High-rubber-permeation and high-strength steel cord for crawler belt and preparation method of high-rubber-permeation and high-strength steel cord

Abstract

The invention relates to the technical field of steel cords, in particular to a high-rubber-permeation high-strength steel cord for a crawler belt and a preparation method thereof.Pretreatment is conducted on a high-carbon steel wire rod and comprises electrolytic pickling, water washing, boron coating and drying; the pretreated wire rod is subjected to dry type medium drawing, a wire obtained through dry type medium drawing is sequentially subjected to degreasing, online heat treatment, water cooling, electrolytic pickling, copper plating, zinc plating, drying, heat diffusion, phosphoric acid washing and soap soaking treatment, and a steel wire with the target diameter is obtained through wet type finish drawing; the steel wires are made into steel cords through a multi-stage twisting process, and online straightening and over-twisting treatment are integrated in the twisting process, so that residual stress is eliminated, and the structure is stabilized. According to the multi-stage and high-precision pull-down process, the steel wire has extremely high tensile strength and fatigue life. Meanwhile, the uniformity, the stability and the low residual torque of the whole structure of the steel cord are guaranteed.

Description

Technical Field

[0001] This invention relates to the technical field of steel cord, specifically to a high-strength steel cord with high adhesive penetration for track use and its preparation method. Background Technology

[0002] Rubber tracks are widely used in construction machinery, agricultural machinery, and special vehicles due to their excellent ground adhesion, shock absorption, and wear resistance. To enhance the load-bearing capacity and fatigue resistance of the tracks, steel cords are typically embedded in the rubber matrix as a reinforcing material. The steel cords not only need to possess high strength and high toughness but also need to ensure good adhesion to the rubber to maintain stable performance under long-term, complex working conditions.

[0003] However, typical operating environments for rubber tracks often involve media such as water, mud, and moist soil. The steel cords inside the track are highly susceptible to corrosion due to moisture seeping through the gaps in the wires. Corrosion of the steel wires weakens the mechanical properties of the cords and their bonding strength with the rubber, leading to failure modes such as cord breakage and adhesive layer peeling, thereby shortening the track's lifespan.

[0004] Existing steel cords for track use mostly employ conventional structures such as 7×7 or 7×(3+9), which offer advantages such as high overall strength and mature twisting technology. However, due to the tight arrangement of the strands in these structures, rubber cannot fully penetrate into the cord core during vulcanization, resulting in voids inside the cord that are not filled with rubber. Once external moisture enters along these microcracks, it can spread to the core wires through these un-penetrated areas, inducing deep corrosion and premature failure.

[0005] To improve rubber penetration performance, some technical solutions improve rubber penetration by adjusting the wire diameter, strand combination, or adding an outer coating structure. For example, CN117758526A discloses a high-penetration radial engineering tire steel cord and its preparation method. By increasing the gap between steel wires through structural design, it can significantly improve rubber penetration performance when applied to rubber products such as tires. At the same time, it enhances the breaking strength of the cord without increasing its diameter and weight, thus giving the tire higher load-bearing capacity.

[0006] However, the lack of precise sub-step control in the manufacturing process of this technology makes it difficult to optimize residual stress and surface quality. These problems not only increase the maintenance cost of the tracks, but also affect the reliability and safety of the mechanical equipment. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a high-strength steel cord with high rubber penetration for track use and its preparation method. By introducing an axially continuous micro-gap design, precise diameter difference control, and staged fine processes (such as vibration-assisted drawing, dynamic tension twisting, and pressure-assisted heat treatment), the invention achieves full rubber penetration, reduces residual stress, and improves fatigue resistance, thereby solving the problems of uneven rubber penetration, insufficient strength, and poor durability in existing technologies.

[0008] To achieve the above objectives, the present invention provides the following technical solution: A high-strength steel cord with high adhesive penetration for track use, wherein the steel cord is a single-strand composite twisted structure, comprising: The central strand consists of three steel wires arranged in a triangular pattern; The intermediate twist strand consists of eight steel wires twisted in a single-layer spiral around the outer periphery of the central strand, and a micro gap is formed between the central strand and the intermediate twist strand that runs through the cord axis. The average width of the micro gap is 0.02~0.05mm. The outer layer of the twisted strand consists of six composite strands twisted together in a spiral manner around the outer periphery of the intermediate twisted strand to form the outermost structure of the cord. Each composite strand is formed by three steel wires twisted together once to form the inner core, and then nine steel wires are twisted together in a single layer in a spiral manner around the outer periphery of the inner core. The diameter of the steel wire in the center twisted strand is larger than that in the outer retwisted strand, so that the rubber can penetrate to the surface of the center strand along the micro-gap during vulcanization.

[0009] A processing method for preparing high-strength steel cord with high adhesive penetration for track use includes the following steps: S1: Pretreatment of high carbon steel wire rod, including electrolytic pickling, water washing, boron coating and drying; S2: Dry intermediate drawing of the pretreated wire rod. S3: Heat treatment and gradient brass plating: The dry-drawn wire is subjected to degreasing, online heat treatment, water cooling, electrolytic pickling, copper plating, zinc plating, drying, thermal diffusion, phosphoric acid washing, and soap immersion treatment in sequence. S4: Perform wet precision drawing to obtain a steel wire of the target diameter; S5: The steel wire is made into steel cord through a multi-stage twisting process, and online straightening and over-twisting treatment are integrated during the twisting process to eliminate residual stress and stabilize the structure.

[0010] The present invention is further configured such that step S1 specifically includes: S11. First, the iron oxide scale on the surface of the wire rod is flexibly peeled off by multiple sets of roller peeling equipment, and then preliminary straightening is performed to eliminate the stress of the wire rod. S12. Immerse the wire rod in the pickling tank for electrochemical rust removal. The sulfuric acid concentration is controlled at 8%~12%, the iron ion concentration is maintained at ≤80g / L, the pickling solution temperature is 40℃~50℃, and the pickling current density is set to 5~10A / dm². S13. Multi-stage counter-current water rinsing is adopted, and hot water at 70℃~80℃ is used in the last stage; S14. Immerse a clean steel wire in a borax solution bath to form a borax film. During this process, the borax concentration is 50~80g / L, and the borax solution temperature is 90℃~100℃. S15. Drying is carried out in a tunnel drying oven, with the drying temperature controlled at 120℃~150℃.

[0011] The present invention is further configured such that step S2, drawing, is divided into three stages: Initial drawing stage: The drawing speed increases linearly from 3.0 m / s to 6.0 m / s; During the intermediate pulling stage: the pulling speed increases linearly from 6.0 m / s to 9.0 m / s; Precision drawing stage: The drawing speed increases from 9.0 m / s and stabilizes at 10.0 m / s. The present invention is further configured such that step S3 specifically includes the following steps: S31. Electrolytic degreasing is performed in an alkaline degreasing solution at 60-80℃ using a current of 5-10A / dm².

[0012] S32. The steel wire is fed into a heating furnace under a protective atmosphere, with the furnace temperature precisely controlled at 960~980℃, and then rapidly cooled.

[0013] S33. After cooling with coolant, electrolytic pickling with the same parameters as in step S12 is performed again to activate the steel wire matrix.

[0014] S34. After the steel wire is rinsed with water, a uniform copper underlayer is deposited in a copper pyrophosphate plating solution at 25~35℃ and pH 10~11.5 at a current density of 0.3~1A / dm². S35. After the steel wire is sprayed and washed with water, it is plated with a layer of zinc in a zinc sulfate plating solution at 30~40℃ and pH value 1~2 at a current density of 1~5A / dm².

[0015] S36. After cleaning and drying, the product enters an induction heating furnace and undergoes thermal diffusion at a temperature of 450~550℃ for 5~15 seconds, allowing copper and zinc atoms to interpenetrate and form a brass layer with adhesive activity.

[0016] S37. The solution is cleaned and activated in a 10% to 20% phosphoric acid solution at 50 to 60°C, and then soaked in a saponification solution at 80 to 90°C to provide a protective and lubricating carrier for the final wet drawing.

[0017] The present invention is further configured such that: step S4 specifically involves fine drawing of the coated steel wire in a fully immersed lubricating coolant, with the drawing speed controlled at 8~15m / s, wherein the lubricant concentration is 5%~10%, the pH value is maintained at 8.0~9.0, and the liquid temperature is constant at 35℃~45℃.

[0018] The present invention is further configured such that step S5 includes the following steps: S51. Twist three steel wires into a central strand with a twist pitch of 5.0~15.0mm; S52. Twist eight steel wires into an intermediate twist strand with a twist pitch of 8.0~24.0mm, and form a micro gap; S53. Twist the six-strand composite yarn into an outer layer of re-twisted strands, with a total re-twisting pitch of 15.0~40.0mm.

[0019] S54. After the twisted steel cord is straightened by the roller straightener, it is then passed through the overtwist device to apply a reverse twist of 180°~360° to the cord, so that the residual twist of the final finished cord is ≤1 turn / 6 meters.

[0020] The present invention is further configured such that: during the entire twisting process, the tension of the single filament is controlled at 8±0.5N and the tension of the take-up is controlled at 15~40N.

[0021] The present invention is further configured such that: the thickness of the brass layer formed in step S36 is 0.18~0.28μm, and the copper content in the coating is 60%~70%, and a gradient structure is formed through thermal diffusion, wherein the copper-zinc ratio of the outer layer is Cu:Zn=60:40, and the copper-zinc ratio of the inner layer is Cu:Zn=70:30.

[0022] The present invention is further configured such that: steel cord is applied to the skeleton reinforcement structure of rubber track.

[0023] Compared with the shortcomings of the prior art, the beneficial effects of the present invention are as follows: Through a multi-layered composite twisting structure, and a precise micro-gap between the center strand and the tundish strand, along with a design where the diameter of the tundish strand wire is slightly larger than that of the outer strand wire, the rubber is effectively ensured to fully penetrate and fill the interior of the steel cord during vulcanization, thereby significantly improving the interfacial bonding strength between the steel cord and the rubber matrix. The multi-stage, high-precision pull-down process endows the steel wire itself with extremely high tensile strength and fatigue life. Simultaneously, meticulously controlled twist pitch, dynamic tension control, segmented twisting, and stable heat treatment processes ensure the uniformity, stability, and low residual torque of the overall steel cord structure, thereby improving its durability and fatigue resistance under dynamic working conditions. Attached Figure Description

[0024] Figure 1 This is a schematic cross-sectional view of the structure of the present invention; Figure 2 This is a schematic diagram of the process of the present invention.

[0025] 1. Center strand, 2. Intermediate twist strand, 3. Outer layer re-twisted strand. Detailed Implementation

[0026] Reference Figures 1 to 2 The embodiments of the present invention will be further described below.

[0027] This invention provides a method for preparing high-strength steel cord with high adhesive penetration for track use. This method involves meticulous pretreatment of high-carbon steel wire rods, multi-stage drawing, optimized heat treatment and coating processes, and a precise twisting process, ultimately producing steel cord that meets the requirements for reinforcing the track skeleton structure.

[0028] The steel cord of this invention adopts a single-strand composite twisting structure, the core of which is to achieve high strength and excellent rubber permeability. The structure mainly includes a center strand, an intermediate twisted strand, and an outer re-twisted strand.

[0029] The center strand consists of three steel wires arranged in a triangular pattern. This triangular arrangement provides good central support and a stable foundation for the subsequent wrapping of the steel wires.

[0030] The triangular arrangement of the three steel wires is more effective at resisting external forces and provides higher tensile strength compared to other arrangements (such as a straight line arrangement). It also provides three-dimensional support points for the wrapping of the intermediate twisted strand, increasing the stability and strength of the overall structure.

[0031] The center twist strand consists of eight steel wires twisted in a single-layer spiral around the outer periphery of the center strand.

[0032] A micro-gap is formed between the center strand and the intermediate twist strand, running through the cord axis, with an average width controlled between 0.02 and 0.05 mm.

[0033] The diameter of the steel wire used in the intermediate twist strand is larger than the diameter of the steel wire used in the outer retwisted strand.

[0034] Eight steel wires are spirally wrapped around the central strand, increasing the overall density and tensile strength of the cord.

[0035] During the twisting process, by precisely controlling the wire diameter, twist pitch and tension, the eight wires can tightly wrap around the central strand. However, due to the triangular arrangement of the three wires in the central strand and the slight deformation of the wires themselves, a small channel is naturally formed that runs through the axial direction.

[0036] The micro-gap design is intended to facilitate efficient rubber penetration during vulcanization. When the steel cord is vulcanized with the rubber composite, the high-viscosity rubber can penetrate deep into the surface of the central strand via capillary action.

[0037] The middle twisted strand uses thicker steel wire, while the outer re-twisted strand uses thinner steel wire. This helps to create micro-gap while maintaining the flexibility of the outer steel wire, facilitating the subsequent twisting of the composite strand. At the same time, the thicker steel wire can better bear stress and provide a more stable channel for rubber penetration.

[0038] The outer layer of retwisted strands consists of six composite strands twisted together in a spiral pattern around the outer periphery of the middle twisted strand, forming the outermost structure of the steel cord.

[0039] Each composite strand consists of three steel wires twisted together to form the inner core, and nine steel wires twisted in a single-layer spiral around the outer periphery of the inner core.

[0040] Composite strands are composed of inner and outer steel wires, which further improves the strength and fatigue resistance of steel cord. The inner core provides core strength, while the outer steel wires increase the contact area and gripping force with the rubber.

[0041] The entire structure adopts a multi-layer spiral structure (three layers of steel wire -> eight steel wires -> six composite strands). This structure provides high strength and high modulus while also giving the steel cord a certain degree of flexibility, allowing it to better adapt to the bending deformation of the rubber track.

[0042] The uniform distribution of the six-strand composite yarn and its tight bond with the intermediate twisted strands ensure the overall stability of the steel cord and provide a wider coating and bonding surface for the rubber.

[0043] The preparation method will be as follows: S1: Pretreatment of high carbon steel wire rod S11: This equipment uses multiple sets of roller-type peeling devices to flexibly remove the iron oxide scale from the surface of high-carbon steel wire rods. By precisely controlling the gap and rotation speed of the rollers, this equipment effectively removes the oxide scale without damaging the substrate. Simultaneously, the peeling process includes preliminary straightening, resolving stress generated during production or transportation of the wire rod and laying the foundation for subsequent processes.

[0044] Compared to traditional pickling or sandblasting, flexible descaling removes oxide scale more gently, reducing damage to the steel wire and improving the quality of subsequent drawing. Preliminary straightening eliminates residual stress, preventing wire breakage or irregular deformation during drawing.

[0045] S12: Immerse the wire rod in the pickling tank for electrochemical rust removal. Specific process parameters are: sulfuric acid concentration controlled at 8%~12%, iron ion concentration maintained at ≤80g / L, pickling solution temperature controlled at 40℃~50℃, and current density set at 5~10A / dm².

[0046] Electrochemical pickling utilizes the synergistic effect of electric current to remove oxide scale more quickly and thoroughly, while avoiding intergranular corrosion that may occur with traditional pickling. Precise control of sulfuric acid concentration, iron ion concentration, temperature, and current density is crucial to ensure effective rust removal while minimizing corrosion of the steel substrate, and to prevent secondary deposition by controlling the iron ion concentration.

[0047] S13: Multi-stage counter-current water rinsing is used to ensure that the acid is completely removed. The final rinsing stage uses hot water at 70℃~80℃.

[0048] Multi-stage countercurrent rinsing effectively removes acid and impurities adhering to the surface of the steel wire. High-temperature hot water rinsing not only removes residual acid and dirt more effectively, but also preheats the steel wire before subsequent processes (such as boron coating), which helps improve the uniformity and adhesion of the borosilicate film and accelerates the drying process.

[0049] S14: Immerse the clean steel wire in the borax solution bath to form a uniform borax film. The borax concentration is controlled at 50~80g / L, and the borax solution temperature is maintained at 90℃~100℃. Borax film is a commonly used lubricant and cold heading agent, playing a crucial role in the steel wire drawing process. It forms a lubricating layer between the wire drawing die and the dies, reducing drawing force, minimizing die wear, and preventing scratches on the steel wire surface. The formation of the borax film at high temperatures facilitates the dissolution and uniform adhesion of borax, forming a dense protective layer.

[0050] S15: The steel wire is dried using a tunnel drying oven, with the drying temperature controlled between 120℃ and 150℃. Thorough drying is crucial to ensuring the steel wire surface is dry, preventing moisture from being carried into the subsequent dry drawing process, which would affect the drawing effect and die life. The tunnel drying oven allows for precise control of temperature and time, ensuring uniform and efficient drying.

[0051] S2: Dry drawing of the pretreated wire rod. The drawing process consists of three stages: Initial drawing stage: The drawing speed increases linearly from 3.0 m / s to 6.0 m / s.

[0052] In the intermediate pulling stage: the pulling speed increases linearly from 6.0 m / s to 9.0 m / s.

[0053] Fine drawing stage: The drawing speed increases from 9.0 m / s and stabilizes at 10.0 m / s.

[0054] In dry drawing, the steel wire gradually decreases in diameter as it passes through the drawing die under the action of a lubricant (such as saponified liquid or graphite powder). Controlling the drawing speed in stages involves gradually transitioning from a relatively large cross-section to a smaller one.

[0055] The linear increase in speed avoids the impact and stress concentration caused by sudden changes in speed on the steel wire, thus ensuring the uniformity of deformation.

[0056] The final speed was stabilized at 10.0 m / s to ensure processing efficiency while avoiding excessive speeds that could lead to lubrication failure, overheating, or fatigue damage to the wire. This gentle acceleration process helps control variations in drawing force and ensures uniform grain deformation and work hardening of the wire at each stage.

[0057] S3: Heat treatment and gradient brass plating. This step is crucial for the preparation of high-adhesion steel cords, aiming to improve the strength and toughness of the steel wires and form a gradient brass layer with excellent adhesive activity.

[0058] S31: Electrolytic degreasing is performed in an alkaline degreasing solution at 60-80℃ using a current of 5-10 A / dm². Alkaline electrolytic degreasing efficiently removes oil, residual soap, and other organic contaminants from the surface of the steel wire, providing a clean surface for subsequent heat treatment and plating. The specific combination of temperature, alkali concentration, and current density ensures thorough and uniform degreasing.

[0059] S32: The steel wire is fed into a heating furnace with a protective atmosphere (such as hydrogen or nitrogen), and the furnace temperature is precisely controlled at 960~980℃, followed by rapid cooling (such as water cooling or mist cooling).

[0060] The brief heat treatment at this high temperature is primarily for recrystallization, refining the grain size. This refined grain structure significantly improves the overall mechanical properties of the steel wire, particularly its strength and toughness. The protective atmosphere prevents oxidation or carburization at high temperatures, ensuring material purity. Rapid cooling inhibits the growth of coarse grains and may introduce a certain degree of martensitic strengthening (depending on the specific steel composition and cooling rate).

[0061] S33: After cooling with coolant, perform electrolytic pickling again, using the same parameters as S12.

[0062] After high-temperature heat treatment and cooling, new oxide layers or contaminants may form on the surface of the steel wire. Repeated electrolytic pickling aims to remove these substances and activate the surface of the steel wire substrate, giving it better coating adhesion.

[0063] S34: After the steel wire is spray-washed, a uniform copper underlayer is deposited in a copper pyrophosphate plating solution at 25-35℃ and pH 10-11.5 at a current density of 0.3-1 A / dm². The copper underlayer serves as a good transition layer between the subsequent brass layer and the steel substrate. Copper has good ductility, which can buffer the difference in thermal expansion coefficients between the steel and the brass layer, improving the adhesion of the coating. The copper pyrophosphate plating solution provides a stable and uniform coating, and the specific pH value and current density ensure the quality and efficiency of the coating.

[0064] S35: After the steel wire is spray-washed with water, it is plated with a zinc layer in a zinc sulfate plating solution at 30-40℃ and pH 1-2, using a current density of 1-5 A / dm². The role of the zinc layer here is to form an alloy with the copper layer, resulting in a uniform brass layer during subsequent thermal diffusion. The zinc sulfate plating solution provides a stable coating at a relatively low pH value, while the high current density ensures the coating formation rate.

[0065] S36: After cleaning and drying, the steel wire enters an induction heating furnace. It undergoes a thermal diffusion treatment at 450~550℃ for 5~15 seconds. This process allows copper and zinc atoms to interpenetrate, forming a brass layer with adhesive activity. The resulting brass layer has a thickness of 0.18~0.28μm and a copper content of 60%~70%. A gradient structure is formed through thermal diffusion, with the outer layer having a copper-zinc ratio of Cu:Zn=60:40 and the inner layer having a copper-zinc ratio of Cu:Zn=70:30.

[0066] Thermal diffusion is the core step in forming brass layers and achieving a gradient structure. By precisely controlling temperature and time, the interdiffusion of copper and zinc atoms at high temperatures is utilized to form alloy layers.

[0067] A copper content of 60%–70% is key to forming excellent brass alloys, providing good strength and ductility. A thickness of 0.18–0.28 μm is optimized to provide sufficient bond strength while avoiding the brittleness that can result from excessively thick layers.

[0068] The gradient structure is designed to optimize rubber wetting and bonding. The outer layer has a Cu:Zn ratio of 60:40, with a slightly higher zinc content, making it easier for the zinc to react chemically or physically with the polar groups in the rubber, providing stronger surface bonding energy. The inner layer has a Cu:Zn ratio of 70:30, with a higher copper content, providing stronger mechanical support and adhesive strength, and serving as a more stable connection with the copper substrate. This gradient design can be viewed as a (Zn-richzone)-(Cu-richzone)-(Culayer)-(Steelsubstrate) structure, maximizing the interfacial bonding between the rubber and the steel cord.

[0069] S37: Cleaned and activated in a 10%–20% phosphoric acid solution at 50–60°C, followed by immersion in a saponification solution at 80–90°C. The phosphoric acid wash further removes surface residues and provides micro-roughness to the wire surface, enhancing subsequent lubrication and bonding with the die. The saponification immersion provides a good lubricating layer, ensuring adequate lubrication and cooling for the final wet drawing, and protecting the brass layer from damage.

[0070] S4: The coated steel wire is finely drawn in a fully submerged lubricating coolant. The drawing speed is controlled at 8~15m / s. The lubricant concentration is 5%~10%, the pH value is maintained at 8.0~9.0, and the liquid temperature is kept constant at 35℃~45℃.

[0071] Wet drawing is the final drawing process performed in a water-based lubricating coolant. Full immersion and optimized lubricant parameters (concentration, pH, temperature) ensure that the steel wire is adequately cooled and lubricated during the drawing process, significantly reducing drawing stress, minimizing die wear, and preventing damage to the brass plating.

[0072] A drawing speed of 8~15m / s is an optimal range that ensures efficiency while taking into account both lubrication and cooling effects and wire quality. The final target diameter is achieved in this step.

[0073] S5: Multi-stage twisting and structural stability: S51: Twist the three steel wires into a center strand according to the preset twist pitch (5.0~15.0mm). The determined twist pitch range is to ensure that the three steel wires in the center strand can form a stable triangular arrangement and to reserve appropriate space for subsequent wrapping.

[0074] S52: Eight steel wires are twisted around the outer periphery of the central strand at a preset twist pitch (8.0~24.0mm), simultaneously forming a micro-gap of 0.02~0.05mm. The twist pitch is selected based on the number and diameter of the steel wires and their wrapping angle with the central strand, aiming to achieve a tight spiral arrangement of the steel wires while precisely controlling the gap between the steel wires to create channels for rubber penetration.

[0075] S53: Six composite strands are twisted together in a spiral pattern around the outer periphery of the intermediate twist strand with a total twist pitch of 15.0~40.0mm to form the overall structure of the steel cord.

[0076] The twisting of the composite strands and the twist pitch of the outer re-twisted strands require precise adjustment to ensure that all strands are evenly distributed, forming a tight and rounded steel cord cross-section. The total re-twisted twist pitch is a crucial parameter determining the overall strength, toughness, and modulus of the steel cord.

[0077] S54: The twisted steel cord is straightened online by a roller straightener, and then the cord is twisted in reverse by 180°~360° by an overtwist device so that the residual twist of the final finished cord is ≤1 turn / 6 meters.

[0078] During the twisting process, the metal material itself generates internal stress, resulting in a certain residual torque in the steel cord. Overtwisting (reverse twisting) is a process to compensate for and release this stress. Applying a reverse twist of 180°~360° can effectively counteract or neutralize the torque generated during twisting, ensuring that the residual torque of the final steel cord is ≤1 turn / 6 meters. The smaller the residual torque, the less likely the steel cord is to undergo torsional deformation during subsequent use, ensuring the structural stability of the cord in the rubber track. During the twisting process, the single filament unwinding tension is controlled at 8±0.5N, and the take-up tension is controlled at 15~40N. This ensures that the steel wire is not overstretched when entering the twisting machine, maintaining its original metallic properties and helping to form the desired gap structure, especially during the tundish twisting process.

[0079] Appropriate winding tension is used to ensure the overall tightness of the steel cord and prevent loosening between the strands. Excessive winding tension may cause excessive deformation of the steel wires, reducing toughness; while insufficient winding tension may cause the steel cord structure to become loose and its strength to decrease.

[0080] Example 1: In the pretreatment stage, the sulfuric acid concentration for S12 electrolytic pickling was set to 8%, the pickling solution temperature was 40°C, and the current density was 5A / dm², aiming to gently but effectively activate the substrate. The boron coating process used a 50g / L borax concentration, operated in a borax solution at 90°C, while DryerS15 was dried at 120°C. In the S2 step before intermediate drawing, the final drawing speed was 10.0m / s.

[0081] In the critical heat treatment and gradient brass plating process, the pH value for the copper underlayer plating was set to 10, and the current density was 0.3 A / dm². The pH value for the zinc layer plating was set to 1, and the current density was 1 A / dm². The thermal diffusion treatment was performed at 450℃ for 5 seconds to form a gradient brass layer with an outer Cu:Zn ratio of 60:40 and an inner Cu:Zn ratio of 70:30, for a total thickness of approximately 0.23 μm.

[0082] In the wet fine drawing step, the lubricant concentration is 5%, the pH value is 8.0, and the liquid temperature is 35℃.

[0083] During the multi-stage twisting and structural stabilization stage, the center strand twist pitch is 5.0 mm, the intermediate twist strand twist pitch is set to 8.0 mm, and the outer composite strand twist pitch is determined to be 15 mm. Finally, a 180° reverse twist is applied through the over-twist device to ensure that the residual twist of the steel cord is ≤1 turn / 6 meters.

[0084] In Example 2, the S12 electrolytic pickling process uses a 12% sulfuric acid concentration in a pickling solution at 50°C and a high current density of 10 A / dm² to enhance surface activation. The boron coating process is adjusted to an 80 g / L borax concentration in a borax solution at 100°C, and the drying temperature is increased to 150°C. In the intermediate drawing step (S2), the final drawing speed remains at 10.0 m / s.

[0085] In the heat treatment and gradient brass plating process, the pH value of the copper underlayer plating was increased to 11.5, and the current density was 1 A / dm². The pH value of the S35 zinc layer plating was increased to 2, and the current density reached 5 A / dm². The thermal diffusion treatment temperature was set at 550℃ for 15 seconds, with the same gradient brass layer structure (outer layer Cu:Zn=60:40, inner layer Cu:Zn=70:30), and the total thickness was approximately 0.23 μm.

[0086] In the wet fine drawing step, the lubricant concentration is increased to 10%, the pH value is set to 9.0, and the liquid temperature is also raised to 45℃.

[0087] During the multi-stage twisting and structural stabilization stage, the center strand twist pitch is 15mm, the intermediate twisted strand twist pitch is 24mm, and the outer composite strand twist pitch is 40mm. Finally, a 360° reverse twist is applied by the over-twisting device to ensure that the residual twist of the steel cord is ≤1 turn / 6 meters.

[0088] Example 3: In the pretreatment stage, high-carbon steel wire rods undergo dry intermediate drawing treatment. The S12 electrolytic pickling step uses a 10% sulfuric acid concentration in a pickling solution at 45°C with a current density of 7.5 A / dm² to ensure complete removal of surface oxide scale and effective activation of the substrate. Subsequently, a boron coating process is used, with a borax concentration of 65 g / L, to form a uniform and dense boron film in a borax solution at 95°C. Drying is completed in a tunnel drying oven at 135°C to ensure complete drying of the wire surface. In the subsequent dry intermediate drawing step, the drawing speed is linearly increased from 3.0 m / s to a final value of 10.0 m / s.

[0089] In the crucial heat treatment and gradient brass plating process, a copper underlayer is formed in a copper pyrophosphate plating bath with a pH of 10.75 at a current density of 0.65 A / dm². Immediately following, a zinc layer is plated in a zinc sulfate plating bath with a pH of 1.5 at a current density of 3 A / dm². Subsequently, a thermal diffusion treatment, the core of the gradient brass layer formation, is performed at 500°C for 10 seconds, allowing copper and zinc atoms to interpenetrate and form a gradient structure with an outer Cu:Zn ratio of 60:40 and an inner Cu:Zn ratio of 70:30, with a total thickness optimized to 0.23 μm.

[0090] The wet fine drawing step uses a 7.5% lubricant concentration, maintains a pH value of 8.5, keeps the liquid temperature constant at 40℃, and performs the final drawing at a speed of 8-15m / s to achieve the target diameter.

[0091] Finally, during the multi-stage twisting and structural stabilization stage, the center strand twist pitch is controlled at 8mm, the intermediate twist strand twist pitch is 18mm, and the outer layer composite strands are twisted, with a total multi-twist twist pitch of 30mm. Finally, a 270° reverse twist is applied to the cord using roller straighteners and an overtwist device, ensuring that the final residual twist is ≤1 turn / 6 meters.

[0092] Comparative Example A This comparative example, by adjusting the twist pitch of the tundish strands, aims to examine its impact on micro-gap formation and subsequent performance. The same S1-S4 process steps as in Example 3 were followed: pretreatment, drawing, heat treatment and plating (both at 500°C for 10 seconds to form a gradient brass layer), and wet fine drawing (lubricant parameters as in Example 3). The overtwist angle remained 270°, the center strand twist pitch was 15 mm, and the outer layer twist pitch was 30 mm. However, the twist pitch of the tundish strands was adjusted to 20 mm.

[0093] The significant result of this comparative example is that, although high strength and low residual torque were maintained while other process parameters were consistent with those of Example 3, the rubber permeability decreased significantly (score of 3 points) due to the abnormality of the microgap. The adhesive strength (16.2 N / mm) and fatigue resistance (750 kcycles) also declined sharply, clearly revealing the necessity of precise control of the microgap for achieving the characteristics of "high-permeability adhesive" and improving overall performance.

[0094] Comparative Example B: By simplifying the thermal diffusion step, the copper-zinc ratio between the inner and outer layers is no longer distinguished. Under the same S1-S5 process steps as in Example 3, the thermal diffusion step is replaced with a one-step homogenization process. Instead of controlling the different copper-zinc ratios between the inner and outer layers, a homogeneous brass layer with an overall copper-zinc ratio of approximately 65:35 is formed, and the thickness remains at approximately 0.23 μm.

[0095] Although the simplified treatment still maintains high tensile strength (2230MPa) and relatively good residual torque, the rubber permeability (8 points), adhesive strength (17.5N / mm), and fatigue resistance (880kcycles) do not reach the optimal level of Example 3. This indicates that the gradient brass layer (outer layer Cu:Zn=60:40, inner layer Cu:Zn=70:30) designed in this invention plays an indispensable role in optimizing the rubber interface bonding and improving the service life of the steel cord.

[0096] Comparative Example C: This comparative example examines the effect of the S54 overtwisting treatment on the structural stability of the steel cord by omitting this step. Under the same S1-S5 process steps as in Example 3, the overtwisting device in S54 is completely removed, and only roller straightening is performed. Therefore, untreated residual torque exists on the surface of the steel cord.

[0097] The following are the results of the comparative AC experiments based on Examples 1-3.

[0098] Based on the above test results: Rubber penetration depth: The rubber penetration depth of Example 3 reached 0.32 mm, which is much higher than that of Comparative Example A (0.08 mm) and Comparative Example C (0.15 mm), verifying the effectiveness of the micro-gap design of the present invention. It is also superior to Comparative Example B (0.26 mm), indicating that the gradient brass layer also plays a positive role in promoting penetration.

[0099] Interfacial adhesion strength: The interfacial adhesion strength of Example 3 is as high as 19.8 N / mm, which is significantly higher than that of Comparative Example A (16.2 N / mm) and Comparative Example B (17.5 N / mm), demonstrating the excellent adhesion effect brought about by the synergistic effect of micro-gap and gradient brass layer.

[0100] Fatigue resistance cycles: Example 3 achieved a fatigue resistance cycle of 980,000 cycles, significantly better than Comparative Example A (750,000 cycles) and Comparative Example B (880,000 cycles). Although Comparative Example C performed reasonably well in terms of fatigue resistance cycles (930,000 cycles), its residual torque was too high, indicating that its structure was not truly stable.

[0101] Residual torque (structural stability): The residual torque of Example 3 is <1 rpm / 6 m, demonstrating the crucial role of overtwisting in reducing residual torque and improving structural stability. Comparative Example A, with a residual torque of <1 rpm / 6 m, although the value is the same as Example 3, shows a significant disadvantage in other performance indicators (such as penetration depth and adhesive strength). This indicates that the <1 rpm / 6 m figure was achieved at the expense of other key performance aspects, thus compromising the true meaning of structural stability.

[0102] Tensile strength of composite materials: In all experimental groups, Examples A, B, C and their embodiments of the present invention maintained high tensile strength, which indicates that the present invention achieves breakthroughs in rubber permeability and adhesive strength while ensuring high strength.

[0103] Cord breaking strength: The cord breaking strength of Example 3 reached 9450N, far exceeding the set minimum requirement of 9120N, and was the highest among all experimental groups. This fully demonstrates that the steel cord of the present invention not only achieves improvements in properties such as "high adhesive penetration" and "high fatigue resistance," but also ensures and even exceeds the required extremely high strength standards. The performance of Comparative Example A (9300N) and Comparative Example B (9400N) was also acceptable, but relatively lower than that of Example 3 of the present invention, indicating that the optimization of other properties of the present invention is comprehensive on the basis of achieving high strength.

[0104] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any ordinary changes and substitutions made by those skilled in the art within the scope of the technical solution of the present invention should be included within the protection scope of the present invention.

Claims

1. A high-strength steel cord with high adhesive penetration for track use, characterized in that, The steel cord is a single-strand composite twisted structure, including: The central strand consists of three steel wires arranged in a triangular pattern; The intermediate twist strand consists of eight steel wires twisted in a single-layer spiral around the outer periphery of the central strand, and a micro gap is formed between the central strand and the intermediate twist strand that runs through the cord axis. The average width of the micro gap is 0.02~0.05mm. The outer layer of the twisted strand consists of six composite strands twisted together in a spiral manner around the outer periphery of the intermediate twisted strand to form the outermost structure of the cord. Each composite strand is formed by three steel wires twisted together once to form the inner core, and then nine steel wires are twisted together in a single layer in a spiral manner around the outer periphery of the inner core. The diameter of the steel wire in the center twisted strand is larger than that in the outer retwisted strand, so that the rubber can penetrate to the surface of the center strand along the micro-gap during vulcanization.

2. A method for preparing the high-strength steel cord with high adhesive penetration for track as described in claim 1, characterized in that, Includes the following steps: S1: Pretreatment of high carbon steel wire rod, including electrolytic pickling, water washing, boron coating and drying; S2: Dry intermediate drawing of the pretreated wire rod; S3: Heat treatment and gradient brass plating: The dry-drawn wire is subjected to degreasing, online heat treatment, water cooling, electrolytic pickling, copper plating, zinc plating, drying, thermal diffusion, phosphoric acid washing and soap immersion treatment in sequence. S4: Perform wet precision drawing to obtain a steel wire of the target diameter; S5: The steel wire is made into steel cord through a multi-stage twisting process, and online straightening and over-twisting treatment are integrated during the twisting process to eliminate residual stress and stabilize the structure.

3. The method for preparing a high-strength steel cord with high adhesive penetration for track according to claim 2, wherein step S1 specifically includes: S11. First, the iron oxide scale on the surface of the wire rod is flexibly peeled off by multiple sets of roller peeling equipment, and then preliminary straightening is performed to eliminate the stress of the wire rod. S12. Immerse the wire rod in the pickling tank for electrochemical rust removal. The sulfuric acid concentration is controlled at 8%~12%, the iron ion concentration is maintained at ≤80g / L, the pickling solution temperature is 40℃~50℃, and the pickling current density is set to 5~10A / dm². S13. Multi-stage counter-current water rinsing is adopted, and hot water at 70℃~80℃ is used in the last stage; S14. Immerse the clean steel wire into the borax solution tank to form a borax film. During this process, the borax concentration is 50~80g / L and the borax solution temperature is 90℃~100℃. S15. Drying is carried out in a tunnel drying oven, with the drying temperature controlled at 120℃~150℃.

4. The method for preparing high-strength steel cord with high adhesive penetration for track use according to claim 3, wherein step S2 drawing is divided into three stages: Initial drawing stage: The drawing speed increases linearly from 3.0 m / s to 6.0 m / s; During the intermediate pulling stage: the pulling speed increases linearly from 6.0 m / s to 9.0 m / s; Fine drawing stage: The drawing speed increases from 9.0 m / s and stabilizes at 10.0 m / s.

5. The method for preparing high-strength steel cord with high adhesive penetration for track according to claim 4, step S3 specifically includes the following steps: S31. Electrolytic degreasing is performed in an alkaline degreasing solution at 60-80℃ using a current of 5-10A / dm². S32. The steel wire is fed into a heating furnace with a protective atmosphere, and the furnace temperature is precisely controlled at 960~980℃, followed by rapid cooling. S33. After cooling with coolant, electrolytic pickling with the same parameters as in step S12 is performed again to activate the steel wire matrix. S34. After the steel wire is washed with spray water, a uniform copper underlayer is plated in a copper pyrophosphate plating solution at 25~35℃ and pH value of 10~11.5 at a current density of 0.3~1A / dm². S35. After the steel wire is sprayed and washed with water, it is plated with a layer of zinc in a zinc sulfate plating solution at 30~40℃ and pH value 1~2 at a current density of 1~5A / dm². S36. After cleaning and drying, it enters the induction heating furnace and undergoes thermal diffusion at a temperature of 450~550℃ for 5~15 seconds, so that copper and zinc atoms can penetrate each other and form a brass layer with adhesive activity. S37. The solution is cleaned and activated in a 10% to 20% phosphoric acid solution at 50 to 60°C, and then soaked in a saponification solution at 80 to 90°C to provide a protective and lubricating carrier for the final wet drawing.

6. The method for preparing high-strength steel cord with high adhesive penetration for track according to claim 5, wherein step S4 specifically involves finely drawing the coated steel wire in a fully immersed lubricating coolant, with the drawing speed controlled at 8~15m / s, wherein the lubricant concentration is 5%~10%, the pH value is maintained at 8.0~9.0, and the liquid temperature is constant at 35℃~45℃.

7. The method for preparing a high-strength steel cord with high adhesive penetration for track according to claim 5, step S5 includes the following steps: S51. Twist three steel wires into a central strand with a twist pitch of 5.0~15.0mm; S52. Twist eight steel wires into an intermediate twist strand with a twist pitch of 8.0~24.0mm, and form a micro gap; S53. Twist the six-strand composite yarn into an outer layer of re-twisted strands, with a total re-twisted twist pitch of 15.0~40.0mm; S54. After the twisted steel cord is straightened by the roller straightener, it is then passed through the overtwist device to apply a reverse twist of 180°~360° to the cord, so that the residual twist of the final finished cord is ≤1 turn / 6 meters.

8. The method for preparing high-strength steel cord with high adhesive penetration for track as described in claim 7, wherein the single filament unwinding tension is controlled at 8±0.5N and the winding tension is controlled at 15~40N throughout the twisting process.

9. The method for preparing high-strength steel cord with high adhesive penetration for track according to claim 7, wherein the thickness of the brass layer formed in step S36 is 0.18~0.28μm, and the copper content in the coating is 60%~70%, and a gradient structure is formed through thermal diffusion, wherein the copper-zinc ratio of the outer layer is Cu:Zn=60:40, and the copper-zinc ratio of the inner layer is Cu:Zn=70:

30.

10. The steel cord according to any one of claims 1 to 9, applied to the skeleton reinforcement structure of a rubber track.

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