Superconducting enameled wire and preparation method thereof

Abstract

The invention belongs to the technical field of superconducting wires, and relates to a superconducting enameled wire and a preparation method thereof. The invention provides a preparation method of a superconducting enameled wire, which comprises the following steps of: coating curing insulating paint on the surface of a superconducting bare wire for multiple times, coating curing hot melting self-adhesive paint for multiple times, and finally preparing a self-adhesive superconducting enameled wire, and heating the self-adhesive superconducting enameled wire under the action of tension and then winding the self-adhesive superconducting enameled wire. The technical problem that the fixing effect and the fixing efficiency are poor when the superconducting wire is wound is solved.

Description

Technical Field

[0001] This invention belongs to the field of superconducting wire technology and relates to a superconducting enameled wire and its preparation method. Background Technology

[0002] Whether it's a superconducting magnet for nuclear magnetic resonance (MRI), an accelerator, or any other type, after the superconducting wire is wound, the superconducting coil must be cured to prevent micro-perturbations that could cause the coil to lose quench when the superconducting magnet operates in low-temperature, high-current, and high-magnetic-field environments. Currently, superconducting wire winding is divided into two methods: dry winding and wet winding. Correspondingly, there are also two types of curing methods. Dry winding typically involves immersing the entire coil in epoxy resin after winding, using vacuum impregnation to achieve a tight bond between turns and layers. This method offers good stability but requires an additional vacuum impregnation process, making it relatively cumbersome and time-consuming. For wet winding, a certain amount of resin is coated onto the wire surface after each turn before winding the next turn. This method can cause pollution to the factory environment. As the resin is wound at high speed to the bobbin, uncured resin splashes around the equipment, causing environmental pollution. Furthermore, to ensure sufficient resin curing, the superconducting coil is typically left to stand for a period after every 3-5 turns to ensure stable bonding between the inner and outer layers. Neither of these methods effectively solves the problem of rapid bonding in superconducting wires. Summary of the Invention

[0003] To overcome the shortcomings of existing technologies, this invention provides a superconducting enameled wire and its preparation method, which simultaneously achieves the solidification and bonding of the coil during the winding process of the superconducting coil. This improves production efficiency while ensuring the bonding strength of the superconducting coil.

[0004] On one hand, the present invention relates to a method for preparing a superconducting enameled wire, which includes: coating a cured insulating varnish onto the surface of a superconducting bare wire in multiple passes, and then coating a cured hot-melt self-adhesive varnish in multiple passes to finally obtain a self-adhesive superconducting enameled wire.

[0005] The self-adhesive superconducting enameled wire is wound under tension after being heated.

[0006] Furthermore, in the method for preparing superconducting enameled wire provided by the present invention, in the multi-pass coating and curing of insulating varnish, the total thickness of the varnish film is 0.05~0.15mm, and the number of passes is 6~12.

[0007] Furthermore, in the method for preparing superconducting enameled wire provided by the present invention, in the multi-pass coating and curing hot-melt self-adhesive varnish, the total thickness of the varnish film is 0.03~0.06mm, and the number of passes is 2~4.

[0008] Furthermore, in the method for preparing superconducting enameled wire provided by the present invention, each time a layer of curing insulating varnish or hot-melt self-adhesive varnish is applied, it is cured by baking after coating, and the curing temperature is independently 200~500℃.

[0009] Furthermore, in the method for preparing superconducting enameled wire provided by the present invention, the tension is 20~150N.

[0010] Furthermore, in the method for preparing superconducting enameled wire provided by the present invention, the length of the wire heated before winding is 40~60cm, and the temperature is 150~350℃.

[0011] Furthermore, in the method for preparing superconducting enameled wire provided by the present invention, the winding speed is 20~60m / min.

[0012] Furthermore, in the method for preparing superconducting enameled wire provided by the present invention, the coefficient of thermal expansion of the hot-melt self-adhesive varnish is 18~19ppm / ℃.

[0013] Furthermore, in the method for preparing superconducting enameled wire provided by the present invention, the solid content of the hot-melt self-adhesive varnish is 20~30wt%, and the viscosity at 25°C is 150~250s.

[0014] On the other hand, the present invention relates to a superconducting enameled wire, which is obtained by the aforementioned method for preparing superconducting enameled wire.

[0015] Compared with the prior art, the technical solution provided by the present invention has at least the following beneficial effects or advantages: (1) The process of winding and curing is integrated, which greatly improves production efficiency. This invention prepares self-adhesive enameled wire by coating the surface of the superconducting bare wire with insulating varnish and hot melt self-adhesive varnish in sequence. The wire can achieve inter-turn bonding by heating during the winding process, which eliminates the independent vacuum impregnation process required by the traditional dry winding method and avoids the long standing time required for resin curing in the wet winding method. Thus, winding and curing are completed simultaneously, which significantly shortens the production cycle and improves the overall efficiency of coil manufacturing.

[0016] (2) Enhanced environmental friendliness and operability of the process. Compared with wet winding, the present invention uses a self-adhesive coating layer that is cured into a film. No additional liquid resin coating is required during wire winding, which completely eliminates the pollution of equipment and environment by resin splashing, improves the working environment, reduces cleaning and maintenance costs, and is more in line with the requirements of green manufacturing.

[0017] (3) Improved uniformity and reliability of coil structure. The self-adhesive varnish melts and bonds during winding heating, achieving tight bonding between turns under tension, forming a coil structure with better overall integrity and more uniform stress distribution. Compared with traditional vacuum impregnation, it avoids the risk of uneven resin penetration or residual air bubbles, which helps to enhance the mechanical stability of the coil under repeated action of low temperature, high magnetic field and electromagnetic force, and reduces the risk of quenching.

[0018] (4) The process is highly adaptable and applicable to various wire specifications. The method described in this invention has wide adaptability to the shape (round wire, flat wire) and size (such as Φ0.1~3.0 mm round wire, 0.5×0.3~5.0×3.0 mm flat wire) of superconducting bare wire. By adjusting parameters such as coating passes, tension, heating temperature and speed, it can flexibly match wires with different copper-to-superconductor ratios (0.6~20.0) and insulation requirements, demonstrating good process versatility and controllability.

[0019] (5) Optimized material matching and interface properties. By limiting the coefficient of thermal expansion of the hot-melt self-adhesive paint (18~19 ppm / ℃), it is better matched with the thermal expansion behavior of superconducting wire (NbTi / Cu composite), reducing the accumulation of thermal stress caused by temperature changes, which helps maintain the adhesion integrity and insulation reliability of the paint layer under low-temperature cycling. At the same time, limiting parameters such as solid content and viscosity of the self-adhesive paint ensures the uniformity of the coating process and the quality of the paint film. Detailed Implementation

[0020] The technical solution of the present invention will be described below with reference to embodiments. However, the present invention is not limited to the following embodiments. Unless otherwise specified, the experimental and detection methods described in each embodiment are conventional methods; the reagents and materials described are commercially available unless otherwise specified. Unless otherwise specified, all percentages in the following embodiments refer to mass percentages. Unless otherwise specified, all proportions in the following embodiments refer to mass ratios.

[0021] The self-adhesive paint used in the following examples is an epoxy self-adhesive paint purchased from "Allentas". Its main components include epoxy resin accelerator, low-temperature curing agent, toughening agent, insulating filler, and diluent. Its solid content is 20-30%, its viscosity is (200±50) s (tested at 25°C using a #4 viscosity cup), and its coefficient of thermal expansion is (18.5±0.5) ppm / °C.

[0022] Example 1 This embodiment provides a specific preparation process for superconducting enameled wire.

[0023] Step 1: The NbTi / Cu superconducting composite ingot is processed through extrusion, drawing, aging heat treatment, twisting, forming and drawing to obtain NbTi / Cu superconducting bare round wire or bare flat wire.

[0024] Step 2: The superconducting bare round / flat wires are subjected to ultrasonic cleaning, annealing, water cooling, and drying in sequence to clean the wire surface and eliminate residual stress inside the wire during the cold working process to a certain extent, so as to obtain a clean, dry superconducting bare wire with moderate hardness.

[0025] Step 3: The bare superconducting wire is passed sequentially through straightening rollers, a varnish tank, and a coating mold to coat the surface with insulating varnish. After coating, the varnish film is cured by baking. During the enameling insulation process, the "varnishing + baking" process needs to be repeated multiple times. Each pass increases the varnish film thickness by micrometers, and the total varnish film thickness is generally between 0.05mm and 0.15mm, resulting in a uniformly coated NbTi enameled superconducting wire.

[0026] Step 4: The NbTi enameled superconducting wire is passed through a self-adhesive varnish tank and a coating mold to achieve self-adhesive varnish coating. After coating, the self-adhesive varnish surface is cured by baking. This process of "self-adhesive varnish coating + curing" generally needs to be repeated 2 to 4 times. The thickness of the self-adhesive varnish is 0.03 to 0.06 mm, and finally self-adhesive NbTi superconducting enameled wire is obtained.

[0027] Step 5: Under a certain tension, the self-adhesive NbTi enameled superconducting wire is tightly wound onto the take-up frame after passing through a heated pipe, ultimately obtaining a stable structure in which the wires adhere to each other.

[0028] Furthermore, the copper-to-superconducting ratio of the superconducting bare round or flat wires mentioned in step one ranges from 0.6 to 20.0, the specifications of the round wires range from Φ0.1mm to Φ3.0mm, and the specifications of the flat wires range from (0.5×0.3)mm to (5.0mm×3.0)mm.

[0029] Furthermore, the temperature of the annealing tube in step two is set between 150 and 400°C. During the wire's travel, the annealing tube is filled with water vapor, which isolates and protects the wire from oxidation at high temperatures. The wire's travel speed is between 5 m / min and 30 m / min.

[0030] Furthermore, the enameled insulation described in step three is generally achieved using different types of insulating varnishes depending on the product's thermal rating and usage requirements. Commonly used varnishes include acetal (Formvar), polyimide (PI), and polyesterimide-polyamide-imide varnish (PEI-PAI). The number of coating coats is generally controlled between 6 and 12, depending on the total film thickness. The baking temperature varies from 200 to 500°C, depending on the coating material.

[0031] Furthermore, the self-adhesive paint described in step four is generally an epoxy-based self-adhesive paint. Depending on actual usage requirements, the self-adhesive paint is typically applied in 2-4 coats, with a thickness generally ranging from 0.02mm to 0.06mm. The baking temperature varies depending on the paint material, generally between 200 and 500℃.

[0032] Furthermore, the tension setting described in step five is generally controlled within the range of 20N to 150N, depending on the copper content and specifications of the wire. The hot air duct length is 50cm, the temperature is generally between 150 and 350℃, and the speed is controlled between 20 and 60m / min, depending on the wire gauge and the thickness of the self-adhesive coating.

[0033] Example 2 This embodiment provides a method for rapid prototyping and insulation of superconducting wires with an insulation specification of Φ1.70mm, including the following steps: Step 1: Prepare NbTi / Cu composite ingots, followed by extrusion and cold drawing. The processing rate of each processing pass is 30%. Four aging heat treatments are performed at intervals during the process. Then, the ingots are twisted and finally processed using a final stretching device to obtain NbTi / Cu composite wires with a specification of Φ1.60mm and a copper super-ratio of 0.8.

[0034] Step 2: Gently place the superconducting NbTi / Cu composite bare wire into an ultrasonic cleaning tank. Use warm water at 50℃±10℃ to ultrasonically clean the wire for at least 1 minute. After cleaning, place the wire into a dryer to remove surface water. After drying, place the wire into a steam annealing tube at an annealing temperature of 280℃±5℃ and a painting speed of 15m / min.

[0035] Step 3: The bare superconducting wire is passed sequentially through straightening rollers, a varnish tank, and a coating mold to coat the wire surface with insulating varnish. After coating, the varnish film is cured by baking. During the enameling insulation process, acetal varnish (Formvar) is used to coat the wire surface. The entire "varnishing + baking" process is repeated 9 times, ultimately yielding a uniformly coated NbTi enameled superconducting wire with a diameter of 1.66 mm. The wire baking temperature is 380℃±5℃.

[0036] Step 4: The NbTi enameled superconducting wire is passed through an epoxy self-adhesive varnish tank (self-adhesive varnish solid content 24%) and a coating mold to achieve self-adhesive varnish coating. After coating, the self-adhesive varnish surface is cured by baking. This process of "self-adhesive varnish coating + curing" is repeated 3 times. The curing temperature is 380℃±5℃ and the self-adhesive varnish thickness is 0.04mm. Finally, a Φ1.70mm self-adhesive NbTi superconducting enameled wire is obtained.

[0037] Step 5: Under a tension of 100N, the Φ1.70mm self-adhesive NbTi enameled superconducting wire is tightly wound onto the take-up frame after passing through the heated pipe. The temperature of the hot air pipe is 240℃±5℃, and the speed of the machine during the winding process is 40m / min.

[0038] The curing degree of the superconducting wire was evaluated by low-temperature excitation test (Dai Guoxi, Wu Beimin, Xin Canjie, et al. Mechanical property test of split superconducting magnet winding and cooling excitation process [J]. Experimental Mechanics, 2025, 40(4):506-514.), and the magnetic field strength was stably reached 1.5T (preset magnetic field target).

[0039] Example 3 This embodiment provides a method for rapid prototyping and insulation of superconducting wires with insulation specifications of (0.76 × 0.56) mm, including the following steps: Step 1: Prepare NbTi / Cu composite ingots, followed by extrusion and cold drawing. The processing rate of each processing pass is 30%. Four aging heat treatments are performed at intervals during the process. Then, the ingots are twisted and processed using a final stretching device and a flat wire rolling device to obtain NbTi / Cu composite wires with specifications of (0.70×0.50) mm and a copper super-ratio of 10.

[0040] Step 2: Gently place the superconducting NbTi / Cu composite bare wire into an ultrasonic cleaning tank. Use warm water at 50℃±10℃ to ultrasonically clean the wire for at least 1 minute. After cleaning, place the wire in a dryer to remove surface water. After drying, place the wire in a steam annealing tube at an annealing temperature of 180℃±5℃ and a painting speed of 25m / min.

[0041] Step 3: The bare superconducting wire is passed sequentially through straightening rollers, a varnish tank, and a coating mold to apply insulating varnish to the wire surface. After coating, the varnish film is cured by baking. During the enameling insulation process, polyesterimide-polyamide-imide varnish (PEI-PAI) is used to coat the wire surface. The entire "varnishing + baking" process is repeated 6 times, ultimately yielding a uniformly coated (0.74 × 0.54) mm NbTi enameled superconducting wire. The wire baking temperature is 240℃ ± 5℃.

[0042] Step 4: The NbTi enameled superconducting wire is passed through an epoxy self-adhesive varnish tank (self-adhesive varnish solid content 24%) and a coating mold to achieve self-adhesive varnish coating. After coating, the self-adhesive varnish surface is cured by baking. This process of "self-adhesive varnish coating + curing" is repeated twice. The curing temperature is 240℃±5℃ and the self-adhesive varnish thickness is 0.02mm. Finally, a (0.76×0.56)mm self-adhesive NbTi superconducting enameled wire is obtained.

[0043] Step 5: Under a tension of 30N, the (0.76×0.56)mm self-adhesive NbTi enameled superconducting wire is tightly wound onto the take-up frame after passing through a heated pipe. The temperature of the hot air pipe is 170℃±5℃, and the speed of the machine during the winding process is 55m / min.

[0044] The curing degree of the superconducting wire was evaluated by low-temperature excitation test (Dai Guoxi, Wu Beimin, Xin Canjie, et al. Mechanical property test of split superconducting magnet winding and cooling excitation process [J]. Experimental Mechanics, 2025, 40(4):506-514.), and the magnetic field strength was stably reached 3.0T (preset magnetic field target).

[0045] Example 4 This embodiment provides a method for rapid prototyping and insulation of superconducting wires with insulation specifications of (4.14 × 2.64) mm, including the following steps: Step 1: Prepare NbTi / Cu composite ingots, followed by extrusion and cold drawing. The processing rate of each processing pass is 30%. Four aging heat treatments are performed at intervals during the process. Then, the ingots are twisted and finally processed using a final stretching device to obtain NbTi / Cu composite wires with specifications of (4.00×2.50) mm and a copper super-ratio of 18.

[0046] Step 2: Gently place the superconducting NbTi / Cu composite bare wire into an ultrasonic cleaning tank. Use warm water at 50℃±10℃ to ultrasonically clean the wire for at least 1 minute. After cleaning, place the wire into a dryer to remove surface water. After drying, place the wire into a steam annealing tube at an annealing temperature of 380℃±5℃ and a painting speed of 8m / min.

[0047] Step 3: The bare superconducting wire is passed sequentially through straightening rollers, a varnish tank, and a coating mold to apply insulating varnish to the wire surface. After coating, the varnish film is cured by baking. During the enameling insulation process, polyesterimide-polyamide-imide varnish (PEI-PAI) is applied to the wire surface in 12 coats, with 6 coats of PEI (inner varnish) and 6 coats of PAI (top varnish), ultimately yielding a uniformly coated (4.08 × 2.58) mm NbTi enameled superconducting wire. The wire baking temperature is 480℃ ± 5℃.

[0048] Step 4: The NbTi enameled superconducting wire was passed through an epoxy self-adhesive varnish tank (self-adhesive varnish solid content 24%) and a coating mold to achieve self-adhesive varnish coating. After coating, the self-adhesive varnish surface was cured by baking. This process of "self-adhesive varnish coating + curing" was repeated 4 times. The curing temperature was 480℃±5℃ and the self-adhesive varnish thickness was 0.06mm. Finally, a (4.14×2.64)mm self-adhesive NbTi superconducting enameled wire was obtained.

[0049] Step 5: Under a tension of 140N, the (4.14×2.64)mm self-adhesive NbTi enameled superconducting wire is tightly wound onto the take-up frame after passing through a heated pipe. The temperature of the hot air pipe is 320℃±5℃, and the speed of the machine during the winding process is 25m / min.

[0050] The curing degree of the superconducting wire was evaluated by low-temperature excitation test (Dai Guoxi, Wu Beimin, Xin Canjie, et al. Mechanical property test of split superconducting magnet winding and cooling excitation process [J]. Experimental Mechanics, 2025, 40(4):506-514.), and the magnetic field strength was stably reached 5.0T (preset magnetic field target).

[0051] Referring to dry winding or wet winding methods, after winding the magnet using self-adhesive varnished wire, the entire magnet or part of the magnet needs to be heated and cured before cooling to achieve the self-adhesive effect. This method generally requires a long heating time to ensure stable curing between turns and layers, which can easily lead to problems such as heating bubbles in the inner layers of the magnet or incomplete curing. Furthermore, the curing effect cannot be effectively determined during the preparation process and can only be confirmed after the magnet excitation results are obtained. Once curing problems occur, they cannot be resolved promptly and effectively, requiring the magnet to be destroyed for analysis. This invention utilizes the superconducting magnet winding process by adding heating tubes to the production line, combining the characteristics of self-adhesive varnish with specific properties (specific coefficient of thermal expansion) to achieve a real-time dynamic adhesion process. Examples 2-4 were verified with 50 batches each, and the pass rate was 100%.

[0052] The embodiments described above are only some, not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely to illustrate preferred embodiments. All other embodiments obtained by those skilled in the art through related deductions and substitutions based on the inventive concept, without inventive effort, are within the scope of protection of the present invention.

Claims

1. A method for producing a superconducting enameled wire, characterized by, The application relates to a self-adhesive superconducting enameled wire. The self-adhesive superconducting enameled wire is wound after heating under tension. The total thickness of the insulating paint film is 0.05-0.15 mm, and the number of coating times is 6-12.

2. The method of making a superconducting enameled wire according to claim 1, characterized in that, The total thickness of the self-adhesive hot-melt enameled paint film is 0.03-0.06 mm, and the number of coating times is 2-4.

3. The method of making a superconducting enameled wire according to claim 1, wherein, The coating is baked after each coating time, and the curing temperature is 200-500 DEG C.

4. The method of making a superconducting enameled wire according to claim 1, characterized in that, The tension is 20-150 N.

5. The method of making a superconducting enameled wire according to claim 1, wherein, The length of the heating before winding is 40-60 cm, and the temperature is 150-350 DEG C.

6. The method of making a superconducting enameled wire according to claim 1, wherein, The winding speed is 20-60 m / min.

7. The method of making a superconducting enameled wire according to claim 1, wherein, The thermal expansion coefficient of the self-adhesive hot-melt enameled paint is 18-19 ppm / DEG C.

8. The method of making a superconducting enameled wire according to claim 1, wherein, The solid content of the self-adhesive hot-melt enameled paint is 20-30 wt%, and the viscosity value at 25 DEG C is 150-250 s.

9. The method of making a superconducting enameled wire according to claim 8, characterized in that, The superconducting enameled wire is prepared by the method.

10. A superconducting enameled wire, characterized by, ​