JPS60235309A - Method of producing nb-ti alloy superconductive wire material coated with enamel insulating coating - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Background and Objectives of the Invention] The present invention relates to superconducting wires, particularly N with an enamel insulation coating.
The present invention relates to a method for manufacturing a b-Ti alloy superconducting wire.

Superconducting magnets, especially superconducting magnets for NMR, require high magnetic field uniformity. In order to obtain high magnetic field uniformity, the most effective means is to improve the winding accuracy of the magnet, but another effective means is to improve the dimensional accuracy of the superconducting wire itself. .

The most common insulation method for superconducting wires used in superconducting magnets is enamel coating.
With the current enamel insulation coating technology, keeping the dimensional tolerance to 5 μm is the limit, especially for long wires of IKm or more. On the other hand, a dimensional accuracy of 2.5 .mu.m is particularly required for wire rods for NMR superconducting magnets.

In order to achieve the precision of magnet winding, it is still necessary to wind the wire with high tension, but when covered with enamel, the Cu part, which is a superconducting stabilizing material, becomes dull and warps, which reduces the mechanical strength of the superconducting wire. decreases and it is impossible to increase the winding tension.

An object of the present invention is to eliminate the drawbacks of the prior art described above and to provide an enamel insulation coated Nb-Ti alloy superconducting wire having high dimensional accuracy.

[Summary of the invention]

The gist of the present invention is to coat a 1Nb-Ti alloy superconducting wire with enamel insulation, such as formal or polyimide, and then subject the wire to a cross-sectional reduction process by drawing or the like.

One of the features of the present invention is that after cross-section reduction processing, heating is performed at a temperature of 350° C. or lower in order to reduce the electrical resistance of the Cu portion, which is a stabilizing material. In addition, the Nb-Ti alloy superconducting material in the present invention includes Nb-Ti
In addition to Nb-Ti, Nb-Tl-Ta, Nb-T
Ternary systems such as 1-Hf, and even Nb-'I"1-Zr-T
A quaternary system such as a can be applied.

In addition, in the present invention, heating at a temperature of 350°C or lower after the cross-section reduction processing is performed under extremely low temperatures (for example, liquid helium temperature 4
．． , 2 K) to lower the electrical resistance (ρa 14.2 K), but the temperature was limited to 350 °C or less because
This is because if it exceeds this value, the superconducting properties of Nb-'pi will deteriorate. There are two methods for heating below 350°C: heating at a temperature below the recrystallization temperature of Cu, and the former is a case where dimensional accuracy and mechanical strength are particularly required;
The latter is applied when dimensional accuracy and low electrical resistance characteristics (ρat4.2K) are required. In the former case, Figure 4 shows the relationship between the heating temperature, tensile strength, and electrical resistance when the wire rod with a reduction in area of 5 inches is further heated in the example shown in Figure 2. As shown, a softening phenomenon is observed at 300°C or higher.

Still, electrical resistance at liquid helium temperature (ρat42K)
starts to drop from 200℃. Therefore, if dimensional accuracy and improvement of electrical resistance characteristics are required, 300 to 350
℃, dimensional accuracy, electrical resistance characteristics, and mechanical strength are required, it is desirable to heat to 200 to 300°C.

The softening temperature is largely influenced by the degree of cross-section reduction, and when the degree of cross-section reduction is large, it tends to shift toward a low temperature side, whereas when it is small, it tends to shift toward a high temperature side. Therefore, it is necessary to determine the heating temperature based on the relationship between the degree of reduction in cross section and the required characteristics.

In the example shown in FIG. 3, changes in dimensional accuracy and significant deterioration of superconducting properties due to heating were not observed up to 350°C.

If dimensional accuracy is required to be improved only in terms of mechanical strength, but not electrical resistance characteristics, it is sufficient to apply cross-sectional reduction processing, and heat treatment is not required.

The electrical resistance of the C11 part, which is a stabilizing material, even below the crystallization temperature (
It is possible to lower ρat4.2K).

[Embodiments of the invention]

The present invention will be explained below with reference to the drawings.

In both figures, a filament of superconducting material made of Nb-Ti is placed in a stabilizing material made of Cu.
-1 ro 1f top , --11, 跣胏姀 LE cold woman 1
It is made of dark blue and has enamel insulation. (a) shows one filament, and (b) shows Nb-'p.
This is an ultra-fine multi-core version of i.

After applying enamel insulation to superconducting wires of any structure,
The cross-section is reduced by drawing a die (further heated at a temperature of 350° C. or less if necessary) and finished to the required dimensions.

Figure 2 shows the cross-sectional area reduction rate, tensile strength, dimensional accuracy, and dielectric breakdown of ultra-fine multifilamentary wires with an outer diameter of 1.0 mm and an insulation thickness of approximately 30 μm after formal insulation, processed at various area reduction rates. This shows the voltage relationship, and it can be seen that the tensile strength and dimensional accuracy are significantly improved by adding cross-section reduction processing.

The dielectric breakdown voltage hardly deteriorates until the area reduction rate is 25%, but it deteriorates when the area reduction rate exceeds 25%, so the area reduction rate is 2.
It is desirable to suppress it to 5% or less.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, dimensional accuracy and mechanical strength can be improved by performing a cross-sectional reduction process such as drawing after enamel insulation coating. In addition, the electrical resistance properties deteriorated by the cross-section reduction process can be recovered by further heat treatment without deteriorating the dimensional accuracy and superconducting properties, and its industrial use value is infinite. be.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view showing an example of superconducting wire fabrication according to an embodiment of the method according to the present invention, and Fig. 2 shows the relationship between the cross-sectional area reduction rate after enamel insulation coating and the required properties of the superconducting wire according to the present invention. FIG. 6 is a graph showing the relationship between heating temperature and required characteristics of the superconducting wire according to the present invention. 1; Filament of superconducting material; 2; Stabilizing material; 6; Enamel insulation coating. Address 1 Diagram No. 2 Appearance 3 Diagram 0 large (5 grade Ji C) (10 units/listen)

Claims (1)

[Claims] 1. A method for manufacturing a Nb-'pi alloy superconducting wire, which comprises applying an enamel insulation coating to the Nl:l-'pi alloy superconducting wire, and then subjecting the wire to cross-sectional reduction processing. 2. The method according to item 1 above, in which the Nb-4''i alloy superconducting wire is a single core wire. 3. The method described in item 1 above, wherein the Nb-Ti alloy superconducting wire is an ultrafine multifilamentary wire. 4. Item 1 above, wherein the area reduction rate is 25 factors or less. 2. The method according to Item 2 or 3. 5 After applying the Nb-']'i alloy-based superconducting mel insulation coating, A method for producing a Nb-'pi alloy superconducting wire, characterized in that the wire is subjected to reduction processing and then heat-treated at a temperature of 350°C or lower. 6. The method described in item 5.