JP2001056028A - Manufacture of bearing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently manufacture a bearing in two-point support structure in a housing of which a sintered body is built into the one having excellent bearing performance under a comparatively simple method. SOLUTION: A material 1A is compressed in the axial direction by inside punches 33B, 34B of upper and lower punches 33, 34 from a state where a housing 21 is fitted in a die 31, the material 1A is fitted in the housing 21 and a core rod 32 having a large diametrical part 32b for dynamic pressure groove formation is inserted into the material 1A. An outer diametrical surface of the material 1A, is cladded on an inner diametrical surface of the housing 21, and an inner diametrical surface of the material IA is pressure welded on the core rod 32. An intermediate undercut part 13 is formed by the large diametrical part 32b on the inner diametrical surface of the material 1A, and axially supporting surfaces 12 are formed on its both sides. A bearing 20A is provided by molding a bearing main body 10A by deforming the material 1A like this and cladding it on the housing 21.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bearing suitable for use in supporting a shaft rotating at a relatively high speed, such as a drive shaft of a spindle motor built in precision equipment, with high precision. The present invention relates to a method of manufacturing a bearing of a type in which a bearing body having a middle relief portion that does not contact a rotating shaft is incorporated in a housing. The bearing body is formed by compressing a material made of a sintered body or a porous body obtained by sizing the sintered body, is impregnated with lubricating oil, and is suitably used as a sintered oil-impregnated bearing.

[0002]

2. Description of the Related Art In a sintered oil-impregnated bearing, the lubricating oil impregnated in a sintered body seeps into an inner diameter surface, and an oil film is formed between the inner diameter surface and a rotating shaft, thereby reducing frictional resistance. It has the characteristic that noise and vibration are suppressed. In addition, as a sintered oil-impregnated bearing with further enhanced vibration and noise suppression effects,
A gap (hereinafter, referred to as a middle relief portion) having an inner diameter slightly larger than the outer diameter of the rotating shaft and not in contact with the rotating shaft is formed on the inner diameter surface at the central portion in the axial direction. As a two-point support structure limited to a surface, there is a structure in which the effect of reducing frictional resistance and the support force of the rotating shaft are further stabilized.

[0003] Sintered oil-impregnated bearings are usually manufactured mainly by the steps of sintering a cylindrical green compact obtained by compression-molding a raw metal powder, sizing the sintered body and finishing it into a final shape. However, as a bearing, there is a type in which a sintered body is incorporated in a housing in addition to a sintered body alone. By the way, in the case where the above-mentioned middle relief portion is formed, if the middle relief portion is formed by machining the sintered body, the pores exposed on the inner diameter surface are crushed, which hinders the circulation operation of the lubricating oil. Become. For this reason, it is preferable to form the middle relief portion at the same time in the sizing step of the sintered body, or to form the middle relief portion by compressing the sintered body again after sizing. In any case, the two inner shafts are separated from each other by causing plastic deformation in the sintered body such that the inner diameter surfaces at both ends in the axial direction project radially inward or the central portion in the axial direction swells radially outward. The supporting surface and the clearance between them are formed on the inner diameter surface at the same time.

[0004]

In the bearing having the above-mentioned two-point support structure, in order to enhance the bearing performance such as the reduction of the frictional resistance and the improvement of the support force of the rotary shaft, the inner diameter of the two separated shaft supporting surfaces and It is required that the coaxiality match with high accuracy and that the supply amount of the lubricating oil to the bearing surface be sufficient. However, although various methods of plastically deforming a sintered body have been conventionally proposed, a certain manufacturing method that is relatively simple and does not sufficiently satisfy requirements for improving bearing performance has been found at present. there were. Also, in a bearing of a type in which a sintered body is incorporated in a housing, even if the bearing is formed into a housing after forming a bearing surface and an intermediate relief portion, the sintered body is deformed due to deformation. In many cases, the inner diameter of the surface is different or the coaxiality is impaired, and it is extremely difficult to size the sintered body after the assembly to form the bearing surface and the middle relief.

Therefore, the present invention provides a bearing having a two-point support structure in which a sintered body is incorporated in a housing, by a relatively simple method, efficiently and with excellent bearing performance (the inner diameter of two bearing surfaces, It is an object of the present invention to provide a method capable of manufacturing a rotating shaft having a coaxiality having the same bearing capacity, lubricating property, and wear resistance.

[0006]

SUMMARY OF THE INVENTION The present invention is directed to a cylindrical member having a central relief portion in which the rotating shaft does not come into contact with an inner diameter surface at a central portion in the axial direction, and rotating at both axial ends on both sides of the central relief portion. A method for manufacturing a bearing in which a bearing body having a bearing surface for supporting a shaft is incorporated in a cylindrical housing, wherein a cylindrical material molded into the bearing body is inserted into the housing, and By inserting a core rod having a large diameter portion capable of forming a relief portion into the material and compressing the material in the axial direction while maintaining the state in which the large diameter portion corresponds to the inner diameter surface of the central portion in the axial direction of the material, The outer diameter surface is pressed against the inner diameter surface of the housing, while the inner diameter surface of the material is pressed against the core rod, and the middle relief portion and the bearing surface are formed on the inner diameter surface. As the material according to the present invention, a sintered body or a porous body obtained by sizing the sintered body as described above is used, and after production, the sintered body is impregnated with a lubricating oil and is suitably used as a sintered oil-impregnated bearing.

In the present invention, for example, a material is coaxially inserted into a housing whose outer diameter is restricted by being fitted into a fitting hole of a molding die, and fitted into an intermediate fitting state, and the core rod is attached. The large diameter portion is inserted into the material so that the large diameter portion corresponds to the inner diameter surface at the central portion in the axial direction of the material. Then, while maintaining this state,
A molding method in which only the material is compressed in the axial direction by a punch is employed. The material compressed in the axial direction is pressed against the inner diameter surface of the housing so that the outer diameter surface swells toward the outer diameter side. In addition, the inner diameter surface of the material is plastically deformed in accordance with the outer diameter surface of the core rod, and a concave portion having a shape corresponding to the large diameter portion of the core rod, that is, a middle relief portion is formed at an axial central portion thereof. On both sides, a bearing surface having a smaller diameter than the middle relief portion is formed. The material is thus plastically deformed and formed into a bearing body, and the outer diameter surface is pressed against the housing inner diameter surface to be integrated with the housing.

According to the present invention, a bearing body formed of a material is incorporated in a housing by adopting a combination of a material and a housing in which such a modification is appropriately made. A bearing having a two-point support structure having a portion can be efficiently manufactured by a relatively simple method. In addition, since the middle relief portion is formed by being pressed against the large diameter portion of the core rod, by forming the large diameter portion accurately, the middle relief portion can be reliably and accurately formed in the desired shape and dimensions. Can be formed.

Further, since the bearing surface formed on the bearing body is formed by strongly pressing the inner diameter surface of the material against the core rod, the inner diameter and the coaxiality match with high accuracy. Further, since the density of the bearing surface can be increased, the wear resistance is improved. On the other hand, the density of the inner diameter surface where the middle relief portion is formed can be finished to the same degree as the bearing surface, so that the lubricating oil in the gap with the rotating shaft has relatively high oil retention, and the bearing surface has Lubricity can be improved. As a result, a bearing having a high level of bearing performance can be manufactured.

In a preferred embodiment of the present invention, a convex portion or a concave portion for forming a dynamic pressure groove is formed on the outer diameter surface of the core rod which is pressed against the inner diameter surfaces of both ends in the axial direction of the material. According to this, in the case of the former convex portion, a dynamic pressure groove corresponding to the shape of the convex portion is formed on the bearing surface. Also,
In the case of the latter concave portion, a bearing surface engraved according to the shape of the concave portion and a dynamic pressure groove between the bearing surfaces are simultaneously formed. When the dynamic pressure grooves are formed on the bearing surface, the dynamic pressure effect generated in the dynamic pressure grooves (the lubricating oil flowing into the dynamic pressure grooves) The support force of the rotating shaft is synergistically increased by the improvement of the rigidity accompanying the high pressure, and the supporting force of the rotating shaft can be further stabilized.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. (1) First Embodiment-FIG. 1 FIGS . 1A to 1C show a bearing forming process according to a first embodiment.
They are shown in the order of (f). In the first embodiment, the housing 21 is fitted to the molding device, and the material 1A fitted in the housing 21 is compressed in the axial direction to manufacture the bearing 20A. The molding device includes a die 31 having a fitting hole 30 into which the housing 21 fits, a core rod 32 inserted into the material 1A, and upper and lower punches 33 and 34. The fitting hole 30 of the die 31 has a shape corresponding to the housing 21, and as shown in FIG. 1 (a), is provided on the entrance side (upper side) of the cylindrical main part 30a via a horizontal step part 30d. An opening 30c having an inner diameter larger than that of the main portion 30a is formed.

As shown in FIG. 1A, the core rod 32
In the vicinity of the upper end portion, a large-diameter portion 32b having a larger diameter than the other main portion (herein referred to as the main body portion 32a).
Are formed coaxially with the main body 32a. The large diameter portion 32b forms a middle relief portion on the inner diameter surface of the material 1A, and its length is, for example, about half of the length of the material 1A. Further, as shown in FIG. 1 (c), the length of the main body 32a above the large diameter portion 32b is such that the large diameter portion 32b is disposed at the axial center of the material 1A and the upper end thereof is the material 1A. It is set to a dimension that can slightly protrude from

As shown in FIG. 1B, the upper punch 33
The outer punch 33A is slidably inserted into the opening 30c of the fitting hole 30, and the inner punch 33B is slidably inserted into the outer punch 33A. The lower punch 34 includes an outer punch 34A slidably inserted into the main portion 30a of the fitting hole 30 and an outer punch 34A.
And an inner punch 34B that is slidably inserted into the inner punch 34B. Inner punch 33 of upper and lower punches 33, 34
The outer diameters of B and 34B are the same. The inner punch 34B of the lower punch 34 has a large diameter portion 32b of the core rod 32.
The lower body portion 32a is slidably inserted. And the main body part 32a above the large diameter part 32b
Are slidably inserted into the inner punch 33B of the upper punch 33.

As shown in FIG. 1 (a), the housing 21 is a cylindrical one having a uniform inner diameter and a flange 23 formed at one end of a main cylindrical portion 22.
The cylindrical portion 22 is fitted to the main portion 30a of the fitting hole 30, and the outer diameter of the flange 23 is fitted to the opening 30c in an intermediate fitting state. As for the length (height) in the axial direction, the cylindrical portion 22 has a main portion 30 a of the fitting hole 30.
And the flange 23 is set shorter than the opening 30c. Further, the inner diameter of the housing 21 is set to a size in which the inner punches 33B, 34B of the upper and lower punches 33, 34 are slidably inserted. Housing 2
Although the material of 1 is arbitrary, for example, a sintered material is used in addition to bronze, brass, an aluminum alloy, and steel. In the case of using a sintered material, if a material having pores larger than the material 1A is used, the oil impregnated in the housing 21 is effectively supplied to the bearing main body side by capillary force, so that the bearing life can be extended. preferable.

The raw material 1A is a sintered body or a porous body formed by sizing the sintered body, and has a simple cylindrical shape having uniform outer and inner diameters. The length of the material 1A in the axial direction is substantially the same as that of the housing 21, and the outer diameter is set to a size fitted into the housing 21. Also,
The inner diameter is set to such a size that the large-diameter portion 32b of the core rod 32 is fitted and a gap is formed between the inner diameter surface and the main body 32a of the core rod 32.

Next, a procedure for manufacturing a bearing by a molding apparatus will be described. [Step 1-Fitting of Housing] As shown in FIG. 1A, the upper end of the lower punch 34 inserted into the main portion 30a of the fitting hole 30 of the die 31 is held at the same level as the step portion 30d. The core rod 32 is protruded from the upper surface of the die 31 by a predetermined length. The housing 21 with the flange 23 facing upward is coaxially fitted to the core rod 32 and set on the outer punch 34A of the lower punch 34. As a setting state of the housing 21, the lower punch 34 may be slightly lowered from the step portion 30d, and the lower end portion of the cylindrical portion 22 may be fitted to the main portion 30a. Next, as shown in FIG. 1B, the upper punch 33 is lowered, and the housing 21 is pushed into the fitting hole 30 and fitted by the outer punch 33A of the upper punch 33. At this time, the large diameter portion 32b of the core rod 32 is attached to the inner punch 33B.
The main body 32a above the core rod 32 is inserted.
Also descend. Further, the lower punch 34 is
Drop with. The housing 21 is in a state where the outer diameter surface is restrained by the die 31.

[Step 2—Compression of Material] The upper punch 33 is raised and temporarily retracted, and as shown in FIG. 1C, the material 1A is fitted to the core rod 32 which has been raised again, and the large diameter portion 32b Is placed at the axial center of the material 1A, and the material 1A is set on the housing 21. Next, as shown in FIG. 1D, the upper punch 33 is lowered again, and the material 1A is pushed into the housing 21 by the inner punch 33B of the upper punch 33 and fitted therein. At this time,
The core rod 32 is lowered together with the material 1A. Next, as shown in FIG. 1E, the inner punches 33B and 34B of the upper and lower punches 33 and 34 are moved toward the material 1A, and only the material 1A is compressed in the axial direction.

The compressed material 1A is subjected to the action of expanding the outer diameter surface, and the outer diameter surface is pressed against the inner diameter surface of the housing 21. The inner diameter of the material 1A is the core rod 3
2 is plastically deformed in accordance with the outer diameter surface of the core rod 32, and its central portion in the axial direction is pressed against the large diameter portion 32b of the core rod 32 to form the middle relief portion 13. Both ends are pressed against the main body portion 32a to be pivotally supported. Formed on surface 12. On the other hand, the housing 21 is made of the material 1
The outer diameter surface is pressed against the inner diameter surface of the fitting hole 30 by receiving pressure from A to the outer diameter side. The material 1A is plastically deformed as described above to be formed into the bearing main body 10A.
Is pressed against the inner diameter surface of the housing 21 to form a bearing 20A in which both are integrated.

[Step 3—Detachment of bearing] The upper punch 33 is raised and retracted, and as shown in FIG. 1 (f), the lower punch 34 is raised together with the core rod 32, and the bearing 20A is pulled out of the die 31. Demold. Thereafter, the core rod 32 is lowered to obtain the bearing 20A. Demolded bearing 2
At 0 A, since the outer diameter surface is restrained from being released by the die 31 and spring back occurs in which the entire diameter increases, the large diameter portion 3
The core rod 32 is mounted on the bearing 20 without the obstacle of 2b.
A can be extracted from A.

According to the first embodiment, the housing 21 is fitted to the die 31 of the molding apparatus.
A bearing 20A having a two-point support structure in which a bearing main body 10A made of a sintered body is incorporated in a housing 21 by a simple method of fitting the raw material 1A therein and then compressing only the raw material 1A in the axial direction. It can be manufactured efficiently. The middle relief portion 13 is a large diameter portion 32 of the core rod 32.
Since the large-diameter portion 32b is formed accurately by pressing the large-diameter portion 32b, the middle relief portion 13 can be formed reliably and precisely according to a desired shape and dimensions.

Since the bearing surface 12 of the bearing 20A is formed by strongly pressing the inner diameter surface of the material 1A against the core rod 32, the inner diameter and the coaxiality match with high precision, and the density is further increased. Excellent in abrasion resistance and rotating shaft support force. On the other hand, since the middle relief portion 13 can be brought into pressure contact with the core rod 32 to have the same density as the bearing surface 12, the oil retention of the lubricating oil can be increased, and the lubricity of the bearing surface 12 can be improved. Is achieved. As a result, bearing 2
0A exhibits excellent bearing performance. In addition, since the degree of compression of both bearing surfaces 12 can be made substantially equal,
The porosity of the bearing surface 12 is equalized, and therefore, the hydraulic pressure generated on the bearing surface 12 is also equalized, and the rotating shaft can be supported in a well-balanced manner.

In the above-described embodiment, the outer diameter of the material 1A is a dimension fitted into the housing 21 (a dimension inserted while sliding). The dimension may be such that a small gap is formed, or the dimension may be such that the inner diameter of the raw material 1A itself is not so large that it is press-fitted into the housing 21. Further, the outer diameter of the housing 21 is a dimension that is fitted in the fitting hole 30 of the die 31 in the middle, but may be a dimension that is press-fitted into the fitting hole 30. If the outer diameter of the housing 21 is such that there is a gap between the outer diameter surface and the fitting hole 30, the material 1
It is not preferable because the diameter of the housing 21 may be increased at the time of compression of A.
That is not the case.

(2) Second Embodiment-FIG. 2 Next, a second embodiment of the present invention will be described. In the second embodiment, as shown in FIG. 2A, the material 1A is previously fitted to the housing 21 by an appropriate device other than the molding device. Next, as shown in FIG. 2B, the material 1A and the housing 21 are fitted and set on the core rod 32. From this state, the housing 2 is
1 is fitted into the fitting hole 30 of the die 31 (the state shown in FIG. 1D), and thereafter, the material 1A is compressed as in the first embodiment.

(3) Third Embodiment—FIGS. 3 and 4 In the third embodiment, as shown in FIG.
2. The core rod 42 for forming a dynamic pressure groove instead of
This is an example in which the material 1 </ b> A is compression-molded by applying to the embodiment or the second embodiment, and a bearing in which a dynamic pressure groove is formed on the shaft support surface 12 is formed. The core rod 42 has a main body portion 42a and a large-diameter portion 42b in the same manner as the core rod 32. Further, as shown in FIG. On the surface, a plurality of V-shaped convex portions 43 are formed in a herringbone shape at equal intervals in the circumferential direction. The convex portion 43 can be formed by means such as cutting or plating of the core rod 42, and has a height of about several μm. The height of the convex portion 43 is the same as the height difference between the large-diameter portion 42b and the small-diameter portion 42a, and it is desirable that the convex portion 43 and the large-diameter portion 42b be flush.

In the third embodiment, as shown in FIG. 3A, in the procedure of the first embodiment or the second embodiment,
The material 1A and the housing 21 are inserted into the fitting holes 30 of the die 31.
And set the inner diameter surfaces of both ends of the material 1A to the core rod 4
The projections 43 correspond to the portions where the two convex portions 43 are formed. From this state, the upper and lower punches 33, 34 as shown in FIG.
The inner punches 33B and 34B are moved toward the material 1A, and only the material 1A is compressed in the axial direction.

The material 1A is plastically deformed as in the first embodiment, and is formed into a bearing body 10C. As shown in FIG. 4B, the protrusion 4 of the core rod 42 is formed on the bearing surface 12 of the bearing body 10C (the housing 21 is omitted in FIG. 4B).
3 forms a herringbone-shaped dynamic pressure groove 14. The bearing body 10C is pressed against the inner diameter surface of the housing 21 to form a bearing 20C.
The mold is released as shown in FIG. Demolded bearing 20C
In this case, since the outer diameter surface is restrained by the die 31 to be released and the whole diameter slightly increases, the bearing 20C can be removed from the core rod 42 without abrasion of the convex portion between the dynamic pressure grooves 14. it can.

Bearing 20 manufactured according to the third embodiment
According to C, in addition to the two-point support structure that supports the rotating shaft on the shaft supporting surface 12, due to the dynamic pressure effect generated in the dynamic pressure groove 14 (improved rigidity due to the high pressure of the lubricating oil flowing into the dynamic pressure groove). The supporting force of the rotating shaft increases synergistically, and the supporting force of the rotating shaft becomes more stable. From the viewpoint that the effect that the lubricating oil concentrates on a part of the dynamic pressure groove 14 and the dynamic pressure rises is sufficiently expected, the bearing 20
C is preferably set so that the rotation direction of the rotating shaft is oriented in the direction of the V-shaped tip of the dynamic pressure groove 14 (the direction of arrow R in FIG. 4B).

The shape of the dynamic pressure groove shown in the third embodiment is arbitrary, and the number thereof is also selected as appropriate. However, from the viewpoint of more stably supporting the rotating shaft, a plurality of grooves are formed on the shaft supporting surface. It is preferable that they are arranged at equal intervals along the circumferential direction. In the third embodiment, the effect of increasing the dynamic pressure is obtained as a herringbone shape, that is, depending on the shape.
The effect can also be obtained depending on the cross-sectional shape of the depth.

The rough shape is a groove extending along the axial direction. When the rotating shaft rotates in only one direction, the end of the rotating shaft in the direction opposite to the rotating direction is the deepest portion. From the section to the direction of rotation of the rotating shaft. When the rotating shaft rotates in both the forward and reverse directions, the middle part in the circumferential direction is set as the deepest part, and the inclination is made so as to gradually become shallower from the deepest part toward both ends in the circumferential direction. The thus formed dynamic pressure groove has a wedge-shaped gap in which the cross-section (cross-section when cut into a circle) becomes shallower in the direction of rotation of the rotary shaft, and the lubricating oil concentrates on the shallow tip of the groove. A wedge effect can be obtained.

Further, the dynamic pressure groove 14 shown in the third embodiment
Is formed by the convex portion 43 formed on the core rod 42, but a dynamic pressure groove can be formed by a concave portion instead of such a convex portion. That is, the pattern of the engraving is opposite to that of the third embodiment, and when the inner diameter surface of the inner diameter small diameter portion of the material 1A is pressed against the core rod, it is introduced into the concave portion formed in the core rod, and the convex portion protrudes. The inner diameter surface of the convex portion functions as a bearing surface, and the groove between the convex portions functions as a dynamic pressure groove. In this case, by further projecting the convex portion, a bearing having a large amount of middle clearance by its height can be obtained. The concave portion formed in the core rod can be formed by means such as electric discharge machining or electrolytic corrosion.

[0031]

As described above, according to the present invention,
The bearing body is configured to be incorporated in the housing,
A two-point support structure bearing with a relatively large middle relief
It can be efficiently manufactured by a relatively simple method. In the bearing manufactured by the present invention, the inner diameter and the coaxiality of the bearing surfaces at both ends in the axial direction are matched with high accuracy, and the density is increased to improve wear resistance.
On the other hand, in the central portion in the axial direction where the middle relief portion is formed,
Since the density is low, the content of lubricating oil and the amount of retained oil are sufficiently ensured. As a result, excellent bearing performance is exhibited.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a manufacturing process of a bearing according to a first embodiment of the present invention in the order of (a) to (f).

FIG. 2 is a longitudinal sectional view showing a part of a manufacturing process of a bearing according to a second embodiment of the present invention in the order of (a) and (b).

FIG. 3 is a longitudinal sectional view showing a part of a manufacturing process of a bearing according to a third embodiment of the present invention in the order of (a) to (c).

FIG. 4A is a partial perspective view of a core rod used in a third embodiment of the present invention, and FIG. 4B is a vertical perspective view showing a part of a bearing manufactured in the third embodiment of the present invention. is there.

[Explanation of symbols]

 1A: Material 10A, 10C: Bearing body 12: Bearing surface 13: Middle relief 20A, 20C: Bearing 21: Housing 32, 42: Core rod 32b, 42b: Large diameter portion of core rod 43: Convex for forming dynamic pressure groove Department

[Procedure amendment]

[Submission date] September 2, 1999 (1999.9.2)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0031

[Correction method] Change

[Correction contents]

[0031]

As described above, according to the present invention,
The bearing body is configured to be incorporated in the housing,
A two-point support structure bearing with a relatively large middle relief
It can be efficiently manufactured by a relatively simple method. In the bearing manufactured by the present invention, the inner diameter and the coaxiality of the bearing surfaces at both ends in the axial direction are matched with high accuracy, and the density is increased to improve wear resistance.
On the other hand, the density of the inner diameter surface where the middle relief is formed is the same as that of the bearing surface.
Can be finished to the same degree,
Some lubricating oils have relatively high oil retention,
Lubricity can be improved. As a result, excellent bearing performance is exhibited.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3J011 AA04 BA02 CA01 CA02 DA02 JA02 LA01 SB19 4K018 CA13 CA15 FA02 JA34 KA03 KA22

Claims (2)

[Claims] An inner surface of a cylindrical, central portion in the axial direction, which has a central relief portion in which the rotary shaft does not contact, and a shaft supporting surface for supporting the rotary shaft at both axial ends on both sides of the central relief portion. A method of manufacturing a bearing, wherein a bearing body having the bearing body is incorporated in a cylindrical housing, wherein a cylindrical material molded into the bearing body is inserted into the housing, and the middle relief portion is formed. By inserting the core rod having the large diameter part obtained into the material and compressing the material in the axial direction while maintaining the state where the large diameter part corresponds to the inner diameter surface in the axial center of the material, the outer diameter surface of the material is obtained. A method for manufacturing a bearing, comprising: pressing an inner diameter surface of a raw material against a core rod while pressing the inner diameter surface of the material against a core rod, and forming the middle relief portion and the bearing surface on the inner diameter surface. 2. A convex portion or a concave portion for forming a dynamic pressure groove is formed on a surface of a core rod which is pressed against an inner diameter surface of the material formed on the shaft supporting surface. 3. The method for producing a bearing according to item 1.