JP3590690B2 - Steel cord for reinforcing rubber products - Google Patents

Description

[0001]
[Industrial applications]
TECHNICAL FIELD The present invention relates to a steel cord for reinforcing rubber products used as a rubber product reinforcing material for automobile tires, conveyor belts, etc., which improves the filling property of rubber into steel cord internal cavities and repeats steel cords. The fatigue strength against a bending load can be improved, thereby significantly improving the durability of a rubber product reinforced by a steel cord.
[0002]
[Prior art]
Steel cords for reinforcing rubber products are hardly twisted with so-called closed twisted cords, in which 5 to 7 strands are tightly twisted and adhered to each other, and so-called open twisted cords, in which strands are loosely twisted together. It is roughly divided into a wire group and another wire group tightly twisted.
FIG. 2 shows an example of a closed twist cord. The steel cord 21 is formed by twisting six side wires 21b in close contact with each other around a core wire 21a. In this steel cord, a hollow portion D exists around a core strand 21a, and since the side strands 21b are in close contact with each other, the steel cord 21 is sandwiched between two rubber sheets and compressed. When the composite sheet is formed, the rubber material does not penetrate into the cavity D, but becomes a composite in which the steel cord is simply wrapped by the rubber sheet, and the rubber material completely enters the cavity D of the steel cord and The sheet and steel cord are not integrated into a complete composite. In the case where this material is incorporated into the tire of an automobile, the rubber material and the steel cord are not sufficiently adhered to each other, which may cause the rubber material to separate from the steel cord and cause a so-called separation phenomenon when the vehicle is running. When the moisture in the rubber material or the moisture penetrating from the cut of the tire reaches the hollow portion D of the steel cord 21, the moisture propagates through the hollow portion D and immediately propagates in the longitudinal direction of the steel cord 21, Corrosion of the steel cord results in a significant decrease in its mechanical strength.
In order to solve this problem, various steel cord structures have been proposed in which a rubber material easily penetrates into the above-mentioned cavity as much as possible. For example, as shown in FIG. 3, the wire diameter of the core element wire 32 is increased, and a gap C is formed between the side element wires 33 which are tightly twisted around the core element wire, as shown in FIG. As shown in FIG. 5, a core wire 42 is provided with a small spiral shape in advance, and a side wire 43 is closely adhered to the core wire and twisted (for example, JP-A-6-191218). An example of such an arrangement is that the core element wire 52 is previously subjected to a wavy shaping of a small amplitude, and the side element wire 53 is closely attached and twisted (for example, JP-A-6-191217).
. Further, a so-called open-twisted steel cord (for example, JP-A-57-43866) in which wires are excessively formed and loosely twisted while providing a gap between the wires (for example, JP-A-57-43866), A so-called flat open-twisted steel cord in which an open-twisted steel cord is crushed flat with a roller to have an elliptical cross-sectional shape (Japanese Patent Laid-Open No. 2-133687) is also one example.
In the structure of the conventional steel cord 31 shown in FIG. 3, the rubber material sufficiently penetrates into the gap between the core strand 32 and the side strand 33, and as a result, a cavity is not formed. Does not propagate, but the diameter of the core element wire 32 is large, so that the diameter of the steel cord 31 is large, and therefore the thickness of the rubber sheet is large. When this is used in an automobile, the diameter of the steel cord 31 is increased, so that the flexibility of the steel cord against bending in the circumferential direction of the tire is poor, and the riding comfort is impaired.
Furthermore, since the core element wire 32 is always in contact with the side element element 33, fretting wear occurs, which results in a high fatigue value and low durability of the steel cord.
Further, in the steel cord 41 shown in FIG. 4 in which the core element wire 42 is spirally curled, the fatigue value is improved since the side element element 43 is not always in contact with the core element element 42, Since the shape is a substantially perfect circular shape, the rigidity of the steel cord against bending is the same in any direction, and a predetermined cornering performance of the tire is ensured (a predetermined lateral rigidity of the tire can be ensured). If the diameter of the steel cord is selected as described above), the rigidity of the tire against bending in the circumferential direction is too high, and the ride quality is deteriorated.
In addition, the steel cord 41 has a larger cord diameter than the close-twisted steel cord 21 as shown in FIG. 2, and the sheet after calendering (rubber coating step) becomes thicker. The required number of steel cords cannot be embedded in the sheet, and the sheet strength is low. Therefore, when this is used for a tire, it is necessary to increase the number of stacked sheets, and as a result, the weight of the tire increases.
The steel cord 51 shown in FIG. 5 in which the core element wire 52 is corrugated is given a substantially track-type (so-called athletic field track) space drawn by the locus of movement of the core element wire 52 (the dotted line in the figure). Since the side strands 53 do not easily enter the (enclosed space), the degree of freedom of the core strands 52 is large to some extent. For this reason, the core element wire 52 is easily moved by an external force generated by a process in which the steel cord is sandwiched between the upper and lower rubber sheets by pressing, vulcanizing and integrating the steel cord, and the stability of the steel cord is reduced. Therefore, handling workability at the time of manufacturing a steel cord or a rubber sheet is deteriorated. Further, since the steel cords 41 and 51 are subjected to a spiral or corrugated crimping process on the core wire, the manufacturing cost is increased accordingly.
Further, in the steel cords 41 and 51, it is necessary to set the twist pitch of the side strands corresponding to the spiral or wavy habit pitch (otherwise, the twisted shape is broken). The adjustment work of the machine is not easy, and there is a problem in handling workability.
In the flat open steel cord 61 shown in FIG. 6, a gap between the wires is required so that the rubber material adheres to the entire circumference of each wire 62 and sufficiently penetrates into the steel cord. It is necessary to make the interval sufficient for the rubber material to enter, that is, 0.02 mm or more. However, if a sufficient gap is provided between the strands as described above, the twisted structure tends to be unstable during the production of the steel cord, causing the strands to be offset or twisted unevenly in the longitudinal direction of the steel cord. Problem. This wire has a relatively large degree of freedom for each wire, so when a steel cord is embedded in a rubber sheet and vulcanized and pressed, the gap created by the external force is reduced by external force, or the gap is shifted due to wire movement. This makes it difficult for the rubber material to sufficiently penetrate into the cord. In this case, buckling is likely to occur due to repeated bending stress, and the life of the steel cord and thus the rubber product is shortened. Further, since the flat open steel cord 61 has a large elongation under a low load, it is difficult to handle in a rubber sheet manufacturing process.
[0003]
[Problems to be solved by the invention]
The present invention forms a required gap between the side strands of a substantially elliptical steel cord having a core strand having a thickness equivalent to that of a large number of side strands, without subjecting the core strands to crimping in advance. The object is to devise the structure so that a predetermined gap is secured and the rubber easily and reliably enters the inside of the steel cord even when the steel cord is sandwiched between rubber sheets and pressed and vulcanized. is there.
[0004]
[Means for Solving the Problems]
The measures taken to solve the above-mentioned problems are constituted by the following elements (a) to (d).
(1) A steel cord having a 1 + 6 structure in which six side strands are arranged around one core strand and twisted,
(B) An open structure in which side wires are twisted around a straight core wire to form a flat open structure in which the cross-sectional shape of the cord is substantially the same as the cord longitudinal direction,
(C) a core element wire is partially cut between two adjacent side element wires during the pressing process;
(D) The maximum amount of interruption of the above-mentioned core strand in one twist pitch of the cord is set to 30% or more and 50% or less of the core strand diameter.
[0005]
[Operation]
The operation will be described with reference to FIG.
The straight core wire 2 is included in the six twisted side wires 3 and the steel cord 1 is crushed into an almost elliptical shape by compression, so that the core wire 2 is formed of the upper and lower side wires. The wire is strongly pressed in between, and is interposed between adjacent side wires to be combined with the side wires. The interrupt has a small portion and a large (maximum interrupt) portion in one twist pitch of the code (see the interrupt state in FIG. 1), and the increase and decrease of interrupts are periodically repeated at one twist pitch interval of the code. The amount of interruption H (see FIG. 1) interrupted between the adjacent side wires 3 and 4 is the amount by which the outer periphery of the core wire 2 protrudes from the common tangent L of the side wires 3 and 4 (shown in FIG. 1). it is a distance of the tangent L ₁ of the common tangent line L and Shinmotosen 2). The amount of interruption H periodically fluctuates between the maximum and the minimum along the steel cord, and the magnitude of the maximum value mainly depends on the compression of the steel cord 1 when the steel cord 1 is crushed into a substantially elliptical shape by compression. It is adjusted according to the magnitude of the force, the magnitude of the twist pitch of the steel cord, and the magnitude of the molding rate of the side strands.
When the steel cord is twisted, the straight core strand becomes the core, so that the twisting structure is stabilized, and it is possible to prevent the side strands from being offset and the side strands from being non-uniformly twisted.
Also, in the state of being formed into a crushed elliptical shape, the core element wire is tightly combined with the side element element, so that the degree of freedom of the side element element is reduced, so that the steel cord is sandwiched between the upper and lower rubber sheets. When pressurizing and vulcanizing, the gap between the side strands hardly fluctuates, and a predetermined gap is maintained. Therefore, the rubber easily penetrates into the steel cord from this gap, and the rubber is sufficiently filled in the steel cord.
When the maximum interrupt amount is small, the above-mentioned effects and effects are reduced. Conversely, when the maximum interrupt amount is large, the above-mentioned effects and effects are large. And damage, resulting in reduced fatigue strength of the steel cord.
When the maximum interruption amount Hmax is less than 0.3 d with respect to the core wire diameter d, the above-described action of the core wire is small, and therefore, the degree of freedom of the side wire is increased, so that the practical use is not practical. Little effect is expected. Conversely, if the maximum interruption amount Hmax exceeds 0.5 d with respect to the core element wire diameter d, the above-mentioned indentation and the decrease in fatigue strength due to damage become remarkable, which is not practically desirable.
Of course, it is practically possible to make the maximum interrupt amount Hmax larger than 0.5 d by applying a special surface treatment to the strands to prevent the above-mentioned indentation and damage. Even if it is larger than 0.5d, the above operation and effect do not increase so much.
The smaller the number of the side strands, the gentler the bend of the core strand, and the above-mentioned action and effect are reduced. Conversely, if the number of the side strands is large, the core strands are sharply bent, so that indentations and damages generated on the strands during press working are increased, and as a result, the fatigue strength of the steel cord is reduced. Therefore, even if the number of side strands is five or seven, the operation and effect of the present invention are not at all generated, but a steel cord having six side strands is most practical.
[0006]
Embodiment
The twist pitch of the steel cord is 6 to 20 mm.
If it is less than 6 mm, the wire is liable to be broken due to extreme processing, and the number of twists per unit length of the steel cord is increased, and the productivity is reduced. In addition, since the habit pitch of the core strand is smaller than the twist pitch of the side strands, if it is less than 6 mm, it is physically difficult to insert the core strand greatly between adjacent side strands.
On the other hand, when the twist pitch of the steel cord is 20 mm or more, the flexibility of the steel cord is reduced and flare is likely to occur, which is not practical.
The diameter of the core element wire is set to 0.2 mm to 0.4 mm.
If the strand is too thin, the strength of the strand will be insufficient, and if it is too thick, the flexibility of the steel cord will be insufficient and the fatigue value will be low. This is even more remarkable in the steel cord of the present invention having an elliptical cross section, and if it exceeds 0.4 mm, it is not practical.
[0007]
【Example】
Next, an embodiment will be described with reference to FIG.
This steel cord 1 is a substantially circular shape having a twist pitch of 16 mm and six side strands formed around one straight core strand 2 having a strand diameter of 0.35 mm and an average cord diameter of 1.07 mm. This is formed into a substantially elliptical shape having a major axis of 1.36 mm and a minor axis of 0.99 mm by a rolling roller. Due to the pressing by the rolling rollers, the core element is plastically deformed and cut between adjacent side elements. FIG. 9 shows enlarged photographs (1 to 8) of enlarged photographs in which each section of the steel cord embedded in resin and cut at intervals of 2 mm in the longitudinal direction of the steel cord is taken. In FIG. 9, the maximum interrupt amount in this embodiment can be measured by measuring the interrupt amount at the maximum interrupt amount (the maximum at one twist pitch of the cord). The third copy has the largest interrupt amount.
In order to confirm the characteristics of the steel cord of the present invention, several steel cords of the present invention (0.32d, 0.43d, 0.48d) with the maximum interrupt amount appropriately changed and several conventional steel cords were compared. Comparative tests were performed with two comparative examples (maximum interruption amounts of 0.17d and 0.58d), and the infiltration rate, rigidity ratio, fatigue resistance and handling workability of rubber were quantitatively evaluated. The evaluation results are as shown in Table 1 below.
[Table 1]
The test conditions and evaluation method for this test are as follows.
The rubber infiltration rate is as follows: each cord is embedded in rubber with a tensile load of 5 kg applied, and after vulcanization, the cord is taken out of the rubber, the cord is disassembled, and a certain length of the strand is observed. The ratio of the length of evidence of contact with the rubber to the observed length was expressed as a percentage. The rubber penetration rate is usually required to be 70% or more.
For fatigue resistance, a three-point pulley bending fatigue tester is used to perform a fatigue test using a composite sheet in which multiple steel cords are embedded in a rubber sheet, and the embedded steel cord breaks through fretting wear, buckling, etc. The number of times of repetition up to the end is counted. Experiment No. The index of the fatigue resistance of the conventional closed-twisted structure of No. 6 is expressed as an index with 100 as the index. The higher the value, the higher the fatigue resistance.
Further, as shown in FIG. 7, the rigidity ratio is a value obtained by measuring a load G when the test piece 71 is held down by 5 mm in a span (SP = 20 mm) of the test piece 71 using a three-point bending tester. The ratio (G / G ₁ ) between the load G for the sample and the load G ₁ for the major axis direction is expressed as a percentage. The smaller the ratio, the higher the circumferential flexibility of the tire when applied to the tire (lower rigidity) and the higher the lateral rigidity (lower lateral flexibility).
As shown in FIG. 8, a test piece 81 was prepared by embedding five test cords 82 in a horizontal row in a rubber sheet 83 having a 100% modulus of 35 kg / cm ^{2, and} subjected to a rigidity test. The dimensions of the rubber sheet 83 are thickness T = 4 mm, width W = 15 mm, and length L = 100 mm. The bending stiffness in the minor axis direction is the bending stiffness of the test code 82 embedded horizontally as shown in FIG. 8A, and the bending stiffness in the major axis direction is as shown in FIG. 8B. In addition, the bending rigidity of the test code 82 embedded vertically is shown.
The handling operability is an evaluation of the complexity of the work during the production of the steel cord and the forming of the composite sheet and the handling operability of the steel cord. As compared with the steel cord of No. 6, a very poor one was evaluated as x, a slightly inferior one was evaluated as Δ, and the one with no difference was evaluated as three ranks.
The evaluation of each steel cord based on the results in Table 1 will be described below.
The conventional steel cord having the cross-sectional shape shown in FIG. 2 (Experiment No. 6) has an extremely inferior rubber penetration rate as compared with the examples of the present invention (Experiment Nos. 1 to 3), and therefore has poor fatigue resistance. However, there are problems such as poor flexibility, lack of flexibility, and a thicker sheet. A conventional steel cord (Experiment No. 7) having a cross-sectional shape shown in FIG. 4 and having a substantially spiral core wire attached to the core wire has a rubber penetration rate of 80, and the rubber penetration rate of the embodiment of the present invention is 100. Considerably lower than The stiffness ratio is 99, which is considerably higher than the stiffness ratio of 93 to 95 of the embodiment of the present invention.
Further, the cord diameter on the minor diameter side is considerably larger than that of the steel cord of the embodiment of the present application. For this reason, when such a cord is used, the seat thickness cannot be reduced, resulting in poor ride comfort.
Furthermore, since it is necessary to subject the core element wire to a spiral curving process, manufacturing costs and equipment costs are increased, and handling operability is somewhat poor.
The steel cord (Experiment No. 8) having a cross section shown in FIG. 5 in which a core element wire is corrugatedly shaped (Experiment No. 8) has a small maximum interruption amount of 0.15 d and a low rubber penetration rate of 60%. . This material has poor handling workability during the production of a steel cord and a rubber sheet, and it is particularly difficult to properly control the tension applied to the steel cord.
The structure is the same as that of the embodiment of the present invention, and is a comparative example in which the maximum interrupt amount is 0.17d, that is, the experiment No. In No. 4, the stability of the steel cord is poor, the rubber penetration rate is only 65%, and the handling workability is poor.
A similar comparative example in which the maximum amount of interruption was 0.58d, that is, Experiment No. The steel cord No. 5 has remarkably low fatigue resistance as compared with the examples of the present invention (Experiments No. 1 to No. 3). This is because the maximum interrupt amount of the cord is too large, and indentation and damage of the wire due to excessive compression processing are remarkable.
As compared with the above-mentioned conventional examples and comparative examples, the examples of the present invention (Experiments No. 1 to No. 3) have an extremely high rubber penetration rate of 100% and a high fatigue resistance of 105 to 108. The rigidity ratio is as small as 93 to 95. For this reason, when it is applied to a tire, the tire has high circumferential flexibility and therefore good riding comfort and high lateral rigidity and therefore good cornering characteristics.
Also, the handling workability is better than the conventional one.
[0008]
[Effect]
The steel cord of the present invention does not have a cavity inside the cord over substantially the entire area in the longitudinal direction of the cord, and has a stable and high rubber penetration property. Further, since the thickness of the sheet when embedded in rubber can be reduced, the tire weight can be reduced, and the fuel efficiency of the vehicle can be improved.
Further, since the rigidity in the circumferential direction (rotational direction) of the tire can be reduced, ride comfort can be improved, and the rigidity in the tire lateral direction can be increased, so that cornering performance can be improved.
Further, since the steel cord of the present invention is extremely excellent in the stability of twisting in the longitudinal direction, the rubber cord is very good as described above, and the workability of the steel cord is very good.
Furthermore, since a straight strand is used as the core strand and the steel cord is twisted, it can be manufactured using any conventional buncher type or tubular type stranding machine, and no twisting failure occurs (core strand) In the prior art shown in FIGS. 4 and 5 in which a twist is generated in advance, a twisting problem is a problem in manufacturing). In addition, in order to adjust the twist pitch of the side strands to the habit pitch of the core strands. Since the pitch adjustment is not necessary, the pitch adjustment of the side strands is simple, handling is easy, and there is no need to pre-curse the core strands. Therefore, the manufacturing cost can be significantly reduced as compared with the conventional example shown in FIGS.
[Brief description of the drawings]
FIG. 1 is a sectional view of a steel cord according to the present invention.
FIG. 2 is a cross-sectional view of a conventional steel cord in which six side strands are closely attached to each other and twisted around a core strand.
FIG. 3 is a cross-sectional view of a conventional steel cord in which a gap is formed between side strands which are tightly twisted around a core strand having a large diameter.
FIG. 4 is a cross-sectional view of a conventional steel cord in which a spiral wire having a small radius is applied to a core wire in advance, and a side wire is closely adhered to the core wire and twisted.
FIG. 5 is a cross-sectional view of a conventional steel cord in which a corrugated core having a small amplitude is applied to a core element wire in advance, and a side element wire is tightly attached thereto and twisted.
FIG. 6 is a sectional view of a conventional flat open twisted steel cord.
FIG. 7 is a schematic view of a rigidity tester.
8A is a perspective view of a test piece in which a steel cord is embedded in a minor axis direction, and FIG. 8B is a perspective view of a test piece in which a steel cord is embedded in a major axis direction.
FIG. 9 is an enlarged photograph of a cross-sectional enlarged photograph of a steel cord (1 + 6 structure) according to an embodiment of the present invention at a pitch of 2 mm at one twist pitch.

Claims (1)

In a steel cord for reinforcing rubber products having a substantially elliptical shape having a core strand of the same thickness as many side strands,
A steel cord of 1 + 6 structure, in which six side strands are arranged around one core strand and twisted,
The open structure in which the side wires are twisted around the straight core wire is compressed to form a flat open structure in which the cross-sectional shape of the cord is almost the same in the longitudinal direction of the cord.
At the time of the pressure processing, the core element wire is partially interrupted between two adjacent side element wires,
The steel cord for reinforcing rubber products as described above, wherein the maximum amount of interruption of the core strand at one twist pitch of the cord is 30% to 50% of the core strand diameter.

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