Anti-wrinkle copper sheath flexible mineral fireproof cable and processing method thereof

Abstract

The invention relates to the technical field of power cables, and discloses an anti-wrinkle copper sheath flexible mineral fireproof cable and a processing method thereof. An insulating layer; an inorganic fiber filler; a copper sheath; and an outer sheath. The processing method comprises the following steps: firstly, stranding a plurality of strands of copper wires into a cable conductor; coating an inorganic material outside the conductor and forming an insulated wire core through a hot pressing process; a plurality of insulating wire cores are twisted and filled with inorganic fibers to form a cable core; secondly, longitudinally coating a copper strip outside the cable core, continuously welding the copper strip, and then rolling the copper strip into a corrugated copper sheath; and finally, a low-smoke halogen-free plastic material is extruded outside the copper sheath to form an outer sheath. Through the cable and the processing method, the cable not only has excellent fireproof, low-smoke, halogen-free and mechanical impact-resistant performances, but also has excellent flexibility and wrinkle-resistant functions, and effectively solves the problems of fireproof safety defects of a traditional organic cable and inconvenience in installation of a rigid mineral cable.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power cable, in particular to a wrinkle-resistant copper sheath flexible mineral fireproof cable and processing method. BACKGROUND

[0002] As a key component of energy transmission and information transmission, power cable plays a vital role in modern buildings, public transportation and industrial facilities. With the increasing emphasis on safety production and public safety, especially in hospitals, tunnels, high-rise buildings and other places where people are densely populated or difficult to evacuate, the safety and reliability of cables under extreme conditions, especially their inherent fireproof performance, are increasingly demanding.

[0003] Currently, there are two technical solutions on the market. One is the traditional cable with organic polymer materials as insulation and sheath, which is widely used in most applications due to its good flexibility. The second is the mineral insulated cable developed to meet the stringent fireproof requirements. This type of cable uses inorganic materials as insulation and metal pipes as sheath, which is applied to special occasions with extremely high fireproof requirements.

[0004] However, the above existing technologies have exposed deficiencies in application. The material nature of organic insulated cable determines that its fireproof performance has defects, it is easy to burn and release toxic gases at high temperatures, and it is difficult to meet the requirements of high fireproof grade and mechanical impact. On the other hand, although the traditional mineral insulated cable has basic fireproof performance, its overall structure is rigid, which leads to poor bending performance and difficult installation and construction. This rigid structure not only limits the continuous production length and conductor cross section of the cable, making it difficult to meet the power supply requirements of long distance and large current, but also makes the copper sheath prone to wrinkle when bending.

[0005] Therefore, the present application proposes a wrinkle-resistant copper sheath flexible mineral fireproof cable and processing method to solve the deficiencies of the prior art. SUMMARY

[0006] The purpose of the present application is to provide a wrinkle-resistant copper sheath flexible mineral fireproof cable and processing method, which aims to solve the technical defects of poor fireproof performance of traditional organic insulated cable, generation of toxic smoke and difficulty in meeting mechanical impact requirements, and overcome the inconvenience of installation caused by the rigid physical structure of organic insulated cable.

[0007] To achieve the above purpose, the present application is realized by the following technical scheme: The present application provides a wrinkle-resistant copper sheath flexible mineral fireproof cable, which comprises, from inside to outside, 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; the copper sheath is provided with a corrugated structure; and the outer sheath is made of low-smoke and halogen-free plastic material.

[0008] The inorganic material used in the insulation layer comprises the following components by mass fraction: Magnesium oxide: 85-95 parts; Sodium silicate: 5-15 parts; The low-smoke halogen-free plastic material comprises the following components by mass fraction: Polyvinyl acetate: 100 parts; Magnesium hydroxide: 130-160 parts; Zinc borate: 8-15 parts; Vinyl trimethoxysilane: 1-2 parts; Auxiliary agent: 1.5-2.5 parts.

[0009] As a preferred technical solution of the first aspect of the present application, the inorganic material is a composite powder with a core-shell structure. The magnesium oxide serves as the core, and the silicon dioxide is coated on the surface of the magnesium oxide as the shell layer. This structure enables uniform distribution of the two components at the micro level, avoiding the agglomeration of magnesium oxide particles caused by traditional physical blending, and at the same time, the dense coating of silicon dioxide improves the dielectric properties and thermal shock resistance of the composite powder.

[0010] As a preferred technical solution of the first aspect of the present application, in the low-smoke halogen-free plastic material, the vinyl trimethoxysilane serves as a coupling agent, one end of which chemically bonds with the surface hydroxyl groups of the magnesium hydroxide, and the other end grafts with the molecular chain of the polyvinyl acetate. This forms a chemical bond between the magnesium hydroxide and the polyvinyl acetate. This chemical bond significantly improves the interfacial compatibility of the inorganic flame retardant and the organic resin matrix, enabling the uniform dispersion of the ultra-high loading of magnesium hydroxide in the polyvinyl acetate, thereby greatly improving the mechanical properties such as tensile strength and elongation at break of the material, and improving its processing flowability.

[0011] As a preferred technical solution of the first aspect of the present application, the twisting 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 technical solution of the first aspect of the present application, the copper sheath is formed by longitudinally wrapping a copper strip, the thickness of the copper sheath is 0.75-0.85 mm, and the corrugation depth of the corrugated structure is 2.8-3.2 mm, and the pitch is 14-16 mm.

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

[0014] The second aspect of the present application provides a processing method of a wrinkle-resistant copper sheath flexible mineral fireproof cable, for preparing the cable according to any one of the preceding aspects, characterized in that comprising the following steps: S1, twisting a plurality of copper wires to form a cable conductor; S2, coating an inorganic material outside the cable conductor to form an insulation layer, and shaping the formed insulated core by a hot-pressing process; S3, twisting a plurality of insulated cores treated by step S2, and filling the gap therebetween with inorganic fiber filler to form a cable core; S4, longitudinally coating a copper strip outside the cable core, and continuously welding along the longitudinal seam of the copper strip to form a sealed tubular sheath, and then performing a corrugation process on the tubular sheath to form a corrugated structure; and 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 technical solution of the second aspect of the present application, the hot-pressing process shaping in step S2 specifically comprises two continuous stages: firstly, flexible pre-compaction is performed on the insulated core; and then, online sintering is performed. The flexible pre-compaction is performed by applying a linear pressure of 50-150 N / cm, which aims to preliminarily increase the bulk density of the insulation layer powder; the heating temperature of the online sintering is set to 300-400℃, and the time of the online sintering is 4-10 seconds, which aims to further solidify the insulation layer to obtain stable mechanical strength and electrical properties.

[0016] As a preferred technical solution of the second aspect of the present application, the preparation process of the inorganic material in step S2 is a specific chemical process for obtaining a core-shell structure powder, specifically comprising: using a liquid phase in-situ coating method, dispersing the magnesium oxide in water to form a slurry, adding a sodium silicate solution dropwise to the slurry, and adjusting the pH value of the reaction system by acid. Under this condition, the sodium silicate undergoes a hydrolysis reaction to generate hydrated silicon dioxide, which is uniformly deposited on the surface of the magnesium oxide particles in-situ to form a coating layer. After washing and drying the reaction product, low-temperature activation treatment is performed at a temperature of 450-550℃ to dehydrate the hydrated silicon dioxide into the final silicon dioxide, thereby obtaining the inorganic material with a core-shell structure. This method ensures the uniformity and compactness of the silicon dioxide shell layer.

[0017] As a preferred technical solution of the second aspect of the present application, the preparation process of the low-smoke halogen-free plastic material in step S5 is a specific reactive extrusion process for realizing the interfacial chemical bonding, which specifically comprises: first, dry interfacial chemical activation treatment of the magnesium hydroxide: the magnesium hydroxide and the vinyl trimethoxysilane are placed in a high-speed mixer, and the temperature of the materials is raised by high-speed shearing and friction heat and controlled at 105-115℃. This step makes the vinyl trimethoxysilane hydrolyze and condense on the surface of the magnesium hydroxide particles to obtain magnesium hydroxide activated powder grafted with vinyl siloxane on the surface. Subsequently, the magnesium hydroxide activated powder obtained in the foregoing is simultaneously fed into a twin-screw extruder with the polyvinyl acetate, zinc borate and additives for melt compatibilization and in-situ grafting reaction extrusion. The temperature of the rear section of the twin-screw extruder is set to 180-190℃, and in this area, the vinyl on the surface of the magnesium hydroxide activated powder reacts with the molecular chain of the polyvinyl acetate to graft, thereby completing forced dispersion, melt plasticization and interfacial chemical bonding in one step in the extruder, and finally the low-smoke halogen-free plastic material is prepared by blending and extrusion.

[0018] In summary, the present application includes at least one of the following beneficial technical effects: 1. The present application uses a liquid phase in-situ reaction method to prepare inorganic insulation materials, and combines with subsequent flexible pre-compaction and online sintering process, so that the insulation layer wrapped outside the twisted copper conductor forms a whole with high mechanical strength and dense structure. This structure solves the technical problem of failure of traditional mineral insulation layer due to powder displacement or insufficient sintering strength under fire and mechanical impact, so that the cable meets the high fireproof grade requirement and maintains the circuit integrity under impact conditions, thereby obtaining excellent flexible mineral fireproof properties.

[0019] 2. The present application sets inorganic fiber filler between the sintered insulation layer and the outer sheath, and uses a copper sheath with a continuous corrugated structure for sealing. The design of the continuous corrugated structure makes the stress evenly dispersed when the cable is bent, effectively overcoming the technical defect that the traditional smooth sheath is prone to wrinkles due to stress concentration, thereby meeting the anti-wrinkle requirement. This structure design significantly improves the overall flexibility of the cable, facilitating continuous manufacturing and installation, and meeting the long-distance and high-current power supply requirements in modern buildings.

[0020] 3. The present application extrudes a specific formula of low-smoke halogen-free outer sheath outside the copper sheath, and the outer sheath material has excellent tensile strength and elongation at break. This design not only provides effective mechanical protection for the internal fireproof functional layer, ensuring the physical integrity of the cable during laying and long-term use, but also has extremely low smoke production when burning. This multi-layer structure from the inside to the outside ensures that the flexible mineral fireproof cable not only has core fireproof performance, but also has high mechanical strength and safety in use. 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] The anti-wrinkle copper sheath flexible mineral fireproof cable provided by the embodiment of the present application comprises, from inside to outside, a cable conductor 1, an insulation layer 2, a copper sheath 4 and an outer sheath 5. When the cable is a multi-core structure, the cable core formed by twisting a plurality of wire cores wrapped by the insulation layer 2 further comprises inorganic fiber filling material 3 for filling the space between the wire cores.

[0028] The cable conductor 1 is the conductive part of the cable, which is formed by twisting a plurality of copper wires in a bundle twisting manner. In a specific embodiment, in order to ensure the flexibility and stability of the cable conductor, the twisting pitch is set to be 9.5-10.5 times the final formed outer diameter of the cable conductor 1.

[0029] The insulation layer 2 is uniformly coated on the outside of the cable conductor 1 and plays the role of electrical insulation and high-temperature isolation. The insulation layer 2 is made of inorganic material, which ensures the fireproof performance of the cable. In a specific embodiment, the thickness of the insulation layer 2 is 1.4-1.6 mm. The inorganic material can be electrical-grade magnesium oxide or mica tape.

[0030] When a multi-core cable is prepared, a plurality of independent wire cores with the insulation layer 2 are first twisted. In the twisting process, the inorganic fiber filling material 3 is used to fill the space between the wire cores, so that the formed cable core structure is full and round. In a specific embodiment, the inorganic fiber filling material 3 can be alkali-free glass fiber rope or alkali-free glass fiber tape, which has excellent temperature resistance and insulation.

[0031] The copper sheath 4 is coated on the outside of the cable core and plays the role of sealing, waterproofing, protecting the internal structure and grounding. It is a metal sheath formed by longitudinally wrapping a copper tape on the outside of the cable core and continuously welding along the butt joint longitudinal seam. In order to realize the flexibility of the cable and prevent it from wrinkling when bent, the surface of the copper sheath 4 is processed into a continuous corrugated structure. In a specific embodiment, the copper tape used to manufacture the copper sheath 4 has a thickness of 0.75-0.85 mm, and the corrugated structure provided thereon has a corrugated depth of 2.8-3.2 mm and a pitch of 14-16 mm.

[0032] The outer sheath 5 is the outermost structure of the cable and provides the final mechanical protection and environmental protection for the cable. The outer sheath 5 is made of low-smoke halogen-free plastic material and is coated on the outside of the copper sheath 4 by extrusion molding. The thickness of the outer sheath 5 is 1.9-2.1 mm.

[0033] Referring to the drawings, Figure 3 .

[0034] Preparation of core material: Example 1: Preparation of inorganic material for insulation layer (by mass fraction): In a reaction vessel, 2000 parts of deionized water was added and stirring was started. 85 parts of magnesium oxide was added and dispersed to form a slurry. While stirring, a solution containing 5 parts of effective silica content of sodium silicate 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 completed, the reaction was continued for 1 hour. The reaction product was washed to 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 produce inorganic material powder A.

[0035] Example 2: Preparation of inorganic material for insulation layer (by mass fraction): In a reaction vessel, 2000 parts of deionized water was added and stirring was started. 95 parts of magnesium oxide was added and dispersed to form a slurry. While stirring, a solution containing 15 parts of effective silica content of sodium silicate 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 completed, the reaction was continued for 1 hour. The reaction product was washed to 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 produce inorganic material powder B.

[0036] Example 3: Preparation of low-smoke halogen-free plastic material for outer sheath: By mass fraction, 130 parts of magnesium hydroxide and 1 part of vinyltrimethoxysilane were placed in a high-speed mixer. High-speed shearing stirring was started, and the temperature of the material was raised to 105°C using friction heat, and maintained at this temperature for 15 minutes to obtain surface-grafted magnesium hydroxide activated powder.

[0037] The above-mentioned magnesium hydroxide activated powder, 100 parts of polyvinyl acetate, 8 parts of zinc borate, and an auxiliary 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 temperature of each zone of the twin-screw extruder was set so that the temperature of the rear reaction zone was 180°C, and the material was extruded by melt compounding and in-situ grafting reaction. After cooling and granulation, 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 mass fraction, 160 parts of magnesium hydroxide and 2 parts of vinyltrimethoxysilane were placed in a high-speed mixer. High-speed shearing stirring was started, and the temperature of the material was raised to 115°C using friction heat, and maintained at this temperature for 15 minutes to obtain surface-grafted magnesium hydroxide activated powder.

[0039] The above-mentioned magnesium hydroxide activated powder, 100 parts of polyvinyl acetate, 15 parts of zinc borate, and an auxiliary consisting of 1.0 part of antioxidant 1010, 0.5 part of antioxidant 168 and 1.0 part of vinyl bis-stearamide are synchronously fed into a twin-screw extruder. The temperature of each zone of the twin-screw extruder is set, and the temperature of the rear reaction zone is 190 DEG C. The melt compatibilization and in-situ grafting reaction extrusion is carried out. After cooling and granulation, low-smoke halogen-free plastic material granules D are prepared.

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

[0041] (S1) Conductor stranding: after drawing T1 oxygen-free copper rod to a specified diameter, 19 strands of copper wire are stranded at a stranding pitch of 9.5 times the total diameter of the conductor to form a cable conductor with a nominal cross-sectional area of 25 mm 2 .

[0042] (S2) Insulation layer preparation: inorganic material powder A (prepared in Example 1) is coated on the outside of the cable conductor by a powder coating device to form an insulation layer with a thickness of 1.4 mm. Subsequently, through a hot press molding device, a flexible pre-compaction is first applied by a linear pressure of 50 N / cm; then it enters an online sintering furnace to perform online sintering at 300 DEG C for 10 seconds to form an insulated core.

[0043] (S3) Cable core cabling: 3 insulated cores treated in step S2 are stranded at a certain pitch, and at the same time, alkali-free glass fiber tape is used to fill the gap therebetween to form a compact cable core.

[0044] (S4) Copper sheath preparation: on the outside of the cable core, T2 electrical copper strip with a thickness of 0.75 mm is longitudinally coated by a copper strip longitudinal forming machine, and continuous welding is performed along the longitudinal seam by argon arc welding to form a sealed tubular sheath. Subsequently, the tubular sheath is processed by a corrugation device to form a corrugated structure with a corrugation depth of 2.8 mm and a pitch of 14 mm.

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

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

[0047] (S1) Conductor stranding: after drawing T1 oxygen-free copper rod to a specified diameter, 19 strands of copper wire are stranded at a stranding pitch of 10.5 times the total diameter of the conductor to form a cable conductor with a nominal cross-sectional area of 25 mm 2 .

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

[0049] (S3) Cable core cabling: Three insulated cores treated in step S2 were twisted at a certain pitch and simultaneously filled with alkali-free glass fiber tape to fill the gaps therebetween to form a compact cable core.

[0050] (S4) Copper sheath preparation: A T2 electrical copper tape with a thickness of 0.85 mm was longitudinally coated on the outer side of the cable core by a copper tape longitudinal forming machine, and continuously welded along the longitudinal seam by argon arc welding to form a sealed tubular sheath. Subsequently, the tubular sheath was processed by a knurling device to form a corrugated structure with a corrugation depth of 3.2 mm and a pitch of 16 mm.

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

[0052] Comparative Example 1: Compared with Example 6, the difference is that in step S2, after coating inorganic material powder B on the outer side of the cable conductor, the flexible pre-compaction and online sintering hot pressing process is not performed, and step S3 is directly entered. The rest are the same.

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

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

[0056] Comparative Example 5: Compared with Example 6, the difference is that the preparation method of the insulating layer material used is physical blending of an equal amount of magnesium oxide powder to the formulation of Example 2 with solid sodium silicate powder, instead of using the liquid in-situ reaction method described in Example 2. The rest are the same.

[0057] Comparative Example 6: Compared with Example 6, the difference is that in step S4, after the sealed tubular sheath is formed, no subsequent embossing is performed to form a corrugated structure, and a smooth copper sheath is obtained. The rest are the same.

[0058] Test Example 1: Bending and Anti-Creasing Performance Test

[0059] In order to verify the bending performance and sheath anti-creasing ability of the cable products prepared in the above examples and comparative example products, the following method is used for testing.

[0060] 1. Preparation and state adjustment of test samples

[0061] 2. Bending test procedure

[0062] (1) Install the sample on the bending test device, and set the diameter of the cylindrical mandrel of the test device to be 10 times the outer diameter of the measured cable sample.

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

[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 scattered natural light or equivalent light source with normal vision, and record whether there are visually observable local wrinkles, creases or cracks.

[0065] 3. Post-bending voltage test procedure (1) Immers the entire sample that has undergone the above bending test in a metal container filled with water, and keep the water temperature at 20°C ± 5°C, with at least 200mm of the sample exposed above the water surface at both ends. The sample is soaked for 1 hour.

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

[0067] (3) During the voltage application, the current of the test loop is monitored. If breakdown occurs, the device will automatically disconnect the voltage and indicate. Record whether the sample passes the test or breakdown occurs.

[0068] Test data is shown in Table 1: Table 1: Test data of bending and anti-wrinkle performance.

[0069] The above test results show that the cable of Example 5 and Example 6 has no wrinkles on the copper sheath after bending and maintains electrical integrity, while Comparative Example 1 and Comparative Example 6 have sheath wrinkles or electrical breakdown.

[0070] This performance difference is due to the specific combination of structure and process. The copper sheath of the example cable has a continuous corrugated structure, which can effectively disperse stress when bending, avoiding local yield and wrinkling of smooth sheath (Comparative Example 6) due to stress concentration. At the same time, the implemented flexible pre-compaction and online sintering process makes the internal inorganic insulation powder form a dense whole layer with self-supporting strength. This structure can maintain its continuity and thickness uniformity when the cable is bent. In contrast, Comparative Example 1, which is not hot-pressed, has a loose powder insulation layer, which displaces particles when bent, forming an electrical weak point, resulting in voltage breakdown.

[0071] The measurable performance parameters confirm that by combining a metal sheath with a corrugated structure and an inorganic insulation layer that has been hot-pressed, the technical problems of sheath wrinkling and insulation failure when the cable is bent 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 examples and the comparative example products under fire and mechanical impact conditions, the following method is used for testing.

[0074] 1. Preparation and installation of test samples Cut 1.2 meters to 1.5 meters of sample from the finished cable of Examples 5-6 and Comparative Examples 1-3, 5-6. Install each sample horizontally on a support in a BS 6387 standard test box. Connect one end of the sample to a three-phase 400V AC power source, and the other end to a set of 3A fuses and indicator lights to form a loop that can monitor the on-off state of the circuit.

[0075] 2. Test steps The test is strictly performed according to the C, W, Z categories in the BS 6387:2013 standard in succession.

[0076] (1) Class C (Fire Resistance Test): A ribbon burner is started in the middle of the sample, and the flame temperature is adjusted and maintained at 950°C (±40°C). The sample is subjected to the flame at this temperature while being subjected to the rated voltage, for a duration of 180 minutes.

[0077] (2) Class W (Fire Resistance plus Spray Test): The flame temperature is adjusted and maintained at 650°C (±40°C). After the sample is subjected to the flame for 15 minutes, a spray head is started above the sample to spray water on the sample at a flow rate of 0.25 L / m 2 for 15 minutes.

[0078] (3) Class Z (Fire Resistance plus Mechanical Impact Test): The flame temperature is adjusted and maintained at 950°C (±40°C). While the sample is subjected to the flame, a mechanical impact device is started. The device impacts the ladder rack carrying the sample at an interval of 30 seconds (±1 second). The test lasts for 15 minutes under the combined action of the flame and the impact.

[0079] 3. Result Determination During the tests of Class C, W, and Z, the integrity of the circuit is determined by observing the status of the indicator light. If the indicator light remains on and the fuse in the circuit is not blown, the sample is determined to pass the test of this class. If the indicator light is off or the fuse is blown at any stage, it is determined to fail and the failed test class is recorded.

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

[0081] Table 2: Fire Resistance, Mechanical Impact Resistance, and Circuit Integrity Test Data Test sample BS 6387 CWZ category test results Example 5 Pass Example 6 Pass Comparative Example 1 Fail (failed in Z category test) Comparative Example 2 Fail (failed in Z category test) Comparative Example 3 Fail (failed in Z category test) Comparative Example 5 Fail (failed in C category test) Comparative Example 6 Pass

[0082] The test results show that the cables of Examples 5 and 6 and Comparative Example 6 pass the full test of fire resistance, spraying, and impact according to BS 6387. In comparison, Comparative Examples 1, 2, and 3 fail at the impact test stage, and Comparative Example 5 fails at the pure burning test stage.

[0083] This performance difference reveals the synergy of material preparation and molding process. Comparative Example 1 fails because the loose powder is displaced under mechanical impact, causing electrical breakdown. Comparative Examples 2 and 3, although hot-pressed, fail because their materials (conventional magnesium oxide or physical blend) lack effective sintering aids, resulting in insufficient mechanical strength of the sintered body, which is difficult to resist impact and damage. Comparative Example 5 fails because it adds a low-melting-point component, which melts at high temperatures of 950°C, destroying the insulation structure.

[0084] The embodiment cable can pass the test because it adopts a specific liquid phase in-situ reaction method combined with 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, the coating layer acts as a high-temperature sintering aid to promote the formation of firm sintering necks between the particles, eventually forming a mechanically strong and structurally stable overall insulation layer. This structure is sufficient to resist the dual effects of high temperature and mechanical impact, thereby solving the technical problem that the insulation layer of the cable is prone to failure due to structural damage in a fire.

[0085] Test Example 3: Smoke density test.

[0086] To verify the smoke production performance of the outer sheath of the cable products prepared in the above embodiments and the comparative example products under burning conditions, the following method is used for testing.

[0087] 1. Preparation of test samples: A sample with a length of 1.0 meter (±5 mm) is cut from the finished cable of Example 5, Example 6, and Comparative Example 4. All samples are conditioned in an environment with a temperature of 23°C ± 2°C and a relative humidity of 50% ± 5% for at least 16 hours before testing.

[0088] 2. Test device and environment: The test is conducted in a 3-meter cubic smoke density test chamber built in accordance with the GB / T 17651.2-1998 (equivalent to IEC 61034-2) standard. The inner wall of the test chamber is black, equipped with a sealed door, a light path system (composed of a white light source and a photoelectric receiver), a fan, and a ring-shaped burning disc for placing the sample.

[0089] 3. Test steps: (1) Place the ring-shaped burning disc containing 1 liter of industrial alcohol in the center of the bottom of the test chamber.

[0090] (2) Horizontally mount the cable sample to be tested above the burning disc at a distance of 70 mm ± 10 mm.

[0091] (3) Close the test chamber door, start the internal fan to mix the air in the chamber uniformly, and then turn off the fan. Calibrate the light path system so that the initial light transmittance is 100%.

[0092] (4) Ignite the alcohol in the burning disc.

[0093] (5) Start the test, and the data acquisition system continuously records the light intensity received by the photoelectric receiver at a time interval not greater than 5 seconds, and converts it to light transmittance.

[0094] (6) The test is stopped after 40 minutes or when the light transmittance reaches a stable minimum value. Record the lowest light transmittance value measured during the entire test process.

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

[0096] Table 3: Smoke density test data. Test sample Minimum light transmittance (%) Example 5 73.8 Example 6 76.1 Comparative Example 4 22.4

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

[0098] The performance difference is derived from the different components of the outer sheath materials and their action mechanisms during combustion. The low-smoke halogen-free plastic material used in Example 5 and Example 6 has magnesium hydroxide in its formula, which undergoes endothermic decomposition and releases crystalline water when heated. This process, on the one hand, delays the combustion rate of the polymer matrix by absorbing heat, and on the other hand, the released water vapor dilutes the concentration of flammable gas and smoke particles in the air. At the same time, zinc borate in the formula acts as a synergistic char-forming agent, promoting the dehydration and carbonization of the polymer matrix during combustion, forming a dense carbon layer.

[0099] This carbon layer acts as a physical barrier, effectively isolating external oxygen from internal unburned materials and inhibiting the escape of flammable volatiles, thereby further reducing the generation of smoke. In contrast, the conventional low-smoke halogen-free polyolefin material used in Comparative Example 4, although it has certain inhibition ability, the carbon layer structure formed by its formula system during combustion is relatively loose or has low carbonization efficiency, and its inhibition effect on smoke is limited. Therefore, the outer sheath material with the specific formula described in the technical solution achieves a lower amount of smoke generation under combustion conditions through the synergistic effect of decomposition and heat absorption, water vapor dilution, and efficient carbonization.

[0100] Test Example 4: Compression resistance test.

[0101] To verify the structural integrity of the cable products prepared in the above examples and the products of the comparative example when subjected to radial pressure, the following steps were used for testing according to the relevant methods in GB / T 13033.1-2007.

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

[0103] 2. Test device and test setting: the test was performed on a universal material testing machine. The machine was equipped with two parallel steel platens with a width of not less than 100 mm. An insulation resistance tester was also provided to monitor the electrical state between the cable conductor and the metal sheath in real time.

[0104] 3. Test Procedure: (1) Place the cable sample horizontally in the center of the lower platen 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 material testing machine, and move the upper platen downward at a constant speed of 5 mm / min (± 1 mm / min) to apply radial pressure to the sample.

[0107] (4) Continuously monitor the applied pressure value and the reading of the insulation resistance tester during the pressure application.

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

[0109] (6) Repeat the test for 3 samples for each type of cable, and take the arithmetic mean as the final result.

[0110] Test data is shown in Table 4.

[0111] Table 4: Crush resistance test data.

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

[0113] The performance difference is due to the geometric configuration of the metal sheath. The copper sheath of Example 5 and Example 6 has a continuous corrugated structure. When radial pressure is applied to the cable, this corrugated structure disperses the concentrated load in the axial direction through the geometry of its wave crests and troughs. This structure is similar to an arch, providing additional structural support, increasing the deformation resistance of the sheath, so that a greater external force is required to cause sufficient deformation of the sheath, thereby extruding the internal insulation layer until its electrical performance fails.

[0114] In contrast, Comparative Example 6 employs a smooth tubular sheath. This structure lacks an effective stress dispersion mechanism when subjected to radial pressure, as the load is directly applied to the point of compression. The smooth tube wall is more susceptible to localized flattening or ovalization under pressure, causing the pressure to be rapidly and concentratedly transmitted to the inner insulation layer, which is crushed at a lower pressure level, resulting in electrical short circuit between the conductor and the sheath. This series of measurable performance parameters indicates that the specific design of setting a corrugated structure on the metal sheath is a direct solution to the technical problem of the insufficient radial crush resistance of the smooth sheath cable.

[0115] Test Example 5: Mechanical property test of outer sheath

[0116] To verify the mechanical properties of the outer sheath materials of the cable products prepared in the above examples and the comparative example products, the following method was used for testing according to GB / T2951.11-2008.

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

[0118] (2) The outer sheath was cut open along the axial direction of the cable and stripped, taking care not to damage the surface of the sheath.

[0119] (3) A standard cutting tool was used to punch out a dumbbell-shaped sample from the flat sheath piece. The length direction of the effective test portion of the sample was consistent with the axial direction of the cable.

[0120] (4) A thickness gauge was used to measure the thickness and width of at least three points in the narrow distance part of the dumbbell-shaped sample, and the average value was calculated to determine the initial cross-sectional area of the sample.

[0121] 2. Test device and environment The test was carried out on an electronic tensile testing machine. The test environment temperature was controlled at 23°C±2°C.

[0122] 3. Test steps: (1) The two ends of the dumbbell-shaped sample were clamped in the upper and lower clamps of the tensile testing machine, respectively, to ensure that the force axis of the sample coincided with the center line of the clamps. The initial gauge length was marked within the gauge length of the sample.

[0123] (2) The tensile testing machine was started to apply a tensile load to the sample at a constant speed of 250mm / min(±50mm / min).

[0124] (3) The data acquisition system of the testing machine recorded the tensile load and the elongation of the gauge length simultaneously until the sample was pulled apart.

[0125] (4) The maximum tensile load at the time of sample fracture and the gauge length at the time of fracture were recorded.

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

[0127] The test data is shown in Table 5. Table 5: Mechanical property test data of outer sheath Test sample Tensile strength (MPa) Elongation at break (%) Example 5 12.8 415 Example 6 13.1 432 Comparative Example 4 8.9 276

[0128] The quantitative data of the above test results show that the tensile strength and elongation at break of the outer sheath materials of Example 5 and Example 6 are significantly higher than those 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 is mainly due to the interfacial bonding state between the components in the material system. In the outer sheath materials of Example 5 and Example 6, ethylene-vinyl acetate copolymer grafted with maleic anhydride is added as a compatibilizer. The polar functional groups (maleic anhydride) in the molecular chain of the compatibilizer can undergo esterification reaction or form hydrogen bonds with the surface of the inorganic flame retardant (magnesium hydroxide), thereby establishing a firm 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 deformed under stress, avoiding stress concentration and premature interfacial debonding.

[0130] In contrast, the conventional low-smoke halogen-free polyolefin material used in Comparative Example 4 has mainly physical mixing between the filler and the polymer matrix, with weak interfacial bonding. When the material is stretched, stress is difficult to transfer effectively, and microcracks are easily generated and rapidly expanded at the interface between the matrix and the filler, leading to the material breaking at a lower stress level and smaller deformation. Therefore, by introducing a specific compatibilizer, the interfacial compatibility between the inorganic filler and the polymer matrix is improved, which is an effective way to solve the technical problem of mechanical property degradation of high-filled flame-retardant materials, and ultimately obtain a sheath material with high tensile strength and elongation at break.

Claims

1. A kink-resistant, copper-sheathed, flexible mineral fire-resistant cable, characterized in that, From inside to outside, it comprises: a cable conductor, which is twisted by multiple copper wires; an insulation layer, which is made of inorganic material; inorganic fiber filler; a copper sheath, which is provided with corrugated structure; an outer sheath, which is made of low-smoke halogen-free plastic material. The inorganic material comprises the following components in mass fraction: Magnesium oxide: 85-95 parts; Sodium silicate: 5-15 parts; The low-smoke halogen-free plastic material comprises the following components in mass fraction: Polyethylene vinyl acetate: 100 parts; Magnesium hydroxide: 130-160 parts; Zinc borate: 8-15 parts; Vinyl trimethoxysilane: 1-2 parts; Auxiliary agent: 1.5-2.5 parts.

2. A kink resistant, copper sheathed, flexible mineral fire resistant cable according to claim 1, characterised in that, The twisting pitch of the cable conductor is 9.5-10.5 times of 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. A kink resistant, copper sheathed, flexible mineral fire resistant cable as claimed in claim 1, wherein, The copper sheath is formed by longitudinal wrapping of copper strip, the thickness of the copper sheath is 0.75-0.85 mm, and the corrugated structure has a corrugated depth of 2.8-3.2 mm and a pitch of 14-16 mm.

4. A kink resistant, copper sheathed, flexible mineral fire resistant cable as claimed in claim 1, wherein, The inorganic fiber filler is alkali-free glass fiber rope or alkali-free glass fiber tape for filling the gap between multiple cable conductors wrapped by insulation layer.

5. A process for the manufacture of a wrinkle-resistant copper-sheathed flexible mineral fire-resistant cable, for the preparation of a wrinkle-resistant copper-sheathed flexible mineral fire-resistant cable as claimed in any one of claims 1 to 4, characterized in that, It comprises the following steps: S1, twisting multiple copper wires to form a cable conductor, and crimping and fixing the end of the cable conductor; S2, wrapping inorganic material outside the cable conductor to form an insulation layer, and forming the insulation wire core by hot pressing process; S3, twisting multiple insulation wire cores treated in step S2, and filling the gap between them with inorganic fiber filler to form a cable core; S4, longitudinally wrapping copper strip outside the cable core, and continuously welding along the longitudinal seam of the copper strip by argon arc welding to form a sealed tubular sheath, and then processing the tubular sheath to form a corrugated structure; S5, extruding low-smoke halogen-free plastic material to cover outside the copper sheath to form an outer sheath.

6. A process for the manufacture of a kink resistant, copper sheathed, flexible mineral fire resistant cable as claimed in claim 5, wherein, In step S2, the hot pressing process forming specifically comprises: First, flexible pre-compacting the insulation wire core; Then, online sintering.

7. A process for the manufacture of a kink resistant, copper sheathed, flexible mineral fire resistant cable as claimed in claim 6, characterised in that, The flexible pre-compacting is performed by applying a linear pressure of 50-150 N / cm; The heating temperature of the online sintering is 300-400 ℃, and the time of the online sintering is 4-10 seconds.

8. A process for the manufacture of a kink resistant, copper sheathed, flexible mineral fire resistant cable as claimed in claim 5, wherein, In step S2, the preparation process of the inorganic material comprises: Using liquid in-situ coating method, dispersing magnesium oxide in water to form slurry, adding sodium silicate solution dropwise and reacting under acidic conditions; After washing and drying the reaction product, low-temperature activation treatment is carried out at 450-550 ℃ to obtain the inorganic material with core-shell structure, which is in powder form.

9. A process for the manufacture of a kink resistant, copper sheathed, flexible mineral fire resistant cable as claimed in claim 5, wherein, In step S5, the preparation process of the low-smoke halogen-free plastic material comprises: First, the magnesium hydroxide is subjected to dry interface chemical activation treatment: the magnesium hydroxide and vinyl trimethoxysilane are placed in a high-speed mixer, the temperature of the materials is raised by high-speed shearing and friction heat and controlled at 105-115℃, to obtain magnesium hydroxide activated powder grafted with vinyl siloxane on the surface; Subsequently, the magnesium hydroxide activated powder is synchronously fed into a twin-screw extruder with polyvinyl acetate, zinc borate and additives, to perform melt compatibilization and in-situ grafting reaction extrusion, the temperature of the rear reaction zone of the twin-screw extruder is 180-190℃, and finally the low-smoke halogen-free plastic material is prepared by blending extrusion.

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