Aluminum-carbon metal matrix composite magnet wire

Abstract

We provide magnet wires having conductive cores made of aluminum and carbon (e.g., carbon nanotubes). [Solution] The magnet wire comprises an insulating layer on the surface of a conductive core. The insulating layer and the conductive core collectively form a fully insulated wire of a coil associated with a magnet. The magnet wire forms a coil of magnet for, for example, an electric motor, generator, transformer, inductor, or speaker.

Description

[Technical Field]

[0001] The disclosed teachings relate to metal composites for magnet wires. [Background technology]

[0002] Magnet wire is a conductive wire coated with a thin insulating layer. In some cases, magnet wire is used to construct transformers, inductors, motors, generators, speakers, hard disk head actuators, electromagnets, and other applications requiring dense coils of insulating wire. The insulator is typically made of a tough polymer, sometimes also called enamel.

[0003] Common materials for magnet wire applications include unalloyed pure metals, particularly copper (Cu). Considering factors such as chemical, physical, and mechanical property requirements, Cu is the first-choice conductor for magnet wire. In one example, magnet wire consists of fully annealed electrolytically refined Cu, tightly wound to form an electromagnetic coil. High-purity oxygen-free Cu grades are used in high-temperature applications in electromechanical devices (e.g., motors, generators) cooled in a reducing atmosphere or by hydrogen gas. Aluminum (Al) magnet wire is sometimes used as an alternative in large transformers and motors. Due to its lower conductivity, Al wire requires approximately 50–60% larger cross-sectional area than Cu wire to achieve equivalent resistance. [Overview of the project] [Means for solving the problem]

[0004] The disclosed technology includes a magnet wire having conductive cores of aluminum and carbon. The magnet wire also comprises an insulating mantle disposed on the conductive core. The insulating mantle and the conductive core are jointly constructed to form a fully insulated wire of a coil of magnet.

[0005] In one example, the carbon content of the conductive core is less than 5 wt%. In another example, the carbon content of the conductive core is primarily (e.g., more than 50%) in the form of carbon nanotubes.

[0006] In one example, an insulated wire may have a substantially circular or substantially rectangular cross-section. In another example, an insulated wire may have a substantially two-dimensional cross-section, where substantially two-dimensional means that the width of the conductive core is substantially greater than its thickness (e.g., 10 times or 1000 times greater).

[0007] In one example, the insulating mantle is formed from a polymer such as polyester-amide-imide. In another example, the insulating mantle is formed from anodized aluminum.

[0008] Magnet wires can be configured to form coils in motors, transformers, generators, speakers, electromagnets, magnetic actuators, or inductors. Magnet wires can have properties such as conductivity of at least 55% IACS (International Annealed Copper Standard), preferably about 60% IACS, an ultimate tensile strength of at least 200 MPa, and / or heat resistance that meets the AT4 specification of International Electrotechnical Commission (IEC) standard 62004 (IEC62004). [Brief explanation of the drawing]

[0009] [Figure 1A] Figure 1A shows a cross-section of a wire-wound coil of magnet wire. [Figure 1B] Figure 1B shows a cross-section of a foil-wound coil of magnet wire. [Figure 2] Figure 2 is a graph showing the strengthening of aluminum (Al) and Al-carbon nanotube (Al-CNT) rods with initial diameters by cold drawing to obtain the desired diameter. [Figure 3]Figure 3 is a graph showing the retention of ultimate tensile strength (UTS) after heating Al and Al-0.5 wt% CNT conductors at various temperatures. [Figure 4] Figure 4 is a graph showing the initial rod diameter required to stretch the rod to a wire having the desired ultimate tensile strength and final wire diameter. [Figure 5] Figure 5 is a graph showing the maximum current in copper (Cu) and Al1350 magnet wires with Class FIW6 polyester-amide-imide (PAI) insulation. [Figure 6] Figure 6 is a graph showing the maximum current for Al1350 and Al-CNT 0.5wt% magnet wires with a 50 μm thick FIW6 PAI insulator and for Al1350 and Al-CNT 0.5wt% magnet wires with a 5 μm thick aluminum oxide (Al-Ox) anodic oxide insulator layer. [Figure 7] Figure 7 is a graph showing the ampere capacitance of 50 mm wide foils as a function of foil thickness for Cu and Al-CNT foils with a 50 μm thick PAI insulator, and Al-CNT and Al1350 foils with a 5 μm thick aluminum oxide (Al-Ox) anodic oxide insulator layer. [Modes for carrying out the invention]

[0010] One or more embodiments of the present disclosure are shown as examples, not limiting, in the drawings of the accompanying drawings, and similar reference numerals indicate similar elements.

[0011] The embodiments described below provide the information necessary to enable those skilled in the art to implement the embodiments and represent the best mode of implementation. By reading the following description in reference to the accompanying drawings, those skilled in the art will understand the concepts of this disclosure and recognize the applications of those concepts not specifically addressed herein. It should be understood that these concepts and applications are within the scope of this disclosure and the accompanying embodiments.

[0012] Magnet wires are used in induction coils for applications such as transformers, motors, generators, speakers, electromagnets, and electromagnetic actuators. The coils may have either an air core or a permeable core containing materials such as cobalt (Co), iron (Fe), nickel (Ni), or alloys thereof, but not limited to these, such as Co-Fe, Ni-Fe, Ni-Fe-Mo, Sendust (Fe-Al-Si), amorphous steel, silicon steel, or ferrite. The disclosed embodiments improve magnet wires, which consist of a metal conductor such as copper (Cu) or aluminum (Al) and a thin insulating coating (e.g., mantle, layer) to prevent short circuits between wires. The improved magnet wires also have various applications such as induction coils in transformers, inductors, motor windings, generators, speakers, electromagnets, or electromagnetic actuators.

[0013] The disclosed embodiments improve conventional magnet wires by replacing or modifying flexible Al magnet wire or foil with stronger Al-carbon nanotube (Al-CNT) composite magnet wire or foil that has substantially the same conductivity but higher tensile strength, higher heat resistance, and higher creep resistance. This technique enables higher amperage capacity and tighter coil winding. Examples of applications for the disclosed magnet wires include electromagnets, transformers, and motors for the automotive and energy industries. As used herein, the term “substantially” may mean a relative majority or dominance.

[0014] While the exact costs of copper and aluminum fluctuate, aluminum has historically been significantly cheaper than copper, making it a preferred choice for economical lightweight magnet applications. Furthermore, aluminum exhibits a density less than one-third that of copper and possesses a conductivity of approximately 60% IACS (International Annealed Copper Standard). These properties further make aluminum attractive for use as a conductor in electromagnets, particularly for lightweight applications. However, aluminum is inherently soft and will break under tensions exceeding approximately 70–100 MPa. The tensile strength of a conductor determines the tension and speed during coil winding, and therefore the tightness and manufacturing efficiency of the coil winding. While higher-strength aluminum alloys are available to allow for tighter windings, the conductivity of these alloys is significantly lower than that of aluminum. Additionally, aluminum has low thermal resistance, and therefore the coil current must be limited to a value that avoids Joule heating to temperatures above approximately 150°C over extended periods. The desired Al composite conductor exhibits similar conductivity to pure Al, but with higher tensile strength, higher creep resistance, and higher heat resistance than pure Al.

[0015] Figures 1A and 1B illustrate different coil types. Specifically, Figure 1A shows a cross-section of a wire-wound coil, and Figure 1B shows a cross-section of a foil-wound coil. As shown in Figure 1A, a wire-wound coil has a substantially circular conductive core of radius r with adequate insulation. In other examples, a wire-wound coil has a conductive core that is substantially square, rectangular, or trapezoidal. As shown in Figure 1B, a foil-wound coil has a substantially two-dimensional conductive core with adequate insulation, where substantially two-dimensional means a width b of the conductive core that is substantially greater than its thickness t. For example, in one embodiment, the width of the conductive core is preferably between 10 and 1000 times its thickness.

[0016] A copper coil comprises a conductive Cu, nickel-plated copper (Ni / Cu), or silver-plated copper (Ag / Cu) core, and a thin insulating layer (e.g., enamel) made of a polymer on the surface thereof to prevent short circuits between wires. An aluminum coil comprises a conductive Al or Al alloy core, and an insulating layer on the surface thereof, which is made of either surface anodization or a thin insulating polymer (e.g., enamel) to prevent short circuits between wires.

[0017] The filling factor f of a coil can be defined by the ratio of the volume of the conductor to the total volume of the conductor, the insulator, and any voids between wires. It can be readily understood that a coil comprising substantially rectangular or square wires has a higher filling factor compared to a coil comprising substantially round wires. Similarly, foil-wound coils generally have a higher filling factor than wire-wound coils.

[0018] Copper has a conductivity of about 5.87×10 7 S / m or 100% IACS and a density of 8.96 g / cm 3 . Compared with copper, Al alloy 1350 has a lower conductivity of about 3.63×10 7 S / m or 61.8% IACS and a lower density of 2.70 g / cm 3 . Since the inductance of a coil is a geometric characteristic, an Al coil having the same dimensions as a copper coil exhibits the same inductance but is approximately 70% lighter. However, the ampacity of an Al coil is generally lower than that of a copper coil, due to the lower conductivity and heat resistance of Al compared with copper.

[0019] As used herein, ampere capacity can refer to the theoretical current-carrying capacity of a wire of a given core, insulating material, and cross-section at ambient temperature, i.e., the current at which it is safe to operate the wire over a long period of time. Often, the ampere capacity of a wire is defined as a derated maximum allowable current, such as 90% of the current at which it is safe to operate the wire over a long period of time. However, it may also be possible to operate the wire for a short period of time at currents higher than those ampere capacities. Furthermore, the ampere capacity of a coil may also depend on the coil design, including but not limited to the coil's geometry, filling density, number of wire turns, core material, and cooling mechanism, such as air cooling or liquid cooling. For the purposes of simplification and exemplification of this disclosure, details of such designs are omitted unless explicitly stated in a given embodiment.

[0020] Since the conductivity of Al1350 is lower than that of copper, the cross-sectional area of ​​an Al magnet wire conductor must be at least 61.8% larger than that of a copper magnet wire conductor (e.g., the ratio of 100% IACS of Cu to 61.8% IACS of Al1350) in order to operate with the same current. Therefore, an Al magnet coil designed for the same current tends to be at least about 50-60% larger than a copper magnet coil. However, even with increased size, the weight of an Al conductor is only about 50% of that of a copper conductor due to the lower density of Al compared to copper. The above simple estimation omits the temperature effects due to Joule heating, thermal conduction, thermal convection, and thermal radiation, some of which will be taken into account in the examples discussed further below.

[0021] The insulating material for magnet wire is selected to withstand the maximum operating temperature of the coil. Table 1 summarizes the temperature limits of various insulators according to the ANSI / NEMA MW1000 2018 standard. Only a few selected wire insulating materials can withstand operating temperatures above 180°C. Polyester-amide-imide (PAI) magnet wire insulating material is a two-part insulating material consisting of a modified polyester base coat and an amide-imide outer coating superimposed on it. PAI is thermally stable up to approximately 200°C, which is considerably higher than the temperature ratings of other magnet wire insulating materials. It exhibits excellent winding properties, thermal shock resistance, and overload resistance. Furthermore, PAI's chemical resistance is extremely effective compared to most solvents and insulating varnishes. For at least these reasons, PAI is a widely used magnet wire insulating material for motors and transformers.

[0022] [Table 1A]

[0023] [Table 1B]

[0024] Wire insulators can hinder heat conduction from the inside to the outside of the coil, which can lead to hot spots within the coil that could damage it. For this reason, thin insulators with high thermal conductivity are preferred.

[0025] Aluminum conductors can also be anodized to form an insulating aluminum oxide (Al-Ox) layer. Al-Ox is an effective insulator and is thermally stable up to temperatures of approximately 500°C. Anodized Al-oxide insulators have a thermal conductivity of 28-35 W / m·K and a thickness of several micrometers, typically 3-10 μm, compared to high-temperature polymer insulators such as PAI, which have a thermal conductivity of 0.26-0.54 W / m·K and a thickness of several tens of micrometers. Therefore, heat in an Al coil with a thin Al-Ox insulator conducts more easily from the inside to the outside of the coil compared to an Al coil with a thick polymer insulator, allowing for higher operating temperatures and, consequently, higher coil amperage. Nevertheless, although anodized Al is thermally stable up to 500°C, Al has low thermal resistance, and therefore, the operating temperature of an Al coil should be limited to approximately 150°C or below over long periods of time.

[0026] The disclosed Al composite wires exhibit higher strength, higher creep resistance, and higher heat resistance than standard Al wires, combining the advantages of Al's low density with the ability to operate at higher currents (e.g., higher amperage capacity) and temperatures for a given wire cross-section. For example, aluminum-carbon nanotube (Al-CNT) metal matrix composite (MMC) magnet wires exhibit similar conductivity to Al, thus providing improved values ​​compared to Al magnet wires, but also exhibiting higher tensile strength, heat resistance, and creep resistance compared to Al magnet wires, as outlined below. Table 2 summarizes the properties of various types of Al magnet wires.

[0027] [Table 2]

[0028] As shown in Table 2, high-conductivity Al such as Al1350 exhibits a conductivity of 61.8% IACS. In comparison, Al-CNT wire with approximately 0.5 wt% CNTs exhibits a conductivity of at least 55% IACS, preferably about 60% IACS. Therefore, the conductivity of Al-CNT wire is approximately 97% of that of Al1350 wire. The thermal coefficient of resistance, which accounts for the increase in resistance with temperature, is 4.29 × 10⁻⁶ for both Al1350 and Al-CNT 0.5 wt%. -3 They are almost the same.

[0029] Magnet wires need to have sufficient mechanical strength to withstand the forces involved in wire drawing and coil winding. Higher tensile strength allows for higher manufacturing speeds and more tightly wound coils. Al1350 exhibits a tensile strength of only about 13 kpsi (90 MPa). In contrast, Al alloys such as 5056 or 6061 exhibit higher tensile strengths than Al1350, at 42 kpsi (290 MPa) and 17 kpsi (117 MPa), respectively. Al alloys such as 5056 or 6061 are used in tightly wound Al coils, but exhibit significantly lower conductivity than Al1350, at only 29% and 47% IACS, respectively. This necessitates further increasing the conductor size for a given amperage capacity, thus losing the weight advantage over copper coils.

[0030] Compared to the aforementioned materials, Al-CNT wires containing approximately 0.5 wt% CNTs exhibit tensile strengths exceeding 29 kpsi (200 MPa) or even 43.5 kpsi (300 MPa), depending on the degree of cold working applied during wire drawing. The higher tensile strength of Al-CNT wires, therefore, offers the advantage of enabling tighter coil winding and higher manufacturing speeds compared to Al1350 wires, and exhibiting conductivity of at least 55% IACS, preferably about 60% IACS, which is about 97% of that of Al1350 and nearly identical or slightly better than that of Al1100.

[0031] Magnet wires must also exhibit threshold heat resistance. Operation at high temperatures must not result in a loss of mechanical strength that could lead to catastrophic failures such as wire thinning, which can result in thermal runaway or wire breakage. Al-CNT wire with approximately 0.5 wt% CNTs exhibits AT4 heat resistance specification according to the International Electrotechnical Commission (IEC) 62004 heat resistance standard. It loses less than 10% of its ultimate tensile strength (UTS) when annealed at 400°C for 1 hour or at 310°C for 400 hours, meaning it can operate continuously for 40 years up to 230°C without significant loss of tensile strength. Al1350, on the other hand, only meets the AT1 level heat resistance specification of the IEC 62004 heat resistance standard, meaning it can only operate for 40 years up to 150°C without significant loss of tensile strength.

[0032] Al-CNT 0.5wt%CNT wires, therefore, operate at higher temperatures than Al1350 wires and can provide a further increase in ampere capacity as long as the temperature remains below the insulator's rated temperature. Table 3 summarizes the temperature and time conditions used during annealing for various AT specifications of the IEC62004 standard. After annealing under the given conditions, 90% of the initial UTS must be retained to pass a particular AT specification.

[0033] [Table 3]

[0034] Table 4 summarizes how various AT specifications translate to 40 years and 400 hours of continuous tolerable operating temperature.

[0035] [Table 4]

[0036] The power lost in a wire is proportional to the resistance of the conductor and the square of the current flowing through the wire. Power loss can sometimes lead to an increase in wire temperature, also known as Joule heating or current heating, and should be limited to prevent the wire from degrading mechanically or electrically.

[0037] More specifically, for a wire having a metal conductor radius r1 and an insulator thickness d = r2 - r1, i.e., a total radius r2, the temperature rise ΔT = T - T0 at the interface between the metal conductor and the wire insulator relative to the ambient temperature T0 can be expressed as follows.

[0038]

number

[0039] Here, I is the current passing through the wire, ρ is the electrical resistivity of the metal conductor, k is the thermal conductivity of the insulator, and h is the heat transfer coefficient to the surroundings. In the case of metals, ρ has the following temperature dependence.

[0040]

number

[0041] Here, ρ0 is the resistivity at ambient temperature, and α is the thermal coefficient of resistance of the metal conductor.

[0042] For a rectangular metal conductor having width b, thickness t, and insulation thickness d, the temperature rise ΔT = T - T0 at the interface between the metal conductor and the wire insulator relative to the ambient temperature T0 can be expressed as follows:

[0043]

number

[0044] The disclosed technology includes compositions for Al-based wires that exhibit similar conductivity to pure Al wire (e.g., Al1350 wire) but have the strength of Al alloy wire (e.g., Al6061 wire) and improved creep resistance compared to Al-based wires. For example, the addition of small amounts of carbon nanotubes (e.g., less than 2 wt%, more preferably less than 1 wt%) to an Al metal matrix provides increased wire tensile strength, higher heat resistance, and higher creep resistance compared to pure Al without CNTs, while maintaining substantially similar conductivity, modulus of elasticity, and coefficient of thermal expansion and thermal resistance. The tensile strength and creep resistance of Al-CNTs increase with increasing CNT weight ratio in the composite material, but the conductivity decreases. Therefore, concentrations of CNTs of 0.1 wt% to 2 wt%, more preferably 0.2 wt% to 1.5 wt%, or even more preferably about 0.5 wt%, can maintain a conductivity of at least 55% IACS, preferably about 60% IACS. In particular, Al-MMC wires with 0.5 wt% CNTs can exhibit strengths exceeding 200 MPa or even 300 MPa while meeting the AT4 specification of the IEC 62004 heat resistance standard for overhead transmission lines (as summarized in Table 1), and can exhibit conductivity close to that of Al1350.

[0045] Al-CNT wires can achieve mechanical strengthening by work and dispersion hardening by continuously reducing the cross-section of the extruded Al-CNT rod through a cold working process (such as, but not limited to, rolling, drawing, or a combination thereof) until the desired diameter of the rod is obtained. During the cold working process to achieve the desired diameter, the grain structure of the rod is refined and the CNTs are more uniformly dispersed in the wire.

[0046] The disclosed embodiments include the application of processed and dispersion-cured Al-CNT magnet wires having a polymer insulator, the application of processed and dispersion-cured Al-CNT magnet wires having an Al-Ox insulator, for example, an anodized surface layer, the application of processed and dispersion-cured Al-CNT foils having a polymer insulator, and the application of processed and dispersion-cured Al-CNT foils having an Al-Ox insulator.

[0047] The following examples demonstrate how Al-CNT composite materials can overcome the shortcomings of conventional Al or Al alloys used in wires or foils for electromagnet coils. In one example, replacing Al1350 magnet wire with Al-CNT magnet wire yields higher strength and higher amperage capacity. In another example, replacing anodized Al1350 foil with anodized Al-CNT foil yields higher strength and higher amperage capacity.

[0048] Figure 2 is a graph comparing the strengthening of a 5mm diameter extruded Al-CNT rod and a 5mm diameter extruded Al(99.7%) rod when the wire size is reduced by continuously applying a cold drawing step. The strengthening of the Al-CNT material is due to work and dispersion hardening, while the strengthening of Al is due to work hardening alone. The CNTs are already dispersed in the Al-CNT rod in the as-extruded state. Therefore, the initial strength of 145 MPa before drawing is already greater than the initial Al strength of 75 MPa. The initial strengthening rate by continuously reducing the wire size by applying cold working is similar for Al-CNT and Al99.7%, but the strengthening rate by continuously reducing the wire size remains constant for Al-CNT, while it decreases significantly for Al99.7%.

[0049] The desired ultimate tensile strength (UTS) and final diameter (D) of the wire. f Initial extrusion diameter (D) of Al-CNT rod for ) i ) can be calculated based on the following mathematical relationships.

[0050] [Numerical]

[0051] Here, A and B are constants depending on the amount of CNT. For a matrix consisting of Al 99.7% combined with a CNT concentration of 0.5 wt%, A and B are about 145 and about 60, respectively.

[0052] Initial thickness (t i ) and final thickness (t f ), a similar exponential relationship also applies to rods that are rolled into thin sheets or foils.

[0053] Figure 3 is a graph showing the retention of UTS after heating Al and Al-CNT wires at various temperatures. As shown, the Al-CNT wire meets the AT4 specification of the IEC62004 standard, while Al or 1xxx series Al only meets the AT1 specification of the IEC62004 standard.

[0054] Figure 4 is a graph that can be used to determine the initial rod diameter required to achieve a desired ultimate tensile strength by cold drawing to a selected final wire diameter. In the example provided in the figure, to achieve a desired UTS of 300 MPa with a final wire diameter of 0.4 mm, the required initial rod diameter is about 5.3 mm. [Examples]

[0055] The following examples show the advantages of using Al-CNT conductors instead of Al conductors in wire-wound coils or foil-wound coils. Furthermore, it is shown that the performance of coils comprising anodized Al-CNT wires or foils competes with that of coils comprising copper-based wires or foils.

[0056] The following properties are used in the calculations below.

[0057] Resistivity ρ0 is 1.71×10 for Cu-8 Ω·m, Al1350 is 2.77 × 10 -8 Ω m, Al-CNT0.5wt% is 2.85×10 -8 The coefficient of thermal resistance is Ω·m. The coefficient of thermal resistance α is approximately 0.00393 for Cu, and 0.00429 for both Al1350 and Al-CNT 0.5wt%.

[0058] The thermal conductivity k of PAI is approximately 0.25 W / m·K, while the thermal conductivity k of the anodized Al layer (Al-Ox) is approximately 28-35 W / m·K. The surface heat transfer coefficient h to ambient air is approximately 12 W / K·m 2 That is the case.

[0059] Copper magnet wires can operate at temperatures up to approximately 180°C. When operating at temperatures exceeding 180°C, they should be plated with nickel or silver to avoid conductor scaling and resulting degradation. For plated copper wires, the operating temperature is limited by the maximum operating temperature of the insulator; for example, with PAI insulators, it is limited to 200°C.

[0060] Aluminum magnet wires, such as 1350Al wire, can only operate up to a temperature of approximately 150°C, which matches their AT1 heat rating. Al-CNT 0.5wt% magnet wire can only operate up to a temperature of 200°C with PAI insulation and 230°C with Al-Ox insulation, which matches their AT4 heat rating.

[0061] (Example 1) Figure 5 shows the ampere capacitance as a function of wire cross-section for Cu wire operating at 150°C, Ni or Ag plated Cu wire at 200°C, Al1350 wire at 150°C, and 0.5 wt% Al-CNT at 200°C. In these cases, fully insulated wires of class FIW6 are assumed (for details on FIW thickness, see, for example, the ANSI / NEMA MW1000-2018 standard or IEC60317-0-7).

[0062] Compared to Cu wires, Al and Al-CNT wires have lower ampere capacitance due to their lower conductivity and higher thermal coefficient of resistance, resulting in relatively higher Joule heating. However, Al-CNT 0.5wt% wires can operate at higher currents and temperatures compared to Al1350 wires due to their higher heat resistance. Therefore, it can be easily understood that Al-CNT 0.5% magnet wires are preferable to Al1350 magnet wires when used with PAI or other high-temperature insulators valued above 150°C.

[0063] (Example 2) Figure 6 shows the ampere capacitance as a function of wire cross-section for Al1350 wire and Al-CNT 0.5wt% wire at 150°C with a class FIW6 PAI insulator, and for Al1350 wire and Al-CNT 0.5wt% wire at 150°C with a 5 μm thick surface anodized (e.g., Al-Ox).

[0064] The ampere capacity of anodized Al and Al-CNT wires is higher than that of Al and Al-CNT wires insulated with PAI class FIW6 because the Al-Ox insulator is thinner and more thermally conductive than PAI class FIW6 insulator. Therefore, it can be easily understood that Al and Al-CNT magnet wires with a thin anodized Al layer exhibit superior performance compared to Al and Al-CNT wires with a thicker PAI insulated magnet wire.

[0065] (Example 3) For coils with polymer-insulated magnet wire, the packing density can be 0.25 to 0.65, while for anodized Al coils, the packing density is 0.85 to 0.995. Therefore, for the same ampere capacity rating, an Al coil with Al-Ox insulation will have a lower coil volume compared to an equivalent coil with thicker high-temperature polymer insulation.

[0066] An Al1350 coil with a packing density of 0.86 is equivalent to a copper coil with a packing density of 0.53 in terms of wire resistance, considering that Al1350 has a conductivity of 61.8% IACS. (The product of packing density and conductivity is equal to 0.86 × 0.618 = 0.53 × 1). However, the weight of the Al conductor is less than half the weight of the equivalent copper conductor (ratio of the product of density and packing density of Al and Cu: 0.86 × 2.7 / 0.53 × 8.96 = 0.49).

[0067] Considering that Al-CNTs have an conductivity of approximately 60% IACS (the product of packing density and conductivity is equal: 0.88 × 0.6 = 0.53 × 1), an Al-CNT 0.5wt% coil with a packing density of 0.88 is equivalent to a copper coil with a packing density of 0.53 in terms of wire resistance. However, the weight of an Al-CNT 0.5wt% conductor is only half the weight of an equivalent copper conductor (ratio of the product of density to packing density for Al-CNT and Cu: 0.88 × 2.7 / 0.53 × 8.96 = 0.50).

[0068] Al-CNT coils can operate up to a temperature of 230°C, which is the heat resistance limit of Al-CNTs. In comparison, Cu coils can operate up to a temperature of 200°C, which is the temperature limit of PAI. Therefore, it can be easily seen that coils having anodized Al-CNT conductors (e.g., Al-Ox insulators) are preferable to coils having copper conductors and high-temperature insulators in terms of coil weight and operating temperature.

[0069] (Example 4) Figure 7 shows the ampere capacitance as a function of conductor thickness t for various 50 mm wide foils. Specifically, these include foils containing Ag or Ni-plated Cu foil with a 50 μm thick PAI insulator operating at 200°C, foils containing 0.5% Al-CNT with a 50 μm thick PAI insulator operating at 200°C, foils containing Al with a 5 μm thick Al-Ox insulator operating at 150°C, and foils containing 0.5 wt% Al-CNT with a 5 μm thick Al-Ox insulator operating at 230°C. The ampere capacitance of the Al-Ox insulated Al-CNT foil is higher than that of the PAI insulated Al-CNT foil, and the ampere capacitance of the PAI insulated Al-CNT foil is higher than that of the Al-Ox insulated Al foil, which is mainly due to the higher operating temperatures of each. The ampere capacity of PAI-insulated copper foil remains the highest compared to Al and Al-CNT foils due to the higher conductivity of Cu compared to Al and Al-CNTs. Therefore, it can be easily understood that a coil having 0.5 wt% anodized Al-CNTs is preferable to a coil having anodized Al or a coil having 0.5 wt% high-temperature PAI-insulated Al-CNTs.

[0070] (Example 5) While previous examples have been described in relation to wire or foil, the heat generated inside a tightly wound coil and the resulting temperature profile are more complex. Most notably, convection acts only on the surface of the coil, while heat conduction acts throughout the coil's volume. The internal portion of the coil can be assumed to be at a constant temperature.

[0071] For a foil-wound coil having an air core, foil thickness t, inner radius r1 and outer radius r2, width b, and filling ratio f, power loss is given by the following:

[0072]

number

[0073] The temperature rise is as follows:

[0074]

number

[0075] A coil with a 100 μm thick Al foil and a 6.5 μm thick Al-Ox insulator (113 μm thick foil) will have a packing density of f = 0.88. The maximum operating temperature is approximately 150°C.

[0076] A coil having a 100 μm thick Al-CNT foil and a 6.5 μm thick Al-Ox insulator (113 μm thick foil) will have a packing density of f = 0.88. The maximum operating temperature is approximately 230°C.

[0077] A coil with a 61 μm thick Cu foil and a 26 μm thick PAI insulator (113 μm thick foil) will have a packing density of f = 0.54. The maximum operating temperature is approximately 200°C.

[0078] The three coils are nearly equivalent in terms of volume and resistance at room temperature, as described in Example 3. However, the weight of the Al and Al-CNT coils is less than half that of the Cu coil, considering the weight of the conductor and insulator.

[0079] A foil-wound coil with outer radii of r1=0.1m and r2=0.15m has 442 turns. For foil with a width of b=0.01m, the ampere capacities of anodized Al, Al-CNT, and PAI-insulated Cu coils are 2.7A, 3.0A, and 2.3A, respectively. This was calculated using Equation 14 of Reeves et al., "Air-cored foil-wound inductor," in Proc. IEE, Vol.125 (1978). Il's guidance is at 54mH.

[0080] Therefore, it can be easily understood that an Al-CNT coil has the same weight as an Al coil, but has a higher amperage capacity due to the higher heat resistance of Al-CNT compared to Al. An Al-CNT coil with an Al-Ox insulator has the same volume as a Cu coil with a PAI insulator, but an Al-CNT coil weighs only about half as much as a Cu coil, but it can be even more easily understood that an Al-CNT coil has a amperage capacity about 30% higher than a Cu coil due to the higher filling density and higher temperature rating of Al-CNT compared to Cu.

[0081] From the above, it will be understood that while specific embodiments of the present invention are described herein for illustrative purposes, various modifications can be made without departing from the scope of the invention.

Claims

[Claim 1] A magnet wire comprising a conductive core containing aluminum and uniformly dispersed carbon, and an insulating layer covering the surface of the conductive core, wherein the carbon is uniformly dispersed in the magnet wire. The insulating layer and the conductive core are jointly configured to form insulating wires for a coil associated with a magnet. The magnet wire has an ultimate tensile strength of at least 200 MPa, The aforementioned magnet wire allows for tighter coil winding compared to Al1350 magnet wire.

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