Method of inspecting welded cage for roller bearing, roller with cage, and welded cage for bearing

Abstract

To provide a welding holder with more excellent fatigue strength than before.SOLUTION: A welding holder comprises a pair of ring parts 11, 11 and a plurality of pillar parts connecting the pair of ring pars to each other. The ring part 11 includes a melt joint part 13 in which a metal material having a length of one round is rolled and both ends of the metal material are melted and joined, where a circumferential dimension of the melt joint part 13 gradually increases from the innermost diameter side portion of the melt joint part 13 to the outermost diameter side portion through a radial intermediate portion.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a rolling bearing, and more particularly to a roller bearing in which the rolling elements are cylindrical. [Background technology]

[0002] Welded cages are known as cages that are incorporated into roller bearings to maintain the spacing between rollers. Welded cages are made by preparing a metal material such as a strip-shaped steel plate in a length that is the circumference of the cage, rolling it, and joining both ends by welding (hereinafter, also referred to as welded parts or welded locations). Examples of such welded cages include those disclosed in JP 2013-160263 A (Patent Document 1), JP 2007-270967 A (Patent Document 2), and JP 2013-108587 A (Patent Document 3).

[0003] In Patent Document 1, a pair of annular portions are provided with notches to prevent the load from concentrating on the welded portion, making it difficult 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] JP 2013-160263 A [Patent Document 2] JP 2007-270967 A [Patent Document 3] JP 2013-108587 A Summary of the Invention [Problem to be solved by the invention]

[0005] In roller bearings that rotatably support parts that are subjected to large accelerations from various directions during revolution, such as planetary gear sets incorporated in automatic transmissions of automobiles and connecting rods in internal combustion engines, the cage is subjected to external forces and therefore needs to be sufficiently strong.

[0006] However, the welded cage in Patent Document 1 has a notch, which causes stress concentration and raises concerns about insufficient fatigue strength. Also, the welded cage in Patent Document 2 has a smaller cross-sectional area at the flat surfaces, which means that its fatigue strength is inferior to other parts that do not have flat portions.

[0007] Furthermore, the welded cage in Patent Document 3 includes many welds, which are weaker than the base material, and so there is concern that the cage may lack strength. In addition to the stress concentration cited in the prior art, welds have the problem that the grains in the welds become coarse due to slow cooling of the molten metal, resulting in insufficient fatigue strength.

[0008] In view of the above-mentioned circumstances, an object of the present invention is to provide a welded cage which improves the fatigue strength of the weld itself without impairing the fatigue strength of the base material, and which has superior fatigue strength to conventional ones and is suitable for roller bearings which are subjected to acceleration due to centrifugal force during revolution. [Means for solving the problem]

[0009] For this purpose, the welded cage for a roller bearing according to the present invention comprises a pair of ring portions and a number of column portions connecting the pair of ring portions, and the ring portions include a fused joint formed by rolling a metal material of one circumference length and melting both ends of the metal material to join them, and is characterized in that the circumferential dimension of the fused joint gradually increases or gradually decreases from the innermost portion of the fused joint through a radially intermediate portion to the outermost portion, or gradually decreases from the innermost portion to the radially intermediate portion and gradually increases from the radially intermediate portion to the outermost portion.

[0010] According to the present invention, when the fusion joint solidifies, heat transfer is promoted toward the larger circumferential dimension, and the thermal gradient can be made larger than in the past. Therefore, the size of the crystal grains can be reduced, and fatigue strength is improved. Regarding the circumferential dimension of the fusion joint, the circumferential dimension of the largest part is preferably at least twice the circumferential dimension of the smallest part. This promotes radial heat removal from the small part to the large part.

[0011] In one aspect of the present invention, the ring portion protrudes in the inner diameter direction from the end of the column portion. According to this aspect, the ring portion has a flange shape, so that the strength is increased, and even when the welded cage revolves and acceleration is applied from various directions, the durability is further improved. The welded cage of the present invention is, for example, an M-type cage. In another aspect, the circumferential dimension of the ring portion is not particularly limited. In a preferred aspect, when the circumferential dimension gradually increases from the innermost part to the outermost part, the fusion joint is provided from the outer diameter surface to the inner diameter surface of the ring portion. And, regarding the circumferential dimension Ld along the outer diameter surface of the fusion joint and the circumferential dimension Lb along the inner diameter surface of the fusion joint, the circumferential dimension Ld is at least twice the circumferential dimension Lb. According to this aspect, in the fusion joint, heat removal to the outer diameter side is promoted, crystal grains are refined, and fatigue strength is improved.

[0012] In one aspect of the present invention, the fusion weld is provided on the outer diameter surface of the ring portion, and the ring portion further includes a diffusion weld on the inner diameter side of the fusion weld, when the diameter gradually increases from the innermost portion to the outermost portion. In another aspect of the present invention, the fusion weld is continuous from the outer diameter surface to the inner diameter surface of the ring portion. The diffusion weld refers to a portion where unmelted metal materials are joined together.

[0013] In another aspect of the present invention, the fusion bond is provided on the inner diameter surface of the ring portion where the fusion bond becomes gradually smaller from the innermost portion to the outermost portion, and the ring portion further includes a diffusion bond on the outer diameter side of the fusion bond.

[0014] In one aspect of the present invention, the molten joint gradually becomes smaller from the innermost portion to the radially intermediate portion and gradually becomes larger from the radially intermediate portion to the outermost portion, and is provided on the inner diameter surface and the outer diameter surface of the ring portion, respectively, and the ring portion further includes a diffusion joint between the molten joint on the inner diameter side and the molten joint on the outer diameter side.

[0015] In a preferred aspect of the invention, the average grain size of the prior austenite grains in the fusion weld is equal to or less than the average grain size of the prior austenite grains in the portion of the ring portion not thermally affected by the fusion weld.

[0016] A roller and cage assembly of the present invention comprises the above-mentioned welded cage for a roller bearing, and rollers assembled into the welded cage for a roller bearing.

[0017] The method for inspecting a welded cage of the present invention includes the steps of grinding the welded cage to expose a cross section including a welded portion, preparing an inspection liquid in which concentrated nitric acid is dissolved in an alcohol solvent, immersing the cross section of the welded portion in the inspection liquid, removing the cross section from the inspection liquid after a time period of 3 to 5 seconds, and judging the shape of the welded portion based on the color change of the cross section. The concentrated nitric acid is a nitric acid solution having a predetermined concentration in the range of 60 to 62% by weight. In another embodiment, the inspection liquid may be one in which picric acid is dissolved in an alcohol solvent. Effect of the Invention

[0018] In this way, the present invention improves the fatigue strength of the welded portion, thereby improving durability even when the present invention is attached to a revolving shaft and is subjected to accelerations from various directions. [Brief description of the drawings]

[0019] [Figure 1] 1 is an overall perspective view showing a welded cage for a roller bearing according to an embodiment of the present invention; [Diagram 2] FIG. 4 is an enlarged perspective view showing a welding point of the embodiment. [Diagram 3]FIG. 4 is an enlarged perspective view showing a welding point of the embodiment. [Figure 4] FIG. 4 is a further enlarged perspective view showing a welding point of the embodiment. [Diagram 5] 3A to 3C are schematic diagrams illustrating typical steps in a manufacturing process for a welded cage for a roller bearing. [Figure 6] FIG. 11 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 photograph showing a fused joint immersed in an inspection solution for a predetermined period of time. [Figure 8] FIG. 2 is a cross-sectional view showing a fusion joint of the present embodiment. [Figure 9] FIG. 11 is a cross-sectional view showing a fusion joint for comparison. [Figure 10] FIG. 4 is a cross-sectional view showing a fusion joint according to a first modified example of the present invention. [Figure 11] FIG. 11 is a cross-sectional view showing another embodiment of the present invention. [Figure 12] FIG. 11 is a cross-sectional view showing a fusion joint according to a second modified example of the present invention. [Figure 13] FIG. 11 is a cross-sectional view showing yet another embodiment of the present invention. [Figure 14] 1 is a photograph showing a cross section of an inspected fusion joint of a test specimen according to the present invention. [Figure 15] 13 is a photograph showing a cross section of an inspected fusion joint of another test specimen according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] 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 roller bearings according to one embodiment of the present invention. Fig. 2 is an enlarged perspective view showing a ring portion of the same embodiment, and shows the circled portion II in Fig. 1. Figs. 3 and 4 are enlarged perspective views showing the ring portion of the same embodiment, with Fig. 3 showing the circled portion III in Fig. 1 and Fig. 4 showing a further enlargement of the central portion of Fig. 3. The welded cage for roller bearings of 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.

[0021] 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. With respect to the multiple columnar portions 16, the central regions of the columnar portions 16 are located on the inner diameter side and extend parallel to the axis O, both ends of the columnar portions 16 are located on the outer diameter side and extend parallel to the axis O, and the intermediate regions of the columnar portions 16 that connect the central regions and the ends extend obliquely with respect to the axis O. The ring portions 11 protrude from both ends of the columnar portions 16 to the inner diameter side. As described above, 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 on a plane including the axis O, the cross sections of the columnar portions 16 and the pair of ring portions 11, 11 are M-shaped. The inner diameter surface of the ring portions 11 in this embodiment is located on the inner diameter side of the central regions of the columnar portions 16.

[0022] A pocket 19 is defined between the pair of ring portions 11, 11 and the circumferentially adjacent column portions 16, 16. A roller (not shown) is disposed in each pocket 19. The shape of the roller is not particularly limited, but may be, for example, a needle roller.

[0023] An inner diameter side roller stopper portion 17 and an outer diameter side roller stopper portion 18 are formed on a pocket surface 16m of each column portion 16 that defines a pocket 19. The inner diameter side roller stopper portion 17 is arranged in a central region of the column portion 16. The outer diameter side roller stopper portions 18 are arranged at both ends of the column portion 16. The inner diameter side and outer diameter side roller stopper portions 17, 18 formed on two pocket surfaces 16m, 16m facing each other across one pocket 19 hold the rollers so that they do not fall out of the pocket 19. This embodiment may be a roller with cage in which a plurality of rollers are incorporated into one welded cage 10 for a roller bearing.

[0024] The welded roller bearing cage 10 is incorporated, for example, into a planetary gear mechanism that includes a sun gear, planetary gears, a ring gear, and a carrier. Specifically, a roller bearing that includes 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.

[0025] Next, the manufacturing process of this embodiment will be described.

[0026] FIG. 5 is a schematic diagram showing a typical process among the manufacturing processes for a welded cage for a roller bearing.

[0027] First, as shown in Fig. 5(a), a strip-shaped steel plate (hereinafter referred to as strip steel or strip plate) is prepared as the material for the welded retainer 10. The material of the strip steel may be cold-rolled steel plate, low carbon steel such as JIS-S15C, or medium carbon steel such as JIS-S45C. Furthermore, in order to refine the crystal grains of the fusion joint 13 described below, it is desirable to use a steel material containing alloy elements that form carbides and refine the crystal grains by the pinning effect.

[0028] Next, as shown in FIG. 5(b), the strip steel is subjected to an M-shape forming process so that the cross section has an M-shape. Here, M-shape refers to plastic deformation so that the widthwise center of the strip steel and both side edges of the strip steel have steps in the radial direction when rolled into a cylindrical shape as described below. The M-shape forming process is performed by sandwiching and pressing the strip steel 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 strip steel are rounded to form chamfered portions 12.

[0029] Next, as shown in Fig. 5(c), a pocket punching process is performed on the steel strip having an M-shaped cross section to form pockets for holding rollers. The pocket punching 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 outside the pockets form the ring portion material 11s of the cage.

[0030] Next, a claw forming process is performed to form a claw-shaped outer diameter side roller stop portion 18 on 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 by a press, thereby molding and forming the column portion 16 so as to expand the circumferential width dimension on the outer diameter side of the end of the column portion 16.

[0031] Thereafter, a cutting process is carried out in which the strip 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 the resulting both sides (ring portion blank 11s) that remain are cut off. The end of the ring portion blank 11s is cut obliquely with respect to the thickness direction of the strip, and is formed into a slant shape when viewed in the width direction of the strip (see FIG. 6). This is hereinafter referred to as the slant end 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 so as to be rounded. By being rounded, the longitudinal direction of the strip steel becomes the circumferential direction of the cage, the thickness direction of the strip steel becomes the radial direction of the cage, the width direction of the strip steel becomes the axial direction of the cage, and the chamfered portion 12 is on the outer diameter side. Furthermore, by the bending process, the interval between the mutually opposing pocket surfaces 16m, 16m becomes narrower 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. Here, it should be noted 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 included in the range of 30° to 80° with respect to the longitudinal direction of the strip steel or the circumferential direction of the cage 10. The outer diameter surfaces of the ends of the bar portions 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 to each other. As a result, the ends of the ring material are welded to each other, and the ring 11 is formed.

[0034] Next, 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 ring portions 11, 11 continuing in the circumferential direction present a smooth cylindrical curved surface.

[0035] Thereafter, a carburizing, quenching and tempering process may be performed as an optional heat treatment process. This heat treatment process improves the strength of the welded cage. When the cage is quenched, the crystal grains are refined by rapid cooling during quenching. In the case of steel with a high carbon content, other heat treatment processes such as nitriding and deep quenching may be performed. In the case of low carbon steel, carburizing and quenching or carbonitriding and quenching are preferable. In the case of a cage that is subjected to particularly high acceleration as in this embodiment, reducing the weight of the cage contributes to improving fatigue strength. In this case, it is preferable 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 manner, the welded cage 10 shown in Fig. 1 is manufactured. Next, rollers (not shown) are fitted into each pocket 19 of the welded cage 10 to manufacture a roller bearing.

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

[0038] FIG. 6 is an enlarged side view showing a state where one circumference of the ring material 11s 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 width direction side edge of the above-mentioned steel strip. In this embodiment, the slant cut ends are faced so that the outer diameter sides are brought close to each other and the inner diameter sides of the ends are made far from each other. Next, the facing ends are brought into contact with each other, and pressed against each other under pressure, and then upset welding is performed by passing a large current through the steel strip to melt and join both ends of the steel strip, thereby creating a circular retainer. Such a welded portion is called a fusion joint 13. In this embodiment, the fusion joint 13 is made of steel strip as a base material.

[0039] 6, the melted regions of the slant ends 13s are larger on the outer diameter side of the ends 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 away from the tip portions.

[0040] FIG. 7 is a photograph showing the fusion joint immersed in the test liquid for a predetermined time, and FIG. 8 is a cross-sectional view showing the fusion joint 13. FIG. 7 and FIG. 8 show cross section VII (FIG. 2, FIG. 4) perpendicular to the axis O. As shown by the arrow R in FIG. 8, when the fusion joint 13 solidifies, heat is mainly dissipated toward the outer diameter surface with a wide width (circumferential dimension Ld). In other words, the arrow R represents the direction of the heat transfer gradient, which is directed toward the outer diameter direction. Accordingly, as shown by the arrow S, the crystal grains grow at an inclination so as to be directed toward the circumferential center of the fusion joint 13 and toward the outer diameter direction. In order to facilitate understanding of this embodiment, FIG. 8 shows the shape of the crystal grains in a schematic manner. The heat transfer gradient of this embodiment shown by the arrow R is steeper than the transfer gradient of the comparative example shown in FIG. 9 described later, that is, the heat transfer is quicker, and the crystal grains are less likely to become coarse.

[0041] As shown in FIGS. 3 and 4, chamfers 12 disappear at the fusion joint 13 when the welding process is completed. The reason for this is that when the molten base material at one end and the molten base material at the other end are joined, the molten metal that has overflowed due to the pressure applied during welding flows into the chamfer 12 and fills the chamfer 12 at that location.

[0042] The fusion joint 13 is trapezoidal when viewed in the direction of axis O. In this embodiment, the circumferential dimension Lc is set to be 1.2 times or more of the circumferential dimension Lb, and the circumferential dimension Ld is set to be 2 times or more of the circumferential dimension Lb (Lc > 1.2Lb and Ld > 2Lb) so that the heat transfer gradient becomes large. Here, preferably, the circumferential dimension Ld is 3 times or more of the circumferential dimension Lb. Also, although the larger circumferential dimension Ld is not particularly limited, the upper limit value is equal to or less than the diameter dimension of the ring portion 11. This is because it is preferable that the volume of the fusion joint is small.

[0043] Referring to FIG. 8, the arc-shaped reference line N represents the radial center of the ring portion 11. The circumferential dimension Lc of the fusion joint 13 at the reference line N satisfies the relationship of Lb < Lc < Ld. That is, the circumferential dimension of the fusion joint 13 gradually increases from the inner diameter side to the outer diameter side.

[0044] In this embodiment, from the viewpoint of fatigue limit, it is desirable that the average grain size number of the prior austenite crystal grains in the fusion joint is equal to or more than that of the base material, and more preferably 8 or more according to the definition of JIS G 0551, that is, the average crystal grain diameter is 22 μm or less. Here, the base material refers to the strip steel.

[0045] Heat affected zones 14, 14 are formed on both circumferential sides of the fusion joint 13. The heat affected zones 14, 14 are regions that are heated to a temperature at which the strip steel does not melt by receiving heat from the fusion joint 13 and in which a change in the structure occurs. The boundary between the fusion joint 13 and the heat affected zone 14 is indicated by a two-dot chain line. The rest of the ring portion 11 corresponds to the non-heat affected zone 15. The boundary between the heat affected zone 14 and the non-heat affected zone 15 is indicated by a two-dot chain line.

[0046] According to this embodiment, the circumferential dimension of the fusion joint 13 gradually increases from the inner diameter side toward the outer diameter side. As a result, the amount of molten metal in the radially intermediate portion including the reference line N is less than the amount of molten metal located along the outer diameter surface, the inner diameter surface, or both of the ring portion 11. In this way, cooling proceeds from the side with less molten metal, so that the molten metal in the radially intermediate portion is more easily cooled, and coarsening of crystal grains can be prevented.

[0047] In this embodiment, in order to prevent welding defects due to a shortage of molten metal, a portion with a large amount of molten metal is arranged on the outer diameter surface of ring portion 11, or on the inner diameter surface of ring portion 11, or on both. This portion is adjacent to the outer diameter surface or the inner diameter surface of ring portion 11 and is easily cooled by dissipating heat into the atmosphere, so that the crystal grains are less likely to become coarse.

[0048] According to this embodiment, in the process of solidifying the molten metal, heat transfer in the outer diameter direction is promoted, making it easier to cool, and the crystal grains are made finer than before, improving the fatigue strength of the welded portion.

[0049] In order to deepen understanding of the effects of this embodiment, a comparative example will be described.

[0050] FIG. 9 is a cross-sectional view showing a fusion joint of the comparative example, and shows the fusion joint 103 in the ring portion 11. The circumferential dimension Lb of the inner diameter surface of the fusion joint 103, the circumferential dimension Lc of the middle portion, and the circumferential dimension Ld of the outer diameter surface are the same or approximately the same. In addition, in the comparative example, the circumferential dimensions Lb, Lc, and Ld are sufficiently secured so that no voids or poor joints are generated. The fusion joint of the comparative example takes time to solidify, and is difficult to cool, especially in the middle portion in the radial direction through which the reference line N passes. That is, the fusion joint of the comparative example has a gentler temperature gradient than the present embodiment, and the crystal grains become coarse. For this reason, there is room for improvement in fatigue strength.

[0051] Next, a method for inspecting the fusion joint will be described.

[0052] First, the axial end of the ring portion of the cage is ground to expose cross section VII (FIGS. 2 and 4). Cross section VII may be a plane oriented in the direction of axis O, and may be substantially perpendicular to axis O. The test specimen is of course after the welding step shown in FIG. 5(e) has been completed, but it is preferable that the test specimen is before heat treatment such as quenching and tempering.

[0053] Next, a test liquid containing nitric acid and alcohol is prepared. The test liquid is nital, specifically, for example, a commercially available nitric acid ethanol solution with a concentrated nitric acid concentration of 3% by volume. Alternatively, the test liquid is prepared by diluting concentrated nitric acid of a predetermined concentration in the range of 60 to 62% by weight with ethanol of a concentration of 99.5% by weight or volume. Alternatively, the test liquid is a nitric acid ethanol solution of a predetermined concentration in which the ratio of concentrated nitric acid to the total is in the range of 3 to 10% by volume. The alcohol in the test liquid may be methanol. Alternatively, the test liquid may be a picric acid alcohol solution.

[0054] Next, when room temperature nital is used as the inspection liquid, the cross section VII of the retainer 10 is immersed in the inspection liquid, and after 3 to 5 seconds, the cross section VII is removed from the inspection 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 preferable to immerse the cross section VII of the retainer 10 for 30 minutes.

[0055] Fig. 14 is a photograph showing the hue obtained by immersing the cross section of the fusion joint of a test specimen according to the present invention in an inspection liquid. The test specimen in Fig. 14 is a test specimen for which the welding process has been completed and which has not yet been heat-treated. In the test specimen before heat treatment shown in Fig. 14, the fusion joint 13 and the base material not affected by heat (hereinafter referred to as non-heat-affected zone 15) turn white, and the heat-affected zone 14 appears dark in color. According to the inspection method of this embodiment, the shape of the fusion joint 13 can be clearly seen.

[0056] Here, it should be noted that among the base materials, the heat-affected zone 14 appears darker than the rest of the base material that has not been affected by heat (non-heat-affected zone 15). When the dipping time exceeds 5 seconds, the entire fusion joint 13, heat-affected zone 14, and non-heat-affected zone 15 become dark, making it difficult to identify the shape of the fusion joint 13. Also, when the dipping time is less than 3 seconds, the hue of the heat-affected zone 14 does not change much, and the color difference between the fusion joint 13 and the heat-affected zone 14 is not prominent, making it difficult to identify the shape of the fusion joint 13.

[0057] The inspection results of another test piece according to the present invention are shown in FIG. 15. The test piece of the present invention shown in FIG. 15 has been heat-treated. As shown in FIG. 15, in the heat-treated test piece, the color difference between the fusion joint 13 and the heat-affected zone 14 is significant, but almost no color difference is seen between the heat-affected zone 14 and the non-heat-affected zone 15.

[0058] Next, a modified example of the present invention will be described. FIG. 10 is a cross-sectional view showing a fusion joint according to a modified example of the present invention, and like the cross-section VII shown in FIGS. 2 and 4, it represents a cut surface obtained by cutting the fusion joint in a plane directed in the axial direction of the cage. For this modified example, the same reference numerals will be given to the components common to the above-described embodiment, and the description will be omitted as much as possible, and the different components will be described below.

[0059] In the ring portion 11 of the modified example, the shape of the fusion joint 23 is triangular, and its circumferential dimension satisfies the relationship of Lc < Ld. The circumferential dimension of the fusion joint 13 gradually increases from the inner diameter side to the outer diameter side, which is common to the embodiment shown in FIG. 8 described above.

[0060] However, in the modified example of FIG. 10, the inner diameter side of the ring portion 11 is diffusion-bonded. In such a diffusion-bonded portion 22, melting of the base material does not occur, but it is heated and bonded at a temperature at which melting does not occur so that non-bonding does not occur.

[0061] Also in the modified example of FIG. 10, as in the embodiment shown in FIG. 8 described above, the heat transfer gradient can be made steep to promote cooling from the inner diameter side to the outer diameter side, the crystal grains of the fusion joint 23 can be made smaller, and the fatigue strength can be increased.

[0062] Next, another embodiment of the present invention will be described. Fig. 11 is a cross-sectional view showing another embodiment of the present invention, and shows a cross section of the fusion joint cut by a plane perpendicular to the axis O of the cage, similar to cross section VII shown in Figs. 2 and 4. In this other embodiment, the same reference numerals are used to designate components common to the above-mentioned embodiment, and explanations thereof are omitted as much as possible, and different components will be described below.

[0063] In another embodiment, the shape of the fused joint 33 is trapezoidal, its circumferential dimension satisfies the relationship Lb>Lc>Ld, and the circumferential dimension of the fused joint 13 gradually decreases from the inner diameter side to the outer diameter side, which differs from the embodiment shown in Figure 8 described above.

[0064] 11, the circumferential dimension of the fusion joint 33 gradually decreases from the inner diameter side toward the outer diameter side (Lb>Lc>Ld). As a result, the amount of molten metal in the radial center portion including the reference line N is less than the amount of molten metal located along the inner diameter surface of the ring portion 11. In this way, cooling progresses in the inner diameter direction from the side with less molten metal to the side with more molten metal, so that the molten metal in the radial center portion is easily cooled, and coarsening of crystal grains can be prevented.

[0065] In another embodiment of the present invention, in order to prevent welding defects due to a shortage of molten metal, a portion with a large amount of molten metal is arranged on the inner diameter surface of the ring portion 11. This portion is adjacent to the outer diameter surface of the ring portion 11 and is easily cooled, so that the crystal grains are less likely to become coarse.

[0066] According to another embodiment, in the process of solidifying the molten metal, heat transfer in the inner diameter direction is promoted, making it easier to cool, and the crystal grains are made finer than before, improving the fatigue strength of the welded area.

[0067] Next, a second modified example of the present invention will be described. FIG. 12 is a cross-sectional view showing a fusion joint portion according to the second modified example of the present invention, and represents a cut surface obtained by cutting the fusion joint portion in a plane directed in the axial direction of the cage, similar to cross-section VII shown in FIGS. 2 and 4. Regarding this second modified example, the same reference numerals will be given to the configurations common to the above-described embodiments, and the description will be omitted as much as possible, and the different configurations will be described below.

[0068] In the ring portion 11 of the second modified example, the shape of the fusion joint portion 43 is triangular, and its circumferential dimension satisfies the relationship of Lb > Lc. The circumferential dimension of the fusion joint portion 13 gradually decreases from the inner diameter side toward the outer diameter side, which is common to the other embodiments shown in FIG. 11 described above.

[0069] However, in the second modified example of FIG. 12, the outer diameter side of the ring portion 11 is diffusion bonded. In such a diffusion bonded portion 44, melting of the base material does not occur, but it is bonded by heating at a temperature at which melting does not occur so that non-bonding does not occur.

[0070] Also in the second modified example of FIG. 12, as in the other embodiments shown in FIG. 11 described above, the heat transfer gradient can be made a steep gradient to promote cooling from the outer diameter side to the inner diameter side, and the crystal grains of the fusion joint portion 43 can be made smaller to increase the fatigue strength.

[0071] Next, still another embodiment of the present invention will be described. FIG. 13 is a cross-sectional view showing still another embodiment of the present invention, and represents a cut surface obtained by cutting the fusion joint portion in a plane perpendicular to the axis O of the cage, similar to cross-section VII shown in FIGS. 2 and 4. Regarding still another embodiment, the same reference numerals will be given to the configurations common to the above-described embodiments, and the description will be omitted as much as possible, and the different configurations will be described below.

[0072] In still another embodiment, the circumferential dimension of the fusion joint portion 53 satisfies the relationship of Lb > Lc < Ld. Specifically, the circumferential dimension of the fusion joint portion 53 gradually increases from the radially intermediate portion on the reference line N toward the inner diameter side, and also gradually increases from the radially intermediate portion toward the outer diameter side.

[0073] 13, the circumferential dimension of the fusion joint 53 is smallest at the radial center where the reference line N passes, gradually increases from the radial center toward the outer diameter side, and gradually increases from the radial center toward the inner diameter side. This results in less molten metal in the radial center compared to the molten metal located along both the outer diameter surface and the inner diameter surface of the ring portion 11. In this way, cooling proceeds from the side with less molten metal, so that the molten metal in the radial center is easily cooled, and coarsening of crystal grains can be prevented.

[0074] In still another embodiment of the present invention, to prevent welding defects due to a shortage of molten metal, portions with a large amount of molten metal are arranged on both the outer diameter surface and the inner diameter surface of the ring portion 11. These portions are adjacent to the outer diameter surface or the inner diameter surface of the ring portion 11 and are easily cooled, so that the crystal grains are less likely to become coarse.

[0075] According to still another embodiment, during the solidification process of the molten metal, heat transfer in the outer diameter direction and the inner diameter direction is promoted, making it easier to cool, and the crystal grains are refined more finely than in the past, improving the fatigue strength of the welded area.

[0076] Although the embodiment of the present invention has been described above with reference to the drawings, the present invention is not limited to the illustrated embodiment. Various modifications and variations can be made to the illustrated embodiment within the same scope as the present invention or within an equivalent scope. For example, a part of the configuration may be extracted from one embodiment described above, and another part of the configuration may be extracted from another embodiment described above, and these extracted configurations may be combined. [Industrial Applicability]

[0077] The present invention is advantageously used in the field of machine elements. [Explanation of symbols]

[0078] 10 welded retainer, 11 ring portion, 11s ring portion material, 13,23,33,43,53,103 fusion joint, 13s slant end, 14 heat-affected zone, 15 non-heat-affected zone, 16 column, 16m pocket surface, 17,18 roller stopper, 19 pocket, 22,44 Diffusion bond, Lb,Lc,Ld Circumferential dimensions, N: Reference line representing the radial center of the ring section, O: Axis line of the cage.

Claims

1. A welded retainer comprising a pair of ring portions and a plurality of column portions connecting the pair of ring portions, the ring portions including a fusion joint portion formed by rolling a metal material having a length corresponding to one circumference and melting both ends of the metal material to join the metal material, The fusion joint is provided from the outer diameter surface to the inner diameter surface of the ring portion, The circumferential dimension of the fusion joint is from the innermost part of the fusion joint through the radially intermediate part to the outermost part of the fusion joint. Gradually growing, or Gradually getting smaller, or gradually decreasing from the innermost portion to the radially intermediate portion, and gradually increasing from the radially intermediate portion to the outermost portion, 1. A welded cage for a roller bearing, wherein the circumferential dimension of the largest portion of said fusion joint is at least twice the circumferential dimension of the smallest portion of said fusion joint.

2. 2. The welded cage for a roller bearing according to claim 1, wherein said ring portion projects radially inward from an end of said column portion.

3. The fused joint gradually increases in size from the innermost portion to the outermost portion, 3. The welded retainer for a roller bearing as described in claim 2, wherein a circumferential dimension Ld of the fusion joint along the outer diameter surface and a circumferential dimension Lb of the fusion joint along the inner diameter surface are such that the circumferential dimension Ld is at least twice the circumferential dimension Lb.

4. A welded retainer comprising a pair of ring portions and a plurality of column portions connecting the pair of ring portions, the ring portions including a fused joint formed by rolling a metal material having a length corresponding to one circumference and melting both ends of the metal material to join the metal material, the circumferential dimension of the fusion joint gradually increases from the innermost portion of the fusion joint through a radially intermediate portion to the outermost portion of the fusion joint, The ring portion protrudes radially inward from an end of the column portion, The fusion joint is provided on an outer diameter surface of the ring portion, The ring portion further includes a diffusion bonded portion on an inner diameter side of the fusion bonded portion.

5. A welded retainer comprising a pair of ring portions and a plurality of column portions connecting the pair of ring portions, the ring portions including a fused joint formed by rolling a metal material having a length corresponding to one circumference and melting both ends of the metal material to join the metal material, The circumferential dimension of the fusion joint gradually decreases from the innermost portion of the fusion joint through a radially intermediate portion to the outermost portion of the fusion joint, The ring portion protrudes radially inward from an end of the column portion, The fusion joint is provided on an inner diameter surface of the ring portion, The ring portion further includes a diffusion bonded portion on an outer diameter side of the fusion bonded portion.

6. A welded retainer comprising a pair of ring portions and a plurality of column portions connecting the pair of ring portions, the ring portions including a fused joint formed by rolling a metal material having a length corresponding to one circumference and melting both ends of the metal material to join the metal material, a circumferential dimension of the fusion joint gradually decreases from an innermost portion of the fusion joint to a radially intermediate portion thereof, and gradually increases from the radially intermediate portion to an outermost portion thereof; The ring portion protrudes radially inward from an end of the column portion, The fusion joint is provided on an inner diameter surface of the ring portion and an outer diameter surface of the ring portion, The ring portion further includes a diffusion welded portion between the fusion welded portion on the inner diameter side and the fusion welded portion on the outer diameter side.

7. A welded retainer comprising a pair of ring portions and a plurality of column portions connecting the pair of ring portions, the ring portions including a fused joint formed by rolling a metal material having a length corresponding to one circumference and melting both ends of the metal material to join the metal material, The circumferential dimension of the fusion joint is from the innermost part of the fusion joint through the radially intermediate part to the outermost part of the fusion joint. Gradually growing, or Gradually getting smaller, or The thickness gradually decreases from the innermost portion to the radially intermediate portion, and gradually increases from the radially intermediate portion to the outermost portion, A welded retainer for a roller bearing, wherein the average grain size of prior austenite crystal grains in the fusion welded portion is equal to or smaller than the average grain size of prior austenite crystal grains in a portion of the ring portion that is not thermally affected by the fusion welded portion.

8. A welded cage for a roller bearing according to any one of claims 1 to 7, and a roller and cage attached thereto, the roller and cage being provided with rollers assembled in the welded cage for the roller bearing.

9. A method for inspecting a welded cage for a roller bearing according to any one of claims 1 to 7, comprising the steps of: grinding the welded retainer to expose a cross section including the weld; A step of preparing a test solution by dissolving concentrated nitric acid in an alcohol solvent; The method for inspecting a welded retainer includes immersing the cross section in the inspection liquid, removing the cross section from the inspection liquid after a period of 3 to 5 seconds, and determining the shape of the weld based on a color change of the cross section.

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