EP0007994B1 - Magnetic core made of a soft magnetic amorphous alloy - Google Patents

Description

The invention relates to a magnetic core made of a soft magnetic amorphous alloy.

Electromagnetic components with cores made of soft magnetic amorphous alloys are already known (DE-A-2546676 and 2 553 003).

As is known, amorphous metal alloys can be produced by cooling an appropriate melt so rapidly that solidification occurs without crystallization. The alloys can be obtained in the form of thin strips, the thickness of which can be, for example, a few hundredths of a mm and the width of which can be from a few mm to several cm.

The amorphous alloys can be distinguished from the crystalline alloys by means of X-ray diffraction measurements. In contrast to crystalline materials, which show characteristic sharp diffraction lines, the intensity in the X-ray diffraction pattern with amorphous metal alloys changes only slowly with the diffraction angle, similarly as is the case with liquids or ordinary glass.

Depending on the production conditions, the amorphous alloys can be completely amorphous or comprise a two-phase mixture of the amorphous and the crystalline state. In general, an amorphous metal alloy is understood to mean an alloy which is at least 50%, preferably at least 80%, amorphous.

For every amorphous metal alloy there is a characteristic temperature, the so-called crystallization temperature. If the amorphous alloy is heated to or above this temperature, it changes to the crystalline state in which it remains even after cooling. In the case of heat treatments below the crystallization temperature, however, the amorphous state is retained.

The previously known soft magnetic amorphous metal alloys have the composition MyX _i -y, where M is at least one of the metals iron, cobalt and nickel, and X is at least one of the so-called glass-forming elements boron, carbon, silicon and phosphorus and y is between about 0.60 and 0.95. In addition to the metals M, the amorphous alloys can also contain other metals, in particular titanium, zircon, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, palladium, platinum, copper, silver or gold, while in addition to the Glass-forming elements X or, where appropriate, the elements aluminum, gallium, indium, germanium, tin, arsenic, antimony, bismuth or beryllium may be present instead of these.

The amorphous soft magnetic alloys are particularly suitable for the production of magnetic cores, since, as already mentioned, they can be produced directly in the form of thin strips without, as with the crystalline soft magnetic metal alloys customary in the art, a large number of rolling steps with numerous Intermediate annealing is required.

Cores with a sheared hysteresis loop are often used for various applications, for example for chokes. In the case of cores made of conventional crystalline soft magnetic alloys, shear is known to be achieved by providing an air gap at least at one point along the core, which extends over the entire core cross section at this point.

Such air gaps often have to be ground in in a relatively complex manner or the core has to be completely cut to produce the air gaps, as is the case, for example, with cutting tape cores, so that additional parts for holding the core together, for example tensioning straps, are required.

From DE-A-1 514 333 a method for obtaining gap-like interruptions in magnetic materials is also known. The known method consists in particular in changing the structure of the magnetic material at the desired point by irradiation with high-energy radiation in such a way that there is no ferro- or ferri-. has more magnetic properties. There is no indication of amorphous magnetic alloys in DE-A-1 514 333.

The object of the invention is to achieve a shear of the hysteresis loop in a simple manner with a magnetic core made of a soft magnetic amorphous alloy.

This is achieved according to the invention in that the amorphous alloy is converted into the crystalline state by local heating at least at one point along the core at least over part of the core cross section at this point.

While the amorphous soft magnetic alloys have a relatively high permeability in the amorphous state, the permeability is considerably reduced by the transition to the crystalline state through local overheating above the crystallization temperature. This results in a crystalline zone which extends at least over part of the core cross section at the heated point and acts in a manner similar to an air gap.

In order to achieve the largest possible difference in permeability between the crystalline zone and the remaining parts of the magnetic core, a completely amorphous soft magnetic alloy can preferably be used as the starting material.

Depending on the intended application of the Magnetic core can be provided one or more crystalline zones distributed over the core, the width of which may also vary over the core cross section.

It is particularly effective in the manner of an air gap if the amorphous alloy is converted into the crystalline state at least at one point in the magnetic core over the entire core cross section at this point.

The magnetic cores according to the application can be produced, for example, by winding an amorphous band into a core or by laminating sheets punched out of amorphous band into a core. Local heating above the crystallization temperature to produce the crystalline zone can then take place, for example, by means of an induction loop placed around the core at the appropriate point. Before the crystalline zone is created, the magnetic cores can be heat-treated in a manner known per se, for example at a temperature below the crystallization temperature in the presence of a magnetic field which magnetizes the magnetic core approximately to saturation. The magnetic field can be a transverse magnetic field or a longitudinal magnetic field.

Especially with larger dimensions, if the core is difficult to heat over the entire cross-section, or in cases where only a certain part of the cross-section is to be converted into the crystalline state, the core can also be layered, for example, from sheets that have been previously at least one point has been converted into the crystalline state over all or part of its cross section. The heating can take place, for example, by resistance heating between two metal cutting edges serving as contacts or also by laser beams.

The invention will be explained in more detail with the aid of a few figures.

Figures 1 to 4 each show a top view schematically different embodiments of a magnetic core according to the invention.

The magnetic core shown in FIG. 1 is constructed, for example, from a number of disks 1 stacked one on top of the other from a soft magnetic amorphous alloy, in each of which a zone 2 has been converted to the crystalline state by inductive heating. If, for example, disks with an inner diameter of 20 mm and an outer diameter of 30 mm made of a soft magnetic amorphous alloy of the composition Fe _0.40 Ni _0.40 P _0.14 B _{0.06 are used} and these are layered to form a 10 mm high core, after appropriate tempering treatment in the magnetic field in the amorphous material, a permeability p. = 250,000 (measured as constant field permeability at 4 mA / cm) can be achieved. Upon transition to the crystalline state by local heating to a temperature above the crystallization temperature of approximately 400 ° C., this permeability in the crystalline zone is reduced to approximately 500. A 5 mm wide crystalline zone 2 therefore corresponds to an apparent air gap with a length of 0.01 mm. Since the average iron path length of the core is 78.5 mm for the dimensions mentioned above, the permeability of the sheared circle is approximately 7630.

FIG. 2 shows a further core, which can, for example, be stacked up from sheet metal or wound from tape in the form of a ring band core. In the amorphous material 11, crystalline zones 12, which extend over the entire core cross section, are generated at four locations on the core circumference by local heating.

FIG. 3 shows a correspondingly constructed magnetic core, in which crystalline zones 22 are generated in the amorphous material 21 at two locations, the boundary surfaces of which are curved. Such crystalline zones, the width of which varies over the core cross section, can be used, for example, to achieve nonlinear characteristic curves.

FIG. 4 shows a magnetic core in which crystalline zones 32 are produced in the amorphous alloy 31 at two locations, each of which extends over only part of the core cross section.

As the exemplary embodiments show, the shear can be varied within wide limits by different selection of the crystalline zones. For example, flat hysteresis loops, perminvar-like loops, strongly sheared linear loops or non-linear characteristics can be achieved.

If several crystalline zones are provided along the circumference of the core, then - similar to a powder core - a uniform shear can be achieved with little magnetic scatter.

The cores can be glued in the usual way, used in protective troughs or cast.

Claims (3)

1. A magnet core consisting of a soft-magnetic amorphous alloy, characterised in that the amorphous alloy (1) is converted by local heating into the crystalline state at at least one point (2) along the core over at least a part of the cross-section of the core at this point.

2. A magnet core as claimed in Claim 1, characterised in that the amorphous alloy (1) is converted into the crystalline state at at least one point (2) along the core over the entire cross-section of the core at this point.

3. A magnet core as claimed in Claim 2, characterised in that the width of the crystalline zone (22) varies over the cross-section of the core.

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