The invention relates to a steel cord adapted to reinforce rubber products, more specifically for heavy duty tires such as the off-the-road tires and earthmover tires.
The large off-the-road pneumatic tires used in heavy construction and earthmoving operations have operating loads and inflation pressures much higher than conventional trucks and lightweight vehicles. Therefore, the radial ply earthmover tires exhibit tremendous load-carrying capacity and need particular reinforcing cords.
JP10131066A discloses a 7×7 cord to meet this load-carrying requirement. JP 2006104636A further discloses a 1×(3+9)+6×(3+9) cord wherein the twisting direction of the strands is the same as the twisting direction of the cord.
Besides, the other concern for the performance of the off-the-road tire is insuring adequate rubber penetration into the cords, which is achieved during the manufacture of the belt layers and in subsequent tire vulcanization. Coupled to this better rubber flow is a desire for higher steel mass and improved wire cut resistance to improve the tires' overall durability. A further requirement for steel cord reinforcing off-road tire is impact resistance capacity, because the surface off the road is not as smooth as the surface of a paved highway. Improved impact resistance capacity not only prolongs the lifetime of the tire but also makes drivers more comfortable when travelling on a bumpy surface.
US2004/0020578A1 discloses a multiple filament diameters in a 7×7 cord design to increase the filament spacings in the cord, which allows better rubber penetration for improved resistance to corrosion as well as superior cut resistance. However, the increased void area in the cord cuts the area of load-bearing steel filaments, which undermines the load-carry capacity of the cord.
It is an object of the invention to provide a multi-strand steel cord with adequate rubber penetration coupled with a maximum load-carry capacity.
A steel cord adapted for the reinforcement of rubber products, comprises a core, this core can be a single wire, a single strand, multiple strands or a polymer element.
The steel cord further comprises three or more outer stands twisted around said core in a cord twisting direction.
Each of the three or more outer strands comprises outer strand filaments lying at the radially external side of the three or more outer strands. The steel outer filaments are twisted in with a strand twisting direction which is the same as the cord twisting direction.
The three or more outer strands have a wavy form.
Preferably, the wavy form is a crimp form obtainable by means of at least one pair of toothed wheels. Crimps may also be obtained by a set of cams. A crimp is a planar wave. However, depending upon the way of twisting, by means of a tubular twisting machine (=cabling) or by means of a double-twister (=bunching) the planar wave may not rotate or rotate.
The wavy form may be a double crimp obtainable by means of two pairs of toothed wheels. The strand is first provided with a first crimp lying in a first plane by the first pair of toothed wheels. The strand is further provided with a second crimp lying in a second plane substantially different from the first plane by the second pair of toothed wheels.
The amplitude of the wavy form ranges from 1.10 to 2.0 times of the diameter of the strand. If the amplitude of the wavy form is smaller than 1.10 times of the diameter of the strand, the spacing between the strands is too small to allow rubber penetration. If the amplitude of the wavy form is bigger than 2.0 times of the diameter of the strand, the spacing between the strands is too big, and cut the load-carrying capacity of the cord.
The pitch of the wavy form ranges from 4.0 to 8.0 times of the diameter of the strand. If the pitch of the wavy form is smaller than 4.0 times of the diameter of the strand, the spacing between the strands is too big, and cut the load-carry capacity of the cord. If the pitch of the wavy form is greater than 8.0 times of the diameter of the strand, the spacing between the strands is too small to allow rubber penetration.
Preferably, the core of the steel cord is a strand of core filaments. The core filaments are twisted in a core twisting direction which is the same as the cord twisting direction.
A steel cord according to the invention may be used as a as reinforcement for an off-the-road tire, e.g. in one of the outermost belt layers of the off-the-road tire.
The invention will now be described into more detail with reference to the accompanying drawings.
Neither the first pair of toothed wheels 22 nor the second pair of toothed wheels 24 needs to be driven by external means. They are both driven and rotated by the passing outer strand 14.
It is important that the second pair of toothed wheel 24 is positioned as close as possible to the first pair of toothed wheels 22 in order to prevent the first crimp from tilting or rotating from plane xz to plane yz under the influence of the second crimp.
Both the first crimp amplitude A1 and the second crimp amplitude A2 may be varied independently of each other. So A1 may be equal to A2 or may be different from A2. Both amplitudes may vary between 1.10 to 2.0 times of the diameter of the outer strand 14. Both the first crimp pitch Pc1 and the second crimp pitch Pc2 may be varied independently of each other. So Pc1 may be equal to Pc2 or may be different from Pc2. The more Pc1 differs from Pc2, the easier it is to prevent the first crimp from tilting. Both pitches may vary between 4.0 to 8.0 times of the diameter of the outer strand 14. it is, however, to be preferred, that in twisted structures at least one, and most preferably both, of the crimp pitches is smaller than the cord twist pitch of steel cord 10.
A 7×7 SSS steel cord 10 according to the invention was built as follows:
Core strand 12 comprises one core filament with diameter of 0.365 mm and six peripheral filaments with diameter of 0.35 twisted around the core filaments in S direction with twisting pitch 18 mm.
Outer strands 14 comprise one core filament with diameter of 0.34 mm and six peripheral filaments 16 with diameter of 0.34 mm twisted around the core filament in S direction with twisting pitch 18 mm and the diameter of the outer strands 14 is 1.02 mm.
Outer strands 14 are further crimped by a pair of toothed wheels into a wavy form, while the amplitude is 1.5 mm, and the pitch is 5.3 mm.
Six outer strands 14 are twisted around the core strand 12 in S direction with twisting pitch 28 mm.
This 7×7 SSS steel cord diameter is around 3.2 mm.
Number | Date | Country | Kind |
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08169886 | Nov 2008 | EP | regional |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2009/065629 | 11/23/2009 | WO | 00 | 5/24/2011 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO2010/060878 | 6/3/2010 | WO | A |
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20110225944 A1 | Sep 2011 | US |