Method for inspecting fluorescent flaw in ceramic sintered body and method for manufacturing ceramic sintered body

Abstract

This method for inspecting a fluorescent flaw in a ceramic sintered body includes a step for applying a phosphor to a surface of a ceramic sintered body, a step for barrel-cleaning the ceramic sintered body to which the phosphor has been attached, and a step for performing fluorescent flaw inspection on the ceramic sintered body after the barrel-cleaning.

Description

Fluorescent flaw detection inspection method for ceramic sintered body and manufacturing method for ceramic sintered body

[0001] The embodiments generally relate to a fluorescent flaw detection inspection method for a ceramic sintered body and a method for manufacturing a ceramic sintered body.

[0002] Ceramic sintered bodies are used in a variety of fields due to their high strength. Examples of ceramic sintered bodies include silicon nitride sintered bodies, aluminum oxide sintered bodies, and zirconium oxide sintered bodies. For example, International Publication WO 2020 / 121752 (Patent Document 1) discloses a bearing ball made of a silicon nitride sintered body. In Patent Document 1, wear resistance is improved by reducing dislocation defects.

[0003] Bearing balls made of sintered ceramics are produced by polishing a base ball made of sintered ceramics. The surface roughness of bearing balls is specified in ASTM F2094. This standard specifies the surface roughness Ra depending on the field in which the bearing ball is to be used. To use a base ball as a bearing ball, it is polished to a surface roughness Ra of 0.01 μm or less. Polishing to an Ra of 0.01 μm or less is sometimes called finish polishing.

[0004] For example, International Publication Nos. WO 2022 / 138579 (Patent Document 2) and WO 2023 / 054611 (Patent Document 3) disclose base balls made of sintered ceramics. In Patent Documents 2 and 3, the polishing efficiency of the base ball is improved by improving the shape of the band-like portion.

[0005] International Publication No. 2020 / 121752 International Publication No. 2022 / 138579 International Publication No. 2023 / 054611 Patent No. 5578429

[0006] A base sphere has, for example, a spherical portion and a band-shaped portion. When a base sphere is subjected to finish polishing, cracks and chips may occur. This occurs because the base sphere has tiny surface defects that cause cracks and chips during finish polishing. Surface defects include cracks, chips, and cracks. Fluorescent flaw detection is a method for measuring surface defects in ceramic sintered bodies. A "crack" is when one object separates into two or more pieces and loses its original shape. A "chipped" object is when part of an object is lost. A "crack" is a fissure. A crack mainly refers to a depth-wise crack that extends from the surface toward the interior.

[0007] Fluorescent flaw detection is an inspection method in which a fluorescent material is applied to the surface of a ceramic sintered body and the presence or absence of defects is determined using ultraviolet light, etc. For example, Japanese Patent No. 5578429 (Patent Document 4) discloses fluorescent flaw detection of a bare sphere.

[0008] Before finish polishing, ceramic sintered bodies have surface irregularities, so the fluorescent material remains in places other than surface defects. This makes it difficult to detect defects using fluorescent flaw detection. Note that "surface irregularities" refer to irregularities made up of the constituent components of the ceramic sintered body. Ceramic sintered bodies are mainly formed from ceramic crystal grains and grain boundary phases, which serve as the base material. The irregularities on the surface of a ceramic sintered body made up of ceramic crystal grains and grain boundary phases are called surface irregularities. For this reason, surface irregularities are distinguished from cracks.

[0009] The embodiment is intended to address such a problem, and one of its objectives is to efficiently inspect surface defects of a ceramic sintered body using fluorescent flaw detection inspection.

[0010] The fluorescent flaw detection inspection method for a ceramic sintered body according to the embodiment includes a step of applying a phosphor to the surface of the ceramic sintered body, a step of barrel cleaning the ceramic sintered body with the phosphor attached, and a step of fluorescent flaw detection inspection of the ceramic sintered body after barrel cleaning.

[0011] 1A and 1B are views showing an example of a ceramic sintered body according to an embodiment, a view showing another example of a ceramic sintered body according to an embodiment, a view showing an example of a barrel cleaning step according to an embodiment, and a view showing an example of a barrel cleaning device according to an embodiment.

[0012] The fluorescent flaw detection inspection method for a ceramic sintered body according to the embodiment includes a step of applying a phosphor to the surface of the ceramic sintered body, a step of barrel cleaning the ceramic sintered body to which the phosphor has been attached, and a step of fluorescent flaw detection inspection of the ceramic sintered body after barrel cleaning. Further, an example of the fluorescent flaw detection inspection method for a ceramic sintered body will be described below.

[0013] First, a process of applying a phosphor to the surface of a ceramic sintered body is performed. Figures 1 and 2 show an example of a ceramic sintered body. In the figures, reference numeral 1 represents the ceramic sintered body, reference numeral 2 represents a spherical portion, and reference numeral 3 represents a strip portion. Figures 1 and 2 show the ceramic sintered body 1, the spherical portion 2, and the strip portion 3.

[0014] Fig. 1 illustrates a ceramic sintered body 1 having a spherical shape with a spherical surface portion 2, and Fig. 2 illustrates a ceramic sintered body 1 having a band-like portion 4 on the circumference of the sphere with the spherical surface portion 2. The band-like portion 4 is provided, for example, along the circumference of the sphere so as to surround the spherical surface portion 2. The ceramic sintered body 1 is not limited to such a shape. The shape of the ceramic sintered body 1 may be, for example, a roll shape, a flat plate shape, or the like.

[0015] The phosphor applied to the ceramic sintered body 1 emits light when irradiated with black light. The applied phosphor may be either a phosphor powder or a phosphor liquid. A phosphor liquid is a solution containing a phosphor. Therefore, examples of the applied phosphor include both a phosphor powder and a phosphor liquid.

[0016] The phosphor used in fluorescent flaw detection testing preferably corresponds to a fluorescent penetrant or a binary penetrant in the JIS standard. Fluorescent flaw detection testing is specified in JIS-Z2343-1 to 3 (2017). JIS-Z-2343 corresponds to ISO 3452-1. Fluorescent flaw detection testing is also specified in ASTM E1417-05.

[0017] For example, the step of applying a phosphor to the surface of the ceramic sintered body 1 may be a method of immersing the surface in a phosphor liquid.

[0018] Next, a process of barrel cleaning the ceramic sintered body to which the phosphor is attached (also referred to as a barrel cleaning process) is performed. Fig. 3 shows an example of the barrel cleaning process. In the figure, reference numeral 1 denotes a ceramic sintered body, and reference numeral 4 denotes a barrel tank. That is, Fig. 3 shows a ceramic sintered body 1 and a barrel tank 4.

[0019] Barrel washing is performed by rotating or rocking a barrel tank 4, which is a washing tank. The barrel tank 4 includes a container capable of accommodating the ceramic sintered body 1. While FIG. 3 illustrates a cylindrical barrel tank 4, various shapes such as a rectangular shape or a cage shape (a container shape with an open top) can be used. The barrel tank 4 may also have a door or a lid. The barrel tank 4 preferably has a mesh shape or holes to facilitate drainage of the washing liquid. The size of the mesh of the mesh shape and the size of the holes of the holes are such that the ceramic sintered body 1 does not fall out.

[0020] First, the ceramic sintered body 1 is placed in the barrel tank 4. It is preferable to place a plurality of ceramic sintered bodies 1 in the barrel tank 4. By placing a plurality of ceramic sintered bodies 1, a plurality of ceramic sintered bodies 1 can be treated in one barrel cleaning step.

[0021] When a phosphor is applied to the surface of the ceramic sintered body 1, the phosphor adheres to areas other than surface defects. The ceramic sintered body 1 has surface irregularities. The ceramic sintered body 1 has ceramic crystal grains and a grain boundary phase as the base material. The ceramic sintered body 1 has a structure in which the ceramic crystal grains and the ceramic crystal grains and the grain boundary phase are intricately intertwined. As a result, minute irregularities are formed on the surface of the ceramic sintered body 1. The phosphor adheres to the minute irregularities. By performing the barrel cleaning process, the phosphor adhering to the surface irregularities and the like in addition to the surface defects can be efficiently removed.

[0022] By placing a plurality of ceramic sintered bodies 1 in the barrel tank 4, the ceramic sintered bodies 1 collide with each other, which has the effect of removing unnecessary phosphor. As a result, for example, the phosphor can be left in surface defects of the ceramic sintered bodies 1, while the phosphor attached to other areas can be removed. This improves the inspection efficiency of the fluorescent flaw detection inspection. It also reduces the cleaning time required to remove unnecessary phosphor from the plurality of ceramic sintered bodies 1. The phosphor may be applied to the ceramic sintered bodies 1 after they are placed in the barrel tank 4, or the ceramic sintered bodies 1 to which the phosphor has been applied in advance may be placed in the barrel tank 4.

[0023] It is preferable to perform barrel cleaning while rotating the barrel tank 4. While FIG. 3 shows an example in which the rotation axis is perpendicular to the vertical direction, this is not limiting. The rotation speed (number of rotations) of the barrel tank 4 is preferably in the range of 1 rpm to 80 rpm. If the rotation speed is less than 1 rpm, the cleaning effect is small. Furthermore, if the rotation speed exceeds 80 rpm, the ceramic sintered bodies 1 may collide violently with each other, resulting in damage. This is particularly likely when the ceramic sintered bodies 1 have a band-shaped portion 3 and the ceramic sintered bodies 1 having a spherical portion 2 are large. For this reason, the rotation speed of the barrel tank 4 is preferably in the range of 1 rpm to 80 rpm, and more preferably in the range of 3 rpm to 40 rpm. Furthermore, the rotation speed of the barrel tank 4 is more preferably in the range of 10 rpm to 30 rpm.

[0024] The barrel cleaning process is preferably carried out by showering cleaning water into the barrel tank 4. Examples of the barrel cleaning process include a shower method and an immersion method. In the immersion method, the rotation of the barrel tank 4 weakens the stress caused by the ceramic sintered bodies 1 colliding with each other, which may reduce the cleaning effect. The shower method can enhance the cleaning effect. Examples of the cleaning water include water and organic solvents. Considering costs, water is preferably used. If necessary, a chemical solution such as an emulsifier may be used.

[0025] The ratio of the ceramic sintered bodies 1 stored in the barrel tank 4 is preferably within a range of 20 vol % to 70 vol % when the storage volume of the barrel tank 4 is taken as 100 vol %. If the ratio is less than 20 vol %, the amount processed at one time is small, which may result in low cleaning efficiency. If the ratio is more than 70 vol %, the rate at which the ceramic sintered bodies 1 collide with each other is low, which may result in low cleaning efficiency.

[0026] The barrel cleaning device that performs the barrel cleaning process has a barrel tank 4 and a rotation mechanism that rotates the barrel tank 4. It also has a cleaning tank that houses the barrel tank 4. In the case of the immersion method, cleaning water is stored in the cleaning tank beforehand. In the case of the shower method, a shower mechanism that sprays cleaning water is provided.

[0027] FIG. 4 shows an example of a barrel cleaning apparatus. In the figure, reference numeral 4 denotes a barrel tank, reference numeral 5 denotes a rotation mechanism, reference numeral 6 denotes a cleaning tank, and reference numeral 7 denotes a shower mechanism. That is, the barrel cleaning apparatus has a barrel tank 4, a rotation mechanism 5, a cleaning tank 6, and a shower mechanism 7. FIG. 4 shows a barrel cleaning apparatus using a shower mechanism 7. In FIG. 4, the barrel tank 4 is oriented laterally relative to the vertical direction, but it may also be oriented vertically or obliquely. Multiple shower mechanisms 7 may be provided. The position at which the shower mechanism 7 is provided is not limited to the upward direction, and cleaning water may be sprayed from the horizontal direction or the downward direction.

[0028] The cleaning water used in the barrel cleaning step may be reused. When reusing, it is preferable to remove any fluorescent material or the like that may have been mixed in during the cleaning step from the used cleaning water before use.

[0029] A rinsing process may be carried out before the barrel cleaning process. The rinsing process may involve spraying a cleaning solution or immersing the barrel in a cleaning solution tank. A shower method may be used to spray the cleaning solution. The barrel may also be immersed in the cleaning solution tank multiple times. By carrying out the rinsing process, easily removable phosphors can be removed in advance. Rinsing is also sometimes called rough cleaning. Furthermore, by carrying out the rinsing process, the frequency of replacing the cleaning solution used in the barrel cleaning process can be reduced. In other words, the cleaning solution can be reused. This means that the amount of waste liquid generated can be reduced.

[0030] An example of the cleaning liquid used in the rinsing step is water. The cleaning liquid used in the rinsing step may also be reused. When reusing the cleaning liquid, it is preferable to remove impurities from the cleaning liquid used in the rinsing step before use.

[0031] The ceramic sintered body 1 preferably has a spherical portion 2. The spherical portion 2 refers to a shape having a curved surface. Examples of the shape of the spherical portion 2 include a sphere, a hemisphere, an ellipsoid, and a roll. The spherical portion 2 may also have a shape having a band-like portion 3 around it. By having the spherical portion 2, the ceramic sintered bodies 1 are less likely to be damaged even if they collide with each other.

[0032] A ceramic sintered body 1 having a band-shaped portion 3 around a spherical portion 2 is called a bare sphere. A compact formed by mixing ceramic powder and sintering additive powder and pressing them in a mold has a band-shaped portion 3 around the spherical portion 2. Sintering the compact produces a ceramic sintered body having a band-shaped portion 3 around the spherical portion 2. The ceramic sintered body 1 may also be subjected to hot isostatic pressing (HIP). HIP is a process that applies high temperature and pressure. HIP is sometimes performed in a nitrogen atmosphere. When a ceramic sintered body is subjected to HIP, the grain boundary phase in the ceramic sintered body 1 may dissolve and move. The grain boundary phase may also react with nitrogen in the nitrogen atmosphere. Therefore, the surface of the ceramic sintered body 1 is easily roughened after HIP. It is difficult to remove unwanted phosphor from a rough surface. In other words, using a barrel cleaning process is effective for fluorescent flaw detection inspection of HIP-treated ceramic sintered bodies 1.

[0033] The spherical portion 2 preferably has a surface roughness Ra of 0.2 μm or more. For example, to make a ceramic sintered body 1 having a spherical portion 2 into a bearing ball, polishing is required. The bearing ball is polished as necessary to have a surface roughness Ra of 0.1 μm or less. For bearing balls, the surface roughness Ra is specified according to the grade in ASTM F2094 by the American Society for Testing and Materials. Therefore, polishing is performed to achieve a surface roughness according to the grade.

[0034] Even when the ceramic sintered body 1 is used as a wear-resistant member other than a bearing ball, surface polishing is performed as necessary. Polishing for use in wear-resistant members such as bearing balls is sometimes called finish polishing. A surface roughness Ra of 0.2 μm or more on the spherical surface 2 indicates the state before finish polishing. Examples of this include the as-sintered surface of the ceramic sintered body 1 and a surface that has been honed. A surface roughness Ra of 0.2 μm or more facilitates adhesion of the applied phosphor due to the anchor effect, making it more likely for the phosphor to remain outside surface defects. The barrel cleaning process can remove phosphor adhering to areas other than surface defects. In other words, the barrel cleaning process can improve the inspection efficiency of fluorescent flaw detection testing of a ceramic sintered body 1 having a spherical surface 2 with a surface roughness Ra of 0.2 μm or more.

[0035] Although there is no particular upper limit to the surface roughness Ra of the spherical surface portion 2, it is preferable that Ra be 10 μm or less. If Ra exceeds 10 μm, it may cause cracks and chips when the ceramic sintered bodies 1 collide with each other. For this reason, it is preferable that the surface roughness Ra of the spherical surface portion 2 be in the range of 0.2 μm to 10 μm, and more preferably 0.2 μm to 5 μm.

[0036] The surface roughness Ra is measured in accordance with JIS-B-0601 (2013), which corresponds to ISO 4287.

[0037] The surface roughness is measured using a SURFCOM 2000 manufactured by Tokyo Seimitsu Co., Ltd., and the evaluation and analysis software for the same is used. Any measuring device having equivalent functions may be used.

[0038] The measurement distance for the surface roughness Ra is 10% or more and 25% or less of the diameter of the spherical portion 2. The measurement conditions are as follows: measurement cutoff wavelength is 0.08 mm, cutoff type is Gaussian, slope correction is least squares linear correction, and λs cutoff ratio is 300. The measurement is performed three times, and the measured value is the average of the three values.

[0039] The diameter of the spherical portion 2 of the ceramic sintered body 1 is preferably 1 mm or more. For example, bearing balls with a diameter of less than 1 mm are used as bearings for fan motors in personal computers, etc. Small bearing balls are used in areas where the load is small, so the impact of defects is small.

[0040] On the other hand, medium-sized and large-sized bearing balls with diameters of 1 mm or more, or even 4 mm or more, are used as bearings for machine tools, automobiles, wind power generation, etc. These fields are subject to heavy loads. Examples of the loads include rotational speed, vibration (vibration of machine tools), and temperature (usage environment). In fields where the loads are heavy, the impact of defects is significant. For this reason, the fluorescent flaw detection inspection method for a ceramic sintered body according to the embodiment is preferably used for a ceramic sintered body 1 in which the diameter of the spherical portion 2 is 1 mm or more.

[0041] Although there is no particular upper limit to the diameter of the ceramic sintered body 1 having the spherical portion 2, it is preferably 60 mm or less. If the diameter exceeds 60 mm, the barrel tank 4 must be enlarged, which may reduce manufacturability. Furthermore, in the ceramic sintered body 1 having the spherical portion 2 and the band-shaped portion 3, the band-shaped portion 3 also becomes larger as the size increases. If the rotation speed of the barrel tank 4 increases, the band-shaped portions 3 may collide and be damaged. For this reason, the diameter of the spherical portion 2 of the ceramic sintered body 1 is preferably within a range of 1 mm to 60 mm, and more preferably 4 mm to 50 mm.

[0042] The ceramic sintered body 1 is preferably one selected from silicon nitride sintered bodies, aluminum oxide sintered bodies, and zirconium oxide sintered bodies. These ceramic sintered bodies can be used for wear-resistant members. Examples of wear-resistant members include bearing balls, rollers, rollers, and friction stir welding tool members. For use as wear-resistant members, it is preferable to polish the surface to an Ra of 0.1 μm or less. Surface defects can cause cracks and chips during polishing. They can also reduce the durability of the wear-resistant member. For this reason, it is effective to inspect for surface defects using a fluorescent flaw detection method.

[0043] Examples of silicon nitride sintered bodies used in wear-resistant members include silicon nitride sintered bodies having a three-point bending strength of 600 MPa or more, or even 800 MPa or more. Examples of aluminum oxide sintered bodies used in wear-resistant members include aluminum oxide sintered bodies having a three-point bending strength of 350 MPa or more. Examples of zirconium oxide sintered bodies used in wear-resistant members include zirconium oxide sintered bodies having a three-point bending strength of 700 MPa or more. Silicon nitride sintered bodies, aluminum oxide sintered bodies, and zirconium oxide sintered bodies are each determined by the component contained in the largest amount. The component contained in the largest amount becomes the base material. Silicon nitride sintered bodies (including sialon (Si-Al-O-N-based ceramics) sintered bodies) contain silicon nitride (including sialon) in the largest amount. Aluminum oxide sintered bodies contain aluminum oxide in the largest amount. Zirconium oxide sintered bodies contain zirconium oxide in the largest amount. The ceramic sintered body 1 may also contain a grain boundary phase.

[0044] The ceramic sintered body 1 is preferably a silicon nitride sintered body. In a silicon nitride sintered body, the silicon nitride crystal grains serving as the base material are columnar crystal grains with an average aspect ratio of 2 or more. The intricate intertwining of the columnar crystal grains contributes to the high strength. In contrast, the aluminum oxide crystal grains serving as the base material for an aluminum oxide sintered body or the zirconium oxide crystal grains serving as the base material for a zirconium oxide sintered body are spherical crystal grains with an average aspect ratio of less than 2. A large number of columnar crystal grains, such as in a silicon nitride sintered body, easily leads to the formation of surface irregularities. In other words, it may be difficult to remove the attached phosphor. The barrel cleaning process can improve the inspection efficiency of the fluorescent flaw detection inspection method. Furthermore, due to the high strength of silicon nitride sintered bodies, they are unlikely to break even if they collide with each other during the barrel cleaning process. From this perspective, a silicon nitride sintered body is also preferable.

[0045] The fluorescent flaw detection method uses ultraviolet light with an irradiance of 1000 μW / cm ２ More than 5000μW / cm ２ The irradiance is preferably within the following range: 1000 μW / cm ２ If the luminescence intensity is less than 5000 μW / cm, the luminescence of the phosphor may be insufficient.２ If the irradiance of ultraviolet light exceeds 1000 μW / cm, there are concerns that it may have adverse effects on the human body. ２ More than 5000μW / cm ２ Below 1500 μW / cm ２ More than 4000μW / cm ２ It is preferable that the illuminance at the measurement location is within the range below. Furthermore, it is preferable that the illuminance at the measurement location is 20 lx (lux) or less. When the illuminance is 20 lx or less, it becomes easier to detect luminescence under black light. The lower limit of the illuminance is not particularly limited, but it is preferable that it is 1 lx or more. Even if it is less than 1 lx, luminescence under black light can be detected. On the other hand, if it is too dark, there is a possibility that a safety problem may occur. For this reason, it is preferable that the illuminance at the measurement location is within the range of 1 lx or more and 20 lx or less.

[0046] The fluorescent flaw detection inspection method for ceramic sintered bodies described above can reduce the amount of fluorescent material attached to areas other than surface defects, thereby improving inspection efficiency. In other words, it can prevent areas that are not defects from being determined to be defects. In other words, it can improve the efficiency of extracting surface defects.

[0047] The fluorescent flaw detection inspection method for a ceramic sintered body according to the embodiment can be used in a method for manufacturing a ceramic sintered body.

[0048] In the method for manufacturing a ceramic sintered body according to the embodiment, a ceramic sintered body that has been determined to be a non-defective product by the fluorescent flaw detection inspection method for a ceramic sintered body according to the embodiment is subjected to polishing.

[0049] The pass / fail judgment using the fluorescent flaw detection inspection method is made based on the brightness and light-emitting area of ​​the fluorescent material remaining on the surface of the ceramic sintered body 1. The deeper the defect, the greater the brightness. Also, the larger the defect, the greater the light-emitting area. The judgment can be made by setting the brightness and light-emitting area according to the defect that will be used to judge pass / fail. The pass / fail judgment can be made visually or by machine judgment using image analysis. The criteria for pass / fail judgment are determined based on the size of the ceramic sintered body, the field of use, etc. Also, a limit sample may be used if necessary. The limit sample is a sample that serves as the standard for making a pass / fail judgment.

[0050] The ceramic sintered body 1 after polishing is preferably a ceramic sintered body for use in bearing balls. The ceramic sintered body 1 that will become a bearing ball after polishing is spherical. The ceramic sintered body 1 before polishing has a sphere or a band-like portion 3 around the sphere. This results in a ceramic sintered body 1 having a spherical portion 2. As described above, the ceramic sintered body 1 having the spherical portion 2 is suitable for the barrel cleaning process.

[0051] If the ceramic sintered body 1 is determined to be a non-defective product by the fluorescent flaw detection inspection method for a ceramic sintered body according to the embodiment, the occurrence of cracks and chips can be suppressed even if polishing is performed. Therefore, the yield of the ceramic sintered body 1 to be polished can be improved. In particular, bearing balls are polished to a surface roughness Ra of 0.1 μm or less, and even 0.01 μm or less. Polishing to reduce the surface roughness places a heavy load on the polishing process. By improving the yield, it is possible to reduce unnecessary polishing processes. By using the fluorescent flaw detection inspection method for a ceramic sintered body according to the embodiment in the method for manufacturing a ceramic sintered body, it is effective not only for improving the yield of the ceramic sintered body 1 to be polished, but also for improving the efficiency of the polishing process.

[0052] (Examples 1 to 11, Comparative Example 1) As the ceramic sintered bodies, silicon nitride sintered bodies and aluminum oxide sintered bodies were prepared. The silicon nitride sintered body had a three-point bending strength of 830 MPa, and the aluminum oxide sintered body had a three-point bending strength of 420 MPa. The ceramic sintered bodies were subjected to HIP treatment.

[0053] The ceramic sintered body had a shape with a band-shaped portion around a spherical portion. A ceramic sintered body with a band-shaped portion around a spherical portion is called a base sphere. The material and size of the base sphere are as shown in Table 1. The method for measuring the surface roughness Ra was as described above.

[0054]

[0055] Base ball 1 is a base ball for obtaining 3 / 16 inch (4.7625 mm) bearing balls. Base balls 2 and 4 are base balls for obtaining 3 / 8 inch (9.525 mm) bearing balls. Base ball 3 is a base ball for obtaining 1 3 / 16 inch (30.1625 mm) bearing balls. Base balls 5 and 6 are base balls for obtaining 7 / 8 inch (22.225 mm) bearing balls.

[0056] A phosphor was applied to each of the bare spheres. The amount of phosphor applied was the same for all. A barrel cleaning process was carried out under the conditions shown in Table 2. Examples 1, 2, and 4 to 11 were subjected to a rinsing cleaning process.

[0057] In Comparative Example 1, after the phosphor was applied, the phosphor was immersed in a cleaning tank once for cleaning. In other words, in Comparative Example 1, 80 blank spheres were subjected to phosphor flaw detection testing without undergoing the barrel cleaning process.

[0058] The barrel cleaning device used had a barrel tank, a rotation mechanism for rotating the barrel tank, and a cleaning tank. In Examples 1, 2, and 4 to 11, a barrel tank with a shower mechanism was used. In Example 3, a system in which cleaning liquid was stored in the cleaning tank and the workpieces were immersed was used.

[0059]

[0060] The above-mentioned barrel cleaning process was carried out to obtain samples for fluorescent flaw detection inspection. In Examples 1 to 8, no damage to the ceramic sintered bodies was observed after the barrel cleaning process. On the other hand, in Examples 9 to 11, a small number of ceramic sintered bodies with damaged band-shaped portions were observed. This is thought to be due to the high rotation speed of the barrel tank.

[0061] Example 9 had more breakages than Examples 10 and 11. This is because Examples 10 and 11 were made of silicon nitride sintered bodies with high strength, while Example 9 was made of aluminum oxide sintered bodies with low strength. It is clear that the barrel cleaning process according to the examples is particularly suitable for silicon nitride sintered bodies.

[0062] 10,000 good products and 5 defective products were prepared as raw spheres (ceramic sintered bodies having a band-shaped portion around the spherical surface) having the aforementioned size. The good products and defective products were randomly mixed and subjected to the barrel cleaning process under the aforementioned conditions. Fluorescent flaw detection testing was then performed to determine whether the five defective products could be detected. The number of good products that were erroneously determined to be defective was also investigated. The results are shown in Table 3. The good products were prepared by removing those that had cracks or chips during the barrel cleaning process.

[0063]

[0064] In Examples 1 to 11, the inspection accuracy was improved. In addition, in Examples 1, 2, and 4 to 11, in which a rinsing process was performed, the inspection accuracy was also improved. Performing a rinsing process can improve the effectiveness of the barrel cleaning process. Furthermore, no bare balls were damaged during the barrel cleaning process. It was found that setting the rotation speed of the barrel tank within the range of 1 rpm to 80 rpm was effective. In Example 3, the inspection accuracy was slightly reduced because a rinsing process was not performed, but sufficient accuracy was obtained for practical purposes.

[0065] In contrast, the inspection accuracy was reduced in Comparative Example 1. There were also many erroneous judgments in which good products were judged to be defective. It was found that the cleaning process of only immersing the product once in a cleaning tank, as in Comparative Example 1, was not able to sufficiently remove unnecessary phosphor. This shows that it is difficult to remove unnecessary phosphor when the surface roughness Ra of the ceramic sintered body is 0.2 μm or more.

[0066] In the examples, good and bad products could be efficiently separated. Therefore, even if a polishing process to a surface roughness Ra of 0.01 μm or less was performed to turn products judged as good into bearing balls, the yield was good. Products judged as bad, as in Comparative Example 1, had cracks and chips during the polishing process. It was found that the examples not only improved the inspection efficiency of the fluorescent flaw detection inspection method, but also had an effect on improving the yield of the manufacturing method of ceramic sintered bodies that includes a polishing process.

[0067] 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. A fluorescent flaw inspection method for a ceramic sintered body, comprising the steps of: applying a phosphor to a surface of the ceramic sintered body; barrel cleaning the ceramic sintered body with the phosphor attached; and performing fluorescent flaw inspection on the ceramic sintered body after barrel cleaning.

2. The inspection method according to claim 1, wherein the barrel cleaning step cleans a plurality of the ceramic sintered bodies in a single step.

3. The inspection method according to claim 1 or 2, wherein in the barrel cleaning step, the rotation speed of a barrel tank in which the ceramic sintered body to which the phosphor is attached is accommodated is 1 rpm or more and 80 rpm or less.

4. The inspection method according to claim 1 or 2, wherein the ceramic sintered body has a spherical portion.

5. The inspection method according to claim 4, wherein the surface roughness Ra of the spherical portion is 0.2 μm or more.

6. The inspection method according to claim 4, wherein the ceramic sintered body has a band-shaped portion.

7. The inspection method according to claim 5, wherein the ceramic sintered body has a band-shaped portion.

8. The inspection method according to claim 1 or 2, wherein the ceramic sintered body is a silicon nitride sintered body.

9. The inspection method according to claim 5, wherein the ceramic sintered body is a silicon nitride sintered body.

10. A method for manufacturing a ceramic sintered body, comprising polishing the ceramic sintered body determined to be a non-defective product by the inspection method according to claim 1.

11. A method for manufacturing a ceramic sintered body, comprising polishing the ceramic sintered body determined to be a non-defective product by the inspection method according to claim 6.

12. The manufacturing method according to claim 10, wherein the ceramic sintered compact after polishing is a ceramic sintered compact for use as a bearing ball.

13. The manufacturing method according to claim 11, wherein the ceramic sintered compact after polishing is a ceramic sintered compact for use as a bearing ball.

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