Pille, Johan (Kortrijksestraat 22, Roeselare, B-8800, BE)
Vanneste, Stijn (Oostrozebekestraat 98, Ingelmunster, B-8770, BE)
Meersschaut, Dirk (Kapt. Com. Vinckestraat 26, Ooigem, B-8710, BE)
Pille, Johan (Kortrijksestraat 22, Roeselare, B-8800, BE)
Vanneste, Stijn (Oostrozebekestraat 98, Ingelmunster, B-8770, BE)
Seynhaeve, Geert (Bekaertstraat 2, Zwevegem, B-8550, BE)
| 1. | A steel cord adapted for the reinforcement of elastomer products, said steel cord comprising a core filament with a core filament diameter and 3N layer filaments twisted around said core filament in the same direction and with the same step, N ranging from four to five, said 3N layer filaments being arranged in an intermediate layer of N filaments and in an outer layer of 2N filaments, the layer filaments in said intermediate layer having an intermediate layer diameter, wherein said core filament diameter is smaller than said intermediate layer diameter. |
| 2. | A steel cord according to claim 1, wherein N equals five. |
| 3. | A steel cord according to any one of the preceding claims, wherein said core filament diameter is greater than the diameter of a circle tangent to each of the crosssections of the intermediate layer filaments in the hollow space that remains free when their cross sections have the highest packing density. |
| 4. | A steel cord according to any one of the preceding claims, wherein all 3N layer filaments have said same intermediate layer diameter. |
| 5. | A steel cord according to any one of claims 1 to 3, wherein said outer layer of 2N filaments has N filaments facing two intermediate layer filaments and having a diameter equal to said intermediate layer diameter and N filaments facing only one intermediate layer filament and having a diameter smaller than said intermediate layer diameter. |
The present invention relates to a steel cord adapted for the reinforcement of elastomer products. The steel cord comprises a core filament with a core filament diameter and layer filaments twisted around the core filament in the same direction and with the same step.
Background of the invention.
Steel cords where all the steel filaments are twisted in the same direction and with the same step are known in the art and are often referred to as "compact steel cords"since they may lead to a compact cross-sectional configuration with a high amount of steel within a limited cross-sectional surface area.
Within the group of compact steel cords, following configurations are widely used in the art of elastomer reinforcement: <BR> <BR> <BR> <BR> - 3xdc# 9xdl CC<BR> <BR> <BR> <BR> <BR> <BR> -1 xdc 1 1 8xdl CC A 3xdc 1 9dl CC is a compact cord comprising three core filaments with a core filament diameter dc and nine layer filaments with a layer filament diameter dl. The core filament diameter dc is somewhat greater than the layer filament dl. Such a compact cord is disclosed in US-A-4, 788, 815.
A 1 xdc I 18xdl CC is a compact cord comprising one core filament with a core filament diameter dc and eighteen layer filaments with a layer filament diameter dl, arranged in an intermediate layer of six filaments and an outer layer of twelve filaments. Such a compact cord is disclosed in EP-B1-0 627 520.
Both compact cords constitute stable constructions and may be used to reinforce the carcass plies of medium to heavy truck and bus radial tires.
A 1 xdc 1 1 8xdl CC construction with its nineteen filaments is used for the higher breaking loads and a 8xdc 1 9xdl CC construction with its twelve filaments is used for the lower breaking loads. The required breaking load is then met by a suitable choice of the filament diameters dc and dl.
By varying the diameters it is technically possible to cover such a broad range of breaking loads so that the carcass plies of practically all current medium and heavy truck and bus radial tires can be reinforced.
Although such a broad range is technically possible, it is, however, not always technically desirable. Increasing the filament diameters in order to obtain higher breaking loads results in decreasing values of fatigue resistance. So the filament diameter range has an upper limit due to technical reasons.
Decreasing the filament diameters in order to obtain lower breaking loads is technically desirable since it results in increasing values of fatigue resistance. Decreasing the filament diameters, however, has also its limits, since further drawing of the high carbon steel filaments is expensive. So the filament diameter range has a lower limit due to economical reasons.
Bearing in mind the lower and the upper limit, it is difficult, if not impossible with the two constructions 3XdC | 9xdl CC and 1 xdc 1 1 8xdl CC to cover the whole range of medium and heavy truck tires with technically and economically feasible steel cords.
Summary of the invention.
It is an object of the present invention to fill in the gap between the two constructions 3xd 9xdl CC and 1xdc # 18xdl CC.
It is another object of the present invention to provide for a stable steel cord construction with an acceptable level of fatigue resistance.
It is a further object of the present invention to provide for a steel cord with a good fretting behavior.
According to the present invention there is provided a steel cord adapted for the reinforcement of elastomer products. The steel cord comprises a core filament with a core filament diameter dc and 3N layer filaments twisted around said core filament in the same direction and with the
same step. N ranges from four to five. The 3N layer filaments are arranged in an intermediate layer of N intermediate layer filaments and in an outer layer of 2N outer layer filaments. The layer filaments in the intermediate layer have an intermediate layer diameter d,. The core filament diameter dc is smaller than the intermediate layer diameter d ;.
This invention cord is a compact cord. The cord has a good fretting behavior, a high breaking load per unit of cross-section and a small diameter. The cord has a symmetric stable construction. It has thirteen to sixteen filaments and fills in the gap between the 3xdc 1 9xdl CC and 1 xdc 1 1 8xdl CC constructions.
The steel cord is adapted for the reinforcement of elastomer products, which means that it has a steel composition along the following lines: a minimum carbon content of 0.60 % (e. g. at least 0.80 %, or at least 0.92 % with a maximum of 1.2 %), a manganese content ranging from 0.20 to 0.90 % and a silicon content ranging from 0.10 to 0.90 %; the sulphur and phosphorous contents are each preferably kept below 0.03 %; additional elements such as chromium (up to 0.2 à 0. 4 %), boron, copper, cobalt, nickel, vanadium... may be added to the composition in order to minimize the amount of deformation needed to obtain a predetermined tensile strength. The steel filaments are generally covered with a coating layer to increase the resistance against corrosion or to enhance the adhesion with rubber. This coating may be a chemical primer or may be a metallic coating. The exact type of coating depends upon the eventual application. Corrosion resistant coatings are zinc or a zinc aluminum alloy. Adhesion coatings are brass in the case of rubber, or a so-called ternary brass such as copper-zinc- nickel (e. g. 64%/35. 5%/0. 5%) and copper-zinc-cobalt (e. g. 64%/ 35.7%/0. 3%), or a copper-free adhesion layer such as zinc-cobalt or zinc-nickel. The final diameters of the steel filaments range from 0.05 mm to 0.60 mm. In case of reinforcement of carcass plies of tires, the filament diameters preferably range from 0.05 mm to 0.35 mm.
N is preferably equal to five, which means that the steel cord comprises sixteen filaments. Five is preferred to four since five filaments in the intermediate layer fill more the intermediate layer in a stable way.
Preferably the core filament diameter de is greater than the diameter of a circle tangent to each of the cross-sections of the intermediate layer filaments in the hollow space that remains free when their cross-sections have the highest packing density.
In a first preferable embodiment of the invention all 3N layer filaments, i. e. all N intermediate layer filaments and all 2N outer layer filaments have a same intermediate layer filament diameter d,. This first preferable embodiment may be summarized by following formula : 1 xdc 1 3Nxdj CC This first embodiment has the advantage that only two different filament diameters are required.
In a second preferable embodiment of the invention the outer layer of 2N filaments has N filaments facing two intermediate layer filaments with a diameter equal to the intermediate layer diameter d, and has N filaments facing only one intermediate layer filament with a diameter smaller than the intermediate layer diameter di.
This second embodiment has the advantage of a so-called Warrington construction with a round cross-section.
Brief description of the drawings.
The invention will now be described into more detail with reference to the accompanying drawings wherein - FIGURE 1 is a cross-section of a first embodiment of a steel cord according to the invention; - FIGURE 2 is an explanatory drawing ; FIGURE 3 is a cross-section of a second embodiment of a steel cord according to the invention.
Description of the preferred embodiments of the invention.
FIGURE 1 shows a cross-section of a first embodiment of a steel cord 10. The steel cord comprises a core filament 12 with a core filament diameter dc. Five intermediate layer filaments 14 form an intermediate layer around core filament 12. The intermediate layer filaments have a diameter d,. Ten outer layer filaments 16 form an outer layer around the intermediate layer. The outer layer filaments 16 also have the same intermediate layer filament diameter du. hall intermediate layer filaments 14 and all outer layer filaments 16 are twisted in the same twisting direction and with the same twisting step so that a compact configuration is formed. The cross-section has the typical form of a pentagon.
The core filament diameter dc is smaller than the intermediate layer filament diameter dy.
Referring to FIGURE 2, the core filament diameter dc is greater than the diameter of a circle 15 tangent to each of the cross-sections of the intermediate layer filaments 16 in the hollow space that remains free when their cross-sections have the highest packing density.
A suitable example of a cord according to the first embodiment of the invention is: 1 x0. 14 115x0. 175 CC twisting step = 11 mm twisting direction = S Other examples are: 1x0.175 # 15x0. 22 CC 1x0. 16 115x0. 20 CC 1x0. 13 115x0. 16 CC
1 x0. 10 15x0. 13 CC FIGURE 3 shows a cross-section of a second embodiment of the steel cord 20 according to the invention. The steel cord 20 comprises a core filament 22. Five intermediate layer filaments 24 with an intermediate layer filament di have been twisted around the core filament 22. An outer layer of outer layer filaments 26,28 is formed around the intermediate layer. Of the outer layer filaments 26,28, those five outer layer filaments 26 facing two intermediate layer filaments 24 have a diameter equal to said intermediate layer diameter di. Five outer layer filaments 28 facing only one intermediate layer filament 24 have a diameter smaller than the intermediate layer diameter d,.
In contrast with FIGURE 1, the cross-section has a round form.
Depending upon the steel composition used and upon the degree of final drawing, the steel cord can be carried out in various tensile versions, ranging from a normal tensile strength to an ultra high tensile strength.
The steel cords according to the invention can be manufactured by means of a tubular twisting machine or preferably by means of a double- twisting device.
Both embodiments may be provided or not with a wrapping filament wrapped around the other filaments. However, for use in carcass plies, the non wrapped version is preferred. In this non wrapped version, non sleeving of the steel cord may be obtained by suitably preforming the outer layer steel filaments so that the outer layer filaments exert a force which is directed radially inward. Such a preforming is disclosed in EP- B 1-0 627 520.
Table 1 hereunder summarizes some properties measured on steel cords according to the first embodiment of the present invention.
Table 1 0. 14 # 15 x 0.175 CC High tensile Super Dimen- strength tensile sions strength s ! ons strength PLE % 0.083 0.080 Diameter cord mm 0,834 0,840 Tensile test not embedded Weight per length g/m 2,984 3,019 Breaking load N 1238 1307 Tensile strength MPa 3261 3404 E-modulus MPa 189986 190397 total elongation at fracture % 2,44 2,36 Tensile test embedded Breaking load N 1346,7 1415,7 Tensile strength MPa 3547 3686 E-modulus MPa 198183 197668 i Total elongation at fracture % 2,1 2,16 Three point bending test not embedded not embedded #k = Ek MPa 152 160 #v = Ev Mpa 513 329 Knee value Mv Nmm 0,4 0,4 A % 19 21 not embedded #k = Ek MPa 152 160 #v = Ev MPa 513 329 Knee value Mv Nmm 0,4 0,4 A % 19 21 Three point bending test embedded #k = Ek MPa 313 306 #v = Ev MPa 855 810 Knee value Mv Nmm 3,6 3,8 A % 31 35 J. L Compression test #k = Rk MPa 172 257 Wk % 0,88 1,28 E compression modulus MPa 6066 7316 Taber stiffness test Not embedded ; Mo TSU 27,6 31 Mo' TSU 1,9 1,5 Ex MPa 171 196 Mo TSU 27,6 31 Mo' TSU 1,9 1,5 Ek MPa 171 196 V % 93 95 Taber stiffness test Embedded M TSU 14@5 13@2 Mo TSU 14, 5, 13, 2 Mo' TSU 1.5 1.2 mo TSU 1, 5 1,2 Ek MPa 431 398 V % 90 91 Three Roller Fatigue test Number of cycli before 20006 30166 fracture
PLE or part load elongation expresses the elongation at very small loads below 50 Newton.
Information about the Taber stiffness test, the three point bending test, and the compression test can be read from L. BOURGOIS, Survey of Mechanical Properties of Steel Cord and Related Test Methods, Special Technical Publication 694, ASTM, 1980.
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