Flexible member and production method therefor

Abstract

This flexible member is a stranded wire or a braided wire including multiple aluminum wires that satisfy formulae (1) and (2).　(1): 0.04≤X≤50 (2): Y≥4.9×10-4×X2+6.8×10-2×X+1.6×10-1 In formulae (1) and (2), X represents the arithmetic average value (mass ppm) of the total content of Fe, Si, Cu, Mg, Ti, Mn, Zn, and Ga which are main impurities in the multiple aluminum wires, and Y represents the arithmetic average wire diameter (mm) of the multiple aluminum wires.

Description

Flexible member and manufacturing method thereof

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

[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 has also been considered. Non-Patent Document 1 discloses the use of 99.9999% pure aluminum stranded wire (49 strands of 0.15 mm diameter wire) in a cryostat.

[0004] "Aluminium Age" newsletter, Japan Aluminum Association, 2017, No. 186, pp. 6-7

[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.

[0007] A first aspect of the present invention is a flexible member that 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 x 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] A second aspect of the present invention is the flexible member according to the first aspect, wherein the number of the plurality of aluminum wires is 7 to 100.

[0009] A third aspect of the present invention is the flexible member according to the first or second aspect, wherein X is 1 mass ppm 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 the first to third aspects, 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 the first to fourth aspects, which is a heat transfer material for cryogenic temperatures.

[0012] A sixth aspect of the present invention is a method for producing a flexible member, which includes twisting or braiding 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 x 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.

[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.

[0014] The results of Table 1 described later are shown in a graph with the horizontal axis being X and the vertical axis being Y. The results of Table 2 described later are shown in a graph with the horizontal axis being X and the vertical axis being Y.

[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 an aluminum wire has generally been set to 0.15 mm (or less), primarily to ensure flexibility. However, as a result of the inventors' studies, it has been found that the thermal conductivity of a flexible member at cryogenic temperatures can be improved by increasing the wire diameter beyond a predetermined value depending on the purity of the aluminum wire. Furthermore, the inventors 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 following describes in detail each requirement specified in this embodiment.

[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 x 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 aluminum wires, and Y is the arithmetic mean wire diameter (mm) of the aluminum wires. This allows for improved thermal conductivity at extremely low temperatures compared to conventional methods.

[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 conditions such as raw materials, materials, and manufacturing equipment, satisfying 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 the same 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 composition of the aluminum wires may consist 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 impurity elements 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 wire 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 compared to conventional methods can be obtained. The inventors also discovered that the range in which even higher thermal conductivity can be obtained at cryogenic temperatures preferably satisfies the following formula (4), and more preferably satisfies the following formula (5): Y≧6.0×10 －４ ×X ２ +1.3 x 10 －１ ×X+1.6×10 －１ ... (4) Y ≥ 6.2 × 10 －４ ×X ２ +2.6 x 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 this 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 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.

[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 listed 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. Multiple aluminum wires of each type were prepared and twisted to produce flexible components. When producing the flexible components, 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 was 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) of Test No. 38 and a Cu flat braided wire (purchased from Kyowa Harmonet, wire diameter φ0.125, tin-plated flat braided copper wire TBC 5.5SQ) of Test No. 39 were also tested. A Cu flat braided wire (purchased from Misawa Electric Wire Co., Ltd., wire diameter φ0.125) No. 39 was prepared.

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

[0030] <Evaluation of Thermal Conductivity 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 by a four-terminal method, and the residual resistance ratio (RRR) and thermal conductivity at cryogenic temperature (4.2 K) (W / m / 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 × 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 was divided by the weight (kg) of the stranded wire to determine the thermal conductivity (W m / K / kg) of the stranded wire at cryogenic temperatures per unit weight. Note that Test No. 10 was a configuration equivalent to the conventional technology, and if it had a higher thermal conductivity of 6.5 (W m / K / kg) or more, it was judged to be pass (◯). The results are shown in Table 1.

[0031]

[0032] The results in Table 1 are examined. Samples Nos. 1 to 9, 11 to 21, and 23 to 28, which met all of 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 plots of ◯ representing examples with a thermal conductivity of 6.5 (W m / K / kg) or more at cryogenic temperatures, and plots of × representing 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 thermal conductivity of 6.5 (W m / K / kg) or more at cryogenic temperatures is achieved.

[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 wire (here, aluminum wire or copper wire) can be derived from the following equation (8) using the equation for cantilever deflection: k = K x E x π x D ４ / (64 x L ３) (8) where 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 wire (m), and D is the diameter of the conductor wire (m). The spring constant of a stranded wire consisting of n conductor wires can be evaluated by k x n. On the other hand, when considering application as a heat transfer material for cryogenic equipment such as superconducting magnets, it is preferable that the yield strength is small and that the wire easily yields. From the above, the flexibility evaluation index of the present disclosure is [reciprocal of the spring constant of the stranded wire] / [yield strength] (m ３ / N ２ Here, the yield strength was measured by performing a tensile test on a conductor (here, an aluminum wire or a copper wire) using a precision universal testing machine AGS-10kNX manufactured by Shimadzu Corporation, and measuring the 0.2% yield strength (N / m ２ The results are shown in Table 2.

[0035]

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

[0037] Figure 2 shows a graph in which the results of Table 2 are arranged with the horizontal axis being X (logarithmic) and the vertical axis being 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] / [proof stress] is 5.0 × 10 －２ (m ３ / N ２ ) are the above examples, and the plots with x are other examples. As shown in Figure 2, by satisfying formula (3) (i.e., being on or below the line of formula (3)), －２ (m ３ / N ２ ) or more [reciprocal of spring constant of twisted wire] / [yield strength].

[0038] This application claims priority from Japanese Patent Application No. 2024-119650, filed July 25, 2024. Japanese Patent Application No. 2024-119650 is incorporated herein by reference.

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 x 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.

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

3. 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 twisting or braiding 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 x 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.

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