Anti-wrinkle copper sheathed flexible mineral fire resistant cable and method of processing

Abstract

The present application relates to the technical field of power cable, and discloses a wrinkle-resistant copper sheath flexible mineral fireproof cable and a processing method, the cable comprising: a cable conductor; an insulation layer; inorganic fiber filler; a copper sheath; and an outer sheath. The processing method comprises the following steps: firstly, twisting a plurality of copper wires into the cable conductor; then, coating the conductor with inorganic material and forming an insulated core through a hot pressing process; then, twisting a plurality of insulated cores and filling them with inorganic fiber to form a cable core; then, longitudinally coating the cable core with a copper strip and continuously welding, and then rolling into a corrugated copper sheath; and finally, extruding a low-smoke and halogen-free plastic material outside the copper sheath to form the outer sheath. Through the cable and the processing method, the cable not only has excellent fireproof, low-smoke and halogen-free and anti-mechanical impact performance, but also has excellent flexibility and wrinkle-resistant function, effectively solving the problems of fire safety defects of traditional organic cables and inconvenience of rigid mineral cable installation.

Description

Technical Field

[0001] This invention relates to the field of power cable technology, and in particular to a wrinkle-resistant copper-sheathed flexible mineral fireproof cable and its processing method. Background Technology

[0002] As a key component for energy transmission and distribution and information transmission, power cables play a vital role in modern buildings, public transportation, and industrial facilities. With increasing societal emphasis on safe production and public safety, particularly in densely populated or difficult-to-evacuate locations such as hospitals, tunnels, and high-rise buildings, increasingly stringent requirements are being placed on the safety and reliability of cables under extreme conditions such as fires, especially their inherent fire resistance.

[0003] Currently, there are two main technical solutions on the market. One is traditional cables using organic polymer materials as insulation and sheathing, which are widely used due to their good flexibility. The other is mineral-insulated cables developed to meet stringent fire protection requirements. These cables use inorganic materials as insulation and metal tubing as sheathing, and are used in special applications with extremely high fire resistance requirements.

[0004] However, the aforementioned existing technologies have all revealed shortcomings in application. The inherent material properties of organic insulated cables determine their inherent fire resistance defects; they are prone to combustion at high temperatures and release toxic gases, making it difficult to meet high fire resistance requirements and mechanical impact requirements. On the other hand, while traditional mineral insulated cables possess basic fire resistance, their overall rigid structure results in poor bending performance and difficult installation. This rigid structure not only limits the continuous production length and conductor cross-section of the cable, making it difficult to adapt to the power supply needs of long distances and high currents, but also makes its copper sheath prone to wrinkling when bent.

[0005] Therefore, this invention proposes a wrinkle-resistant copper-sheathed flexible mineral fireproof cable and its processing method to overcome the shortcomings of the prior art. Summary of the Invention

[0006] The purpose of this invention is to provide a wrinkle-resistant copper-sheathed flexible mineral fireproof cable and its processing method, which aims to solve the technical defects of traditional organic insulated cables, such as poor fire resistance, the generation of toxic smoke, and difficulty in meeting mechanical impact requirements, as well as the inconvenience of installation caused by the rigid physical structure of organic insulated cables.

[0007] To achieve the above objectives, the present invention provides the following technical solution: The first aspect of this invention provides a wrinkle-resistant copper-sheathed flexible mineral fire-resistant cable, comprising, from the inside out: a cable conductor, an insulation layer, an inorganic fiber filler, a copper sheath, and an outer sheath. The cable conductor is composed of multiple strands of copper wire twisted together; the copper sheath has a corrugated structure; and the outer sheath is made of a low-smoke, halogen-free plastic material.

[0008] The insulating layer is made of inorganic material comprising the following components in parts by weight: Magnesium oxide: 85-95 parts; Sodium silicate; 5-15 parts; The low-smoke halogen-free plastic material comprises the following components in parts by weight: Polyvinyl acetate: 100 parts; Magnesium hydroxide: 130-160 parts; Zinc borate: 8-15 parts; Vinyltrimethoxysilane: 1-2 parts; Additives: 1.5-2.5 parts.

[0009] As a preferred embodiment of the first aspect of the present invention, the inorganic material is a composite powder with a core-shell structure. Magnesium oxide serves as the core, and silicon dioxide forms the shell coating the surface of the magnesium oxide. This structure enables the two components to achieve uniform distribution at the microscopic level, avoiding the agglomeration of magnesium oxide particles caused by traditional physical blending. Simultaneously, the dense coating of silicon dioxide improves the dielectric properties and thermal shock resistance of the composite powder.

[0010] In a preferred embodiment of the first aspect of this invention, in the low-smoke halogen-free plastic material, the vinyltrimethoxysilane acts as a coupling agent, with one end chemically bonded to the surface hydroxyl groups of magnesium hydroxide and the other end grafted onto the molecular chain of polyethylene vinyl acetate, thereby forming a chemical bond between magnesium hydroxide and polyethylene vinyl acetate. This chemical bond significantly improves the interfacial compatibility between the inorganic flame retardant and the organic resin matrix, allowing the ultra-high filler content of magnesium hydroxide to be uniformly dispersed in polyethylene vinyl acetate, thereby greatly improving the tensile strength, elongation at break, and other mechanical properties of the material, and improving its processing fluidity.

[0011] As a preferred embodiment of the first aspect of the present invention, the stranding pitch of the cable conductor is 9.5-10.5 times the diameter of the cable conductor; the thickness of the insulation layer is 1.4-1.6 mm; and the thickness of the outer sheath is 1.9-2.1 mm.

[0012] As a preferred embodiment of the first aspect of the present invention, the copper sheath is formed by longitudinal wrapping of copper strip, the thickness of the copper sheath is 0.75-0.85mm, and the corrugation depth of the corrugated structure is 2.8-3.2mm, and the pitch is 14-16mm.

[0013] As a preferred embodiment of the first aspect of the present invention, the inorganic fiber filler is an alkali-free glass fiber rope or alkali-free glass fiber tape used to fill the gaps between cable conductors after multiple insulation layers have been wrapped.

[0014] The second aspect of this invention provides a method for processing a wrinkle-resistant copper-sheathed flexible mineral fire-resistant cable, used to prepare the cable described in any of the aforementioned schemes, characterized by comprising the following steps: S1, stranding multiple copper wires to form a cable conductor; S2, covering the outside of the cable conductor with an inorganic material to form an insulation layer, and shaping the formed insulated core by a hot pressing process; S3, stranding multiple insulated cores processed in step S2, and filling the gaps with inorganic fiber filler to form a cable core; S4, longitudinally wrapping the outside of the cable core with copper strip, and continuously welding along the longitudinal seam of the copper strip to form a sealed tubular sheath, and then corrugating the tubular sheath to form a corrugated structure; S5, extruding a low-smoke halogen-free plastic material to cover the outside of the copper sheath to form an outer sheath.

[0015] As a preferred embodiment of the second aspect of the present invention, the hot pressing process in step S2 specifically includes two consecutive stages: first, the insulated wire core is flexibly pre-compacted; then, online sintering is performed. The flexible pre-compacting is carried out by applying a linear pressure of 50-150 N / cm, which aims to initially increase the packing density of the insulating powder. The online sintering temperature is set to 300-400℃, and the online sintering time is 4-10 seconds. This step aims to further solidify the insulating layer to obtain stable mechanical strength and electrical properties.

[0016] As a preferred embodiment of the second aspect of this invention, the preparation process of the inorganic material in step S2 is a specific chemical process for obtaining a core-shell structured powder, specifically including: using a liquid-phase in-situ coating method, dispersing magnesium oxide in water to form a slurry, adding sodium silicate solution dropwise to the slurry, and adjusting the pH of the reaction system with acid. Under these conditions, sodium silicate undergoes a hydrolysis reaction to generate hydrated silica, which is uniformly deposited in-situ on the surface of the magnesium oxide particles to form a coating layer. After washing and drying, the reaction product is subjected to a low-temperature activation treatment at 450-550°C to dehydrate the hydrated silica and convert it into final silica, thereby obtaining the inorganic material with a core-shell structure. This method ensures the uniformity and density of the silica shell layer.

[0017] As a preferred embodiment of the second aspect of the present invention, the preparation process of the low-smoke halogen-free plastic material in step S5 is a specific reactive extrusion process to achieve the interfacial chemical bonding, specifically including: First, dry interfacial chemical activation treatment of the magnesium hydroxide: placing the magnesium hydroxide and the vinyltrimethoxysilane in a high-speed mixer, and using high-speed shearing and frictional heat to raise the material temperature and control it at 105-115℃. This step causes the vinyltrimethoxysilane to undergo hydrolysis and condensation on the surface of the magnesium hydroxide particles, obtaining activated magnesium hydroxide powder with vinylsiloxane grafted on the surface. Subsequently, the aforementioned activated magnesium hydroxide powder, along with the polyethylene vinyl acetate, zinc borate, and additives, are simultaneously fed into a twin-screw extruder for melt compatibilization and in-situ grafting reaction extrusion. The temperature of the reaction zone in the middle and rear section of the twin-screw extruder is set to 180-190℃. In this zone, the vinyl groups on the surface of the magnesium hydroxide activated powder undergo a grafting reaction with the molecular chains of polyethylene vinyl acetate, thereby completing forced dispersion, melt plasticization and interfacial chemical bonding in one step within the extruder, and finally producing the low-smoke halogen-free plastic material through blending extrusion.

[0018] In summary, the present invention has at least one of the following beneficial technical effects: 1. This invention utilizes a liquid-phase in-situ reaction method to prepare inorganic insulating materials, combined with subsequent flexible pre-compaction and online sintering processes, to create an insulating layer with high mechanical strength and a dense structure encasing the stranded copper conductor. This structure solves the technical problem of traditional mineral insulation layers failing under fire and mechanical impact due to powder displacement or insufficient sintering strength, enabling the cable to meet high fire resistance requirements and maintain circuit integrity under impact conditions, thus achieving excellent flexible mineral fire-resistant properties.

[0019] 2. This invention utilizes inorganic fiber filler between the sintered insulation layer and the outer sheath, and seals it with a copper sheath featuring a continuous corrugated structure. This continuous corrugated structure design allows for uniform stress distribution during cable bending, effectively overcoming the technical defect of traditional smooth sheaths that are prone to wrinkling due to stress concentration, thus meeting the requirements for wrinkle prevention. This structural design significantly improves the overall flexibility of the cable, facilitating continuous manufacturing and installation, and meeting the long-distance, high-current power supply needs of modern buildings.

[0020] 3. This invention involves extruding a low-smoke, halogen-free outer sheath with a specific formulation onto the copper sheath. This outer sheath material possesses excellent tensile strength and elongation at break. This design not only provides effective mechanical protection for the internal fire-resistant functional layer, ensuring the physical integrity of the cable during laying and long-term use, but also results in extremely low smoke production during combustion. This multi-layered structure from the inside out collectively ensures that this flexible mineral fire-resistant cable possesses core fire-resistant performance while also exhibiting high mechanical strength and operational safety. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the cable structure of the present invention. Figure 1 ; Figure 2 This is a schematic diagram of the cable structure of the present invention. Figure 2 ; Figure 3 This is a schematic diagram of the processing method of the present invention.

[0022] The components are: 1. Cable conductor; 2. Insulation layer; 3. Inorganic fiber filler; 4. Copper sheath; 5. Outer sheath. Detailed Implementation

[0023] The following is in conjunction with the appendix Figure 1 - Appendix Figure 3 The present invention will be further described in detail below.

[0024] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0025] Main ingredients: Magnesium oxide, CAS: 1309-48-4; Sodium silicate, CAS: 1344-09-8; Polyvinyl acetate, CAS: 24937-78-8; Magnesium hydroxide, CAS: 1309-42-8; Zinc borate, CAS: 1332-07-6; Vinyltrimethoxysilane, CAS: 2768-02-7; Additives: Antioxidant 1010, CAS: 6683-19-8; Antioxidant 168, CAS: 31570-04-4; Vinyl bis-stearamide, CAS: 110-30-5; Copper materials for conductors: T1 oxygen-free copper rod, conforming to GB / T 3952.1-2008 standard; Copper material for copper sheath: T2 electrical copper strip, conforming to GB / T 2059-2017 standard.

[0026] See attached document Figure 1 and Figure 2 .

[0027] This invention provides a wrinkle-resistant copper-sheathed flexible mineral fire-resistant cable. Referring to the accompanying drawings, the cable comprises, from the inside out, a cable conductor 1, an insulation layer 2, a copper sheath 4, and an outer sheath 5. When the cable has a multi-core structure, the cable core, formed by stranding multiple cores wrapped in the insulation layer 2, also includes an inorganic fiber filler 3 for filling the gaps between the cores.

[0028] Cable conductor 1 is the conductive part of the cable, which is formed by stranding multiple copper wires together. In one specific embodiment, to ensure the flexibility and stability of the cable conductor, the stranding pitch is set to 9.5-10.5 times the final outer diameter of cable conductor 1.

[0029] Insulation layer 2 is uniformly wrapped around the outside of cable conductor 1, serving as electrical insulation and high-temperature isolation. This insulation layer 2 is made of inorganic materials, ensuring the cable's fire resistance. In one specific embodiment, the thickness of insulation layer 2 is 1.4-1.6 mm. The inorganic material can be electrical-grade magnesium oxide or mica tape.

[0030] When manufacturing multi-core cables, multiple independent cores, each with an insulation layer 2, are first stranded together. During the stranding process, inorganic fiber filler 3 is used to fill the gaps between the cores, resulting in a full and rounded cable core structure. In one specific embodiment, the inorganic fiber filler 3 can be alkali-free glass fiber rope or alkali-free glass fiber tape, which possesses excellent temperature resistance and insulation properties.

[0031] The copper sheath 4 covers the outside of the cable core, serving functions such as sealing, waterproofing, protecting the internal structure, and grounding. It is a metal sheath formed by longitudinally wrapping copper strip around the outside of the cable core and continuously welding it along its longitudinal joint. To achieve cable flexibility and prevent wrinkling during bending, the surface of the copper sheath 4 is processed into a continuous corrugated structure. In one specific embodiment, the copper strip used to manufacture the copper sheath 4 has a thickness of 0.75-0.85 mm, the corrugation depth of the corrugated structure is 2.8-3.2 mm, and the pitch is 14-16 mm.

[0032] The outer sheath 5 is the outermost layer of the cable, providing final mechanical and environmental protection. This outer sheath 5 is made of low-smoke, halogen-free plastic material and is extruded over the copper sheath 4. The thickness of the outer sheath 5 is 1.9-2.1 mm.

[0033] See attached document Figure 3 .

[0034] Preparation of core materials: Example 1: Preparation of inorganic materials for insulating layers (by parts by mass): 2000 parts of deionized water were added to a reaction vessel, and stirring was started. 85 parts of magnesium oxide were added and dispersed evenly to form a slurry. While stirring, a sodium silicate solution containing an effective silica content equivalent to 5 parts was slowly added dropwise, and the pH of the reaction system was maintained at 6.0 by adding dilute sulfuric acid dropwise. After the addition was complete, the reaction continued for 1 hour. The reaction product was washed until neutral, filtered, and dried at 120°C for 8 hours. Finally, the dried powder was subjected to low-temperature activation treatment at 450°C for 2 hours in a muffle furnace, cooled, and sieved to obtain inorganic material powder A.

[0035] Example 2: Preparation of inorganic materials for insulating layers (by parts by mass): 2000 parts of deionized water were added to a reaction vessel, and stirring was started. 95 parts of magnesium oxide were added and dispersed evenly to form a slurry. While stirring, a sodium silicate solution containing an effective silica content equivalent to 15 parts was slowly added dropwise, and the pH of the reaction system was maintained at 6.5 by adding dilute sulfuric acid dropwise. After the addition was complete, the reaction continued for 1 hour. The reaction product was washed until neutral, filtered, and dried at 120°C for 8 hours. Finally, the dried powder was subjected to low-temperature activation treatment at 550°C for 2 hours in a muffle furnace, cooled, and sieved to obtain inorganic material powder B.

[0036] Example 3: Preparation of low-smoke halogen-free plastic material for outer sheath: By weight, 130 parts magnesium hydroxide and 1 part vinyltrimethoxysilane were placed in a high-speed mixer. High-speed shear stirring was started, and the material temperature was raised to 105°C by frictional heat. The mixture was then kept at this temperature and stirred for 15 minutes to obtain surface-grafted activated magnesium hydroxide powder.

[0037] The above-mentioned activated magnesium hydroxide powder, along with 100 parts of polyethylene vinyl acetate, 8 parts of zinc borate, and an additive consisting of 0.5 parts of antioxidant 1010, 0.5 parts of antioxidant 168, and 0.5 parts of vinyl bis-stearamide, were simultaneously fed into a twin-screw extruder. The temperatures of each zone of the twin-screw extruder were set so that the temperature of the rear reaction zone was 180°C, and melt compatibilization and in-situ grafting reaction extrusion were carried out. After cooling and pelletizing, low-smoke halogen-free plastic material granules C were obtained.

[0038] Example 4: Preparation of low-smoke halogen-free plastic material for outer sheath: By weight, 160 parts of magnesium hydroxide and 2 parts of vinyltrimethoxysilane were placed in a high-speed mixer. High-speed shear stirring was started, and the material temperature was raised to 115°C by frictional heat. The mixture was then kept at this temperature and stirred for 15 minutes to obtain surface-grafted activated magnesium hydroxide powder.

[0039] The above-mentioned activated magnesium hydroxide powder, along with 100 parts of polyethylene vinyl acetate, 15 parts of zinc borate, and an additive consisting of 1.0 part of antioxidant 1010, 0.5 parts of antioxidant 168, and 1.0 part of vinyl bis-stearamide, were simultaneously fed into a twin-screw extruder. The temperatures of each zone of the twin-screw extruder were set so that the temperature of the rear reaction zone was 190°C, and melt compatibilization and in-situ grafting reaction extrusion were carried out. After cooling and pelletizing, low-smoke halogen-free plastic material granules D were obtained.

[0040] Example 5: A processing method for a wrinkle-resistant copper-sheathed flexible mineral fireproof cable.

[0041] (S1) Conductor stranding: After drawing the T1 oxygen-free copper rod to the specified diameter, take 19 strands of copper wire and strand them at a spacing of 9.5 times the total conductor diameter to form a conductor with a nominal cross-sectional area of ​​25mm². 2 The cable conductor.

[0042] (S2) Insulation layer preparation: Inorganic material powder A (prepared from Example 1) is coated on the outside of the cable conductor using a powder coating device to form an insulation layer with a thickness of 1.4 mm. Subsequently, a linear pressure of 50 N / cm is applied to the outside of the cable conductor for flexible pre-compaction using a hot pressing device; then, the conductor is sintered in an online sintering furnace at 300°C for 10 seconds to form an insulated wire core.

[0043] (S3) Cable core assembly: Take 3 insulated wire cores that have been processed in step S2, twist them together at a certain pitch, and simultaneously fill the gaps with alkali-free glass fiber tape to form a compact cable core.

[0044] (S4) Copper sheath preparation: On the outside of the cable core, a 0.75mm thick T2 electrical copper strip is longitudinally wrapped using a copper strip longitudinal wrapping forming machine, and argon arc welding is used to continuously weld along the longitudinal seam to form a sealed tubular sheath. Subsequently, the tubular sheath is corrugated using a corrugating device to form a corrugated structure with a corrugation depth of 2.8mm and a pitch of 14mm.

[0045] (S5) Outer sheath extrusion: Low-smoke halogen-free plastic material particles C (prepared from Example 3) are plasticized and extruded in a single screw extruder and extruded to cover the outside of the corrugated copper sheath to form an outer sheath with a thickness of 1.9 mm. After cooling and shaping, the final cable product is obtained.

[0046] Example 6: A processing method for a wrinkle-resistant copper-sheathed flexible mineral fireproof cable.

[0047] (S1) Conductor stranding: After drawing the T1 oxygen-free copper rod to the specified diameter, take 19 strands of copper wire and strand them at a spacing of 10.5 times the total conductor diameter to form a conductor with a nominal cross-sectional area of ​​25mm². 2 The cable conductor.

[0048] (S2) Insulation layer preparation: Inorganic material powder B (prepared from Example 2) is coated on the outside of the cable conductor using a powder coating device to form an insulation layer with a thickness of 1.6 mm. Subsequently, a linear pressure of 150 N / cm is applied to the outside of the cable conductor for flexible pre-compaction using a hot pressing molding device; then, the conductor is sintered in an online sintering furnace at 400°C for 4 seconds to form an insulated wire core.

[0049] (S3) Cable core assembly: Take 3 insulated wire cores that have been processed in step S2, twist them together at a certain pitch, and simultaneously fill the gaps with alkali-free glass fiber tape to form a compact cable core.

[0050] (S4) Copper sheath preparation: On the outside of the cable core, a 0.85mm thick T2 electrical copper strip is longitudinally wrapped using a copper strip longitudinal wrapping forming machine, and argon arc welding is used to continuously weld along the longitudinal seam to form a sealed tubular sheath. Subsequently, the tubular sheath is corrugated using a corrugating device to form a corrugated structure with a corrugation depth of 3.2mm and a pitch of 16mm.

[0051] (S5) Outer sheath extrusion: Low-smoke halogen-free plastic material particles D (prepared from Example 4) are plasticized and extruded in a single screw extruder and extruded to cover the outside of the corrugated copper sheath to form an outer sheath with a thickness of 2.1 mm. After cooling and shaping, the final cable product is obtained.

[0052] Comparative Example 1: Compared with Example 6, the difference is that in step S2, after coating the outside of the cable conductor with inorganic material powder B, the flexible pre-compaction and online sintering hot pressing process is not performed, and the process proceeds directly to step S3. All other steps are the same.

[0053] Comparative Example 2: Compared with Example 6, the difference is that in step S2, the insulating layer material used for coating is replaced with conventional electrical-grade magnesium oxide powder, instead of the inorganic material powder B prepared in Example 2. All other aspects are the same.

[0054] Comparative Example 3: Compared with Example 6, the difference is that the insulating layer material used was prepared by a traditional physical blending method (i.e., mechanically mixing magnesium oxide powder and fumed silica powder in equal amounts as in Example 2), instead of the liquid-phase in-situ coating method described in Example 2. All other aspects are the same.

[0055] Comparative Example 4: Compared with Example 6, the difference is that in step S5, the material used for extruding the outer sheath is replaced with conventional commercially available low-smoke halogen-free polyolefin cable material, instead of the low-smoke halogen-free plastic material particles D prepared in Example 4. All other aspects are the same.

[0056] Comparative Example 5: Compared with Example 6, the difference is that the insulating layer material used was prepared by physically blending magnesium oxide powder in the same amount as the formulation in Example 2 with solid sodium silicate powder, instead of using the liquid-phase in-situ reaction method described in Example 2. All other aspects are the same.

[0057] Comparative Example 6: Compared with Example 6, the difference is that in step S4, after forming the sealed tubular sheath, no subsequent corrugating process is performed to form a corrugated structure, resulting in a smooth copper sheath. All other aspects are the same.

[0058] Test Example 1: Bending and Wrinkle Resistance Test.

[0059] To verify the bending performance and sheath wrinkle resistance of the cable products prepared in the above embodiments and the comparative products, the following methods were used for testing.

[0060] 1. Preparation and Conditioning of Test Samples: Samples with a length of not less than 2 meters were cut from the finished cables of Examples 5, 6, Comparative Example 1, and Comparative Example 6. All samples were placed in an environment with a temperature of 20℃±5℃ and a relative humidity of 40%-60% for at least 24 hours.

[0061] 2. Bending Test Procedure This test shall be performed in accordance with the bending test method specified in GB / T12706.1-2020.

[0062] (1) Install the sample on the bending test device. The diameter of the cylindrical mandrel of the test device is set to 10 times the outer diameter of the cable sample being tested.

[0063] (2) Start the device, bend the sample around the cylinder by 90 degrees, return to the initial position, and then bend it in the opposite direction by 90 degrees to return to the initial position. This process is counted as one cycle, and a total of 3 cycles are executed.

[0064] (3) After the bending process is completed, remove the sample and inspect the outer surface of the copper sheath of the bent part of the sample under diffused natural light or equivalent light source with normal vision, and record whether there are any visible local wrinkles, folds or cracks.

[0065] 3. Voltage test procedure after bending: (1) Immerse the entire sample that has undergone the above bending test into a metal container filled with water. The water temperature should be maintained at 20℃±5℃, and both ends of the sample should be at least 200mm above the water surface. The soaking time is 1 hour.

[0066] (2) Using a power frequency withstand voltage tester, apply an AC voltage of 3.5kV between the cable conductor and the water (connected via a grounded container). The voltage rises smoothly from zero to the set value and is maintained for 60 seconds.

[0067] (3) Monitor the current in the test circuit during voltage application. If breakdown occurs, the device will automatically disconnect the voltage and issue an indication. Record whether the sample passes the test or breaks down.

[0068] Test data are shown in Table 1: Table 1: Test data on bending and wrinkle resistance.

[0069] The test results above show that the copper sheath of the cables in Examples 5 and 6 did not wrinkle and maintained electrical integrity after bending, while Comparative Examples 1 and 6 showed sheath wrinkles or electrical breakdown.

[0070] This performance difference stems from a specific combination of structure and process. The copper sheath of the cable in this example has a continuous corrugated structure, which effectively disperses stress during bending, preventing localized yielding and wrinkling caused by stress concentration in a smooth sheath (Comparative Example 6). Simultaneously, the flexible pre-compacting and in-line sintering processes create a dense, self-supporting monolithic layer of inorganic insulating powder. This structure maintains its continuity and thickness uniformity during cable bending. In contrast, Comparative Example 1, which was not thermoformed, has a loose powder insulation layer. During bending, the particles shift, creating electrical weak points and leading to voltage breakdown.

[0071] Measurable performance parameters confirm that by combining a corrugated metal sheath with a thermoformed inorganic insulation layer, the technical problems of sheath wrinkling and insulation failure during cable bending are solved.

[0072] Test Example 2: Fire resistance, mechanical impact resistance and circuit integrity test.

[0073] To verify the circuit integrity of the cable products prepared in the above embodiments and the comparative products under fire and mechanical impact conditions, the following methods were used for testing.

[0074] 1. Preparation and Installation of Test Samples: Cut samples with lengths of 1.2 to 1.5 meters from the finished cables of Examples 5-6 and Comparative Examples 1-3 and 5-6. Install each sample horizontally on a bracket inside a BS 6387 standard test chamber. Connect one end of the sample to a three-phase 400V AC power supply, and the other end to a set of 3A fuses and indicator lights to form a loop for monitoring circuit continuity.

[0075] 2. Test Procedure This test is strictly performed in accordance with the three categories C, W and Z in BS 6387:2013 standard.

[0076] (1) Class C (Fire resistance test): Start the ribbon propane burner located in the middle of the sample, adjust and maintain the flame temperature at 950℃ (±40℃). Apply flame to the sample at this temperature while applying the rated voltage, and continue burning for 180 minutes.

[0077] (2) Class W (Fire Resistance Test with Spray): Adjust and maintain the flame temperature at 650℃ (±40℃), apply the flame to the sample for 15 minutes, and while maintaining the flame, start the spray head located above the sample at a rate of 0.25 L / m. 2 A flow rate of ·s was used to spray water onto the sample. The test lasted for 15 minutes under the combined effects of flame and water spray.

[0078] (3) Class Z (Fire Resistance and Mechanical Impact Test): The flame temperature is adjusted and maintained at 950℃ (±40℃). While the flame is applied to the sample, the mechanical impact device is activated. The device impacts the ladder supporting the sample once every 30 seconds (±1 second). The test lasts for 15 minutes under the combined action of flame and impact.

[0079] 3. Result Judgment: Throughout the C, W, and Z category tests, the circuit integrity is determined by observing the status of the indicator lights. If the indicator lights remain illuminated and the fuses in the circuit do not blow, the sample is considered to have passed that category of the test. If the indicator lights go out or the fuses blow at any point, the test is considered a failure, and the failed test category is recorded.

[0080] The test data is shown in Table 2.

[0081] Table 2: Test data on fire resistance, mechanical impact resistance and circuit integrity. Example 5 pass Example 6 pass Comparative Example 1 Failed (failed in Z-category test) Comparative Example 2 Failed (failed in Z-category test) Comparative Example 3 Failed (failed in Z-category test) Comparative Example 5 Failed (failed in Category C test) Comparative Example 6 pass

[0082] Test results show that the cables of Examples 5 and 6, and Comparative Example 6, passed all tests of BS 6387 for fire resistance, spraying, and impact. In contrast, Comparative Examples 1, 2, and 3 failed in the impact test, while Comparative Example 5 failed in the pure combustion test.

[0083] This performance difference reveals the synergistic effect of material preparation and molding processes. Comparative Example 1, lacking hot pressing, experienced electrical breakdown due to displacement of its loose powder under mechanical impact. Comparative Examples 2 and 3, although hot-pressed, lacked effective sintering aids in their materials (conventional magnesium oxide or physical blends), resulting in sintered bodies with insufficient mechanical strength, making them unable to withstand impact and thus prone to failure. Comparative Example 5, due to the addition of low-melting-point components, melted at 950°C, destroying its insulating structure.

[0084] The cable in this example passed testing because it employed a specific combination of a liquid-phase in-situ reaction method and a hot-pressing process. The former forms a uniform silica coating layer on the surface of magnesium oxide particles. In the subsequent hot-pressing process, this coating layer acts as a high-temperature sintering aid, promoting the formation of strong sintering necks between particles, ultimately resulting in a high-mechanical-strength, structurally stable integral insulation layer. This structure is sufficient to withstand the combined effects of high temperatures and mechanical impact, thus solving the technical problem of cable insulation failure due to structural damage during fires.

[0085] Test Example 3: Smoke density test.

[0086] To verify the smoke generation performance of the outer sheath of the cable products prepared in the above embodiments and the comparative products under combustion conditions, the following methods were used for testing.

[0087] 1. Preparation of Test Samples: Samples with a length of 1.0 meter (±5 mm) were cut from the finished cables of Examples 5, 6, and Comparative Example 4. All samples were conditioned for at least 16 hours in an environment with a temperature of 23℃±2℃ and a relative humidity of 50%±5% before testing.

[0088] 2. Test Apparatus and Environmental Testing: The test was conducted in a 3-meter cubic smoke density test chamber constructed in accordance with GB / T 17651.2-1998 (equivalent to IEC 61034-2). The test chamber had black inner walls and was equipped with a sealed door, an optical system (consisting of a white light source and a photodetector), a fan, and an annular combustion pan for placing the samples.

[0089] 3. Testing steps: (1) Place the annular combustion pan containing 1 liter of industrial alcohol at the bottom center of the test chamber.

[0090] (2) Place the cable sample to be tested horizontally 70mm±10mm above the combustion pan.

[0091] (3) Close the test chamber door, turn on the internal fan to mix the air inside the chamber evenly, and then turn off the fan. Calibrate the optical path system to ensure that the initial light transmittance is 100%.

[0092] (4) Ignite the alcohol in the combustion plate.

[0093] (5) At the start of the experiment, the data acquisition system continuously records the light intensity received by the photoelectric receiver at intervals of no more than 5 seconds and converts it into light transmittance.

[0094] (6) The test shall continue for 40 minutes or until the light transmittance reaches a stable minimum value. Record the lowest light transmittance value measured during the entire test.

[0095] The test data is shown in Table 3.

[0096] Table 3: Smoke density test data. Example 5 73.8 Example 6 76.1 Comparative Example 4 22.4

[0097] The quantitative data from the above test results show that, under the same combustion conditions, the minimum light transmittance measured for the cable samples of Examples 5 and 6 is significantly higher than that of the cable sample of Comparative Example 4. Higher light transmittance corresponds to lower smoke concentration, revealing a performance difference in the combustion smoke generation characteristics of the outer sheath materials of the two samples.

[0098] The performance difference stems from the different components of the outer sheath material and their mechanisms of action during combustion. In the low-smoke halogen-free plastic materials used in Examples 5 and 6, the magnesium hydroxide in the formulation undergoes endothermic decomposition upon heating, releasing water of crystallization. This process, on the one hand, slows down the combustion rate of the polymer substrate by absorbing heat, and on the other hand, the released water vapor dilutes the concentration of combustible gases and smoke particles in the air. Simultaneously, zinc borate in the formulation acts as a synergistic charring agent, promoting the dehydration and carbonization of the polymer substrate during combustion, forming a dense char layer.

[0099] This char layer acts as a physical barrier, effectively isolating external oxygen from contact with internal unburned materials and inhibiting the escape of combustible volatiles, thereby further reducing smoke generation. In contrast, the conventional low-smoke halogen-free polyolefin material used in Comparative Example 4, while possessing some smoke-suppressing ability, has a relatively loose char layer structure or low char-forming efficiency during combustion, resulting in limited smoke suppression. Therefore, the specific outer sheath material described in this technical solution achieves lower smoke generation under combustion conditions through the synergistic effect of decomposition heat absorption, water vapor dilution, and efficient char formation.

[0100] Test Example 4: Crush Resistance Test.

[0101] To verify the structural integrity of the cable products and comparative products prepared in the above embodiments when subjected to radial pressure, the following steps were performed in accordance with the relevant methods in GB / T 13033.1-2007.

[0102] 1. Preparation of test samples: Samples with a length of 300 mm were cut from the finished cables of Examples 5, 6 and Comparative Example 6. All samples were placed in an environment at a temperature of 20℃±5℃ for at least 3 hours before testing.

[0103] 2. Test Setup and Configuration: The test is conducted on a universal testing machine. The machine is equipped with two parallel steel pressure plates with a width of not less than 100 mm. An insulation resistance tester is also provided for real-time monitoring of the electrical condition between the cable conductor and the metal sheath.

[0104] 3. Testing steps: (1) Place the cable sample horizontally at the center of the lower pressure plate of the testing machine.

[0105] (2) Connect the two test terminals of the insulation resistance tester to the conductor and copper sheath of the sample, respectively.

[0106] (3) Start the universal testing machine. The upper platen moves downward at a constant speed of 5 mm / min (±1 mm / min) to apply radial pressure to the sample.

[0107] (4) During the pressurization process, continuously monitor the applied pressure value and the reading of the insulation resistance tester.

[0108] (5) When the reading of the insulation resistance tester drops sharply or electrical continuity occurs between the conductor and the copper sheath, immediately stop the test machine and record the pressure value displayed by the test machine at this time. This value is recorded as the crush resistance of the sample.

[0109] (6) Test three samples of each type of cable repeatedly and take the arithmetic mean as the final result.

[0110] The test data is shown in Table 4.

[0111] Table 4: Test data on crush resistance performance.

[0112] The quantitative data from the above test results show that the cable samples of Examples 5 and 6 can withstand significantly higher crushing forces than the cable sample of Comparative Example 6. This difference directly reflects the difference in the radial mechanical pressure resistance performance of different sheath structures.

[0113] This performance difference stems from the geometry of the metal sheath. The copper sheaths of Examples 5 and 6 have a continuous corrugated structure. When radial pressure is applied to the cable, this corrugated structure, through the geometry of its crests and troughs, disperses the concentrated load axially. This structure, similar to an arch, provides additional structural support and increases the sheath's resistance to deformation. Therefore, a greater external force is required to cause sufficient deformation in the sheath, which in turn compresses the inner insulation layer until its electrical performance fails.

[0114] In contrast, Comparative Example 6 uses a smooth tubular sheath. Under radial pressure, this structure directs the load to the pressure point, lacking an effective stress dispersion mechanism. The smooth tubular wall is more prone to localized flattening or elliptic deformation under pressure, causing the pressure to be rapidly and concentratedly transmitted to the internal insulation layer, leading to its collapse at relatively low pressure levels and resulting in an electrical short circuit between the conductor and the sheath. These measurable performance parameters indicate that the specific design of incorporating a corrugated structure on the metallic sheath is a direct solution to the technical problem of insufficient radial crush resistance in smooth-sheathed cables.

[0115] Test Example 5: Mechanical performance test of the outer sheath.

[0116] To verify the mechanical properties of the outer sheath material of the cable products prepared in the above embodiments and the comparative product, the following methods were used for testing in accordance with GB / T2951.11-2008.

[0117] 1. Preparation of test samples: (1) Take a section from each of the finished cables of Example 5, Example 6 and Comparative Example 4.

[0118] (2) Cut along the cable axis and peel off the outer sheath, taking care to avoid damaging the surface of the sheath.

[0119] (3) Using a standard cutter, punch out dumbbell-shaped specimens from the flat sheath. Make sure the length of the effective test section of the specimen is aligned with the axial direction of the cable.

[0120] (4) Use a thickness gauge to measure the thickness and width at at least three points in the narrow section in the middle of the dumbbell-shaped specimen, and calculate the average value to determine the initial cross-sectional area of ​​the specimen.

[0121] 2. The test setup and environmental tests were conducted on an electronic tensile testing machine. The ambient temperature was controlled at 23℃±2℃.

[0122] 3. Testing steps: (1) Clamp both ends of the dumbbell-shaped specimen in the upper and lower clamps of the tensile testing machine, ensuring that the force axis of the specimen coincides with the center line of the clamp. Mark the initial gauge length within the gauge spacing of the specimen.

[0123] (2) Start the tensile testing machine and apply a tensile load to the specimen at a constant speed of 250 mm / min (±50 mm / min).

[0124] (3) The data acquisition system of the testing machine synchronously records the tensile load and the elongation of the gauge length until the specimen is broken.

[0125] (4) Record the maximum tensile load and gauge length at the time of fracture when the specimen breaks.

[0126] (5) Calculate the tensile strength of the material based on the recorded maximum tensile load and the initial cross-sectional area of ​​the specimen. Calculate the elongation at break of the material based on the recorded gauge length at fracture and the initial gauge length.

[0127] The test data is shown in Table 5. Table 5: Test data of mechanical properties of the outer sheath. Example 5 12.8 415 Example 6 13.1 432 Comparative Example 4 8.9 276

[0128] The quantitative data from the above test results show that the outer sheath materials of Examples 5 and 6 have significantly higher tensile strength and elongation at break than the outer sheath material of Comparative Example 4. This performance difference directly reflects the decisive influence of different sheath material formulations on their physical and mechanical properties.

[0129] The performance difference mainly stems from the interfacial bonding state between the components within the material system. In the outer sheath materials of Examples 5 and 6, an ethylene-vinyl acetate copolymer grafted with maleic anhydride was added as a compatibilizer. The polar functional groups (maleic anhydride) in the compatibilizer molecular chain can undergo esterification or form hydrogen bonds with the surface of the inorganic flame retardant (magnesium hydroxide), thereby establishing a strong interfacial layer between the inorganic filler and the polymer matrix (EVA). This interfacial structure can effectively transfer stress from the matrix to the high-strength inorganic filler when the polymer is subjected to stress and deformation, avoiding stress concentration and premature interfacial debonding.

[0130] In contrast, the conventional low-smoke halogen-free polyolefin material used in Comparative Example 4 primarily involves a physical mixture between the filler and the polymer matrix, resulting in weak interfacial bonding. When the material is subjected to tension, stress is difficult to transfer effectively, and microcracks easily form and rapidly propagate at the matrix-filler interface, leading to material fracture at relatively low stress levels and with minimal deformation. Therefore, this technical solution improves the interfacial compatibility between the inorganic filler and the polymer matrix by introducing a specific compatibilizer. This is an effective way to solve the technical problem of decreased mechanical properties in highly filled flame-retardant materials, ultimately yielding a sheath material with high tensile strength and elongation at break.

Claims

1. A wrinkle-resistant copper-sheathed flexible mineral fire-resistant cable, characterized in that, From the inside out, it includes: The cable conductor is made of multiple strands of copper wire twisted together. An insulating layer, wherein the insulating layer is made of inorganic material; Inorganic fiber filler; A copper sheath, wherein the copper sheath has a corrugated structure; The outer sheath is made of low-smoke halogen-free plastic material; The inorganic material comprises the following components in parts by mass: Magnesium oxide: 85-95 parts; Sodium silicate: 5-15 parts; The low-smoke halogen-free plastic material comprises the following components in parts by weight: Polyvinyl acetate: 100 parts; Magnesium hydroxide: 130-160 parts; Zinc borate: 8-15 parts; Vinyltrimethoxysilane: 1-2 parts; Additives: 1.5-2.5 parts; The preparation process of the inorganic material includes: Magnesium oxide was dispersed in water to form a slurry using a liquid-phase in-situ coating method, and sodium silicate solution was added dropwise and reacted under acidic conditions. The reaction product was washed and dried, and then subjected to low-temperature activation treatment at 450-550℃ to obtain the inorganic material with a core and shell structure, wherein the inorganic material is in powder form. The preparation process of the low-smoke halogen-free plastic material includes: First, magnesium hydroxide is subjected to dry interfacial chemical activation treatment: magnesium hydroxide and vinyltrimethoxysilane are placed in a high-speed mixer, and the material temperature is raised and controlled at 105-115℃ by high-speed shearing and frictional heat to obtain activated magnesium hydroxide powder with vinylsiloxane grafted on the surface. Subsequently, magnesium hydroxide activated powder, polyethylene vinyl acetate, zinc borate, and additives are simultaneously fed into a twin-screw extruder for melt compatibilization and in-situ grafting reaction extrusion. The temperature of the reaction zone in the middle and later sections of the twin-screw extruder is 180-190℃. Finally, the low-smoke halogen-free plastic material is obtained by blending and extrusion.

2. The anti-wrinkle copper-sheathed flexible mineral fire-resistant cable according to claim 1, characterized in that, The stranding pitch of the cable conductor is 9.5-10.5 times the diameter of the cable conductor; the thickness of the insulation layer is 1.4-1.6 mm; and the thickness of the outer sheath is 1.9-2.1 mm.

3. The anti-wrinkle copper-sheathed flexible mineral fire-resistant cable according to claim 1, characterized in that, The copper sheath is formed by longitudinally wrapping copper strips, the thickness of the copper sheath is 0.75-0.85mm, and the corrugation depth of the corrugated structure is 2.8-3.2mm, with a pitch of 14-16mm.

4. The anti-wrinkle copper-sheathed flexible mineral fire-resistant cable according to claim 1, characterized in that, The inorganic fiber filler is an alkali-free glass fiber rope or alkali-free glass fiber tape used to fill the gaps between cable conductors after multiple insulation layers have been wrapped.

5. A method for processing a wrinkle-resistant copper-sheathed flexible mineral fire-resistant cable, used to prepare a wrinkle-resistant copper-sheathed flexible mineral fire-resistant cable as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Twist multiple copper wires together to form a cable conductor, and crimp the ends of the cable conductor to fix them. S2. An inorganic material is wrapped around the outside of the cable conductor to form an insulation layer, and the insulated core is formed by hot pressing. S3. Twist together multiple insulated wire cores processed in step S2, and fill the gaps with the inorganic fiber filler to form a cable core. S4. On the outside of the cable core, a copper strip is longitudinally wrapped and argon arc welding is used to continuously weld along the longitudinal seam of the copper strip to form a sealed tubular sheath. The tubular sheath is then corrugated to form a corrugated structure. S5. Extruding low-smoke halogen-free plastic material to cover the outside of the copper sheath, forming an outer sheath.

6. The processing method of a wrinkle-resistant copper-sheathed flexible mineral fire-resistant cable according to claim 5, characterized in that, In step S2, the hot pressing process specifically includes: First, the insulated wire core is flexibly pre-compacted; Then, online sintering is performed.

7. The processing method of a wrinkle-resistant copper-sheathed flexible mineral fire-resistant cable according to claim 6, characterized in that, The flexible pre-compression is achieved by applying a linear pressure of 50-150 N / cm; The heating temperature for online sintering is 300-400℃, and the online sintering time is 4-10 seconds.

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