JPH10177913A - Supeconductive coil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a cryogenic superconductive coil which is enhanced in performance and stability by a method wherein a spool made of low-thermal change glass or ceramic of prescribed expansion coefficient is used. SOLUTION: A protrudent or columnar spool made of low-thermal change glass or ceramic of expansion coefficient 3.8×10<-6> (1/ deg.C) or below in a temperature range of 300k to 4.2k can be used, and it is preferable that the spool is made of high silicata glass, borosilicata low-alkali glass, high-strength glass or low-thermal change ceramic. Fiber-reinforced plastic where low-thermal change glass fiber or ceramic fiber is used as reinforcing fiber can be used. A coil bobbin formed of low thermal-change glass or fiber-reinforced plastic where low thermal-change glass or the like is used as reinforcing fiber is coated with a material layer of low friction coefficient, whereby a coil bobbin more enhanced in stability can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting coil used at a very low temperature.

[0002]

2. Description of the Related Art A superconducting coil device comprises a superconducting conductor wound around a bobbin and a layered coil element formed by interposing a spacer between layers or winding the superconducting conductor along a spiral groove engraved on the outer peripheral surface. A plurality of layers are sequentially and concentrically stacked. Conventionally, a metal frame such as stainless steel and aluminum or glass fiber reinforced plastic has been used as the reel, and a fiber reinforced plastic composed of a combination of an organic fiber having a negative coefficient of thermal expansion or an inorganic fiber and a fiber having a negative coefficient of thermal expansion as those having improved properties thereof. Proposed.

[0003]

The applications of superconducting coils are diverse, but increasing the current density of the superconducting wire is extremely important for improving the performance of the coil itself. This greatly depends on the stability of the superconducting wire wound on the bobbin. The physical stability of a superconducting wire wound around a bobbin is closely related to the electrical stability of the superconducting coil itself. Usually, as the bobbin, a metal such as stainless steel or aluminum or a glass fiber reinforced plastic (GFRP) using ordinary E-glass is used. First, these are wound at room temperature to form liquid nitrogen (LNT). ) Or when cooled to liquid helium temperature (LHeT), both shrink greatly in the circumferential direction of the bobbin and shrink slightly in the axial direction. On the other hand, when the superconducting wire is excited at a very low temperature, it expands in the circumferential direction due to the repulsive force derived from the Lorentz force, and the winding moves in a direction away from the bobbin. Further, when the temperature is extremely low in the axial direction, the size of the superconducting wire changes more than the small shrinkage in the axial direction of the bobbin due to the large shrinkage resulting from the positive expansion of the superconducting wire in the vertical direction. These two movements combine to cause microscopic movement between the superconducting wires, causing disturbance due to frictional heating of the surface, and the superconducting coil reaches quench.

A fiber reinforced plastic using negatively swelling organic fibers such as high-strength polyethylene has been proposed as a bobbin having improved large shrinkage, but has a problem in heat resistance. In other words, the superconducting coil is impregnated with a resin such as epoxy after winding to improve the fixation of the superconducting wire to the bobbin.However, since the curing temperature exceeds the heat resistance of the organic fiber, it is compressed and deformed by the winding tension of the superconducting wire. Or a loss of high strength or negative expansion characteristics, resulting in a winding frame having a high strength of contraction and a low elastic modulus, and the characteristics of a superconducting coil using the same are low. Further, a metal electrode is attached to the superconducting coil bobbin. At this time, the superconducting wire is soldered to the electrode, but heat is applied to the bobbin, and the performance thereof is impaired because the superconducting wire becomes higher than the heat resistant temperature of the organic fiber. In addition, a fiber reinforced plastic reel using these organic fibers has a drawback that compression or bending strength is low and compression creep occurs with time. The superconducting coil bobbin has a superconducting wire wound with a large tension applied to suppress the movement of the wire. In the case of coil bobbins using these organic fiber reinforced plastics, the winding tension added for compressive creep decreases with time and the superconducting wire becomes mobile, so the superconducting coil becomes unstable and quench at a low current value. Become. In a multi-layer coil, a superconducting wire is wound in a multi-layer by applying a large tension. However, the super-conducting wire is deformed by a large compressive or bending stress, and the coil characteristics are low.

As described above, there is a mechanical factor centering on the movement of the wire as a factor of the quench of the coil, which includes a difference in heat shrinkage characteristics between the bobbin and the superconducting wire. Coefficient. The superconducting wire is wound around the winding frame with tension applied, and the frictional force F is F = μN and the frictional heat W is W = μNs where μ is the friction coefficient, N is the normal component of tension, that is, the normal force, and s is This is the moving distance of the superconducting wire. Here, GFRP and metals such as stainless steel and aluminum which have been conventionally used as winding frames have a high friction coefficient and generate high frictional heat when the superconducting wire moves, so that the coil is quenched at a low current value. In addition, in the case of a metal bobbin such as stainless steel or aluminum, it is conductive, and in particular, in the case of an alternating current, Joule heat is generated due to eddy current, so that it becomes unstable. SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to obtain a high-performance and stable superconducting coil.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a cryogenic superconducting coil in which a superconducting wire is wound around a cylindrical or column-shaped winding frame, wherein the winding frame is made of low heat-change glass or ceramic, or a fiber or ceramic of these low heat-change glass. A superconducting coil characterized by being made of a fiber-reinforced plastic obtained by integrally molding a fiber and a resin, or having a layer of a material having a low friction coefficient formed on the surface thereof.

As the low thermal change glass or ceramic used in the present invention, a wide range of glass can be used as long as the average coefficient of thermal expansion from 300 K to 4.2 K is 3.8 × 10 ⁻⁶ (1 / ° C.) or less. However, for example, high silicate glass, borosilicate low alkali glass, high strength glass and low heat change ceramic are particularly preferable. Examples are quartz glass,
Vycor glass, Pyrek glass, S-glass, T
-Glass, R-glass and the like.

[0008] These low change glass or ceramics can be used as a coil bobbin by forming a pipe by a melting method, a hot pressing method, a rubber forming method or the like. These bobbins are made of only low-shrinkage or low-expansion glass or ceramics, and therefore have an excellent feature that the dimensional change is extremely small even when cooled from room temperature to extremely low temperature. It is also possible to use a fiber-reinforced plastic having this low-change glass fiber or ceramic fiber as a reinforcing fiber. Examples of the forming method include roving of the present fiber, filament winding method in which a fabric is impregnated with a matrix resin and winding around a mandrel, sheet winding method, tape winding method in which a unidirectional or woven fabric tape prepreg is wound around a mandrel, and autoclave. Method, and the like. The low change glass or ceramic used may be in the form of short fibers or particles in addition to the long fibers. In that case, various methods such as the SMC method, the BMC method, the injection method, and the resin injection method can be adopted.

[0009] The fiber-reinforced plastics obtained by these methods are all composed of a combination of low heat change glass fibers or ceramic fibers and a matrix resin. As the matrix used here, epoxy resin, unsaturated polyester resin, vinyl ester resin, urethane resin, thermosetting resin such as acrylate resin and polyethylene, polypropylene, polybutene, polyvinyl alcohol, polyamide, polyamide imide, polyether imide, Thermoplastic resins such as aramid, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyarylate, polyphenylene sulfide, polysulfone, polyetheretherketone, and polyetherketoneketone can be used. At this time, the matrix resin shows a positive expansion characteristic that shrinks greatly as the temperature decreases, but by optimizing the processing conditions in each molding method, it is possible to make the thermal strain a characteristic close to that of the low heat-change glass or ceramics itself. is there.

This will be described below with reference to the filament winding method. The dimensional change with temperature of a cylinder or cylinder formed by winding a roving with a low heat change glass as a reinforcing fiber and changing the winding angle while changing the winding angle depends on the winding angle as shown in FIG. A low shrinkage and a high shrinkage in the axial direction can be achieved. It is appropriate that the orientation angle is ± 35 to 90 degrees with respect to the axial direction. When the temperature of the superconducting coil bobbin using the low heat change glass obtained in this manner is changed from room temperature to extremely low temperature, the outer peripheral thermal strain is almost zero. On the other hand, since the contraction of the superconducting wire itself is very large, the winding tension of the superconducting wire itself increases significantly at extremely low temperatures. When the superconducting coil is energized, Lorentz force acts on the superconducting wire, and the superconducting wire expands in the radial direction, reducing the tension applied to the wire.However, the ratio is relatively small, and the superconducting wire retains a large winding tension. Become. The mixing ratio of the fibers and the matrix resin in the composite material is preferably 35 to 85%, more preferably 40 to 70%, as a fiber volume fraction (Vf). If Vf is less than 35%, the effect of reinforcing the fiber is not exhibited, and if it exceeds 85%, the mechanical properties deteriorate, which is not preferable. On the other hand, in the case of GFRP using ordinary E glass, both the glass fiber and the matrix resin have large shrinkage, so that the shrinkage is large in the circumferential direction regardless of the winding angle. Further, a coil bobbin using a metal such as stainless steel or aluminum has a larger shrinkage than GFRP.

On the other hand, a coil bobbin of FRP using organic fibers of negative expansion has been proposed for thermal distortion in the circumferential direction. In this case, since the circumferential direction of the bobbin expands at an extremely low temperature, the winding tension of the superconducting wire can be kept high. However, as a drawback common to organic fibers but not inorganic fibers, compression creep occurs and the winding tension decreases with time. When an excessive tension is applied to a superconducting wire in a multilayer winding or the like, there is a problem that compression or bending deformation occurs. In this respect, the fiber reinforced plastic using the glass fiber or the ceramic fiber as well as the coil bobbin made of the low heat change glass or the ceramic itself, which is an inorganic material, has a substantially extremely low compression creep and a remarkably high resistance to compression and bending stress. G
When FRP or metal is used as the winding frame of a superconducting coil, the biggest problem is that the coil is easily quenched due to the loosening of the superconducting wire due to large circumferential contraction.
When fiber-reinforced plastics using organic fibers with negative expansion are used, the tension is loosened over time, and the coil bobbin is deformed due to excessive tension, making it easier for the wire to move, and consequently the direction in which the coil is easily quenched. Is to change. The superconducting coil using the winding frame according to the present invention has substantially no thermal distortion in the circumferential direction at cryogenic temperatures, so that the initial winding tension is kept high and stable over time. A high-performance coil having high quench resistance and high current density can be obtained.

Next, the friction coefficient of the coil bobbin material will be described. The superconducting wire wound around the coil bobbin moves to a stable position due to the balance between the thermal stress caused by the difference in the coefficient of thermal expansion between the coil bobbin and the impregnated epoxy and the initial winding tension and Lorentz force. Focusing now on the relationship between the coil bobbin and the superconducting wire, frictional heat is generated between the two along with the movement of the superconducting wire in proportion to the friction coefficient. By forming a material layer having a low coefficient of friction on a coil bobbin made of the low heat deformation glass, ceramics or fiber reinforced plastic using these fibers according to the present invention, a more stable coil bobbin can be produced. Examples of the low friction coefficient material include a polymer of α-olefin having 1 to 4 fluorine substitutions or a fluorine-based polymer composed of a copolymer thereof, a polymer containing paraffin, wax, ethylene, or propylene as a monomer or copolymer. An olefin-based polymer composed of a polymer, a molybdenum compound such as molybdenum disulfide, and the like can be given. Of these, particularly preferred are polytetrafluoroethylene (Teflon), high molecular weight polyethylene, and as a method for laminating these materials, various methods such as a solution coating method, a melt coating method, a thermal spraying method, a vapor deposition method, a sputtering method, and a plasma heavy method. It is possible to adopt a method.

[0013]

EXAMPLE A coil bobbin using the low heat change glass or ceramics of the present invention was prepared as follows. Pyrex and silicon nitride are used as glass and ceramics, respectively.
mm and a molded body having a thickness of 13 mm were obtained. Also, for FRP, T glass (Nitto Bo) and Quolzell (Saint-Gobain) were used as reinforcing fibers, and epoxy resin was used as a matrix. Epicoat 827 (oiled shell) 100 Epicure YH-300 (oiled shell) 80 EMI-24 (oiled shell) 1 Next, various fibers were wound around a mandrel while being impregnated with an epoxy resin to form a cylinder. Next, while keeping this on a mandrel, 100 ° C. × 2 hr, and then 130 ° C.
The molded article was cured at × 3 hr to obtain a molded article having a fiber volume content of 65%. Among them, low heat change ceramics and T glass fiber reinforced plastic cylinders are made of Teflon and molybdenum disulfide (M
A film of oS ₂ ) was formed on the surface. As for the method, the former is applied, dried and baked by a solvent sol spray method, and then the latter is applied by sputtering to a thickness of 15 μm.
A μm film was formed. Each of the thus obtained cylinders was joined to a flange made of the same material to obtain a coil bobbin bobbin. A 1.2 mmφ superconducting conductor was wound around this with a tension of 10 kgf. Thereafter, the coil was impregnated with the epoxy resin and cured under the same conditions to complete a superconducting coil.

[0014]

[Comparative Example] The following was prepared as a comparative example and compared. E-glass as a normal glass or FRP as an E-glass fiber (Nitto Boseki), a high-strength polyethylene fiber (Toyobo, SK-60) and a high-strength polyethylene fiber / alumina fiber (Sumitomo Chemical, Altex) ) =
Using the 50/50 (volume ratio) and the epoxy as a matrix, a pipe having the same shape as that of the example was prepared by a filament winding method. Aluminum pipe was also studied as metal. A flange made of the same material was joined to each of the thus obtained cylinders, a superconducting coil was prepared under the same conditions, and the characteristics were examined. Table 1 shows the results.

[0015]

[Table 1]

(Coefficient of thermal expansion) A strain gauge was attached to the outer surface of the bobbin, immersed in liquid He, and the dimensional change in the circumferential direction was measured. The measurement position was measured at five points at equal intervals (7.5 cm) with both ends opened by 10 cm, and the average value was obtained. When forming a bobbin from glass or metal itself, a 5 mm cube test piece was cut out from these flat plates. Also FRP
In the case of (1), the lath fiber itself was used as a sample, though it was a reinforcing fiber.
For these, TMA (Thermal Machine)
liquid Heal from the room temperature by the Ionic Analyzer) method.
It was immersed in the sample and the dimensional change in the circumferential direction was measured. (Coefficient of friction) A sample of 10 × 10 × 5 mm was cut out from each coil bobbin, and 5 mm which was a matrix of a superconducting wire was cut out.
The coefficient of friction was measured in liquid He by pressing CuNi of φ while applying a force of 10N. (Stress relaxation) A sample of 10 × 10 × 5 mm was cut out from each coil bobbin, and the crosshead interval was set to 5 in liquid He.
mm and apply a compressive stress of 30 MPa for 100 min.
Later stresses were measured. The stress relaxation rate (X) was measured as follows. X = σ / σ ₀ × 100% σ ₀ : initial stress 30 MPa σ: stress after 100 min (compressive stress) From each pipe, x (tangential direction as viewed from pipe cross section), y (pipe longitudinal direction), z (x, A rectangular parallelepiped having a length of 5, 10, 5 mm (in the direction of 90 ° with respect to the y-axis) was cut out, and the compression characteristics were measured at room temperature at a speed of 1 mm / min in the x-direction. From this, the compression strength and compression elastic modulus were calculated. (Initial Coil Characteristics) The training characteristics were examined by immersing the superconducting coil device in liquid He. 50H coil device
The current value when a voltage was generated by connecting to a z power supply and gradually increasing the current from 0 was defined as a quench current value (Iq). This operation was repeated to determine the maximum current value (Iq). (Coil durability) The coil characteristics after operation for 20,000 hours were examined by the above-described method.

[0017]

According to the present invention, it has become possible to provide a stable and high-performance superconducting coil which has a small number of times of training and a high maximum current value even after long-term use, as well as initial coil characteristics.

[Table 2]

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI B29K 263: 00 309: 08

Claims (8)

[Claims] 1. A cryogenic superconducting coil in which a superconducting wire is wound around a cylindrical or columnar winding frame, wherein the winding frame is 300K.
The average coefficient of thermal expansion up to 4.2K is 3.8 × 10 ⁻⁶
A superconducting coil made of low heat change glass or ceramic having a temperature of (1 / ° C.) or less. 2. A fiber reinforced plastic obtained by integrally molding a low heat-change glass fiber or a ceramic fiber and a matrix resin having an average coefficient of thermal expansion of 3.8 × 10 ⁻⁶ (1 / ° C.) or less from 300K to 4.2K. A superconducting coil characterized by using a winding frame. 3. The winding frame is provided with a roving of the low heat-deformable glass or ceramics fiber of ± 35 to the axial direction of the coil.
3. A fiber reinforced plastic wound at an angle of 90 degrees and integrally formed with a matrix resin.
The superconducting coil as described. 4. The superconducting coil according to claim 1, wherein a molybdenum compound layer is formed on the surface of the bobbin. 5. The superconducting coil according to claim 1, wherein a fluorine compound layer is formed on a surface of the bobbin. 6. A paraffin or olefin compound layer is formed on the surface of a bobbin.
4. The superconducting coil according to claim 3. 7. The superconducting coil according to claim 1, wherein a polyolefin or a copolymer layer thereof is formed on the surface of the bobbin. 8. The superconducting coil according to claim 1, wherein a silicon compound layer is formed on the surface of the bobbin.