Flexible member and method of manufacturing the same

Abstract

To provide a flexible member in which thermal conductivity at an extremely low temperature is improved more than before, and to provide a method for producing the same.SOLUTION: A flexible member, which is a stranded wire or a braided wire comprising a plurality of aluminum wires satisfying the following formulae (1) and (2): 0.04 ≤ X ≤ 50 (1) Y ≥ 4.9 * 10 - 4 * X2 + 6.8 * 10 - 2 * X + 1.6 * 10 - 1 (2) In Expressions (1) and (2), X is an arithmetic average (mass ppm) of a total content of Fe, Si, Cu, Mg, Ti, Mn, Zn, and Ga that are each a main impurity in the plurality of aluminum wires, and Y is an arithmetic average wire diameter (mm) of the plurality of aluminum wires.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to flexible members and methods of making the same. [Background technology]

[0002] Conventionally, flexible members, which are twisted or braided wires containing multiple conductors, have been made of copper-based materials such as copper or copper alloys, which have high electrical conductivity. However, from the perspective of reducing workloads through weight reduction, a shift from copper-based materials to aluminum-based materials is being considered.

[0003] The use of the flexible member as a cryogenic heat transfer material is also being considered. Non-Patent Document 1 discloses the use of 99.9999% pure aluminum stranded wire (49 strands of 0.15 mm diameter wire twisted together) in a cryostat. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Newsletter "Aluminum Age", Japan Aluminum Association, 2017, No. 186, pp. 6-7 Summary of the Invention [Problem to be solved by the invention]

[0005] In the prior art disclosed in Non-Patent Document 1, sufficient consideration has not been given to improving the thermal conductivity of flexible members at cryogenic temperatures, and there is room for improvement.

[0006] An object of the present disclosure is to provide a flexible member having improved thermal conductivity at cryogenic temperatures compared to conventional flexible members, and a method for manufacturing the same. [Means for solving the problem]

[0007] Aspect 1 of the present invention is A flexible member that is a twisted or braided wire containing a plurality of aluminum wires that satisfy the following formulas (1) and (2): 0.04≦X≦50 (1) Y ≥ 4.9 × 10 -4 ×X 2 +6.8×10 -2 ×X+1.6×10 -1 ···(2) In formulas (1) and (2), X is the arithmetic mean value (ppm by mass) of the total content of Fe, Si, Cu, Mg, Ti, Mn, Zn, and Ga, which are major impurities in the plurality of aluminum wires, and Y is the arithmetic mean wire diameter (mm) of the plurality of aluminum wires.

[0008] Aspect 2 of the present invention is In the flexible member according to aspect 1, the number of the plurality of aluminum wires is 7 to 100.

[0009] Aspect 3 of the present invention is 3. The flexible member according to claim 1, wherein X is 1 ppm by mass or less and Y is 0.3 mm or more.

[0010] A fourth aspect of the present invention is The flexible member according to any one of aspects 1 to 3, wherein X and Y further satisfy the following formula (3): Y≦-0.4×ln(X)+2.3 (3)

[0011] A fifth aspect of the present invention is The flexible member according to any one of Aspects 1 to 4 is a heat transfer material for cryogenic use.

[0012] A sixth aspect of the present invention is The method for manufacturing a flexible member includes subjecting a plurality of aluminum wires that satisfy the following formulas (1) and (2) to a twisted or braided wire processing. 0.04≦X≦50 (1) Y ≥ 4.9 × 10 -4 ×X 2 +6.8×10 -2 ×X+1.6×10 -1 ···(2) In formulas (1) and (2), X is the arithmetic mean value (ppm by mass) of the total content of Fe, Si, Cu, Mg, Ti, Mn, Zn, and Ga, which are major impurities in the plurality of aluminum wires, and Y is the arithmetic mean wire diameter (mm) of the plurality of aluminum wires. [Effects of the Invention]

[0013] According to this embodiment, it is possible to provide a flexible member having improved thermal conductivity at cryogenic temperatures compared to conventional flexible members, and a method for manufacturing the same. [Brief explanation of the drawings]

[0014] [Figure 1] The results of Table 1 below are shown in a graph, with X on the horizontal axis and Y on the vertical axis. [Figure 2] The results of Table 2 below are shown in a graph, with X on the horizontal axis and Y on the vertical axis. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present inventors have conducted various studies to realize a flexible member with improved thermal conductivity at cryogenic temperatures compared to conventional flexible members. As disclosed in Non-Patent Document 1, in conventional technology, the wire diameter of aluminum wires has generally been set to 0.15 mm (or less), mainly to ensure flexibility. However, as a result of the inventors' studies, they have found that the thermal conductivity of flexible members at cryogenic temperatures can be improved by increasing the wire diameter beyond a predetermined value depending on the purity of the aluminum wire. Furthermore, they have found a predetermined relationship between purity and wire diameter, and have found that by satisfying this relationship, improved thermal conductivity at cryogenic temperatures compared to conventional flexible members can be obtained. The details of each requirement stipulated in this embodiment are shown below.

[0016] The flexible member according to this embodiment is a twisted or braided wire including a plurality of aluminum wires that satisfy the following formulas (1) and (2). 0.04≦X≦50 (1) Y ≥ 4.9 × 10 -4 ×X 2 +6.8×10 -2 ×X+1.6×10 -1 ···(2) In formulas (1) and (2), X is the arithmetic mean value (ppm by mass) of the total content of Fe, Si, Cu, Mg, Ti, Mn, Zn, and Ga, which are major impurities in the plurality of aluminum wires, and Y is the arithmetic mean wire diameter (mm) of the plurality of aluminum wires. This provides improved thermal conductivity at cryogenic temperatures compared to conventional materials.

[0017] A twisted or braided wire including a plurality of aluminum wires can be made more flexible than a solid aluminum wire having the same cross-sectional area as the twisted or braided wire.

[0018] The aluminum wires have an arithmetic mean value X of the total content of Fe, Si, Cu, Mg, Ti, Mn, Zn, and Ga, which are major impurity elements (hereinafter also referred to as "major impurities") inevitably introduced due to the conditions of raw materials, materials, manufacturing equipment, etc., and satisfy the above formula (1) (i.e., 0.04 mass ppm to 50 mass ppm). By satisfying the above formula (1) and the formula (2) described below, improved thermal conductivity at cryogenic temperatures can be obtained. If X exceeds 50 ppm, the thermal conductivity at cryogenic temperatures may be significantly reduced, and sufficient thermal conductivity at cryogenic temperatures may not be obtained even if formula (2) is satisfied. Alternatively, the arithmetic mean wire diameter Y of the aluminum wires may need to be significantly increased, which may significantly reduce flexibility. Furthermore, setting X to less than 0.04 mass ppm significantly increases manufacturing costs. Here, the "arithmetic mean value" of the physical property values ​​of a plurality of aluminum wires (including the arithmetic mean diameter described later) refers to the arithmetic mean value of the physical property values ​​measured for each aluminum wire. Note that if a plurality of aluminum wires are prepared by the same method (including raw materials), the physical property value of one of the aluminum wires may be used as the "arithmetic mean value of the physical property values."

[0019] The aluminum wires may have a composition composed of Al and unavoidable impurities. The unavoidable impurities may include elements introduced due to the conditions of raw materials, materials, manufacturing equipment, etc. In addition to the eight major impurities described above, the unavoidable impurities may include V, Cr, Zr, Li, Be, B, Na, K, Ca, Ni, Co, Ge, As, Se, Mo, Ag, Cd, In, Sn, Sb, Ba, La, Ce, Pt, Hg, Pb, Bi, Th, and U (also referred to simply as "29 elements"). The arithmetic mean value of the total content of elements excluding Th and U from the 29 elements (hereinafter also referred to as "27 elements") may be equal to or less than half, or even less than one-quarter, of the arithmetic mean value of the total content of the major impurities. Note that the amount of unavoidable impurities other than the eight major impurity elements and the 27 elements is extremely small, so the total content of the unavoidable impurities may be the total content of the eight major impurity elements and the 27 elements. That is, the arithmetic mean value of the total content of unavoidable impurities may be 2 times or less, 1.5 times or less, or 1.25 times or less of the arithmetic mean value X of the total content of major impurities.

[0020] The above-mentioned component composition (amount of impurities) is measured by the method described in the examples below.

[0021] The flexible member according to this embodiment further satisfies the above formula (2). The inventors newly discovered that the thermal conductivity of the flexible member at cryogenic temperatures depends on the purity and diameter of the aluminum wire, and discovered the above formula (2) by examining in detail the relationship between purity and wire diameter that provides high thermal conductivity at cryogenic temperatures in the examples described below. By satisfying this formula (2) together with the above formula (1), improved thermal conductivity at cryogenic temperatures can be achieved compared to conventional products. The present inventors have also found that the range in which even higher thermal conductivity can be obtained at extremely low temperatures preferably satisfies the following formula (4), and more preferably satisfies the following formula (5). Y ≥ 6.0 × 10 -4 ×X 2 +1.3×10 -1 ×X+1.6×10 -1 ···(4) Y ≥ 6.2 × 10 -4 ×X 2 +2.6×10 -1 ×X+1.2×10 -1 ···(5)

[0022] In the flexible member according to this embodiment, X is preferably 1 mass ppm or less and Y is preferably 0.3 mm or more, and more preferably 0.5 mm or more, which makes it possible to obtain even higher thermal conductivity at cryogenic temperatures.

[0023] The present inventors have newly discovered that the flexibility of a flexible member depends on the purity and diameter of the aluminum wire, and by examining the relationship between purity and diameter in detail in the examples described below, have found that it is preferable to further satisfy the following formula (3): By satisfying formula (3), high flexibility can be obtained. Y≦-0.4×ln(X)+2.3 (3)

[0024] In this embodiment, the number of the aluminum wires is preferably 7 to 100. By having 7 or more wires, the thermal conductivity of the flexible member at cryogenic temperatures can be further improved. Furthermore, by having 100 or less wires, the flexibility of the flexible member can be improved.

[0025] The flexible member according to this embodiment mainly includes the above-described plurality of aluminum wires, and may further include other conductive wires (such as copper wires). In the flexible member according to this embodiment, the number of the above-described plurality of aluminum wires is preferably 80% or more of the total number of conductive wires, more preferably 90% or more, and most preferably 100% (i.e., the flexible member is made up of the above-described plurality of aluminum wires).

[0026] The flexible member according to this embodiment has sufficient thermal conductivity even at extremely low temperatures, and can therefore be suitably used, for example, as a heat transfer material for extremely low temperatures. Heat transfer materials for extremely low temperatures are used, for example, for cooling superconducting magnets for MRI and NMR, superconducting quantum computers, etc. In particular, it is preferable to use the flexible member as a heat transfer material for extremely low temperatures in contact with an extremely low temperature part, for example, between 1 K and 60 K, as this will significantly enhance the effects of this embodiment.

[0027] The method for manufacturing a flexible member according to this embodiment includes subjecting the plurality of aluminum wires described above to a twisting or braiding process. The processing method is not particularly limited, and the wires can be processed using a twisting machine or a braiding machine. [Example]

[0028] Aluminum wires with different major impurity contents and wire diameters were prepared, as shown in Table 1. The component compositions of the aluminum wires, including the major impurity contents, were measured by glow discharge mass spectrometry. Although not shown in Table 1, the total content of the 27 elements in each aluminum wire was less than one-quarter of the total content of the major impurities. A plurality of aluminum wires of each type were prepared and twisted to produce flexible members. When producing the flexible members, the number of aluminum wires in the twisted wire was appropriately set so that the thermal conductivity (thermal conductivity of the aluminum wire × cross-sectional area perpendicular to the longitudinal direction of the twisted wire) of the twisted wire would be approximately the same, based on a standard wire diameter of 0.16 mm (or 0.20 mm), which is similar to the conventional wire diameter of 0.15 mm. Furthermore, for comparison, a Cu flat braided wire (purchased from Kyowa Harmonet, wire diameter φ0.125, tin-plated flat braided copper wire TBC 5.5SQ) for test No. 38 and a Cu flat braided wire (purchased from Misawa Electric Wire, wire diameter φ0.125) for test No. 39 were prepared.

[0029] The flexible members of Test Nos. 1 to 39 were evaluated as follows.

[0030] <Thermal conductivity evaluation at cryogenic temperatures> For each aluminum wire, the resistivity at 300 K (ρ300 K) (Ω·m) and the resistivity at 4.2 K (ρ4.2 K) (Ω·m) were measured using the four-terminal method, and the residual resistance ratio (RRR) and thermal conductivity (W / m / K) at cryogenic temperature (4.2 K) of each aluminum wire were calculated using the following equations (6) and (7). RRR=ρ 300K / ρ 4.2K ···(6) Thermal conductivity = 1 / (1.8 x 10 -7 ×4.2 2 +1.1 / RRR / 4.2)···(7) Furthermore, the total cross-sectional area of ​​the stranded wire (m 2 ) to determine the thermal conductivity (W·m / K) of the stranded wire at cryogenic temperatures. Furthermore, the thermal conductivity of the stranded wire at cryogenic temperatures per unit weight (W·m / K / kg) was determined by dividing the thermal conductivity of the stranded wire at cryogenic temperatures by the weight (kg) of the stranded wire. Note that Test No. 10 is a configuration equivalent to conventional technology, and if it had a higher thermal conductivity of 6.5 (W·m / K / kg) or more, it was judged to have passed (〇). The results are shown in Table 1.

[0031] [Table 1]

[0032] Consider the results in Table 1. Samples Nos. 1 to 9, 11 to 21, and 23 to 28, which met all the requirements of this embodiment, had improved thermal conductivity at cryogenic temperatures compared to the prior art. On the other hand, Test No. 10, and Test Nos. 22 and 29 to 39, which correspond to the prior art, did not meet the requirements of this embodiment and were inferior in thermal conductivity at cryogenic temperatures.

[0033] Figure 1 shows a graph of the results of Table 1, with X (logarithmic) on the horizontal axis and Y on the vertical axis. The dashed line in Figure 1 is the curve showing the right side of Y = Equation (2), with O plots indicating examples with a thermal conductivity of 6.5 (W·m / K / kg) or higher at cryogenic temperatures, and X plots indicating other examples. As shown in Figure 1, by satisfying Equation (2) (i.e., being on or above the curve of Equation (2)), it can be seen that a material has a thermal conductivity of 6.5 (W·m / K / kg) or higher at cryogenic temperatures.

[0034] <Flexibility evaluation> Furthermore, the flexibility of the flexible members of Test Nos. 1 to 39 was evaluated as follows. It is preferable that the flexible member has a large vibration damping property (i.e., a small spring constant). The spring constant of the conductor (here, aluminum wire or copper wire) can be derived from the following equation (8) using the equation for cantilever deflection. k=K×E×π×D 4 / (64×L 3 )···(8) Here, k is the spring constant (N / m), K is the shape factor of the wire with one end fixed, E is Young's modulus (GPa), L is the length of the conductor (m), and D is the diameter of the conductor (m). The spring constant of a stranded wire consisting of n conductors can be evaluated by k × n. On the other hand, when considering application as a cryogenic heat transfer material to cryogenic equipment such as superconducting magnets, it is preferable that the material has a low yield strength and easily yields. From the above, the flexibility evaluation index of this disclosure is [reciprocal of the spring constant of the stranded wire] / [yield strength] (m 3 / N 2Here, the yield strength was measured by performing a tensile test on a conductor (here, aluminum wire or copper wire) using a Shimadzu Corporation precision universal testing machine AGS-10kNX, and measuring the 0.2% yield strength (N / m 2 ) was decided. The results are shown in Table 2.

[0035] [Table 2]

[0036] Consider the results in Table 2. Test Nos. 1 to 10, 12 to 22, 26 to 34, and 36 to 37 satisfy formula (3), and the ratio of [reciprocal of the spring constant of the stranded wire] / [yield strength] is 5.0 × 10 -2 (m 3 / N 2 ) or more, and had high flexibility.

[0037] Figure 2 shows a graph of the results of Table 2, with the horizontal axis representing X (logarithm) and the vertical axis representing Y. The dashed line in Figure 2 is the straight line that corresponds to the right side of Y = Equation (3), and the circle plots indicate that [reciprocal of the spring constant of the twisted wire] / [yield strength] is 5.0 x 10 -2 (m 3 / N 2 ) are examples above, and the plots with × are other examples. As shown in Figure 2, by satisfying equation (3) (i.e., being on or below the line of equation (3)), -2 (m 3 / N 2 ) or more [reciprocal of the spring constant of the twisted wire] / [yield strength].

Claims

1. A flexible member that is a twisted or braided wire containing a plurality of aluminum wires that satisfy the following formulas (1) and (2): 0.04≦X≦50 (1) Y≧4.9×10 －４ ×X ２ +6.8×10 －２ ×X+1.6×10 －１ ・・・(2) In formulas (1) and (2), X represents the arithmetic mean value (ppm by mass) of the total content of Fe, Si, Cu, Mg, Ti, Mn, Zn, and Ga, which are major impurities in the plurality of aluminum wires, and Y represents the arithmetic mean wire diameter (mm) of the plurality of aluminum wires.

2. The flexible member according to claim 1 , wherein the number of the plurality of aluminum wires is 7 to 100.

3. 2. The flexible member according to claim 1, wherein X is 1 mass ppm or less and Y is 0.3 mm or more.

4. The flexible member according to claim 1 , wherein X and Y further satisfy the following formula (3): Y≦-0.4×ln(X)+2.3...(3)

5. The flexible member according to any one of claims 1 to 4, which is a heat transfer material for cryogenic temperatures.

6. A method for manufacturing a flexible member, comprising: subjecting a plurality of aluminum wires that satisfy the following formulas (1) and (2) to a twisted or braided wire processing. 0.04≦X≦50 (1) Y≧4.9×10 －４ ×X ２ +6.8×10 －２ ×X+1.6×10 －１ ・・・(2) In formulas (1) and (2), X represents the arithmetic mean value (ppm by mass) of the total content of Fe, Si, Cu, Mg, Ti, Mn, Zn, and Ga, which are major impurities in the plurality of aluminum wires, and Y represents the arithmetic mean wire diameter (mm) of the plurality of aluminum wires.

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