Endless belt power transmission systems or components – Positive drive pulley or guide roll
Patent
1997-05-19
1998-11-03
Hannon, Thomas R.
Endless belt power transmission systems or components
Positive drive pulley or guide roll
29892, F16H 5530
Patent
active
058300953
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a sprocket made of low carbon steel, the carbon content of which is not more than 0.25 wt %, and a manufacturing method thereof.
BACKGROUND ART
Conventionally, carbon steel of which the carbon content is 0.40 to 0.50 wt % (referred to as medium carbon steel in this specification hereinafter), for example, carbon steel of S45C stipulated in JIS is used for a sprocket to transmit power in a motorcycle.
The process of manufacturing a sprocket includes, for example, 15 processes of (a) to (j) as shown in FIGS. 7 and 8. When the teeth portion of a sprocket undergo a heat-treatment in the teeth portion quenching process shown in FIG. 8(g), hardness of the teeth portion is set at 35 to 50 of the Rockwell hardness C, so that the anti-abrasion property can be enhanced.
On the other hand, there is provided a sprocket made of carbon steel, the carbon content of which is not more than 0.25 wt % (referred to as low carbon steel in this specification hereinafter), for example, low carbon steel of SPH to S20C stipulated in JIS. The above sprocket is used in some regions because a plate of low carbon steel is inexpensive.
It is well known that even the hardness of low carbon steel is somewhat increased when it is heated to a temperature not lower than the A.sub.3 transformation point and then dipped in water so as to be quenched. There is provided a sprocket, the teeth portion of which undergo a heat treatment so that the hardness can be increased. However, when the matter is considered from an essential viewpoint, it is impossible to quench low carbon steel, and it is difficult to sufficiently increase the hardness of low carbon steel.
In the case of a sprocket made of medium carbon steel, it is possible to sufficiently increase the hardness of the teeth portion. Therefore, the sprocket made of medium carbon steel is excellent in the anti-abrasion property. However, the material cost of medium carbon steel is high, and further distortions and cracks tend to occur in the process of press forming since the hardness is high. Due to the above characteristic of medium carbon steel, it is difficult to manufacture a sprocket mainly by means of press forming. Therefore, it is necessary to conduct machining in the five essential manufacturing processes including an outside diameter cutting process, inside diameter cutting process, teeth cutting process, mounting hole drilling process and mounting hole chamfering process. Since the number of processes is increased, the manufacturing cost is high. Further, a large quantity of chips are produced in the process of machining, and it is complicated to remove the produced chips. Furthermore, due to the abrasion of a cutting tool, errors tend to occur in the manufacturing process. Accordingly, it is necessary to pay close attention in order to stabilize the machining accuracy when the sprocket is manufactured.
On the other hand, in the case of a sprocket made of low carbon steel, the following advantages are provided. The material cost is reduced. Due to the characteristic of low carbon steel, no distortions are generated in the process of press forming. Therefore, it is not necessary to machine after-processing such as finishing. Accordingly, it is possible to manufacture a sprocket mainly by means of press forming. Further, the manufacturing process of a sprocket made of low carbon steel is simpler than that of a sprocket made of medium carbon steel. Therefore, the manufacturing cost can be greatly reduced. In spite of the above advantages, the sprocket made of low carbon steel is disadvantageous in that it is impossible to provide a sufficiently high hardness and further the anti-abrasion property is greatly deteriorated.
DISCLOSURE OF THE INVENTION
The present invention has been accomplished by the inventors who discovered that even the hardness of low carbon steel can be increased to a value close to the theoretical maximum quenching hardness when it is cooled more quickly than it is cooled being dipped in water. It is an objec
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Metsugi Fumihiko
Ohata Akihito
Takamori Norihiko
Takeda Shunji
Yoshiie Akihito
Hannon Thomas R.
Sunstar Engineering Inc.
Uni-Sunstar B.V.
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