A method for preparing a b1 class cable of an optimal economic structure

Abstract

The application discloses a preparation method of B1-grade cable with optimal economic structure, and comprises the following steps: S1, preparing silane cross-linked polyolefin insulation material; S2, preparing fire-resistant B1-grade cable insulation core by adopting an extrusion die method with automatically adjusted extrusion coating pressure; S3, cabling and filling; S4, manufacturing an outer sheath (5) to complete the preparation of the B1-grade cable; the silane cross-linked polyolefin insulation material comprises the following materials in parts by weight: base resin, 40-45 parts; flame retardant, 45-50 parts; functional additive, 4-10 parts; cross-linking agent, 1-5 parts. The B1-grade cable has the same structure form and outer diameter as common cables, the cost of the cable and construction is greatly reduced, and the B1-grade cable is manufactured by realizing optimal economic structure design.

Description

Technical Field

[0001] This invention relates to the field of cable manufacturing technology, and in particular to a method for manufacturing a B1 grade cable with an optimal economic structure. Background Technology

[0002] GB31247-2014, "Classification of Flame Retardant Performance of Cables and Optical Fibers," is a mandatory standard in my country that is a transformation of the EU standard EN13501-6:2014 and aligns with advanced international standards. Compared with the previous Chinese standard GB / T19666-2005, "General Rules for Flame Retardant and Fire-Resistant Wires, Cables, and Optical Fibers," GB31247 not only specifies the halogen-free (W), low-smoke (D), low-toxicity (U), and flame-retardant performance indicators for flame-retardant cables, but also specifies heat release (heat release during cable combustion), smoke emission (smoke emission during cable combustion), combustion growth rate index (the rate of increase in combustion intensity, i.e., the ease of fire control), and combustion drip / particulate level (the degree of dripping of combustible material from the cable). Furthermore, it scientifically classifies flame-retardant cables according to their combustion performance (B1, B2, and B3 levels) to allow for the selection of flame-retardant cables for different applications and requirements in building construction. Among them, Class B1 cables (control cables or power cables) are the plastic insulated cables with the highest existing fire performance requirements.

[0003] B1-grade cables (control cables or power cables) must meet both the general performance requirements of their respective product standards (GB / T9330 for control cables and GB / T12706 for power cables) and the B1-grade flammability requirements of GB31247 standard. However, in my country, both control cables and power cables use flammable cross-linked polyethylene (XLPE) extruded insulation to ensure that the mechanical properties and insulation resistance of the cable insulation meet the product standard requirements (tensile strength not less than 12.5 N / mm², elongation not less than 200%, and insulation resistance constant Ki not less than 3.67 MΩ•km). However, for B1-grade cables, if flammable XLPE insulation is used, without a sufficiently reliable fireproof and heat-insulating protective layer (i.e., a firewall) between the cable core and outer sheath, the XLPE will absorb heat, melt, crack, and release flammable gases and heat during cable combustion, thus igniting a chain reaction in other insulation layers. This results in the thermal propagation of the flame, causing the B1-grade cable to fail the flammability test.

[0004] Therefore, almost all existing B1-grade control cables and small-section B1-grade power cables in my country use cross-linked polyethylene insulation with 1-2 layers of fire-resistant fiber tape wrapped around it, and a layer of flame-retardant polyolefin oxygen barrier or fireproof mud extruded as a firewall to protect the insulation from flame propagation. At the same time, the cable sheath uses expensive B1-grade special sheath material. As a result, the material usage of existing B1-grade control cables and small-section B1-grade power cables has increased dramatically, the manufacturing process has increased, and the cable outer diameter is 30% or more larger than that of ordinary cables. This not only increases the cost of cables and labor, but also occupies building space, increases construction difficulty, and increases project cost. Summary of the Invention

[0005] The purpose of this invention is to provide an optimal and economical method for manufacturing B1-grade cables, in order to address the technical problems of reducing the manufacturing cost of B1-grade cables and improving their intelligence.

[0006] The objective of this invention is achieved by the following technical solution: a method for manufacturing a B1 grade cable with an optimal economic structure, wherein the B1 grade cable includes multiple conductors, each conductor is provided with a mica wrapping layer, an insulation layer is provided outside the mica wrapping layer, a wrapping layer is provided outside the insulation layer, a filler layer is provided between the insulation layer and the wrapping layer, an outer sheath is provided outside the wrapping layer, and the insulation layer is made of silane cross-linked polyolefin insulation material; The method for manufacturing the B1 grade cable includes the following steps: S1: Preparation of silane crosslinked polyolefin insulating material; S2: Fire-resistant B1 grade cable insulation cores are prepared by using an extrusion die matching method with automatically adjusted extrusion coating pressure; S3: Cable formation and filling; S4: Fabricate the outer sheath to complete the preparation of the B1 grade cable; The extrusion die matching method automatically adjusts the distance between the inner ends of the extrusion die to change the amount of covering pressure on the extruded insulation layer (2), thereby controlling the tightness of the covering between the insulation layer (2) and the mica wrapping layer (7). The silane crosslinked polyolefin insulation material comprises the following materials in parts by weight: matrix resin: 40-45 parts; flame retardant: 45-50 parts; functional additives: 4-10 parts; crosslinking agent: 1-5 parts.

[0007] Furthermore, the matrix resin comprises: POE: 28-30 parts; EPR: 12-15 parts; The flame retardant comprises: inorganic flame retardant: 38-40 parts; organic flame retardant: 7-10 parts; The functional additives include: compatibilizer: 1.5-3 parts; hydrophobic agent: 0.5-2 parts; lubricant: 0.5-1 part; shell-forming agent: 1-3 parts; antioxidant: 0.5-1 part; The crosslinking agent includes: peroxide initiator: 0.2~1 part; silane crosslinking agent: 0.7~3 parts; catalyst: 0.1~1 part.

[0008] Preferably, the matrix resin comprises: 30 parts POE; 15 parts EPR; The flame retardant comprises: 40 parts of inorganic flame retardant; and 10 parts of organic flame retardant. The functional additives include: compatibilizer: 1.5 parts; hydrophobic agent: 0.5 parts; lubricant: 0.5 parts; shell-forming agent: 1 part; antioxidant: 0.5 parts; The crosslinking agent comprises: peroxide initiator: 0.2 parts; silane crosslinking agent: 0.7 parts; catalyst: 0.1 parts.

[0009] Furthermore, the preparation method of the silane crosslinked polyolefin insulation material includes the following sub-steps: Prepare material A; material A is a grafting matrix, which includes POE, EPR, compatibilizer, antioxidant, peroxide initiator and silane crosslinking agent; Prepare component B; component B is a flame-retardant functional masterbatch, which includes inorganic flame retardants, organic flame retardants, shell-forming agents, hydrophobic agents, lubricants, and antioxidants; For the finished product mixing, firstly, the grafted base material, flame-retardant functional masterbatch, and catalyst are added to a low-speed mixer and mixed at room temperature for 5-10 minutes to ensure uniform dispersion of each component; then, the lumps are removed, and the product is vacuum-sealed and packaged to obtain the final silane cross-linked polyolefin insulation material.

[0010] Furthermore, the preparation method of the grafted base material is as follows: First, POE, EPR, compatibilizer and antioxidant are added to a high-speed mixer and mixed for 1-2 minutes. Then, peroxide initiator and silane crosslinking agent are added, and mixing continues for 3-5 minutes to allow the liquid to be fully absorbed until the resin surface is dry. Finally, the material is added to a parallel co-rotating twin-screw extruder for melt grafting reaction. The material completes the grafting reaction in the extruder, is extruded and granulated to obtain the grafted base material. The preparation method of the flame-retardant functional masterbatch is as follows: First, the flame-retardant functional masterbatch is added to a high-speed mixer and mixed at high speed for 5-10 minutes at a temperature of 60-80℃; then, the mixed hot material is added to a mixer or a twin-screw extruder for plasticizing and granulation, with the temperature controlled at 130℃-150℃, and extruded and granulated to obtain the flame-retardant functional masterbatch.

[0011] Furthermore, the filling layer is filled with basalt fiber rope; the wrapping layer is wrapped with inorganic mineral composite tape; and the outer sheath is a general-purpose thermoplastic flame-retardant polyolefin outer sheath.

[0012] Furthermore, the extrusion die-fitting method is implemented using an extrusion die with automatically adjustable pressure for insulation-coated cores. This extrusion die automatically adjusts the distance between the inner ends of the extrusion die to change the coating pressure on the extruded insulation layer, thereby controlling the tightness of the coating between the insulation layer and the mica wrapping layer, and completing the preparation of the fire-resistant B1 grade cable insulation core.

[0013] Furthermore, the automatic pressure adjustment extrusion die for the insulated sheathed wire core includes: a die head body, an extrusion die cover at the front end of the die head body, an extrusion die core inside the extrusion die cover, the extrusion die core being connected to an adjustment rod, and the adjustment rod being connected to a servo motor via a transmission mechanism.

[0014] Furthermore, the extrusion die cover is also equipped with a die cover locker and a pressure sensor; the die adjusting rod is also equipped with a flow divider cone, and the flow divider cone is equipped with a flow divider cone set nut.

[0015] Furthermore, the following steps are included before the outer sheath is manufactured: The optical fiber is embedded in a flame-retardant layer using a spiral embedding method. The flame-retardant layer is disposed between the wrapping layer and the outer sheath. The optical fiber is used to connect to the terminal to accurately locate the fault point.

[0016] Furthermore, embedding the optical fiber into the flame-retardant layer specifically includes the following steps: The cable core that has been completed and cabled is heated to 40-60℃ using a preheating device; The rotating head begins to revolve around the cable core at a set speed. The rotational speed is precisely matched according to the required helical pitch and the cable core travel speed. The calculation formula is as follows: Rotational speed = Production line speed / Helix pitch; At the moment the optical fiber contacts the cable core, the surface of the cable core is locally heated or coated with a layer of EVA hot melt adhesive using a micro hot air gun or a micro adhesive applicator, so that the optical fiber is slightly adhered to the cable core and prevented from shifting before entering the extruder die. The fiber optic cable core is immediately fed into the extruder head and covered with an outer sheath.

[0017] Furthermore, a stress anomaly early warning method based on polarized light time-domain reflectometry (POTDR) is adopted to achieve full-process monitoring of fiber embedding.

[0018] The beneficial effects of this invention are as follows: This invention utilizes silane cross-linked polyolefin insulation that meets standard requirements for mechanical and dielectric properties and has excellent combustion performance (including flame retardancy). This greatly simplifies the cable structure, making the structure and outer diameter of B1-grade cables consistent with ordinary cables. Cable and construction costs are significantly reduced, achieving the goal of designing and manufacturing B1-grade cables with the best economic structure.

[0019] The extrusion die-fitting method used in this invention solves the problem of adhesion between the silane cross-linked polyolefin insulation and the mica tape wrapped conductive core of fire-resistant B1 grade cables caused by existing extrusion processes, which leads to problems with the mechanical properties of the fire-resistant B1 grade cable insulation. As a result, the measured values ​​of tensile strength, elongation and insulation resistance of the fire-resistant B1 grade cable insulation are consistent with the qualified data.

[0020] This invention adds optical fibers during the manufacturing process of B1-grade cables, enabling real-time monitoring of the cable's usage and significantly improving its safety and intelligence. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of a Class B1 cable structure. Figure 2 A schematic diagram of a Class B1 cable structure with added optical fiber; Figure 3 This is a schematic diagram of the insulation core structure of a fire-resistant B1 grade cable. Figure 4 Schematic diagram of an extrusion die structure for automatically adjusting pressure of insulated wire cores; Figure 5 This is a schematic diagram of the automatic control principle for adjusting the inner distance. Figure 6 It is an extrusion die; Figure 7 It is an extrusion die; Figure 8 It is a semi-extrusion die; In the figure, 1-conductor, 2-insulation layer, 3-filler layer, 4-wrapping layer, 5-outer sheath, 6-optical fiber, 7-mica wrapping layer, 8-transmission mechanism, 9-servo motor, 10-diverter cone set nut, 11-diverter cone, 12-die adjusting rod, 13-die head body, 14-extrusion die core, 15-die cover locker, 16-pressure sensor, 17-extrusion die cover. Detailed Implementation

[0023] 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 described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0024] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0025] See Figures 1 to 8 A method for manufacturing a Class B1 cable with an optimal economic structure is disclosed. The Class B1 cable includes multiple conductors 1, each conductor 1 having an insulation layer 2, an outer wrapping layer 4, a filler layer 3 between the insulation layer 2 and the outer wrapping layer 4, an outer sheath 5 outside the outer wrapping layer 4, and a mica wrapping layer 7 between the conductors 1 and the insulation layer 2. The insulation layer 2 is made of silane cross-linked polyolefin insulation material; the filler layer 3 is filled with basalt fiber rope; the outer wrapping layer 4 is an inorganic mineral composite tape wrapping layer; and the outer sheath 5 is a general-purpose thermoplastic flame-retardant polyolefin outer sheath.

[0026] In this embodiment, the method for manufacturing a Class B1 cable includes the following steps: S1: Preparation of silane crosslinked polyolefin insulating material; S2: Fire-resistant B1 grade cable insulation cores are prepared by using an extrusion die matching method with automatically adjusted extrusion coating pressure; S3: Cable formation and filling; S4: Fabricate the outer sheath 5 to complete the preparation of the B1 grade cable.

[0027] To address the chain reaction problem caused by the flammable cross-linked polyethylene (XLPE) insulation in B1-grade cables, this invention considers replacing flammable XLPE insulation with flame-retardant XLPE insulation. However, existing flame-retardant XLPE insulation materials contain over 60% flame retardant in their formulations, resulting in a significant decrease in tensile strength, elongation, and insulation resistance, failing to meet product standards. Therefore, this invention develops a silane-crosslinked XLPE insulation material that meets technical requirements for combustion performance, tensile strength, elongation, and insulation resistance, all of which meet product standards. This material is used as the insulation for B1-grade cables, eliminating the need for an additional cable core "firewall." The outer sheath uses only conventional flame-retardant XLPE, and the cable structure and outer diameter are identical to ordinary cables, saving significant amounts of flame-retardant or fire-resistant materials and reducing production steps. Compared to similar B1-grade cables, this not only reduces material costs by 30% or more but also significantly lowers the overall cost of engineering cables.

[0028] To reduce the impact of flame retardants on the tensile strength, elongation, and hydrophobicity of cross-linked polyolefin insulation, this invention specifically selected and modified the amount and type of flame retardant in the silane cross-linked olefin, the characteristics and type of the base resin, and the characteristics and amount of the compatibilizer, ultimately determining the formulation combination of the silane cross-linked polyolefin. Specifically, the silane cross-linked polyolefin insulation material comprises the following materials in parts by weight: base resin: 40-45 parts; flame retardant: 45-50 parts; functional additives: 4-10 parts; cross-linking agent: 1-5 parts. Specifically, the matrix resin includes: POE: 28-30 parts; EPR: 12-15 parts; the flame retardant includes: inorganic flame retardant: 38-40 parts; organic flame retardant: 7-10 parts; the functional additives include: compatibilizer: 1.5-3 parts; hydrophobic agent: 0.5-2 parts; lubricant: 0.5-1 part; shell-forming agent: 1-3 parts; antioxidant: 0.5-1 part; the crosslinking agent includes: peroxide initiator: 0.2-1 part; silane crosslinking agent: 0.7-3 parts; catalyst: 0.1-1 part.

[0029] Preferably, the matrix resin comprises: 30 parts POE; 15 parts EPR; the flame retardant comprises: 40 parts inorganic flame retardant; 10 parts organic flame retardant; the functional additives comprise: 1.5 parts compatibilizer; 0.5 parts hydrophobic agent; 0.5 parts lubricant; 1 part shell-forming agent; 0.5 parts antioxidant; and the crosslinking agent comprises: 0.2 parts peroxide initiator; 0.7 parts silane crosslinking agent; and 0.1 parts catalyst.

[0030] POE's main components are ethylene-octene and butene-butene, while EPR's main component is ethylene-propylene. Both materials improve tensile strength and elongation. POE exhibits excellent toughness and elongation, while EPR facilitates the compatibility of materials with different polarities, thus enhancing tensile strength and elongation. The inorganic flame retardant mainly consists of magnesium hydroxide, aluminum hydroxide, and a water-based inorganic flame retardant with low hygroscopicity and good hydrophobicity. The organic flame retardant mainly consists of nitrogen series compounds, red phosphorus compounds, and organosilicon compounds. The surface of the inorganic flame retardant powder was treated to improve the tensile strength, elongation, and hydrophobicity (hygroscopic resistance) of polyolefins while ensuring halogen-free, low-smoke, and flame-retardant combustion performance. The addition of organic flame retardants serves two purposes: firstly, to reduce the amount of inorganic flame retardants used and minimize their negative effects; and secondly, to improve the combustion performance of polyolefins, as well as tensile strength, elongation, and insulation resistance.

[0031] The compatibilizer mainly consists of four polymer compatibilizers grafted with maleic anhydride, including POE-MAH (maleic anhydride polyolefin elastomer) and EVA-MAH (maleic anhydride ethylene-vinyl acetate copolymer). Both POE-MAH and EVA-MAH are excellent compatibilizers, possessing very good flexibility and superior compatibilizing properties. They facilitate the uniform mixing of materials with different polarities (such as plasticizers and flame retardants), enhancing bonding strength and thus improving the tensile strength, elongation, and insulation resistance of polyolefins. The hydrophobic agent mainly consists of special silane coupling agents, titanates, etc., and its purpose is to improve the water resistance of polyolefins, reduce hygroscopicity, and enhance insulation resistance.

[0032] In this embodiment, the preparation method of the silane crosslinked polyolefin insulation material includes the following sub-steps: Preparation of material A; material A is a grafting matrix; Prepare material B; material B is a flame-retardant functional masterbatch. Mix the finished products.

[0033] Specifically, the preparation method of the grafted base material includes: Ingredients: Weigh POE, EPR, compatibilizer, antioxidant, peroxide initiator, and silane crosslinking agent according to weight parts. Mixing: Add the resin (except for peroxide and silane) to a high-speed mixer and mix for 1-2 minutes. Then add the peroxide and silane crosslinking agent and continue mixing for 3-5 minutes until the liquid is fully absorbed and the resin surface is dry. Control points: The temperature should not exceed 40℃ to prevent premature reaction. Grafting reaction and granulation: Add the mixed material to a parallel co-rotating twin-screw extruder for melt grafting reaction. The temperature of each zone of the screw is controlled at 140℃-180℃ (feeding section 140-150℃, reaction section 160-170℃, die head 170-180℃), and the screw speed is 200-400 rpm. The material completes the grafting reaction in the extruder, is extruded and granulated to obtain the grafted base material (material A), and then sealed and packaged.

[0034] The preparation method of flame-retardant functional masterbatch includes: Ingredients: Weigh out inorganic flame retardant, organic flame retardant, shell-forming agent, hydrophobic agent, lubricant, and remaining antioxidant according to weight parts. Mixing: Add all the above powdered and granular additives to a high-speed mixer and mix at 60-80℃ for 5-10 minutes to fully activate and homogenize the powders. Granulation: Add the mixed hot material to a mixer or twin-screw extruder for plasticizing and granulation. Temperature control must be below the crosslinking initiation temperature, and the temperature of each zone must be strictly controlled between 130℃ and 150℃. Extrusion granulation yields the flame-retardant functional masterbatch (B material).

[0035] The preparation method of the finished product mixture includes: 1. Finished product mixing: The prepared material A (grafted base material), the prepared material B (flame retardant functional masterbatch), and the catalyst are added to a low-speed mixer in proportion and mixed at room temperature for 5-10 minutes to ensure uniform dispersion of each component. 2. Sieving and packaging: The uniformly mixed material is sieved (40-60 mesh) to remove lumps, and then vacuum-sealed and packaged to obtain the final silane cross-linked polyolefin insulation material.

[0036] This invention utilizes a compound of inorganic / organic flame retardants (40+10 parts) with the addition of a specific "shell-forming agent" to enable the material to rapidly form a dense char layer during combustion, preventing dripping and meeting the heat release and smoke toxicity requirements of GB 31247 for Class B1 cables. A two-step process separates the "grafting reaction" from the "flame retardant filling," avoiding interference from a large amount of flame retardant on the silane grafting reaction. Simultaneously, the elastomer properties of POE and EPR are utilized to compensate for the reduced flexibility caused by high-filling flame retardants. Adding the catalyst separately afterwards avoids catalyst failure or pre-crosslinking during high-temperature granulation, ensuring uniform and stable crosslinking degree and good surface finish in the final product during warm water crosslinking. The addition of hydrophobic and lubricating agents improves the flowability of the high-filling system during extrusion, resulting in a smooth and flat surface of the final cable insulation layer.

[0037] The following series of experiments further illustrates the performance of silane crosslinked polyolefin insulation materials: The insulating materials in Examples 1-3 and Comparative Examples 1-2 were all prepared by the above-described method. The weight percentages of each component in Examples 1-3 and Comparative Examples 1-2, as well as the resulting insulating materials, are shown in Table 1.

[0038] Table 1: Components of Examples and Comparative Examples (Unit: Parts by Weight)

[0039] The performance test results are shown in Table 2. Table 2: Comparison of Performance Test Results and B1 Level Compliance

[0040] Experimental results show that Examples 1-3 all meet the GB 31247 B1 grade requirements and exhibit stable performance. Comparative Example 1, due to insufficient peroxide, suffers from inadequate cross-linking, resulting in decreased mechanical and combustion properties. Comparative Example 2, lacking a shell-forming agent, fails to form a char layer, leading to severe dripping during combustion and failing to meet B1 grade requirements. The silane cross-linked polyolefin insulation material used in this invention not only solves the problem of unqualified mechanical properties due to adhesion of the fire-resistant core insulation, but also, through the use of fire-resistant materials as filler and a basalt wrapping fire-retardant layer with a temperature and fire resistance of 1000°C and above, forms a heat-insulating and flame-retardant cable structure. This results in the cable core having only two wrapping layers and no extruded oxygen barrier layer, allowing the outer sheath to be made of ordinary thermoplastic flame-retardant polyolefin, and the cable outer diameter being 20%-30% smaller than current B1 grade cables.

[0041] Furthermore, for the silane crosslinked polyolefin insulation material of the above formulation combination, three existing extrusion methods (extrusion, tube extrusion, and semi-tube extrusion) are respectively used. Figures 6 to 8 As shown in the figure, the bare copper conductor insulation cores of B1 grade cables were extruded separately. The results were as follows: the elongation of silane cross-linked polyolefin insulation of B1 grade cables (bare copper conductor) extruded by extrusion and semi-extrusion die-fitting methods was mostly unqualified. The reason is that the extrusion method makes the plastic stretch ratio and tensile stress large, which leads to increased tensile strength and decreased elongation, resulting in unqualified performance. However, the silane cross-linked polyethylene insulation of B1 grade cables (bare copper conductor) extruded by extrusion die-fitting method has low insulation tensile stress, and its tensile strength and elongation are excellent, meeting the product standard requirements. Moreover, the insulation resistance of silane cross-linked polyolefin also meets the product standard requirements (see Table 3).

[0042] Table 3 Insulating mechanical and dielectric properties of silane-crosslinked polyolefins

[0043] However, when using extrusion molding to wrap fire-resistant B1 grade cables, the conductor of the fire-resistant B1 grade cable is not a bare copper conductor, but a core with fire-resistant mica tape wrapped around it (see...). Figure 3When using silane cross-linked polyolefin extruded fire-resistant B1 grade cable with mica tape wrapped around the conductive core, the silane cross-linked polyolefin adheres tightly to the mica tape-wrapped conductive core and is difficult to peel off. There are two main reasons for this: First, the silane cross-linked polyolefin contains highly polar aluminum hydroxide and magnesium oxide, which significantly increase the polarity of the material surface. Mica, a silicate mineral, is also polar. In addition, the mica tape itself contains a large amount of adhesive. Therefore, under high temperature and pressure extrusion, the insulation layer adheres tightly to the mica tape, strengthening the molecular forces (i.e., van der Waals forces) between the plastic and the mica tape, resulting in adhesion much stronger than non-polar materials (such as PE). Thus, when tensile tests are conducted on insulation samples, the inner surface of the insulation tears due to adhesion when separating from the mica tape, leading to unsatisfactory tensile strength and elongation test results. This phenomenon also exists for other existing cross-linked polyolefin extruded fire-resistant cable conductors.

[0044] To address the adhesion problem between silane cross-linked polyolefin and the mica tape core wrapped in fire-resistant B1 grade cables, this invention employs an extrusion die-fitting method that automatically adjusts the extrusion pressure of the silane cross-linked polyolefin insulation layer. This method controls the tightness between the insulation layer and the core, facilitating non-destructive peeling of the insulation layer. Consequently, the tensile strength and elongation test results of the silane cross-linked polyolefin insulation are accurate and valid, meeting standard requirements.

[0045] See Figure 4 This invention provides an automatically adjustable pressure extrusion die for insulating cores. This die automatically adjusts the distance between the inner ends of the extrusion die to change the pressure exerted on the extruded insulation layer 2, thereby controlling the tightness of the insulation layer 2 and the mica wrapping layer 7, and completing the preparation of the fire-resistant B1 grade cable insulation core; the fire-resistant B1 grade cable insulation core is formed from the inside out. Further, the automatically adjustable pressure extrusion die for insulating cores includes: a die head body 13, with an extrusion die cover 17 at the front end of the die head body 13, an extrusion die core 14 inside the extrusion die cover 17, the extrusion die core 14 being connected to an adjusting rod 12, the adjusting rod 12 being connected to a servo motor 9 via a transmission mechanism 8, and the extrusion die cover 17 also having a die cover lock 15 and a pressure sensor 16; the adjusting rod 12 also has a flow divider cone 11, and the flow divider cone 11 has a flow divider cone set nut 10.

[0046] It should be noted that the extrusion die-fitting process for automatically adjusting the pressure of the silane cross-linked polyolefin insulated core is as follows: the die nozzle of the extrusion die is a horizontal receiving tube. Its main function is to reduce the extrusion pressure of the molten plastic in the die cavity along the oblique direction through the die nozzle in the horizontal direction, thereby reducing the pressure of the plastic-coated core. Since the entire die nozzle does not extend into the die cap hole, like in extrusion die-fitting, it maintains the characteristics of pressure extrusion (rather than stretch extrusion as in tube extrusion or semi-tube extrusion), ensuring that the tensile strength and elongation of the silane cross-linked polyolefin insulation meet the requirements.

[0047] The relationship between the extrusion coating pressure and the inner end distance of silane cross-linked polyolefin insulated wire cores is as follows: the larger the inner end distance *e* of the extrusion die, the wider the flow channel of the molten plastic between the inner end distances *e*, the lower the pressure on the wire core, and the looser the insulation coating of the mica tape-wrapped wire core; the smaller the inner end distance, the narrower the flow channel of the molten plastic between the inner end distances, the higher the pressure on the wire core, and the tighter the insulation coating of the mica tape-wrapped wire core. In practice, the inner end distance is usually set between 1.5 and 4.5 mm. Within this range, the silane cross-linked polyolefin extrusion pressure (which corresponds to the wire core coating pressure) is most suitable. It avoids the situation where the inner end distance is too small (less than 1.5 mm), resulting in excessively tight insulation coating of the wire core, and also avoids the situation where the inner end distance is too large (greater than 4.5 mm), resulting in an excessively large gap between the insulation layer and the wire core, which does not meet the process requirements.

[0048] For this purpose, the present invention also includes an automatic distance adjustment control system for the inner end, the automatic control working principle of which is as follows (e.g. Figure 5 As shown, the pressure data within the inner end distance control range (1.5~4.5mm) is pre-input into the pressure controller (installed in the extruder control hub). When the inner end distance is less than 1.5mm, the pressure sensor transmits the pressure data (exceeding the set lower limit) to the controller, which then transmits the command to the servo motor control system. At this time, the servo motor drives the die adjusting rod of the extrusion die to rotate counterclockwise, increasing the inner end distance of the die. When the inner end distance is greater than 4.5mm, the pressure sensor transmits the pressure data (exceeding the set upper limit) to the controller, which then transmits the command to the... In the servo motor control system, the servo motor drives the mold core adjusting rod to rotate clockwise, reducing the distance between the inner ends of the mold core. When the distance between the inner ends is within the range of 1.5 to 4.5 mm, the controller will not send a command to start the servo motor to the servo motor control system. At this time, the pressure of the silane cross-linked polyolefin extruded wire core and the tightness of the wrapped wire core meet the process requirements. Under these conditions, the silane cross-linked polyolefin insulation layer and the mica tape wrapped wire core are easy to peel off, and the inner surface of the insulation will not be damaged due to adhesion, thus affecting the actual test values ​​of the mechanical properties (tensile strength and elongation) of the insulation.

[0049] This invention solves the problem that existing extrusion processes cause adhesion between the silane cross-linked polyolefin insulation and the mica tape-wrapped conductive core of fire-resistant B1 grade cables, leading to problems with the mechanical properties of the insulation. As a result, the measured values ​​of tensile strength, elongation, and insulation resistance of the fire-resistant B1 grade cable insulation are consistent with the qualified data.

[0050] This invention, by developing and employing silane cross-linked polyolefin insulation material extruded over B1-grade cable insulation, not only solves the defects of poor mechanical properties and insulation resistance of cross-linked polyolefins, but also matches the flammability (including flame retardancy) of the cable insulation with the technical requirements of B1-grade cables. This reduces the need for extruded firewalls (flame-retardant polyolefin or fire-retardant mud inner sheath) in the core of existing B1-grade control cables and small-section power cables, lowers the cost of the outer sheath, and greatly simplifies the structure and manufacturing process of B1-grade cables. Under these conditions, the material structure selection for the core and outer sheath of the B1-grade cable of this application is as follows: Core filling: In this application, the gaps in the cable core of the B1 grade cable are filled and compacted with basalt fiber under high pressure during the cable core cabling process. The purpose of this is that basalt fiber can withstand temperatures of over 1000℃, which is compatible with the B1 grade combustion test temperature (while the commonly used fiberglass rope begins to soften at 350℃~400℃). It has good heat insulation, flame retardant and fire resistance for the cable core, and blocks the ventilation and oxygen supply effect of the gaps in the cable core, which is beneficial to improving the combustion performance of the B1 grade cable.

[0051] The inner lining of the cable core is wrapped with an inorganic mineral composite tape (2 layers, each layer 0.19 mm thick) coated with metal hydrate. This wrapping serves to tighten the stranded cable core and improve its flame retardant properties.

[0052] Outer sheath: The outer sheath is made of thermoplastic polyolefin extrusion. This sheath is made of conventional flame-retardant polyolefin sheath material, which is 30% or more cheaper than the existing B1 grade special sheath material. Because this sheath material has good shelling and charring properties when burning, it does not produce burning drips and protects the cable core (without spreading the flame), thus exhibiting excellent combustion performance.

[0053] The technical means employed in this invention (including the preparation of silane cross-linked polyolefin insulation material and the insulation core of fire-resistant B1 grade cable, etc.) are all aimed at achieving the optimal cost under the premise of simultaneously meeting the general technical requirements for cables (mechanical and electrical properties, etc. as specified in GB / T 12706 and GB / T 9330 standards) and the combustion performance requirements of B1 grade cables (GB 31247). As can be seen from the experiments, the B1 grade cable of this application, due to the use of silane cross-linked polyolefin insulation that meets the standard requirements for mechanical and dielectric properties and has excellent combustion performance (including flame retardancy), greatly simplifies the cable structure, making the structural form and outer diameter of the B1 grade cable consistent with ordinary cables, and greatly reducing the cable and construction costs, thus achieving the goal of designing and manufacturing B1 grade cables with the best economic structure.

[0054] Table 4 compares the material cost and cable outer diameter of the B1 grade cable of the present invention with those of existing B1 grade cables; Table 5 compares the measured values ​​and standard values ​​of the combustion performance of the B1 grade cable of the present invention.

[0055] Table 4 25mm 2 Comparison of material costs and cable outer diameter between Class B1 cables with conductor oxygen barrier structures and Class B1 cables of the present invention.

[0056] Table 5. Test data on the combustion performance of Class B1 cables of this invention.

[0057] In some embodiments, to enhance the intelligence of Class B1 cables, the following steps are included before fabricating the outer sheath 5: The optical fiber 6 is embedded in the flame-retardant layer using a spiral embedding method. The flame-retardant layer is disposed between the wrapping layer 4 and the outer sheath 5. The optical fiber 6 is used to connect to the terminal to monitor the operating temperature of each section of the B1 grade cable of this application in real time. Once the load is too large or a short circuit occurs, the fault location can be monitored and alarmed immediately to accurately locate the fault point.

[0058] In this embodiment, embedding the optical fiber 6 into the flame-retardant layer specifically includes the following steps: Step 1: Cable core preparation and preheating The cable core, which has already been cabled (the cable core consists of insulated wire cores, filler ropes, and cable ties), is heated to 40-60℃ using a preheating device. The purpose of preheating is to improve the surface activity of the cable core, which facilitates subsequent material bonding, and at the same time reduces thermal shock during optical fiber embedding.

[0059] Step 2: Spiral Guiding and Pre-embedding of Optical Fibers Start the rotating device: The rotating head begins to revolve around the cable core at a set speed. The rotation speed is precisely matched to the required helical pitch (e.g., 200-500mm) and the cable core travel speed (production line speed). Calculation formula: Rotation speed (rpm) = Production line speed (m / min) / Helical pitch (m) Precision Laying Out: The optical fiber is led out from the laying out unit and maintained at a constant low tension (typically 2-5N) by a tension controller. Helical Forming: The optical fiber is guided to the cable core surface by guide wheels on a rotating disk. Due to the combined motion of the rotating disk and the linear motion of the cable core, the optical fiber is precisely laid on the cable core surface at a preset helical angle and pitch. At the instant the optical fiber contacts the cable core, a micro-heat gun (80-100℃) or a micro-application device mounted on the rotating disk is used to locally heat the cable core surface or apply a very thin layer of EVA hot melt adhesive. This step allows the optical fiber to slightly adhere to the cable core, preventing it from shifting before entering the extruder die.

[0060] Step 3: Simultaneous extrusion coating (shaping) The cable core with the laid optical fiber immediately enters the extruder head. Core design: A pressure-type core is used to ensure that the molten flame-retardant filler material (temperature approximately 120-150℃) wraps around the cable core and the spirally wound optical fiber with uniform pressure. Fusion mechanism: The high-temperature melt completely encapsulates the optical fiber and fuses it with the surface of the underlying cable core. Due to the extremely small diameter of the optical fiber (typically 0.9mm) and the good fluidity of the material, the melt can fully fill the tiny gaps around the optical fiber, forming a bubble-free, tightly bonded "optical fiber-flame-retardant layer" composite. Water tank cooling: After extrusion, the fiber is cooled and shaped using segmented water tanks, ensuring it is firmly locked inside the flame-retardant layer.

[0061] Furthermore, when embedding fiber 6, a stress anomaly early warning method based on polarized light time-domain reflectometry (POTDR) can be used to monitor the loss changes of the fiber in real time throughout the embedding process. If a sudden increase in loss or fiber breakage is detected, an alarm will be triggered and the system will immediately shut down.

[0062] Specifically, the implementation process of the stress anomaly early warning method based on polarized light time-domain reflectometry (POTDR) includes: Step 1, System Initialization Before starting the fiber embedding process on the production line, a system initialization operation is performed first. The operator starts the POTDR monitoring system through the human-machine interface. The system automatically performs a self-test, checking whether the laser output power, detector bias voltage, and data acquisition card communication status are normal. After the self-test passes, the system enters the baseline calibration stage.

[0063] The purpose of baseline calibration is to obtain the polarization characteristic distribution of a reference fiber under stress-free conditions, serving as a benchmark for subsequent anomaly detection. The specific operation involves connecting a sensing fiber (from the same batch as the fiber used in the production line) at least 100 meters in length to the POTDR system before the fiber embedding process begins. The system injects optical pulses into the fiber with a set pulse width (typically 50 to 100 nanoseconds) and repetition frequency (typically 1 kHz). The polarization state generator sequentially generates three mutually orthogonal polarization states in a time-division multiplexing mode, each lasting for one complete measurement cycle. Backscattered Rayleigh light enters the full polarization state detection device via a circulator. This device decomposes the scattered light into multiple components, including horizontal, vertical, 45-degree linear polarization, and right-hand circular polarization. These components are converted into electrical signals by a photodetector and digitized by a high-speed acquisition card. The processor accumulates and averages the data from multiple pulse acquisitions under each polarization state to eliminate random noise. The number of accumulations is typically set to 256 or 512 to obtain a curve with a sufficient signal-to-noise ratio. After processing, backscattered power curves for each of the three polarization states are obtained. The processor calculates the Stokes parameters at various locations along the fiber based on these three curves, and then calculates the degree of polarization (DOP) distribution curve along the fiber length. Simultaneously, the processor differentiates the DOP curve to obtain the derivative curve of the natural logarithm of DOP with respect to distance, which is the reference attenuation rate curve. This curve is saved in system memory as a benchmark for subsequent real-time monitoring.

[0064] After baseline calibration is completed, the system automatically checks whether the DOP curve is smooth and whether the reference attenuation rate is within the expected range (e.g., attenuation rate not exceeding 0.1 per kilometer). If it exceeds the range, the system prompts the operator to check the fiber optic cable or system status. After calibration is successful, the system enters standby mode, waiting for the production line start signal.

[0065] Step 2: Real-time data acquisition and trigger synchronization After the production line starts, the PLC system sends a production line operation status signal to the POTDR monitoring system. Upon receiving this signal, the monitoring system begins to perform data acquisition tasks cyclically at fixed intervals (usually set to 100 to 200 milliseconds). At the beginning of each acquisition cycle, the FPGA (Field Programmable Gate Array) generates a trigger pulse, simultaneously driving the laser driver to emit a light pulse from the narrow-linewidth pulsed laser. The width of this light pulse determines the spatial resolution: for example, a 50-nanosecond pulse width corresponds to approximately 5 meters of spatial resolution, and a 100-nanosecond pulse width corresponds to approximately 10 meters of spatial resolution. When the fiber embedding speed on the production line is relatively fast, a wider pulse can be selected to ensure the signal-to-noise ratio; when higher positioning accuracy is required, a narrower pulse is selected. After the light pulse is emitted, it passes through a polarization state generator. The polarization state generator integrates an electro-optic modulator and a polarization controller. The FPGA controls the polarization state generator to output three different polarization states sequentially according to a preset timing sequence: the first is horizontal linear polarization, the second is 45-degree linear polarization, and the third is right-hand circular polarization. The duration of each polarization state is equal to the maximum time required for a light pulse to travel one round trip in the optical fiber (corresponding to the total length of the fiber), typically tens of microseconds. The three polarization states are output sequentially to complete one full polarization state measurement cycle, with a total time of approximately 100 microseconds, far less than the 100-millisecond acquisition cycle. Therefore, multiple pulse accumulations can be performed on the same polarization state within one acquisition cycle.

[0066] The optical pulse is injected into the sensing fiber via a circulator. The backscattered Rayleigh light returns along the original path of the fiber and enters the fully polarized state detection device via the circulator. This device contains a polarization beam splitter and multiple waveplates, capable of decomposing the incident light into horizontal, vertical, 45-degree linearly polarized, and right-hand circularly polarized components. These components are received by four independent photodetectors. The detectors are made of indium gallium arsenide, with a bandwidth of 200 MHz and a responsivity of not less than 0.9 amperes / watt. The weak current signal output by the detector is converted into a voltage signal by a transimpedance amplifier, and then digitally sampled by an analog-to-digital converter at a rate of not less than 200 megasamples / second, with a quantization resolution of 12 bits.

[0067] The digital signal after analog-to-digital conversion is fed into the FPGA in real time. The FPGA internally incorporates multiple accumulators, each corresponding to a polarization state component and a specific distance gate. For the same polarization state, the FPGA accumulates and averages the sampled values ​​of multiple consecutive pulses (e.g., 256 pulses) at the same distance gate. The averaged data is then transmitted to the digital signal processor (DSP) via interrupt or direct memory access.

[0068] Step 3: Signal preprocessing and parameter calculation After receiving the raw data from each acquisition cycle, the DSP first performs denoising and baseline correction. Due to potential dark current and temperature drift in the photodetector and amplifier circuits, the DSP first subtracts pre-measured dark background noise, then digitally filters the signal to remove high-frequency noise components. The filtering algorithm uses a finite impulse response low-pass filter with a cutoff frequency set to 20 MHz, suppressing noise while preserving the edge characteristics of loss abrupt changes. The denoised data corresponds to the backscattered power at each distance gate (i.e., each location on the fiber) under three polarization states. The DSP calculates the Stokes parameters for each location based on these power values. The four components of the Stokes parameters represent the total light intensity, the difference in intensity between horizontal and vertical linear polarization, the difference in intensity between 45 degrees and 135 degrees linear polarization, and the difference in intensity between right-handed and left-handed circular polarization. These parameters are calculated entirely based on power measurements under the three polarization states, requiring no external reference.

[0069] After obtaining the Stokes parameters, the DSP calculates the degree of polarization (DOP) at each location. The degree of polarization is defined as the modulus of the Stokes vector (i.e., the composite vector of the three polarization-dependent components) divided by the total light intensity. This value reflects the degree of light polarization: in an ideal stress-free fiber, the backscattered light has a high degree of polarization and attenuates slowly along the fiber; when the fiber is subjected to local stress, the degree of polarization at that location attenuates more rapidly. The DSP calculates the DOP point-by-point, obtaining the DOP distribution curve along the fiber length within the current acquisition period.

[0070] Simultaneously, the DSP executes the three-point method algorithm to calculate the birefringence vector distribution. The three-point method is based on the Stokes parameters at three adjacent locations along the fiber, obtaining the polarization mode dispersion vector per unit length at each location through matrix operations. The magnitude of this vector reflects the strength of local birefringence, and its direction reflects the orientation of the principal axis of birefringence. Compared to a single DOP index, the birefringence vector provides richer stress information, such as distinguishing between tensile and bending stresses.

[0071] To facilitate subsequent anomaly detection, the DSP also performs differentiation on the DOP curve, calculating the derivative of the natural logarithm of DOP with respect to distance, to obtain the DOP attenuation rate curve for the current period. This curve is then compared point-by-point with the reference attenuation rate curve stored during baseline calibration.

[0072] Step 4: Anomaly Detection and Early Warning Output The anomaly detection algorithm integrates three independent detection metrics: polarization anomaly index, adjacent period correlation coefficient, and kurtosis coefficient. The polarization anomaly index is obtained as follows: the DSP subtracts the DOP attenuation rate curve of the current period from the reference attenuation rate curve point by point, and takes the absolute value to obtain the polarization anomaly index curve. The peak position on this curve corresponds to the region in the optical fiber where stress anomalies may occur. The system sets a basic threshold; when the polarization anomaly index at a certain point exceeds this threshold, a level one warning is triggered.

[0073] The correlation coefficient between adjacent periods is calculated as follows: The DSP performs a sliding window correlation operation on the fiber length between the DOP curves of the current period and the previous period. Specifically, a fixed-length window (e.g., 50 meters wide) is selected, and a segment of the DOP curve within the window of the current period is compared with the DOP curve at the same position in the previous period to calculate the correlation coefficient. The closer the correlation coefficient is to 1, the more stable the polarization characteristics of that fiber segment; a significant decrease in the correlation coefficient indicates a change in the stress state of that fiber segment. The system sets a lower threshold for the correlation coefficient; when the correlation coefficient of a window falls below this threshold, it is determined that there is a stress anomaly within that window.

[0074] The kurtosis coefficient is calculated as follows: The DSP first calculates the DOP difference curve between the current cycle and the previous cycle, i.e., subtracting the differences point by point. Then, the kurtosis coefficient is calculated on the difference curve using a sliding window method. The kurtosis coefficient reflects the peak of the difference curve: if a sudden stress change occurs at a certain location, the difference curve will show a steep peak near that location, and the kurtosis coefficient will increase significantly. The system sets a kurtosis coefficient threshold; when this threshold is exceeded, it helps to determine the presence of stress anomalies.

[0075] The final comprehensive judgment adopts a multi-indicator fusion strategy. The system only outputs the corresponding warning level when at least two indicators simultaneously reach their respective warning thresholds. This design effectively avoids false alarms caused by noise or random fluctuations of a single indicator.

[0076] The warning levels are divided into three levels: Level 1 is the lowest level, which only records the abnormal location and issues an audible and visual alert, while the production line continues to operate; Level 2 is the medium level, where the system sends a deceleration command to the PLC via industrial Ethernet, reducing the production line speed to 50% to 80% of its original speed, while closely monitoring the changing trends of abnormal indicators in subsequent cycles; Level 3 is the highest level, where the system immediately sends an emergency stop command to the PLC, triggers a high-decibel audible and visual alarm, and clearly displays the distance value of the fault location on the human-machine interface.

[0077] Step 5: PLC linkage and defect segment location The warning signal is sent to the PLC controller on the production line via an industrial Ethernet protocol (such as Profinet or Ethernet / IP) or a hard-wired I / O port. After receiving the instructions at different levels, the PLC executes the corresponding actions: for a level 1 warning, only the event is recorded and production is not interfered with; for a level 2 warning, the speed of the traction motor is adjusted by the frequency converter to reduce the speed; for a level 3 alarm, the power supply to the traction motor is cut off and the emergency brake is activated.

[0078] After an alarm or warning occurs, the system needs to convert the fiber optic distance (length measured from the OTDR port) measured by the OTDR into the actual location of the cable core on the production line so that operators can accurately locate and remove defective sections. This conversion relies on a speed-time synchronization mapping algorithm.

[0079] The DSP records the current position of the cable core tip during each acquisition cycle. This position is fed back to the PLC in real time by the production line encoder, and the PLC periodically sends this value to the POTDR system via Ethernet. The system maintains a speed-time history buffer of several minutes, storing the instantaneous speed of the production line at each moment. When an anomaly is detected at distance location zd, the system calculates the optical distance from the anomaly point to the OTDR port based on the propagation speed of the light pulse in the optical fiber (approximately 2.05 × 10^8 m / s). Then, the system queries the actual physical location on the cable core corresponding to this optical distance: since the optical fiber is helically embedded with a flame-retardant layer, its actual length is slightly longer than the cable core length. The system pre-stores a ratio factor (typically 1.01 to 1.05) between the helical pitch and the cable core length. Dividing the optical distance by this ratio factor yields the actual physical distance on the cable core.

[0080] After obtaining the physical distance on the cable core, the system searches backwards from the speed-time history buffer: calculating backwards from the current moment, integrating the production line speed until the integrated distance equals the physical distance. During integration, the system discretizes continuous speed values ​​into a sum of time steps multiplied by instantaneous speeds. When the error between the integrated distance and the target distance is less than a set tolerance (e.g., 0.5 meters), the corresponding moment is the production moment when the defective segment passed a fixed reference point (e.g., the extruder die). The system uses this moment, along with intervals extending forward and backward by a certain length (e.g., 2 meters forward and backward), as the range of defective segments to be eliminated.

[0081] Finally, the system generates a record containing information such as the warning level, defect distance, production time, and defect range, stores it in the local database, and displays it through the human-machine interface.

[0082] Step Six: Data Storage and Quality Traceability For each warning or alarm event, the system saves a complete original data packet, including: the time of the event, the production line speed curve, the backscattered power curves for the three polarization states, the calculated DOP curve, the birefringence vector distribution curve, the intermediate indicators used for anomaly determination (polarization anomaly index curve, correlation coefficient curve, kurtosis coefficient curve), and the final determination result. This data is stored in binary format on a local solid-state drive, with a storage capacity sufficient to support the amount of data generated during a month of continuous production.

[0083] Meanwhile, the system provides a data export interface, which can upload historical data to the factory's quality management system (QMS) via Ethernet. The QMS can perform statistical analysis on the long-term accumulated data, such as statistically analyzing the distribution pattern of defects along the cable length, the defect incidence rate at different production speeds, and the stress sensitivity of different batches of optical fibers, thereby providing a basis for process optimization.

[0084] In addition, the system supports post-event playback. Operators can select any historical time period on the human-machine interface, and the system will retrieve the raw data for that time period, re-execute the signal processing and anomaly detection algorithms, and graphically display the evolution of the DOP curve and polarization anomaly index curve over time. This function is invaluable for analyzing the causes of intermittent faults and verifying the effectiveness of parameter adjustments.

[0085] Furthermore, to ensure the reliability of the POTDR monitoring system itself, a periodic self-test function is designed. Every hour, the system automatically performs a short-distance fiber optic test, coupling a portion of the optical pulses to an internal reference fiber (approximately 100 meters long, fixed inside the system) to check whether key parameters such as laser power, detector responsivity, and acquisition card noise level are within normal ranges. If the self-test detects an anomaly, the system will display maintenance information on the human-machine interface and decide whether to suspend the production line or switch to a backup monitoring channel based on the severity of the fault. Redundant power supplies and watchdog timers can also be configured. The watchdog timer runs independently on the FPGA, checking the DSP's program execution status every second. If the DSP fails to feed the watchdog in time due to a software fault, the watchdog timer will trigger a hardware reset and simultaneously send a monitoring system fault signal to the PLC. The PLC can then choose to continue production or suspend production according to a preset strategy. This design ensures that even if the monitoring system itself malfunctions, it will not cause unexpected shutdowns to the production line.

[0086] In summary, the B1-grade cable provided by this invention uses silane cross-linked polyolefin insulation that meets standard requirements for mechanical and dielectric properties and has excellent combustion performance (including flame retardancy). This greatly simplifies the cable structure, making the structural form and outer diameter of the B1-grade cable consistent with ordinary cables. The cable and construction costs are greatly reduced, achieving the goal of designing and manufacturing B1-grade cables with the best economic structure.

[0087] It should be noted that, for the sake of simplicity, the foregoing embodiments are all described as a series of actions. However, those skilled in the art should understand that this application is not limited to the described order of actions, because according to this application, some steps can be performed in other orders or simultaneously. Furthermore, those skilled in the art should also understand that the embodiments described in the specification are preferred embodiments, and the actions involved are not necessarily essential to this application.

[0088] Furthermore, the terms "connection" and "setting" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "connection" or "setting" may explicitly or implicitly include one or more of that feature. Moreover, the terms "connection," "setting," etc., are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of the invention described herein can be implemented in sequences other than those illustrated or described herein.

[0089] The above embodiments describe the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Modifications and variations made by those skilled in the art without departing from the spirit and scope of the invention should be within the protection scope of the appended claims.

Claims

1. A method for manufacturing a B1 grade cable with an optimal economic structure, the B1 grade cable comprising a plurality of conductors (1), each conductor (1) having a mica wrapping layer (7) outside, an insulation layer (2) outside the mica wrapping layer (7), a wrapping layer (4) outside the insulation layer (2), a filler layer (3) between the insulation layer (2) and the wrapping layer (4), and an outer sheath (5) outside the wrapping layer (4), characterized in that, The insulating layer (2) is made of silane cross-linked polyolefin insulating material; The method for manufacturing the B1 grade cable includes the following steps: S1: Preparation of silane crosslinked polyolefin insulating material; S2: Fire-resistant B1 grade cable insulation cores are prepared by using an extrusion die matching method with automatically adjusted extrusion coating pressure; S3: Cable formation and filling; S4: Make the outer sheath (5) to complete the preparation of the B1 grade cable; The extrusion die matching method automatically adjusts the distance between the inner ends of the extrusion die to change the amount of covering pressure on the extruded insulation layer (2), thereby controlling the tightness of the covering between the insulation layer (2) and the mica wrapping layer (7). The silane crosslinked polyolefin insulating material comprises the following parts by weight: matrix resin: 40-45 parts; flame retardant: 45-50 parts; functional additives: 4-10 parts; crosslinking agent: 1-5 parts; The extrusion die matching method is achieved by using an automatic pressure adjustment extrusion die for insulating coated wire cores. The automatic pressure adjustment extrusion die for insulating coated wire cores includes: a die head body (13), an extrusion die cover (17) is provided at the front end of the die head body (13), an extrusion die core (14) is provided inside the extrusion die cover (17), the extrusion die core (14) is connected to the die adjustment rod (12), and the die adjustment rod (12) is connected to the servo motor (9) through the transmission mechanism (8). The extrusion die cover (17) is also provided with a die cover locker (15) and a pressure sensor (16); the die adjusting rod (12) is also provided with a flow divider cone (11), and the flow divider cone (11) is provided with a flow divider cone set nut (10).

2. The method for manufacturing a B1-grade cable with an optimal economic structure as described in claim 1, characterized in that, The matrix resin comprises: POE: 28-30 parts; EPR: 12-15 parts; The flame retardant comprises: inorganic flame retardant: 38-40 parts; organic flame retardant: 7-10 parts; The functional additives include: compatibilizer: 1.5-3 parts; hydrophobic agent: 0.5-2 parts; lubricant: 0.5-1 part; shell-forming agent: 1-3 parts; antioxidant: 0.5-1 part; The crosslinking agent includes: peroxide initiator: 0.2~1 part; silane crosslinking agent: 0.7~3 parts; catalyst: 0.1~1 part.

3. The method for manufacturing a B1-grade cable with an optimal economic structure as described in claim 2, characterized in that, The preparation method of the silane crosslinked polyolefin insulation material includes the following sub-steps: Prepare material A; material A is a grafting matrix, which includes POE, EPR, compatibilizer, antioxidant, peroxide initiator and silane crosslinking agent; Prepare material B; material B is a flame retardant functional masterbatch, which includes inorganic flame retardants, organic flame retardants, shell-forming agents, hydrophobic agents, lubricants, and antioxidants; For the finished product mixing, firstly, add the grafted base material, flame retardant functional masterbatch and catalyst into a low-speed mixer and mix for 5-10 minutes at room temperature to ensure that the components are evenly dispersed. Then, the lumps are removed, and the product is vacuum-sealed and packaged to obtain the final silane cross-linked polyolefin insulation material.

4. The method for manufacturing a B1-grade cable with an optimal economic structure as described in claim 3, characterized in that, The preparation method of the grafted base material is as follows: First, POE, EPR, compatibilizer and antioxidant are added to a high-speed mixer and mixed for 1-2 minutes. Then, peroxide initiator and silane crosslinking agent are added and mixed for another 3-5 minutes to allow the liquid to be fully absorbed until the resin surface is dry. Finally, the material is added to a parallel co-rotating twin-screw extruder for melt grafting reaction. The material completes the grafting reaction in the extruder, is extruded and granulated to obtain the grafted base material. The preparation method of the flame-retardant functional masterbatch is as follows: First, the flame-retardant functional masterbatch is added to a high-speed mixer and mixed at high speed for 5-10 minutes at a temperature of 60-80℃; then, the mixed hot material is added to a mixer or a twin-screw extruder for plasticizing and granulation, with the temperature controlled at 130℃-150℃, and extruded and granulated to obtain the flame-retardant functional masterbatch.

5. The method for manufacturing a B1-grade cable with an optimal economic structure as described in claim 1, characterized in that, The filling layer (3) is filled with basalt fiber rope; the wrapping layer (4) is wrapped with inorganic mineral composite tape; the outer sheath (5) is a general thermoplastic flame-retardant polyolefin outer sheath.

6. A method for manufacturing a B1-grade cable with an optimal economic structure as described in any one of claims 1 to 5, characterized in that, Before making the outer sheath (5), the following steps are also included: The optical fiber (6) is embedded in the flame-retardant layer by means of spiral embedding. The flame-retardant layer is disposed between the wrapping layer (4) and the outer sheath (5). The optical fiber (6) is used to connect with the terminal to accurately locate the fault point.

7. The method for manufacturing a B1-grade cable with an optimal economic structure as described in claim 6, characterized in that, The embedding of the optical fiber (6) into the flame-retardant layer specifically includes the following steps: The cable core that has been completed and cabled is heated to 40-60℃ using a preheating device; The rotating head begins to revolve around the cable core at a set speed. The rotational speed is precisely matched according to the required helical pitch and the cable core travel speed. The calculation formula is as follows: Rotational speed = Production line speed / Helix pitch; At the moment when the optical fiber (6) contacts the cable core, the surface of the cable core is locally heated or coated with a layer of EVA hot melt adhesive by using a micro hot air gun or a micro glue applicator, so that the optical fiber (6) is slightly adhered to the cable core to prevent it from shifting before entering the extruder die. The cable core with the laid optical fiber is immediately fed into the extruder head and covered with an outer sheath (5).

8. The method for manufacturing a B1-grade cable with an optimal economic structure as described in claim 6, characterized in that, A stress anomaly early warning method based on polarized light time domain reflectance (POTDR) is adopted to realize the whole process monitoring of fiber (6) embedding.

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