JPS596005B2 - Stabilized coated superconducting wire and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an aluminum stabilized coated superconducting wire and a method for manufacturing the same.

Thanks to advances in research on stability in strong magnetic fields, superconducting wires are made by embedding a large number of very thin superconducting materials (e.g. 10 μφ x 10,000 wires) in a normal conducting metal with low electrical resistance, and then twisting them into the superconducting material. Processed so-called ultra-fine multicore twisted superconducting wire (finemul
(ti-twisted wire) has come to be mainly used.

Figure 1 shows a cross section of an example of this ultra-fine multicore twisted superconducting wire, in which 1 is made of various alloy-based superconducting materials such as Nb-Ti alloy, and many of the wires are made of normal conductive metal 2 such as oxygen-free copper. It is embedded and twisted, and the outermost layer is covered with an insulating layer 3.

Conventionally, most of the wires have been ultrafine multicore twisted superconducting wires coated with oxygen-free copper stabilizing coating as described above. On the other hand, regarding stabilized superconducting wires using high-purity aluminum (99.99% or more) as the normal conductive metal coated around a single superconducting material, for example,
It has already been proposed in No. 24, and the advantages of using high-purity aluminum are as follows. 0) High-purity aluminum has a lower electrical resistance than oxygen-free copper, and in particular in a magnetic field, it becomes significantly lower due to the difference in magnetic resistance, increasing the stability of the wire.

(T■j) Since high-purity aluminum has higher thermal conductivity than oxygen-free copper, the stability of the wire increases.

← Therefore, if the same stability is expected, less amount of high-purity aluminum is required, which reduces the overall volume of the wire, resulting in an increase in current density. (: High-purity aluminum has a lower specific gravity than oxygen-free copper, so the weight of the entire wire is significantly reduced, and this effect is doubled by the effect of (c). The oxide film is thin and strong, and has a high withstand voltage.
It also has good thermal conductivity, making it an excellent electrical insulating film. As described above, high-purity aluminum stabilized coated superconducting wire has superior performance compared to oxygen-free copper stabilized coated superconducting wire, so it is expected to be used as a conductor for DC superconducting cables and superconducting wire for magnetic levitation trains in the future. Ru.

Furthermore, it is clear that a multicore superconducting wire with a high-purity aluminum stabilization coating in which many thin superconducting materials are embedded in order to prevent flux jumps in strong magnetic fields has excellent superconducting properties with excellent stability.

Although high-purity aluminum stabilized coated superconducting wires are expected to have such excellent features, there are problems with conventional methods such as the difference in deformation resistance between high-purity aluminum and superconducting materials, and the fact that high-purity aluminum softens due to heat generated during processing. It was extremely difficult to put it into practical use. The present invention provides a stabilized multicore superconducting wire that does not have the difficulties of the above-mentioned manufacturing method and has the features (a) to (e) above, and also provides an industrial method that allows it to be manufactured easily and at low cost. The purpose is to provide a manufacturing method.

The present invention is characterized in that a single-core or multi-core linear superconducting material is embedded in a stabilizing coating layer made of a high-purity aluminum-alumina alloy containing 0.005% to 5% by weight of alumina. This is a stabilized coated superconducting wire.

The stabilizing coating layer made of a high-purity aluminum-alumina alloy in the present invention is made of an alloy in which fine alumina is dispersed in high-purity aluminum. ) has high electrical conductivity and thermal conductivity, practically 99.99 (fl)
Higher purity is desirable.

In addition, in the present invention, the superconducting material refers to, for example, Nb-*:(
It means Ti alloy, Nb-Zr alloy, and other superconducting materials. In the present invention, alumina is 0.005 to 5
．． The reason for setting it to 0% by weight is that if the content is less than 0.005%, the improvement in strength and heat resistance due to the alumina content will not be sufficient, and if it exceeds 5.0%, the workability will decrease.

FIG. 2 is a diagram showing a softening curve of a high-purity aluminum-alumina alloy obtained by a powder method in comparison with that of ordinary high-purity aluminum.

In the figure, a is a 1.0 mmφ aluminum wire with a purity of 99.99 (!) obtained by ordinary melting casting, rolling, and wire drawing processing, and B, c, and d are surface oxidized aluminum wires with a purity of 99.99.
% of high-purity aluminum powder was obtained through the steps of isostatic molding, pressure sintering, isostatic extrusion, and wire drawing. l
High-purity aluminum-alumina alloy wires of φ are shown, and the alumina content and particle size of the raw material powder are as follows. That is, there is a correlation between the particle size of the raw material powder and the alumina content of the alloy, and the smaller the particle size, the greater the alumina content.

The surface of the raw aluminum powder is usually naturally oxidized in the air, and in the present invention, no special oxidation treatment is generally required, and the alumina content is controlled by the particle size of the raw aluminum powder. From FIG. 2, it can be seen that the high-purity aluminum-alumina alloy obtained by the powder method has superior heat resistance and tensile strength near room temperature, which is about 1.3 times higher than that of ordinary high-purity aluminum.

Moreover, the higher the alumina content, the higher the tensile strength. Furthermore, these wires were annealed at 3000-400℃ for 10 hours, the resistivity at liquid helium temperature (4.2"K) was measured, and the ratio between the resistivity at room temperature and the ratio was determined. The results are shown in Table 1. As shown.

It is almost comparable to the obtained high-purity aluminum wire, and moreover, it has the low deformation resistance and softening temperature mentioned above, which are the reasons why high-purity aluminum has not been used as a stabilizing coating layer for conventional aluminum-coated multicore superconducting wires. This is extremely meaningful from an industrial perspective because it can improve the low temperature. The manufacturing method of the present invention will be explained below with reference to the drawings and examples.

Example: FIG. 3 is a diagram showing the manufacturing process in Example 1 of the stabilized coated superconducting wire of the present invention.

This example shows the case of manufacturing a stabilizing coated superconducting wire in which seven cores of Nb-Ti alloy superconducting material are embedded in a high purity aluminum-alumina alloy stabilizing coating layer. First, 99.
After melting with 99% high-purity aluminum, it was made into powder by an atomization method. A powder of 150 mesh or less (alumina content 0.01%) obtained by sieving this powder is
It was molded into a cylindrical block using 00 kg of pressure. This was sintered under pressure at 600°C in a vacuum, and then cut to a diameter of 24 mm and a length of 80 mm without any lubricating oil. Powder sintering in this case may be performed using other methods, such as a method in which pressure molding is followed by non-pressure sintering in the presence of a liquid phase. Next, seven holes of 531mm diameter were drilled in the longitudinal direction of this block, and a superconducting material core material of Nb55-Ti45 alloy of 5m1Jmm diameter was inserted into each of these holes, which was degassed in a vacuum and subjected to electron beam welding. It was sealed and sealed.

This composite billet was hydrostatically extruded into a composite wire rod of 5 mm diameter using a die with a total angle of 3 (j) and a die diameter of 5 mm. This wire was further drawn and twisted if necessary to obtain a wire with a diameter of 0.32 mm. Next, this Q wire was drawn with a skin pass to make it 0.26 mmφ, and then 30
Heat treatment was performed at 00 to 400°C, and finally anodization treatment was performed to obtain an aluminum stabilization coated ultrafine multicore superconducting wire as shown in FIG.

In Fig. 4, 4 is a superconducting material with a diameter of 0.050mm, 5 is a high-purity aluminum-alumina alloy 6 is a thickness of 0.005mm
mm thick anodized insulating layer. When this electric wire was compared with an oxygen-free copper stabilized coated ultrafine multicore twisted superconducting wire having the same degree of stability as 1, the following values were obtained.

This shows that the superconducting wire manufactured according to the present invention has extremely excellent performance.

In the above examples, the case where the hydrostatic extrusion process is performed once is shown, but the hydrostatic extrusion process may be repeated multiple times as necessary depending on the wire size, or the stretching process after the hydrostatic extrusion process is performed. In addition to wire drawing, processing methods such as swaging and rolling may be used.

Further, in the examples, a powder of 150 mesh or less prepared by the atomization method was used as the raw material powder, but the particle size is appropriately selected depending on the desired alumina content.

That is, when it is desired to obtain a product with a high alumina content, a product with a smaller particle size is used. Further, the raw material powder may be one obtained by a method other than the above, for example, an alkyl aluminum powder. If the natural oxide on the surface of the raw material powder is insufficient in alumina content, an appropriate amount of alumina powder may be added and mixed separately when forming the powder compact.
Further, the powder compaction step in the present invention is not limited to static pressure molding, and powder compaction may be performed by a conventional press in which powder is placed in a mold. Additionally, the composite billet used in hydrostatic extrusion may be cased with metal such as copper or aluminum when the alumina content in the high-purity aluminum is high. Further, the number of core materials of the superconducting material may be one or more than two.

As described above, the stabilizing coating layer of the present invention is made of a high-purity aluminum-alumina alloy containing 0.005 to 50% by weight of alumina, which has good heat resistance and high strength. Since there is no difficulty in processing due to differences in aluminum, softening, etc., it is easy to manufacture and enables industrial production, and the high-purity aluminum-alumina alloy has electrical conductivity comparable to that of ordinary high-purity aluminum at extremely low temperatures. Since it has thermal conductivity, it has the advantage that a stabilized coated superconducting wire with extremely good characteristics can be obtained.

In addition, in the present invention, high-purity aluminum powder with naturally surface oxidized surface is used, and since it is compression molded, there is no need to separately add and mix alumina powder, so there is an advantage that manufacturing is easy and manufacturing cost is low.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a cross section of one inch of the ultrafine multicore twisted superconducting wire. FIG. 2 is a diagram showing a softening curve of a high-purity aluminum-alumina alloy obtained by a powder method in comparison with that of ordinary high-purity aluminum. FIG. 3 is a diagram showing the manufacturing process in an embodiment of the stabilized coated superconducting wire of the present invention. FIG. 4 is a sectional view of the final product obtained by the manufacturing process shown in FIG. 3. 1, 4...Superconducting material, 2...
・Normal conductive metal, 3... Insulating layer, 5...
High purity aluminum-alumina alloy, 6...Anodized insulating layer.

Claims (1)

[Scope of Claims] 1 A single-core or multi-core linear superconducting material is embedded in a stabilizing coating layer made of a high-purity aluminum-alumina alloy containing 0.005 to 5.0% by weight of alumina. A stabilized coated superconducting wire featuring: 2. A composite billet is created by making multiple holes in the longitudinal direction in a block made by compressing and sintering high-purity aluminum powder with surface oxidation, and inserting a rod made of superconducting material into each hole. A method for producing an aluminum stabilized coated conductive wire, which comprises subjecting the wire to one-time hydrostatic extrusion and then drawing it to a predetermined size by processing such as swaging and rolling.