JPH0146962B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a multi-core superconducting wire, particularly a method using hydrostatic extrusion. As shown in Figure 6, multicore superconducting wires are made of copper,
A plurality of superconducting materials 31 made of Nb-Ti, Nb-Zr, Nb ₃ Sn, V ₃ Ga, etc. are arranged in a matrix 21 of a stabilizing material made of aluminum or the like. Conventionally, multi-core superconducting wires having such a configuration have been manufactured by the following method. (1) Multiple wires or rods made of superconducting material prepared separately are inserted into a tube made of stabilizing material prepared in advance, and multiple pieces of the composite material obtained are inserted into a large diameter tube made of stabilizing material prepared separately. After inserting the large diameter tube, the end of the large diameter tube is vacuum degassed and sealed by electron beam welding or the like to create a composite billet. Thereafter, this composite billet is hot extruded or isostatically extruded, and then, if necessary, the area is reduced by drawing or the like to form a thin wire. (2) Separately prepared rods or wires made of superconducting material are inserted into each hole of a perforated rod (billet) made of stabilizing material prepared in advance, and the ends are vacuum degassed and then subjected to electron beam welding, etc. Seal and process in the same way as (1). In either method, at the time of assembling the composite billet, clearance is required between the superconducting material rod or wire and the stabilizing material tube or porous rod (billet) that accommodates it so that they can be inserted into each other. There is a gap between the two even after insertion. In other words, the two are only mechanically fitted. If this gap is too large, wrinkles will form on the inner surface of the tube during extrusion, reducing adhesion to the wire or rod, leading to failure in the extrusion process or breakage during subsequent area reduction processes such as drawing. On the other hand, if you try to reduce the clearance at the expense of workability when mating, the air, moisture, etc. that have entered the gap cannot be removed during vacuum degassing, and this expands during extrusion, causing it to flow outside. This may cause blistering or rupture of the layer, or decreased adhesion between the superconducting material and the stabilizing material, resulting in wire breakage during area reduction processing. Therefore, in the composite billet before extrusion, it is desirable that there be no gaps between the stabilizing material and the superconducting material, and also that there be no air or moisture at the interface. An object of the present invention is to provide a method that eliminates the drawbacks of the prior art described above, allows smooth extrusion and subsequent area reduction processing, and allows production of multi-core superconducting wires with excellent adhesive properties. It is in. According to the present invention, such an object is achieved by forming a composite material, which is one of the structural members of a composite billet, by hydrostatic extrusion and, if necessary, adding a drawing process. Composite billets can also be achieved by isostatic extrusion. In this case, high-purity copper or aluminum, which has good electrical and thermal conductivity, is generally used as the stabilizing material, but if the superconducting part in the multi-core superconducting wire is compound-based, the components of those compounds It is also possible to use an alloy containing one of the following. Therefore, it is possible to use not only alloy-based superconducting materials that are generally used as superconducting materials, but also superconducting materials made of residual components of compound-based components. Of course, if necessary for the production or performance of superconducting wires, materials other than stabilizing materials and superconducting materials, such as Ta, Nb, copper, Cu-Ni alloys, etc., may be used as part of the composite billet assembly. It can be used as Referring now to the drawings, FIG. 1 shows a billet for composite materials. This billet includes a stabilizing material such as a pipe 2 made of oxygen-free copper, a billet 3 made of a superconducting material such as Nb-Ti alloy, and a plug 4 that seals the front and back of these.
It consists of 1,42. To create this billet, use the prepared billet 3.
This is done by fitting the pipe 2 and the pipe 2 into each other, vacuuming the inside with the plugs 41 and 42 attached, and electron beam welding the boundary between the pipe 2 and the plugs 41 and 42. The tip of the plug 41 may be processed in advance or may be processed after welding. Of course, either one of the plugs 41 and 42 may be airtightly fixed to the end of the pipe 2 in advance. As shown in Fig. 2, this billet 1 will be
The container 5 of the hydrostatic extruder is filled with a pressurized medium 6, and the stem 7 is moved to release the pressurized medium 6.
By further applying pressure, the composite material 11 is extruded from the die 8 and has the desired shape and dimensions. The temperature during extrusion is selected at such a temperature that the billet 1 has sufficient deformability, and there is no thermal influence on the constituent materials, no danger of mutual reactions, etc., or at least a minimum. In ordinary extrusion, priority is given to obtaining deformability, so for example, when combining copper and Nb-Ti alloy,
450-650℃, in combination with Cu-Su alloy and Nb
A fairly high temperature level of 600 to 750°C is required, and in reality, there is a very high risk of thermal effects on the constituent materials and mutual reactions between the constituent materials. However, in the case of isostatic extrusion, industrially sufficient processing can be achieved even at considerably low temperatures, so it is preferable that the temperature is lower than that of ordinary extrusion.
Temperatures can be selected over a fairly wide range from below 450°C to room temperature. The composite material 11 obtained in this manner is then subjected to drawing processing as required, and formed into a predetermined shape and size. In many cases, the cross-sectional shape of the composite material 11 is
As shown in the figure, it is assumed to be hexagonal, but other shapes may be used. The molding of this composite material 11 is performed when the material is of a large size, so it is much easier to form the composite material 11 than when inserting thin pieces together. Furthermore, since a long composite material 11 can be obtained, assembly of a long composite billet can also be improved. FIG. 3 shows a composite billet assembled using such composite material 11. This billet 9
is made in almost the same way as the previous billet 1. That is, the composite material 1 of a predetermined length obtained in the previous step
1 are orderly inserted into a pipe 2 made of oxygen-free copper, for example, in a predetermined number, the inside thereof is vacuum degassed, and the space between the plugs 41, 42 and the pipe 2 is welded and sealed.
In this case, not only the composite material 11 but also other materials such as wires made of oxygen-free copper or the like can be inserted into the pipe 2 as required. The composite billet 9 is then hydrostatically extruded as shown in FIG. 5, and then subjected to processes such as drawing, forming a composite billet, and isostatically extruding as required to form a stabilized copper material as shown in FIG. superconducting wire 91
It is put into practical use as Hydrostatic extrusion of this composite billet 9
Since the composite material 11 is metallically bonded to the Nb-Ti alloy and has no gaps, the advantages of hydrostatic extrusion are increased, and the work can be carried out more smoothly. The yield of extruded material can be further improved by making the non-uniform portion of the metal flow shorter. The obtained superconducting wire 91 is then processed as necessary.
Fine detailing and multi-core construction are carried out through processes such as drawing, composite billet formation, and hydrostatic extrusion, but the advantages of using the unique composite material 11 are utilized in each of these processes, making each process smooth. can be carried out. The above has described the advantages of using the unique composite material 11 in terms of workability in extrusion and subsequent area reduction processes such as drawing. This phenomenon also appears in the superconducting properties of multicore superconducting wires. It is known that the critical current value of Nb-Ti alloy superconducting materials in liquid helium increases as the degree of cold working increases. Taking this type of material as an example, using a composite material 11 that is hydrostatically extruded at a temperature range from room temperature to 450°C or less as a material for a multi-core billet means that the degree of cold working is extremely increased, and the critical The current value will improve. Furthermore, since the interfacial adhesion is good and the material flow is uniform during processing, variations in the copper ratio and superconducting properties in the longitudinal direction are reduced. Taking Nb ₃ Sn superconducting wire produced by the bronze method as an example, manufacturing copper-tin alloy coated niobium wire for multi-core billet assembly by isostatic extrusion of multi-core materials improves interfacial adhesion and reduces the final process. It has the effect of uniformizing the formation of the Nb ₃ Sn layer during the heat treatment of
The critical current value is high and uniform in the longitudinal direction. [Example 1] Pre-prepared outer diameter 160mm, wall thickness 13mm, length 1200mm
Nb in a mm copper tube with an outer diameter of 146 mm and a length of 1100 mm
- Insert a titanium alloy billet, then cap both ends with copper plugs, vacuum degas and seal with electric welding. Extrude the billet using castor oil as a pressure medium at a temperature of 300℃ and a maximum extrusion pressure of 1400Kg. / ^cm2
By isostatically extruding the material to an outer diameter of 25 mm, a material with a copper ratio of 0.44 and a Nb-Ti portion diameter of approximately 20.8 mm was obtained. This material was cold drawn, made into a hexagonal cross-sectional wire with a distance across flats of 3.14, and cut to a length of 1100 mm.
The 1560 pieces are 160mm in outer diameter, 12mm in wall thickness, and 1200 in length.
A composite billet was prepared by filling an oxygen-free copper pipe of mm in size and sealing both ends in the same manner as described above. Thereafter, this composite billet was hydrostatically extruded to an outer diameter of 28 mm using the same pressure medium, extrusion temperature, and extrusion pressure as described above, and then cold drawn to an outer diameter of 1 mm to obtain a wire with a copper ratio of 1 and an Nb- Copper-stabilized Nb− with a Ti diameter of about 20μ
We manufactured Ti ultrafine multicore superconducting wire. [Comparative Example 1] A separately prepared Nb-Ti wire with a hexagonal cross-section of 2.37 mm on opposite sides and 500 mm in length was placed inside a copper tube with a hexagonal cross-section of 3.14 mm on opposite sides, 0.18 mm in wall thickness, and 500 mm in length. The specified number of material created by inserting the
Aligned and filled into a copper tube with a wall thickness of 12 mm and a length of 600 mm.
Thereafter, a composite billet prepared by sealing both ends in the same manner as described above was hydrostatically extruded to an outer diameter of 28 mm under the same extrusion conditions as in Example 1, and then wire-drawn to an outer diameter of 1 mm in the same manner as described above. 1.1, the diameter of the Nb-Ti part is approx.
A 18μ multicore superconducting wire was obtained. [Comparative Example 2] The coated billet obtained in Comparative Example 1 was heated to a temperature of 650°C.
After hot extrusion to an outer diameter of 50 mm at a maximum extrusion pressure of 2,500 tons at ℃, the wire was thinned to an outer diameter of 1 mm by cold drawing. The experimental results for each of the above examples are shown in the table below.

[Table] The critical current values in the table were measured using a manufactured multi-core superconducting wire with an outer diameter of 1 mm in 4.2K helium under a 7.5T magnetic field. As is clear from these results, Example 1 according to the present invention shows good results in all characteristics, but Comparative Example 1 tends to have strong wrinkles on the billet surface due to gaps in the material. Therefore, the extrusion is unstable compared to Example 1, and there is also concern about the subsequent pullability. Furthermore, regarding the critical current value, the characteristics deteriorated by about 20% compared to Example 1, although this may be due to the somewhat increased copper ratio. Furthermore, in Comparative Example 2, there remain concerns about difficulty in extrusion due to buckling of the billet, or about pullability due to the occurrence of wrinkles. Furthermore, because the temperature during extrusion is high, brittle reactants are generated at the interface with copper, Nb-Ti, and the non-uniformity of the filament itself is also affected, which may reduce subsequent drawing performance. Furthermore, the critical current value is approximately 30% lower than that of Example 1, which is 650
It is believed that such poor properties were caused by thermal deterioration due to hot extrusion at .degree. C. and non-uniform changes in the filament. [Example 2] Pre-prepared outer diameter 160mm, inner diameter 91mm, length 1200mm
A Nb hollow billet with an outer diameter of 90 mm and a length of 1100 mm was inserted into a Cu-10% Sn hollow billet with a
A billet formed by sealing both ends in the same manner as in the previous example was extruded at a temperature of 350°C using castor oil as a pressure medium.
By hydrostatically extruding the material to an outer diameter of 29 mm at a maximum extrusion pressure of 1400 Kg/cm ² , a material with a Cu-Sn alloy ratio of 2 and a Nb portion diameter of approximately 16 mm was obtained. This was repeatedly cold drawn and intermediate annealed to form a hexagonal cross-section wire with a distance across flats of 2.1 mm, and 4,300 wires of a specified length were made into copper tubes with an outer diameter of 160 mm, a wall thickness of 6 mm, and a length of 1200 mm. When the composite billet, which was packed in an array and sealed at both ends in the same manner as in the previous example, was hydrostatically extruded to an outer diameter of 25 mm under the same extrusion conditions as above,
Extrusion was extremely smooth, and the extruded material did not show any swelling or wrinkles, and was very sound. The extruded material was then subjected to repeated cold drawing and intermediate annealing to reduce its area, but the work was carried out smoothly without any problems such as blistering, constriction, or wire breakage. As is clear from the above description, according to the present invention, extrusion and subsequent area reduction processing can be carried out smoothly by using hydrostatic extrusion in both molding of composite materials and multi-core superconducting materials. With,
High-quality ultrafine multicore superconducting wires with excellent adhesive properties and good superconducting properties can be obtained at a high yield, and their industrial utility value is extremely high. One way to obtain a composite material with excellent adhesive properties is to insert a Nb-Ti alloy rod into a copper tube and then draw it out. It must be sufficiently cleaned and cold worked with an area reduction rate of 70% or more. In all of the previous examples, the stabilizing material is copper, but the present invention is applicable to the production of superconducting wires using aluminum or its alloy as a stabilizing material, or to coating a single core wire with a Cu-Ni alloy. Of course, it is also possible to manufacture superconducting wires such as multi-core wires.

[Brief explanation of drawings]

1 to 5 are explanatory diagrams showing an example of the method according to the present invention, and FIG. 6 is an explanatory diagram showing an example of a multicore superconducting wire. 1... billet, 2... stabilizing material pipe,
3... Billet of superconducting material, 41 and 42... Plug, 5... Container of hydrostatic extruder, 6... Pressure medium, 7... Stem, 8... Die, 9... Composite billet, 11... Composite material, 91...Superconducting wire.

Claims (1)

[Claims] 1 A solid billet made of a superconducting material is inserted into a hollow body made of a stabilizing material, the resulting billet is made into a composite material by hydrostatic extrusion, and multiple pieces of this composite material are inserted into a hollow body made of a stabilizing material. 1. A method for producing a multicore superconducting wire, the method comprising isostatically extruding a composite billet obtained by filling a composite billet into a composite billet, characterized in that the hydrostatic extrusion is carried out at a billet temperature of 450° C. or lower.