Magnetic core

Abstract: A magnetic core comprises at least one layer of magnetic film (1) composed of an amorphous alloy and an electrically insulating film (2) made of polyimide. Powder materials (3) having a property for alleviating mutual influence between the magnetic film and the insulating film during a heat treatment thereof is sticked on a surface of the magnetic film or the insulating film. The magnetic film and the electrically insulating film are alternately wound up in a predetermined shape with powder material interposed there­ between to thereby form a magnetic core.

Description: The present invention relates to a magnetic core and, more particularly, to a high power pulse magnetic core such as a saturable core impulse source for lasers as an induction core for a linear accelerator. Generally, a high power pulse magnetic core, for example an induction core of a linear accelerator, operates essentially as a 1 : 1 transformer and accelerates the beam of charged particles in the center of the core by a voltage which appears across a gap. Recently, there has been proposed a pulse source adapted for lasers of the type of a magnetic pulse compressor which operates with high power and high voltage. The pulse compressor serves to convert a pulse generated by the power source having a wide pulse width into a high power pulse having a relatively narrow pulse width. This conversion is achieved by utilizing a saturation phenomenon of the magnetic core incorporated in the pulse compressor. In a conventional technology, the magnetic core for the high power pulse generation is made of a material having a high saturation magnetic flux density and a high rectangular ratio of a magnetization curve. For this purpose, a magnetic core is widely utilized which is formed by alternately laminating or winding a thin metallic film made of an iron based amorphous alloy or cobalt based amorphous alloy and an electrically insulating film made of a polymeric film such as polyimide film. The magnetic core formed by alternately laminating or winding the polymeric film such as the polyimide film as the insulating layer and the magnetic film is then thermally heated. However, the polymeric film is liably subjected to the heat shrinkage by such heat treatment and, hence, the heat shrinkage adversely affects the magnetic film to apply compression stress, resulting in the lowering of the rectangular ratio of the magnetization curve and degrading the magnetic characteristic of the magnetic core. JP-A 62-61308 discloses a process for producing an amorphous wound core wherein a fine powderlike oxide dissolved in a solvent is sprayed on one surface of an amorphous magnetic thin belt in order to form an insulating film thereon. The magnetic thin belt and the insulating film are wound up to produce the wound core, with the magnetic thin belt being heated up. Thus, a repetitive two-layer structure is produced. JP-A 60-165705 discloses a wound iron core being produced by winding many sheets of amorphous ribbons together with non-magnetic thin belts being inserted between the ribbons. JP-A 61-8903 describes a method for coating a surface of an amorphous alloy thin belt with an insulation film of chromic acid salt for producing iron core material of a wound transformer. EP-A 0 214 305 discloses a core made of thin amorphous alloy strips. The core is formed as a repetitive two-layer structure which consists of the amorphous alloy strips and interposed adhesive of borosiloxan resin to achieve a direct fixed contact between the amorphous layers. US-A 4,558,297 is directed to a saturable core which consists of a coiled thin strip of an amorphous magnetic alloy. An electrically insulating film of organic material having a low heat resistance is interposed between neighboring coil layers of the coiled thin strip. The thin strip is subjected to a heat treatment. An object of the present invention is to subsstantially eliminate the defects or drawbacks encountered with the prior technology described above and to provide a magnetic core having a high rectangular ratio of the magnetization curve even after the heat treatment of the magnetic core and having an improved magnetic characteristic. This and other objects can be achieved according to the present invention in one aspect by providing a magnetic core in accordance with claim 1. In a preferred embodiment, the magnetic film is made of an amorphous alloy and the electrically insulating film is made of a polyimide. The substance is composed of powder material of such as oxide, nitrate or carbonate of magnesium, silicon or the like. In another aspect of the present invention, a magnetic core according to claim 18 is provided. According to the magnetic core of the characters described above, the substance such as powder materials having a property for alleviating the mutual influence between the magnetic film consisting preferably of amorphous alloy and an electrically insulating film such as polyimide film is interposed therebetween. The magnetic film and the electrically insulating. film are alternately wound up with the powder materials interposed therebetween to form a magnetic core. Accordingly, the magnetic core has a high rectangular ratio of the magnetization curve after the heat treatment. Fig. 1 is a perspective view, partially broken away, of one embodiment of a magnetic core according to the present invention; and Fig. 2 is also a perspective view of another embodiment of a magnetic core according to the present invention. Fig. 1 shows a perspective view, partially broken away for showing a wound-up condition of layers, of a magnetic core prepared in accordance with one embodiment of the present invention, in which a magnetic film layer 1 and an electrically insulating film layer 2, both described in detail hereinafter by way of preferred examples, are wound up around a core rod or mandrel. A material or substance 3, such as powders, is sticked on the surface of the magnetic film 1 or the insulating film 2 by the manner described herein later. As described, for example with reference to Fig. 1, the material 3 is sticked on the magnetic film 1 and, accordingly, the material will be referred to as a material interposed between the films 1 and 2, i.e. an interposed material, herein for the sake of convenience. According to the present invention, the material or substance for forming the magnetic film is not limited to a specific one, but it is preferred to utilize an iron based amorphous alloy ribbon, a cobalt based amorphous alloy ribbon or a crystalline iron based magnetic alloy film with an ultrafine grain structure precipitated by crystallization from the amorphous state. The crystalline iron based magnetic alloys have the composition represented by formula: (Fe 1-g N g ) 100-h-i-j-k-l-m Cu h Si i B j N′ k N″ l Z m wherein N represents at least one selected from the group consisting of Co and Ni; N′represents at least one selected from the group consisting of Nb, W, Ta, Zr, Hf, Ti and Mo; N″ represents at least one selected from the group consisting of V, Cr, Mn, Al, elements in the platinum group, Sc, Y, rare earth elements, Au, Zn, Sn, and Re; Z represents at least one selected from the group consisting of C, Ge, P, Ga, Sb, In, Be and As; and g, h, i, j, k, l, m represent numbers satisfying 0≦ g ≦ 0.5, 0.1 ≦ h ≦ 3, 0≦ i ≦ 30, 0 ≦ j ≦ 25, 0 ≦ i+j ≦ 35, 0,1 ≦ k ≦ 30, 0 ≦ 1 ≦ 10 and 0≦ m ≦ 10; at least 50% of alloy structure being ultrafine grain having an average grain size of less than 50 nm (500Å) The iron based amorphous alloy has the composition represented by the formula: (Fe 1-a-b M a M′ b ) 100-c Y c wherein M represents at least one selected from the group consisting of Co and Ni; M′ represents at least one selected from the group consisting of Ti, V, Cr, Mn, Cu, Zr, Nb, Mo, Ta, and W; Y represents at least one selected from the group consisting of B, Si, C and P; and a, b, and c represent numbers satisfying 0 ≦ a ≦ 0.4 ; 0 ≦ b ≦ 0.15 and 14 ≦ c ≦ 25, respectively. The cobalt based amorphous alloys have the composition represented by the formula : (Co 1-c-d Fe c M″ d ) 100-f (Si 1-e B e ) f wherein M″ represents at least one selected from the group consisting of V, Cr, Mn, Ni, Cu, Nb, and Mo; and c, d, e and f represent numbers satisfying 0.01 ≦ c ≦ 0.10, 0 ≦ d ≦ 0.10, 0.2 ≦ e ≦ 0.9 and 20≦ f ≦ 30, respectively. Such ribbon may be easily produced by rapid quenching from the melt, for example, to an alloy having predetermined metal composition. It is preferred, but not limited, for the film to have a thickness of less than 40 µm, and more specifically, to 12 to 30 µm. The interposed material 3, in Fig. 1, for example, is not limited to a specific material as far as the material has a property to withstand against the heating during the heat treatment. In this meaning, however, it may be preferred for the interposed material to be formed with a material having an electrically insulating property for further ensuring the insulation between the laminated magnetic films. Furthermore, in consideration of the workability or handling efficiency of the interposed material when the interposed material is inserted between the magnetic film and the insulating film, powder materials may be preferred for the interposed material. As a method or process of interposing the powder material between the magnetic film and the insulating film, a powder sticking method in which the powder materials are sticked on the surface of the insulating film or magnetic film will be preferably utilized for easy and simple operation efficiency. The following methods will be referred to for sticking the powder materials on the surface of the magnetic thin metal film, for example: 1. A method in which powders are dispersed in water to form a suspension into which the magnetic film is immersed; 2. A method utilizing an electrophoresis treatment; and A method in which powders are sprayed on the surface of the magnetic film by spraying means. However, as these methods are themselves per se known, the explanation thereof is omitted herein. With the powder sticking methods described above, it is possible to stick the powder material on one or both surfaces of the magnetic film, but the objects and effects of the present invention can be more effectively achieved by sticking the powder materials on both surfaces of the magnetic film for the reason that, when the magnetic film and the insulating film are wound up for forming a magnetic core, the insulating films between which one magnetic film is interposed less affect the interposed magnetic film. The electrically insulating film is not specifically limited as regards the material thereof, but it is found that the usage of the polyimide film, which is thermally shrunk at a high temperature, attains a suitable effect, and the magnetic core will attain more remarkable effects when combining the polyimide film and the iron based amorphous film having relatively large magnetostriction. The substance of the powder materials to be sticked is not specifically limited, but powders having an electrically insulating property such as at least one selected from oxide, nitrate or carbonate or least one selected from magnesium, silicon, aluminium, zirconium or titanium may be preferred and, particularly, the magnesium, silicon or aluminium oxide may be most preferred for the reason that these oxides can easily be handled and obtained with relatively low cost. Furthermore, according to the present invention, there is no limitation to the grain size of the powder, but it may be preferred for the grain to have a diameter (which herein means the diameter of most small ball including powder) of 0.05 to 40 µm. This is because the objects and effects of the present invention are hardly achieved when the grain diameter is too small and, on the other hand, when the grain diameter is too large, a magnetic substance space factor is extremely lowered when manufacturing the magnetic core from the magnetic film. In consideration of these facts, it is preferred for the grain of the powder to have a diameter of 0.5 to 10 µm. One method of concretely producing the magnetic core, for example as shown in Fig. 1, according to the present invention will be described hereunder. A magnetic film and an electrically insulating film are preliminarily prepared and powder materials, preferably having an electrically insulating property, are sticked by, for example, dispersing the powder materials into water to form a suspension, immersing at least one of the magnetic film and the insulating film and then drying the immersed one. The thus prepared magnetic film and the insulating film are alternately wound up around a reel or mandrel, for example, in a state such as shown in Fig. 1, in which the powder materials are sticked on the surface of the magnetic film 1. The magnetic core is then finally produced by the heat treatment of the thus wound-up core. The magnetization characteristic such as the rectangular ratio of the produced magnetic core will be improved by carrying out the heat treatment in a D.C. or A.C. magnetic field. In such heat treatment, it is preferred that the magnetic field has an intensity of about 39,8 to 7960 A/m (0.5 to 100 Oe (oersted)), preferably of about 159,2 to 1592 A/m (2 to 20 Oe). The combination of the magnetic film and the electrically insulating film may be optionally selected according to the present invention in accordance with the characteristics of the produced magnetic core to be required. For example, more than two insulating film layers are wound up in a case where strong electric insulation is required and, on the other hand, more than two magnetic thin metal film layers are wound up in a case where a strong magnetized characteristic is required. Concrete examples of the present invention will be described hereunder in comparison with comparative examples. (Example 1) An amorphous ribbon having a composition of Fe₇₈Si₉B₁₃ (at%) and having a thickness of 22 µm was immersed in a suspension which was prepared by diffusing magnesium oxide (MgO) powders (1wt%) into water to thereby stick the powders on the surface of the amorphous ribbon. The immersed amorphous ribbon was thereafter put in an electric furnace and heated to a temperature of about 150° to dry the same. The thus prepared amorphous ribbon and a polyimide film (Commercial Name: UPILEX, produced by UBE KOSAN, Thickness: 5 µm) were alternately wound up around a magnetic core having an outer diameter of 50mm, an inner diameter of 30mm and a height of 13mm. The thus formed magnetic core was then heat treated for two hours at a constant temperature of 380° in a D.C. constant magnetic field of 796 A/m (10 Oe). (Comparative Example 1) A magnetic core was prepared and formed by substantially the same manner as that described with reference to the Example 1 except that no powder was sticked to the amorphous ribbon. (Example 2) An amorphous ribbon having a composition of Fe₇₈Si₉B₁₃ (at%) and having a thickness of 22 µm was immersed in a dispersion solution which was prepared by diffusing magnesium oxide (MgO) powders (1wt%) into water to thereby stick the powders on the surface of the amorphous ribbon. The immersed amorphous ribbon was thereafter put in an electric furnace and heated to a temperature of about 150° to dry the same. The thus prepared two amorphous ribbons and one amorphous ribbon on which the MgO powders were not sticked were laminated in a sandwiched manner to form three amorphous alloy ribbon layer. The amorphous ribbon layers and one polyimide film having a thickness of 7.5 µm were then wound up around a magnetic core having an outer diameter of 50mm, an inner diameter of 30mm and a height of 13mm. The thus formed magnetic core was then heat treated for two hours at a constant temperature of 380° in a D.C. constant magnetic field of 796 A/m (10 Oe). (Comparative Example 2) A magnetic core was prepared and formed in substantially the same manner as that described with reference to the Example 2 except that no powder was sticked to the amorphous alloy ribbon. (Example 3) An amorphous alloy ribbon having a composition of (Co 0. 94 Fe 0. 06 )₇₀Ni₃Nb₁Si₁1B₁₅ (at%) and having a thickness of 16 µm was immersed in a dispersion solution which was prepared by diffusing magnesium oxide (MgO) powders (1wt%) into water to thereby stick the powders on the surface of the amorphous alloy ribbon. The immersed amorphous alloy ribbon was thereafter put in an electric furnace and heated to a temperature of about 150° to dry the same. The thus prepared amorphous alloy ribbon and a polyimide film having a thickness of 7.5µm were alternately wound up around a magnetic core having an outer diameter of 50mm, an inner diameter of 30mm and a height of 13mm. The thus formed magnetic core was then heat treated for one hour at a constant temperature of 420° in a D.C. constant magnetic field of 796 A/m (10 Oe). (Comparative Example 3) A magnetic core was prepared and formed in substantially the same manner as that described with reference to the Example 3 except that no powder was sticked to the amorphous alloy ribbon. (Example 4) An amorphous alloy ribbon having a composition of Fe₈₁Si 3. 5 B 13. 5 C₂ (at%) and having a thickness of 22 µm was immersed in a dispersion solution which was prepared by diffusing magnesium oxide (MgO) powders (1wt%) into water to thereby stick the powders on the surface of the amorphous alloy ribbon. The immersed amorphous ribbon was thereafter put in an electric furnace and heated to a temperature of about 150° to dry the same. The thus prepared amorphous alloy ribbon and a polyimide film having a thickness of 7.5 µm were alternately wound up around a magnetic core having an outer diameter of 50mm, an inner diameter of 30mm and a height of 13mm. The thus formed magnetic core was then heat treated for two hours at a constant temperature of 360° in a D.C. constant magnetic field of 796 A/m (10 Oe). (Comparative Example 4) A magnetic core was prepared and formed in substantially the same manner as that described with reference to the Example 4 except that no powder was sticked to the amorphous alloy ribbon. (Example 5) An amorphous alloy ribbon having a composition of Fe₆₇Co₁₈Si₁B₁₄ (at%) and having a thickness of 22 µm was immersed in a dispersion solution which was prepared by diffusing magnesium oxide (MgO) powders (1wt%) into water to thereby stick the powders on the surface of the amorphous alloy ribbon. The immersed amorphous ribbon was thereafter put in an electric furnace and heated to a temperature of about 150° to dry the same. The thus prepared amorphous alloy ribbon and a polyimide film having a thickness of 7.5 µm were alternately wound up around a magnetic core having an outer diameter of 50mm, an inner diameter of 30mm and a height of 13mm. The thus formed magnetic core was then heat treated for two hours at a constant temperature of 320° in a D.C. constant magnetic field of 796 A/m (100e). (Comparative Example 5) A magnetic core was prepared and formed in substantially the same manner as that described with reference to the Example 5 except that no powder was sticked to the amorphous alloy ribbon. (Example 6) An amorphous alloy thin film having a composition of Fe₇₈Si₉B₁₃ (at%) and having a thickness of 22 µm was immersed in a dispersion solution which was prepared by diffusing silicon dioxide (SiO) powders (1wt%) into water to thereby stick the powders on the surface of the amorphous alloy ribbon. The immersed amorphous ribbon was thereafter put in an electric furnace and heated to a temperature of about 150° to dry the same. The thus prepared amorphous alloy ribbon and a polyimide film having a thickness of 7.5 µm were alternately wound up around a magnetic core having an outer diameter of 50mm, an inner diameter of 30mm and a height of 13mm. The thus formed magnetic core was then heat treated for two hours at a constant temperature of 380° in a D.C. constant magnetic field of 796 A/m (10 Oe). (Comparative Example 6) A magnetic core was prepared and formed in substantially the same manner as that described with reference to the Example 6 except that no powder was sticked to the amorphous alloy ribbon. With respect to the thus prepared twelve magnetic cores, rectangular ratios of the magnetization curves, maximum magnetic flux densities, coercive forces and magnetic flux density swing were examined under the condition of a constant temperature. The rectangular ratios, the maximum magnetic flux densities and the coercive forces were measured by a D.C. automatic hysteresis loop tracer at an applied field of 796 A/m (10 Oe). The magnetic flux density swing (Δ B) wasΔ B= Br + Bm. The results of the measurements are summarized in the following Table 1. Fig. 2 shows a perspective view of a magnetic core prepared in accordance with another embodiment of the present invention, in which the magnetic core is prepared by alternately laminating magnetic film layers 4 and electrically insulating film layers 5. These magnetic film layers 4 and insulating film layers 5 are generally formed by punching a thin magnetic metal plate and a thin insulating plate in the shape of discs, for example, and such discs are laminated alternately as shown. According to the present invention, a material or substance 6, such as powders, is sticked on the surface of the magnetic film layers 4 or the insulating film layers 5. In the practical production of the magnetic core, however, it may be preferred to produce the magnetic core by winding the magnetic thin metal film and the insulating film around the mandrel, for example as shown in Fig. 1, in comparison with the magnetic core produced by alternately laminating these discs such as shown in Fig. 2, in consideration of the actual product and apparatus to be used.

Claims: A magnetic core comprising at least one layer of magnetic film and an electrically insulating film characterized in that a substance (3) is interposed between the magnetic film (1) and the electrically insulating film (2), the material of said substance being heat-resistant and being different from same of the magnetic film and the insulating film, and the magnetic film and the electrically insulating film are alternately wound up in a predetermined shape with the substance interposed therebetween. A magnetic core according to claim 1, wherein said magnetic film (1) is composed of an iron based amorphous alloy. A magnetic core according to claim 1, wherein said magnetic film (1) is composed of a cobalt based amorphous alloy. A magnetic core according to claim 1 or 2, wherein said magnetic film (1) has a thickness of less than 40µm. A magnetic core according to claim 4, wherein said magnetic film (1) has a thickness of 12 to 30µm. A magnetic core according to any of claims 1 to 5, wherein said electrically insulating film (2) is made of a substance having a thermally shrinkable property. A magnetic core according to claim 6, wherein said electrically insulating film (2) is a polyimide. A magnetic core according to any of claims 1 to 7, wherein said substance (3) interposed between said magnetic film (1) and said electrically insulating film (2) has an electrically insulating property. A magnetic core according to claim 8, wherein said substance (3) is powder of at least one selected from oxide, nitrate or carbonate having an electrically insulating property. A magnetic core according to claim 9, wherein said oxide, nitrate, or carbonate is at least one selected from oxide, nitrate or carbonate of magnesium, silicon, aluminium, zirconium or titanium. A magnetic core according to claim 9 or 10, wherein said powder has a grain diameter of 0.05 to 40µm. A magnetic core according to claim 11, wherein said powder has a grain diameter of 0.5 to 10µm. A magnetic core according to any of claims 9 to 11, wherein said powder is sticked on a surface of said magnetic film (1). A magnetic core according to any of claims 9 to 13, wherein said powder is sticked by immersing said magnetic film (1) in a dispersion solution prepared by dispersing said powder in water. A magnetic core according to any of claims 9 to 12, wherein said powder is sticked on a surface of said electrically insulating film (2). A magnetic core according to any of claims 1 to 15, wherein said magnetic film (1) is composed of three laminated layers having an intermediate layer on which said substance is not disposed. A magnetic core according to any of claims 1 to 16, wherein the heat treatment is performed in a magnetic field having an intensity of 39,8 to 7960, preferably 159,2 to 1592 A/m (0.5 to 100, preferably 2 to 20, oersted). A magnetic core comprising at least one layer of magnetic film generally of a disc shape and at least one layer of electrically insulating film generally of a disc shape characterized in that a substance (6) is interposed between the magnetic film (4) and the electrically insulating film (5), the material of said substance being heat-resistant and being different from same of the magnetic film and the magnetic film and the electrically insulating film are alternately laminated with the substance interposed therebetween.

Inventors: KUSAKA TAKAO, OKAMURA MASAMI, SAWA TAKAO, YAMAUCHI YOSHIYUKI, KUSAKA, TAKAO, OKAMURA, MASAMI, SAWA, TAKAO, YAMAUCHI, YOSHIYUKI
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1990
Main classification: H01F3
IPC codes: H01F1, H01F3