Double-row conical roller bearing

Abstract

To provide a double-row conical roller bearing with improved rolling fatigue service, capable of reliably suppressing propagation of cracks from a raceway surface toward the inside.SOLUTION: A double-row conical roller bearing 1 comprises an outer ring 2 and an inner ring 5. The outer ring 2 has outer ring raceway surfaces 9A, 9B as raceway surfaces on an inner peripheral surface. The inner ring 5 has inner ring raceway surfaces 9C, 9D as raceway surfaces on an outer peripheral surface. The maximum compressive residual stress in an axial direction of the raceway surfaces in an area within a depth of 0.1 mm from at least any raceway surface 9 of the outer ring 2 and the inner ring 5 is 1400 MPa or more.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a double row tapered roller bearing. [Background technology]

[0002] Double-row tapered roller bearings are used in railway vehicle axles. Double-row tapered roller bearings are also used in automobile axles, machine tools, pumps, etc. In particular, double-row tapered roller bearings used in railway vehicle axles are important infrastructure, so high reliability is required.

[0003] However, nonmetallic inclusions exist along the fiber flow in the base metal of the metallic material that constitutes the outer and inner rings of the bearing. It is technically impossible to eliminate nonmetallic inclusions in metallic materials. Nonmetallic inclusions that exist along the fiber flow near the raceway surfaces of the outer and inner rings cause spalling of the raceway surfaces. It is necessary to suppress the propagation of cracks that originate from nonmetallic inclusions and move inward from the raceway surfaces of the outer and inner rings along the fiber flow. Suppressing the propagation of cracks prevents spalling of the raceway surfaces caused by nonmetallic inclusions, and improves the rolling fatigue life of the bearing.

[0004] A method for improving the rolling fatigue life of bearings is proposed, for example, in JP 2019-095044 A (Patent Document 1). In JP 2019-095044 A, compressive residual stress is imparted near the raceway surface by machining such as burnishing. This fills the gap between the nonmetallic inclusions and the base material, preventing the gap from acting as an open crack. This improves the rolling fatigue life of the bearing.

[0005] Japanese Patent Application Publication No. 2003-301850 (Patent Document 2) focuses on the relationship between the fiber flow angle with respect to the raceway surface and the square root length of internal defects, and the rolling fatigue life. In Japanese Patent Application Publication No. 2003-301850, the fiber flow angle with respect to the raceway is set to 15° or less, and the square root length of internal defects is set to 0.3 mm or less. This improves the rolling fatigue life of the bearing. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2019-095044 A [Patent Document 2] JP 2003-301850 A Summary of the Invention [Problem to be solved by the invention]

[0007] The technology disclosed in JP 2019-095044 A does not mention the effect of suppressing crack propagation by applying compressive residual stress to the base material. As disclosed in JP 2003-301850 A, it is difficult to control the fiber flow angle relative to the raceway surface to be small, and even if it is possible, the manufacturing cost will rise. In particular, if the fiber flow angle is reduced for all of the multiple rows of raceways, the manufacturing cost will rise.

[0008] The present invention has been made in view of the above problems, and an object of the present invention is to provide a double row tapered roller bearing capable of suppressing the propagation of cracks from the raceway surface toward the inside and improving the rolling fatigue life. [Means for solving the problem]

[0009] A double row tapered roller bearing according to the present disclosure includes an outer ring and an inner ring. The outer ring has an outer ring raceway surface as a raceway surface on its inner circumferential surface. The inner ring has an inner ring raceway surface as a raceway surface on its outer circumferential surface. The maximum value in the raceway surface axial direction in an area within a depth of 0.1 mm from the raceway surface of at least one of the outer ring and the inner ring is 1400 MPa or more. Note that the direction along the axial direction and parallel to the raceway surface is referred to as the "raceway surface axial direction" below. The "raceway surface axial direction" is not limited to a direction completely parallel to the raceway surface, but includes a direction that is approximately equal to the direction parallel to the raceway surface but has a slight angle with respect to the parallel direction, that is, a direction along the direction parallel to the raceway surface. Effect of the Invention

[0010] According to the present disclosure, it is possible to provide a double-row tapered roller bearing capable of suppressing the propagation of cracks from the raceway surface toward the inside and improving the rolling fatigue life. [Brief description of the drawings]

[0011] [Figure 1] 1 is a schematic diagram of a double row tapered roller bearing according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a schematic cross-sectional view taken along line II-II in FIG. [Diagram 3] FIG. 2 is a schematic diagram showing how burnishing is performed on a raceway surface of a bearing. [Figure 4] FIG. 2 is a schematic diagram showing an aspect in which shot peening is performed on a raceway surface of a bearing. [Diagram 5] FIG. 5 is a schematic diagram of the raceway surface of the bearing after shot peening in FIG. 4. [Figure 6] FIG. 4 is a schematic diagram showing the final state of the raceway surface after shot peening. [Figure 7] FIG. [Figure 8] FIG. 4 is an enlarged view of the first row outer ring raceway surface. [Figure 9] FIG. 4 is an enlarged view of the second row outer ring raceway surface. [Figure 10] FIG. 4 is a schematic diagram for explaining the definition of the angle of the fiber flow with respect to the outer ring raceway surface. [Figure 11] FIG. 1 is a schematic diagram of a model of a cracked base material analyzed by the finite element method. [Figure 12] FIG. 12 is a schematic enlarged view of a portion XII enclosed by a dotted line in FIG. [Figure 13] 12 is a schematic diagram showing how the line contact area moves over time in the model of FIG. 11. [Figure 14] 14 is a graph showing calculated values, by the finite element method, of stress intensity factors in the models of FIGS. 11 to 13 to which no compressive residual stress is imparted. [Figure 15]14 is a graph showing calculated values, by the finite element method, of stress intensity factors in the models of FIGS. 11 to 13 to which compressive residual stress has been imparted. [Figure 16] 1 is a graph showing the relationship between the depth from the raceway surface and the residual stress in the outer ring of each prototype. [Figure 17] 1 is a graph showing the relationship between compressive residual stress imparted to a prototype and bearing life. [Figure 18] 1 is a schematic cross-sectional view of a double row tapered roller bearing to which the present embodiment is applied. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the following drawings, the same or corresponding parts are given the same reference numerals, and the description thereof will not be repeated as long as they have the same functions, etc. For convenience of explanation, the X-direction, Y-direction, and Z-direction are introduced.

[0013] (Double row tapered roller bearing) FIG. 1 is a schematic diagram of a double row tapered roller bearing according to the present embodiment. FIG. 2 is a schematic cross-sectional view taken along line II-II in FIG. 1. Referring to FIGS. 1 and 2, a double row tapered roller bearing 1 mainly includes an outer ring 2, which is a raceway ring having an annular shape, an inner ring 5, which is a raceway ring having an annular shape and is disposed on the inner circumferential side of the outer ring 2, a plurality of rollers 6 as rolling elements, and a cage 7 that defines the arrangement of the plurality of rollers 6. A bolt hole 8 is formed in the outer ring 2. The bolt hole 8 is formed so as to extend along the axial direction of the double row tapered roller bearing. In addition, two outer ring raceway surfaces 9A and 9B are formed as raceway surfaces 9 on the inner circumferential surface of the outer ring 2.

[0014] Two inner rings 5 ​​are arranged adjacent to each other in the X direction. An inner ring spacer 4 may or may not be sandwiched between the two inner rings 5. The two inner rings 5 ​​and the inner ring spacer 4 each have an annular shape. Each of the two inner rings 5 ​​has a groove 19, the bottom of which serves as a raceway surface, formed on an outer circumferential surface 16 facing the outer ring 2. In other words, the double row tapered roller bearing 1 has two rows of grooves 19. Two inner ring raceway surfaces 9C, 9D serving as raceway surfaces 9 are formed on the outer circumferential surface of the inner ring 5.

[0015] Of the raceway surfaces 9, raceway surfaces 9A and 9C are disposed on the left side in the X direction in Fig. 2. Roller 6 is disposed so as to be sandwiched between raceway surfaces 9A and 9C. Of the raceway surfaces 9, raceway surfaces 9B and 9D are disposed on the right side in the X direction in Fig. 2. Roller 6 is disposed so as to be sandwiched between raceway surfaces 9B and 9D. Roller 6 has a conical shape.

[0016] The maximum value of the compressive residual stress in the raceway axial direction in a region within 0.1 mm deep from the raceway surface 9 of at least one of the outer ring 2 and the inner ring 5 is 1400 MPa or more. Here, a region within 0.1 mm deep means a region having a dimension of 0.1 mm or less in a direction perpendicular to the raceway surface 9 toward the inside of the base material of the outer ring 2 or the inner ring 5. In particular, it is preferable that the maximum value in the raceway axial direction in a region within 0.1 mm deep from the two adjacent outer ring raceways 9A, 9B of the outer ring 2 is 1400 MPa or more. The compressive residual stress is measured by X-ray diffraction.

[0017] The maximum value of the compressive residual stress in the region within 0.1 mm deep from the outer ring raceways 9A, 9B may be 1400 MPa or more not only in the raceway axial direction but also in the circumferential direction (direction along the arc of the annular shape). It is more preferable that the maximum value of the compressive residual stress in the region within 0.1 mm deep from the outer ring raceways 9A, 9B in the raceway axial direction is, for example, 1600 MPa or more, and even more preferable that it is 1800 MPa or more.

[0018] The raceway surface 9 is machined from the viewpoint of setting the maximum value of the compressive residual stress in the raceway surface axial direction within a depth of 0.1 mm from the raceway surface 9 to 1400 MPa or more. The raceway surface 9 is particularly subjected to burnishing. From the viewpoint of the manufacturing process, as with the viewpoint of the product, the raceway surface 9 may be formed (burnished) so that the maximum value of the compressive residual stress in the raceway surface axial direction within a depth of 0.1 mm from the outer ring raceway surfaces 9A, 9B is 1400 MPa or more not only in the raceway surface axial direction but also in the circumferential direction (direction along the arc of the annular shape). It is more preferable that the maximum value of the compressive residual stress in the raceway surface axial direction within a depth of 0.1 mm from the outer ring raceway surfaces 9A, 9B is 1600 MPa or more, for example, and even more preferable that the maximum value is 1800 MPa or more.

[0019] Fig. 3 is a schematic diagram showing how burnishing is performed on the raceway surface of a bearing. With reference to Fig. 3, burnishing is performed by bringing a burnishing tool 25 into contact with an unmachined portion 9E of the raceway surface 9 with a pressing load F while rotating the outer ring 2 or the inner ring 5, and moving the burnishing tool 25 in the direction M indicated by the arrow in the figure along the raceway surface axial direction (X direction). In this way, the raceway surface 9 is burnished.

[0020] FIG. 3 shows an example of burnishing the outer ring raceway 9A of the outer ring 2. The front direction (Y direction) of the paper in FIG. 3 is the circumferential direction of the outer ring 2. The burnishing tool 25 is fed in the X direction by a distance P during one rotation of the outer ring 2 in the circumferential direction. The amount of movement of the burnishing tool 25 per one rotation of the workpiece is called the feed pitch. At this time, as shown in FIG. 3, a waviness 15 is formed on the outer ring raceway 9A, the period of which is a distance P equal to the feed pitch. The waviness 15 means a waveform in which the height of the outer ring raceway 9A in the Z direction (depth direction) repeats highs and lows at a constant period P along the axial direction of the raceway surface of the outer ring raceway 9A. In other words, the wavelength of the waviness 15 is equal to the feed pitch P of the burnishing tool. The waviness is inevitably generated by the burnishing process, and the smaller the difference h in height between the highest and lowest parts of the waviness 15 along the Z direction, the better, and it is preferably 1 μm or less.

[0021] Burnishing is characterized by the formation of waviness 15 on the raceway surface 9 (outer ring raceway surfaces 9A, 9B or inner ring raceway surfaces 9C, 9D). Burnishing involves processing that crushes the original roughness of the surface of the workpiece. This results in the formation of waviness 15 as a characteristic uneven shape as described above. By confirming the presence of waviness 15, it can be determined that the outer ring raceway surface 9A has been burnished.

[0022] It is preferable that the wavelength (feed pitch P) of the waviness 15 is equal to or less than the diameter in the raceway axial direction (along the raceway axial direction) of the contact ellipse when it is assumed that the burnishing tool 25 is in elastic contact with the raceway surface 9. In this way, it is possible to obtain the effect of improving the surface roughness of the workpiece by the burnishing process to a level that does not require re-polishing and super-finishing as post-processes.

[0023] For example, if the raceway surface 9 is subjected to machining other than burnishing, a post-process such as regrinding is required. In contrast, if burnishing is performed, compressive residual stress is imparted to the vicinity of the raceway surface 9 and the roughness of the raceway surface 9 can be improved. For this reason, if burnishing is performed, no post-process is required. Therefore, using burnishing can reduce costs compared to using machining other than burnishing.

[0024] However, from the viewpoint of making the maximum value of the compressive residual stress in the region within a depth of 0.1 mm from the raceway surface 9 1400 MPa or more, the machining applied to the raceway surface 9 is not limited to burnishing. Instead of burnishing, the machining may be any one selected from the group consisting of shot peening, UIT (Ultrasonic impact treatment), cavitation peening, laser peening, cold rolling, and rolling.

[0025] FIG. 4 is a schematic diagram showing how the raceway surface of a bearing is shot peened. FIG. 5 is a schematic diagram of the raceway surface of the bearing after the shot peening of FIG. 4. Referring to FIG. 4, in the shot peening, for example, a ball 17 is collided with an unmachined portion 9E that is to become the outer ring raceway surface. The ball 17 moving at high speed in the direction of the arrow M1 in the figure collides with the outer ring raceway surface 9A, bounces off, and moves in the direction of the arrow M2 in the figure. This collision forms a round indentation 9F on the outer ring raceway surface 9A as shown in FIG. 5. If countless balls 17 collide with different positions on the outer ring raceway surface 9A, multiple round indentations 9F are formed. The balls 17 may be made of iron or non-ferrous metal. By forming the indentation 9F, residual stress is imparted to the area adjacent to the raceway surface of the base material.

[0026] Fig. 6 is a schematic diagram showing the final state of the raceway surface after shot peening. Referring to Fig. 6, a high surface roughness is required in the final stage, particularly for the raceway surfaces 9 of the outer ring 2 and the inner ring 5. For this reason, the raceway surfaces 9 are subjected to superfinishing on the surfaces on which a plurality of indentations 9F are formed, as shown in Fig. 5. This forms the outer ring raceway surface 9A.

[0027] FIG. 7 is an enlarged schematic view of the outer ring. As an example of the appearance of the outer ring 2 as shown in FIG. 7, consider a case where the outer ring 2 has two rows of outer ring raceway surfaces, an outer ring raceway surface 9A and an outer ring raceway surface 9B. FIG. 8 is an enlarged view of the first row outer ring raceway surface. FIG. 9 is an enlarged view of the second row outer ring raceway surface. With reference to FIG. 8 and FIG. 9, the dotted lines in these figures indicate the direction in which the fiber flow 21 extends. The angle of the fiber flow 21 of the outer ring raceway surface 9A in the first row of the two rows of outer ring raceway surfaces 9A and 9B (see FIG. 8: first row raceway surface) at the center in the axial direction (X direction) relative to the outer ring raceway surface 9A differs by 10° or more from the angle of the fiber flow 21 of the outer ring raceway surface 9B in the second row (see FIG. 9: second row raceway surface) relative to the outer ring raceway surface 9B at the center in the axial direction. Specifically, the fiber flow 21 in FIG. 8 (the direction of the dotted line in FIG. 8) is approximately parallel to the outer ring raceway surface 9A. That is, the fiber flow 21 in Fig. 8 forms an angle of approximately zero with the outer ring raceway surface 9A. On the other hand, the fiber flow 21 in Fig. 9 (in the direction of the dotted line in Fig. 9) has an angle θ1 with the outer ring raceway surface 9B. The angle θ1 in Fig. 9 is, for example, 10° or more. Note that the angle θ1 may be 15° or less, or may exceed 15°. The same is true for the two rows of inner ring raceway surfaces 9C, 9D of the inner ring 5.

[0028] 8 and 9, in this specification, the angle of the fiber flow 21 with respect to the outer ring raceway surfaces 9A, 9B is defined as the angle of the fiber flow 21 with respect to the outer ring raceway surfaces 9A, 9B at a position closest to the outer ring raceway surfaces 9A, 9B in the radial direction (for example, at the axial center position). The same applies to the angle of the fiber flow 21 with respect to the inner ring raceway surfaces 9C, 9D. The radial direction is the direction extending radially from the center of the annular shape of the outer ring 2, etc. In other words, the radial direction corresponds to the direction in which the diameter dimension extends.

[0029] FIG. 10 is a schematic diagram for explaining the definition of the angle of the fiber flow relative to the outer ring raceway surface. Referring to FIG. 10, for example, even in one outer ring raceway surface 9B cut in cross section as shown here, if the axial position (left and right direction in FIG. 10) is different, the angle between the outer ring raceway surface 9B and the fiber flow 21 is different. Even if the axial position of the outer ring raceway surface 9B is the same, if the circumferential position (direction in which the circumference of the outer ring 2 in FIG. 10 extends) is different, the angle between the fiber flow 21 and the outer ring raceway surface 9B is different from each other. In other words, the angles of the fiber flow 21 relative to the outer ring raceway surface 9B at five points A, B, C, D, and E indicated by arrows in FIG. 10 differ from each other by, for example, about 3° to 5°. This is the same for the outer ring raceway surface 9A and the inner ring raceway surface.

[0030] Therefore, in this specification, for example, the "angle between the outer ring raceway surface 9B and the fiber flow 21" (same as the angle of the fiber flow 21 with respect to the outer ring raceway surfaces 9A, 9B) on the right side of the two rows in FIG. 10 is defined as follows. That is, the above "angle" is the average value of the angles between the raceway surface and the fiber flow 21 at the axial center position of the outer ring raceway surface 9A at a total of five points that are 72° apart in phase from the center of the bearing in the circumferential direction as representative values. That is, the above "angle" is the average value of the angles of the fiber flow 21 with respect to the outer ring raceway surface 9B at five points A, B, C, D, and E indicated by arrows in FIG. 10. The position of point A may be, for example, a position equal to the phase of one end of the letters of the model number attached to the bearing, but is not limited to this. In FIG. 10, the outer ring raceway surface 9A and the outer ring raceway surface 9B are formed on separate outer rings 2 (there are two outer rings 2). 2, they may be arranged in double rows on the same (single) outer ring 2. The same applies to the angles formed between the inner ring raceway surfaces 9C, 9D and the fiber flow 21.

[0031] (Background and issues that led to the effects of this embodiment) Here, we will once again provide a detailed explanation of the comparative examples (conventional background art) that led to the advantageous effects of this embodiment and the problems they face (including those described in the Background Art and Problems to be Solved sections above).

[0032] In the manufacturing process of double row tapered roller bearings, one or two outer rings 2 having an outer ring raceway surface on their inner circumferential surface are prepared. One or two inner rings 5 ​​having an inner ring raceway surface on their outer circumferential surface are prepared. When one outer ring 2 and one inner ring 5 are prepared, two rows of raceway surfaces are formed thereon. When two outer rings 2 and two inner rings 5 ​​are prepared, one row of raceway surfaces is formed on each of the two.

[0033] The outer ring 2 and the inner ring 5 are formed of, for example, high carbon chromium bearing steel SUJ2 as specified by the JIS standard. However, this is not limiting and other steel types may be used. When manufacturing the outer ring 2 and the inner ring 5, the above-mentioned bearing steel is punched out by hot forging to form an annular shape. The punched-out formed product contains more nonmetallic inclusions on the inside than on the outside in the radial direction. In particular, the outer ring 2 has a raceway 9 formed on its inner peripheral surface, and therefore contains more nonmetallic inclusions in the area adjacent to the raceway 9.

[0034] During hot forging (punching process), the fiber flow bends in the area adjacent to the raceway surface 9. For this reason, the angle of the fiber flow 21 with respect to the raceway surface 9 tends to become larger. This tendency differs between the double-row raceway surfaces 9. For example, when the outer ring raceway surfaces 9A and 9B are used as the double-row raceway surfaces 9, the angle of the fiber flow 21 with respect to one outer ring raceway surface 9A tends to be larger than the angle of the fiber flow 21 with respect to the other outer ring raceway surface 9B. In this way, a difference in the angle of the fiber flow 21 with respect to the raceway surface 9 between the double-row raceway surfaces inevitably occurs. For example, the difference in angle may be 10° or more as described above.

[0035] Furthermore, the nonmetallic inclusions in the base material of the bearing steel are elongated along the fiber flow 21. As a result, multiple tiny nonmetallic inclusions are connected together and exist as a single long nonmetallic inclusion in the base material of the bearing steel. For this reason, together with the large number of nonmetallic inclusions near the raceway surface 9 and the fact that the angle of the fiber flow 21 with respect to the raceway surface 9 tends to be large, the nonmetallic inclusions are likely to be exposed on the raceway surface, particularly in the outer ring 2 of the double row tapered roller bearing.

[0036] Non-metallic inclusions exposed on the raceway surface 9 have a greater impact on the rolling fatigue life of a bearing than non-metallic inclusions present inside the base material. Specifically, the outer ring 2 of a double-row tapered roller bearing 1 is prone to flaking of the raceway surface 9 caused by exposed non-metallic inclusions. The challenge is to prevent the reduction in rolling fatigue life caused by such flaking. It is possible to take some measures by reducing the number of non-metallic inclusions by improving the cleanliness of the base material (steel). However, even if you do so, it is not possible to completely eliminate non-metallic inclusions in the steel.

[0037] The larger the angle between the raceway surface 9 and the fiber flow 21, the more likely peeling occurs. From this viewpoint, it is preferable that the angle between the raceway surface 9 and the fiber flow 21 is 15° or less. Therefore, in the final product, it is necessary to process the double row raceway surfaces 9 so that the above-mentioned angle is 15° or less. However, such processing is difficult due to the shape of the double row tapered roller bearing 1 and the bending of the fiber flow 21. Although such processing is possible, the manufacturing cost will rise. Specifically, the shape at the time of hot forging is devised, and the portion where the fiber flow 21 is bent is removed by post-processing. This makes it possible to prevent the angle of the fiber flow 21 closest to the raceway surface 9 from becoming large. However, doing so increases the manufacturing cost due to the increase in the amount of processing and the deterioration of the yield.

[0038] The angle between the raceway surface 9 and the fiber flow 21 is measured as follows. First, the raceway ring is cut to expose the raceway surface 9. The cross section of the exposed raceway surface 9 is etched by an etching method shown in JIS G0553:2019 "Method of testing macrostructure of steel" or the like to reveal the fiber flow. After that, the angle of the fiber flow 21 with respect to the raceway surface 9 is measured using an optical microscope or the like.

[0039] (Action and effect) The present embodiment, which has been developed in consideration of the above background and problems, provides the following configuration and effects.

[0040] A double row tapered roller bearing 1 according to the present disclosure includes an outer ring 2 and an inner ring 5. The outer ring 2 has outer ring raceway surfaces 9A, 9B as raceway surfaces on its inner circumferential surface. The inner ring 5 has inner ring raceway surfaces 9C, 9D as raceway surfaces on its outer circumferential surface. The maximum compressive residual stress in the raceway surface axial direction in a region within a depth of 0.1 mm from the raceway surface 9 of at least one of the outer ring 2 and the inner ring 5 is 1400 MPa or more.

[0041] By preventing the crack from progressing inward along the nonmetallic inclusions, the occurrence of peeling of the raceway surface 9 due to the nonmetallic inclusions exposed on the raceway surface 9 can be prevented. This can improve the rolling fatigue life of the double row tapered roller bearing 1. The crack progresses from the raceway surface 9 to the inside due to the oil pressure generated when the contact surface pressure between the rolling elements and the raceway surface 9 is applied to the lubricant that has penetrated into the crack. Therefore, by imparting a high compressive residual stress to the region within a depth of 0.1 mm from the raceway surface 9, the force that tends to expand the crack due to the oil pressure of the lubricant is canceled. This can suppress the progress of the crack. In this case, by setting the maximum value of the compressive residual stress in the region within a depth of 0.1 mm from the raceway surface to 1400 MPa or more, the progress of the crack to the inside can be effectively suppressed. This suppression effect can be obtained even if the extension angle of the fiber flow to the raceway surface is large and nonmetallic inclusions are exposed on the raceway surface. Furthermore, even if multiple tiny nonmetallic inclusions are connected together to form a single long nonmetallic inclusion within the base material of the bearing steel, the above effect can be obtained.

[0042] The compressive residual stress in the region within a depth of 0.1 mm from the raceway surface only needs to be 1400 MPa or more in maximum, and does not have to be 1400 MPa or more in other regions. However, if there is a region in the base material where the compressive residual stress is 1400 MPa or more, even if it is localized, the compressive residual stress will be high overall, even if the surrounding regions do not also have a compressive residual stress of 1400 MPa or more. For example, the outer ring 2, etc., which has a maximum value of 1400 MPa or more, will have a high compressive residual stress overall, compared to the outer ring 2 or inner ring 5, which is not controlled at all so that the maximum value of the compressive residual stress is 1400 MPa or more and has a relatively low compressive residual stress overall. For this reason, as described above, the propagation of cracks can be effectively suppressed.

[0043] The compressive residual stress is preferably such that the maximum value in the raceway axial direction is 1400 MPa or more. The maximum value of the compressive residual stress along a direction other than the raceway axial direction may be less than 1400 MPa. This is because cracks preferentially propagate in the axial direction.

[0044] In the above double row tapered roller bearing 1, the maximum value of the compressive residual stress in the raceway surface axial direction, particularly in the region within a depth of 0.1 mm from the outer ring raceway surfaces 9A, 9B of the outer ring 2, is preferably 1400 MPa or more. As described above, the outer ring 2 is more likely to have dense nonmetallic inclusions on the raceway surface 9 (outer ring raceway surfaces 9A, 9B) than the inner ring 5. For this reason, by increasing the compressive residual stress, particularly in the region adjacent to the raceway surface 9 of the outer ring 2, the effect of suppressing crack propagation and peeling of the raceway surface 9 is enhanced. In addition, the outer ring raceway surfaces 9A, 9B of the double row tapered roller bearing 1 are more likely to form a larger angle with the fiber flow 21 than the inner ring raceway surfaces 9C, 9D. For this reason, by increasing the compressive residual stress, particularly in the region adjacent to the raceway surface 9 of the outer ring 2, the effect of suppressing crack propagation and peeling of the raceway surface 9 is enhanced.

[0045] The double row tapered roller bearing 1 has two rows of at least one of the outer ring raceway surfaces 9A, 9B and the inner ring raceway surfaces 9C, 9D. The angle of the fiber flow 21 at the axial center of the first row raceway surface 9A (9C) in the first row of the two rows of raceway surfaces 9A, 9B (9C, 9D) to the first row raceway surface 9A (9C) differs by 10° or more from the angle of the fiber flow 21 at the axial center of the second row raceway surface 9B (9D) in the second row adjacent to the first row of the two rows of raceway surfaces 9A, 9B (9C, 9D) to the second row raceway surface 9B (9D). Such a feature may be present.

[0046] The above double row tapered roller bearing 1 has two rows of inner ring raceways 9C, 9D. The angle of the fiber flow 21 at the axial center of the first row inner ring raceway 9C in the first row of the two rows of inner ring raceways 9C, 9D, to the first row inner ring raceway 9C differs by 10° or more from the angle of the fiber flow 21 at the axial center of the second row inner ring raceway 9D in the second row adjacent to the first row of the two rows of inner ring raceways 9C, 9D, to the second row inner ring raceway 9D. Such a feature may be present.

[0047] Crack propagation and delamination on the raceway surface 9 are likely to occur at locations where the angle of the fiber flow 21 with respect to the raceway surface 9 is larger. Therefore, even by imparting compressive residual stress to only one of the two rows of raceway surfaces 9, a crack propagation suppression effect can be obtained compared to the case where compressive residual stress is not imparted to either of the two rows of raceway surfaces 9.

[0048] As described above, the difference in the angle between the fiber flow 21 and one of the two rows of raceway surfaces 9 inevitably occurs in the manufacturing process. It is possible to intentionally form the angle of the fiber flow 21 of the other of the two rows of the raceway surface 9 to be small by any method, at the expense of making the angle of the fiber flow 21 of one of the two rows of the raceway surface 9 large. Here, the small angle of the fiber flow 21 of the other of the two rows of the raceway surface 9 to be small is, for example, 15° or less. In this case, if burnishing is performed on the raceway surface 9 with the larger angle, it is possible to suppress the propagation of cracks from the raceway surface 9 with the larger angle. Therefore, the manufacturing cost can be reduced compared to the case where processing is performed on both of the two rows to make the angle 15° or less.

[0049] In the above double row tapered roller bearing 1, waviness 15 may be formed on raceway surface 9. Waviness 15 is formed by burnishing raceway surface 9. Mechanical processing such as burnishing can impart compressive residual stress to the area adjacent to raceway surface 9. Therefore, double row tapered roller bearing 1 having waviness 15 on raceway surface 9 has the effect of suppressing the growth of cracks due to compressive residual stress, and the associated effect of improving the rolling fatigue life. EXAMPLES

[0050] An investigation was conducted to confirm the effect of compressive residual stress on cracks that originate from nonmetallic inclusions in the base material of the outer ring 2 or the inner ring 5 and exist along the fiber flow 21.

[0051] Specifically, both numerical analysis and prototype testing were performed in the investigation. The numerical analysis is as follows. FIG. 11 is a schematic diagram of a model of a base material having a crack, analyzed by the finite element method. FIG. 12 is a schematic enlarged view of the portion XII surrounded by a dotted line in FIG. 11. Referring to FIG. 11 and FIG. 12, for example, a model in which a part of the outer ring 2o of the bearing is cut out is used for the analysis. A model in which a part of the inner ring of the bearing is cut out can also be used for the analysis. The model of the bearing has an outer ring raceway 9Ao. In the model of FIG. 11, the fiber flow 21 extends along the X direction perpendicular to the load movement direction M3 accompanying the movement of the rolling element. The fiber flow 21 has an angle θ2 with respect to the outer ring raceway 9Ao. More specifically, the angle θ2 means an angle with respect to the outer ring raceway 9Ao on the ZX plane when the Z direction is defined as being perpendicular to the outer ring raceway 9Ao and extending in the depth direction toward the inside of the outer ring 2o.

[0052] The outer ring raceway surface 9Ao has a line contact region 18 with which the rolling elements come into contact. The line contact region 18 is a region where the outer ring raceway surface 9Ao and the surface of the rolling elements come into linear contact along the X direction (axial direction). In other words, the outer ring raceway surface 9Ao receives a load from the rolling elements at the portion where the outer ring raceway surface 9Ao and the surface of the rolling elements come into contact. The load causes the outer ring and the rolling elements to elastically deform. This contact region then becomes a line contact region 18 that has a certain area and extends along the X direction. The circumferential direction of the outer ring raceway surface 9Ao, which has an annular shape, is along the Y direction in the figure.

[0053] The outer ring 2o and the rolling elements rotate, and the rolling elements move on the outer ring raceway 9Ao in the load movement direction M3 shown by the arrow in Fig. 11. For this reason, the load that the outer ring raceway 9Ao receives from the rolling elements moves in the load movement direction M3 over time. As shown in Fig. 12, a crack 27 formed in the outer ring 2o extends from the outer ring raceway 9Ao toward the inside of the outer ring 2o, for example in a semi-elliptical shape at an angle θ3 with respect to the outer ring raceway 9Ao. Using the finite element method, the stress intensity factor K IThe stress intensity factor K was calculated for both the model with compressive residual stress on the outer ring raceway 9Ao and the model without compressive residual stress. I The stress intensity factor K was calculated and the two were compared. For the model without compressive residual stress, all other conditions were the same as for the model with compressive residual stress. I The calculated position (calculation point) is tip 27P of crack 27. Of crack 27, tip 27P is disposed at the deepest position in the Z direction within outer ring 2o.

[0054] The above "the line contact area 18 passes through the formation part of the crack 27" will be explained next. FIG. 13 is a schematic diagram showing the manner in which the line contact area moves over time in the model of FIG. 11. Referring to FIG. 13, the rolling element rolls on the outer ring raceway surface 9Ao. As a result, the position of the line contact area 18 changes over time along the Y direction. That is, the line contact area 18 is located at the position of the line contact area 18A at time t=0. However, with the movement in the load movement direction M3, the line contact area 18 is located at the position of the line contact area 18B at time t=n1. Also, the line contact area 18 is located at the position of the line contact area 18C at time t=n2. The position of the line contact area 18 moves over time along the circumferential direction of the outer ring raceway surface 9Ao having an annular shape. Therefore, the line contact area 18 approaches the formation part of the crack 27 located at a certain position in the circumferential direction over time, overlaps with the formation part of the crack 27, and then moves away from the formation part of the crack 27. Therefore, the line contact area 18 passes through the formation part of the crack 27.

[0055] In the models of Figures 11 to 13, the extension length of the crack 27 (the dimension in the major axis direction of the semi-elliptical crack 27 in Figure 12) was set to 50 µm. The half-width of the crack 27 (the dimension in the minor axis direction of the semi-elliptical crack 27 in Figure 12) was set to 30 µm. The maximum contact pressure between the outer ring raceway surface 9Ao and the rolling element was set to 2.5 GPa, and the half-width of contact (half the value of the width in the Y direction of the line contact area 18) was set to 100 µm. The compressive residual stress imparted to the model was set to 1000 MPa almost over the entire model in both the circumferential and axial directions. It was assumed that the oil pressure applied to the crack 27 by the lubricating oil was the average contact pressure applied evenly on the crack 27. Under the above conditions, the stress intensity factor K I was calculated.

[0056] Fig. 14 is a graph showing calculated values ​​of stress intensity factors, calculated by the finite element method, for the models of Figs. 11 to 13 to which compressive residual stress is not applied. Fig. 15 is a graph showing calculated values ​​of stress intensity factors, calculated by the finite element method, for the models of Figs. 11 to 13 to which compressive residual stress is applied. With reference to Figs. 14 and 15, the horizontal axis of each graph shows the relative position of the contact center with respect to the crack center. The vertical axis of each graph shows the stress intensity factor K I The angles shown in the legend correspond to the inclination angle θ3 of the crack 27 in FIG.

[0057] From Fig. 14 and Fig. 15, the larger the inclination angle θ3 of the crack 27, the larger the stress intensity factor K I In addition, the stress intensity factor K I is the stress intensity factor K in a model without compressive residual stress I This confirmed that the application of compressive residual stress has the effect of suppressing the propagation of cracks caused by nonmetallic inclusions.

[0058] The prototype tests were as follows. Several prototype angular contact ball bearings were prepared using bearing steel containing a large number of nonmetallic inclusions. Some of these prototypes were given a maximum 1400 MPa compressive residual stress in the raceway axial direction in an area within 0.1 mm depth from the raceway surface of the outer and inner rings by burnishing. These are hereinafter referred to as prototype A. Others of these prototypes were given a maximum 1200 MPa compressive residual stress in the raceway axial direction in an area within 0.1 mm depth from the raceway surface of the outer and inner rings by burnishing. These are hereinafter referred to as prototype B. Unlike prototype A, prototype B was not given a maximum compressive residual stress of 1400 MPa or more. Prototype A and prototype B were made differently by changing the indentation load of the burnishing process. In other words, the compressive residual stress of prototype A was made higher by increasing the indentation load of the burnishing process compared to prototype B. For still other prototypes, the outer and inner rings were not burnished, and the above-mentioned compressive residual stress was not, at least intentionally, imparted. These are referred to below as prototype C. Fatigue tests were conducted on each of these prototypes, and the rolling fatigue lives were compared. Eight pieces each of prototype A and prototype B, and 25 pieces of prototype C were prepared and tested.

[0059] The angular contact ball bearing used in this prototype test is a different type of bearing from the double row tapered roller bearing used in the explanation of this embodiment. However, spalling on the raceway surface of an angular contact ball bearing is caused by non-metallic inclusions exposed on the raceway surface, similar to the spalling mechanism of a double row tapered roller bearing. Therefore, testing a prototype angular contact ball bearing allows for evaluation with the same reliability as testing a prototype double row tapered roller bearing. The reason why an angular contact ball bearing was used in this prototype test instead of a double row tapered roller bearing was due to considerations of the difficulty of manufacturing and the cost.

[0060] The prototype angular ball bearing used in this prototype test had the bearing model number 7206, and the maximum surface pressure of the outer ring was 3.00 GPa. The contact angle of the angular ball bearing was 27°, and the rotational speed of the outer ring was 3100 rpm. VG56 was used as the lubricant.

[0061] FIG. 16 is a graph showing the relationship between the depth from the raceway surface of the outer ring of each prototype and the residual stress. Referring to FIG. 16, the horizontal axis of the graph shows the depth distance from the raceway surface of the outer ring of each prototype. The vertical axis of the graph shows the axial residual stress at each position. A residual stress value less than 0 indicates compressive residual stress, and a residual stress value greater than 0 indicates tensile residual stress. As shown in FIG. 16, in prototype A, the maximum value of compressive residual stress in the raceway surface axial direction at a depth of 50 μm from the raceway surface is 1400 MPa or more. In prototype B, the maximum value of compressive residual stress in the raceway surface axial direction at a depth of 30 μm from the raceway surface is 1200 MPa or more. On the other hand, almost no compressive residual stress was applied to prototype C.

[0062] Fig. 17 is a graph showing the relationship between compressive residual stress imparted to a prototype and bearing life. Referring to Fig. 17, the horizontal axis of the graph shows the test time of the angular ball bearing prototype. The vertical axis of the graph shows the cumulative fracture probability of the angular ball bearing prototype on a logarithmic scale. The test time (L10) until the cumulative fracture probability of each of prototypes A to C reaches 10% is considered to be the life of that prototype (bearing).

[0063] As can be seen from Figure 17, the L10 life of prototype C was 31.66 hours, and that of prototype B was 42.79 hours, with no significant difference being observed between them. Meanwhile, the L10 life of prototype A was 588.31 hours, demonstrating a significant improvement in rolling fatigue life compared to prototypes B and C. Note that the filled dots in each figure indicate that the raceway surface had peeled off at that time, and the open dots in each figure indicate that the test was discontinued because the raceway surface did not peel off. Testing was discontinued after 1,000 hours for prototypes A and B, and 300 hours for prototype C.

[0064] From the above, it was confirmed that applying a compressive residual stress of up to 1400 MPa or more in the raceway axial direction near the raceway surface improves the rolling fatigue life compared to cases where it is not applied. In other words, applying a compressive residual stress of up to 1400 MPa or more in the raceway axial direction suppresses the propagation of cracks from non-metallic inclusions. This shows that even if the fiber flow extends at a large angle relative to the raceway surface and non-metallic inclusions are exposed on the raceway surface, it is possible to suppress the occurrence of peeling on the raceway surface caused by these inclusions. On the other hand, if the compressive residual stress in the raceway axial direction is up to about 1200 MPa, there is almost no effect in improving the rolling fatigue life.

[0065] (Examples) An application example of the present embodiment will be described below with reference to FIG.

[0066] FIG. 18 is a schematic cross-sectional view of a double row tapered roller bearing to which this embodiment is applied. As with other cross-sectional views, the left-right direction of the drawing is the X direction (axial direction), and the up-down direction of the drawing is the Z direction. Referring to FIG. 18, the double row tapered roller bearing of this embodiment is used, for example, as a railway vehicle axle bearing 101. The railway vehicle axle bearing 101 mainly includes an outer ring 102, two inner rings 105, a plurality of rollers 106 as rolling elements, and a cage 107. The inner ring 105 is press-fitted into the shaft end of the axle (not shown). Annular members, that is, a front cover 142 and a rear cover 144, are arranged on both sides of the pair of inner rings 105 in the axial direction. The front cover 142 is fastened to the axle by using a bolt and a nut. This positions and fixes the pair of inner rings 105, and thus the entire bearing. The outer ring 102 is fixed to an axle box (not shown). A spacer may be interposed between the pair of inner rings 105 .

[0067] In Fig. 18, a convex portion 105a is formed on the end face of the inner ring 105, and concave portions 142a, 144a are formed on the end faces of the front cover 142 and the rear cover 144. Specifically, a concave portion 142a is formed on the end face of the front cover 142, and a convex portion 105a is formed on the end face of the inner ring 105 in the first row of the double rows. When the concave portion 142a and the convex portion 105a are fitted together, an axial clearance δa is formed between the bottom surface of the concave portion 142a and the end face of the convex portion 105a. A radial clearance δb is formed between the inner peripheral surface of the concave portion 142a and the outer peripheral surface of the convex portion 105a.

[0068] A recess 144a is formed on the end surface of the rear cover 144, and a protrusion 105a is formed on the end surface of the inner ring 105 of the second row of the double rows. When the recess 144a and the protrusion 105a are engaged with each other, an axial clearance δa is formed between the bottom surface of the recess 144a and the end surface of the protrusion 105a. A radial clearance δb is formed between the inner peripheral surface of the recess 144a and the outer peripheral surface of the protrusion 105a. The arrangement of the recess and the protrusion of the recess-protrusion engagement may be reversed from that shown in FIG. 18. That is, a recess may be formed in the inner ring 105, and protrusions may be formed in the front cover 142 and the rear cover 144.

[0069] The axial clearance δa and radial clearance δb are both set to approximately 0.1 mm to 0.5 mm. In particular, if the radial clearance δb is a tight fit with interference, it will make the bearing difficult to disassemble, requiring special jigs or presses, which will increase the amount of work required for inspection. Therefore, it is preferable for the radial clearance δb to be a loose fit.

[0070] The grease applied to the gaps in the fitting portions is desirably the same type as the lubricating grease filled in the railway vehicle axle bearing 101. The lubricating grease filled in the railway vehicle axle bearing 101 is, for example, a urea-based grease.

[0071] An oil thrower may be interposed between the inner ring 105 and the front cover 142. In addition to the rear cover 144 or instead of the rear cover 144, a slinger may be provided.

[0072] Sealing devices 130 are disposed on both ends of the outer ring 102. The sealing devices 130 serve to prevent leakage of grease sealed inside the railway vehicle axle bearing 101 and to prevent the intrusion of foreign matter from the outside.

[0073] The above railway vehicle axle bearing 101 in FIG. 18 has the same characteristics as the double row tapered roller bearing 1 in FIGS. 1 and 2, and therefore exerts the effect of suppressing the growth of cracks.

[0074] The embodiments and examples disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0075] Various aspects of the present disclosure are summarized below as appendices. (Appendix 1) an outer ring having an outer ring raceway surface as a raceway surface on an inner circumferential surface; an inner ring having an inner ring raceway surface as a raceway surface on an outer peripheral surface, A double-row tapered roller bearing, wherein the maximum value of compressive residual stress in the axial direction of the raceway surface in a region within a depth of 0.1 mm from the raceway surface of at least one of the outer ring and the inner ring is 1400 MPa or more.

[0076] (Appendix 2) At least one of the outer ring raceway surface and the inner ring raceway surface has two rows of raceway surfaces, 2. The double row tapered roller bearing according to claim 1, wherein an angle of a fiber flow at an axial center of a first row raceway surface in a first row of said two row raceway surfaces, relative to said first row raceway surface, differs by 10° or more from an angle of a fiber flow at an axial center of a second row raceway surface in a second row adjacent to the first row of said two row raceway surfaces, relative to said second row raceway surface.

[0077] (Appendix 3) 3. The double row tapered roller bearing according to claim 1 or 2, wherein the raceway surface is formed with undulations.

[0078] (Appendix 4) 4. The double-row tapered roller bearing according to claim 3, wherein the waviness has a wavelength equal to or less than a diameter in an axial direction of the raceway surface of a contact ellipse when it is assumed that a burnishing tool is in elastic contact with the raceway surface.

[0079] (Appendix 5) 5. A double-row tapered roller bearing according to any one of claims 1 to 4, as a bearing for a railway vehicle axle.

[0080] (Appendix 6) preparing an outer ring having an outer ring raceway surface as a raceway surface on an inner circumferential surface; preparing an inner ring having an inner ring raceway surface as a raceway surface on an outer circumferential surface; and machining the raceway surface. a manufacturing method for a double row tapered roller bearing, wherein in the step of machining the raceway surface, at least one of the outer ring and the inner ring is formed so that the maximum value of compressive residual stress in the axial direction of the raceway surface in a region within a depth of 0.1 mm from the raceway surface is 1400 MPa or more.

[0081] (Appendix 7) Appendix 7. A method for manufacturing a double row tapered roller bearing as described in Appendix 6, wherein in the step of machining the raceway surface, the raceway surface of at least one of the outer ring and the inner ring is machined so as to be formed so that a maximum value of compressive residual stress in the axial direction of the raceway surface in a region within a depth of 0.1 mm from the raceway surface is 1400 MPa or more.

[0082] (Appendix 8) 8. The method for manufacturing a double row tapered roller bearing according to claim 7, wherein the machining is burnishing.

[0083] (Appendix 9) In the burnishing process, a burnishing tool is moved in an axial direction of the raceway surface while being pressed into contact with the raceway surface, so that a waviness is formed on the raceway surface. 9. A method for manufacturing a tapered roller bearing as described in Appendix 8, wherein the waviness has a wavelength equal to or less than a diameter in the axial direction of the raceway surface of a contact ellipse when it is assumed that the burnishing tool is in elastic contact with the raceway surface. [Explanation of symbols]

[0084] 1 double row tapered roller bearing, 2,2o,102 outer ring, 4 inner ring spacer, 5,105 inner ring, 6,106 roller, 7,107 cage, 8 bolt hole, 9 raceway surface, 9A,9B,9Ao outer ring raceway surface, 9C,9D inner ring raceway surface, 9E unmachined portion, 9F indentation, 15 waviness, 16 outer peripheral surface, 17 ball, 18,18A,18B,18C line contact area, 19 groove, 21 fiber flow, 25 burnishing tool, 27 crack, 27P tip, 101 railroad vehicle axle bearing, 105a convex portion, 130 sealing device, 142 front cover, 142a,144a concave portion, 144 rear cover.

Claims

1. an outer ring having an outer ring raceway surface as a raceway surface on an inner circumferential surface; an inner ring having an inner ring raceway surface as a raceway surface on an outer peripheral surface, A double-row tapered roller bearing, wherein a maximum value of compressive residual stress in an axial direction of the raceway surface in a region within a depth of 0.1 mm from the raceway surface of at least one of the outer ring and the inner ring is 1400 MPa or more.

2. At least one of the outer ring raceway surface and the inner ring raceway surface has two rows of raceway surfaces, 2. The double row tapered roller bearing according to claim 1, wherein an angle of a fiber flow at an axial center of a first row raceway surface in a first row among said two row raceway surfaces, relative to said first row raceway surface, differs by 10° or more from an angle of a fiber flow at an axial center of a second row raceway surface in a second row adjacent to the first row among said two row raceway surfaces, relative to said second row raceway surface.

3. 2. The double row tapered roller bearing according to claim 1, wherein undulations are formed on the raceway surface.

4. 4. The double row tapered roller bearing according to claim 3, wherein the waviness has a wavelength equal to or less than a diameter in the axial direction of the raceway surface of a contact ellipse when it is assumed that a burnishing tool is in elastic contact with the raceway surface.

5. 2. The double row tapered roller bearing according to claim 1, which is used as a bearing for a railway vehicle axle.

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