A low-cost internal tin method for assembling Nb3Sn CuNb composite sheaths

Abstract

The present application discloses a low-cost internal tin method Nb 3 The SnCuNb composite sheath assembly method comprises: respectively extruding a first oxygen-free copper rod to obtain an oxygen-free copper tube, an outer oxygen-free copper rod and a square oxygen-free copper rod, wherein the specifications of the outer oxygen-free copper rod and the square oxygen-free copper rod are both smaller than those of the oxygen-free copper rod; stretching the oxygen-free copper tube to obtain an outer square inner circle oxygen-free copper tube; inserting a cleaned Nb rod into the cleaned outer square inner circle oxygen-free copper tube, and closely arranging the Nb rod, the cleaned outer oxygen-free copper rod, the square oxygen-free copper rod and the square oxygen-free copper-zinc rod into the cleaned oxygen-free copper sheath, and filling the gaps generated in the process with a second oxygen-free copper rod to obtain an Nb 3 Sn CuNb composite sheath. The use of drilled porous copper ingots has high drilling processing fees and the porous copper ingots cannot be used, which seriously affects production efficiency and has high costs.

Description

Technical Field

[0001] The present application relates to the technical field of superconducting materials, and in particular to a low-cost internal tin method for assembling a Nb3Sn CuNb composite sheath. Background Art

[0002] Nb3Sn (niobium tin) superconducting wire has a high critical current density and is an important raw material for manufacturing high-field magnets. The internal tin method is one of the main methods for preparing Nb3Sn superconducting wires. At present, the Nb3Sn superconducting wires with the highest performance and the widest application in the world are all prepared by the internal tin method. Among them, the CuNb (copper niobium alloy) composite sheath is usually obtained by drilling, that is, drilling holes in oxygen-free copper ingots according to the design drawings to obtain porous copper ingots, and inserting Nb rods into the porous copper ingots to obtain CuNb composite sheaths.

[0003] At present, the internal tin method Nb3Sn CuNb (niobium tin copper niobium alloy) composite sheath uses drilled porous copper ingots. The drilling processing cost is high, and there is a risk of drilling deviation during the drilling process. The straightness of the drilled holes is also prone to deviation. Once the above problems occur, the porous copper ingot cannot be used, which seriously affects production efficiency and is costly. Summary of the invention

[0004] The embodiment of the present application provides a low-cost internal tin method Nb3Sn CuNb composite sheath assembly method to solve the problems of using drilled porous copper ingots in the prior art, high drilling processing fees, and the inability to use porous copper ingots, which seriously affects production efficiency and is costly.

[0005] On the one hand, the embodiment of the present application provides a low-cost internal tin method Nb3SnCuNb composite sheath assembly method, comprising the following steps:

[0006] Step 1: Extruding the first oxygen-free copper rod to obtain an oxygen-free copper tube, an outer oxygen-free copper rod and a square oxygen-free copper rod, wherein the outer oxygen-free copper rod and the square oxygen-free copper rod are smaller in specifications than the oxygen-free copper rod;

[0007] Step 2: Stretch the oxygen-free copper tube to obtain an oxygen-free copper tube with a square outer surface and a round inner surface, and hone the inner hole to ensure that the inner hole is smooth and free of foreign matter;

[0008] Step 3: inserting the cleaned Nb rod into the cleaned outer square inner circle oxygen-free copper tube, and closely arranging the Nb rod together with the cleaned outer square oxygen-free copper rod, the square oxygen-free copper rod, and the square oxygen-free copper-zinc rod into the cleaned oxygen-free copper sheath, during which the gaps between the Nb rod, the cleaned outer square oxygen-free copper rod, the square oxygen-free copper rod, and the square oxygen-free copper-zinc rod are filled with a second oxygen-free copper rod to obtain a Nb3SnCuNb composite sheath, wherein the specification of the second oxygen-free copper rod is smaller than that of the first oxygen-free copper rod.

[0009] Optionally, the square oxygen-free copper-zinc rod is obtained by stretching the oxygen-free copper-zinc rod, and the specifications of the square oxygen-free copper-zinc rod are smaller than those of the oxygen-free copper-zinc rod, wherein the specifications of the oxygen-free copper-zinc rod are φ[100, 300mm]×[200, 1000mm], its composition includes [0.5, 5]wt% Zn, and the extrusion ratio is [5, 30].

[0010] Optionally, the outer oxygen-free copper rod is an octagonal oxygen-free copper rod.

[0011] Optionally, the method also includes: capping and sealing the two ends of the obtained Nb3Sn CuNb composite sheath, performing extrusion and stretching to obtain a CuNb composite rod, inserting a SnTi alloy rod into the center of the CuNb composite rod through a drilling hole and stretching to obtain subcomponents, bundling the subcomponents into Ta tubes in sequence, and then inserting them into oxygen-free copper tubes to obtain the final Nb3Sn blank of the internal tin method, and obtaining the Nb3Sn composite wire of the internal tin method after multiple stretching passes.

[0012] Optionally, the specification of the first oxygen-free copper rod in step 1 is φ[100, 300 mm]×[200, 1000 mm], and the specification of the oxygen-free copper tube obtained after extrusion is φ[40, 80 mm] / φ[20, 60 mm].

[0013] Optionally, in step 2, the secondary processing rate of the outer square and inner circle oxygen-free copper pipe is [5%, 20%], the specification of the outer square and inner circle oxygen-free copper pipe is H [8, 20mm] / φ[6, 15mm], the honing processing amount is [0.005, 0.01mm], and the surface roughness Ra is [0.05, 0.2μm].

[0014] Optionally, in step 3, the processing rate of the square oxygen-free copper rod is [5%, 20%], and the specification of the square oxygen-free copper rod is H [8, 20mm]; the processing rate of the square oxygen-free copper rod is [5%, 20%], and the specification of the square oxygen-free copper rod is H [3, 9mm]; the processing rate of the oxygen-free copper-zinc rod is [5%, 20%], and the specification of the square oxygen-free copper-zinc rod is H [3, 9mm].

[0015] Optionally, in step 3, the specification of the Nb rod is φ[5.5, 14.5 mm]×[200, 1000 mm] and the specification of the oxygen-free copper sheath is φ[180, 300 mm] / φ[160, 280 mm]×[200, 1000 mm].

[0016] A low-cost internal tin method Nb3Sn CuNb composite sheath assembly method in this application has the following advantages:

[0017] An oxygen-free copper tube with an outer square and an inner circle is obtained by extrusion-stretching-honing. The oxygen-free copper tube with an outer square and an inner circle, the oxygen-free copper rod, the square oxygen-free copper rod and the square oxygen-free copper-zinc rod are used to replace the traditional process of drilling holes in the porous copper ingots in the process of assembling the Nb3Sn CuNb composite sheath by the internal tin method, so that no drilling cost is generated in the process of assembling the Nb3Sn CuNb composite sheath by the internal tin method, and only the cost of extrusion and mechanical processing is generated in the whole process, thereby avoiding the high drilling cost and greatly reducing the processing cost of the Nb3Sn CuNb composite sheath by the internal tin method; the use of octagonal oxygen-free copper rods and oxygen-free copper tubes and the symmetrical assembly greatly increase the filling rate of the CuNb composite sheath and ensure the uniformity of the deformation of the core wire in the subsequent process; the use of the square oxygen-free copper-zinc rod enables the presence of Zn element in the process of heat treatment of the Nb3Sn composite wire by the internal tin method, which can promote the diffusion of the Sn element, so that the wire forms a more uniform Nb3Sn phase and ensures that the wire has stable performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 A schematic diagram of the cross-sectional structure of a CuNb composite sheath in a low-cost internal tin method Nb3Sn CuNb composite sheath assembly method provided in an embodiment of the present application.

[0020] Explanation of the accompanying numbers: 1- oxygen-free copper-zinc rod, 2- Nb rod, 3- outer square and inner round copper tube, 4- octagonal copper rod, 5- square copper rod. DETAILED DESCRIPTION

[0021] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0022] The embodiment of the present application provides a low-cost internal tin method Nb3Sn CuNb composite sheath assembly method, including the following steps. It should be noted that the operation steps of the internal tin method Nb3Sn CuNb composite sheath assembly in this embodiment can be the following steps 1-3, but are not limited to the order of steps 1-3, and the local operation order can be adjusted appropriately. Specifically:

[0023] Step 1: Extruding the first oxygen-free copper rod to obtain an oxygen-free copper tube, an outer oxygen-free copper rod and a square oxygen-free copper rod, wherein the outer oxygen-free copper rod and the square oxygen-free copper rod are smaller in specifications than the oxygen-free copper rod;

[0024] Step 2: Stretch the oxygen-free copper tube to obtain an oxygen-free copper tube with a square outer surface and a round inner surface, and hone the inner hole to ensure that the inner hole is smooth and free of foreign matter;

[0025] Step 3: inserting the cleaned Nb rod into the cleaned outer square inner circle oxygen-free copper tube, and closely arranging the Nb rod together with the cleaned outer square oxygen-free copper rod, the square oxygen-free copper rod, and the square oxygen-free copper-zinc rod into the cleaned oxygen-free copper sheath, during which the gaps between the Nb rod, the cleaned outer square oxygen-free copper rod, the square oxygen-free copper rod, and the square oxygen-free copper-zinc rod are filled with a second oxygen-free copper rod to obtain a Nb3SnCuNb composite sheath, wherein the specification of the second oxygen-free copper rod is smaller than that of the first oxygen-free copper rod.

[0026] Optionally, the square oxygen-free copper-zinc rod is obtained by stretching the oxygen-free copper-zinc rod, and the specifications of the square oxygen-free copper-zinc rod are smaller than those of the oxygen-free copper-zinc rod, wherein the specifications of the oxygen-free copper-zinc rod are φ[100, 300mm]×[200, 1000mm], its composition includes [0.5, 5]wt% Zn, and the extrusion ratio is [5, 30].

[0027] Optionally, the outer oxygen-free copper rod is an octagonal oxygen-free copper rod.

[0028] Optionally, the method also includes: capping and sealing the two ends of the obtained Nb3Sn CuNb composite sheath, performing extrusion and stretching to obtain a CuNb composite rod, drilling a hole in the center of the CuNb composite rod, inserting a SnTi alloy rod and stretching to obtain subcomponents, bundling the subcomponents into Ta tubes in sequence, and then inserting them into oxygen-free copper tubes to obtain the final Nb3Sn blank of the internal tin method, and obtaining the Nb3Sn composite wire of the internal tin method after multiple stretching passes.

[0029] Optionally, the specification of the first oxygen-free copper rod in step 1 is φ[100, 300 mm]×[200, 1000 mm], and the specification of the oxygen-free copper tube obtained after extrusion is φ[40, 80 mm] / φ[20, 60 mm].

[0030] Optionally, in step 2, the secondary processing rate of the outer square and inner circle oxygen-free copper pipe is [5%, 20%], the specification of the outer square and inner circle oxygen-free copper pipe is H [8, 20mm] / φ[6, 15mm], the honing processing amount is [0.005, 0.01mm], and the surface roughness Ra is [0.05, 0.2μm].

[0031] Optionally, in step 3, the processing rate of the square oxygen-free copper rod is [5%, 20%], and the specification of the square oxygen-free copper rod is H [8, 20mm]; the processing rate of the square oxygen-free copper rod is [5%, 20%], and the specification of the square oxygen-free copper rod is H [3, 9mm]; the processing rate of the oxygen-free copper-zinc rod is [5%, 20%], and the specification of the square oxygen-free copper-zinc rod is H [3, 9mm].

[0032] Optionally, in step 3, the specification of the Nb rod is φ[5.5, 14.5 mm]×[200, 1000 mm] and the specification of the oxygen-free copper sheath is φ[180, 300 mm] / φ[160, 280 mm]×[200, 1000 mm].

[0033] Combination Figure 1 , Figure 1 The cross-sectional structure diagram of the CuNb composite sheath in the low-cost internal tin method Nb3Sn CuNb composite sheath assembly method of the present invention is shown. In which, taking the outer oxygen-free copper rod as an octagonal oxygen-free copper rod as an example, three specific processing process embodiments are given.

[0034] A low-cost internal tin method Nb3Sn CuNb composite sheath assembly method comprises the following steps:

[0035] Step 1: With an extrusion ratio of [5, 30], the first oxygen-free copper rod with a specification of φ[100, 300mm]×[200, 1000mm] is extruded to obtain an oxygen-free copper tube and a smaller oxygen-free copper rod, the smaller oxygen-free copper rod is φ[40, 80mm], and then the smaller oxygen-free copper rod is stretched with a pass processing rate of [5%, 20%] to obtain an outer square oxygen-free copper rod with a specification of H [8, 20mm] and a specification of H [3, 9mm] square oxygen-free copper rod; and the oxygen-free copper tube obtained after extruding the first oxygen-free copper rod has a specification of φ[40, 80mm] / φ[20, 60mm]; the oxygen-free copper-zinc rod with a specification of φ[100, 300mm]×[200, 1000mm] is extruded to obtain a smaller square oxygen-free copper-zinc rod, and the specification of the smaller oxygen-free copper-zinc rod is φ[40, 80mm]; the oxygen-free copper-zinc rod comprises [0.5, 5]wt% Zn, and then the smaller oxygen-free copper-zinc rod is stretched with a pass processing rate of [5%, 20%] to obtain a square oxygen-free copper-zinc rod with a specification of H [3, 9mm].

[0036] Step 2: Stretch the oxygen-free copper tube obtained in step 1 to obtain an oxygen-free copper tube with an outer square and inner circle, and hone the inner hole to ensure that the inner hole is smooth and free of foreign matter; the secondary processing rate of the outer square and inner circle oxygen-free copper pipe is [5%, 20%], and the specifications of the obtained outer square and inner circle oxygen-free copper tube are H [8, 20mm] / φ[6, 15mm], the honing processing amount is [0.005, 0.01mm], and the surface roughness Ra is [0.05, 0.2μm].

[0037] Step 3: insert the cleaned Nb rod into the cleaned outer square inner circle oxygen-free copper tube to form an oxygen-free copper sheath, wherein the specification of the Nb rod is φ[5.5, 14.5mm]×[200, 1000mm], and it is closely arranged together with the cleaned outer square oxygen-free copper rod, the square oxygen-free copper rod, and the square oxygen-free copper-zinc rod into the cleaned oxygen-free copper sheath, the specification of the oxygen-free copper sheath is φ[180, 300mm] / φ[160, 280mm]×[200, 1000mm], and the gap is filled with a second oxygen-free copper rod of smaller specification to obtain a Nb3Sn CuNb composite sheath.

[0038] Step 4: Cover and seal the two ends of the Nb3Sn CuNb composite sheath obtained in step 3, perform extrusion and stretching to obtain a CuNb composite rod, drill a hole in the center of the CuNb composite rod, insert the SnTi alloy rod and stretch it to obtain subcomponents, bundle the subcomponents into Ta tubes in sequence, and then load them into oxygen-free copper tubes to obtain the final Nb3Sn billet of the internal tin method, and obtain the Nb3Sn composite wire of the internal tin method after multiple stretching passes.

[0039] Embodiment 1,

[0040] Step 1: With an extrusion ratio of 5, a first oxygen-free copper rod with a specification of φ100×200mm is extruded to obtain an oxygen-free copper tube and a smaller oxygen-free copper rod, the smaller oxygen-free copper rod having a specification of φ[40, 80mm], and then the smaller oxygen-free copper rod is stretched with a pass processing rate of 5% to obtain an outer square oxygen-free copper rod with a specification of H 8mm and a square oxygen-free copper rod with a specification of H 3mm; and the oxygen-free copper tube obtained after extruding the first oxygen-free copper rod has a specification of φ44mm / φ20mm, and the smaller oxygen-free copper rod has a specification of φ40mm; an oxygen-free copper-zinc rod with a specification of φ100mm×200mm is extruded to obtain a smaller oxygen-free copper-zinc rod, the smaller oxygen-free copper-zinc rod having a specification of φ40mm; the oxygen-free copper-zinc rod comprises 0.5wt% of Zn, and then the smaller oxygen-free copper-zinc rod is stretched with a pass processing rate of 5% to obtain a square oxygen-free copper-zinc rod with a specification of H 3mm.

[0041] Step 2: The oxygen-free copper tube obtained in step 1 is stretched to obtain an oxygen-free copper tube with an outer square and inner circle, and the inner hole is honed to ensure that the inner hole is smooth and free of foreign matter; the secondary processing rate of the outer square and inner circle oxygen-free copper pipe is 5%, and the specification of the outer square and inner circle oxygen-free copper tube obtained is H 8mm / φ6mm, the honing processing amount is 0.005mm, and the surface roughness Ra is 0.05μm.

[0042] Step 3: insert the cleaned Nb rod into the cleaned outer square inner circle oxygen-free copper tube to form an oxygen-free copper sheath, wherein the specification of the Nb rod is φ5.5mm×200mm, and it is closely arranged together with the cleaned outer square oxygen-free copper rod, the square oxygen-free copper rod, and the square oxygen-free copper-zinc rod into the cleaned oxygen-free copper sheath, the specification of the oxygen-free copper sheath is φ180mm / φ160mm×200mm, and the gap is filled with a second oxygen-free copper rod of smaller specification to obtain a Nb3Sn CuNb composite sheath.

[0043] Step 4: Cover and seal the two ends of the Nb3Sn CuNb composite sheath obtained in step 3, perform extrusion and stretching to obtain a CuNb composite rod, drill a hole in the center of the CuNb composite rod, insert the SnTi alloy rod and stretch it to obtain subcomponents, bundle the subcomponents into Ta tubes in sequence, and then load them into oxygen-free copper tubes to obtain the final Nb3Sn billet of the internal tin method, and obtain the Nb3Sn composite wire of the internal tin method after multiple stretching passes.

[0044] For the same number of cores, the assembly method saves 100 yuan / kg compared to the drilling method.

[0045] Embodiment 2,

[0046] Step 1: With an extrusion ratio of 30, the first oxygen-free copper rod with a specification of φ300mm×1000mm is extruded to obtain an oxygen-free copper tube and a smaller oxygen-free copper rod, the smaller oxygen-free copper rod having a specification of φ80mm, and then the smaller oxygen-free copper rod is stretched with a pass processing rate of 20% to obtain an outer square oxygen-free copper rod with a specification of H 20mm and a square oxygen-free copper rod with a specification of H 9mm; and after the first oxygen-free copper rod is extruded, the oxygen-free copper tube has a specification of φ55mm / φ35mm, and the smaller oxygen-free copper rod has a specification of φ(55mm); the oxygen-free copper-zinc rod with a specification of φ300mm×1000mm is extruded to obtain a smaller square oxygen-free copper-zinc rod, the smaller oxygen-free copper-zinc rod having a specification of φ55mm; the oxygen-free copper-zinc rod contains 2.25wt% Zn, and then the smaller oxygen-free copper-zinc rod is stretched with a pass processing rate of 20% to obtain a square oxygen-free copper-zinc rod with a specification of H 9mm.

[0047] Step 2: The oxygen-free copper tube obtained in step 1 is stretched to obtain an oxygen-free copper tube with an outer square and inner circle, and the inner hole is honed to ensure that the inner hole is smooth and free of foreign matter; the secondary processing rate of the outer square and inner circle oxygen-free copper pipe is 20%, and the specification of the obtained outer square and inner circle oxygen-free copper tube is H 20mm / φ15mm, the honing processing amount is 0.01mm, and the surface roughness Ra is 0.2μm.

[0048] Step 3: insert the cleaned Nb rod into the cleaned outer square inner circle oxygen-free copper tube to form an oxygen-free copper sheath, wherein the specification of the Nb rod is φ14.5mm×200mm, and it is closely arranged together with the cleaned outer square oxygen-free copper rod, the square oxygen-free copper rod, and the square oxygen-free copper-zinc rod into the cleaned oxygen-free copper sheath, the specification of the oxygen-free copper sheath is φ300mm / φ280mm, and the gap is filled with a second oxygen-free copper rod of smaller specification to obtain a Nb3Sn CuNb composite sheath.

[0049] Step 4: Cover and seal the two ends of the Nb3Sn CuNb composite sheath obtained in step 3, perform extrusion and stretching to obtain a CuNb composite rod, drill a hole in the center of the CuNb composite rod, insert the SnTi alloy rod and stretch it to obtain subcomponents, bundle the subcomponents into Ta tubes in sequence, and then load them into oxygen-free copper tubes to obtain the final Nb3Sn billet of the internal tin method, and obtain the Nb3Sn composite wire of the internal tin method after multiple stretching passes.

[0050] For the same number of cores, the assembly method saves 150 yuan / kg compared to the drilling method.

[0051] Embodiment 3,

[0052] Step 1: With an extrusion ratio of 15, a first oxygen-free copper rod with a specification of φ290mm×500mm is extruded to obtain an oxygen-free copper tube and a smaller oxygen-free copper rod, the smaller oxygen-free copper rod having a specification of φ[40,80mm], and then the smaller oxygen-free copper rod is stretched with a pass processing rate of 15% to obtain an outer square oxygen-free copper rod with a specification of H 15mm and a square oxygen-free copper rod with a specification of H 6mm, and after the first oxygen-free copper rod is extruded, the specification of the oxygen-free copper tube is φ75mm / φ50mm, and the specification of the smaller oxygen-free copper rod is φ75mm; an oxygen-free copper-zinc rod with a specification of φ290mm×500mm is extruded to obtain a smaller oxygen-free copper-zinc rod, the smaller oxygen-free copper-zinc rod having a specification of φ75mm; the oxygen-free copper-zinc rod comprises 5wt% of Zn, and then the oxygen-free copper-zinc rod is stretched with a pass processing rate of 15% to obtain a square oxygen-free copper-zinc rod with a specification of H6mm.

[0053] Step 2: The oxygen-free copper tube obtained in step 1 is stretched to obtain an oxygen-free copper tube with an outer square and inner circle, and the inner hole is honed to ensure that the inner hole is smooth and free of foreign matter; the secondary processing rate of the outer square and inner circle oxygen-free copper pipe is 15%, the specification of the outer square and inner circle oxygen-free copper pipe is H 15mm / φ10mm, the honing processing amount is 0.007mm, and the surface roughness Ra is 0.1μm.

[0054] Step 3: insert the cleaned Nb rod into the cleaned outer square inner circle oxygen-free copper tube to form an oxygen-free copper sheath, wherein the Nb rod has a specification of φ9.5mm×500mm, and is densely packed together with the cleaned outer square oxygen-free copper rod, the square oxygen-free copper rod, and the square oxygen-free copper-zinc rod into the cleaned oxygen-free copper sheath, the specification of the oxygen-free copper sheath is φ250mm / φ230mm×500mm, and the gap is filled with a small-sized oxygen-free copper rod to obtain a Nb3Sn CuNb composite sheath.

[0055] Step 4: Cover and seal the two ends of the Nb3Sn CuNb composite sheath obtained in step 3, perform extrusion and stretching to obtain a CuNb composite rod, drill a hole in the center of the CuNb composite rod, insert the SnTi alloy rod and stretch it to obtain subcomponents, bundle the subcomponents into Ta tubes in sequence, and then load them into oxygen-free copper tubes to obtain the final Nb3Sn billet of the internal tin method, and obtain the Nb3Sn composite wire of the internal tin method after multiple stretching passes.

[0056] For the same number of cores, the assembly method saves 130 yuan / kg compared to the drilling method.

[0057] Although the preferred embodiments of the present application have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0058] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims

1. A low-cost internal tin method Nb3Sn CuNb composite sheath assembly method, characterized in that: The following steps are involved: Step 1: Extruding the first oxygen-free copper rod to obtain an oxygen-free copper tube, an octagonal oxygen-free copper rod, and a square oxygen-free copper rod, wherein the heights of the octagonal oxygen-free copper rod and the square oxygen-free copper rod are both smaller than those of the first oxygen-free copper rod; Step 2: stretching the oxygen-free copper tube to obtain an oxygen-free copper tube with a square outer surface and a round inner surface, and honing the inner hole; Step 3: inserting the cleaned Nb rod into the cleaned outer square inner circle oxygen-free copper tube, and the overall structure after the Nb rod is inserted into the outer square inner circle oxygen-free copper tube and the cleaned octagonal oxygen-free copper rod, square oxygen-free copper rod, and square oxygen-free copper-zinc rod are closely packed into the cleaned oxygen-free copper sheath. In the process, the gaps between the Nb rod, the cleaned octagonal oxygen-free copper rod, the square oxygen-free copper rod, and the square oxygen-free copper-zinc rod are filled with a second oxygen-free copper rod to obtain a Nb3Sn CuNb composite sheath, wherein the specification of the second oxygen-free copper rod is smaller than that of the first oxygen-free copper rod.

2. A low-cost internal tin method Nb3Sn CuNb composite sheath assembly method as claimed in claim 1, characterized in that: The square oxygen-free copper-zinc rod is obtained by stretching the oxygen-free copper-zinc rod, and the specification of the square oxygen-free copper-zinc rod is smaller than that of the oxygen-free copper-zinc rod, wherein the specification of the oxygen-free copper-zinc rod is φ[100, 300] mm×H[200, 1000] mm, its composition includes [0.5, 5] wt% Zn, and the extrusion ratio is [5, 30].

3. A low-cost internal tin method Nb3Sn CuNb composite sheath assembly method as claimed in claim 1, characterized in that: The method also includes: capping and sealing the two ends of the CuNb composite sheath of the Nb3Sn obtained, performing extrusion and stretching to obtain a CuNb composite rod, inserting a SnTi rod into the center of the CuNb composite rod through a drilling hole and stretching to obtain subcomponents, first loading the subcomponents into a Ta tube in sequence, and then inserting them into an oxygen-free copper tube to obtain a final Nb3Sn blank of the internal tin method, and obtaining an Nb3Sn composite wire of the internal tin method after multiple stretching passes.

4. A low-cost internal tin method Nb3Sn CuNb composite sheath assembly method as claimed in claim 1, characterized in that: The specification of the first oxygen-free copper rod in step 1 is φ[100, 300] mm×H[200, 1000] mm, and the specification of the oxygen-free copper tube obtained after extrusion is φ[40, 80] mm / φ[20, 60] mm.

5. A low-cost internal tin method Nb3Sn CuNb composite sheath assembly method as claimed in claim 1, characterized in that: In step 2, the secondary processing rate of the outer square and inner circle oxygen-free copper pipe is [5%, 20%], the specification of the outer square and inner circle oxygen-free copper pipe is H[8, 20] mm / φ[6, 15] mm, the honing processing amount is [0.005, 0.01] mm, and the surface roughness Ra is [0.05, 0.2] μm.

6. A low-cost internal tin method Nb3Sn CuNb composite sheath assembly method as claimed in claim 1, characterized in that: In the step 3, the processing rate of the octagonal oxygen-free copper rod is [5%, 20%], and the specification of the octagonal oxygen-free copper rod is H[8, 20] mm; the processing rate of the square oxygen-free copper rod is [5%, 20%], and the specification of the square oxygen-free copper rod is H[3, 9] mm; the processing rate of the square oxygen-free copper-zinc rod is [5%, 20%], and the specification of the square oxygen-free copper-zinc rod is H[3, 9] mm.

7. The low-cost internal tin method Nb3Sn CuNb composite sheath assembly method according to claim 1, characterized in that: The specification of the Nb rod in step 3 is φ[5.5, 14.5] mm×H[200, 1000] mm. The specification of the oxygen-free copper sheath is outer diameter [180, 300] mm / inner diameter [160, 280] mm×H[200, 1000] mm.

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