Low-relaxation steel core semi-duralumin overhead conductor and preparation method thereof

Abstract

The present invention provides a low-relaxation steel-core semi-durized aluminum overhead conductor, comprising a reinforcing core and a conductor layer disposed on the outer periphery of the reinforcing core. The reinforcing core is twisted from a plurality of zinc-aluminum-coated steel wire strands, each comprising a steel core and a zinc-aluminum coating disposed on the outer periphery of the steel core. The conductor layer is twisted from a plurality of semi-durized aluminum strands. The reinforcing core of the present invention has been stabilized, achieving a total elongation of ≥4.0% under maximum force and a stress relaxation rate of ≤4% for 1000 hours under a load of 80% of the rated tension. This prevents stress relaxation during installation of the low-relaxation steel-core semi-durized aluminum overhead conductor, which would otherwise increase line sag. The conductor layer utilizes high-temperature-treated semi-durized aluminum strands with a conductivity of ≥63% IACS, resulting in a low DC resistance. The conductor can withstand continuous high-temperature operation above 230°C, doubling its transmission capacity. The conductor migration point temperature is ≤70°C, fully utilizing the small thermal expansion coefficient of steel wire to achieve low sag performance.

Description

Technical Field

[0001] The invention relates to the technical field of overhead conductors, in particular to a low-relaxation steel core semi-hard aluminum overhead conductor and a preparation method thereof. Background Art

[0002] After nearly 50 years of rapid construction, my country's overhead transmission lines have formed a vast AC / DC transmission network with the highest voltage levels, largest system scale, and strongest resource allocation capabilities in the world. However, electricity demand in eastern and coastal regions has been rapidly increasing, and given the growing urgency of environmental protection, building new transmission corridors is becoming increasingly difficult. At the same time, the proportion of clean renewable energy generation, such as photovoltaics, wind power, hydropower, and biomass, is gradually increasing. However, the seasonal, intermittent, and volatile nature of renewable energy generation places new demands on transmission lines. Therefore, transmission line characteristics should be aligned with those of renewable energy sources, increasing line load utilization hours and addressing the grid's capacity to absorb peak loads.

[0003] Overhead conductors, as carriers of electrical energy, have a transmission capacity that depends solely on the conductor itself, without considering connections or transmission system terminals. When current flows through the conductor, the conductor's resistance causes a thermal effect. Long-term load operation can reduce the conductor's strength or cause permanent deformation, posing safety risks. Currently, high-temperature, low-sag conductors, such as Invar core heat-resistant aluminum alloy conductors and carbon fiber soft aluminum conductors, are primarily used for line expansion and retrofitting, but these are expensive. Developing new overhead conductors with low sag, low energy consumption, high capacity, and low cost has become a research and development direction for researchers. Summary of the Invention

[0004] The purpose of the present invention is to overcome and supplement the deficiencies in the prior art and provide a low-relaxation steel-core semi-duralumin overhead conductor and a preparation method thereof, thereby solving the problem of increased sag in transmission lines caused by stress relaxation during the installation of ordinary conductors, while also increasing the long-term allowable operating temperature of the conductors and improving the transmission capacity of the line.

[0005] The technical solution adopted in the present invention is:

[0006] A low-relaxation steel core semi-hard aluminum overhead conductor, comprising a reinforcing core and a conductor layer arranged on the periphery of the reinforcing core, wherein the reinforcing core is formed by twisting a plurality of zinc-aluminum-coated steel wire single wires, and the zinc-aluminum-coated steel wire single wire comprises a steel core wire and a zinc-aluminum coating arranged on the periphery of the steel core wire; and the conductor layer is formed by twisting a plurality of semi-hard aluminum single wires.

[0007] Preferably, the low-relaxation steel core semi-hard aluminum overhead conductor, wherein the steel core wire comprises the following components, calculated by mass percentage: C 0.85-1.0wt%, Mn 0.80-1.0wt%, Si 0.65-0.80wt%, Cr 0.05-0.08%, Al 0.01-0.03wt%, V≤0.05wt%, P≤0.02wt%, S≤0.01wt%, the total of other impurity elements ≤0.03wt%, and the balance is iron.

[0008] Preferably, the low-relaxation steel core semi-duralumin overhead conductor, wherein, by mass percentage, the semi-duralumin single wire comprises the following components: Fe 0.06-0.12wt%, Si 0.03-0.06wt%, B 0.01-0.03wt%, Cu≤0.005wt%, Mn+Ti+V+Cr≤0.02wt%, the sum of other impurity elements ≤0.03wt%, and the balance is aluminum.

[0009] A method for preparing a low-relaxation steel core semi-duralumin overhead conductor, comprising the following steps:

[0010] 1) Preparation of zinc-aluminum coated steel wire

[0011] Step S1. Wire rod preparation: The steel core wire comprises the following components: C 0.85-1.0 wt%, Mn 0.80-1.0 wt%, Si 0.65-0.80 wt%, Cr 0.05-0.08%, Al 0.01-0.03 wt%, V ≤ 0.05 wt%, P ≤ 0.02 wt%, S ≤ 0.01 wt%, and the sum of other impurity elements ≤ 0.03 wt%, with the remainder being iron. Raw materials are weighed according to the above components and molten iron is smelted. The molten iron is then subjected to desulfurization, deoxidation, and refining treatments in sequence, and then cast and rolled into wire rod with a diameter of 5.0-8.0 mm.

[0012] Step S2. Pickling the wire rod: Pickling the wire rod to remove the surface oxide layer;

[0013] Step S3. Lead bath phosphating: The pickled wire rod is heated to 850-900°C for a lead bath, with the lead bath temperature controlled at 480-500°C to form a lead layer on the surface of the wire rod. The leaded wire rod is then immersed in a phosphate solution for 10-15 minutes to form a phosphate film on the surface of the wire rod through phosphating.

[0014] Step S4. Steel core wire drawing: The phosphated wire rod is drawn through a device in multiple passes into a steel core wire with a diameter of 2.0 to 3.5 mm. The drawn steel core wire is coiled on a reel;

[0015] Step S5. Pickling the steel core wire: The coiled steel core wire is unwound by a pay-off device and then passed through a pickling tank to remove surface oxides in the presence of acid. The pickled steel core wire is then drawn out, washed with water, and then dried.

[0016] Step S6. Dip Coating: The dried steel core wire is preheated in an industrial frequency furnace under the protection of a protective gas at a temperature of 550-600°C. The preheated steel core wire is then introduced into a hot-dip galvanized aluminum bath for continuous dipping, forming a uniform zinc-aluminum coating on the surface of the steel core wire. After the coating is formed, the wire is cooled to obtain a zinc-aluminum coated steel wire.

[0017] 2) Reinforcement core preparation

[0018] Step S7. Twisting the reinforcing core: twisting a plurality of zinc-aluminum coated steel wires with a strength of ≥2100 MPa in an orderly manner around the axis to obtain a reinforcing core;

[0019] Step S8. Stabilization Treatment: The stranded reinforcing core is continuously subjected to a load of 35-45% of the maximum tension that the stranded reinforcing core can withstand. Under the protection of a protective gas, the steel core is heated to 340-360°C by a heater and the wire is taken up at a take-up speed of 30-50 m / min.

[0020] 3) Conductor layer preparation

[0021] Step S9. Aluminum Rod Rolling: The semi-duralumin single wire comprises the following components, calculated by mass percentage: Fe 0.06-0.12 wt%, Si 0.03-0.06 wt%, B 0.01-0.03 wt%, Cu ≤ 0.005 wt%, Mn + Ti + V + Cr ≤ 0.02 wt%, and the sum of other impurity elements ≤ 0.03 wt%, with the balance being aluminum. Raw materials are weighed according to the above components to produce molten aluminum. The aluminum is then refined, deslagging, allowed to stand, degassed, filtered, and then rolled into aluminum rods having a diameter of 9.5 mm to 12 mm using continuous casting and rolling equipment.

[0022] Step S10. Aluminum wire drawing: cold drawing the rolled aluminum rod into aluminum wire of desired shape and specification through a wire drawing device;

[0023] Step S11. Annealing: The drawn aluminum wire is placed in an annealing furnace for annealing, and then naturally cooled to room temperature to obtain a semi-hard aluminum wire with a conductivity of ≥63% IACS and a strength of ≥100 MPa;

[0024] Step S12. Conductor layer stranding: Place the reinforcing core at the axis, and strand several semi-duralumin single wires concentrically on the outer surface of the reinforcing core layer by layer in an orderly manner. Adjacent layers rotate in different directions around the reinforcing core to obtain a low-relaxation steel core semi-duralumin overhead conductor.

[0025] Preferably, in the method for preparing the low-relaxation steel core semi-duralumin overhead conductor, the elongation of each drawing pass in step S4 is 1.10-1.20, the mold is matched according to the wire diameter during drawing, the angle of the mold working area is 12-15°, and the length of the mold sizing area is 35-55% of the mold hole diameter.

[0026] Preferably, in the method for preparing the low-relaxation steel core semi-hard aluminum overhead conductor, in step S6, the hot-dip galvanized aluminum bath contains a zinc-aluminum alloy liquid, the zinc-aluminum alloy liquid includes 88-94wt% Zn, the sum of other impurity elements ≤0.5wt%, and the balance is aluminum, and the temperature of the zinc-aluminum alloy liquid is 480-600°C; and the steel core wire is continuously immersed in the hot-dip galvanized aluminum bath for 15-25m / min.

[0027] Preferably, in the method for preparing the low-relaxation steel core semi-hard aluminum overhead conductor, one or more layers of zinc-aluminum-coated steel wire are twisted around the axis in step S7, and when the multiple layers are twisted, adjacent layers rotate in different directions around the axis, and the axis is composed of zinc-aluminum-coated steel wire.

[0028] Preferably, in the method for preparing the low-relaxation steel core semi-hard aluminum overhead conductor, the axial core wire is a stranded combination of one zinc-aluminum coated steel wire and six zinc-aluminum coated steel wires, and the stranding pitch is 18 to 24 times the nominal diameter.

[0029] Preferably, in the method for preparing the low-relaxation steel core semi-hard aluminum overhead conductor, the axial core wire is a zinc-aluminum coated steel wire single wire, which is twisted into 6 layers and 12 layers on the outside, the 6 layers of zinc-aluminum coated steel wire single wire and the 12 layers of zinc-aluminum coated steel wire single wire are rotated in opposite directions, the 6 layers of zinc-aluminum coated steel wire single wire twist pitch is 20 to 26 times the nominal diameter of the layer, and the 12 layers of zinc-aluminum coated steel wire single wire twist pitch is 16 to 22 times the nominal diameter of the layer;

[0030] Preferably, in the method for preparing the low-relaxation steel core semi-hard aluminum overhead conductor, the annealing temperature in step S11 is 260-280°C and the annealing time is 4-6 hours; in step S12, the twist pitch of the aluminum single wires in the outermost conductor layer is 10-14 times the nominal diameter of the layer; the twist pitch of the aluminum single wires in the remaining conductor layers is 12-16 times the nominal diameter of the conductor in that layer, and the ratio of the twist pitch of any layer to the nominal diameter of the conductor in that layer should not be greater than the ratio of the twist pitch of the adjacent inner layer to the nominal diameter of the conductor in that layer.

[0031] Advantages of the present invention:

[0032] (1) Compared with the prior art, the low-relaxation steel core semi-hard aluminum overhead conductor and its preparation method of the present invention are as follows: adding 0.85-1.0wt% C, 0.80-1.0wt% Mn and 0.65-0.80wt% Si elements to the steel can control the microstructure and ensure the strength of the steel wire rod; adding 0.05-0.08% Cr and ≤0.05wt% V for microalloying treatment can further optimize the strength and hardness of the steel wire rod without affecting the toughness and plasticity of the steel wire rod; adding 0.01-0.03wt% Al for deoxidation of molten steel, dispersing fine aluminum oxide and refining the microstructure can ensure low wire rod drawing and fatigue performance of the steel core wire; the steel core wire is continuously coated in a high-temperature zinc-aluminum bath to repair defects caused by drawing stress, and aluminum elements are enriched in the surface of the steel core wire, so that the zinc-aluminum coating is more firmly attached to the surface of the steel core wire; the stabilization treatment uses protective gas to protect the reinforcing core, so that the zinc-aluminum coating will not oxidize, maintain the metallic luster, and ensure its corrosion resistance.

[0033] (2) The low-relaxation steel core semi-hard aluminum overhead conductor and its preparation method of the present invention have a reinforced steel core that has been stabilized. Under the action of maximum force, the total elongation is ≥4.0%; under 80% of the rated tension load, the stress relaxation rate for 1000 hours is ≤4%; so that the low-relaxation steel core semi-hard aluminum overhead conductor will not experience stress relaxation during engineering installation, which will lead to an increase in line sag; the conductor layer adopts a semi-hard aluminum single wire treated at high temperature, with a conductivity of ≥63% IACS, and the conductor has a low DC resistance; the conductor can withstand continuous high-temperature operation above 230°C, and can double the conductor transmission capacity; the conductor migration point temperature is ≤70°C, and when operating at high temperatures above 70°C, the advantage of the small thermal expansion coefficient of the steel wire can be fully utilized to achieve low sag performance of the conductor.

[0034] (3) The low-relaxation steel core semi-duralumin overhead conductor provided by the present invention is applied to the construction of overhead power lines. It has the technical advantages of high strength, low sag, high current carrying capacity, low energy consumption, corrosion resistance, and low price. It can solve some technical bottlenecks in the field of overhead power transmission and is suitable for capacity expansion and transformation of old lines and construction of new lines, bringing huge economic and social benefits to the power transmission and transformation industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The present invention is a process flow chart of a method for preparing a low-relaxation steel core semi-duralumin overhead conductor.

[0036] Figure 2 It is a schematic diagram of the structure of the aluminum-clad copper conductor of the present invention.

[0037] Figure 3 This is a schematic diagram of the end face structure of the low-relaxation steel core semi-duralumin overhead conductor prepared in Example 1.

[0038] Figure 4Schematic diagram of the cross-sectional structure of the low-relaxation steel core semi-duralumin overhead conductor prepared in Example 1.

[0039] Figure 5 This is a schematic diagram of the end face structure of the low-relaxation steel core semi-duralumin overhead conductor prepared in Example 2.

[0040] Figure 6 This is a schematic cross-sectional view of the low-relaxation steel core semi-duralumin overhead conductor prepared in Example 2.

[0041] Explanation of the reference numerals: 1-reinforcement core, 1-1 zinc-aluminum coated steel wire single wire, 1-11 steel core wire, 1-12 zinc-aluminum coating, 2-conductor layer, 2-1 semi-duraluminum single wire. DETAILED DESCRIPTION

[0042] The present invention will be further described below with reference to specific drawings and embodiments.

[0043] Example 1

[0044] like Figure 2-3 A low-relaxation steel core semi-hard aluminum overhead conductor comprises a reinforcing core 1 and a conductor layer 2 arranged on the periphery of the reinforcing core 1. The reinforcing core 1 is formed by twisting a plurality of zinc-aluminum-coated steel wire single wires 1-1. The zinc-aluminum-coated steel wire single wire 1-1 comprises a steel core wire 1-11 and a zinc-aluminum coating 1-12 arranged on the periphery of the steel core wire 1-11; the conductor layer 2 is formed by twisting a plurality of semi-hard aluminum single wires 2-1.

[0045] like Figure 1 The method for preparing the low-relaxation steel core semi-duralumin overhead conductor of this embodiment comprises the following steps:

[0046] 1) Preparation of zinc-aluminum coated steel wire

[0047] Step S1. Wire rod preparation: The steel core wire 1-11 comprises the following components: C 0.858 wt%, Mn 0.987 wt%, Si 0.655 wt%, Cr 0.05%, Al 0.027 wt%, V 0.04 wt%, P 0.012 wt%, S 0.004 wt%, the total content of other impurity elements is 0.016 wt%, and Fe 97.344 wt%. According to the above composition ratio, the raw materials are smelted in molten iron at a furnace temperature of 1320°C, and then the molten iron is transferred to a converter and desulfurized by adding magnesium particles using the KR method. The molten iron is then transferred to an LF furnace for refining and deoxidation with aluminum, and then to an RH furnace for vacuum degassing. Finally, the molten iron is cast and rolled into a wire rod with a diameter of 5.0 mm by continuous casting.

[0048] Step S2: Pickling the wire rod: Immerse the wire rod in 34% industrial hydrochloric acid for 10 minutes to remove the oxide layer on the wire rod surface;

[0049] Step S3. Lead bath phosphating: The pickled wire rod is heated to 850°C for a lead bath. The lead bath temperature is controlled at 490°C and the wire rod is kept in the lead bath for 10 seconds to form a lead layer on the wire rod surface. The leaded wire rod is then immersed in a phosphate solution for 12 minutes to form a phosphate film on the wire rod surface, which facilitates lubrication during drawing.

[0050] Step S4. Steel core wire drawing: The phosphated 5.0 mm diameter wire rod is drawn through an 11-die wire drawing apparatus into a 2.22 mm diameter steel core wire 1-11. The drawn steel core wire 1-11 is coiled using a coiling tool. The wire rod drawing process uses 11 passes. The die dimensions, die working area angle, and sizing zone length are shown in Table 1.

[0051] Table 1

[0052]

[0053] Step S5. Pickling the Steel Core Wire: A coiled steel core wire 1-11 with a diameter of 2.22 mm is unwound at a speed of 22 m / min through a pay-off device and passed through a pickling tank filled with 34% industrial hydrochloric acid. The wire is continuously immersed in the tank for 40 seconds to remove surface oxides from the steel core wire 1-11. The pickled steel core wire is then immediately introduced into a water tank, where the surface of the steel core wire 1-11 is cleaned using ultrasonic waves and clean water. After being removed from the water tank, the cleaned steel core wire 1-11 is blown dry with a heater.

[0054] Step S6. Dip coating: The dried steel core wire 1-11 is preheated in an industrial frequency furnace under a nitrogen atmosphere having a purity of 99.99%, with the preheating temperature controlled at 560° C. The preheated steel core wire 1-11 is introduced into a hot-dip galvanized aluminum bath containing a zinc-aluminum alloy solution containing 90 wt% Zn, ≤0.5 wt% of other impurity elements, and the balance aluminum, with the temperature of the zinc-aluminum alloy solution controlled within a range of 500° C. The steel core wire 1-11 is continuously routed in the galvanized aluminum bath at a routing speed of 22 m / min and immersed in the bath for 6 seconds. The steel core wire 1-11 is continuously routed in the hot-dip galvanized aluminum bath and then vertically withdrawn from the zinc-aluminum alloy solution. A uniform zinc-aluminum coating 1-12 is formed on the surface of the steel core wire 1-11 by gravity and the adhesion of the alloy solution. After the coating is formed, it is solidified and cooled in a cooling device, thereby obtaining a single steel wire 1-1 with a zinc-aluminum coating.

[0055] After testing, the diameter of the zinc-aluminum coated steel wire single wire 1-1 after coating is 2.35mm, and the tensile strength is ≥2320MPa.

[0056] 2) Reinforcement core preparation

[0057] Step S7. Twisting the reinforcing core: twisting a plurality of zinc-aluminum coated steel wires 1-1 with a strength of ≥2100 MPa around the axis to obtain a reinforcing core 1;

[0058] A 2.35mm zinc-aluminum coated steel wire single wire 1-1 is used as the axis 1-1-1, and 6 layers 1-1-2 and 12 layers 1-1-3 are formed outside the axis 1-1-1. The twisting pitch is 20 times the nominal diameter of the 12 layers of the reinforcing core. The cross-sectional area of ​​the twisted reinforcing core 1 is 82.41mm 2 , the maximum tensile force that the stranded reinforcement core 1 can withstand is 181.63kN;

[0059] Step S8. Stabilization: The stranded reinforcement core 1 is continuously subjected to a rated tensile load of 64 ± 0.5 kN (181.63 kN x 35%). The steel core is heated to 345 ± 5°C using a heater under a nitrogen atmosphere of 99.99% purity for stabilization. The wire is then wound at a speed of 35 m / min. Due to the argon atmosphere, the zinc-aluminum coating of the reinforcement core 1 is prevented from oxidation during the stabilization process.

[0060] The reinforcing core 1 prepared in Example 1 after stabilization treatment was tested to have a tight structure, the zinc-aluminum coating maintained its metallic luster, and no oxidation occurred. At the maximum tensile force of 176.18 kN, the total elongation was 4.6%; under the application of a rated tensile load of 140.94 kN (176.18 kN×80%), the stress relaxation rate after 1000 hours was 3.88%.

[0061] 3) Conductor layer preparation

[0062] Step S9. Aluminum rod rolling: The semi-duraluminum single wire 2-1 comprises the following components by mass percentage: Fe 0.06-0.12wt%, Si 0.03-0.06wt%, B 0.01-0.03wt%, Cu≤0.005wt%, Mn+Ti+V+Cr≤0.02wt%, the sum of other impurity elements≤0.03wt%, and the balance being aluminum. Raw materials are weighed according to the above components, and molten aluminum is smelted at a furnace temperature of 740°C. The molten aluminum is refined by introducing a 6AB refining agent from Pyrotech into the aluminum liquid through 99.99% nitrogen. After the refining is completed, the slag on the surface of the aluminum liquid is scraped off with a slag skimmer. After standing for 20 minutes, the aluminum liquid is drawn out and degassed online through a degassing device through 99.99% nitrogen. The aluminum liquid then flows through a filter box and is filtered using a 40-mesh ceramic filter plate. Finally, the 710±5°C aluminum liquid is rolled into aluminum rods with a diameter of 9.5mm through a continuous casting and rolling machine.

[0063] Step S10. Aluminum wire drawing: The rolled aluminum rod is cold-drawn into 54 coils of aluminum wire with a diameter of 3.90 mm through a wire drawing device;

[0064] Step S11. Annealing: A 3.90 mm round aluminum wire is placed in an annealing furnace and heat treated at 265±5°C for 6 hours. The wire is then naturally cooled to room temperature to obtain a semi-hard aluminum wire 2-1. Testing shows that the semi-hard aluminum wire 2-1 has a conductivity of 63.3-63.6% IACS and a strength of 110-125 MPa.

[0065] Step S12. Conductor layer twisting: Figure 4 , place the strengthening core 1 at the axis center, and divide 54 semi-hard aluminum single wires 2-1 into 12 layers, 18 layers, and 24 layers, and twist them concentrically on the outer surface of the strengthening core 1 in an orderly manner. Adjacent layers are rotated in different directions around the strengthening core 1 to obtain a low-relaxation steel core semi-hard aluminum overhead conductor; the twisting pitch of the 12-layer aluminum single wires 2-1-1 is 15.5 times the nominal diameter of the layer; the twisting pitch of the 18-layer aluminum single wires 2-1-2 is 13.5 times the nominal diameter of the layer; the twisting pitch of the 24-layer aluminum single wires 2-1-3 is 11.5 times the nominal diameter of the layer.

[0066] In this embodiment 1, a 645 / 80 type low-relaxation steel core semi-hard aluminum overhead conductor is prepared. The aluminum cross-sectional area of ​​the conductor layer 2 is 645.08 mm 2 The cross-sectional area of ​​the steel core of the reinforcing core 1 is 82.41mm 2 The reinforcing core 1 is a stabilized low-relaxation steel core, and the strength of the zinc-aluminum-coated steel wire single wire is ≥2200MPa. The reinforcing core 1 has a total elongation of 4.6% at a maximum tensile force of 176.18kN. The reinforcing core 1 has a stress relaxation rate of 3.88% after 1000 hours under a rated tensile load of 140.94kN (176.18kN×80%). The conductor layer 2 is an annealed semi-hard aluminum single wire, and the conductivity of the aluminum wire is ≥63.3%IACS and the strength is ≥110MPa. It can withstand continuous high-temperature operation of 230°C. The migration point temperature of the conductor is 45°C.

[0067] Example 2

[0068] like Figure 2 and Figure 5 A low-relaxation steel core semi-hard aluminum overhead conductor comprises a reinforcing core 1 and a conductor layer 2 arranged on the periphery of the reinforcing core 1. The reinforcing core 1 is formed by twisting a plurality of zinc-aluminum-coated steel wire single wires 1-1. The zinc-aluminum-coated steel wire single wire 1-1 comprises a steel core wire 1-11 and a zinc-aluminum coating 1-12 arranged on the periphery of the steel core wire 1-11; the conductor layer 2 is formed by twisting a plurality of semi-hard aluminum single wires 2-1.

[0069] like Figure 1 The method for preparing the low-relaxation steel core semi-duralumin overhead conductor of this embodiment comprises the following steps:

[0070] 1) Preparation of zinc-aluminum coated steel wire

[0071] Step S1. Wire rod preparation: The steel core wire 1-11 comprises the following components: C 0.988 wt%, Mn 0.817 wt%, Si 0.796 wt%, Cr 0.075%, Al 0.018 wt%, V 0.036 wt%, P 0.011 wt%, S 0.004 wt%, the total content of other impurity elements is 0.023 wt%, and Fe 97.232 wt%. According to the above composition ratio, the raw materials are smelted in molten iron at a furnace temperature of 1380°C, and then the molten iron is transferred to a converter and desulfurized by adding magnesium particles using the KR method. The molten iron is then transferred to an LF furnace for refining and deoxidation with aluminum, and then to an RH furnace for vacuum degassing. Finally, the molten iron is cast and rolled into a wire rod with a diameter of 8.0 mm by continuous casting.

[0072] Step S2. Pickling the wire rod: Immerse the 8.0 mm wire rod in 38% industrial hydrochloric acid for 16 minutes to remove the oxide layer on the wire rod surface;

[0073] Step S3. Lead bath phosphating: The pickled wire rod is heated to 900°C for a lead bath. The lead bath temperature is controlled at 500°C and the wire rod is kept in the lead bath for 10 seconds to form a thin lead layer on the wire rod surface. The leaded wire rod is then immersed in a phosphate solution for 15 minutes to form a phosphate film on the wire rod surface, which facilitates lubrication during drawing.

[0074] Step S4. Steel core wire drawing: Phosphate-treated 8.0 mm diameter wire rod is drawn through a 12-die wire drawing apparatus into steel core wires 1-11 with a diameter of 3.42 mm. The drawn steel core wires 1-11 are coiled using a coiling machine. The wire rod drawing process uses 12 passes. The die dimensions, die working area angle, and sizing zone length are shown in Table 2.

[0075] Table 2

[0076]

[0077] Step S5. Pickling the Steel Core Wire: A coiled steel core wire 1-11 with a diameter of 3.42 mm is unwound at a speed of 20 m / min through a pay-off device and passed through a pickling tank filled with 38% industrial hydrochloric acid. The wire is continuously immersed in the tank for 50 seconds to remove surface oxides from the steel core wire 1-11. The pickled steel core wire is then immediately introduced into a water tank, where the surface of the steel core wire 1-11 is cleaned using ultrasonic waves and clean water. After being removed from the water tank, the cleaned steel core wire 1-11 is blown dry with a heater.

[0078] Step S6. Dip coating: The dried steel core wire 1-11 is preheated in an industrial frequency furnace under the protection of argon gas with a purity of 99.99% at a preheating temperature of 600° C. The preheated steel core wire 1-11 is introduced into a hot-dip galvanized aluminum bath containing a zinc-aluminum alloy solution containing 90 wt% Zn, ≤0.5 wt% of other impurity elements, and the balance aluminum, with the temperature of the zinc-aluminum alloy solution controlled within a range of 600° C. The steel core wire 1-11 is continuously routed in the galvanized aluminum bath at a routing speed of 17 m / min and immersed in the bath for 8 seconds. The steel core wire 1-11 is continuously routed in the hot-dip galvanized aluminum bath and then vertically withdrawn from the zinc-aluminum alloy solution. A uniform zinc-aluminum coating 1-12 is formed on the surface of the steel core wire 1-11 by gravity and the adhesion of the alloy solution. After the coating is formed, it is solidified and cooled in a cooling device, thereby obtaining a single steel wire 1-1 with a zinc-aluminum coating.

[0079] After testing, the diameter of the zinc-aluminum coated steel wire single wire 1-1 after coating is 3.56mm, and the tensile strength is ≥2280MPa.

[0080] 2) Reinforcement core preparation

[0081] Step S7. Twisting the reinforcing core: Use a 3.56mm zinc-aluminum coated steel wire single wire 1-1 as the axis 1-1-1, and twist six zinc-aluminum coated steel wire single wires 1-1-2 outside the axis 1-1-1. The twisting pitch of the zinc-aluminum coated steel wire single wires 1-1-2 is 235mm. The nominal diameter of the six layers of the reinforcing core is 10.68mm, and the twisting pitch is 22 times the nominal diameter of the six layers of the reinforcing core. The cross-sectional area of ​​the twisted reinforcing core 1 is 69.68mm. 2 , the maximum tensile force that the stranded reinforcing core 1 can withstand is 156.41kN;

[0082] Step S8. Stabilization: The stranded reinforcement 1 is continuously subjected to a rated tensile load of 66±0.5 kN (156.41 kN x 42%). The reinforcement is heated to 355±5°C under a 99.99% pure argon atmosphere for stabilization. The wire is then taken up at a speed of 45 m / min. Due to the nitrogen atmosphere, the zinc-aluminum coating of the reinforcement 1 is prevented from oxidizing during the stabilization process.

[0083] The reinforcing core 1 prepared in Example 2 was tested to have a tight structure, the zinc-aluminum coating maintained its metallic luster, and no oxidation occurred. At a maximum tensile force of 148.77 kN, the total elongation was 4.5%; when a rated tensile load of 119.02 kN (148.77 kN×80%) was applied to the reinforcing core 1, the stress relaxation rate after 1000 hours was 3.92%.

[0084] 3) Conductor layer preparation

[0085] Step S9. Aluminum rod rolling: The semi-duralumin single wire 2-1 comprises the following components by mass percentage: Fe 0.1131wt%, Si 0.0324wt%, B 0.0142wt%, Cu 0.0015wt%, Mn+Ti+V+Cr 0.0149wt%, and the sum of other impurity elements 0.029wt%. Al 99.7949 wt %, raw materials were weighed according to the above composition, and aluminum liquid was melted at a furnace temperature of 740°C. The molten aluminum liquid was refined by introducing a 6AB refining agent from Pyrotech into the aluminum liquid through 99.99% nitrogen. After refining, the slag on the surface of the aluminum liquid was scraped off with a slag skimmer. After standing for 20 minutes, the aluminum liquid was drawn out and degassed online through a degassing device with 99.99% nitrogen. The aluminum liquid then flowed through a filter box and was filtered using a 40-mesh ceramic filter plate. Finally, the 720±5°C aluminum liquid was rolled into aluminum rods with a diameter of 12 mm through a continuous casting and rolling machine.

[0086] Step S10. Aluminum single wire drawing: 12mm aluminum rod is cold drawn into 23 coils with a cross-sectional area of ​​19.35mm through a wire drawing device. 2 Trapezoidal aluminum single wire 2-1;

[0087] Step S11. Annealing treatment: The drawn trapezoidal aluminum single wire 2-1 is placed in an annealing furnace and heat treated at a furnace temperature of 270±5°C for 5 hours. The semi-hard aluminum single wire 2-1 is then naturally cooled to room temperature. Testing shows that the conductivity of the trapezoidal semi-hard aluminum single wire 2-1 is 63.3-63.6% IACS and the strength is 110-120 MPa.

[0088] Step S12. Conductor layer twisting: Figure 6 The reinforcing core 1 is placed at the axis center, and 23 semi-hard aluminum single wires 2-1 are divided into 9 layers and 14 layers, and are concentrically twisted in an orderly manner on the outer surface of the reinforcing core 1. Adjacent layers are rotated in different directions around the reinforcing core 1 to obtain a low-relaxation steel core semi-hard aluminum overhead conductor; the twisting pitch of the 9-layer aluminum single wires 2-1-1 is 14 times the nominal diameter of the layer; the twisting pitch of the 14-layer aluminum single wires 2-1-2 is 11 times the nominal diameter of the layer.

[0089] In this embodiment 2, a 445 / 70 type low-relaxation steel core semi-hard aluminum overhead conductor is prepared. The aluminum cross-sectional area of ​​the conductor layer 2 is 445.05 mm 2 The cross-sectional area of ​​the steel core of the reinforcing core 1 is 69.68mm 2The reinforcing core is a stabilized low-relaxation steel core, and the strength of the zinc-aluminum-coated steel wire single wire is ≥2135MPa. The total elongation of the reinforcing core 1 is 4.5% at a maximum tensile force of 148.77kN. The stress relaxation rate of the reinforcing core 1 is 3.92% after 1000 hours under a rated tensile load of 119.02kN (148.77kN×80%). The conductor layer 2 is an annealed semi-hard aluminum single wire with a conductivity of ≥63.3%IACS and a strength of ≥110MPa. It can withstand continuous high-temperature operation of 230°C. The migration point temperature of the conductor is 40°C.

[0090] Finally, it should be noted that the above specific implementation methods are only used to illustrate the technical solutions of the present invention and are not limiting. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present invention, which should all be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a low-relaxation steel core semi-duralumin overhead conductor, characterized in that: A low-relaxation steel core semi-hard aluminum overhead conductor comprises a reinforcing core (1) and a conductor layer (2) arranged on the periphery of the reinforcing core (1), wherein the reinforcing core (1) is formed by twisting a plurality of zinc-aluminum coated steel wire single wires (1-1), and the zinc-aluminum coated steel wire single wire (1-1) comprises a steel core wire (1-11) and a zinc-aluminum coating (1-12) arranged on the periphery of the steel core wire (1-11); and the conductor layer (2) is formed by twisting a plurality of semi-hard aluminum single wires (2-1); The preparation method comprises the following steps: 1) Preparation of zinc-aluminum coated steel wire Step S1. Wire rod preparation: The steel core wire (1-11) comprises the following components: C 0.85-1.0 wt%, Mn 0.80-1.0 wt%, Si 0.65-0.80 wt%, Cr 0.05-0.08%, Al 0.01-0.03 wt%, V ≤0.05 wt%, P ≤0.02 wt%, S ≤0.01 wt%, the sum of other impurity elements ≤0.03 wt%, and the balance being iron. Raw materials are weighed according to the above components and molten iron is smelted. The molten iron is then subjected to desulfurization, deoxidation, and refining treatments in sequence, and then cast and rolled into wire rods with a diameter of 5.0-8.0 mm. Step S2. Pickling the wire rod: Pickling the wire rod to remove the surface oxide layer; Step S3. Lead bath phosphating: The pickled wire rod is heated to 850-900°C for a lead bath, with the lead bath temperature controlled at 480-500°C, to form a lead layer on the surface of the wire rod. The leaded wire rod is then immersed in a phosphate solution for 10-15 minutes to form a phosphate film on the surface of the wire rod through phosphating treatment; Step S4. Steel core wire drawing: The phosphated wire rod is drawn through a device through multiple passes into a steel core wire (1-11) with a diameter of 2.0 to 3.5 mm, and the drawn steel core wire (1-11) is coiled through a coiling tool; Step S5. Pickling the steel core wire: The coiled steel core wire (1-11) is unwound by a pay-off device and then passed through a pickling tank to remove surface oxides of the steel core wire under the action of acid. The pickled steel core wire (1-11) is drawn out, washed with water, and then dried. Step S6. Dip coating: preheating the dried steel core wire (1-11) in an industrial frequency furnace under the protection of a protective gas, controlling the preheating temperature to be 550-600°C, introducing the preheated steel core wire (1-11) into a hot-dip galvanized aluminum bath for continuous dipping, forming a uniform zinc-aluminum coating on the surface of the steel core wire, and cooling the coating after formation, thereby obtaining a zinc-aluminum coated steel wire single wire (1-1); the hot-dip galvanized aluminum bath contains a zinc-aluminum alloy liquid, the zinc-aluminum alloy liquid includes 88-94 wt% Zn, the sum of other impurity elements is ≤0.5 wt%, and the balance is aluminum; 2) Preparation of reinforcement core Step S7. Twisting the reinforcing core: twisting a plurality of zinc-aluminum coated steel wires (1-1) having a strength ≥ 2100 MPa in an orderly manner around the axis to obtain a reinforcing core (1); Step S8. Stabilization treatment: The stranded reinforcing core (1) is continuously subjected to a load of 35-45% of the maximum tension that the stranded reinforcing core (1) can withstand. Under the protection of a protective gas, the steel core is heated to 340-360° C. by a heater, and the wire is taken up at a take-up speed of 30-50 m / min. 3) Conductor layer preparation Step S9. Aluminum rod rolling: The semi-duralumin single wire (2-1) comprises the following components, calculated by mass percentage: Fe 0.06-0.12 wt%, Si 0.03-0.06 wt%, B 0.01-0.03 wt%, Cu ≤ 0.005 wt%, Mn + Ti + V + Cr ≤ 0.02 wt%, and the sum of other impurity elements ≤ 0.03 wt%, with the balance being aluminum. Raw materials are weighed according to the above components to produce molten aluminum. The aluminum liquid is then refined, deslagging, allowed to stand, degassed, filtered, and then rolled into aluminum rods with a diameter of 9.5 mm to 12 mm using continuous casting and rolling equipment. Step S10. Aluminum wire drawing: cold drawing the rolled aluminum rod into aluminum wire of desired shape and specification through a wire drawing device; Step S11. Annealing treatment: placing the drawn aluminum single wire in an annealing furnace for annealing, and then naturally cooling to room temperature to obtain a semi-hard aluminum single wire (2-1) with a conductivity of ≥63% IACS and a strength of ≥100 MPa; Step S12. Conductor layer stranding: The reinforcing core (1) is placed at the axis center, and a plurality of semi-durable aluminum single wires (2-1) are sequentially and concentrically stranded layer by layer on the outer surface of the reinforcing core (1). Adjacent layers are rotated in different directions around the reinforcing core (1) to obtain a low-relaxation steel core semi-durable aluminum overhead conductor.

2. The method for preparing a low-relaxation steel core semi-duralumin overhead conductor according to claim 1, characterized in that: The elongation of each drawing pass in step S4 is 1.10-1.

20. During drawing, the die is matched according to the wire diameter. The angle of the die working area is 12-15 degrees, and the length of the die sizing area is 35-55% of the die hole diameter.

3. The method for preparing a low-relaxation steel core semi-duralumin overhead conductor according to claim 1, characterized in that: In step S6, the temperature of the zinc-aluminum alloy liquid is 480-600° C.; the steel core wire is continuously immersed in the hot-dip galvanized aluminum bath for a time of 15-25 m / min.

4. The method for preparing a low-relaxation steel core semi-duralumin overhead conductor according to claim 1, characterized in that: In step S7, one or more layers of zinc-aluminum coated steel wire are twisted around the axis. When multiple layers are twisted, adjacent layers rotate in different directions around the axis. The axis is composed of zinc-aluminum coated steel wire.

5. The method for preparing a low-relaxation steel core semi-duralumin overhead conductor according to claim 1, characterized in that: The core wire is a zinc-aluminum coated steel wire stranded with six zinc-aluminum coated steel wire strands, and the stranding pitch is 18 to 24 times the nominal diameter.

6. The method for preparing a low-relaxation steel core semi-duralumin overhead conductor according to claim 1, characterized in that: The core wire is a zinc-aluminum coated steel wire single wire, and 6 layers and 12 layers are twisted outside. The rotation direction of the 6-layer zinc-aluminum coated steel wire single wire is opposite to that of the 12-layer zinc-aluminum coated steel wire single wire. The twisting pitch of the 6-layer zinc-aluminum coated steel wire single wire is 20 to 26 times the nominal diameter of the layer, and the twisting pitch of the 12-layer zinc-aluminum coated steel wire single wire is 16 to 22 times the nominal diameter of the layer.

7. The method for preparing a low-relaxation steel core semi-duralumin overhead conductor according to claim 1, characterized in that: In step S11, the annealing temperature is 260-280°C, and the annealing time is 4-6 hours. In step S12, the twist pitch of the aluminum single wires in the outermost conductor layer is 10-14 times the nominal diameter of the layer; the twist pitch of the aluminum single wires in the remaining conductor layers is 12-16 times the nominal diameter of the conductor in the layer, and the ratio of the twist pitch of any layer to the nominal diameter of the conductor in the layer should not be greater than the ratio of the twist pitch of the adjacent inner layer to the nominal diameter of the conductor in the adjacent inner layer.

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