Raw material for ceramic ball, device for processing ceramic molded body, and method for processing ceramic molded body

Abstract

A raw material for a ceramic ball according to an embodiment is characterized by having a sphericity of 2% or less and an arithmetic average roughness Ra of 0.2 [mu] m to 2 [mu] m (inclusive). The maximum cross-sectional height (Rt) of the raw material for ceramic balls is preferably 4 [mu] m or more and 20 [mu] m or less. Furthermore, when the surface roughness Ra in the circumferential direction of the band-shaped portion trace is Ra1 and the surface roughness Ra in the circumferential direction perpendicular to the band-shaped portion trace is Ra2, it is preferable that Ra1 / Ra2 be 0.2-2 inclusive.

Description

Technical Field

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

[0002] Ceramic balls are used in various bearings. Ceramic balls used in bearings are called bearing balls. As bearing balls, ceramic sintered bodies such as silicon nitride sintered bodies, alumina sintered bodies, zirconia sintered bodies, and alusil high silicon heat-resistant aluminum alloy sintered bodies can be listed. Alusil high silicon heat-resistant aluminum alloy sintered bodies are made by mixing alumina and zirconia.

[0003] The surface roughness and material properties of bearing balls are graded according to ASTM (American Society for Testing and Materials)-F2094. Grades corresponding to the application areas of bearings are being sought. As bearing balls, spherical ceramic balls are being sought. For example, in ASTM-F2094, the surface roughness of bearing balls is specified to be less than Ra0.013μm.

[0004] To obtain a true spherical ceramic ball, the raw material for the ceramic ball must be ground. The so-called raw material for the ceramic ball refers to the ceramic sintered body before it is formed into a ceramic ball through grinding. The raw material for the ceramic ball is sometimes called the ball material.

[0005] For example, Japanese Patent Gazette No. 4761613 (Patent Document 1) and Japanese Patent Gazette No. 3853197 (Patent Document 2) disclose raw materials for ceramic balls having a band-shaped portion. Since the raw materials for ceramic balls are manufactured by molding, a band-shaped portion must be formed. In Patent Documents 1 and 2, the grinding efficiency of the raw materials for ceramic balls is improved by working on the shape of the band-shaped portion, etc. Although the grinding efficiency is improved in the raw materials for ceramic balls of Patent Documents 1 and 2, no further improvement in the grinding efficiency is found due to the presence of the band-shaped portion.

[0006] On the other hand, Japanese Patent Application Laid-Open No. 2000-185976 (Patent Document 3) discloses producing a raw material for ceramic balls by tumbling granulation.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent No. 4761613

[0010] Patent Document 2: Japanese Patent No. 3853197

[0011] Patent Document 3: Japanese Patent Application Publication No. 2000-185976 Summary of the invention

[0012] Problems to be solved by the invention

[0013] As shown in Patent Document 3, a ceramic molded body is obtained by tumbling granulation, and no band-shaped portion is formed in the raw material for ceramic balls formed by sintering the ceramic molded body. The grinding efficiency of the raw material for ceramic balls is improved according to the extent that there is no band-shaped portion in the raw material for ceramic balls. However, tumbling granulation causes insufficient densification of the molded body due to weak pressurization pressure. If the insufficiently densified molded body is sintered, the density of the sintered body, i.e., the raw material for ceramic balls, is also reduced.

[0014] Patent document 3 is considered to be effective for small-diameter bearing balls with a diameter of less than 4.5 mm. Bearing balls with a diameter of less than 4.5 mm have been used in hard disk drives (HDDs) and the like. The load applied to the bearing balls by the motor of the HDD is relatively small. In the field of large loads, the durability of the bearing balls based on rolling granulation is insufficient.

[0015] The embodiment is to provide a raw material for ceramic balls having good grinding efficiency and excellent durability.

[0016] Means used to solve problems

[0017] The raw material for ceramic balls involved in the embodiment is characterized in that the sphericity is less than 2%, and the arithmetic mean roughness Ra is greater than 0.2μm and less than 2μm. The sphericity of the raw material for ceramic balls can be obtained as follows: as a perfect roundness ((maximum diameter-minimum diameter) / average diameter) based on a projection image when projected onto a plane from one direction, or as an average value of multiple perfect roundnesses based on multiple projection images when projected onto a plane from each of multiple directions. For example, the perfect roundness of the projection image can be obtained from 8 diameters equally separated with the center of gravity of the projection image as the center. That is, the raw material for ceramic balls involved in the embodiment is characterized in that the perfect roundness obtained from 8 diameters equally separated with the center of gravity of the projection image when projected onto a plane from any direction is less than 2%, and the arithmetic mean roughness Ra is greater than 0.2μm and less than 2μm. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is an external view showing an example of a material for a ceramic ball having a band-shaped portion.

[0019] Figure 2 This is an external view showing an example of a ceramic ball material from which the strip-shaped portion is sufficiently removed according to the embodiment.

[0020] Figure 3 The diagram exemplifies a substantially circular projection image projected onto a plane and eight equally spaced diameters centered on the center of gravity of the projection image.

[0021] Figure 4 It is a diagram showing an example of a processing device for producing a ceramic molded body of a raw material for ceramic balls according to an embodiment.

[0022] Figure 5 This is a conceptual diagram for explaining an example of the displacement amount of the outer peripheral surface of the ceramic molded body used for manufacturing the raw material for ceramic balls according to the embodiment.

[0023] Figure 6 This is an external view showing an example of a spherical ceramic molded body used for producing a raw material for a ceramic ball according to an embodiment. DETAILED DESCRIPTION

[0024] The raw material for ceramic balls according to the embodiment is characterized in that the sphericity is less than 2% and the arithmetic mean roughness Ra is greater than 0.2 μm and less than 2 μm. The raw material for ceramic balls according to the embodiment refers to a ceramic sintered body before forming a ceramic ball by grinding. The raw material for ceramic balls is sometimes referred to as a ball material.

[0025] Figure 1 An example of a conventional raw material for a ceramic ball having a band-shaped portion is shown in FIG. Figure 1 In the figure, symbol 1A is a raw material for a ceramic ball obtained by sintering a ceramic molded body having a band-shaped portion, symbol 2A is a spherical portion of the raw material for a ceramic ball 1A, and symbol 3A is a band-shaped portion of the raw material for a ceramic ball 1A. Figure 2 An example of a raw material for ceramic balls according to an embodiment is shown in FIG. Figure 2 In the embodiment, reference numeral 1 is a ceramic molded body 13 ( Figure 6 Raw materials for ceramic balls obtained by sintering (as shown in the figure).

[0026] The raw materials 1A for ceramic balls in the past are as follows Figure 1 As shown in FIG. 1 , the ceramic ball raw material 1 according to the embodiment has a spherical portion 2A and a band portion 3A formed around the circumference of the spherical portion 2A. Figure 2 As shown, it has a spherical portion 2, but does not have Figure 1 The strip-shaped portion 3A shown.

[0027] The sphericity of the ceramic ball material 1 is 2% or less. For example, the roundness of the ceramic ball material 1 obtained from eight equally spaced diameters centered at the center of gravity of a projection image when projected onto a plane from one direction is 2% or less. Figure 3 1 shows an example of a substantially circular projection image 1E projected onto a plane and eight diameters r1 to r8 equally spaced about the center of gravity of the projection image. Figure 3In the figure, reference numeral 1E is a projection image of the ceramic ball material 1, and reference numerals r1 to r8 are eight diameters.

[0028] The shape measurement using the projection image 1E was performed using an optical three-dimensional shape measuring device. The three-dimensional shape measuring device used was VR-5000 manufactured by KEYENCE, and the analysis was performed using the analysis software of the device. Any measuring device having equivalent functions may be used.

[0029] First, eight equally separated diameters r1 to r8 are measured from a projection image 1E when the material 1 for a ceramic ball is projected onto a plane from an arbitrary direction. Figure 3 The diameter is measured at the place where the circumference of the projection image 1E is divided into 8 equal parts. The diameters r1 to r8 are respectively taken as the measured diameters. The maximum value of the measured diameters r1 to r8 is set as rmax, the minimum value is set as rmin, and the average value is set as the average diameter. The roundness of the projection image 1E of the raw material 1 for ceramic balls can be calculated by the following formula.

[0030] Roundness (%) = (|rmax-rmin| / average diameter) × 100

[0031] Thus, it is known that the smaller the value of roundness is, the closer it is to a perfect circle. In addition, the so-called "high roundness" and "good roundness" indicate that the numerical value of roundness is small. On the contrary, "low roundness" and "poor roundness" indicate that the numerical value of roundness is large. Furthermore, the sphericity of the raw material 1 for ceramic balls can be obtained as a single roundness based on a projection image 1E when projected onto a plane from one direction, or as an average value of multiple roundnesses based on multiple projection images 1E when projected onto a plane from each of multiple directions.

[0032] In addition, the raw material 1 for ceramic balls is characterized in that the sphericity (i.e., one perfect roundness obtained from one projection image 1E, or the average value of multiple perfect roundnesses obtained from multiple projection images 1E) is 2% or less. The sphericity of the raw material 1 for ceramic balls is 2% or less, which means that the raw material 1 for ceramic balls has a shape that is close to a perfect sphere (the projection image is a perfect circle). Since the projection image 1E of the raw material 1 for ceramic balls is close to a perfect circle, it does not substantially have an elliptical shape. In addition, the raw material 1 for ceramic balls does not substantially have a band-shaped portion ( Figure 1 The sphericity of the raw material 1 for ceramic balls is preferably 2% or less, and more preferably within the range of 0% to 1.5%.

[0033] In addition, the arithmetic mean roughness Ra of the raw material 1 for ceramic balls is greater than 0.2 μm and less than 2 μm. The arithmetic mean roughness Ra can be measured in accordance with JIS-B-0601 (2013). In addition, the measurement of surface roughness stipulates that the measurement length is greater than 0.8 mm. JIS-B-0601 corresponds to ISO4287. The surface roughness measuring instrument stipulates the use of SURFCOM2000 manufactured by Tokyo Seimitsu Co., Ltd., and the evaluation and analysis software of the device is used for analysis. The measuring device can be any device with equivalent functions.

[0034] Regardless of where the surface of the raw material 1 for ceramic balls is measured, the arithmetic mean roughness Ra is within the range of 0.2 μm to 2 μm. To make the arithmetic mean roughness Ra lower than 0.2 μm, a grinding process of the raw material 1 for ceramic balls is necessary. In addition, if the arithmetic mean roughness Ra is larger than 2 μm, it may become a cause of breakage during grinding due to large surface unevenness. Therefore, the arithmetic surface roughness Ra of the raw material 1 for ceramic balls is preferably within the range of 0.2 μm to 2 μm, and more preferably within the range of 0.5 μm to 1.0 μm. Furthermore, as mentioned above, the arithmetic surface roughness Ra is determined according to the grade of the bearing ball in ASTM-F2094. The maximum Ra is 0.013 μm. The arithmetic surface roughness Ra of the raw material 1 for ceramic balls is 0.2 to 2 μm. Therefore, it can be distinguished from a ceramic ball that has been ground and can be used as a bearing ball.

[0035] In addition, the surface of the raw material 1 for ceramic balls is preferably a sintered surface, a surface that has been honed, or a surface that has been cleaned. The so-called sintered surface is the surface of the ceramic sintered body after the sintering process. Honing and cleaning have the effect of removing dirt on the surface of the sintered surface. Therefore, honing and cleaning can be distinguished from grinding.

[0036] As described later, in order to control the sphericity of the raw material 1 for ceramic balls, the band-shaped portion 11 ( Figure 4 By controlling the removal of the band-shaped portion 11 of the ceramic molded body 9, the arithmetic surface roughness Ra of the sintered surface (including the sintered surface that has been subjected to a honing process or a cleaning process) can be controlled. For example, as in Patent Document 3, no pressure is applied during tumbling granulation, thereby increasing the arithmetic surface roughness Ra.

[0037] In addition, the maximum cross-sectional height Rt of the surface of the raw material 1 for ceramic balls is preferably greater than 4 μm and less than 20 μm. The maximum cross-sectional height Rt is also determined by the same method as the arithmetic mean roughness Ra mentioned above. In order to make the maximum cross-sectional height Rt of the raw material 1 for ceramic balls lower than 4 μm, grinding of the raw material 1 for ceramic balls is necessary. In addition, if the maximum cross-sectional height Rt is greater than 20 μm, there is a possibility that the burden of grinding the raw material 1 for ceramic balls used to manufacture ceramic balls (such as bearing balls) may increase. Therefore, the maximum cross-sectional height Rt is preferably greater than 4 μm and less than 20 μm, and more preferably in the range of greater than 5 μm and less than 17 μm.

[0038] In addition, when the arithmetic surface roughness Ra in the circumferential direction of the band-shaped portion mark is defined as Ra1 and the surface roughness Ra in the circumference in the direction perpendicular to the band-shaped portion mark is defined as Ra2, it is preferred that Ra1 / Ra2 is 0.2 or more and 2 or less. In addition, the band-shaped portion mark is preferably removed from the ceramic molded body 9 after removing the band-shaped portion 11 ( Figure 4 The strip-shaped portion trace is formed by sintering after removing the strip-shaped portion (as shown in the figure). The strip-shaped portion trace is discernible because it can be seen in a strip shape after the strip-shaped portion is removed. In addition, the strip-shaped portion trace can usually be confirmed by visual inspection. In addition, when the strip-shaped portion trace is difficult to discern, it is stipulated that Ra1 / Ra2 can also be obtained by measuring the arithmetic surface roughness Ra of the circumference in any circumferential direction and the circumference in the direction perpendicular thereto.

[0039] As mentioned above, the arithmetic surface roughness Ra of the raw material 1 for ceramic balls is greater than 0.2 μm and less than 2 μm. Moreover, Ra1 / Ra2 is greater than 0.2 and less than 2, which means that the arithmetic surface roughness Ra has no directionality. Thus, the deviation of the cutting amount during grinding can be controlled. As a result, the grinding cost can be reduced.

[0040] In addition, when the maximum cross-sectional height Rt of the band-shaped portion mark of the raw material 1 for ceramic balls in the circumferential direction is set to Rt1 and the maximum cross-sectional height Rt of the circumference in the direction perpendicular to the band-shaped portion mark is set to Rt2, it is preferred that Rt1 / Rt2 is greater than 0.2 and less than 2. In addition, when it is difficult to distinguish the band-shaped portion mark, it is stipulated that Rt1 / Rt2 can also be calculated by measuring the maximum cross-sectional height Rt of the circumference in any circumferential direction and the circumference in the direction perpendicular thereto. Rt1 / Rt2 is greater than 0.2 and less than 2, which means that Rt has no directionality. As a result, the deviation of the cutting amount during the grinding process of the raw material 1 for ceramic balls can be suppressed. As a result, the grinding cost can be reduced.

[0041] Furthermore, the arithmetic surface roughness Ra, the maximum cross-sectional height Rt, Ra1 / Ra2, and Rt1 / Rt2 can be used in combination, respectively. Furthermore, by satisfying all of them, a synergistic effect can be obtained.

[0042] In addition, the ceramic ball material 1 is preferably one selected from silicon nitride sintered body, alumina sintered body, zirconia sintered body, and alusil high silicon heat-resistant aluminum alloy sintered body. More preferably, the ceramic ball material 1 is silicon nitride sintered body.

[0043] The silicon nitride sintered body preferably has a three-point bending strength of 850 MPa or more or a fracture toughness of 6 MPa·m 1 / 2 The three-point bending strength is measured according to JIS-R-1601 (2008). In addition, the fracture toughness is measured according to the IF method of JIS-R-1607 (2015) and obtained by the new original formula. In addition, JIS-R-1601 corresponds to ISO14704. In addition, JIS-R-1607 corresponds to ISO15732.

[0044] For alumina sintered bodies, the three-point bending strength is 450-550 MPa and the fracture toughness is 4 MPa·m 1 / 2 In addition, for zirconia sintered bodies and Alusil high silicon heat-resistant aluminum alloy sintered bodies, the three-point bending strength is 800-1000MPa and the fracture toughness is 6MPa·m 1 / 2 about.

[0045] The silicon nitride sintered body is mainly composed of silicon nitride grains with an aspect ratio of 1.5 or more, and further more than 2. The wear resistance of the silicon nitride sintered body is improved by the complex entanglement of slender silicon nitride grains. The zirconium oxide sintered body is mainly composed of zirconium oxide grains with an aspect ratio of less than 1.5. The alusil high silicon heat-resistant aluminum alloy sintered body is also mainly composed of alusil high silicon heat-resistant aluminum alloy grains with an aspect ratio of less than 1.5. Therefore, the wear resistance of the silicon nitride sintered body is improved.

[0046] On the other hand, the silicon nitride sintered body is mainly composed of elongated silicon nitride grains, so the arithmetic surface roughness Ra and the maximum cross-sectional height Rt tend to be large. As described above, by controlling the arithmetic surface roughness Ra and the maximum cross-sectional height Rt, the grinding cost can be reduced, and a ceramic ball material 1 with excellent wear resistance can be provided.

[0047] In addition, a bearing ball can be obtained by grinding the raw material 1 for ceramic balls. A bearing ball is cited as an example of a ceramic ball that has been ground. The arithmetic surface roughness Ra of the bearing ball after grinding is less than 0.1 μm. In addition, the arithmetic surface roughness Ra is specified as less than 0.013 μm in ASTM-F2094. As the grade of the bearing ball increases, the arithmetic surface roughness Ra decreases. In order to form the raw material 1 for ceramic balls into bearing balls, grinding to reduce the arithmetic surface roughness Ra is necessary.

[0048] In addition, the bearing ball preferably has a diameter of 5 mm or more. In order to improve the wear resistance of the bearing ball, it is preferred to prepare a dense ceramic molded body at the stage of the ceramic molded body 9. It is effective to adopt molding to obtain a dense ceramic molded body 9. The diameter of the bearing ball is not particularly limited, but is preferably less than 70 mm. The diameter of the bearing ball may also exceed 70 mm, but there is a possibility of increased manufacturing costs. Therefore, the diameter of the bearing ball is preferably more than 5 mm and less than 70 mm, and more preferably in the range of more than 8 mm and less than 55 mm.

[0049] The ceramic balls manufactured from the ceramic ball raw material 1 are used as bearing balls. In addition, they can also be used as a medium used in the mixing process. Therefore, the ceramic balls manufactured from the ceramic ball raw material 1 represent both bearing balls and medium.

[0050] Next, a method for producing the ceramic ball material 1 will be described. The method for producing the ceramic ball material 1 is not particularly limited as long as it has the above-mentioned structure, but the following is a method for obtaining a good yield.

[0051] The raw material 1 for ceramic balls can be manufactured by sintering a spherical ceramic molded body from which the strip-shaped portion is sufficiently removed using a processing device 100 described later. The processing device 100 is characterized in that it comprises: a molded body fixing portion that sandwiches and fixes the spherical portion so that the ceramic molded body having the spherical portion and the strip-shaped portion formed around the circumference thereof can be rotated; and a processing portion that contacts the strip-shaped portion and removes the strip-shaped portion.

[0052] Figure 4 An example of a ceramic molded body processing device is shown in FIG. Figure 5 An example of a method for measuring the displacement of the peripheral surface of a ceramic molded body is shown in FIG. In the figure, symbol 4 is a part of the molded body fixing portion, i.e., a rotating shaft end (upper rotating shaft end), symbol 5 is another part of the molded body fixing portion, i.e., a rotating shaft end (lower rotating shaft end), symbol 6 is a processing fixture as a processing portion, symbol 7 is a processing fixture fixing portion, symbol 8 is a displacement measuring portion, symbol 9 is a ceramic molded body having a strip portion, symbol 10 is a spherical portion, symbol 11 is a strip portion, symbol 12 is a control portion, symbol 100 is a processing device, symbol R is a central curve of the outer periphery of the strip portion 11, symbol V is a straight line (rotation axis) connecting the rotating shaft ends 4 and 5, and symbol H is the displacement.

[0053] Hereinafter, a method for producing a ceramic ball material 1 (including a method for processing a ceramic molded body 9) using a silicon nitride sintered body will be described as an example.

[0054] First, prepare Figure 4The ceramic molded body 9 having the band-shaped portion 11 shown in the figure. A raw material powder slurry made by mixing silicon nitride powder, sintering aid powder and binder is molded. The mold is molded using a mold whose inner surface is spherical. By using an upper mold and a lower mold whose inner surfaces are spherical, a ceramic molded body 9 having a spherical portion 10 and a band-shaped portion 11 formed around the circumference can be manufactured.

[0055] The ceramic molded body 9 installed in the processing device 100 may be a molded body before or after the CIP process. The ceramic molded body 9 installed in the processing device 100 is preferably a molded body before the CIP process. This is because the molded body after the CIP process becomes somewhat hardened by the CIP process, so there is a possibility that the load of removing the strip-shaped portion 11 by the processing device 100 increases. The molded body after the CIP process is referred to as a CIP body.

[0056] Furthermore, the ceramic molded body 9 installed in the processing device 100 is not limited to the case of a molded body before CIP treatment. The ceramic molded body 9 installed in the processing device 100 may also be a molded body after at least one of the CIP treatment process, degreasing process and calcining process is implemented. The molded body after the degreasing process is implemented is called a degreased body. The molded body after the calcining process is implemented is called a calcined body. The so-called calcining process is a heat treatment at a lower temperature than the sintering process described later. Furthermore, when the ceramic molded body 9 installed in the processing device 100 is a degreased body and a calcined body, it also becomes somewhat harder as when it is a CIP body. Therefore, there is a possibility that the load of the process of removing the strip-shaped portion 11 is somewhat increased. The following describes the case where the ceramic molded body 9 installed in the processing device 100 is a molded body before CIP treatment.

[0057] Next, the band-shaped portion 11 of the ceramic molded body 9 before the CIP treatment is removed to obtain a spherical ceramic molded body 13 ( Figure 6 The strip-shaped portion 11 is removed by Figure 4 The processing device 100 shown is carried out.

[0058] The molding fixing part of the processing device 100 has rotating shaft ends 4 and 5. For convenience, the rotating shaft end 4 is sometimes referred to as the upper rotating shaft end 4, and the rotating shaft end 5 is sometimes referred to as the lower rotating shaft end 5. The top ends of the upper rotating shaft end 4 and the lower rotating shaft end 5 have fixing parts for fixing the ceramic molding 9. The ceramic molding 9 is fixed between the upper rotating shaft end 4 and the lower rotating shaft end 5. At this time, it is preferred as Figure 4 As shown, the strip-shaped portion 11 is arranged horizontally. By arranging the strip-shaped portion 11 horizontally, the process of removing the strip-shaped portion 11 becomes easy.

[0059] Next, the fixed ceramic molded body 9 is rotated. After the ceramic molded body 9 is fixed between the upper rotating shaft end 4 and the lower rotating shaft end 5, the rotating shaft ends 4 and 5 themselves are rotated around the rotating shaft V. The processing jig 6 is brought into contact with the band-shaped portion 11 of the ceramic molded body 9 rotating together with the rotating shaft ends 4 and 5. The band-shaped portion 11 is gradually removed by bringing the processing jig 6 into contact with the rotating band-shaped portion 11 of the ceramic molded body 9.

[0060] In addition, the surface (horizontal surface) containing the center curve R of the outer periphery of the strip-shaped portion 11 of the fixed ceramic molded body 9 is set to be orthogonal to the rotation axis V. Moreover, the displacement measuring unit 8 sequentially measures the displacement of the outer peripheral surface of the strip-shaped portion 11 rotating around the rotation axis V on the surface containing the center curve R. The so-called displacement measuring unit 8 refers to a device that measures the displacement of the object (the distance from the sensor to the object) by detecting the physical change of the object through a plurality of sensor elements and calculating the change as a distance. The displacement measuring unit 8 converts the displacement of the outer periphery of the strip-shaped portion 11 into digital data and sends it to the control unit 12.

[0061] The control unit 12 preferably has the following functions: a function of measuring the variation value of the outer peripheral surface of the strip-shaped portion 11 based on the displacement amount of the outer peripheral surface of the strip-shaped portion 11 measured by the displacement amount measuring unit 8 (variation value measuring function), and a function of adjusting the processing amount of the strip-shaped portion 11, that is, the force of the processing fixture 6 clamping the strip-shaped portion 11 according to the variation value (processing amount adjusting function). For example, the control unit 12 is composed of a computer with a processor, and the variation value measuring function and the processing amount adjusting function are realized by the processor executing a computer program. In addition, in the variation value of the outer peripheral surface of the strip-shaped portion 11, in addition to the displacement amount of the outer peripheral surface of the strip-shaped portion 11, the deviation of the rotation axis V from the center of the ceramic molded body 9 is also considered.

[0062] By setting the surface including the center curve R of the outer periphery of the strip-shaped portion 11 of the fixed ceramic molded body 9 to be orthogonal to the rotation axis V, the rotation direction of the strip-shaped portion 11 and the circumferential direction of the strip-shaped portion 11 become the same. As a result, the processing fixture 6 can be made to abut the rotating strip-shaped portion 11 vertically. In addition, the rotation speed of the ceramic molded body 9 can be listed as being in the range of 30 rpm or more and 250 rpm or less. If the rotation speed is lower than 30 rpm, there is a possibility that the processing time becomes longer. In addition, if the rotation speed exceeds 250 rpm, there is a possibility that the ceramic molded body 9 is damaged. Therefore, the rotation speed is preferably in the range of 30 rpm or more and 250 rpm or less, and more preferably in the range of 50 rpm or more and 200 rpm or less.

[0063] The displacement measuring unit 8 is a unit that measures the amount of the strip portion 11 of the rotating ceramic molded body 9 that is cut away as the displacement amount. The displacement measuring unit 8 is preferably a laser ( Figure 4A laser displacement meter (indicated by the dashed arrow shown). If it is a laser displacement meter, the displacement amount of the outer peripheral surface of the strip portion 11 can be measured without contacting the rotating ceramic molding 9.

[0064] In addition, the displacement amount measuring unit 8 has a function of measuring the variation value of the outer peripheral surface of the strip portion 11 based on the displacement amount of the outer peripheral surface of the strip portion 11. Figure 5 FIG. shows a conceptual diagram of measuring the displacement amount of the outer peripheral surface of the strip portion 11. Figure 5 In FIG., the ceramic molding 9 is rotated counterclockwise (to the left), but the rotation direction is arbitrary.

[0065] If the strip portion 11 of the ceramic molding 9 is gradually removed by the processing jig 6, the distance between the surface on the side of the displacement amount measuring unit 8 of the ceramic molding 9 and the displacement amount measuring unit 8 changes according to the degree of removal. This changed distance becomes the displacement amount H. The difference between the maximum value and the minimum value of the displacement amount H is called the variation value. That is, the variation value (the original Japanese text is "ブレ値") can be obtained by the following formula.

[0066] Variation value = Maximum value of displacement amount H - Minimum value of displacement amount H

[0067] Preferably, the control unit 12 has a function of adjusting the processing amount of the strip portion 11 according to this variation value. The function of adjusting the processing amount of the strip portion 11 is: by moving the processing jig 6 in the depth direction of the strip portion 11 (the radial direction of the ceramic molding 9), the amount of contact between the processing jig 6 and the strip portion 11, that is, the applied force, changes. In addition, if the control unit 12 automatically moves the processing jig 6 by feedback of the displacement amount H obtained by the displacement amount measuring unit 8, the mass productivity of the spherical ceramic molding 13 is improved. In addition, while rotating the ceramic molding 9, the strip portion 11 is removed, and the variation value is measured until the sphericity of the ceramic molding 9 becomes 2% or less. Thus, the sphericity of the raw material 1 of the sintered ceramic ball can be controlled to 2% or less.

[0068] In addition, after removing the strip portion 11, by changing the fixing position of the ceramic molding 9 by 90°, a method of measuring the variation value of the spherical surface portion 10 in the same manner as the measurement of the variation value of the above-mentioned strip portion 11 in this state is also effective. A method of fixing the strip portion in contact with the rotating shaft ends 4 and 5 and confirming the sphericity of the ceramic molding 9 by measuring the variation value of the spherical surface portion 10 is also effective.

[0069] In addition, the portion of the processing fixture 6 that contacts the strip-shaped portion 11 of the ceramic molded body 9 (hereinafter referred to as the "contact portion") is preferably abrasive paper. In addition, the contact portion of the processing fixture 6 is preferably composed of tungsten carbide (WC) as the main component. Grinding paper is sometimes also called sandpaper or sandpaper. Grinding paper is made by coating abrasive material. By changing the particle size of the abrasive material, the removal amount and surface roughness can be controlled. Grinding paper of the same mesh number can be used, or it can be changed to grinding paper of different mesh numbers in the middle. The mesh number of the grinding paper is preferably within the range of more than P100 and less than P600. The larger the mesh number of the grinding paper, the finer the texture. If it is lower than P100, there is a possibility that the surface of the strip-shaped portion 11 of the ceramic molded body 9 becomes rough. If the surface of the strip-shaped portion 11 becomes rough, there is a possibility that the surface of the raw material (sintered body) for ceramic balls becomes rough. In addition, if it exceeds P600, there is a possibility that the processing efficiency decreases. Therefore, the mesh number of the grinding paper is preferably P100 or more and P600 or less, and more preferably P150 or more and P400 or less. In addition, the grinding paper can refer to JIS-R-6252 (2022) and JIS-R-6010 (2000). These JIS standards correspond to ISO3366 (1999), ISO21948 (2001), ISO21950 (2001), ISO6344-1 to 3 (1998), etc.

[0070] In addition, the grinding paper can be attached to the base material of the processing fixture 6, or the grinding paper can be fixed around. The method of fixing the grinding paper around is preferably to add tension to the grinding paper to the extent of describing a circular arc (including a bow shape). As methods for fixing the grinding paper around, there can be listed a method of stretching the grinding paper straightly, a method of stretching it in a manner of describing a circular arc, and the like. As described above, when the ceramic molded body 9 having the strip-shaped portion 11 is rotated while the strip-shaped portion 11 is removed, the contact with the strip-shaped portion 11 can be softened by arranging the grinding paper in an arc shape. In this way, the strip-shaped portion 11 can be removed evenly. In addition, the method of fixing the surrounding can adopt various methods such as fixing up and down, left and right, and the entire circumference.

[0071] In addition, the so-called WC as the main component refers to a WC (tungsten carbide) containing 50% by mass or more. Such a material is sometimes also called a superhard alloy. As a superhard alloy, WC contains one or more selected from Fe (iron), Ni (nickel), and Co (cobalt). The material with WC as the main component is suitable for the process of removing the strip portion because of its hardness. In addition, by making the top of the contact part of the processing fixture 6 containing WC flat, the removal amount and surface roughness can be controlled.

[0072] The above example illustrates a method of removing the strip-shaped portion 11 while rotating the ceramic molded body 9 having the strip-shaped portion 11. However, the method is not limited to this method, and a method of fixing the ceramic molded body 9 having the strip-shaped portion 11 and moving the contact portion of the processing jig 6 around the strip-shaped portion 11 is also effective. In addition, in the strip removal process of hard materials such as CIP bodies, degreased bodies, or calcined bodies, there is a method of rolling the ceramic molded body 9 on a rotating grinding plate. In addition, there is a method of performing the strip removal process of the ceramic molded body 9 by rolling.

[0073] As described above, by using the processing device involved in the embodiment, the strip-shaped portion 11 can be removed from the ceramic molded body 9 having the spherical portion 10 and the strip-shaped portion 11 formed around the circumference. As a result, a spherical ceramic molded body 13 without the strip-shaped portion 11 can be obtained. In addition, the molded body chips generated by removing the strip can be used again as a raw material. Since the ceramic molded body 9 is processed, it is possible to reuse the molded body chips. It is considered that the spherical ceramic molded body 13 can also be subjected to CIP treatment as needed.

[0074] Next, a degreasing process is performed on the spherical ceramic molded body 13. The degreasing process is performed by heating at a temperature of 500° C. to 800° C. for 1 hour to 4 hours in a non-oxidizing atmosphere to degrease most of the organic binder added in advance. Examples of the non-oxidizing atmosphere include a nitrogen atmosphere and an argon atmosphere. If necessary, the treatment may be performed in an oxidizing atmosphere such as an air atmosphere to control the amount of organic matter remaining in the degreased body.

[0075] Next, a sintering step of the degreased body is performed. The sintering step is preferably performed in a temperature range of 1650°C to 2000°C. As a non-oxidizing atmosphere, a nitrogen atmosphere or a reducing atmosphere containing nitrogen is preferred. In addition, the pressure in the sintering furnace is preferably a pressurized atmosphere.

[0076] If the sintering is performed at a low temperature state of less than 1650°C, the grain growth of the silicon nitride grains is insufficient, and it is difficult to obtain a dense sintered body. On the other hand, if the sintering is performed at a high temperature of more than 2000°C, there is a concern that it will decompose into Si and N2 when the atmosphere pressure in the furnace is low, so it is preferred to control the sintering temperature within the above range. In addition, the sintering time is preferably within the range of more than 3 hours and less than 12 hours.

[0077] In addition, a roasting process may be performed as needed before the sintering process. The so-called roasting process is a process of performing heat treatment at a lower temperature than the sintering process described later. In addition, the temperature of the roasting process is higher than the temperature of the degreasing process and lower than the temperature of the sintering process.

[0078] In addition, after the sintering step, HIP (hot isostatic pressing) treatment is preferably performed. HIP treatment is to perform HIP treatment on the sintered body. The step of sintering the degreased body is called the first sintering step, and the step of performing HIP treatment on the sintered body is called the second sintering step.

[0079] The HIP treatment is preferably performed at a temperature of 1600°C to 1900°C and a pressure of 80MPa to 200MPa. By performing the HIP treatment, the pores in the sintered body can be reduced. Thus, a dense sintered body can be obtained. If the pressure is lower than 80MPa, the effect of the load pressure is insufficient. In addition, if it is higher than 200MPa, there is a possibility that the load of the manufacturing device becomes high.

[0080] The sintering step is completed, and the ceramic ball material 1 is completed. In addition, the sintered ceramic ball material 1 may be subjected to honing as needed. Honing is a process of removing foreign matter such as dust by spraying abrasive grains on the surface of the sintered body.

[0081] The obtained raw material 1 for ceramic balls has a sphericity of 2% or less and a surface roughness Ra of 0.2 μm or more and 2 μm or less. In addition, by grinding the raw material 1 for ceramic balls, a bearing ball can be formed. The surface roughness Ra of the bearing ball is set to 0.1 μm or less. In addition, grinding is set to a surface roughness corresponding to the grade specified in ASTM-F2094.

[0082] (Example)

[0083] (Examples 1 to 6, Comparative Examples 1 to 6)

[0084] First, a ceramic molded body 9 having a spherical portion 10 and a band-shaped portion 11 formed around the circumference is prepared. The ceramic molded bodies 9 according to Examples 1 to 5 are used to obtain a silicon nitride sintered body. The ceramic molded body 9 according to Example 6 is used to obtain an alumina sintered body.

[0085] In order to manufacture the ceramic ball raw material 1 according to Examples 1 to 6, the ceramic molded body 9 is Figure 4 The processing device 100 shown implements the stripping processing. A portion of the processing fixture 6 of the processing device 100 is used as abrasive paper. Abrasive paper with a mesh size of more than P100 and less than P600 is used as the abrasive paper. In addition, the spherical portion 10 of the ceramic molded body 9 is fixed up and down on the rotating shaft ends 4 and 5, and is arranged in a manner such that the strip portion 11 is horizontal. In addition, a laser displacement meter is used as the displacement measuring unit 8. The displacement H is calculated by the laser displacement meter, and the processing fixture 6 is automatically moved according to the change value calculated from the displacement H. The same is true for the processing of the raw materials for the ceramic balls involved in Comparative Example 1.

[0086] In Examples 1 to 6 and Comparative Example 1, the ceramic molded body 9 obtained by molding was subjected to stripping processing using the processing device 100. In Comparative Examples 2 to 4 and 6, no stripping processing was performed. In Comparative Example 5, a ceramic molded body without a strip-shaped portion was produced by rolling granulation. In Comparative Examples 1 to 5, an alumina molded body was used. In Comparative Example 6, an alumina molded body was used.

[0087] A raw material for ceramic balls formed of a silicon nitride sintered body or an alumina sintered body is manufactured by subjecting the ceramic molded body to a degreasing process, a sintering process, and a HIP process, respectively. Furthermore, the degreased body used to manufacture the raw material for ceramic balls 1 involved in Examples 1 to 6 is obtained by degreasing the spherical ceramic molded body 13. The same is true for the degreased body used to manufacture the raw material for ceramic balls involved in Comparative Example 1. The degreased body used to manufacture the raw material for ceramic balls involved in Comparative Examples 2 to 4 and 6 is obtained by degreasing the ceramic molded body 9 having the band-shaped portion 11. The degreased body used to manufacture the raw material for ceramic balls involved in Comparative Example 5 is obtained by degreasing the ceramic molded body without the band-shaped portion 11.

[0088] The sphericity, arithmetic surface roughness Ra, maximum cross-sectional height Rt, Ra1 / Ra2, and Rt1 / Rt2 of the ceramic ball material obtained after the HIP process were measured.

[0089] Ra1 and Rt1 are values ​​in the circumferential direction of the strip-shaped portion mark. In addition, Ra2 and Rt2 are values ​​in the perpendicular direction to the strip-shaped portion mark. The measurement results are shown in Table 1.

[0090] Table 1

[0091]

[0092] The diameter of about 10 mm in Example 1 and Comparative Examples 2 and 5 is a raw material for ceramic balls used to make bearing balls with a diameter of 3 / 8 inch. In addition, the diameter of about 31 mm in Examples 2 to 3, 6 and Comparative Examples 1, 3, 6 is a raw material for ceramic balls used to make bearing balls with a diameter of 1-3 / 16 inch. In addition, the diameter of about 47 mm in Examples 4 to 5 and Comparative Example 4 is a raw material for ceramic balls used to make bearing balls with a diameter of 1-7 / 8 inch. In addition, although Comparative Example 1 uses the same processing device 100 for strip processing as Examples 1 to 6, the sphericity of the spherical ceramic molded body 9 before obtaining the raw material for ceramic balls is poor.

[0093] Using the ceramic ball materials according to the examples and comparative examples shown in Table 1, the polishing efficiency and yield were investigated.

[0094] The grinding efficiency was measured by measuring the time required for finishing grinding to achieve a surface roughness Ra of 0.005 μm, which is the surface roughness of a bearing ball corresponding to Grade 5 of ASTM-F2094.

[0095] The ratio of the time taken for the finish grinding process of the Example was calculated when the finish grinding process time of Comparative Examples 2 to 4 and Comparative Example 6 was set to 100. When the ratio of the grinding time was 70% or less, it was regarded as "improvement", and when it was in the range of more than 70 and 100 or less, it was regarded as "maintained".

[0096] Specifically, for the bearing balls with a diameter of 3 / 8 inches manufactured from the raw materials for ceramic balls involved in Example 1 and Comparative Examples 2 and 5, the grinding time of Comparative Example 2 was set to 100. In addition, for the bearing balls with a diameter of 1-3 / 16 inches manufactured from the raw materials for ceramic balls involved in Examples 2 to 3 and 6 and Comparative Examples 1, 3 and 6, the grinding time of Comparative Example 3 was set to 100. In addition, for the bearing balls with a diameter of 1-7 / 8 inches manufactured from the raw materials for ceramic balls involved in Examples 4 to 5 and Comparative Example 4, the grinding time of Comparative Example 4 was set to 100.

[0097] Regarding the yield rate, the ratio of the broken raw materials for ceramic balls during the above-mentioned fine grinding process was investigated. 1,000 fine grinding processes were performed respectively, and the ratio of the number of broken raw materials for ceramic balls was investigated. When the ratio of the broken raw materials for ceramic balls was above 0% and below 0.5%, it was regarded as "improved", when it was above 0.5% and below 3%, it was regarded as "maintained", and when it was above 3%, it was regarded as "defective". The results are shown in Table 2.

[0098] Table 2

[0099] Grinding efficiency Yield Example 1 improve improve Example 2 improve improve Example 3 improve improve Example 4 improve improve Example 5 improve improve Example 6 improve improve Comparative Example 1 maintain maintain Comparative Example 2 - maintain Comparative Example 3 - maintain Comparative Example 4 - maintain Comparative Example 5 maintain bad Comparative Example 6 - maintain

[0100] As can be seen from Table 2, the raw materials for ceramic balls involved in the embodiments have improved grinding efficiency and yield compared with the comparative examples. Correspondingly, the improvement in grinding efficiency and yield is small for those with less belt processing as in Comparative Example 1. In addition, the yield is reduced due to insufficient strength for those formed by rolling granulation as in Comparative Example 5. It is found that it is not suitable for finishing with a surface roughness Ra of about 0.005 μm. In addition, it is found that it is also effective for ceramic sintered bodies other than silicon nitride sintered bodies as in Example 6.

[0101] Several embodiments of the present invention are illustrated above, but these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other ways, and various omissions, substitutions, changes, etc. can be made without departing from the scope of the main purpose of the invention. These embodiments and their modifications are included in the scope and main purpose of the invention, and are also included in the invention recorded in the claims and their equivalents. In addition, the above-mentioned embodiments can also be implemented by combining with each other.

Claims

1. A raw material for ceramic balls, characterized in that: The sphericity is less than 2%, The arithmetic mean roughness Ra is 0.2 μm or more and 2 μm or less.

2. The raw material for ceramic balls according to claim 1, characterized in that: The maximum cross-sectional height Rt is greater than or equal to 4 μm and less than or equal to 20 μm.

3. The raw material for ceramic balls according to claim 1 or 2, wherein: When the surface roughness Ra of the circumferential direction of the strip-shaped portion mark is Ra1 and the surface roughness Ra of the circumference in the direction perpendicular to the strip-shaped portion mark is Ra2, Ra1 / Ra2 is 0.2 or more and 2 or less.

4. The raw material for ceramic balls according to claim 1 or 2, wherein: When the maximum cross-sectional height Rt of the strip-shaped portion mark in the circumferential direction is defined as Rt1 and the maximum cross-sectional height Rt of the circumference in the direction perpendicular to the strip-shaped portion mark is defined as Rt2, Rt1 / Rt2 is greater than or equal to 0.2 and less than or equal to 2.

5. The raw material for ceramic balls according to claim 1 or 2, characterized in that: The raw material for the ceramic ball is one selected from the group consisting of a silicon nitride sintered body, an alumina sintered body, a zirconia sintered body, and an alusil high-silicon heat-resistant aluminum alloy sintered body.

6. The raw material for ceramic balls according to claim 3, characterized in that: The raw material for the ceramic ball is one selected from the group consisting of a silicon nitride sintered body, an alumina sintered body, a zirconia sintered body, and an alusil high-silicon heat-resistant aluminum alloy sintered body.

7. A bearing ball, characterized in that: The ceramic ball is obtained by grinding the raw material for ceramic balls according to claim 1.

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

9. A ceramic molded body processing device, characterized in that: It has: a molded body fixing portion that sandwiches and fixes the spherical portion so as to rotate a ceramic molded body having a spherical portion and a band-shaped portion formed around the circumference thereof; and A processing portion abuts against the strip-shaped portion and removes the strip-shaped portion.

10. The ceramic molded body processing device according to claim 9, characterized in that: Further possesses: a displacement measuring unit for measuring the displacement of the outer peripheral surface of the rotating belt-shaped portion; a variation value measuring unit that measures a variation value of an outer peripheral surface of the strip-shaped portion based on the displacement amount; and A processing amount adjustment unit adjusts the processing amount of the strip-shaped portion by the processing unit according to the variation value.

11. The ceramic molded body processing device according to claim 9 or 10, characterized in that: In the processing portion, a portion in contact with the belt-shaped portion is abrasive paper.

12. The ceramic molded body processing device according to claim 9 or 10, characterized in that: In the processed portion, a portion in contact with the strip-shaped portion contains WC as a main component.

13. A method for processing a ceramic molded body, characterized in that: A ceramic formed body processing device according to claim 9 or 10 is used.

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