Method for measuring indentation resistance, method for predicting indentation resistance of rolling bearings, method for selecting machining conditions, method for selecting bearing material quality, method for selecting polishing conditions, and bearing manufacturing method

Abstract

The present invention provides a method for measuring the indentation resistance of the outer and inner ring raceways, eliminating the need for test piece preparation and testing. The method involves determining: a first curve showing the yield shear stress in the depth direction of the raceway surface of a rolling bearing material before machining; a second curve showing the static shear stress in the depth direction of the raceway surface after machining; and a third curve showing the static shear stress in the depth direction of the raceway surface when a rolling element contacts the raceway surface and a static load is applied. Area A is defined as the area enclosed by the first and second curves and the third curve, and the correlation between Area A and the indentation depth of the raceway is determined.

Description

Technical Field

[0001] The present invention relates to a method for measuring indentation resistance, a method for predicting indentation resistance of a rolling bearing, a method for selecting machining conditions, a method for selecting bearing material quality, a method for selecting polishing conditions, and a bearing manufacturing method. Background Art

[0002] It is known that in rolling bearings, if excessive loads are applied while stationary, Hertzian contact occurs between the outer and inner raceways of the rolling bearing and the rolling elements, leaving permanent deformation (Brinell indentations). If such indentations exist, the sound and vibration characteristics of the rolling bearing will be affected when it is used. For example, in rolling bearings used in high-speed rotation applications such as machine tools, even a tiny indentation of about 1 μm can cause abnormal noise and vibration. Therefore, when designing rolling bearings, the static limit load (basic static load rating) is determined by the contact stress. In JISB 1519 (2009), for example, the contact stress of radial ball bearings other than thrust ball bearings and self-aligning ball bearings is set to 4.2 GPa.

[0003] Furthermore, with the trend toward miniaturization of rolling bearings, driven by the pursuit of lower fuel consumption in automobiles and other applications, there is a need for resistance to plastic deformation, sufficient to withstand excessive loads. Traditionally, improving the plastic deformation resistance of rolling bearings has hinged on balancing the hardness of the outer and inner raceways of the bearings with the amount of retained austenite. By increasing the hardness of the bearing raceways and reducing retained austenite, a soft structure in steel, measures have been implemented to improve resistance to permanent deformation and indentation.

[0004] For example, Patent Document 1 describes a technique of subjecting high-carbon chromium bearing steel to carbonitriding and tempering, and Patent Document 2 describes a technique of subjecting the raceway surfaces of bearing inner and outer rings to cryogenic treatment.

[0005] However, if one attempts to improve indentation resistance only through such heat treatment and composition adjustment, special heat treatments such as carbonitriding and cryogenic treatment require a long time, and separate steps for carbonitriding and cryogenic treatment are required, increasing manufacturing costs.

[0006] On the other hand, the formation of indentations is the plastic deformation of the raceway surface and can be considered a simple material yield phenomenon. There are various methods for strengthening materials, including heat treatment and composition adjustment, as well as work hardening. The inventors of this application have discovered that by mechanically processing a material that has been hardened to the maximum extent by heat treatment, such as quenched steel, it is possible to further improve indentation resistance. Mechanical processing methods include polishing, shot peening, and other methods, which can also be implemented industrially.

[0007] In particular, the polishing process can suppress deterioration of surface properties such as shot peening, and can suppress machining allowances in the finishing process performed as needed in the subsequent process.

[0008] Prior art literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application Laid-Open No. 2015-200351

[0011] Patent Document 2: Japanese Patent Application Laid-Open No. 2000-274440 Summary of the Invention

[0012] Technical problem that the invention aims to solve

[0013] However, it is difficult to predict the appropriate amount of machining required to improve the indentation resistance of rolling bearings for each bearing material, requiring extensive trial production, evaluation, and research. Consequently, test specimens must be produced with varying treatment conditions, machining conditions, and alloy compositions, each requiring evaluation, which increases costs and time.

[0014] The present invention was completed with the above-mentioned problems in mind, and its purpose is to provide a method for measuring the indentation resistance of the outer ring and inner ring raceway surfaces when the outer ring raceway surfaces and inner ring raceway surfaces are hardened by machining, which does not require the preparation and testing of test pieces, as well as a method for predicting the indentation resistance of a rolling bearing, a method for selecting machining conditions and the quality of the bearing material after heat treatment, and a bearing manufacturing method.

[0015] In addition, the object of the present invention is to provide a method for selecting optimal polishing processing conditions and a bearing manufacturing method for improving indentation resistance when the raceway surfaces of bearing raceways such as the outer ring raceway surface and the inner ring raceway surface are hardened by polishing, without the need for test piece production and testing, through calculation-based verification.

[0016] Technical means to solve the problem

[0017] The formation of indentations in rolling bearings is the result of plastic deformation caused by the surface contact between the rolling elements and the raceway rings. The theory of Hertzian contact explains the stress that produces this plastic deformation. On the other hand, if a load exceeding the yield stress is applied to the metal, plastic deformation occurs. In order to continue this plastic deformation, a greater load is required, and a phenomenon called "work hardening" occurs. In addition, it has the following characteristics: once the load is released from the work-hardened metal, it will not deform unless a load equal to or greater than the load is applied. If these phenomena are combined, the area that is deformed due to the contact between the rolling element and the raceway ring will not deform within this range if machining is applied in advance according to the stress field of the Hertzian contact generated between the two, and the difference between the two contributes to the formation of indentations.

[0018] That is, the deformation of the material can be explained based on the Hertzian contact theory, and if a calibration curve is experimentally prepared, the amount of indentation formed by the applied machining can be predicted only by geometric calculations.

[0019] Furthermore, for example, when performing a polishing process as a machining process, the optimal machining conditions can be selected by considering the size of the polishing ball attached to the front end of the polishing tool, the material constituting the polishing ball, the polishing load, etc. during the prediction.

[0020] The present invention is based on such findings, and in order to solve the above-mentioned problems, provides a method for measuring indentation resistance as shown in the following (1).

[0021] (1) A method for measuring indentation resistance of a rolling bearing having a plurality of rolling elements rotatably held between raceways having machined raceway surfaces, wherein:

[0022] Find:

[0023] a first curve showing a yield shear stress in a depth direction of a raceway surface of a material forming the rolling bearing before machining of the raceway surface;

[0024] a second curve showing a static shear stress in a depth direction of the raceway surface in a state where the raceway surface is machined; and

[0025] A third curve shows the static shear stress in the depth direction of the raceway surface when the rolling element is in contact with the raceway surface and a static load is applied thereto.

[0026] Furthermore, an area enclosed by areas above the first and second curves and below the third curve is defined as area A, and a correlation between the area A and the indentation depth of the raceway ring is determined.

[0027] In addition, in order to solve the above-mentioned problems, the present invention provides a method for predicting the indentation resistance of a rolling bearing as shown in the following (2), a method for selecting machining conditions as shown in the following (3), a method for selecting the quality of bearing materials as shown in the following (4), and a bearing manufacturing method as shown in the following (5).

[0028] (2) A method for predicting the indentation resistance of a rolling bearing, characterized in that:

[0029] The indentation resistance of the raceway ring is predicted based on the indentation resistance measuring method described in (1) above.

[0030] (3) A method for selecting machining conditions, characterized in that the method for predicting the indentation resistance of a rolling bearing described in (2) above is used,

[0031] Based on the correlation between the area A and the indentation depth of the raceway ring, the area A is calculated in a manner such that the indentation resistance of the raceway ring is of an arbitrary size, the second curve is calculated in a manner such that the area A becomes the area A, and then the machining conditions are determined in a manner such that the second curve becomes the area A.

[0032] (4) A method for selecting the quality of a bearing material, characterized in that the method for predicting the indentation resistance of a rolling bearing described in (2) above is used,

[0033] Based on the correlation between the area A and the indentation depth of the raceway ring, the area A is calculated in a manner such that the indentation resistance of the raceway ring is of any size, the first curve is calculated in a manner such that the area A becomes the first curve, and then the quality of the bearing material after heat treatment is determined in a manner such that the first curve becomes the first curve.

[0034] (5) A bearing manufacturing method, characterized in that it includes at least one of the steps of the method for predicting the indentation resistance of a rolling bearing described in (2), the method for selecting machining conditions described in (3), and the method for selecting the quality of a bearing material described in (4).

[0035] It should be noted that, in this specification, the inventions according to (1) to (5) above are referred to as the "first invention group."

[0036] Furthermore, in order to solve the above-mentioned problems, the present invention provides a method for selecting polishing conditions as shown in the following (6) to (10).

[0037] (6) A method for selecting polishing processing conditions, characterized in that the method for selecting polishing processing conditions is a method for selecting processing conditions for polishing processing performed on a raceway surface of a bearing raceway ring,

[0038] Find:

[0039] a first curve showing a yield shear stress in a depth direction of the raceway surface of a material forming the bearing raceway ring before the raceway surface is subjected to the polishing process;

[0040] a second curve showing a static shear stress in a depth direction of the raceway surface when the raceway surface has been subjected to the polishing process; and

[0041] A third curve shows the static shear stress in the depth direction of the raceway surface when the rolling element is in contact with the raceway surface and a static load is applied thereto.

[0042] The area above the first and second curves and below the third curve is defined as area A.

[0043] The area above the first curve and below the third curved surface is defined as area S.

[0044] A processing condition satisfying the area A < the area S is selected.

[0045] (7) The method for selecting polishing conditions as described in (6) above is characterized in that:

[0046] The polishing process is performed using a polishing tool with a polishing ball installed at the front end.

[0047] When the value obtained by dividing the radius of the polishing ball by the groove radius of the bearing raceway is set as the polishing tool selection index B,

[0048] B≤1.

[0049] (8) The method for selecting polishing conditions as described in (7) above is characterized in that:

[0050] The correlation between the polishing indentation resistance index α represented by (the area S−the area A) / the area S and the polishing ball selection index B is determined.

[0051] (9) The method for selecting polishing conditions as described in (8) above is characterized in that:

[0052] Based on the correlation between the polishing indentation resistance index α and the polishing ball selection index B, the size, material, and polishing load of the polishing ball are determined so as to maximize the polishing indentation resistance index α.

[0053] (10) The method for selecting polishing conditions according to any one of (7) to (9) above, characterized in that:

[0054] As the polishing ball, a material having a Young's modulus of 200 GPa or more is selected.

[0055] In addition, the present invention provides a bearing manufacturing method shown in the following (11).

[0056] (11) A bearing manufacturing method, characterized in that:

[0057] The method includes a polishing step using the polishing conditions selected based on the method for selecting the polishing conditions described in any one of (6) to (10).

[0058] It should be noted that, in this specification, the inventions according to (6) to (11) above are referred to as the "second invention group."

[0059] Effects of the Invention

[0060] According to the present invention involved in the above-mentioned "First Invention Group", there is no need for test piece preparation and testing, and it is possible to measure the indentation resistance of the bearing raceway ring, predict the indentation resistance, select the machining conditions, select the quality of the bearing material after heat treatment, and manufacture bearings with excellent indentation resistance.

[0061] In addition, according to the present invention involved in the above-mentioned "Second Invention Group", a method for selecting processing conditions and a bearing manufacturing method can be provided, which can select the optimal processing conditions for improving indentation resistance when the raceway surfaces of the bearing raceways, such as the outer ring raceway surface and the inner ring raceway surface, are hardened by polishing through calculation-based verification, without the need for test piece preparation and testing. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 It is a partially cutaway perspective view showing a radial ball bearing as an example of a rolling bearing.

[0063] Figure 2 This is a schematic diagram used to illustrate static shear stress.

[0064] Figure 3 This is a schematic diagram for explaining the calculation method of area S.

[0065] Figure 4 This is a schematic diagram for explaining the calculation method of area A.

[0066] Figure 5 This is a graph showing the relationship between the area A and the indentation depth of the raceway ring for explaining the present invention according to the first invention group in the first embodiment.

[0067] Figure 6This is a graph showing the correlation between the polishing ball selection index B and the polishing indentation resistance index α when the polishing tool, the material of the ball, and the polishing load are changed in the second embodiment for explaining the present invention according to the second invention group.

[0068] Figure 7 This is a graph showing the relationship between the polishing ball selection index B and the polishing indentation resistance index α when the polishing load is changed in the second embodiment for explaining the present invention according to the second invention group.

[0069] Figure 8 This is a graph showing the relationship between the polishing ball selection index B and the polishing indentation resistance index α when the material of the polishing ball is changed in the second embodiment for explaining the present invention according to the second invention group.

[0070] Explanation of symbols

[0071] 1 radial ball bearing

[0072] 2 Outer ring raceway surface

[0073] 3 outer ring

[0074] 4 Inner ring raceway

[0075] 5 Inner circle

[0076] 6 Balls

[0077] 7 Cage DETAILED DESCRIPTION

[0078] Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be applied with appropriate modifications within the scope of the present invention.

[0079] In the embodiments described below, the embodiment for describing the present invention pertaining to the above-mentioned “first invention group” will be referred to as the “first embodiment,” and the embodiment for describing the present invention pertaining to the above-mentioned “second invention group” will be referred to as the “second embodiment.”

[0080] <First embodiment>

[0081] First, the first embodiment will be described.

[0082] In the present invention, the type and structure of the rolling bearing are not limited. Figure 1The radial ball bearing shown in the figure includes an outer ring 3 having an outer ring raceway 2 on its inner circumference; an inner ring 5 having an inner ring raceway 4 on its outer circumference; and a plurality of balls 6, each serving as a rolling element, disposed between the outer ring raceway 2 and the inner ring raceway 4. The balls 6 are arranged at equal intervals in the circumferential direction and are held in a cage 7 so that they can roll freely.

[0083] The outer ring raceway surface 2 and the inner ring raceway surface 4 are machined. The machining is not limited, but lapping and shot peening are preferred.

[0084] Polishing is a machining method in which a device with a spherical, high-hardness tip, serving as a machining jig, is pressed against the outer ring raceway 2 and inner ring raceway 4, causing the outer ring 3 and inner ring 5 to rotate about their axes, thereby applying compressive stress to the outer ring raceway 2 and inner ring raceway 4. Shot peening, on the other hand, is a machining method in which high-hardness, roughly spherical projectiles are sprayed onto the outer ring raceway 2 and inner ring raceway 4. By adjusting the processing conditions, such as the size, material, and spray velocity of the roughly spherical projectiles, the quality can be adjusted to the same level as polishing.

[0085] However, in rolling bearings, when a static load is applied, the raceway ring undergoes plastic deformation due to contact with the rolling elements, sometimes resulting in indentations on the raceway surface. The amount of deformation due to plastic deformation is determined based on the relative relationship between the static yield shear stress of the material forming the rolling bearing and the static shear stress generated inside the raceway ring due to Hertzian contact between the rolling elements and the raceway ring. Figure 2 As shown in the figure, the static shear stress is the static shear stress (τ st ).

[0086] exist Figure 3 The figure shows "Curve a," which represents the yield shear stress in the depth direction of the raceway surface of the rolling bearing's material, and "Curve b," which represents the static shear stress in the depth direction of the raceway surface generated within the raceway ring when a predetermined static load is applied. As shown in the figure, a region (the shaded area in the figure) is formed where the static shear stress shown by Curve b is higher than the yield shear stress of the rolling bearing's material shown by Curve a. The amount of plastic deformation of the raceway surface can be estimated based on the size of this "area S." The smaller this area S, the less likely it is to undergo plastic deformation, and thus, the less likely it is to form indentations on the raceway surface.

[0087] In addition, Figure 3 In the figure, for convenience, “curve a” is represented by a straight line, but it is actually a substantially straight line. Figure 4The same is true for "curve a" in .

[0088] Similarly, when machining the raceway surface, the contact between the machining jig (a spherical tip in the case of polishing, or a roughly spherical projection in the case of shot peening) and the raceway surface can be considered to be Hertzian contact. Furthermore, it can be considered that a static shear stress exceeding the yield shear stress of the rolling bearing material is introduced before the static load is applied.

[0089] Figure 4 The figure also shows "Curve a" (first curve) which represents the yield shear stress in the depth direction of the raceway surface of the material forming the rolling bearing before the raceway surface is machined, "Curve c" (second curve) which represents the static shear stress in the depth direction of the raceway surface when the raceway surface is machined under specified conditions, that is, when the raceway surface is machined, and "Curve b" (third curve) which represents the static shear stress in the depth direction of the raceway surface when a specified static load is applied, that is, when the rolling element is in contact with the raceway surface and a static load is applied.

[0090] exist Figure 4 In the figure, the "area A" (plastic deformation index) of the region (shaded area in the figure) enclosed by curves a (first curve) and c (second curve) and below b (third curve) can be used to predict the indentation resistance of the raceway ring obtained under machining conditions. It should be noted that each curve can be obtained by the following calculation.

[0091] At the contact point between the raceway ring and the rolling element, if the vertical stress generated relative to the tangential direction of the rolling element is σ x (unit: MPa), the vertical stress generated relative to the normal direction is σ z (unit: MPa), the static shear stress τst generated inside the raceway ring can be expressed by the following formula (1) and calculated using a known elasticity theory solution.

[0092] [Formula 1]

[0093]

[0094] In the case of point contact, the vertical stress σ x and σ zFor example, the calculation can be performed using Hanson's elastic theory solution (Hanson, MT and Johnson, T., "The Elastic Field for Spherical Hertzian Contact of Isotropic Bodies Revisited: Some Alternative Expressions", Transactions of the ASME, Journal of Tribology, Vol. 115 (1993), pp. 327-332). The maximum contact pressure q using Hertzian contact is max , contact surface radius a, Poisson's ratio ν, σ x and σ z It is represented by the following formulas (2) to (7).

[0095] [Formula 2]

[0096]

[0097] [Formula 3]

[0098]

[0099] [Formula 4]

[0100]

[0101] [Formula 5]

[0102]

[0103] [Formula 6]

[0104]

[0105] [Formula 7]

[0106]

[0107] Here, x=rcosθ(r>0), when x>0, θ=0, and when x<0, θ=π. The maximum contact surface pressure q of Hertzian contact max The contact surface radius a can be calculated by referring to "Introduction to Ball Bearing Design Calculation" (Junzo Okamoto, 2011), etc.

[0108] It should be noted that in the case of line contact, for example, Smith's elastic theory solution (Smith, JO, Liu, CK and Ill U., "Stress Due to Tangential and Normal Loads on an Elastic Solid With Application to Some Contact Stress Problems", Transaction of the ASME, Journal of Applied Mechanics, Vol. 20 (1953), pp. 157-166) or Tanaka's calculation formula (Naoyuki Tanaka, "On the calculation of internal stress in elliptical contact", Proceedings of the Japan Society of Mechanical Engineers C, Vol. 61, No. 660 (2001), pp. 265-269) can be used for calculation.

[0109] In addition, if 0.2% endurance is set as σ 0.2 , the Vickers hardness of the raceway ring is set to HV, then the yield shear stress τ of the material forming the rolling bearing is y (Unit: MPa) is represented by the following formula (8).

[0110] [Formula 8]

[0111]

[0112] Then, each curve is calculated according to the above formula, and the difference between curve a, curve b, and curve c at the same depth from the surface is integrated in the depth direction from the surface, thereby determining the area A.

[0113] Alternatively, for ease of calculation, the segmented quadrature method can be used to approximate the area. Specifically, the contact point between the raceway and the rolling element is divided into a number of small intervals ΔZ relative to the normal to the rolling element, and the areas of these intervals are summed. For more accurate calculations, it is best to reduce the small interval ΔZ, but 0.01 mm is a reasonable value. Even with further reductions, the difference in the calculated area A is negligible.

[0114] It should be noted that the present invention is a method for measuring and predicting the amount of indentation formation that is applicable to the following situations, namely, situations where metal is mechanically processed using the theory of Hertzian contact, such as in roller polishing, and the theory of deformation correlation, such as in rolling bearings, is generated by Hertzian contact, and the present invention is used to control the conditions for mechanical processing of the amount of indentation formation and the selection of the quality of bearing materials after heat treatment.

[0115] <Examples of the First Embodiment>

[0116] The following examples and comparative examples will specifically illustrate the effects of the present invention according to the first invention group, but the present invention is not limited thereto. The area A obtained as described above is found to have a high correlation with the indentation depth of the raceway surface as shown below.

[0117] (Preparation of test pieces)

[0118] A steel ball is pressed against a flat-plate-shaped test piece simulating the raceway ring of a rolling bearing, and the depth of the indentation produced on the surface of the test piece is measured. The test pieces are all made of bearing steel (SUJ2 steel) and are subjected to quenching and tempering. In Example 1, quenching at 840°C and tempering at 180°C are performed, and in Example 2, quenching at 840°C and tempering at 300°C are performed. Then, after plane finishing, polishing is performed in Examples 1 and 2. In Comparative Example 1, quenching at 840°C and tempering at 180°C are performed, and in Comparative Example 2, quenching at 840°C and tempering at 300°C are performed. Then, in Comparative Examples 1 and 2, polishing is not performed, and only plane finishing is performed. In addition, the polishing conditions are as follows: the front end shape of the polishing tool is set to The slip ratio was set to 100%, the circumferential speed to 100 m / min, the tool feed rate to 0.05 mm / rev, and the tool penetration to 0.3 mm. Furthermore, during machining, filtered working fluid was used, and the maximum contact pressure, calculated as 9.2 GPa, was calculated assuming that the polishing load resulted only in elastic deformation.

[0119] (Indentation test)

[0120] In the indentation test, a test piece of a flat plate shape simulating a rolling bearing raceway was made of bearing steel, a 3 / 8 inch steel ball after quenching and tempering was used, and a load was applied in a manner such that the maximum contact surface pressure of the test piece was 5.0 GPa, 5.5 GPa, and 6.0 GPa. Then, a 3-dimensional surface property measuring machine (CCI) manufactured by Taylor Hobson was used to measure the depth of the indentation generated on the surface of the test piece. The results of the indentation test and the calculation results of area A are shown in Table 1. By comparing the results of Example 1 and Comparative Example 1, and Example 2 and Comparative Example 2, polishing was performed to confirm the reduction in the indentation depth.

[0121] In addition, Figure 5 In the figure, the relationship between the area A and the indentation depth of the raceway ring is shown in a graph. Figure 5 As shown, a good correlation was observed between the calculated area A and the measured indentation depth.

[0122] In this way, if the area A can be calculated, the indentation depth can be predicted. Therefore, there is no need to perform an indentation resistance evaluation test every time a test piece is produced. The indentation resistance of the bearing raceway after machining can be predicted, and a bearing with excellent indentation resistance can be provided.

[0123] In addition, based on the correlation between area A and the indentation depth of the raceway ring, area A is calculated in a manner such that the indentation resistance of the raceway ring is of an arbitrary size. In addition, a second curve is calculated in a manner such that area A becomes the second curve, and then the machining conditions can be determined in a manner such that the second curve becomes the second curve.

[0124] Furthermore, based on the correlation between area A and the indentation depth of the raceway ring, area A is calculated in a manner such that the indentation resistance of the raceway ring is of an arbitrary size, and a first curve is calculated in a manner such that the area A becomes the first curve. Thereafter, the quality of the bearing material after heat treatment can be determined in a manner such that the first curve becomes the first curve.

[0125] Furthermore, a bearing having excellent indentation resistance can be manufactured by a bearing manufacturing method that includes at least one of the above-mentioned methods for predicting the indentation resistance of a rolling bearing, selecting machining conditions, and selecting the quality of a bearing material.

[0126] [Table 1]

[0127]

[0128] <Second embodiment>

[0129] Next, a second embodiment will be described.

[0130] In the second embodiment, the type and structure of the rolling bearing are also not limited. For example, Figure 1 The outer ring raceway surface 2 and the inner ring raceway surface 4 are subjected to a lapping process as a machining process.

[0131] When the raceway surface is polished, the tip of the spherical polishing tool contacts the raceway surface, so it can also be considered as Hertzian contact. In addition, it can be considered that a shear stress exceeding the yield shear stress of the material forming the rolling bearing is pre-introduced before applying the static load.

[0132] Therefore, as reference Figure 3 As described above, between "curve a," which represents the yield shear stress in the depth direction of the raceway surface of the rolling bearing's material, and "curve b," which represents the static shear stress in the depth direction of the raceway surface generated within the raceway ring when a predetermined static load is applied, the amount of plastic deformation of the raceway surface can be estimated based on the size of "area S," the region where the static shear stress shown by curve b is higher than the yield shear stress of the rolling bearing's material shown by curve a. The smaller this area S, the less likely it is to undergo plastic deformation, and thus, the less likely it is to form indentations on the raceway surface.

[0133] In addition, as reference Figure 4As described, based on the "area A" (plastic deformation index) of the area (shaded part in the figure) surrounded by curves above curve a (first curve) and curve c (second curve) and below curve b (third curve), the indentation resistance of the raceway ring obtained under the conditions of polishing can be predicted.

[0134] It should be noted that each curve can be obtained according to the above-mentioned equations (1) to (8).

[0135] Then, each curve is calculated according to the above formula, and the difference between curve a, curve b, and curve c at the same depth from the surface is integrated in the depth direction from the surface, thereby determining the area S or the area A.

[0136] Alternatively, for ease of calculation, the segmented quadrature method can be used to approximate the area. Specifically, the contact point between the raceway and the rolling element is divided into a number of small intervals ΔZ relative to the normal to the rolling element, and the areas of these intervals are summed. For more accurate calculations, it is best to reduce the small interval ΔZ, but 0.01 mm is a reasonable value. Even with further reductions, the difference between the calculated areas S and A becomes negligible.

[0137] To improve the indentation resistance of bearing raceways through polishing, the area enclosed by the areas above curves a and c and below curve b is defined as Area A, and the area enclosed by the areas above curve a and below curve b is defined as Area S. It is necessary to satisfy "Area A < Area S." It should be noted that if "Area A = Area S," the polishing process will not provide sufficient hardening and will not contribute to improved indentation resistance.

[0138] In order to perform a polishing process on the raceway surface of a bearing raceway, the polishing ball selection index B, obtained by dividing the radius of the polishing ball used as the polishing tool by the groove radius of the bearing raceway, must be ≤ 1. Furthermore, if B > 1, the ball at the tip of the polishing tool cannot be inserted into the groove of the bearing raceway, making it impossible to perform the desired polishing process.

[0139] In addition, when the value obtained by subtracting the area A from the area S and dividing it by the area S, that is, "(area S-area A) / area S", is set as the polishing indentation resistance index α, as shown in the examples described later, there is a correlation between the polishing indentation resistance index α and the polishing ball selection index B. And, as described later, Figures 6-8 As shown, when the polishing ball selection index B is set to "x" (horizontal axis) and the polishing indentation resistance index α is set to "y" (vertical axis) in the xy coordinate, the larger the polishing indentation resistance index α is, the more effectively the indentation resistance of the bearing raceway caused by the polishing process is improved.

[0140] That is, it is preferable to determine the size, ie, radius, material of the polishing ball, and polishing load so that the polishing indentation resistance index α is maximized in the xy coordinates.

[0141] In addition, the material of the polishing ball affects the polishing process conditions. Here, as shown in the examples described below, there is a correlation between the Young's modulus of the polishing ball and its indentation resistance. The larger the Young's modulus of the material, the larger the polishing indentation resistance index α.

[0142] Specifically, it is preferred to select a material having a Young's modulus greater than that of iron (Young's modulus 200 GPa), for example, preferably silicon nitride (Young's modulus 320 GPa), more preferably tungsten carbide (Young's modulus 550 GPa) or other materials known as superhard alloys, or diamond (Young's modulus 786 GPa).

[0143] As described above, the indentation resistance of the bearing raceway during polishing varies significantly depending on the ball size of the polishing tool, the material of the ball, and the applied polishing load. Therefore, as in the present invention, by determining the ball size and material, as well as the polishing load, based on the correlation between the polishing ball selection index B and the polishing indentation resistance index α, and maximizing the polishing indentation resistance index α, optimal polishing conditions for improving the indentation resistance of the bearing raceway can be selected without requiring test piece preparation or testing.

[0144] Furthermore, the present invention according to the aforementioned "Second Invention Group" provides a method for manufacturing a rolling bearing, comprising a polishing step for polishing the inner ring raceway surface and the outer ring raceway surface under the optimal processing conditions selected as described above. It should be noted that other than the polishing step, conventional manufacturing methods may be appropriately performed.

[0145] <Example according to the second embodiment>

[0146] The effects of the selected polishing processing conditions (tool selection) on the indentation resistance of the bearing raceway ring were verified based on calculations. It should be noted that the following verification examples are given to specifically illustrate the effects of the present invention involved in the second invention group, but the present invention is not limited to these.

[0147] The indentation resistance of various bearing raceways during polishing was verified. The bearings tested were angular contact ball bearing inner rings, and the main bearing shapes are shown in Table 2. The bearings tested were made of carbonitrided steel, and the rolling elements were ceramic. In Table 2, "PCD" stands for the rolling element pitch diameter.

[0148] [Table 2]

[0149]

[0150] Table 3 lists the polishing tools used in this verification. Each tool differed in the size of the ball at the tip and the applicable polishing load. The ball was made of silicon nitride (Young's modulus 320 GPa, Poisson's ratio 0.26), tungsten carbide (Young's modulus 550 GPa, Poisson's ratio 0.22), or diamond (Young's modulus 786 GPa, Poisson's ratio 0.2).

[0151] [Table 3]

[0152]

[0153] Table 4 summarizes the results of the polishing ball selection index B for each bearing, organized by polishing tool. Furthermore, to perform polishing on the bearing raceway, the polishing ball selection index B must be at least 1. As mentioned above, if the polishing ball selection index B is greater than 1, the ball at the tip of the polishing tool cannot be inserted into the groove of the bearing raceway, preventing the desired polishing process. Therefore, in Table 4, values ​​with a polishing ball selection index B greater than 1 are indicated as "-."

[0154] [Table 4]

[0155]

[0156] Then, the rolling elements were in contact with the bearing raceway surface, and a static load of 4.6 GPa was applied at the maximum contact surface pressure. Curves a, b, and c were obtained, respectively, to calculate Area A and Area S. It should be noted that in Table 4, for bearing and tool combinations not marked with a "-," as described later, the condition "Area A < Area S" can be satisfied by appropriately selecting the polishing ball material and the polishing load.

[0157] Next, the polishing indentation resistance index α, which is "(area S-area A) / area S", was calculated based on area A and area S, and its correlation with the polishing ball selection index B was examined. Figure 6 A graph showing the xy coordinates of the polishing ball selection index B as "x" (horizontal axis) and the polishing indentation resistance index α as "y" (vertical axis) when the polishing tool, ball material and polishing load are changed. Figure 6 As shown, there is a correlation between the polishing indentation resistance index α and the polishing ball selection index B. As the polishing ball selection index B increases, the polishing indentation resistance index α increases. However, after the polishing ball selection index B reaches a certain value, the polishing indentation resistance index α decreases. Thus, it can be said that the optimal ball size for the polishing tool corresponds to the groove radius of the bearing raceway ring through verification based on calculations.

[0158] Then, in Figure 7The figure shows the relationship between the polishing ball selection index B and the polishing indentation resistance index α when the polishing load is changed in the verification of the polishing tool 1 or 2 using the polishing ball made of super-hard alloy. Figure 7 As shown, calculation-based verification confirms that the greater the polishing load, the higher the indentation resistance of the bearing raceway. Furthermore, the smaller the polishing ball, the higher the indentation resistance of the bearing raceway. However, in practice, when using a polishing tool, there are limits to the maximum applicable polishing load due to the durability of the ball. Therefore, it is necessary to select the desired polishing tool based on the optimal combination of ball size and polishing load.

[0159] Figure 8 The figure shows the relationship between the polishing ball selection index B and the polishing indentation resistance index α when the polishing ball material is varied, during a test conducted on bearings 3 to 9 using a polishing tool 2 at a polishing load of 2000 N. It should be noted that in this test (based on calculations), in addition to the aforementioned silicon nitride (Young's modulus 320 GPa, Poisson's ratio 0.26), the superhard alloy tungsten carbide (Young's modulus 550 GPa, Poisson's ratio 0.22), and diamond (Young's modulus 786 GPa, Poisson's ratio 0.2), iron (Young's modulus 200 GPa, Poisson's ratio 0.28) was also used as the polishing ball material.

[0160] like Figure 8 As shown, it can be confirmed that the indentation resistance of the polishing ball increases in the order of iron, silicon nitride, superhard alloy (tungsten carbide), and diamond. In other words, the higher the Young's modulus, the higher the indentation resistance. In addition, in this verification, it can be confirmed that if the polishing ball is composed of a material with a Young's modulus of iron of 200GPa or more, the indentation resistance of the bearing raceway can be improved.

[0161] As described above, the indentation resistance of the bearing raceway caused by polishing varies significantly depending on the size of the polishing tool, i.e., the polishing ball, the material of the ball, and the applied polishing load. Therefore, by determining the size and material of the polishing ball, as well as the polishing load, to maximize the polishing indentation resistance index α based on the correlation between the polishing ball selection index B and the polishing indentation resistance index α, as in the present invention, the production and testing of test pieces are eliminated, and optimal polishing processing conditions (tool selection) for improving the indentation resistance of the bearing raceway can be achieved.

[0162] While various embodiments have been described above with reference to the accompanying drawings, the present invention is not limited to these examples. Those skilled in the art will be able to devise various variations or modifications within the scope of the claims, and these variations or modifications will naturally fall within the technical scope of the present invention. Furthermore, the various components of the above embodiments may be arbitrarily combined without departing from the spirit of the invention.

[0163] In addition, this application is based on the Japanese patent application (Japanese Patent Application No. 2020-080615) filed on April 30, 2020 and the Japanese patent application (Japanese Patent Application No. 2021-023516) filed on February 17, 2021, the contents of which are incorporated herein by reference.

Claims

1. A method for measuring indentation resistance of a rolling bearing having a plurality of rolling elements rotatably held between raceways having machined raceway surfaces, wherein: Find: a first curve showing a yield shear stress in a depth direction of a raceway surface of a material forming the rolling bearing before machining of the raceway surface; a second curve showing a static shear stress in a depth direction of the raceway surface when the raceway surface is machined; as well as A third curve shows the static shear stress in the depth direction of the raceway surface when the rolling element is in contact with the raceway surface and a static load is applied thereto. Furthermore, an area enclosed by areas above the first and second curves and below the third curve is defined as area A, and a correlation between the area A and the indentation depth of the raceway ring is determined.

2. A method for predicting the indentation resistance of a rolling bearing, characterized in that: The indentation resistance of the raceway ring is predicted based on the indentation resistance measuring method according to claim 1 .

3. A method for selecting machining conditions, characterized in that: Using the method for predicting the indentation resistance of a rolling bearing according to claim 2, Based on the correlation between the area A and the indentation depth of the raceway ring, the area A is calculated in a manner such that the indentation resistance of the raceway ring is of an arbitrary size, the second curve is calculated in a manner such that the area A becomes the area A, and then the machining conditions are determined in a manner such that the second curve becomes the area A.

4. A method for selecting bearing material quality, characterized in that: Using the method for predicting the indentation resistance of a rolling bearing according to claim 2, Based on the correlation between the area A and the indentation depth of the raceway ring, the area A is calculated in a manner such that the indentation resistance of the raceway ring is of any size, the first curve is calculated in a manner such that the area A becomes the first curve, and then the quality of the bearing material after heat treatment is determined in a manner such that the first curve becomes the first curve.

5. A bearing manufacturing method, characterized in that: The method comprises at least one step of the method for predicting the indentation resistance of a rolling bearing according to claim 2, the method for selecting machining conditions according to claim 3, and the method for selecting the quality of a bearing material according to claim 4.

6. A method for selecting polishing conditions, characterized in that: The method for selecting the polishing processing conditions is a method for selecting the processing conditions for the polishing processing performed on the raceway surface of the bearing raceway ring. Find: a first curve showing a yield shear stress in a depth direction of the raceway surface of a material forming the bearing raceway ring before the raceway surface is subjected to the polishing process; a second curve showing a static shear stress in a depth direction of the raceway surface when the raceway surface has been subjected to the polishing process; as well as A third curve shows the static shear stress in the depth direction of the raceway surface when the rolling element is in contact with the raceway surface and a static load is applied thereto. The area above the first and second curves and below the third curve is defined as area A. The area above the first curve and below the third curved surface is defined as area S. A processing condition satisfying the area A < the area S is selected.

7. The method for selecting polishing conditions according to claim 6, wherein: The polishing process is performed using a polishing tool with a polishing ball installed at the front end. When the value obtained by dividing the radius of the polishing ball by the groove radius of the bearing raceway is set as the polishing tool selection index B, B≤1。 8. The method for selecting polishing conditions according to claim 7, wherein: The correlation between the polishing indentation resistance index α represented by (the area S−the area A) / the area S and the polishing ball selection index B is determined.

9. The method for selecting polishing conditions according to claim 8, wherein: Based on the correlation between the polishing indentation resistance index α and the polishing ball selection index B, the size, material, and polishing load of the polishing ball are determined so as to maximize the polishing indentation resistance index α.

10. The method for selecting polishing conditions according to any one of claims 7 to 9, wherein: As the polishing ball, a material having a Young's modulus of 200 GPa or more is selected.

11. A bearing manufacturing method, characterized in that: A polishing process comprising a polishing process step using the polishing process conditions selected by the method for selecting polishing process conditions according to any one of claims 6 to 10.

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