Crosslinked polyethylene power cable with flame-retardant layer and production process

Abstract

The invention belongs to the technical field of power cables, and particularly provides a cross-linked polyethylene power cable with a flame-retardant layer, which comprises a conductor, a conductor shielding layer, a cross-linked polyethylene insulating layer, an insulating shielding layer, a metal shielding layer, a flame-retardant layer and an outer sheath layer which are sequentially arranged from inside to outside, the conductor is formed by twisting a plurality of metal single wires; the conductor shielding layer is made of a semi-conductive material and tightly coats the periphery of the conductor; the cross-linked polyethylene insulating layer is formed through a cross-linking process and has good insulating performance; the insulation shielding layer is made of a semi-conductive material and wraps the periphery of the cross-linked polyethylene insulation layer; the metal shielding layer is formed by wrapping or weaving a copper strip or a copper wire; the flame-retardant layer is made of a halogen-free flame-retardant material and comprises magnesium hydroxide, aluminum hydroxide and a phosphorus-nitrogen flame retardant, and a reinforcing material is added into the flame-retardant layer; and the outer sheath layer is made of high-density polyethylene.

Description

Technical Field

[0001] This invention relates to the field of power cable technology, specifically to a cross-linked polyethylene power cable with a flame-retardant layer and its manufacturing process. Background Technology

[0002] Currently, the widely used power cables on the market have revealed numerous problems in actual use. On the one hand, they are significantly inadequate in terms of safety, especially in terms of flame retardancy. The insulation and sheathing materials of traditional power cables are mostly ordinary polymer materials. These materials are highly flammable when exposed to high temperatures or open flames, and release large amounts of toxic and harmful gases during combustion. This not only causes the fire to spread rapidly, posing a serious threat to human life, but also hinders rescue efforts during a fire, leading to frequent major property damage and casualties. For example, in densely populated urban areas, once a power cable catches fire, its poor flame retardancy often causes the fire to expand rapidly in a short period, bringing catastrophic consequences to surrounding residents and commercial facilities. On the other hand, in terms of performance, traditional cables also struggle to meet the ever-increasing and complex power demands. As power systems develop towards higher voltage and larger capacity, higher requirements are placed on the insulation performance, transmission efficiency, and stability of cables. Under long-term high voltage, the insulation layer of traditional cables is prone to aging and breakdown, affecting the cable's normal service life and the reliability of power transmission. Furthermore, the selection of conductor structure and materials also limits the cable's transmission capacity, failing to effectively reduce resistance and improve transmission efficiency, resulting in significant energy waste. Meanwhile, with increasing environmental awareness and increasingly stringent environmental policies, the negative environmental impacts of traditional cables during production and use are gradually attracting attention. Some materials and processes used in their production not only consume large amounts of resources and energy but also generate pollutants, damaging the ecological environment. Furthermore, after cables are scrapped, the difficulty in degrading and recycling their materials further exacerbates environmental pollution. In summary, developing a new type of power cable with excellent flame retardant properties, good electrical properties, high mechanical strength, and environmental protection and energy saving has become a key issue that the power industry urgently needs to address. This invention was developed based on this background. Summary of the Invention

[0003] In view of this, the present invention provides a cross-linked polyethylene power cable with a flame-retardant layer and a manufacturing process thereof, in order to solve the technical problems mentioned in the background art.

[0004] The technical solution of the present invention is as follows: In a first aspect, the present invention proposes a cross-linked polyethylene power cable with a flame-retardant layer, comprising, from the inside out, a conductor, a conductor shielding layer, a cross-linked polyethylene insulation layer, an insulation shielding layer, a metal shielding layer, a flame-retardant layer, and an outer sheath layer. The conductor is composed of multiple stranded metal wires. If it is a copper conductor, its purity is not less than 99.95%; if it is an aluminum conductor, its purity is not less than 99.7%. The diameter of the conductor wires ranges from 0.5mm to 3.0mm, depending on the cable specifications. It employs either compacted stranding or profiled stranding, with a compaction coefficient of not less than 0.9, to improve the conductor's fill factor and the overall compactness of the cable. The conductor shielding layer is made of a semi-conductive material with a carbon black content of 2%-4%. It is tightly wrapped around the outer periphery of the conductor through an extrusion process. The extrusion temperature is controlled at 120℃-140℃, and the thickness is 0.5mm-0.8mm, ensuring good adhesion to the conductor and stable semi-conductive properties. The insulating shielding layer is made of a semi-conductive material with a carbon black content of 2%-4%. It is extruded onto the outer periphery of the cross-linked polyethylene insulating layer using an extruder. The extrusion process parameters are the same as those of the conductor shielding layer, and the thickness is 0.5mm-0.8mm, ensuring good contact with the insulating layer and the metal shielding layer and stabilizing the electric field distribution. The semiconductive material uses low-density polyethylene (LDPE) as the base resin. Considering the flowability requirements of the semiconductive material during extrusion, an appropriate amount of lubricant zinc stearate (accounting for 0.2%-0.5% of the total mass of the semiconductive material) is added to reduce the friction between the material and the inner wall of the equipment, ensuring the smoothness of the extrusion process, so that the material has good processability while meeting electrical performance requirements.

[0005] The metal shielding layer is made of copper strip or copper wire wrapped or braided. If copper strip is used for wrapping, the thickness of the copper strip is 0.1mm-0.3mm, and the wrapping overlap rate is 15%-25%; if copper wire is used for braiding, the diameter of the copper wire is 0.1mm-0.3mm, and the braiding density is 80%-95%, which effectively shields electromagnetic interference and ensures the transmission performance of the cable. The flame-retardant layer is made of halogen-free flame-retardant material, containing 40%-50% magnesium hydroxide, 20%-30% aluminum hydroxide, and 10%-20% phosphorus-nitrogen flame retardant (preferably melamine polyphosphate (MPP) and triphenyl phosphate (TPP)). It also contains 10%-15% reinforcing materials such as glass fiber (5μm-10μm diameter) or carbon fiber (7μm-10μm diameter) to improve mechanical properties. The flame-retardant layer is formed by extrusion, with the extrusion temperature controlled at 150℃-170℃, screw speed at 35r / min-55r / min, thickness at 1.5mm-2.0mm, oxygen index exceeding 35%, and passes the UL94-V0 standard in vertical burning tests, demonstrating excellent flame-retardant performance.

[0006] To improve the interfacial bonding between the fiber and the flame-retardant matrix, the fiber surface is treated with a silane coupling agent to introduce active groups that can chemically react with the matrix resin, thereby enhancing the chemical bonding between the fiber and the matrix and significantly improving the interfacial strength of the composite material, thus fully leveraging the reinforcing effect of the fiber.

[0007] The outer sheath is made of high-molecular materials such as polyethylene, specifically high-density polyethylene (HDPE), with the addition of antioxidants 1010 and 168 (mass ratio 1:1) at a concentration of 0.1%-0.5% (preferably 0.1%-0.3%), and ultraviolet absorber benzophenone at a concentration of 0.2%-0.6% (preferably 0.2%-0.4%) to improve the aging resistance of the outer sheath. The outer sheath is formed on top of the flame-retardant layer using an extrusion process at a temperature of 200℃-220℃ and a screw speed of 40r / min-60r / min. The thickness of the outer sheath is determined according to the cable specifications, generally ranging from 1.5mm to 3.0mm, serving to protect the internal structure of the cable and enhance its wear and corrosion resistance. In some optional embodiments, the conductor is a copper conductor or an aluminum conductor, and the single wires of the conductor are subjected to compaction stranding or shaped stranding. During the compaction process, the pressure is controlled at 10MPa-15MPa, and the shaped stranding is carried out using a special mold to ensure that the stranded conductor is tight and stable, thereby improving the conductor's fill factor and the overall compactness of the cable.

[0008] In some optional embodiments, the carbon black in the semiconductive materials of the conductor shielding layer and the insulating shielding layer undergoes surface treatment, with a particle size between 20nm and 40nm, to ensure good semiconducting properties and compatibility with adjacent layers. During the mixing process, a twin-screw mixer is used, with a mixing temperature of 130℃-150℃, a screw speed of 40r / min-60r / min, and a mixing time of 10min-15min, to ensure that the carbon black is uniformly dispersed in the semiconductive material matrix. In some optional embodiments, the degree of crosslinking of the crosslinked polyethylene insulation layer reaches more than 90%, which is achieved by a peroxide crosslinking process, with the amount of peroxide added being 0.8%-1.2%, the crosslinking temperature being 170℃-200℃, and the crosslinking time being 10min-30min. In some optional embodiments, the flame-retardant layer has a thickness of 1.5mm-2.0mm, an oxygen index of 35% or higher, and passes the UL94-V0 standard in vertical burning tests. During the preparation of the flame-retardant layer, the halogen-free flame-retardant material and reinforcing material are premixed in a high-speed mixer for 5-8 minutes at a mixing speed of 1000-1500 r / min. Then, the mixture is granulated using a twin-screw extruder at a granulation temperature of 160℃-180℃ and a screw speed of 50-70 r / min. The granules are then extruded to form the flame-retardant layer. In some optional embodiments, the outer sheath layer includes additives such as antioxidants and ultraviolet absorbers. The amount of antioxidant 1010 and 168 compound (mass ratio 1:1) added is 0.1%-0.3%, and the amount of ultraviolet absorber benzophenone is 0.2%-0.4%, to improve the aging resistance of the outer sheath layer. During the mixing process, high-density polyethylene and additives are mixed in a high-speed mixer at a mixing temperature of 80℃-100℃ for 8min-12min to ensure that the additives are uniformly dispersed in the high-density polyethylene. Then, the outer sheath layer is extruded and formed using an extruder.

[0009] Secondly, the present invention also provides a manufacturing process for a cross-linked polyethylene power cable with a flame-retardant layer as described above, comprising the following steps: Conductor preparation: After drawing and annealing, the metal raw materials (copper or aluminum) are stranded according to the design requirements to obtain the conductor.

[0010] Conductor shielding layer extrusion: Semiconducting material is uniformly coated onto the surface of a conductor using an extruder to form a conductor shielding layer.

[0011] Cross-linked polyethylene insulation extrusion: After the polyethylene raw material is mixed evenly with the peroxide cross-linking agent and additives, the cross-linked polyethylene insulation layer is extruded outside the conductor shielding layer through an extruder. After extrusion, it enters the vulcanization pipeline and is kept at a temperature of 170℃-200℃ for 10min-30min to complete the cross-linking. The peroxide cross-linking agent is one of dicumyl peroxide (DCP), di-tert-butyl peroxide (DTBP), or 2,5-dimethyl-2,5-di-tert-butylperoxide (Bi25); the additive is one of triallyl cyanurate (TAC), triallyl isocyanurate (TAIC), or 1,2-polybutadiene (1,2-PBR); the ratio of polyethylene raw material to peroxide cross-linking agent and additives is 100:(0.8-1.2):(0.4-0.6).

[0012] Extrusion of the insulating shielding layer: Semiconducting material is coated onto the surface of a cross-linked polyethylene insulating layer using an extruder to form an insulating shielding layer. The extrusion process parameters are the same as those for the conductor shielding layer extrusion. The extruder used is a single-screw extruder of the same specifications as that used for the conductor shielding layer extrusion, ensuring uniform extrusion of the semiconducting material, good adhesion between the insulating shielding layer and the cross-linked polyethylene insulating layer, uniform thickness, and stable electric field distribution. Metal shielding layer fabrication: A metal shielding layer is fabricated on the outside of the insulating shielding layer using a wrapping machine or braiding machine, controlling the wrapping overlap rate or braiding density to meet requirements. The copper wire braiding machine employs high-speed automated equipment. During the braiding process, the braiding angle and copper wire tension are adjusted to ensure uniform braiding density, ranging from 80% to 95%.

[0013] Flame retardant layer preparation: After mixing the halogen-free flame retardant material with the reinforcing material, the flame retardant layer is extruded outside the metal shielding layer through an extruder. Specifically, the halogen-free flame retardant material and the reinforcing material are first premixed in a high-speed mixer for 5-8 minutes at a mixing speed of 1000-1500 r / min. Then, the mixture is granulated through a twin-screw extruder at a granulation temperature of 160℃-180℃ and a screw speed of 50-70 r / min to obtain flame retardant granules. The flame retardant granules are then extruded through a single-screw extruder at an extrusion temperature of 150℃-170℃ and a screw speed of 35-55 r / min to ensure uniform flame retardant layer thickness and stable flame retardant performance. Outer Sheath Extrusion: After mixing high-density polyethylene with additives, the outer sheath layer is extruded over the flame-retardant layer using an extruder. The ratio of high-density polyethylene to antioxidant and ultraviolet absorber is 100:(0.1-0.5):(0.2-0.6). Specifically, high-density polyethylene, antioxidant, and ultraviolet absorber are mixed in a high-speed mixer at a mixing temperature of 80℃-100℃ and a mixing time of 8min-12min to ensure uniform dispersion of the additives. The extrusion temperature for polyethylene is 200℃-220℃, and the screw speed is 40r / min-60r / min. By adjusting the extrusion process parameters, the outer sheath layer is ensured to have uniform thickness, a smooth surface, and good wear resistance and corrosion resistance.

[0014] Cable cabling: Multiple insulated cores with outer sheaths are twisted together at a specific pitch and direction to form the cable core, and filler material is used to fill the gaps between the cores. The filler material is a flame-retardant, non-hygroscopic material, such as flame-retardant polypropylene rope or fiberglass rope. During the filling process, the filler material is kept tight and uniform to improve the overall structural stability of the cable. Inspection and Packaging: The electrical, mechanical and flame-retardant properties of the finished cables are tested. After passing the tests, the cables are packaged and put into storage.

[0015] In some optional embodiments, during conductor fabrication, the die selection during the wire drawing process is determined based on the material of the metal raw material and the target single wire diameter. The surface roughness Ra of the die's inner hole is not higher than 0.2 μm to ensure the surface quality of the metal single wire. The annealing current is 100A-150A (copper) or 80A-120A (aluminum), the annealing time is 10s-15s, and the annealing furnace is protected by nitrogen with a nitrogen purity of not less than 99.99% to prevent metal oxidation. In some optional embodiments, during cable cabling, the stranding pitch is 15 to 20 times the cable's outer diameter, and the stranding pitch is precisely controlled by adjusting the speed and traction speed of the cabling machine. The filler is a flame-retardant, non-hygroscopic material, which is dried before filling to a moisture content of less than 0.1%, ensuring filling effectiveness and overall cable performance.

[0016] Compared with the prior art, the present invention has the following beneficial effects: The flame-retardant layer of the cable of this invention uses a special formula of halogen-free flame-retardant material, in which magnesium hydroxide, aluminum hydroxide and phosphorus-nitrogen flame retardants work together to make the oxygen index of the flame-retardant layer as high as 35% or more, and can successfully pass the UL94-V0 vertical burning test.

[0017] The cross-linked polyethylene insulation layer of this invention achieves a high degree of cross-linking of over 90% through a precisely controlled peroxide cross-linking process. This gives the insulation layer excellent electrical insulation properties, enabling it to withstand higher voltages and effectively reducing leakage and breakdown.

[0018] The metal shielding layer provided by this invention, whether wrapped with copper tape or braided with copper wire, can provide a highly efficient electromagnetic shielding effect for cables.

[0019] The conductor provided by this invention is made of multiple metal single wires twisted together. Based on different metal materials (copper conductor purity not less than 99.95%, aluminum conductor purity not less than 99.7%) and cable specifications, the diameter of each single wire is rationally selected within the range of 0.5mm-3.0mm. Compact stranding or profile stranding methods are used, with a compaction coefficient not less than 0.9. This not only improves the conductor's fill factor and the overall compactness of the cable but also enhances the cable's mechanical strength, enabling it to withstand greater tensile and bending forces. This reduces problems such as conductor breakage and insulation damage caused by external forces during installation and use, thereby extending the cable's service life and reducing maintenance costs. The flame-retardant layer provided by this invention uses halogen-free flame-retardant materials, which avoids the harm to the environment and human body caused by the release of toxic hydrogen halide gas during combustion of traditional halogen-containing flame-retardant materials, and meets environmental protection requirements. Attached Figure Description

[0020] 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 embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of a cross-linked polyethylene power cable with a flame-retardant layer proposed in this invention. Detailed Implementation

[0022] The present invention will be further described below through embodiments, but is not limited to these embodiments. Experimental methods not specifically described in the embodiments generally use conventional conditions and conditions described in the manual, or conditions recommended by the manufacturer. The general equipment, materials, reagents, etc., used are all commercially available unless otherwise specified.

[0023] Reference Figure 1The present invention provides a cross-linked polyethylene power cable with a flame-retardant layer, comprising, from the inside out, a conductor 1, a conductor shielding layer 2, a cross-linked polyethylene insulation layer 3, an insulation shielding layer 4, a metal shielding layer 5, a flame-retardant layer 6, and an outer sheath layer 7. The present invention will be described below with reference to specific embodiments.

[0024] Example 1: 1kV copper conductor cross-linked polyethylene power cable Step 1, Conductor preparation: Select electrolytic copper with a purity of 99.95% and draw it into a single wire with a diameter of 0.5 mm using a cemented carbide mold (internal hole roughness Ra0.2μm) at a drawing speed of 10m / min.

[0025] The single-line annealing process is carried out in a continuous annealing furnace with an annealing current of 80A and a time of 5s, under nitrogen protection (purity 99.99%).

[0026] The seven annealed single wires were compacted and stranded at a compaction pressure of 10 MPa and a stranding pitch ratio of 25, resulting in a conductor outer diameter of 1.6 mm and a compaction coefficient of 0.91.

[0027] Step 2, conductor shielding layer extrusion: Semiconducting material (carbon black content 2%, particle size 20nm) is processed by a twin-screw mixer (130℃, 40r / min, 10min).

[0028] A 65mm single-screw extruder is used, with an extrusion temperature of 120℃, a screw speed of 20r / min, and a 0.5mm thick shielding layer is formed around the conductor. The traction speed is 15m / min.

[0029] Step 3, Extrusion of cross-linked polyethylene insulation layer: Polyethylene raw material is mixed with peroxide (DCP) and additive (TAC) at a ratio of 100:0.8:0.4 (mass ratio).

[0030] The extrusion is performed using an 80mm single-screw extruder at an extrusion temperature of 160℃ and a screw speed of 30r / min, forming a 1.0mm thick insulating layer.

[0031] Enter the vulcanization pipeline: crosslinking at 170℃ for 10 min, nitrogen pressure 0.2MPa, cool to 40℃ and discharge.

[0032] Step 4, Extrusion of the insulating shielding layer: The process is the same as that of the conductor shielding layer, forming a 0.5mm thick shielding layer outside the insulating layer.

[0033] Step 5, Metal shielding layer fabrication: Use 0.1mm diameter copper wire, braided by a high-speed braiding machine with a braiding density of 80% and a braiding angle of 45°.

[0034] Step 6, Flame retardant layer preparation: Halogen-free flame retardant material (40% magnesium hydroxide, 30% aluminum hydroxide, 20% phosphorus and nitrogen) and carbon fiber (7μm diameter, 10%) are premixed in a high-speed mixer for 5 minutes (1000r / min).

[0035] Granulation is performed using a twin-screw extruder (160℃, 50r / min), followed by extrusion using an 80mm single-screw extruder (140℃, 25r / min) to form a 1.0mm thick flame-retardant layer outside the metal shielding layer.

[0036] Step 7, Outer Sheath Extrusion: High-density polyethylene is mixed with antioxidant 1010 / 168 compound (0.1%) and benzophenone-based ultraviolet absorber (0.2%) in a high-speed mixer (80℃, 8min).

[0037] The extrusion is performed using a 90mm single-screw extruder at a temperature of 160℃ and a screw speed of 30r / min, forming a 1.5mm thick outer sheath.

[0038] Step 8, Cable cabling: Single insulated wire cores are directly cabled (no need for multi-core twisting), and the gaps between the cable cores are filled with flame-retardant polypropylene rope (0.1% moisture content).

[0039] Step 9, Inspection and Packaging: Conduct various tests on the electrical performance, mechanical performance, and flame retardant performance of the completed cables. After passing the tests, the cables are packaged and put into storage.

[0040] In this embodiment, electrical performance testing includes insulation resistance testing (using an insulation resistance tester, test voltage 1000V, insulation resistance not less than 1000MΩ·km), withstand voltage testing (AC withstand voltage test, test voltage is 2.5 times the rated voltage of the cable, duration 5min, no breakdown or flashover phenomenon), etc.; mechanical performance testing includes tensile strength testing (tensile strength not less than 15MPa), bending test (bending radius is 10 times the outer diameter of the cable, no insulation layer cracking, conductor breakage, etc. after 10 bends), etc. Flame retardant performance was tested according to the UL94 standard, with a vertical burning test, and passed the UL94-V0 standard.

[0041] Oxygen Index (OI) Test Principle: The Oxygen Index (OI) refers to the minimum oxygen concentration required for a material to sustain combustion in an oxygen-nitrogen mixture under specified test conditions, expressed as a volume percentage. A higher OI indicates better flame retardant properties. When the OI of a flame-retardant layer reaches 32% or higher, it means that it can only sustain combustion in an environment with an oxygen content of 32% or higher, and is difficult to burn in normal air (containing approximately 21% oxygen), thus possessing good flame retardant capabilities.

[0042] Sample preparation: Cut standard samples with a length of 80mm-150mm, a width of 10mm±0.5mm, and a thickness of 1.0mm-2.5mm (consistent with the actual thickness of the flame retardant layer) from the flame retardant layer of the cable, ensuring that the sample surface is flat and free of burrs.

[0043] Test standard: Performed in accordance with GB / T 2406.2-2009 "Determination of flammability of plastics by oxygen index method - Part 2: Room temperature test".

[0044] Test process: The sample is vertically fixed inside the combustion cylinder, and an oxygen-nitrogen mixture is introduced into the cylinder. The volume fraction of oxygen and nitrogen is adjusted by a gas flow controller.

[0045] Ignite the tip of the sample with the tip igniter, ensuring that the entire tip of the sample is ignited, and record the ignition time.

[0046] Observe the combustion of the sample: if the combustion time of the sample exceeds 3 minutes or the combustion length exceeds 50 mm (calculated from the ignition end), reduce the oxygen concentration; if the sample extinguishes within 3 minutes or the combustion length does not reach 50 mm, increase the oxygen concentration.

[0047] Repeatedly adjust the oxygen concentration until the lowest oxygen concentration that the sample can just sustain combustion is found. This concentration is the oxygen index of the flame retardant layer.

[0048] Judgment requirements: The test result must reach more than 35% to meet the performance indicators of the flame retardant layer and ensure that the cable has a good flame retardant effect.

[0049] The final results of Example 1 are as follows: Insulation resistance: 1200MΩ・km, withstand voltage test (2.5kV, 5min) with no breakdown.

[0050] Flame retardant performance: Oxygen index 35%, UL94-V0 rating passed.

[0051] Mechanical properties: tensile strength 16MPa, no damage in bending test (radius 16mm).

[0052] Example 2: 10kV aluminum conductor cross-linked polyethylene power cable Step 1, Conductor preparation: Aluminum ingots with a purity of 99.7% are drawn into 1.5mm single wires (die roughness Ra0.2μm) at a drawing speed of 12m / min.

[0053] Single-wire annealing: 80A current, 10s time, nitrogen protection.

[0054] Using a special die, six single wires are twisted together to form a conductor with an outer diameter of 4.0 mm and a compression factor of 0.92.

[0055] Step 2, conductor shielding layer extrusion: semiconducting material (carbon black content 3%, particle size 30nm) is mixed (140℃, 50r / min, 12min).

[0056] A 65mm extruder (130℃, 40r / min) is covered with a 0.6mm thick shielding layer, and the traction speed is 20m / min.

[0057] Step 3, cross-linked polyethylene insulation layer extrusion: Polyethylene is mixed with DTBP (1.0%) and TAIC (0.5%), and extruded into a 4.5mm thick insulation layer using a 90mm extruder (170℃, 35r / min).

[0058] The vulcanized pipe was crosslinked at 185℃ for 20 minutes (nitrogen gas 0.25MPa), and then cooled to 45℃.

[0059] Step 4, Extrusion of the insulating shielding layer: The process is the same as that of the conductor shielding layer, forming a 0.6mm thick shielding layer outside the insulating layer.

[0060] Step 5: Fabrication of the metal shielding layer: Wrap a 0.2mm thick copper strip with an overlap of 20% and a tension of 15N.

[0061] Step 6: Preparation of flame retardant layer: Premix flame retardant material (45% magnesium hydroxide, 25% aluminum hydroxide, 15% phosphorus and nitrogen) with glass fiber (8μm in diameter, 15%) for 6 min (1200r / min).

[0062] After granulation (170℃, 60r / min), an 80mm extruder (160℃, 40r / min) forms a 1.7mm thick flame-retardant layer.

[0063] Step 7, Outer Sheath Extrusion: High-density polyethylene is mixed with antioxidant (0.3%) and ultraviolet absorber (0.4%) (90℃, 10min).

[0064] A 100mm extruder (180℃, 45r / min) extrudes a 2.0mm thick outer sheath.

[0065] Step 8, Cable Assembly: Single-core cable assembly, filled with flame-retardant fiberglass rope (moisture content 0.08%), with a twist pitch of 15 times the outer diameter.

[0066] Step 9, Inspection and Packaging: Conduct various tests on the electrical performance, mechanical performance, and flame retardant performance of the completed cables. After passing the tests, the cables are packaged and put into storage.

[0067] The final results for Example 2 are as follows: Insulation resistance: 1500MΩ・km, withstand voltage test (25kV, 5min) with no breakdown.

[0068] Flame retardant performance: Oxygen index 37%, UL94-V0 rating passed.

[0069] Mechanical properties: tensile strength 17MPa, no damage in bending test (radius 40mm).

[0070] Example 3: 35kV Copper Conductor Cross-linked Polyethylene Power Cable Step 1, Conductor preparation: 99.96% copper material is drawn into a 3.0mm single wire at a drawing speed of 8m / min and an annealing current of 150A for 15s.

[0071] 19 single wires tightly twisted together (pressure 15MPa), pitch ratio 18, conductor outer diameter 10.0mm, compaction coefficient 0.93.

[0072] Step 2, conductor shielding layer extrusion: semiconductive material (4% carbon black, 40nm particle size) is mixed (150℃, 60r / min, 15min).

[0073] A 90mm extruder (140℃, 60r / min) is used to coat a 0.8mm thick shielding layer.

[0074] Step 3, Extrusion of cross-linked polyethylene insulation layer: Polyethylene is mixed with 25 (1.2%) and 1,2-PBR (0.6%), and extruded into a 9.0 mm thick insulation layer using a 120 mm extruder (180℃, 50 r / min).

[0075] Crosslinking of vulcanized pipes at 200℃ for 30 minutes (nitrogen 0.3MPa).

[0076] Step 4: Extrusion of the insulating shielding layer: Same parameters as the conductor shielding layer, covering with a 0.8mm thick shielding layer.

[0077] Step 5: Fabrication of the metal shielding layer: Wrap with 0.3mm copper tape, with an overlap rate of 25% and a tension of 20N.

[0078] Step 6: Preparation of flame retardant layer: Premix flame retardant material (50% magnesium hydroxide, 20% aluminum hydroxide, 10% phosphorus and nitrogen) with glass fiber (10 μm diameter, 10%) for 8 min (1500 r / min).

[0079] After granulation (180℃, 70r / min), a 2.5mm thick flame-retardant layer is formed by a 100mm extruder (180℃, 55r / min).

[0080] Step 7, Outer Sheath Extrusion: High-density polyethylene is mixed with antioxidant (0.5%) and ultraviolet absorber (0.6%) (100℃, 12min).

[0081] A 120mm extruder (200℃, 60r / min) extrudes a 3.0mm thick outer sheath.

[0082] Step 8, Cable cabling: Single-core cable, filled with flame-retardant material, with a stranding pitch of 20 times the outer diameter.

[0083] Step 9, Inspection and Packaging: Conduct various tests on the electrical performance, mechanical performance, and flame retardant performance of the completed cables. After passing the tests, the cables are packaged and put into storage.

[0084] The final results of Example 3 are as follows: Insulation resistance: 2000MΩ・km, withstand voltage test (87.5kV, 5min) with no breakdown.

[0085] Flame retardant performance: Oxygen index 39%, UL94-V0 rating passed.

[0086] Mechanical properties: tensile strength 19MPa, no damage in bending test (radius 100mm).

[0087] Comparative Example 1 Comparative Example 1 lacks step 6, the preparation of the flame-retardant layer, compared to Example 2. The final results of the comparative example are as follows: Flame retardant performance: oxygen index 28%, UL94-V2 rating (burning time 40s, dripping material ignites cotton).

[0088] Insulation performance: Breakdown after withstand voltage test (25kV, 3min).

[0089] Mechanical properties: tensile strength 12MPa, insulation layer cracked after bending test.

[0090] The above description represents preferred embodiments in conjunction with preferred embodiments, but it should not be construed as limiting the specific embodiments of the present invention to those described. For those skilled in the art, various variations and substitutions can be made without departing from the research concept of the present invention, and all such variations and substitutions are included within the scope defined by the present invention.

Claims

1. A cross-linked polyethylene power cable with a flame-retardant layer, characterized in that, It includes, from the inside out, a conductor, a conductor shielding layer, a cross-linked polyethylene insulation layer, an insulation shielding layer, a metal shielding layer, a flame-retardant layer, and an outer sheath layer; The conductor is made of multiple stranded metal wires; The conductor shielding layer is made of a semi-conductive material and is tightly wrapped around the outer periphery of the conductor. The cross-linked polyethylene insulation layer is formed through a cross-linking process and has good insulation properties; The insulating shielding layer is made of a semi-conductive material and is wrapped around the periphery of the cross-linked polyethylene insulating layer. The metal shielding layer is made of copper strip or copper wire wrapped or woven together; The flame-retardant layer is made of halogen-free flame-retardant material, including 40%-50% magnesium hydroxide, 20%-30% aluminum hydroxide, and 10%-20% phosphorus-nitrogen flame retardant, and 10%-15% reinforcing material is added to the flame-retardant layer, wherein the reinforcing material is glass fiber or carbon fiber. The outer sheath is made of high-density polyethylene.

2. The cross-linked polyethylene power cable with a flame-retardant layer according to claim 1, characterized in that, The conductor is a copper conductor or an aluminum conductor, and the individual wires of the conductor are tightly stranded or profiled stranded to improve the conductor's fill factor and the overall compactness of the cable.

3. The cross-linked polyethylene power cable with a flame-retardant layer according to claim 1, characterized in that, The carbon black content in the semiconductive materials of the conductor shielding layer and the insulating shielding layer is 2%-4% to ensure good semiconducting performance and compatibility with adjacent layers.

4. The cross-linked polyethylene power cable with a flame-retardant layer according to claim 1, characterized in that, The cross-linking degree of the cross-linked polyethylene insulation layer reaches more than 90%, which is achieved by a peroxide cross-linking process. The amount of peroxide added is 0.8%-1.2%, the cross-linking temperature is 170℃-200℃, and the cross-linking time is 10min-30min.

5. The cross-linked polyethylene power cable with a flame-retardant layer according to claim 1, characterized in that, The copper strip of the metal shielding layer has a thickness of 0.1mm-0.3mm and a wrapping overlap rate of 15%-25%; or the copper wire has a diameter of 0.1mm-0.3mm and a weaving density of 80%-95%.

6. The cross-linked polyethylene power cable with a flame-retardant layer according to claim 1, characterized in that, The thickness of the flame-retardant layer is 1.0mm-2.5mm.

7. The cross-linked polyethylene power cable with a flame-retardant layer according to claim 1, characterized in that, The outer sheath layer contains antioxidants and ultraviolet absorbers, with the amount of antioxidants added being 0.1%-0.5% and the amount of ultraviolet absorbers added being 0.2%-0.6%.

8. A manufacturing process for a cross-linked polyethylene power cable with a flame-retardant layer as described in any one of claims 1-7, characterized in that, Includes the following steps: Conductor preparation: After the metal raw materials are drawn and annealed, they are stranded according to the design requirements to obtain the conductor; Conductor shielding layer extrusion: Semiconducting material is uniformly coated onto the surface of a conductor using an extruder to form a conductor shielding layer; Cross-linked polyethylene insulation layer extrusion: After the polyethylene raw material is mixed evenly with peroxide cross-linking agent and additives, the cross-linked polyethylene insulation layer is extruded outside the conductor shielding layer through an extruder. After extrusion, it enters the vulcanization pipeline and is kept at a temperature of 170℃-200℃ for 10min-30min to complete the cross-linking. Extrusion of insulating shielding layer: Semiconducting material is coated onto the surface of cross-linked polyethylene insulation layer through an extruder to form an insulating shielding layer. The extrusion process parameters are the same as those for conductor shielding layer extrusion. Metal shielding layer fabrication: Copper strips or wires are used to create a metal shielding layer outside the insulating shielding layer using a wrapping machine or braiding machine, controlling the wrapping overlap rate or braiding density to meet the requirements; Flame retardant layer preparation: After mixing halogen-free flame retardant material with reinforcing material, the flame retardant layer is extruded outside the metal shielding layer through an extruder, and the extrusion temperature is controlled at 140℃-180℃; Outer sheath extrusion: After mixing high-density polyethylene with additives, the outer sheath is extruded over the flame-retardant layer using an extruder. The extrusion temperature is controlled between 160℃ and 200℃. Cable cabling: Multiple insulated wire cores with outer sheaths are twisted together according to a certain pitch and direction to form a cable core, and filler is used to fill the gaps between the cable cores; Inspection and Packaging: The completed cables are subjected to various tests, including electrical performance, mechanical performance, and flame retardancy performance. After passing the tests, they are packaged and put into storage.

9. The manufacturing process of a cross-linked polyethylene power cable with a flame-retardant layer according to claim 8, characterized in that, In the conductor manufacturing process, the selection of the die during the wire drawing process is determined based on the material of the metal raw material and the target single wire diameter.

10. The manufacturing process of a cross-linked polyethylene power cable with a flame-retardant layer according to claim 8, characterized in that, During the cable cabling process, the stranding pitch is 10 to 20 times the outer diameter of the cable, and the filler is a flame-retardant, non-hygroscopic material.

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