JP2020031128A - Superconducting coil and manufacturing method thereof - Google Patents

Abstract

To provide a superconducting coil and a manufacturing method thereof that performs more reliable control of a quench.SOLUTION: A superconducting coil according to an embodiment includes a superconducting wire, a fiber braid, and a cured resin. The fiber braid covers the outer periphery of the superconducting wire. The cured resin is impregnated into at least a part of the fiber braid. The cured resin includes a resin base material, a curing agent, and first and second particles. The first and second particles are particles of an inorganic material. The first particles have a larger particle size than a gap of the fiber braid. The second particles have a smaller particle size than the gap.SELECTED DRAWING: Figure 2

Description

  Embodiments of the present invention relate to a superconducting coil and a method for manufacturing the same.

  A superconducting coil is an electromagnet using a superconductor, can flow a large current without generating heat, and is used for various applications requiring a large magnetic force.

The superconductor may change from a superconducting state to a normal conducting state due to application of disturbance (superconducting breakdown, hereinafter referred to as quench). In a superconducting coil, for example, if a crack occurs in an insulator (for example, a resin) that electrically insulates the superconductors, heat may be generated in the vicinity of the crack to cause quench. If quench occurs in the superconducting coil through which a large current flows, the superconducting coil may be destroyed.
For this reason, in the superconducting coil, various techniques have been developed to prevent quench.

JP-A-9-63366

It is desired to suppress the quench of the superconducting coil more reliably.
An object of the present invention is to provide a superconducting coil in which quench is more reliably suppressed and a method for manufacturing the same.

  A superconducting coil according to one embodiment includes a superconducting wire, a fiber braid, and a cured resin. The fiber braid covers the outer periphery of the superconducting wire. The cured resin is impregnated into at least a part of the fiber braid. The cured resin includes a resin base material, a curing agent, and first and second particles. The first and second particles are particles of an inorganic material. The first particles have a larger particle size than the interstices of the fiber braid. The second particles have a smaller particle size than the gap.

FIG. 2 is a partial cross-sectional view of the superconducting coil according to the embodiment. FIG. 2 is an enlarged sectional view illustrating a part of FIG. 1 in an enlarged manner. It is an expanded sectional view near the superconducting wire of the superconducting coil concerning an embodiment. FIG. 4 is an enlarged cross-sectional view of the superconducting coil according to Comparative Example 1 near a superconducting wire. It is an expanded sectional view near the superconducting wire of the superconducting coil concerning comparative example 2. It is a flowchart showing an example of the manufacturing process of a superconducting coil. 9 is a graph illustrating an example of a relationship between an added amount Rp of second particles and a void content.

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

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

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

The superconducting wire 12 has a superconductor at least in part. The superconducting wire 12 may be long (linear, rod-shaped), and its cross-sectional shape can be appropriately selected, such as a circle or a flat angle. In FIG. 1, the superconducting wire 12 is represented as a square wire (a wire having a square cross section).
Here, one superconducting wire 12 is wound four times in parallel and three steps (three layers) up and down. This is an example, and the number of layers of the superconducting wire 12 and the number of turns in one layer can be appropriately set.

The superconducting wire 12 may have a composite structure in which a superconductor filament (ultrafine wire) is embedded in a stabilizing material (for example, Cu or a Cu alloy (bronze)) (not shown). As the filament of the superconductor, for example, an ultrafine wire of a metal-based superconductor such as NbTi or Nb ₃ Sn can be used.

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

As shown in FIG. 3, the fiber braid 13 has a gap 132 in the mesh of the 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 smaller one of the widths Wx and Wy is defined as the width Ws of the gap 132. This is because when the widths Wx and Wy have different sizes, it is determined whether or not first and second particles 22 and 23 to be described later can pass through the gap 132 by the smaller of the widths Wx and Wy. It is because it is thought that it is decided by one.
The width Ws of the gap 132 is, for example, about 1 to 2 μm.
This width Ws can be measured by observing 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 the resin matrix 21. The cured resin 14 (resin matrix 21) has an insulating property and prevents a short circuit between the superconducting wires 12.
For the resin matrix 21 for this purpose, various materials (resin base material), for example, a thermosetting resin such as an epoxy resin, a phenol resin, a urea resin, and a melamine resin can be used.

Hereinafter, an epoxy resin to which a curing agent and a diluent are appropriately added will be described as an example of the thermosetting resin. That is, the resin matrix 21 is a resin component of the resin cured product 14 and includes an epoxy resin (resin base material) and an appropriate amount of a curing agent.
The resin base material may be any compound that has two or more three-membered rings composed of two carbon atoms and one oxygen atom in one molecule and is curable. The type of the resin base is not particularly limited.
The curing agent is a liquid material having low viscosity at room temperature or low temperature. The curing agent is preferably an amine, more preferably a polyetheramine, an aliphatic amine, or an alicyclic amine. Note that a diluent is appropriately added. In some cases, the resin matrix 21 (superconducting coil 10) is formed without adding a diluent.

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

As the first particles 22 having a relatively large particle diameter, at least one of fused silica, crystalline silica, alumina, and magnesium oxide can be selected.
As the second particles 23 having a relatively small particle diameter, at least one of fumed silica (Fumed Silica), fumed alumina (Fumed Alumina), colloidal silica, colloidal alumina, and bentonite can be selected.
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 obtained by refining or modifying micro-layered minerals such as bentonite. For example, "Kunipia F (trade name)", which is bentonite refined, or "S-BEN (organic bentonite, which is obtained by modifying montmorillonite," (Trade name) "," ORGANITE (trade name) ", and the like.

  When the width Ws of the gap 132 of the fiber braid 13 is about 1 to 2 μm, preferably, the particle diameter (diameter) of the first particles 22 is about 2 μm to 15 μm, and the average particle diameter (diameter) of the second particles 23. Is 1 nm to 500 nm, more preferably, the particle diameter (diameter) of the first particles 22 is about 3 μm to 5 μm, and the average particle diameter (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 a particle size distribution is obtained by calculation from an intensity distribution pattern of the diffraction / scattered light emitted from the particle group.
In the present embodiment, the laser diffraction / scattering method is used (measurement can be performed by, for example, LA-700 manufactured by HORIBA).

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 the average particle diameter of the powder are determined from the isotherm.
First, the relationship (adsorption isotherm) between the amount V of gas molecules (adsorbate) adsorbed on the powder and P / P0 (relative pressure, P0 is the saturated vapor pressure) is measured. The specific surface area is determined by applying the BET equation to this isotherm. Further, the average particle size of the second particles 23 is calculated from the specific surface area. For example, this calculation can be performed by assuming that all the second particles 23 are true spheres having the same diameter.
In the present embodiment, among them, a transmission electron microscope (TEM) is used (for example, it can be measured by H-F7100FA manufactured by Hitachi High-Tech Corporation).

  The resin matrix 21 (resin component) includes 100 parts by mass of an epoxy main agent (resin main agent) and, for example, 40 parts by mass of a curing agent. Note that the amount of the curing agent is appropriately changed depending on the state of the epoxy main agent.

  The filling amount of the first particles 22 with respect to 100 parts by mass of the epoxy main agent in the resin matrix 21 is preferably 100 to 300 parts by mass, and more preferably 120 to 200 parts by mass. If the filling amount is too small, the strength and insulation of the cured resin 14 may be insufficiently improved. If the filling amount is too large, the viscosity of the resin mixture before curing (the mixture of the resin matrix 21, the first and second particles 22, 23) becomes too high, and it becomes difficult to pass through the gaps of the fiber braid 13 (insufficient). Impregnation).

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

The filling amount of the second particles 23 with respect to 100 parts by mass of the epoxy main agent in the resin matrix 21 is preferably 0.75 to 2.0 parts by mass, more preferably 1.0 to 1.5 parts by mass. .
If the filling amount is too small, the improvement of the impregnating property of the resin mixture (clogging of the fiber braid 13 and prevention of 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 gaps in the fiber braid 13 (insufficient impregnation).
As described below, by filling the second particles 23 in an appropriate amount, the impregnation property of the resin mixture is improved, and the generation of voids can be reduced.

As shown in Comparative Example 2 to be described later, the resin cured product 14 is formed of particles having a particle diameter close to the width Ws of the gap 132 of the fiber braid 13 (particles having an intermediate particle diameter between the first and second particles 22 and 23). That is, it is desirable that the third particles 25) described later are not substantially contained.
From this viewpoint, the content of particles having a particle diameter 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 base agent. It is as follows.

The ratio of the amount (mass) of the first particles 22 to the second particles 23 (the mass of the first particles: the mass of the second particles) is preferably 100: 1 to 150: 1, and more preferably. Is from 120: 1 to 130: 1. If the amount of the second particles 23 relative to the first particles 22 is too small, the fiber braid 13 may be clogged due to the first particles 22. 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 for preventing the aggregation of the first particles 22. For this reason, if the second particles 23 are too small or too large with respect to the first particles 22, this lubricating action will be impaired.

(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 illustrating the vicinity of the superconducting wire 12 of the superconducting coil according to Comparative Example 1 in an enlarged manner.

The cured resin 14x of Comparative Example 1 includes the resin matrix 21 and the first particles 22, but does not include 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 include the second particles 23 (fine particles), the first particles 22 are deposited separately from the resin matrix 21 and the layer (deposited layer) L is easily formed.

  This layer L prevents the resin matrix 21 from passing through the fiber braid 13. For this reason, impregnation of the resin matrix 21 into the superconducting wire 12 and the fiber braid 13 is impeded, and, for example, voids B (unimpregnated portions of the resin matrix 21) are likely to be generated in the vicinity of the superconducting wire 12 or in the mesh of the fiber braid 13.

  The superconducting wire 12 and the fiber-resin composite structure (composite structure of the fiber braid 13 and the cured resin 14x) receive an electromagnetic force due to the excitation current. For this reason, stress concentrates in the vicinity of the superconducting wire 12 or in the unimpregnated portion of the mesh of the fiber braid 13, and there is a possibility that the stress may be a starting point of cracks. If a crack occurs around the superconducting wire 12, heat may be generated to induce quench.

(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 those in FIGS.
FIG. 5 is an enlarged cross-sectional view illustrating the vicinity of the superconducting wire 12 of the superconducting coil according to Comparative Example 2 in an enlarged manner.

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

  For this reason, the third particles 25 are likely to be clogged in the gaps (mesh) 131 of the fiber braid 13. The clogging prevents the resin matrix 21 from passing through the fiber braid 13, and the void B is easily generated near the superconducting wire 12. As described above, the void B can cause cracks and, consequently, quench.

  As can be understood from the above, in the present embodiment, the first particles 22 having a particle size sufficiently larger than the width Ws and the width Ws are not used, and the third particles 25 having a particle size close to the width Ws of the gap 131 of the fiber braid 13 are not used. The second particles 23 having a sufficiently smaller particle size are used. Since the second particles 23 at the small grain boundaries function as a lubricant for the first particles 22, aggregation of the first particles 22 (generation of the layer L described above) is prevented, and impregnation of the resin matrix 21 is prevented. (Reduction of void B).

(Preparation of superconducting coil 10)
Hereinafter, creation of the superconducting coil 10 will be described.
FIG. 6 is a flowchart illustrating an example of a manufacturing process of the superconducting coil 10. The superconducting coil 10 can be prepared by a coating impregnation method as shown below.

(1a) Winding of Superconducting Wire 12 of First Layer (Step S1 (1))
The first layer superconducting wire 12 is wound around the bobbin 11. At this time, the superconducting wire 12 is covered with the tubular fiber braid 13. The same applies to the following.
(1b) Impregnation of the first layer (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 the fiber braid 13). This resin composition reaches the superconducting wire 12 through the mesh of the fiber braid 13. That is, the resin composition is filled in the mesh of the fiber braid 13 and between the fiber braid 13 and the superconducting wire 12.

(2a) Winding of Superconducting Wire 12 of Second Layer (Step S1 (n))
The second layer of superconducting wire 12 is wound on the first layer of superconducting wire 12.
(2b) Impregnation of the second layer (Step S2 (n))
The resin composition is applied to the second superconducting wire 12 (covered with the fiber braid 13). The resin composition is filled in the mesh of the second-layer fiber braid 13 and between the fiber braid 13 and the superconducting wire 12.
Further, 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 forms the superconducting wire 12 and the fiber braid. 13 is impregnated without defects.

  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, superconducting coil 10 is created.

Hereinafter, examples will be described.
Here, the content of the first particles 22 was kept constant and the content (addition amount Rp) of the second particles 23 was changed from 0 to 2.0 parts by mass with respect to 100 parts by mass of the epoxy base agent. Thus, a superconducting coil was manufactured.
The addition amount Rp is expressed in units of phr (per handed resin), that is, as the size of the mass of the second particles 23 with respect to 100 mass of the epoxy main agent.

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

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

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

  Although several embodiments of the present invention have been described, these embodiments are provided by way of example and are not intended to limit the scope of the invention. These new embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and gist of the invention, and are also included in the inventions described in the claims and their equivalents.

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

Claims (10)

A superconducting wire,
A fiber braid covering the outer periphery of the superconducting wire,
And a cured resin impregnated into at least a part of the fiber braid,
The cured resin,
A resin base,
A curing agent,
A first particle of an inorganic material having a particle size larger than a gap of the fiber braid;
A second particle of an inorganic material having a particle size smaller than the gap.
Superconducting coil. The superconducting coil according to claim 1, wherein the first particles have a particle size of 2 μm to 15 μm. The superconducting coil according to claim 1, wherein the 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 includes 100 parts by mass of the resin base material and 300 parts by mass or less of the first particles. The superconducting coil according to claim 4, wherein the cured resin includes 100 parts by mass of the resin base material and 0.75 parts by mass or more of 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. The superconducting coil according to any one of claims 1 to 6, wherein the first particles include at least one of fused silica, crystalline silica, alumina, and magnesium oxide. The superconducting coil according to any one of claims 1 to 7, wherein the second particles include one or more of fumed silica, fumed alumina, colloidal silica, colloidal alumina, and bentonite. The resin base 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,
A step of applying a resin mixture to the wound superconducting wire,
Curing the resin mixture,
A first particle of the inorganic material, wherein the resin mixture has a particle diameter larger than a gap between the resin base material, the curing agent, and the fiber braid; and a second particle of the inorganic material, which has a smaller particle diameter than the gap. And a method for producing a superconducting coil including particles.

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