Halogen-free low-smoke flame-retardant control cable without combustion drippings and its preparation method

Abstract

The application discloses a halogen-free low-smoke flame-retardant control cable without combustion dripping matters and a preparation method thereof. The control cable comprises a shaped cable, an oxygen barrier and flame-retardant layer, a buffer pad layer, a metal armor and a composite outer sheath. The shaped cable comprises a plurality of control line units, the plurality of control line units are reversely twisted into a cable in two layers, ceramic flame-retardant separation strips with radial protrusions are arranged between the two layers, and the interspaces of the plurality of control line units are filled with dot-shaped skeleton filling bodies. The oxygen barrier and flame-retardant layer is composed of an inner layer glass fiber ceramic tape and an outer layer glass fiber ceramic tape which are spirally wound in positive and negative directions. The buffer pad layer is extruded on the outer layer of the oxygen barrier and flame-retardant layer, and a plurality of hollow ceramic fiber tube bundles are uniformly distributed in the buffer pad layer along the axial direction. The composite outer sheath comprises a polyolefin matrix layer and a ceramic dip-coated protective sheath arranged from inside to outside. The control cable solves the problems in the prior art, such as that the resin matrix melts after being heated, the inorganic fillers lose the constraint, and the molten materials drip along the outer wall of the cable under the action of gravity.

Description

Technical Field

[0001] This invention relates to the field of cable manufacturing technology, specifically to a halogen-free, low-smoke, flame-retardant control cable with no burning drips and its preparation method. Background Technology

[0002] Flame-retardant control cables are cables specifically designed to prevent or delay the spread of flames in fire conditions. They are primarily used for transmitting control signals, measurement signals, operating commands, and low-voltage electrical energy (typically 450 / 750V and below).

[0003] Its core feature is its "flame retardant" characteristic, which means that after the cable itself or an external fire source ignites, the flame can extinguish itself within a limited range, preventing the flame from spreading rapidly along the cable path and buying valuable time for personnel evacuation, equipment shutdown and fire rescue.

[0004] The common structure of traditional flame-retardant control cables is: conductor - single-layer insulation - fully filled cable core - integrated extruded inner lining - continuous steel tape armor wrapping - single-layer sheath. These cables typically use highly filled flame-retardant polyolefin materials containing aluminum hydroxide and magnesium hydroxide. When heated, the resin matrix melts, the inorganic filler loses its binding force, and the molten material drips down the outer wall of the cable under its own weight. The dripping material ignites surrounding combustibles, expanding the fire's spread. Summary of the Invention

[0005] This invention provides a halogen-free, low-smoke, flame-retardant control cable with no burning drips and its preparation method. The purpose is to solve the problems existing in the background technology, such as the resin matrix melting when heated, the inorganic filler losing its binding, and the molten material dripping along the outer wall of the cable under its own weight.

[0006] The technical solution provided by this invention is as follows: A halogen-free, low-smoke, flame-retardant control cable with no burning drips includes, from the inside out, a molded cable, an oxygen-barrier flame-retardant layer, a buffer layer, a metal armor, and a composite outer sheath. The formed cable includes multiple control line units, which are twisted into cables in reverse in two layers, inner and outer. A radially protruding ceramic flame-retardant separator is arranged between the inner and outer layers, and the gaps between the multiple control line units are filled with dot-shaped skeleton fillers. The oxygen-barrier flame-retardant layer is composed of an inner layer of glass fiber ceramic tape and an outer layer of glass fiber ceramic tape wound in opposite directions, and flame-retardant microcapsules are filled in the interlayer between the inner layer of glass fiber ceramic tape and the outer layer of glass fiber ceramic tape. The buffer pad is extruded over the oxygen-barrier flame-retardant layer. Multiple hollow ceramic fiber tube bundles are evenly distributed in a ring along the axial direction inside the buffer pad. The hollow ceramic fiber tube bundles are sealed and filled with liquid boron-based heat-absorbing flame-retardant liquid. The composite outer sheath comprises a polyolefin matrix layer and a ceramic-coated protective sleeve arranged from the inside out.

[0007] Optionally, the outer wall of the buffer pad layer is integrally formed with positioning ribs; The metal armor is made of multiple arc-shaped galvanized steel sheets spliced ​​together with snap fasteners at both ends. The inner side of the arc-shaped galvanized steel sheets is provided with a slot that matches the limiting rib. Flame-retardant sealing strips are embedded in the splicing gaps of the arc-shaped galvanized steel sheets.

[0008] Optionally, the control line unit includes a conductor, an insulating layer, and a flame-retardant outer sheath; The raw material components of the insulating layer, by weight, include: 40 parts LLDPE, 22 parts EVA, 30 parts ultrafine aluminum hydroxide, 2.8 parts organic modified montmorillonite, 3.2 parts phosphorus-based charring agent, and 2 parts composite antioxidant. The flame-retardant outer layer is made by extruding a blend of EVA, ultrafine magnesium hydroxide, borosilicate ceramic powder, and closed-cell foamed microspheres. After extrusion, it undergoes low-temperature in-situ foaming and high-temperature rapid sintering at a temperature greater than or equal to 300°C to form a sealed ceramic shell.

[0009] Optionally, the cross-section of the ceramic flame-retardant separator is a semi-circular ring with an inner diameter of 1.0mm to 1.5mm, and one is arranged every 35mm to 45mm along the circumferential direction of the cable. The dotted skeleton filler is made of expanded graphite coated with glass fiber bundles.

[0010] Optionally, the inner diameter of the hollow ceramic fiber tube bundle is 0.5 mm, and the center-to-center distance between adjacent hollow ceramic fiber tube bundles inside the buffer pad layer is 4 mm to 6 mm. The length of a single arc-shaped galvanized steel sheet is 80mm to 120mm, the overlap width of the interlocking of adjacent arc-shaped galvanized steel sheets is 3mm to 5mm, and the width of the flame-retardant sealing strip embedded in the splice seam is 2mm.

[0011] This invention also provides a method for preparing a halogen-free, low-smoke, flame-retardant control cable with no burning drips, comprising the following steps: Multiple conductors are twisted together, and joint defects are repaired. The diameter of a single conductor is >0.2mm, and the spacing between adjacent joints is controlled to be ≥320mm. By employing a segmented temperature control method, an insulating layer and a flame-retardant outer sheath are sequentially extruded onto the conductor to obtain a control line unit. Multiple control line units are twisted in opposite directions in two layers, and radially protruding ceramic flame-retardant separators are arranged between the inner and outer layers. Dot-shaped skeleton fillers are filled into the gaps of the multiple control line units to obtain a shaped cable. An inner layer of glass fiber ceramic tape and an outer layer of glass fiber ceramic tape are spirally wound in opposite directions on the formed cable, and flame-retardant microcapsules are filled in the interlayer between the inner layer of glass fiber ceramic tape and the outer layer of glass fiber ceramic tape to obtain an oxygen-barrier flame-retardant layer. An integrally extruded buffer pad layer is formed outside the oxygen-barrier flame-retardant layer. Hollow ceramic fiber tube bundles are arranged in the buffer pad layer. Liquid boron-based heat-absorbing flame-retardant liquid is sealed and filled inside the hollow ceramic fiber tube bundles. Limiting ribs are extruded on the outer wall of the buffer pad layer. The product is assembled and sealed using multiple arc-shaped galvanized steel sheets with snap-fit ​​ends. The inner side of the arc-shaped galvanized steel sheet has a slot that matches the limiting rib. Flame-retardant sealing strips are embedded in the splicing gaps of the arc-shaped galvanized steel sheet. The slot is engaged with the limiting rib to obtain metal armor; A composite outer sheath, consisting of a polyolefin matrix layer arranged from the inside out and a ceramic-coated protective sleeve, is formed on the metal armor to obtain the halogen-free, low-smoke, flame-retardant control cable that produces no burning droplets.

[0012] Optionally, the method of segmented temperature control, wherein an insulating layer and a flame-retardant outer layer are sequentially extruded onto the conductor, includes: The body of the insulation extruder is temperature controlled in four stages: 120℃, 135℃, 150℃, and 160℃. The temperature of the die head is controlled at 155±5℃. After the insulation layer is extruded, a flame-retardant outer layer is continuously extruded online. The foaming and setting temperature of the flame-retardant outer layer is controlled at 85±5℃.

[0013] Optionally, the process involves twisting multiple control line units in reverse layers (inner and outer), and placing radially protruding ceramic flame-retardant separators between the inner and outer layers. Dot-shaped skeleton fillers are then filled into the gaps between the multiple control line units to obtain a shaped cable, comprising: The inner layer control line units are twisted clockwise, and the outer layer control line units are twisted counterclockwise. If the conductor is a rigid conductor, the cabling pitch of the rigid conductor is controlled to be ≤18 times the outer diameter of the cable; if the conductor is a flexible conductor, the cabling pitch of the flexible conductor is controlled to be ≤15 times the outer diameter of the cable. During the cabling process, ceramic flame-retardant separators are pasted at equal intervals between layers. Multiple control line units are interspersed with expanded graphite-coated fiberglass bundles at fixed points to form a dotted skeleton filler, without overall full-section filling.

[0014] Optionally, the inner layer of glass fiber ceramic tape has an overlap rate of 16%, the outer layer of glass fiber ceramic tape is reverse-wound with an overlap rate of 20%, and the flame-retardant microcapsule is a phosphorus-nitrogen-based expandable flame-retardant microcapsule.

[0015] Optionally, the buffer pad layer is integrally extruded using a special-shaped co-extrusion die, and the extrusion temperature is 130℃~142℃; Hollow ceramic fiber tube bundles are arranged in the buffer pad layer, and limiting ribs are extruded on the outer wall of the buffer pad layer, including: While the buffer pad is being extruded, a hollow ceramic fiber tube bundle is fed into the buffer pad at a uniform speed through a feeding fixture, and an annular limiting rib is extruded integrally on the outer wall of the buffer pad simultaneously.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. This invention uses a single-core independent flame-retardant outer sheath and a high-temperature individually ceramicized and locked insulating molten core to suppress molten droplet shedding from the core source; the cable core is equipped with ceramic flame-retardant separators and dot-shaped skeleton fillers, and a high-temperature formed internal rigid support mesh to support the molten material and block the molten core from falling.

[0017] 2. The double-layered oxygen-barrier flame-retardant layer with the front and back wrapping, combined with the interlayered flame-retardant microcapsules, releases the drug and absorbs heat upon ignition, and seals off oxygen, slowing down the combustion and melting of the inner substrate; the buffer layer contains hollow ceramic fiber tubes filled with boron-based flame-retardant liquid, which absorb heat and cool down over a large area during high-temperature vaporization, reducing the amount of melt generated. 3. The segmented, snap-fit ​​metal armor forms a cage-like structure to support the molten material, while the double-layer composite outer sheath ceramicizes and seals the outer substrate upon contact with fire. This cable achieves full-layer synergistic anti-melting and dripping resistance, and also boasts advantages such as low smoke, halogen-free properties, bending resistance, and lightweight design, thus solving the ignition hazard caused by dripping during combustion of traditional cables. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of a halogen-free, low-smoke, flame-retardant control cable with no burning drips, as described in an embodiment of the present invention. Figure 2 This is a partial structural diagram of the metal armor in an embodiment of the present invention.

[0019] The attached figures are labeled as follows: 1-Control line unit, 101-Conductor, 102-Insulation layer, 103-Flame-retardant outer sheath, 2-Ceramic flame-retardant separator strip, 3-Dot-shaped skeleton filler, 4-Oxygen-barrier flame-retardant layer, 401-Inner layer glass fiber ceramic tape, 402-Outer layer glass fiber ceramic tape, 403-Flame-retardant microcapsule, 5-Buffer pad layer, 501-Hollow ceramic fiber tube bundle, 502-Heat-absorbing flame-retardant liquid, 503-Limiting rib, 6-Metal armor, 601-Arc-shaped galvanized steel sheet, 602-Card slot, 603-Flame-retardant sealing strip, 7-Composite outer sheath, 701-Polyolefin matrix layer, 702-Ceramic dip-coated protective sleeve. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in conjunction with the accompanying drawings is intended merely to illustrate selected embodiments of the invention and is not intended to limit the scope of protection claimed by the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0021] like Figure 1 As shown, the present invention provides a halogen-free, low-smoke, flame-retardant control cable with no burning drips, comprising, from the inside out, a shaped cable, an oxygen-barrier flame-retardant layer 4, a buffer layer 5, a metal armor 6, and a composite outer sheath 7.

[0022] The formed cable includes multiple control line units 1, which are twisted into cables in reverse in two layers, inner and outer. A radially protruding ceramic flame-retardant separator 2 is arranged between the inner and outer layers, and the gaps between the multiple control line units 1 are filled with dot-shaped skeleton fillers 3.

[0023] The oxygen-barrier flame-retardant layer 4 is composed of an inner layer of glass fiber ceramic tape 401 and an outer layer of glass fiber ceramic tape 402 wound in opposite directions, and flame-retardant microcapsules 403 are filled in the interlayer between the inner layer of glass fiber ceramic tape 401 and the outer layer of glass fiber ceramic tape 402.

[0024] The buffer layer 5 is extruded over the oxygen-barrier flame-retardant layer 4. Multiple hollow ceramic fiber tube bundles 501 are evenly distributed in a ring along the axial direction inside the buffer layer 5. The hollow ceramic fiber tube bundles 501 are sealed and filled with liquid boron-based heat-absorbing flame-retardant liquid 502.

[0025] The composite outer sheath 7 includes a polyolefin matrix layer 701 and a ceramic-coated protective sheath 702 arranged from the inside out.

[0026] Specifically, control line unit 1 is the smallest electrical transmission unit of the cable. Multiple control line units 1 are divided into inner and outer layers and twisted in opposite directions. The torsional stress during the forming process is offset by the opposite twisting direction, which improves the roundness of the cable core. From the inside out, each control line unit 1 consists of a conductor 101, an insulation layer 102, and a flame-retardant outer sheath 103. Unlike the traditional single-layer insulation core structure, it relies on the insulation layer for electrical insulation protection, and the outer layer is equipped with an independent flame-retardant outer sheath 103 to form a single flame-retardant shell. When the cable is exposed to open flame, each control line unit 1, relying on the flame-retardant outer sheath 103, first forms a ceramic seal, which can individually bind its own molten insulation substrate, preventing the molten material of the single core from dripping, thus laying the foundation for no dripping at the micro-unit level of the cable.

[0027] The ceramic flame-retardant separator 2 has a semi-circular cross-section and is positioned at the gap between adjacent control line units 1. It is evenly distributed along the circumference of the cable core and mainly serves a dual function of zoning and limiting, as well as three-dimensional support. On the one hand, it separates the densely arranged wire cores into independent areas, preventing multiple wire cores from collapsing and causing local material accumulation and falling after the cable is squeezed and softened by high temperature. On the other hand, the component itself is made of ceramicizable polymer material, which has moderate elasticity at room temperature to adapt to cable bending and laying. Under the high temperature environment of a fire, it quickly hardens into a rigid support rib, building a radial support skeleton inside the cable core to support the molten material inside and prevent the molten material from seeping downwards along the gaps between the wire cores.

[0028] The dotted skeleton filler 3 fills the gaps between control line units using an intermittent, fixed-point filling method, abandoning the traditional process of full-section filling of the entire flame-retardant rope. It uses expanded graphite coated with continuous fiberglass bundles. The fiberglass bundles themselves are high-temperature resistant and do not soften at high temperatures, permanently remaining as a rigid support skeleton in the cable core gaps. The expanded graphite coating expands rapidly upon heating, automatically sealing the filling gaps and blocking the downward flow of molten resin. This intermittent dotted arrangement significantly reduces filler material usage, lowers cable weight, and improves cable bending flexibility while ensuring flame-retardant support.

[0029] The oxygen-barrier flame-retardant layer 4 is wrapped around the outer surface of the cable core. It is formed by the inner layer of fiberglass ceramic tape 401 and the outer layer of fiberglass ceramic tape 402, which are wound in opposite directions. The double-layer winding in opposite directions can effectively eliminate wrapping gaps and improve overall airtightness. The cavity between the two layers of tape is uniformly filled with granular flame-retardant microcapsules 403, which can seal phosphorus and nitrogen flame-retardant agents. Under normal storage conditions, the flame-retardant microcapsules 403 are sealed and stable without breakage. In the event of a fire, the external high temperature penetrates the sheath, and the flame-retardant microcapsules 403 rupture due to heat. The phosphorus and nitrogen flame-retardant agents sealed inside are released instantaneously. On the one hand, they absorb ambient heat to reduce the temperature rise, and on the other hand, they decompose to generate inert flame-retardant gas to fill the interlayer space, prevent oxygen from diffusing inward, and inhibit the violent combustion and melting of the inner polymer material.

[0030] The buffer layer 5 is integrally extruded using halogen-free, low-smoke, elastic flame-retardant material, tightly encapsulating the oxygen-barrier flame-retardant layer 4, serving as a buffer against pressure and integrating heat storage and flame retardancy. Hollow ceramic fiber tube bundles 501 are uniformly arranged in a ring along the cable axis inside the buffer layer 5. The hollow ceramic fiber tube bundles 501 are sealed with a heat-absorbing flame-retardant liquid 502, which can be a liquid boron-based component. When the cable is subjected to external pressure, the buffer layer 5 elastically deforms to buffer stress, protecting the inner cable core from mechanical damage. In high-temperature environments, the hollow ceramic fiber tube bundles 501 expand and crack due to heat, and the internal heat-absorbing flame-retardant liquid 502 rapidly vaporizes and absorbs heat, extensively absorbing heat from the buffer layer 5 and the inner cable core, slowing down the melting rate of the insulation, filling, and other polymer substrates, and reducing the amount of molten material generated from the middle layer.

[0031] The metal armor 6 is located on the outside of the buffer pad layer 5, serving as the core mechanical support structure for this cable. It adopts a segmented snap-fit ​​assembly instead of the traditional continuous steel strip wrapping process. The entire structure relies on the snap-fit ​​between the steel sheet and the buffer pad layer 5 to achieve radial and axial limiting and fixation. The steel sheet has good dimensional stability at high temperatures and does not soften or deform, forming a cage-like metal enclosure. Once the inner layers of material melt due to heat, the molten material is caught and blocked by the inner wall of the metal armor 6. The metal armor 6 supports all the molten material, completely blocking the downward dripping path of the molten material. This is the key structure to achieve a fire-free dripping effect on the entire cable.

[0032] The composite outer sheath 7, as the outermost protective structure of the cable, consists of a polyolefin matrix layer 701 and a ceramic-coated protective sleeve 702 from the inside out. The polyolefin matrix layer 701 is extruded to ensure a tight fit between the composite outer sheath 7 and the surface of the metal armor 6, providing excellent tear resistance and bending resistance to meet the requirements of complex laying conditions such as outdoor and trench installations. The ceramic-coated protective sleeve 702 is formed through post-immersion coating and curing. The coating contains silicon-based ceramic carbon-forming components, which sinter in a short time when exposed to open flame to form a dense and hard ceramic shell, completely encapsulating the inner matrix and preventing flame and oxygen from eroding inward. At the same time, it encapsulates the molten matrix of the sheath, preventing the outer sheath from melting and dripping.

[0033] In other embodiments, the outer wall of the buffer pad 5 is integrally formed with a limiting rib 503.

[0034] The metal armor 6 is made of multiple arc-shaped galvanized steel sheets 601 spliced ​​together with snap fasteners at both ends. The inner side of the arc-shaped galvanized steel sheet 601 is provided with a slot 602 that matches the limiting rib 503. The splicing gap of the arc-shaped galvanized steel sheet 601 is embedded with a flame-retardant sealing strip 603.

[0035] Specifically, during the extrusion molding process, the outer wall of the buffer pad 5 is simultaneously extruded with an annular limiting rib 503. The limiting rib 503 and the body of the buffer pad 5 are of the same material and have a solid bond with no risk of falling off.

[0036] like Figure 2 As shown, the metal armor 6 is composed of multiple arc-shaped galvanized steel sheets 601 spliced ​​together end to end with snap fasteners. The inner side of the arc-shaped galvanized steel sheets 601 has a pre-made groove 602. During assembly, the groove 602 is precisely fitted onto the outer side of the limiting rib 503, realizing axial anti-movement and circumferential anti-loosening of the metal armor 6. The gaps between the interlocking arc-shaped galvanized steel sheets 601 are pre-embedded with flame-retardant sealing strips 603. At room temperature, the flame-retardant sealing strips 603 fill the gaps to prevent dust and moisture. When heated at high temperature, the flame-retardant sealing strips 603 foam and expand to fill the gaps, sealing the air gaps of the metal armor 6 and preventing air from entering the interior and aiding combustion.

[0037] In other embodiments, the raw material components of the insulation layer 102, by weight, include: 40 parts LLDPE, 22 parts EVA, 30 parts ultrafine aluminum hydroxide, 2.8 parts organically modified montmorillonite, 3.2 parts phosphorus-based charring agent, and 2 parts composite antioxidant. The aluminum hydroxide undergoes low-temperature endothermic decomposition, the modified montmorillonite migrates upon heating to form a barrier film, and the phosphorus-based charring agent catalyzes char formation; the multiple components synergistically inhibit the insulation from melting and flowing upon heating.

[0038] Specifically, LLDPE (linear low-density polyethylene) is used as the base resin for insulation layer 102. Its molecular main chain has a linear structure and short branches are evenly distributed. It has excellent low-temperature resistance, tear resistance, and bending resistance, which can ensure that insulation layer 102 will not crack when laid at room temperature and low temperature. Its melt flow rate is suitable for cable extrusion process. After being blended with EVA, it improves the interfacial compatibility of inorganic fillers and avoids filler agglomeration that causes insulation voids and defects, thus providing basic mechanical and processing properties for the formulation.

[0039] EVA (ethylene-vinyl acetate copolymer) is selected from grades with VA (vinyl acetate) content of 18% to 22%. The molecular chain has polar vinyl acetate groups, which can significantly improve the bonding force between inorganic powders such as aluminum hydroxide and montmorillonite and polyolefin matrix, and solve the problems of brittleness and easy breakage of high-filled halogen-free materials during extrusion. It works in conjunction with LLDPE to control melt viscosity, adapt to high-speed insulation extrusion production, and optimize the insulation flexibility of finished products.

[0040] The ultrafine standard for ultrafine aluminum hydroxide is a powder particle size D50 ≤ 2.0 μm. The raw material is subjected to airflow ultrafine pulverization and surface activation treatment with silane coupling agent; it is heated at 220℃~280℃ to remove crystal water, absorb a large amount of heat to reduce the temperature rise of the substrate, and decompose to generate inert alumina powder to fill the pores of the carbon layer, blocking oxygen penetration. It is the core halogen-free flame retardant and smoke suppressant component of the system, which delays polymer melting by relying on the dual effects of physical heat absorption and solid phase barrier.

[0041] Organically modified montmorillonite is made from natural montmorillonite through quaternary ammonium salt cation intercalation. It is transformed from a hydrophilic inorganic powder into an oleophilic filler. During processing, it is exfoliated into nanosheets that are uniformly dispersed inside the resin. When heated, the sheets migrate and stack towards the insulating surface to form a dense inorganic barrier film, which prevents heat and oxygen from being conducted inward, constrains the flow of molten resin, and inhibits the dripping of molten insulation from the microstructure.

[0042] The phosphorus-based charring agent is an intumescent flame retardant component made of ammonium polyphosphate and pentaerythritol. Under high temperature conditions, it gradually dehydrates and catalyzes the cross-linking and carbonization of the matrix resin, forming a porous intumescent char layer on the surface of the insulating layer 102. The char layer isolates the heat source and oxygen, encapsulates the internal molten resin, effectively locks the melt to prevent it from flowing and falling, and forms a high and low temperature segmented flame retardant synergistic system with ultrafine aluminum hydroxide.

[0043] The composite antioxidant is composed of hindered phenol as the main antioxidant and phosphite as the auxiliary antioxidant. During the high-temperature stage of extrusion processing, it captures free radicals, inhibits high-temperature oxidation and coking of the resin, and eliminates coke particles on the insulation surface. During the long-term use of the cable, it resists heat, oxygen, and ultraviolet aging, delays the hardening and brittleness of the insulation, and stabilizes the insulation performance and flame retardant effect of the product in the long term.

[0044] In other embodiments, the flame-retardant outer sheath 103 is formed by extruding a blend of EVA, ultrafine magnesium hydroxide, borosilicate ceramic powder, and closed-cell foamed microspheres. After extrusion, it undergoes low-temperature in-situ foaming to form a microporous flexible layer that adapts to cable bending. It is then rapidly sintered at a temperature greater than or equal to 300°C to form a sealed ceramic shell that firmly wraps the inner insulation layer.

[0045] In other embodiments, the ceramic flame-retardant separator 2 has an inner diameter of 1.0mm to 1.5mm, and one is arranged every 35mm to 45mm along the circumference of the cable. This allows for uniform support around the entire circumference without occupying too much cable core space.

[0046] In other embodiments, the inner diameter of the hollow ceramic fiber tube bundle 501 is 0.5 mm, and the center-to-center distance between adjacent hollow ceramic fiber tube bundles 501 inside the buffer pad layer 5 is 4 mm to 6 mm.

[0047] The length of a single arc-shaped galvanized steel sheet 601 is 80mm to 120mm, the overlap width of the interlocking of adjacent arc-shaped galvanized steel sheets 601 is 3mm to 5mm, and the width of the flame-retardant sealing strip 603 embedded in the splice seam is 2mm.

[0048] Specifically, the inner diameter of the hollow ceramic fiber tube bundle 501 is fixed at 0.5mm. The center-to-center distance between adjacent hollow ceramic fiber tube bundles 501 inside the buffer pad 5 is 4mm to 6mm. The uniform ring arrangement ensures that all areas of the pad can absorb heat and avoid excessive local temperature rise. The length of the single-segment arc-shaped galvanized steel sheet 601 is 80mm to 120mm. The standardized segment size facilitates prefabrication and mass production in the factory. The overlap width of the interlocking buckles of adjacent arc-shaped galvanized steel sheets 601 is 3mm to 5mm to ensure that the buckle connection is firm and not easy to fall off. The width of the flame-retardant sealing strip 603 embedded in the splice seam is uniformly set at 2mm, matching the size of the gap of the arc-shaped galvanized steel sheet 601. After foaming, it completely fills the splice gap, taking into account both the ease of assembly and the high-temperature sealing and flame-retardant effect.

[0049] This invention provides a method for preparing a halogen-free, low-smoke, flame-retardant control cable with no burning drips, comprising the following steps: S1. Twist the multi-strand conductor 101 together, repair the joint defects, the diameter of the single wire of conductor 101 is >0.2mm, and control the distance between adjacent joints to ≥320mm.

[0050] S2. Using a segmented temperature control method, an insulating layer 102 and a flame-retardant outer layer 103 are sequentially extruded onto the conductor 101 to obtain the control line unit 1.

[0051] S3. Twist multiple control line units 1 in reverse between inner and outer layers, and lay radially protruding ceramic flame-retardant separator strips 2 between the inner and outer layers. Fill the gaps of multiple control line units 1 with dot-shaped skeleton fillers 3 to obtain a shaped cable.

[0052] S4. The inner layer of glass fiber ceramic tape 401 and the outer layer of glass fiber ceramic tape 402 are spirally wound in opposite directions on the formed cable, and flame-retardant microcapsules 403 are filled in the interlayer between the inner layer of glass fiber ceramic tape 401 and the outer layer of glass fiber ceramic tape 402 to obtain the oxygen-barrier flame-retardant layer 4.

[0053] S5. An integrally extruded buffer layer 5 is formed outside the oxygen-barrier flame-retardant layer 4. Hollow ceramic fiber tube bundles 501 are arranged in the buffer layer 5. Liquid boron-based heat-absorbing flame-retardant liquid 502 is sealed and filled inside the hollow ceramic fiber tube bundles 501. Limiting ribs 503 are extruded on the outer wall of the buffer layer 5.

[0054] S6. The multi-segment arc-shaped galvanized steel sheet 601 is assembled and sealed by snap-fit ​​at both ends. The inner side of the arc-shaped galvanized steel sheet 601 is provided with a slot 602 that matches the limiting rib 503. The splicing gap of the arc-shaped galvanized steel sheet 601 is embedded with a flame-retardant sealing strip 603.

[0055] S7. Connect the slot 602 with the limiting rib 503 to obtain the metal armor 6.

[0056] S8. A composite outer sheath 7, comprising a polyolefin matrix layer 701 and a ceramic-coated protective sleeve 702 arranged from the inside out, is formed on the outside of the metal armor 6 to obtain a halogen-free, low-smoke, flame-retardant control cable with no burning drips.

[0057] Specifically, S1 is the conductor stranding process. High-purity oxygen-free copper raw material can be used to process conductor 101. Multiple strands of copper wire are neatly stranded. For single wire diameters > 0.2mm, phosphor bronze is used to braze broken wires. After welding, the weld joint is finely ground to remove protrusions, burrs, and other joint defects. This process strictly limits the spacing between adjacent welded joints to ≥ 320mm to avoid concentrated joints causing localized high resistance and overheating during operation. The stranding pitch is strictly controlled during the stranding process to ensure that conductor 101 has a compact structure, without loose strands, skipped wires, or scattered strands, and has a smooth and clean surface, providing a flat substrate for the subsequent extrusion of the insulation layer 102.

[0058] S2 is the process for preparing the control line unit by double-layer extrusion. It adopts a four-segment temperature-controlled extrusion equipment. The insulation layer 102 is first extruded on the outside of the conductor 101. The melt flow is controlled by temperature control parameters to ensure that the insulation layer 102 has a uniform thickness and is free of bubbles and char particles. After the insulation layer 102 is extruded and shaped, the flame-retardant outer layer 103 is continuously coated online using a co-extrusion die head. The flame-retardant outer layer 103 mixture is foamed in situ at low temperature. The flexibility is improved by the foaming structure. Thus, the conductor 101, insulation layer 102 and flame-retardant outer layer 103 are integrated to form a single control line unit 1, realizing independent flame-retardant protection for single-core cables.

[0059] S3 divides multiple prepared control line units 1 into inner and outer layers, and twists them into a cable using opposite twisting directions: the inner layer is twisted clockwise and the outer layer is twisted counterclockwise, to counteract the internal stress generated by twisting and improve the roundness of the cable core. During cable formation, semi-circular ceramic flame-retardant separators 2 are equidistantly embedded along the circumference of the cable core to separate each group of control line units 1 and prevent them from being compressed and clustered. The remaining gaps in the control line units 1 are intermittently filled with dot-shaped skeleton fillers 3 made of expanded graphite-coated glass fiber bundles. This abandons the traditional full-section full-filling process and builds a multi-point three-dimensional support skeleton inside the cable core to obtain a well-formed cable.

[0060] S4 is the process of preparing an oxygen-barrier and flame-retardant layer by reverse wrapping. A double-layer reverse wrapping machine is used to wrap the outer layer of the formed cable. First, the inner layer of glass fiber ceramic tape 401 is spirally wound, and then the outer layer of glass fiber ceramic tape 402 is wound in the opposite direction. The two layers of tape are wound in opposite directions, which can reduce the wrapping gap and improve the sealing of the wrapping. Particle flame-retardant microcapsules 403 are evenly sprinkled in the cavity formed by the inner layer of glass fiber ceramic tape 401 and the outer layer of glass fiber ceramic tape 402. The flame-retardant microcapsules 403 can be prevented from falling off by the double-layer tape wrapping and limiting. The combination of the three forms an oxygen-barrier and flame-retardant layer 4 with oxygen barrier and drug storage and slow release functions.

[0061] S5 uses halogen-free, low-smoke, flame-retardant, and elastic raw materials. A buffer pad 5 is integrally extruded on the outside of the oxygen-barrier flame-retardant layer 4 using a special shaped extrusion mold. During the extrusion process, a continuous feeding fixture is used to evenly distribute hollow ceramic fiber tube bundles 501 pre-loaded with heat-absorbing flame-retardant liquid 502 along the cable axis and in a ring shape to control the extrusion temperature and prevent the tube bundles from being damaged by high-temperature extrusion. While the buffer pad 5 is being extruded, annular limiting ribs 503 are integrally extruded on the outer wall of the pad. The limiting ribs 503 and the buffer pad 5 are of the same material and integral structure, which are firm and do not fall off. They are used for subsequent metal armor 6 assembly and positioning.

[0062] S6 and S7 are the snap-fit ​​assembly process for metal armor. Pre-fabricated arc-shaped galvanized steel sheets 601 are used to assemble the metal armor 6. During assembly, the pre-reserved groove 602 on the inner side of the arc-shaped galvanized steel sheet 601 is aligned with the limiting rib 503 on the outer wall of the buffer pad layer 5 and clamped in place. The ends of the arc-shaped galvanized steel sheet 601 are overlapped end to end through a pre-set snap-fit ​​structure, and the overlap size meets the process specifications. Before assembly, flame-retardant sealing strips 603 are pre-filled into the gaps between the arc-shaped galvanized steel sheets 601. After all the armor is assembled, it is shaped as a whole by a rolling equipment to eliminate defects such as warped edges, loose edges, and flared mouths, forming a cage-like metal armor 6 that can be mechanically supported.

[0063] S8 is a double-layer coating molding composite outer sheath process. Before the sheath is formed, a rotary negative pressure cleaning device is used to thoroughly clean the dust and metal debris on the outer wall of the metal armor 6 to prevent impurities from being embedded in the sheath and forming weak points in flame retardancy. After cleaning, a polyolefin matrix layer 701 is extruded on the outside of the metal armor 6 to ensure that the matrix layer is tightly attached to the outer surface of the armor without any voids or bulges. After the polyolefin matrix layer 701 cools and sets, a silicon-based ceramic coating is dipped into its outer surface and cured at room temperature to form a ceramic dip-coated protective sleeve 702. The polyolefin matrix layer 701 and the ceramic dip-coated protective sleeve 702 together form the composite outer sheath 7, ultimately producing a halogen-free, low-smoke, flame-retardant control cable with no burning drips.

[0064] In other embodiments, a segmented temperature control method is used to sequentially extrude an insulating layer and a flame-retardant outer layer onto the conductor. This includes: controlling the temperature of the body of the insulation extruder in four stages, namely 120°C, 135°C, 150°C, and 160°C, controlling the temperature of the die head at 155±5°C, and continuously extruding the flame-retardant outer layer online after the insulation layer is extruded. The foaming and setting temperature of the flame-retardant outer layer is controlled at 85±5°C.

[0065] Specifically, the control line unit 1 is manufactured using a segmented precision temperature-controlled co-extrusion process. An insulation layer 102 and a flame-retardant outer layer 103 are sequentially and continuously extruded over the conductor 101. A dual-head online extrusion system is configured, with an independent extruder for the insulation layer 102. The extruder body is divided into four stepped temperature control sections along the material conveying direction, with the four temperature zones set at 120℃, 135℃, 150℃, and 160℃ respectively. The 120℃ section is responsible for preheating and melting the raw materials to prevent powder agglomeration; the 135℃ section allows for thorough mixing and plasticization of the resin and various flame-retardant additives; the 150℃ section stabilizes the melt viscosity to ensure uniform material mixing; and the 160℃ section achieves stable melt pressure conveying. The die temperature control of the insulation extruder is set to 155±5℃ to precisely regulate the discharge flow rate and forming state, preventing die scorch buildup, uneven insulation thickness, and localized material shortages. This ensures that the insulation layer 102 tightly covers the outer periphery of the conductor 101, with a smooth surface free of pores and coke particles.

[0066] After the insulation layer 102 is extruded and shaped, the production line is not interrupted. The flame-retardant outer layer 103 is extruded online synchronously through the online auxiliary extruder head. After the flame-retardant outer layer 103 mixture is extruded, it immediately enters the constant temperature foaming and shaping channel. The channel temperature is strictly limited to 85±5℃. Within this temperature range, the closed-cell foamed microspheres are stably foamed and shaped, which not only ensures that the flame-retardant outer layer 103 has excellent bending flexibility at room temperature, but also retains the internal closed microporous structure, laying the structural foundation for the overall ceramic molding at high temperature above 300℃. Finally, the integrated molding structure is stable.

[0067] In other embodiments, in step S3, multiple control line units 1 are twisted together in reverse, with inner and outer layers, and radially protruding ceramic flame-retardant separator strips 2 are arranged between the inner and outer layers. Dot-shaped skeleton fillers 3 are filled into the gaps between the multiple control line units 1 to obtain a shaped cable, including: S301. Twist the inner layer control line unit 1 in a clockwise direction and twist the outer layer control line unit 1 in a counterclockwise direction. If conductor 101 is a hard conductor, control the cabling pitch of the hard conductor to be ≤18 times the outer diameter of the cabling; if conductor 101 is a soft conductor, control the cabling pitch of the soft conductor to be ≤15 times the outer diameter of the cabling.

[0068] S302. During the cabling process, ceramic flame-retardant separator strips 2 are pasted at equal intervals between layers. Multiple control line units are interspersed with expanded graphite-coated fiberglass bundles to form a dotted skeleton filler 3, without overall full-section filling.

[0069] Specifically, step S3 involves layering and reverse twisting multiple control line units 1, and laying ceramic flame-retardant separators 2 and dotted skeleton fillers 3 to achieve neat and orderly cable core formation. This is divided into two sub-processes: S301 and S302. S301: Layered Differentiated Twisting Control: All control line units 1 are divided into inner core groups and outer core groups. The inner control line units 1 are twisted and arranged in a clockwise direction, while the outer control line units 1 are twisted in a counterclockwise direction. The forward and reverse twisting is used to offset the torsional internal stress generated during cable formation, thereby improving the roundness and structural stability of the entire cable core. The pitch parameters are differentiated according to the material of conductor 101. Hard conductors have high rigidity and weak deformation ability, so the cable formation pitch is controlled to be ≤18 times the outer diameter of the cable to avoid loose and misaligned cores. Soft conductors are made of multiple strands of fine copper wire and have excellent flexibility. The cable formation pitch is tightened to ≤15 times the outer diameter of the cable to prevent core movement and displacement during laying and dragging, ensuring a compact and orderly cable core arrangement.

[0070] S302. Fixed-point layout of separators and fillers: During the entire process of cable laying, semi-circular ceramic flame-retardant separators 2 are continuously pasted at set intervals along the interlayer position of the cable core circumference. The ceramic flame-retardant separators 2 are used to separate adjacent control line units 1 to prevent the core from collapsing after softening due to heat. The scattered gaps between control line units 1 are only filled with point-like skeleton fillers 3 made of expanded graphite-coated fiberglass bundles. This method abandons the traditional method of filling the entire cross-section of flame-retardant rope. Instead, it uses intermittent point-like support to construct a three-dimensional mesh inside the cable core. This reduces the amount of filler material and the weight of the cable. At the same time, it relies on the high-temperature resistant fiberglass skeleton to support the molten material in the later stage and block the combustion dripping channel from inside the cable core.

[0071] In other embodiments, the inner layer of the double-layer glass fiber ceramic tape 401 has a wrapping overlap rate of 16%, and the outer layer of glass fiber ceramic tape 402 is wrapped in the opposite direction with an overlap rate of 20%. Phosphorus-nitrogen-based expandable flame-retardant microcapsule particles (i.e., flame-retardant microcapsules 403) are continuously and uniformly sprinkled in the gaps between the double-layer glass fiber ceramic tape wrapping.

[0072] Specifically, during the molding of the oxygen-barrier flame-retardant layer 4, the wrapping parameters of the two layers of fiberglass ceramic tape are set differently. The inner layer of fiberglass ceramic tape 401 is wrapped in a forward spiral, and the overlap rate of the tape is controlled to be fixed at 16%. This overlap ratio can ensure that the inner layer is completely covered without exposed gaps, and will not cause the tape to wrinkle or local accumulation and bulge due to excessive overlap. The outer layer of fiberglass ceramic tape 402 adopts a spiral winding direction opposite to that of the inner layer, and the wrapping overlap rate is set at 20%. The larger overlap allowance, combined with the reverse wrapping structure, can seal the overlap gaps of the inner layer, forming an interlaced and sealed double-layer encapsulation cavity, which greatly improves the overall sealing performance of the oxygen-barrier flame-retardant layer 4.

[0073] Within the interlayer cavity formed by the inner layer of fiberglass ceramic tape 401 and the outer layer of fiberglass ceramic tape 402, phosphorus-nitrogen expandable flame-retardant microcapsule particles are uniformly and continuously sprinkled in at a constant speed as the wrapping progresses, forming flame-retardant microcapsules 403. The covering and limiting effect of the double-layer tape body can prevent the flame-retardant microcapsules 403 from falling off and scattering. Under normal conditions, the flame-retardant microcapsules 403 are sealed and stable, and the agent does not leak out. When exposed to high temperature and open flame, the outer shell of the flame-retardant microcapsules 403 breaks, and the internal phosphorus-nitrogen flame-retardant components decompose and absorb heat, releasing inert flame-retardant gas, filling the interlayer space and preventing oxygen from penetrating into the cable core. Together with the double-layer fiberglass substrate, it achieves the functions of heat insulation and oxygen isolation, and inhibits the melting and dripping of the substrate.

[0074] In other embodiments, the buffer pad 5 is integrally extruded using a non-standard co-extrusion die, and the extrusion temperature is controlled at 130℃~142℃.

[0075] Hollow ceramic fiber tube bundles 501 are arranged in the buffer pad layer 5, and limiting ribs 503 are extruded on the outer wall of the buffer pad layer 5. This includes: while the buffer pad layer 5 is being extruded, the hollow ceramic fiber tube bundles 501 are fed into the buffer pad layer 5 at a uniform speed through a feeding tool, and the annular limiting ribs 503 are extruded synchronously and integrally on the outer wall of the buffer pad layer 5.

[0076] Specifically, the buffer layer 5 is made of halogen-free, low-smoke, elastic, and flame-retardant raw material, and is integrally extruded using a customized co-extrusion die. The overall extrusion temperature is controlled within the range of 130℃ to 142℃. This temperature range ensures that the matrix resin is fully plasticized and has moderate fluidity, achieving complete molding of the buffer layer. It also avoids heat damage to the hollow ceramic fiber tube bundle 501 caused by excessively high temperatures, while preventing problems such as poor material plasticization, cracking, and material shortage in the buffer layer due to excessively low temperatures.

[0077] During the extrusion molding process of the buffer pad 5, the internal components are laid out and the outer wall structure is formed simultaneously. The production line is equipped with a special continuous feeding fixture, which feeds hollow ceramic fiber tube bundles 501 pre-filled with heat-absorbing and flame-retardant liquid 502 into the molten pad material at a uniform speed and at equal intervals, following the extrusion speed. The tube bundles are evenly arranged in a ring around the circumference of the cable and are completely wrapped and fixed by the molten pad material. Relying on the outer contour structure of the special mold, a ring-shaped limiting rib 503 is extruded in an integral manner on the outer wall of the buffer pad 5. The limiting rib 503 and the buffer pad 5 are homogeneous integral extrusion structures, which are firmly bonded and do not delaminate or fall off. When assembling the metal armor 6 later, the slot 602 of the arc-shaped galvanized steel sheet 601 can accurately engage the limiting rib 503 to achieve axial and circumferential limiting and fixing of the armor.

[0078] Example 1 This embodiment provides a method for preparing a 450 / 750V halogen-free, low-smoke, flame-retardant control cable. The control cable adopts a layered cabling structure with 16 core control line units 1, including an inner layer of 8 control line units 1 and an outer layer of 8 control line units 1. The overall structure adopts the above-mentioned single-core independent ceramic protection, interlayer partition strip support, dotted skeleton filling, double-layer reverse oxygen barrier, built-in heat-absorbing tube bundle buffer pad layer, segmented snap-fit ​​armor, and double-layer ceramic composite sheath structure, which is completely different from the conventional cable structure.

[0079] I. Raw material ratio 1. Weight proportion of raw material 102 for insulation layer The composition consists of 40 parts LLDPE, 22 parts EVA, 30 parts ultrafine aluminum hydroxide, 2.8 parts organically modified montmorillonite, 3.2 parts phosphorus-based charring agent, and 2 parts composite antioxidant. The ultrafine aluminum hydroxide has a D50 ≤ 2.0 μm and is activated by silane. The EVA is selected from grades with a VA content of 18% to 22%. The organically modified montmorillonite is a quaternary ammonium salt intercalated oleophilic modified powder.

[0080] 2. Flame-retardant outer coating material ratio 103 EVA, ultrafine magnesium hydroxide, borosilicate ceramic powder, and closed-cell foamed microspheres are blended together to suit low-temperature in-situ foaming and high-temperature ceramic molding processes.

[0081] The specific weight proportions of the above components are as follows: EVA 38 parts, ultrafine magnesium hydroxide 52 parts, borosilicate ceramic powder 6 parts, and closed-cell foamed microspheres 4 parts. These components work synergistically to adapt to low-temperature in-situ foaming and high-temperature rapid ceramicizing processes. The mixture is halogen-free, low-smoke, and highly flame-retardant, and can be stably extruded. It maintains flexibility at room temperature and can rapidly form a dense ceramic protective shell at high temperatures. Detailed description of the functions of each component: 1. EVA: Copolymer resin with VA content of 18% to 22% is selected as the matrix binder. It has excellent powder wettability and foaming properties, and can firmly encapsulate inorganic powder and foamed microspheres, ensuring extrusion layering quality and room temperature bending toughness. 2. Ultrafine magnesium hydroxide: Activated powder with D50≤2.0μm is used as the main flame retardant and smoke suppressant component. When heated to about 280℃, it dehydrates and absorbs heat, dilutes oxygen, and decomposes to generate an inert magnesium oxide refractory layer, which inhibits the combustion and melting of the substrate. 3. Borosilicate ceramic powder: a special vitrification aid that can cross-link and sinter with magnesium hydroxide decomposition products at high temperatures, promoting the rapid formation of a continuous, dense, and high-strength hard ceramic shell and preventing the leakage and dripping of molten materials; 4. Closed-cell foamed microspheres: Temperature-controlled physical foaming components that are stably foamed at a setting temperature of 85±5℃ to form a uniform and closed microporous structure, reducing coating hardness and improving the overall flexibility of the cable, while not damaging the high-temperature ceramicization performance, providing bidirectional structural support for cable bending at room temperature and flame-retardant protection at high temperature.

[0082] II. Preparation process is as follows S1, Conductor stranding process Conductor 101 is prepared by stranding multiple strands of high-purity oxygen-free copper wire, with a single wire diameter greater than 0.2mm. Broken wires are brazed with phosphor bronze, and after welding, protrusions and burrs are removed through fine grinding. The spacing between adjacent welded joints is strictly controlled to be ≥320mm to prevent concentrated heat generation at the joints. The stranding pitch is standardized throughout the process to ensure that conductor 101 has a compact structure, free of loose strands, skipped wires, and scattered strands, with a smooth and flat surface, providing a high-quality substrate for subsequent double-layer extrusion coating.

[0083] S2, Segmented Temperature-Controlled Double-Layer Co-Extrusion Preparation Control Line Unit The extrusion equipment employs a dual-head inline extrusion system. The insulation extruder features four-stage temperature control at 120℃, 135℃, 150℃, and 160℃, with a constant die temperature of 155±5℃. The 120℃ stage preheats the raw material to prevent agglomeration; the 135℃ stage ensures thorough mixing and plasticization of the powder and resin; the 150℃ stage stabilizes the melt viscosity; and the 160℃ stage provides stable pressure and uniform discharge, guaranteeing a uniform thickness, pore-free, and particle-free insulation layer 102. After extrusion and shaping of the insulation layer 102, a flame-retardant outer layer 103 is continuously extruded online. The flame-retardant outer layer 103 enters a constant-temperature shaping channel, where the foaming and shaping temperature is strictly controlled at 85±5℃, achieving low-temperature in-situ microporous foaming. The resulting control line unit 1 exhibits excellent flexibility and possesses a high-temperature ceramic-like basic structure.

[0084] S3, Layered reverse cabling, laying separator strips and dotted fillers The 16 control wire units 1 are divided into an inner layer of 8 wires and an outer layer of 8 wires, and a differentiated reverse twisting process is performed: the inner layer control wire units 1 are twisted clockwise, and the outer layer control wire units 1 are twisted counterclockwise, to offset the torsional stress of the cable and improve the roundness of the cable core. This embodiment adopts a soft conductor structure and strictly controls the cable pitch to ≤15 times the outer diameter of the cable to prevent dragging and movement during laying. Throughout the cable laying process, semi-circular ceramic flame-retardant separators 2 are evenly distributed between the layers of the cable core, with a diameter of 1.2 mm and a spacing of 40 mm. Expanded graphite-coated glass fiber bundles are interspersed at specific points in the scattered gaps of the wire core to form a dotted skeleton filler 3, instead of using the traditional full-section full-filling process, to construct a lightweight three-dimensional high-temperature resistant support skeleton.

[0085] S4, Double-layer differentiated wrapping molding oxygen-barrier and flame-retardant layer A reverse double-layer wrapping process is adopted. The inner layer, fiberglass ceramic tape 401, is spirally wrapped in the forward direction with a fixed overlap rate of 16%, ensuring full coverage without any exposed areas. The outer layer, fiberglass ceramic tape 402, is spirally wound in the reverse direction with a fixed overlap rate of 20%, and the double layers interlock to seal the wrapping gaps. Phosphorus-nitrogen-based expandable flame-retardant microcapsule particles are continuously, uniformly, and at a constant speed sprinkled into the cavity between the two tapes, forming a sealed flame-retardant microcapsule 403 storage interlayer. The double-layer tape body limits and prevents the flame-retardant microcapsules 403 from falling off, constructing a multi-layer flame-retardant structure that isolates oxygen, absorbs heat, and releases the drug.

[0086] S5, constant temperature extruded buffer pad, pre-embedded tube bundle and integrally formed limiting rib The buffer pad 5 is made from halogen-free, low-smoke, elastic flame-retardant raw materials and is extruded in an integrated manner using a customized co-extrusion die. The overall extrusion temperature is strictly controlled between 130℃ and 142℃ to ensure full plasticization and molding of the material, while preventing high-temperature damage to the hollow ceramic fiber tube bundles 501. During the extrusion process, a special feeding fixture uniformly and circumferentially distributes the hollow ceramic fiber tube bundles 501 inside the pad at the inside of the pad. The inner diameter of the tube bundle is 0.5mm, and the center distance between adjacent tube bundles is 5mm. The inside of the tube bundle is pre-sealed and filled with liquid boron-based heat-absorbing flame-retardant liquid 502. Simultaneously with the extrusion of the buffer pad 5, an integral annular limiting rib 503 is extruded on the outer wall. The rib is homogeneous with the pad, resulting in a strong structure without delamination or detachment.

[0087] S6, Segmented snap-fit ​​assembled metal armor Prefabricated arc-shaped galvanized steel sheets 601, each 90mm in length, are used for assembly. The inner groove 602 of the arc-shaped galvanized steel sheet 601 precisely engages with the outer wall limiting rib 503 of the buffer pad layer 5, achieving dual axial and circumferential limiting. The overlap width of the interlocking buckles of adjacent arc-shaped galvanized steel sheets 601 is 4mm, and a 2mm wide flame-retardant sealing strip 603 is embedded in the splicing gap. After all the arc-shaped galvanized steel sheets 601 are assembled, they are shaped as a whole using a rolling mill to eliminate defects such as warping, loosening, and flared openings, forming a sealed cage-like bottom metal armor 6.

[0088] S7, Double-layer composite outer sheath molding Before molding, a rotary negative pressure cleaning device is used to thoroughly clean the outer wall of the metal armor 6 to remove metal debris and dust, eliminating any weak points in the flame retardancy of the sheath. After cleaning, a polyolefin matrix layer 701 is extruded to ensure a tight fit without bulges or gaps. After the matrix layer cools and sets, a silicon-based ceramic coating is applied to the entire cable, which is then cured at room temperature to form a ceramic-coated protective sheath 702. This results in a complete, halogen-free, low-smoke flame-retardant control cable with no burning droplets.

[0089] III. Results of Finished Product Performance Testing The finished cable prepared by this invention was compared with a traditional halogen-free low-smoke flame-retardant control cable of the same specification (traditional structure: conductor-single-layer insulation-full filling-integral inner lining-continuous steel tape armor-single-layer sheath) for benchmark testing. The traditional halogen-free low-smoke flame-retardant control cable of the same specification, model WDZB1-KYJY23, was selected. The results are as follows: 1. Bundled burning B1 level test (according to national standard GB 31247): The present invention controls the cable to burn continuously for 40 minutes without producing any molten drips, the flame self-extinguishes rapidly, and the carbon layer of the cable core is intact and hardened into porcelain; the traditional cable burning process continuously produces molten drips, and the drips can ignite the combustibles below.

[0090] 2. Smoke density test (according to national standard GB 17651): The smoke density Ds of the control cable of this invention is 106, which meets the low smoke standard; the smoke density of traditional cables of the same type is generally ≥130, and the smoke suppression performance is significantly better than that of traditional cables.

[0091] 3. Halogen-free acid gas test: The present invention controls the cable to burn without hydrogen halides or corrosive acid gas release, meeting the fire protection requirements of high-risk locations.

[0092] 4. Mechanical and weather resistance: The control cable of this invention can withstand repeated bending at -40℃ for 20 times without cracking or delamination; it can withstand a power frequency withstand voltage of 3kV / 5min without breakdown, and the elongation at break of the sheath is 190%.

[0093] 5. Structural stability: After high-temperature combustion, the internal skeleton of the control cable remains intact, with no core collapse or material flow. In contrast, traditional cables suffer from severe collapse of the high-temperature filling layer and softening and sagging of the inner lining.

[0094] The above description is merely the preferred embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A halogen-free, low-smoke, flame-retardant control cable with no burning drips, characterized in that, This includes, from the inside out, a molded cable, an oxygen-barrier and flame-retardant layer, a cushioning layer, a metal armor, and a composite outer sheath; The formed cable includes multiple control line units, which are twisted into cables in reverse in two layers, inner and outer. A radially protruding ceramic flame-retardant separator is arranged between the inner and outer layers, and the gaps between the multiple control line units are filled with dot-shaped skeleton fillers. The oxygen-barrier flame-retardant layer is composed of an inner layer of glass fiber ceramic tape and an outer layer of glass fiber ceramic tape wound in opposite directions, and flame-retardant microcapsules are filled in the interlayer between the inner layer of glass fiber ceramic tape and the outer layer of glass fiber ceramic tape. The buffer pad is extruded over the oxygen-barrier flame-retardant layer. Multiple hollow ceramic fiber tube bundles are evenly distributed in a ring along the axial direction inside the buffer pad. The hollow ceramic fiber tube bundles are sealed and filled with liquid boron-based heat-absorbing flame-retardant liquid. The composite outer sheath includes a polyolefin matrix layer and a ceramic-coated protective sleeve arranged from the inside out; The control line unit includes a conductor, an insulating layer, and a flame-retardant outer layer. The flame-retardant outer layer is rapidly sintered at a temperature greater than or equal to 300°C to form a sealed ceramic shell. The outer wall of the buffer pad is integrally formed with a limiting rib; the metal armor is spliced ​​together by multiple arc-shaped galvanized steel sheets with snap fasteners at both ends, and the inner side of the arc-shaped galvanized steel sheets is provided with a groove that matches the limiting rib, and the splicing gap of the arc-shaped galvanized steel sheets is embedded with a flame-retardant sealing strip.

2. The halogen-free, low-smoke, flame-retardant control cable with no burning drips according to claim 1, characterized in that, The raw material components of the insulating layer, by weight, include: 40 parts LLDPE, 22 parts EVA, 30 parts ultrafine aluminum hydroxide, 2.8 parts organic modified montmorillonite, 3.2 parts phosphorus-based charring agent, and 2 parts composite antioxidant. The flame-retardant outer layer is formed by extruding EVA, ultrafine magnesium hydroxide, borosilicate ceramic powder, and closed-cell foamed microspheres to form a sealed ceramic shell.

3. The halogen-free, low-smoke, flame-retardant control cable with no burning drips according to claim 1 or 2, characterized in that, The ceramic flame-retardant separator has a semi-circular cross-section with an inner diameter of 1.0mm to 1.5mm, and one is arranged every 35mm to 45mm along the circumference of the cable. The dotted skeleton filler is made of expanded graphite coated with glass fiber bundles.

4. The halogen-free, low-smoke, flame-retardant control cable with no burning drips according to claim 1, characterized in that, The inner diameter of the hollow ceramic fiber tube bundle is 0.5 mm, and the center distance between adjacent hollow ceramic fiber tube bundles inside the buffer pad layer is 4 mm to 6 mm. The length of a single arc-shaped galvanized steel sheet is 80mm to 120mm, the overlap width of the interlocking of adjacent arc-shaped galvanized steel sheets is 3mm to 5mm, and the width of the flame-retardant sealing strip embedded in the splice seam is 2mm.

5. A method for preparing a halogen-free, low-smoke, flame-retardant control cable with no combustion drippings, characterized in that, Includes the following steps: Multiple conductors are twisted together, and joint defects are repaired. The diameter of a single conductor is >0.2mm, and the spacing between adjacent joints is controlled to be ≥320mm. By employing a segmented temperature control method, an insulating layer and a flame-retardant outer sheath are sequentially extruded onto the conductor to obtain a control line unit. Multiple control line units are twisted in opposite directions in two layers, and radially protruding ceramic flame-retardant separators are arranged between the inner and outer layers. Dot-shaped skeleton fillers are filled into the gaps of the multiple control line units to obtain a shaped cable. An inner layer of glass fiber ceramic tape and an outer layer of glass fiber ceramic tape are spirally wound in opposite directions on the formed cable, and flame-retardant microcapsules are filled in the interlayer between the inner layer of glass fiber ceramic tape and the outer layer of glass fiber ceramic tape to obtain an oxygen-barrier flame-retardant layer. An integrally extruded buffer pad layer is formed outside the oxygen-barrier flame-retardant layer. Hollow ceramic fiber tube bundles are arranged in the buffer pad layer. Liquid boron-based heat-absorbing flame-retardant liquid is sealed and filled inside the hollow ceramic fiber tube bundles. Limiting ribs are extruded on the outer wall of the buffer pad layer. The product is assembled and sealed using multiple arc-shaped galvanized steel sheets with snap-fit ​​ends. The inner side of the arc-shaped galvanized steel sheet has a slot that matches the limiting rib. Flame-retardant sealing strips are embedded in the splicing gaps of the arc-shaped galvanized steel sheet. The slot is engaged with the limiting rib to obtain metal armor; A composite outer sheath, consisting of a polyolefin matrix layer arranged from the inside out and a ceramic-coated protective sleeve, is formed on the outside of the metal armor to obtain the halogen-free, low-smoke, flame-retardant control cable that produces no burning droplets. The method of segmented temperature control involves sequentially extruding an insulating layer and a flame-retardant outer layer onto the conductor. This includes: controlling the temperature of the insulation extruder body in four stages, namely 120°C, 135°C, 150°C, and 160°C, controlling the temperature of the die head at 155±5°C, and continuously extruding the flame-retardant outer layer online after the insulation layer is extruded. The foaming and setting temperature of the flame-retardant outer layer is controlled at 85±5°C.

6. The method according to claim 5, characterized in that, The process involves twisting multiple control line units in reverse, with inner and outer layers, and placing radially protruding ceramic flame-retardant separators between the inner and outer layers. Dot-shaped skeleton fillers are then filled into the gaps between the multiple control line units to obtain a shaped cable, comprising: The inner layer control wire units are twisted clockwise, and the outer layer control wire units are twisted counterclockwise. If the conductor is a rigid conductor, the cabling pitch of the rigid conductor is controlled to be ____ times the outer diameter of the cable; if the conductor is a flexible conductor, the cabling pitch of the flexible conductor is controlled to be ____ times the outer diameter of the cable. During the cabling process, ceramic flame-retardant separators are pasted at equal intervals between layers. Multiple control line units are interspersed with expanded graphite-coated fiberglass bundles at fixed points to form a dotted skeleton filler, without overall full-section filling.

7. The method according to claim 5, characterized in that, The inner layer of glass fiber ceramic tape has an overlap rate of 16%, and the outer layer of glass fiber ceramic tape is reverse-wound with an overlap rate of 20%. The flame-retardant microcapsules are phosphorus-nitrogen-based expandable flame-retardant microcapsules.

8. The method according to any one of claims 5, 6 or 7, characterized in that, The buffer pad layer is integrally extruded using a special-shaped co-extrusion die, with an extrusion temperature of 130°C to 142°C. Hollow ceramic fiber tube bundles are arranged in the buffer pad layer, and limiting ribs are extruded on the outer wall of the buffer pad layer, including: While the buffer pad is being extruded, a hollow ceramic fiber tube bundle is fed into the buffer pad at a uniform speed through a feeding fixture, and an annular limiting rib is extruded integrally on the outer wall of the buffer pad simultaneously.

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