CN114974724A - Preparation method of NbTi superconducting wire for liquid-helium-free superconducting magnet - Google Patents
Preparation method of NbTi superconducting wire for liquid-helium-free superconducting magnet Download PDFInfo
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Abstract
The invention relates to a preparation method of an NbTi superconducting wire for a liquid-helium-free superconducting magnet, which comprises the following steps: processing an oxygen-free copper single-core ingot sheath and an oxygen-free copper composite sheath; uniformly wrapping the Nb barrier layer around the NbTi ingot, placing the NbTi ingot into an oxygen-free copper single-core ingot sheath, performing vacuum electron beam welding to obtain an NbTi single-core ingot, and performing superconducting induction heating on the NbTi single-core ingot to obtain an NbTi single-core rod; uniformly arranging a plurality of NbTi single core rods and oxygen-free copper rods with the same specification in an oxygen-free copper composite sheath, performing vacuum electron beam welding to obtain an NbTi composite ingot, performing superconducting induction heating on the NbTi composite ingot, and performing reverse extrusion to obtain an NbTi composite rod; obtaining an NbTi composite bare wire by adopting a mode of combining horizontal stretching and vertical stretching on the NbTi composite rod; the NbTi composite bare wire is insulated by painting to obtain the NbTi superconducting wire used for the liquid-free helium magnet. The method is optimized in the aspects of raw materials, design, processing technology and enamelled insulation, and the self heat-conducting performance of the superconducting wire is greatly improved.
Description
Technical Field
The invention belongs to the technical field of superconducting materials, and relates to a preparation method of an NbTi superconducting wire for a liquid-helium-free superconducting magnet.
Background
With the increasing global medical level, the installation popularity of Magnetic Resonance Imaging (MRI) devices has also expanded from developed countries to developing countries. The country also begins to develop from provincial meeting, city and county level cities to county and county level cities. For a conventional 1.5T (tesla, magnetic field unit) MRI apparatus, its superconducting magnet must be immersed in a 2000 liter liquid helium environment for operation, and liquid helium is a scarce strategic resource, basically depending on import. On the other hand, the price of liquid helium per liter is hundreds of RMB, the cost pressure of the hospital is high due to the regular maintenance and supplement of the liquid helium, and the normal detection and treatment of the hospital are influenced in the maintenance process. Therefore, various large MRI research and development and manufacturing enterprises begin research and development work of liquid-helium-free superconducting magnets from the comprehensive consideration of multiple factors such as customer use requirements and cost reduction.
One of the biggest difficulties in developing a superconducting magnet without liquid helium is the problem of heat conduction of the superconducting coil, which also puts more strict requirements on the preparation of the superconducting wire. For a conventional Wire In Channel (WIC) NbTi superconducting Wire, the following factors are considered: 1. the copper ratio of the wire is larger than that of the common wire, and the corresponding wire has larger volume when the same current carrying is realized, so the liquid helium amount required during cooling and heat dissipation is larger; 2. the polyester yarn is adopted for weaving insulation, the thickness is thicker, the compactness is general, and the heat conduction between turns and layers of the wire rod is not facilitated. The lack of thermal conductivity of conventional WIC superconducting wires therefore limits their mass application in the field of liquid helium free magnets. For conventional NbTi painted wires, the following are considered: 1. the wire NbTi core wires are generally uniformly distributed from inside to outside, and particularly the core wires in the central area are relatively hindered in heat dissipation and heat transmission. 2. The wire rod generally adopts an NbTi single core rod with a copper ratio of 0.5, so that a copper layer around a single NbTi core wire is thin, a heat transmission channel is relatively narrow, and the rapid transmission of heat is not facilitated. 3. Lacquered insulation of superconducting wires generally uses conventional acetal lacquers, the excellent insulation at low temperatures also meaning relatively poor thermal conductivity. In view of the above, it is very important to develop an NbTi superconducting wire for a liquid helium-free superconducting magnet.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a preparation method of an NbTi superconducting wire for a liquid-helium-free superconducting magnet, which is optimized in the aspects of raw materials, design, processing technology, enamelled insulation and the like, so that the heat-conducting property of the superconducting wire is greatly improved. The NbTi superconducting wire processed by the process has excellent heat-conducting property at low temperature and high production efficiency, can be customized and designed according to the batch requirements of customers, and can meet the special requirements of different customers on the superconducting wire for the liquid-helium-free magnet.
In order to achieve the purpose, the invention adopts the following technical scheme:
a preparation method of an NbTi superconducting wire for a liquid-helium-free superconducting magnet is characterized by comprising the following steps of:
s1, processing the oxygen-free copper single-core ingot sheath and the upper and lower covers matched with the two ends of the sheath, and processing the oxygen-free copper composite sheath and the upper and lower covers matched with the two ends of the sheath;
s2, uniformly wrapping the Nb barrier layer around the NbTi ingot, placing the NbTi ingot into an oxygen-free copper single-core ingot sheath, matching the two ends of the oxygen-free copper single-core ingot sheath with a sleeve and a lower cover, performing vacuum electron beam welding to obtain an NbTi single-core ingot, performing superconducting induction heating on the NbTi single-core ingot, and performing reverse extrusion on the NbTi single-core ingot after heat preservation is finished to obtain an NbTi single-core rod;
s3, uniformly arranging a plurality of NbTi single core rods and oxygen-free copper rods with the same specification in an oxygen-free copper composite sheath, wherein the plurality of NbTi single core rods are arranged inwards from the outermost layer close to the inner wall of the sheath, two ends of the oxygen-free copper composite sheath are provided with an upper cover and a lower cover, vacuum electron beam welding is carried out to obtain an NbTi composite ingot, the NbTi composite ingot is subjected to superconducting induction heating, and the NbTi composite ingot is subjected to reverse extrusion after heat preservation is finished to obtain an NbTi composite rod;
s4, obtaining the NbTi composite bare wire by combining horizontal stretching and vertical stretching of the NbTi composite rod;
s5, adopting a thin-layer multi-coating painting insulation process to the NbTi composite bare wire to finally obtain the NbTi superconducting wire for the liquid-free helium magnet.
Further, the oxygen-free copper single-core ingot sheath and the upper and lower covers matched with the two ends of the sheath are processed in S1, the oxygen-free copper composite sheath and the upper and lower covers matched with the two ends of the sheath are made of 6N-grade high-purity oxygen-free copper raw materials, and the purity requirement is more than 99.9999%.
Further, the thickness of the Nb barrier layer in the S2 is 0.3mm, the diameter of the NbTi ingot is phi 143.2mm, the length is less than or equal to 1200mm, the outer diameter of the oxygen-free copper single-core ingot sheath is phi 250.0mm, the inner diameter is phi 144.5mm, and the copper ratio of the NbTi single-core ingot is 0.9-1.1.
Furthermore, the arrangement of the NbTi single core rods in the S3 is close to the inner wall of the oxygen-free copper composite sheath, so that when the NbTi composite wire is stretched to the phi 1.000mm specification, the shortest distance between the NbTi core wire and the oxygen-free copper shell at the outer side of the wire is less than 25 mu m.
Furthermore, the magnetic induction intensity in the space for carrying out superconducting induction heating on the NbTi single-core ingot in the S2 and the NbTi composite ingot in the S3 is 0.4-0.5T, the induction heating heat preservation temperature is controlled to be 740-760 ℃, and the rotating speed of the NbTi single-core ingot in the heating process is 300 r/min; and carrying out reverse extrusion on the NbTi single-core ingot and the NbTi composite ingot, wherein the speed of the extrusion process is controlled to be 40-60 mm/s.
Furthermore, the number of the NbTi single core rods in the S3 ranges from 36 to 180, and the corresponding copper ratio of the composite ingot ranges from 5 to 7.
Further, when the diameter of the NbTi composite rod is more than phi 10mm in the S4, a mode of horizontally stretching a die is adopted; when the diameter of the NbTi composite rod is less than or equal to phi 10mm, a vertical stretching mode is adopted, and the uniformity of wire deformation is improved in a pressure drawing mode in the vertical stretching.
Further, the painting insulation process of the S5 is carried out through 16-20 mould painting processes, the total thickness of the paint layer is 0.05-0.10 mm, and the overall dimension precision of the painted wire is controlled within +/-0.003 mm.
Further, the painting process in S5 employs a novel filler modified acetal paint.
Compared with the prior art, the invention has the following beneficial effects:
1. the purity of the high-purity oxygen-free copper raw material in the NbTi wire is required, the influence of impurity introduction on the heat conductivity of the wire is avoided from the source of the raw material, the purity of the oxygen-free copper required by the product must reach 6N level, and compared with the conventionally used high-purity oxygen-free copper material, the copper material of 6N level has smaller resistance at low temperature, is more beneficial to heat transmission and strongly ensures the stable operation of the liquid-free helium magnet;
2. according to the invention, the NbTi single-core ingot is assembled by adopting the thick-wall copper pipe, so that sufficient copper layer wrapping is ensured around the NbTi core wire in the finally-formed NbTi single-core rod, an effective channel is provided for heat transmission, thereby avoiding heat accumulation and being beneficial to improving the heat-conducting property of the superconducting wire;
3. the extrusion process adopts a mode of 'superconducting induction heating and reverse extrusion', the superconducting induction heating frequency is extremely low (the heating frequency can reach 5Hz at the lowest), the penetration depth of the corresponding induced current is deep, the superconducting induction heating can be directly heated to the core part of the ingot blank, the temperature difference of the core surface is effectively controlled (controlled within 10 ℃), the heating efficiency of the superconducting ingot blank is greatly improved on the premise of ensuring uniform material heating, no relative motion exists between the ingot blank and the extrusion cylinder in the reverse extrusion mode, therefore, no external friction force exists, the deformation of the extruded product core wire is uniform as a whole, and the yield is high. Compared with the conventional extrusion process, the mode of superconducting induction heating and reverse extrusion has low process cost and high production efficiency, and the most important is that the deformation of the core wire of the wire rod is uniform, so that the stability of the superconducting performance of the wire rod is effectively improved;
4. the composite ingot blank assembly adopts the thin-wall sheath, and the NbTi single-core rods are uniformly distributed near the inner wall of the sheath, so that the NbTi core wires of the finally prepared wire are relatively distributed and are close to the edge of the wire, thereby being beneficial to the heat exchange between the NbTi core wires and the substrate high-purity oxygen-free copper in the superconducting wire and effectively improving the thermal stability of the superconducting wire. Under the process, when the wire rod is stretched to the specification of phi 1.000mm, the minimum distance between the corresponding outermost layer core wire and the sheath copper layer is less than or equal to 25 mu m; under the conventional process, the NbTi single core rods are generally uniformly distributed from the inner layer to the outer layer and are closely arranged, and particularly, under the condition that the heat exchange limitation of the core NbTi single core rods and the NbTi core wires is blocked, the thermal stability between the core wires and the core wires is greatly different;
5. when the specification of the composite wire is less than or equal to phi 10mm, a mode of combining vertical stretching and pressure drawing is adopted, a pressurizing device is used for pressurizing the inside of a drawing die device, lubricating liquid can be strongly attached to the surface of the wire under the action of high pressure, the friction between the wire and a die is greatly reduced, the surface state of the wire after drawing is improved, meanwhile, along with the great reduction of the friction force, the processing rate of the wire in each pass is adjusted and increased, the processing rate is increased to 25-30% from 15% -20%, the wire stretching process is normal after adjustment, and the production stretching efficiency is greatly improved; during vertical drawing, the wire and the die are easier to keep coaxial, so that drawing is smoother, and the roundness and dimensional accuracy of the drawn wire are ensured;
6. according to the invention, a thin-layer multi-coating painting insulation mode is adopted, the painting pass is generally controlled to be 16-20, the total thickness of a paint layer is generally controlled to be 0.05-0.10 mm, the painting pass and the painting amount of each pass can be properly adjusted according to the specification of a product and the required paint film thickness, the size precision of the wire rod is effectively ensured, the painting defect is reduced, the RRR value of the superconducting wire rod is improved, the quench protection of the superconducting wire rod in a liquid helium-free environment is enhanced, and the size fluctuation of the superconducting painted product after insulation can be controlled to be less than +/-0.005 mm; in addition, the painting process adopts novel filler modified acetal paint with both thermal conductivity and low temperature resistance. By adding quantitative modified nano silicon powder filler into the conventional acetal paint, the low-temperature insulation property of a paint film can be ensured, and the thermal conductivity of the acetal paint is improved to 0.4W/(m.K) from 0.2W/(m.K), so that the thermal conductivity of the wire is greatly improved;
7. the invention can be customized according to the batch requirements of customers, and meets the special requirements of different customers on the superconducting wire for the liquid-helium-free magnet.
Other features of the present invention and advantages thereof will become apparent from the following detailed description of exemplary embodiments thereof, which proceeds with reference to the accompanying drawings.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description, serve to explain the principles of the invention.
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without inventive exercise.
FIG. 1 is a sectional view of a 36NbTi composite ingot having a copper ratio of 7 and a core number of 7 according to example 1 of the present invention;
FIG. 2 is a sectional view of an NbTi composite ingot having a copper ratio of 5 and a core number of 180 in example 2 of the present invention.
Detailed Description
Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. When the following description refers to the accompanying drawings, like numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of apparatus consistent with certain aspects of the invention, as detailed in the appended claims.
In order to make those skilled in the art better understand the technical solution of the present invention, the following detailed description of the present invention is provided with reference to the accompanying drawings and examples.
A preparation method of NbTi superconducting wire for a liquid helium-free superconducting magnet is characterized by comprising the following steps:
s1, processing the oxygen-free copper single-core ingot sheath and the upper and lower covers matched with the two ends of the sheath, and processing the oxygen-free copper composite sheath and the upper and lower covers matched with the two ends of the sheath; the oxygen-free copper single-core ingot sheath and the upper cover and the lower cover matched with the oxygen-free copper single-core ingot sheath at two ends are processed, the oxygen-free copper composite sheath and the upper cover and the lower cover matched with the oxygen-free copper composite sheath at two ends adopt high-purity oxygen-free copper raw materials of 6N grade, and the purity requirement of the high-purity oxygen-free copper raw materials is more than 99.9999 percent. The invention requires the purity of high-purity oxygen-free copper raw materials in the NbTi wire rod, and avoids the influence of impurity introduction on the heat conductivity of the wire rod from the source of the raw materials. The purity of the oxygen-free copper required by the product must reach 6N level, and compared with a conventionally used high-purity oxygen-free copper material, the copper material of 6N level has smaller resistance at low temperature, is more favorable for heat transmission, and strongly ensures the stable operation of the liquid-free helium magnet. The outer diameter of the oxygen-free copper single-core ingot sheath is phi 250.0mm, the inner diameter of the oxygen-free copper single-core ingot sheath is phi 144.5mm, the wall thickness of the oxygen-free copper composite ingot sheath is 12-18 mm, the NbTi single-core ingot sheath is assembled by adopting a thick-wall oxygen-free copper single-core ingot sheath, sufficient copper layer wrapping around an NbTi core wire in a finally-formed NbTi single core rod is guaranteed, an effective channel is provided for heat transmission, heat accumulation is avoided, and the heat conducting performance of a superconducting wire rod is improved. The NbTi composite ingot adopts the thin-wall oxygen-free copper composite sheath, and NbTi single-core rods are uniformly distributed near the inner wall of the sheath, so that the finally prepared wire NbTi core wires are relatively distributed and are close to the edge of the wire, heat exchange between the NbTi core wires in the superconducting wire and the substrate high-purity oxygen-free copper is facilitated, and the thermal stability of the superconducting wire is effectively improved. Under the process, when the wire rod is stretched to the specification of phi 1.000mm, the minimum distance between the corresponding outermost layer core wire and the sheath copper layer is less than or equal to 25 mu m. Under the conventional process, the NbTi single core rods are generally uniformly distributed from the inner layer to the outer layer and are closely arranged, and particularly, the heat exchange limit of the core NbTi single core rods and the NbTi core wires is blocked, so that the thermal stability between the core wires is greatly different.
S2, uniformly wrapping the Nb barrier layer around the NbTi ingot, placing the NbTi ingot into an oxygen-free copper single-core ingot sheath, matching the two ends of the oxygen-free copper single-core ingot sheath with a sleeve and a lower cover, performing vacuum electron beam welding to obtain an NbTi single-core ingot, performing superconducting induction heating on the NbTi single-core ingot, and performing reverse extrusion on the NbTi single-core ingot after heat preservation is finished to obtain a hexagonal NbTi single-core rod; the thickness of the Nb barrier layer is 0.3mm, the diameter of the NbTi ingot is phi 143.2mm, the length of the NbTi ingot is 500 mm-1200 mm, and the copper ratio of the NbTi single-core ingot is 0.9-1.1;
the hexagonal NbTi single core rod has thicker copper layer, so that the wrapped NbTi core wire has enough heat transfer area, and when a plurality of NbTi single core rods are assembled in a secondary composite mode, a heat transfer channel between the core wire and the core wire is wider, and the heat transfer inside the core wire is facilitated.
Carrying out superconducting induction heating on the NbTi single-core ingot, wherein the magnetic induction intensity in an induction heating space is 0.4-0.5T, the induction heating heat preservation temperature is controlled at 740-760 ℃, the rotating speed of the NbTi single-core ingot in the heating process is 300r/min, carrying out reverse extrusion on the NbTi single-core ingot, and the speed in the extrusion process is controlled at 40-60 mm/s; the friction force of the backward extrusion is small, which is beneficial to the deformation of the NbTi single-core ingot.
The superconducting induction heating frequency is extremely low, the heating frequency can reach 5Hz at the lowest, the corresponding induced current penetration depth is deep, the superconducting ingot blank can be directly heated to the core part of the ingot blank, the temperature difference of the core surface is effectively controlled, the temperature is controlled within 10 ℃, the superconducting ingot blank heating efficiency is greatly improved on the premise of ensuring the uniform material heating, no relative motion exists between the ingot blank and an extrusion cylinder in a reverse extrusion mode, therefore, no external friction force exists, the deformation of the extruded product core wire is uniform as a whole, and the yield is high.
Compared with the conventional extrusion process, the mode of combining superconducting induction heating and reverse extrusion has low process cost and high production efficiency, and the most important is that the core wire of the wire rod deforms uniformly, so that the stability of the superconducting performance of the wire rod is effectively improved.
S3, uniformly arranging a plurality of NbTi single-core rods and oxygen-free copper rods with the same specification in an oxygen-free copper composite sheath, matching two ends of the oxygen-free copper composite sheath with an upper cover and a lower cover, performing vacuum electron beam welding to obtain an NbTi composite ingot, performing superconducting induction heating on the NbTi composite ingot, and performing reverse extrusion on the NbTi composite ingot after heat preservation to obtain an NbTi composite rod; the NbTi single core rod is arranged in the area of the oxygen-free copper composite sheath closest to the outer layer, so that when the NbTi composite wire is stretched to the required specification of a product, the distance between the NbTi core wire and the oxygen-free copper outside the wire rod is less than 25 mu m.
Because the sheath wall of the oxygen-free copper composite ingot is thin, once the core wire generates heat, the heat can be quickly conducted to the copper matrix, so that the heat is taken away by the circulating refrigeration equipment, and the stability of the wire is improved.
The magnetic induction intensity in the space for carrying out superconducting induction heating on the NbTi composite ingot is 0.4-0.5T, and the induction heating heat preservation temperature is controlled to be 740-760 ℃. The number of the NbTi single core rods is 36-180, and the corresponding composite ingot copper ratio ranges from 0.6-10. The mode that adopts induction heating makes the heating of material more even, and heating efficiency is higher.
S4, obtaining the NbTi composite bare wire by combining horizontal stretching and vertical stretching of the NbTi composite rod; when the diameter of the NbTi composite rod is larger than phi 10mm, a horizontal die stretching mode is adopted; when the diameter of the NbTi composite rod is less than or equal to phi 10mm, a vertical drawing mode is adopted, a pressurizing device is used for pressurizing the inside of a drawing die device, lubricating liquid can be strongly attached to the surface of a wire under the action of high pressure, the friction between the wire and a die is greatly reduced, the surface state of the wire after drawing is improved, simultaneously, along with the great reduction of friction force, the processing rate of each pass of the wire is adjusted and increased, the processing rate is increased to 25-30% from 15% -20%, the drawing process of the wire after adjustment is normal, the production drawing efficiency is greatly improved, the uniformity of deformation of a core wire is improved by adopting a pressure drawing mode in the vertical drawing, the wire and the die are easier to keep a coaxial state, the drawing is smoother, and the roundness and the size precision of the wire after drawing are also ensured.
S5, adopting a thin-layer multi-coating painting insulation process for the NbTi composite bare wire to finally obtain the NbTi superconducting wire for the liquid-free helium magnet; the painting insulation process ensures the uniformity of the wire through 16-20 mould painting processes, the total thickness of the paint layer is 0.05-0.10 mm, the painting passes and the painting amount of each pass can be properly adjusted according to the specification of the product and the required paint film thickness, the size precision of the wire is effectively ensured, the painting defects are reduced, the RRR value of the superconducting wire is improved, and the quench protection of the superconducting wire in a liquid helium-free environment is enhanced. The size fluctuation of the superconducting painting product after insulation can be controlled below +/-0.005 mm. In addition, the painting process adopts novel filler modified acetal paint with both thermal conductivity and low temperature resistance. By adding quantitative modified nano silicon powder filler into the conventional acetal paint, the low-temperature insulation property of a paint film is ensured, and the thermal conductivity of the acetal paint is improved to 0.4W/(m.K) from 0.2W/(m.K), so that the thermal conductivity of the wire is greatly improved.
The following is described with reference to specific process procedures:
example 1:
as shown in fig. 1, the present invention provides a method for preparing an NbTi superconducting wire for a liquid-helium-free superconducting magnet, which comprises the following steps:
s1, processing the oxygen-free copper single-core ingot sheath and the upper and lower covers matched with the two ends of the sheath, and processing the oxygen-free copper composite sheath and the upper and lower covers matched with the two ends of the sheath; the oxygen-free copper single-core ingot sheath and the upper cover and the lower cover matched with the oxygen-free copper single-core ingot sheath at two ends are processed, the oxygen-free copper composite sheath and the upper cover and the lower cover matched with the oxygen-free copper composite sheath at two ends adopt high-purity oxygen-free copper raw materials of 6N grade, and the purity requirement of the high-purity oxygen-free copper raw materials is more than 99.9999 percent.
S2, uniformly wrapping the Nb barrier layer around the NbTi ingot, placing the NbTi ingot into an oxygen-free copper single-core ingot sheath, matching the two ends of the oxygen-free copper single-core ingot sheath with a sleeve and a lower cover, performing vacuum electron beam welding to obtain the NbTi single-core ingot, performing superconducting induction heating on the NbTi single-core ingot, performing reverse extrusion on the NbTi single-core ingot after heat preservation is finished, performing multi-pass cold drawing, and sawing the NbTi single-core ingot into a large copper ratio hexagonal NbTi single core rod with the size of H21.5 x 800 mm; the thickness of the Nb barrier layer is 0.3mm, the diameter of the NbTi ingot is phi 143.2mm, the length of the NbTi ingot is 500mm, the outer diameter of the oxygen-free copper single-core ingot sheath is phi 250.0mm, the inner diameter of the oxygen-free copper single-core ingot sheath is phi 144.5mm, and the copper ratio range of the NbTi single-core ingot is 0.9-1.1;
carrying out superconducting induction heating on the NbTi single-core ingot, wherein the magnetic induction intensity in an induction heating space is 0.4-0.5T, the induction heating heat preservation temperature is controlled at 740-760 ℃, the rotating speed of the NbTi single-core ingot in the heating process is 300r/min, carrying out reverse extrusion on the NbTi single-core ingot, and the speed in the extrusion process is controlled at 40-60 mm/s;
s3, uniformly arranging 36NbTi single core rods and a plurality of oxygen-free copper rods with the same specification in an oxygen-free copper composite sheath, matching two ends of the oxygen-free copper composite sheath with an upper cover and a lower cover, performing vacuum electron beam welding to obtain an NbTi composite ingot, performing superconducting induction heating on the NbTi composite ingot, and performing reverse extrusion on the NbTi composite ingot after heat preservation to obtain the NbTi composite rod;
the NbTi single core rods are arranged in the area, closest to the inner wall, of the oxygen-free copper composite sheath, the oxygen-free copper rods are positioned in the 36NbTi single core rods, and the distance between the NbTi core wire and the oxygen-free copper outside the wire rod is less than 25 micrometers when the NbTi composite wire is stretched to the required specification of a product.
The wall thickness of the oxygen-free copper composite ingot sheath is 12mm, the magnetic induction intensity in an induction heating space for carrying out superconducting induction heating on the NbTi composite ingot is 0.4-0.5T, and the induction heating heat preservation temperature is controlled at 740-760 ℃. The number of the NbTi single core rods is 36, and the corresponding copper ratio of the composite ingot is 7.
S4, obtaining the NbTi composite bare wire by combining horizontal stretching and vertical stretching of the NbTi composite rod; when the diameter of the NbTi composite rod is larger than phi 10mm, a horizontal die stretching mode is adopted, the copper ratio is accurately controlled in the process, and meanwhile, the influence of impurities on the surface after extrusion on subsequent stretching is avoided, so that the surface of the material is scalped, the outer diameter is scalped from phi 61.50mm to phi 60.50mm, the outer diameter is scalped from phi 52.00mm to phi 51.10mm, and the final designed copper ratio is 6.968. In the stretching process, a multi-pass aging heat treatment process is carried out according to the product performance requirement so as to improve the superconducting performance of the NbTi wire; when the diameter of the NbTi composite rod is less than or equal to phi 10mm, a vertical stretching mode is adopted, the uniformity of deformation of the core wire is improved by adopting a pressure drawing mode in the vertical stretching, the average processing amount of each pass is controlled to be 28 percent, and finally, the round wire bare wire with the phi 1.500mm specification is prepared by twisting and final stretching.
S5, adopting a thin-layer multi-coating painting insulation process for the NbTi composite bare wire to finally obtain an NbTi superconducting wire for a liquid-free helium magnet; and after 16 times of repeated painting and baking, the finished wire rod with the specification of phi 1.560mm is finally obtained, the uniformity of the wire rod is ensured by multi-time painting, the total thickness of a paint layer is 0.05-0.10 mm, and the dimensional accuracy of the whole painted wire rod is controlled to be +/-0.003 mm. The novel filler modified acetal paint is adopted in the painting process, so that the thermal conductivity is stronger.
At this point, the final product obtained was sampled and tested, and the critical current Ic at 7.102, 4T, 4.2K was measured at the ingot head to be 825A. The critical current Ic at the tail of the ingot is 841A under the actual copper ratio of 6.913, 4T and 4.2K. The closest distance between the core wire at the outermost layer of the wire rod and the inner wall of the oxygen-free copper pipe is 21 mu m.
Example 2
As shown in fig. 2, the present invention provides a method for preparing an NbTi superconducting wire for a liquid-helium-free superconducting magnet, which comprises the following steps:
s1, processing the oxygen-free copper single-core ingot sheath and the upper and lower covers matched with the two ends of the sheath, and processing the oxygen-free copper composite sheath and the upper and lower covers matched with the two ends of the sheath; the oxygen-free copper single-core ingot sheath and the upper cover and the lower cover matched with the oxygen-free copper single-core ingot sheath at two ends are processed, the oxygen-free copper composite sheath and the upper cover and the lower cover matched with the oxygen-free copper composite sheath at two ends adopt high-purity oxygen-free copper raw materials of 6N grade, and the purity requirement of the high-purity oxygen-free copper raw materials is more than 99.9999 percent.
S2, uniformly wrapping the Nb barrier layer around the NbTi ingot, placing the NbTi ingot into an oxygen-free copper single-core ingot sheath, matching the two ends of the oxygen-free copper single-core ingot sheath with a sleeve and a lower cover, performing vacuum electron beam welding to obtain the NbTi single-core ingot, performing superconducting induction heating on the NbTi single-core ingot, performing reverse extrusion on the NbTi single-core ingot after heat preservation is finished, performing multi-pass cold drawing, and sawing the NbTi single-core ingot into a large copper ratio hexagonal NbTi single core rod with the size of H21.5 x 800 mm; the thickness of the Nb barrier layer is 0.3mm, the diameter of the NbTi ingot is phi 143.2mm, the length of the NbTi ingot is 1200mm, the outer diameter of the oxygen-free copper single-core ingot sheath is phi 250.0mm, the inner diameter of the oxygen-free copper single-core ingot sheath is phi 144.5mm, and the copper ratio range of the NbTi single-core ingot is 0.9-1.1;
carrying out superconducting induction heating on the NbTi single-core ingot, wherein the magnetic induction intensity in an induction heating space is 0.4-0.5T, the induction heating heat preservation temperature is controlled at 740-760 ℃, the rotating speed of the NbTi single-core ingot in the heating process is 300r/min, carrying out reverse extrusion on the NbTi single-core ingot, and the speed in the extrusion process is controlled at 40-60 mm/s;
s3, uniformly arranging 180NbTi single core rods and a plurality of oxygen-free copper rods with the same specification in an oxygen-free copper composite sheath, matching two ends of the oxygen-free copper composite sheath with an upper cover and a lower cover, performing vacuum electron beam welding to obtain an NbTi composite ingot, performing superconducting induction heating on the NbTi composite ingot, and performing reverse extrusion on the NbTi composite ingot after heat preservation to obtain the NbTi composite rod;
the NbTi single core rod is arranged in the area of the oxygen-free copper composite sheath closest to the inner wall, so that when the NbTi composite wire is stretched to the required specification of a product, the distance between the NbTi core wire and the oxygen-free copper outside the wire rod is less than 25 mu m.
The wall thickness of the oxygen-free copper composite ingot sheath is 18 mm. The magnetic induction intensity in an induction heating space for carrying out superconducting induction heating on the NbTi composite ingot is 0.4-0.5T, and the induction heating heat preservation temperature is controlled at 740-760 ℃. The number of the NbTi single core rods is 180, and the corresponding copper ratio of the composite ingot is 5.
S4, obtaining the NbTi composite bare wire by combining horizontal stretching and vertical stretching of the NbTi composite rod; when the diameter of the NbTi composite rod is larger than phi 10mm, a horizontal die stretching mode is adopted, the copper ratio is accurately controlled in the process, and meanwhile, the influence of impurities on the surface after extrusion on subsequent stretching is avoided, so that the surface of the material is scalped, the outer diameter is scalped from phi 61.50mm to phi 60.50mm, the outer diameter is scalped from phi 52.00mm to phi 51.10mm, and the final designed copper ratio is 6.968. In the stretching process, a multi-pass aging heat treatment process is carried out according to the product performance requirement so as to improve the superconducting performance of the NbTi wire; when the diameter of the NbTi composite rod is less than or equal to phi 10mm, a vertical stretching mode is adopted, the uniformity of deformation of the core wire is improved by adopting a pressure drawing mode in the vertical stretching, the average processing amount of each pass is controlled to be 28 percent, and finally, the round wire bare wire with the phi 1.500mm specification is prepared by twisting and final stretching.
S5, flattening the NbTi composite bare wire processed by the S4, and precisely controlling the wire to be processed to 1.23 × 0.78mm by a four-roller mill, wherein 4R angles are controlled to be 0.50 +/-0.10 mm. And painting the flat wire formed by rolling, adopting novel filler modified acetal paint with both heat conductivity and low temperature resistance in the painting process, repeatedly painting and baking for 20 times, wherein the total thickness of a paint layer is 0.05-0.10 mm, the overall size precision of the painted wire is controlled within +/-0.003 mm, and finally obtaining the finished wire with the specification of phi 1.31 x 0.86 mm.
The foregoing are merely exemplary embodiments of the present invention, which enable those skilled in the art to understand or practice the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention.
It is to be understood that the present invention is not limited to what has been described above, and that various modifications and changes may be made without departing from the scope thereof. The scope of the invention is limited only by the appended claims.
Claims (9)
1. A preparation method of NbTi superconducting wire for a liquid helium-free superconducting magnet is characterized by comprising the following steps:
s1, processing the oxygen-free copper single-core ingot sheath and the upper and lower covers matched with the two ends of the sheath, and processing the oxygen-free copper composite sheath and the upper and lower covers matched with the two ends of the sheath;
s2, uniformly wrapping the Nb barrier layer around the NbTi ingot, placing the NbTi ingot into an oxygen-free copper single-core ingot sheath, matching the two ends of the oxygen-free copper single-core ingot sheath with a sleeve and a lower cover, performing vacuum electron beam welding to obtain an NbTi single-core ingot, performing superconducting induction heating on the NbTi single-core ingot, and performing reverse extrusion on the NbTi single-core ingot after heat preservation is finished to obtain an NbTi single-core rod;
s3, uniformly arranging a plurality of NbTi single core rods and oxygen-free copper rods with the same specification in an oxygen-free copper composite sheath, wherein the plurality of NbTi single core rods are arranged inwards from the outermost layer close to the inner wall of the sheath, two ends of the oxygen-free copper composite sheath are provided with an upper cover and a lower cover, vacuum electron beam welding is carried out to obtain an NbTi composite ingot, the NbTi composite ingot is subjected to superconducting induction heating, and the NbTi composite ingot is subjected to reverse extrusion after heat preservation is finished to obtain an NbTi composite rod;
s4, obtaining the NbTi composite bare wire by combining horizontal stretching and vertical stretching of the NbTi composite rod;
s5, adopting a thin-layer multi-coating painting insulation process to the NbTi composite bare wire to finally obtain the NbTi superconducting wire for the liquid-free helium magnet.
2. The method as claimed in claim 1, wherein the step of S1, the oxygen-free copper single core ingot sheath and the upper and lower covers fitted at both ends thereof are processed, the oxygen-free copper composite sheath and the upper and lower covers fitted at both ends thereof are made of high purity oxygen-free copper material of 6N grade, and the purity requirement is more than 99.9999%.
3. The method of claim 1, wherein the thickness of the Nb barrier layer in S2 is 0.3mm, the diameter of the NbTi ingot is phi 143.2mm, the length is less than or equal to 1200mm, the outer diameter of the oxygen-free copper single-core ingot sheath is phi 250.0mm, the inner diameter is phi 144.5mm, and the copper ratio of the NbTi single-core ingot is 0.9-1.1.
4. The method as claimed in claim 1, wherein the NbTi single core rod of S3 is disposed close to the inner wall of the oxygen-free copper composite sheath, so as to ensure that the shortest distance between the NbTi core wire and the oxygen-free copper sheath outside the wire is less than 25 μm when the NbTi composite wire is drawn to Φ 1.000 mm.
5. The method of claim 1, wherein the magnetic induction intensity in the space for superconducting induction heating of the NbTi single-core ingot in S2 and the NbTi composite ingot in S3 is 0.4-0.5T, the induction heating temperature is controlled at 740-760 ℃, and the rotation speed of the NbTi single-core ingot during heating is 300 r/min; and carrying out reverse extrusion on the NbTi single-core ingot and the NbTi composite ingot, wherein the speed of the extrusion process is controlled to be 40-60 mm/s.
6. The method as claimed in claim 1, wherein the number of NbTi single core rods in S3 is 36-180, and the corresponding copper ratio of the composite ingot is 5-7.
7. The method of claim 1, wherein in S4, when the diameter of the NbTi composite rod is greater than Φ 10mm, a die horizontal drawing mode is adopted; when the diameter of the NbTi composite rod is less than or equal to phi 10mm, a vertical stretching mode is adopted, and the uniformity of wire deformation is improved in a pressure drawing mode in the vertical stretching.
8. The method for preparing the NbTi superconducting wire for the liquid helium-free superconducting magnet as claimed in claim 1, wherein the painting insulation process of S5 is performed by 16-20 mould painting processes, the total thickness of the paint layers is 0.05-0.10 mm, and the overall dimensional accuracy of the painted wire is controlled within +/-0.003 mm.
9. The method of claim 1, wherein the step of S5 adopts a novel filler modified acetal paint.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116741460A (en) * | 2023-08-15 | 2023-09-12 | 西安聚能超导线材科技有限公司 | Preparation method of NbTi/Cu superconducting composite wire with ultralow copper ratio |
| CN116759154A (en) * | 2023-08-16 | 2023-09-15 | 西安聚能超导线材科技有限公司 | Preparation method of superconducting wire with short production period and ultra-low copper ratio |
| CN117457283A (en) * | 2023-12-22 | 2024-01-26 | 西安聚能超导线材科技有限公司 | Preparation method of superconducting composite rod, superconducting composite rod and superconducting wire |
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Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116741460A (en) * | 2023-08-15 | 2023-09-12 | 西安聚能超导线材科技有限公司 | Preparation method of NbTi/Cu superconducting composite wire with ultralow copper ratio |
| CN116741460B (en) * | 2023-08-15 | 2023-11-10 | 西安聚能超导线材科技有限公司 | Preparation method of NbTi/Cu superconducting composite wire with ultralow copper ratio |
| CN116759154A (en) * | 2023-08-16 | 2023-09-15 | 西安聚能超导线材科技有限公司 | Preparation method of superconducting wire with short production period and ultra-low copper ratio |
| CN116759154B (en) * | 2023-08-16 | 2023-11-17 | 西安聚能超导线材科技有限公司 | Preparation method of superconducting wire with short production period and ultra-low copper ratio |
| CN117457283A (en) * | 2023-12-22 | 2024-01-26 | 西安聚能超导线材科技有限公司 | Preparation method of superconducting composite rod, superconducting composite rod and superconducting wire |
| CN117457283B (en) * | 2023-12-22 | 2024-04-02 | 西安聚能超导线材科技有限公司 | Preparation method of superconducting composite rod, superconducting composite rod and superconducting wire |
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