KR100209438B1 - Magnetic cores utilizing metallic glass ribbons and mica paper interlaminar insulation - Google Patents

Abstract

The present invention provides magnetic cores made from ferromagnetic metal glass ribbons and mica paper insulation. The ribbon and the insulation are co-wound to constitute alternating concentric rings of the layers. The wound iron core is then annealed in vacuo or in an inert atmosphere such as dry nitrogen or argon gas. Co-wound iron cores of this type exhibit good magnetics at high susceptibility and high voltage hold off between adjacent layers and are particularly suitable for pulsed power applications.

Description

Magnetic core using metallic glass ribbon and mica interlayer insulation

1 is a perspective view of an insulated annular core showing a cut surface of a metal ribbon and insulating tape by cutting a quarter of the iron core.

FIG. 2 is a perspective view of an annular core, schematically showing the winding used to provide a magnetic field to the iron core material during annealing.

3 is a schematic of the B-H loop of a soft ferromagnetic material showing properties for pulsed current applications, such as residual magnetization, maximum induction, and possible flux changes.

* Explanation of symbols for main parts of the drawings

1: mica paper insulation

2: metallic glass ribbon

2: iron core 22: insulated wire

The present invention relates to a magnetic core made from a ferromagnetic metallic glass ribbon. More specifically, the present invention relates to a core provided with interlaminar insulation made of mica paper.

Magnetic cores using ferromagnetic metal glass ribbons are used for pulse power applications at very high magnetization rates resulting in induction voltages as large as 100 volts between adjacent layers of magnetic materials. In the absence of suitable insulation between these layers, interlaminar eddy currents are created that result in increased iron loss and impair the good magnetism of the metal glass ribbons.

In order to obtain optimal magnetics in magnetic cores made from metallic glass ribbons, annular iron cores are first wound into their final shape and then annealed with the surrounding magnetic field applied to the toroid. This annealing acts to relieve the in-ribbon bending stress due to the bending of the ribbon in the iron core as well as the stress in the metal glass ribbon resulting from the rapid cooling during the casting of the ribbon. During annealing, the applied magnetic field acts to induce an easy orientation of magnetization along the field directions. By dulling the iron core made from the metallic glass ribbons, magnetic cores with nearly square B-H loops can be produced.

The square BH loop, defined as a BH loop with a high ratio of remanent magnetization to maximum induction, has a positive maximum from the negative remanence of the iron core. When magnetized by induction, it provides the maximum change in the magnetic flux in the iron core. The relevant properties of the soft magnetic materials for pulsed power applications are shown in FIG. 3. The vertical axis 31 is magnetic induction or B field and the horizontal axis 35 is applied magnetic field or H field. The maximum change in induction (called the maximum induction change) ΔB 34 is achieved by first resetting the core by applying a magnetic field to the core when detecting a negative magnetic field. This magnetic field Hm 39 should be several times the coercive field Hc 38. Induction in the core reaches a negative maximum induction -Bm 37 when the applied magnetic field is -Hm 39. The core then returns to the negative saturated residual magnetic flux density -Br 36. When a quantum field is applied, the magnetic induction in the iron core changes from the negative saturated residual magnetic flux density 36 to the positive maximum induction + Bm 32. The maximum possible variation in induction ΔB 34 can be about twice as large as Bm 32 and is made when the loop is nearly square and Br 33 is as large as Bm 32. Large magnetic induction changes are important for iron cores used in high power pulse applications. For example, when iron cores are used as inductors, annular windings are placed around the iron cores. The voltage that can be applied to the windings for a given time without reducing the iron core saturation and inductance of the inductor depends on the product of the cross-sectional area of the iron core and the change in induction of the magnetic material used for the iron core. Large induction variations allow the use of iron cores with smaller cross-sectional areas, and thus the use of iron cores with smaller volumes and weights.

While annealing is important to achieve maximum induction change in pulsed power applications, the annealing should not damage any insulation in the iron core. Therefore, the insulation present in the iron core before annealing is typically 300-400 for 1-2 hours for high-induction metal glass alloys. It must be able to withstand the annealing temperature.

Current methods for producing metallic glass cores include dip coating of metal alkoxides already developed for polycrystalline magnetic materials as disclosed in US Pat. No. 2,796,364. The use of metal glasses of magnesium methylate in methyl alcohol is described in IEEE Conference Record of the 15th Power Modulator Symposium, published by Institute of Electrical and Electronic Engineers, 345, East 47th Street, New York, 10017, New York. pp. 22-27, all rights reserved for metal glasses for magnetic switches of Carl H. Smith, published in 1982. These coatings are annealed to convert the metal alkoxide remaining on the ribbon surface after solvent evaporation into a metal oxide coating. IEEE Transactions on Magnetics, Vol. MAG-20, no. 5, September 5, 1984, pp. Poems published in 1320-1322. H. Smith, D. Appeared and H. H. Gel-sol coating of metal glass by dip coating the ribbons in a colloidal suspension of silica in alcohol is also used, as described in Liberman's paper Step dB / dt magnetization under the thickness dependency of progeny in amorphous FeBSiC ribbons. Although these insulating coatings withstand the temperatures required for self-annealing, both of these insulation methods provide a voltage hold off, limited at most to tens of volts. This limited voltage hold off is due to the thickness of the coatings, typically on the order of 100-200 nm in association with the surface roughness of the metal glass ribbons. Therefore, the magnetic cores produced using these isolation methods are limited in their use in applications with relatively low susceptibility, resulting in only low induced voltages between adjacent layers of the iron core.

Other insulation materials that have been tested for metallic glass cores are PARYLENE polymer films of deposited carbide oxides such as SiO and SiO ₂ and Union Carbide Corporation. For example, IEEE Conference Record of the 16th Power Modulator Symposium, published by Institute of Electrical and Electronic Engineers, 345, East 47th Street, New York, 10017, New York, USA. pp. 240-244, All Rights Reserved. 1984 by Carl H., Smith and David M., Nassin. See the magnetic properties of metal glasses under rapid pulses. These deposition methods are performed in a vacuum chamber and are therefore very difficult and expensive to handle the continuous length metal glasses required for large magnetic cores.

Another method of making metallic glass cores with interlayer insulation is to co-wind the metallic glass ribbon with a thin polymer film. This method is described in Journal of Applied Physics, Vol. 57, No. 1, April 1985, pp. Published in 3508-3510. Wheelton, S, S, Rosenblum and the City. H. Smith, reviewed in Investigation of Metglas Toroid Fabrication Techniques for a Heavy Ion Fusion Drivier. This iron core manufacturing method provides a voltage hold-off of several hundred volts per insulation, depending on the insulation thickness.

METGLAS with nominal composition of Fe ₆₆ Co ₁₈ B ₁₅ Si ₁ A series of alloys, such as alloy 2605C0 (METGLAS is an allied-signal, a registered trademark of Incorporated), can be annealed on a supply spool and then carefully rewound with an annular iron core with a polymer insulation. The relatively high induced magnetic anistropy energy of these alloys interferes with the tendency of the mutual reaction between magnetic strain and strain energy, resulting in irregular magnetization directions in the ribbon, thus squaring the BH loops. Decreases. Strain energy is derived from flexural stresses in the ribbon resulting from the rewinding of the ribbon after annealing. Therefore, iron cores with magnets almost similar to the iron cores annealed in their final shapes can be produced from high magnetic anisotropic energy ribbons. However, since annealing softens iron-based alloys, rewinding should be done at lower speeds more carefully than when winding up non-annealed ribbons.

METGLAS alloys with nominal compositions of Fe ₈₁ B _13.5 Si _3.5 C ₂ and Fe ₇₈ B ₁₃ Si ₁₉ respectively, such as metal glass alloys with very low organic magnetotropic anisotropy energies, such as 2605SC and 2605S-2, It cannot be annealed and rewound as iron cores without a significant reduction in the squareization of their BH loops compared to the BH loops produced when annealed in shape. The magnetisms of three sets of iron cores of three different metallic glass alloys are shown in Table I below. Two iron cores in each set were annealed under suitable conditions for the alloy. One iron core in each set was placed between each 25μ metal glass ribbon layer. It was rewound after annealing with polyester (MYLAR) tape. For each set, the reduction of the saturated residual magnetic flux density Br and the maximum induction B ₁ at 1 Hersted (10 e = 80 A / M) is noteworthy. The possible induction change from -Br to + B ₁ is given as ΔB for each iron core.

Most polymers do not withstand the annealing temperatures required for metallic glasses. Those that can withstand annealing temperatures, such as polyimides, are expensive. In addition, when co-wound together with metallic glass ribbons, polyimides tend to stress magnetic materials due to different heat shrinkage upon cooling after annealing. This stress tends to damage the magnets of the iron cores through the mutual reaction of magnetostriction and stress. See, for example, Smith and Natsin.

Magnetics measured from dc BH loops are shown in Table II for METGLAS alloys 2605 SC and 2605 C0. Two toroids were wound from each alloy ribbon, one 12 Metal glass ribbons were wound together with KAPTON tape, and the other one was wound without polyimide tape. The iron cores were then annealed with the magnetic field under the appropriate conditions for each alloy. Iron cores with polyimide insulation exhibit reduced ΔB values compared to iron cores without polyimide insulation. The reduction is greatest in METGLAS alloy 2065SC with smaller induced magnetic anisotropy energy.

Therefore, conventional coatings for metallic glass ribbons upon annealing provide good magnetics but have a relatively low voltage hold off. Conventional methods of co-winding metallic glass ribbons with polymers have adequate voltage hold off, but yield magnetically damaged sashes, especially when formed from glass alloys with low induced magnetic anisotropy energy. Accordingly, a method of iron core insulation is desired that is suitable for use with various metal glass alloys and provides magnetic cores with suitable interlayer insulation and optimum magnetisms.

The present invention provides an iron core having excellent magnetics at high interlayer voltage hold off and high susceptibility, and which is effectively produced by quickly winding an annealed ductile metal glass ribbon to form an iron core which is subsequently annealed in its wound shape. . Generally speaking, the iron core includes ferromagnetic metal glass alloys and mica paper insulation having at least 80% glassy structure. The metal ribbon and the insulation are co-wound to form an iron core, the metal and the insulation being alternating layers thereof. The iron core is then annealed in the shape wound up thereon to provide a magnetic core with a rectangular B-H loop and a high available flux swing. Mica paper insulation provides a voltage hold-off above 300 volts and is not affected by annealing temperatures and does not apply any stress to the magnetic ribbon. As mentioned above, co-wound iron cores together with mica are particularly suitable for the use of metal glass ribbons with high magnetic strain and low anisotropic energy. Such iron cores are used at high susceptibility in pulsed power applications. Also suitable for use as the ribbon component of the iron cores are nanocrystalline alloys and polycrystalline magnetic alloys.

According to the present invention, a magnetic core, indicated as 10 in FIG. Self core (iron core) 10 is approximately 15-50 About 5-25 thick metal ribbons2 It is made by co-winding as a toroid with mica paper insulation 1 of thickness. The winding is done so that the layer of ribbon 2 and the layer of insulating material 1 form alternating concentric layers. One example of a metal glass ribbon suitable for the assembly of iron core 10 is EMTGLAS alloy 2605 C0. An example of a mica insulator material suitable for the assembly of iron core 10 is SAMICA 4100 from Essex Grum, Incorporated, New Hampshire. Mica paper is a uniform soluble sheet of pure mica flakes. Natural mica is first broken into small flakes and then suspended in the fluid. Mica paper is extracted from the fluid on the web and dried in a manner similar to conventional paper making methods. After the winding process, the iron core is annealed in vacuo or in an inert atmosphere such as dry nitrogen or argon gas. Suitable annealing for this alloy is about 1-10 325 iron core at a heating rate of Heated to a temperature of about 325 Hold the iron core for 120 minutes at a temperature of about 1-10 cooling the core at a rate of / min. As shown in FIG. 2, the magnetic field of 800-1600 A / m is maintained in the iron core by passing a current 21 through the insulated wire 22 surrounding the iron core 10 during the entire annealing cycle, or at least during the cooling part of the annealing cycle. . The magnetic field is calculated by multiplying the strength (A) of current 21 through line 22 by the number of revolutions of line 22 through the center of iron core 10 and completely surrounding the core 10 and dividing by the average circumference (m) of iron core 10 . The current is supplied by voltage source 26 and regulated by variable resistor 25. The advantages provided by the co-wound iron cores assembled according to the invention become apparent when comparing the magnetic properties of these iron cores with the magnetic properties of the iron cores produced by conventional methods. High energy pulses typically use large voltages. To deal with these high voltages, inductors or transducers using magnetic cores with magnetic flux handling capacity greater than or equal to the pulse duration multiplied by the voltage per line turn applied as a winding around the iron core I need it. The magnetic flux treatment capacity of the iron core is equal to the cross-sectional area of the magnetic material multiplied by the maximum magnetic induction change of the magnetic material.

The present invention provides a method of winding magnetic cores from ribbons of such metallic glass alloys. According to the invention, the ribbons in the wound shape constitute iron cores with good magnetic properties. Advantageously, ribbons made of certain magnetic alloys can be wound in the non-annealed state, and therefore in the less crunch state, allowing for a faster winding speed and less interruption of the winding operation due to the rupture of the ribbon.

Related magnets measured for dc B-H loops of a pair of iron cores wound in the presence and absence of mica insulation and annealed at appropriate temperatures are indicated in Application III. There is little magnetic degradation for any of the alloys.

As can be seen by comparing the results of Table III with those of the prior art, the method of the present invention has a much larger flux swing value (ΔB) than previously possible and provides magnetic cores with less B ₁ / Br degradation. .

Claims (8)

A mica paper insulation material comprising a ferromagnetic metal glass alloy ribbon having a glass structure of at least 80% and having a thickness of 15-50 micrometers, and a uniform flexible sheet of pure thermo-flakes having a thickness of 5-25 micrometers; The ribbon and insulation are co-wound to form a core with alternating layers of metal and insulation, which cores are wound and annealed to maintain a high interlayer voltage hold-off. And a magnetic core having excellent magnetism at high magnetization rate. The magnetic core of claim 1, wherein the annealing step is performed in a state in which a magnetic field is applied. The magnetic core of claim 1, wherein the metal glass is a magnetostrictive iron alloy. The magnetic core of claim 1, wherein the metal glass has a nominal composition selected from the group consisting of Fe ₆₆ Co ₁₈ B ₁₅ Si ₁ , Fe ₈₁ B _13.5 Si _3.5 C _2, and Fe ₇₈ B ₁₃ Si ₉ . The magnetic core of claim 1, wherein the alloy has a crystalline structure or a semicrystalline structure after annealing. The magnetic core of claim 1 wherein the metallic glass is a cobalt-based alloy having a saturation magnetostriction of less than about 1 ppm (part per million). (a) co-winding mica paper insulation consisting of ferromagnetic metallic glass alloy glass and uniform flexible sites of pure mica flakes having a thickness of 5-25 micrometers to form a core with alternating layers of metal and insulation; (b) A method of manufacturing a magnetic core having excellent magnetism at high interlayer voltage hold-off and high susceptibility, including annealing the core after the co-winding, while maintaining its glass structure. 8. The method of claim 7, wherein the annealing step is performed under magnetic field application.