JPH08115813A - Superconducting coil - Google Patents

Abstract

PURPOSE: To provide a superconducting coil in which a strain characteristic from room temperature up to a cryogenic temperature state is not changed by a repetitive heat cycle by a method wherein a reinforcing fiber roving comprised by combining organic fibers having a negative coefficient of thermal expansion and glass fibers are wound on a spool at a specific angle against the axial direction of the coil, and the wound product is integrally molded with resin. CONSTITUTION: In a superconducting coil for a cryogenic temperature, in which a superconducting wire is wound on a cylindrical or piller-shaped spool, a reinforcing fiber roving comprised of combination of organic fibers having a negative coefficient of thermal expansion and glass fibers are wound on a spool at an angle of ±40-90 deg. against the axial direction of the coil, and the wound product i integrally molded with resin to obtain a superconducting coil comprised of a fiber-reinforced plastic. In the superconducting coil, the volume ratio of the organic fiber to the glass fiber is (90:10) to (30:70). Thereby, it is possible to obtain the superconducting coil in which the number of training operation is small, whose maximum current value is high and stable and whose performance is high.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting coil which is cooled to an extremely low temperature and used.

[0002]

2. Description of the Related Art In a superconducting coil device, a superconducting conductor is wound on a winding frame, and layer coil elements in which the superconducting conductor is wound along a spiral groove formed between layers with a spacer or engraved on the outer peripheral surface are sequentially formed. Concentric layers are formed. Conventionally, a metal such as aluminum or glass fiber reinforced plastic is used as the reel.

[0003]

Although the superconducting coil has a wide variety of applications, increasing the current density of the superconducting wire is extremely important for improving the performance of the coil itself. And, this largely depends on the stability of the superconducting wire wound around the bobbin. The physical stability of the superconducting wire wound around the bobbin is closely related to the electrical stability of the superconducting coil itself. Usually, the reel is made of metal such as stainless steel or aluminum, or glass fiber reinforced plastic (G
FRP) is used, but when they are wound at room temperature and cooled to liquid nitrogen (LNT) or liquid helium temperature (LHeT), they both largely contract in the circumferential direction of the reel and slightly contract in the axial direction. On the other hand, when the superconducting wire is excited at an extremely low temperature, it expands in the circumferential direction due to the repulsive force resulting from the Lorentz force, and the winding moves in the direction away from the winding frame. Further, when the temperature becomes extremely low in the axial direction, the size of the superconducting wire changes more than the small amount in the axial direction of the winding frame due to the large contraction caused by the positive expansion in the vertical direction. These two movements are combined to cause microscopic mutual movements between the superconducting wires, causing a disturbance due to frictional heat generation on the surface, and the superconducting coil is quenched. Further, in the case of stainless steel or aluminum frame, since it is conductive, Joule heat is generated due to eddy current, especially in an alternating current, so that it becomes unstable.

In order to improve the coil performance, a large diameter,
It is necessary to make the superconducting wire long and secure the length of the superconducting wire. On the other hand, in order to use the cryogenic measurement with LHeT, it is necessary to reduce the thickness of the coil bobbin itself to reduce the heat capacity,
It is important for improving cooling efficiency. On the other hand, for the coil, when the superconducting wire is wound around the winding frame, it is necessary to apply a certain tension in advance to suppress the movement of the superconducting wire. It can be said that the higher the tension is to a certain limit, the higher the effect of suppressing the wire rod and the higher the quenching resistance. Considering this and the technological trend of large diameter thinning of the reel, it is important that the reel itself has high rigidity. If a material with low compressive strength and elastic modulus is used as the material forming this reel, it will be deformed over time due to high pre-tension during coil making, and the strain characteristics from room temperature to cryogenic temperature will be repeated. This causes a disadvantage that the coil characteristics change depending on the cycle and the coil characteristics change. The present invention has been made to solve the above problems,
The purpose is to obtain a high-performance and stable superconducting coil.

[0005]

DISCLOSURE OF THE INVENTION The present invention relates to a cryogenic superconducting coil in which a superconducting wire is wound around a cylindrical or columnar winding frame, in which the winding frame has a negative expansion coefficient of organic fiber and glass fiber. The superconducting coil is characterized in that it is made of a combination of the above and is made of a fiber reinforced plastic obtained by integrally molding the resin and the resin.

The negative expansion organic fibers used in the present invention are high-strength and high-modulus fibers such as polyethylene, aramid, polyarylate (wholly aromatic polyester), P
Fibers of BZ polymer (polybenzbisoxazole, polybenzbisthiazole, etc.) may be mentioned, with polyethylene fibers being particularly preferred. All of these fibers have the peculiar property that they expand as the temperature decreases, and because they have a much lower specific gravity than glass fibers,
It is possible to obtain a reinforcing fiber having a high specific strength, a high specific elastic modulus and a light weight.

On the other hand, all of these organic fibers have a common drawback that they are extremely low in compression, bending and properties as compared with inorganic fibers such as metal and ceramics. However, in general, inorganic fibers are excellent in compression and bending characteristics, but both show only positive expansion characteristics. Among the inorganic fibers, carbon fiber has a small negative expansion property, is excellent in compression and bending characteristics, and has a small specific gravity, which is preferable, but it has a problem in insulation performance and is limited in use as a winding frame of a coil. On the contrary,
Although glass fiber shows only positive expansion characteristics, it has excellent compression and bending characteristics and good insulation performance. Regarding the positive swelling property, which is a drawback, it is possible to satisfy the required performance requirements by appropriately mixing and using the organic fiber having the negative swelling property. The significance of mixing and using another glass fiber is that organic fibers generally have low adhesiveness with matrix resins. On the other hand, the glass fiber is well compatible with the resin and has high interlaminar shear strength derived from the adhesiveness at the fiber / matrix interface.
This reduces the possibility of occurrence of microcracks and the like due to thermal shock when the temperature is lowered from room temperature, and a stable molded product is obtained.

Here, the glass fibers are E glass, S glass,
A wide range of materials such as F glass can be used, but S-glass and F-glass are particularly preferred. The mixing ratio of the organic fiber and the glass fiber is 90/10 to 30/70, preferably 80/20 to 35/75 in terms of volume ratio. If the glass fiber content is less than 10%, the effect of improving the compression characteristics is small,
Further, when the organic fiber content is less than 30%, the negative expansion property becomes small.

Next, the dimensional change will be described in detail. All of these organic fibers have the unique property of having a negative expansion coefficient (extending when the temperature is lowered from room temperature). On the other hand, glass fiber has a positive expansion coefficient. On the other hand, the matrix resin exhibits a positive expansion, but the fiber reinforced plastic (FRP) made of a mixed fiber of organic fiber and glass fiber continuously changes depending on the mixing ratio of both. Figure 1 shows high strength, high modulus polyethylene fiber (DF) and T-glass (GF).
2 shows the coefficient of thermal expansion in the fiber direction of the unidirectionally reinforced FRP using. In this example, it can be seen that negative expansion occurs when DF is 40 vol% or more. It is also possible to wind a DF / GF mixed fiber to form a cylinder or a cylinder.

At this time, the matrix resin exhibits positive expansion, but the cylinder or column formed by winding the filaments of these fibers has a negative expansion coefficient in the circumferential direction and an axial direction by selecting the mixing ratio of DF and GF. Can have a positive expansion coefficient. As the matrix used here, an epoxy resin, an unsaturated polyester resin, a vinyl ester resin, a urethane resin, a urethane acrylate resin or the like can be used, but an epoxy resin is particularly preferable. Although all of these matrix resins exhibit positive expansion, DF fibers exhibiting negative expansion and GF fibers exhibiting positive expansion are used, and the filament is wound by changing the winding angle, and the dimensions of the formed cylinder or cylinder with temperature increase. The change depends on the winding angle as shown in FIG. 2, and by appropriately selecting it, the negative expansion coefficient in the circumferential direction and the positive expansion in the axial direction can be obtained. The negative expansion in the circumferential direction is much higher than the negative expansion coefficient of the fiber itself. Orientation angle is ± 40-9 with respect to the axial direction
0 degree is suitable, but it is preferably ± 47 to ± 85 degrees. If the angle is less than ± 40 degrees, the positive expansion in the circumferential direction (contracting as the temperature becomes lower) increases. On the other hand, in the case of GFRP, since both glass fiber and matrix resin have positive expansion, only the characteristic of normal expansion, which is a characteristic of ordinary materials, can be obtained regardless of the winding angle. Therefore, the superconducting coil using the reel according to the present invention can be a high-performance coil that is stable, has high quench resistance, and has a large current density. When GFRP is used as a bobbin of a superconducting coil, the biggest problem is that the coil is easily quenched due to loosening of the superconducting wire accompanying a large contraction in the circumferential direction.

In the present invention, when a high-strength, high-modulus organic negative expansion fiber such as polyethylene, aramid, polyarylate, or PBZ polymer is combined with a glass fiber excellent in compression resistance and bending characteristics, a fiber molded product is obtained. Training work is easy, and the maximum current value is high and stable by using a fiber reinforced plastic integrally molded with winding resin so that the angle is ± 40 degrees to ± 90 degrees with respect to the axis. It is intended to provide a high-performance superconducting coil. As a method of mixing the organic fiber and the glass fiber, a method of uniformly mixing one or more kinds of the organic fiber and the glass fiber in a yarn unit and winding the mixture,
Any method such as a method of winding a yarn in which organic fibers and glass fibers are uniformly mixed in a filament unit, a method of alternately laminating organic fibers and glass fibers, and a method of winding are possible. The most effective method is to uniformly mix the organic fiber and the glass fiber with a filament or a yarn and wind them. In this case, the mixing ratio is appropriately set by changing the number of filaments of the organic fiber and the glass fiber, or the ratio of the number of windings of both, for example, the ratio of one glass fiber for every two organic fibers. be able to. Examples of the molding method include a filament winding method or a tape winding method in which the present fiber is wound around a mandrel while being impregnated with a matrix resin in a thread or tape shape.

The mixing ratio of the fibers and the matrix resin in the above composite material is 35 to 8 as the volume molecular weight (Vf) of the fibers.
5% is preferable, and 40 to 70% is more preferable. When the fiber Vf is less than 35%, the reinforcing effect of the fiber does not appear, and when it exceeds 85%, it is difficult to impregnate the matrix resin and the mechanical properties of the composite material deteriorate, which is not preferable.

[0013]

EXAMPLE A cylindrical fiber reinforced plastic (FRP) comprising negative expansion fibers of the present invention was prepared as follows. As the organic negative expansion fiber, high-strength polyethylene fiber (Toyobo,
Dyneema SK60), aramid fiber (Japanese aramid fiber, Twaron HM), polyarylate fiber (Kuraray, Becton), polybenzbisoxazole fiber, etc.,
Various cylindrical FRPs were prepared by filament winding method by uniformly mixing or alternately laminating these and glass fibers (Nitto Boseki, T) with each other. Epoxy resin was used as the matrix, and a uniform mixed resin dope was prepared in the following proportions. Epicoat-827 (oiled shell) 100 Epicure-YH-300 (oiled shell) 80 EMI-24 (oiled shell) 1 Next, various fibers were impregnated with an epoxy resin and wound around a mandrel to form a cylindrical shape. Next, while keeping it on the mandrel, 100 ° C x 2 hr, then 130 ° C x 3
Curing and molding with hr, fiber volume content 65%, outer diameter 100
A molded body having a size of mm × length of 500 mm and a wall thickness of 13 mm was obtained.
A flange made of GFRP was adhered to each of the cylinders thus obtained to obtain a coil winding frame. 1.2mm to this
After winding one layer of a φ superconductor with a tension of 10 kg, a superconducting coil was completed. The results of these evaluations are shown in Table 1.

[0014]

[Table 1]

(Coefficient of thermal expansion) Strain gauges were attached to the outer peripheral surface and the inner peripheral surface of the reel, and then immersed in liquid He to measure the dimensional change in the circumferential direction. Both the inner and outer sides of the measurement position were 10 cm apart at both ends, and five points were measured at equal intervals (120 cm) to obtain an average value. (Quench current) The superconducting coil device was immersed in liquid He, and the quench current of the coil after continuous operation for 10,000 hours was measured. The results are shown by the maximum current density reached by repeated training and the number of trainings at that time. The superconducting critical current value used at this time was 1850.
A. (Compression characteristic) Length from each pipe in the x (full tangential direction from the pipe cross section), y (longitudinal direction of the pipe), and z (90 ° to the x and y axes) direction is 5, 10, 5 mm. The rectangular parallelepiped 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 compressive strength and the compressive elastic modulus were calculated.

[0016]

According to the present invention, it is possible to provide a stable and high-performance superconducting coil in which the number of trainings is small, the maximum current value is high.

[Brief description of drawings]

FIG. 1 is a mixture ratio of high-strength and high-modulus polyethylene fiber (DF) and glass fiber (GF) and its unidirectionally reinforced FRP.
The figure which shows the relationship of the thermal expansion coefficient of the fiber direction.

FIG. 2 is a diagram showing a relationship between a winding angle and a coefficient of thermal expansion of a molded product using various fibers.

Claims (2)

[Claims] 1. A cryogenic superconducting coil in which a superconducting wire is wound around a cylindrical or columnar winding frame, wherein the winding frame comprises a roving of a reinforcing fiber made of a combination of an organic fiber having a negative expansion coefficient and a glass fiber, ± 40 to the coil axis
A superconducting coil, which is made of fiber-reinforced plastic which is wound at an angle of 90 degrees and is integrally molded with resin. 2. The superconducting coil according to claim 1, wherein the volume ratio of the organic fiber to the glass fiber is 90:10 to 30:70.