Multi-row tapered roller bearing

Abstract

A multi-row tapered 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 the inner peripheral surface. The inner ring (5) has inner ring raceway surfaces (9C, 9D) on the outer peripheral surface as raceway surfaces. The maximum value of 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 at least 1400 MPa.

Description

Technical Field

[0001] The invention relates to a multi-row tapered roller bearing. Background Art

[0002] Multi-row tapered roller bearings are used in railway vehicle axles. Multi-row tapered roller bearings are also used in automobile axles, machine tools, pumps, etc. In particular, multi-row tapered roller bearings used in railway vehicle axles are important infrastructure and therefore require high reliability.

[0003] However, in the base metal material constituting the outer ring and inner ring of the bearing, non-metallic inclusions exist along the fiber flow. It is technically impossible to eliminate non-metallic inclusions in the metal material. Near the raceway surfaces of the outer ring and the inner ring, the non-metallic inclusions existing along the fiber flow become the cause of the raceway surface peeling. It is required to suppress the progress of cracks starting from the non-metallic inclusions, along the fiber flow and from the raceway surface of the outer ring and the inner ring toward the inside. If the progress of the crack is suppressed, the peeling of the raceway surface caused by non-metallic inclusions can be prevented, and the rolling fatigue life of the bearing can be improved.

[0004] For example, Japanese Patent Publication No. 2019-095044 proposes a method for improving the rolling fatigue life of a bearing. In Japanese Patent Publication No. 2019-095044, compressive residual stress is applied near the track surface by machining such as polishing. As a result, the gap between the non-metallic inclusions and the base material can be filled, and the gap can be suppressed from acting as an open crack. Therefore, the rolling fatigue life of the bearing can be improved.

[0005] Japanese Patent Publication No. 2003-301850 focuses on the relationship between the angle of the fiber flow relative to the raceway surface and the square root length of the internal defect and the rolling fatigue life. In Japanese Patent Publication No. 2003-301850, the angle of the fiber flow relative to the raceway ring is less than 15°, and the square root length of the internal defect is less than 0.3 mm. This can improve the rolling fatigue life of the bearing.

[0007] According to the technology disclosed in Japanese Patent Publication No. 2019-095044, there is no mention of the effect of suppressing crack progression caused by applying compressive residual stress to the base material. As disclosed in Japanese Patent Publication No. 2003-301850, it is difficult to control to reduce the fiber flow angle relative to the track surface, and even if it is possible, the manufacturing cost will rise. In particular, if all of the multi-row track wheels are processed to reduce the fiber flow angle, the manufacturing cost will rise. Summary of the invention

[0008] The present invention has been made in view of the above technical problems. An object of the present invention is to provide a double-row tapered roller bearing that can suppress crack propagation from the raceway surface toward the inside and improve rolling fatigue life.

[0009] The multi-row tapered roller bearing according to the present disclosure includes an outer ring and an inner ring. The outer ring has an outer ring track surface as a track surface on the inner circumferential surface. The inner ring has an inner ring track surface as a track surface on the outer circumferential surface. The maximum value of the track surface axial direction of at least any one of the outer ring and the inner ring within a depth of 0.1 mm from the track surface is 1400 MPa or more. In addition, the direction along the axial direction and parallel to the track surface will be referred to as the "track surface axial direction" below. The "track surface axial direction" is not limited to the direction that is completely parallel to the track surface, but includes a direction that is approximately equal to the direction parallel to the track surface but has a small angle relative to the parallel direction, that is, a direction along the direction parallel to the track surface. The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a schematic diagram of the double-row tapered roller bearing according to the present embodiment. Figure 2 It is along Figure 1 Schematic cross-sectional view of line II-II. Figure 3 This is a schematic diagram showing a method of performing a polishing process on the raceway surface of a bearing. Figure 4 This is a schematic diagram showing a method of performing shot peening on the raceway surface of a bearing. Figure 5 yes Figure 4 Schematic diagram of the raceway surface of a bearing after shot peening. Figure 6 This is a schematic diagram showing the final form of the raceway surface after shot peening. Figure 7 It is an enlarged schematic diagram of the outer ring. Figure 8 This is an enlarged view of the first row of outer ring track surface. Fig. 9 This is an enlarged view of the second row outer ring track surface. Fig.10 This is a schematic diagram for explaining the definition of the angle of the fiber flow with respect to the outer ring raceway surface. Fig.11 This is a schematic diagram of a model of a base material with a crack analyzed by the finite element method. Fig.12 Is Fig.11 A schematic enlarged view of section XII surrounded by a dotted line. Fig.13 It means in Fig.11 Schematic diagram of how the line contact area moves over time in the model. Fig.14 It means that no compressive residual stress is applied. Figure 11 to Figure 13 A curve chart of the stress amplification factor in the model calculated using the finite element method. Fig.15 It means that compressive residual stress is applied. Figure 11 to Figure 13 A curve chart of the stress amplification factor in the model calculated using the finite element method. Fig.16 This is a graph showing the relationship between the depth from the raceway surface and the residual stress of the outer ring of each trial product. Fig.17 This is a graph showing the relationship between the compressive residual stress applied to the prototype and the bearing life. Fig.18 This is a schematic cross-sectional view of a double-row tapered roller bearing to which the present embodiment is applied. DETAILED DESCRIPTION

[0012] Hereinafter, the embodiments of the present invention will be described with reference to the accompanying drawings. In addition, in the following drawings, the same reference numerals are given to the same or corresponding parts, and their descriptions will not be repeated as long as they have the same functions. In addition, for the convenience of description, the X direction, Y direction, and Z direction are introduced.

[0013] (Multi-row tapered roller bearings) Figure 1 It is a schematic diagram of the double-row tapered roller bearing according to the present embodiment. Figure 2 It is along Figure 1 Schematic cross-sectional view of line II-II. Figure 1 and Figure 2 The multi-row tapered roller bearing 1 mainly includes: an outer ring 2 as a track wheel having an annular shape; an inner ring 5 arranged on the inner circumference of the outer ring 2 and serving as a track wheel having an annular shape; a plurality of rollers 6 as rolling elements; and a retainer 7 for limiting 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 in a manner extending in the axial direction of the multi-row tapered roller bearing. In addition, two outer ring track surfaces 9A and 9B as track surfaces 9 are formed on the inner circumferential surface of the outer ring 2.

[0014] The two inner rings 5 ​​are arranged adjacent to each other in the X direction. The inner ring spacer 4 may or may not be sandwiched between the two inner rings 5. Both the two inner rings 5 ​​and the inner ring spacer 4 have an annular shape. In each of the two inner rings 5, a groove 19 whose bottom surface is a raceway surface is formed on the outer peripheral surface 16 facing the outer ring 2. That is, two rows of grooves 19 are formed in the multi-row tapered roller bearing 1. Two inner ring raceway surfaces 9C and 9D are formed on the outer peripheral surface of the inner ring 5 as the raceway surface 9.

[0015] The track surface 9A and the track surface 9C of the track surface 9 are arranged Figure 2 The roller 6 is arranged in a manner of being sandwiched between the track surface 9A and the track surface 9C. The track surface 9B and the track surface 9D in the track surface 9 are arranged at Figure 2 The roller 6 is arranged to be sandwiched between the track surface 9B and the track surface 9D. The roller 6 has a conical shape.

[0016] The maximum value of the compressive residual stress in the axial direction of the raceway surface in the 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. Here, the region within a depth of 0.1 mm refers to a region within a dimension of 0.1 mm from the raceway surface 9 in a direction perpendicular to the raceway surface 9 and toward the inside of the parent material of the outer ring 2 or the inner ring 5. In particular, the maximum value of the axial direction of the raceway surface in the region within a depth of 0.1 mm from the outer ring raceway surfaces 9A and 9B arranged in two rows of the outer ring 2 is preferably 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 axial direction of the raceway surface within the depth of 0.1 mm from the outer ring raceway surface 9A, 9B, and in the circumferential direction (along the circular arc of the annular shape) can be 1400 MPa or more. The maximum value of the compressive residual stress in the axial direction of the raceway surface within the depth of 0.1 mm from the outer ring raceway surface 9A, 9B is, for example, more preferably 1600 MPa or more, and further preferably 1800 MPa or more.

[0018] From the viewpoint of setting the maximum value of the compressive residual stress in the axial direction of the raceway surface within a depth of 0.1 mm from the raceway surface 9 to 1400 MPa or more, the raceway surface 9 is machined. The raceway surface 9 is particularly polished. From the viewpoint of the manufacturing process, as from the viewpoint of the physical structure, the maximum value of the compressive residual stress in not only the axial direction of the raceway surface but also the circumferential direction (along the direction of the circular arc of the annular shape) within a depth of 0.1 mm from the outer ring raceway surfaces 9A and 9B can be set to 1400 MPa or more (polishing). The maximum value of the compressive residual stress in the axial direction of the raceway surface within a depth of 0.1 mm from the outer ring raceway surfaces 9A and 9B is preferably processed to 1600 MPa or more, and further preferably processed to 1800 MPa or more.

[0019] Figure 3 This is a schematic diagram showing how the raceway surface of a bearing is polished. Figure 3 In the polishing process, while rotating the outer ring 2 or the inner ring 5, the polishing tool 25 is brought into contact with the unprocessed portion 9E of the raceway surface 9 with a press load F, and the polishing tool 25 is moved in the axial direction (X direction) of the raceway surface in the direction of the arrow M in the figure. Thus, the raceway surface 9 is polished.

[0020] exist Figure 3 , as an example, a method of performing a lapping process on the outer ring raceway surface 9A of the outer ring 2 is shown. Figure 3 The front direction (Y direction) of the paper is the circumferential direction of the outer ring 2. During the time it takes for the outer ring 2 to rotate one circle in the circumferential direction, the polishing tool 25 is transported a distance P in the X direction. Thus, the movement amount of the polishing tool 25 per one rotation of the workpiece is called the feed pitch. Figure 3 As shown, a corrugation 15 having a period equal to the feed pitch P is formed on the outer ring raceway surface 9A. The corrugation 15 represents a waveform whose height in the Z direction (depth direction) of the outer ring raceway surface 9A is repeated at a certain period P along the axial direction of the raceway surface of the outer ring raceway surface 9A. That is, the wavelength of the corrugation 15 is equal to the feed pitch P of the polishing tool. The corrugation is necessarily generated by polishing, but the difference h between the height position of the highest part and the lowest part of the corrugation 15 along the Z direction is as small as possible, preferably less than 1 μm.

[0021] The characteristic of the polishing process is that by performing this process, a corrugation 15 is formed on the raceway surface 9 (outer ring raceway surface 9A, 9B or inner ring raceway surface 9C, 9D). In the polishing process, the roughness originally possessed by the surface of the workpiece is crushed. Thus, the corrugation 15 as a characteristic concave-convex shape as described above is formed. By confirming the presence of the corrugation 15, the polishing process of the outer ring raceway surface 9A can be identified.

[0022] The wavelength (feed pitch P) of the corrugation 15 is preferably less than the diameter of the contact ellipse in the axial direction of the track surface (along the axial direction of the track surface) when the polishing tool 25 is assumed to be in elastic contact with the track surface 9. In this way, the surface roughness of the workpiece caused by the polishing process can be improved to a level that does not require regrinding and super finishing as a post-process.

[0023] For example, in the case where the track surface 9 is subjected to mechanical processing other than polishing, a post-process such as regrinding is required. In contrast, if polishing is performed, compressive residual stress is applied near the track surface 9, and the roughness of the track surface 9 can be increased. Therefore, if polishing is performed, a post-process is not required. Therefore, if polishing is used, the cost can be reduced compared to the case where mechanical processing other than polishing is used.

[0024] However, from the viewpoint of setting the maximum value of the compressive residual stress in the region within a depth of 0.1 mm from the track surface 9 to 1400 MPa or more, the mechanical processing performed on the track surface 9 is not limited to the polishing process. As the mechanical processing, instead of the polishing process, any one selected from the group consisting of shot peening, UIT (Ultrasonic impact treatment), cavitation hardening, laser hardening, cold rolling, and rolling may be performed.

[0025] Figure 4 This is a schematic diagram showing a method of performing shot peening on the raceway surface of a bearing. Figure 5 yes Figure 4 Schematic diagram of the bearing raceway surface after shot peening. Figure 4 In shot peening, for example, the ball 17 collides with the unprocessed portion 9E that is to become the outer raceway surface. The ball 17, which is moving at high speed in the direction of the arrow M1 in the figure, collides with the outer raceway surface 9A and rebounds to move in the direction of the arrow M2 in the figure. Through this collision, a surface such as Figure 5 The circular indentation 9F shown. If numerous balls 17 collide with different positions on the outer ring raceway surface 9A, multiple circular indentations 9F are formed. In addition, the balls 17 can be iron or non-ferrous metal. By forming the indentation 9F, residual stress is applied to the area adjacent to the raceway surface of the base material.

[0026] Figure 6 This is a schematic diagram showing the final form of the raceway surface after shot peening. Figure 6 , especially for the raceway surface 9 of the outer ring 2 and the inner ring 5, a high surface roughness is finally obtained. Figure 5 As shown, raceway surface 9 is subjected to super finishing on the surface where a plurality of indentations 9F are formed. Thus, outer ring raceway surface 9A is formed.

[0027] Figure 7 is an enlarged schematic diagram of the outer ring. Figure 7 As shown in FIG. 1 , as an example of the external appearance of the outer ring 2 , a case where the outer ring 2 has two rows of outer ring raceway surfaces, namely, an outer ring raceway surface 9A and an outer ring raceway surface 9B is considered. Figure 8 This is an enlarged view of the first row of outer ring track surface. Fig. 9 This is an enlarged view of the second row outer ring raceway surface. Figure 8 and Fig. 9 The dotted lines in these figures indicate the extending direction of the fiber flow 21. The outer raceway surface 9A (refer to FIG. 1 ) located in the first row of the two rows of outer raceway surfaces 9A and 9B is Figure 8 The fiber flow 21 at the center of the axial direction (X direction) of the first row of raceway surfaces) is at an angle relative to the outer raceway surface 9A to the outer raceway surface 9B located in the second row (refer to Fig. 9 : The fiber flow 21 at the axial center of the second row of raceway surfaces) is at an angle of more than 10° relative to the outer raceway surface 9B. Specifically, Figure 8 Fiber flow 21( Figure 8 The dotted line direction) is roughly parallel to the outer ring raceway surface 9A. That is, Figure 8 The angle between the fiber flow 21 and the outer raceway surface 9A is substantially zero. Fig. 9 Fiber flow 21( Fig. 9 The dashed line direction) has an angle θ1 with the outer ring raceway surface 9B. Fig. 9 The angle θ1 of the inner ring 5 is, for example, not less than 10°. The angle θ1 may be not more than 15°, but may be greater than 15°. The same is true for the two rows of inner ring raceway surfaces 9C and 9D of the inner ring 5.

[0028] In addition, if Figure 8 and Fig. 9 As shown, in this specification, the angle of the fiber flow 21 relative to the outer ring track surface 9A, 9B is defined as the angle of the fiber flow 21 relative to the outer ring track surface 9A, 9B at the position closest to the outer ring track surface 9A, 9B in the radial direction (for example, at the position of the axial center). This is also the same for the angle of the fiber flow 21 relative to the inner ring track surface 9C, 9D. The radial direction refers to the direction extending radially from the center of the circular ring shape such as the outer ring 2. That is, the radial direction corresponds to the extension direction of the diameter dimension.

[0029] Fig.10 This is a schematic diagram for explaining the definition of the angle of the fiber flow relative to the outer raceway surface. Fig.10 For example, even in an outer ring raceway surface 9B obtained by cutting the cross section shown here, if its axial direction ( Fig.10If the position of the outer raceway surface 9B in the left and right direction is different, the angle between the outer raceway surface 9B and the fiber flow 21 will also be different. In addition, even if the axial position of the outer raceway surface 9B is equal, if its circumferential direction ( Fig.10 The angle between the outer ring 2 and the fiber flow 21 is different. That is, Fig.10 The angles of the fiber flows 21 at the five points A, B, C, D, and E indicated by the arrows in the middle relative to the outer raceway surface 9B differ from each other by, for example, about 3° to 5°. This is the same for both the outer raceway surface 9A and the inner raceway surface.

[0030] Therefore, in this specification, for example Fig.10 The "angle between the outer raceway surface 9B and the fiber flow 21" on the right side of the two-row arrangement (the same as the angle between the fiber flow 21 and the outer raceway surface 9A, 9B) is defined as follows. That is, the above "angle" is the average value of the angle between the raceway surface and the fiber flow 21 at the axial center position of the outer raceway surface 9A at a total of 5 locations with a phase difference of 72° from the bearing center in the circumferential direction as a representative value. That is, the above "angle" is Fig.10 The average value of the angles of the fiber flow 21 relative to the outer ring raceway surface 9B at the five points A, B, C, D, and E indicated by the arrows in the figure. The position of point A may be, for example, a position that is equal in phase to one end of the lettering attached to the bearing model, but is not limited thereto. Fig.10 In the embodiment, the outer ring raceway surface 9A and the outer ring raceway surface 9B are formed on different outer rings 2 (having two outer rings 2). Although such a structure is also possible, it is also possible to Figure 2 The angles formed between the inner raceway surfaces 9C and 9D and the fiber flow 21 are also the same.

[0031] (Background and technical issues for achieving the effects of the present embodiment) Here, comparative examples (conventional background technologies) and technical problems thereof (including those described in the above-mentioned background technology column and problem to be solved column) that achieve the effects of the present embodiment will be described again in detail.

[0032] In the manufacturing process of a multi-row tapered roller bearing, one or two outer rings 2 having outer ring raceways on the inner circumference are prepared. One or two inner rings 5 ​​having inner ring raceways on the outer circumference are prepared. When one outer ring 2 and one inner ring 5 are prepared, two rows of raceways are formed there. When two outer rings 2 and two inner rings 5 ​​are prepared, one row of raceways is formed for 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 specified in 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 bearing steel is punched out during hot forging to form a circular ring shape. The punched formed product contains more non-metallic inclusions on the inner side of the radial outer side. In particular, in the outer ring 2, since the raceway surface 9 is formed on its inner circumferential surface, more non-metallic inclusions are contained in the area adjacent to the raceway surface 9.

[0034] During hot forging (punching process), the fiber flow bends in the area adjacent to the track surface 9. Therefore, there is a tendency for the angle of the fiber flow 21 relative to the track surface 9 to become larger. This tendency varies between multiple rows of track surfaces 9. For example, when the outer ring track surfaces 9A and 9B are used as two rows of track surfaces 9, the angle of the fiber flow 21 relative to one outer ring track surface 9A tends to be larger than the angle of the fiber flow 21 relative to the other outer ring track surface 9B. In this way, a difference in the angle of the fiber flow 21 relative to the track surface 9 between multiple rows of track surfaces is inevitable. For example, the difference in the angle is sometimes greater than 10° as described above.

[0035] In addition, the non-metallic inclusions in the base material of the bearing steel are stretched along the fiber flow 21. As a result, a plurality of tiny non-metallic inclusions are connected in the base material of the bearing steel and exist as a single long non-metallic inclusion. Due to the above situation, the number of non-metallic inclusions near the track surface 9 is large and the angle of the fiber flow 21 relative to the track surface 9 is easy to increase. In the outer ring 2 of the multi-row tapered roller bearing, in particular, the non-metallic inclusions are easily exposed on the track surface.

[0036] Compared with non-metallic inclusions existing inside the base material, non-metallic inclusions exposed on the raceway surface 9 have a greater impact on the rolling fatigue life of the bearing. Specifically, the outer ring 2 of the multi-row tapered roller bearing 1 is prone to peeling of the raceway surface 9 due to exposed non-metallic inclusions. Suppressing the reduction in rolling fatigue life caused by this peeling becomes a technical problem. Some countermeasures can be implemented by improving the cleanliness of the base material (steel) to reduce non-metallic inclusions. However, even so, non-metallic inclusions in steel cannot be completely eliminated.

[0037] The larger the angle between the track surface 9 and the fiber flow 21, the easier it is for peeling to occur. From this point of view, the angle between the track surface 9 and the fiber flow 21 is preferably less than 15°. Therefore, in the final product, it is necessary to process the above-mentioned angle of each of the multiple rows of track surfaces 9 to be less than 15°. However, due to the shape of the multiple-row tapered roller bearing 1 and the curvature of the fiber flow 21, such processing is difficult. Although such processing can be performed, the manufacturing cost will rise. Specifically, effort is spent on the shape during hot forging, and the curved parts of the fiber flow 21 are removed by post-processing. In this way, the angle of the fiber flow 21 closest to the track surface 9 can be avoided from becoming larger. However, in this way, the manufacturing cost rises due to the increase in processing amount and the deterioration of the yield.

[0038] The angle between the track surface 9 and the fiber flow 21 is measured as follows. First, the track wheel is cut to expose the track surface 9. The cross section of the exposed track surface 9 is etched by an etching method such as JIS G0553:2019 "Macrostructure test method for steel" to expose the fiber flow. Thereafter, the angle of the fiber flow 21 relative to the track surface 9 is measured by an optical microscope or the like.

[0039] (Effect) In view of the above background and technical problems, this embodiment achieves the following structure and effects.

[0040] The multi-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 track surfaces 9A and 9B as track surfaces on the inner circumferential surface. The inner ring 5 has inner ring track surfaces 9C and 9D as track surfaces on the outer circumferential surface. The maximum value of the compressive residual stress in the axial direction of the track surface in the region within a depth of 0.1 mm from the track 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 cracks along the non-metallic inclusions from progressing inward, the occurrence of peeling of the track surface 9 caused by the non-metallic inclusions exposed on the track surface 9 can be prevented. As a result, the rolling fatigue life of the multi-row tapered roller bearing 1 can be improved. The progress of the crack from the track surface 9 to the inside is caused by the oil pressure generated by the contact surface pressure between the rolling element and the track surface 9 applied to the lubricating oil that has penetrated into the crack. Therefore, by applying a high compressive residual stress to the area within a depth of 0.1 mm from the track surface 9, the force of crack expansion caused by the oil pressure of the lubricating oil can be eliminated. As a result, the progress of the crack can be suppressed. At this time, by setting the maximum value of the compressive residual stress in the area within a depth of 0.1 mm from the track surface to more than 1400 MPa, the progress of the crack to the inside can be effectively suppressed. This suppression effect can be obtained even when the extension angle of the fiber flow relative to the track surface is large and the non-metallic inclusions are exposed on the track surface. Furthermore, this effect can be obtained even when a plurality of minute non-metallic inclusions are connected and exist as a single long non-metallic inclusion in the base material of the bearing steel.

[0042] In addition, the maximum value of the compressive residual stress in the area within a depth of 0.1 mm from the raceway surface only needs to be above 1400 MPa, and it is not necessary to be above 1400 MPa in other areas. However, even if it is local, if there is an area with a compressive residual stress of 1400 MPa or more in the base material, the surrounding area will not reach 1400 MPa or more, and the compressive residual stress will be higher as a whole. For example, if the maximum value of the compressive residual stress is not controlled to be above 1400 MPa, the compressive residual stress of the outer ring 2 with a maximum value of 1400 MPa or more will be higher as a whole compared to the outer ring 2 or the inner ring 5 with relatively low compressive residual stress as a whole. Therefore, as described above, the progress of cracks can be effectively suppressed.

[0043] In addition, the maximum value of the compressive residual stress, especially in the axial direction of the raceway surface, is preferably 1400 MPa or more. The maximum value of the compressive residual stress in directions other than the axial direction of the raceway surface may be less than 1400 MPa. This is because cracks preferentially propagate in the axial direction.

[0044] In the above-mentioned multi-row tapered roller bearing 1, the maximum value of the compressive residual stress in the axial direction of the raceway surface of the region within a depth of 0.1 mm from the outer ring raceway surface 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 non-metallic inclusions closely present on the raceway surface 9 (outer ring raceway surface 9A, 9B) than the inner ring 5. Therefore, by increasing the compressive residual stress in the region adjacent to the raceway surface 9 of the outer ring 2, the effect of suppressing the progress of cracks and the peeling of the raceway surface 9 can be improved. In addition, the angle formed by the outer ring raceway surface 9A, 9B of the multi-row tapered roller bearing 1 and the fiber flow 21 is likely to be larger than the angle formed by the inner ring raceway surface 9C, 9D and the fiber flow 21. For this reason, by increasing the compressive residual stress in the region adjacent to the raceway surface 9 of the outer ring 2, the effect of suppressing the progress of cracks and the peeling of the raceway surface 9 can also be improved.

[0045] In the above-mentioned multi-row tapered roller bearing 1, at least one of the two rows of outer ring raceway surfaces 9A, 9B and the inner ring raceway surfaces 9C, 9D is provided. The angle of the fiber flow 21 at the axial center of the first row raceway surface 9A (9C) of the two rows of raceway surfaces 9A, 9B (9C, 9D) relative to the first row raceway surface 9A (9C) is different from the angle of the fiber flow 21 at the axial center of the second row raceway surface 9B (9D) of the two rows of raceway surfaces 9A, 9B (9C, 9D) relative to the second row raceway surface 9B (9D) at the axial center of the second row adjacent to the first row of the two rows of raceway surfaces 9A, 9B (9C, 9D) by more than 10°. Such a feature may also be provided.

[0046] In the above-mentioned multi-row tapered roller bearing 1, there are two rows of inner ring raceway surfaces 9C and 9D. The angle of the fiber flow 21 at the axial center of the first row of the two rows of inner ring raceway surfaces 9C and 9D relative to the first row of the inner ring raceway surface 9C is different from the angle of the fiber flow 21 at the axial center of the second row of the two rows of inner ring raceway surfaces 9C and 9D relative to the second row of the inner ring raceway surface 9D located in the second row adjacent to the first row. Such a feature may also be provided.

[0047] The progress of cracks and peeling on the track surface 9 are likely to occur at a portion where the fiber flow 21 has a larger angle with respect to the track surface 9. Therefore, even if compressive residual stress is applied to only one of the two tracks 9, the crack progress suppression effect can be obtained compared to the case where compressive residual stress is not applied to either of the two tracks 9.

[0048] In addition, as described above, in the manufacturing process, a difference in the angle between the fiber flow 21 and one side of the two rows of track surfaces 9 is inevitably generated. Consider using any method to intentionally form a fiber flow 21 in the other of the two rows to reduce the angle of the track surface 9 at the expense of increasing the angle of the fiber flow 21 in one of the two rows relative to the track surface 9. Here, the small angle of the fiber flow 21 in the other of the two rows relative to the track surface 9 is, for example, 15° or less. In this case, if the track surface 9 with the larger angle is polished, the progress of cracks from the track surface 9 with the larger angle can be suppressed. Therefore, compared with the case where the angle of the two rows is processed to be less than 15°, the manufacturing cost can be reduced.

[0049] In the above-mentioned multiple-row tapered roller bearing 1, the corrugations 15 may be formed on the raceway surface 9. The corrugations 15 are formed by polishing the raceway surface 9. By machining such as polishing, compressive residual stress can be applied to the region adjacent to the raceway surface 9. Therefore, the multiple-row tapered roller bearing 1 having the corrugations 15 on the raceway surface 9 can obtain the effect of suppressing the progress of cracks caused by the compressive residual stress and the effect of improving the rolling fatigue life accompanying this. [Example 1]

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

[0051] Specifically, the investigation involved both numerical analysis and prototype testing. The numerical analysis was as follows. Fig.11 This is a schematic diagram of the base material model with cracks analyzed by the finite element method. Fig.12 Is Fig.11 A schematic enlarged view of the portion XII surrounded by a dotted line. Fig.11 and Fig.12 For example, a model in which a portion of the outer ring 2o of the bearing is sheared is used for analysis. In the analysis, a model in which a portion of the inner ring of the bearing is sheared can also be used. This model of the bearing has an outer ring raceway surface 9Ao. Fig.11 In the model, 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 relative to the outer ring track surface 9Ao. More specifically, the angle θ2 refers to the angle relative to the outer ring track surface 9Ao on the ZX plane when a Z direction perpendicular to the outer ring track surface 9Ao and extending in the depth direction toward the inside of the outer ring 2o is defined.

[0052] The outer ring track surface 9Ao has a line contact area 18 that contacts the rolling element. The line contact area 18 is an area where the outer ring track surface 9Ao and the surface of the rolling element are in linear contact along the X direction (axial direction). That is, in the portion where the outer ring track surface 9Ao contacts the surface of the rolling element, the outer ring track surface 9Ao receives a load from the rolling element. The outer ring and the rolling element are elastically deformed due to the load. Thus, the contact area becomes a line contact area 18 having a certain area and extending along the X direction. The circumference of the annular outer ring track surface 9Ao is along the Y direction of the figure.

[0053] The outer ring 2o and the rolling elements rotate, and the rolling elements move on the outer ring raceway surface 9Ao. Fig.11 The load movement direction M3 indicated by the arrow in the middle moves. Therefore, the load received by the outer ring raceway surface 9Ao from the rolling element moves in the load movement direction M3 as time passes. Fig.12 As shown in FIG. 1 , the crack 27 formed in the outer ring 2o extends from the outer ring raceway surface 9Ao toward the inside of the outer ring 2o and extends in a semi-elliptical shape at a certain angle θ3 relative to the outer ring raceway surface 9Ao. The stress expansion coefficient K when the line contact area 18 passes through the formation portion of the crack 27 is calculated by the finite element method. I The stress expansion coefficient K is calculated for both the model in which compressive residual stress is applied to the outer ring raceway surface 9Ao and the model in which compressive residual stress is not applied. I The two are compared. In addition, for the model without compressive residual stress, all conditions except compressive residual stress are the same as those of the model with compressive residual stress. Stress expansion coefficient K I The calculated position (calculated point) is the front end 27P of the crack 27. The front end 27P of the crack 27 is arranged at the deepest position in the Z direction inside the outer ring 2o.

[0054] Next, the above-mentioned “the line contact region 18 passes through the formation portion of the crack 27 ” will be described. Fig.13 It means in Fig.11 Schematic diagram of how the line contact area moves over time in the model. 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 with time along the Y direction. That is, the line contact area 18 exists at the position of the line contact area 18A at time t=0. However, as the load movement direction M3 moves, the line contact area 18 exists at the position of the line contact area 18B at time t=n1. In addition, the line contact area 18 exists at the position of the line contact area 18C at time t=n2. The position of the line contact area 18 moves with time along the circumferential direction of the annular outer ring raceway surface 9Ao. Therefore, as time passes, the line contact area 18 approaches the formation portion of the crack 27 existing at a certain position in the circumferential direction and overlaps with the formation portion of the crack 27, and then moves away from the formation portion of the crack 27. Therefore, the line contact area 18 passes the formation portion of the crack 27.

[0055] exist Figure 11 to Figure 13 In the model, the extension length of crack 27 ( Fig.12 The half width of the crack 27 ( Fig.12 The dimension of the semi-elliptical crack 27 in the short axis direction) is 30μm. The maximum contact surface pressure between the outer ring raceway surface 9Ao and the rolling element is 2.5GPa, and the contact half width (the value of half the width of the line contact area 18 in the Y direction) is 100μm. The compressive residual stress applied to the model is almost entirely 1000MPa in the circumferential and axial directions. It is assumed that the oil pressure applied to the crack 27 by the lubricating oil is the average contact surface pressure applied evenly to the crack 27. Based on the above conditions, the stress expansion coefficient K is calculated. I .

[0056] Fig.14 It means that no compressive residual stress is applied. Figure 11 to Figure 13 A graph showing the calculated values ​​of the stress amplification factor in the model using the finite element method. Fig.15 This indicates that compressive residual stress is applied. Figure 11 to Figure 13 The curve diagram of the stress amplification factor in the model obtained by the finite element method. Fig.14 and Fig.15 The horizontal axis of each curve represents the relative position of the contact center to the crack center. The vertical axis of each curve represents the stress expansion coefficient K obtained by numerical analysis. I In addition, the angles shown in the legend correspond to Fig.12 The inclination angle θ3 of the crack 27 in the image is θ3.

[0057] from Fig.14 and Fig.15 It can be seen that the greater the inclination angle θ3 of the crack 27, the greater the stress expansion coefficient K I In addition, the stress magnification coefficient K in the model with compressive residual stress isI Compared with the stress expansion factor K in the model without compressive residual stress I Therefore, by applying the compressive residual stress, the effect of suppressing the progress of cracks caused by non-metallic inclusions can be obtained.

[0058] The trial production test is as follows. A plurality of angular contact ball bearing trial products are prepared using bearing steel containing a large amount of non-metallic inclusions. A portion of these trial products is subjected to a compressive residual stress of up to 1400 MPa in the axial direction of the raceway surface in the region within a depth of 0.1 mm from the raceway surface of the outer ring and the inner ring by polishing. These are hereinafter referred to as trial product A. For another portion of these trial products, a compressive residual stress of up to 1200 MPa in the axial direction of the raceway surface is applied to the region within a depth of 0.1 mm from the raceway surface of the outer ring and the inner ring by polishing. These are hereinafter referred to as trial product B. Trial product B, unlike trial product A, does not apply a compressive residual stress of up to 1400 MPa or more. Trial product A and trial product B can be distinguished by changing the press-in load of the polishing process. That is, by making the press-in load of the polishing process of trial product A greater than the press-in load of the polishing process of trial product B, the compressive residual stress can be increased. For another portion of these trial products, polishing is not performed on the outer ring and the inner ring, at least the above-mentioned compressive residual stress is not intentionally applied. These are hereinafter referred to as trial products C. Fatigue tests were performed on each of these trial products, and rolling fatigue lives were compared. In addition, eight trial products A and eight trial products B and 25 trial products C were prepared and tested.

[0059] In addition, the angular contact ball bearing used in this trial test is different from the bearing type of the multi-row tapered roller bearing used in the description of this embodiment. However, the peeling of the raceway surface of the angular contact ball bearing is caused by the non-metallic inclusions exposed on the raceway surface, similar to the peeling mechanism of the multi-row tapered roller bearing. Therefore, if the prototype of the angular contact ball bearing is tested, it is possible to conduct an evaluation with the same reliability as when the prototype of the multi-row tapered roller bearing is tested. The reason for using angular contact ball bearings instead of multi-row tapered roller bearings in this trial test is the result of considering the difficulty and cost of manufacturing.

[0060] The angular contact ball bearing prototype used in this trial production test has a bearing model of 7206, and the maximum surface pressure of the outer ring is 3.00 GPa. The contact angle of the angular contact ball bearing is 27°, and the rotation speed of the outer ring is 3100 rpm. VG56 is used as the lubricant.

[0061] Fig.16 This is a graph showing the relationship between the depth from the raceway surface and the residual stress of the outer ring of each trial product. Fig.16The horizontal axis of the curve represents the depth distance of the outer ring of each trial product from the track surface. The vertical axis of the curve represents the axial residual stress at each position. If the residual stress value is less than 0, it indicates compressive residual stress, and if the residual stress value exceeds 0, it indicates tensile residual stress. Fig.16 As shown in Fig. 2, in the case of trial product A, the maximum value of the compressive residual stress in the axial direction of the raceway surface at a depth of 50 μm from the raceway surface is 1400 MPa or more. In the case of trial product B, the maximum value of the compressive residual stress in the axial direction of the raceway surface at a depth of 30 μm from the raceway surface is 1200 MPa or more. On the other hand, almost no compressive residual stress is applied to trial product C.

[0062] Fig.17 This is a graph showing the relationship between the compressive residual stress applied to the prototype and the bearing life. Fig.17 The horizontal axis of the curve represents the test time of the angular contact ball bearing prototype. The vertical axis of the curve uses a logarithmic scale to represent the cumulative failure probability of the angular contact ball bearing prototype. The test time (L10) until the cumulative failure probability of each prototype A to C reaches 10% is regarded as the life of the prototype (bearing).

[0063] Depend on Fig.17 It can be seen that the L10 life of trial product C is 31.66 hours, and the L10 life of trial product B is 42.79 hours, and there is no significant difference between them. On the other hand, the L10 life of trial product A is 588.31 hours, and it can be confirmed that the rolling fatigue life is greatly improved compared with trial products B and C. In addition, the filled points in each figure indicate that the track surface peeled off at that time, and the blank points in each figure indicate that the test was terminated because the track surface did not peel off. The test was terminated after 1000 hours for trial products A and B, and after 300 hours for trial product C.

[0064] Thus, it was confirmed that if a compressive residual stress of a maximum of 1400MPa or more is applied in the axial direction of the track surface near the track surface, the rolling fatigue life can be improved compared to the case where this is not done. That is, if a compressive residual stress of a maximum of 1400MPa or more is applied in the axial direction of the track surface, the progress of cracks from non-metallic inclusions can be suppressed. It can be seen that even in the case where the extension angle of the fiber flow relative to the track surface is large and non-metallic inclusions are exposed on the track surface, the occurrence of track surface peeling caused by them can be suppressed. On the other hand, if the maximum compressive residual stress in the axial direction of the track surface is about 1200MPa, the effect of improving the rolling fatigue life is almost invisible.

[0065] (Application example) Below, use Fig.18 An application example of the above-mentioned present embodiment will be described.

[0066] Fig.18 This 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. Fig.18 The multi-row tapered roller bearing of this embodiment is used, for example, as a bearing 101 for a railway vehicle axle. The bearing 101 for a railway vehicle axle mainly includes an outer ring 102, two inner rings 105, a plurality of rollers 106 as rolling elements, and a retainer 107. The inner ring 105 is pressed into the shaft end of the axle (not shown). Annular components, namely, a front cover 142 and a rear cover 144, are arranged on both axial sides of the pair of inner rings 105. Bolts and nuts are used to fasten the front cover 142 to the axle. In this way, the pair of inner rings 105 and thus the entire bearing are positioned and fixed. The outer ring 102 is fixed to the axle box (not shown). A spacer may also be sandwiched between the pair of inner rings 105.

[0067] exist Fig.18 In the embodiment, a convex portion 105a is formed on the end surface of the inner ring 105, and concave portions 142a and 144a are formed on the end surfaces of the front cover 142 and the rear cover 144. Specifically, a concave portion 142a is formed on the end surface of the front cover 142, and a convex portion 105a is formed on the end surface of the inner ring 105 of the first row among the multiple rows. When the concave portion 142a and the convex portion 105a are fitted, an axial gap δa is formed between the bottom surface of the concave portion 142a and the end surface of the convex portion 105a. A radial gap 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 recessed portion 144a is formed on the end surface of the rear cover 144, and a convex portion 105a is formed on the end surface of the inner ring 105 of the second row among the multiple rows. When the recessed portion 144a and the convex portion 105a are engaged with each other, an axial gap δa is formed between the bottom surface of the recessed portion 144a and the end surface of the convex portion 105a. A radial gap δb is formed between the inner circumferential surface of the recessed portion 144a and the outer circumferential surface of the convex portion 105a. In addition, the arrangement of the recessed and convex portions engaged with each other may be different from the arrangement of the recessed and convex portions. Fig.18 That is, the concave portion may be formed on the inner ring 105 and the convex portion may be formed on the front cover 142 and the rear cover 144.

[0069] The axial clearance δa and the radial clearance δb are both about 0.1 mm or more and 0.5 mm or less. In particular, if the radial clearance δb is set to a tight fit with a tightening amount, the disassembly of the bearing will deteriorate, so a special fixture or press is required, which increases the man-hours for inspection. Therefore, the radial clearance δb is preferably a loose fit (clearance fit).

[0070] The grease applied to the gap of the fitting portion is preferably the same type as the grease sealed in the railway vehicle axle bearing 101. The grease sealed in the railway vehicle axle bearing 101 is, for example, urea-based grease.

[0071] An oil remover may also be provided between the inner ring 105 and the front cover 142. In addition to the rear cover 144 or as an alternative to the rear cover 144, an oil slinger may also be provided.

[0072] Seals 130 are disposed at both ends of the outer ring 102. The seals 130 have a function of preventing leakage of grease sealed inside the railway vehicle axle bearing 101 and preventing foreign matter from entering from the outside.

[0073] Above Fig.18 The railway vehicle axle bearing 101 has Figure 1-2 The double-row tapered roller bearing 1 has the same features as the double-row tapered roller bearing 1, and therefore, can achieve the effect of suppressing the progress of cracks.

[0074] The embodiments and examples disclosed herein are illustrative in all respects and should not be construed as restrictive. The scope of the present invention is indicated by the claims rather than the above description, and is intended to include all modifications within the meaning and scope equivalent to the claims.

[0075] Hereinafter, each embodiment of the present disclosure will be summarized and described as a supplement. (Note 1) A multi-row tapered roller bearing, comprising: an outer ring having an outer ring raceway surface as a raceway surface on an inner circumferential surface; and The inner ring has an inner ring raceway surface as a raceway surface on the outer peripheral surface, The maximum value of the 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] (Note 2) A multi-row tapered roller bearing as described in Supplementary Note 1, wherein: A raceway surface having two rows of at least one of the outer raceway surface and the inner raceway surface, The angle of the fiber flow at the axial center of the first row of the two rows of track surfaces relative to the first row of track surfaces differs by more than 10° from the angle of the fiber flow at the axial center of the second row of the two rows of track surfaces adjacent to the first row of track surfaces relative to the second row of track surfaces.

[0077] (Note 3) A multi-row tapered roller bearing as described in Supplement 1 or 2, wherein: Corrugations are formed on the track surface.

[0078] (Note 4) A multi-row tapered roller bearing as described in Supplementary Note 3, wherein: The above-mentioned corrugation has a wavelength that is smaller than the diameter in the axial direction of the raceway surface of a contact ellipse assumed when the polishing tool is in elastic contact with the above-mentioned raceway surface.

[0079] (Note 5) A multi-row tapered roller bearing as described in any one of Supplementary Notes 1 to 4, wherein: The above-mentioned multiple-row tapered roller bearing is used as a bearing for a railway vehicle axle.

[0080] (Note 6) A method for manufacturing a multi-row tapered roller bearing, comprising: The steps of preparing an outer ring having an outer ring track surface as a track surface on the inner circumference; and preparing an inner ring having an inner ring track surface as a track surface on the outer circumference; and processing the track surface, 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 the compressive residual stress in the raceway surface axial direction in a region within a depth of 0.1 mm from the raceway surface is 1400 MPa or more.

[0081] (Note 7) The method for manufacturing a multi-row tapered roller bearing as described in Supplementary Note 6, wherein: In the process of machining the raceway surface, at least one of the raceway surfaces of the outer ring and the inner ring is machined so that the maximum value of the axial compressive residual stress of the raceway surface in an area within a depth of 0.1 mm from the raceway surface is greater than 1400 MPa.

[0082] (Note 8) The method for manufacturing a multi-row tapered roller bearing as described in Supplementary Note 7, wherein: The above-mentioned machining is polishing.

[0083] (Note 9) The method for manufacturing a multi-row tapered roller bearing as described in Supplementary Note 8, wherein: In the polishing process, the polishing tool is pressed and contacted with the track surface while the polishing tool moves axially along the track surface, thereby forming ripples on the track surface. The corrugation has a wavelength that is smaller than a diameter in the axial direction of the raceway surface of a contact ellipse assumed when the polishing tool is in elastic contact with the raceway surface. It should be understood that although the embodiments of the present invention have been described, the embodiments disclosed this time are illustrative in all points and do not constitute limitations. The scope of the present invention is indicated by the claims, and is intended to include all changes within the meaning and scope equivalent to the claims.

Claims

1. A multi-row tapered roller bearing, characterized in that: include: an outer ring having an outer ring raceway surface as a raceway surface on an inner circumferential surface; and an inner ring, wherein the inner ring has an inner ring raceway surface as a raceway surface on an outer peripheral surface, The maximum value of the 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.

2. The multi-row tapered roller bearing according to claim 1, characterized in that: having two rows of at least one of the outer raceway surface and the inner raceway surface, An angle of the fiber flow at the axial center of the first row of the two rows of track surfaces relative to the first row of track surfaces differs by more than 10° from an angle of the fiber flow at the axial center of the second row of the two rows of track surfaces adjacent to the first row of the two rows of track surfaces relative to the second row of track surfaces.

3. The multi-row tapered roller bearing according to claim 1, characterized in that: Corrugations are formed on the track surface.

4. The multi-row tapered roller bearing according to claim 3, characterized in that: The corrugation has a wavelength that is smaller than a diameter in the axial direction of the raceway surface of a contact ellipse assumed when the polishing tool is in elastic contact with the raceway surface.

5. The multi-row tapered roller bearing according to claim 1, wherein: The multi-row tapered roller bearing is used as a bearing for a railway vehicle axle.

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