Endless belt power transmission systems or components – Friction drive belt – Including discrete embedded fibers
Reexamination Certificate
2000-04-14
2002-04-23
Bucci, David A. (Department: 3682)
Endless belt power transmission systems or components
Friction drive belt
Including discrete embedded fibers
C474S264000
Reexamination Certificate
active
06375590
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a toothed belt for power transmission, and more particularly to a power-transmission toothed belt for use in general industrial machineries. The toothed belt of the type concerned is used for transmitting power from one pulley to another rotated at low speeds under heavily-loaded conditions.
2. Description of the Related Art
A toothed belt for driving a camshaft of an automobile engine is used under the conditions where the low-temperature resistance, high-temperature resistance, flexing resistance and quietness are severely required. Currently, the toothed belt is produced by vulcanizing and pressing (or otherwise molding) a rubber composition containing, as major ingredients, hydrogenated nitrile rubber and zinc polymethacrylate after several additives are blended with the rubber composition.
On the other hand, toothed belts designed for use in general industrial machineries are mainly used for the purpose of transmitting power between two shafts and they operate at low speeds under heavily loaded conditions. Under such conditions, the high-temperature resistance and quietness, such as required in an application to automobile engines, are not necessary. More specifically, a heat resistance on the order of 80° C. is sufficient, and a low-temperature resistance enough to withstand the room temperature is satisfactory. In addition, the flexing resistance is not highly demanded. In the manufacture of the toothed belts for general industrial machineries, urethane rubber is selected for this purpose as a main component because the urethane rubber can provide sufficient physical properties even when the rigidity thereof is increased within a certain range. The urethane rubber is vulcanized and pressed or otherwise molded into a toothed belt with a tensile member made of aromatic polyamide fibers being embedded in the urethane rubber.
The toothed belts designed for use in general industrial machineries may occasionally be used at high speeds. In this instance, a rubber portion forming teeth (hereinafter referred to as “tooth rubber”) of the toothed belts becomes soft due to high self-heating properties of the urethane rubber. As a consequence, the rigidity of tooth rubber decreases, tending to cause a breakage of teeth present on the toothed belts. This same teeth breakage problem may also occur when the toothed belts are used under high temperature environmental conditions.
Thus rubber compositions are used for automobile engines to produce a toothed belt for general industrial machineries. However, since the conventional toothed belts for automobile engines are designed for use under relatively low load conditions, if components of the rubber composition are changed to withstand the heavily loaded conditions, the high-temperature resistance, low-temperature resistance, flexing resistance and quietness are lost.
In addition, since aromatic polyamide fibers are used in making the tensile member of the conventional toothed belts, the dimensional stability of the tensile member is relatively low because the fibers are likely to undergo elongation and contraction when subjected to changes in the temperature, humidity or the like environmental condition. Use of such dimensionally unstable tensile members brings about remarkable changes in the tooth-belt tension, leading to reduction of the lifetimes of the toothed belts and peripheral devices as well as the generation of unpleasant operation noises.
Furthermore, since the aromatic polyamide fibers poorly adhere to the urethane rubber, a peel-off problem of the tooth rubber may arise. In addition, it is difficult to improve the bonding strength between the fibers. Thus, in heavily loaded, high-speed applications, the toothed belt encounters a tooth-breakage problem as well as a breakage of the toothed belt.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a toothed belt having qualities suitable for use in general industrial machineries.
Another object of the present invention is to provide a toothed belt formed from a rubber composition which is capable of withstanding heavily loaded, high-speed conditions.
A further object of the present invention is to provide a toothed belt formed from a rubber composition which has a formulation improved to increase the lifetime of the toothed belt and lower operation noises of the toothed belt.
Still another object of the present invention is to improve the affinity between a rubber composition and a tensile member of the tooth belt thereby increasing the bonding strength a between rubber and the tensile member to such an extent that the tooth rubber peel-off problem from the toothed belt is completely prevented.
In one aspect, the present invention provides a toothed belt comprising a cured rubber belt body formed primarily from a vulcanizable rubber composition containing hydrogenated nitrile rubber and zinc polymethacrylate, and a tensile member embedded in the belt body, wherein the rubber composition is comprised of zinc polymethacrylate and hydrogenated nitrile rubber having an iodine value of 4-28 g which are blended together in a ratio of 22:78 to 45:55 parts by weight.
In a toothed belt having a belt body formed from a vulcanizable rubber composition containing hydrogenated nitrile rubber and zinc polymethacrylate, the zinc polymethacrylate forms a higher-order network structure in a polymer of the belt body. Accordingly, a proportion of the zinc polymethacrylate must be held down to some extent; otherwise, in an application where the toothed belt is driven to run at high speeds along a complicated path, the toothed belt would encounter a problem that the flexing resistance is remarkably reduced and the belt body separates or peels off from the tensile member.
However, since the general industrial machineries require heavy duty power transmission, toothed belts used therein operate at relatively low speeds because they are mainly used for the purpose of achieving power transmission between two shafts. In the present invention, this particular use or application is perceived, and the aforesaid higher-order network structure forming-function of the zinc polymethacrylate is utilized so that a rubber composition containing hydrogenated nitrile rubber and zinc polymethacrylate can possess an on-load performance (load-bearing properties) which is improved to the level of urethane rubber. The on-load performance is particularly chosen from among many performances of the conventional toothed belts required for use in the general industrial machineries.
To improve the on-load performance, the present invention sets the blending ratio of zinc polymethacrylate and hydrogenated nitrile rubber to be in a range of 22:78 to 45:55 parts by weights. If the proportion of zinc polymethacrylate is below 22 parts by weight, a belt body formed after vulcanization of the rubber composition achieves an insufficient on-load performance and, hence, the belt body is not suitable for use in the general industrial machineries requiring heavy duty power transmission. Conversely, if the proportion of zinc polymethacrylate exceeds 45 parts by weight, the hardness of the belt body is increased to a level which makes the flexing resistance and quietness of the toothed belt unsatisfactory even in an application to the general industrial machineries.
Preferred examples of the hydrogenated nitrile rubber used in the present invention include hydrogenated nitrile rubber with a nitrile content of 30 to 50% and having an iodine value of 4-28 g. These examples include a 90-98% hydrogenated nitrile rubber which is available in the market (under the product name “Z-pole series” of Nippon Zeon Co, Ltd.
If the iodine value is not greater than 4 g, a great amount of vulcanizing agent added to provide prescribed rubber properties exerts a negative influence to the resorcin-formalin-latex of the tensile member (core) such that an unnecessarily great rigidity is provided to the toothed belt, tending to lower the f
Arai Tatsuo
Kikuchi Hiroshi
Tomobuchi Masato
Dann Dorfman Herrell and Skillman, P.C.
Skillman Henry H.
Tsubakimoto Chain Co.
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