Methods for identifying welded cages for roller bearings, caged rollers, fusion joints, and quality assurance methods for welded cages for roller bearings.

Abstract

The welded retainer has a base material (15) extending circumferentially and a welded portion (13) formed by welding one end and the other end of the base material together. The welded retainer uses a plurality of pockets formed at intervals circumferentially on the base material to hold the roller. The welded portion includes a fusion joint (13a) on one radial side and a diffusion joint (13b) on the other radial side. The radial dimension of the fusion joint is more than 70% and less than 95% of the radial dimension of the welded portion.

Description

Technical Field

[0001] The present invention relates to a welded retainer, which is made into a ring shape by preparing a strip of base material with pre-formed pockets and rounding the base material and joining the two ends of the base material by welding. Background Technology

[0002] Welded cages are known as cages installed in roller bearings to maintain the spacing between rollers. Welded cages are formed by preparing a strip of metal material, such as a strip of steel plate, of a length equal to the circumference of the cage, rounding it, and then welding the two ends together (hereinafter also referred to as welded portions or welded areas). Currently known examples of such welded cages include Japanese Patent Application Publication No. 2013-160263 (Patent Document 1), Japanese Patent Application Publication No. 2007-270967 (Patent Document 2), and Japanese Patent Application Publication No. 2013-108587 (Patent Document 3).

[0003] In Patent Document 1, cuts are made in a pair of annular portions to avoid load concentration at the welded area, making it difficult to disconnect at the welded area. In Patent Document 2, the outer peripheral surface of the cage is formed as a flat surface at the circumferential position including the welded area. In Patent Document 3, the welded areas of one annular portion and the other annular portion are set at different circumferential positions, and a welded area is also provided in the column portion.

[0004] Prior art literature

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2013-160263

[0007] Patent Document 2: Japanese Patent Application Publication No. 2007-270967

[0008] Patent Document 3: Japanese Patent Application Publication No. 2013-108587 Summary of the Invention

[0009] The problem that the invention aims to solve

[0010] However, the existing welding retainer described above presents the following problem: The amount of molten metal at the weld joint is not specified in the prior art. The amount of molten metal affects the strength of the weld joint, therefore, the strength of the weld joint cannot be managed in the prior art.

[0011] For example, when molten metal overflows and forms a bulge, stress concentration occurs near the bulge at the weld joint. This reduces the strength of the weld joint.

[0012] Furthermore, in the existing technology, no indicators affecting the strength of the welded part, such as surface hardness or molten state, are defined, so the strength of the welded part cannot be managed.

[0013] Especially in vehicles equipped with internal combustion engines and automatic transmissions, when roller bearings are installed on revolving components such as planetary gears in the planetary gear mechanism inside the automatic transmission and connecting rods inside the internal combustion engine, centrifugal force will act on these roller bearings. Therefore, the cages installed in the roller bearings are required to have a specified fatigue strength to prevent fatigue failure at the welded joints.

[0014] The present invention addresses the aforementioned practical situation by aiming to improve the fatigue strength of welded parts. Furthermore, the present invention addresses the management of the fatigue strength of welded parts. The object of the present invention is to provide a weld retainer capable of quality management of welded parts.

[0015] Solution for solving the problem

[0016] To achieve this objective, the welded cage for roller bearings of the present invention comprises a base material extending circumferentially and a welded portion formed by welding one end and the other end of the base material together. The welded cage for roller bearings retains rollers by having a plurality of pockets spaced apart circumferentially on the base material. The welded portion of the welded cage includes a fusion joint on one radial side and a diffusion joint on the other radial side. The radial dimension of the fusion joint is 70% or more and 95% or less of the radial dimension of the welded portion.

[0017] The value obtained by dividing the radial dimension of the fused joint by the radial dimension of the welded area is called the fusion length ratio. According to the present invention, since the fusion length ratio is set to 70% or more, the proportion of the fused joint in the welded area increases, the tensile strength of the welded area increases, and the fatigue limit of the weld cage can be ensured. Furthermore, since the fusion length ratio is set to 95% or less, the amount of molten metal in the welded area is not excessive, preventing the welded area from bulging more than 0.3 mm from the inner or outer diameter surface of the ring. Therefore, stress concentration can be suppressed or prevented. It should be noted that the radial dimension of the welded area is the radial dimension after welding and before grinding, or it can be the radial dimension after welding and grinding. Grinding is arbitrary.

[0018] In one embodiment of the invention, the fusion joint is provided along the outer diameter surface of the welded portion, and the diffusion joint is provided along the inner diameter surface of the welded portion. In another embodiment, the fusion joint is provided along the inner diameter surface of the welded portion, and the diffusion joint is provided along the outer diameter surface of the welded portion.

[0019] When the two ends of the base material are welded together, a radial bulge is often formed on the surface of the weld joint. The height (bulge amount) of this bulge is preferably low. This is because if the bulge becomes significant, stress concentration will occur near the bulge when the cage is subjected to centrifugal force during rotation. As a preferred embodiment of the invention, the bulge amount of the inner diameter surface of the weld joint is less than 0.3 mm, based on the inner diameter surface of the base material. According to this embodiment, stress concentration at the weld joint is mitigated, and durability is improved even if the invention is subjected to deformation into an elliptical shape due to centrifugal force generated by rotation. Incidentally, the radial dimension of the fused joint of the invention can also be a dimension measured including the bulge amount of the fused joint, or it can be a dimension measured after the bulge of the fused joint has been removed by grinding.

[0020] As a more preferred embodiment of the present invention, the outer diameter surface of the welded portion is ground, and the outer diameter surface of the welded portion has the same curvature as the outer diameter surface of the base material. According to the above embodiment, the outer diameter of the retainer can be guided. As a more preferred embodiment, the fusion joint is disposed on the outer diameter side of the weld retainer, and this fusion joint is ground. According to the above embodiment, when the outer peripheral surface of the welded portion has a bulge, the bulge of the fusion joint, which has a large amount of molten metal, can be removed by grinding the outer diameter of the weld retainer, thus ensuring the outer diameter guiding surface of the weld retainer and suppressing stress concentration at a lower cost than grinding the inner diameter. As another embodiment, the inner diameter surface of the welded portion has a bulge.

[0021] After welding, the weld retainer is preferably subjected to heat treatment such as carburizing, quenching, and tempering. As one aspect of the invention, the welded portion is subjected to carburizing, quenching, and tempering to achieve a surface hardness of 600 Hv or higher and a tensile strength of 1100 MPa or higher.

[0022] The caged roller of the present invention comprises the above-described welded cage for roller bearings and a roller held in a pocket of the welded cage for roller bearings.

[0023] The method for identifying fused joints of the present invention involves grinding a welded cage for a roller bearing to create a cross-section at the welded portion of the cage. After etching the cross-section with a nitric acid alcohol solution, a digital image is captured. Digital image processing is then performed on the digital image to identify the boundary between the fused joint and any other portion. This cross-section can be a plane parallel to the cage's axis, but is preferably a flat cross-section intersecting the axis, intersecting both the outer and inner diameter surfaces of the welded portion. Digital image processing includes, for example, performing image processing in the order of grayscale conversion, histogram flattening, low-pass filtering, and binarization, but is not limited to this.

[0024] The quality confirmation method for the welded cage of the roller bearing of the present invention involves heat treating the welded cage described above, followed by a tensile test that causes the welded portion to fracture, to confirm whether the tensile strength of the welded portion, as determined by the tensile test, is within a specified range. The heat treatment may be, for example, carburizing, quenching, and tempering, but is not limited to this.

[0025] Invention Effects

[0026] Thus, according to the present invention, the proportion of the molten joint in the welded area can be increased and the surface bulge of the welded area can be reduced, thereby improving the fatigue strength of the welded area. Furthermore, by defining surface hardness and molten state as indicators affecting the strength of the welded area, the strength of the welded area can be managed. Attached Figure Description

[0027] Figure 1 This is an overall perspective view of a welded cage for a roller bearing, which is an embodiment of the present invention.

[0028] Figure 2 This is an enlarged perspective view showing the welding area in this embodiment.

[0029] Figure 3 This is an enlarged perspective view showing the welding area in this embodiment.

[0030] Figure 4 This is a perspective view showing the welded portion of this embodiment in a further enlarged manner.

[0031] Figure 5 This is a simplified diagram showing representative steps in the manufacturing process of welded cages for roller bearings.

[0032] Figure 6 This is an enlarged side view showing the inclined ends of the ring material approaching each other.

[0033] Figure 7 It is a digital image representing the welding area of ​​this embodiment (Example 1).

[0034] Figure 8 It is a digital image representing the welded area in Comparative Example 1.

[0035] Figure 9 It is a digital image representing the welded area in Comparative Example 2.

[0036] Figure 10 This is a digital image showing the welding area in Embodiment 2 of the present invention.

[0037] Figure 11 Yes Figure 10 The image was obtained by digital processing.

[0038] Figure 12 Yes Figure 11 The image was obtained by digital processing.

[0039] Figure 13 Yes Figure 12 The image was obtained by digital processing.

[0040] Figure 14 Yes Figure 13 The image was obtained by digital processing.

[0041] Figure 15 Yes Figure 14 The image was obtained by digital processing.

[0042] Figure 16 Yes Figure 15 The image was obtained by digital processing.

[0043] Figure 17 This is a digital image showing the welding area in Embodiment 3 of the present invention. Detailed Implementation

[0044] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Figure 1 This is an overall perspective view of a welded cage for a roller bearing, which is an embodiment of the present invention. Figure 2 This is an enlarged perspective view showing the ring portion of this embodiment, illustrating... Figure 1 The circled part II in the middle. Figure 3 and Figure 4 This is an enlarged perspective view showing the ring portion of this embodiment. Figure 3 express Figure 1 The circled part III, Figure 4 It is Figure 3 The figure is a further enlarged view of the central part. The welded cage for the roller bearing of this embodiment (hereinafter also simply referred to as cage 10) has a pair of rings 11, 11 and a plurality of columns 16 that join the pair of rings 11, 11 together.

[0045] In the following description, the center of cage 10 will be referred to as axis O. Cage 10 is an M-type cage. (Refer to...) Figure 1Regarding the multiple columns 16 of the M-type cage, the central region of the column 16 extends parallel to the axis O on the inner diameter side, and the two ends of the column 16 extend parallel to the axis O on the outer diameter side. The intermediate region of the column 16, which connects the central region and the ends, extends obliquely relative to the axis O. Rings 11 extend from both ends of the column 16 toward the inner diameter side. Thus, the rings 11 are inwardly projecting flanges, and are therefore also called flanges. That is, when the cage 10 is cut using a plane containing the axis O, the cross-section of the column 16 and the pair of rings 11, 11 is M-shaped. In this embodiment, the inner diameter surface of the rings 11 is located on the inner diameter side closer to the central diameter side than the central region of the column 16.

[0046] A pocket 19 is formed between a pair of ring portions 11, 11 and adjacent circumferentially oriented column portions 16, 16. Rollers (not shown) are disposed in each pocket 19. The rollers are not particularly limited in shape; for example, they may be needle rollers.

[0047] In each column portion 16, an inner diameter side roller anti-detachment portion 17 and an outer diameter side roller anti-detachment portion 18 are formed on the pocket surface 16m that divides the pocket 19. The inner diameter side roller anti-detachment portions 17 are arranged in the central region of the column portion 16. The outer diameter side roller anti-detachment portions 18 are arranged at both ends of the column portion 16. The inner diameter side and outer diameter side roller anti-detachment portions 17 and 18 formed on two pocket surfaces 16m, 16m opposite each other with a pocket 19 respectively retain the rollers (not shown) to prevent them from falling out of the pocket 19. In this embodiment, a roller bearing with a cage can also be used, in which multiple rollers are inserted into a welded cage 10.

[0048] The roller bearing with welded cage 10 is inserted into a planetary gear mechanism (not shown), for example, which includes a sun gear, planetary gears, a ring gear, and a planet carrier. Specifically, the roller bearing with the roller bearing with welded cage 10 is inserted into the center of a planetary gear that is rotatable and supported by a planet carrier. The planetary gear and the roller bearing with welded cage 10 revolve as the planet carrier rotates. Alternatively, the roller bearing with welded cage 10 is inserted into the pivot (not shown) of the connecting rod of an internal combustion engine, and revolves with the pivot as the connecting rod moves.

[0049] Next, the manufacturing process of this embodiment will be described.

[0050] Figure 5 This is a simplified diagram showing representative steps in the manufacturing process of welded cages for roller bearings. First, as... Figure 5 As shown in (a), the strip of steel (hereinafter referred to as strip, strip plate, or base material) is prepared to become the raw material for the weld retainer 10. Examples of materials for the strip include cold-rolled steel plates such as JIS-SPC, JIS-SCM415, and JIS-SCM420. Alternatively, low-carbon steel such as JIS-S15C and medium-carbon steel such as JIS-S45C can be used.

[0051] Next, as Figure 5 As shown in (b), an M-shaped template forming process is performed on the strip to make its cross-sectional shape into an M-shape. Here, "M-shape" refers to plastic deformation in which the central portion of the strip in the width direction and the two side edges of the strip have a radial height difference when the strip is rounded into a cylindrical shape as described later. The M-shaped template forming process is performed by clamping and pressing the strip between forming rollers consisting of an upper mold with a convex central portion and a lower mold with a concave central portion. At this time, the corners of the two edges of the strip in the width direction are rounded to form chamfered portions 12.

[0052] Next, as Figure 5 As shown in (c), a pocket-cutting process is performed on a strip with an M-shaped cross-section to form pockets for retaining rollers. The pocket-cutting process is performed by preparing a punch with a cutting blade and pressing the tip of the punch against the strip along its thickness direction. The portion of strip remaining between adjacent pockets forms the column portion 16 of the retainer. Furthermore, the portion of strip remaining outside the pockets in the width direction forms the ring portion 11s of the retainer.

[0053] Next, a claw forming process is performed to form a claw-shaped outer diameter side roller anti-detachment part 18 at the end of the column 16. In the claw forming process, the end of the column 16 is fixed and pressed from the inner diameter side by stamping, thereby widening and forming the circumferential width dimension of the outer diameter side of the end of the column 16.

[0054] Then, a cutting process is performed to cut the strip to a length that is the circumference of the retainer 10, which is a specified length. The cutting is performed transversely through the pocket 19, resulting in the remaining two sides (ring material 11s) being cut off. The ends of the ring material 11s are cut at an angle relative to the thickness direction of the strip, and are obliquely shaped when viewed from the width direction of the strip (see reference). Figure 6 Hereinafter, this will be referred to as the inclined end 13s. The ladder-shaped cage material is cut out through a cutting process.

[0055] Next, as Figure 5 As shown in (d), a bending process is performed to round the strip steel by bending it into a cylindrical shape after cutting it into a length equal to one circumference. Through rounding, the length direction of the strip steel becomes the circumferential direction of the cage, the thickness direction becomes the radial direction of the cage, and the width direction becomes the axial direction of the cage; the chamfer 12 is on the outer diameter side. Furthermore, through the bending process, the spacing between the opposing pocket surfaces 16m, 16m narrows in the central region of the column portion 16. As a result, the inner diameter side of the central region of the column portion 16 forms the inner diameter side roller anti-detachment portion 17. Incidentally, as... Figure 6As shown, the inclined cutting ends are positioned opposite each other on the outer diameter side. The inclination angle of the cutting surface is a specified value that is between 30° and 80° relative to the length direction of the strip or the circumferential direction of the cage 10. The outer diameter surfaces of the ends of the columns 16 that are not connected in the circumferential direction are ground to form curved surfaces belonging to a common cylinder.

[0056] Next, as Figure 5 As shown in (e), a welding process is performed to join the two ends (inclined ends 13s, 13s) of the bent steel plate together. Thus, the ends of the ring material are welded together to form the ring 11.

[0057] Next, as needed, a first grinding process is performed to grind the outer diameter surface of the cylindrical welded cage 10 joined by welding. Here, a smooth cylindrical curved surface is presented at the outer diameter surface of the circumferentially connected rings 11, 11. The first grinding process can be omitted.

[0058] Then, preferably, carburizing, quenching, and tempering can be performed as a heat treatment process. This heat treatment process increases the strength of the welded cage. When the cage is quenched, the crystal grains are refined by the rapid cooling during quenching. In the case of steel with a high carbon content, other heat treatment processes such as nitriding or overall quenching can be performed. In the case of low carbon steel, carburizing and quenching or carburizing and nitriding quenching is preferred. In the case of a cage subjected to acceleration generated by centrifugal force as in this embodiment, the lightweighting of the cage contributes to the improvement of fatigue strength. In this case, it is preferable to use strips of JIS-SCM415, JIS-SCr415, high-tensile steel, etc., and perform carburizing, quenching, and tempering or carburizing and nitriding quenching and tempering.

[0059] In this way, it is manufactured Figure 1 The welded cage 10 is shown. Next, rollers (not shown) are inserted into each pocket 19 of the welded cage 10 to manufacture a roller bearing.

[0060] The aforementioned welding process will be described in detail.

[0061] Figure 6 This is an enlarged side view showing the state in which the inclined ends 13s, 13s of the ring-shaped raw material 11s, made of metal, are brought close to each other after rounding a circumference of the raw material 11s. The ring-shaped raw material is the width-direction side edge of the aforementioned strip. In this embodiment, the outer diameter sides of the inclined cut ends are brought close to each other while the inner diameter sides are moved away from each other. Next, the facing ends are brought into contact and pressure is applied to press the ends together. The two ends of the strip are melted and joined together by resistance welding with a large current flowing through the strip, forming a circular retainer. In this embodiment, the welded portion 13 uses the strip as the base material.

[0062] It should be noted that, in Figure 6 In the inclined ends 13s, the melting area of ​​the inclined ends 13s is large on the outer diameter side where the pointed front portions of the inclined ends 13s are close to each other. In contrast, the melting area of ​​the inclined ends 13s is small on the inner diameter side where the inclined ends 13s are away from the front end.

[0063] Figure 7 The image is an image obtained by taking a picture of the welded part 13 in this embodiment using a digital imaging device (hereinafter also referred to as Embodiment 1). This image is obtained by using... Figure 4 The annular portion 11 is cut at a section VII perpendicular to the axis O, and the cut surface is immersed in a nitric acid alcohol solution to change its color, and then photographed, as described below. The welded portion 13 utilizes the aforementioned... Figure 6 The welding method shown includes a white fusion joint 13a on one radial side and a gray diffusion joint 13b on the other radial side. Since one end is joined to the other, the circumferential center surface of the welded portion 13 is referred to as the joint surface 13c for convenience. Furthermore, the base material 15 is heated during welding. The base material adjacent to the circumferential sides of the welded portion 13 is referred to as the heat-affected zone 14.

[0064] Instructions for making Figure 7 The steps for the cross-section shown are as follows. First, prepare a test solution containing nitric acid and alcohol. The test solution is a nitric acid alcohol solution, specifically, for example, a commercially available concentrated nitric acid ethanol solution with a concentration of 3% by volume. Alternatively, the test solution is prepared by diluting concentrated nitric acid of a specified concentration, comprising 60-62% by weight, with ethanol of a concentration of 99.5% by weight or volume. Alternatively, the test solution is a nitric acid ethanol solution of a specified concentration, comprising concentrated nitric acid in a ratio of 3-10% by volume to the total. It should be noted that the alcohol in the test solution can also be methanol. Alternatively, the test solution can also be a picric acid alcohol solution.

[0065] Next, using a room temperature nitric acid alcohol solution as the test solution, section VII ( of the cage 10) Figure 4 The section VII of the cage 10 is immersed in the inspection solution and removed from the solution after a period of 3 to 5 seconds. The shape of the weld is determined based on the color change of section VII. It should be noted that when using a room temperature picric acid alcohol solution, it is preferable to immerse section VII of the cage 10 for 30 minutes.

[0066] The fusion joint 13a is the portion joined by the complete melting and incorporation of the base material during welding. In the fusion joint 13a, carbides from the base material melt into the matrix phase. Therefore, when the fusion joint section is corroded with a nitric acid alcohol solution, it appears white compared to incompletely fused portions such as the diffusion joint 13b or the heat-affected zone 14. While the aforementioned fusion joint exhibits high joint strength, molten metal overflows, and the surface of the welded area tends to bulge significantly. This results in stress concentration near the bulge, leading to a decrease in fatigue strength.

[0067] The diffusion joint 13b is the portion joined by butt welding where the base material does not melt during the welding process. In the diffusion joint 13b, the carbides of the base material do not fuse into the matrix phase; instead, metal atoms diffusely bond with each other. Therefore, when the cross-section of the diffusion joint is etched with a nitric acid alcohol solution, it acquires the same hue as the heat-affected zone, making it distinguishable by comparison with molten metal. While the diffusion joint described above has lower bond strength than a fusion joint, the lack of molten metal reduces the likelihood of overflow, resulting in less surface bulging at the welded area.

[0068] The heat-affected zone 14 is the part in which the composition of the base material changes due to the heating of the weld joint.

[0069] It should be noted that, as a variation not shown in the figure, in relation to... Figure 6 Conversely, in the case of an inclined cut where the outer diameter sides of the ends are far apart and the inner diameter sides of the ends are close to each other, the welded part becomes... Figure 7 The shapes are opposite. That is, the white fused joint 13a is disposed on the inner diameter side, and the gray diffused joint 13b is disposed on the outer diameter side.

[0070] Return the description Figure 7 In this embodiment, the white fusion joint 13a is disposed on the outer diameter side, and the gray diffusion joint 13b is disposed on the inner diameter side. The fusion joint 13a is an isosceles triangle whose circumferential dimension increases as it approaches the outer diameter surface 11d of the ring portion 11. The centerline of this isosceles triangle coincides with the joint surface 13c. When the radial dimension Lr of the welded portion 13, i.e., the dimension Lr from the outer diameter surface 11d to the inner diameter surface 11c, is set to 100%, the radial dimension La of the diffusion joint 13b at the joint surface 13c is within the range of 70% or more and 95% or less. Moreover, the radial dimension Lr-La of the diffusion joint 13b at the joint surface 13c is within the range of 30% or less and 5% or more.

[0071] In this embodiment, the weld portion 13 has a melt length ratio La / Lr that is within the range of 70% to 95%, resulting in reduced bulging and no stress concentration, thus ensuring fatigue strength. Furthermore, by including it within this range, this embodiment sufficiently contains molten metal, ensuring the required bond strength.

[0072] A comparative example will be described to facilitate understanding of Example 1 described above.

[0073] Figure 8 This is a digital image showing the welded portion of Comparative Example 1. In the annular portion 111 of Comparative Example 1, the diffusion joint 13b occupies the entire joint surface 13c, extending from the outer diameter surface 11d to the inner diameter surface 11c. That is, the welded portion 13 does not include the fusion joint (melt length ratio La / Lr = 0%). Moreover, although the diffusion joint 13b protrudes at the outer diameter surface 11d, it does not protrude at the inner diameter surface 11c.

[0074] Figure 9 This is a digital image showing the welded portion of Comparative Example 2. In the annular portion 112 of Comparative Example 1, the fusion joint 13a occupies the entire joint surface 13c, extending from the outer diameter surface 11d to the inner diameter surface 11c. The welded portion 13 does not include the diffusion joint (melt length ratio La / Lr = 100%). The circumferential dimension of the fusion joint 13a increases towards the outer diameter side, thus its shape, when viewed from the axial direction, becomes an isosceles trapezoid. Furthermore, the fusion joint 13a bulges at both the outer diameter surface 11d and the inner diameter surface 11c.

[0075] Fatigue strength tests were conducted at the welded portion 13 of the test body in Example 1, the welded portion 13 of the test body in Comparative Example 1, and the welded portion 13 of the test body in Comparative Example 2. It should be noted that, to avoid stress concentration caused by bulging, each test body was manufactured such that the bulge of the inner diameter surface 11c relative to the arc forming the inner diameter of the ring was less than 0.3 mm. Furthermore, fatigue strength tests were also conducted on their base materials, and the fatigue limit was determined. The fatigue limit refers to the stress at which the test body will not break even after being subjected to more than 10 million repeated loads (pulsating bending loads in this test), and is determined based on the repeated loads. The fatigue strength index is set as the fatigue limit. For these test bodies, M-shaped welded retainers with an outer diameter of 22 mm, an inner diameter of 14 mm, and a width of 14 mm were prepared. The axial dimension of the ring (base material thickness) was 0.7 mm. The material was set as JIS-SCM415, and carburizing, quenching, and tempering were performed after welding. After carburizing, quenching, and tempering, the depth (effective hardened layer depth) from the surface with a hardness of 513 Hv is 0.06 mm, and the surface hardness is approximately 600 Hv. The measurement results for the ring are shown in Table 1.

[0076] [Table 1]

[0077] Table 1 Comparison of weld length ratio and fatigue limit

[0078] Melt length percentage Fatigue limit MPa 0 401 70 879 100 823 (Base material) 837

[0079] In Example 1, the melt length ratio La / Lr was 70%, and the fatigue limit was 879 MPa. In Comparative Example 1, the melt length ratio La / Lr was 0%, and the fatigue limit was 401 MPa. In Comparative Example 2, the melt length ratio La / Lr was 100%, and the fatigue limit was 823 MPa. It should be noted that the fatigue limit of the base material was 837 MPa. From the above, it can be seen that, according to Example 1, a fatigue limit equal to or greater than that of the base material can be obtained.

[0080] Next, a method for calculating the melt length ratio La / Lr of the welded part 13 by performing image processing on the digital image of the welded part 13 will be explained.

[0081] Figure 10 Embodiment 2, relating to this implementation, is a digital image showing the welded portion 13 of Embodiment 2. This digital image is obtained by utilizing... Figure 4 The ring portion 11 is cut through section VII, which is perpendicular to the axis O. The cut surface is then immersed in a nitric acid alcohol solution under specified conditions to change its color and is photographed.

[0082] Figure 10 In order to identify the fused joint using digital image processing, the image processing software ImageJ was used for image processing. Figure 11 It is Figure 10 The image is converted into an 8-bit grayscale image. Figure 12 It is Figure 11 The magnified image obtained by cropping the central part of the image. Figure 13 Yes Figure 12 The image was obtained by performing histogram flattening on the image. Figure 14 Is Figure 13 The image obtained by applying a low-pass filter to the spatial frequency of the image to remove high-frequency noise is obtained. This low-pass filter is a process in ImageJ's bandpass filter where the low-frequency component is set to a range of 1000 pixels and the high-frequency component is set to a range of 20 pixels. Figure 15 Yes Figure 14 The image was obtained by performing histogram flattening on the image. Figure 16 Yes Figure 15 The image was binarized, and in ImageJ's Threshold settings, the black side threshold was set to 20 and the white side threshold was set to 180. This resulted in an image where the space outside the fused joint 13a and the ring 11 was white, and everything else was black. Figure 16Furthermore, the radial dimension La of the fusion joint 13a and the radial dimension Lr of the welded portion 13 were measured.

[0083] Following the steps described above, an image of another embodiment 3 was obtained ( Figure 17 Furthermore, the radial dimension La of the fusion joint 13a and the radial dimension Lr of the welded portion 13 were measured. In another embodiment 3, the outer diameter surface of the ring portion 11 was ground to form an arc shape in a manner mimicking the outer diameter surface of the ring portion. In contrast, in embodiment 2, as... Figure 16 As shown, the outer circumferential surface of the welded part is raised relative to the outer diameter surface of the ring 11.

[0084] It should be noted that in Examples 2 and 3, carburizing, quenching, and tempering were performed after welding. The carburized portion along the surface of the ring 11 appears black, therefore... Figure 16 and Figure 17 In the examples, the white fused joint 13a is reduced in appearance, but in Examples 2 and 3, since melting begins from the outer diameter surface, the black carburized portion on the outer diameter surface is the fused area. Therefore, in Figure 16 and Figure 17 In this case, the radial dimension La of the fused joint 13a can be measured starting from the outer diameter surface of the ring 11.

[0085] Next, we will explain the methods for detecting poor welding.

[0086] As test specimens, welded retainers with a melt length ratio La / Lr of 0% were prepared using both carburizing, quenching, and tempering methods. Surface hardness, tensile strength, and symmetrical alternating fatigue limit were measured at the weld site and the base material, respectively. Furthermore, as test specimens, welded retainers with a melt length ratio La / Lr of 70% were prepared using carburizing, quenching, and tempering methods. Surface hardness, tensile strength, and symmetrical alternating fatigue limit were measured at the weld site. Moreover, as test specimens, welded retainers with a melt length ratio La / Lr of 100% were prepared using carburizing, quenching, and tempering methods. Surface hardness, tensile strength, and symmetrical alternating fatigue limit were measured at the weld site. The results are shown in Table 2.

[0087] [Table 2]

[0088] Table 2 compares the surface hardness and tensile strength obtained according to different heat treatment states and melt length ratios.

[0089]

[0090] Referring to Table 2, in terms of surface hardness after welding and before carburizing, quenching, and tempering, the weld area (413 Hv) is 2.3 times that of the base material (180 Hv). This is because when the ends of the base materials are welded together and placed in air, the surface of the weld area cools and hardens. Upon subsequent carburizing, quenching, and tempering, the weld area (605 Hv) becomes equal to the base material (603 Hv).

[0091] Describe the tensile strength of the welded joints related to the molten state (melt length ratio La / Lr of 0%, 70%, 100%, and the base material unaffected by heat) and the tensile strength before and after carburizing, quenching, and tempering. For tensile testing, refer to... Figure 7 A region including the welded portion 13 and the base material 15 on both circumferential sides is cut out from the ring portion 11. A tensile load perpendicular to the joint surface 13c is applied to the cut test piece, and the tensile load at the welded portion is measured. Furthermore, only the base material 15 is cut out, and the tensile load on the base material 15 is measured. The tensile strength is set as the value obtained by dividing the maximum tensile load until the test piece breaks by the cross-sectional area of ​​the non-welded portion of the ring portion (i.e., the base material). The cross-sectional area is the area of ​​a flat cut surface orthogonal to the circumference of the ring portion 11.

[0092] In test specimens with a melt length ratio La / Lr = 0% after welding and before carburizing, quenching, and tempering, the tensile strength of the weld (555 MPa) was greater than that of the base metal (466 MPa). This was attributed to the higher surface hardness of the weld (413 Hv) compared to the base metal (180 Hv). Conversely, in test specimens with a melt length ratio La / Lr = 0% after carburizing, quenching, and tempering, although the surface hardness of the weld (605 Hv) was equal to that of the base metal (603 Hv), the tensile strength of the weld (893 MPa) was lower than that of the base metal (1185 MPa). Therefore, even with tensile testing in test specimens before carburizing, quenching, and tempering, a decrease in the fatigue limit of the welded cage with a melt length ratio La / Lr = 0% could not be detected.

[0093] According to Table 2, in the test pieces with a melt length ratio La / Lr = 0% after carburizing, quenching, and tempering, the surface hardness of the weld (605Hv) is equal to that of the base material (603Hv). Regarding tensile strength, the weld with a melt length ratio La / Lr = 0% is lower than that of the base material, while the weld with a melt length ratio La / Lr = 100% is higher than that of the base material. The symmetrical alternating fatigue limit exhibits the same tendency as the tensile strength.

[0094] According to Table 2, in order to detect the decrease in fatigue limit using tensile tests, the surface hardness (Vickers hardness) of the welded part is preferably 90% or more and 110% or less of the surface hardness (Vickers hardness) of the base material.

[0095] When describing heat treatment, methods include, for example, integral quenching, carburizing and quenching, carburizing and nitriding, high-frequency quenching, and laser quenching. Heat treatment other than carburizing and quenching may also be applied to the welded cage of this embodiment. To increase bending fatigue strength, carburizing and quenching or carburizing and nitriding may be performed, and the surface hardness of the welded cage is preferably 600 Hv or higher.

[0096] From the viewpoint of suppressing the bulging of the inner diameter surface 11c (or outer diameter surface 11d) of the ring at the welding site, excessive increase in the amount of molten metal should be prevented. Therefore, in this embodiment, a melt length ratio La / Lr of 95% or less is preferred.

[0097] To improve the fatigue limit of the welded part to be equal to that of the base material, it is preferable that the tensile strength of the welded part is equal to that of the base material, and more preferably 1100 MPa or more. Furthermore, it is preferable to perform heat treatment such as carburizing, quenching and tempering on the welded cage to make the surface hardness of the welded cage (welded part and base material) 600 Hv or more.

[0098] In particular, the weld portion with a melt length ratio La / Lr = 70% exhibits a greater symmetrical alternating fatigue limit than the weld portions with melt length ratios La / Lr = 0% and 100%, similar to the base material. Therefore, it can be concluded that the weld portion with a melt length ratio La / Lr = 70% has a superior fatigue limit compared to the weld portions with melt length ratios La / Lr = 0% and 100%.

[0099] The embodiments of the present invention have been described above with reference to the accompanying drawings; however, the present invention is not limited to the structures of the illustrated embodiments. Various modifications and variations can be applied to the illustrated embodiments within the same or equivalent scope as the present invention. For example, a portion of the structure can be extracted from one of the above embodiments, and another portion of the structure can be extracted from another of the above embodiments, and these extracted structures can be combined.

[0100] Industrial availability

[0101] The present invention can be advantageously utilized at the rotation center of a rolling bearing that rotates on its own axis while also revolving around a central point.

[0102] Symbol explanation:

[0103] 10 Welded cage for roller bearings, 11, 111, 112 Ring, 11c Inner diameter surface, 11d Outer diameter surface, 11s Ring raw material, 13 Welded part, 13a Melt joint, 13b Diffusion joint, 13c Joint surface, 13s Inclined end, 14 Heat-affected zone, 15 Base material, 16 Column, 16m Pocket surface, 17, 18 Roller anti-detachment part, 19 Pocket, La Radial dimension of melt joint, Lr Radial dimension of welded part, La / Lr Melt length ratio, O axis.

Claims

1. A welded cage for roller bearings, comprising a circumferentially extending base material and a welded portion formed by welding one end and the other end of the base material together, wherein the welded cage for roller bearings retains rollers by means of a plurality of pockets spaced apart circumferentially in the base material, wherein... The welded portion includes a fusion joint on one radial side and a diffusion joint on the other radial side. The fusion joint is the part joined by the complete melting and incorporation of the base material during welding. The diffusion joint is the part where the base material is not melted during welding and is joined by butt joint. The radial dimension of the fused joint is more than 70% and less than 95% of the radial dimension of the welded part.

2. The welded cage for roller bearings according to claim 1, wherein, The fusion joint is provided along the outer diameter surface of the welded area, and the diffusion joint is provided along the inner diameter surface of the welded area.

3. The welded cage for roller bearings according to claim 1, wherein, The bulge of the inner diameter surface of the welded part is less than 0.3 mm, based on the inner diameter surface of the base material.

4. The welded cage for roller bearings according to claim 1, wherein, The outer diameter surface of the welded part is ground, and the outer diameter surface of the welded part has the same curvature as the outer diameter surface of the base material.

5. The welded cage for roller bearings according to claim 1, wherein, The welded area is subjected to carburizing, quenching and tempering treatment to achieve a surface hardness of 600Hv or higher and a tensile strength of 1100MPa or higher.

6. A roller with a cage, comprising: Welded cage for roller bearings according to any one of claims 1 to 5; and The roller is held in the pocket.

7. A method for identifying fused joints, wherein, A cross-section is created at the welded portion by grinding the welded cage of the roller bearing according to any one of claims 1 to 4. Digital images were captured after the cross-section was etched using a nitric acid alcohol solution. The digital image is processed to identify the boundary between the fused joint and the portion outside the fused joint.

8. A method for quality verification of welded cages for roller bearings, wherein, The welded cage for the roller bearing according to any one of claims 1 to 4 is subjected to heat treatment. After the heat treatment, a tensile test is performed to cause the welded part to break, and it is confirmed whether the tensile strength of the welded part, as determined by the tensile test, is within the specified range.

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