External multi-conductor coaxial heat tracing band and preparation process thereof
By using a circular heating tape structure and multiple sets of outer conductors, the problem of poor contact of the conductor during longitudinal torsion is solved, achieving stable heating and flexibility, adapting to bending at any angle, and extending service life.
Patent Information
- Application Number
- CN202511831969.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2025-11-07
- Filing Date
- 2025-12-05
- Publication Date
- 2026-03-06
AI Technical Summary
Existing heat tracing cables have a large difference in bending radius between the inner and outer conductors when twisted in the longitudinal direction, which makes them prone to separation, resulting in poor contact and fire risk. They also cannot bend freely 360 degrees.
The heating cable adopts an overall circular structure with an internal central conductor and multiple sets of outer peripheral conductors connected in parallel. It uses high-temperature resistant conductive paint and a high-elasticity insulation layer. The outer peripheral conductors can be bent without obstruction, and the insulation and sheath layers can be bent in any direction. The conductive paint penetrates deep into the gaps for adhesion, and the insulation layer is fixed by locking protrusions and trapezoidal grooves.
It achieves stable contact between conductors, and multiple sets of outer conductors can replace damaged conductors to maintain heating function. It is flexible, adaptable to bending at any angle, and extends service life and stability.
Smart Images
Figure CN121619686A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the technical field of heat tracing cables, specifically to an external multi-conductor coaxial heat tracing cable and its manufacturing process. Background Technology
[0002] Electric heat tracing tape is a device that uses electrical energy to generate heat. It typically consists of a core tape, metal wires, insulating materials, a metal shielding mesh, and an outer sheath. When powered on, the electric heat tracing tape generates heat, which is transferred to the object being heated through heat transfer, thus raising the temperature of the object. Electric heat tracing tape is safe, reliable, and easy to install, and is widely used in various applications requiring heat tracing and insulation. Most existing heat tracing tapes typically have two parallel conductors in their core, with PTC heating material filling the space between them.
[0003] The existing technical solutions mentioned above have the following defects: most of the heat tracing cables are flat or elliptical in shape, and can only be bent and twisted in the horizontal direction. They cannot bend freely in 360 degrees. When twisted in the longitudinal direction, the bending radius of the inner and outer conductors is very different. The conductor is easy to separate from the internal PTC heating material. In the case of poor contact, it is very easy to start a fire. Summary of the Invention
[0004] The purpose of this invention is to provide an external multi-conductor coaxial heat tracing cable and its preparation process.
[0005] To achieve the above objectives, the present invention provides the following technical solution: The device includes a circular heat tracing cable body, a central conductor within the heat tracing cable body, a PTC intermediate resistance layer surrounding the central conductor, a PTC heating layer surrounding the PTC intermediate resistance layer, several equally spaced outer conductors fixedly abutting against the outer edge of the PTC heating layer, an insulating layer fixedly surrounding the outer conductors on the outer edge of the PTC heating layer, a metal shielding mesh surrounding the outer edge of the insulating layer, an outer sheath layer surrounding the outer edge of the metal shielding mesh, and a conductive paint coating on the outer edge of the PTC heating layer to adhere and fix the outer conductors. The outer conductors are circular, strip-shaped, or square, and their structure is either spirally twisted or woven mesh, or a combination of two of these.
[0006] By adopting the above technical solution, all outer conductors are connected to one power pole and the center conductor is connected to the other power pole during use. Current flows through the PTC heating layer for continuous heating. The outer conductors are connected in parallel and do not interfere with each other. Compared with traditional flat heating cables, this type of heating cable has several advantages. First, the PTC heating layer has a uniform texture and heats evenly. Second, because there are multiple sets of outer conductors, the center conductor can be thickened. Therefore, if one outer conductor fails due to accidental damage, the other outer conductors can still work normally. The PTC heating layer is a layered structure that wraps around the center conductor, so the contact area with the outer conductors is large. When the resistance of the PTC heating layer increases due to heat generation, the current will preferentially bypass this link while maintaining normal heating effect. Therefore, the service life and stability are far superior to existing single-conductor heating cables.
[0007] Meanwhile, the intermediate resistance layer of PTC plays a role in adjusting the resistance between the central conductor and the PTC heating layer. The material of the intermediate resistance layer of PTC is basically the same as that of the PTC heating layer, with the addition of carbon powder or silver powder to improve its conductivity. As a transition layer, it ensures that the current can pass smoothly between the central conductor and the PTC heating layer.
[0008] The conductive paint is a high-temperature resistant epoxy resin-based conductive paint with good flexibility and conductivity. It can be FEVE. One type of FEVE can be formulated by weight as follows: 35-55 parts fluororesin, 15-25 parts carbon black, and 35-50 parts solvent. The solvent is one of aromatic hydrocarbons, esters, or ketones. It is baked into shape during use at a baking temperature of 245-250 degrees Celsius. The resistivity of the above conductive paint in liquid state is tested to be 56-58 mΩ. The surface resistivity of the conductive paint after drying is 0.9-1.5 mΩ, the tensile strength is 22-24 MPa, and the breaking strength is 130-150%. The strength and conductivity meet the strength requirements of the heat tracing cable.
[0009] The coating thickness is between 20-40 micrometers, and it can initially fix all the outer conductors as an adhesive during the production process. When the heat tracing cable is subjected to external force and torsional deformation, there will be a tendency for relative displacement between the outer conductors and the PTC heating layer. The conductive paint penetrates into the gaps between the spiral stranded or mesh structure of the outer conductors to form a firm wrap, effectively bonding the two so that they will not have relative displacement and ensuring normal circuit connection. The heat tracing cable is circular in shape, with the outer conductors evenly distributed around the perimeter of the central conductor, and the outer conductors themselves are shaped to bend without obstruction. The insulation layer and sheath layer are made of highly elastic material, so they can be bent and twisted in any direction. In this external outer conductor structure, the conductive paint plays a very significant role. The stranded outer conductors can also have additional tensile ropes set at the center to further improve the overall tensile strength of the heat tracing cable.
[0010] Furthermore, one of the materials of the PTC heating layer can be made of polymer-based PTC materials, including medium-low temperature PTC materials and high-temperature resistant PTC materials. The medium-low temperature PTC material includes the following raw materials in parts by weight: 70-80 parts of polyethylene material, 3-5 parts of toughening agent, 18-20 parts of carbon black, 0.9-1.2 parts of antioxidant and 0.4-0.6 parts of calcium carbonate, 0.2-0.4 parts of crosslinking agent, and 0.3-0.6 parts of zinc oxide. The toughening agent is one or more of POE plastic and EEA plastic. The high-temperature resistant PTC material includes the following raw materials in parts by weight: 80-85 parts of fluoropolymer and 5-15 parts of carbon black. The fluoropolymer is one or more of polytetrafluoroethylene, tetrafluoroethylene-ethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and trifluorochloroethylene-ethylene copolymer.
[0011] By adopting the above technical solutions, the medium and low temperature PTC material can withstand a heating temperature of 140-150℃ and a high temperature of 210℃, while the high temperature PTC material has a heating temperature of 190-210℃ and can withstand a high temperature of 250℃. Among them, the high temperature PTC material uses fluororesin with added carbon black as a conductive modifier to improve conductivity, which is very similar to the material properties of conductive paint, thus resulting in better bonding effect during the bonding process.
[0012] Furthermore, the inner side of the insulating layer is fixedly provided with a number of equally spaced inverted trapezoidal engaging protrusions surrounding the PTC heating layer, and the PTC heating layer is provided with trapezoidal grooves that engage with the engaging protrusions.
[0013] By adopting the above technical solution, the inverted trapezoidal locking protrusion and the trapezoidal groove cooperate and lock together, effectively fixing the insulation layer to the PTC heating layer during the torsion process of the heat tracing cable, allowing the relative displacement of the two during torsion, which further ensures the structural strength while improving the overall flexibility of the heat tracing cable.
[0014] Furthermore, a method for preparing an external multi-conductor coaxial heat tracing cable includes the following steps: S1. Preparation of PTC intermediate resistance layer: Weigh each component of PTC material and add 3-5 parts of carbon powder to the mixer to obtain a mixture of PTC intermediate resistance layer material. S2, Preparation of PTC material: Weigh each component and add it to a mixer to mix and obtain a PTC material mixture; S3. The PTC intermediate resistance layer material mixture is gradually cooled to below the melting temperature by natural cooling, and then the PTC intermediate resistance layer material mixture is extruded by a vacuum extruder to wrap around the outer edge of the central conductor. S4. The PTC material mixture is gradually cooled to below the melting temperature by natural cooling. Then, the PTC material mixture is extruded by a vacuum extruder and wrapped around the outer edge of the PTC middle resistance layer. After solidification, it is naturally cooled to obtain the PTC heating layer. A trapezoidal groove is simultaneously opened when the PTC heating layer is extruded by setting a cutting block at the extruder head. S5. Wait for the PTC heating layer in step S4 to cool and solidify naturally. S6. Attach, wrap, or braid the outer conductor to the PTC heating layer so that the outer conductor contacts the PTC heating layer, then apply conductive paint and dry it at 248℃-250℃ to form the final product. S7. Align the PTC heating layer and the trapezoidal groove and extrude an insulating layer; S8. After the insulation layer has cured and cooled, a sheath layer is extruded onto its surface.
[0015] The vacuum extrusion process is a molding process that uses a negative pressure environment in the extrusion equipment to remove gas from the material. This process uses a screw extruder in conjunction with a vacuum pump to form a pressure reduction zone. Mechanical extrusion promotes the raw material to enter the exhaust section in a thin film state to achieve double degassing. This can effectively eliminate bubble defects caused by residual gas during high-pressure extrusion, resulting in higher quality finished products.
[0016] In summary, the beneficial technical effects of the present invention are as follows: 1. It adopts a center conductor and outer conductors. When one set of outer conductors fails due to accidental damage, the other sets of outer conductors can still work normally, thus ensuring that the heating tape maintains a stable heating function. The outer conductors can be one of stranded or mesh, or a combination of both. The gaps facilitate the penetration of conductive paint for deep bonding, resulting in better bending performance and structural strength. The outer conductors are evenly distributed around the center conductor, and the outer conductors themselves are shaped to bend without obstruction. The insulation layer and sheath layer are made of highly elastic material, so they can be bent and twisted in any direction.
[0017] 2. Because multiple sets of outer conductors are set up in conjunction with the central conductor, the total power limit is larger, and there are more options for adjusting the heating power. The number of outer conductors to be activated can be selected according to actual needs, thereby adjusting the heating power.
[0018] 3. When a heating link in the PTC heating layer shows an increase in resistance due to local aging, the current will preferentially connect to the area next to this link with lower resistivity to establish a new heating link. Compared with traditional heating tapes, the PTC heating layer with a layered structure that wraps around the central conductor has a larger contact area between the central conductor, the outer conductor and the PTC heating layer, and more selectable link areas. This maintains normal heating effect while producing a long service life and stable heating effect.
[0019] 4. The design incorporates interlocking ridges and trapezoidal grooves, which effectively fix the insulation layer to the PTC heating layer during the torsion process of the heat tracing cable, allowing for relative displacement between the two during torsion. This ensures structural strength while improving the overall flexibility of the heat tracing cable. Attached Figure Description
[0020] The accompanying drawings are provided to further illustrate the invention and form part of the specification, but do not constitute a limitation thereof. In the drawings: Figure 1 This is a schematic diagram of the installation of existing heat tracing cables in actual use; Figure 2 This is a diagram illustrating damage to existing heat tracing cables in actual use; Figure 3 This is a schematic diagram of the overall cross-sectional structure of the present invention; Figure 4 This is a schematic diagram of the structure of the central conductor and the outer conductor in this invention; Figure 5 This is a schematic diagram of the spiral-twisted outer edge conductor structure in this invention; Figure 6 This is a schematic diagram of the braided mesh outer conductor structure in this invention; Figure 7 It is an experimental diagram of existing traditional flat wire tracing tape and its bending in all directions. Figure 8 This is an experimental diagram of the overall structure of the heat tracing cable in this invention and its bending in all directions.
[0021] In the diagram, 1 is the center conductor; 2 is the PTC intermediate resistance layer; 3 is the PTC heating layer; 4 is the outer conductor; 5 is the insulation layer; 6 is the metal shielding mesh; 7 is the outer sheath layer; 8 is the conductive paint; 9 is the snap-fit protrusion; and 91 is the trapezoidal groove. Detailed Implementation
[0022] The present invention will be further described in detail below with reference to the accompanying drawings.
[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0024] Please see Figures 3-6 The present invention provides the following technical solution: The system includes a circular heat tracing cable body. Inside the heat tracing cable body is a central conductor 1. A PTC intermediate resistance layer 2 surrounds the central conductor 1. A PTC heating layer 3 surrounds the PTC intermediate resistance layer 2. Several equally spaced outer conductors 4 are fixedly arranged along the outer edge of the PTC heating layer 3. An insulation layer 5 is fixedly arranged around the outer edge of the PTC heating layer 3, enclosing the outer conductors 4. A metal shielding mesh 6 surrounds the outer edge of the insulation layer 5. An outer sheath layer 7 surrounds the outer edge of the metal shielding mesh 6. Conductive paint 8 is coated on the outer edge of the PTC heating layer 3 to adhere and fix the outer conductors 4. The outer conductors 4 are circular, strip-shaped, or square, and their structure is either spirally twisted or woven mesh, or a combination of both. During use, all outer conductors 4 are connected to a power source. One pole, the center conductor 1, is connected to the other pole of the power supply. Current flows through the PTC heating layer 3 for continuous heating. The outer conductors 4 are connected in parallel and do not interfere with each other. Compared with traditional flat heating cables, this type of heating cable has several advantages. First, the PTC heating layer is of uniform texture and heats evenly. Second, because there are multiple sets of outer conductors 4, the center conductor 1 can be thickened. Therefore, if one outer conductor 4 fails due to accidental damage, the other outer conductors 4 can still work normally. The PTC heating layer is a layered structure that wraps around the center conductor 1, so the contact area with the outer conductors 4 is large. When the resistance of the PTC heating layer increases due to heat generation, the current will preferentially bypass this link while maintaining normal heating effect. Therefore, in terms of service life and stability, it is far superior to the existing single conductor structure heating cables.
[0025] Meanwhile, the PTC intermediate resistance layer 2 serves to adjust the resistance between the central conductor 1 and the PTC heating layer 3. The material of the PTC intermediate resistance layer 2 is basically the same as that of the PTC heating layer 3, with additional carbon powder or silver powder added to improve its conductivity. As a transition layer, it ensures that the current can pass smoothly between the central conductor 1 and the PTC heating layer 3.
[0026] Conductive paint 8 is a high-temperature resistant epoxy resin-based conductive paint 8, which has good flexibility and conductivity. It can be FEVE. One of the FEVE components can be formulated by weight as follows: 35-55 parts fluororesin, 15-25 parts carbon black, and 35-50 parts solvent. The solvent is one of aromatic hydrocarbons, esters, or ketones. It is baked into shape during use. The baking temperature is 245-250 degrees Celsius. The resistivity of the above conductive paint 8 in liquid state is 56-58 mΩ. The surface resistivity of the conductive paint 8 after drying is 0.9-1.5 mΩ, the tensile strength is 22-24 MPa, and the breaking strength is 130-150%. The strength and conductivity meet the strength requirements of the heat tracing cable.
[0027] The coating thickness is between 20-40 micrometers, and it can be used as an adhesive to initially fix all the outer conductors 4 during the production process. When the heat tracing cable is subjected to external force and torsion deformation, there will be a tendency for relative displacement between the outer conductors 4 and the PTC heating layer 3. The conductive paint 8 penetrates into the gaps between the spiral stranded structure or mesh structure of the outer conductors 4 to form a firm wrap, effectively bonding the two so that they will not have relative displacement and ensuring the normal connection of the circuit. The heat tracing cable is circular in shape, with the outer conductors 4 evenly distributed around the periphery of the central conductor 1, and the outer conductors 4 themselves are shaped to bend without obstruction. The insulation layer 5 and the sheath layer are made of high elastic material, so they can be bent and twisted in any direction. In this external outer conductor 4 structure, the conductive paint 8 plays a very significant role. The stranded outer conductors 4 can also have an additional tensile rope set at the center to further improve the overall tensile strength of the heat tracing cable.
[0028] One of the available materials for the PTC heating layer 3 is made of polymer-based PTC material, including medium-low temperature PTC material and high-temperature resistant PTC material. The medium-low temperature PTC material includes the following raw materials by weight: 70-80 parts polyethylene material, 5 parts POR / EEA plastic, 18-20 parts carbon black, 0.9-1.2 parts antioxidant, and 0.4-0.6 parts calcium carbonate. The high-temperature resistant PTC material includes the following raw materials by weight: 80-85 parts fluoropolymer and 5-15 parts carbon black. The fluoroplastic is one or more of polytetrafluoroethylene, tetrafluoroethylene-ethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and trifluorochloroethylene-ethylene copolymer. The medium-low temperature PTC material has a heating temperature of 140-150℃ and can withstand a high temperature of 210℃. The high-temperature resistant PTC material has a heating temperature of 190-210℃ and can withstand a high temperature of 250℃.
[0029] The inner side of the insulation layer 5 is fixedly provided with several equally spaced inverted trapezoidal engaging protrusions 9 surrounding the PTC heating layer 3. The PTC heating layer 3 has trapezoidal grooves 91 that cooperate with the engaging protrusions 9. The inverted trapezoidal engaging protrusions 9 and the trapezoidal grooves 91 cooperate with each other to engage, effectively fixing the insulation layer 5 to the PTC heating layer 3 during the torsion process of the heat tracing cable. This allows for relative displacement between the two during torsion, further ensuring the structural strength while improving the overall flexibility of the heat tracing cable.
[0030] A method for preparing an external multi-conductor coaxial heat tracing cable includes the following steps; S1, Preparation of PTC intermediate resistance layer 2: Weigh each component of PTC material, and add 3-5 parts of carbon powder to the mixer to obtain a mixture of PTC intermediate resistance layer 2 materials; S2, Preparation of PTC material: Weigh each component and add it to a mixer to mix and obtain a PTC material mixture; S3. The PTC intermediate resistance layer 2 material mixture is gradually cooled to below the melting temperature by natural cooling, and then the PTC intermediate resistance layer 2 material mixture is extruded by a vacuum extruder to wrap around the outer edge of the central conductor 1. S4. The PTC material mixture is gradually cooled to below the melting temperature by natural cooling. Then, the PTC material mixture is extruded by a vacuum extruder and wrapped around the outer edge of the PTC middle resistance layer 2. After solidification, it is naturally cooled to obtain the PTC heating layer 3. A trapezoidal groove is simultaneously opened when the PTC heating layer 3 is extruded by setting a cutting block at the extruder head. S5. Wait for the PTC heating layer 3 in step S4 to cool and solidify naturally. S6. Attach, wrap or braid the outer conductor 4 to the PTC heating layer 3 so that the outer conductor 4 contacts the PTC heating layer 3, then apply conductive paint 8 and then dry it at 248℃-250℃ to form the product. S7. Align the PTC heating layer 3 and the trapezoidal groove and extrude the insulating layer 5; S8. After the insulation layer 5 has cured and cooled, a sheath layer is extruded onto its surface.
[0031] refer to Figures 7-8 The product of this invention can be bent at any angle while ensuring heating effect. The central conductor 1 will not move relative to the heating element at any angle. It is suitable for installation methods that wrap heated items at any angle. It has good adaptability to various irregular objects and effectively solves the problem of traditional flat wire heating tape being easily twisted and burned. At the same time, it has an all-round passage and multi-angle self-heating.
[0032] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.
[0033] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. An over-the-wire multi-conductor coaxial heat tracing band comprising a generally circular heat tracing band body, characterized in that: The heat tracing band body is internally provided with a center conductor (1), the center conductor (1) is wrapped with a PTC intermediate resistance layer (2), the PTC intermediate resistance layer (2) is wrapped with a PTC heating layer (3), the outer edge of the PTC heating layer (3) is fixedly provided with a plurality of outer edge conductors (4) distributed at equal intervals, and the outer edge of the PTC heating layer (3) is fixedly provided with an insulating layer (5) wrapping the outer edge conductors (4).
2. An external multi-conductor coaxial heat tracing band according to claim 1, characterized in that: The outer edge of the insulating layer (5) is wrapped with a metal shielding net (6), the outer edge of the metal shielding net (6) is wrapped with an outer sheath layer (7), and the outer edge of the PTC heating layer (3) is coated with a conductive paint (8) for adhesively fixing the outer edge conductors (4).
3. An external multi-conductor coaxial tracing band according to claim 2, characterized in that: The outer edge conductors (4) are in one or more of a circular shape, a strip shape and a square shape, and the outer edge conductors (4) are in one or a combination of the other of a spiral twisted shape and a woven mesh shape, and one of the conductive paints (8) is FEVE.
4. An external multi-conductor coaxial heat tracing band according to claim 1, characterized in that: The center conductor (1) and the outer edge conductors (4) are made of one or more of tin-plated copper, nickel-plated copper and silver-plated copper, and the PTC intermediate resistance layer (2) is conductive between the PTC heating layer (3) and the center conductor (1).
5. An external multi-conductor coaxial heat tracing band according to claim 1, characterized in that: The PTC heating layer (3) is a high-molecular-based PTC material, including a low-temperature PTC material and a high-temperature PTC material.
6. An external multi-conductor coaxial tracing band according to claim 5, characterized in that, The low-temperature PTC material includes the following raw materials by weight: 70-80 parts of polyethylene material, 3-5 parts of toughening agent, 18-20 parts of carbon black, 0.9-1.2 parts of antioxidant, 0.4-0.6 parts of calcium carbonate, 0.2-0.4 parts of crosslinking agent, and 0.3-0.6 parts of zinc oxide, wherein the toughening agent is one or more of POE plastic and EEA plastic.
7. An external multi-conductor coaxial tracing band according to claim 6, characterized in that The high-temperature PTC material includes the following raw materials by weight: 80-85 parts of fluorine resin, 5-15 parts of carbon black, and the fluorine plastic is one or more of polytetrafluoroethylene, tetrafluoroethylene-ethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer and trifluorochloroethylene-ethylene copolymer.
8. An external multi-conductor coaxial heat tracing band according to claim 1, characterized in that: The inner side of the insulating layer (5) is fixedly provided with a plurality of equidistantly distributed inverted trapezoidal clamping ribs (9) around the PTC heating layer (3), and the PTC heating layer (3) is provided with trapezoidal grooves (91) matched with the clamping ribs (9).
9. A method of making an external multi-conductor coaxial heat tracing band according to claims 1-5, wherein, The method comprises the following steps: S1, preparation of the PTC intermediate resistance layer (2): weighing each component of the PTC material and additionally adding 3-5 parts of carbon powder into a mixer to obtain a PTC intermediate resistance layer (2) material mixture; S2, preparation of the PTC material: weighing each component and adding it into a mixer to obtain a PTC material mixture; S3, gradually cooling the PTC intermediate resistance layer (2) material mixture to below the melting temperature by natural cooling, and then using a vacuum extruder to extrude the PTC intermediate resistance layer (2) material mixture around the center conductor (1); S4, gradually cool the PTC material mixture below the melting temperature by natural cooling, then use a vacuum extruder to extrude the PTC material mixture to wrap the outer edge of the PTC intermediate resistance layer (2), and after solidification, naturally cool to obtain a PTC heating layer (3), and by setting a cutting block in the extruder extrusion head, open a trapezoidal groove at the same time when the PTC heating layer (3) is extruded and formed; S5, wait for the PTC heating layer (3) to be naturally cooled and formed in step S4; S6, wrap or weave the outer edge conductor (4) to the PTC heating layer (3), so that the outer edge conductor (4) is in contact with the PTC heating layer (3), then coat the conductive paint (8), and then dry and form under the condition of 248-250℃; S7, align the PTC heating layer (3) and the trapezoidal groove to extrude and wrap the insulating layer (5); S8, after the insulating layer (5) is solidified and cooled, extrude and wrap the sheath layer on the surface thereof.