JPH03152884A - Superconductive wire and junction method therefor - Google Patents

Abstract

PURPOSE:To enhance a proximity effect in bonding by reducing oxide at the surfaces of metallic superconductive element wires so as to bring them into contact with each other under pressure. CONSTITUTION:Metallic superconductive element wires 2 are embedded in a stable material 3, thus obtaining a superconductive wire 1. A plurality of superconductive wires 1 are connected, thereby forming an elongated object. In this connection, the stable material 3 is peeled off at the end of the superconductive wire 1 so that the metallic superconductive element wire is exposed to the exterior. The exposed superconductive element wires 4, 5 to be connected are superposed each other to be heated in pressure-contact while being held by a sheath member 6 having a U-shaped cross section. The inside of the sheath member 6 is coated with wax 7 containing a reducing agent. Oxide on the surfaces of metallic superconductive element wires 4, 5 can be reduced to be gasified and dispersed by heating in pressure-contact at the first stage, and the wires 4, 5 are brought into contact with each other under pressure at contact surfaces without foreign matter by heating in pressure-contact at the second stage.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention connects superconducting fine multi-wires together, and
Superconducting wire suitable for obtaining close connection and method for joining the same,
The present invention also relates to magnetic levitation trains and other devices equipped with the superconducting wire.

[Conventional technology]

The superconducting wire for connection is a large number of metal superconducting wires made of copper (Cυ).
A superconducting fine multi-wire is used, which is embedded in a stabilizing material such as or aluminum (All) and drawn to a desired outer diameter.

To connect such superconducting fine multi-wires, a method has conventionally been adopted in which the ends of the superconducting wires are overlapped and fixed using In solder or the like, as described in Japanese Patent Application Laid-Open No. 50-92698. In this method, electrical connection is made through a normal conductive layer, so when used in a DC magnet or the like that targets persistent current, there is a drawback that the current decreases over time. Also, JP-A-1989-1983. -4.82
As described in Publication No. 95, the stabilizing material is removed with chemicals to expose the superconducting wire, the superconducting wires are overlapped and twisted, and then a sleeve of stabilizing material is inserted and soldered. A method has been proposed in which the superconducting 3-conductor wires in the overlapped portion are fixed by injecting However, this method involves intertwining and connecting superelectric wire operators.
When the superconducting wires are simply entangled, reaction products with oxygen are generally present on the surface of the superconducting wires, so a connection aiming at persistent current has the disadvantage that the current decreases.

[Problem to be solved by the invention]

- The conventional technology described in F does not take into consideration the cleaning of the surface of the metal superconducting strands, and as a result, true direct connection between the metal superconducting strands cannot be achieved, and there are problems with the permanent electrical properties associated with this. Ta. In other words, there has been no connection path that creates a proximity effect between superconducting strands.

Furthermore, even if the stabilizing material is removed with chemicals to expose the metal superconducting strands and the chemicals are washed off with water, reaction products with oxygen will still exist on the surface of the metal superconducting strands, resulting in the above-mentioned proximity effect. There was a problem that it was not sufficient.

The first object of the present invention is to provide a highly reliable superconducting wire with permanent electrical properties by making such a connection with a high proximity effect, a method for joining the same, and an electromagnet provided with the same. The purpose is to provide devices such as magnetic levitation trains.

Here, to briefly explain the process of the invention, an oxide film, which is a reaction product with oxygen, exists on the surface of the metal superconducting wire exposed as described above. Therefore, if this surface product can be removed during bonding, metal superconducting wires can be connected to each other with a proximity effect of 1. After various studies on the method, it was found that it is best to use the brazing filler metal described later for metal superconducting wire materials such as Nb-Ti, Nb, and Sn.The brazing filler metal is P, which has a strong bonding force with oxygen. Those containing reducing agents such as elements are good, and the effect is small when used alone, and metal alloys containing P elements etc. are used.
It has been found that materials that melt at 0°C are suitable.

[Means to solve the problem]

In order to achieve the above object, the Kawa conductor wire according to the present invention has a plurality of metal superconducting element wires that are exposed at the end of each unit superconducting wire in which a plurality of metal superconducting element wires are embedded in a stabilizing material. In the connected superconducting wires, the metal superconducting wires at the connection part are filled with a brazing material around them with the surface oxide film removed and are in close contact with each other, and an exterior member is placed around the brazing material. is installed. Here, the unit superconducting wire may have a coil portion or may be simply linear.

If wires are joined together, they become long electric wires.

Furthermore, the superconducting wire bonding force method according to the present invention is a process of superimposing metal superconducting strands exposed at the ends of each unit superconducting wire in which a plurality of metal superconducting strands are embedded in a stabilizing material. , a step of enclosing a brazing material and an exterior member in the overlapped portion, compressing the exterior member, and increasing the temperature to reduce the surface of the metal superconducting wire with a reducing agent added to the brazing material. removing the oxide film formed on the overlapping portion, and filling the periphery of the metal superconducting element wires in the overlapping portion with the oxide film removed on the surface thereof and bringing them into close contact with each other; This includes: Here, a method is preferable in which the reducing agent is gasified by an increase in temperature, and the oxide film is removed using the gas. In addition, the brazing filler metal is a reducing agent that has a flux effect, or an element that forms an oxide that is more effective than the oxidation of the superconducting wire or stabilizing material, such as P, Zn, Cd, Mg, 1-i, H''
.

Made of at least one material of Zr, F'100
A material having a melting temperature of 800°C is preferable. Here, as the R material of the brazing filler metal to which the reducing agent is added, CIJ,
Ag, Nb, Si, Ni, 811. Examples include AIJ. In addition, a brazing material is laminated and integrated on one side of the exterior member, and a metal superconducting wire is wrapped in the integrally fixed member with the brazing material inside, and then pressurized and the temperature is increased. Good. Further, it is preferable that the temperature of the brazing material be increased by electrical heating or ultrasonic oscillation.

Here, P is particularly good as a reducing agent, and the oxide film on the surface is removed by the reduction reaction described below.

4P+5TiO2→2 P2O5+ 5 T j ・
...(1) Furthermore, in the reaction formula "-", the metal superconducting wire is N b
-"l' The reaction of P with respect to Ti oxide in the case of the i system has been shown, but normally, when the stabilizing material around the metal superconducting wire is removed and the metal superconducting wire is exposed, the stabilization occurs. The reducing agent of the present invention also acts to reduce such oxides.Stabilizing materials When is Cu, the reduction reaction of P to its oxide is as follows.

2P+5Cu20−+P2O5+ 10(:u −・
・(2) 2Cu3P+5Cu20-+P2O5+16C
u - (3) In addition, the exposed metal superconducting strands overlapped with each other is wrapped with the other exterior member in which the brazing material is laminated in advance, and electricity is passed between the exterior members by the first stage of energization, and the solder material is heated. By partially melting the material and gasifying the reducing agent element during melting, reducing and cleaning the surface of the metal superconducting wire, and then applying heat and pressure by applying electricity in the second stage. At the same time that the metal superconducting strands are closely connected to each other, the remainder of the brazing material melts and flows around the connected metal superconducting strands, filling the space in the terminal with the brazing material and fixing it. It is better to have

The exterior members are those used for the stabilizing material and the rotating components, such as Cu or heat shield, and these are U-shaped, cylindrical, elliptical, angular, etc. so that they can easily wrap the superconducting wire. Good.

Moreover, the electromagnet according to the present invention is an electromagnet in which a coil of superconducting wire is wound around the core.

The coil is made of a superconducting wire having the joint portion. This electromagnet can be used for the magnetic floating-1-train and M
In addition to those used in RI, it also includes those used in magnetic confinement type nuclear fusion devices.

Further, a magnetically levitated train according to the present invention includes a car body, a superconducting magnet provided at the bottom of the car body, and a levitation coil and a propulsion guide coil provided in a guideway. The superconducting wire, which is a component of the superconducting magnet, is made of the superconducting wire described above.

Furthermore, a nuclear magnetic resonance imaging apparatus (MRI) according to the present invention
a self-shield and a first
A vacuum isolation tank surrounding the first and second shields, a liquid helium tank provided between the first shield and the second shield, and a liquid helium tank provided in the liquid helium tank. In the nuclear magnetic resonance imaging diagnostic apparatus equipped with a superconducting magnet, the superconducting wire that is a component of the superconducting magnet is made of the superconducting wire described above.

[Effect]

In the joint parts of the superconducting wires according to the present invention, the oxide film on the surface of the metal superconducting wires is removed and they are directly overlapped with each other, and are filled with brazing material and tightly connected, so that the proximity effect is eliminated. A sufficient amount can be obtained, and deterioration of the properties as a superconducting wire can be prevented.

By adding a reducing agent such as P to the brazing filler metal to be filled in advance, the oxide film on the surface of the metal superconducting wire can be removed by pressurization, heating, etc. during the bonding process, and the filling can be carried out. Therefore, it is possible to easily achieve a bonded state in which a sufficient proximity effect can be obtained.

It is preferable to use a resistance welder as the joining device. This is because heating and pressure can be applied at the same time, and bonding can be achieved in a short time. Since most of the bonding is done in the atmosphere, the shorter the bonding time, the less reaction with oxygen and the better the bonded part can be obtained.

Further, in order to achieve the object of the present invention, the resistance welding machine preferably employs a two-stage heating and pressurizing method. In other words, the first stage 11 is to melt the - part of the brazing material, remove the oxide film on the surface of the metal superconducting wires, and bring the metal superconducting wires into contact with each other by applying pressure. In the step, the remaining brazing material is melted and the oxide film on the surface of the metal superconducting wire is extruded and flows around the metal superconducting wire to cover it, and the overlapping parts of the exterior members are metallically joined by the brazing material. It is something that will be done.

The brazing filler metal used at this time needs to have a high vapor pressure and contain an element that has a strong affinity for oxygen as a reducing agent. This is because the stabilizing agent is removed using nitric acid, etc.
After washing with water, an oxide film bonded to oxygen exists on the surface of the metal superconducting wire such as Nb-'T'i. To remove this oxide film, heat is applied to activate the surface.
At the same time, if an element having a strong affinity for oxygen 1 2 is supplied there, the oxide film on the surface of the metal superconducting wire will inevitably be removed.

The most notable of these effects is ■). Since P is unstable in the rB form, it is generally supplied by alloying it with other elements. That is, Cu and A are alloyed with P.
g, Si, Ni, Sn, Zn.

Cd, Au, etc. are used. Furthermore, although it is desirable that these alloys have a low melting temperature, the active action of P must be present as a necessary condition. For that purpose, it is necessary to heat it to 500°C to 800°C. For example, when Cu is used as a stabilizing material, the alloy is 15%Ag, 3.5%P, 9.5%
Sn, 0.5% Au, remaining Cu (melting temperature: about 600°C)
8.4% P, residual Cu (melting temperature 715°C), 15% Ag, 5% P, residual Cu (melting temperature approximately 700°C)
) are good, and when AQ is used as a stabilizing material, those with components such as 10% Si, 0.1% P, and the remainder AQ (melting temperature about 570° C.) are used.

On the other hand, the material of the exterior member is preferably the same as the stabilizing material that wraps the superconducting wire, Cu or AQ is used, and the shape is preferably U-shaped, circular, etc., so that it can wrap around the superconducting wire and tighten it. . The above-mentioned P-containing alloy is used as the brazing filler metal to be placed on the joint surface using a general method. That is,
Apply the powder as a paste. A number of methods can be applied, such as spraying by thermal spraying, wrapping with foil, or cladding the bonding terminal in advance. The thickness of the brazing filler metal should be the minimum necessary, 10 to 50 μm.
Thickness level applies.

An electromagnet formed of a superconducting wire having the above-mentioned joint portion can sufficiently obtain the advantages 1 to 1 as a superconducting magnet, and can also maintain performance more stably in magnetic levitation trains and MRI.

〔Example〕

Hereinafter, the superconducting wire and the method for joining the same according to the present invention will be explained in detail.

The basic joining method is shown in Figure 1. This is a combination of current-carrying resistance heating and pressure bonding equipment and superconducting wire as the material to be bonded. That is, the superconducting wire 1 is made of Nb-T as shown in FIG.
It consists of an i-based metal superconducting wire 2 and a stabilizing material 3 made of Cu. The end of this superconducting wire 1 that will be the joint is 60
%HNO3 to remove the stabilizing material 3 from that part. The exposed metal superconducting wires 4 and 5 are overlapped and installed in a U-shaped exterior member 6. A brazing filler metal 7 made of a P-containing alloy is arranged on the joint surface of the exterior member 6. This joining joint is installed between the electrodes 8 of the current-carrying resistance heating and pressurizing device. Then, electricity is applied between the electrodes 8 to heat them.

3 to 5 show the joining process using the U-shaped exterior member 6. FIG. 3(a) shows the assembled state, and the energized electrodes are omitted. In this embodiment, four metal superconducting strands 4 and 5 are shown.

An oxide film 9 is formed around this superconducting wire. These overlapping wires 4 and 5 are loaded into the exterior member 6. A brazing material 7 is attached to the inside (joining surface) of the exterior member 6 in advance. In this case, the pressing force Pa and the current Ia
is zero as shown in FIG. 3(b).

FIG. 4(a) shows the state of electrical heating and pressurization in the first stage. First, the exterior member 6 is pressurized pb, and as a result, the overall adhesion is increased, a current 1b flows, and the exterior member 6 is heated ((+) in FIG. 4).

As a result, the brazing filler metal 7 is partially melted and phosphorus vapor is generated, which reduces and removes the oxide film on the adjacent metal superconducting wires 4 and 5. The so-called clean surface is exposed. 12 indicates what has been removed. At the same time, a portion of the connection between the metal superconducting wires 4 and 5 progresses.

FIG. 5(a) shows the state of electrical heating and pressurization in the second stage. As shown in FIG. 5(b), the metal superconducting wires 4 and 5 are sufficiently connected by the pressure Pc, and the brazing material 7 is sufficiently melted by the heating current 1c, and the superconducting element is removed. The oxide film 12 on the surface of the wire is extruded and filled around it. At the same time, by pressurizing Pc, the exterior member 6 is lowered and is metallically joined via the brazing material 7.
Further, the gap between the connected superconducting wires 4 and 5 is filled with the brazing material 7. In this case, the condition that the second stage is somewhat higher in both the pressing force and the current applied than the first stage further improves the connection state. By such a two-stage heating and pressing method, the metal superconducting strands have a proximity effect and are metallically fixed, thereby achieving a persistent current.

<Example 1> A superconducting wire 1 having a diameter of 1.0 mm was selected. In its cross section, 40 metal superconducting wires 2 (diameter 50 μm) are embedded in the stabilizing copper 3. Oxygen-free Cu U on the exterior member 6
15% Ag in the brazing filler metal 7 inside the shape.3.
A foil with a thickness of about 40 μm and containing 5% P, 9.5% Sn, 0.5% Au, and residual Cu (melting temperature: about 600° C.) was used. In order to expose the metal superconducting strands at the joint, the stabilized copper was removed with nitric acid and washed with water. The connection was made using a resistance welding machine, and the first stage applied a pressure load of 35 cycles for 30 cycles.
kgf, the current was 1.6 KA, and in the second stage, the pressure load was 4.0 kgf and the current was 2.0 kgf in 6 cycles.
．． It was held at OK Hachi. Note that Mo material was used for the electrode.

16- <Example 2> The superconducting wire 1 and the exterior member 6 were made of the same materials as in Example 1,
The exposure method for metal superconducting wires was carried out in the same manner. Exterior member 6
A foil with a thickness of about 40 μm and containing 8.4% P and residual Cu (melting temperature 715° C.) was used as the brazing filler metal 7 placed on the joint surface of the bonding material 7, and bonding was performed using a resistance welding machine using electrical heating and pressure. The connection conditions were the same as in Example 1.

<Example 3> The same materials as in Example 1 were used for the superconducting wire 1 and the exterior member 6,
The exposure method for metal superconducting wires was also processed in the same manner. Brazing material 7
15%Ag, 5%P, residual Cu (W4 melting temperature approx. 700℃
) was used to clad the joint surface of the exterior member 6. The cladding thickness is approximately 40 μm. Bonding was similarly carried out under the above conditions using a resistance welding machine using electrical heating and pressurization.

<Comparative example 1> The same superconducting wire J as in Example 1 was overlapped with an overlap of 20 mII+.

Stabilized copper pieces were soldered together at 200°C using In solder.

<Comparative Example 2> The same superconducting wire 1 as in Example 1 was prepared by removing stabilized copper with nitric acid,
Pb-8 was heated to 230℃ after twisting the piled superconducting strands and inserting a sleeve of Cu stabilizing material.
n solder was injected and fixed.

The relationship between the magnetic field and current in liquid He for the joined bodies bonded and connected in the above Examples and Comparative Examples is 41! I decided. The results are shown in FIG. All measurements were made with a U-shaped holder and a distance between voltage terminals of 30 mm.

As can be seen from FIG. 6, the superconducting wires produced in Examples 1, 2, and 3 of the present invention were 480A to 625A at a temperature of about ○T.
The current value decreases as the magnetic field increases, but
This is unique to the superconducting wire itself, and is not due to connection. - - The superconducting wire of Comparative Example 1 has a very poor value, and Comparative Example 2 is better than Comparative Example 1, but is much worse when compared with the present invention.

In these comparative examples, the reduction is clearly due to the influence of the connection part. These results show that the superconducting wire of the present invention is extremely superior.

In addition, when looking at the cross section of the joint, in the case of the present invention, the metal superconducting wires are brought close to each other and are well connected. The stabilizing materials were joined together.

Other materials such as aluminum can also be used for exterior parts.
Further, as the brazing filler metal, alloys containing 1゛1, alloys containing Hf and Zr, alloys containing Mg, etc. can be used. Furthermore, the bonding of the present invention can be achieved by using an ultrasonic welding machine or the like instead of the current-carrying resistance heating or pressurizing device as the bonding device. Furthermore, since the shorter the bonding time, the less damage to the superconducting wire, it has been confirmed that a more preferable joint can be obtained by bonding in an atmosphere of zero temperature such as liquid N2.

The shape of the joint may be such that the superconducting wires 1 and 1' are connected from the same direction into a sleeve-shaped exterior member 6 as shown in FIG.
may be provided, and the filling metal superconducting strands]] may be interposed.

FIG. 9 shows a schematic cross-sectional view of a magnetic float 190 top row type equipped with electromagnets according to the invention. The superconducting electromagnet 13 disposed at the bottom of the vehicle body consists of a magnetic core and a coil made of superconducting wire wound around the magnetic core (not shown). A superconducting wire having a joint portion according to the present invention is used in this coil. Moreover, FIG. 10 shows a schematic cross-sectional view of the main part of the MRI according to the present invention. A superconducting magnet (not shown) is disposed in the liquid helium tank 14, and the superconducting wire having the above-mentioned structure according to the present invention is used as a component of the superconducting magnet. Both of these magnetic levitation trains and MRI,
Stable performance can be obtained.

〔Effect of the invention〕

According to the superconducting wire according to the present invention, since the joint portion thereof has a structure in which a sufficient proximity effect can be obtained, the characteristics of a superconducting wire having zero resistance can be efficiently obtained.

According to the joining method according to the present invention, a superconducting wire that can sufficiently obtain the above-mentioned proximity effect can be easily obtained.

Electromagnet, magnetic levitation train and MT-? according to the present invention? , I can obtain stable performance over a long period of time by using the above superconducting wire.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a main part of a device 6 for explaining the joining method according to the present invention, FIG. 2 is a perspective view of a superconducting wire, and FIGS.
b) to 5(a) and (b) are explanatory diagrams of the joining process of the present invention, FIG. 6 is a diagram of the relationship between the magnetic field and current of the superconducting wire, and FIG.
8 and 8 are cross-sectional views of main parts showing different embodiments of the present invention, FIG. 9 is a schematic curved view of a magnetically levitated train according to the present invention, and FIG. 0 is a cross-sectional view of main parts of an MRI according to the present invention. Show the diagram. ]...Superconducting wire, 2, 4. ．． 5... Metal superconducting wire, 3... Stabilizing material, 6... Exterior member, 7... Brazing material, 9... Oxide film, 13... Superconducting magnet.

Claims (1)

[Scope of Claims] 1. A superconducting wire in which metal superconducting element wires exposed at the ends of each unit superconducting wire in which a plurality of metal superconducting wires are embedded in a stabilizing material are connected to each other, The metal superconducting wires in the connection part have their surface oxide film removed and are filled with a brazing material so that they are in close contact with each other, and an exterior member is placed around the brazing material. superconducting wire. 2. A step of overlapping the exposed metal superconducting wires at the ends of each unit superconducting wire in which a plurality of metal superconducting wires are embedded in a stabilizing material, and a wax containing a reducing agent in the overlapping portion. a step of wrapping the material and the exterior member, a step of compressing the exterior member, and a step of heating the exterior member to remove an oxide film formed on the surface of the metal superconducting wire by the reducing agent in the brazing material. A method for joining superconducting wires, comprising the steps of: filling the spaces between the superconducting wires with the brazing material and joining the superconducting wires to each other; 3. The method of joining superconducting wires according to claim 2, wherein the reducing agent is gasified by increasing the temperature, and the oxide film is removed by the gas. 4. In claim 2 or 3, the brazing filler metal contains P as a reducing agent.
, Zn, Cd, Mg, Ti, Hf, and Zr.
A method for joining superconducting wires, which are made of different materials and have a melting temperature of 500 to 800°C. 5. In any one of claims 2 to 4, a brazing material is laminated and integrated on one surface of the exterior member, a metal superconducting wire is wrapped in the integrated member with the brazing material inside, and then processing is performed. A method for joining superconducting wires that is compressed and heated. 6. A method for joining superconducting wires according to any one of claims 2 to 5, wherein the temperature of the brazing material is increased by electrical heating or ultrasonic oscillation. 7. An electromagnet in which a coil of superconducting wire is wound around a core, wherein the coil is the superconducting wire according to claim 1. 8. A magnetic levitation train comprising a car body, a superconducting magnet provided at the bottom of the car body, and a levitation coil and a propulsion guide coil provided in a guideway, in which a superconductor that is a component of the superconducting magnet is provided. A magnetic levitation train, wherein the line is the superconducting line according to claim 1. 9. A self-shield, a first shield and a second shield disposed within the self-shield, a vacuum isolation tank surrounding the first and second shields, and a vacuum isolation tank provided between the first shield and the second shield. In a nuclear magnetic resonance imaging diagnostic apparatus comprising a liquid helium tank and a superconducting magnet disposed in the liquid helium tank, the superconducting wire that is a component of the superconducting magnet is the superconducting wire according to claim 1. A nuclear magnetic resonance imaging diagnostic apparatus characterized by: