High-flexibility medium-low voltage insulated cable and preparation method thereof

Abstract

The application belongs to the technical field of cable materials, and particularly relates to a high-flexibility medium-low voltage insulated cable and a preparation method thereof. The cable comprises a plurality of asymmetrically arranged cores, a compressible deformation zone, a low-friction isolation layer and a spiral buffer layer. The compressible deformation zone is arranged in a staggered manner with the spiral buffer layer. Through the synergistic effect of asymmetric core arrangement, directional compressible deformation and limited relative displacement along the radial compressible deformation zone direction, multi-stage dispersion of bending stress is realized, and the repeated bending life and insulation performance of the cable can be improved. The cable has the advantages of small minimum bending radius, high bending recovery rate, good insulation resistance retention rate and excellent low-temperature resistance, and is suitable for flexible connection and high-reliability application in complex wiring environments.

Description

Technical Field

[0001] This invention belongs to the field of cable material technology, specifically relating to a highly flexible medium- and low-voltage insulated cable and its preparation method. Background Technology

[0002] Medium and low voltage power cables are mainly used in power supply applications such as industrial equipment, mobile power supply equipment, building construction, rail transportation, and ships. Compared with fixed-lay cables, cables in these environments typically need to withstand greater bending deformation and local compression. Therefore, in addition to meeting conductivity and insulation performance requirements, they also need to possess good flexibility and bending resistance. Existing highly flexible cables typically improve their bending performance by increasing the flexibility of the insulation material, adding buffer layers, or using flexible sheaths. For example, by setting elastic ropes and elastic particles between the cores, a certain amount of deformation space can be provided when the cable is subjected to external forces. Some flexible cables also have buffer strips, foamed rubber strips, buffer bladders, etc., between the filler layer and the outer sheath to absorb external forces when elastic or compressive deformation occurs.

[0003] Currently, existing medium-voltage power cables with bending resistance in the industry mostly utilize structures such as supports, elastic components, and air bladders to disperse and release bending stress and compressive force, thereby balancing the internal stress state of the cable and optimizing its overall bending performance. However, these existing technical solutions largely rely on adding flexible materials, buffer components, or reserving elastic space to improve the cable's flexibility. The relatively regular arrangement of the internal conductors in these cables results in a lack of effective guidance and restraint mechanisms for the relative displacement of the conductors during bending. When the cable undergoes bending deformation, the inner conductors are subjected to compression, while the outer conductors are subjected to tension. The degree of deformation varies significantly among the conductors, which can easily lead to mutual compression, displacement, and restraint between the conductors, causing the local insulation layer to experience large concentrated strain. Especially under repeated bending conditions, if the internal conductors cannot achieve orderly displacement and coordinated deformation, the bending deformation will continue to concentrate in localized areas and gradually propagate to the insulation layer, filler layer, and outer sheath. Under long-term cyclic action, cable insulation structures are prone to fatigue damage and localized stress concentration, leading to a gradual decrease in overall flexibility and ultimately reducing the stability of long-term cable operation. Furthermore, simply thickening the elastic filler material or buffer layer, while improving the cable's deformation adaptability to some extent, results in drawbacks such as increased overall cable outer diameter, loose internal structure, and unstable bending response. The solution using spirally wound elastic buffer material only provides external buffering protection and cannot actively regulate or coordinate the spatial displacement of the multiple internal cores, making it difficult to fundamentally improve the cable's bending resistance.

[0004] Therefore, in order to develop a highly flexible medium- and low-voltage insulated cable that combines high flexibility and good electrical performance, this invention proposes a highly flexible medium- and low-voltage insulated cable and its preparation method. Summary of the Invention

[0005] The purpose of this invention is to provide a highly flexible medium- and low-voltage insulated cable and its manufacturing method. This invention reconfigures the internal macroscopic spatial structure of the cable, causing multiple cores to form an asymmetrical spatial arrangement within the cross-section, and creating directional compressible deformation zones with predetermined compression space between the cores. Simultaneously, a low-friction isolation structure allowing limited relative displacement along the radial direction of the compressible deformation zone is provided on the outside of the cores, and a helical elastic buffer structure that forms a misalignment with the compressible deformation zone is provided on the outside. When the cable bends, the cores located on the inside of the bend can move towards and compress the predetermined compressible deformation zone, while the cores located on the outside of the bend can obtain corresponding displacement space. Controlled relative slippage can occur between the cores and adjacent structures, thereby reducing mutual restraint between the cores. At the same time, the outer helical elastic buffer structure undergoes radial and circumferential composite deformation as the cable bends, further dispersing the external stress generated during the bending process. Therefore, the overall bending deformation of the cable is distributed to multiple structural components such as the spatial displacement of the conductor, the compression of the compressible deformation zone, and the deformation of the spiral buffer layer. This allows the bending stress to be transmitted and released step by step along the radial and circumferential directions of the cable, reducing the concentrated deformation borne by the local insulation structure and improving the structural stability of the cable under repeated bending conditions.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A highly flexible medium- and low-voltage insulated cable and its manufacturing method, comprising the following steps: Unless otherwise specified, the parts in this invention refer to parts by mass.

[0007] A highly flexible medium- and low-voltage insulated cable includes an insulated core, a low-friction isolation layer disposed outside the insulated core, a spiral buffer layer disposed around the insulated core, an outer insulating protective layer disposed outside the spiral buffer layer, and a sheath layer disposed outside the outer insulating protective layer. The insulated core includes a flexible conductor and a flexible insulating layer covering the flexible conductor. The insulated cores are arranged asymmetrically in the cross-section of the cable. A radially compressible deformation zone extending along the length of the cable is provided between adjacent insulated cores, and the radially compressible deformation zone has a predetermined initial deformation space. The spiral path of the spiral buffer layer and the radially compressible deformation zone are initially circumferentially misaligned on the assembly reference cross-section.

[0008] Preferably, the insulated wire cores are arranged in a non-equidistant angle and non-equidistant spacing manner within the cross-section of the cable, and the ratio of the maximum net gap to the minimum net gap between adjacent insulated wire cores is 1.3-2.5; Preferably, the radially compressible deformation zone extends along the cable axis and the cross-sectional area of ​​the deformation zone enclosed by the insulated wire cores accounts for 8%-25% of the area of ​​the internal gap enclosed by the outer contours of the four insulated wire cores; Preferably, the radially compressible deformable region is composed of at least one of thermoplastic polyolefin elastomer, polyolefin elastomer, ethylene-vinyl acetate copolymer, ethylene-propylene-diene terpolymer and polyethylene; Preferably, the low-friction isolation layer comprises at least one of polyester film, polytetrafluoroethylene film, and polyethylene tape, and is wound in a spiral manner around the outside of the insulated wire core to generate a limited relative displacement between the insulated wire core and the buffer layer along the radial compressible deformation zone direction. Preferably, the spiral buffer layer is made of at least one of elastic nonwoven tape, polyester fiber reinforced elastic tape and thermoplastic elastomer tape, and the extending direction of the spiral buffer layer forms an angle of 30°-60° with the extending direction of the radially compressible deformation zone. Preferably, the insulated core comprises a flexible conductor and a flexible insulating layer covering the outside of the flexible conductor. The flexible insulating layer comprises 38 parts of ethylene propylene rubber, 22 parts of polyolefin elastomer, 15 parts of polyethylene, 8 parts of ethylene-vinyl acetate copolymer, 3 parts of maleic anhydride-grafted polyolefin, 8 parts of magnesium hydroxide, 3 parts of aluminum hydroxide, 1.5 parts of silica, 0.8 parts of antioxidant, and 0.7 parts of crosslinking aid.

[0009] Method for manufacturing highly flexible medium and low voltage insulated cables: S1. Extruding flexible insulating material onto the outside of a flexible conductor and cross-linking it to form an insulated wire core; S2. A low-friction isolation layer is formed on the outside of the insulated wire core; S3. Arrange the insulated wire cores in an asymmetrical spatial position to create a radially compressible deformation zone between adjacent insulated wire cores; S4. An elastic foam material is provided in the radially compressible deformation zone so that it extends along the cable direction and maintains a predetermined initial deformation space. S5. An elastic buffer strip is spirally wrapped around the outside of multiple insulated wire cores, so that the spiral buffer strip and the radial compressible deformation zone form a misalignment relationship in the cross section. S6. An outer insulating protective layer and an outer sheath are formed sequentially on the outside of the spiral buffer layer; S7. Perform pre-forming treatment and continuous thermal stabilization treatment on the obtained cable to maintain the predetermined spatial positional relationship between the asymmetrical core arrangement, the radial compressible deformation zone and the spiral buffer layer, and reduce the residual shrinkage stress of the outer insulation protective layer and the sheath layer during the forming and cooling process.

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention, through the combination of asymmetrical core arrangement and directional compressible deformation zone, enables the cable to form a directional deformation space inside when it bends. The bending deformation no longer depends entirely on the elasticity of the insulation material itself, but can be actively distributed by the internal spatial structure. At the same time, the core displacement, the compression of the compressible deformation zone, and the radial and circumferential composite deformation of the external spiral buffer layer work together from the inside out to achieve multi-level release of bending stress.

[0011] 2. This invention, by setting a low-friction isolation structure, enables the conductor to generate a limited relative displacement along the radial compressible deformation zone during bending, reducing the compression and tension between adjacent conductors and lowering the additional strain of the local insulation layer; the bending deformation is distributed across multiple structural areas, avoiding repeated large compression, tension, or shear deformation at a single location, which helps reduce local fatigue of the insulation layer and sheath, and improves the stability of repeated bending; and without simply reducing the stiffness of each layer of material, it takes into account both flexibility and the necessary spatial constraints between conductors and the overall structural integrity of the cable.

[0012] 3. By adjusting the relative spacing between wire cores, the size of the compressible deformation zone, the low-friction isolation structure, and the pitch and winding angle of the spiral buffer layer, this invention can structurally adjust the flexibility and bending response of the cable according to different usage environments, which facilitates parametric preparation and stable, continuous industrial production. Attached Figure Description

[0013] Figure 1 This is a flowchart of the manufacturing process of the present invention.

[0014] Figure 2 This is a dual Y-axis schematic diagram showing the bending recovery rate and insulation resistance retention rate after 50,000 cycles for some embodiments and comparative examples.

[0015] Figure 3 This is a schematic diagram of the cable cross-section structure in Example 1. Detailed Implementation

[0016] The technical solution of the present invention will be clearly and completely described below through some embodiments and experimental examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0017] This invention provides a highly flexible medium- and low-voltage insulated cable and its manufacturing method, the technical solution of which is as follows:

[0018] Example 1 1. Raw materials and formula The raw materials used in this cable include: EPDM purchased from Henan Yuecheng Waterproof Materials Co., Ltd., CAS No. 25038-36-2, polymer grade, impurities ≤0.5%, dense granules, used to provide low-temperature flexibility and elasticity; POE purchased from Wanhua Chemical, CAS No. 26221-73-8, polymer grade, D90≤3mm, impurities ≤0.5%, granular, used to improve flexibility and resistance to repeated deformation; LDPE purchased from Yanshan Petrochemical Co., Ltd., CAS No. 9002-88-4, purity ≥99%, granules, D90≤3mm, used as... Matrix and extrusion processing components: EVA was purchased from Yanshan Petrochemical Co., Ltd., CAS No. 24937-78-8, purity ≥99%, granules, D90≤3mm, VA content 18-28%, used to improve flexibility and filler compatibility; maleic anhydride-grafted polyolefin was purchased from Nanjing Sutai Polymer Technology Co., Ltd., CAS No. 9003-07-0, grafting rate 1.0-1.5%, granules, used to improve the interfacial bonding between polar fillers and polyolefins; magnesium hydroxide was purchased from Aladdin Reagent (Shanghai) Co., Ltd., for cable flame retardant grade, CAS No. 1309-4 2-8, purity ≥98.5%, D50=1.5-2.5μm, used for halogen-free flame retardant and endothermic fillers; Aluminum hydroxide purchased from Aladdin Reagent (Shanghai) Co., Ltd., is cable flame retardant grade, CAS number 21645-51-2, purity ≥99.5%, D50=1.5-2.5μm, used for halogen-free flame retardant and endothermic fillers; Silica purchased from Aladdin Reagent (Shanghai) Co., Ltd., CAS number 112945-52-5, purity ≥99.8%, native particle size approximately 12nm, used for rheology adjustment and reinforcement; Antioxidant 1010 purchased from BASF, CA S-grade material (6683-19-8), purity ≥98%, powder, used for resistance to thermo-oxidative aging; TAIC powder (CAS number 1025-15-6), purchased from Hunan Fangruida Technology Co., Ltd., purity ≥98%, powder, used to promote cross-linking; polyester fiber reinforced elastic tape (Zhejiang Aoya Elastic Fabric Co., Ltd.), with tensile breaking strength ≥120N / mm, elongation resilience ≥92%, and water absorption <0.5%; closed-cell POE / EVA elastic foam strip (Taishan Dayuan New Material Technology Co., Ltd.), with closed-cell rate ≥90% and density 0.08-0.20g / cm³. 3 Compression set (23℃, 25% compression for 24h) ≤15%.

[0019] Based on 100 parts by weight of the base resin and additives for the insulating layer, the formulation consists of 38 parts EPDM, 22 parts POE, 15 parts LDPE, 8 parts EVA, 3 parts maleic anhydride-grafted polyolefin, 8 parts Mg(OH)2, 3 parts Al(OH)3, 1.5 parts fumed SiO2, 0.8 parts antioxidant 1010, and 0.7 parts TAIC. Four flexible conductors of the same specification are used, each with a cross-sectional area of ​​25 mm².2 The four insulated cores are not arranged at equal angles or spacing within the cross-section, but rather asymmetrically. The minimum net gap between adjacent insulated cores is 4.0 mm, and the maximum net gap is 7.2 mm, with a ratio of 1.8 between the maximum and minimum net gaps. The "net gap between adjacent insulated cores" refers to the shortest distance between the outer surfaces of the outer sheath / insulation layer of two adjacent insulated cores within the cable cross-section, excluding the conductor and insulation layer thickness. The area containing the maximum net gap forms the main directional compressible deformation zone, which uses closed-cell POE / EVA elastic foam strips with an approximately elliptical cross-section, a major axis of 5.0 mm, a minor axis of 3.0 mm, and extends continuously along the cable axis. The compressible deformation zone comprises 16% of the area of ​​the deformation zone enclosed by the multiple cores, which is also 16% of the area of ​​the internal gap enclosed by the outer contours of the four insulated cores. Each insulated core is wrapped with a 0.05mm thick PTFE low-friction insulating tape with a 12% overlap. A spiral buffer layer is formed on the outside of the four insulated cores, with a width of 15mm, a thickness of 0.40mm, and a pitch of 50mm. The center trajectory of the spiral buffer layer is offset from the center line of the compressible deformation zone by approximately 45° circumferentially, meaning they are not in the same radial direction. The average thickness of the insulation layer is controlled at 1.8mm, the outer insulation protective layer thickness is 0.8mm, and the sheath thickness is 2.5mm. The finite relative displacement in this invention refers to the spatial displacement of the insulated core relative to adjacent structures during cable bending, used to release bending strain. This displacement direction is constrained by the position of the radial compressible deformation zone, and the displacement range is jointly limited by the core arrangement, the foam deformation space, the spiral buffer layer, and the outer protective layer.

[0020] 2. Preparation method (1) Flexible conductor pretreatment: Select soft copper monofilaments with diameter and resistivity that meet the requirements of medium and low voltage power cables, and form a 25mm² conductor by multiple strands. The stranding pitch is controlled at 15 times the outer diameter of the conductor to make the conductor itself have a certain flexibility. After stranding, clean the surface of the conductor to remove oil and metal dust, and preheat it at 85℃ to keep the surface of the conductor dry.

[0021] (2) Premixing and granulation of insulating materials: Weigh out 38 parts EPDM, 22 parts POE, 15 parts LDPE, 8 parts EVA, 3 parts maleic anhydride grafted polyolefin, 8 parts magnesium hydroxide, 3 parts aluminum hydroxide, 1.5 parts silicon dioxide, 0.8 parts antioxidant 1010 and 0.7 parts TAIC by weight. Maleic anhydride-grafted polyolefin was pre-dried at 80℃ for 3 hours, then added to a mixer along with EPDM and POE. The mixture was stirred at 110℃ for 5 minutes at a speed of 40 r / min to ensure thorough dispersion of the maleic anhydride-grafted polyolefin in the continuous phase. LDPE and EVA were then added, and mixing continued at 115℃ for 5 minutes. After mixing, pre-mixed magnesium hydroxide, aluminum hydroxide, and silica were added in two batches, mixing for 2 minutes after each addition to prevent localized agglomeration. Once the system temperature was maintained at 115℃, antioxidant 1010 was added, and mixing continued for 3 minutes. The mixture was then discharged and passed through a two-roll mill at a temperature of 110℃, repeated four times. When the material temperature dropped below 115℃, TAIC was added and mixed until the TAIC was uniformly dispersed. After mixing, the mixture was granulated using a twin-screw extruder at a temperature of 120℃. The granules were then cooled and dried to obtain insulating granules.

[0022] (3) Insulation layer extrusion and continuous crosslinking: The obtained insulation granules are added to a 90mm insulation extruder, and the temperatures of each zone are controlled at 105℃, 115℃, 125℃, 135℃ and 140℃ respectively, with the die head temperature controlled at 140℃. The flexible conductor, preheated to 80℃, is placed into the die head of the extruder so that the insulation material covers the outer periphery of the conductor, with an insulation layer thickness of about 1.8mm. After extrusion, the insulation layer immediately enters the continuous crosslinking equipment for crosslinking. The effective heating crosslinking section length is controlled at 20m, the crosslinking section temperature is controlled at 200℃, and the cable speed is controlled at 10m / min, so that the cable stays in the effective crosslinking section for 120s. After crosslinking is completed, it enters the staged cooling section, first cooled with 45℃ warm water, and then finally cooled with room temperature water, so that the insulation layer temperature is reduced to below 40℃ to reduce the internal residual stress caused by rapid cooling.

[0023] (4) Low friction isolation layer treatment and four-core cabling: After the insulation extrusion is completed, the four cores are treated with low friction isolation layer. A PTFE tape with a thickness of 0.05mm is spirally wound around the outer periphery of the core with an overlap rate of 12%. The winding tension is controlled at 8N so that the PTFE tape is close to the insulation layer but not excessively compressed, thereby forming a low friction isolation layer between the two. After processing, four-core cabling is performed. A specialized cabling mold controls the relative positions of the four cores within the cross-section, resulting in a non-equidistant arrangement. During cabling, POE / EVA elastic foam strips are placed at the predetermined maximum net gap position as compressible deformation zones. The foam strips do not completely fill the space between adjacent cores during assembly; instead, an initial free deformation gap of 1.5mm is maintained, forming initial deformation space. The maximum spacing between adjacent cores is controlled at 7.2mm, and the minimum spacing at 4.0mm, ensuring a maximum net gap to minimum net gap ratio of 1.8. The cabling tension is controlled at 50N to prevent excessive tension from prematurely damaging the compressible deformation zone. The initial free deformation gap refers to the unfilled space between the outer surface of the foam material and the outer surface of the adjacent insulated core within the assembly reference cross-section, along the main compressible deformation zone in the radial direction.

[0024] (5) Forming a spiral buffer layer and outer layer: After completing the four-core arrangement, a spiral buffer layer is formed on its outer side. A polyester fiber reinforced elastic tape with a width of 15mm and a thickness of 0.40mm is spirally wound with a pitch of 50mm. During the winding process, by adjusting the circumferential position of the wrapping guide head, at the assembly reference cross section, the center trajectory of the spiral buffer tape is initially offset by about 45° from the center line of the inner compressible deformation zone along the circumferential direction. Because the spiral buffer tape uses a 50mm fixed pitch spiral wrapping, the circumferential phase of the two cross sections changes cyclically along the cable axis according to the pitch period, avoiding complete overlap between the maximum constraint direction of the outer spiral buffer layer and the inner compressible deformation zone. When the cable bends, the inner core first undergoes limited displacement. The inner core moves towards the compressible deformation zone and compresses the foam material. At the same time, the PTFE interface allows The core wire generates a limited relative displacement along the radial compressible deformation zone, and the outer core wire gains relative expansion space. The outer spiral elastic buffer band undergoes radial compression and circumferential stretching, so that the bending deformation is jointly borne by the displacement of the inner core wire, the compression of the elastic foam, and the deformation of the outer spiral band. Subsequently, an outer insulating protective layer is extruded outside the spiral buffer layer, using flexible polyolefin material, at an extrusion temperature of 145℃. During the extrusion process, the geometric position of the spiral buffer layer is kept from significant displacement. After the outer insulating protective layer is formed, the sheath layer is extruded at an extrusion temperature of 155℃, and the outer diameter of the sheath is controlled by a sizing sleeve.

[0025] (6) Cable pre-forming and continuous thermal stabilization treatment: After completing the above steps, the obtained cable is continuously pulled to the pre-forming device under a tension of 50N. First, the cable is passed through the first pre-forming zone with a length of 2m and a temperature of 70℃. The lower temperature is used to gradually release the internal stress of the external insulation protective layer and the sheath layer, while avoiding significant compression of the compressible deformation zone. Then, the cable is introduced into the flexible sizing mold for the second stage of pre-forming. The maximum adjacent core spacing is controlled to be 7.2mm and the minimum adjacent core spacing is 4.0mm, so that the ratio of the maximum adjacent core spacing to the minimum adjacent core spacing is 1.8. At the same time, the long axis of the compressible deformation zone is kept at 5.0mm and the short axis is kept at 3.0mm, and an initial free deformation gap of 1.5mm is retained. The pre-forming process maintains the cross-sectional geometry of each component inside the cable core and no longer forcibly maintains the circumferential misalignment angle of the entire length, thereby avoiding excessive compression of the spiral buffer layer and the compressible deformation zone during the pre-forming process. After the cross-section is pre-shaped, the cable is sent into a continuous hot air thermal stabilization treatment zone. Circulating hot air is used as the heat exchange medium, the chamber temperature is set at 135℃, the effective constant temperature heating zone physical length is 5m, the production line traction speed is 10m / min, the cable passes through the constant temperature zone for 30s, the initial temperature of the cable before entering the thermal stabilization zone is 60℃, and the hot air circulation speed is controlled at 3.5m / s to enhance convective heat transfer and reduce the temperature difference between the inside and outside of the cable cross-section. It was measured that under the above conditions, the outer surface of the cable sheath can quickly reach 130℃, and the internal temperature of the cable can reach 128℃. This allows the external insulation protective layer, sheath layer, and internal elastic buffer layer to gradually release thermal shrinkage stress and form a stable spatial fit. During the thermal stabilization process, low-tension traction is used to prevent axial movement of the four insulated cores and to maintain the predetermined cross-sectional shape of the compressible deformation zone. After thermal stabilization treatment, a staged cooling process is performed. First, a slow cooling process using 55°C warm water is initiated, followed by a second cooling process using 35°C warm water. Finally, room temperature water is used for cooling to room temperature. Throughout the cooling process, the traction speed is kept constant to avoid significant radial shrinkage stress on the outer sheath and insulation layer due to sudden cooling. After cooling, the cable's outer diameter and cross-sectional structure are inspected, resulting in a structurally stable, highly flexible, medium-low voltage insulated cable. Within an assembly reference cross-section perpendicular to the cable axis, the four insulated cores are numbered C1, C2, C3, and C4, and a two-dimensional coordinate system is established with the cable cross-section center as the reference. The center coordinates of each insulated core are (X1, Y1), (X2, Y2), (X3, Y3), and (X4, Y4), respectively. The net gap between adjacent insulated cores is defined as g. 12 g 23 g 34 and g 41 Where: minimum net clearance g min =min(g 12 ,g 23 ,g34 ,g 41 Maximum net clearance g max =max(g 12 ,g 23 ,g 34 ,g 41 ).

[0026] Examples 2-6 differ from Example 1 in operating parameters, but the other process steps and the range of raw material selection are the same.

[0027] The specific changes in operating parameters are summarized in Table 1.

[0028] Table 1. Parameter variations of high-flexibility medium and low voltage insulated cables in Examples 1-6 ; Comparative Example 1 Unlike Example 1, this comparative example changes the four insulated wire cores in Example 1 to be arranged at equal angles and equal intervals, so that the spacing between each adjacent wire core is 5.5mm. The remaining process parameters are the same as in Example 1.

[0029] Comparative Example 2 Unlike Example 1, this comparative example omits the independent compressible deformation zone and uses a common elastic filler material that matches the gap between the insulated wire cores to directly fill all the gaps between the wire cores, so that no initial compression space is retained inside. The remaining process parameters are the same as in Example 1.

[0030] Comparative Example 3 Unlike Example 1, this comparative example omits the PTFE low-friction isolation layer, allowing the outer surface of the insulated core to directly contact the adjacent buffer material. The remaining process parameters are the same as in Example 1.

[0031] Comparative Example 4 Unlike Example 1, this comparative example omits the 50mm pitch spiral elastic buffer strip and replaces it with an elastic strip with a thickness of 0.4mm and a width of 15mm, which is continuously set along the cable axis. The remaining process parameters are the same as in Example 1.

[0032] Comparative Example 5 Unlike Example 1, this comparative example keeps the pitch, thickness and overlap of the spiral buffer layer unchanged, but changes its circumferential position so that the spiral buffer trajectory coincides with the center direction of the compressible deformation zone, that is, the misalignment angle is 0°. The remaining process parameters are the same as those in Example 1.

[0033] Comparative Example 6 Unlike Example 1, this comparative example increases the maximum adjacent spacing of the four wires to 12.0 mm while maintaining the minimum net gap at 4.0 mm, resulting in a maximum / minimum net gap ratio of 3.0. The remaining process parameters are the same as in Example 1.

[0034] Comparative Example 7 Unlike Example 1, this comparative example keeps the width, thickness and overlap of the spiral buffer strip unchanged, but reduces the spiral angle of the spiral buffer strip to 20° by changing the spiral winding parameters. The remaining process parameters are the same as in Example 1.

[0035] Comparative Example 8 Unlike Example 1, this comparative example replaces the low-friction isolation layer with a PTFE film and uses a silicone oil-impregnated ordinary polyester film. The remaining process parameters are the same as in Example 1.

[0036] Comparative Example 9 Unlike Example 1, this comparative example adds high-hardness EPDM particles to the compressible deformation zone to form a "high-resilience-filled" deformation zone, while the remaining process parameters are the same as in Example 1.

[0037] Comparative Example 10 Unlike Example 1, this comparative example adds a flexible guide limiting strip extending along the cable axis to the inner core of the compressible deformation zone, based on the structure of Example 1. The guide limiting strip is made of flexible TPU material, with an arc-shaped cross section, a thickness of about 1.0 mm and a width of about 3.0 mm, forming an initial movable gap of about 0.5 mm between it and the adjacent core. The remaining process parameters are the same as those in Example 1.

[0038] Experimental Example 1 The results of minimum non-destructive bending radius, bending recovery rate, insulation resistance retention rate after 50,000 cycles, bending results after 100,000 cycles, appearance cracks, maximum compression rate, deformation zone recovery rate, maximum displacement of inner core, sheath condition after bending at -20℃, and low-temperature insulation resistance retention rate of the highly flexible medium and low voltage insulated cables prepared in Test Examples 1-6 and Comparative Examples 1-10 are summarized in Table 2.

[0039] (1) Minimum non-destructive bending radius and bending recovery rate test: The purpose of the test is to evaluate the minimum bending space required for the cable during a single bending process and the structural recovery ability after the bending is removed. First, the actual outer diameter D of the finished cable is measured. The sample length is determined according to the target bending radius, bending angle and the effective clamping length required at both ends of the clamp. Then, the sample is installed on the bending clamp, with one end fixed and the other end gradually bent along the cylindrical mandrel. Pre-tests are conducted in the range of 6D-20D. The bending radius is gradually reduced from the larger bending radius. After determining the adjacent radius range where the first structural damage occurs, bending tests are conducted in this range with a step size of 0.1D. Each bending radius is held for 30s, and the condition of the sample is checked. The minimum measured bending radius without the above-mentioned structural damage is defined as the minimum non-destructive bending radius of the sample and expressed as a multiple of the actual outer diameter D. A bending recovery test was performed at a determined test bending radius. Using the straight center axis of the specimen before bending as a reference line, the specimen was bent to the specified radius and held for 60 seconds. The maximum lateral offset σ0 of the specimen's center axis relative to the reference line was measured while holding the bending state. After the external force was removed, the specimen was left to stand in an environment of 23±2℃ for 10 minutes, and then the maximum residual lateral offset σ of the specimen's center axis relative to the initial reference line was measured again. r The bending recovery rate η is calculated according to the following formula: η = (σ0 - σ) r ) / σ0×100%; In the formula: η is the bending recovery rate; σ0 is the maximum lateral offset relative to the initial straight reference under the specified bending state; σ r The maximum residual lateral offset after the bending load is removed and the plant is left to stand for 10 minutes.

[0040] (2) Repeated bending life test: The purpose of the test is to simulate the working state of repeated bending of cables in mobile equipment. The specific test method is as follows: Fix the sample on the reciprocating bending tester, fix both ends of the sample, use an 8D bending radius at the bending center, and use a 180° reciprocating bending direction. That is, the sample bends from one side to the other side and then returns to the original position as one cycle. Control the bending speed to 30 times / min. Record the appearance of the sample once every 1000 cycles, and measure the outer diameter and insulation resistance of the sample. Continue for 100,000 cycles. Stop the test and record the failure cycle number when the sample shows the following conditions: obvious cracks in the sheath, the insulation layer is broken, the conductor is broken, the insulation resistance drops by more than one order of magnitude of the initial value, and the cable shows obvious permanent flat deformation.

[0041] (3) Insulation resistance and withstand voltage retention test before and after bending: First, select a finished cable sample with a length of 1m and place it for 16h in an environment of 23±2℃ and relative humidity of 45%-55%. There is no metal shielding layer inside the cable. When testing the insulation resistance of the core to the outer insulation, the outer surface of the outer sheath of the sample is tightly wrapped with metal foil as a temporary external measuring electrode. The length of the metal foil wrapping is consistent with the effective test length of the cable. The metal foil is grounded. A 500V insulation resistance tester is used to complete the measurement of two types of insulation resistance in sequence: the insulation resistance between cores and the insulation resistance between each insulated core and the external metal foil electrode. For each group of samples, the insulation resistance of all pairs of wire cores and the wire core to the metal foil electrode were measured separately. All measured absolute values ​​were recorded, and the arithmetic mean was taken as the initial insulation resistance R0 of the sample. Then, 50,000 reciprocating bends were performed according to the repeated bending test method. After bending, the sample was placed in an environment of 23±2℃ and 45%-55% relative humidity for 2 hours, and the measurement was performed again in the same manner. The arithmetic mean was taken as the insulation resistance R1 after bending. The insulation resistance retention rate can be calculated using the following formula: K R =R1 / R0×100%; Where: K R R0 represents the insulation resistance retention rate after 50,000 cycles; R1 represents the insulation resistance of the sample before the bending test; R2 represents the insulation resistance of the sample after 50,000 repeated bending cycles.

[0042] (4) The compression-recovery and relative displacement test of the compressible deformation zone is an important test to verify the structural mechanism of the present invention. It is used to prove that the core can move towards the predetermined deformation zone during bending and that the compressible deformation zone bears part of the bending deformation. The specific test method is as follows: Take a 300mm long sample from each group of cables, mark the position of the four cores on the cross section, and use a micrometer or industrial CT to measure the center coordinates of the cores in the unstressed state; then install the sample in the bending fixture, bend it 90° with an 8D radius, hold it for 60s, and measure the center position of the four cores again in the holding state. The maximum displacement of the inner core refers to the unidirectional projected displacement of the center of the inner core along the compression direction of the compression deformation zone (not the planar displacement modulus). Calculate the distance that the inner core moves towards the compressible deformation zone and the radial offset distance of the outer core. After the bending is released, let it stand for 10 minutes, and measure the cross section again. Calculate the compression rate and recovery rate of the compressible deformation zone. The maximum compression rate and the recovery rate of the deformation zone can be calculated by the following formula: C = (H0 - H1) / H0 × 100%; R C =(H2-H1) / (H0-H1)×100%; In the formula: C is the maximum compression ratio; R CH0 represents the recovery rate of the deformation zone; H1 represents the initial height of the compressible deformation zone; H2 represents the maximum compression height; and H3 represents the recovery height after unloading.

[0043] (5) Low-temperature bending test: This test is used to evaluate the bending stability of cable materials and macrostructure under low-temperature conditions, and to prevent sheath cracking or insulation damage caused by increased material rigidity in low-temperature environments. The specific test method is as follows: Place the sample in a low-temperature test chamber and keep it at -20℃ for 4 hours to allow the cable to reach a stable temperature. Then, bend the sample around a cylindrical mandrel of a specified diameter at 180° in the low-temperature environment, with the bending speed controlled at 5-10s / bend, and complete 3 times consecutively. After bending, keep the sample in the low-temperature environment for 10 minutes, and then restore it to an environment of 23±2℃. Afterward, observe whether cracks, cleavage, obvious whitening, delamination or local deformation appear in the sheath and ends, and then perform insulation resistance and withstand voltage checks. This test comprehensively reflects whether the sheath material, insulation layer, and internal macrostructure of the cable can remain intact when subjected to bending deformation under low temperature conditions, avoiding sheath cracking, insulation damage, and decline in electrical performance caused by low-temperature embrittlement or increased rigidity. If there are no cracks, ruptures, obvious whitening, delamination, or local deformation in the sheath and ends after low-temperature bending, and the insulation resistance and withstand voltage tests are qualified, it indicates that the cable has good low-temperature bending stability.

[0044] (6) Calculation of the radial compressible deformation zone area: In the cross-section perpendicular to the cable axis, the area of ​​the continuous gap region enclosed by the outer surfaces of the insulation layers of the four insulated cores facing the inner area of ​​the cable core is S0, and S1 is the cross-sectional area of ​​the radial compressible deformation zone. Therefore, the proportion of the radial compressible deformation zone area η can be calculated by the following formula: η = S1 / S0 × 100%; In the formula: η is the area ratio of the radially compressible deformation zone; S0 is the area of ​​the continuous void region enclosed by the outer surface of the insulation layer of the four insulated wire cores facing the inner area of ​​the cable core; S1 is the cross-sectional area of ​​the radially compressible deformation zone.

[0045] Table 2. Test results of bending performance and insulation performance after repeated bending for Examples 1-6 and Comparative Examples 1-10 ;

[0046] Table 3. Test results of compression-recovery and low-temperature bending properties of the compressible deformation zone in Examples 1-6 and Comparative Examples 1-10 ; Analysis of the data in Tables 2 and 3 shows that Example 1, employing a superior adjacent core spacing ratio, a moderate compressible deformation zone area ratio, and a staggered spiral buffer structure, exhibits the most balanced overall performance. It has a lower minimum bending radius, a higher bending recovery rate, and both high compressibility and recovery rates in the compressible deformation zone. The inner cores show a larger relative displacement, resulting in a high insulation resistance retention rate after long-term repeated bending, even after low-temperature bending. This indicates that bending deformation is effectively distributed across multiple structural regions and does not concentrate on the insulation layer. In Example 2, reducing the spacing ratio increases the minimum bending radius and decreases core displacement. While the insulation resistance retention rate remains high after long-term bending, flexibility is acceptable, but deformation dispersion ability decreases. In Example 3, increasing the spacing ratio increases core displacement and compression rate, but slightly increases the minimum bending radius and increases permanent structural deformation, indicating that greater asymmetry is not always better. In Example 4, reducing the compressible zone area ratio causes the compression rate and core displacement to begin decreasing, while the minimum bending radius increases. The recovery rate and long-term insulation retention rate decrease, indicating that an excessively small deformation zone leads to more bending deformation being transferred to the insulation layer. In Example 5, reducing the helical pitch resulted in performance similar to Example 1. In Example 6, increasing the helical pitch increased the minimum bending radius but decreased the recovery rate and long-term insulation retention rate, indicating that increasing the helical unit spacing weakened the dispersion effect. In summary, appropriate asymmetric spacing, sufficient but not excessive compressible space, and a reasonable helical pitch collectively form a stable multi-stage deformation path.

[0047] Comparative Example 1: Removing the asymmetrical core arrangement and adopting an equal-spacing, equal-angle arrangement increased the minimum bending radius, resulted in a low recovery rate, and very small compression rate and core displacement. Anomalies appeared in the early cycle count, indicating that the regular arrangement lacked displacement difference and could not effectively drive directional compression. Comparative Example 2: Removing the compressible deformation zone and filling it with ordinary elastic filler resulted in a larger minimum bending radius, earlier anomalies, and low compression rate and displacement, indicating that ordinary filler could not provide effective deformation space in the predetermined direction. Comparative Example 3: Removing the low-friction isolation layer allowed the compressible zone to still generate some compression, but the core displacement was limited, the recovery rate decreased, and anomalies appeared earlier, indicating that motion resistance needed to be reduced to achieve controlled slippage. Comparative Example 4: Replacing the helical buffer layer with an axially continuous elastic band resulted in a larger bending radius, a low recovery rate, and earlier anomalies, indicating that the axial structure could not gradually release radial and circumferential deformation. Comparative Example 5: Aligning the helix and compressible zone in the same direction resulted in a larger bending radius, a lower recovery rate, and earlier anomalies, indicating that deformation in the same direction tends to concentrate, while misalignment can be dispersed. Comparative Example 6, by increasing the spacing ratio too much, resulted in high compression ratio and displacement, but low recovery rate and early anomalies, indicating that excessive asymmetry leads to excessive local deformation and reduces long-term stability. Comparative Example 7, by changing the helix angle, showed a decline in performance and early anomalies, indicating that geometric parameters need to be matched. Comparative Example 8, by replacing PTFE with ordinary polyester film, showed acceptable initial minimum bending radius and recovery rate, but decreased long-term insulation resistance retention and deformation zone recovery rate, indicating that initial lubrication does not equate to long-term stable slip. Comparative Example 9, by adding high-hardness EPDM particles to the compressible zone, showed an increase in deformation zone recovery rate, while compression ratio and core displacement decreased. Comparative Example 10, by adding a flexible guide limit strip, showed an increase in the minimum bending radius, indicating that appropriate guidance can improve structural stability.

[0048] In summary, the flexibility of the cable of this invention is not achieved by a single material, but by the combined effect of multiple materials. This invention constructs a structure of "asymmetric core arrangement—directional compressible deformation—controllable relative slippage—misaligned spiral buffer—multi-stage synergistic release of bending stress." When the cable bends, the cores on the inner side of the bend can move towards the compressible deformation zone and compress the area, generating compressive deformation. The outer cores adjust their spacing accordingly with the bend. Simultaneously, the low-friction interface structure allows for smooth relative displacement of the cores, and the misaligned spiral buffer layer simultaneously generates circumferential and radial deformation, further improving the cable's flexibility. Through the combination of these structures, the bending stress and deformation originally concentrated on the insulation layer can be effectively distributed to multiple structural areas of the cable. Test results highly match the mechanism of this structure, confirming that the macroscopic structure designed in this invention can effectively improve the cable's service life under repeated bending, ensure the retention of insulation performance, and optimize the cable's low-temperature bending stability.

Claims

1. A highly flexible medium- and low-voltage insulated cable, characterized in that: The cable includes an insulated core, a low-friction isolation layer disposed outside the insulated core, a spiral buffer layer disposed around the insulated core, an outer insulating protective layer disposed outside the spiral buffer layer, and a sheath layer disposed outside the outer insulating protective layer. The insulated core includes a flexible conductor and a flexible insulating layer covering the flexible conductor. The insulated cores are arranged asymmetrically in the cross-section of the cable. A radially compressible deformation zone extending along the length of the cable is provided between adjacent insulated cores, and the radially compressible deformation zone has a predetermined initial deformation space. The spiral path of the spiral buffer layer and the radially compressible deformation zone are initially circumferentially misaligned on the assembly reference cross-section.

2. The highly flexible medium- and low-voltage insulated cable according to claim 1, characterized in that: The insulated wire cores are arranged in a non-equidistant angle and non-equidistant spacing manner within the cross-section of the cable, and the ratio of the maximum net gap to the minimum net gap between adjacent insulated wire cores is 1.3-2.

5.

3. The highly flexible medium- and low-voltage insulated cable according to claim 1, characterized in that: The radially compressible deformation zone extends along the cable axis and its cross-sectional area is such that the area of ​​the deformation zone enclosed by the insulated wire cores accounts for 8%-25% of the area of ​​the internal gap enclosed by the outer contours of the four insulated wire cores.

4. The highly flexible medium- and low-voltage insulated cable according to claim 1, characterized in that: The radially compressible deformable region is composed of at least one of thermoplastic polyolefin elastomer, polyolefin elastomer, ethylene-vinyl acetate copolymer, ethylene-propylene-diene terpolymer and polyethylene.

5. The highly flexible medium- and low-voltage insulated cable according to claim 1, characterized in that: The low-friction isolation layer comprises at least one of polyester film, polytetrafluoroethylene film, and polyethylene tape, and is wound in a spiral manner around the outside of the insulated wire core to generate a limited relative displacement between the insulated wire core and the buffer layer along the radial compressible deformation zone direction.

6. The highly flexible medium- and low-voltage insulated cable according to claim 1, characterized in that: The spiral buffer layer is made of at least one of elastic nonwoven tape, polyester fiber reinforced elastic tape and thermoplastic elastomer tape, and the extension direction of the spiral buffer layer forms an angle of 30°-60° with the extension direction of the radially compressible deformation zone.

7. The highly flexible medium- and low-voltage insulated cable according to claim 1, characterized in that: The insulated core includes a flexible conductor and a flexible insulating layer covering the outside of the flexible conductor. The flexible insulating layer includes 38 parts of ethylene propylene rubber, 22 parts of polyolefin elastomer, 15 parts of polyethylene, 8 parts of ethylene-vinyl acetate copolymer, 3 parts of maleic anhydride grafted polyolefin, 8 parts of magnesium hydroxide, 3 parts of aluminum hydroxide, 1.5 parts of silicon dioxide, 0.8 parts of antioxidant, and 0.7 parts of crosslinking aid.

8. The method for preparing a highly flexible medium- and low-voltage insulated cable according to any one of claims 1-7, characterized in that: Includes the following steps: S1. Extruding flexible insulating material onto the outside of a flexible conductor and cross-linking it to form an insulated wire core; S2. A low-friction isolation layer is formed on the outside of the insulated wire core; S3. Arrange the insulated wire cores in an asymmetrical spatial position to create a radially compressible deformation zone between adjacent insulated wire cores; S4. An elastic foam material is provided in the radially compressible deformation zone so that it extends along the cable direction and maintains a predetermined initial deformation space. S5. An elastic buffer strip is spirally wrapped around the outside of multiple insulated wire cores, so that the spiral buffer strip and the radial compressible deformation zone form a misalignment relationship in the cross section. S6. An outer insulating protective layer and an outer sheath are formed sequentially on the outside of the spiral buffer layer; S7. Perform pre-forming treatment and continuous thermal stabilization treatment on the obtained cable to maintain the predetermined spatial positional relationship between the asymmetrical core arrangement, the radial compressible deformation zone and the spiral buffer layer, and reduce the residual shrinkage stress of the outer insulation protective layer and the sheath layer during the forming and cooling process.

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