Textiles: spinning – twisting – and twining – Strand structure – Covered or wrapped
Reexamination Certificate
2000-02-18
2001-08-14
Falik, Andy (Department: 3765)
Textiles: spinning, twisting, and twining
Strand structure
Covered or wrapped
C057S902000, C152S556000, C152S451000, C152S527000
Reexamination Certificate
active
06272830
ABSTRACT:
TECHNICAL FIELD
This invention relates to steel cords for reinforcing elastomeric articles and, more particularly, to steel cords which form a portion of the carcass of an endless track.
BACKGROUND ART
The use of endless tracks on vehicles is becoming increasingly more popular, especially in agricultural applications. An endless track is a belt that has no distinct beginning or ending and is made of elastomeric materials reinforced by steel cords. The radially outermost portion of the track has a ground engaging tread, similar to that on a tire. The primary purpose of a track is to provide a larger surface area of contact between the vehicle and the ground. This is especially useful in keeping the vehicle afloat when running on soft surfaces, such as muddy ground.
The endless track generally contains multiple regions having steel cord reinforcement. A first steel cord reinforced region is the carcass. The carcass is an elastomeric layer having a circumferentially oriented steel cord. This steel cord lays in a longitudinal direction and is spirally wrapped around the circumference of the endless track from a first edge to a second edge. This cord carries substantially all of the tensile working load of the track, and as a result, is generally the thickest steel cord in the track. Typically, an endless track will have at least two plies positioned radially outwardly of the carcass. Each ply contains a steel wire reinforcement. The steel wire reinforcement of these plies is laid at a bias angle with respect to the equatorial plane of the track. The most common arrangement for these plies is that the steel wire reinforcement of the first ply is at an angle opposite the steel wire reinforcement of the second ply. Commonly a third ply will be placed radially outwardly of the bias angled plies. The steel wire reinforcement of this third ply generally is laid at an angle perpendicular to the equatorial plane.
Currently, the steel cord reinforcing the carcass is formed from seven strands of seven steel wires. As shown in
FIG. 1
, each strand includes a single core wire that is helically wrapped by a sheath of six wires. A first strand then makes up the core of the steel cord and the six remaining strands are helically wrapped around the first strand to form the completed steel cord.
Although the current steel cord construction provides sufficient support to handle the tensile working load of the track, the cord experiences a problem known as “wire migration.” The wire forming the core of the first stand of the cord tends to break after being subjected to the bending stresses of an extended service life. After continued service, an end of the broken wire migrates through the surrounding sheath and remaining strands and punctures the elastomeric material forming part of the carcass. As a result, the end of the broken wire protrudes from the track. Although the protruding wire does not cause a failure of the track, the protruding wire reduces the aesthetics of the track and may open a passageway for moisture to penetrate to the steel cord.
SUMMARY OF THE INVENTION
This invention provides to a steel cord for reinforcing elastomeric articles. The steel cord has a plurality of strands. Each strand has a core and a sheath. The sheath is a plurality of steel filaments helically wrapped about the core. A first strand extends longitudinally through the center of the cord. The remaining strands are helically wrapped about the first strand. The core of the first strand is a plurality of filaments twisted together.
In the preferred embodiment, three filaments form the core of the first strand. These three filaments are twisted in an S-direction at a lay length of 7 mm. The sheath of the first strand is helically wound about the core in an S-direction at a lay length of 14 mm. The sheath of each remaining strand is helically wound about the core of the respective remaining stand in a Z-direction at a lay length of 29 mm. The remaining strands are helically wound about the first strand in an S-direction at a lay length of 40 mm.
Definitions
For ease of understanding this disclosure, the following terms are disclosed.
“Carcass” means the first reinforced layer of the track located radially outwardly of the interior surface of the track. The carcass is an elastomeric layer having steel cord reinforcement. The steel cord reinforcement is generally spirally wrapped around the circumference of the track and travels from a first edge to a second edge.
“Circumferential” means lines or directions extending along the perimeter of the track surface parallel to the equatorial plane and perpendicular to the axial direction.
“Cord” denotes a plurality of bundles or strands of grouped filaments of high modulus material.
“Equatorial Plane (EP)” means the plane perpendicular to the axial direction of the track and passing through the center of the track.
“Lay length” means the distance at which a twisted filament or strand travels to make a 360 degree rotation about another filament or strand.
“Longitudinal” means in a circumferential direction.
“Ply” means a continuous layer of elastomeric material having parallel cords.
“Radial” or “radially” mean directions toward or away from the centroid of the track. The centroid of the track is located at the intersection of a line drawn from the upper and lower sections of the track and the forward and rear sections of the track when mounted on a drive device.
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Morgan John Gomer
Sinopoli Italo Marziale
Falik Andy
King David L
The Goodyear Tire & Rubber Company
Whitman Dan
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