JPH04137315A - Superconductor and superconductive coil and their manufacture - Google Patents

Abstract

PURPOSE:To reduce hysteresis and heating factors in the case of a repeated load so as to prevent quenching by working a multi-core compound superconductor whose surface is subjected to insulation treatment such a way that the shape of a cross section vertical to the longitudinal direction of the superconductor becomes approximately a square. CONSTITUTION:Working rolls 5a, 5b whose end portions in the upward and downward directions are flat and lateral direction working rolls 6a, 6b with flat end portions arranged in shifting by each 90 deg. from the rolls 5a, 5b are so arranged as the working surfaces of superconductors after completion of their surface insulation treatment are flush with each other. The intervals among those four working rolls 5a, 5b, 6a, 6b are adjusted so that the upward, downward, right and left directions of the superconductor are simultaneously formed according to a prescribed degree of processing. A portion of void is Nb-Ti line, and a portion that looks white is Cu. The external surface is covered with enamel insulating covering 4. The length of a linear portion on the cross section vertical to the longitudinal direction of the superconductor is at approximately 90%.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a superconductor, a method for reinforcing the same, and a superconducting coil and a method for manufacturing the same.
The present invention relates to a technology for reducing plastic strain heat generation, which is one of the causes of mechanical disturbance in superconducting wires that exhibit superconducting phenomena in e.g.

[Prior Art] Superconducting materials (for example, Nb-Ti wires) that exhibit superconducting phenomena when cooled with liquid He are generally heated in Cu or AQ, which has high thermal conductivity (these are referred to as stabilizing materials). By incorporating a large number of ultra-fine wires, it is used as a superconductor in multicore composites.

This superconductor has been previously described in the 6th book of ``Fundamentals of Superconductivity Engineering''.
It is manufactured by the method described in Vol. 1, No. 4, Nuclear Fusion Research P317 (1989).

The above conventional technique will be explained using FIG. 8.

First, a superconducting material such as Nb-Ti81 is embedded in a stabilizing material, and then the superconducting material and the stabilizing material are aggregated (80) to form a multicore composite superconductor.

Next, the core wires of this multicore composite superconductor are twisted (twist 82) in stabilizing equipment, and then shaped into the desired shape (
83) Do.

Next, the multi-core composite superconductor is heat-treated (85) and then wire-drawn, and then the surface of the enamel coating is coated with #! Edge roasting process 86).

FIG. 9 shows an enlarged longitudinal sectional view of the superconductor manufactured as described above.

The superconductor shown in this cross-section is actually about 2 a
It has a size of about n x 1 mm, and has about 2000 or more ultrafine wires made of superconducting material embedded therein.

In the figure, the white parts are Nb-Ti wires, and the white parts are Cu, and their volume ratio is 1:1.

Next, a superconducting coil obtained by winding the multi-core composite superconductor in multiple layers will be described.

Conventionally, this superconducting coil has a power of approximately 2w×1■, for example.
of superconductor 1 was wound around the form more than 1000 times, and
It is manufactured by impregnating it with epoxy at ~150°C and molding it into a racetrack shape.

FIG. 4 is a partially enlarged sectional view showing a cross section of this superconducting coil taken in a direction perpendicular to the direction in which the superconducting coil is wound in multiple layers.

As shown in the figure, this superconducting coil is made by laminating superconductors 1 and using glass cloth (GFR) as an insulating material between each layer.
P) 2 is placed. Furthermore, as a result of the epoxy impregnation, the outside of one corner of the superconductor is filled with epoxy 3.

[Problem to be solved by the invention] In the above-mentioned conventional technology, the yield stress of Nb-Ti wire, which is generally used as a superconducting material, is high, but the yield stress of Cu (pure mesh) and AI (pure aluminum), which are stabilizing materials, is high. is low.

Furthermore, in the above-mentioned prior art superconductor manufacturing method, the surface is subjected to insulation treatment such as enamel coating at about 300 to 350° C. after wire drawing, so the yield stress of Cu and the like is reduced. Therefore, the superconductor exhibits hysteresis under repeated load conditions.

This hysteresis will be explained using FIG. 3.

Figure 3 shows the stress and stress inside the superconductor under repeated loads.
It is a graph showing a strain state.

The vertical axis shows stress and the horizontal axis shows strain.

As shown in the figure, the superconductor, which is a composite of Nb-Ti wire and copper, has the characteristic of exhibiting hysteresis even under repeated loads of low stress, as shown by the broken line.

In the conventional technology, the energy indicated by the area of this hysteresis is converted into heat, which increases the consumption of He, which is an expensive coolant, and furthermore, the quenching state that transitions from the superconducting state to the normal conducting state increases. There is a problem that occurs.

Next, a superconducting coil manufactured using the above-mentioned conventional superconductor will be explained.

FIG. 5 shows the amount of thermal contraction of the material constituting this superconducting coil.

In the figure, the vertical axis indicates the amount of thermal contraction in percentage, and the horizontal axis indicates temperature.

Further, FIG. 6 is a graph showing the restraint strain generated in the epoxy portion of the coil.

In the figure, the vertical axis shows the epoxy part restraint strain in percentage, and the horizontal axis shows the temperature.

As shown in FIG. 5, the amount of thermal shrinkage of epoxy is extremely large compared to other constituent materials. Therefore, as shown by the broken line in FIG. 6, in the prior art, the epoxy has a tensile strain of about 1.25% during epoxy molding and cooling to a liquid He temperature of 4.2 K, which functions as a superconducting coil. will be loaded. Considering other factors such as electromagnetic force during excitation and vibration during running, it is thought that a tensile strain of approximately 1.35% will be repeatedly applied.

On the other hand, the tensile strength σB of epoxy at 4.2 is approximately 130
Since the MPa and longitudinal elastic modulus E are approximately 6 GPa, the strain σII/E will be approximately 2.2% when brittle fracture occurs, and therefore, 2 to 2.5% is considered to be the allowable strain. Therefore, the current coil has a problem in that the safety factor is not very high from the viewpoint of epoxy cracking.

Next, FIG. 7 shows the temperature dependence of the thermal conductivity of the superconducting coil constituent material.

The vertical axis in the figure shows thermal conductivity, and the horizontal axis shows temperature.

Compared to the thermal conductivity of superconductors, the thermal conductivity of epoxy is approximately 1
/1000, which poses a problem that if heat is generated due to epoxy cracking or other factors, it will hinder the diffusion of heat.

The purpose of the present invention is to provide a method for increasing the yield stress of a stabilizing material such as Cu, reducing the hysteresis of a superconductor under repeated loads, reducing heat generation factors, and preventing quenching, and a method for preventing quenching of a superconductor at a corner. To provide a superconducting coil and a method for manufacturing the same, which increase the degree of adhesion between superconductors and improve the flow of heat in the lateral direction when manufacturing the coil by reducing the radius (R) and winding the coil in multiple layers. be.

[Means for Solving the Problem] The above object is constituted by a step of processing a multi-core composite superconductor whose surface is insulated so that its shape in a cross section perpendicular to the length direction is approximately square. This can be achieved by a method for manufacturing superconductors.

Furthermore, this can be achieved by a method of manufacturing a superconducting coil in which the superconductor is wound in multiple layers around a mold while applying tension to the superconductor.

[Function] In a superconductor whose surface has been insulated, the yield strength of its stabilizing material is reduced, so by subjecting it to area reduction rolling after the insulating treatment, the superconductor is work hardened and its yield stress increases. As a result, the yield stress of the superconductor increases, preventing heat generation due to plastic deformation.

Prevents quenching.

Further, by making the longitudinal cross-sectional shape of the superconductor substantially square, it is possible to prevent the formation of large spaces at corners. Therefore, in order to manufacture superconducting coils,
In the case of multilayer winding, the amount of adhesive having poor thermal conductivity can be reduced, and the degree of adhesion between superconductors is improved, improving the cooling effect. As a result, quenching is prevented.

[Example] Next, an embodiment of the present invention will be described using the drawings.

A first embodiment of the present invention will be described using FIGS. 1 and 2.

FIG. 1 is an explanatory diagram for explaining part of the method for manufacturing a superconductor according to this example.

Moreover, FIG. 2 is an enlarged cross-sectional view in the longitudinal direction of the superconductor manufactured by the method according to this example.

The method for manufacturing a superconductor according to this embodiment is such that a rolling forming step using processing rolls 5a, 5b, 6a, and 6b as shown in FIG. 1 is added to the conventional manufacturing method shown in FIG. It is.

That is, the processing rolls 5a, 5 having flat ends in the vertical direction
b, and horizontal processing rolls 6a and 6b with flat ends arranged 90 degrees apart from this, so that the processing surfaces of the superconductor that has undergone surface insulation treatment and become the workpiece are on the same plane. Place it like this.

The intervals between these four processing rolls 5a are adjusted, and the superconductor whose surface insulation treatment has been completed is simultaneously formed to a predetermined degree of processing in the vertical and horizontal directions.

Note that the processing roll is non-active and rotates by friction due to the movement of the superconductor 1, so that the enamel layer is not damaged. Even when rolled to a working degree of 15%, there was no insulation peeling of Enamel 4.

FIG. 2 shows an enlarged cross-sectional view in the longitudinal direction when the superconductor manufactured by the conventional method shown in FIG. 9 was rolled and formed by 10% by the method according to this embodiment.

In the figure, the white part is the Nb-Ti wire, and the white part is the Cu wire. Note that an enamel insulation coating 4 is applied to the outer surface.

As shown in the figure, in the superconductor according to the second embodiment, the length of the straight part of the shape in the cross section perpendicular to the length direction is:
Compared to the length of the same portion of the superconductor according to the prior art shown in FIG. 9, the length is improved in both the upper and lower and left and right sides.

The higher the ratio of this straight line portion, the better. In this example, it is approximately 90%.

As a result, the radius of curvature of the cross-sectional corner portion, which is approximately 0.4 mm in the conventional technology, can be reduced to approximately 0.18 mm, and in order to manufacture the superconducting coil described later,
When wound in multiple layers, the degree of adhesion between superconductors is improved, the cooling effect can be improved, and quenching can be prevented.

Next, using FIG. 10, the results of a tensile test of the superconductor according to this example will be shown.

This tensile test is a well-known test method, and the vertical axis in the figure shows stress and the horizontal axis shows strain.

In addition, the figure (a) shows a conventional superconductor, and the figure (b) shows a 1o
The stress-strain relationship of the superconductor processed by % in this example is indicated by a 0 mark.

The 0.2% yield stress care for superconductors is 290 MPa with the conventional technology, but with the technology of this example, it is
It becomes 60 MPa, which is about 1.6 times. This thing,
It can be seen that the rolling process has a large effect of improving yield stress.

As shown in the figure, the Nb-Ti wire has a high yield stress (1
400 MPa), it is thought that the reason for the improvement in the yield stress of the superconductor is that the yield stress of Cu, indicated by the * symbol, increased from about 100 MPa to 250 MPa.

In addition, as a result of a tensile test performed on 5% and 15% workpieces, the 0.2% yield stress was 420 MPa and 420 MPa, respectively.
490MPa, and if the working degree is 5% or more, it will be about 1.
It can be seen that the yield stress increases by more than 5 times, indicating that the rolling process is sufficiently effective.

Next, a second embodiment of the present invention will be described using FIG. 11.

FIG. 11 is a process diagram showing the superconducting coil manufacturing method according to this example.

In the superconducting coil manufacturing method according to this embodiment, first, the superconductor 1 manufactured by the conventional method is rolled using processing rolls 5 and 6, and then the yield stress σa of the superconductor 1 is approximately 300 MPa, which is slightly higher than the yield stress σa of the superconductor 1. While applying a tension of , it is wound in multiple layers around a racetrack-shaped formwork 7 with glass cloth 2 (see FIG. 4) interposed as an insulating material between each layer. Here, the glass cloth 2 is interposed between each layer of the superconductor 1.
This is to prevent scratches from occurring on the enamel layer 4 treated on the surface of the superconductor 1 at the corners of the formwork 7, etc., as the superconductor 1 is wound while being pulled.

When a predetermined number of turns (dimensions) is reached, the coil is fixed to the formwork 7 and placed in 4 baths of an organic adhesive such as epoxy, and the entire coil is impregnated with epoxy 3.

Next, after a predetermined period of time has elapsed, the temperature is returned to room temperature and the formwork 7 is removed, thereby completing the superconducting coil 8.

As shown in this example, when winding the superconductor around the formwork,
When the superconductor is wound under a tension of 300 MPa, cooled to room temperature after epoxy molding, and the mold is removed, the epoxy 3 is subjected to a compressive strain of approximately 0.4%, as shown in Figure 6 above. It will be done.

Also, the difference in thermal shrinkage between epoxy 3 and superconductor is about 0.
Since the amount is 4%, it cancels out the thermal distortion caused by the difference in the amount of thermal shrinkage when the epoxy mold is cooled from the temperature to room temperature. Thereafter, by cooling the liquid He to a temperature of 4.2 K, a tensile strain of about 0.85% is applied to the epoxy 3.

In the conventional superconductor manufacturing method, the amount of strain in epoxy is about 1.25%, so in the method according to this embodiment, the amount of tensile strain can be reduced by about 0.4%.

Even when considering the allowable strain of epoxy 3 of 2%, the electromagnetic force due to excitation, and the vibration stress during operation, the superconductor manufacturing method according to this example has the effect of securing a safety factor of about twice. .

Note that if only compressive residual stress is to be generated in the epoxy 3, the rolling process is not necessary.

Next, using FIG. 12, the plastic strain behavior when the superconducting coil according to this example is repeatedly loaded is shown.

In this figure, the rolling process of the superconductor is 10%.

Further, in the same figure, the vertical axis shows the applied stress σ, and the horizontal axis shows the plastic strain ε.

The plastic strain of the as-rolled material, marked O, and after the epoxy impregnation treatment after rolling, marked Δ, are as follows:
・Plastic strain ε at the second repetition indicated by marks and mu marks,
It is a very large value compared to , and it can be seen that the behavior is not much different from the behavior of superconducting coils manufactured by conventional methods.

However, after 10% rolling, tension was applied at 300 Pa,
In the superconductor 1 of this example considering the epoxy 3 impregnation treatment, there is no big difference in plastic strain between the first time ■ and the second time marked 1.
It can be seen that this is effective in reducing the plastic strain ε.

Therefore, conventional coil manufacturing methods include rolling and 30%
Strong winding at 0 MPa has a great effect of suppressing the amount of heat generated by the superconductor itself due to repeated loads.
It has the effect of preventing quenching.

I thought that stretching the unprocessed material above the yield stress would have the same effect as hardening it by rolling, but the first
As shown in Figure 3, it was found that the material behaved almost the same as the unprocessed material and had no effect, probably because it was softened by heat treatment similar to epoxy impregnation treatment after tensioning.

Next, the effect of making the cross-sectional shape of the superconductor substantially square will be explained.

As mentioned above, FIG. 2 shows a cross section of the superconductor 1 after being rolled.

As mentioned above, compared to the cross section of the conventional method shown in Figure 8, the radius of curvature of the corner part was 0.4 x m, but now it is 0.18 mm.
, and the flatness of both the top and bottom and left and right surfaces has been improved, so when winding in multiple layers as shown in Figure 4, the amount of epoxy 3 that is filled into the gaps between the superconductors 1 is reduced. The amount of heat generated due to epoxy cracking is reduced,
It has the effect of preventing quenching.

Further, by winding strongly at 300 MPa, the glass cloth 3 placed between each layer of the superconductor 1 is fixed more closely, so that the shape of the superconducting coil 8 is stabilized.

Furthermore, even if heat is generated within the superconducting coil 8 for some reason, it is cooled by liquid He through the superconductor 1 (see FIG. 7), which has a high thermal conductivity, and the effect of suppressing heat generation is increased.

If the above superconducting coil is used as a magnetic levitation means.

Quenching can be prevented and an efficient magnetic levitation device can be obtained.

Note that the same effect can be obtained by manufacturing a superconducting coil by winding a superconductor manufactured by a conventional method in multiple layers and then rolling it.

In the superconductor manufacturing method shown in FIG. 9, the material is twisted to reduce AC loss, and then shaped into a shape. However, if the rolling process is performed thereafter, the twist will return and there is a concern that the superconductor 1 will be twisted. For this purpose, when fabricating the superconducting coil 8, as shown in FIG. 11, rolling is performed during the series of steps of tightly winding the superconductor 1 while applying tension, so that the untwisted superconductor 1 can be untwisted. can be prevented.

[Effects of the Invention] According to the present invention, since plastic working is applied to the superconductor as the final step of manufacturing the superconductor, the yield strength increases and quenching can be prevented. In addition, since the cross section of the superconductor in the longitudinal direction is approximately rectangular, the flatness of this cross section on both the top and bottom, left and right sides is improved, and the radius of curvature of the corner portion is reduced, so it is possible to wind the superconducting coil in multiple layers. When this happens, the degree of adhesion between superconductors is improved, heat flow improves, and the cooling effect increases. As a result, quenching can be prevented.

In addition, if a superconducting coil is manufactured by wrapping a superconductor in multiple layers and impregnating it with epoxy while applying tension to the formwork, and then removing the formwork at room temperature, compressive residual stress can be generated in the epoxy, and the temperature of the liquid He It is possible to suppress the tensile strain that occurs in epoxy when it is cooled to a certain temperature. In addition, in the case of multilayer winding, by rolling the superconductor and then applying tension and winding it tightly, plastic strain due to repeated loading can be reduced, which has the effect of suppressing the amount of heat generated by the superconductor itself. Furthermore, by including the rolling process in a series of steps of strong winding while applying tension, there is an effect of preventing the untwisting phenomenon of the superconductor.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram for explaining part of the method for manufacturing a superconductor according to the first embodiment, and FIG. 2 is an enlarged cross-sectional view in the longitudinal direction of the superconductor manufactured by the method according to the first embodiment. , Figure 3 is a graph explaining the stress/strain state inside the conductor under repeated loads, Figure 4 is an enlarged cross-sectional view of a superconducting coil made by multilayer winding of superconductors manufactured by the conventional method, and Figure 6 is the inside of the superconducting coil. Figures 5 and 7 are graphs showing the thermal contraction amount and thermal conductivity temperature characteristics of the superconducting coil constituent materials. Figure 8 is a graph showing the behavior of constraint strain occurring in the epoxy. Figure 9 is an enlarged cross-sectional view of a superconductor manufactured by a conventional method, Figure 1o is a stress-strain diagram of a superconductor obtained by tensile experience, and Figure 11 is a diagram of a superconductor produced by a conventional method.
Process diagram showing the superconducting coil manufacturing method according to the example, 1st
Figure 2 is a graph showing the plastic strain behavior when a superconducting coil is repeatedly loaded, and Figure 13 is a graph showing the plastic strain behavior when a superconducting coil made using a superconductor produced using a conventional method is repeatedly loaded. be. 1... superconductor, 5 a, 5 b, 6 a
, 6 b - rolling roll, 2... glass cloth, 3... epoxy, 4... enamel coating layer, 7...
・Formwork, 8...Superconducting coil.

Claims (10)

[Claims] 1. A multicore composite superconductor characterized by having a substantially rectangular shape in a cross section perpendicular to the length direction. 2. A multi-core composite superconductor characterized in that it has two sets of substantially parallel sides, and the total length of the straight portions is 90% or more of the total length of the cross-sectional periphery. 3. 1. A method for strengthening a multi-core composite superconductor, which comprises processing the multi-core composite superconductor so that the cross-section perpendicular to the length direction has a substantially rectangular shape. 4. A method for strengthening a multi-core composite superconductor, comprising processing the multi-core composite superconductor using two sets of rolls whose processing surfaces are parallel to each other on the same plane. 5. A method for manufacturing a multi-core composite superconductor, comprising the step of processing the multi-core composite superconductor whose surface is insulated so that its shape in a cross section perpendicular to the length direction is approximately square. A method for producing a superconductor, characterized by: 6. The process of processing the above-mentioned multicore composite superconductor so that the cross section perpendicular to the length direction has a substantially rectangular shape is performed using two sets of rolls whose processing surfaces are parallel to each other on the same plane. 6. The method for manufacturing a superconductor according to claim 5, wherein the step is processing a composite superconductor. 7. A superconducting coil manufactured by winding the multicore composite superconductor according to claim 1 or 2 in multiple layers. 8. A method for manufacturing a superconducting coil, which is manufactured by winding a superconductor in multiple layers around a formwork and impregnating it with an adhesive, the method comprising: winding the superconductor in multiple layers around the formwork while applying tension to the superconductor. . 9. In a method for manufacturing a superconducting coil in which a multi-core composite superconductor is wound in multiple layers around a formwork and impregnated with an adhesive, 1. A method for manufacturing a superconducting coil, comprising: processing the superconductor so that it has a substantially rectangular shape in cross section; and winding the superconductor in multiple layers around a formwork while applying tension to the superconductor. 10. A magnetic levitation device characterized in that the superconducting coil according to claim 7 is used as a magnetic levitation means.