramic ball base ball formed by a die 20 for storing a punch is characterized by having an inclined portion 18 at the intersection of the substantially hemispherical concave portion and the flat portion of the upper and lower punches. It is preferable that the inclined portion 18 between the substantially hemispherical concave portion and the flat portion of the upper and lower punches is an R surface and / or a chamfer. Further, as shown in FIGS. 4A and 4B, the radius and chamfer length of the R surface of the inclined portion 18 between the substantially hemispherical concave portion of the upper and lower punches and the flat portion 19 are c, When the length is h, it is preferable that 1> c / h ≧ 0.05.

The method for producing a ceramic ball element ball according to the present invention includes a substantially hemispherical concave portion at the center of the pressing surface, a flat portion around the concave portion, and an inclined portion at an intersection of the concave portion and the flat portion. Using a ceramic ball base ball molding die formed by a punch and a die containing these upper and lower punches, the ceramic powder has at least 0.1 to 5 parts by weight of an organic binder, and the center particle size Is 10 to 150 μm, the ratio of bulk density ρa to tap bulk density ρt, (ρa / ρt) is a granulated powder having a pressure of 0.7 or more in the axial direction of the upper and lower punches, and the entire circumferential direction in the center A ceramic ball base ball molded body having a belt-like portion protruding outward and having an inclined portion between the spherical portion and the belt-like portion is sintered and then sintered to obtain a ceramic ball base ball. The granulated powder preferably has an aspect ratio of 2 or less. The granulated powder preferably has a maximum particle size of 300 μm or less. The granulated powder is preferably a ceramic slurry obtained by mixing at least a ceramic powder, an organic binder, and a solvent and having a solid content of 45% or more by spray drying.

According to the ceramic ball base ball, the ceramic ball base ball mold, and the method for manufacturing the ceramic ball base ball of the present invention, when manufacturing the ceramic ball base ball having a band-shaped portion, cracking during press molding, during sintering Generation of ceramic balls can be produced with high yield.

It is the schematic diagram which showed an example of the ceramic ball base ball of this invention. It is sectional drawing which showed the metal mold | die for ceramic ball base ball shaping | molding of this invention. (A) (b) It is the expanded sectional view which showed a part of ceramic ball base ball of this invention. (A) (b) It is the expanded sectional view which showed a part of the metal mold | die for ceramic ball base ball shaping | molding of this invention. It is sectional drawing which showed the conventional metal mold | die for ball molding of ceramic balls. It is the schematic diagram which showed the conventional ceramic ball elementary ball.

Embodiments of the present invention will be specifically described below, but the present invention is not limited to the following embodiments. It should be understood that the following embodiments are appropriately modified and improved within the scope of the present invention based on the common general knowledge of those skilled in the art without departing from the gist of the present invention.

  The ceramic ball base ball of the present invention is obtained by adding additives such as a sintering aid and a binder to various ceramic raw material powders, mixing, pulverizing, granulating with a spray dryer, etc., as shown in FIG. A granulated powder is inserted between the upper and lower punches having a substantially hemispherical concave part in the part, a flat part around the concave part, and an inclined part at the intersection of the concave part and the flat part. It can be obtained by applying pressure to the punch 1 and the lower punch 2 in the vertical direction, press-molding the granulated powder to produce a compact, and sintering the compact.

As shown in FIG. 1, the obtained ceramic ball base ball 9 of the present invention has a substantially spherical spherical surface portion 6 at both ends, and a belt-like portion 7 protruding outward in the entire circumferential direction at the center portion. Since the formed ceramic ball base ball has the inclined portion 8 between the spherical surface portion 6 and the belt-like portion 7, when press molding, the powder easily moves at the boundary between the spherical surface portion and the belt-like portion, and the belt-like shape. Since the difference in the compressibility of the powder between the portion and the spherical portion is small, the molding density unevenness is small, and cracks are unlikely to occur at the boundary between the belt-like portion and the spherical portion of the molded ceramic ball. Further, in this sintering process after molding, cracks toward the inside of the element sphere are less likely to occur with this part as a base point, so the defect rate of sintering cracks in the element sphere is reduced. Further, the density unevenness of the elementary spheres is reduced, and even when sintered and processed for use in a bearing or the like, problems caused by the characteristic difference due to the density unevenness are less likely to occur.

In the ceramic ball base ball of the present invention, when the inclined portion is an R surface and / or a chamfer, the powder easily moves at the boundary between the spherical surface portion and the belt-like portion when press forming, and the belt-like portion and the spherical surface. Since the difference in the compressibility of the powder between the parts is small, the molding density unevenness is small, and cracks are less likely to occur at the boundary between the belt-like part and the spherical part of the ceramic ball molded body during molding. As for the inclined portion, only the R surface or a chamfered shape may be used, but a shape obtained by combining the R surface and the chamfer may be used.

In the ceramic ball base ball of the present invention, as shown in FIGS. 3 (a) and 3 (b), when the radius of the R surface and the length of the chamfer are C, and the protruding height of the belt-like portion is H, 1 It is preferable that> C / H ≧ 0.05. When the C / H is 0.05 or more, the powder becomes easier to move at the boundary between the spherical portion and the belt-like portion during press molding, and cracks occur at the boundary between the belt-like portion and the spherical portion of the ceramic ball molded body. Is more preferable because it is less likely to occur. When the C / H is 1 or more, the size of the inclined portion is unnecessarily large, and the processing time for processing the ceramic ball base ball into a ceramic ball product ball is undesirably long. For the same reason, it is more preferable that 0.5 ≧ C / H ≧ 0.1. As shown in FIGS. 3 (a) and 3 (b), C indicates the radius of curvature of the radius of the R surface and the length of the chamfer, and indicates the chamfer length in the case of chamfering. As shown in FIG. 3, the protruding height H of the belt-shaped portion is a distance between the extended line of the spherical surface portion, the intersection of the belt-shaped portion side surface, and the belt-shaped portion circumferential surface. The radius of the R surface, the length C of the chamfer, and the protrusion height H of the belt-like portion are measured by a contour measuring instrument.

In the ceramic ball base ball of the present invention, as shown in FIG. 1, when the length connecting the vertices of the spherical portions on both sides of the ceramic ball base ball is A and the width of the belt-like portion is D, D / A By setting it as ≧ 0.05, breakage during molding is less likely to occur, and the yield of elementary balls can be improved. Further, it is more preferable that D / A ≦ 0.5. This is because when the D / A exceeds 0.5, the width of the belt-like portion becomes too large, and the processing time until obtaining the ceramic ball product ball becomes long. More preferably, 0.3 ≧ D / A ≧ 0.1.

In the ceramic ball base ball of the present invention, it is preferable to provide an R portion having a radius of 0.1 mm or more at the corner of the belt-like portion. This is because, when the base ball is processed into a product ball, there is an effect of preventing the occurrence of defects on the surface of the product ball due to the corners of the belt-shaped portion hitting the grindstone and being chipped.

As the material of the ceramic ball base ball of the present invention, since ceramic balls are used for bearings and the like and wear resistance is required, silicon nitride, sialon, silicon carbide, alumina, hard and excellent in wear resistance, Zirconia or the like can be used. Among these, silicon nitride is preferable because it has a high hardness and excellent wear resistance, and thus the effect of the ceramic ball base ball of the present invention is great. In particular, ceramics using silicon nitride as the main crystal and MgO and rare earth oxide as a sintering aid are preferred because they have high strength and high toughness and are excellent in fatigue characteristics. In a ceramic having silicon nitride as a main crystal, a grain boundary phase containing Mg and rare earth is formed by using a sintering aid of 2 to 5% by mass MgO and 2 to 5% by mass rare earth oxide. Are included in a linear distance of 10 μm. As a result, a ceramic having material properties of a bending strength of 700 MPa or more at normal temperature and a fracture toughness of 6 MPa · m ^1/2 or more can be obtained. For this reason, when it is used as a bearing ball, a sufficient life is shown. As the rare earth oxide, Y ₂ O ₃ is preferable from the viewpoint of making the bending strength 700 MPa or more. It should be noted that at least one of the metals in groups 4a, 5a, and 6a of the periodic table, such as Ti, V, Nb, W, and Mo, is used for ceramics using silicon nitride as a main crystal and MgO and rare earth oxide as a sintering aid. It is preferable to include seeds in an amount of 0.05 to 2% by mass in terms of oxides, because there is an effect of improving strength and toughness.

As shown in FIG. 2, the ceramic ball base ball molding die 25 of the present invention has upper and lower punches 11 and 12 each having a substantially hemispherical concave portion 16 having a radius E at the center of the pressing surface and a flat portion 19 around the concave portion 16. In the ceramic ball base ball molding die constituted by the dies 20 for storing these upper and lower punches, the upper and lower punches are formed with an inclined portion 18 between the substantially hemispherical concave portion 16 and the flat portion 19. This reduces the cracking defect rate of the base ball and significantly improves the punch life. The pressing direction and the vertical cross section of the upper and lower punches 11 and 12 are substantially circular, and the pressing direction and the vertical cross section of the die 20 are substantially circular with an inner diameter F. Moreover, the depth from the flat part 19 of the substantially hemispherical recessed part 16 of an up-and-down punch is shown by G. Note that the inclined portion 18 is specifically an R surface and / or a chamfer.

The ceramic ball base ball molding die 25 of the present invention is such that the radius of the R surface and the chamfer length of the inclined portion 18 between the substantially hemispherical concave portion 16 and the flat portion 19 of the upper and lower punches are c, When the length is h, it is preferable that 1> c / h ≧ 0.05. When the c / h is 0.05 or more, during press molding, the powder is more easily moved at the boundary between the spherical surface portion and the belt-shaped portion, and cracks are formed at the boundary between the belt-shaped portion and the spherical surface portion of the ceramic ball molded body. Is more preferable because it is less likely to occur. Further, when the c / h is 1 or more, the size of the inclined portion of the ceramic ball base ball obtained by sintering after press molding becomes larger than necessary, and the ceramic ball base ball becomes a ceramic ball product ball. This is not preferable because the processing time in processing into a long time becomes long. For the same reason, it is more preferable that 0.5 ≧ c / h ≧ 0.1. The radius of the R surface of the inclined portion 18 and the chamfering length c are as shown in FIGS. 4 (a) and 4 (b). As shown in FIG. 4, the length h of the flat portion refers to the distance from the intersection of the extension line of the substantially hemispherical concave portion 16 and the extension line of the flat portion 19 to the side surfaces of the upper and lower punches. The radius of the R surface of the inclined portion 18 and the chamfering length c and the flat portion length h are measured by a contour measuring instrument.

In the ceramic ball base ball molding die of the present invention, the surface roughness Ra of the substantially hemispherical concave portion and the flat portion of the upper and lower punches and the inclined portion between the substantially hemispherical concave portion and the flat portion is 0.2 μm or less. Then, when press-molding, the powder is more likely to move at the boundary between the spherical surface portion and the belt-shaped portion, and cracks are less likely to occur at the boundary between the belt-shaped portion and the spherical surface portion of the ceramic ball molded body. Further preferable surface roughness is Ra 0.1 μm or less.

The method for producing a ceramic ball element ball according to the present invention includes a substantially hemispherical concave portion at the center of the pressing surface, a flat portion around the concave portion, and an inclined portion at an intersection of the concave portion and the flat portion. Using a ceramic ball base ball molding die formed by a punch and a die containing these upper and lower punches, the ceramic powder has at least 0.1 to 5 parts by weight of an organic binder, and the center particle size Is 10 to 150 μm, the ratio of bulk density ρa to tap bulk density ρt, (ρa / ρt) is a granulated powder having a pressure of 0.7 or more in the axial direction of the upper and lower punches, and the entire circumferential direction in the center In addition, a ceramic ball base ball molded body having a band-like portion protruding outward and having an inclined portion between the spherical portion and the belt-like portion is sintered and then sintered to obtain a ceramic ball base ball. Here, the ceramic powder has at least 0.1 to 5 parts by mass of an organic binder, a center particle size of 10 to 150 μm, a ratio of bulk density ρa to tap bulk density ρt, and (ρa / ρt) of 0. Since the granulated powder having a particle size of 7 or more is used, the fluidity of the raw material is improved, and there is an effect that the problem that cracks occur at the boundary between the belt-like portion and the spherical portion is less likely to occur.

In the method for producing a ceramic base ball of the present invention, since the granulated powder has an organic binder in an amount of 0.5 to 5 parts by mass, the strength of the ceramic ball molded body after press molding can be obtained. The problem of cracking at the time of molding at the boundary is less likely to occur. This is because when the organic binder is less than 0.1 parts by mass, the strength of the molded body is low and cracking is likely to occur during molding. When the organic binder exceeds 5 parts by mass, the granulated powder becomes too hard, and press It is because it becomes difficult to compress at the time of shaping | molding, the adhesiveness between granulated powders worsens, and a shaping | molding crack may generate | occur | produce. A preferable range of the organic binder is 0.2 to 2 parts by mass. As the organic binder, PVB (polyvinyl butyral), acrylic, or the like can be used, but PVB (polyvinyl butyral) is preferable from the viewpoint of preventing cracks during molding.

When the center particle diameter of the granulated powder is 10 to 150 μm, the ratio of the bulk density ρa and the tap density ρt, and (ρa / ρt) being 0.7 or more, the fluidity of the granulated powder becomes better,
This is because, during press molding, the powder easily moves at the boundary between the spherical surface portion and the belt-shaped portion, and cracks are less likely to occur at the boundary between the belt-shaped portion and the spherical surface portion of the ceramic ball molded body. If the center particle diameter of the granulated powder is less than 10 μm, the granulated powder becomes smaller and the fluidity becomes worse, and cracking may occur during press molding. This is because if the thickness exceeds 150 μm, the granulated powder becomes large and defects may remain in the sintered ceramic ball base ball. A preferred range of the center particle size of the granulated powder to be used is 50 to 120 μm. A more preferable range is 70 to 110 μm. The center particle size of the granulated powder is measured by a method based on JIS R1639-1 “Fine Ceramics-Measuring Method of Granule Characteristics-Part 1: Particle Size Distribution”.

Moreover, it is more preferable that the ratio (ρa / ρt) of the bulk density ρa and the tap bulk density ρt is 0.7 or more. The larger the ratio (ρa / ρt) of the bulk density ρa and the tap bulk density ρt, the smaller the influence on the degree of filling when vibration is applied to the powder, and an index indicating the fluidity of the granulated powder. Therefore, if the ratio of the bulk density ρa and the tap bulk density ρt, (ρa / ρt) is 0.7 or more, the fluidity of the raw material is improved, so that cracking occurs at the boundary between the belt-shaped part and the spherical part. The effect is that problems are less likely to occur. The ratio (ρa / ρt) of the bulk density ρa and the tap bulk density ρt is more preferably 0.8 or more. The bulk density ρa and the tap bulk density ρt are measured by a method based on JIS R1639-1 “Fine Ceramics-Measuring Method of Granule Characteristics-Part 2: Bulk Density”.

In the method for producing a ceramic ball sphere according to the present invention, it is preferable that an aspect ratio of the granulated powder is 2 or less. When the granulated powder has an aspect ratio of 2 or less, the form of the granulated powder is isotropic, so that the fluidity of the granulated powder is further improved. At the boundary, the powder easily moves and cracks are less likely to occur at the boundary between the band-shaped portion and the spherical portion of the ceramic ball molded body. The aspect ratio of the granulated powder is calculated as (major axis / minor axis) by taking an SEM photograph of the granulated powder, measuring the major axis and minor axis of the granulated powder by image analysis.

Moreover, it is preferable that the maximum particle diameter of the granulated powder is 300 μm or less. This is because if the maximum particle size of the granulated powder exceeds 300 μm, the granulated powder becomes large and defects may remain in the sintered ceramic ball base ball. More preferably, the maximum particle size is 250 μm or less. In order to set the maximum particle size of the granulated powder to 300 μm or less, it can be achieved by passing the granulated powder through a sieve having a mesh size exceeding 300 μm and removing particles having a particle size exceeding 300 μm.

The granulated powder is preferably a ceramic slurry obtained by mixing at least a ceramic powder, an organic binder, and a solvent and having a solid content of 45% or more by spray drying. When the solid content is 45% or more, the degree of filling of the ceramic powder in the granulated powder after spray drying increases, so there is no need to apply more pressure than necessary in the axial direction of the upper and lower punches during press molding, There is an effect that the problem that a crack occurs at the boundary between the portion and the spherical portion is less likely to occur.

As ceramic powder, ceramic balls such as silicon nitride, sialon, silicon carbide, alumina, zirconia, etc., which are hard and excellent in wear resistance, are obtained because ceramic balls are used for bearings and the like, and wear resistance is required. Preference is given to using powder. In the case of silicon nitride, a powder obtained by mixing silicon nitride powder having a pregelatinization rate of 70% or more and an average particle size of 5 μm or less and a sintering aid powder is preferable. Examples of the sintering aid powder include MgO, Al ₂ O ₃ , Rare earth oxides are used. In particular, silicon nitride ceramics using MgO and rare earth oxides as sintering aids are preferred because they have high strength and high toughness and are excellent in fatigue characteristics.

In the method for producing a ceramic ball base ball of the present invention, it is preferable that the pressing force in the axial direction of the upper and lower punches during press molding is 5 to 50 MPa. This is because if the pressing force in the axial direction of the upper and lower punches is less than 5 MPa, the strength of the ceramic ball base ball is insufficient, and handling becomes difficult, and if it exceeds 50 MPa, This is because cracks may occur at the boundary of the spherical portion.

Since the ceramic ball base ball manufacturing method of the present invention is press-molded using the upper and lower punches having inclined portions at the intersections between the concave portions and the flat portions, the band-shaped portion and the spherical portion of the ceramic ball molded body at the time of press molding It is possible to prevent the occurrence of cracks at the boundary of the ceramic ball. However, after press molding, if the molded ceramic ball sphere is subjected to CIP using a rubber mold having a hardness of 20 to 100, the ceramic ball This is preferable because the effect of preventing the occurrence of cracks at the boundary between the belt-like portion of the sphere and the spherical portion is increased. The CIP pressure Pc is preferably 50 ≧ Pc / Pp> 1 when the pressing force Pp in the axial direction of the upper and lower punches during press molding is used. If Pc / Pp> 1, even if there is a microcrack in the ceramic ball base ball during press molding, the pressure is applied isotropically in the CIP, so that the crack can be reduced. . If Pc / Pp exceeds 50, the pressure of CIP becomes excessive and increases the equipment cost, which is not preferable. More preferably, 20 ≧ Pc / Pp ≧ 2. The hardness of the rubber mold refers to the durometer hardness measured by the method specified in the durometer hardness test of JIS-K6253. The measurement was performed with a type A durometer, and the durometer scale within 15 seconds after the pressing surface of the durometer was in close contact was defined as the durometer hardness of the rubber.

Examples of the present invention will be described below.
Example 1
Si ₃ N ₄ having an average particle size of 1.0 μm and a pregelatinization rate of 90% as a main raw material
As a sintering aid, 5% by weight of Y ₂ O ₃ powder, 2% by weight of MgO powder, and 1.2% by weight of SiO ₂ powder were added to 91.8% by weight of the powder. Further, 0.5 parts by mass of polyvinyl butyral as an organic binder is added to parts by mass, and the solid content (powder weight / (powder weight + solvent weight)) of the solvent (ethyl alcohol) is 50% with respect to the powder. And mixed and ground by a ball mill using silicon nitride balls to prepare a ceramic slurry. Thereafter, the ceramic slurry was spray-dried using a spray dryer, and then passed through a sieve having an opening of 150 μm to remove coarse particles, whereby spherical granulated powder 1 was prepared. At this time, the center particle diameter of the granulated powder and the bulk density ρa / tap bulk density ρt were adjusted by adjusting the operating conditions of the spray dryer. As shown in Table 1, the mean particle diameter of the granulated powder 1 60 [mu] m, bulk density .rho.a is 0.76 g / cm ^3, a tap bulk density ρt is 0.80 g / cm ^3, a bulk density .rho.a / tapped bulk density ρt is The aspect ratio of the granulated powder was 0.95 and 1.2.

  On the other hand, in the shape shown in FIG. 2, as shown in Table 2, a hemispherical shape having an inner diameter F of 18.7 mm, a radius E of 8.97 mm, and a depth G of 8.33 mm at the center of the pressing surface of the upper and lower punches. A ceramic ball base ball molding die having a concave portion, a flat portion of 0.41 mm around the concave portion, and an R surface having a radius of 0.013 m at the intersection of the semicircular concave portion and the flat portion of the upper and lower punches was prepared. . The material of the mold was die steel (equivalent to JIS SKD11), and the surface roughness of the pressing surface of the upper and lower punches was 0.1 μm in Ra.

This mold is set in a press molding machine, the granulated powder is filled between the upper and lower punches of the mold, and as shown in Table 2, pressurizing is performed in the axial direction of the upper and lower punches at a press pressure of 25 MPa, and 500 pieces are continuously formed. Then, a molded body of ceramic ball spheres was prepared. Table 2 shows the results of visually confirming the state of occurrence of cracks in this molded body. The molded body in which no crack was generated was inserted into a rubber mold having a hardness of 35, and CIP molding was performed at a press pressure of 120 MPa. Then, after heating to 500 degreeC in air | atmosphere and performing binder removal, it heated and sintered at 1800 degreeC in nitrogen, and the ceramic ball elementary ball was obtained. The obtained ceramic ball base ball has the shape shown in FIG. 1, and the dimensions are as shown in Table 3. The length A connecting the vertices of the spherical portions on both sides is 14 mm, the diameter of the belt portion is 14.6 mm, the belt portion The width D was 1 mm, an R surface was formed between the belt-like portion and the spherical portion, the radius C of the R surface was 0.01 mm, and the protrusion height of the belt-like portion was 0.32 mm. Table 3 shows the results of confirming the occurrence of cracks after sintering of the obtained ceramic ball spheres using a fluorescent flaw detection test.

  Thereafter, the obtained ceramic ball base ball is ground using a known ball grinder. At this time, the time until the band-like portion of the ceramic ball sphere disappeared was recorded.

(Examples 2 to 7)
As shown in Table 2, the same procedure as in Example 1 was carried out except that the radius c of the R surface at the intersection of the semicircular recess and the flat part of the upper and lower punches of the ceramic ball molding die of Example 1 was changed. Ceramic ball balls of Examples 2 to 7 were produced. The size of the ceramic ball base ball was the same as that of the ceramic ball base ball of Example 1 except that the radius C of the R surface between the belt-like portion and the spherical portion was changed. The results are shown in Table 3. The ceramic ball base balls of Examples 2 to 7 are made into polishing balls using a well-known ball polishing machine as in Example 1. The polishing time until the band-like portion of the ceramic ball sphere disappears in the case of Example 1, where (◎) is the same level (◎), and the polishing time is increased within a range of 5% Are shown in Table 3 as (Δ) and (Δ) where the polishing time increased by more than 5%.

(Examples 8 to 12)
The inclined portion between the concave semicircular concave portion and the flat portion of the upper and lower punches of the ceramic ball molding die of Example 4 is chamfered, and the depth G of the concave portion of the upper and lower punches and the length h of the flat portion of the upper and lower punches are shown. The ceramic ball base balls of Examples 8 to 12 were produced in the same manner as in Example 4 except that the pressure was changed to 2 as shown in FIG. The size of the ceramic ball element ball is the same as that of Example 4 except that the inclined portion between the belt-like portion and the spherical portion is chamfered, the width D of the belt-like portion, and the protrusion height H of the belt-like portion is changed. It was similar to a sphere. The results are shown in Tables 2 and 3. Further, the ceramic ball base balls of Examples 8 to 12 are formed into polishing balls using a known ball polishing machine as in Example 4.

(Examples 13 to 15)
The same procedure as in Examples 4, 8, and 9 was performed except that the press pressure at the time of press forming was 110 MPa and CIP was not performed after press forming on the ceramic ball base balls of Examples 4, 8, and 9. Ceramic ball balls of Examples 13, 14, and 15 were obtained. The results are shown in Tables 2 and 3. Further, the ceramic ball base balls of Examples 13 to 15 are made into polishing balls by using a known ball polishing machine in the same manner as in Examples 4, 8, and 9.

(Examples 16 and 17)
The characteristics of the granulated powder used for the production of the ceramic ball base ball of Example 6 were changed to the granulated powder 2 shown in Table 1, and the depth of the concave portion of the upper and lower punches of the ceramic ball molding die of Example 6 was changed. The thickness G, the R surface radius c of the inclined portion, the length h of the flat portion of the upper and lower punches, and the surface roughness of the pressing surface of the upper and lower punches are changed as shown in Table 1, and the press pressure during press molding is 49 MPa. Except that, ceramic ball base balls of Examples 16 and 17 were produced in the same manner as Example 6. The dimensions of the ceramic ball base ball were the same as the ceramic ball base ball of Example 6 except that the width D of the belt-like portion, the radius R of the inclined portion C, and the protrusion height H of the belt-like portion were changed. . The results are shown in Table 1. Further, the ceramic ball base balls of Examples 16 and 17 are formed into polishing balls using a known ball polishing machine in the same manner as in Example 6.

(Examples 18 and 19)
Table 1 shows the radius c of the R surface between the semicircular recess and the flat portion of the upper and lower punches of the ceramic ball molding die of Example 16, the recess depth G of the upper and lower punches, and the length h of the flat portion of the upper and lower punches. The ceramic ball base balls of Examples 18 and 19 were produced in the same manner as Example 16 except that the changes were made as shown in FIG. The dimensions of the ceramic ball base ball are the same as those of Example 16 except that the radius C of the R surface between the belt-like portion and the spherical portion, the width D of the belt-like portion, and the protrusion height H of the belt-like portion are changed. It was similar to a sphere. The results are shown in Table 1. Further, the ceramic ball base balls of Examples 18 and 19 are formed into polishing balls using a known ball polishing machine as in Example 16.

(Examples 20 to 22)
The inner diameter F of the die of the ceramic ball molding die of Example 16, the radius E of the concave portion at the center of the pressing surface of the upper and lower punches, the radius c of the R surface between the semicircular concave portion and the flat portion of the upper and lower punches, Ceramic ball balls of Examples 20 to 22 were produced in the same manner as in Example 16 except that the depth G of the recesses and the width h of the flat part of the upper and lower punches were changed as shown in Table 2. The dimensions of the ceramic ball base ball are as follows: the length A connecting the apexes of the spherical portions on both sides of the ceramic ball base ball, the diameter B of the strip portion, the radius C of the R surface between the strip portion and the spherical portion, the width of the strip portion D, the same as the ball of the ceramic ball of Example 16, except that the height H of the protruding portion of the belt-like portion was changed. The results are shown in Table 1. Furthermore, the ceramic ball base balls of Examples 20 to 22 are made into polishing balls using a known ball polishing machine as in Example 16.

(Example 23)
A ceramic ball ball of Example 23 was manufactured in the same manner as in Example 16 except that the granulated powder 3 shown in Table 1 was used in the method of manufacturing the ceramic ball ball of Example 16.

(Comparative Example 1)
The ceramic ball base ball of Comparative Example 1 was produced in the same manner as in Example 1 except that the inclined portion was not provided at the intersection of the semicircular concave portion and the flat portion of the upper and lower punches of the ceramic ball molding die of Example 1. did. The dimensions of the ceramic ball base ball of Comparative Example 1 were the same as those of the ceramic ball base ball of Example 1 except that no inclined part was provided between the belt-like part and the spherical part. The results are shown in Tables 2 and 3. The ceramic ball base ball of Comparative Example 1 is made into a polishing ball using a known ball polishing machine as in Example 1.

(Comparative Examples 2 to 4)
Comparative Example 2 is the same as Comparative Example 1 except that the depth G of the concave portion of the upper and lower punches and the width h of the flat portion of the upper and lower punches of the ceramic ball molding die of Comparative Example 1 are changed as shown in Table 2. ˜4 ceramic balls were produced. The ceramic ball balls of Comparative Examples 2 to 4 were the same as the ceramic ball balls of Comparative Example 1 except that the width D of the belt-like portion and the height H of the protrusion of the belt-like portion were changed. The results are shown in Tables 2 and 3. The ceramic ball base spheres of Comparative Examples 2 to 4 are made into polishing balls using a known ball polishing machine as in Comparative Example 1.

The ceramic ball base ball obtained by the ceramic ball base mold of the present invention shown in Examples 1 to 23 and the method of manufacturing the ceramic ball base ball is compared with the ceramic ball base ball of Comparative Examples 1 to 4, It can be seen that the generation of cracks occurring during press molding and sintering can be reduced. In particular, CIP molding is performed after press molding, and the pressure is manufactured by a manufacturing method having a relationship of 50 ≧ Pc / Pp> 1, and the radius of the R surface and the length of the chamfer are set to C, and the protrusion height of the band-shaped portion C / H when the thickness is H is a more preferable range of 0.5 ≧ C / H ≧ 0.1, the length connecting the vertices of the spherical portions on both sides of the ceramic ball base ball is A, and the band shape In Examples 8 and 9, in which D / A when the width of the part is D is 0.3 ≧ D / A ≧ 0.1, which is a more preferable range, cracks during sintering after molding also occur. It can be seen that there is an effect of reducing the processing time for making the product ball.

It goes without saying that the present invention is not limited to the above-described embodiments and can be implemented in various forms without departing from the gist of the present invention. For example, as the material of the ceramic ball element ball, in addition to the silicon nitride material, a high hardness material such as a silicon carbide material, a zirconia material, or an alumina material can be used.

As described above, the ceramic ball base ball and ceramic ball molding die of the present invention. According to the method for manufacturing a ceramic ball base ball, it is possible to prevent the generation of cracks during molding and sintering and to manufacture the ceramic ball base ball with high efficiency.
For this reason, it becomes possible to apply to the ceramic ball used for a bearing ball etc.

1: Upper punch 2: Lower punch 3: Tip part of upper punch 4: Tip part of lower punch 5: Conventional ceramic ball element 6: Spherical surface part 7: Strip part 8: Inclined part 9: Ceramic ball element of the present invention Sphere 11: Upper punch 12: Lower punch 13: Upper punch tip 14: Lower punch tip 15: Conventional ceramic ball molding die 16: Upper / lower punch recess 18: Upper / lower punch slope 19: Upper / lower punch Flat part 20: Die 25: Mold for molding ceramic balls of the present invention

Claims (8)

Has a substantially spherical shape of the spherical portion at both ends, in the ceramic balls unfinished ball that strip portion which projects outwardly is formed over the entire circumference in the central portion, have a sloped portion between the spherical portion and the belt portion , Where the inclined portion is an R surface and / or a chamfer, the radius of the R surface and the length of the chamfer are C, and the protruding height of the belt-shaped portion is H, 1> C / H ≧ 0. A ceramic ball base ball characterized by being 05 . 2. The D / A ≧ 0.05 according to claim 1 , wherein A is a length connecting the vertices of spherical portions on both sides of the ceramic ball base ball, and D is a width of the band-shaped portion. Ceramic ball baseball. 3. The ceramic ball base ball according to claim 2 , wherein D / A ≦ 0.5. In an upper and lower punch having a substantially hemispherical concave portion in the center of the pressing surface and having a flat portion around it, and a ceramic ball base ball molding die formed by a die for storing these upper and lower punches, have a slope portion at the intersection of the concave portions and the flat portion of the substantially hemispherical, the inclined portion between the concave portion and the flat portion of the substantially hemispherical of the upper and lower punches is R surface and / or chamfering, of the upper and lower punches When the radius of the R surface and the chamfering length of the inclined portion between the substantially hemispherical concave portion and the flat portion are c and the length of the flat portion is h, 1> c / h ≧ 0.05. A die for forming ceramic balls. Formed by an upper and lower punch having a substantially hemispherical concave portion at the center of the pressing surface, a flat portion around the concave portion, and an inclined portion between the concave portion and the flat portion, and a die for storing these upper and lower punches. Where the inclined portion is an R surface and / or a chamfer, the radius and chamfer length of the R surface of the inclined portion are c, and the length of the flat portion is h, 1> c / h ≧ Using a ceramic ball base ball mold of 0.05 , the ceramic powder has at least 0.1 to 5 parts by weight of an organic binder, a center particle size of 10 to 150 μm, a bulk density ρa and a tap. The ratio of the bulk density ρt, (ρa / ρt) is 0.7 or more, and the granulated powder is pressed in the axial direction of the upper and lower punches with a pressing force in the range of 5 to 50 MPa, and the entire circumferential direction in the center With a belt-like portion protruding outward, and a spherical portion and a belt After obtaining a ceramic balls unfinished ball formed body having an inclined portion between the parts, a manufacturing method of the ceramic balls unfinished ball, characterized in that to obtain a ceramic balls unfinished ball and sintered. 6. The method for producing a ceramic ball base ball according to claim 5, wherein the granulated powder has an aspect ratio of 2 or less. The method for producing a ceramic ball sphere according to claim 5 or 6, wherein the granulated powder has a maximum particle size of 300 µm or less. The granulated powder of at least a ceramic powder, a ceramic slurry obtained by an organic binder, a solvent were mixed, to claim 5, characterized in that solids may a ceramic slurry is 45% or more spray dried 8. A method for producing a ceramic ball base ball according to 7 .

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