Flame and fire retardant cable

Abstract

The application belongs to the technical field of cables and specifically relates to a flame-retardant fire-resistant cable, which comprises, from inside to outside, a conductor, an insulation layer, a fire-resistant layer, a microporous vacuum composite armor layer and an outer sheath, the microporous vacuum composite armor layer is formed by overlapping and wrapping the microporous vacuum composite strip on the outside of the fire-resistant layer, the microporous vacuum composite strip comprises a plurality of microporous vacuum composite segments and flexible metal connecting pieces, adjacent microporous vacuum composite segments are connected through the flexible metal connecting pieces, each microporous vacuum composite segment comprises a microporous metal framework and a metal foil encapsulation layer wrapped on the outer surface of the microporous metal framework; the application integrates the functions of armoring, heat insulation and fire resistance in the same structural layer, significantly simplifies the structure and eliminates the risk of interlayer peeling, the segmented independent vacuum unit provides redundant protection, the low equivalent thermal conductivity makes the heat insulation performance excellent, the all-metal structure is fire-resistant and non-combustible, the high-temperature non-toxic smoke, and the rigid-flexible coupling design ensures that the cable has mechanical protection and bending laying capacity.

Description

Technical Field

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

[0002] Flame-retardant and fire-resistant cables are cables that can maintain the integrity of the circuit for a certain period of time under fire conditions. They are widely used in aerospace, nuclear power facilities and other places where power supply safety requirements are extremely high.

[0003] Currently, flame-retardant and fire-resistant cables typically employ a multi-layered composite structure to achieve fire resistance. A typical structure, from the inside out, consists of: a conductor, an insulation layer, a fire-resistant layer (such as a mica tape wrapping layer), a thermal insulation layer (such as ceramicized silicone rubber, aerogel felt, or other low thermal conductivity materials), an armor layer (steel tape or wire), and an outer sheath. In engineering applications, while this layered approach combines multiple functions, it also leads to problems such as a bulky structure, poor inter-layer reliability, a single function of the armor layer, and functional fragmentation.

[0004] Specifically, to achieve the triple functions of fire resistance, heat insulation, and armoring, the conductor needs to be covered with multiple materials layer by layer. This results in a significant increase in the cable's outer diameter, higher costs, and limited installation space. Simultaneously, the thermal expansion coefficients of each layer differ significantly. Under normal operating thermal cycles and the high temperatures of a fire, relative slippage or even peeling can easily occur between the layers, directly affecting structural integrity and fire resistance. Furthermore, the metal armor only provides mechanical protection and lacks heat insulation capabilities. In a fire, it can become a channel for heat conduction into the interior, necessitating the addition of an extra insulation layer, further complicating the structure. While the fire-resistant layer provides insulation protection in flames and the insulation layer blocks heat conduction, their complementary functions and different materials make them difficult to integrate into a single functional layer, hindering structural simplification. Summary of the Invention

[0005] The purpose of this invention is to provide a flame-retardant and fire-resistant cable that solves the technical problems of functional separation between the armor layer and the insulation layer, bulky structure, and poor interlayer reliability in the prior art.

[0006] This invention discloses a flame-retardant and fire-resistant cable, comprising: It includes, from the inside out, a conductor, an insulating layer, a fire-resistant layer, a microporous vacuum composite armor layer, and an outer sheath; The microporous vacuum composite armor layer is formed by overlapping and wrapping microporous vacuum composite strips around the outside of the refractory layer. The microporous vacuum composite strips include multiple microporous vacuum composite segments and flexible metal connectors. Adjacent microporous vacuum composite segments are connected by the flexible metal connectors. Each of the microporous vacuum composite segments includes a microporous metal framework and a metal foil encapsulation layer covering the outer surface of the microporous metal framework. The microporous metal framework has a three-dimensional interconnected microporous structure with a porosity of 60%–95% and a pore size of 10 μm–200 μm. The internal air pressure... The metal foil encapsulation layer forms an airtight seal to maintain a vacuum state within the microporous metal skeleton.

[0007] This application integrates armoring, heat insulation, and fire resistance into the same structural layer, significantly simplifying the structure and eliminating the risk of interlayer peeling. The segmented independent vacuum units provide redundant protection, and the low equivalent thermal conductivity results in excellent heat insulation performance. Furthermore, the all-metal structure is fire-resistant and non-combustible, and produces no toxic fumes at high temperatures. In addition, the rigid-flexible coupling design ensures that the cable has both mechanical protection and bending laying capability.

[0008] Based on the above technical solution, the solution of this application can be further improved as follows: Preferably, the microporous metal skeleton has a porosity of 70% to 90%, a pore size of 20 μm to 100 μm, and a thickness of 0.5 mm to 5 mm. This solution achieves a better balance between mechanical strength, thermal insulation performance, and bending flexibility, ensuring sufficient vacuum insulation space, further reducing solid-phase heat conduction, and effectively suppressing gas heat transfer while giving it higher specific strength and compressive bearing capacity. It also ensures mechanical protection stiffness and avoids bending stress concentration caused by excessive thickness of a single section, so that the strip has both structural compactness and laying flexibility after wrapping.

[0009] Preferably, the microporous metal skeleton is foamed metal, and is selected from one or more of foamed nickel, foamed copper, and foamed stainless steel. By adopting this solution, flexible adaptation and functional synergy at the material level can be achieved, enabling the microporous metal skeleton to achieve an optimized balance between support stiffness, vacuum insulation performance, fire resistance rating and engineering adaptability, and significantly improving its comprehensive applicability under different working conditions.

[0010] Preferably, the metal foil encapsulation layer is stainless steel foil or aluminum foil with a thickness of 0.05mm to 0.2mm. This solution can achieve a balance between airtight sealing reliability, mechanical protection capability and strip flexibility, so that the metal foil encapsulation layer can effectively maintain the vacuum state inside the micropores while taking into account the flexibility required for cable bending and laying and the durability for long-term use.

[0011] Preferably, the flexible metal connector is a metal corrugated pipe made of 304 stainless steel or 316L stainless steel, with a wall thickness of 0.15mm to 0.30mm, a corrugated shape of U-shape or S-shape, a peak height of 2mm to 5mm, a wave pitch of 3mm to 8mm, and a smooth transition between the peaks and troughs. This design creates a reliable transition area between the microporous vacuum composite sections, balancing mechanical flexibility and structural integrity. While maintaining vacuum sealing and mechanical protection capabilities, it also provides the flexibility required for cable bending and laying, achieving a balance between rigidity and flexibility, uniform load transfer, and long-term reliability.

[0012] Preferably, the flexible metal connector is a metal braided mesh sleeve made of 304 or 316L stainless steel wire with a wire diameter of 0.2mm to 0.5mm, a braiding density of 70% to 85%, and a braiding angle of 30° to 45°. With this solution, a mechanically continuous and flexible connection is formed between the microporous vacuum composite sections. While transmitting axial tensile loads, it has extremely low bending stiffness, so that the entire strip has both the longitudinal strength required for mechanical protection and the flexible bending performance required for cable laying.

[0013] Preferably, the length of the microporous vacuum composite section is 50mm to 500mm, the length of the flexible metal connector is 20mm to 80mm, and the ratio of the length of the microporous vacuum composite section to the length of the flexible metal connector is 1:1 to 10:1. This solution allows the microporous vacuum composite tape to maintain a high proportion of effective vacuum insulation area and continuous mechanical protection capabilities, while achieving smooth bending of the entire tape through deformation compensation in the flexible connection area. This balances the continuity of insulation protection with the adaptability to cable bending installation.

[0014] Preferably, the outer surface of the metal foil encapsulation layer is coated with a fire-retardant coating, which is a ceramicized silicone rubber fire-retardant coating with a thickness of 0.1mm to 0.5mm. This solution combines the ability to generate a ceramic protective layer in situ at high temperatures, further enhancing the fire resistance reliability and structural integrity of the microporous vacuum composite armor layer 4 under extreme fire conditions.

[0015] Preferably, the microporous vacuum composite tape is overlapped and wrapped, with an overlap rate of 15% to 25%, a wrapping angle of 15° to 45°, and a wrapping tension of 5N to 50N. By adopting this solution, the microporous vacuum composite armor layer forms a continuous and complete protective barrier during the cabling and wrapping process, while retaining the bending compliance capability given by the segmented flexible design of the tape, ultimately achieving a unified function of mechanical protection, fireproofing and heat insulation, and laying flexibility.

[0016] Preferably, the fire-resistant layer is a ceramicized silicone rubber layer or a mica tape layer; the ceramicized silicone rubber layer is formed by extruding ceramicized silicone rubber material or wrapping ceramicized silicone rubber tape; the mica tape layer is formed by wrapping mica tape. By adopting this solution, the fire-resistant layer solution can be flexibly selected according to the specific application scenario of the cable, and both solutions can serve as a fire barrier adjacent to the insulation layer, directly resisting the erosion impact of flames on the insulation layer and conductor in the event of a fire, and maintaining the insulation integrity.

[0017] Through the above technical solution, the present invention achieves the following beneficial effects: 1. This application integrates armoring, heat insulation, and fire resistance into one through a microporous vacuum composite armoring layer, eliminating the need for separate armoring and heat insulation layers, significantly simplifying the cable structure, reducing the cable outer diameter, and lowering material costs; 2. This application integrates armor and thermal insulation functions into the same structural layer, instead of relying on multiple layers. Therefore, there is no interlayer interface problem in multi-layer composite structures, which completely eliminates the risk of slippage and peeling caused by the difference in thermal expansion coefficients between layers, and greatly improves the long-term operational reliability of the cable. 3. This application uses a segmented independent vacuum unit design to make each micropore vacuum composite section an independent and sealed vacuum chamber, which provides redundant protection capabilities. The vacuum failure of a single micropore vacuum composite section will not affect other sections, avoiding the drawbacks of "single-point leakage and overall failure" in traditional continuous vacuum layers, and significantly improving the service reliability of the cable under complex working conditions. 4. This application achieves an equivalent thermal conductivity of ≤0.01W / (m·K) through the synergistic effect of the high vacuum state inside the micropores and the low solid-phase thermal conductivity of the microporous metal skeleton, which is far superior to traditional thermal insulation materials such as ceramicized silicone rubber and aerogel felt, and can achieve better thermal insulation effect with thinner thickness. 5. The microporous metal skeleton and metal foil encapsulation layer of this application are both non-combustible metal materials, which have high temperature resistance, meet the standard requirements for fire-resistant cables, and do not produce toxic fumes at high temperatures; 6. This application uses a segmented structure with alternating rigid microporous vacuum composite sections and flexible metal connectors to enable the entire microporous vacuum composite tape to maintain excellent mechanical protection capabilities while possessing compliant bending performance, thus overcoming the technical difficulties of applying rigid vacuum insulation structures to cables. 7. This application has good airtightness through metal foil encapsulation layer, and combined with the high structural strength of the microporous metal skeleton itself, it can effectively maintain the vacuum degree of the internal micropores and has a long service life. 8. The overlapping wrapping design of the microporous vacuum composite tape in this application not only eliminates the overlap gaps between the tapes, ensuring the continuity and airtightness of the armor layer in the circumferential direction and effectively blocking the intrusion of flames and high-temperature gases, but also achieves overall flexibility through the relative sliding between the tapes, so that the armor layer does not suffer structural damage when the cable is bent, and has excellent mechanical protection and fireproof and heat insulation performance. Attached Figure Description

[0018] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0019] Figure 1 This is a radial cross-sectional view of the flame-retardant and fire-resistant cable described in an embodiment of the present invention; Figure 2 for Figure 1 Schematic diagram of the microporous vacuum composite armor layer; Figure 3 for Figure 2 Radial cross-sectional view of the microporous vacuum composite section; Explanation of reference numerals in the attached figures: 1. Conductor; 2. Insulating layer; 3. Fire-resistant layer; 4. Microporous vacuum composite armor layer; 41. Microporous vacuum composite strip; 411. Microporous vacuum composite section; 4111. Microporous metal skeleton; 4112. Metal foil encapsulation layer; 4113. Fireproof coating; 412. Flexible metal connector; 5. Outer sheath. Detailed Implementation

[0020] The embodiments of the technical solution of the present invention will now be described in detail with reference to the accompanying drawings. These embodiments are merely illustrative of the technical solution of the present invention and are therefore intended to limit the scope of protection of the present invention.

[0021] In this application, unless otherwise expressly specified and limited, the terms "installation" and "connection" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0022] To better understand the above technical solutions, the following will provide a detailed description of the technical solutions in conjunction with the accompanying drawings and specific embodiments.

[0023] Example: like Figure 1 As shown in the illustration, this application discloses a flame-retardant and fire-resistant cable. By integrating armored mechanical protection with vacuum high-efficiency thermal insulation, it significantly reduces the outer diameter and improves structural compactness while achieving excellent fire resistance and thermal insulation performance. It is particularly suitable for critical power supply circuits in space-constrained and harsh fire environments such as fire protection systems, emergency lighting, nuclear power facilities, rail transportation, ships, and high-end industrial equipment. Specifically, it includes, from the inside out, a conductor 1, an insulation layer 2, a fire-resistant layer 3, a microporous vacuum composite armor layer 4, and an outer sheath 5.

[0024] like Figure 2 As shown, the microporous vacuum composite armor layer 4 is formed by overlapping and wrapping the microporous vacuum composite strip 41 around the refractory layer 3. The microporous vacuum composite strip 41 includes multiple microporous vacuum composite segments 411 and flexible metal connectors 412. Adjacent microporous vacuum composite segments 411 are connected by flexible metal connectors 412, thereby forming a segmented structure along the length of the strip.

[0025] It should be noted that the microporous vacuum composite tape 41 forms a continuous spiral coating layer outside the fire-resistant layer 3. The overlapping area between adjacent tapes eliminates radial gaps, ensuring the sealing integrity of the microporous vacuum composite armor layer 4 and preventing flames and high-temperature gases from entering the cable through the lap joint. At the same time, since the lap joint in the width direction of the tape is a non-rigid fixed connection, each loop of tape can undergo a slight relative slippage when the cable is bent, so that the microporous vacuum composite armor layer 4 remains flexible as a whole, avoiding the risk of plastic deformation or breakage when bending traditional integral rigid armor.

[0026] Understandably, the microporous vacuum composite section 411 is the smallest structural unit that undertakes both armor protection and vacuum insulation functions; while the flexible metal connector 412 connects the various rigid microporous vacuum composite sections 411 into a complete strip, so that the entire strip maintains high strength in most areas while having the flexibility to adapt to cable bending and twisting. This "alternating rigidity and flexibility" structure makes the microporous vacuum composite armor layer 4 as a whole flexible, and the bending radius can be controlled within the range required by cable industry standards (such as ≤15 times the cable outer diameter), meeting the requirements of cable coiling, transportation and laying.

[0027] Understandably, since each microporous vacuum composite section 411 is an independent sealed vacuum unit, even if a vacuum failure occurs in one of the composite sections due to accidental external impact or high-temperature deformation, only the thermal insulation performance of that section will be affected, while the vacuum thermal insulation function of the remaining sections remains unchanged, ensuring that the overall fire resistance and thermal insulation performance of the cable will not experience a precipitous decline. This redundant design of "single-segment failure, localized impact" significantly improves the reliability and service life of the cable under extreme operating conditions.

[0028] like Figure 3 As shown, each microporous vacuum composite segment 411 includes a microporous metal skeleton 4111 and a metal foil encapsulation layer 4112 covering the outer surface of the microporous metal skeleton 4111. The microporous metal framework 4111 has a three-dimensional interconnected microporous structure with a porosity of 60%–95% and a pore size of 10 μm–200 μm, and an internal air pressure. The metal foil encapsulation layer 4112 forms an airtight seal to maintain the vacuum state inside the microporous metal skeleton 4111.

[0029] It should be noted that the microporous metal skeleton 4111 itself possesses high mechanical strength, effectively resisting external extrusion, impact, and other mechanical forces, thus fulfilling the mechanical protective function of the armor layer. Simultaneously, its three-dimensional interconnected microporous structure and porosity of 60%–95% ensure isotropic mechanical properties, avoiding the weak overlapping areas present in traditional wrapping armor, and providing a continuous internal space for vacuum evacuation, which is fundamental to achieving vacuum insulation. Finally, by optimizing the pore structure design and controlling the pore size within the range of 10μm–200μm, not only can the convective heat transfer of residual gas within the micropores be effectively suppressed, but the uniform stress distribution through small pores also significantly improves the specific strength and compressive load-bearing capacity of the skeleton, enabling the microporous vacuum composite armor layer 4 to maintain lightweight while possessing outstanding mechanical reliability.

[0030] It is understandable that the three-dimensional interconnected micropores of the microporous metal framework 4111 are in a high vacuum state. This results in a very small number of gas molecules within the micropores, significantly suppressing gas heat conduction and convection. Although vacuum insulation panels can achieve low thermal conductivity below 100 Pa, this application employs more stringent vacuum requirements (…). The purpose is to compensate for the additional heat flow caused by solid-state thermal conduction in the microporous metal skeleton 4111. Simultaneously, the porous structure of the microporous metal skeleton 4111 effectively reduces the solid-state heat transfer path, resulting in a low solid-state thermal conductivity. Under the synergistic effect of the high vacuum and low solid-state thermal conductivity, the equivalent thermal conductivity of the microporous vacuum composite armor layer 4 can be as low as ≤0.01 W / (m·K), significantly better than traditional thermal insulation materials such as ceramicized silicone rubber (thermal conductivity approximately 0.2–0.3 W / (m·K)).

[0031] Understandably, both the microporous metal skeleton 4111 and the metal foil encapsulation layer 4112 are non-combustible metal materials, capable of withstanding temperatures above 800℃, meeting the requirements of GB / T19216.21 (Class A flame temperature 950~1000℃, continuous fire supply time 90min) and GA306 fire-resistant cable standards. In high-temperature fire environments, the microporous metal skeleton 4111 maintains structural integrity and does not burn or decompose like organic insulation materials. Simultaneously, the vacuum microporous structure continuously provides insulation, delaying heat conduction to the internal conductor 1.

[0032] Through the above design, the present invention has the following technical effects: 1. By integrating armor, heat insulation, and fire resistance into one through the microporous vacuum composite armor layer 4, the cable structure is significantly simplified, the outer diameter of the cable is reduced, and the material cost is lowered, eliminating the need for separate armor and heat insulation layers.

[0033] Second, the armoring and thermal insulation functions are integrated into the same structural layer, instead of relying on multiple layers. Therefore, there is no interlayer interface problem in multi-layer composite structures, which completely eliminates the risk of slippage and peeling caused by the difference in thermal expansion coefficients between layers, and greatly improves the long-term operational reliability of the cable.

[0034] Third, the segmented independent vacuum unit design makes each micropore vacuum composite section 411 an independent and sealed vacuum chamber, which provides redundant protection capabilities. The vacuum failure of a single micropore vacuum composite section 411 will not affect other sections, avoiding the drawbacks of "single-point leakage and overall failure" in traditional continuous vacuum layers, and significantly improving the service reliability of the cable under complex working conditions.

[0035] Fourth, through the synergistic effect of the high vacuum state inside the micropores and the low solid-phase thermal conductivity of the microporous metal skeleton 4111, the equivalent thermal conductivity is as low as ≤0.01W / (m·K), which is far superior to traditional thermal insulation materials such as ceramicized silicone rubber and aerogel felt, and can achieve better thermal insulation effect with thinner thickness.

[0036] 5. Both the microporous metal skeleton 4111 and the metal foil encapsulation layer 4112 are non-combustible metal materials with high temperature resistance, meeting the requirements of fire-resistant cable standards such as GB / T19216.21 and GA306, and do not produce toxic fumes at high temperatures.

[0037] VI. The segmented structure, combined with the alternating arrangement of rigid microporous vacuum composite section 411 and flexible metal connector 412, enables the entire microporous vacuum composite tape 41 to maintain excellent mechanical protection capabilities while possessing compliant bending performance, thus overcoming the technical difficulties of applying rigid vacuum insulation structures to cables.

[0038] VII. The metal foil encapsulation layer 4112 has good airtightness, and combined with the high structural strength of the microporous metal skeleton 4111 itself, it can effectively maintain the internal micropore vacuum and has a long service life.

[0039] 8. The overlapping wrapping design of the microporous vacuum composite tape 41 not only eliminates the overlap gaps between the tapes, ensuring the continuity and airtightness of the armor layer in the circumferential direction and effectively blocking the intrusion of flames and high-temperature gases, but also achieves overall flexibility through the relative sliding between the tapes, so that the armor layer does not suffer structural damage when the cable is bent, and has excellent mechanical protection and fireproof and heat insulation performance.

[0040] In some embodiments, the microporous metal skeleton 4111 has a porosity of 70% to 90%, a pore size of 20 μm to 100 μm, and a thickness of 0.5 mm to 5 mm.

[0041] Through the above design, a better balance between mechanical strength, thermal insulation performance and bending flexibility is achieved: its high porosity ensures sufficient vacuum insulation space and further reduces solid-phase heat conduction; while the optimized pore size range effectively suppresses gas heat transfer and gives it higher specific strength and compressive load-bearing capacity; the thickness design ensures mechanical protection stiffness and avoids bending stress concentration caused by excessive thickness in a single section, so that the strip has both structural compactness and laying flexibility after wrapping.

[0042] In some embodiments, the microporous metal framework 4111 is a foamed metal, selected from one or more of foamed nickel, foamed copper, and foamed stainless steel.

[0043] Understandably, nickel foam has certain oxidation resistance, is lightweight and has good flexibility, making it easy to bend and form strips; copper foam has moderate thermal conductivity and good processability, which is conducive to the uniform control of microporous structure; and stainless steel foam has high strength, excellent temperature resistance and corrosion resistance, and can maintain the integrity of the skeleton structure under harsh fire environment and harsh working conditions.

[0044] It should be noted that for single-core AC cables, if the armor layer uses magnetic metal materials, eddy current losses and hysteresis losses will occur under the action of an alternating magnetic field, leading to abnormal heating of the armor layer and thus reducing the cable's current carrying capacity. To avoid the above problems, the foam metal constituting the microporous metal skeleton 4111 should be selected from non-magnetic metals, specifically foamed copper or austenitic foamed stainless steel (such as 304L or 316L). In this way, while ensuring that the armor layer achieves mechanical protection and vacuum insulation functions, the additional losses caused by magnetic armor are eliminated, ensuring that the electrical transmission efficiency of the cable is not affected.

[0045] Through the above design, flexible material adaptation and functional synergy can be achieved according to the performance requirements of different application scenarios. This enables the microporous metal skeleton 4111 to achieve an optimized balance between support stiffness, vacuum insulation performance, fire resistance rating and engineering adaptability, significantly improving its comprehensive applicability under different working conditions.

[0046] In some embodiments, the metal foil encapsulation layer 4112 is a stainless steel foil or an aluminum foil with a thickness of 0.05 mm to 0.2 mm, and the edges can be sealed by laser welding.

[0047] Understandably, stainless steel foil has high strength, excellent corrosion resistance and oxidation resistance, and can effectively resist external mechanical damage and environmental erosion, making it suitable for forming a long-term reliable airtight seal; while aluminum foil has low density and good ductility, making it easy to adhere to the surface of the microporous metal skeleton 4111 and achieve tight coverage.

[0048] It should be noted that by limiting the thickness to the range of 0.05mm to 0.2mm, a dense and reliable hermetically sealed structure can be formed to ensure that the high vacuum inside the microporous metal skeleton 4111 is maintained for a long time. At the same time, it can avoid excessive rigidity of the strip due to excessive thickness of the encapsulation layer, and ensure that the armor layer has good flexibility when wrapping and bending, and that the encapsulation layer will not crack.

[0049] Through the above design, a balance can be achieved between airtight sealing reliability, mechanical protection capability and strip flexibility, so that the metal foil encapsulation layer 4112 can effectively maintain the vacuum state inside the micropores while taking into account the flexibility required for cable bending and laying and the durability for long-term use.

[0050] In some embodiments, the flexible metal connector 412 is a metal bellows, made of 304 stainless steel or 316L stainless steel, with a wall thickness of 0.15mm to 0.30mm, a corrugated shape of U-shaped or S-shaped, a peak height of 2mm to 5mm, a wave pitch of 3mm to 8mm, and a smooth transition between the peaks and troughs.

[0051] Metal bellows is a continuous thin-walled tube structure with transverse corrugations. Its continuous tube wall can uniformly transmit tensile, bending and torsional loads. The bending stiffness can be flexibly adjusted by the waveform parameters. It has excellent resilience and good long-term reliability. It is also easy to laser weld with the metal foil encapsulation layer 4112 of the front and rear microporous vacuum composite sections 411 to form a continuous and sufficiently long circumferential weld, which is stable. It also makes the surface of the microporous vacuum composite strip 41 continuous and flat, which is conducive to the tight wrapping of the outer sheath 5.

[0052] Regarding the limitations on various structural parameters of metal bellows, it is understandable that: The material is limited to 304 stainless steel or 316L stainless steel. Both are non-combustible metals with excellent high-temperature resistance and are compatible with the 4112 metal foil encapsulation layer material, which facilitates overall welding. The wall thickness is limited to 0.15mm to 0.30mm, which achieves an optimized balance between bending flexibility and structural strength. Its upper limit ensures that the bending moment of the corrugated pipe is controllable and does not affect the overall flexibility of the cable, while the lower limit ensures that the corrugated pipe has sufficient compressive and torsional strength and fatigue life. The corrugated shape is limited to U-shaped or S-shaped corrugations. U-shaped corrugations have uniform stress distribution and long fatigue life, while S-shaped corrugations can accommodate more corrugations and have better compliance. Both waveforms are continuous curved surfaces with smooth transitions and uniform stress distribution, which can effectively avoid stress concentration at sharp corners and improve fatigue resistance. The height of the crest is limited to 2mm to 5mm to ensure that the corrugations have sufficient geometric depth to form an effective flexible deformation zone, while controlling the overall thickness of the armor strip to prevent excessive increase. The wave pitch is limited to 3mm to 8mm to provide a sufficient number of corrugations per unit length to increase the flexibility and deformation capacity, while avoiding excessively sparse corrugations that could cause excessive deformation of a single corrugation and enter the plastic zone. The smooth transition between the crests and troughs ensures that the bending stress is evenly distributed along the waveform profile, eliminating local high-stress areas and improving long-term reliability under repeated bending and thermal cycling conditions.

[0053] Through the above design, the metal corrugated pipe forms a reliable transition area between the microporous vacuum composite section 411, which takes into account both mechanical flexibility and structural integrity. This allows the armor tape to maintain vacuum sealing and mechanical protection capabilities while also having the flexibility required for cable bending and laying, thus achieving a balance between rigidity and flexibility, uniform load transfer, and long-term reliability.

[0054] In some embodiments, the flexible metal connector 412 is a metal woven mesh sleeve made of 304 or 316L stainless steel wire with a wire diameter of 0.2mm to 0.5mm, a weaving density of 70% to 85%, and a weaving angle of 30° to 45°.

[0055] Metal braided mesh sheaths are continuous mesh tubular structures made of multiple strands of metal wires woven together in a certain pattern. They can transmit tensile, torsional, and bending loads and provide bending flexibility. Compared with metal corrugated pipes, braided mesh sheaths have lower bending stiffness, better torsional compliance, and are lighter in weight. They also generate almost no springback stress when bent, making them better suited for scenarios involving repeated cable coiling and laying cables with small bending radii.

[0056] Regarding the limitations on various structural parameters of the metal woven mesh sleeve, it is understandable that: The material is limited to 304 or 316L stainless steel wire; both are non-combustible metals with excellent high temperature resistance, and stainless steel wire has high tensile strength and fatigue limit, which can ensure that the woven mesh sleeve can withstand alternating stress for a long time without breaking during cable bending and operation. The wire diameter is limited to 0.2mm to 0.5mm; the lower limit ensures that the single wire has sufficient tensile strength and wear resistance to prevent wire breakage due to excessive force during braiding or cable bending, while the upper limit controls the single wire diameter to prevent the mesh sleeve from being too stiff, which would affect the overall flexibility and bending compliance of the cable; and the finer wire diameter can make the mesh sleeve surface smoother, which is beneficial for the outer sheath 5 to cover. The weaving density is limited to 70% to 85%; the lower limit ensures that the netting has sufficient structural density and strength to reliably transmit axial tension and prevent loosening; the upper limit ensures a certain mesh opening to avoid the netting becoming too dense and rigid, losing its flexibility; and retaining a small amount of gaps also facilitates the sliding between the wires when bending, making the netting easier to deform. The weaving angle is limited to 30° to 45°. The lower limit ensures that the woven mesh can generate sufficient radial shrinkage when subjected to axial tension, so as to achieve effective load transfer and avoid locking between the filaments when bending. The upper limit avoids that the axial stiffness is insufficient due to the excessive weaving angle, resulting in excessive axial elongation deformation when subjected to tension, which would affect the dimensional stability of the connection structure. Within this angle range, it will have both moderate axial stiffness and good bending compliance, and while transferring the mechanical continuity of the strip along the length direction, it will not significantly constrain the relative bending between the microporous vacuum composite sections 411.

[0057] Through the above design, the metal braided mesh sleeve forms a mechanically continuous and flexible connection between the microporous vacuum composite sections 411, which has extremely low bending stiffness while transmitting axial tensile loads, so that the entire strip has both the longitudinal strength required for mechanical protection and the flexible bending performance required for cable laying.

[0058] It should be noted that when a single-core cable transmits alternating current, the alternating magnetic field around it induces an electromotive force in adjacent metal components. If the material has high permeability, significant hysteresis and eddy current losses will occur, leading to localized heating, increasing additional losses in the cable line, and affecting long-term operational stability. To avoid these problems, for single-core cables, the flexible metal connector 412 is preferably made of 316L stainless steel. After cold forming, 316L stainless steel has an extremely low martensite content, and its relative permeability can be maintained at a low level, thereby effectively suppressing magnetic losses and heating.

[0059] In some embodiments, the length of the microporous vacuum composite section 411 is 50mm to 500mm, the length of the flexible metal connector 412 is 20mm to 80mm, and the ratio of the length of the microporous vacuum composite section 411 to the length of the flexible metal connector 412 is 1:1 to 10:1.

[0060] The length of the microporous vacuum composite section 411 is limited to 50mm to 500mm; the lower limit ensures that a single composite section has sufficient axial accommodation space to avoid excessively thin sections leading to too many encapsulation seams, while the upper limit prevents the rigid section from being too long, causing excessive local curvature when the cable bends, making the composite section unable to follow the bending trajectory of the cable.

[0061] The length of the flexible metal connector 412 is limited to 20mm to 80mm; it is used to balance bending compensation capability and armor continuity. Its lower limit provides sufficient deformation space for the connector so that it can fully absorb the relative angle between adjacent rigid sections and avoid bending stress concentration; the upper limit prevents the proportion of flexible sections from being too high, which would weaken the overall thermal insulation and mechanical protection continuity of the armor layer.

[0062] The length ratio of the microporous vacuum composite section 411 to the flexible metal connector 412 is limited to 1:1 to 10:1. The lower limit avoids that the flexible metal connector 412 accounts for too high a proportion, resulting in too little area that actually undertakes the armoring and heat insulation functions, thus weakening the overall performance. The upper limit prevents the microporous vacuum composite section 411 from being too long, which would lead to insufficient flexibility of the entire strip and enable it to meet the minimum bending radius requirements of the cable. This achieves a balance between the continuity of heat insulation protection and the ability to bend compliantly according to the specific working conditions.

[0063] Through the above design, the microporous vacuum composite tape 41 maintains a high proportion of effective vacuum insulation area and continuous mechanical protection capability, while achieving smooth bending of the entire tape through deformation compensation of the flexible connection area, thereby achieving a balance between the continuity of thermal insulation protection and the adaptability of cable bending laying.

[0064] In some embodiments, such as Figure 3 As shown, the outer surface of the metal foil encapsulation layer 4112 is coated with a fire-retardant coating 4113, which is a ceramicized silicone rubber fire-retardant coating with a thickness of 0.1 mm to 0.5 mm.

[0065] It should be noted that the ceramicized silicone rubber fireproof coating has flexibility and good adhesion at room temperature, and can tightly cover the surface of the metal foil encapsulation layer 4112. It can also deform synchronously with the bending and wrapping of the microporous vacuum composite section 411 without cracking or falling off. Under the high temperature of a fire, the ceramicized silicone rubber coating can be transformed in situ into a dense ceramic protective layer. In conjunction with the internal vacuum insulation structure, it can block the direct ablation of the metal foil encapsulation layer 4112 and the airtight weld from the outside, and continuously play a vacuum insulation role from the inside. This enhances the fire resistance reliability of the microporous vacuum composite section 411 without significantly increasing the thickness of the strip.

[0066] Understandably, the coating thickness is limited to 0.1mm to 0.5mm. The lower limit ensures that the coating can form a continuous ceramic protective layer with sufficient thickness at high temperatures, avoiding incomplete coverage or local cracking after ceramicization due to excessively thin coating, thus losing its protective function. The upper limit controls the coating thickness to avoid significantly increasing the overall thickness and outer diameter of the microporous vacuum composite section 411, while also taking into account material costs.

[0067] Through the above design, the microporous vacuum composite section 411, on the basis of the original vacuum insulation and mechanical protection functions, is superimposed with the ability to generate a ceramic protective layer in situ at high temperature, which further enhances the fire resistance reliability and structural integrity of the microporous vacuum composite armor layer 4 under extreme fire conditions.

[0068] In some embodiments, such as Figure 2 As shown, the microporous vacuum composite tape 41 is overlapped and wrapped, with an overlap rate of 15% to 25%, a wrapping angle of 15° to 45°, and a wrapping tension of 5N to 50N.

[0069] It should be noted that the overlap rate is limited to 15% to 25%, which ensures the continuous sealing and airtightness of the microporous vacuum composite armor layer 4 in the circumferential direction. This effectively blocks the intrusion of flames and high-temperature gases, avoids a significant increase in the local thickness and outer diameter of the armor layer, and saves on material usage.

[0070] It should be noted that the wrapping angle is limited to 15° to 45°, which achieves a balance between the smoothness of the wrapping process and the uniformity of the armor structure, ensuring that the strip is uniformly wrapped with a reasonable helix angle, forming a continuous armor layer with balanced mechanical and protective properties in all directions.

[0071] It should be noted that the wrapping tension is limited to 5N to 50N. This ensures that the strip fits tightly and eliminates slack gaps, while preventing structural damage to the flexible metal connector 412 due to excessive tension. This ensures that the microporous vacuum composite armor layer 4 after wrapping has both structural tightness and functional integrity.

[0072] Through the above design, the microporous vacuum composite armor layer 4 forms a continuous and complete protective barrier during the cabling and wrapping process, while retaining the bending compliance capability given by the segmented flexible design of the strip, ultimately achieving a unified function of mechanical protection, fireproofing and heat insulation and laying flexibility.

[0073] In some embodiments, the fire-resistant layer 3 is a ceramicized silicone rubber layer or a mica tape layer; the ceramicized silicone rubber layer is a flexible elastomer at room temperature, which can be transformed in situ into a dense ceramic shell at high temperature, possessing both room temperature flexibility and high temperature fire resistance; while the mica tape layer is a strip-shaped fire-resistant material that does not burn or decompose in flames and can withstand high temperatures for a long time, and is a mature material for the fire-resistant layer 3; both can provide an effective thermal barrier for the interior, and can be flexibly selected according to different application scenarios and cost requirements of the cable.

[0074] The ceramicized silicone rubber layer is formed by extruding ceramicized silicone rubber material or wrapping ceramicized silicone rubber tape. Extrusion results in a uniform thickness, smooth surface, tight adhesion, and strong interfacial bonding, which is beneficial for the subsequent wrapping of the microporous vacuum composite armor layer 4, resulting in high production efficiency and suitability for large-scale continuous production. Wrapping offers high process flexibility, suitable for small-batch, multi-specification production needs, and allows for stress release through interlayer slippage during cable bending, helping to maintain cable flexibility. Both molding methods can meet the functional requirements of the fire-resistant layer, and the appropriate process can be selected based on cable specifications and batch requirements.

[0075] The mica tape layer is formed by wrapping mica tape. The wrapping process allows the mica tape to form a continuous overlapping fire-resistant barrier in the circumferential direction. The double-layer structure of the overlapping area can further enhance the fire resistance reliability. Moreover, the wrapping process is mature and easy to operate.

[0076] Through the above design, the fire-resistant layer 3 scheme can be flexibly selected according to the specific application scenario of the cable. Both schemes can serve as a fire barrier adjacent to the insulation layer 2, directly resisting the burning impact of flames on the insulation layer 2 and conductor 1 in the event of a fire, and maintaining the insulation integrity.

[0077] In some embodiments, the outer sheath 5 is an extruded layer of low-smoke, halogen-free, flame-retardant polyolefin material, which integrates low-smoke, halogen-free, and flame-retardant properties. It produces low smoke during combustion, does not release corrosive or toxic gases, and is self-extinguishing when the flame is removed. It also ensures visibility, avoids secondary hazards, and inhibits the spread of flames along the cable. At the same time, the extrusion molding process gives the sheath a uniform and dense covering quality, which can fit tightly and provide reliable mechanical protection and environmental isolation for the cable, ensuring its comprehensive reliability during laying and long-term operation.

[0078] In this embodiment, a method for preparing the above-mentioned flame-retardant and fire-resistant cable is also provided, including the following steps: Step S1: Prepare foam metal using electrodeposition or powder metallurgy sintering; and control the porosity to be 60%–95%, the pore size to be 10 μm–200 μm, and the thickness to be 0.5 mm–5 mm.

[0079] Step S2: Cut the foam metal into strips with a width of 20mm to 80mm, and mark them into segments according to a preset length, with each segment being 50mm to 500mm long.

[0080] Step S3: Place the segmented foam metal strips in a vacuum sealing device and evacuate to a vacuum level of ≤1×10⁻⁶. - ³ Pa (considering the possibility of trace gas release during long-term use after encapsulation, a more stringent vacuum level is used during encapsulation). While maintaining a vacuum, a metal foil (stainless steel or aluminum foil, 0.05mm–0.2mm thick) is coated onto the outer surface of the strip. The edges are sealed by laser welding, with a weld width of 0.5mm–2mm, forming a microporous vacuum composite section 411. The vacuuming time is 30min–120min to ensure sufficient gas removal from the three-dimensionally interconnected micropores. Post-weld leak detection using helium mass spectrometry is performed, with a leak rate ≤1×10⁻⁶. -9 Pa·m³ / s.

[0081] Step S4: Perform ultrasonic cleaning or chemical degreasing on the outer surface of the metal foil encapsulation layer 4112 of the microporous vacuum composite section 411 formed in step S3 to remove surface oil and oxides.

[0082] Step S5: On the outer surface of the metal foil encapsulation layer 4112 after cleaning in step S4, first reserve a 5mm to 15mm uncoated area at both ends as the welding area for subsequent laser welding (the uncoated area at the ends is achieved by: masking both ends of the strip segment with high-temperature resistant tape before coating, and removing the masking tape after coating; or wiping off the end coating with solvent after coating). Then, apply a primer for pretreatment. The primer is a silane or siloxane adhesive accelerator with a coating thickness of 1μm to 10μm and air-dry at room temperature for 10 to 20 minutes. Then, apply a fire-retardant coating 4113 on the primer layer. The fire-retardant coating 4113 is a ceramicized silicone rubber fire-retardant coating with a coating thickness of 0.1mm to 0.5mm and cures at room temperature for 24 hours or at 80 to 120°C for 2 to 4 hours. The primer is used to enhance the interfacial bonding strength between the ceramicized silicone rubber fire-retardant coating and the metal foil encapsulation layer 4112.

[0083] Step S6: The microporous vacuum composite segment 411, after being encapsulated and coated with a fire-retardant coating 4113, is alternately arranged with the flexible metal connector 412 and connected by laser welding to form a continuous microporous vacuum composite strip 41. The laser welding is carried out in an argon protective atmosphere, with a welding power of 500W to 2000W and a welding speed of 1m / min to 3m / min. During laser welding, a water-cooled fixture is used to locally cool the microporous vacuum composite segment 411 to ensure that the welding heat-affected zone does not extend to the vacuum encapsulation area. After welding, the vacuum encapsulation layer near the welding area (within 5mm to 20mm of the weld seam) is subjected to local helium mass spectrometry leak detection.

[0084] Step S7: On the outside of the cable core where conductor 1, insulation layer 2, and fire-resistant layer 3 have been prepared, the above-mentioned microporous vacuum composite tape 41 is wrapped around the outside of the cable core in an overlapping wrapping manner. The overlap rate is 15% to 25%, the wrapping angle is 15° to 45°, and the wrapping tension is controlled at 5N to 50N. The specific tension should be determined according to the cable specifications and tape width to ensure that the wrapping is tight and does not damage the vacuum encapsulation of the microporous vacuum composite section 411, thus forming a microporous vacuum composite armor layer 4. During the wrapping process, the bending radius should be controlled to avoid cracks in the fireproof coating 4113 due to excessive tensile or compressive stress.

[0085] Step S8: After wrapping, perform helium mass spectrometry leak detection on the finished cable, with a leak rate ≤1×10⁻⁶. -9 Pa·m³ / s, ensuring that the vacuum seal is not damaged during the wrapping process; when checking for leaks after wrapping, attention should be paid to the possibility that the fireproof coating 4113 may cover the tiny leaks on the surface of the metal foil encapsulation layer 4112.

[0086] Step S9: Extrude a halogen-free, low-smoke, flame-retardant polyolefin outer sheath 5 over the microporous vacuum composite armor layer 4.

[0087] Numerous specific details are set forth in this specification. However, it will be understood that embodiments of the invention may be practiced without these specific details. In some instances, well-known methods, structures, and techniques have not been shown in detail so as not to obscure the understanding of this specification.

[0088] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A fire-retardant, fire-resistant cable, characterized in that, It includes, from the inside out, a conductor, an insulating layer, a fire-resistant layer, a microporous vacuum composite armor layer, and an outer sheath; The microporous vacuum composite armor layer is formed by overlapping and wrapping microporous vacuum composite strips around the outside of the refractory layer. The microporous vacuum composite strips include multiple microporous vacuum composite segments and flexible metal connectors. Adjacent microporous vacuum composite segments are connected by the flexible metal connectors. Each of the microporous vacuum composite segments includes a microporous metal framework and a metal foil encapsulation layer covering the outer surface of the microporous metal framework. The microporous metal framework has a three-dimensional interconnected microporous structure with a porosity of 60%–95% and a pore size of 10 μm–200 μm. The internal air pressure... The metal foil encapsulation layer forms an airtight seal to maintain a vacuum state within the microporous metal skeleton.

2. The flame-retardant and fire-resistant cable according to claim 1, characterized in that, The microporous metal skeleton has a porosity of 70% to 90%, a pore size of 20 μm to 100 μm, and a thickness of 0.5 mm to 5 mm.

3. The flame-retardant and fire-resistant cable according to claim 1, characterized in that, The microporous metal framework is foam metal, and is selected from one or more of foam nickel, foam copper, and foam stainless steel.

4. The flame-retardant and fire-resistant cable according to claim 1, characterized in that, The metal foil encapsulation layer is stainless steel foil or aluminum foil, with a thickness of 0.05mm to 0.2mm.

5. The flame-retardant and fire-resistant cable according to claim 1, characterized in that, The flexible metal connector is a metal corrugated pipe made of 304 stainless steel or 316L stainless steel, with a wall thickness of 0.15mm to 0.30mm, a corrugated shape of U-shape or S-shape, a peak height of 2mm to 5mm, a wave pitch of 3mm to 8mm, and a smooth transition between the peaks and troughs.

6. The flame-retardant and fire-resistant cable according to claim 1, characterized in that, The flexible metal connector is a metal woven mesh sleeve made of 304 or 316L stainless steel wire with a wire diameter of 0.2mm to 0.5mm, a weaving density of 70% to 85%, and a weaving angle of 30° to 45°.

7. The flame-retardant and fire-resistant cable according to claim 1, characterized in that, The length of the microporous vacuum composite section is 50mm to 500mm, the length of the flexible metal connector is 20mm to 80mm, and the ratio of the length of the microporous vacuum composite section to the length of the flexible metal connector is 1:1 to 10:

1.

8. The flame-retardant and fire-resistant cable according to claim 1, characterized in that, The outer surface of the metal foil encapsulation layer is coated with a fire-retardant coating, which is a ceramicized silicone rubber fire-retardant coating with a thickness of 0.1 mm to 0.5 mm.

9. The flame-retardant and fire-resistant cable according to claim 1, characterized in that, The microporous vacuum composite tape is overlapped and wrapped, with an overlap rate of 15% to 25%, a wrapping angle of 15° to 45°, and a wrapping tension of 5N to 50N.

10. The flame-retardant and fire-resistant cable according to claim 1, characterized in that, The refractory layer is a ceramicized silicone rubber layer or a mica tape layer; the ceramicized silicone rubber layer is formed by extruding ceramicized silicone rubber material or wrapping ceramicized silicone rubber tape; the mica tape layer is formed by wrapping mica tape.

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