Welded cage for roller bearing, roller with cage, method for distinguishing fusion joint, and method for verifying the quality of welded cage for roller bearing

Abstract

To enhance fatigue strength of a welding holder to enable quality control of the welding holder.SOLUTION: A welding holder comprises a base material 15 extending in a circumferential direction, and a welding portion 13 where one end and the other end of the base material are joined to each other by welding, where the welding holder holds rollers with a plurality of pockets formed in the base material at intervals in the circumferential direction. The welding portion includes a fused junction part 13a on one side in a radial direction and a diffused junction part 13b on the other side in the radial direction. A radial dimension of the fused junction part is 70% or more and 95% or less of a radial dimension of the welding portion.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a welded cage that is fabricated into a ring shape by preparing a strip-shaped base material with pockets formed in advance, rolling the base material, and joining both ends of the base material by welding.

[0002] Welded cages are known as cages that are incorporated into roller bearings and maintain the spacing between the rollers. The welded cage is made by preparing a metal material such as a strip of steel plate in a length that is the circumference of the cage, and then welding it together. First, both ends are joined by welding (hereinafter, also referred to as the welded portion or the welded portion). Conventionally, the contact cage has been disclosed in Japanese Patent Laid-Open No. 2013-160263 (Patent Document 1), Japanese Patent Laid-Open No. 2007-270967 ( Patent Document 2) and JP-A-2013-108587 (Patent Document 3).

[0003] In Patent Document 1, notches are provided in a pair of annular portions to prevent load concentration at the welded portion, making it difficult for the cage to separate at the welded portion. In Patent Document 2, the outer peripheral surface of the cage is formed into a flat surface at a circumferential position including the welded portion. In Patent Document 3, the welded portions of one annular portion and the other annular portion are located at different circumferential positions, and welded portions are also provided on the column portions. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-160263 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-270967 [Patent Document 3] Japanese Patent Application Laid-Open No. 2013-108587 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the above-described conventional welded retainer has the following problem: the amount of molten metal at the weld is not specified in the conventional technique. Since the amount of molten metal affects the strength of the weld, the conventional technique makes it impossible to control the strength of the weld.

[0006] For example, if the molten metal overflows and forms a bulge, stress will be concentrated in the welded area near the bulge, which will reduce the strength of the welded area.

[0007] Furthermore, in the prior art, the strength of the welded portion cannot be controlled because the indicators that affect the strength of the welded portion, such as the surface hardness and the fusion state, are not defined.

[0008] In particular, in vehicles equipped with internal combustion engines and automatic transmissions, roller bearings are mounted on revolving components such as planetary gears of planetary gear mechanisms inside automatic transmissions and connecting rods inside internal combustion engines, and centrifugal forces act on these roller bearings. For this reason, cages incorporated into roller bearings are required to have a certain level of fatigue strength to prevent fatigue failure at welded points.

[0009] In view of the above-mentioned circumstances, an object of the present invention is to increase the fatigue strength of welded portions. Another object of the present invention is to manage the fatigue strength of welded portions. An object of the present invention is to provide a welded cage that allows quality control of welded portions. [Means for solving the problem]

[0010] For this purpose, the welded cage for a roller bearing according to the present invention is a welded cage comprising a base material extending in the circumferential direction and a welded portion formed by joining one end and the other end of the base material together by welding, and which holds rollers in a plurality of pockets formed at intervals in the circumferential direction in the base material, the welded portion of the welded cage including a fused joint on one radial side and a diffusion joint on the other radial side, and the radial dimension of the fused joint being 70% or more and 95% or less of the radial dimension of the welded portion.

[0011] The value obtained by dividing the radial dimension of the fused joint by the radial dimension of the welded portion is called the fusion length ratio. According to the present invention, by setting the fusion length ratio to 70% or more, the proportion of the fused joint in the welded portion increases, increasing the tensile strength of the welded portion and ensuring the fatigue limit of the welded cage. Furthermore, by setting the fusion length ratio to 95% or less, the amount of molten metal at the welded portion is prevented from becoming excessively large, preventing the welded portion from protruding 0.3 mm or more from the inner or outer diameter surface of the ring portion. Therefore, stress concentration can be suppressed or prevented. Note that the radial dimension of the welded portion refers to the radial dimension after welding and before polishing, but it may also be the radial dimension after welding and polishing. Polishing is optional.

[0012] In one aspect of the invention, the fusion bond is located along the outer diameter of the weld and the diffusion bond is located along the inner diameter of the weld. In another aspect, the fusion bond is located along the inner diameter of the weld and the diffusion bond is located along the outer diameter of the weld.

[0013] When welding the ends of the base material together, a radial protrusion often forms on the surface of the weld. It is preferable that the height (protrusion amount) of the weld be low. If the protrusion at the weld becomes significant, stress concentration occurs near the protrusion when the cage revolves and is subjected to centrifugal force. In a preferred aspect of the present invention, the protrusion amount on the inner diameter surface of the weld is 0.3 mm or less, based on the inner diameter surface of the base material. This aspect alleviates stress concentration at the weld, improving durability even when the present invention is subjected to elliptical distortion due to centrifugal force caused by revolution. It should be noted here that the radial dimension of the fused joint of the present invention may be measured to include the protrusion amount of the fused joint, or may be measured after removing the protrusion of the fused joint by grinding.

[0014] In a further preferred aspect of the present invention, the outer diameter surface of the welded portion is polished, and the outer diameter surface of the welded portion has the same curvature as the outer diameter surface of the base material. According to this aspect, the cage can be guided to the outer diameter. In a further preferred aspect, the fusion bonded portion is disposed on the outer diameter side of the welded cage, and the fusion bonded portion is polished. According to this aspect, when the outer peripheral surface of the welded portion has a protrusion, the protrusion of the fusion bonded portion, which has a large amount of melted metal and results in a large protrusion, can be removed by polishing the outer diameter of the welded cage, ensuring an outer diameter guide surface for the welded cage and suppressing stress concentration at a lower cost than polishing the inner diameter. In another aspect, the inner diameter surface of the welded portion has a protrusion.

[0015] After welding, the welded cage is preferably subjected to a heat treatment such as carburizing, quenching, and tempering. In one aspect of the present invention, the welded portion is subjected to carburizing, quenching, and tempering, so that the surface hardness is 600 Hv or more and the tensile strength is 1100 MPa or more.

[0016] The roller and cage assembly of the present invention comprises the above-mentioned welded cage for a roller bearing, and rollers held in the pockets of the welded cage for a roller bearing.

[0017] The method for identifying a fused joint of the present invention involves polishing the welded cage for a roller bearing to create a cross section of the welded portion of the welded cage for a roller bearing, corroding the cross section with a nitric acid alcohol solution, taking a digital image of the cross section, and digitally processing the digital image to identify the boundary between the fused joint and other portions. This cross section may be a plane parallel to the axis of the cage, but is preferably a flat cross section intersecting the axis and intersecting the outer and inner diameter surfaces of the welded portion. Digital image processing includes, but is not limited to, image processing in the following order: grayscale conversion, histogram equalization, low-pass filtering, and binarization.

[0018] The quality confirmation method for a welded cage for a roller bearing of the present invention involves subjecting the welded cage for a roller bearing described above to a heat treatment, then conducting a tensile test to fracture the weld after the heat treatment, and confirming whether the tensile strength of the weld measured by the tensile test is within a predetermined range. The heat treatment may be, for example, carburizing, quenching, and tempering, but is not limited to this. [Effects of the Invention]

[0019] In this way, the present invention can increase the fatigue strength of a welded portion by increasing the proportion of the fused joint in the welded portion while reducing the protrusion of the welded portion surface. Furthermore, the strength of a welded portion can be controlled by defining the surface hardness and molten state as indicators that affect the strength of the welded portion. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is an overall perspective view showing a welded cage for a roller bearing according to an embodiment of the present invention; [Figure 2] FIG. 2 is an enlarged perspective view showing a welding point of the embodiment. [Figure 3] FIG. 2 is an enlarged perspective view showing a welding point of the embodiment. [Figure 4] FIG. 2 is a perspective view showing a further enlarged view of a welding portion of the embodiment. [Figure 5] 3A to 3C are schematic diagrams illustrating a typical process among the manufacturing processes of a welded cage for a roller bearing. [Figure 6] FIG. 10 is an enlarged side view showing the state in which the slant ends of the ring portion material are brought close to each other. [Figure 7] 1 is a digital image showing a welding point in the same embodiment (Example 1). [Figure 8] 10 is a digital image showing the welded portion of Comparative Example 1. [Figure 9] 10 is a digital image showing the welded portion of Comparative Example 2. [Figure 10] 10 is a digital image showing a welded portion of Example 2 of the present invention. [Figure 11] This is a digitally processed image of the image in Figure 10. [Figure 12] This is a digitally processed image of the image in Figure 11. [Figure 13] This is a digitally processed image of the image in FIG. [Figure 14] This is a digitally processed image of the image in FIG. [Figure 15] This is a digitally processed image of the image in FIG. [Figure 16] This is a digitally processed image of the image in FIG. [Figure 17] 10 is a digital image showing a welded portion of Example 3 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Fig. 1 is an overall perspective view showing a welded cage for a roller bearing according to one embodiment of the present invention. Fig. 2 is an enlarged perspective view showing the ring portion of the same embodiment, and represents the circled area II in Fig. 1. Figs. 3 and 4 are enlarged perspective views showing the ring portion of the same embodiment, with Fig. 3 representing the circled area III in Fig. 1 and Fig. 4 being a further enlargement of the central portion of Fig. 3. The welded cage for a roller bearing according to this embodiment (hereinafter also simply referred to as cage 10) comprises a pair of ring portions 11, 11 and a plurality of pillar portions 16 connecting the pair of ring portions 11, 11 together.

[0022] In the following description, the center of the cage 10 is referred to as the axis O. The cage 10 is an M-type cage. Referring to FIG. 1 , with respect to the numerous bar portions 16 of the M-type cage, the central regions of the bar portions 16 are located on the inner diameter side and extend parallel to the axis O, both end portions of the bar portions 16 are located on the outer diameter side and extend parallel to the axis O, and intermediate regions of the bar portions 16 connecting the central regions and the end portions extend obliquely with respect to the axis O. The ring portions 11 protrude from both end portions of the bar portions 16 toward the inner diameter side. As such, the ring portions 11 are inward flanges and are therefore also referred to as flange portions. In other words, when the cage 10 is cut along a plane including the axis O, the cross sections of the bar portions 16 and the pair of ring portions 11, 11 are M-shaped. In this embodiment, the inner diameter surface of the ring portions 11 is located on the inner diameter side of the central regions of the bar portions 16.

[0023] Pockets 19 are defined between the pair of ring portions 11, 11 and the circumferentially adjacent column portions 16, 16. Rollers (not shown) are disposed in each pocket 19. The shape of the rollers is not particularly limited, but may be, for example, needle rollers.

[0024] An inner diameter side roller stop portion 17 and an outer diameter side roller stop portion 18 are formed on a pocket surface 16m of each column portion 16 that defines a pocket 19. The inner diameter side roller stop portion 17 is arranged in a central region of the column portion 16. The outer diameter side roller stop portions 18 are arranged at both ends of the column portion 16. The inner diameter side and outer diameter side roller stop portions 17, 18 formed on two opposing pocket surfaces 16m, 16m that sandwich one pocket 19 hold rollers (not shown) so that they do not fall out of the pocket 19. This embodiment may also be a roller and cage combination in which multiple rollers are incorporated into a single welded cage 10 for a roller bearing.

[0025] The welded roller bearing cage 10 is incorporated, for example, into a planetary gear mechanism (not shown) that includes a sun gear, planetary gears, ring gears, and a carrier. Specifically, a roller bearing equipped with the welded roller bearing cage 10 is incorporated into the center of a planetary gear that is rotatably supported by the carrier. As the carrier rotates, the planetary gear and the welded roller bearing cage 10 revolve. Alternatively, the welded roller bearing cage 10 is incorporated into a pivot shaft (not shown) of a connecting rod of an internal combustion engine, and revolves together with the pivot shaft as the connecting rod moves.

[0026] Next, the manufacturing process of this embodiment will be described.

[0027] Figure 5 is a schematic diagram showing a typical process in the manufacturing process of a welded cage for a roller bearing. First, as shown in Figure 5(a), a strip-shaped steel plate (hereinafter referred to as strip steel, strip plate, or base material) that will serve as the material for the welded cage 10 is prepared. Examples of materials for the strip steel include cold-rolled steel plates such as JIS-SPC, JIS-SCM415, and JIS-SCM420. Alternatively, low-carbon steel such as JIS-S15C or medium-carbon steel such as JIS-S45C may also be used.

[0028] Next, as shown in FIG. 5(b), the steel strip is subjected to an M-shape forming process so that the cross section has an M-shape. Here, "M-shape" refers to plastic deformation that creates a radial step between the widthwise center of the steel strip and both side edges of the steel strip when rolled into a cylindrical shape, as described below. The M-shape forming process is carried out by sandwiching and pressing the steel strip between forming rolls consisting of an upper die with a convex center and a lower die with a concave center. At this time, the corners of both widthwise edges of the steel strip are rounded, forming chamfered portions 12.

[0029] Next, as shown in Figure 5(c), a pocketing process is performed on the steel strip having an M-shaped cross section to form pockets for holding rollers. The pocketing process is performed by preparing a punch with a punching blade and pressing the tip of the punch against the steel strip in the thickness direction to punch out the steel strip. The portions of the steel strip remaining between adjacent pockets form the column portions 16 of the cage. The portions of the steel strip remaining widthwise outward of the pockets form the ring portion material 11s of the cage.

[0030] Next, a claw forming process is carried out to form a claw-shaped outer diameter side roller stop portion 18 at the end of the column portion 16. In the claw forming process, the end of the column portion 16 is fixed and pressed from the inner diameter side using a press, thereby molding and forming the end of the column portion 16 so that the width dimension in the circumferential direction on the outer diameter side is increased.

[0031] Thereafter, a cutting process is carried out in which the strip steel is cut to a predetermined length, which is the circumferential length of the cage 10. The cutting is carried out across the pocket 19, and as a result, both sides (ring portion blank 11s) that remain are cut. The ends of the ring portion blank 11s are cut obliquely with respect to the thickness direction of the strip steel, and are formed into a slant shape when viewed in the width direction of the strip steel (see Figure 6). This is hereinafter referred to as the slant end portion 13s. A ladder-shaped cage blank is cut out by the cutting process.

[0032] Next, as shown in FIG. 5(d), a bending process is performed in which the strip steel cut to a length equivalent to one circumference is bent into a cylindrical shape. By rolling, the longitudinal direction of the strip steel is aligned with the circumferential direction of the cage, the thickness direction of the strip steel is aligned with the radial direction of the cage, the width direction of the strip steel is aligned with the axial direction of the cage, and the chamfered portion 12 is positioned on the outer diameter side. Furthermore, the bending process narrows the gap between the opposing pocket surfaces 16m, 16m in the central region of the bar portion 16. As a result, the inner diameter side of the central region of the bar portion 16 forms the inner diameter side roller stop portion 17. It should be noted here that, as shown in FIG. 6, the slant-cut ends face each other on the outer diameter side. The inclination angle of the cut surface is a predetermined value within a range of 30° to 80° relative to the longitudinal direction of the strip steel or the circumferential direction of the cage 10. The outer diameter surfaces of the ends of each bar portion 16 that are not connected in the circumferential direction are ground to form a curved surface belonging to a common cylinder.

[0033] Next, as shown in FIG. 5(e), a welding process is performed to join both ends (slant ends 13s, 13s) of the bent steel plate together. As a result, the ends of the ring material are welded together. , a ring portion 11 is created.

[0034] Next, if necessary, a first grinding step is performed to grind the outer diameter surface of the cylindrical welded cage 10 joined by welding. Here, the outer diameter surfaces of the circumferentially connected ring portions 11, 11 present a smooth cylindrical curved surface. The first grinding step can be omitted.

[0035] Thereafter, preferably, a carburizing, quenching, and tempering process may be performed as a heat treatment process. This heat treatment process improves the strength of the welded cage. When quenching the cage, rapid cooling during quenching refines the crystal grains. In the case of steel with a high carbon content, other heat treatment processes such as nitriding and through-hardening may be performed. In the case of low-carbon steel, carburizing and quenching or carbonitriding and quenching are preferred. In the case of a cage that is subjected to acceleration due to centrifugal force, as in this embodiment, reducing the weight of the cage contributes to improving fatigue strength. In this case, it is desirable to use a strip of JIS-SCM415, JIS-SCr415, high-tensile steel, or the like, and to perform carburizing, quenching, and tempering or carbonitriding and quenching and tempering.

[0036] In this way, the welded cage 10 shown in FIG. 1 is manufactured. Next, each of the welded cages 10 is A roller bearing is manufactured by fitting rollers (not shown) into the pockets 19.

[0037] The above-mentioned welding process will now be described in detail.

[0038] FIG. 6 is an enlarged side view showing a state in which a ring material 11s of one circumference is rolled and the slant ends 13s, 13s of the metal ring material 11s are brought close to each other. The ring material is the widthwise side edge of the aforementioned steel strip. In this embodiment, the slant-cut ends are faced so that the outer diameter sides are close to each other and the inner diameter sides of the ends are far from each other. Next, the facing ends are brought into contact and pressed together under pressure, and then upset welding is performed, in which a large current is passed through the steel strip, to melt and join both ends of the steel strip, thereby creating a circular cage. In this embodiment, the base material for the welded portion 13 is the steel strip.

[0039] 6, the melted regions of the slant ends 13s are larger on the outer diameter side of the end where the tapered tip portions of the slant ends 13s are close to each other. In contrast, the melted regions of the slant ends 13s are smaller on the inner diameter side of the slant ends 13s, which are farther from the tip portions.

[0040] FIG. 7 shows an image of the welded portion 13 of this embodiment (hereinafter also referred to as Example 1) captured with a digital imaging device. The image was taken after cutting the ring portion 11 at cross section VII perpendicular to the axis O in FIG. 4, immersing the cut surface in a nitric acid alcohol solution to discolor it using the following procedure, and then photographing it. The welded portion 13 was produced using the welding method shown in FIG. 6 and includes a whitish fusion welded portion 13a on one radial side and a grayish diffusion welded portion 13b on the other radial side. Because one end and the other end are joined, the circumferential center surface of the welded portion 13 is conveniently referred to as the welded surface 13c. Furthermore, the base material 15 is heated by welding. The base material adjacent to both circumferential sides of the welded portion 13 is referred to as the heat-affected zone 14.

[0041] The procedure for creating the cut surface shown in Figure 7 will be described below. First, a test solution containing nitric acid and alcohol is prepared. The test solution is nital, specifically, for example, a commercially available concentrated nitric acid-ethanol solution with a nitric acid concentration of 3% by volume. Alternatively, the test solution is prepared by diluting concentrated nitric acid of a predetermined concentration within the range of 60 to 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 predetermined concentration in which the ratio of concentrated nitric acid to the total is within the range of 3 to 10% by volume. The alcohol in the test solution may be methanol. Alternatively, the test solution may be a picric acid-alcohol solution.

[0042] Next, when room temperature nital is used as the test liquid, the cross section VII (Fig. 4) of the retainer 10 is immersed in the test liquid, and after 3 to 5 seconds, the cross section VII is removed from the test liquid and the shape of the weld is determined based on the color change of the cross section VII. When room temperature picric acid alcohol solution is used, it is desirable to immerse the cross section VII of the retainer 10 for 30 minutes.

[0043] The fusion bonded portion 13a is formed by the complete melting of the base material during welding. In the fusion bonded portion 13a, the carbides of the base material dissolve into the matrix phase. Therefore, when the cross section of the fusion bonded portion is corroded with a nitric acid alcohol solution, it appears whiter than incompletely melted portions such as the diffusion bonded portion 13b and the heat-affected zone 14. While such fusion bonds exhibit high joint strength, the molten metal tends to overflow, causing the surface of the weld to bulge significantly. This causes stress concentration near the bulge, reducing fatigue strength.

[0044] The diffusion-bonded portion 13b is formed by butting the base material without melting it during welding. In the diffusion-bonded portion 13b, the carbides of the base material do not dissolve into the matrix phase, and the metal atoms diffuse to form a bond. Therefore, when the cross section of the diffusion-bonded portion is etched with a nitric acid alcohol solution, it takes on the same color as the heat-affected zone, making it easy to distinguish from the molten metal. Compared to fusion bonding, this type of diffusion bonding has a lower bond strength, but because the metal does not melt, it is less likely to protrude, and the surface of the weld tends to be less raised.

[0045] The heat-affected zone 14 is a zone in which the composition of the base material has changed due to the heating caused by welding.

[0046] As a modified example (not shown), in the case of a slant cut in which the outer diameter sides of the end portions are farther apart and the inner diameter sides of the end portions are closer to each other, the welding points have the opposite shape to that of Figure 7. That is, the whitish fused joint 13a is located on the inner diameter side, and the grayish diffusion joint 13b is located on the outer diameter side.

[0047] Returning to FIG. 7, in this embodiment, the white fusion bonded portion 13a is located on the outer diameter side, and the gray diffusion bonded portion 13b is located on the inner diameter side. The fusion bonded portion 13a is an isosceles triangle whose circumferential dimension increases toward the outer diameter surface 11d of the ring portion 11. The center line of this isosceles triangle coincides with the bonding surface 13c. If 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 taken as 100%, the radial dimension La of the diffusion bonded portion 13b at the bonding surface 13c is in the range of 70% to 95%. Furthermore, the radial dimension Lr-La of the diffusion bonded portion 13b at the bonding surface 13c is in the range of 30% to 5%.

[0048] In this embodiment, the welded portion 13 has a fusion length ratio La / Lr in the range of 70% to 95%, which reduces swelling at the welded portion 13, prevents stress concentration, and ensures fatigue strength. Furthermore, by having this range, the present embodiment can contain a sufficient amount of molten metal and ensure the necessary joint strength.

[0049] To facilitate understanding of the above-described first embodiment, a comparative example will be described.

[0050] 8 is a digital image showing the welded portion of Comparative Example 1. In the ring portion 111 of Comparative Example 1, the diffusion-bonded portion 13b occupies the entire bonding surface 13c, extending from the outer diameter surface 11d to the inner diameter surface 11c. In other words, the welded portion 13 does not include a fusion-bonded portion (fusion length ratio La / Lr = 0%). Furthermore, the diffusion-bonded portion 13b bulges on the outer diameter surface 11d but does not bulge on the inner diameter surface 11c.

[0051] FIG. 9 is a digital image showing the welded portion of Comparative Example 2. In the ring portion 112 of Comparative Example 1, the fused joint 13a occupies the entire joining surface 13c, extending from the outer diameter surface 11d to the inner diameter surface 11c. The welded portion 13 does not include a diffusion-welded portion (fusion length ratio La / Lr = 100%). The circumferential dimension of the fused joint 13a increases toward the outer diameter, so that its shape when viewed from the axial direction is a trapezoid with a foot. Furthermore, the fused joint 13a protrudes from the outer diameter surface 11d and the inner diameter surface 11c.

[0052] Fatigue strength tests were conducted on the welded portion 13 of the specimens of Example 1, Comparative Example 1, and Comparative Example 2. To prevent stress concentration due to the protrusion, each specimen was prepared so that the protrusion of the inner diameter surface 11c relative to the circular arc constituting the inner diameter of the ring portion was 0.3 mm or less. Furthermore, fatigue strength tests were also conducted on these base materials to measure their fatigue limits. The fatigue limit refers to the stress at which the specimen does not break even when subjected to a repeated load (a pulsating bending load in this test) of 10 million or more cycles, and is determined from the repeated load. The fatigue limit was used as an index of fatigue strength. These test specimens were M-shaped welded cages with an outer diameter of 22 mm, an inner diameter of 14 mm, and a width of 14 mm. The axial dimension of the ring portion (base material plate thickness) was 0.7 mm. The material was JIS-SCM415, and carburized, quenched, and tempered after welding. After carburizing, quenching and tempering, the depth from the surface where the hardness reaches 513Hv (effective hardened layer depth) is 0.06mm, and the surface hardness is approximately 600Hv. The measurement results for the ring part are shown in Table 1.

[0053] [Table 1]

[0054] 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. The fatigue limit of the base material was 837 MPa. From the above, it was found that Example 1 can achieve a fatigue limit equal to or greater than that of the base material.

[0055] Next, a method for determining the fusion length ratio La / Lr of the welded portion 13 by image processing a digital image of the welded portion 13 will be described.

[0056] FIG. 10 is a digital image showing the welded portion 13 of Example 2 of this embodiment, which was taken by cutting the ring portion 11 at cross section VII perpendicular to the axis O in FIG. 4, immersing the cut surface in a nitric acid alcohol solution under predetermined conditions to discolor it, and then photographing it.

[0057] To identify the fused joint in Figure 10, image processing was performed using the image processing software ImageJ. Figure 11 is an image converted to 8-bit grayscale from the image in Figure 10. Figure 12 is an enlarged image of the center of the image in Figure 11. Figure 13 is an image obtained by histogram equalization of the image in Figure 12. Figure 14 is an image obtained by applying a low-pass filter to the spatial frequency of the image in Figure 13 to remove high-frequency noise. This low-pass filter was created by setting the low-frequency component to a range of 1000 pixels and the high-frequency component to a range of 20 pixels using ImageJ's band-pass filter. Figure 15 is an image obtained by histogram equalization of the image in Figure 14. Figure 16 is an image obtained by binarizing the image in Figure 15, with the black threshold set to 20 and the white threshold set to 180 in ImageJ's threshold settings. In this way, an image (Figure 16) was obtained in which the space outside the fused joint 13a and ring portion 11 was white and the rest was black. Then, the radial dimension La of the fusion joint 13a and the radial dimension Lr of the welded portion 13 were measured.

[0058] The image of Alternative Example 3 (FIG. 17) was obtained using the above-described procedure. The radial dimension La of the fusion joint 13a and the radial dimension Lr of the welded portion 13 were then measured. In Alternative Example 3, the outer diameter surface of the ring portion 11 was ground into an arc shape that conformed to the outer diameter surface of the ring portion. In contrast, in Example 2, as shown in FIG. 16, the outer peripheral surface of the welded portion is raised relative to the outer diameter surface of the ring portion 11.

[0059] In Examples 2 and 3, carburizing, quenching, and tempering were performed after welding. Because the carburized portion along the surface of the ring portion 11 is black, the white fusion bonded portion 13a appears smaller in Figures 16 and 17. However, in Examples 2 and 3, melting begins from the outer diameter surface, so the black carburized portion on the outer diameter surface is the fusion region. Therefore, in Figures 16 and 17, the radial dimension La of the fusion bonded portion 13a can be measured starting from the outer diameter surface of the ring portion 11.

[0060] Next, a method for detecting welding defects will be described.

[0061] As test specimens, welded cages with a fusion length ratio La / Lr = 0% were prepared without carburizing, quenching, and tempering, and the surface hardness, tensile strength, and alternate fatigue limit were measured at the welded area and the rest of the base material. Also, as test specimens, welded cages with a fusion length ratio La / Lr = 70% were prepared with carburizing, quenching, and tempering, and the surface hardness, tensile strength, and alternate fatigue limit were measured at the welded area. Also, as test specimens, welded cages with a fusion length ratio La / Lr = 100% were prepared with carburizing, quenching, and tempering, and the surface hardness, tensile strength, and alternate fatigue limit were measured at the welded area. The measurement results are shown in Table 2.

[0062] [Table 2]

[0063] Referring to Table 2, after welding and before carburizing, quenching, and tempering, the surface hardness of the welded area (413 Hv) is 2.3 times that of the base material (180 Hv). This is because when the ends of the base material are welded together and left in the air, the surface of the weld cools and hardens. After carburizing, quenching, and tempering, the welded area (605 Hv) becomes equivalent to the base material (603 Hv).

[0064] The tensile strength for the fused states of the welded portion (when the fusion length ratio La / Lr was 0%, 70%, and 100%, and for the base material not affected by heat), as well as the tensile strength before and after carburizing, quenching, and tempering, will be described. For the tensile test, referring to FIG. 7 , a region including the welded portion 13 and the base material 15 on both sides in the circumferential direction was cut out from the ring portion 11, and a tensile load was applied to the cut-out test piece in a direction perpendicular to the joining surface 13c to measure the tensile load at the welded portion. Furthermore, only the base material 15 was cut out, and the tensile load of the base material 15 was measured. The tensile strength was determined by dividing the maximum tensile load until the test piece broke by the cross-sectional area of ​​the unwelded portion of the ring portion (i.e., the base material). The cross-sectional area was the area of ​​a flat cut surface perpendicular to the circumferential direction of the ring portion 11.

[0065] After welding but before carburizing, quenching, and tempering, the test piece with a fusion length ratio La / Lr = 0% had a higher tensile strength at the welded area (555 MPa) than the tensile strength of the base material (466 MPa). This is thought to be because the surface hardness of the welded area (413 Hv) was higher than that of the base material (180 Hv). - On the other hand, in the case of a test piece with a fusion length ratio La / Lr=0% after carburizing, quenching, and tempering, the surface hardness of the welded area (605Hv) is equivalent to that of the base material (603Hv), but the tensile strength of the welded area (893MPa) is lower than that of the base material (1185MPa). Therefore, even if a tensile test is performed on a test piece before carburizing, quenching, and tempering, it is not possible to detect a decrease in the fatigue limit of a welded cage with a fusion length ratio La / Lr=0%.

[0066] From Table 2, it can be seen that for test pieces with a fusion length ratio La / Lr = 0% after carburizing, quenching and tempering, the surface hardness of the welded area (605Hv) is equivalent to that of the base material (603Hv). With regard to tensile strength, the welded area with a fusion length ratio La / Lr = 0% is smaller than that of the base material, and the welded area with a fusion length ratio La / Lr = 100% is larger than that of the base material. The reversed fatigue limit shows the same trend as the tensile strength.

[0067] From Table 2, in order to detect a decrease in fatigue limit by tensile testing, it is preferable that the surface hardness (Vickers hardness) of the welded portion is 90% or more and 110% or less of the surface hardness (Vickers hardness) of the base material.

[0068] Regarding heat treatment, examples of heat treatment include through hardening, carburizing and quenching, carbonitriding, induction hardening, and laser hardening. The welded cage of this embodiment may be subjected to heat treatment other than carburizing and quenching. To increase the bending fatigue strength, carburizing and quenching or carbonitriding are preferably performed, and the surface hardness of the welded cage is preferably 600 Hv or more.

[0069] In order to prevent the inner diameter surface 11c (or the outer diameter surface 11d) of the ring portion from swelling up at the welding point, it is necessary to prevent the amount of molten metal from becoming excessively large. For this reason, in this embodiment, it is desirable that the molten length ratio La / Lr is 95% or less.

[0070] To raise the fatigue limit of the welded area to that of the base material, it is desirable that the tensile strength of the welded area be equivalent to that of the base material, more preferably 1100 MPa or more. It is also desirable to subject the welded cage to heat treatment such as carburizing, quenching, and tempering to raise the surface hardness of the welded cage (welded area and base material) to 600 Hv or more.

[0071] In particular, the welded area with a fusion length ratio La / Lr = 70% is equivalent to the base material, and the reverse fatigue limit is greater than the welded areas with a fusion length ratio of 0% and 100%. This indicates that the fatigue limit of the welded area with a fusion length ratio La / Lr = 70% is superior to that of the welded areas with a fusion length ratio of 0% and 100%.

[0072] Although the embodiments of the present invention have been described above with reference to the drawings, the present invention is not limited to the illustrated embodiments. Various modifications and variations can be made to the illustrated embodiments within the same scope as the present invention or within an equivalent scope. For example, some components may be extracted from one embodiment described above, and other components may be extracted from another embodiment described above, and these extracted components may be combined. [Industrial Applicability]

[0073] The present invention can be advantageously used at the center of rotation of a rolling bearing that revolves while rotating on its own axis. [Explanation of symbols]

[0074] 10 Welded cage for roller bearing, 11,111,112 Ring part, 11c inner diameter surface, 11d outer diameter surface, 11s ring material, 13 welding point, 13a fusion joint, 13b diffusion joint, 13c joint surface, 13s slant end, 14 heat affected zone, 15 Base material, 16 Column part, 16m Pocket surface, 17,18 Roller stopper, 19 Pocket, La: Radial dimension of fusion joint, Lr: Radial dimension of welded part, La / Lr melt length ratio, O axis.

Claims

1. A welded cage includes a base material extending in a circumferential direction and welded portions formed by joining one end and the other end of the base material together by welding, and holds rollers in a plurality of pockets formed at intervals in the circumferential direction in the base material, the welded portion includes a fusion welded portion on one side in the radial direction and a diffusion welded portion on the other side in the radial direction, The fusion joint is formed by completely melting and weld-joining the base materials, The diffusion bonded portion is formed by joining the base materials by butting them together without melting them in a welding process, A welded cage for a roller bearing, wherein the radial dimension of the fusion joint is 70% or more and 95% or less of the radial dimension of the welded portion.

2. 2. The welded cage for a roller bearing according to claim 1, wherein the fusion weld is located along an outer diameter surface of the welded portion, and the diffusion weld is located along an inner diameter surface of the welded portion.

3. 3. The welded cage for a roller bearing according to claim 1, wherein the amount of rise of the inner diameter surface of the welded portion is 0.3 mm or less with respect to the inner diameter surface of the base material.

4. 4. The welded cage for a roller bearing according to claim 1, wherein the outer diameter surface of the welded portion is polished, and the outer diameter surface of the welded portion has the same curvature as the outer diameter surface of the base material.

5. 5. The welded cage for a roller bearing according to claim 1, wherein the welded portion is subjected to carburizing, quenching and tempering treatment, so that the surface hardness is 600 Hv or more and the tensile strength is 1100 MPa or more.

6. A roller and cage assembly comprising the welded cage for a roller bearing according to any one of claims 1 to 5 and rollers held in the pockets.

7. a cross section is formed at the welded portion by polishing the welded cage for a roller bearing according to any one of claims 1 to 4; taking a digital image of the cross section after etching it with a nitric acid alcohol solution; The method for identifying a fused joint includes digitally processing the digital image to identify the boundary between the fused joint and other portions.

8. The welded cage for a roller bearing according to any one of claims 1 to 4 is subjected to a heat treatment, A quality confirmation method for a welded cage for a roller bearing, comprising: performing a tensile test that fractures the welded portion after the heat treatment; and confirming whether the tensile strength of the welded portion measured by the tensile test is within a predetermined range.

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