A double-layer differential steel wire structure for polyethylene composite pipe and a pretreatment method

Abstract

The application relates to the technical field of pressure pipelines, and discloses a double-layer differentiated steel wire structure for a polyethylene composite pipe and a pretreatment method, which comprises, from inside to outside, an inner-layer polyethylene pipe body, a double-layer differentiated steel wire reinforcing framework and an outer-layer polyethylene covering pipe body, the double-layer differentiated steel wire reinforcing framework is covered on the outer periphery of the inner-layer polyethylene pipe body, the double-layer differentiated steel wire reinforcing framework comprises an inner-layer steel wire layer, a separation buffer layer and the separation buffer layer, the inner-layer steel wire layer is formed by spirally winding a plurality of first steel wires at a first spiral winding angle alpha 1 along the circumferential surface of the inner-layer polyethylene pipe body; the application is provided with differentiated double-layer steel wires with different diameters and differentiated spiral winding angles, the inner-layer thick steel wires mainly bear axial tensile load on the large-inclination side, and the long-term creep elongation of the pipe is effectively inhibited; the outer-layer thin steel wires are spirally wound in a nearly circumferential direction and mainly resist internal pressure in the circumferential direction, the inner and outer layers are spirally wound in opposite directions to form a bidirectional complementary stress system, and the load distribution is more balanced.

Description

Technical Field

[0001] This invention relates to the field of pressure pipeline technology, and in particular to a double-layer differentiated steel wire structure for polyethylene composite pipes and a pretreatment method thereon. Background Technology

[0002] Polyethylene composite pipes are widely used in medium- and high-pressure fluid transportation scenarios such as municipal water supply and drainage, oil and gas transportation, chemical fluid transportation, and mine backfilling due to their advantages such as corrosion resistance, smooth inner wall and low transportation resistance. The current mainstream products adopt a single-layer steel wire winding reinforcement structure, which uses only a single specification of steel wire wound at a fixed helix angle on the outside of the inner liner pipe, and the outer layer is directly covered with polyethylene. This type of traditional structure has shortcomings in mechanical performance: the single layer of steel wire bears the dual loads of axial tension and circumferential internal pressure of the pipe at the same time. It is difficult to take into account the axial and circumferential force requirements at the winding angle. If the winding angle is too small, the axial tensile and creep resistance of the pipe is poor, and axial elongation and tensile deformation of the pipe section are likely to occur under long-term pressure transportation. If the winding angle is increased to improve the circumferential pressure bearing capacity, the axial rigidity of the pipe will decrease, and tensile cracking is very likely to occur under laying, backfilling and temperature difference expansion and contraction conditions.

[0003] While some existing double-layer steel wire composite pipe solutions add two layers of steel wire to improve load-bearing capacity, they generally use steel wires of equal diameter and similar winding angles, failing to achieve differentiated stress matching between the two layers. There is no dedicated modified buffer transition structure between the two layers, and the specifications and winding angles of the inner and outer layers of steel wire are not differentiated, resulting in an imbalance in axial and circumferential load distribution. Both layers of steel wire simultaneously bear bidirectional loads, and the superimposed stress easily leads to localized overload and breakage of the steel wires. Furthermore, the unreasonable matching of the spiral directions of the two layers of steel wires causes mutual compression and friction between the layers, leading to wear, corrosion, and potential wire breakage under long-term dynamic pressure. Simultaneously, traditional steel wire surfaces are only simply derusted and coated with ordinary primer, with the steel wire metal coating and polyethylene matrix relying solely on physical adhesion, resulting in weak interfacial bonding. Under alternating water pressure and media penetration, the interface is prone to separation. Conventional steel wire pretreatment only involves basic degreasing, resulting in low peel strength between the steel wire and plastic interface, making it difficult to meet the requirements of high-pressure, long-life pipeline projects. Summary of the Invention

[0004] This invention proposes a double-layer differentiated steel wire structure and pretreatment method for polyethylene composite pipes to solve the problems of existing pipes having difficulty in balancing axial and circumferential load-bearing capacity, direct contact between double-layer steel wires leading to frictional corrosion and wire breakage, and insufficient bonding strength between steel wires and polyethylene.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A double-layer differentiated steel wire structure for polyethylene composite pipes, comprising, from the inside out: Inner polyethylene pipe body; A double-layer differentiated steel wire reinforced skeleton is wrapped around the outer periphery of the inner polyethylene tube; The outer polyethylene-coated tube body is injection-molded over the double-layer differentiated steel wire reinforced skeleton; The double-layer differentiated steel wire reinforced skeleton includes: The inner steel wire layer is formed by spirally winding multiple first steel wires around the circumference of the inner polyethylene tube with a first spiral winding angle α1, where α1 is the angle between the axis of the first steel wire and the axis of the composite tube. An isolation buffer layer is continuously wrapped around the outer surface of the inner steel wire layer, burying and filling the steel wire intersection nodes of the inner steel wire layer, and forming an elastic transition interface with uniform thickness. The outer steel wire layer is formed by multiple second steel wires spirally wound around the outer surface of the isolation buffer layer at a second spiral winding angle α2, where α2 is the angle between the axis of the second steel wire and the axis of the composite pipe.

[0006] Preferably, the first spiral winding angle α1 satisfies 50°≤α1≤60°, and the second spiral winding angle α2 satisfies 75°≤α2≤90°.

[0007] Preferably, the range of the first spiral winding angle α1 is 55°±3°, the range of the second spiral winding angle α2 is 80°±5°, and α1+α2∈[125°,150°].

[0008] Preferably, the inner steel wire layer and the outer steel wire layer are wound in opposite directions to form a bidirectional complementary reverse winding structure; the first steel wire and the second steel wire are respectively disposed on both sides of the isolation buffer layer and arranged in a non-contact cross-layer staggered manner.

[0009] Preferably, the diameter d1 of the first steel wire and the diameter d2 of the second steel wire satisfy a differential relationship: d1>d2, where d1=2.0–3.0mm and d2=1.0–2.0mm;

[0010] Furthermore, the surface of the first steel wire is activated by atmospheric pressure plasma and then coated with a silane coupling agent transition film to form a chemically bonded interface layer.

[0011] Preferably, the thickness δ of the isolation buffer layer satisfies 0.5–2.5 mm, and δ / d1 ∈ [0.3, 1.0]; The wall thickness t1 of the inner polyethylene pipe, the thickness δ of the isolation buffer layer, and the wall thickness t2 of the outer polyethylene-coated pipe satisfy the proportional relationship t1:δ:t2=(3–5):(0.5–1.5):(2.5–4).

[0012] Preferably, the insulating buffer layer is composed of a nano-silica modified polyethylene composite material, comprising the following components by weight percentage: High-density polyethylene or medium-density polyethylene matrix 90–97.0 wt%; Surface-modified nano-silica 3.0–7.0 wt%; Maleic anhydride-grafted polyethylene compatibilizer 2.5–5.0 wt%; Antioxidant system 0.5–1.5 wt%; The surface of the surface-modified nano-silica is pre-modified with γ-methacryloxypropyltrimethoxysilane, and the amount of the modifier is 1–5% of the mass of the surface-modified nano-silica, so that the linear thermal expansion coefficient (CTE) of the isolation buffer layer is ≤1.5×10. -4 / ℃, forming a gradual gradient transition between the CTE of the inner polyethylene pipe body and the CTE of the outer polyethylene-coated pipe body.

[0013] A pretreatment method for double-layer differentiated steel wire in polyethylene composite pipes, used in the aforementioned double-layer differentiated steel wire structure for polyethylene composite pipes, includes the following steps: S1. Steel wire surface degreasing and cleaning: High-strength steel wire is continuously drawn through an alkaline degreasing solution or organic solvent cleaning section to remove surface oil and then dried with hot air. S2. Atmospheric pressure plasma activation treatment: The cleaned steel wire is put into the atmospheric pressure plasma jet treatment station, and the surface of the steel wire is continuously scanned and activated in an argon / oxygen mixed plasma atmosphere. The process conditions are: discharge power 3–8kW, nozzle distance from the steel wire surface 5–15mm, steel wire feed speed 8–15m / min, Ar:O2 volume ratio = (9:1)–(19:1). S3. Preparation of silane coupling agent primer: Select one or a combination of two of γ-glycidoxypropyltrimethoxysilane or γ-aminopropyltriethoxysilane as the silane coupling agent, dissolve it in a mixed solvent of ethanol / deionized water at a concentration of 0.5–3.0 wt%, with water accounting for 10–20 vol%, adjust the pH to 4.0–5.0 with acetic acid, and hydrolyze and activate for 30–60 min to obtain the primer. S4. Immediately immerse the plasma-activated steel wire obtained in step S2 into the primer liquid of step S3 or spray the primer liquid through a nozzle, and then flash dry it in a tunnel at 80–110℃ for 10–30s to form a silane coupling agent chemical bonding transition film with a thickness of 50–300nm on the surface of the steel wire. The silanol group Si–OH in the transition film forms M–O–Si covalent bonds with the metal oxide on the surface of the steel wire.

[0014] Preferably, in step S2, the steel wire surface is coated with a brass or zinc layer. The oxygen component of the argon / oxygen mixed plasma performs controlled micro-oxidation on the metal oxides on the coating surface to generate SiO. X / CuO X / ZnOX The mixed active interface increases the bonding strength between the silane coupling agent and the coating in the subsequent step S4 by more than 30%.

[0015] Preferably, step S5 is added after step S4: the surface-pretreated steel wire is drawn out from the wire feeding reel, and through a closed-loop tension control unit composed of a magnetic powder brake and a servo motor, the wire feeding tension of a single steel wire is stabilized within the range of 50–80N, with a tension fluctuation range of ≤±1%, and the wire diameter deviation Δd is monitored in real time with a laser diameter gauge, which is ≤±0.02mm.

[0016] The technical effects and advantages provided by the present invention in the above technical solution are as follows: (1) The present invention sets up a double layer of steel wires with different thicknesses and different spiral winding angles. The inner layer of thick steel wires with a large inclination angle focuses on bearing the axial tensile load, effectively inhibiting the long-term creep elongation of the pipe. The outer layer of thin steel wires is wound in a near-circumferential direction to mainly resist the circumferential internal pressure. The inner and outer layers have opposite spiral directions to form a two-way complementary force system, and the load distribution is more balanced. The two layers of steel wires are completely separated by the isolation buffer layer and arranged in a non-contact staggered manner to avoid friction and wear between the steel wire layers. Compared with the traditional single-layer steel wire pipe, the axial tensile strength and circumferential burst pressure are effectively improved, and the bearing stability of large-diameter high-pressure transportation conditions is effectively enhanced.

[0017] (2) The intermediate isolation buffer layer of the present invention is made of silane-modified nano-silica modified polyethylene composite material. The linear thermal expansion coefficient is between that of the inner and outer polyethylene tubes, forming a gradual gradient thermal expansion transition, which can effectively weaken the interlayer thermal stress generated by the hot and cold cycle; and the buffer layer can completely bury and fill the inner steel wire cross protrusion node, forming a uniform and smooth elastic transition interface, and dispersing and absorbing the concentrated shear stress of the steel wire node through the elastic deformation of the material.

[0018] (3) The steel wire of the present invention is first degreased and dried to remove oil stains, and then activated by argon-oxygen atmospheric pressure plasma controllable micro-etching to generate a multi-metal oxide active interface. Then, a silane coupling agent is coated to form a nanoscale covalent bond transition film. The steel wire metal coating and the polyethylene matrix are doubly bonded by M–O–Si covalent bonds and molecular chain entanglement. The steel wire-PE interface peel strength is increased from about 60 N / cm in the traditional way to more than 110 N / cm, and the interface bonding strength is greatly improved. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of the composite pipe of the present invention; Figure 2 This is a schematic diagram of the structure of the double-layer differentiated steel wire reinforced skeleton of the present invention; Figure 3 This is a schematic diagram of the structure of the present invention with a single first steel wire and a second steel wire wound together; Figure 4 This is a flowchart of the steel wire pretreatment process of the present invention; Figure 5 This is a flowchart illustrating the forming process of the double-layer differentiated steel wire reinforced skeleton of the present invention. In the diagram: 1. Inner polyethylene pipe; 2. Double-layer differentiated steel wire reinforcement skeleton; 21. Inner steel wire layer; 211. First steel wire; 22. Isolation buffer layer; 23. Outer steel wire layer; 231. Second steel wire; 3. Outer polyethylene coated pipe. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] like Figures 1-3 As shown, a double-layer differentiated steel wire structure for polyethylene composite pipe includes, from the inside out, an inner polyethylene pipe body 1, a double-layer differentiated steel wire reinforcing skeleton 2, and an outer polyethylene-coated pipe body 3. The double-layer differentiated steel wire reinforcing skeleton 2 covers the outer periphery of the inner polyethylene pipe body 1, and the outer polyethylene-coated pipe body 3 is injection molded and melt-coated outside the double-layer differentiated steel wire reinforcing skeleton 2. The double-layer differentiated steel wire reinforcement skeleton 2 includes an inner steel wire layer 21, an isolation buffer layer 22, and an outer steel wire layer 23. The inner steel wire layer 21 is formed by spirally winding multiple first steel wires 211 around the circumference of the inner polyethylene pipe body 1 at a first spiral winding angle α1, where α1 is the angle between the axis of the first steel wire 211 and the axial direction of the composite pipe. Its function is to bear the axial tensile load of the pipe and resist the axial creep elongation of the pipe. The isolation buffer layer 22 continuously covers the outer surface of the inner steel wire layer 21, burying and filling the steel wire intersection nodes of the inner steel wire layer 21, and forming a uniform thickness elastic transition interface. The outer steel wire layer 23 is formed by multiple second steel wires 231 spirally wound around the outer surface of the isolation buffer layer 22 at a second spiral winding angle α2, where α2 is the angle between the axis of the second steel wire 231 and the axis of the composite pipe. The winding direction of the inner steel wire layer 21 is opposite to that of the outer steel wire layer 23, forming a bidirectional complementary winding structure with opposite winding directions. The first steel wire 211 of the inner steel wire layer 21 and the second steel wire 231 of the outer steel wire layer 23 are arranged in a non-contact, cross-layer staggered manner on both sides of the isolation buffer layer 22. The interlayer stress at the steel wire crossing position is absorbed by the elastic deformation of the isolation buffer layer 22.

[0023] As mentioned above, the first spiral winding angle α1 satisfies 50°≤α1≤60°, and the second spiral winding angle α2 satisfies 75°≤α2≤90°.

[0024] Specifically, the range of the first spiral winding angle α1 is 55°±3°, and the range of the second spiral winding angle α2 is 80°±5°, and α1+α2∈[125°,150°].

[0025] The diameter d1 of the first steel wire 211 and the diameter d2 of the second steel wire 231 satisfy the relationship: d1>d2, where d1=2.0–3.0mm and d2=1.0–2.0mm, and the axial tensile modulus is increased by relying on the thicker steel wire; The tensile strength of the first steel wire 211 and the second steel wire 231 is ≥1000MPa, preferably high carbon high strength steel wire with a tensile strength ≥1800MPa. The surfaces of the first steel wire 211 and the second steel wire 231 are provided with a metal coating, which is a brass coating or a zinc coating with a coating thickness of 0.3–8μm. The surface of the first steel wire 211 is activated by atmospheric pressure plasma and then coated with a silane coupling agent transition film to form a chemically bonded interface layer, so that the interfacial peel strength between the steel wire and polyethylene is ≥110N / cm.

[0026] The thickness δ of the isolation buffer layer 22 satisfies 0.5–2.5 mm, and δ / d1∈[0.3, 1.0]. The wall thickness t1 of the inner polyethylene pipe body 1, the thickness δ of the isolation buffer layer 22 and the wall thickness t2 of the outer polyethylene-coated pipe body 3 satisfy the proportional relationship t1:δ:t2=(3–5):(0.5–1.5):(2.5–4).

[0027] Three typical wall thickness ratio examples are set up, as shown in the table below:

[0028] The inner polyethylene tube body 1 is extruded at a temperature range of 190-220℃, with an extrusion die pressure of 12-18MPa and a cooling water temperature of 20-30℃, ensuring that the outer diameter tolerance of the inner liner tube is ≤±0.3mm, providing a regular cylindrical matrix for subsequent spiral winding of steel wire.

[0029] The matching parameters for the inner steel wire diameter d1 and the isolation buffer layer thickness δ are shown in the table below:

[0030] The isolation buffer layer is formed by extrusion coating process with an extrusion temperature of 185~210℃. After extrusion, it is leveled by calendering roller to ensure that the uniformity of the layer thickness is ≤±0.1mm. It completely wraps the inner steel wire protrusions and forms a smooth cylindrical outer surface for the outer steel wire to be wound.

[0031] The aforementioned isolation buffer layer 22 is composed of nano-silica modified polyethylene composite material, and includes the following components by weight percentage: High-density polyethylene or medium-density polyethylene matrix 90–97.0 wt%; Surface-modified nano-silica 3.0–7.0 wt%; Maleic anhydride-grafted polyethylene compatibilizer 2.5–5.0 wt%; Antioxidant system 0.5–1.5 wt%; Optional hollow polydimethylsiloxane microspheres, 0–0.5 wt%; The surface of the surface-modified nano-silica is pre-modified with γ-methacryloxypropyltrimethoxysilane, and the amount of modifier is 1–5% of the mass of the surface-modified nano-silica, so that the linear thermal expansion coefficient CTE of the isolation buffer layer 22 is ≤1.5×10. -4 / ℃, a gradual gradient transition is formed between the CTE of the inner polyethylene tube 1 and the CTE of the outer polyethylene-coated tube 3.

[0032] Three sets of gradient formulation examples are set up, as shown in the table below:

[0033] At the same time, such as Figures 4-5 As shown, the present invention also provides a pretreatment method for double-layer differentiated steel wire for polyethylene composite pipes, used in the above-mentioned double-layer differentiated steel wire structure for polyethylene composite pipes, comprising the following steps: S1. Steel wire surface degreasing and cleaning: High-strength steel wire is continuously drawn through an alkaline degreasing solution or organic solvent cleaning section to remove surface oil and then dried with hot air. S2. Atmospheric pressure plasma activation treatment: The cleaned steel wire is put into the atmospheric pressure plasma jet treatment station, and the surface of the steel wire is continuously scanned and activated in an argon / oxygen mixed plasma atmosphere. The process conditions are: discharge power 3–8kW, nozzle distance from the steel wire surface 5–15mm, steel wire feed speed 8–15m / min, Ar:O2 volume ratio = (9:1)–(19:1). After treatment, the surface energy of the steel wire can reach ≥60mN / m, and the surface micro-etching roughness Ra reaches 0.8–1.6μm. S3. Preparation of silane coupling agent primer: Select one or a combination of two of γ-glycidoxypropyltrimethoxysilane or γ-aminopropyltriethoxysilane as the silane coupling agent, dissolve it in a mixed solvent of ethanol / deionized water at a concentration of 0.5–3.0 wt%, with water accounting for 10–20 vol%, adjust the pH to 4.0–5.0 with acetic acid, and hydrolyze and activate for 30–60 min to obtain the primer. S4. Immediately immerse the plasma-activated steel wire obtained in step S2 into the primer liquid of step S3 or spray the primer liquid through a nozzle, and then flash dry it in a tunnel at 80–110℃ for 10–30s to form a silane coupling agent chemical bonding transition film with a thickness of 50–300nm on the surface of the steel wire. The silanol group Si–OH in the transition film forms M–O–Si covalent bonds with the metal oxide on the surface of the steel wire, and at the same time, its organic functional group ends form physical / chemical entanglement and anchoring with the subsequent injection-molded polyethylene molecular chains.

[0034] In step S2, the steel wire surface is coated with a brass or zinc layer. The oxygen component of the argon / oxygen mixed plasma performs controlled micro-oxidation on the metal oxides on the coating surface, generating SiO2. X / CuO X / ZnO X The mixed active interface increases the bonding strength between the silane coupling agent and the coating in the subsequent step S4 by more than 30%.

[0035] Step S4 is followed by step S5: the pre-treated steel wire is wound onto the I-beam reel, and a closed-loop tension control system is configured for the wire release before winding: a magnetic powder brake and a servo motor are adjusted in real time, and a laser diameter measuring instrument is used to collect the steel wire diameter in real time.

[0036] Process control indicators: 1. The stable tension range for a single steel wire is 50-80N, 70-80N for high-pressure pipes, and 50-65N for low-pressure pipes; 2. Tension fluctuation range ≤ ±1% to avoid uneven winding density; 3. Laser diameter measurement monitors the steel wire diameter deviation Δd≤±0.02mm in real time. If the deviation exceeds the limit, an automatic alarm is triggered and the tension compensation is finely adjusted to ensure that the pre-tightening force of the inner and outer steel wires is uniform and consistent, and there is no internal stress concentration after the pipe is formed.

[0037] For degreasing and cleaning the surface of steel wire, two cleaning methods can be selected, which can be switched according to the degree of oil contamination on the steel wire: Alkaline degreasing route: 5-10 wt% sodium hydroxide + 2 wt% trisodium phosphate mixed degreasing solution, temperature 50-60℃, soak and wash for 10-20 seconds; Organic solvent cleaning route: Anhydrous ethanol + acetone 3:1 mixed solvent, spray cleaning for 5 seconds, after cleaning, hot air drying at 100-120℃, drying length 2m, completely remove moisture and residual solvent, after drying the steel wire surface is free of oil spots and water stains.

[0038] The following table shows an example of atmospheric pressure plasma activation process parameters:

[0039] Argon gas is used as a carrier gas to ionize and generate plasma. The oxygen component can controllably oxidize the coating on the steel wire surface to generate CuO. X / ZnO X / SiO X The mixed active interface enhances the chemical bonding ability of subsequent silane coupling agents, increasing the interfacial adhesion strength by more than 30%. The effective duration of the active window on the treated steel wire surface is ≤60s, and it must immediately enter the silane primer process to prevent the surface from repassivating.

[0040] In step 3, the silane system is implemented in two ways: single-component and compound-component. The solvent system is a mixture of ethanol and deionized water. Acetic acid is used to adjust the pH to 4.0–5.0. Hydrolysis is carried out for 30–60 minutes to fully activate the silanol groups. The formulation examples are shown in the table below:

[0041] The compound silane has metal coating bonding and PE organic entanglement, and the interfacial peel strength is better than that of the single component, making it the preferred solution.

[0042] The following table compares the performance of the structure of this invention with that of traditional single-layer steel wire polyethylene composite pipe:

[0043] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A double-layer differentiated steel wire structure for polyethylene composite pipes, characterized in that, From the inside out, the following are included: Inner polyethylene tube (1); A double-layer differentiated steel wire reinforced skeleton (2) is wrapped around the outer periphery of the inner polyethylene tube (1); The outer polyethylene-coated pipe body (3) is injection-molded over the double-layer differentiated steel wire reinforced skeleton (2); The double-layer differentiated steel wire reinforced skeleton (2) includes: The inner steel wire layer (21) is formed by spirally winding multiple first steel wires (211) around the circumference of the inner polyethylene pipe body (1) at a first spiral winding angle α1, where α1 is the angle between the axis of the first steel wire (211) and the axis of the composite pipe; An isolation buffer layer (22) is continuously wrapped around the outer surface of the inner steel wire layer (21), burying and filling the steel wire intersection nodes of the inner steel wire layer (21) and forming an elastic transition interface with uniform thickness. The outer steel wire layer (23) is formed by multiple second steel wires (231) spirally wound around the outer surface of the isolation buffer layer (22) at a second spiral winding angle α2, where α2 is the angle between the axis of the second steel wire (231) and the axis of the composite pipe.

2. The double-layer differentiated steel wire structure for polyethylene composite pipes according to claim 1, characterized in that: The first spiral winding angle α1 satisfies 50°≤α1≤60°, and the second spiral winding angle α2 satisfies 75°≤α2≤90°.

3. The double-layer differentiated steel wire structure for polyethylene composite pipes according to claim 2, characterized in that: The range of the first spiral winding angle α1 is 55°±3°, and the range of the second spiral winding angle α2 is 80°±5°, and α1+α2∈[125°,150°].

4. The double-layer differentiated steel wire structure for polyethylene composite pipes according to claim 1, characterized in that: The inner steel wire layer (21) and the outer steel wire layer (23) are wound in opposite directions to form a bidirectional complementary reverse winding structure. The first steel wire (211) and the second steel wire (231) are respectively located on both sides of the isolation buffer layer (22) and are arranged in a non-contact cross-layer staggered manner.

5. The double-layer differentiated steel wire structure for polyethylene composite pipes according to claim 1, characterized in that: The diameter d1 of the first steel wire (211) and the diameter d2 of the second steel wire (231) are set differently: d1>d2, where d1=2.0–3.0mm and d2=1.0–2.0mm; The surface of the first steel wire (211) is activated by atmospheric pressure plasma and then coated with a silane coupling agent transition film to form a chemically bonded interface layer.

6. The double-layer differentiated steel wire structure for polyethylene composite pipes according to claim 5, characterized in that: The thickness δ of the isolation buffer layer (22) satisfies 0.5–2.5 mm, and δ / d1 ∈ [0.3, 1.0]; The wall thickness t1 of the inner polyethylene tube (1), the thickness δ of the isolation buffer layer (22), and the wall thickness t2 of the outer polyethylene-coated tube (3) satisfy the proportional relationship t1:δ:t2=(3–5):(0.5–1.5):(2.5–4).

7. The double-layer differentiated steel wire structure for polyethylene composite pipes according to claim 1, characterized in that: The isolation buffer layer (22) comprises the following components by weight percentage: High-density polyethylene or medium-density polyethylene matrix 90–97.0 wt%; Surface-modified nano-silica 3.0–7.0 wt%; Maleic anhydride-grafted polyethylene compatibilizer 2.5–5.0 wt%; Antioxidant system 0.5–1.5 wt%; The surface of the surface-modified nano-silica is pre-modified with γ-methacryloxypropyltrimethoxysilane, and the amount of the modifier is 1–5% of the mass of the surface-modified nano-silica, so that the linear thermal expansion coefficient CTE of the isolation buffer layer (22) is ≤1.5×10. -4 / ℃, a gradual gradient transition is formed between the CTE of the inner polyethylene tube (1) and the CTE of the outer polyethylene-coated tube (3).

8. A pretreatment method for double-layer differentiated steel wire in polyethylene composite pipes, used in the double-layer differentiated steel wire structure for polyethylene composite pipes according to any one of claims 1 to 7, characterized in that, Includes the following steps: S1. Steel wire surface degreasing and cleaning: High-strength steel wire is continuously drawn through an alkaline degreasing solution or organic solvent cleaning section to remove surface oil and then dried with hot air. S2. Atmospheric pressure plasma activation treatment: The cleaned steel wire is put into the atmospheric pressure plasma jet treatment station, and the surface of the steel wire is continuously scanned and activated in an argon / oxygen mixed plasma atmosphere. The process conditions are: discharge power 3–8kW, nozzle distance from the steel wire surface 5–15mm, steel wire feed speed 8–15m / min, Ar:O2 volume ratio = (9:1)–(19:1). S3. Preparation of silane coupling agent primer: Select one or a combination of two of γ-glycidoxypropyltrimethoxysilane or γ-aminopropyltriethoxysilane, dissolve them in a mixed solvent of ethanol / deionized water at a concentration of 0.5–3.0 wt%, with water accounting for 10–20 vol%, adjust the pH to 4.0–5.0 with acetic acid, and hydrolyze and activate for 30–60 min to obtain the primer. S4. Immediately immerse the plasma-activated steel wire obtained in step S2 into the primer liquid of step S3 or spray the primer liquid through a nozzle, and then flash dry it in a tunnel at 80–110℃ for 10–30s to form a silane coupling agent chemical bonding transition film with a thickness of 50–300nm on the surface of the steel wire. The silanol groups (Si–OH) in the transition film form M–O–Si covalent bonds with the metal oxides on the surface of the steel wire.

9. The method for pretreatment of double-layer differentiated steel wire for polyethylene composite pipes according to claim 8, characterized in that: In step S2, the high-strength steel wire has a brass or zinc plating layer on its surface. The oxygen component of the argon / oxygen mixed plasma performs controlled micro-oxidation on the metal oxides on the plating surface to generate SiO. X / CuO X / ZnO X Hybrid active interface.

10. The method for pretreatment of double-layer differentiated steel wire for polyethylene composite pipes according to claim 9, characterized in that: Step S4 is followed by step S5: the surface-pretreated steel wire is drawn out from the wire feeding reel and controlled by a closed-loop tension control unit consisting of a magnetic powder brake and a servo motor, so that the wire feeding tension of a single steel wire is stabilized in the range of 50–80N, with a tension fluctuation range of ≤±1%, and the steel wire diameter deviation Δd is monitored in real time with a laser diameter measuring instrument, which is ≤±0.02mm.

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