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Title:
STEEL CORD WITH FULL ELASTOMER PENETRATION
Document Type and Number:
WIPO Patent Application WO/2013/107570
Kind Code:
A1
Abstract:
A steel cord (10) adapted for the reinforcement of elastomers, comprises a first group and a second group, the second group being helically twisted around the first group with a cord twisting step, the first group comprising a first number of first steel filaments (12), the first number ranging between three and eight, the second group comprising a second number of second steel filaments (14), the second number being equal to or greater than the first number, the first filaments having a twisting step greater than 300mm, both the first steel filaments (12) and the second steel filaments (14) being preformed. The steel cord has a PLE at a tensile tension of 50 Newton between 0.08% and 0.25%. This steel cord has measurable deformation to achieve full elastomer penetration, but also maintains the process-ability and functionality for elastomer reinforcement.

Inventors:
ZHANG QINXIA (CN)
LIU XING (CN)
ZHU HONGZHEN (CN)
Application Number:
PCT/EP2012/075247
Publication Date:
July 25, 2013
Filing Date:
December 12, 2012
Export Citation:
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Assignee:
BEKAERT SA NV (BE)
International Classes:
D07B1/06; D07B7/02
Domestic Patent References:
WO2002088459A12002-11-07
WO1995016816A11995-06-22
WO1999028547A11999-06-10
WO2002088459A12002-11-07
Foreign References:
JPH0533277A1993-02-09
Attorney, Agent or Firm:
MESSELY, Marc (Bekaertstraat 2, Zwevegem, BE)
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Claims:
Claims

1. a steel cord (10) comprising a first group and a second group, said second group being helically twisted around said first group with a cord twisting step, said first group comprising a first number of first steel filaments (12), said first number ranging between three and eight, said second group comprising a second number of second steel filaments (14), said second number being equal to or greater than said first number, said first filaments (12) having a twisting step greater than 300mm, both said first steel filaments (12) and said scond steel filaments (14) being preformed, characterized in that said steel cord (10) has a PLE at a tensile tension of 50 Newton between 0.08% and 0.25%.

2. a steel cord according to claim 1 , wherein said steel cord (10) has a PLE at a tensile tension of 50 Newton between 0.10% and 0.18%.

3. a steel cord according to claim 1 , wherein said second steel filament (14) has a PLE at a tensile tension of 50 Newton between 0.9% and 2.0%.

4. a steel cord according to claim 3, wherein said second steel filament (14) has a PLE at a tensile tension of 50 Newton between 1.0% and 1.2%.

5. a steel cord according to claim 1 , wherein said first steel filament (12) has a PLE at a tensile tension of 50 Newton between 0.4% and 1.0%.

6. a steel cord according to claim 5, wherein said first steel filament (12) has a PLE at a tensile tension of 50 Newton between 0.65% and 0.75%.

7. a steel cord according to claim 1 , wherein said first number is 4.

8. a steel cord according to clainn 7, wherein said second number is 6.

9. a steel cord according to claim 1 , wherein said first filament (12) is

preformed into a spatial wavy form.

10. a steel cord according to claim 9, wherein said spatial wavy form has a first crimp and a second crimp, the first crimp lying in a plane that is

substantially different from the plane of the second crimp.

1 1. a steel cord according to claim 1 , wherein said second filament (14) is

polygonally preformed.

Description:
Steel cord with full elastomer penetration

Description

Technical Field

[1 ] The invention relates to a steel cord adapted for the reinforcement of

elastomers such as rubber conveyor belts, pneumatic tyres, rubber hoses, rubber timing belts or timing belts in polyurethane. The steel cord has an open structure to allow full rubber penetration.

Background Art

[2] Steel cords with twisted steel filaments are known in the art, particularly in the art of rubber reinforcement, and more particularly in the art of pneumatic tyre reinforcement.

[3] One of the major requirements put upon steel cords is full penetration of the elastomer such as rubber. This means that rubber must be able to penetrate into the cord between the composing elements and fill all possible interstices in order to reduce fretting and tension between the elements and to avoid moisture from travelling along the cord, which would cause a lot of corrosion and which would considerably reduce the life of the cord and the rubber product.

[4] To achieve full rubber penetration, prior arts provide solutions to deform the steel filaments and to construct an open steel cord. WO95/16816A1 discloses a technology to polygonally deform steel filaments without extra energy. WO99/28547A1 discloses a technology to crimp steel filaments in two planes. WO02/088459A1 discloses a steel cord comprising a first group and a second group. The second group is helically twisted around the first group with a cord twisting step. The first group comprises a first number of first steel filaments. The first number ranges between three and eight. The second group comprises a second number of second steel filaments. The second number is equal to or greater than the first number. The first filaments having a twisting step greater than 300mm. At least one of the second filaments is polygonally preformed in order to allow rubber penetration. [5] Although prior arts provide a few ways to make open steel cord and to allow rubber penetration, how much deformation on the steel cord can achieve full rubber penetration is still unknown.

Disclosure of Invention

[6] The primary object of the invention is to provide a steel cord with

measurable deformation to achieve full rubber penetration.

[7] The second object of the invention is to provide a steel cord with full

rubber penetration without weakening the process-ability and functionality of the steel cord for elastomer reinforcement.

[8] According to a first aspect of the invention a product is claimed that a steel cord comprising a first group and a second group, the second group being helically twisted around the first group with a cord twisting step, the first group comprising a first number of first steel filaments, the first number ranging between three and eight, the second group comprising a second number of second steel filaments, the second number being equal to or greater than the first number, the first filaments having a twisting step greater than 300mm, both the first steel filaments and the second steel filaments are preformed. The steel cord has a PLE at a tensile tension of 50 Newton between 0.08% and 0.25%. More preferably, the steel cord has a PLE at a tensile tension of 50 Newton between 0.10% and 0.18%. The second steel filament has a PLE at a tensile tension of 50 Newton between 0.9% and 2.0%, and more preferable between 1 .0% and 1 .2%, while the first steel filament has a PLE at a tensile tension of 50 Newton between 0.4% and 1 .0%, and more preferable between 0.65% and 0.75%. The first number is 4, while the second number is 6. The first steel filaments are preformed into a spatial wavy form, and more preferable the spatial wavy form has a first crimp and a second crimp, while the first crimp lying in a plane that is substantially different from the plane of the second crimp. The second steel filaments are polygonally preformed. Brief Description of Figures in the Drawings

[9] Figure 1 describes a first preferred embodiment of the invention.

[10] Figure 2 illustrates the tensile tension and elongation curves for steel cords with different PLE.

Mode(s) for Carrying Out the Invention

[1 1 ] Figure 1 illustrate a steel cord incorporating present invention, wherein steel cord 10 comprises a first group of filaments 12 and a second group of filaments 14. The second group is helically twisted around the first group with a cord twisting step. The first group comprises 4 first steel filaments 12, while the second group comprises 6 second steel filaments 14. The first filaments 12 have a twisting step greater than 300mm. Both the first steel filaments 12 and the second steel filaments 14 are

preformed. Therefore, there are spaces between the filaments.

[12] To achieve full rubber penetration, the steel cord has a PLE at a tensile tension of 50 Newton between 0.08% and 0.25%. More preferably, the steel cord has a PLE at a tensile tension of 50 Newton between 0.10% and 0.18%. In the tyre making process, steel cord is under a tensile tension between 8 Newton and 12 Newton in the calendaring operation, where steel cords are merged into rubber matrix. To make sure there are always spaces for rubber to penetrate between the filaments, the steel cord PLE at a tensile tension of 50 Newton should not below 0.08%, because too low PLE means the openings between steel filaments may close under the tensile tension between 8 Newton and 12 Newton in the calendaring operation. On the other hand, although bigger steel cord PLE brings better rubber penetration, the upper limit for steel cord PLE is around 0.25%. Steel cords are embedded in pneumatic tyres as tensile reinforcement, while steel cord with PLE bigger than 0.25% means a very open cord, which may firstly cause troubles in the construction of the steel cord because the steel cord is too loose, and secondly cause troubles in tyre making process, for example rough ply or un-even spacing, which will lead to un-uniformity in tyre and destroy dynamic balance of the tyre, and thirdly cannot exert enough strength in a tyre because big PLE means big elongation under tension and steel cord with big PLE cannot exert the same strength as steel cord with small PLE in the same condition.

Therefore, steel cord PLE should between 0.08% and 0.25%, and more preferable between 0.10% and 0.18%.

[13] Based on the similar reasoning, to achieve desired steel cord PLE, there are low and upper limits for the steel filaments. The second steel filament should has a PLE at a tensile tension of 50 Newton between 0.9% and 2.0%, and more preferable between 1 .0% and 1 .2%, while the first steel filament has a PLE at a tensile tension of 50 Newton between 0.4% and 1 .0%, and more preferable between 0.65% and 0.75%. Comparatively, the second steel filament needs bigger PLE than the first steel filament, to make spaces between the second filaments to achieve full rubber penetration.

[14] Contrastive test on 4+6x0.30mm steel cord also confirms above reasoning.

First filament diameter (mm) 0.30 0.30 0.30 0.30 0.30

First filament PLE at 50N (%) 0.4 0.65 0.7 0.75 1 .0

First filament lay length (mm) >300 >300 >300 >300 >300

First filament twisting direction S S S S S

Second filament diameter 0.30 0.30 0.30 0.30 0.30 (mm)

Second filament PLE at 50N 0.9 1 .0 1 .1 1 .2 2.0 (%)

Second filament lay length 18 18 18 18 18 (mm)

Second filament twisting S S s S S direction

Steel cord lay length (mm) 18 18 18 18 18

Steel cord twisting direction S S s S S

Steel cord PLE at 50N (%) 0.08 0.10 0.14 0.18 0.25

Polymer penetration (% loss in 50 5 0 0 0 pressure)

E-modulus (GPa) 175 175 175 175 175 [15] Figure 2 illustrates the tensile tension and elongation curves for steel cords with different PLE, wherein line 22 represents steel cord with PLE 0.08%, 24 for PLE 0.14%, and 26 for PLE 0.25%. The three lines have same gradient because the three steel cords have same E-modulus, while the structural elongation is different because the openness of the steel cord is different. Therefore, line 22, 24, and 26 parallel and offset to each other. Under the same elongation at E, line 22 will exert F2, line 24 F4, and line 26 F6. Hence, steel cord with PLE bigger than 0.25% may not exert enough force for polymer reinforcement.

[16] To compensate the force drop from F2 to F4 because of the increase of PLE, high tensile or super tensile, even ultra tensile steel filaments can be used. In the above contrastive test, high tensile steel filaments, tensile strength higher than 3800-2000xd (filament diameter in mm) MPa, are used to achieve a steel cord E-modulus as high as 175Gpa.

[17] The first steel filament is preformed into a spatial wavy form, and more preferable the spatial wavy form has a first crimp and a second crimp, while the first crimp lying in a plane that is substantially different from the plane of the second crimp. Since the first filaments are inside the cord and not twisted or twisted in a twisting step greater than 300mm, the spatial wavy form on the first steel filaments makes sure that there are always spaces between first steel filaments to achieve full rubber penetration.