JP7143147B2 - Superconducting coil and its manufacturing method - Google Patents

Description

TECHNICAL FIELD Embodiments of the present invention relate to superconducting coils and methods of manufacturing the same.

A superconducting coil is an electromagnet that uses a superconductor, does not generate heat, can pass a large current, and is used in various applications that require a large magnetic force.

A superconductor may change from a superconducting state to a normal conducting state by the application of a disturbance (superconducting breakdown, hereinafter referred to as quench). In a superconducting coil, for example, if a crack occurs in an insulator (for example, resin) that electrically insulates between superconductors, heat is generated in the vicinity of the crack, possibly causing quenching. If a quench occurs in a superconducting coil through which a large current flows, the superconducting coil may be destroyed.
Therefore, various techniques have been developed to prevent quenching in superconducting coils.

JP-A-9-63366

It is desired to suppress the quenching of the superconducting coil more reliably.
SUMMARY OF THE INVENTION An object of the present invention is to provide a superconducting coil and a method of manufacturing the same in which quenching is suppressed more reliably.

A superconducting coil according to one aspect has a superconducting wire, a fiber braid, and a cured resin. The fiber braid covers the outer circumference of the superconducting wire. At least part of the fiber braid is impregnated with the cured resin. The cured resin contains a resin main agent, a curing agent, and first and second particles. The first and second particles are particles of an inorganic material. The first particles have a particle size larger than the interstices of the fiber braid. The second particles have a particle size smaller than this gap.

1 is a partial cross-sectional view of a superconducting coil according to an embodiment; FIG. 2 is an enlarged cross-sectional view showing an enlarged part of FIG. 1; FIG. 3 is an enlarged cross-sectional view of the vicinity of a superconducting wire of the superconducting coil according to the embodiment; FIG. 8 is an enlarged cross-sectional view of the vicinity of a superconducting wire of a superconducting coil according to Comparative Example 1. FIG. 8 is an enlarged cross-sectional view of the vicinity of a superconducting wire of a superconducting coil according to Comparative Example 2. FIG. FIG. 3 is a flowchart showing an example of a manufacturing process of a superconducting coil; 5 is a graph showing an example of the relationship between the amount Rp of second particles added and the content of voids.

Hereinafter, embodiments of the superconducting coil will be described in detail with reference to the drawings.

FIG. 1 is a partial cross-sectional view showing a superconducting coil 10 according to an embodiment. FIG. 2 is an enlarged cross-sectional view showing an enlarged portion R (near superconducting wire 12) in FIG. FIG. 3 is an enlarged view showing the fiber braid 13 in an enlarged manner.

Superconducting coil 10 has bobbin 11 , superconducting wire 12 , fiber braid 13 , and cured resin 14 .
The bobbin 11 is divided into a central shaft 11A and side plates 11B. A superconducting wire 12 covered with a fiber braid 13 is wound around the central shaft 11A. The pair of side plates 11B hold the superconducting wire 12 wound around the central axis 11A from left and right.

Superconducting wire 12 has a superconductor at least in part. The superconducting wire 12 may be long (linear or bar-shaped), and its cross-sectional shape can be selected appropriately from round, rectangular, or the like. Note that FIG. 1 shows the superconducting wire 12 as a square wire (a wire having a square cross section).
Here, one superconducting wire 12 is wound four times in parallel over three levels (three layers). This is just an example, and the number of layers of the superconducting wire 12 and the number of turns in one layer can be set as appropriate.

The superconducting wire 12 may be a composite structure (not shown) in which superconducting filaments (ultrafine wires) are embedded in a stabilizing material (eg, Cu or Cu alloy (bronze)). As the filament of the superconductor, for example, an ultrafine wire of a metallic superconductor such as NbTi, Nb ₃ Sn or the like can be used.

A fiber braid 13 is a combination of fibers 131 arranged in two or more directions. Fiber braid 13 has a cylindrical shape and covers the outer periphery of superconducting wire 12 .
Fibers 131 are generally made of an insulating material to prevent short circuits between superconducting wires 12 . As the fibers 131, for example, glass, carbon, or organic polymer fibers can be used.

As shown in FIG. 3, fiber braid 13 has interstices 132 within the mesh of fibers 131 . Here, since the fibers 131 are arranged in two directions, the size of the gap 132 is defined by the widths Wx and Wy in the two directions.
The width Ws of the gap 132 is the smaller one of the widths Wx and Wy. The reason for this is that if the widths Wx and Wy are different, whether the first and second particles 22 and 23 described later can pass through the gap 132 depends on the smaller width Wx and Wy. This is because it is thought that it depends on the person.
The width Ws of the gap 132 is, for example, approximately 1 to 2 μm.
This width Ws can be measured by observation using an electron microscope (SEM).

The cured resin 14 has a resin matrix 21 (resin component), first particles 22 and second particles 23 .
The cured resin 14 is obtained by impregnating the fiber braid 13 with the resin matrix 21 and curing it. The cured resin 14 (resin matrix 21 ) has insulating properties and prevents short circuits between the superconducting wires 12 .
For the resin matrix 21 for this purpose, various materials (resin base resin), for example, thermosetting resins such as epoxy resin, phenol resin, urea resin, and melamine resin can be used.

Hereinafter, as the thermosetting resin, an epoxy resin to which a curing agent and a diluent are appropriately added will be described as an example. That is, the resin matrix 21 is a resin component of the cured resin 14 and contains an epoxy resin (resin main ingredient) and an appropriate amount of curing agent.
The resin main agent may be a curable compound having two or more three-membered rings composed of two carbon atoms and one oxygen atom in one molecule. The type of resin base is not particularly limited.
The curing agent is a liquid material with low viscosity at room temperature or low temperature. Curing agents are preferably amines, more preferably polyetheramines, aliphatic amines, or cycloaliphatic amines. A diluent is added as appropriate. In some cases, the resin matrix 21 (superconducting coil 10) is created without adding a diluent.

The first and second particles 22 and 23 are particles of an inorganic material and filled in the resin matrix 21 (inorganic filler) to improve the strength and insulation of the cured resin 14 .
Here, the first particles 22 have a particle size larger than the width Ws of the gaps 132 of the fiber braid 13, and the second particles 23 have a particle size smaller than the width Ws.
Since the first and second particles 22 and 23 have a particle diameter different from the width Ws of the gaps 132 of the fiber braid 13, they are less likely to be caught in the mesh of the fiber braid 13 and clog the fiber braid 13. Become. Further, since the first and second particles 22 and 23 having different particle diameters are mixed, a deposited layer (a layer L described later) of the first particles 22 or the second particles 23 is formed on the fiber braid 13. can also be prevented from forming. Therefore, resin matrix 21 can pass through gaps 131 of fiber braid 13 and impregnate superconducting wire 12 and fiber braid 13 without defects.

At least one of fused silica, crystalline silica, alumina, and magnesium oxide can be selected for the first particles 22 having a relatively large particle size.
At least one of fumed silica, fumed alumina, colloidal silica, colloidal alumina, and bentonites can be selected for the relatively small second particles 23 .
Among them, fumed silica is generally produced by reacting silicon tetrachloride gas with a mixed gas of oxygen and hydrogen, and is available, for example, as "AEROSIL (trade name)".
Bentonites are produced by refining or modifying microlayered minerals such as bentonite. Examples include "Kunipia F (trade name)," which is refined bentonite, and "S-BEN (product name)," which is organic bentonite by modifying montmorillite. product name)”, “ORGANITE (product name)”, and the like.

When the width Ws of the gaps 132 of the fiber braid 13 is about 1 to 2 μm, preferably the particle size (diameter) of the first particles 22 is about 2 μm to 15 μm, and the average particle size (diameter) of the second particles 23 is about 2 μm to 15 μm. is 1 nm to 500 nm, more preferably, the particle size (diameter) of the first particles 22 is about 3 μm to 5 μm, and the average particle size (diameter) of the second particles 23 is 10 nm to 100 nm.

The particle size of the first particles 22 can be measured by a laser diffraction/scattering method or an electron microscope. In the laser diffraction/scattering method, a particle group is irradiated with laser light, and the particle size distribution is obtained by calculation from the intensity distribution pattern of the diffracted/scattered light emitted therefrom.
In the present embodiment, among these methods, the laser diffraction/scattering method is used (for example, LA-700 manufactured by HORIBA can be used for measurement).

On the other hand, the particle size of the second particles 23 can be measured by a BET (Brunauer, Emmett, Teller) method or an electron microscope.
In the BET method, the adsorption isotherm of a group (powder) of the second particles 23 is measured, and the specific surface area and average particle diameter of the powder are obtained from this isotherm.
First, the relationship (adsorption isotherm) between the adsorption amount V of the gas molecules (adsorbate) to the powder and P/P0 (relative pressure, P0 being the saturated vapor pressure) is measured. Apply the BET equation to this isotherm to determine the specific surface area. Furthermore, the average particle diameter of the second particles 23 is calculated from the specific surface area. For example, this calculation becomes possible by assuming that all the second particles 23 are true spheres having the same diameter.
In the present embodiment, among these, a transmission electron microscope (TEM) is used (for example, it can be measured by H-F7100FA manufactured by Hitachi High-Tech Co., Ltd.).

The resin matrix 21 (resin component) contains 100 parts by mass of epoxy main agent (resin main agent) and, for example, 40 parts by mass of a curing agent. In addition, the amount of the curing agent is appropriately changed according to the state of the epoxy main agent.

The filling amount of the first particles 22 is preferably 100 to 300 parts by mass, more preferably 120 to 200 parts by mass, with respect to 100 parts by mass of the epoxy main agent in the resin matrix 21 . If the filling amount is too small, the strength and insulating properties of the cured resin 14 may not be sufficiently improved. If the filling amount is too large, the viscosity of the resin mixture (the mixture of the resin matrix 21 and the first and second particles 22 and 23) before curing increases, making it difficult to pass through the gaps of the fiber braid 13 (insufficient impregnation).

The shape of the first particles 22 is preferably nearly spherical. Impregnability of the resin mixture can be improved. The aspect ratio of the first particles 22 is preferably 1.0 to 1.5, for example.

The filling amount of the second particles 23 is preferably 0.75 to 2.0 parts by mass, more preferably 1.0 to 1.5 parts by mass with respect to 100 parts by mass of the epoxy main agent in the resin matrix 21. .
If the filling amount is too small, the impregnating property of the resin mixture (prevention of clogging of the fiber braid 13 and formation of a deposited layer of the first particles 22 or the second particles 23) may be insufficient. If the filling amount is too large, the viscosity of the resin mixture increases, making it difficult to pass through the interstices of the fiber braid 13 (insufficient impregnation).
As will be described later, by filling an appropriate amount of the second particles 23, the impregnating property of the resin mixture can be improved and the generation of voids can be reduced.

As shown in Comparative Example 2, which will be described later, the cured resin 14 contains particles having a particle size close to the width Ws of the gap 132 of the fiber braid 13 (particles having a particle size intermediate between the first and second particles 22 and 23). That is, it is desirable to substantially not contain third particles 25) described later.
From this point of view, the content of particles having a particle size of more than 500 nm and less than 2 μm is preferably 2.0 parts by mass or less, more preferably 1.5 parts by mass, with respect to 100 parts by mass of the epoxy main agent. It is below.

The ratio of the amount (mass) of the first particles 22 and the second particles 23 (mass of the first particles: mass of the second particles) is preferably 100: 1 to 150: 1, more preferably is between 120:1 and 130:1. If the amount of the second particles 23 relative to the first particles 22 is too small, clogging of the fiber braid 13 due to the first particles 22 may occur. If the amount of the second particles 23 relative to the first particles 22 is too large, the fiber braid 13 may be clogged due to the second particles 23 .
Basically, the second particles 23 function as a so-called lubricant to prevent the aggregation of the first particles 22 . Therefore, if the second particles 23 are too small or too large with respect to the first particles 22, this lubricating effect will be hindered.

(Comparative example 1)
A superconducting coil according to Comparative Example 1 will be described with reference to FIG. The same reference numerals are used for the same reference numerals as those in FIGS.
FIG. 4 is an enlarged cross-sectional view showing the vicinity of superconducting wire 12 of a superconducting coil according to Comparative Example 1 in an enlarged manner.

The resin cured product 14 x of Comparative Example 1 contains the resin matrix 21 and the first particles 22 but does not contain the second particles 23 .
Since the particle size of the first particles 22 is larger than the width Ws of the gap 131 of the fiber braid 13, the fiber braid 13 is not clogged. However, since the cured resin 14x does not contain the second particles 23 (fine particles), the first particles 22 are separated from the resin matrix 21 and deposited to form a layer (deposition layer) L easily.

This layer L prevents the resin matrix 21 from passing through the fiber braid 13 . For this reason, impregnation of the superconducting wire 12 and the fiber braid 13 with the resin matrix 21 is hindered, and for example, voids B (non-impregnated portions of the resin matrix 21) tend to occur in the vicinity of the superconducting wire 12 and in the mesh of the fiber braid 13.

The superconducting wire 12 and the fiber-resin composite structure (the composite structure of the fiber braid 13 and the cured resin 14x) receive an electromagnetic force from the exciting current. Therefore, stress concentrates on the vicinity of the superconducting wire 12 and on the non-impregnated portion of the mesh of the fiber braid 13, which may become the origin of cracks. If a crack occurs around superconducting wire 12, it may generate heat and induce quenching.

(Comparative example 2)
A superconducting coil according to Comparative Example 2 will be described with reference to FIG. The same reference numerals are used for the same reference numerals as in FIGS.
FIG. 5 is an enlarged cross-sectional view showing the vicinity of superconducting wire 12 of a superconducting coil according to Comparative Example 2 in an enlarged manner.

The resin cured product 14 y of Comparative Example 2 contains the resin matrix 21 and the third particles 25 but does not contain the first and second particles 22 and 23 .
The third particles 25 are particles of an inorganic material having a particle size greater than 500 nm and less than 2 μm. That is, for example, it has an intermediate particle size between the first particles 22 with a particle size of about 2 μm to 15 μm and the second particles 23 with a particle size of about 1 nm to 500 nm, for example. In other words, the particle diameter of the third particles 25 is relatively close to the width Ws of the gaps 132 of the fiber braid 13 (for example, about 1 to 2 μm).

Therefore, the third particles 25 tend to clog the gaps (mesh) 131 of the fiber braid 13 . This clogging prevents the resin matrix 21 from passing through the fiber braid 13 , and voids B are likely to occur in the vicinity of the superconducting wire 12 . As described above, this void B can cause cracks and eventually quenching.

As can be seen from the above, in the present embodiment, the third particles 25 having a particle size close to the width Ws of the gaps 131 of the fiber braid 13 are not used, and the first particles 22 having a particle size sufficiently larger than the width Ws and the width Ws Second particles 23 having a sufficiently smaller particle size are used. The second particles 23 with small grain boundaries function as a lubricant for the first particles 22, thereby preventing aggregation of the first particles 22 (generation of the layer L described above) and impregnating the resin matrix 21. improvement (reduction of generation of voids B).

(Creation of superconducting coil 10)
The fabrication of the superconducting coil 10 will be described below.
FIG. 6 is a flowchart showing an example of the manufacturing process of the superconducting coil 10. As shown in FIG. The superconducting coil 10 can be produced by a coating impregnation method as described below.

(1a) Winding of first-layer superconducting wire 12 (step S1(1))
A bobbin 11 is wound with a first layer of superconducting wire 12 . At this time, the superconducting wire 12 is covered with the tubular fiber braid 13 . The same shall apply hereinafter.
(1b) First layer impregnation (step S2(1))
A resin composition containing a resin matrix 21, first particles 22, and second particles 23 is applied to the first layer of superconducting wire 12 (covered with fiber braid 13). This resin composition reaches superconducting wire 12 through the mesh of fiber braid 13 . That is, the resin composition is filled between the fiber braid 13 and between the fiber braid 13 and the superconducting wire 12 .

(2a) Winding of second layer of superconducting wire 12 (step S1(n))
The superconducting wire 12 of the second layer is wound on the superconducting wire 12 of the first layer.
(2b) Second layer impregnation (step S2(n))
A resin composition is applied to the second layer of superconducting wire 12 (covered with fiber braid 13). The resin composition is filled between the fiber braid 13 of the second layer and between the fiber braid 13 and the superconducting wire 12 .
Moreover, the resin matrix 21 applied in step S2(1) is disposed between the first layer and the second layer, passes through the gap 131 of the fiber braid 13 below the second layer, and superconducting wire 12 and the fiber braid. 13 impregnated without defects.

Thereafter, similarly, the third layer of superconducting wire 12 is wound and the resin composition is applied. If the number of layers n is 4 or more, this winding and application are repeated.

As described above, when the winding application is completed, the bobbin 11 (resin composition) is heated to cure the resin composition to obtain a cured resin 14 . As a result, the superconducting coil 10 is produced.

Examples are described below.
Here, with respect to 100 parts by mass of the epoxy main agent, the content of the first particles 22 is constant, and the content of the second particles 23 (addition amount Rp) is varied between 0 and 2.0 parts by mass. Then, a superconducting coil was produced.
The addition amount Rp is expressed in units of phr (per handled resin), that is, the size of the second particles 23 in parts by mass with respect to 100 parts by mass of the epoxy main agent.

The resin matrix 21 used an epoxy resin to which a curing agent was appropriately added.
The content of the first particles 22 was 180 parts by mass with respect to 100 parts by mass of the epoxy main agent.
The width Ws of the gap of the fiber braid 13 was 1 μm.
The material of the first particles 22 was spherical silica (MSS-6 manufactured by Admatechs) with a particle size of 6 μm.
The material of the second particles 23 is Aerosil (AEROSIL RY200S manufactured by EVONIK) with an average particle size of 12 nm.

A cross section of the superconducting coil 10 thus produced was observed with an electron microscope (SEM), and the amount of voids generated (void content rate Rb [%]) near the superconducting wire 12 was measured.
The following table and Figure 7 summarize the results.

Here, the case where the content Rp of the second particles 23 is 0 is taken as a comparative example (corresponding to the aforementioned comparative example 1), and the others are taken as examples.
As shown in FIG. 7, the void content rate Rb [%] changes according to the addition amount Rp [phr] of the second particles 23 .
When the addition amount Rp of the second particles 23 is around 0.75 parts by mass, the void content rate Rb is greatly reduced. That is, from the viewpoint of improving the reliability of the superconducting coil 10, the amount of the second particles 23 added is preferably 0.75 parts by mass or more.

While several embodiments of the invention have been described, these embodiments have been presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, replacements, and modifications can be made without departing from the scope of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are included in the scope of the invention described in the claims and its equivalents.

10: superconducting coil, 11: bobbin, 11A: center shaft, 11B: side plate, 12: superconducting wire, 13: fiber braid, 14: cured resin, 21: resin matrix, 22: first particles, 23: second particles, 131: fibers, 132: interstices

Claims (10)

a superconducting wire;
a fiber braid covering the outer periphery of the superconducting wire;
and a cured resin impregnated into at least part of the fiber braid,
The cured resin is
a resin base;
a curing agent;
first particles of an inorganic material having a particle size larger than the interstices of the fiber braid;
a second particle of an inorganic material having a particle size smaller than the gap;
superconducting coil. 2. The superconducting coil according to claim 1, wherein the first particles have a particle size of 2 μm to 15 μm. 3. The superconducting coil according to claim 1, wherein said second particles have an average particle size of 1 nm to 500 nm. The superconducting coil according to any one of claims 1 to 3, wherein the cured resin contains 100 parts by mass of the main resin and 100 to 300 parts by mass of the first particles. 5. The superconducting coil according to claim 4, wherein the cured resin contains 100 parts by mass of the resin main agent and 0.75 parts by mass or more of the second particles. The superconducting coil according to any one of claims 1 to 5, wherein the first particles have an aspect ratio of 1.0 to 1.5. 7. The superconducting coil according to any one of claims 1 to 6, wherein the first particles contain one or more of fused silica, crystalline silica, alumina, and magnesium oxide. 8. The superconducting coil according to any one of claims 1 to 7, wherein the second particles contain one or more of fumed silica, fumed alumina, colloidal silica, colloidal alumina, and bentonites. The resin main agent is an epoxy resin,
The superconducting coil according to any one of claims 1 to 8, wherein the curing agent contains at least one of polyetheramine, aliphatic amine, and alicyclic amine. A step of winding a superconducting wire covered with a fiber braid around a bobbin;
applying a resin mixture to the wound superconducting wire;
and curing the resin mixture;
The resin mixture comprises a resin main agent, a curing agent, first particles of an inorganic material having a particle size larger than the interstices of the fiber braid, and second particles of an inorganic material having a particle size smaller than the interstices. and a method of making a superconducting coil.

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