Textiles: spinning – twisting – and twining – Strand structure – Covered or wrapped
Reexamination Certificate
2000-06-02
2002-07-02
Worrell, Danny (Department: 3765)
Textiles: spinning, twisting, and twining
Strand structure
Covered or wrapped
C057S204000, C057S206000, C057S207000, C057S211000, C057S212000, C057S213000, C057S214000, C057S215000, C057S218000, C057S219000, C057S230000, C057S231000, C057S236000, C057S237000
Reexamination Certificate
active
06412263
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates, in general, to reinforcing steel cords for a variety of rubber products, such as tires and conveyor belts, and, more particularly, to a reinforcing steel cord formed by twisting a plurality of external element wires around a twisted flat core, thus having a plurality of interspaces between the core and the wires in addition to a plurality of interspaces between the wires, the steel cord thus allowing the rubber material to be more effectively penetrated into the cord through the interspaces during a production process of the rubber products and being free from an undesirable movement of the core within the cord, and being improved in its ageing adhesive force with the rubber material, the present invention also relating to a method and device for producing such steel cords.
2. Description of the Prior Art
As well known to those skilled in the art, steel cords are used as reinforcing materials for rubber products or elastomer products, such as tires or conveyor belts. The steel cords, used as the reinforcing materials for such rubber products, are superior in desired characteristics, such as strength, modulus, heat resistance and fatigue resistance, in comparison with other conventional reinforcing materials, such as organic or inorganic fibers. Therefore, the steel cords have been more preferably used as reinforcing materials of such rubber products than such other reinforcing materials. Particularly when such steel cords are used as the material of the carcass or the steel belt layer of a radial tire, the steel cords remarkably improve the fretting resistance, durability and steering response of the tire.
A steel cord, used as a reinforcing material for radial tires or conveyor belts, is typically formed by twisting a plurality of element wires together to form a strand structure or by twisting a plurality of strands together to form a wire rope structure. In order to allow such steel cords to perform a desired reinforcing function within a rubber product, it is necessary for the steel cords to be physically, chemically and firmly integrated with the rubber material.
FIGS. 1
to
5
are sectional views, respectively showing examples of conventional reinforcing steel cords for radial tires.
FIG. 1
shows a steel cord, which has a double layer twisted structure and is typically used as the belt layer material of steel belted radial tires for large-scaled vehicles, such as trucks or buses. AS shown in the drawing, the steel cord
1
has a 3+6 element wire structure wherein six external element wires
1
b
are twisted around a core to form a double layer twisted structure, with the core being formed by twisting three core element wires la together to form a core.
However, the above double layer twisted steel cord
1
is problematic in that it is somewhat complex in structure since it has many element wires. In addition, the above steel cord
1
has to be produced through two twisting processes, or a primary twisting process of twisting the three core element wires la to form a core and a second twisting process of twisting the six external element wires
1
b
around the core to form a cord. This finally complicates the process of producing the reinforcing steel cords in addition to an increase in the production cost of the steel cords. In the above steel cord
1
, a central space H is formed at the center of the three twisted core element wires
1
a
, but it is almost impossible for the rubber material to be penetrated into the central space H during a tire production process. This steel cord
1
is thus undesirably reduced in its ageing adhesive force with the rubber material.
Another problem experienced in the above steel cord
1
resides in that the cord
1
is somewhat heavy and has a large diameter, thus being not agreeable with the recent trend of lightness of tires or of an improvement in maximum safe mileage.
In an effort to overcome the above-mentioned problems of the double layer twisted steel cord
1
, a steel cord, having a single layer twisted open structure, has been proposed as disclosed in Japanese Laid-open Publication No. Heisei. 6-65,877. This Japanese steel cord, shown in
FIG. 2
of the accompanying drawings, has a small diameter in addition to a simple construction. This steel cord is also produced through a single process free from the primary twisting step of forming the twisted core different from the steel cord
1
of FIG.
1
. As shown in the drawing, a plurality of element wires, for example, six element wires
2
a
are twisted together to form a steel cord
2
while being respectively and exceedingly preformed. This steel cord
2
is, thereafter, externally forced to be somewhat flattened, thus having a generally elliptical cross-section. In the above steel cord
2
, a plurality of interspaces S are formed between the element wires
2
a.
The above steel cord
2
is produced through a single twisting process, thus simplifying the cord production process in addition to a reduction in the cord production cost. In the above steel cord
2
, the element wires
2
a
are somewhat loosely integrated since they are respectively and exceedingly preformed during the process of producing the cord
2
, thus forming the desired interspaces S between the wires
2
a
. Due to such interspaces S, the rubber material is allowed to be penetrated into the steel cord
2
during a process of producing a steel belted radial tire. In addition, since each flat surface of the above steel cord
2
is almost kept on the same plane within the total length of the cord
2
, it is possible to reduce the thickness of a resulting tire while preferably reducing the weight of the tire.
However, the above steel cord
2
is problematic in that since the element wires
2
a
are loosely twisted together while being respectively preformed, the cord
2
is exceedingly high in its elongation even in the case of application of low load. This cord
2
is thus difficult to be handled by a worker during a tire production process. In order to preform the element wires
2
a
within a predetermined range, it is necessary to mechanically process the element wires
2
a
using a specific preforming jig, such as a plate-type preforming device or a rotary-type preforming device. In such a case, severe friction is generated at the contact portions between the element wires
2
a
and the jig, thus undesirably removing brass coating layers from the surfaces of the element wires
2
a
and damaging the wires
2
a
. This finally reduces the rubber adhesive force and buckling fatigue resistance of the steel cord
2
.
Particularly, the above steel cord
2
is very difficult to handle during a process of producing desired rubber products having the cords
2
and necessarily has a fine difference in the low load elongation between the wires
2
a
. Therefore, it is difficult to regularly array the steel cords
2
within a topping sheet, thus resulting in irregular quality of resulting topping sheets. In the case of tires using belt layers made of such steel cords
2
, the steel cords
2
may be easily loosened during a rotation of the tires on a street. This may finally allow the belt layers to be unexpectedly deformed, thus reducing the steering response of the tires and occasionally causing safety hazards.
FIG. 3
shows a conventional steel cord
3
, which has a 1+6 element wire structure wherein six external element wires
3
b
are twisted around a core
3
a
, made of one core element wire having a circular cross-section, to form a cord. On the other hand,
FIG. 4
shows another conventional steel cord
4
, which has a 1+6 element wire structure, with six external element wires
4
b
being twisted around a core
4
a
, made of one core element wire, to form a steel cord in the same manner as that described for the cord
3
of FIG.
3
. However, the core
4
b
of this steel cord
4
is rolled by a press roll pair to have a flat cross-section different from the that of the cord
3
.
In the steel cords
3
and
4
each
Lee Byung-Ho
Lim Seung-Ho
Hongduk Steel Cord Co., Ltd.
Hurley Shaun R
Perman & Green LLP
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