Login| Sign Up| Help| Contact|

Patent Searching and Data


Title:
OPEN STEEL CORD
Document Type and Number:
WIPO Patent Application WO/2012/055677
Kind Code:
A2
Abstract:
Open steel cord with a structure of n×1 has a high elongation at break being not less than 4%, open steel cord has a lay length being more than 10 mm, the steel filaments in open steel cord are helically preformed, and the ratio of the preforming height of steel filament and the diameter of steel filament is not less than 5.0. Open steel cord has high elongation at break, high elongation under low load and full rubber penetration. The open steel cord is used as reinforcing element in a rubber product.

Inventors:
CHENG ZHICHAO (CN)
HIMPE STIJN (BE)
LUO YIWEN (CN)
ZHANG AIJUN (CN)
Application Number:
PCT/EP2011/067259
Publication Date:
May 03, 2012
Filing Date:
October 04, 2011
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
BEKAERT SA NV (BE)
CHENG ZHICHAO (CN)
HIMPE STIJN (BE)
LUO YIWEN (CN)
ZHANG AIJUN (CN)
International Classes:
D07B1/06
Domestic Patent References:
WO2007128335A12007-11-15
Foreign References:
US5707467A1998-01-13
EP1344864A22003-09-17
US4938015A1990-07-03
Attorney, Agent or Firm:
MESSELY, Marc (Zwevegem, BE)
Download PDF:
Claims:
Claims

1. Open steel cord with a structure of ηχ1 having a high elongation at break being not less than 4%, said open steel cord having a lay length being more than 10 mm, the steel filaments in said open steel cord being helically preformed, characterized in that the ratio of the preforming height of said steel filament and the diameter of said filament is not less than 5.0.

2. Open steel cord as claimed in claim 1 , characterized in that said ratio of said preforming height of said filament and said diameter of said steel filament is between 5.0 and 8.0.

3. Open steel cord as claimed in claim 1 or 2, characterized in that said lay length is between 12mm and 20mm.

4. Open steel cord as claimed in any one of claim 1 to 3, characterized in that the elongation of said open steel cord under a load of 20 N is not less than 1.00%.

5. Open steel cord as claimed in any one of claim 1 to 4, characterized in that the elongation of said open steel cord under a load of 50 N is not less than 1.50%.

6. Open steel cord as claimed in any one of claim 1 to 5, characterized in that the diameter of said steel filament is between 0.15 and 0.5mm.

7. Open steel cord as claimed in any one of claim 1 to 6, characterized in that said n is from 2 to 8.

8. Open steel cord as claimed in claim 7, characterized in that said n is 4, 5 or 6.

9. Use of open steel cord according to any one of preceding claims as reinforcing element in a rubber product.

10. Use of open steel cord as claimed in claim 9, characterized in that said rubber product is a 0 degree belt layer or a protecting layer in a pneumatic tire.

Description:
OPEN STEEL CORD

Description

Technical Field

[0001] The present invention relates to a steel cord, particularly relates to an

open steel cord with high elongation at break. The present invention also relates to a rubber product reinforced by the steel cord.

Background Art

[0002] Steel cord with high elongation at break, high low load elongation and full rubber penetration is always required in market, especially being as reinforcing element for 0 degree belt layer and protecting layer in tires.

[0003] High elongation (HE) leads to a good anti-impacting or anti-cutting

property. Especially for protecting layer, high elongation steel cord is quite required for great anti-impacting or anti-cutting property when, for example, the rubber tire runs over a stone or like.

[0004] Usually, for a steel cord reinforcing 0 degree belt layer in a rubber tire, elongation under a low load (LLE) is required to be high. In case of insufficient LLE, the ply will not expand to the desired dimension. As a result, the cross section of the vulcanized tire will be different from the tire design, leading to unfavourable stress distribution in the tire and a reduction of tire lifetime.

[0005] Furthermore full rubber penetration which means 100% rubber penetration is also desired. The better the rubber penetration, the better the fatigue. To a full rubber penetration steel cord, the friction between the filaments is low, and the wear of the filaments is low. And there is no space to let the moisture penetrating into the cord, as a result no corrosion occurs. Thus the fatigue resistance of the steel cord is good, and the useful time of the steel cord is long. Always, the more open the structure of steel cord, the better the rubber penetration. [0006] But to the prior steel cord as a reinforcing element in rubber product, even in 0° belt layer and protecting layer of rubber tire, high elongation at break, full rubber penetration and high LLE can not present at the same time.

[0007] To prior HE cord which has come into the market, the strands in the steel cord are twisted in a small lay length (smaller than 4mm) to get HE and high LLE. But the drawback is that the filaments are arranged too close that there is little space among the filaments to let rubber penetrating in. The rubber penetration of such HE steel cord is so bad that the fatigue is not good. Further, prior HE cord consists of multi-strand with small lay length normally, the production cost is very high.

[0008] US 5707467 discloses a steel cord with high elongation at break more than 5%. The steel filaments are helically preformed before being twisted into the cord, and the ratio of preforming height and filament diameter is from 1.05 to 2.0. The twisting pitch (lay length) is in the range of 8-15. The elongation under a load of 70N is from 1.18% to 1.57% . Due to the small preforming value, the LLE is not big although the elongation at break is great. Such steel cord can not be provided for reinforcing 0° belt layer in rubber tire. And the figuration of tire reinforced by the steel cord is very bad for its low LLE. Thus the life time of the tire is too short.

[0009] EP 1344864 also discloses a steel cord comprising coil preformed

filaments. The LLE under a load of 50N is less than 0.2%. Such steel cord is not suitable for reinforcing 0° belt layer or protecting layer in rubber tire for its poor LLE.

[0010] US 4938015 discloses an open cord for good penetration of rubber. The open structure is formed by rolling the round steel cord into ellipse. But during the rolling, there will be a strength loss. Although the steel cord has high rubber penetration, the elongation at break of the steel cord is not so high. As a result the anti-impacting or anti-cutting property of rubber product is not good, thus the life time of the rubber product is low. Disclosure of Invention

[001 1 ] It is one object of the present invention to solve the problems above.

[0012] It is another object of the present invention to provide an open steel cord with high elongation at break, full rubber penetration and high low load elongation.

[0013] It is further an object of the present invention to provide a use of the steel cord as reinforcing element in a rubber product.

[0014] According to the present invention, open steel cord with a structure of ηχ 1 has a high elongation at break being not less than 4%, the open steel cord has a lay length being more than 10 mm, the steel filaments in open steel cord are helically preformed, and the ratio of the preforming height of steel filament and the diameter of steel filament is not less than 5.0.

[0015] For the high lay length (more than 10mm) and high preforming ratio (not less than 5.0), the steel cord has high elongation at break, high low load elongation (LLE) and a very open structure with full rubber penetration.

[0016] The high LLE and high elongation at break is obtained by preforming the steel filament before being twisted to form open steel cord. The higher the preforming ratio, the higher the LLE and elongation at break. The preforming ratio is defined by the ratio of the preforming height of steel filament and the diameter of steel filament.

[0017] The high preforming ratio leads to high LLE and elongation at break, the higher the preforming ratio, the higher the LLE and elongation at break.

[0018] Preferably, the preforming ratio is between 5.0 and 10.0.

[0019] More preferably, the preforming ratio is between 5.0 and 8.0. Thus the open HE steel cord has high LLE and is also easy to be manufactured.

[0020] Additionally, the preforming length is determined by the desired LLE and determined preforming height.

[0021 ] The elongation under break is not less than 4%. Preferably the elongation under break is not less than 4.5%.

[0022] Preferably, the elongation of open steel cord under a load of 20 N is not less than 1 .00%, preferably not less than 1 .10%, and smaller than 2.00%.

[0023] Preferably, the elongation of open steel cord under a load of 50 N is not less than 1 .50%, preferably not less than 1 .60% , and smaller than 3.00%. [0024] Compared with prior mono-strand HE cord which is twisted by one step, such as HE cord described in US 5707467, the LLE of present invention steel cord is much higher. While using invention steel cord as reinforcing element in rubber tire, the figuration of tire can reach the tire requirement and the life time of the tire is better.

[0025] US 5707467 discloses a mono-strand HE steel cord comprising preformed filaments and twisted by one step. But the preforming ratio of filament is so small that the LLE is very small. The elongation under a load of 35N is between 0.71 % and 1.00% (of course, the elongation under a load of 20N is smaller than 1.00%), and the elongation under a load of 70N is between 1.18% and 1.57%. They are quite smaller than the LLE of present invention. And the filament in US 5707467 is preformed by zigzag lined rollers which is only available for small performing ratio that big preforming ratio can not be achieved.

[0026] According to the present invention, the steel filament is preformed by a sleeve that the preforming ratio is very big. The open HE steel cord comprising such preformed steel filaments has high LLE.

[0027] The open steel cord is twisted in one step. The lay length (or twisting pitch) of the open steel cord is more than 10 mm. The bigger the lay length, the smaller the elongation at break. However, in the case of the present invention cord, the bigger lay length is compensated by the great preforming ratio so that a high elongation at break is obtained. Preferably, the lay length is between 12mm and 20mm. The lay length relates to the diameter of the steel filament and to the number of the steel filament: It means that the lay length increases with the increasing of the diameter of the steel filament and the lay length increases with an increase in the number of steel filaments.

[0028] As a result of combination of big lay length and high preforming ratio, open steel cord has a very open structure. The steel cord will only close while putting under high tension and - since the initial elongation is mainly structural and elastic - the cord will come back to its original state when the tension is removed. Such very open structure will bring a full rubber penetration to the steel cord. Furthermore both the elongation at break and LLE are high.

[0029] Compared with prior HE cord with multi-strand, the open structure is a great advantage. Although prior HE cord with multi-strand has high LLE, the steel cord is a close cord for its low lay length. The rubber penetration is 0% tested by air drop method while embedding such cord into rubber. This means that the invention steel cord has full rubber penetration which means 100% rubber penetration. The invention cord is more suitable for reinforcing rubber product than prior HE cord with multi-strand.

[0030] Preferably, the diameter of the steel filament is between 0.15 and 0.5mm.

[0031 ] As open steel cord with structure of ηχ 1 is manufactured by one step, n is from 2 to 8 preferably. While n is more than 10, to achieve a great effect, the diameter of steel filament decreases with the increasing of the number of steel filaments.

[0032] Compared with prior HE cord with multi-strand, the invention steel cord has better rubber penetration and lower production cost, and compared with prior HE cord with mono-strand, the invention steel cord has better LLE.

[0033] To such open steel cord with high elongation at break, full rubber

penetration and high low load elongation, it can be used as reinforcing element in a rubber product. Preferably rubber product is 0 degree belt layer or protecting layer in a pneumatic tire.

Brief Description of Figures in the Drawings

[0034] Figure 1 shows the manufacturing process of 6x 1 open HE cord.

[0035] Figure 2a-2d show the different cross-section views of 6x 1 open HE cord.

[0036] Figure 3 shows the preforming height of the filament separated from 6x 1 open HE cord.

[0037] Figure 4 shows the cross-section view of 4x 1 open HE cord.

[0038] Figure 5 shows the cross-section view of 7x 1 open HE cord.

[0039] Figure 6 shows the tensile curve of the invention steel cord and prior steel cord. Mode(s) for Carrying Out the Invention

[0040] The steel filament may be made from a wire rod.

[0041] The wire rod composition has a minimum carbon content of 0.70%, a

maximum carbon content of about 1.10%, a manganese content ranging from 0.40% to 0.70%, a silicon content ranging from 0.15% to 0.30%, a maximum sulphur content of 0.03%, a maximum phosphorus content of 0.30%, all percentages being percentages by weight. Usually there are only traces of copper, nickel, aluminium, titanium, and nitrogen and / or chromium, except for very high tensile strengths.

[0042] The wire rod is firstly cleaned by mechanical descaling and / or by

chemical pickling in a H2SO 4 or HCI solution in order to remove the oxides present on the surface. The wire rod is then rinsed in water and is dried. The dried wire rod is then subjected to a first series of dry drawing operations in order to reduce the diameter until a first intermediate diameter.

[0043] At this first intermediate diameter, e.g. at about 3.0 to 3.5 mm, the dry drawn steel filament is subjected to a first intermediate heat treatment, called patenting. The steel filament is then ready for further mechanical deformation.

[0044] Thereafter the steel filament is further dry drawn from the first intermediate diameter until a second intermediate diameter in a second number of diameter reduction steps. The second diameter typically ranges from 1.0 mm to 2.5 mm.

[0045] At this second intermediate diameter, the steel filament is subjected to a second patenting treatment to allow for transformation to pearlite.

[0046] After this second patenting treatment the steel filament is provided with a brass coating: copper is plated on the steel filament and zinc is plated on the copper. A thermo-diffusion treatment is applied to form the brass coating.

[0047] Additionally the steel filament may be provided with an organo functional silane coating upon the brass coating.

[0048] Then steel filament is subjected to a final series of cross-section

reductions by means of wet drawing machines. The final product is a round steel filament with a carbon content above 0.60 percent by weight, with a tensile strength typically above 3800-2000D MPa and adapted for the reinforcement of rubber products.

[0049] The steel filaments adapted for reinforcing tire typically have a final

diameter ranging from 0.15 mm to 0.50 mm, e.g. from 0.20 mm to 0.40 mm. Examples of filament diameters are 0.20 mm, 0.22 mm, 0.245 mm, 0.28 mm, 0.30 mm, 0.32 mm, 0.35 mm, 0.38 mm, 0.40 mm.

[0050] After the above processes, the steel filament will be picked up by a spool for the following processes, such as deforming and twisting to form a cord.

[0051] Figure 1 shows the manufacturing process of 6x 1 open HE cord. Six steel filaments 10 with a diameter of 0.26mm are guided from the spools 12 to pass through the deforming device sleeves 14. Each steel filament 10 passes over one sleeve 14. Each sleeve causes a plastic bending to the steel filament. However, the steel filaments rotate when passing over the sleeves due to the downstream twisting operation. This bending combined with the rotation and with the linear speed of the steel filaments result in a helical preforming. Thus the steel filaments 10 are helically preformed by sleeves 14. Then the steel filaments 10 are gathered in device 16 wherein the steel filaments are twisted to form a 6x 1 open HE cord 18.

[0052] According to the present invention, any deforming device which can make big deformation known by the person skilled in the art is available.

Preferably deforming device is sleeve deforming device. During the preforming process, the diameter of sleeve is determined by the desired preforming height of steel filament. And during the twisting process wherein the steel filaments are twisted into a steel cord, the high lay length is obtained. The high preforming ratio of steel filament and high lay length of steel cord lead to HE, high LLE and full rubber penetration of steel cord.

[0053] Figure 2a to 2d show the different cross-section views of different parts along the length of 6x 1 open HE cord 18. The elongation at break of steel cord 18 is 5.01 %, the elongation under a load of 20 N is 1.33% and the elongation under a load of 50 N is 1.79%. And the preforming ratio of the filament 10 is 5.96. The lay length of steel cord 18 is 16mm. The optical diameter of the steel cord 18 is 1.68. The diameter is measured by optical projection at the cross-section of the steel cord. From the diameter, it is very clear that the steel cord is very open that the rubber penetration is very good. And actually the rubber penetration is 100% measured by air drop testing method.

[0054] The preforming ratio is the ratio of preforming height and diameter of steel filament. The preforming height is measured by optical measuring method. First cut the steel cord into short, then separate the steel filaments into individual filaments from the steel cord, then measure the preforming height by optical measuring method. Always there is a wave form of the steel filament after optical projection. The distance in perpendicular between the highest point of wave form and the lowest point of wave form is preforming height (including two times diameter). Figure 3 shows the preforming height 20 of the filament 10 separated from 6x 1 open HE cord 18.

[0055] Figure 4 illustrates a 4x 1 open HE cord. The steel cord 22 comprising 4 steel filaments 24 with a diameter of 0.35mm. The elongation at break of steel cord 22 is 5.33%, and the elongation under a load of 20 N is 1.41 % and the elongation under a load of 50 N is 1.67%. The preforming ratio of the filament 24 is 5.54. The lay length of steel cord 22 is 14mm.

[0056] Figure 5 illustrates a 7x 1 open HE cord. The steel cord 26 comprising

seven steel filaments 28 with a diameter of 0. 245mm. The elongation at break of steel cord 26 is 4.75%, and the elongation under a load of 20 N is 1.30% and the elongation under a load of 50 N is 1.53%. The preforming ratio of the filament 28 is 6.07. The lay length of steel cord 26 is 17mm.

[0057] Besides, the steel cord can be 3x 1 , 5x 1 , 8x 1 , 9x 1 and etc.

[0058] All the steel cords above have full rubber penetration and high LLE.

[0059] A comparison test is carried out between the invention steel cord 18 and prior art normal HE steel cord A. Steel cord A is a multi-strand structure of 3x4 with small strand lay length lower than 4mm. Steel cord A has an elongation at break more than 4%. Figure 7 shows tensile curve, curve 30 is steel cord 18 and curve 32 is steel cord A. From Figure 7, it is clear that the invention cord 18 has the similar strain and stress curve with prior art steel cord A. It shows the invention cord 18 has the similar elongation at break and LLE with prior art steel cord A. But the rubber penetration of invention steel cord 18 is 100%, and the rubber penetration of prior art steel cord A is 0%. Additionally the production cost of invention cord 18 is quite lower than prior art steel cord A, for steel cord 18 is twisted by one step in big lay length wherein the prior art steel cord A should be twisted by two steps at least in very small lay length.

Open HE cord with high LLE and full rubber penetration is suitable for reinforcing rubber product, particularly reinforcing 0 degree belt layer or protecting layer in a pneumatic tire. The steel cord has a good fatigue resistance and a long lifetime. The tire also has a long lifetime.