JPH0735557B2 - Superconducting wire manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for manufacturing a superconducting wire.

[Prior art and its problems]

Conventionally, as a method for producing a superconducting conductor containing a superconducting filament such as Nb ₃ Sn or V ₃ Ga, the following is known.

(A) A large number of holes are formed in the axial direction in a billet made of Cu-Sn bronze with a circular cross section, and a core material made of Nb rods is inserted into each of the holes, then extruded and then surface-reduced. To obtain a superconducting conductor by applying diffusion heat treatment to this wire.

(B) A complex in which a large number of Nb cores are embedded in a Cu-Sn bronze matrix obtained in the intermediate step of (a), by forming a large number of holes in a copper billet having a circular cross section in the axial direction. A method of obtaining a superconducting conductor by inserting a core material composed of "rods", extruding the core material, and further reducing the surface of the core material into a wire material, and subjecting the wire material to diffusion heat treatment.

These are the cases of Nb ₃ Sn, but the same applies to the case of V ₃ Ga.

In this way, a large number of holes are formed in the axial direction in the billet having a circular cross section, the core material is inserted into each of the holes, and the core material is extruded and further surface-reduced to produce a superconducting wire. The holes are conventionally arranged as shown in FIG. 3 or FIG. That is, FIG. 3 shows an example in which one hole 2a is formed in the center of the billet 1, six holes 2b are formed around the hole, and 12 holes 2c are formed around the hole 2a. They are equal. In this example, the number of holes around the center is up to two layers, but three or more layers may be formed.
The number of holes in the layer and above is [the number of holes in the inner layer + 6]. FIG. 4 is an example in which the central hole is omitted in the arrangement of the holes in FIG.

It is known that in the arrangement of holes as shown in FIG. 3, the core material located at the center is easily broken during the surface-reduction processing after the extrusion processing. If surface reduction processing is continued even after the central core material is broken, the core material around the core material will also be broken, and eventually the wire material will be broken, making it impossible to process. In order to eliminate such a defect, the hole arrangement shown in FIG. 4 was devised, and normally, the superconducting wire rod is manufactured with this arrangement.

By the way, when carrying out the above-described manufacturing method, there are some restrictions. First, the outer diameter of the billet is constant because it is regulated by the extruder. Also, the distance between adjacent holes affects the minimum wall thickness between holes (hereinafter referred to as "hole thickness"), but it is not preferable that this hole thickness be too thin. A wall thickness of 4 mm or more is required. Furthermore, the wall thickness between the hole closest to the billet outer peripheral surface and the billet outer peripheral surface (hereinafter referred to as the outermost wall thickness) must be sufficiently larger than the above hole thickness, for example, 100 mm.
For φ billet, it is desirable that it is 6 mm or more.

Under such restrictions, if the area occupied by each material forming the superconducting wire is determined, the diameter of the hole formed in the billet is naturally determined. For example, the billet outer diameter is 100 mm,
60% of billet material occupied area, 40% of core material occupied area,
If the hole thickness is 4 mm, the hole arrangement shown in Fig. 3 has a hole diameter of 14.51 mm and the outermost wall thickness is 5.8 mm, and the hole arrangement shown in Fig. 4 has a hole diameter of 14.91 mm, The outer wall thickness is 4.8 mm. As can be seen from this, when the holes are arranged as shown in FIG. 4, the outermost wall thickness becomes smaller than that in the case where the holes are arranged as shown in FIG.

If the outermost wall thickness becomes thin, the outermost core material may peel off during extrusion or subsequent surface reduction processing,
Not preferable. Particularly in the extrusion process, the core material of the outermost layer tends to be displaced to the outside of the billet stage, so that the core material is likely to be peeled off. That is, the arrangement of the holes in FIG. 4 can prevent the disconnection due to the breakage of the central core material, but under the same condition, the outermost wall thickness becomes thin, so that the core material is likely to be peeled off.

[Means for solving problems and their effects]

The present invention, in view of the problems of the prior art as described above, there is no disconnection due to the breakage of the central core material, and further provides a method for producing a superconducting wire rod without peeling of the core material. Billet with circular cross section, 3 around the center axis
Book, [the number of holes in the inner layer + 6] holes are formed around the book so that the intervals between adjacent holes are equal, and after inserting the core material into each hole, extruding this and further reducing the surface area It is characterized by being processed into a wire rod.

According to this method, since the core material is not arranged at the center of the billet, the core material is unlikely to break, and the outermost wall thickness can be increased, so that the core material can be prevented from peeling off.

Hereinafter, examples of the present invention will be described in detail.

〔Example〕

This example forms a large number of holes in a copper billet, in which a large number of Nb in a Cu-Sn bronze matrix is used as a core material.
After inserting the composite rod in which the core is embedded, extrusion processing and surface reduction processing are performed. Each condition is as follows.

Copper billet: Outer diameter 100mm Hole thickness 4mm Core material Composite rod: Cu-14.5wt% Sn bronze Nb Number of cores 367 cores Cu-Sn bronze / Nb ratio 3.0 Diffusion barrier: Nb foil Occupied area: Copper 60% Diffusion barrier 8 % Nb core 8% Cu-Sn bronze 24% Under these conditions, as shown in Fig. 1, there are three holes 2a around the center axis of the billet 1 and nine holes 2b around it. And the diameter of each hole is 18.26 mm,
The outermost wall thickness is 7.0 mm, the diameter of the composite rod is 16.33 mm,
The thickness of the diffusion barrier will be 0.96 mm.

If the holes are arranged as shown in Fig. 3 under the same conditions, the diameter of each hole is 14.51 mm, the outermost wall thickness is 5.8 mm, the composite rod diameter is 12.98 mm, and the diffusion barrier thickness is 0.77 mm. .

If the holes are arranged as shown in Fig. 4 under the same conditions, the diameter of each hole is 14,91 mm, the outermost wall thickness is 4.8 mm, the composite rod diameter is 13.33 mm, and the diffusion barrier thickness is 0.79 mm. Become.

Based on the above design values, as an example, first, a billet as shown in FIG. 1 was manufactured, and a Nb foil was wound around a composite rod processed to an outer diameter of 16.33 mm to a thickness of 0.96 mm to form a core material. The composite billet was prepared by inserting the core material into each hole of the billet.

Next, as Comparative Example 1, a billet as shown in FIG. 3 was produced, and a composite rod processed to have an outer diameter of 12.98 mm had a thickness of 0.7.
A Nb foil was wound to have a thickness of 7 mm to prepare a core material, and the core material was inserted into each hole of the billet to prepare a composite billet.

Further, as Comparative Example 2, a billet as shown in FIG. 4 was produced, and a composite rod processed to have an outer diameter of 13.33 mm had a thickness of 0.7.
A Nb foil was wound so as to be 9 mm to prepare a core material, and the core material was inserted into each hole of the billet to prepare a composite billet.

These composite billets are heated to about 800 ° C and extruded,
Composite base materials each having an outer diameter of 25 mm were obtained. At this time, the core material of the composite base material of Comparative Example 2 was partially peeled off at the extrusion start portion, but the surface was normal except for this. The composite base materials of Example and Comparative Example 1 had no problem. When the cross-sectional shape was observed, it was found that in any of the composite base materials, the core material was relatively displaced outward from the billet stage.

Next, the normal part of these composite base materials was subjected to surface reduction processing to an outer diameter of 10 mm by repeating groove roll processing and annealing, and then further surface reduction processing was carried out by repeating drawing and annealing with a round die. For annealing, the cross-sectional area of the wire is approximately
Every 20% reduction, it was performed under the condition of 550 ° C x 30 minutes.

In this process, during the wire drawing from 1.5 mmφ to 1.4 mmφ, Comparative Example 1
The wire was broken. As a result of checking the remaining sample, 2.
It was found that in the 0 mm sample, the central core material was broken at some places, and as the processing proceeded, this expanded to the whole core material. Therefore, the processing of Comparative Example 1 is interrupted here, and the processing of Example and Comparative Example 2 is further advanced to finally obtain 0.75 mmφ.
I got the wire.

Each of the finished wires was glass braided to a thickness of about 0.05 mm and cut into a length of 1.1 m.
30mm, 10mm long stainless steel tube tightly wound, 67 in vacuum
Diffusion heat treatment was performed at 0 ° C. for 5 days. Next, a lead wire for voltage measurement was attached at a position 5 cm from both ends of this coil (that is, the interval was 1 m). Thereafter, this coil was impregnated with epoxy to fix the winding.

Next, each coil was inserted into the magnet in the cryostat, and the critical current was measured under the conditions of 4.2K and 10T. The reference of the critical current was a current value of 100 μV for voltage generation in a 1 m coil. The measured value of the critical current of each coil is
162A and 114A in Comparative Example 2. When converted into a critical current density, it was 0.92 × 10 ⁵ A / cm ² in Example, and Comparative Example 2 was
It was 0.65 × 10 ⁵ A / cm ² .

When checking the remaining sample, in the wire rod of Comparative Example 2,
From the time of 1 mmφ or less, the diffusion barriers of the six cores out of the 18 cores started to damage, and at 0.75mm, these six cores were divided at intervals of about 100mm. It turned out that it was done. This is probably because the outermost wall thickness is thin. No abnormality was found in the wire rods of the examples.

The effectiveness of the present invention has been clarified by the above prototypes.

In the above embodiment, the case where three holes in the center are the first layer and the holes are formed up to the second layer has been described. However, when the billet diameter is large and holes are formed up to the third layer, the second hole is formed. Like In other words, the number of holes in the second layer and above is [number of holes in the inner layer + 6]
It will be a book.

The present invention is not limited to the above-described embodiment, but can be similarly applied to the following cases, for example.

When the billet is copper and the core material is a composite rod with multiple Nb cores embedded in a Cu-Sn bronze matrix (without diffusion barrier).

When the billet is Cu-Sn bronze and the core is Nb bar.

When the billet is copper and the core material is a composite rod in which multiple V cores are embedded in a Cu-Ga bronze matrix (when there is no diffusion barrier).

When the billet is copper and the core material is composed of a composite rod in which a large number of V cores are embedded in a Cu-Ga bronze matrix and a diffusion barrier coated on the composite bar.

When the billet is Cu-Ga bronze and the core is V bar.

〔The invention's effect〕

As described above, according to the present invention, since the core material is not arranged at the center of the billet, the core material is less likely to be broken during the surface-reduction processing, and the outermost wall thickness can be made thicker than before, so that the core material can be peeled off. It is possible to prevent sticking out. Therefore, there is an advantage that a wire having a smaller diameter can be smoothly processed without causing wire breakage and breakage of the core material.

[Brief description of drawings]

1 and 2 are end views of the billet used in the manufacturing method of the present invention, and FIGS. 3 and 4 are end views of the billet used in the conventional manufacturing method. 1-Billet, 2a / 2b / 2c-hole.

Claims (7)

[Claims] 1. A billet having a circular cross section is formed with three holes around the central axis thereof and [the number of holes in the inner layer + 6] around the central axis so that the intervals between adjacent holes are equal. A method for manufacturing a superconducting wire, comprising inserting a core material into a hole, extruding the core material, and further reducing the surface area of the core material to obtain a wire material. 2. The manufacturing method according to claim 1, wherein the billet is copper, and the core material is a composite rod in which a large number of Nb cores are embedded in a Cu—Sn bronze matrix. . 3. The manufacturing method according to claim 1, wherein the billet is copper, and the core material is a composite rod in which a large number of Nb cores are embedded in a Cu—Sn bronze matrix and a composite rod thereon. Consisting of a diffusion barrier coated on. 4. The manufacturing method according to claim 1, wherein the billet is Cu—Sn bronze and the core is an Nb rod. 5. The manufacturing method according to claim 1, wherein the billet is copper and the core material is a composite rod in which a large number of V cores are embedded in a Cu-Ga bronze matrix. . 6. The manufacturing method according to claim 1, wherein the billet is copper, and the core material is a composite rod in which a large number of V cores are embedded in a Cu-Ga bronze matrix, and a composite rod thereon. Consisting of a diffusion barrier coated on. 7. The manufacturing method according to claim 1, wherein the billet is Cu-Ga bronze and the core is a V rod.