Method of manufacturing inner and outer races of deep groove...

Details Method of manufacturing inner and outer races of deep groove... Method of manufacturing inner and outer races of deep groove...

1999-08-25

2003-09-16

King, Roy (Department: 1742)

Metal treatment

Process of modifying or maintaining internal physical...

Carburizing or nitriding using externally supplied carbon or...

C148S659000

Reexamination Certificate

active

06620262

ABSTRACT:

This is a national phase application based on International Application PCT/JP98/05965 filed Dec. 25, 1998. International Application PCT/JP98/05965 was not published under PCT Article 21(2) in the English Language.
TECHNICAL FIELD
This invention relates to a continuous annealing furnace, to a roller bearing, to an annealing method and to a method for manufacturing an inner ring and an outer ring for a deep groove ball bearing. In particular, this invention relates to a technique which is useful for the manufacturing machine parts mainly concerning a roller bearing to be employed in various portions of a two-wheeler, a motor car, an agricultural machinery, a construction machine, etc.
BACKGROUND ART
(1)
FIG. 1
illustrates a method of manufacturing an inner ring and an outer ring for a deep groove ball bearing which involves a turning work after a heat treatment, and which is generally employed in view of saving the manufacturing cost.
As for the raw round bar, a steel round bar which has been rolled is generally employed as it is (S
1
). Then, a hot forging is performed generally using a multi-stage former thereby to produce a rough ring to be subsequently finished into an inner ring or an outer ring (S
2
). After this hot forging, by means of softening, the hardness of the rough ring is lowered or the microstructure of the rough ring is improved for the convenience of the following steps (S
3
). Then, a cold rolling work (hereinafter, referred to as CRF working) is performed (S
4
). By the way, this CRF working is performed, as schematically shown in
FIG. 5
, for thinning the cross-section of the rough ring
23
and at the same time, for enlarging the diameter of the rough ring
23
by rolling the rough ring
23
interposed between a molding roll
21
and a mandrel
22
under a load of “W” on the rough ring
23
.
FIG. 3
illustrates a forging process wherein the aforementioned CRF working is not employed. Namely, in order to fabricate forged rings
1
and
2
, a ring
3
and a fraction
4
are discarded as a scrap. On the other hand, when the CRF working is employed, small forged rings
5
and
6
are produced as shown in FIG.
4
(D) in a hot forging step, and then, these forged rings
5
and
6
are diametrally enlarged to form CRF rings
7
and
8
as shown in FIG.
4
(E). Therefore, the ring
3
shown in FIG.
3
(D) is no more required to be produced, and the fraction
4
shown in FIG.
3
(D) can be also made smaller as represented by a fraction
12
as shown in FIG.
4
(D). Furthermore, a groove
7
a
or
8
a
may be formed on the raceway surface of the CRF ring
7
or
8
, respectively, at the occasion of obtaining a diametrally enlarged CRF ring
7
or
8
, thereby minimizing as much as possible the magnitude of turning, thus resulting in an excellent saving of material.
Next, a sizing of the ring is performed (S
5
) as shown in FIG.
1
. Subsequently, the entire surface of the CRF ring is subjected to a turning work (S
6
) thereby to remove an oxide layer or a decarbonized layer that has been formed during the forging or annealing, or thereby to form the CRF ring into a deep groove ball bearing after a heat treatment or grinding. Depending on certain circumstances, a flash that may happen to be formed during the hot forging may be removed by means of grinding before the aforementioned turning work. Then, the ring is subjected to a quenching and an annealing thereby to obtain a suitable hardness of the ring required for the bearing (S
7
). Next, the raceway surface and the fitting surface of the ring is subjected to a grinding work thereby to manufacture an inner ring and an outer ring (S
8
).
Japanese Patent Publication H6-83872 discloses a method wherein a rough ring is subjected to a turning work thereby making the ring fixed in configuration and in weight prior to the CRF working, and then, the resultant ring is subjected to a high precision CRF working in which the ring is completely finished to form a raceway surface groove as well as a sealing groove which are desired as a deep groove ball bearing, thereby making it possible to omit the subsequent turning work, and to save the manufacturing cost.
By the way, this CRF working is a process, as mentioned above, for enlarging the diameter of the rough ring (such as a forging ring or a turning ring) thereby to make the rough ring into a CRF ring. Therefore, although it is possible to adjust the thickness and the magnitude of enlarging the diameter of the ring, it is impossible to control the dimension in the lateral direction of the ring, thus allowing a flash to be generated in the lateral direction of the ring.
In the case of the method disclosed in Japanese Patent Publication H6-83872 where a high precision CRF working is performed, a flash extending in the lateral direction is caused to be generated, or fine cracks due to the cold working are also caused to be generated at the edge portion of a sealing groove forming a complicated configuration or of a race groove. Therefore, not only a full-face turning work for adjusting the dimension or for making the volume constant is required to be performed prior to the CRF working, but also a finishing turning work for removing the fine cracks is required to be performed after the CRF working. Further, when a complicated configuration is to be obtained through a high-precision CRF working, the working time would be prolonged and the cost for the CRF working would be increased.
On the other hand, in the method where a turning work is not performed prior to the CRF working as shown in
FIG. 1
, a groove (the groove
7
a
or
8
a
in
FIG. 4
) is usually formed on the raceway surface at the occasion of enlarging the diameter of the ring by making use of the CRF working so as to minimize as much as possible the magnitude of turning. However, the magnitude of turning is excessively minimized, the decarbonized layer that has been formed during the hot forging or softening may be left remained after the turning work, thus raising a problem in terms of the function of the bearing. As a result, a full-face turning work is also required to be performed on the ring after the CRF working, thus leaving a room for further improvement regarding the reduction of manufacturing cost through a simplification of manufacturing steps.
Since the bearing is subject to a repeated load at a small contacting surface thereof, i.e. between the raceway surface thereof and a rolling element, the bearing is generally formed of a hard steel which is capable of withstanding this repeated load (stress) and has a uniform structure and an excellent abrasion resistance. Therefore, a high carbon chromium bearing steel (SUJ2) which is defined in the JISG 4805 is typically employed for the bearing. This bearing steel is featured in that, in view of ensuring a high hardness, the content of carbon in this raw material is as high as about 1%.
Therefore, when this bearing steel is heated at a high temperature in the air atmosphere in the manufacturing steps thereof, the surface of the bearing steel is decarbonized, thus failing to obtain a predetermined hardness if this heat-treated bearing steel is to be employed as it is. This means that if a decarbonized layer is left remained on the rolling contact surface of the bearing after the manufacture thereof, the capabilities of the bearing such as the life and abrasion resistance thereof may be deteriorated.
In the ordinary manufacturing method of the bearing ring, a method wherein a steel bar obtained from rolling is directly formed into a rectangular ring by means of a hot forging, and then, the resultant ring is subjected to a finishing work by means of turning work, or a method wherein a tubular material is subjected to a finishing work by means of turning work has been employed. There are also known various working methods for forming a ring. In any of these working methods however, a spheroidizing annealing is performed prior to the turning work in order to facilitate the workability of raw material.
The decarburization of the bearing steel is caused to occur

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