Extrusion insulation low-voltage power cable and preparation method thereof

Abstract

The invention relates to the technical field of cable preparation, in particular to an extruded insulation low-voltage power cable and a preparation method thereof.The preparation method comprises the steps that metal wires are twisted into a conductor according to preset twisting parameters, and the conductor is preprocessed; extruding an insulating layer on the surface of the pretreated conductor by using a screw extruder to obtain an insulated wire core; monitoring the diameter of the insulated wire core in real time by using a laser diameter measuring instrument, and determining the fluctuation characteristic type of the diameter of the wire core under a first preset condition; obtaining the eccentricity of the insulating layer and the void ratio between the insulating layer and the conductor; judging the qualification of the extrusion process according to the extrusion comprehensive quality index; under the condition that the extrusion process is unqualified, the qualification of the extrusion process is secondarily judged according to the insulation performance evaluation value; under the condition that the extrusion process is judged to be unqualified for the second time, an adjustment strategy of the extrusion process is determined; and after the insulated wire cores qualified in the extrusion process are twisted into a cable, an outer protective sleeve is extruded. The production efficiency and the product stability of the cable are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of cable preparation, and in particular to an extruded insulated low-voltage power cable and a preparation method thereof. Background Art

[0002] Extruded insulated low-voltage power cable is a type of cable product widely used in power distribution networks, industrial equipment and building electrical systems. The conductor is coated with a polymer insulation layer (such as polyvinyl chloride (PVC), cross-linked polyethylene (XLPE), etc.) through an extrusion process. It has the characteristics of simple structure, stable electrical performance, good mechanical strength and easy installation. With the increasing requirements for safety and energy efficiency of power systems, cables need to meet higher insulation reliability, heat resistance and environmental protection standards. However, traditional extruded insulated cables still face many challenges in material selection, process control and structural design, such as uneven thickness of the insulation layer, interface defects, thermal stress cracking and other problems, which can easily lead to partial discharge, insulation aging and even short circuit failures. In addition, factors such as fluctuations in process parameters, material impurities or insufficient stability of extrusion equipment during the production process further affect the long-term service performance of the cable.

[0003] Chinese patent application publication number CN120183781A discloses an extruded insulated low-voltage power cable and its preparation method. The method comprises: subjecting copper rods to wire drawing and annealing to produce copper wire, and then twisting multiple copper wires to form a copper core; extruding an insulating material around the outer periphery of the copper core, and cross-linking the insulating material to form an insulating layer to produce a cable; wrapping an inner lining layer around the outer surface of the cable, and then wrapping an outer sheath around the outer periphery of the inner lining to produce an extruded insulated low-voltage power cable. However, the prior art suffers from the following problems: The prior art fails to fully consider the effect of the extrusion process on the thickness distribution of the insulation layer, which may result in localized uneven thickness, causing electric field distribution distortion, accelerating insulation aging, and degrading the long-term electrical performance of the cable. Summary of the Invention

[0004] To this end, the present invention provides an extruded insulated low-voltage power cable and a preparation method thereof, so as to overcome the problem in the prior art that the influence of the thickness uniformity of the insulation layer on the electrical performance of the cable is not considered, resulting in accelerated aging of the insulation layer.

[0005] To achieve the above object, the present invention provides an extruded insulated low-voltage power cable and a preparation method thereof, comprising:

[0006] Twisting the metal wires into a conductor according to preset twisting parameters, and pre-treating the conductor, wherein the twisting parameters include twist pitch, twist tightness, and single wire diameter and number;

[0007] Using a screw extruder to extrude an insulation layer on the surface of the pretreated conductor to obtain an insulated wire core;

[0008] A laser diameter gauge is used to monitor the diameter of the insulated wire core in real time, and a wire core diameter fluctuation characteristic type under a first preset condition is determined. The first preset condition is that the wire core diameter remains within a preset diameter range and the wire core diameter is detected to exceed the preset diameter range for the first time. The wire core diameter fluctuation characteristic types include periodic fluctuation and non-periodic fluctuation.

[0009] Collecting a cross-sectional grayscale image of a preset point in an abnormal extrusion section under non-periodic fluctuation conditions to obtain the eccentricity of the insulation layer and the void ratio between the insulation layer and the conductor, wherein the abnormal extrusion section is a wire core section monitored for a preset time under a first preset condition;

[0010] The qualification of the extrusion process is determined by the comprehensive extrusion quality index determined by eccentricity and void ratio;

[0011] Under the condition that the extrusion process fails, the insulation performance evaluation value is obtained through electrical performance testing, and the qualification of the extrusion process is secondarily determined based on the insulation performance evaluation value;

[0012] Under the condition that the extrusion process is determined to be unqualified for the second time, determining an adjustment strategy for the extrusion process based on a difference between a preset insulation performance evaluation value and the insulation performance evaluation value, including increasing the melt temperature of the insulation material based on the average surface roughness of the insulation layer, or reducing the extrusion speed based on the surface defect index of the insulation layer;

[0013] The insulated wire cores that have passed the extrusion process are twisted into cables and then extruded with an outer protective sheath.

[0014] Furthermore, the process of determining the type of wire core diameter fluctuation characteristics under the first preset condition includes:

[0015] Based on the condition that the wire core diameter is detected to be outside the preset diameter range for the first time, the wire core diameter is continuously monitored for a preset time period and a diameter fluctuation curve is drawn;

[0016] Compare the diameter fluctuation curve with the operating cycle of the screw and traction roller respectively;

[0017] Based on the result that the fluctuation period of the wire core diameter coincides with any period of the screw and the traction roller, it is determined that the fluctuation characteristic of the wire core diameter is a periodic fluctuation;

[0018] Based on the result that the fluctuation period of the wire core diameter does not coincide with the operating period of the screw and the traction roller, it is determined that the fluctuation characteristics of the wire core diameter are non-periodic fluctuations;

[0019] The preset duration is greater than the duration of at least three cycles of the maximum cycle of the screw and the traction roller.

[0020] Furthermore, the process of determining the comprehensive quality index of the extruded package includes:

[0021] Using an industrial camera in combination with image analysis software, grayscale images of cross sections of preset points in an abnormal extrusion section under non-periodic fluctuations are collected, wherein the preset points include the point with the largest diameter and the point with the smallest diameter;

[0022] Obtain the maximum and minimum thicknesses of the insulation layer in the grayscale image, as well as the area of ​​the dark region between the insulation layer and the conductor in the grayscale image, where the void ratio is the percentage of the dark region area to the area of ​​the core cross section;

[0023] The eccentricity and void ratio were obtained by calculation respectively;

[0024] The maximum values ​​of eccentricity and void ratio at the preset points are taken and calculated using a weighted algorithm to obtain the comprehensive quality index of the extruded package.

[0025] Furthermore, the eligibility of the extrusion process is determined based on the comprehensive extrusion quality index, where:

[0026] If the comprehensive extrusion quality index is less than the first preset quality index, the extrusion process is determined to be unqualified, the die core of the extruder is calibrated, and the extrusion pressure is increased according to the void ratio;

[0027] If the comprehensive extrusion quality index is greater than or equal to the first preset quality index and less than the second preset quality index, the extrusion process is judged to be unqualified, and the qualification of the extrusion process is re-judged based on the insulation performance evaluation value;

[0028] If the comprehensive extrusion quality index is greater than or equal to the second preset quality index, the extrusion process is determined to be qualified and the next step of cabling is entered.

[0029] Furthermore, the insulation performance evaluation value is determined by insulation resistance and dielectric loss factor.

[0030] Furthermore, the qualification of the extrusion process is determined again based on the insulation performance evaluation value, wherein:

[0031] If the insulation performance evaluation value is less than a preset insulation performance evaluation value, the extrusion process is determined to be unqualified for the second time, and an adjustment strategy for the extrusion process is determined according to the difference between the preset insulation performance evaluation value and the insulation performance evaluation value;

[0032] If the insulation performance evaluation value is greater than or equal to the preset insulation performance evaluation value, the extrusion process is judged to be qualified for the second time, and the next step of cabling is entered.

[0033] Furthermore, the adjustment strategy of the extrusion process is determined according to the insulation performance evaluation difference, wherein:

[0034] If the insulation performance evaluation difference is less than a preset evaluation difference, determining that the adjustment strategy for the extrusion process is to increase the melt temperature of the insulation material according to the average surface roughness of the insulation layer;

[0035] If the insulation performance evaluation difference is greater than or equal to the preset evaluation difference, determining that the adjustment strategy for the extrusion process is to reduce the extrusion speed according to the surface defect index of the insulation layer;

[0036] The insulation performance evaluation difference is the difference between the preset insulation performance evaluation value and the insulation performance evaluation value.

[0037] Furthermore, several adjustment methods are provided for the melt temperature of the insulating material, and each adjustment method has a different adjustment range for the melt temperature.

[0038] Furthermore, the extrusion speed is negatively correlated with the surface defect index of the insulation layer, and the surface defect index of the insulation layer is determined by the surface crack size.

[0039] The present invention also provides an extruded insulated low-voltage power cable, the conductor material of which is copper, and the insulation layer material and the outer protective sheath material are polyvinyl chloride.

[0040] Compared with the prior art, the beneficial effect of the present invention is that the present invention fully considers the influence of the thickness uniformity of the insulation layer on the electrical performance of the cable, monitors the diameter of the insulation core in real time through a laser diameter gauge, and accurately determines the type of core diameter fluctuation characteristics. For non-periodic fluctuations, the cross-sectional grayscale image of the preset point of the abnormal extrusion section is collected to accurately obtain the eccentricity of the insulation layer and the void ratio between the insulation layer and the conductor, and the comprehensive quality index of the extrusion is determined accordingly. Through a multi-dimensional and refined detection method, the problem of uneven thickness of the insulation layer can be discovered in time, and the electric field concentration or poor heat dissipation caused by local thickness being too thin or too thick can be avoided, thereby effectively delaying the accelerated aging of the insulation layer and improving the service life and reliability of the cable.

[0041] Furthermore, the present invention establishes a multi-level judgment mechanism. Initially, the extrusion process is assessed based on the comprehensive extrusion quality index. If the extrusion process fails, a secondary judgment is performed using insulation performance evaluation values ​​obtained through electrical performance testing. Targeted adjustment strategies are then developed based on the different judgment results. This intelligent adjustment approach can quickly and accurately resolve problems that arise during the extrusion process, reduce scrap rates, improve production efficiency, and ensure consistently high-quality extrusion.

[0042] Furthermore, the present invention scientifically and reasonably sets various judgment parameters. At the same time, several adjustment methods are set for the melt temperature of the insulating material, and each adjustment method has a different adjustment range for the melt temperature. The extrusion speed is negatively correlated with the surface defect index of the insulating layer and the defect index is determined according to the surface crack size. Through flexible adjustment methods, it can adapt to different production conditions and quality requirements, further enhancing the practicality and flexibility of the preparation method of the present invention.

[0043] Furthermore, the extruded insulated low-voltage power cable provided by the present invention utilizes copper, a material with excellent electrical conductivity, as its conductor, ensuring efficient current transmission and reducing power loss. Both the insulation layer and outer protective sheath are made of polyvinyl chloride, a material with excellent insulation, chemical resistance, and flame retardancy, effectively protecting the conductor and preventing electrical leakage and fire. Furthermore, the preparation method of the present invention ensures the quality of the insulation layer and outer protective sheath, improving the overall performance of the cable. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 This is a flow chart of a method for preparing an extruded insulated low-voltage power cable according to an embodiment of the present invention;

[0045] Figure 2 This is a flow chart of determining the eligibility of an extrusion process according to an extrusion comprehensive quality index according to an embodiment of the present invention;

[0046] Figure 3 This is a flow chart of a method for secondary determining the eligibility of an extrusion process according to an insulation performance evaluation value according to an embodiment of the present invention;

[0047] Figure 4 This is a flow chart of an embodiment of the present invention for determining an adjustment strategy for an extrusion process based on an insulation performance evaluation difference. DETAILED DESCRIPTION

[0048] In order to make the objects and advantages of the present invention more clearly understood, the present invention is further described below in conjunction with embodiments; it should be understood that the specific embodiments described herein are merely used to explain the present invention and are not intended to limit the present invention.

[0049] The preferred embodiments of the present invention are described below with reference to the accompanying drawings. It should be understood by those skilled in the art that these embodiments are only used to explain the technical principles of the present invention and are not intended to limit the scope of protection of the present invention.

[0050] It should be pointed out that the data in this embodiment are obtained by comprehensive analysis and evaluation of the historical test data and the corresponding historical test results of the three months before this test. It can be understood by those skilled in the art that the present invention can determine the above parameters for a single item by selecting the value with the highest proportion as the preset standard parameter based on the data distribution, using weighted summation to use the obtained value as the preset standard parameter, substituting each historical data into a specific formula and using the value obtained by the formula as the preset standard parameter or other selection methods, as long as the present invention can clearly define the different specific situations in the single determination process through the obtained values.

[0051] See also Figures 1 to 4 As shown, they are respectively a flow chart of a method for preparing an extruded insulated low-voltage power cable according to an embodiment of the present invention; a flow chart of determining the eligibility of an extrusion process according to an extrusion comprehensive quality index according to an embodiment of the present invention; a flow chart of secondary determining the eligibility of an extrusion process according to an insulation performance evaluation value according to an embodiment of the present invention; and a flow chart of determining an adjustment strategy for an extrusion process according to an insulation performance evaluation difference according to an embodiment of the present invention.

[0052] The method for preparing an extruded insulated low-voltage power cable according to an embodiment of the present invention comprises:

[0053] Step S1, twisting metal wires into a conductor according to preset twisting parameters, and pre-processing the conductor, wherein the twisting parameters include twisting pitch, twisting tightness, and single wire diameter and number;

[0054] Step S2, using a screw extruder to extrude an insulating layer on the surface of the pretreated conductor to obtain an insulated wire core;

[0055] Step S3: Using a laser caliper to monitor the diameter of the insulated wire core in real time, and determining a type of wire core diameter fluctuation characteristic under a first preset condition, wherein the first preset condition is that the wire core diameter remains within a preset diameter range and the wire core diameter is detected to exceed the preset diameter range for the first time. The wire core diameter fluctuation characteristic types include periodic fluctuation and non-periodic fluctuation.

[0056] Step S4, collecting a cross-sectional grayscale image of a preset point in the abnormal extrusion section under the non-periodic fluctuation condition to obtain the eccentricity of the insulation layer and the void ratio between the insulation layer and the conductor, wherein the abnormal extrusion section is a core section monitored for a preset time under the first preset condition;

[0057] Step S5, judging the eligibility of the extrusion process according to the comprehensive extrusion quality index determined by the eccentricity and the void ratio;

[0058] Step S6: If the extrusion process fails, obtain an insulation performance evaluation value through an electrical performance test, and re-determine the eligibility of the extrusion process based on the insulation performance evaluation value;

[0059] Step S7, if the extrusion process is determined to be unqualified after the second determination, determining an adjustment strategy for the extrusion process based on the difference between the preset insulation performance evaluation value and the insulation performance evaluation value, including increasing the melt temperature of the insulating material based on the average surface roughness of the insulating layer, or reducing the extrusion speed based on the surface defect index of the insulating layer;

[0060] Step S8, twisting the insulated wire cores that have passed the extrusion process into cables and then extruding an outer protective sheath.

[0061] In the embodiment of the present invention, a wire stranding machine is used to strand copper wires according to preset stranding parameters, wherein the stranding pitch is set to 15 mm, the stranding tightness is set to 85%, the single wire diameter is 0.5 mm, and the number of single wires is 19.

[0062] Specifically, the pretreatment includes removing dust and impurities on the conductor surface by high-pressure air blowing, increasing the surface roughness by mechanical grinding, and coating a layer of antioxidant on the conductor surface to prevent the conductor from oxidation. The antioxidant is, for example, a rosin solution or a silane coupling agent, which is not specifically limited.

[0063] Specifically, the initial parameters of the screw extruder include: the feed section temperature is set to 130°C, the compression section temperature is set to 160°C, the metering section temperature is set to 190°C, the die head temperature is set to 200°C, the screw speed is set to 30rpm, the extrusion pressure is set to 18MPa, and the extrusion speed is set to 15m / min, but the above values ​​are not limited to these, and those skilled in the art can adjust the above values ​​according to actual needs.

[0064] Specifically, the laser diameter gauge is set 1.5m behind the extruder die outlet and in front of the cooling water trough. This setting can quickly capture the diameter data of the newly extruded insulated wire core and promptly reflect the working status of the die. Once the die is blocked, the extrusion pressure is unstable, etc., resulting in abnormal diameter, rapid feedback can be provided to adjust the extruder parameters to ensure initial accuracy.

[0065] Specifically, when the extruder starts running, the insulated wire core will have an unstable diameter range. After the wire core diameter remains within the preset diameter range, the situation where the wire core diameter exceeds the preset diameter range is recorded as the first preset condition. The preset diameter range is [4.85, 5.00], and the diameter unit is mm.

[0066] Specifically, the process of determining the type of wire core diameter fluctuation characteristics under the first preset condition includes:

[0067] Based on the condition that the wire core diameter is detected to be outside the preset diameter range for the first time, the wire core diameter is continuously monitored for a preset time period and a diameter fluctuation curve is drawn;

[0068] Compare the diameter fluctuation curve with the operating cycle of the screw and traction roller respectively;

[0069] Based on the result that the fluctuation period of the wire core diameter coincides with any period of the screw and the traction roller, it is determined that the fluctuation characteristic of the wire core diameter is a periodic fluctuation;

[0070] Based on the result that the fluctuation period of the wire core diameter does not coincide with the operating period of the screw and the traction roller, it is determined that the fluctuation characteristics of the wire core diameter are non-periodic fluctuations;

[0071] The preset duration is greater than the duration of at least three cycles of the maximum cycle of the screw and the traction roller.

[0072] In the embodiment of the present invention, the preset duration is set to 15s, but the value is not limited thereto, and those skilled in the art may adjust the value according to actual needs.

[0073] Specifically, for periodic fluctuations, check the screw and traction roller for wear or eccentricity, and replace or correct the screw or traction roller.

[0074] Specifically, the present invention uses continuous monitoring and curve drawing within a preset time period, combined with cross-comparison between the operating cycles of the screw and traction roller, to quickly identify the root cause of the fluctuation and reduce manual troubleshooting time; the preset time period covers more than three times the maximum cycle of the equipment, ensuring that the sampled data fully contains periodic characteristics, avoiding misjudgment due to insufficient monitoring time, and improving the statistical significance of the analysis results.

[0075] Specifically, the process of determining the comprehensive quality index of extruded packages includes:

[0076] Using an industrial camera in combination with image analysis software, grayscale images of cross sections of preset points in an abnormal extrusion section under non-periodic fluctuations are collected, wherein the preset points include the point with the largest diameter and the point with the smallest diameter;

[0077] Obtain the maximum and minimum thicknesses of the insulation layer in the grayscale image, as well as the area of ​​the dark region between the insulation layer and the conductor in the grayscale image, where the void ratio is the percentage of the dark region area to the area of ​​the core cross section;

[0078] The eccentricity and void ratio were obtained by calculation respectively;

[0079] The maximum values ​​of eccentricity and void ratio at the preset points are taken and calculated using a weighted algorithm to obtain the comprehensive quality index of the extruded package.

[0080] Specifically, image analysis software such as Halcon, OpenCV, and MATLAB are not specifically limited.

[0081] Specifically, eccentricity = (maximum thickness - minimum thickness) / (maximum thickness + minimum thickness), comprehensive extrusion quality index = first weight coefficient × eccentricity threshold / eccentricity + second weight coefficient × void ratio threshold / void ratio, wherein the first weight coefficient is 0.6, the eccentricity threshold is 0.16, the second weight coefficient is 0.4, and the void ratio threshold is 0.08.

[0082] Specifically, the qualification of the extrusion process is determined based on the comprehensive extrusion quality index, where:

[0083] If the comprehensive extrusion quality index is less than the first preset quality index, the extrusion process is determined to be unqualified, the die core of the extruder is calibrated, and the extrusion pressure is increased according to the void ratio;

[0084] If the comprehensive extrusion quality index is greater than or equal to the first preset quality index and less than the second preset quality index, the extrusion process is judged to be unqualified, and the qualification of the extrusion process is re-judged based on the insulation performance evaluation value;

[0085] If the comprehensive extrusion quality index is greater than or equal to the second preset quality index, the extrusion process is determined to be qualified and the next step of cabling is entered.

[0086] In the embodiment of the present invention, the first preset quality index is set to 0.8, and the second preset quality index is set to 0.98, but the above values ​​are not limited thereto, and those skilled in the art may adjust the above values ​​according to actual needs.

[0087] Specifically, the extrusion pressure is positively correlated with the void ratio, that is, the greater the void ratio, the greater the increase in the extrusion pressure. The adjustment range of the extrusion pressure is 15 to 25 MPa.

[0088] Specifically, the insulation performance evaluation value is jointly determined by the insulation resistance and the dielectric loss factor, and the insulation performance evaluation value = the third weight coefficient × insulation resistance / insulation resistance threshold + the fourth weight coefficient × dielectric loss factor threshold / dielectric loss factor, wherein the third weight coefficient is 0.55, the insulation resistance threshold is 1000MΩ·km, the fourth weight coefficient is 0.45, and the dielectric loss factor threshold is 0.02.

[0089] Specifically, the insulation resistance is obtained by testing with a miniature high resistance meter, and the dielectric loss factor is obtained by testing with an automatic dielectric loss tester. A 5 mm wide line segment is selected from the above-mentioned cross section along the long-range direction of the insulated wire core, and several points are selected on the outer surface of the insulation layer of the line segment for testing. There is no limit on the number of points. The lowest resistance and the highest dielectric loss factor are taken from the test data to calculate the insulation performance evaluation value.

[0090] Specifically, the qualification of the extrusion process is determined twice based on the insulation performance evaluation value, where:

[0091] If the insulation performance evaluation value is less than a preset insulation performance evaluation value, the extrusion process is determined to be unqualified for the second time, and an adjustment strategy for the extrusion process is determined according to the difference between the preset insulation performance evaluation value and the insulation performance evaluation value;

[0092] If the insulation performance evaluation value is greater than or equal to the preset insulation performance evaluation value, the extrusion process is judged to be qualified for the second time, and the next step of cabling is entered.

[0093] In the embodiment of the present invention, the preset insulation performance evaluation value is 0.95, but the above value is not limited thereto, and those skilled in the art can adjust the above value according to actual needs.

[0094] Specifically, the adjustment strategy of the extrusion process is determined according to the insulation performance evaluation difference, where:

[0095] If the insulation performance evaluation difference is less than a preset evaluation difference, determining that the adjustment strategy for the extrusion process is to increase the melt temperature of the insulation material according to the average surface roughness of the insulation layer;

[0096] If the insulation performance evaluation difference is greater than or equal to the preset evaluation difference, determining that the adjustment strategy for the extrusion process is to reduce the extrusion speed according to the surface defect index of the insulation layer;

[0097] The insulation performance evaluation difference is the difference between the preset insulation performance evaluation value and the insulation performance evaluation value.

[0098] In the embodiment of the present invention, the preset evaluation difference value is 0.15, but the above value is not limited thereto, and those skilled in the art can adjust the above value according to actual needs.

[0099] Specifically, if the extrusion speed is too fast, the shear force and tensile force applied to the insulating material during the extrusion process will increase, which may easily lead to defects such as micropores and cracks inside the insulating layer, reducing the insulation performance; if the melt temperature is too low, the insulating material cannot be fully melted, resulting in a rough surface and granular protrusions on the surface of the extruded insulating layer, and there may be unmelted impurities inside, thereby reducing the insulation resistance, increasing the dielectric loss factor, and reducing the insulation performance evaluation value.

[0100] Specifically, there are several adjustment methods for the melt temperature of the insulating material, and each adjustment method has a different adjustment range for the melt temperature.

[0101] If the average surface roughness of the insulating layer is less than the preset roughness, the melt temperature is increased to the corresponding value using the first temperature adjustment coefficient 1.02;

[0102] If the average surface roughness of the insulating layer is greater than or equal to the preset roughness, the melt temperature is increased to the corresponding value using the second temperature adjustment coefficient of 1.05;

[0103] The melt temperature is the metering section temperature.

[0104] In the embodiment of the present invention, the preset roughness value is 1.2 μm, but the above value is not limited thereto, and those skilled in the art can adjust the above value according to actual needs.

[0105] Specifically, the roughness is obtained by testing with a contact roughness meter.

[0106] Specifically, the extrusion speed is negatively correlated with the surface defect index of the insulation layer, which is determined by the surface crack size.

[0107] Specifically, if the surface defect index of the insulating layer is less than the first preset defect index, the extrusion speed is reduced to a corresponding value using the first speed adjustment coefficient of 0.98;

[0108] If the surface defect index of the insulating layer is greater than or equal to the first preset defect index and less than the second preset defect index, the extrusion speed is reduced to a corresponding value using a second speed adjustment coefficient of 0.95;

[0109] If the surface defect index of the insulating layer is greater than or equal to the second preset defect index, the extrusion speed is reduced to a corresponding value using a third speed adjustment coefficient of 0.92.

[0110] In the embodiment of the present invention, the first preset defect index is set to 0.85, and the second preset defect index is set to 0.98, but the above values ​​are not limited thereto, and those skilled in the art may adjust the above values ​​according to actual needs.

[0111] Specifically, the surface defect index of the insulating layer = depth weight coefficient × crack depth / crack depth threshold + length weight coefficient × crack length / crack length threshold, wherein the depth weight coefficient is 0.6, the crack depth threshold is 50 μm, the length weight coefficient is 0.4, and the crack length threshold is 5 mm.

[0112] Specifically, the surface crack size is obtained through industrial microscope detection, and the surface crack size includes crack length and crack depth.

[0113] The extruded insulated low-voltage power cable according to the embodiment of the present invention has a conductor made of copper, and an insulation layer and an outer protective sheath made of polyvinyl chloride.

[0114] Thus far, the technical solutions of the present invention have been described in conjunction with the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art may make equivalent changes or substitutions to the relevant technical features, and the technical solutions after such changes or substitutions will fall within the scope of protection of the present invention.

[0115] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing an extruded insulated low-voltage power cable, characterized in that: include: Twisting the metal wires into a conductor according to preset twisting parameters, and pre-treating the conductor, wherein the twisting parameters include twist pitch, twist tightness, and single wire diameter and number; Using a screw extruder to extrude an insulation layer on the surface of the pretreated conductor to obtain an insulated wire core; A laser diameter gauge is used to monitor the diameter of the insulated wire core in real time, and a wire core diameter fluctuation characteristic type under a first preset condition is determined. The first preset condition is that the wire core diameter remains within a preset diameter range and the wire core diameter is detected to exceed the preset diameter range for the first time. The wire core diameter fluctuation characteristic types include periodic fluctuation and non-periodic fluctuation. Collecting a cross-sectional grayscale image of a preset point in an abnormal extrusion section under non-periodic fluctuation conditions to obtain the eccentricity of the insulation layer and the void ratio between the insulation layer and the conductor, wherein the abnormal extrusion section is a wire core section monitored for a preset time under a first preset condition; The qualification of the extrusion process is determined by the comprehensive extrusion quality index determined by eccentricity and void ratio; Under the condition that the extrusion process fails, the insulation performance evaluation value is obtained through electrical performance testing, and the qualification of the extrusion process is secondarily determined based on the insulation performance evaluation value; Under the condition that the extrusion process is determined to be unqualified for the second time, determining an adjustment strategy for the extrusion process based on a difference between a preset insulation performance evaluation value and the insulation performance evaluation value, including increasing the melt temperature of the insulation material based on the average surface roughness of the insulation layer, or reducing the extrusion speed based on the surface defect index of the insulation layer; The insulated wire cores that have passed the extrusion process are twisted into cables and then extruded with an outer protective sheath.

2. The method for preparing an extruded insulated low-voltage power cable according to claim 1, wherein: The process of determining the type of wire core diameter fluctuation characteristics under the first preset condition includes: Based on the condition that the wire core diameter is detected to be outside the preset diameter range for the first time, the wire core diameter is continuously monitored for a preset time period and a diameter fluctuation curve is drawn; Compare the diameter fluctuation curve with the operating cycle of the screw and traction roller respectively; Based on the result that the fluctuation period of the wire core diameter coincides with any period of the screw and the traction roller, it is determined that the fluctuation characteristic of the wire core diameter is a periodic fluctuation; Based on the result that the fluctuation period of the wire core diameter does not coincide with the operating period of the screw and the traction roller, it is determined that the fluctuation characteristics of the wire core diameter are non-periodic fluctuations; The preset duration is greater than the duration of at least three cycles of the maximum cycle of the screw and the traction roller.

3. The method for preparing an extruded insulated low-voltage power cable according to claim 2, characterized in that: The process of determining the comprehensive quality index of extruded packages includes: Using an industrial camera in combination with image analysis software, grayscale images of cross sections of preset points in an abnormal extrusion section under non-periodic fluctuations are collected, wherein the preset points include the point with the largest diameter and the point with the smallest diameter; Obtain the maximum and minimum thicknesses of the insulation layer in the grayscale image, as well as the area of ​​the dark region between the insulation layer and the conductor in the grayscale image, where the void ratio is the percentage of the dark region area to the area of ​​the core cross section; The eccentricity and void ratio were obtained by calculation respectively; The maximum values ​​of eccentricity and void ratio at the preset points are taken and calculated using a weighted algorithm to obtain the comprehensive quality index of the extruded package.

4. The method for preparing an extruded insulated low-voltage power cable according to claim 3, characterized in that: The qualification of the extrusion process is determined based on the comprehensive extrusion quality index, where: If the comprehensive extrusion quality index is less than the first preset quality index, the extrusion process is determined to be unqualified, the die core of the extruder is calibrated, and the extrusion pressure is increased according to the void ratio; If the comprehensive extrusion quality index is greater than or equal to the first preset quality index and less than the second preset quality index, the extrusion process is judged to be unqualified, and the qualification of the extrusion process is re-judged based on the insulation performance evaluation value; If the comprehensive extrusion quality index is greater than or equal to the second preset quality index, the extrusion process is determined to be qualified and the next step of cabling is entered.

5. The method for preparing an extruded insulated low-voltage power cable according to claim 4, characterized in that: The insulation performance evaluation value is determined by the insulation resistance and the dielectric loss factor.

6. The method for preparing an extruded insulated low-voltage power cable according to claim 5, characterized in that: The qualification of the extrusion process is determined secondary based on the insulation performance evaluation value, among which: If the insulation performance evaluation value is less than a preset insulation performance evaluation value, the extrusion process is determined to be unqualified for the second time, and an adjustment strategy for the extrusion process is determined according to the difference between the preset insulation performance evaluation value and the insulation performance evaluation value; If the insulation performance evaluation value is greater than or equal to the preset insulation performance evaluation value, the extrusion process is judged to be qualified for the second time, and the next step of cabling is entered.

7. The method for preparing an extruded insulated low-voltage power cable according to claim 6, characterized in that: The adjustment strategy of the extrusion process is determined based on the insulation performance evaluation difference, where: If the insulation performance evaluation difference is less than a preset evaluation difference, determining that the adjustment strategy for the extrusion process is to increase the melt temperature of the insulation material according to the average surface roughness of the insulation layer; If the insulation performance evaluation difference is greater than or equal to the preset evaluation difference, determining that the adjustment strategy for the extrusion process is to reduce the extrusion speed according to the surface defect index of the insulation layer; The insulation performance evaluation difference is the difference between the preset insulation performance evaluation value and the insulation performance evaluation value.

8. The method for preparing an extruded insulated low-voltage power cable according to claim 7, characterized in that: There are several adjustment methods for the melt temperature of the insulating material, and each adjustment method has a different adjustment range for the melt temperature.

9. The method for preparing an extruded insulated low-voltage power cable according to claim 8, characterized in that: The extrusion speed is negatively correlated with the surface defect index of the insulation layer, which is determined by the surface crack size.

10. An extruded insulated low-voltage power cable used in the method for preparing an extruded insulated low-voltage power cable according to any one of claims 1 to 9, characterized in that: The conductor material is copper, and the insulation layer material and outer protective sheath material are polyvinyl chloride.

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