Extrusion molding process of low-wind-resistance overhead insulated wire

Abstract

The invention discloses an extrusion molding process of a low-wind-resistance overhead insulated wire. The process comprises the following stages: a plasticizing stage; in the forming stage, a wire core or a conductor penetrates through the semi-extruded tube type mold; in the shaping stage, after the plastic extrusion material is cooled by a cooling water tank or a cooling pipeline, an amorphous plastic state is changed into a shaped solid state; the semi-extruded tube type die comprises a die core and a die sleeve, the die core is sleeved with the die sleeve, the die sleeve is arranged in the machine head, and a hole matched with the periphery of the insulated wire is formed in the end of the die sleeve. The mold disclosed by the invention can be mounted in a plastic extruding machine, so that a special-shaped cable, such as a cable with a groove, is obtained; the wire structure and the corresponding mold structure are tightly matched, the structural parameters of the extrusion mold can be directly calculated according to related formulas, workers do not need to measure the structural parameters every time, a parameter value adjusting method is set, formula calculation is more accurate, and therefore cost is reduced, and working efficiency is improved.

Description

Technical Field

[0001] The invention relates to the field of low wind resistance overhead insulated cables, and in particular to an extrusion process for low wind resistance overhead insulated conductors. Background Art

[0002] The research and development of low-wind resistance insulated wires is of great significance to improving the stability and reliability of distribution network operation and reducing operation and maintenance costs. However, due to the influence of the special-shaped extrusion process of the insulation layer, there are few research results on the extrusion process of low-wind resistance insulated wires at home and abroad, and the research on the extrusion process of low-wind resistance insulated wires is still in its infancy.

[0003] For example, the invention patent with publication number CN118789787A discloses an extruder, which solves the technical problem of heating and softening the crushed material in the preheating section to reduce the gap between the crushed material particles, and when the softened plastic raw material enters the exhaust section, the crushed material is softened and extruded, and the gas in the crushed material is further discharged, which effectively avoids the phenomenon of uneven distribution of components when the raw material is melted, and avoids the generation of bubbles inside the plastic when it is melted, which affects the extrusion quality. The invention patent with publication number CN118789780A and CN118832823A also deals with round cables. Fig.11 As shown, there are few related technologies for extrusion molding of special-shaped cables. Therefore, there is an urgent need for a mold and a corresponding extrusion process to realize the extrusion processing of special-shaped wires to meet industrial needs. Summary of the invention

[0004] Purpose of the invention: To solve the problems of the prior art, the present invention provides an extrusion process for low wind resistance overhead insulated conductors.

[0005] Technical solution: The present invention discloses an extrusion process for low wind resistance overhead insulated conductors, which process includes the following stages:

[0006] Plasticizing stage: The screw of a specific shape in the extruder rotates in the heated barrel to squeeze the plastic sent from the hopper forward, so that the plastic is plasticized evenly and the plastic is changed from a granular solid to a plastic viscous fluid;

[0007] Forming stage: Due to the rotation and pressure of the screw, the viscous fluid is pushed to the die head, and through the semi-extrusion die in the die head, the viscous fluid is formed into extruded materials of various sizes and shapes required for the insulated wire, and is coated on the wire core or conductor; the wire core or conductor passes through the semi-extrusion die;

[0008] Forming stage: After the plastic extruded material is cooled in a cooling water tank or cooling pipe, it changes from an amorphous plastic state to a formed solid state, thereby obtaining an outer protective layer of the insulated wire; the outer protective layer includes an insulating layer and a conductor shielding layer;

[0009] In one embodiment, the semi-extrusion tube mold includes a mold core and a mold sleeve, the mold core sleeve is arranged in the mold sleeve, and the mold sleeve includes an upper connecting column and a lower connecting column. After the upper connecting column and the lower connecting column are connected, they are arranged in the machine head, and the end of the upper connecting column away from the lower connecting column is provided with a hole matching the outer periphery of the insulated wire.

[0010] Further, including:

[0011] The inner periphery of the hole is provided with a plurality of protrusions, the protrusions match the grooves on the outer periphery of the insulating layer, the number of the protrusions matches the number of the grooves on the outer periphery of the conductor, and the Taguchi analysis method is used to verify and adjust the calculated hole structure.

[0012] Further, including:

[0013] The height H and width L of the protrusion are obtained according to the depth d and width s of the groove, and the corresponding calculation formula is:

[0014] H=d*k d ; L = s * k s ; (1)

[0015] Among them, k d is the correction factor corresponding to the groove depth, k s is the correction factor corresponding to the groove width.

[0016] Further, including:

[0017] The grooves are arranged in a circular array on the insulating layer of the insulated wire, and the number of the grooves is 6, 8, 10 or 12. When the wind speed is greater than 25 m / s, the more the number of grooves, the lower the corresponding wind resistance coefficient.

[0018] Further, including:

[0019] The size of the outer circle of the upper connecting column is expressed as:

[0020] T=D+2×TH+φ; (2)

[0021] Wherein, D is the outer diameter of the wire core in the conductor, TH is the extrusion thickness of the viscous fluid in the screw, and φ is an adjustment parameter, and its setting range is 1.0 to 1.5 mm.

[0022] Further, including:

[0023] The method of verifying and adjusting the structural parameters of the hole by using the Taguchi analysis method comprises the following steps:

[0024] S1 sets three groove depth d values, three groove width s values ​​and three chamfer radii R according to the actual groove structure required, and designs 9 combinations based on the L9 orthogonal table of 3 factors and 3 levels in the Taguchi analysis method;

[0025] S2 uses a KSM measuring system to detect the size of the cable structure corresponding to the combination in 9. The KSM measuring system uses a camera connected to a computer to take pictures of the cable structure and measure and analyze relevant parameters of the cable;

[0026] S3 cuts uniform insulation slices from the trial-produced cable, places the insulation slices under the KSM measurement system, observes them and exports projection images;

[0027] S4 imports the exported projection image into the processing software, and the processing software adjusts the projection image to coincide with the current mold image, thereby obtaining the height and width dimensions of the hole structure in the mold, and thereby obtaining the corresponding correction factor according to the height and width of the hole structure.

[0028] Further, including:

[0029] In step S4, the corresponding correction factor is obtained according to the height and width of the hole structure, which specifically includes: obtaining 9 different k based on the data under 9 sizes. d , k s , the final value adopts the corresponding average value.

[0030] Further, including:

[0031] The surface of the insulating layer of the insulated wire is provided with a water drop-shaped structure, which is a circular array of grooves on the surface of the insulating layer. The radius of curvature R of the arcs at both ends of the groove is 2.4 mm, and the depth d of the groove is 1.09 mm.

[0032] Further, including:

[0033] The opening angle of each groove is 30° to 60°. The groove includes a left arc and a right arc opposite to the left arc. The opening angle is an angle formed by the intersection of the tangent of the left arc and the tangent of the right arc.

[0034] Further, including:

[0035] The extruder is set to: use a screw speed of 65.4RPM and a wire drawing speed of 23.3m / min, the average thickness of the insulation layer is 3.4-3.6mm, the deviation is controlled within 0.2mm, and the surface of the insulation layer is smooth and even.

[0036] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0037] The present invention first proposes an extrusion die, which can be installed in an extruder to obtain a special-shaped cable, such as a cable with a groove; the conductor structure of the present invention and the corresponding die structure are closely matched, and the structural parameters of the extrusion die can be directly calculated according to relevant formulas, and workers are no longer required to measure each time. In addition, the present application provides a parameter value adjustment method to make the formula calculation more accurate, thereby not only reducing costs but also improving work efficiency;

[0038] Secondly, the surface of the insulating layer of the insulated wire of the present invention is provided with a water drop-shaped structure, which is a groove in a circular array on the surface of the insulating layer. The radius of curvature of the arcs at both ends of the groove is 2.4 mm, the depth of the groove is 1.09 mm, and the number of the grooves in the circular array on the surface of the insulating layer is 12. Therefore, the opening angle of the groove is 30°, and the wind resistance is far better than that of the existing insulated cables on the market. By specially setting the surface structural parameters of the insulating layer, the optimal structural state is achieved, so that the wind resistance coefficient of 0.75 can be achieved;

[0039] Then, in order to minimize the impact of shrinkage during cooling on the structure, the extrusion process of the present invention uses a low-shrinkage two-step silane cross-linked polyethylene material during product trial production. A small amount of polypropylene is added to the formula of this material to delay the crystallization of polyethylene, thereby reducing the shrinkage of the material during cooling.

[0040] Finally, the dimensions of the relevant parameters of the mold sleeve of the present invention can be directly calculated through the wire core and the extrusion thickness, and manual measurement is no longer required. The mold design is convenient. In order to prevent the materials of the raised part from squeezing each other during expansion rather than expanding outward uniformly, causing the protrusion to become shallower and narrower, the raised structure is enlarged in proportion during mold design, that is, the curvature remains unchanged and the depth is deepened, so that the obtained wire is more in line with the actual size requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a flow chart of the extrusion process stages described in an embodiment of the present invention;

[0042] Figure 2 Schematic diagram of the types of extrusion dies and their corresponding structures, where (a) is a tube extrusion die, (b) is an extrusion die, and (c) is a semi-tube extrusion die;

[0043] Figure 3 A schematic diagram of temperature control of various regions of an extruder according to an embodiment of the present invention;

[0044] Figure 4 A schematic diagram of a wire structure according to an embodiment of the present invention;

[0045] Figure 5 A schematic diagram of parameters corresponding to the groove structure described in an embodiment of the present invention;

[0046] Figure 6 A schematic diagram of parameter combination in the Taguchi analysis method according to an embodiment of the present invention;

[0047] Figure 7 A schematic diagram of observing the insulation appearance through the KSM measurement system according to an embodiment of the present invention;

[0048] Figure 8 This is a schematic diagram of comparing the insulation appearance and the mold shape using CAD according to an embodiment of the present invention;

[0049] Fig. 9 A comparison of the differences between the design parameters of the extrusion die described in the embodiment of the present invention and the parameters of the produced low wind pressure insulated wire;

[0050] Fig.10 is a schematic diagram of holes corresponding to the mold sleeve after the parameters are adjusted according to an embodiment of the present invention;

[0051] Fig.11 It is a schematic diagram of the structure of a common round wire in the background technology;

[0052] Fig.12 A schematic diagram of the structure of the golf-like cable of the present invention;

[0053] Fig.13 It is a schematic diagram of the structure of the dune-like cable of the present invention;

[0054] Fig.14 The wind resistance coefficient diagram of the low wind resistance insulated cable in different shapes of the present invention;

[0055] Fig.15 The wind resistance coefficient diagram of the low wind resistance insulated cable with different slot numbers of the present invention;

[0056] Fig.16 The wind resistance coefficient diagram of the low wind resistance insulated cable under different curvature radii of the present invention;

[0057] Fig.17 The wind resistance coefficient diagram of the low wind resistance insulated cable at different groove depths of the present invention;

[0058] Fig.18 This is a wind tunnel test result diagram of the wind resistance performance verification test of the present invention;

[0059] Fig.19 This is a simulation experiment diagram of the low wind resistance insulated cable of the present invention at a wind speed of 10 m / s;

[0060] Fig. 20 This is a simulation experiment diagram of the low wind resistance insulated cable of the present invention at a wind speed of 15 m / s;

[0061] Fig.21This is a simulation experiment diagram of the low wind resistance insulated cable of the present invention at a wind speed of 20 m / s;

[0062] Fig. 22 This is a simulation experiment diagram of the low wind resistance insulated cable of the present invention at a wind speed of 25 m / s;

[0063] Fig.23 This is a simulation experiment diagram of the low wind resistance insulated cable of the present invention at a wind speed of 30 m / s;

[0064] Fig.24 This is a simulation experiment diagram of the low wind resistance insulated cable of the present invention at a wind speed of 35 m / s;

[0065] Fig.25 This is a simulation experiment diagram of the low wind resistance insulated cable of the present invention at a wind speed of 40 m / s;

[0066] Fig.26 This is a simulation experiment diagram of the low wind resistance insulated cable of the present invention at a wind speed of 45 m / s;

[0067] Fig. 27 This is a simulation experiment diagram of the low wind resistance insulated cable of the present invention at a wind speed of 50 m / s;

[0068] Fig.28 It is a structural schematic diagram of the extruder according to an embodiment of the present invention;

[0069] Fig.29 This is a schematic diagram of the extrusion process described in an embodiment of the present invention;

[0070] Fig.30 This is another schematic diagram of the extrusion process described in an embodiment of the present invention. DETAILED DESCRIPTION

[0071] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0072] like Figure 1 As shown, the present invention discloses an extrusion process for low wind resistance overhead insulated conductors, the process comprising the following stages:

[0073] Among them, the main basis of extrusion is the plasticity of plastics. The completion of plastic molding in the extruder is a complex physical process, which includes the process of crushing, melting, plasticizing, exhausting, compacting and finally molding. The basic principle of plastic extrusion:

[0074] A screw with a specific shape rotates in a heated barrel to extrude the plastic sent from the hopper forward, making the plastic evenly plasticized (i.e. melted). The plastic is extruded into continuous plastic layers of various shapes required through a machine head and molds of different shapes, and then extruded onto the conductor or wire core.

[0075] Plasticizing stage: The screw of a specific shape in the extruder rotates in the heated barrel to squeeze the plastic sent from the hopper forward, so that the plastic is plasticized evenly and the plastic is changed from a granular solid to a plastic viscous fluid, such as Fig.29 and Fig.30 shown.

[0076] In this embodiment, if Fig.28 As shown, the extruder includes a head and a barrel which are connected to each other. The head is arranged at the head of the barrel, a screw is arranged in the barrel, a heater is arranged at the outer periphery of the barrel, a hopper is arranged at the tail of the barrel, and an electric motor is also arranged to provide drive, as well as a support and a base plate to support the barrel and other components.

[0077] In this embodiment, selecting a suitable screw speed can control the extrusion thickness and the amount of glue output, and a suitable pulling speed can ensure the thickness of the insulation layer. After multiple verifications, a screw speed of 65.4RPM and a wire-taking pulling speed of 23.3m / min are used, and the average insulation thickness is 3.4-3.6mm, the deviation is controlled within 0.2mm, and the insulation surface is smooth and even.

[0078] like Figure 3 As shown, the temperature of each zone of the extruder is set, and consistent temperature control is maintained in all trial productions. In this embodiment, the barrel of the extruder in this embodiment includes 6 zones, and the temperatures are set to 160 degrees Celsius, 165 degrees Celsius, 170 degrees Celsius, 180 degrees Celsius, 185 degrees Celsius and 190 degrees Celsius respectively. The head includes 4 zones, and the temperatures are set to 205, 205, 215, and 225 respectively.

[0079] Forming stage: Due to the rotation of the screw and the pressure, the viscous fluid is pushed toward the die, and through the semi-extrusion die inside the die, the viscous fluid is formed into extruded materials of various sizes and shapes required for the insulated wire, and is coated on the wire core or conductor; the wire core or conductor passes through the semi-extrusion die.

[0080] In this embodiment, if Figure 2 As shown, the extrusion mold is composed of a mold core and a mold sleeve. The extrusion molds used are classified according to the cooperation between the mold core and the mold sleeve. There are three types, namely, tube extrusion type, extrusion type and semi-extrusion type.

[0081] Since the voltage level of low wind resistance overhead insulated cables is 10kV, the State Grid's bidding documents require that the insulation eccentricity be ≤10%. Large eccentricity will cause uneven voltage distribution, which can easily damage the insulation layer of cables with high voltage levels. Therefore, considering that the tube extrusion die cannot provide the extrusion force required to form structures such as grooves, and the eccentricity of the extrusion die is difficult to control, a semi-tube extrusion die is selected for the production of low wind resistance overhead insulated conductors.

[0082] Forming stage: After the plastic extruded material is cooled in a cooling water tank or cooling pipe, it changes from an amorphous plastic state to a formed solid state, thereby obtaining an outer protective layer of the insulated wire; the outer protective layer includes an insulating layer and a conductor shielding layer.

[0083] Furthermore, in this embodiment, in order to reduce the large eccentricity caused by the material sagging due to gravity, water cooling is used to quickly shape the molten plastic.

[0084] In this embodiment, in order to minimize the impact of shrinkage during cooling on the structure, a low-shrinkage two-step silane cross-linked polyethylene material was selected during product trial production. A small amount of polypropylene was added to the formula of this material to delay the crystallization of polyethylene, thereby reducing the shrinkage of the material during cooling.

[0085] Therefore, the above extruder adopts Φ65+120 machine to produce 10kV rated voltage low wind resistance overhead insulated wire. The cooling water tank of the equipment has 80m, which can better cool the wire core, reduce the shape change and insulation sagging eccentricity difficult to control. In order to better control the insulation eccentricity, an imported SIKORA deflectometer is installed at 8m of the insulation outlet to reduce the insulation eccentricity.

[0086] In this embodiment, the semi-extrusion tube mold includes a mold core and a mold sleeve, the mold core sleeve is arranged in the mold sleeve, and the mold core adopts the mold core of a conventional semi-extrusion tube mold according to the size of the mold core and the mold sleeve. The mold sleeve includes an upper connecting column and a lower connecting column. After the upper connecting column and the lower connecting column are connected, they are arranged in the machine head. The end of the upper connecting column away from the lower connecting column is provided with a hole matching the outer periphery of the insulated wire. The main structure of the hole is the outer periphery shape of the wire. The inner periphery of the hole is provided with a plurality of protrusions, and the protrusions match the grooves on the outer periphery of the insulating layer. The number of the protrusions matches the number of the grooves on the outer periphery of the wire. The Taguchi analysis method is used to verify and adjust the calculated hole structure. That is, the annularly arranged protrusions corresponding to the hole and the part connected thereto form a structure matching the wire.

[0087] The wire structure in this embodiment is as follows Figure 4 In addition, this application also considers Fig.12 , Fig.13 The wire structure shown, Fig.12 , Fig.13 It is a schematic diagram of the structure of the golf-like conductor and the structure of the dune-like cable. Fig.14 It is a diagram of the drag coefficient of low-drag insulated cables in different shapes.

[0088] The structure of the water drop-shaped wire in the present application includes a conductor layer and an outer protective layer, wherein the outer protective layer is wrapped around the outer side of the conductor layer, wherein the conductor layer includes a plurality of aluminum single wires, wherein the outer protective layer includes an insulating layer and a conductor shielding layer, and wherein the surface of the insulating layer is provided with a water drop-shaped structure, such as Figure 4 and Figure 5 As shown, the water drop-like structure is a groove in a circular array on the surface of the insulating layer, the radius of curvature of the arcs at both ends of the groove is 2.4 mm, the depth of the groove is 1.09 mm, the number of the grooves in the circular array on the surface of the insulating layer is 12, and the opening angle of the groove is 30°.

[0089] The conductor layer includes 37 aluminum single wires, the diameter of the aluminum single wire is 2.9 mm, and the cross-sectional area of ​​the conductor layer is 244.39 mm 2 .

[0090] The insulating layer is made of cross-linked polyethylene, the average thickness of the insulating layer is not less than 3.40 mm, the thickness at the thinnest part is not less than 2.96 mm, and the maximum eccentricity is 15%.

[0091] The conductor shielding layer includes a base material and carbon black.

[0092] The conductor shielding layer is a non-metallic layer extruded on the conductor layer. The non-metallic layer has the same potential as the aluminum single wire. The average thickness of the conductor shielding layer is 0.60 mm, and the thinnest thickness is 0.44 mm.

[0093] The matrix material is a cross-linked semi-conductive inner shielding material.

[0094] The low wind resistance cable with fan-shaped outer strands has been found through field tests to reduce its drag coefficient and wind pressure to less than 70% of ordinary cables within the wind speed range of 30 to 60 m / s. Four types of grooved cables are now used as research objects, indicating that within the range of 10 to 20 m / s, the cable wind resistance coefficient increases linearly with the increase of the cable cross-sectional roughness. Within the range of 20 to 60 m / s, the cable wind resistance coefficient is determined by a two-variable quadratic function consisting of the number of cross-sectional grooves and the groove radius.

[0095] The convex arc of the outer single wire of the low-drag cable is changed to a concave arc, and the wind resistance coefficient of the cable is reduced by designing the depth of the concave arc. For insulated cables, the surface shape of the insulation layer can be optimized and designed using the fluid mechanics turbulence theory to effectively reduce wind resistance. At present, due to the influence of the special-shaped extrusion process of the insulation layer, there are few research results on low-drag insulated cables at home and abroad, and the research on low-drag insulated cables is still in its infancy. Therefore, the process of obtaining the best model based on the following experiments is as follows:

[0096] According to the theory of flow around cylinders, the surface of the insulating layer is designed to imitate the golf ball shape, water drop shape, and sand dune shape. The specific analysis steps are as follows:

[0097] The surface structure of the insulation layer is designed for golf-like surface structure, water drop-like structure of free fall motion, and sand dune-like structure. These three types are compared with ordinary insulated cables by CFD simulation. The turbulence model of low wind resistance insulated cable uses Shear Stress Transport k-εModel during CFD simulation, and the finite volume method and SIMPLEC algorithm are used to solve it. The momentum, turbulent kinetic energy k and turbulent dissipation rate ε are all discrete in second-order precision format. The air density and viscosity are both default values, and the cable model size is consistent with the actual size. During the simulation, the wind speed ranges from 10m / s-50m / s, the interval is 5m / s, and the wind deflection angle is 90°. Through CFD simulation, it can be concluded that the wind resistance of low wind resistance insulated cable is better than that of ordinary round cable at wind speeds above 20m / s. Among them, the wind resistance coefficient of water drop-like insulated cable decreases significantly with the increase of wind speed when it is 20m / s~50m / s, which is better than the other three cables.

[0098] ① When there are dimples on the golf-like surface, the dimples promote turbulent transition, and the turbulent boundary layer is less likely to separate, which reduces the low-pressure area behind the ball and reduces the resistance, thus increasing the flying distance of the golf ball.

[0099] ② The water drop-like shape of free fall is a streamlined shape, characterized by a smooth front and a flat rear, which reduces the pressure difference resistance of the object flowing around;

[0100] ③ The stress-bearing parts of the dune-like shape that are subject to large wind resistance will gradually deform and eventually form a shape with minimal wind resistance. The formation of this shape is conducive to the flow of wind, that is, the wind flow resistance is small.

[0101] Then, different groove numbers, groove depths, and curvature radii of the arcs at both ends of the grooves were designed for the teardrop-shaped structure, and the actual objects were made and compared with ordinary round cables in wind tunnel experiments. The cable was made by a frame stranding machine and an extruder, and the wind tunnel experiment was carried out in a low-speed reflux wind tunnel laboratory. The laboratory can generate wind speeds of 0m / s to 60m / s, with a uniform wind field and continuously adjustable wind speed. The wind tunnel experiment wind speed loading interval is 5m / s, the sampling frequency is 1000Hz, the sampling time is 30s, and the cable length is 1m fixed on the bracket. The bracket is equipped with a six-dimensional force balance. The wind resistance of the cable can be obtained based on the force applied to the bracket before and after the experiment. The calculation formula for the wind resistance coefficient of the cable is as follows:

[0102]

[0103] Among them, C d is the wind resistance coefficient of the cable, F D is the resistance of the cable, ρ is the air density, V is the actual wind speed, D is the diameter of the cable, and L is the effective length of the cable.

[0104] Through wind tunnel experiments on cables with different teardrop-shaped structures and ordinary insulated cables, it was found that the radius of curvature of the arcs at both ends of the groove has a greater effect on wind resistance than the depth of the groove. Too deep grooves may even have a negative effect on wind resistance. As for the number of grooves, by comparing the calculated data of different numbers of grooves under the same groove shape, it was found that the number of grooves is negatively correlated with wind resistance.

[0105] The first step is to study the effect of the number of grooves on the wind resistance coefficient of low wind resistance insulated cables. The number of grooves is equal to 360° divided by the opening angle of the cable surface. Due to the limitations of processing technology and installation grip requirements, the number of grooves is generally set to an even number and not more than 12. Therefore, four cable models are designed for comparative analysis, in which the radius of curvature R of the arc at both ends of the groove is 0.6mm, and the groove depth d is 1.2mm. When the number of grooves C is 6, 8, 10, and 12, respectively, the corresponding opening angles are 60°, 45°, 36°, and 30°. As follows Fig.15 The figure shows the cable drag coefficient under different slot numbers. It can be concluded that when the wind speed is greater than 25m / s, the more slots there are, the lower the drag coefficient.

[0106] The second step is to study the effect of the radius of curvature of the arc at both ends of the groove on the wind resistance coefficient of the low wind resistance insulated cable. Due to the limitation of processing technology and the thickness of the outer insulation layer is generally 3mm to 3.4mm, the radius of curvature of the arc at both ends of the groove is generally in the range of 0.6mm to 2mm. Therefore, two cable models are designed for comparative analysis, in which the groove depth d is 1.2mm, the number of grooves C is 12, and the curvature radius R is 0.6mm and 2mm respectively. As follows Fig.16 The figure shows the wind resistance coefficient of the cable under different curvature radii. It can be concluded that the larger the curvature radius, the lower the wind resistance coefficient.

[0107] The third step is to study the effect of groove depth on the wind resistance coefficient of low wind resistance insulated cables. Too deep grooves will reduce the contact surface of the hardware, causing problems with the installation grip. Therefore, when the number of grooves does not exceed 10, the groove depth is generally not more than 1.5mm, and when the number of grooves does not exceed 12, the groove depth is not more than 1.2mm. Therefore, three cable models are designed for comparative analysis, in which the curvature radius R is 2mm, the number of grooves C is 12, and the groove depths d are 1mm, 1.2mm, and 1.5mm respectively. As follows Fig.17 The figure shows the cable drag coefficient at different groove depths. It can be concluded that when the wind speed is less than 30m / s, the smaller the groove depth, the lower the drag coefficient. When the wind speed is greater than 30m / s, the drag coefficient is the smallest when the groove depth is 1.2mm.

[0108] In summary, the curvature radius and the number of grooves of the outer surface structure of the teardrop-shaped insulated cable are inversely proportional to the drag coefficient. At low wind speeds, the groove depth is proportional to the drag coefficient, and at high wind speeds, the drag coefficient is optimal when the groove depth is about 1.2 mm. At the same time, due to the limitations of the outer insulation size, processing technology, installation grip requirements and other conditions, various structural parameters need to be comprehensively considered when developing and selecting low-drag insulated cables.

[0109] Finally, according to the structural parameter design results and the strong wind resistance requirements, eight types of teardrop-shaped low wind resistance insulated cables, R2d1.2C8, R2d1.2C10, R2d1.2C12, R2d1.5C10, R0.6d1.2C8, R0.6d1.2C10, R0.6d1.2C12, and R2.4d1.09C12, were selected for trial production and wind resistance performance verification tests. The wind resistance performance verification test, i.e., wind tunnel test results, are as follows Fig.18 shown.

[0110] Fig.19 , Fig. 20 , Fig.21 , Fig. 22 , Fig.23 , Fig.24 , Fig.25 , Fig.26 and Fig. 27 The simulation test graphs are from 10m / s to 50m / s respectively, and finally the R2.4d1.09C12 type is obtained, that is, the curvature radius is 2.4mm, the groove depth is 1.09mm, the number of grooves is 12, and the opening angle is 30°. At this time, the teardrop-shaped low wind resistance insulated cable has the best strong wind resistance performance, which is 30% higher than that of ordinary insulated cables.

[0111] The insulation layer is made of black cross-linked polyethylene, with an average minimum thickness of 3.40 mm, a minimum thickness of 2.96 mm at the thinnest point, and a maximum eccentricity of 15%. The insulation eccentricity calculation formula is:

[0112]

[0113] The conductor shielding layer is a non-metallic layer extruded on the cable conductor and has the same potential as the conductor. Its average thickness is 0.60mm and the thinnest thickness is 0.44mm. The base material of the conductor shielding layer is a cross-linked semi-conductive inner shielding material, which is usually consistent with the material of the conductor and has a density of 1.2g / cm 3 .

[0114] Based on the above-mentioned wire structure, the height H and width L of the protrusion corresponding to the extrusion die of the present application are obtained according to the depth d and width s of the groove, and the corresponding calculation formula is:

[0115] H=d*k d ; L = s * k s ; (1)

[0116] Among them, k d is the correction factor corresponding to the groove depth, k s is the correction factor corresponding to the groove width.

[0117] Furthermore, in this embodiment, the structural parameters of the hole are verified and adjusted using the Taguchi analysis method, including the following steps:

[0118] S1 sets three groove depth d values, three groove width s values ​​and three chamfer radii R according to the actual groove structure required, and designs 9 combinations based on the L9 orthogonal table of 3 factors and 3 levels in the Taguchi analysis method;

[0119] S2 uses a KSM measuring system to detect the size of the cable structure corresponding to the combination in 9. The KSM measuring system uses a camera connected to a computer to take pictures of the cable structure and measure and analyze relevant parameters of the cable;

[0120] S3 cuts a uniform insulation layer slice from the trial-produced cable, and places the insulation slice under the KSM measurement system to observe and export the projection image; Figure 7 shown.

[0121] S4 imports the exported projection image into processing software, such as CAD software, and the processing software adjusts the projection image to coincide with the current mold image, thereby obtaining the height and width of the hole structure in the mold, and then obtaining the corresponding correction factor according to the height and width of the hole structure, such as Figure 8 shown.

[0122] Further, including:

[0123] In step S4, the corresponding correction factor is obtained according to the height and width of the hole structure, which specifically includes: obtaining 9 different k based on the data under 9 sizes. d , k s , the final value adopts the corresponding average value.

[0124] In this embodiment, the structure of the groove is described by three parameters, namely the groove depth d, the groove width and the chamfer radius R of the groove.

[0125] According to the actual needs of the groove structure, the depth d is planned to be set to three values ​​of 1.5mm, 2.0mm, and 2.5mm, the groove width is planned to be set to three values ​​of 4.0mm, 4.5mm, and 5.0mm, and the chamfer radius R is planned to be set to three values ​​of 1.00mm, 1.25mm, and 1.5mm.

[0126] Furthermore, according to the Taguchi analysis method, L9 (3 3 ) orthogonal array, 9 combinations were designed, such as Figure 6 shown.

[0127] The KSM measuring system is used to detect the cable structure dimensions. The system uses a camera connected to a computer to take pictures and measure and analyze relevant parameters.

[0128] Furthermore, the KSM measuring system is used to detect the cable structure dimensions. The system uses a camera connected to a computer to take pictures and measure and analyze relevant parameters.

[0129] Furthermore, the exported images are imported into CAD, the projection images are adjusted to overlap with the mold images, and quantitative analysis is performed to compare the differences between the design parameters and the actual parameters.

[0130] In the above case, the depth d and width s are approximately 1 / 2 of the die design value due to the extrusion effect, while the arc of the chamfer is relatively uniform and does not differ much from the design value. Therefore, for the design of d and s, the correction factor k is calculated respectively. d and k S , k d =2.0137, k S =1.9899. Therefore, according to the above method, multiply the values ​​of d and s by the corresponding correction factors to obtain the design parameters of the mold. Fig. 9 As shown, it is a schematic diagram comparing the difference between the extrusion die design parameters before parameter adjustment and the actual finished product parameters, that is, comparing the die parameters with the wire insulation outer layer parameters. Fig.10 This is a schematic diagram of the holes of the mold sleeve obtained after parameter adjustment.

[0131] Furthermore, this embodiment also includes:

[0132] The size of the outer circle of the upper connecting column is expressed as:

[0133] T=D+2×TH+φ; (2)

[0134] Wherein, D is the outer diameter of the wire core in the conductor, TH is the extrusion thickness of the viscous fluid in the screw, and φ is an adjustment parameter, and its setting range is 1.0-1.5 mm. Since the extrusion thickness is the thickness of the outer insulating layer, it is multiplied by 2 because the outer diameter of the upper connecting column includes two extrusion thicknesses, that is, the extrusion layer wraps around D, so the extrusion thickness is counted twice. Therefore, in this embodiment, the mold is redesigned for the shape of the target, and the mold after adjustment can produce the insulation layer of the low wind resistance overhead insulated cable of the target shape.

[0135] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Moreover, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0136] Although the preferred embodiments of the present invention have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0137] Obviously, those skilled in the art can make various changes and modifications to the embodiments of the present invention without departing from the spirit and scope of the embodiments of the present invention. Thus, if these modifications and variations of the embodiments of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. An extrusion process for low wind resistance overhead insulated conductors, characterized in that: The process consists of the following stages: Plasticizing stage: The screw of a specific shape in the extruder rotates in the heated barrel to squeeze the plastic sent from the hopper forward, so that the plastic is plasticized evenly and the plastic is changed from a granular solid to a plastic viscous fluid; Forming stage: Due to the rotation and pressure of the screw, the viscous fluid is pushed to the die head, and through the semi-extrusion die in the die head, the viscous fluid is formed into extruded materials of various sizes and shapes required for the insulated wire, and is coated on the wire core or conductor; the wire core or conductor passes through the semi-extrusion die; Forming stage: After the plastic extruded material is cooled in a cooling water tank or cooling pipe, it changes from an amorphous plastic state to a formed solid state, thereby obtaining an outer protective layer of the insulated wire; the outer protective layer includes an insulating layer and a conductor shielding layer; The semi-extrusion tube mold comprises a mold core and a mold sleeve, wherein the mold core sleeve is arranged in the mold sleeve, and the mold sleeve is arranged in the machine head, and one end of the mold sleeve is provided with a hole matching the outer circumference of the insulated wire.

2. The extrusion process of low wind resistance overhead insulated conductor according to claim 1, characterized in that: The inner periphery of the hole is provided with a plurality of protrusions, the protrusions match the grooves on the outer periphery of the insulating layer, the number of the protrusions matches the number of the grooves on the outer periphery of the conductor, and the Taguchi analysis method is used to verify and adjust the calculated hole structure.

3. The extrusion process of low wind resistance overhead insulated conductor according to claim 2, characterized in that: The height H and width L of the protrusion are obtained according to the depth d and width s of the groove, and the corresponding calculation formula is: H=d*k d ;L=s*k s ;(1) Among them, k d is the correction factor corresponding to the groove depth, k s is the correction factor corresponding to the groove width.

4. The extrusion process of low wind resistance overhead insulated conductor according to claim 3, characterized in that: The grooves are arranged in a circular array on the insulating layer of the insulated wire, and the number of the grooves is 6, 8, 10 or 12. When the wind speed is greater than 25 m / s, the more the number of grooves, the lower the corresponding wind resistance coefficient.

5. The extrusion process of low wind resistance overhead insulated conductor according to claim 4, characterized in that: The size of the outer circle of the upper connecting column is expressed as: T=D+2×TH+φ;(2) Wherein, D is the outer diameter of the wire core in the conductor, TH is the extrusion thickness of the viscous fluid in the screw, and φ is an adjustment parameter, and its setting range is 1.0 to 1.5 mm.

6. The extrusion process of low wind resistance overhead insulated conductor according to claim 4, characterized in that: The method of verifying and adjusting the structural parameters of the hole by using the Taguchi analysis method comprises the following steps: S1 sets three groove depth d values, three groove width s values ​​and three chamfer radii R according to the actual groove structure required, and designs 9 combinations based on the L9 orthogonal table of 3 factors and 3 levels in the Taguchi analysis method; S2 uses a KSM measuring system to detect the size of the cable structure corresponding to the combination in 9. The KSM measuring system uses a camera connected to a computer to take pictures of the cable structure and measure and analyze relevant parameters of the cable; S3 cuts uniform insulation slices from the trial-produced cable, places the insulation slices under the KSM measurement system, observes them and exports projection images; S4 imports the exported projection image into the processing software, and the processing software adjusts the projection image to coincide with the current mold image, thereby obtaining the height and width dimensions of the hole structure in the mold, and thereby obtaining the corresponding correction factor according to the height and width of the hole structure.

7. The extrusion process of low wind resistance overhead insulated conductor according to claim 6, characterized in that: In step S4, the corresponding correction factor is obtained according to the height and width of the hole structure, which specifically includes: obtaining 9 different k based on the data under 9 sizes. d , k s , the final value adopts the corresponding average value.

8. The extrusion process of low wind resistance overhead insulated conductor according to claim 2, characterized in that: The surface of the insulating layer of the insulated wire is provided with a water drop-shaped structure, which is a circular array of grooves on the surface of the insulating layer. The radius of curvature R of the arcs at both ends of the groove is 2.4 mm, and the depth d of the groove is 1.09 mm.

9. The extrusion process of low wind resistance overhead insulated conductor according to claim 8, characterized in that: The opening angle of each groove is 30° to 60°. The groove includes a left arc and a right arc opposite to the left arc. The opening angle is an angle formed by the intersection of the tangent of the left arc and the tangent of the right arc.

10. The extrusion process of low wind resistance overhead insulated conductor according to claim 1, characterized in that: The extruder is set to: use a screw speed of 65.4RPM and a wire drawing speed of 23.3m / min, the average thickness of the insulation layer is 3.4-3.6mm, the deviation is controlled within 0.2mm, and the surface of the insulation layer is smooth and even.

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