Outer ring for a shell-type radial needle bearing and manufacturing method thereof

Abstract

An outer ring 6a for a shell-type radial needle bearing having a cylindrical shape with a bottom is achieved for which fatigue life of the bottom plate section 9a and the continuous section between the bottom plate section 9a and the cylindrical section 8a is improved, as well as the anti-corrosion characteristic of the outer ring 6a is improved and the outer ring 6a can be prevented from coming out of the bearing without an increase in cost. After obtaining an intermediate raw material 35 having a cylindrical section and a bottom plate section from a metal raw material, shot peening is performed on the intermediate material 35 to create residual compressive stress in the surface and surface layer section on the outer surface side of the cylindrical section 8a and the bottom plate section 9a such that the residual compressive stress in the surface layer section on the outer surface side is greater than the in the surface layer section on the inner surface side, and from the surface to a depth of 0.03 mm is 700 mpa to 1600 mpa.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a FIG. 4 is a graph illustrating the test results of testing that was performed for learning the effects that the dimension of the thickness of the bottom plate section of the outer ring has on durability of the outer ring.to 1.2 mm, and in some cases, 1.5 mm to 2 mm, the thickness dimension (T) of the bottom plate section 9a is taken to be 1.2 mm to 3 1.25 mm.

The thickness of the opening end section of the cylindrical section 8a is thin, and this thin section is bent inward in the radial direction to form an inward facing flange section 10, and this inward flange section 10 prevents the plurality of needles 7 that are arranged between the inner circumferential surface (outer raceway) of the cylindrical section 8a and the outer circumferential surface (inner raceway) of the shaft section 4, which is an inside member, from coming out. There is no particular need for there to be residual compressive stress in the surface layer section on the outer surface side of the inward facing flange section 10. However, similarly, when performing shot peening of the outer surface side of the cylindrical section 8a and the bottom plate section 9a, the projectile material hits against the inward facing flange section 10, so residual compressive stress in the surface layer section of this inward facing flange section 10 is allowable. By devising the direction for projecting the projectile material, the inward facing flange 10 can prevent the projectiles from entering inside the outer ring 6a with great energy. Therefore, when performing shot peening, it is not particularly necessary to close off the opening section of the outer ring 6a.

In the present invention, when performing shot peening in order to create residual compressive stress in the surface layer section on the outer surface side, a known shot peening apparatus can be used. The material, the particle size, the projection time and the like of the projectiles are set appropriately according to the desired value of the residual compressive stress and the shape and size of the outer ring 6a. These conditions differ case by case, so as necessary, the appropriate values are found by performing testing.

In the present invention, in case that anti-corrosion coating is performed for the surface on the outer surface side of the outer ring 6a, when the shot peening conditions are set according to the desired value of the residual compressive stress and the like, the adhesion characteristics of the anti-corrosion coating should be taken into consideration at the same time, and by optimizing the conditions, such as the material of the projectile, it is possible to obtain a surface on the outer surface side that has excellent adhesion that corresponds well with the type of anti-corrosion coating. As a result, it is also possible at the same time to improve the anti-corrosion properties of the outer ring 6a. The adhesion can be adjusted by controlling the surface roughness of the surface on the outer surface side of the cylindrical section 8a and the bottom plate section 9a.

Similarly, by optimizing the shot peening conditions according to the existence conditions of oxides on the surface of the outer ring 6a before assembly, it is also possible to remove the oxides from the surface at the same time when the value of the residual compressive stress is adjusted by shot peening. As a result, it is also possible at the same time to improve the ease of assembly of the outer ring 6.

Furthermore, it is also possible to optimize the shot peening conditions from the aspect of preventing the outer ring 6a from coming out from the circular hole 3 in the yoke 1a, 1b, and at the same time when the value of the residual compressive stress is adjusted, it is possible to provide an outer circumferential surface to the cylindrical section 8a of the outer ring 6a that will make it difficult for the outer ring 6a to come out from the circular hole 3. In this case as well, the performance of this can be adjusted by controlling the surface roughness of the outer surface side of the cylindrical section 8a of the outer ring 6a.

From the aspects described above, it is also preferable that shot peening be actively performed for the outer circumferential surface of the cylindrical section 8a in addition to the outside surface of the bottom plate section 9a, and the bent section 16, which is the continuous section between the bottom plate section 9a and cylindrical section 8a, which require improved rigidity.

Moreover, surface processing such as surface preparation for improving the surface characteristics of the outside surface of the bottom plate section and the outer circumferential surface of the cylindrical section of the outer ring can be performed by etching such as surface texturing, however, performing this kind of processing separately becomes additional surface processing, which brings about much labor and a large increase in costs, and performing such surface processing cannot provide the surface layer section of the outer surfaces the residual compressive stress required for the present invention. On the other hand, when performing the surface improvement as described above, conventional shot blast conditions may not be sufficient in order to sufficiently increase the effect, and processing may have to be repeatedly performed multiple times. However, by using the conditions of the present invention, it is, as a role, possible to simultaneously obtain both the effect of providing the required residual compressive stress and the effect of surface improvement.

Next, of the method for manufacturing the outer ring for shell-type radial needle bearing of the present invention, an example of the method for manufacturing an outer ring 6a, of which the thickness dimension (t) of the cylindrical section 8a and the thickness dimension (T) of the bottom plate section 9a are different, will be explained with reference to FIG. 2. First, as raw material, a metal plate having a thickness dimension that is equal to or greater than the thickness dimension of the bottom plate section of the outer ring 6a to be manufactured is pulled from a coil 18 as illustrated in FIG. 2(A), then this metal plate is punched to obtain a circular disk shaped raw material plate 19 as illustrated in FIG. 2(B). Next, this raw material plate 19 is plastically deformed and drawn between the outer circumferential surface of a first punch 20 and the inner circumferential surface of a first die 21 as illustrated in FIG. 2(C) to form a cylindrical shape having a bottom and obtain a first intermediate raw material 22 that has a cylindrical shape and a bottom. One half (½) of the difference between outer diameter of the first punch 20 and the inner diameter of the first die 21 is less than the thickness dimension of the raw plate 19 and, except for the spring back amount, nearly coincides with the thickness dimension (t) of the cylindrical section 8a. Therefore, through this drawing process, the thickness dimension of the raw plate 19 is reduced and the portion that will become the cylindrical section 8a is formed. On the other hand, the thickness dimension of the portion that will become the bottom plate section 9a is nearly the same as the thickness dimension of the raw plate 19. This kind of drawing process is performed in a plurality of stages. Therefore, there is a plurality of sets of the first punch 20 and first die 21, the shapes of which slightly differ from each other.

Next, as illustrated in FIG. 2(D), of the first intermediate raw material 22, the tip end section of the portion that will become the cylindrical section 8a is pressed between a second punch 23 and second die 24, to form a second intermediate raw material 25 having a thin section that will become the inward facing flange section 10.

Next, as illustrated in FIG. 2(E), with the second intermediate raw material 25 held by a third die 26, the portion of this second raw material 25 that will become the bottom plate section 9a is pressed between the tip end surface of a third punch 27 and the tip end surface of a counter punch (not illustrated in the figure), to form a third intermediate raw material 28 having a partial spherical convex curved surface 12 in the center section on the inner surface of the portion that will become the bottom plate section 9a.

Then, as illustrated in FIG. 2(F), this third intermediate raw material 28 is held between a fourth punch 29 and a fourth die 30, and the excess portion on the tip end section of the thin section that will become the inward facing flange section 10 is removed (trimmed), to obtain a fourth intermediate raw material 31.

Next, as illustrated in FIG. 2(G) and FIG. 2(H), with this fourth intermediate raw material 31 being held by a fifth die 32, the thin portion of this fourth intermediate raw material 31 is sequentially bent using a preliminary bending punch 33 and finishing bending punch 34, to form this thin section into the inward facing flange section 10, obtaining the final intermediate raw material 35 illustrated in FIG. 2(H). This final intermediate raw material 35 corresponds to the intermediate raw material of the present invention having a cylindrical section and bottom plate section.

Next, heat treatment is performed in order to increase the hardness of the inner surface of the cylindrical section 8a that will function has the outer raceway to the necessary level. Finally, shot peening is performed on this final intermediate raw material 35 to create residual compressive stress in the surface layer sections of the surfaces of the cylindrical section 8a and the bottom plate section 9a.

The outer ring 6a, which is constructed as described above so as to have construction according to the present invention, has construction that is able to keep friction loss that occurs at the area of contact between the end surface of the shaft section 4 of a joint cross 2 of a universal joint and the inner surface of the bottom plate section 9a low, so it is possible to improve the fatigue strength of the bottom plate section 9a and the continuous section between the bottom plate section 9a and the cylindrical section 8a without the outer diameter dimension or thickness of the outer ring 6a becoming large, and without the shape of the bottom plate section 9a becoming complex. Furthermore, by improving adhesion of an anti-corrosion coating or by eliminating the effect of oxides, it is also possible to improve the resistance to corrosion of the outer ring 6a. Furthermore, by adjusting the surface properties of the outer circumferential surface of the cylindrical section 8a of the outer ring 6a, the outer ring 6a can be prevented from coming out and it is possible to provide an outer ring 6a that will have not positional shifting in rotation of the universal joint and the like.

In the embodiment described above, the case of manufacturing the outer ring for a shell-type radial needle bearing of the present invention by performing a drawing process of a raw metal (ferrous alloy) plate that can be hardened by at least heat treatment was explained. However, the outer ring for a shell-type radial needle bearing of the present invention can be manufactured by performing cold forging, which is a kind of plastic working, of a column shaped raw material such as disclosed in JP22008-188610. In this case as well, an intermediate raw material that is cylindrical shaped with a bottom is formed such that the thickness dimension of the bottom plate section is greater than the thickness dimension of the cylindrical section, and heat treatment to improve surface hardness, and shot peening to create residual compressive stress in the outer surface are performed on this intermediate raw material. In the case of manufacturing the outer ring for a shell-type radial needle bearing by this kind of cold forging, in exchange for increasing equipment costs by having to increase the strength of the dies, and to increase the capacity of the press when compared with the case of drawing raw plate, it is possible to improve the material yield. Therefore, in the case of mass production, it is possible keep manufacturing costs low when compared with the drawing process.

EXAMPLE

Testing that was performed in order to confirm the effect of the present invention will be explained. In this testing, as illustrated in FIG. 3, the cylindrical section 8a of a sample outer ring 6a was fitted inside a hole 37 of a holder 36 using an interference fit. This hole 37 is a through hole, so the bottom plate section 9a of the outer ring 6a was not backed up. In this state, a plurality of needles 7 and the shaft section 4 of a joint cross 2 were inserted into the outer ring 6a, and the tip end surface of the shaft section 4 was brought into contact with the inner surface of the bottom plate 9a. A pressure rod 38 was used to press the tip end surface of the shaft section 4 against the inner surface of the bottom plate section 9a with a fluctuating load that fluctuates within the range of 500 N to 1500 N, and number of times the load was applied until damage such as cracking occurred in the sample outer ring 6a was measured.

As samples, three of each kind of three types of samples, having a bottom plate thickness (T) of 0.84 mm, 1 mm and 1.2 mm, were made for a total of nine samples, were made, and sixteen samples having sixteen different values of residual compressive stress in the surface layer section of the outer surface side of the cylindrical section and the bottom plate section of the outer ring 6a were prepared. The nine samples having different bottom plate thicknesses had values of residual compressive stress in the surface layer section of 1000 MPa to 1200 MPa. Also, the sixteen samples having different residual compressive stress had a bottom plate thickness (T) of 1.25 mm. The outer diameter of the outer ring in all of the samples was 16 mm, the thickness (t) of the cylindrical section was 1 mm in all of the samples, and the material was SCM415 in all of the samples. Shot peening to create residual compressive stress was not performed for the inner surface of the outer ring, so the only residual compressive stress in the inner surface was that due to the drawing process. Therefore, the value of the residual compressive stress in the inner surface of the outer ring was about the same level as in the outer surface side before shot peening was performed. The results of the testing performed under these conditions are given in FIG. 4 and FIG. 5.

FIG. 4 illustrates the effect that the thickness (T) of the bottom plate section has on the durability (the number of times an axial load is repeated until damage occurs). As can be seen from FIG. 4, when the thickness (T) was 0.84 mm, the outer ring became damaged after the load was repeatedly applied 120,000 to 200,000 times, when the thickness (T) was 1 mm, damage to the outer ring occurred after the load was repeatedly applied 740,000 to 1 million times, and when the thickness (T) was 1.2 mm, the number of times the load was repeatedly applied before damage occurred greatly increased to 10 million to 11 million times.

On the other hand, FIG. 5 illustrates the effect that the value of the residual compressive stress in the surface layer section has on durability (the number of times an axial load is repeated until damage occurs). As can be seen from FIG. 5, when the residual compressive stress was 460 MPa to 560 MPa, damage occurred after the load was repeatedly applied 180,000 to 940,000 times, however, when the residual compressive stress was 830 MPa to 1290 MPa, the number of times the load was repeatedly applied before damage occurred greatly increased to 3.15 million to 10 million times.

In testing the durability of the outer ring for a shell-type radial needle bearing in which normally 1 million times is the OK level, when the residual compressive stress exceeds 700 MPa, the load could be repeatedly applied 3 million times or more, and when the residual compressive stress exceeds 1100 MPa, the load could be repeatedly applied 10 million times or more before damage occurred. In testing, when damage did not occur even after applying the load 10 million times, testing was ended as being OK.

INDUSTRIAL APPLICABILITY

The present invention can be suitably applied to the outer ring for a shell-type radial needle bearing that is assembled in the rotation support section of a joint cross type universal bearing for an automobile, however, the invention is not limited to this, and can be widely applied to the outer ring of shell-type radial needle bearings having a cylindrical shape with a bottom that are assembled in various kinds of machinery for which strength of the bottom plate and anti-corrosion of the outer ring are required.

EXPLANATION OF REFERENCE NUMBERS

• 1a, 1b Yoke
• 2 Joint cross
• 3 Circular hole
• 4 Shaft section
• 5 Shell-type radial needle bearing
• 6, 6a Outer ring
• 7 Needle
• 8, 8a Cylindrical section
• 9, 9a Bottom plate
• 10 Inward facing flange section
• 11 Outer raceway
• 12 Convex curved surface
• 13 Inner raceway
• 14 Stepped section
• 15 Seal member
• 16 Bent section
• 18 Coil
• 19 Raw plate
• 20 First punch
• 21 First die
• 22 First intermediate raw material
• 23 Second punch
• 24 Second die
• 25 Second intermediate raw material
• 26 Third die
• 27 Third punch
• 28 Third intermediate raw material
• 29 Fourth punch
• 30 Fourth die
• 31 Fourth intermediate raw material
• 32 Fifth die
• 33 Preliminary bending punch
• 34 Finishing bending punch
• 35 Final intermediate raw material
• 36 Holder
• 37 Hole
• 38 Pushing rod

Claims

1. An outer ring for a shell-type radial needle bearing that is formed using a metallic material into a single bottomed cylindrical shaped member, comprising:

a cylindrical section having an outer raceway formed around the inner circumferential surface thereof; and

a bottom plate section that closes off an opening on one end of the cylindrical section,

the outer ring used in a state that the cylindrical section is fitted and fastened inside a circular hole that is formed in an outside member; a plurality of needles are located between the outer raceway and an inner raceway formed around an outer circumferential surface of an end section of a circular column shaped inside member so as to be able to roll freely; and an end surface of the inside member comes in contact with a center section of the inner surface of the bottom plate section,

wherein the residual compressive stress is given by performing a way of creating the residual compressive stress on the outer surface side of the cylindrical section and the bottom plate section, such that the value of residual compressive stress existing on the inner surface side of the cylindrical section and the bottom plate section after the way is performed is the same level as the value of residual compressive stress existing on the outer surface side of the cylindrical section and the bottom plate section before the way is performed, and the value of the this residual compressive stress is larger in the surface layer section on the outer surface side of the cylindrical section and the bottom plate section than in the surface layer section on the inner surface side of the cylindrical section and bottom plate section after the way is performed; and

of the surface layer section on the outer surface side of the cylindrical section and the bottom plate section, the size of the residual compressive stress in the surface layer section from the surface to a depth of 0.03 mm is 1100 mpa to 1600 mpa.

2. The outer ring for a shell-type radial needle bearing according to claim 1, wherein the ratio between the thickness dimension of the bottom plate section and the thickness dimension of the cylindrical section is in the range 1.05 to 2 1.25.

3. The outer ring for a shell-type radial needle bearing according to claim 2, wherein the thickness dimension of the bottom plate section is 1.2 mm to 3 1.25 mm.

4. The outer ring for a shell-type radial needle bearing according to claim 1, wherein there are no oxides on the surface on the outer surface side of the cylindrical section and the bottom plate section.