Textiles: spinning – twisting – and twining – Strand structure – Covered or wrapped
Reexamination Certificate
1999-07-19
2001-07-03
Worrell, Danny (Department: 3765)
Textiles: spinning, twisting, and twining
Strand structure
Covered or wrapped
C057S237000, C057S902000, C152S527000, C152S556000
Reexamination Certificate
active
06253536
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a steel cord for radial tires, and more particularly relates to a steel cord for radial tires having a construction including a “2+5” bi-diametric cord formed by twisting a core and a strand in such a fashion that they have the same twist pitch length and the same twist direction, so that the number of processing steps for the twisting process is reduced from two to one, thereby reducing the manufacturing costs while achieving an improvement in productivity.
2. Description of the Prior Art
In a steel cord having a two-layer twisted construction, a core, which forms a first layer of the steel cord, and a strand, which forms a second layer of the steel cord, are typically different from each other in terms of twist pitch length and twist direction as follows:
Steel Cord Construction: 1×3(0.20)+6(0.35)
Twist Pitch Length of Core: 10 mm
Twist Pitch Length of Strand: 18 mm
Twist Direction of Core: S (Right)
Twist Direction of Strand: Z (Left)
For this reason, it is impossible to carry out the twisting process for the manufacture of such a cord using a single processing step. Conventionally, the twisting process has been carried out using two processing steps. However, this results in an increase in the manufacturing costs for cords. Furthermore, the contact between the core and strand is rendered to be a point contact. Where such a cord is applied to a tire, a stress concentration occurs at portions of the cord, where point contacts are formed, during the use of the tire. Due to such a stress concentration, a fretting phenomenon occurs which results in a degradation in the durability of the tire.
In order to reduce the above mentioned drawback, a method for the manufacture of steel cords having a two-layer twisted construction has been proposed in which a steel cord is formed by twisting a core and a strand in such a fashion that they have different twist pitch lengths while having the same twist direction as follows:
Steel Cord Construction: 1×2+7(0.30)
Twist Pitch Length of Core: 8 mm
Twist Pitch Length of Strand: 16 mm
Twist Direction of Core: S (Right)
Twist Direction of Strand: S (Right)
In this case, it is still impossible to carry out the twisting process for the manufacture of such a cord using a single processing step because the core and strand are different in terms of twist pitch length. Consequently, the twisting process has been carried out using two processing steps in accordance with this method. For this reason, an increase in the manufacturing costs for cords is still involved. Although line contacts are formed between the core and strand by virtue of the same twist direction, they are unstable because the core and strand have different twist pitch lengths. In other words, although this method can reduce the durability degradation of the tire to a some degree, it has a limitation in completely eliminating the fundamental problems.
Meanwhile, in the case of a cord layered with topping rubber, an insufficient penetration of the topping rubber into the core layer may occur. Where such a cord is applied to a tire, such an insufficient penetration of the topping rubber results in a movement of the core layer. As a result, corrosion of the cord caused by moisture or salt is accelerated, thereby greatly degrading the durability of the tire.
SUMMARY OF THE INVENTION
Therefore, an object of the invention is to eliminate the above mentioned problems and to provide a steel cord for radial tires having a construction formed by twisting a core and a strand in such a fashion that they have the same twist pitch length and the same twist direction, so that the number of processing steps for the twisting process is reduced from two to one, thereby reducing the manufacturing costs while achieving an improvement in productivity, and so that the core and strand are in stable and almost complete line contact with each other, thereby achieving an improvement in the durability of tires to which the steel cord is applied.
In accordance with the present invention, this object is accomplished by providing a steel cord for radial tires and a radial tire using the steel cord in a belt, a carcass, or a chafer thereof, the steel cord comprising: a core layer having two filaments twisted to have a twist pitch length of 10 mm to 22 mm; a strand layer having five filaments twisted to have the same twist pitch length and the same twist direction as the core layer; and said filaments of said core and strand layers being made of a carbon steel having a carbon content ranging from 0.70% to 0.96% by weight and being plated with brass at respective surfaces thereof to obtain an enhanced adhesion force to rubber, said filaments having a tensile strength of 260 kgf/mm
2
to 385 kgf/mm
2
prior to twisting thereof to form said steel cord.
In accordance with the present invention, the core and strand layers have the same twist direction and the same twist pitch length. Accordingly, the core and strand are not in point contact with each other, but is in line contact with each other. Therefore, the steel cord of the present invention minimizes the occurrence of the fretting phenomenon. In addition, the twisting process for the manufacture of the cord construction according to the present invention can be achieved using a single processing step, as compared to those for conventional constructions involving two processing steps.
REFERENCES:
patent: 4609024 (1986-09-01), Yatsunami et al.
patent: 4690191 (1987-09-01), Kawasaki
patent: 5213640 (1993-05-01), Ikehara
patent: 5598693 (1997-02-01), Yanagisawa et al.
patent: 5706641 (1998-01-01), Ishizaka
patent: 5802829 (1998-09-01), Yamanaka
patent: 5968651 (1999-10-01), De Vos et al.
Fish & Richardson P.C.
Hankook Tire Co., Ltd.
Worrell Danny
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