Steel cord for rubber reinforcement

Abstract

This invention provides a steel wire cord with a structure of nx1, where n is the number of steel monofilaments in the steel wire cord. The elongation of the steel wire cord at 2.5N to 50N is less than 1.2%, and the lay length is greater than 16mm. When unwound from the steel wire cord, each steel monofilament has a helical wave form, with a wavelength L in mm and a wave height H in mm, where L is greater than 16mm. The spatial volume Vs of each steel monofilament satisfies Vs = L x H. 2 xπ / 4, and Vs>20mm 3 The steel wire cord of this invention is beneficial for stress distribution.

Description

Technical Field

[0001] This invention relates to a steel cord (or steel cord) for rubber reinforcement. It also relates to a rubber article reinforced with steel cord. Background Technology

[0002] Steel wire cord is widely used as a reinforcing component in rubber products (such as rubber belts, rubber tires, hoses, etc.).

[0003] As a reinforcing component in rubber products, steel cord requires certain strength, corrosion resistance, fatigue resistance, rubber permeability, and rubber bonding properties. Rubber permeability is a property of steel cord, indicating the degree to which rubber can penetrate the steel cord. Rubber permeates the steel cord and fills the gaps between the wires, thereby reducing internal cavities and preventing moisture from entering. This also avoids corrosion of the steel wires, ensuring a long service life. Steel cord typically requires high rubber permeability.

[0004] Open-type steel cord is a type of steel cord developed for high rubber permeability. Open-type steel cord refers to steel cord with a considerable number of gaps between the steel wires, which allows rubber to penetrate the cord relatively easily.

[0005] US4258543 discloses an open-type steel cord having 3 to 5 steel wires, and the diameter of the open-type steel cord is larger than the diameter of the same cord in a compact geometry.

[0006] However, sometimes, in the shoulder section of the tire, the open steel cords separate from the rubber, which is called the shoulder separation problem, and this problem can lead to tire failure. Summary of the Invention

[0007] The main objective of this invention is to solve the problems of the prior art.

[0008] The first objective of this invention is to provide a steel wire cord.

[0009] A second object of the present invention is to provide a tire reinforced with the steel cord of the present invention.

[0010] According to a first aspect of the present invention, a steel wire cord is provided. The steel wire cord has an nx1 structure, where n is the number of steel monofilaments in the cord. The elongation of the steel wire cord at 2.5 N to 50 N is less than 1.2%, and the lay length is greater than 16 mm. When unwound from the steel wire cord, each steel monofilament has a helical wave form, the helical wave having a wavelength L in mm and a wave height H in mm, where L is greater than 16 mm. The spatial volume Vs of each steel monofilament satisfies Vs = LxH. 2 xπ / 4 and Vs>20mm 3 .

[0011] The large volume of steel monofilaments is beneficial for stress distribution around and along the length of the steel cord. This is especially true in the tire shoulder area, where stress concentration is significant and can sometimes lead to tire shoulder separation. The use of steel cords in this invention produces better stress distribution, thereby reducing the risk of tire shoulder separation.

[0012] Preferably, Vs is greater than 23mm 3 More preferably, Vs is greater than 30mm. 3 Preferably, Vs is greater than 35mm. 3 Vs is preferably less than 200mm. 3 .

[0013] When the steel filaments are untied from the steel cord, each filament is observed to be in the form of a helical wave, i.e., a three-dimensional wave. When the steel filaments are projected onto a screen, their outlines are two-dimensional waves with wavelength and wave height, and the wavelength and wave height of the two-dimensional wave outlines are regarded as the wavelength and wave height of the helical wave of the steel filaments.

[0014] Preferably, the wavelength L is greater than 20 mm. More preferably, the wavelength L is greater than 24 mm and less than 40 mm.

[0015] Preferably, the steel wire cord has a twist pitch greater than 20 mm. More preferably, the steel wire cord has a twist pitch greater than 24 mm and less than 40 mm.

[0016] According to the present invention, the steel wire cord has an elongation at break of less than 5.0%.

[0017] "Elongation at 2.5N to 50N" is the elongation between 2.5N and 50N, expressed as a percentage.

[0018] According to the present invention, n ranges from 2 to 7.

[0019] Preferably, the steel monofilament has a tensile strength greater than 4000-2000 x D MPa when unwound from the steel cord, where D is the diameter of the steel monofilament expressed in mm. More preferably, the steel monofilament has a tensile strength greater than 4200-2000 x D MPa. The higher tensile strength of the steel monofilament facilitates a reduction in the diameter of both the steel monofilament and the steel cord, thereby contributing to tire weight reduction.

[0020] One application of the steel wire cord of the present invention is for rubber reinforcement.

[0021] According to a second aspect of the invention, a tire is provided. The tire includes at least one belt layer, at least one carcass layer, at least one tread layer, and a pair of bead portions. The belt layer and / or the carcass layer includes at least one steel cord with a structure of n x 1, where n is the number of steel monofilaments in the steel cord. The steel cord has an elongation of less than 1.2% at 2.5 N to 50 N and a lay length greater than 16 mm. Each steel monofilament, when unwound from the steel cord, has a helical wave shape, the helical wave having a wavelength L in mm and a wave height H in mm, where L is greater than 16 mm. The spatial volume Vs of each steel monofilament satisfies Vs = L x H. 2 xπ / 4 and Vs>20mm 3 . Attached Figure Description

[0022] Figure 1 The steel wire cord of the present invention is described.

[0023] Figures 2a to 2b It describes the steel monofilaments unwound from the steel wire cord and their corresponding wavelengths and wave heights. Detailed Implementation

[0024] The steel monofilaments of steel wire cord are made of wire rod (or wire rod).

[0025] The wire rod is first cleaned by mechanical rust removal and / or chemical pickling in H2SO4 or HCl solution to remove surface oxides. The wire rod is then rinsed in water and dried. The dried wire rod is then subjected to a first series of dry drawing operations to reduce its diameter until a first intermediate diameter is reached.

[0026] At this first intermediate diameter D1, for example, at approximately 3.0 mm to 3.5 mm, the dry-drawn steel monofilament undergoes a first intermediate heat treatment called lead quenching (or lead bath quenching, patenting). Lead quenching refers to first austenitizing up to a temperature of approximately 1000°C, and then transforming from austenite to pearlite at a temperature of approximately 600°C to 650°C. The steel monofilament is then ready for further mechanical deformation.

[0027] Subsequently, in a second series of diameter reduction steps, the steel monofilament is further dry-drawn from the first intermediate diameter until a second intermediate diameter is reached. The second diameter typically ranges from 1.0 mm to 2.5 mm.

[0028] At this second intermediate diameter, the steel monofilament undergoes a second lead quenching treatment, namely, re-austenitization at a temperature of about 1000°C, followed by quenching at a temperature of 600°C to 650°C to allow transformation into pearlite.

[0029] If the total reduction in the first and second dry drawing steps is not too large, a direct drawing operation can be performed from the wire rod until the second intermediate diameter.

[0030] Following this second lead quenching process, the steel monofilament typically has a brass coating: copper is plated onto the steel monofilament, and zinc is plated onto the copper. A heat diffusion treatment is applied to form the brass coating. Alternatively, the steel monofilament may be provided with a ternary alloy coating, comprising copper, zinc, and a third alloy of cobalt, titanium, nickel, iron, or other known metals.

[0031] The brass-plated or ternary alloy-plated steel monofilaments are then subjected to a final series of cross-sectional reductions using a wet drawing machine. The final product is a steel monofilament with a carbon content of more than 0.70% by weight, or not less than 0.80% by weight, or even more than 0.90% by weight, and a tensile strength (TS) typically greater than 3000 MPa, suitable for reinforcing rubber products.

[0032] Steel monofilaments suitable for tire reinforcement typically have a final diameter D ranging from 0.05 mm to 0.60 mm, for example, from 0.10 mm to 0.40 mm. Examples of wire diameters are 0.10 mm, 0.12 mm, 0.15 mm, 0.175 mm, 0.18 mm, 0.20 mm, 0.22 mm, 0.245 mm, 0.28 mm, 0.30 mm, 0.32 mm, 0.35 mm, 0.38 mm, and 0.40 mm. The diameter D of the steel monofilament is preferably in the range of 0.10 mm to 0.50 mm.

[0033] Multiple steel monofilaments are twisted together to form a steel cord using existing steel cord manufacturing processes (i.e., cabling or bundling processes). Prior to twisting, the steel monofilaments are pre-shaped using existing pre-forming methods. By adjusting the pre-forming of the steel monofilaments, a predetermined wave height is achieved. Similarly, by adjusting the pre-forming and twisting processes, a predetermined wavelength is achieved, resulting in unwound steel monofilaments with a predetermined spatial volume. Although the wavelength and wave height of the steel monofilaments are measured when they are unwound from the steel cord, the unwinding operation does not substantially change their wavelength or wave height.

[0034] Figure 1An embodiment of the invention is shown. The steel cord 100 comprises four steel monofilaments 105 with a diameter of 0.38 mm. Figure 2a This shows the steel monofilament 105 unwound from the steel wire cord 100. Figure 2b The wavelength L and wave height H of steel monofilament 105 are shown according to the measurement method. Details of the measurement method for wavelength and wave height are as follows:

[0035] First, cut the steel cord 100 into samples of a certain length, such as 100-150mm, and then untangle the steel monofilaments 105 from the steel cord samples.

[0036] -Second, project a steel wire 105 onto the screen and create the outline of the middle part of the steel wire 105.

[0037] - Third, measure the distance between two subsequent wavelengths (i.e., from one peak to the next second peak) and divide by two to determine the wavelength; measure the distance between the valley and the imaginary baseline between the two peaks to determine the wave height. - Fourth, repeat 5 identical steel wires 105 and calculate the average value, which is the wavelength L and the wave height H.

[0038] Table 1 below summarizes the performance of the steel wire cord of the present invention compared with a reference steel wire cord.

[0039] Table 1

[0040]

[0041] Fatigue testing is used to determine the degree of separation between the steel wire cord and the rubber. The fatigue test involves the following steps:

[0042] - Melt the steel cord into 15 small pieces, each 330mm long. Cut the small pieces in the center to obtain 30 small steel cord samples, ensuring that the cut ends of the small steel cord samples are not flared.

[0043] - Prepare a rubber strip measuring 203mm x 35mm x 6.4mm (length x width x height) and a rubber cap of the same size as the rubber strip;

[0044] - Place the end portion of a small steel wire cord sample (12.5mm in length, including the cut end) on a rubber strip. Arrange 15 small steel wire cord samples along one side of the rubber block, and place another 15 small steel wire cord samples along the opposite side of the rubber strip. Ensure that one small steel wire cord sample on one side of the rubber strip has the same horizontal axis as the corresponding small steel wire cord sample on the opposite side. Place a rubber cover on the rubber strip and small steel wire cord samples to form a rubber block, and then cure the rubber block. - Mark the small steel wire cord samples 2, 4, 6, 9, 11, and 13 along the length of the rubber block. Cut the rubber block to remove small pieces approximately 22mm long. Ensure that two small steel wire cord samples are inserted into the center of each small piece. Then, use two clamps to fix the steel wire cord of each small piece along the vertical axis. Then, apply vibration force to the small piece at a predetermined frequency and amplitude at room temperature and record the repeated cycles of vibration force until the steel wire cord separates from the small piece.

[0045] Compared to reference steel wire cords, the steel wire cords of the present invention have a better ability to withstand more vibrations until they separate from the rubber block, which proves that the steel wire cords of the present invention contribute to better stress distribution.

Claims

1. A steel cord of structure nx 1, n being the number of steel filaments of said steel cord, said steel cord having an elongation at 2.5 N to 50 N of less than 1.2% and a lay length of more than 20 mm, each of said steel filaments having the form of a helical wave when uncoiled from said steel cord, the helical wave having a wavelength L expressed in mm and a wave height H expressed in mm, characterized in that, Where L is greater than 16mm, the spatial volume Vs of each steel wire satisfies: Vs = L x H 2 x π / 4 and Vs > 20 mm 3 and the Vs is less than 200 mm 3 and n ranges from 2 to 7.

2. Steel cord according to claim 1, characterized in that, said Vs is greater than 23 mm 3 .

3. Steel cord according to claim 2, characterized in that, said Vs is greater than 30 mm 3 .

4. Steel cord according to claim 3, characterized in that, Vs is greater than 35 mm 3 .

5. Steel cord according to any one of claims 1 to 4, characterized in that, The wavelength L is greater than 20 mm.

6. Steel cord according to claim 5, characterized in that, The wavelength L is greater than 24 mm and less than 40 mm.

7. Steel cord according to any one of claims 1 to 4, characterized in that, The twist pitch of the steel wire cord is greater than 24 mm and less than 40 mm.

8. Steel cord according to any one of claims 1 to 4, characterized in that, The steel wire cord has a breaking elongation of less than 5.0%.

9. Steel cord according to any one of claims 1 to 4, characterized in that, The tensile strength of the steel monofilament when it is untied from the steel wire cord is greater than 4000-2000xD MPa, where D is the diameter of the steel monofilament expressed in mm.

10. Steel cord according to claim 9, characterized in that, The steel monofilament has a tensile strength greater than 4200-2000 x D MPa.

11. The use of the steel wire cord as claimed in any one of claims 1 to 10 for rubber reinforcement.

12. A tire comprising at least one belt layer, at least one carcass layer, at least one tread layer, and a pair of bead portions, characterized in that, The belt layer and / or the carcass layer comprise at least one steel cord as claimed in any one of claims 1 to 10.

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