Fireproof flame-retardant sheathed cable and production process thereof

Abstract

The application relates to the technical field of electric wire and cable, in particular to a fireproof and flame-retardant sheath cable and a production process thereof. The cable comprises, from inside to outside, a high-purity aluminum conductor, an XLPE insulation layer, a wrapping layer, an inner lining layer, a metal shielding layer and a red polyolefin ST8 sheath layer; the shielding layer is subjected to laser overlapping welding and spiral embossing. The production process comprises the steps of conductor tight pressing and twisting, warm water crosslinking after insulation extrusion molding, steel belt laser welding, inner protection and sheath extrusion. The application realizes fireproof standard of B2ca sa1 a1 level for the cable through the six-layer integrated structure design and the flame-retardant modification of the sheath material, cooperates with high-precision production process control, makes the cable have high insulation reliability, excellent radial sealability and construction flexibility, and solves the problems of substandard fireproof grade of the existing cable, easy insulation aging and poor sealability of the shielding layer.

Description

Technical Field

[0001] This invention relates to the field of wire and cable technology, specifically to a fire-resistant and flame-retardant sheathed cable and its manufacturing process. Background Technology

[0002] In the field of railway power transmission, the quality stability, insulation performance, and fire-retardant properties of cables directly affect the safety and reliability of power transmission. Especially in special environments such as tunnels, forests, and public facilities, cables not only need to possess extremely high fire resistance ratings but also must maintain structural strength and environmental resistance under complex physical conditions. According to the requirements of railway construction and high-end industrial applications, cables often need to meet B2ca-sa1-a1 fire resistance requirements and strictly comply with international standards such as UNE-EN 60228 and IEC 60502.

[0003] While current cable technology has made some progress in material selection and structural design, issues remain, such as insufficient fire resistance and flame retardancy in some cables, and the potential for smoke release during fires. Furthermore, the thermal stability and dielectric properties of the insulation layer during long-term operation still have room for improvement, and the sealing and structural stability of the metal shielding layer exhibit limitations in resisting corrosion or physical impacts. At the production level, existing technologies lack systematic standards for raw material selection, refined control of production processes, and end-to-end inspection of finished products, leading to fluctuations in product quality when meeting the demands of high-end applications.

[0004] Patent CN112735652B discloses a fire-retardant cable and a wrapping mechanism for producing fire-retardant cables. The cable includes a core, insulation layer, shielding layer, and inner and outer protective layers, and is equipped with a specialized wrapping device to improve production efficiency. This technical solution enhances the cable's fire resistance through a multi-layered protective structure; however, its innovation mainly focuses on improving the wrapping mechanism. It lacks in-depth material ratio optimization for achieving higher fire resistance requirements (such as B2ca-sa1-a1 level) for the sheath material, and further improvements are needed in the standardized quality control throughout the entire production process.

[0005] Patent CN120452911A discloses a flame-retardant B1-grade fire-resistant cable, whose cable core is externally covered with a ceramicized silicone rubber composite tape layer, a halogen-free, low-smoke, high-flame-retardant tape layer, and a metal longitudinal sheath layer, enabling it to maintain operation for a certain period without being broken down under high-temperature flames. While this solution improves the cable's fire resistance, it still falls short in terms of the systematic production process control required for specific high-end scenarios such as railways. In particular, there is still room for optimization and improvement in the closed-loop quality management throughout the entire lifecycle, from design and raw material selection to production, processing, finished product inspection, and storage and delivery. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] To address the shortcomings of existing technologies, this invention provides a fire-resistant and flame-retardant sheathed cable and its manufacturing process, thus solving the problems mentioned in the background art.

[0008] (II) Technical Solution

[0009] To achieve the above objectives, this invention provides a fire-resistant and flame-retardant sheathed cable and its manufacturing process. The aim is to obtain a power transmission cable with B2casa1 a1 fire resistance rating, high insulation reliability, and high structural stability through specific structural design and material modification, combined with high-precision production process control.

[0010] In a first aspect, the present invention provides a fire-resistant and flame-retardant sheathed cable, model WDFS YJLY53 AL 3 / 3Kv, wherein the cable comprises, from the inside out, a conductor, an XLPE insulation layer, a wrapping layer, an inner lining layer, a metal shielding layer, and a red polyolefin ST8 sheath layer.

[0011] According to the present invention, the conductor of the cable is made of high-purity aluminum wire with a purity of not less than 99.7%. The high-purity aluminum wire is drawn to a preset diameter by a multi-head wire drawing machine, and the wire diameter deviation is controlled within ±0.02mm. The surface roughness Ra value of the conductor is less than or equal to 1.6 micrometers.

[0012] According to the present invention, the XLPE insulation layer is formed by extruding silane cross-linked polyethylene material at high temperature and then reacting it with warm water or steam. The thickness of the insulation layer is 2.0 mm to 2.5 mm, and the inner wall of the insulation layer is tightly attached to the outer surface of the conductor.

[0013] According to the present invention, the metal shielding layer is a tin-plated steel strip with a thickness of 0.15 mm. The metal shielding layer is formed by laser continuous welding process to form a longitudinal overlapping weld. The overlap width of the overlapping weld is 10 mm to 12 mm. The surface of the metal shielding layer is provided with spiral grooves. The pitch of the grooves is 2.5 mm to 3.3 mm, that is, there are 3 to 4 grooves distributed within each 1 cm length.

[0014] According to the present invention, the red polyolefin ST8 sheath layer is extruded from a halogen-free, low-smoke, flame-retardant polyolefin composition. The thickness of the sheath layer is 2.0 mm to 3.0 mm. Two purple longitudinal stripes are co-extruded at corresponding positions in the circumferential direction of the sheath layer. The width of the purple longitudinal stripes is 8 mm to 10 mm, and the depth of the stripes embedded in the surface of the sheath layer is 0.2 mm to 0.5 mm.

[0015] Secondly, the present invention provides a manufacturing process for the above-mentioned fire-resistant and flame-retardant sheathed cable, comprising the following steps:

[0016] S10: Conductor stranding: Multiple high-purity aluminum wires are stranded using a stranding machine. The stranding pitch is set to 12 to 16 times the outer diameter of the conductor. During the stranding process, the tension fluctuation of a single wire is controlled within 5% of the rated value through a tension feedback system. The stranded conductor is then compacted using a compaction die with a compaction coefficient of 0.90 to 0.93.

[0017] S20: Insulation layer extrusion: The conductor is introduced into the extrusion production line, and XLPE insulation material is continuously extruded on the outer surface of the conductor. The barrel temperature of the extruder is set to 120 to 145°C, 155 to 165°C, and 170 to 185°C from the feeding section to the homogenization section, respectively. The die head temperature is set to 190 to 210°C. The extruded wire core enters the steam crosslinking chamber and is steamed in the steam crosslinking chamber at 80 to 95°C for 8 to 12 hours to achieve a crosslinking degree of more than 80%.

[0018] S30: Wrapping and inner liner processing: Water-blocking tape and low-smoke halogen-free high flame-retardant tape are overlapped and wrapped on the outer surface of the cross-linked wire core, with a wrapping overlap rate of 20% to 25%. Then, a polyolefin inner liner is wrapped on the outside of it by an extruder, with a thickness of 1.8 mm to 2.0 mm.

[0019] S40: Metal shielding layer processing: A 0.15mm thick tin-plated steel strip is wrapped around the inner lining layer using a longitudinal wrapping forming machine. The steel strip joints are overlapped and welded using a laser welding machine. The laser power is set to 1500 to 2500W, and the welding speed is 2 to 10 meters per minute. After welding, the steel strip enters a corrugating machine, where a spiral pattern is pressed onto the surface of the steel strip by rotating corrugating rollers. The corrugating depth is controlled between 0.8mm and 1.2mm.

[0020] S50: Co-extrusion of the sheath layer: A dual-extrusion process is adopted. The main extruder extrudes the red polyolefin ST8 sheath material, while the auxiliary extruder simultaneously extrudes the purple polyolefin marking material. The two melt streams merge in the die and then coat the outside of the metal shielding layer. The extrusion temperature is controlled between 150 and 180°C, and then the material enters a cooling water tank for cooling.

[0021] S60: Finished Product Inspection and Packaging: The finished cables are inspected for appearance, dimensions, electrical performance and fire resistance. After passing the inspection, the cables are packaged in wooden fumigated cable reels and heat-shrink capped at the ends.

[0022] In some embodiments, the method for preparing the XLPE insulating material in step S20 includes:

[0023] 100 parts of low-density polyethylene, 1.5 to 2.5 parts of vinyltrimethoxysilane, 0.05 to 0.15 parts of initiator dicumyl peroxide, and 0.2 to 0.5 parts of antioxidant 300 are mixed evenly and subjected to a grafting reaction in a twin-screw extruder to obtain silane-grafted polyethylene material. The silane-grafted polyethylene material is then mixed with catalyst masterbatch at a mass ratio of 95:5 before use.

[0024] In some embodiments, in step S50, the components of the red polyolefin ST8 sheath material, by weight, include:

[0025] 40 to 60 parts of linear low-density polyethylene, 20 to 35 parts of ethylene-vinyl acetate copolymer, 80 to 120 parts of magnesium hydroxide flame retardant, 5 to 10 parts of red phosphorus flame retardant, 3 to 8 parts of nano-montmorillonite, 3 to 5 parts of red masterbatch, and 1 to 2 parts of silane coupling agent KH550.

[0026] In some embodiments, the preparation process of the red polyolefin ST8 sheath material is as follows:

[0027] Linear low-density polyethylene and ethylene vinyl acetate copolymer are added to a mixer and melt-mixed at 140 to 160°C for 5 to 10 minutes. Then, magnesium hydroxide pretreated with silane coupling agent, red phosphorus flame retardant and nano montmorillonite are added, and the temperature is raised to 170 to 180°C and the mixing continues for 15 to 20 minutes. Finally, red masterbatch is added, and the mixture is granulated by a two-stage extruder and air-cooled to obtain the finished product.

[0028] In some embodiments, in step S40, the laser welding adopts an overlapping welding process, the depth of the weld pool at the welding position is controlled between 0.18 mm and 0.25 mm, ensuring that the weld completely penetrates the upper steel strip and fuses with the lower steel strip, and the width of the weld surface is between 1.2 mm and 1.8 mm.

[0029] In some embodiments, in step S40, the ratio of the rotational speed of the corrugated roller to the cable traction speed is adjusted in real time by a PLC control system to keep the corrugation spacing fluctuation within ±0.1mm.

[0030] In some embodiments, step S60, the electrical performance test includes:

[0031] At 20℃, the conductor resistance is measured using a high-voltage DC resistance tester, and the resistance value per kilometer is not greater than the specified standard value. At room temperature, a 3.5kV AC voltage is applied to the finished cable for 5 minutes, and the insulation layer is observed to see if it breaks down or flashes.

[0032] In some embodiments, step S60, the fire resistance performance test includes:

[0033] A 5-meter-long cable sample was taken and placed on a combustion test rack conforming to EN 50399. A 20.5kW ribbon propane burner was used as the ignition source, and the ignition time was 20 minutes. The damaged length, peak smoke production rate, total smoke production, and flame spread distance were recorded. The technical parameters must meet the requirements for B2ca sa1 a1 level determination.

[0034] In some embodiments, step S60, the mechanical performance test includes:

[0035] Take a sheath test piece and stretch it on a tensile testing machine at a speed of 250 mm per minute. Record the load and elongation at break. Calculate the tensile strength as 12.5 to 15.0 MPa and the elongation at break as 160% to 220%.

[0036] In some embodiments, step S60, the bending performance test includes:

[0037] Wrap the cable around a cylinder with a diameter 20 times the outer diameter of the cable, making 3 turns in each direction. Observe whether cracks appear at the weld of the metal shielding layer and whether whitening or cracks appear on the surface of the sheath.

[0038] In some embodiments, in step S10, the high-purity aluminum wire enters the stranding machine.

[0039] In some embodiments, in step S30, the polyolefin inner liner is extruded using an extrusion die, and the stretch ratio between the die core and the die sleeve is controlled at 1.2 to 1.5, so that the inner liner generates inward radial pressure after cooling and shrinking, tightly binding the inner wrapping layer.

[0040] In some embodiments, in step S40, the tin-plated steel strip passes through a set of tension adjusting rollers and a centering sensor before longitudinal wrapping, and the edge position of the steel strip is adjusted by a hydraulic servo system so that the position of the overlapping weld seam is always kept directly above the cable cross-section.

[0041] In some embodiments, in step S50, the difference between the melt index of the purple polyolefin marking material and the melt index of the red polyolefin ST8 sheath material is controlled to be within 1.0 g per 10 minutes (under test conditions of 190°C and 2.16 kg) to form a stable co-extrusion interface.

[0042] In some embodiments, in step S50, the length of the cooling water tank is allocated as follows: the length of the first section of the cooling water tank is 8 to 10 meters, the length of the second section of the cooling water tank is 12 to 15 meters, and the length of the third section of the cooling water tank is 10 to 12 meters.

[0043] In some embodiments, during the packaging process of the finished cable, a rubber pad with a thickness of 0.5 mm to 1.0 mm is laid on the inside of the cable reel. After the cable is wrapped, the outermost layer is wrapped with two layers of polyethylene moisture-proof film and reinforced with nylon strapping in a grid pattern.

[0044] According to the present invention, a stable electrical transmission channel is formed by adopting a six-layer integrated structure of "conductor insulation wrapping inner lining shielding sheath" combined with high-purity aluminum conductor and silane cross-linked polyethylene insulation. By introducing a high proportion of magnesium hydroxide, red phosphorus, and nano-montmorillonite into the sheath material, when a fire occurs, magnesium hydroxide decomposes upon heating, releasing moisture and absorbing a large amount of heat; red phosphorus forms a dense carbonized layer; and nano-montmorillonite forms a physical barrier on the surface, collectively restricting the penetration of heat into the interior and the diffusion of smoke outward.

[0045] According to the present invention, the metal shielding layer adopts a laser overlapping welding process instead of the traditional seamless butt welding or lap welding method. Utilizing the high energy density of the laser, a deep-penetration weld is formed in the overlapping area of ​​the steel strip, making the shielding layer a complete metal tubular structure. Combined with the electrochemical protection of the tin plating layer, this isolates the steel strip substrate from the corrosion of moisture and acidic gases. Simultaneously, the high-density spiral corrugated design (3 to 4 corrugations within 1 cm) allows the metal tube wall to absorb stress through minute corrugated deformation when the cable is bent, preventing weld cracking and improving the cable's flexibility when laid in confined spaces such as tunnels.

[0046] According to this invention, the production process employs gradient cooling, tension closed-loop control, and co-extrusion marking technology. By adjusting the cooling water temperature in stages, the internal stress of the sheath layer after extrusion is eliminated, preventing cracking during long-term use. A comprehensive process parameter recording and finished product inspection system incorporates key variables such as raw material purity, extrusion temperature, welding power, and cooling rate into a standardized control framework, ensuring that the final cable consistently meets B2ca, sa1, and a1 fire resistance standards and relevant international electrical standards.

[0047] In some embodiments, in the conductor stranding step S10, the surface of the compaction die is coated with a diamond-like carbon (DLC) film, the film having a thickness of 2 to 3 micrometers, a hardness of 2500 to 3000 HV, and a coefficient of friction of less than 0.1. By reducing the frictional force during the compaction process, the degree of work hardening on the conductor surface is reduced, maintaining the toughness of the aluminum conductor and preventing microcracks from forming during subsequent bending tests.

[0048] In some embodiments, in step S20, the extruder screw is a barrier-type compounding screw with a length-to-diameter ratio (L / D) of 25 to 30 and a compression ratio of 2.5 to 3.2. The barrier section on the screw generates a shearing effect on the melt, which fully disperses the silane-grafted polyethylene and catalyst masterbatch, eliminating crystal points and gel particles in the insulating layer.

[0049] In some embodiments, in step S30, the single-layer thickness of the low-smoke halogen-free high flame-retardant strip is 0.15 mm to 0.20 mm, and its warp and weft tensile strength is not less than 200 N per 10 mm. By overlapping and wrapping, a fire-resistant barrier is formed outside the insulation layer, which slows down the thermal decomposition rate of the insulation layer when attacked by external flames.

[0050] In some embodiments, in step S40, the laser welding machine is equipped with a weld seam tracking system, which uses a laser scanner to collect the height and position information of the steel strip edge in real time, and feeds it back to the actuator to adjust the focal length and horizontal position of the laser head to compensate for welding deviations caused by steel strip fluctuations.

[0051] In some embodiments, in step S40, the surface hardness of the embossing roll is 58 to 62 HRC, and the surface is polished to a mirror finish. During the embossing process, a small amount of volatile stamping oil is sprayed onto the surface of the steel strip to lubricate the embossing interface and prevent the tin plating layer from peeling off or scratching during extrusion.

[0052] In some embodiments, in step S50, the nano-montmorillonite in the red polyolefin ST8 sheath material is organically modified with hexadecyltrimethylammonium bromide. The interlayer spacing of the modified montmorillonite is increased from 1.2 nm to 2.5 to 3.5 nm, making it easier to peel into nanoscale sheets in the polyolefin matrix, thereby improving the oxygen index and drip protection performance of the material.

[0053] In some embodiments, in step S50, the average particle size D50 of the magnesium hydroxide flame retardant is 0.8 to 1.5 micrometers, and the specific surface area is 4 to 8 square meters per gram. Using magnesium hydroxide with a small particle size and narrow distribution ensures flame retardant efficiency while reducing the impact on the machinability of the sheath material.

[0054] In some embodiments, in step S50, the compression ratio of the co-extrusion die is designed to be 1.5 to 2.0, and the die gap is set to 1.1 times the design thickness of the sheath. Through reasonable die design, appropriate extrusion back pressure is generated, improving the density and surface finish of the sheath layer.

[0055] In some embodiments, step S60, the finished product inspection further includes a smoke toxicity test. The cable material is placed in a toxicity testing furnace and thermally decomposed at 800°C. The smoke is collected and analyzed by ion chromatography to determine the content of acidic gases such as hydrogen halides, sulfur dioxide, and nitrogen oxides. The weighted average toxicity index must be less than 5.

[0056] In some embodiments, step S60, the finished product inspection further includes a thermal aging test. The cable sample is placed in a constant temperature aging chamber at 135°C for 168 hours, then removed and cooled to room temperature. The tensile strength change rate of the sheath and insulation is tested, requiring that the change rate of strength and the change rate of elongation both not exceed ±25%.

[0057] In some embodiments, the color difference value Delta E of the two purple longitudinal stripes at 180° corresponding positions of the red polyolefin ST8 sheath layer is controlled within 1.0. By precisely controlling the feed rate and pressure of the auxiliary extruder, the stripes maintain a consistent width throughout their entire length, without any breaks or drift.

[0058] In some embodiments, a flame-retardant waterproof sealant is used to fill the space between the inner lining layer and the metal shielding layer of the cable. The sealant is a mixture of polybutene copolymer, white oil, hydrophobic fumed silica, and a flame retardant, with a dropping point temperature not lower than 80°C. The sealant fills the corrugated gaps in the shielding layer, preventing moisture from penetrating longitudinally along the cable.

[0059] In some embodiments, the production process further includes an online deviation measurement step. After the insulation extrusion and sheath extrusion processes, an ultrasonic deviation meter is installed to monitor the thickness of the cable at various points along the circumference in real time. When the thickness difference exceeds 0.1 mm, the die head adjustment mechanism is automatically triggered to compensate.

[0060] In some embodiments, in step S40, the weld area after laser welding is subjected to online eddy current testing. The continuity of the weld is detected by a testing coil, and when a missing weld or a weak weld is found, the system automatically records the defect location and marks it on the sheath surface.

[0061] In some embodiments, in step S10, a very thin layer of antioxidant grease is coated on the surface of the stranded conductor. The grease is composed of synthetic ester oil and benzotriazole derivatives, and the coating amount is controlled at 0.5 to 1.0 grams per square meter to prevent surface oxidation of the aluminum conductor during production turnover.

[0062] In some embodiments, in step S20, the water circulation system of the warm water crosslinking tank is equipped with an ion exchange resin filter. By removing calcium and magnesium ions from the water, scale deposits are prevented from forming on the insulation surface during the crosslinking process, thus maintaining the smoothness of the insulation surface.

[0063] In some embodiments, in step S50, the red polyolefin ST8 sheath material is treated with a dehumidifying dryer before extrusion. The drying temperature is 70 to 80°C, and the moisture content after drying is controlled below 0.02%, eliminating microporous defects inside the sheath layer.

[0064] In some embodiments, the red polyolefin ST8 sheath material further comprises 2 to 5 parts of an organosilicon lubricant. This lubricant migrates to the surface during extrusion, reducing friction between the sheath and the die, increasing extrusion speed, and improving the abrasion resistance of the finished cable.

[0065] According to the present invention, the problems of existing cables, such as substandard fire resistance, easy aging of insulation, poor sealing of shielding layer, and large quality fluctuations, are solved through the above-mentioned specific technical means. The laser-overlapped weld of the cable of the present invention provides excellent radial sealing performance, and the combination of tin-plated steel strip and flame-retardant sheath gives it an expected service life of up to 40 years in acidic or alkaline soil environments. At the same time, the high-frequency corrugation process (3 to 4 per centimeter) significantly reduces the bending stiffness of the cable, allowing its bending radius to be reduced to 12 times the cable outer diameter, which greatly facilitates construction and wiring in narrow spaces such as railway tunnels.

[0066] Furthermore, this invention, through in-depth optimization of the raw material formulation, particularly the application of flame retardant compounding and nano-modification technology, enables the cable to meet the high flame retardancy requirements of B2ca grade while maintaining excellent physical and mechanical properties. The sheath tensile strength reaches over 12.5 MPa, far exceeding that of ordinary polyolefin materials. Precise process control throughout the entire process, from ultrasonic cleaning of the conductor to gradient cooling of the sheath, from weld seam tracking in laser welding to toxicity analysis of the finished product, forms a complete and quantifiable quality assurance system, ensuring that every reel of cable delivered meets the stringent standards of international railway power transmission.

[0067] The red sheath and purple stripe design of this invention's cable, achieved through dual-machine co-extrusion technology, ensures that the markings do not peel off or fade under conditions of friction and scratches, providing a clear identification feature for the cable's later maintenance. By standardizing packaging, storage, and delivery processes, from fumigation of the wooden trays to end-of-line heat shrink sealing, all environmental factors are prevented from causing secondary damage to product quality, ensuring consistent quality from the production workshop to the construction site.

[0068] In some embodiments, during step S40, high-purity argon gas is purged into the welding area as a protective gas during laser welding. The argon gas flow rate is controlled at 15 to 25 liters per minute to prevent oxidation of the high-temperature molten pool and ensure the toughness and corrosion resistance of the weld metal.

[0069] In some embodiments, during step S50, 0.5 to 1.5 parts of UV absorber UV 326 are added to the red polyolefin ST8 sheath material. By absorbing ultraviolet energy from sunlight, photo-oxidative aging of the cable is prevented in outdoor forests, public facilities, and other open-air installation scenarios.

[0070] In some embodiments, step S60 involves performing a partial discharge test on the finished cable. At 1.73 times the rated voltage, the partial discharge quantity is no greater than 5 pC, ensuring that there are no tiny air gaps or impurities inside the insulation layer, thus improving the cable's operational stability under high-voltage electric fields.

[0071] In some embodiments, the insulation layer extrusion in step S20 employs a two-step crosslinking process. Rapid crosslinking is achieved through the high temperature of a steam crosslinking chamber, thereby increasing the degree of crosslinking of the insulation.

[0072] In some embodiments, in step S40, the profile of the corrugated roll is designed as a sinusoidal waveform. The corrugation depth is 6 to 8 times the thickness of the steel strip. The smooth transition of the sinusoidal waveform reduces stress concentration at the corrugation point and improves the fatigue life of the cable.

[0073] In some embodiments, in step S50, the sheath extruder employs a vacuum exhaust device. An exhaust port is provided in the middle of the screw, and the vacuum level is controlled at -0.08 to -0.09 MPa to forcibly remove low-molecular-weight volatiles and residual moisture from the melt.

[0074] In some embodiments, step S60 involves subjecting the cable to rodent resistance testing. 0.1 to 0.3 parts of a bittering agent (such as capsaicin) are added to the sheath material, and simulation experiments are conducted to verify the cable's protective capability against rodents and other animals in tunnel or public facility environments.

[0075] In some embodiments, step S60 involves a water absorption test on the cable. The sheath sample is immersed in distilled water at 70°C for 14 days, and the weight gain per unit area is measured. The weight gain is no greater than 1.0 mg / cm², ensuring the volume stability of the sheath in a humid environment.

[0076] In some embodiments, in step S10, the wire drawing machine uses a fully synthetic emulsified wire drawing oil. The concentration of the wire drawing oil is controlled at 8% to 12%, the temperature is controlled at 35 to 45°C, and the pH value is maintained at 8.5 to 9.5. Good lubrication and cooling ensure that the aluminum wire surface is free of black streaks and scratches.

[0077] In some embodiments, in step S40, the laser welding machine uses a fiber laser. The fiber core diameter is 50 to 100 micrometers, and the beam quality factor M2 is less than 1.2. Through high-quality, small-spot focusing, a narrow and deep weld morphology is achieved, reducing the size of the heat-affected zone.

[0078] In some embodiments, in step S50, 1 to 3 parts of nano-zinc oxide are added to the red polyolefin ST8 sheath material. Besides its synergistic flame-retardant effect, nano-zinc oxide also has antibacterial and antifungal properties, preventing the cable from becoming moldy in humid and bacteria-prone environments such as forests.

[0079] In some embodiments, in step S30, the inner lining is extruded using a tube extrusion method to reduce the adhesion between the inner lining and the wrapping layer, facilitating cable end stripping and joint fabrication.

[0080] In some embodiments, step S60 involves conducting an acid and alkali corrosion resistance test on the cable. The sample is immersed in a 10% sulfuric acid solution and a 10% sodium hydroxide solution, respectively, and left at room temperature for 168 hours. The cable should show no blistering, discoloration, or significant decrease in strength on the sheath surface.

[0081] In some implementations, each cable reel of the finished cable is tagged with an RFID tag. The tag stores the cable's unique code, production date, raw material batch number, process parameters for each step, and inspector information, enabling information-based traceability throughout the product's entire lifecycle.

[0082] This invention, through a series of precise technical features and process steps, constructs a railway power transmission cable with extremely high safety boundaries and environmental adaptability. Its B2ca sa1 a1 fire resistance rating effectively reduces the flame spread rate and total smoke production during a fire, buying crucial time for personnel evacuation and firefighting. The combination of laser-overlap welding shielding structure and high-density corrugated processing ensures electromagnetic shielding while giving the cable excellent mechanical reliability and construction flexibility. Closed-loop quality control throughout the entire process fundamentally eliminates product performance uncertainties, providing solid hardware support for the long-term safe operation of railway power systems. Attached Figure Description

[0083] Figure 1 This is a schematic diagram of the cross-sectional structure of the cable of the present invention.

[0084] In the diagram: 1. Conductor; 2. XLPE insulation layer; 3. Wrapping layer; 5. Inner lining layer; 6. Metal shielding layer; 7. Red polyolefin ST8 sheath layer. Detailed Implementation

[0085] 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.

[0086] This invention provides a fire-resistant and flame-retardant sheathed cable, model number WDFS YJLY53 AL 3 / 3Kv. The cable's radial structure, from the inside out, includes a conductor 1, an XLPE insulation layer 2, a wrapping layer 3, an inner liner layer 5, a metal shielding layer 6, and a red polyolefin ST8 sheath layer 7. In terms of spatial layout, the conductor 1 is located at the very center of the cable. The XLPE insulation layer 2 is extruded around the conductor's outer perimeter. The wrapping layer 3 covers the XLPE insulation layer 2. The inner liner layer 5 is extruded around the wrapping layer 3. The metal shielding layer 6 is longitudinally wrapped around the outer surface of the inner liner layer 5. The red polyolefin ST8 sheath layer 7 serves as the outermost structure, covering the metal shielding layer.

[0087] According to the present invention, the conductor is made of high-purity aluminum wire with a purity of not less than 99.7%. This high-purity aluminum wire is drawn in multiple passes using a multi-head drawing machine, with the wire diameter deviation controlled within ±0.02 mm, and the surface roughness Ra value of the conductor controlled below 1.6 micrometers. During processing, the conductor is stranded using a stranding machine, with the stranding pitch set to 12 to 16 times the outer diameter of the conductor. The stranded conductor is then compacted using a compaction die, with the compaction coefficient set in the range of 0.90 to 0.93. The surface of the compaction die is coated with a diamond-like carbon (DLC) film with a thickness of 2 to 3 micrometers, the film having a hardness of 2500 to 3000 HV and a coefficient of friction of less than 0.1.

[0088] The XLPE insulation layer has a thickness of 2.0 mm to 2.2 mm. This insulation layer is composed of silane cross-linked polyethylene material, continuously extruded onto the outer surface of the conductor through a three-layer co-extrusion production line. During extrusion, a barrier-type compounding screw is used in the extruder, with a length-to-diameter ratio (L / D) of 25 to 30 and a compression ratio of 2.5 to 3.2. The extruder barrel temperature is set at 120 to 145°C, 150 to 170°C, and 175 to 185°C from the feeding section to the homogenization section, respectively, while the die head temperature is set at 190 to 210°C. The extruded wire core enters a steam cross-linking chamber and is steamed at 80 to 95°C for 8 to 12 hours to achieve a cross-linking degree of over 80%. The preparation of XLPE insulation material involves mixing 100 parts of low-density polyethylene, 1.5 to 2.5 parts of vinyltrimethoxysilane, 0.05 to 0.15 parts of initiator dicumyl peroxide, and 0.2 to 0.5 parts of antioxidant 300, performing a grafting reaction in a twin-screw extruder, and granulating the mixture to obtain silane-grafted polyethylene material. Finally, the grafted material is mixed with catalyst masterbatch at a mass ratio of 95:5 for use.

[0089] The wrapping layer is composed of overlapping low-smoke, halogen-free, highly flame-retardant tapes, with an overlap rate of 20% to 25%. The single-layer thickness of the flame-retardant fiberglass tape is 0.15 mm to 0.20 mm, and its warp and weft tensile strength is not less than 200 N / 10 mm. The inner lining layer covers the outside of the wrapping layer, with a thickness of 1.0 mm to 1.5 mm. It is made of polyolefin material and extruded through an extrusion die, with the stretch ratio between the die core and the die sleeve controlled at 1.2 to 1.5.

[0090] The metal shielding layer is made of 0.15mm thick tin-plated steel strip. This shielding layer is wrapped around the inner lining layer using a longitudinal wrapping forming machine and then continuously overlapped and welded using a fiber laser. The fiber core diameter of the fiber laser is 50 to 100 micrometers, and the beam quality factor M2 is less than 1.2. The laser power is set to 1500 to 2500W, and the welding speed is 5 to 10 meters per minute. The overlap width of the weld seam is 2.0mm to 3.0mm, the molten pool depth is controlled at 0.18mm to 0.25mm, and the weld surface width is 1.2mm to 1.8mm. High-purity argon gas is purged into the welding area at a flow rate of 15 to 25 liters per minute during the welding process. The surface of the metal shielding layer has spiral grooves with a groove pitch of 2.5mm to 3.3mm, i.e., 3 to 4 grooves distributed per 1cm length, and the groove depth is controlled at 0.8mm to 1.2mm. The surface hardness of the embossed roll is 58 to 62 HRC, the profile is designed as a sine wave, and the embossing depth is 6 to 8 times the thickness of the steel strip. The space between the inner liner and the metal shielding layer is filled with a flame-retardant waterproof paste, which is a mixture of polybutene copolymer, white oil, hydrophobic fumed silica and flame retardant, with a dropping point temperature of not less than 80°C.

[0091] The thickness of the red polyolefin ST8 sheath layer is 2.0 mm to 3.0 mm. This sheath layer is extruded from a halogen-free, low-smoke, flame-retardant polyolefin composition. Two purple longitudinal stripes are co-extruded at 180° positions along the circumference of the sheath layer, with a stripe width of 2.0 mm to 3.0 mm and an embedding depth of 0.2 mm to 0.5 mm. The components of the red polyolefin ST8 sheath material, by weight, include: 40 to 60 parts of linear low-density polyethylene, 20 to 35 parts of ethylene-vinyl acetate copolymer, 80 to 120 parts of magnesium hydroxide flame retardant, 5 to 10 parts of red phosphorus flame retardant, 3 to 8 parts of nano-montmorillonite, 3 to 5 parts of red masterbatch, 1 to 2 parts of silane coupling agent KH550, 2 to 5 parts of silicone lubricant, 0.5 to 1.5 parts of UV absorber UV 326, and 1 to 3 parts of nano-zinc oxide.

[0092] The magnesium hydroxide flame retardant has an average particle size (D50) of 0.8 to 1.5 micrometers and a specific surface area of ​​4 to 8 square meters per gram. Nano-montmorillonite is organically modified with hexadecyltrimethylammonium bromide, resulting in a layer spacing of 2.5 to 3.5 nm. The sheath material is prepared as follows: linear low-density polyethylene and ethylene-vinyl acetate copolymer are added to a mixer and melt-mixed at 140 to 160°C for 5 to 10 minutes; then magnesium hydroxide pretreated with a silane coupling agent, red phosphorus flame retardant, and nano-montmorillonite are added, and the mixture is heated to 170 to 180°C and continued to be mixed for 15 to 20 minutes; finally, red masterbatch and other additives are added, and the mixture is granulated using a two-stage extruder.

[0093] The sheath extrusion employs a dual-extrusion process, with the main extruder handling the red sheath material and the auxiliary extruder handling the purple marking material. The extrusion temperature is controlled between 150 and 180°C, and the extruders are equipped with vacuum exhaust devices, maintaining a vacuum level of -0.08 to -0.09 MPa. The compression ratio of the co-extrusion die is designed to be 1.5 to 2.0, and the die gap is set to 1.1 times the designed sheath thickness. The melt flow index difference between the purple marking material and the red sheath material is controlled within 1.0 g / 10 min (190°C, 2.16 kg). After extrusion, the material enters a cooling water tank.

[0094] The specific steps of the production process are as follows:

[0095] S10: Conductor stranding: Multiple high-purity aluminum wires are stranded together in a stranding machine. The tension fluctuation of a single wire is controlled within 5% of the rated value.

[0096] S20: Insulation Layer Extrusion: A two-step cross-linking process is used, with a steam boiler in the steam cross-linking chamber equipped with a temperature-controlled steam circulation system. S30: Wrapping and Lining Layer Processing: Low-smoke, halogen-free, high-flame-retardant tape is overlapped and wrapped around the insulated core, followed by extrusion of a polyolefin liner. S40: Metal Shielding Layer Processing: Tin-plated steel strip is longitudinally wrapped by tension adjusting rollers and centering sensors, and then overlapped and welded using a laser welding machine. The welding machine is equipped with a weld seam tracking system and performs online eddy current flaw detection on the weld seam. Subsequently, a spiral pattern is pressed using a PLC-controlled corrugating machine, with volatile stamping oil sprayed during the corrugating process. S50: Sheath Co-extrusion: The sheath material is dehumidified and dried at 70-80℃ before extrusion, reducing the moisture content to below 0.02%. A dual-machine co-extrusion process is used to mark the stripes. S60: Finished Product Inspection and Packaging: Finished products shall undergo inspection for appearance, dimensions, electrical properties (DC resistance at 20℃, AC withstand voltage of 3.5kV / 5min, 1.73U0 partial discharge test), fire resistance (EN 50399 standard B2ca sa1 a1 grade), smoke toxicity (weighted average toxicity index less than 5), mechanical properties (tensile strength 12.5 to 15.0 MPa, elongation at break 160% to 220%), heat aging test (135℃ / 168h), bending properties, rodent resistance test, and water absorption test. Upon passing inspection, finished products shall be packaged in wooden fumigated cable reels lined with rubber pads, with heat-shrink caps at the ends and RFID electronic tags attached.

[0097] Example 1: In this example, the composition ratio of the red polyolefin ST8 sheath material is as follows: 50 parts linear low-density polyethylene, 25 parts ethylene vinyl acetate copolymer, 100 parts magnesium hydroxide, 8 parts red phosphorus, 5 parts nano montmorillonite, 4 parts red masterbatch, and 1.5 parts KH550. The corrugation pitch of the metal shielding layer is set to 2.8 mm (approximately 3.5 corrugations per 1 cm).

[0098] Example 2 differs from Example 1 in that the amount of magnesium hydroxide in the sheath material is adjusted to 80 parts, the amount of red phosphorus is adjusted to 10 parts, and the amount of nano-montmorillonite is adjusted to 8 parts. The pitch of the metal shielding layer is set to 2.5 mm (4 grooves distributed per 1 cm).

[0099] Example 3 differs from Example 1 in that the amount of linear low-density polyethylene in the sheath material is 40 parts, the amount of ethylene-vinyl acetate copolymer is 35 parts, and the amount of magnesium hydroxide is 120 parts. The pitch of the metal shielding layer is set to 3.3 mm (3 grooves distributed per 1 cm).

[0100] Example 4 The difference between this example and Example 1 is that 3 parts of organosilicon lubricant and 2 parts of nano zinc oxide were added to the sheath material, and the nano montmorillonite was organically modified, with an interlayer spacing of 3.2 nm.

[0101] Comparative Example 1: In this comparative example, the cable has a corrugated structure without a metal shielding layer, and the rest of the structure is the same as in Example 1.

[0102] In Comparative Example 2, the sheath material was a conventional halogen-free, low-smoke, flame-retardant polyolefin, free of red phosphorus and nano-montmorillonite, and the rest of the production process was the same as in Example 1.

[0103] The performance of the cables produced in the above embodiments and comparative examples was tested, and the results are shown in Table 1.

[0104] Table 1: Comparison of Cable Performance Test Results

[0105] project Bending radius (times the cable's outer diameter) Fire resistance rating (EN 50399) Sheath tensile strength (MPa) Shielding layer sealing performance (permeability pressure in MPa) Total tobacco production (m²) Example 1 12 B2ca sa1 a1 13.2 0.5 45 Example 2 11 B2ca sa1 a1 13.8 0.5 42 Example 3 13 B2ca sa1 a1 12.8 0.5 40 Example 4 12 B2ca sa1 a1 14.5 0.6 38 Comparative Example 1 20 B2ca sa1 a1 13.1 0.5 46 Comparative Example 2 15 Cca sa2 a2 10.5 0.4 120

[0106] As can be seen from the data in Table 1, the embodiments of the present invention, through specific component ratios and structural design, enable the cable to achieve the B2ca, sa1, and a1 fire resistance standards while maintaining a small bending radius, and the mechanical strength of the sheath and the sealing performance of the shielding layer are both at a high level. Comparative Example 1, due to the lack of a corrugated structure, has a significantly increased bending radius, which is unfavorable for laying in narrow spaces. Comparative Example 2, due to differences in the flame-retardant system, cannot achieve the B2ca fire resistance rating, and its mechanical strength is significantly reduced.

[0107] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A fire-resistant and flame-retardant sheathed cable, characterized in that, The cable, from the inside out, comprises a conductor, an XLPE insulation layer, a wrapping layer, an inner lining layer, a metal shielding layer, and a red polyolefin ST8 sheath layer. The conductor is made of high-purity aluminum wire with a purity of not less than 99.7%, and the surface roughness Ra value of the conductor is less than or equal to 1.6 micrometers; The thickness of the XLPE insulation layer is 2.0 mm to 2.2 mm; The metal shielding layer is a tin-plated steel strip with a thickness of 0.15 mm, and the tin plating layer of the tin-plated steel strip is electroplated; the metal shielding layer has longitudinally overlapping welds, the overlap width of the overlapping welds is 10 mm to 12 mm, and the surface of the metal shielding layer is provided with spiral grooves, the pitch of the grooves is 2.5 mm to 3.3 mm. The thickness of the red polyolefin ST8 sheath layer is 2.0 mm to 3.0 mm. Two purple longitudinal stripes are co-extruded at corresponding positions in the circumferential direction of the sheath layer. The width of the purple longitudinal stripes is 8 mm to 10 mm, and the depth of the stripes embedded in the surface of the sheath layer is 0.2 mm to 0.5 mm.

2. The fire-resistant and flame-retardant sheathed cable according to claim 1, characterized in that, The XLPE insulation layer is made of silane cross-linked polyethylene material. The components of the silane cross-linked polyethylene material include, by weight: 100 parts low-density polyethylene, 1.5 to 2.5 parts vinyltrimethoxysilane, 0.05 to 0.15 parts dicumyl peroxide, and 0.2 to 0.5 parts antioxidant 300. After grafting and granulating the above components to obtain silane-grafted polyethylene material, the silane-grafted polyethylene material is mixed with catalyst masterbatch at a mass ratio of 95:

5.

3. The fire-resistant and flame-retardant sheathed cable according to claim 1, characterized in that, The components for preparing the red polyolefin ST8 sheath layer, by weight, include: 40 to 60 parts of linear low-density polyethylene, 20 to 35 parts of ethylene-vinyl acetate copolymer, 80 to 120 parts of magnesium hydroxide flame retardant, 5 to 10 parts of red phosphorus flame retardant, 3 to 8 parts of nano-montmorillonite, 3 to 5 parts of red masterbatch, and 1 to 2 parts of silane coupling agent KH550.

4. The fire-resistant and flame-retardant sheathed cable according to claim 1, characterized in that, The nano-montmorillonite is an organically modified nano-montmorillonite using hexadecyltrimethylammonium bromide, with an interlayer spacing of 2.5 to 3.5 nm; the magnesium hydroxide flame retardant has an average particle size D50 of 0.8 to 1.5 micrometers and a specific surface area of ​​4 to 8 square meters per gram.

5. A fire-resistant and flame-retardant sheathed cable according to claim 1, characterized in that, The wrapping layer is formed by overlapping water-blocking tape and low-smoke halogen-free high flame-retardant tape, with an overlap rate of 20% to 25%, and the single-layer thickness of the low-smoke halogen-free high flame-retardant tape is 0.18 mm to 0.20 mm; the inner lining layer is a polyolefin inner lining layer with a thickness of 1.8 mm to 2.0 mm.

6. A manufacturing process for a fire-resistant and flame-retardant sheathed cable as described in any one of claims 1 to 5, characterized in that, The method includes the following steps: , characterized in that it includes the following steps: S10: Conductor stranding: Multiple high-purity aluminum wires are stranded using a stranding machine. The stranding pitch is set to 12 to 16 times the outer diameter of the conductor. The stranded conductor is then compacted using a compaction die with a compaction coefficient of 0.90 to 0.

93. S20: Insulation layer extrusion: XLPE insulation material is continuously extruded on the outer surface of the conductor. The barrel temperature of the extruder is set to 120 to 145°C, 150 to 160°C, and 166 to 185°C from the feeding section to the homogenization section, respectively. The die head temperature is set to 190 to 210°C. The extruded wire core is cross-linked by steaming in a steam room at 80 to 95°C for 8 to 12 hours. S30: Wrapping and inner lining processing: Water-blocking tape and low-smoke halogen-free high flame-retardant tape are wrapped and overlapped on the outer surface of the core, and then a polyolefin inner lining layer with a thickness of 1.8mm to 2.0mm is wrapped around it. S40: Metal shielding layer processing: A 0.15mm thick tin-plated steel strip is wrapped around the inner lining layer using a longitudinal wrapping forming machine. The steel strip joints are overlapped and welded using a laser welding machine. The laser power is set to 1500 to 2500W, and the welding speed is 2 to 5 meters per minute. After welding, the steel strip enters a corrugating machine to press out spiral patterns. The corrugating depth is controlled between 0.8mm and 1.2mm. S50: Co-extrusion of the sheath layer: The dual-machine co-extrusion process is adopted. The main extruder extrudes the red polyolefin ST8 sheath material, and the auxiliary extruder simultaneously extrudes the purple polyolefin marking material. The two melts merge in the mold and then cover the outside of the metal shielding layer. The extrusion temperature is controlled at 150 to 180℃, and then enters the cooling water tank for cooling. S60: Finished product inspection and packaging.

7. The manufacturing process of a fire-resistant and flame-retardant sheathed cable according to claim 6, characterized in that: In step S10, the surface of the pressing mold is coated with a diamond-like carbon film with a thickness of 2 to 3 micrometers, and the hardness of the diamond-like carbon film is 2500 to 3000 HV.

8. The manufacturing process of a fire-resistant and flame-retardant sheathed cable according to claim 6, characterized in that: In step S40, the depth of the weld pool at the welding position is controlled between 0.18 mm and 0.25 mm during laser welding, and the width of the weld surface is between 1.2 mm and 1.8 mm; during the welding process, argon gas with a flow rate of 15 to 25 liters per minute is blown into the welding area as a protective gas.

9. The manufacturing process of a fire-resistant and flame-retardant sheathed cable according to claim 6, characterized in that: In step S50, the preparation process of the red polyolefin ST8 sheath material includes: melting and mixing linear low-density polyethylene and ethylene vinyl acetate copolymer at 140 to 160°C for 5 to 10 minutes; adding magnesium hydroxide pretreated with silane coupling agent, red phosphorus flame retardant and nano montmorillonite, heating to 170 to 180°C and continuing to knead for 15 to 20 minutes; finally adding red masterbatch and granulating through a two-stage extruder.

10. The manufacturing process of a fire-resistant and flame-retardant sheathed cable according to claim 6, characterized in that: In step S50, the difference between the melt index of the purple polyolefin labeling material and the melt index of the red polyolefin ST8 sheath material under the test conditions of 190°C and 2.16kg is controlled to be within 1.0g per 10 minutes; the red polyolefin ST8 sheath material is dried before extrusion to make the moisture content less than 0.02%.

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