A method for detecting a break in a superconducting wire

Abstract

The application belongs to the technical field of superconducting material, and discloses a kind of superconducting wire broken wire detection method.The method comprises: after the fracture of superconducting wire, forming fracture, the fracture is composed of convex fracture and concave fracture;Selecting concave fracture, sampling, polishing multiple times, recording the abnormal change of cross section at each time of polishing, obtaining the broken wire process and fracture starting position of superconducting wire.The superconducting wire broken wire detection method provided by the application is used to solve the problem of difficult to find the starting position of broken wire, and can overcome the difficulty of difficult to master the broken wire process and difficult to find the starting position of broken wire.

Description

Technical Field

[0001] This invention belongs to the field of superconducting materials technology and discloses a method for detecting wire breakage in superconducting wires. Background Technology

[0002] Currently, the most widely used superconducting material is low-temperature superconducting wire. Every year, a large number of these wires are used in various fields, including nuclear magnetic resonance imaging (MRI), nuclear magnetic resonance spectrometry (NMR), large particle accelerators and superconducting energy storage systems (SMES), and magnetic confinement fusion devices (Tokamak). Superconducting wires are mainly made from various high-purity metal materials, assembled, extruded, and drawn in multiple stages to form the final wire. Due to the large number of cores and the thin diameter of superconducting wires, the processing is very difficult, and wire breakage is common during drawing or stretching. Analyzing the causes of wire breakage and pinpointing the exact location of the fracture is crucial for the subsequent design and control of key aspects of superconducting material production.

[0003] CN112024622B discloses an apparatus and method for drawing and detecting niobium-tritin (Nb3Sn) superconducting wires. This method utilizes a laser diameter gauge for horizontal and vertical measurements; employs a high-speed camera for 360° imaging and data processing to create real-time images of the wire cross-section; uses a pressure sensor to collect real-time data on the deformation force during wire processing; and uses a high-speed camera and data processing to collect real-time images of the lubricating fluid surface. By analyzing these four parameters in real-time, the plastic deformation during wire processing is assessed, identifying any potential breakage points and enabling online real-time monitoring of wire uniformity to obtain plastic deformation data. However, this method is only applicable to niobium-tritin superconducting wires and lacks universal applicability for different sample specifications and breakage types. Therefore, overcoming the challenges of using complex testing instruments and conditions, and providing a more cost-effective and universally applicable breakage detection method for superconducting wires is of great significance. Summary of the Invention

[0004] The purpose of this invention is to provide a method for detecting wire breakage in superconducting wires, which solves the problem of difficulty in finding the starting point of the breakage and overcomes the difficulties in grasping the breakage process and finding the starting point of the breakage.

[0005] To achieve the above objectives, the present invention provides a method for detecting wire breakage in superconducting wires to meet this need in the art.

[0006] On the one hand, the present invention provides a method for detecting broken superconducting wires, which includes: after the superconducting wire breaks, a fracture surface is formed, wherein the fracture surface is composed of a convex fracture surface and a concave fracture surface;

[0007] Select a concave fracture surface, take a sample, and perform multiple grinding operations. Record any abnormal changes in the cross-section during each grinding operation to obtain the breakage process and fracture initiation location of the superconducting wire.

[0008] During the stretching process, the internal components of superconducting wires are subjected to both compressive and tensile stresses. When a component within the wire breaks, the unstretched portion of that component will not experience tensile stress, but only radial compressive stress and frictional forces from surrounding components to complete its stretching deformation. In multi-core structures, if an internal component breaks or undergoes other uneven deformation, the stress and deformation within the wire become even more uneven, ultimately leading to wire breakage. After fracture, superconducting wires exhibit two types of fracture surfaces: one where the inner components are longer than the outer components (protruding outwards), called a convex fracture; and another where the inner components are shorter than the outer components (concave inwards), called a concave fracture. The interior of the most convex and concave points of these two fracture surfaces marks the starting point of the wire's fracture. Due to the unique structure of superconducting wires, the choice of fracture surface for analysis cannot be arbitrary. When selecting a fracture surface, the concave fracture surface is better suited to preserve the integrity of the internal components during fracture because the area to be tested is located in the internal depression. It is also less likely to be damaged by external impacts. Therefore, the concave fracture surface should be selected for testing during sampling.

[0009] Furthermore, in the superconducting wire breakage detection method provided by the present invention, the multiple grinding processes sequentially include coarse grinding, fine grinding, and final grinding. The single grinding amount of the coarse grinding is 1 to 2 mm, the single grinding amount of the fine grinding is 0.5 to 1 mm, and the single grinding amount of the final grinding is 0.1 to 0.2 mm.

[0010] During the rough grinding process, the complete composite structure cannot be observed on the cross-section. Some sub-components are missing or abnormally deformed. Continued grinding will gradually reveal the complete sub-component structure. This process allows for a large amount of grinding.

[0011] After the rough grinding stage, the morphology and structure of the subcomponents tended to be normal, but some subcomponents still had abnormal deformations inside, requiring repeated grinding through fine grinding. However, this process required reducing the amount of grinding. During the fine grinding process, it could be observed in the cross-section that most of the abnormal deformations were gradually recovering and tending to be normal.

[0012] After rough grinding and fine grinding, the starting position of the fracture can be roughly determined but not precisely located. At this time, the sample needs to be ground for the final time. The amount of grinding must be strictly controlled during this process. After grinding in small amounts and multiple times, the starting position of the fracture can be accurately located.

[0013] Furthermore, in the superconducting wire breakage detection method provided by the present invention, the coarse grinding is performed until a single core wire or a single sub-component in the superconducting wire is missing, while the other core wires or sub-components are in normal shape, then the fine grinding is performed;

[0014] When the area of ​​the single core wire or single sub-component obtained from the coarse grinding is close to the shape of other core wires or sub-components, the final grinding is performed.

[0015] Furthermore, in the superconducting wire breakage detection method provided by the present invention, after the rough grinding or fine grinding is completed, polishing is performed, and metallographic analysis is performed after polishing. The metallographic image obtained from the metallographic analysis is used to determine whether the grinding stage is completed.

[0016] Furthermore, in the superconducting wire breakage detection method provided by the present invention, the thicker the wire diameter at the time of breakage, the longer the sampling length; the sampling length is 20mm to 40mm.

[0017] Furthermore, in the superconducting wire breakage detection method provided by the present invention, during the multiple polishing process, the upper and lower surfaces of the sample obtained by sampling are parallel.

[0018] Compared with the prior art, the technical solution provided by the present invention has the following beneficial effects or advantages:

[0019] The technical solution provided by this invention has low requirements for instruments and equipment. It does not require professional testing instruments or a strict testing environment. It can accurately locate the broken wire position through simple metallographic analysis, saving testing costs and having high detection efficiency. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the fracture surface of an NbTi type superconducting wire.

[0022] Figure 2 This is a metallographic image of the fracture surface after rough grinding.

[0023] Figure 3 This is a metallographic image of the fracture surface after fine grinding.

[0024] Figure 4 This is a metallographic diagram of the fracture surface after final grinding. Detailed Implementation

[0025] The technical solution of the present invention will be described below with reference to the embodiments. However, the present invention is not limited to the following embodiments.

[0026] Unless otherwise specified, the experimental and detection methods described in the following embodiments are conventional methods; unless otherwise specified, the reagents and materials are commercially available.

[0027] Example 1

[0028] This embodiment provides a process for detecting wire breakage in NbTi type superconducting wires.

[0029] Step 1: Count the number of breaks in this NbTi superconducting wire. A total of 3 breaks were recorded, and 6 fracture surfaces were collected, including 3 concave fracture surfaces and 3 convex fracture surfaces. Since the concave fracture surface better preserves the state at the time of fracture and is not damaged by external impacts, one φ1.60mm concave fracture surface was selected for grinding and testing. Figure 1 As shown;

[0030] Step 2: Prepare metallographic samples from the collected concave fracture surfaces. First, cut a 20mm length of sample from the concave fracture end and mount it to the appropriate size using a mounting machine. Begin rough grinding from one side of the fracture. Grind 1.5mm at a time during the rough grinding stage, ensuring the upper and lower surfaces of the mounted sample are parallel. Use different types of sandpaper for grinding, then polish. The polished sample is ready for metallographic analysis. Analysis of the metallographic image after one grinding stage revealed severe abnormal deformation in the cross-section and a large number of missing core wires, making it impossible to determine the fracture initiation point; further grinding was required. After three grinding stages, some core wires appeared on the cross-section, with only a few showing abnormal deformation. After six rough grinding stages, with a total grinding amount of approximately 9mm, the abnormal deformation on the cross-section weakened, with only a single missing core wire remaining; the remaining core wires were in normal shape. The rough grinding stage was complete. Figure 2 This is a metallographic image of the fracture surface after rough grinding.

[0031] Step 3: After rough grinding, fine grinding of the sample will be performed. At this point, only a single core wire in the wire cross-section shows abnormal deformation. Further grinding requires reducing the amount of material removed per pass. In the first pass of fine grinding, the amount removed is 1mm. The metallographic image shows the missing core wire beginning to appear, but its area is smaller compared to other core wires. Grinding continues, and with each pass, the area of ​​this core wire gradually increases. After four passes of fine grinding, with a removal amount of approximately 4mm, the abnormal core wire's shape and size are similar to the surrounding core wires but slightly smaller. At this point, the fine grinding stage can be ended. Figure 3 This is a metallographic image of the fracture surface after fine grinding.

[0032] Step 4: After completing the fine grinding stage, only one core wire on the wire cross-section differs from the others. At this point, the grinding amount needs to be even smaller, about 1mm each time. After three grinding passes, the metallographic image of the cross-section shows that the abnormally deformed core wire has returned to normal. This indicates that this core wire is the starting point of the wire breakage, approximately 15mm from the break location. The breakage also started from this point. Figure 4 This is a metallographic diagram of the fracture surface after final grinding.

[0033] Example 2

[0034] This embodiment provides a process for detecting wire breakage in Nb3Sn type superconducting wires.

[0035] Step 1: Count the number of breaks in this Nb3Sn type superconducting wire. There were a total of 2 breaks. Four fracture points were collected, including 2 concave fracture points and 2 convex fracture points. One of the concave fracture points with a diameter of 2.76mm was selected for grinding and testing.

[0036] Step 2: Prepare metallographic samples from the collected concave fracture surfaces. First, cut a 25mm long sample from the concave fracture end and mount it to the appropriate size using a mounting machine. Begin rough grinding from one side of the fracture. Each rough grinding step involves 1mm to 1.5mm of grinding. During grinding, ensure the upper and lower surfaces of the mounted sample are parallel. Use different types of sandpaper for grinding, then polish. The polished sample is ready for metallographic analysis. Analysis of the metallographic image after one grinding step revealed severe abnormal deformation in most sub-components of the cross-section, making it impossible to determine the fracture initiation point; further grinding is required. After four grinding steps, some sub-components on the cross-section returned to normal shape, with only a few showing abnormal deformation. After seven rough grinding steps, with a total grinding amount of approximately 9.6mm, most sub-components on the cross-section returned to normal, with only three sub-components exhibiting abnormal morphology. After nine grinding steps, with a total grinding amount of approximately 11mm, only one sub-component showed abnormal morphology, and all surrounding sub-components returned to normal. At this point, the rough grinding stage is complete.

[0037] Step 3: After rough grinding, fine grinding of the sample will be carried out. At this time, only a single sub-component in the wire cross-section has abnormal deformation. Further grinding requires reducing the amount of grinding per pass. In the first pass of fine grinding, the grinding amount is 0.8mm-1mm. Metallographic images show that inside the abnormal sub-component, some core wires are missing and some core wires are abnormally deformed. Continue grinding. After each pass, the missing core wires gradually appear and their shape returns to normal. After 5 passes of fine grinding, when the grinding amount is about 4mm, only 1 core wire is found to be abnormally deformed. At this point, the fine grinding stage ends.

[0038] Step 4: After completing the fine grinding stage, there is only one core wire on the cross-section of the wire that differs from the other core wires. The area is small, so the amount of grinding needs to be even smaller, about 0.5mm-1mm each time. After three grindings, the cross-sectional metallographic image shows that the area of ​​the abnormally deformed core wire gradually increases and returns to the same shape as the surrounding core wires. It can be determined that this core wire is the starting point of the wire breakage, about 16.5mm away from the breakage location.

[0039] In summary, the technical method for detecting the breakage process of superconducting wires provided by this invention can overcome the problems of different sample specifications and types, and is applicable to the breakage detection of most multi-core wires. It overcomes the difficulties of using complex testing instruments and testing conditions, and can be completed through a simple metallographic polishing method, which is low in cost and high in efficiency.

[0040] As described above, the basic principles, main features, and advantages of the present invention have been well described. The above embodiments and specifications are merely descriptions of preferred embodiments of the present invention, and the present invention is not limited to the above embodiments. Various changes and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit and scope of the present invention should fall within the protection scope defined by the present invention.

Claims

1. A method for detecting wire breakage in superconducting wires, characterized in that, include: When a superconducting wire breaks, a fracture surface is formed, which consists of a convex fracture surface and a concave fracture surface. Select a concave fracture surface, take a sample, and perform multiple grinding operations. Record the abnormal changes in the cross-section after each grinding operation to obtain the breakage process and fracture initiation location of the superconducting wire. The multiple polishing processes sequentially include coarse polishing, fine polishing, and final polishing. The single polishing amount for coarse polishing is 1~2mm, the single polishing amount for fine polishing is 0.5~1mm, and the single polishing amount for final polishing is 0.1~0.2mm. If the coarse grinding is performed until a single core wire or a single sub-component in the superconducting wire is missing, while the other core wires or sub-components are in normal shape, then the fine grinding is performed. When the area of ​​the single core wire or single sub-component obtained from the coarse grinding is close to the area of ​​other core wires or sub-components, the final grinding is performed.

2. The method for detecting broken wires in superconducting wires according to claim 1, characterized in that, After the coarse grinding or fine grinding is completed, polishing is performed. After polishing, metallographic analysis is performed, and the metallographic image obtained from the metallographic analysis is used to determine whether the current grinding stage is completed.

3. The method for detecting broken wires in superconducting wires according to claim 1, characterized in that, The thicker the wire diameter at break, the longer the sampling length; the sampling length is 20mm~40mm.

4. The method for detecting broken wires in superconducting wires according to claim 1, characterized in that, During the multiple polishing processes, the upper and lower surfaces of the sample obtained from the sampling are parallel.

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