Alignment device for ceramic ball material, alignment method, and inspection method

Abstract

An alignment device for a ceramic ball material according to an embodiment of the present invention aligns a ceramic ball material in which a spherical surface part and a belt-shaped part are formed. In the alignment device, grooves are formed in an opposing manner along the outer circumferences of respective rollers of a pair of rollers that receive the ceramic ball material. In the alignment device, each roller is rotated in the same direction so that a straight line that connects both poles of the spherical surface part on the pair of rollers is parallel to the rotation axis of each roller.

Description

Alignment device, alignment method, and inspection method for ceramic ball materials

[0001] The embodiments relate to an apparatus, an alignment method, and an inspection method for materials for ceramic balls.

[0002] Various ceramic materials possess properties such as high hardness, insulation, and wear resistance. Fine ceramics, in particular, which have high purity and uniform particle size, exhibit properties that make them useful in a variety of fields, including capacitors, actuator materials, and refractory materials. Ceramic materials are used in balls, a product that takes advantage of their wear resistance and insulation properties. These ceramic balls are used in bearings, jigs, tools, gauges, solenoid valves, check valves, and various valves. Among these, ceramic balls for bearing applications (ceramic bearing balls) are made from materials such as aluminum oxide, silicon nitride, and zirconium oxide (Patent Documents 1 and 2). For example, Patent Document 1 discloses a bearing ball made from a silicon nitride material, and Patent Document 2 discloses a bearing ball made from a zirconium oxide material.

[0003] In the process of producing ceramic ball materials, which are sintered bodies used to produce ceramic balls, including these ceramic bearing balls, a method of sintering a ball-shaped compact (hereinafter simply referred to as a "compact") is used. Furthermore, press molding using a mold is used as a molding method. Press molding generally involves inserting powder between an upper punch and a lower punch and applying pressure to obtain a compact. Because the compact is formed by uniaxial loads from above and below, cold isostatic pressing (CIP) is used to obtain a homogeneous compact (also called a "CIP compact") by applying pressure from all directions (Patent Document 3). According to Patent Document 3, a gap must be provided between the tips of the upper and lower punches during press molding to protect the mold. Therefore, the compact has a spherical portion and a band-like portion due to the gap, and therefore the ceramic ball material also has a spherical portion and a band-like portion.

[0004] Before removing the band-shaped portion from the ceramic ball material, the surface condition, such as color unevenness and the presence or absence of scratches, and the dimensions of the ceramic ball material are inspected. These surface condition inspections have been performed visually. In response to this, a method for inspecting ceramic ball materials using an alignment device has been disclosed (Patent Document 4). According to Patent Document 4, a positioning body with a row of positioning portions reciprocates relative to a receiving body having a groove to align the ceramic ball material.

[0005] Japanese Patent Laid-Open No. 6-48813 Japanese Patent Laid-Open No. 60-18620 International Publication No. 2023 / 003040 Japanese Patent Laid-Open No. 2003-171013

[0006] However, in the method of aligning ceramic ball materials by reciprocating a positioning body as described in Patent Document 4, the aligned ceramic ball materials are stationary, so if an image is taken from one direction, such as from the top, only one side (hemisphere) of the ceramic ball material is inspected. Therefore, to inspect the other side, it is necessary to change the imaging direction. Furthermore, with the method described in Patent Document 4, since the aligned ceramic ball materials are stationary, it is not possible to image the entire periphery of the ceramic ball material, making it impossible to inspect the dimensions of the ceramic ball material.

[0007] The problem to be solved by the present invention is to provide an apparatus, an alignment method, and an inspection method for aligning materials for ceramic balls, which can align materials for ceramic balls efficiently and effectively.

[0008] According to an embodiment, an alignment device for ceramic ball materials aligns ceramic ball materials having spherical portions and strip-shaped portions. The alignment device comprises a pair of rollers that receive the ceramic ball materials, each of which has a groove formed along its outer periphery so that the groove faces the outer periphery. The alignment device rotates each roller in the same direction so that a line connecting the two poles of the spherical portions on the pair of rollers is parallel to the rotation axis of each roller.

[0009] 1 is a diagram showing an example of a ceramic ball material used in an apparatus for aligning ceramic ball materials according to an embodiment; FIG. 2 is a diagram showing an example of a die press; FIG. 3 is a diagram showing an example of an apparatus for aligning ceramic ball materials according to an embodiment; FIG. 4 is a top view showing a state of an apparatus for aligning ceramic ball materials according to an embodiment; FIG. 5 is a diagram showing a rotation axis of ceramic ball materials used in an apparatus for aligning ceramic ball materials according to an embodiment; FIG. 6 is a cross-sectional view showing a state of alignment by an apparatus for aligning ceramic ball materials according to an embodiment; FIG. 7 is a conceptual diagram showing a state of inspection by an apparatus for aligning ceramic ball materials according to an embodiment; FIG. 8 is a diagram showing dimensions of the ceramic ball material of FIG. 1; FIG. 9 is a diagram showing an example of a groove portion of a roller of an apparatus for aligning ceramic ball materials according to an embodiment; FIG. 11 is a diagram showing a flowchart of an inspection method for ceramic ball materials according to an embodiment; Embodiment

[0010] Hereinafter, embodiments of an apparatus, an alignment method, and an inspection method for ceramic ball materials will be described in detail with reference to the drawings.

[0011] A ceramic ball material is shown in Figure 1. In Figure 1, reference numeral 1 denotes a ceramic ball material (e.g., a ceramic bearing ball material), reference numeral 2 denotes a spherical portion, and reference numeral 3 denotes a strip portion. Also, Figure 2 shows a press die for molding the ceramic ball material 1. In Figure 2, reference numeral 4 denotes a press die, and reference numeral 5 denotes a punch portion.

[0012] An alignment device for ceramic ball raw materials 1 according to an embodiment aligns ceramic ball raw materials having spherical portions and strip-shaped portions. The alignment device comprises a pair of rollers that receive the ceramic ball raw materials, each of which has a groove formed along the outer periphery, facing each other. The alignment device rotates each roller in the same direction so that a line connecting both poles of the spherical portion on the pair of rollers is parallel to the rotation axis of each roller. Here, the two poles are the two poles V and W on the outer periphery (outermost surface) of the spherical portion 2 that are located farthest from the strip-shaped portion 3. The line connecting both poles V and W is designated as line C1.

[0013] 3 shows an example of an alignment device for a ceramic ball material 1 according to an embodiment. In FIG. 3, reference numeral 6 denotes an alignment device for a ceramic ball material 1, reference numeral 7 denotes a front roller, reference numeral 8 denotes a rear roller, reference numeral 71 denotes a front rotation shaft that is the rotation shaft (shaft) of the front roller 7, reference numeral 81 denotes a rear rotation shaft that is the rotation shaft of the rear roller 8, reference numeral 9 denotes a groove portion of the front roller 7, and reference numeral 10 denotes a groove portion of the rear roller 8. The front roller 7 and the rear roller 8 form a pair of rollers. The groove portion 9 of the front roller 7 is arranged to face the groove portion 10 of the rear roller 8.

[0014] FIG. 3A is a top view of the alignment device 6. The actual alignment device 6 includes a drive section and a base section, but for the sake of explanation, FIG. 3A shows only the rollers 7 and 8, whose rotation axes 71 and 81 are parallel to each other. The rotating front roller 7 and rear roller 8 each have a cylindrical shape with a plurality of grooves 9 and 10 formed along the circumferential direction and having a depth in the radial direction on the side surface. In FIG. 3 and other figures, the axial direction of the rotation axes 71 and 81 is defined as the X-axis direction, the direction in which the rollers 7 and 8 are aligned is defined as the Z-axis direction, and the direction perpendicular to the X-axis and Z-axis directions is defined as the Y-axis direction. When viewed from above, the rollers 7 and 8 rotate forward (in the negative direction of the Z-axis).

[0015] Figure 3(B) is a front view of the alignment device 6, seen from the front roller 7 side. In the front view, the front surface of the front roller 7, on which the grooves 9 are formed, is rotating from the top to the bottom (negative direction of the Y axis). Figure 3(C) is a side view of the alignment device 6. The front roller 7 and rear roller 8 are rotating in the same counterclockwise direction. The rotation directions of the rollers 7 and 8 may be clockwise as long as they are the same.

[0016] In Fig. 3, three rows of grooves 9 are formed in the front roller 7, but in the embodiment, this is not limited to this and one, two, or four or more rows of grooves 9 may be formed. Also, in Fig. 3, the shape of the grooves 9, 10 in the cross section including the rotation shaft 71 is semicircular, but it may be a similar shape such as a U-shape or V-shape. The number of rows and cross-sectional shape of the grooves 10 of the rear roller 8 are also the same as those of the front roller 7.

[0017] The rollers 7 and 8 are preferably made of a material that does not scratch the ceramic ball material 1 when it comes into contact with the ceramic ball material 1, and does not rub against the material to contaminate the surface of the ceramic ball material 1. Furthermore, the rollers 7 and 8 are preferably made of a smooth surface so that dirt that could cause false detection is less likely to adhere to them. Therefore, the rollers 7 and 8 are preferably made of plastics such as polyamide (PA), polycarbonate (PC), polybutylene terephthalate (PBT), polyethylene terephthalate (PET), or plastics coated with these plastics.

[0018] The alignment device 6 rotates the rollers 7 and 8 in the same direction so that a line C1 connecting the poles V and W of the spherical surface 2 of the ceramic ball material 1 on the rollers 7 and 8 is parallel to the rotation axes 71 and 81. The line C1 being parallel to the rotation axes 71 and 81 means that the line C1 is parallel to the rotation axes 71 and 81 when the alignment device 6 is viewed at least from above (the negative direction of the Y axis) and from the front (the positive direction of the Z axis). In this specification, "parallel" is not limited to when the angle between the perpendicular to the first line and the second line is 90°, but also includes when the angle between the perpendicular to the first line and the second line is slightly deviated between 70° and 110°. More preferably, "parallel" includes when the angle between the perpendicular to the first line and the second line is 80° and 100°.

[0019] Furthermore, the fact that the line C1 is parallel to the rotation axes 71 and 81 means that, when the alignment device 6 is viewed at least from above (the negative direction of the Y axis) and from the front (the positive direction of the Z axis), the diameter C2 of the band-shaped portion 3 (a line segment having both ends on the surface of the band-shaped portion 3) is perpendicular to the rotation axes 71 and 81. In this specification, "perpendicular" is not limited to when the angle between the first line and the second line is 90°, but also includes when the angle between the first line and the second line is slightly deviated and is between 70° and 110°. More preferably, "perpendicular" includes when the angle between the first line and the second line is between 80° and 100°.

[0020] 4A and 4B are top views showing the alignment state by the alignment device 6. FIG. 4A shows the state immediately after the ceramic ball material 1 is placed across the groove 9 of the front roller 7 and the groove 10 of the rear roller 8. In this case, the orientation of the strip-shaped portion 3 is random. Also, while FIG. 4 only shows misalignment along two axes (X-axis and Z-axis), in reality, complex misalignment along three axes occurs in the ceramic ball material 1. FIG. 4B shows the state in which the rollers 7 and 8 rotate in the same direction from the state shown in FIG. 4A at a rotational speed equal to or greater than a threshold, causing the ceramic ball material 1 to rotate so that the orientation of the strip-shaped portion 3 is perpendicular to the rotation axes 71 and 81.

[0021] Furthermore, Fig. 4(C) shows a state in which the ceramic ball material 1 in Fig. 4(B) has been rotated 90° around the Y-axis. After being rotated 90° around the Y-axis, the rollers 7 and 8 slowly rotate in the same direction at a rotation speed below a threshold, causing the ceramic ball material 1 to rotate so that the diameter C2 of the band-shaped portion 3 is parallel to the rotation axes 71 and 81. For example, a suction pad is attached to the ceramic ball material 1 in Fig. 4(B) and lifted up, and the ceramic ball material 1 is rotated 90° around the Y-axis, and then the suction is released and the ceramic ball material 1 is returned to its original position.

[0022] 5A and 5B are diagrams showing the rotation axis of the ceramic ball material 1. FIG. 5A corresponds to FIG. 4B. FIG. 5A shows a front view (shown on the left) and a top view (shown on the right) in which the rotation axis is the straight line C1 connecting the two poles V and W of the spherical portion 2. In contrast, FIG. 5B corresponds to FIG. 4C. FIG. 5B shows a front view (shown on the left) and a top view (shown on the right) in which the rotation axis is the diameter C2 of the strip portion 3.

[0023] In Fig. 4(B), the material 1 for a ceramic ball rotates in the state shown in Fig. 5(A) where the line C1 connecting the poles V and W serves as the rotation axis. In Fig. 4(C), the material 1 for a ceramic ball rotates in the state shown in Fig. 5(B) where the diameter C2 of the strip-shaped portion 3 serves as the rotation axis.

[0024] 6A and 6B are front views showing the alignment state by the alignment device 6. Fig. 6A shows a case where the shape of the groove 9 in the cross section including the front rotation axis 71 is V-shaped. In Fig. 6A, the belt-like portion 3 of the ceramic ball material 1 is inclined, and both the spherical portion 2 and the belt-like portion 3 are in contact with the groove 9.

[0025] If the rollers 7 and 8 (shown in FIG. 3A) rotate in the same direction in the state shown in FIG. 6A, the rotation of the ceramic ball material 1 becomes unstable. By rotating the rollers 7 and 8 in the same direction at a rotational speed equal to or greater than a threshold value, the ceramic ball material 1 gradually changes direction in an attempt to stabilize, reaching the state shown in FIG. 6B. FIG. 6B corresponds to FIGS. 4B and 5A. FIG. 6B shows a state in which the ceramic ball material 1 is rotating so that the line C1 is parallel to the rotation axes 71 and 81. In this case, the groove portion 9 does not contact the strip portion 3 of the ceramic ball material 1, but only the spherical portion 2.

[0026] 6(B), the rotation of the ceramic ball material 1 becomes stable when the rollers 7 and 8 rotate at a rotation speed equal to or higher than the threshold value. That is, when the ceramic ball material 1 rotates, the spherical portions 2 that face each other across the vertical center line of the ceramic ball material 1 come into point contact with the side surfaces of the grooves 9 and 10, thereby achieving stable rotation of the ceramic ball material 1.

[0027] 7A and 7B are conceptual diagrams showing the state of inspection by the alignment device 6 as seen from the front. Fig. 7A shows a case where the ceramic ball material 1, whose straight line C1 has been made parallel to the rotation axes 71 and 81 by the alignment device 6, is inspected from above by the inspection camera 11. The inspection camera 11 has an inspection area 12 with high inspection accuracy and a blind spot area 13 with low inspection accuracy. For this reason, the ceramic ball material 1 is rotated appropriately to inspect the inspection area 12 by the inspection camera 11.

[0028] In FIG. 7(B), the ceramic ball material 1 is rotated 90° around the Y-axis from the state shown in FIG. 7(A). FIG. 7(B) corresponds to FIGS. 4(C) and 5(B). By rotating the rollers 7 and 8 at a rotational speed below the threshold, the portion that was in the blind spot 13 in FIG. 7(A) moves into the inspection area 12, making it possible to inspect the entire surface of the ceramic ball material 1 in the inspection area 13. Note that the rotation of the ceramic ball material 1 shown in FIG. 7(B) may be performed on rollers other than the rollers 7 and 8 shown in FIG. 7(A), or may be performed on the rollers 7 and 8 shown in FIG. 7(A). When rotating on the rollers 7 and 8, rotating the rollers 7 and 8 at a low speed below the threshold allows the ceramic ball material 1 to be rotated once or a few times with minimal misalignment of the band-shaped portion 3.

[0029] The ceramic ball material 1 preferably contains, as a main component (50 mass% or more), one or more of aluminum oxide (alumina), silicon nitride, boron nitride, zirconium oxide (zirconia), silicon carbide, and aluminum nitride contained in the raw ceramic powder. Furthermore, the ceramic ball material 1 more preferably contains 85 mass% or more of one or more of aluminum oxide, silicon nitride, boron nitride, zirconium oxide, silicon carbide, and aluminum nitride. Ceramic bearing balls, which are an example of ceramic balls produced by polishing the ceramic ball material 1, use the above-mentioned materials. In particular, silicon nitride sintered bodies have excellent wear resistance and are effective as ceramic bearing balls.

[0030] Furthermore, if the ceramic powder used as the raw material for the ceramic ball material 1 contains 85 mass % or more of any one of aluminum oxide, silicon nitride, boron nitride, and zirconium oxide, the resulting ceramic sintered body will also contain 85 mass % or more of any one of aluminum oxide, silicon nitride, boron nitride, and zirconium oxide. In addition to these main components, the ceramic sintered body may contain 15 mass % or less of a sintering aid.

[0031] For example, the aluminum oxide sintered body or the zirconium oxide sintered body has a Vickers hardness of about 1200 or more and 1700 or less. On the other hand, the toughness value is 3 MPa m １／２ 6MPa・m or more １／２ In contrast, silicon nitride sintered bodies have a high Vickers hardness of 1400 or more and 1800 or less. Also, the toughness value is 5 MPa m １／２ 10MPa・m or more １／２ The toughness is high, at about the same level as above. Silicon nitride sintered bodies have both high toughness and Vickers hardness, which gives them excellent wear resistance. This is because silicon nitride sintered bodies have a structure that is mainly composed of β-type silicon nitride crystal grains. β-type silicon nitride crystal grains have a long, thin shape, and these long, thin crystal grains are intricately intertwined, which is why they achieve high toughness.

[0032] Polishing is also preferred for turning spherical ceramic sintered bodies into ceramic bearing balls. The spherical ceramic sintered bodies after the sintering process are called ceramic ball material 1. The ceramic ball material 1 becomes a sphere with a band-like portion 3 resulting from the band-like portion of the compact, as shown in Figure 1. The ceramic ball material 1 polished into a sphere is called a ceramic ball, for example, a ceramic bearing ball.

[0033] Next, the conditions for aligning the actual ceramic ball material 1 using the alignment device 6 will be described. Figure 8 shows the dimensions of the ceramic ball material 1 in Figure 1. When the band-shaped portion 3 is oriented horizontally, symbol H represents the width (diameter) of the spherical portion 2, symbol h represents the width of the band-shaped portion 3, symbol D represents the width (diameter) of the band-shaped portion 3, and symbol T represents the thickness of the band-shaped portion 3. Because the band-shaped portion 3 is to be removed by polishing, it is preferable that the values ​​of the width h and thickness T of the band-shaped portion 3 be as small as possible.

[0034] Conversely, from the viewpoint of ease of producing a green body by press molding, it is preferable to increase the values ​​of the width h and the thickness T. In this case, the shape of the ceramic ball material 1 produced by sintering the green body will vary. In the alignment device 6, it is possible to align ceramic ball materials 1 of various shapes by changing the size and shape of the rollers 7 and 8. Furthermore, it can be said that it is more cost-effective to align and inspect ceramic ball materials 1 of similar shapes using the same rollers 7 and 8 without changing the rollers 7 and 8.

[0035] 9A and 9B show XZ cross-sectional views of the groove 9 (similar to the groove 10) of the front roller 7. In Fig. 9A, the groove 9 has a V-shape. Symbol A denotes the angle of the bottom of the groove 9, symbol d denotes the depth of the groove 9, and symbol L denotes the distance of the opening of the groove 9. In Fig. 9A, the angle A is 90°. To prevent the material 1 for a ceramic ball from falling, it is preferable that the distance L of the opening of the groove 9 be shorter than the width H (shown in Fig. 8) of the material 1 for a ceramic ball and the diameter D of the strip portion 3.

[0036] As explained with reference to Figure 6, the principle behind the orientation of the ceramic ball material 1 is due to the action of the spherical portion 2 and the strip-shaped portion 3 simultaneously coming into contact with the surface of the groove 9 and rotating unevenly. In Figure 9(B) , the angle A is large in relation to the diameter D of the ceramic ball material 1. In this case, if the material rotates while only the strip-shaped portion 3 is in contact with the groove 9, the spherical portion 2 tends to meander so as to come into contact with the groove 9.

[0037] Conversely, in Figure 9(C), the angle A is small in relation to the diameter D of the ceramic ball material 1. In this case, because the depth d of the groove 9 is large, the ceramic ball material 1 moves (reciprocates) significantly in the positive and negative directions of the Z axis in response to the rotation of the rollers 7 and 8, which makes it easy for the orientation of the ceramic ball material 1 to shift. As a result, proper photography cannot be performed in the photography step ST3 (shown in Figure 10 described later) after alignment, leading to a decrease in inspection accuracy. To prevent a decrease in inspection accuracy, the angle A of the groove 9 is preferably 60° or more and 120° or less.

[0038] 9A to 9C, the deepest part of the groove 9 (the part deepest from the surface of the rollers 7 and 8) is an intersection of surfaces (lines) and is difficult to machine. In Fig. 9D, a machined groove 14 is formed in the deepest part of the groove 9 to make the surface easier to machine.

[0039] In the above-described FIGS. 9A to 9D, the inclined surfaces of the grooves 9 are flat (straight lines), whereas in FIG. 9E, the inclined surfaces of the grooves 9 are curved (curved lines). Symbol R denotes the radius of curvature of the grooves 9, symbol d denotes the depth of the grooves 9, symbol L denotes the distance between the openings of the grooves, and symbol L1 denotes the distance between the vertices of the circumferential shape. When the circumferential shape is semicircular, the distance L1 is greater than the distance L due to the space between the rollers 7 and 8. Furthermore, when the radius of curvature R is greater than the radius of curvature when the distances L and L1 are equal, the distance L1 becomes smaller (L > L1), and when the radius of curvature R becomes smaller, the distance L becomes smaller (L1 > L). If the diameter D of the ceramic ball material 1 is smaller than the minimum value of the distances L and L1, the ceramic ball material 1 will fall off the alignment device 6. For this reason, it is preferable that the grooves 9 have a shape with dimensions that match the diameter D of the ceramic ball material 1.

[0040] In Fig. 9(E), the shape of the groove 9 is concave, whereas in Fig. 9(F), it is convex. In this case, the radius of curvature of the groove 9 is negative. The way the curved surface bends varies depending on the value of the radius of curvature, but if the distance between the vertices of the diagonally opposite curved surfaces is L2, then the distance L or L2 becomes a minimum value. If the diameter D of the material 1 for ceramic balls is smaller than the minimum value of the distance L or the distance L2, the material 1 for ceramic balls will fall off the alignment device 6. For this reason, it is preferable that the groove 9 has a shape with dimensions that match the diameter D of the material 1 for ceramic balls.

[0041] Next, a method for aligning and inspecting the ceramic ball materials 1 using the alignment device 6 will be described. Fig. 10 is a flowchart showing an inspection method including steps in the method for aligning the ceramic ball materials 1. In this embodiment, the case where the ceramic ball materials 1 are silicon nitride ceramics will be described as an example.

[0042] The method for aligning the ceramic ball raw materials 1 on which the band-shaped portions 3 are formed includes an arrangement step ST1 and a roller rotation step ST2. In the arrangement step ST1, the ceramic ball raw materials 1 on which the spherical portions 2 and the band-shaped portions 3 are formed are arranged on rollers 7 and 8, each having grooves 9 and 10 formed along its outer periphery. In the roller rotation step ST2, the rollers 7 and 8 are rotated in the same direction so that a line C1 connecting the poles V and W of the spherical portions 2 on the rollers 7 and 8 is parallel to the rotation axes 71 and 81 of the rollers 7 and 8. For example, in the roller rotation step ST2, the rollers 7 and 8 are rotated in the same direction at a rotational speed equal to or greater than a threshold value.

[0043] In addition, the roller rotation step ST2 of the method for aligning the ceramic ball material 1 on which the band-shaped portion 3 is formed rotates the rollers 7 and 8 so that when the ceramic ball material 1 rotates on the rollers 7 and 8, the points of the spherical portion 2 facing each other across the vertical center line of the ceramic ball material 1 come into point contact with the side surfaces of the groove portions 9 and 10.

[0044] The ceramic ball material 1 having the strip-shaped portion 3 formed thereon may be any material as long as it is spherical and has the strip-shaped portion 3. A method for improving the yield (number of good products / number of manufactured products) will be described below.

[0045] Here, a method for preparing a green body before producing the ceramic ball material 1 (before sintering) will be described using silicon nitride as an example. When one or more of aluminum oxide, boron nitride, and zirconium oxide are used as the main component (50 mass% or more), silicon nitride should be replaced with these components. In the examples of this embodiment, uniaxial pressing is used as a method for obtaining a green body, but the forming method is not limited to this.

[0046] First, appropriate amounts of sintering aids, additives, solvents, binders, etc. are added to the silicon nitride raw material, mixed, crushed, and granulated using a spray dryer. This process produces a granulated powder of the raw powder. Furthermore, when the total of the silicon nitride powder and sintering aid powder is 100% by mass, the silicon nitride powder is preferably 85% by mass or more. The additive is a plasticizer, etc. The solvent is water or an organic solvent. Examples of organic solvents include alcohol, ketone, and benzene. The binder is an organic substance. The amount of binder added is preferably 3% by mass or more and 20% by mass or less when the total of the silicon nitride powder and sintering aid powder is 100% by mass. Adjusting the binder amount allows for adjustment of the shape retention and density uniformity of the compact during uniaxial pressing and CIP. Furthermore, granulation allows for uniform mixing of the silicon nitride powder and sintering aid powder.

[0047] Next, the granulated powder is subjected to uniaxial pressing. An example of uniaxial pressing is a die molding method using an upper punch and a lower punch as shown in FIG. 2. The shape of the green body can be adjusted by changing the shape of the die. A spherical green body can be obtained by making the insides of the upper punch and the lower punch hemispherical. The band-like portion of the green body obtained by uniaxial pressing corresponds to the band-like portion 3 of the ceramic ball material 1 shown in FIG. 1.

[0048] Next, the green body is subjected to a CIP process. A rubber mold is used during the CIP process. The green body is formed using granulated powder. When isostatic pressure is applied to the green body during the CIP process, the granulated powder is crushed, thereby suppressing density variations. By using granulated powder to form the green body, the silicon nitride powder and sintering aid powder are uniformly dispersed, and density variations can be suppressed. If the pressure applied to the green body during the CIP process is uneven, some of the granulated powder will not be crushed and will remain. The remaining uncrushed parts will cause density variations.

[0049] Next, a degreasing step is performed to degrease the compact after the CIP treatment. The degreasing step is a step in which the compact is heated to a temperature equal to or higher than the decomposition temperature of organic components such as binders to evaporate the organic components. The degreasing step may be performed in a nitrogen atmosphere or in the air atmosphere. A degreased body can be obtained by the degreasing step.

[0050] Next, a sintering process is performed to sinter the degreased body. The sintering process is preferably performed at a temperature of 1700°C or higher and 2000°C or lower. The sintering process is preferably performed in a nitrogen atmosphere. The sintering pressure is preferably within a range of atmospheric pressure to 300 MPa or lower. The atmospheric pressure is 0.10133 MPa (=1 atm). The sintered body obtained by the sintering process may be subjected to a HIP (hot isostatic pressing) process. This process allows the production of a ceramic ball material 1. The ceramic ball material 1 is a ceramic sintered body having a theoretical density of 98% or higher.

[0051] Next, the ceramic ball material 1 is subjected to a placement step ST1 and a roller rotation step ST2. First, in the placement step ST1, the ceramic ball material 1 having the spherical portion 2 and the band-shaped portion 3 is placed on rollers 7 and 8, each of which has grooves 9 and 10 formed along its outer periphery. For example, the rollers 7 and 8 have an outer diameter of 6 mm and semicircular grooves 9 and 10 (diameter L: 4 mm in FIG. 9(E) ). The distance (gap) between the rollers 7 and 8 is 1 mm. The groove 9 of the front roller 7 and the groove 10 of the rear roller 8 are aligned on the same line. For example, one ceramic ball material 1 having a diameter D (shown in FIG. 8 ) of 7 mm is placed in the pair of grooves 9 and 10 between the rollers. When placing the ceramic ball material 1 in the placement step ST1, the rollers 7 and 8 may be stationary or may be rotating at a low speed.

[0052] Next, in the roller rotation step ST2, the rollers 7 and 8 are rotated in the same direction at a rotational speed equal to or greater than a threshold value. This rotation places the ceramic ball material 1 in the state shown in FIGS. 4(B), 5(A), and 6(B). The rotational speed of the rollers 7 and 8 varies depending on the outer diameter of the ceramic ball material 1, the diameter of the rollers 7 and 8, the shape of the grooves 9 and 10, and the diameter of the grooves 9 and 10. In the above example, the threshold rotational speed of the rollers 7 and 8 is 60 rpm, and the rotational speed of the rollers 7 and 8 is preferably in the range of 60 to 180 rpm. If the rotation of the rollers 7 and 8 is too slow, it takes a long time for the material to align. Conversely, if the rotation of the rollers 7 and 8 is too fast, the rotation of the ceramic ball material 1 becomes unstable, and in extreme cases, the material for a ceramic ball 1 may fall off the grooves 9 and 10. By rotating under appropriate conditions, the rotational axis of the strip-shaped portion 3 and the rotational axis of the rollers 7 and 8 are aligned parallel to each other.

[0053] In addition, in the rotation process of the ceramic ball material 1, when the ceramic ball material 1 rotates, spherical portions facing each other across the vertical center line of the ceramic ball material 1 come into point contact with the side surfaces of the grooves 9 and 10.

[0054] The track is unstable if the strip portion 3 of the ceramic ball material 1 is in point contact with the side surfaces of the grooves 9 and 10. For this reason, the rotation speed of the rollers 7 and 8 is increased or decreased so that the spherical portion 2 is in point contact with the side surfaces.

[0055] According to the above-described steps ST1 and ST2, the ceramic ball material 1 can be aligned efficiently and effectively.

[0056] Next, the method for inspecting the ceramic ball material 1 includes the above-described placement step ST1 and roller rotation step ST2, as well as a photographing step ST3 and an inspection step ST4. In the photographing step ST3, the inspection camera 11 photographs the ceramic ball material 1 as it rotates on the rollers 7 and 8, thereby obtaining images (a plurality of still images and moving images) of the ceramic ball material 1 viewed from multiple directions. In the inspection step, the ceramic ball material 1 is inspected using the images. In the photographing step ST3, photographs are taken while the rollers 7 and 8 are rotating, but the present invention is not limited to this case. In the photographing step ST3, photographs may be taken by repeatedly starting and stopping the rotation of the rollers 7 and 8 and photographing.

[0057] Next, the inspection process ST4 will be described. The rotation speed of the ceramic ball material 1 in the photographing process ST3 depends on the accuracy of the device for acquiring the image, but may be a rotation speed equal to or higher than the threshold value for alignment, or may be a rotation speed slower than that for alignment. In the case of a rotation speed slower than that for alignment, the rotation speed may be less than the threshold value at which the orientation can be maintained. The reason why rotation at a slow speed below the threshold is acceptable is that, since the inspection process ST4 only requires an image for one rotation, no orientation shift occurs even if the rotation is slow for about one rotation.

[0058] In order to improve the inspection accuracy, the ceramic ball material 1 may be rotated more than once during the photographing. Furthermore, the rollers that rotate the ceramic ball material 1 in the photographing step ST3 may not be the rollers 7 and 8 that were used for alignment, but the aligned ceramic ball material 1 may be moved to other rollers and rotated for photographing.

[0059] According to the above-described steps ST1 to ST4, there is no need to provide multiple inspection cameras 11, and inspection can be performed efficiently and effectively using images of the ceramic ball material 1 viewed from multiple directions without moving the inspection camera 11.

[0060] Furthermore, the method for inspecting the material 1 for a ceramic ball may include a ball rotating step ST5, a roller rotating step ST6, and a photographing step ST7, as shown in Fig. 10. In the ball rotating step ST5, the material 1 for a ceramic ball is rotated so that the rotation axis of the material 1 for a ceramic ball is changed from the straight line C1 to the diameter C2 of the band-shaped portion 3. For example, a suction pad is attached to the material 1 for a ceramic ball in Fig. 4(B) and lifted up, and the material 1 for a ceramic ball is rotated 90° around the Y-axis, and then the suction is released and the material 1 for a ceramic ball is returned to its original position, resulting in the state shown in Fig. 4(C).

[0061] In the roller rotation process ST6, the rollers 7 and 8 are rotated in the same direction so that a straight line C1 connecting the poles V and W of the spherical portion 3 on the rollers 7 and 8 is perpendicular to the rotation axes 71 and 81 of the rollers 7 and 8. For example, unlike the roller rotation process ST2, the roller rotation process ST6 rotates the rollers 7 and 8 in the same direction at a rotation speed below a threshold (a rotation speed at which the orientation of the band-shaped portion 3 can be maintained).

[0062] In the photographing process ST7, similar to the photographing process ST3, the material 1 for a ceramic ball is photographed in accordance with the rotation of the rollers 7 and 8. The photographing process ST3 described above photographs the material 1 for a ceramic ball rotating on the rollers 7 and 8 in a state where the straight line C1 connecting both poles of the spherical portion 2 is parallel to the rotation axes 71 and 81 of the rollers 7 and 8. On the other hand, the photographing process ST7 photographs the material 1 for a ceramic ball rotating on the rollers 7 and 8 in a state where the straight line C1 is perpendicular to the rotation axes 71 and 81. In the inspection process ST4 following the photographing process ST7, the material 1 for a ceramic ball is inspected based on the image obtained in the photographing process ST3 and the image obtained in the photographing process ST7.

[0063] Furthermore, in steps ST5 to ST7, the ceramic ball material 1 is photographed after being rotated 90° around the Y axis. This is because blind spots occur when photographing only in the photographing step ST3. For example, when photographing the ceramic ball material 1 rotating by the rotation of the rollers 7 and 8 from above, it is difficult to photograph the surface near the rotation axis of the ceramic ball material 1 (blind spot area 13 shown in FIG. 7 ).

[0064] In the method for inspecting the material for a ceramic ball 1, the plurality of rotation axes of the material for a ceramic ball 1 are the straight line C1 and the diameter C2 of the band-shaped portion 3.

[0065] In the roller rotation step ST2, the rollers 7 and 8 rotate the material 1 for a ceramic ball with the diameter C2 of the band-shaped portion 3 perpendicular to the rotation axes 71 and 81. At this time, the material 1 for a ceramic ball rotates around the axis of rotation, which is the straight line C1 connecting both poles of the spherical portion 2. Therefore, when the material 1 for a ceramic ball is photographed from above, the outer periphery of the material 1 for a ceramic ball is photographed with the band-shaped portion 3 of the material 1 at the approximate center, as shown in FIG. 4(B). After the photographing is completed, the material 1 for a ceramic ball is rotated 90° around the Y-axis in the ball rotation step ST5. Then, in the roller rotation step ST6, the material 1 rotates around the diameter C2 of the band-shaped portion 3 as the axis of rotation, as shown in FIG. 4(C). Therefore, it becomes possible to photograph the vicinity of the apex of the spherical portion 2 and the protruding portion of the band-shaped portion 3, which were blind spots when photographing during rotation in the photographing step ST3 (FIG. 4(B)).

[0066] In the ball rotation step ST5, the ceramic ball material 1 can be rotated by 90° around the Y-axis by using a suction pad or by clamping with a clip or clamp. The ceramic ball material 1 can be lifted up and rotated by 90°.

[0067] The photographing in the photographing step ST7 may be performed using the same rollers 7 and 8 as those used in the photographing step ST3, or may be performed using rollers different from the rollers 7 and 8. When photographing using the same rollers 7 and 8, the photographing may be performed at a slower rotation speed than when aligning. Although the rotation is performed around two points on the opposite side of the band-shaped portion as the rotation axis, as described above, one rotation of the ceramic ball material 1 is sufficient for the inspection in the inspection step ST4, and therefore, no misalignment occurs even if the rotation is slow, as long as it is about one rotation.

[0068] Ceramic balls (e.g., ceramic bearing balls) can be manufactured by polishing the ceramic ball material 1 after inspection in the inspection process ST4. A typical example of sphere polishing is surface plate processing. For example, the ceramic ball material 1 is inserted between parallel surface plates. The movement of the polishing surface plate allows the ceramic ball material 1 to be polished into a perfect sphere. The surface roughness of bearing balls is specified in ASTM F2094. Depending on the application, bearing balls are polished to a surface roughness Ra conforming to ASTM F2094, ISO 26602, or JIS R1669. Higher grades of bearing balls are sometimes mirror-finished to a surface roughness Ra of 0.01 μm or less.

[0069] According to the above-described steps ST1 to ST7, an image obtained in the photographing step ST3 while rotating the ceramic ball material 1 on the first rotation axis (straight line C1) and an image obtained in the photographing step ST7 while rotating the ceramic ball material 1 on the second rotation axis (diameter C2 of the band-shaped portion 3) can be used for inspection, thereby improving the accuracy of the inspection in addition to the above-described effects. This is because the image portion of the blind spot region 13 that cannot be obtained in the photographing step ST3 can be complemented by the image obtained in the photographing step ST7.

[0070] Although several embodiments of the present invention have been described above, these embodiments are presented by way of example only and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, modifications, etc. can be made without departing from the spirit of the invention. Modifications of these embodiments are included within the scope and spirit of the invention, as well as within the scope of the invention and its equivalents as set forth in the claims. Furthermore, the above-described embodiments can be implemented in combination with each other.

Claims

1. An apparatus for aligning ceramic ball materials, which aligns ceramic ball materials having spherical and band-shaped portions, comprising a pair of rollers that receive the ceramic ball materials, each of which has a groove formed along the outer periphery so that the rollers are rotated in the same direction so that a straight line connecting both poles of the spherical portions on the pair of rollers is parallel to the rotation axis of each roller.

2. The apparatus for aligning materials for ceramic balls as described in claim 1, wherein the rollers are rotated so that when the material for ceramic balls rotates on the pair of rollers, points of the spherical portion opposing each other across the vertical center line of the material for ceramic balls come into point contact with the side surface of the groove portion.

3. A method for aligning ceramic ball materials, which aligns ceramic ball materials having a spherical portion and a band-shaped portion, comprising: a placement step of placing the ceramic ball materials on a pair of rollers, each of which has a groove portion formed in such a way that the groove portion faces the outer periphery; and a roller rotation step of rotating each of the pair of rollers in the same direction so that a straight line connecting both poles of the spherical portion on each of the pair of rollers is parallel to the rotation axis of each of the pair of rollers.

4. A method for aligning ceramic ball materials as described in claim 3, wherein said roller rotating step rotates each of said rollers so that when said ceramic ball material rotates on said pair of rollers, points of said spherical portions opposing each other across a vertical center line of said ceramic ball material come into point contact with the side surface of said groove portion.

5. A method for inspecting materials for ceramic balls, comprising: a placement step and a roller rotating step as described in claim 3 or 4; a photographing step of taking photographs as the material for ceramic balls rotates on the pair of rollers, thereby obtaining images of the material for ceramic balls viewed from a plurality of directions; and an inspection step of inspecting the material for ceramic balls using the images.

6. A method for inspecting a material for a ceramic ball as described in claim 5, wherein the photographing step comprises photographing the material for a ceramic ball rotating on the pair of rollers in a state where a straight line connecting both poles of the spherical portion is parallel to the rotation axis of each of the rollers, and photographing the material for a ceramic ball rotating on the pair of rollers in a state where a straight line connecting both poles of the spherical portion is perpendicular to the rotation axis of each of the rollers.

7. The method for inspecting materials for ceramic balls as described in claim 5, wherein the roller rotation process rotates each of the rollers at a rotational speed equal to or greater than a threshold value so that a straight line connecting both poles of the spherical portion is parallel to the rotation axis of each of the rollers, and rotates each of the rollers at a rotational speed less than the threshold value so that a straight line connecting both poles of the spherical portion is perpendicular to the rotation axis of each of the rollers.