EP2171729B1 - Method for production of a magnet core - Google Patents

Description

The invention relates to a method for producing a magnetic core according to the preamble of claim 1. Such a method is for example from the EP 0794 541 A known.

Magnet cores, which are formed from a spirally wound metal strip, so-called ring band cores, are used, for example, in current transformers, power transformers, current-compensated radio interference suppression chokes, starting current limiters, storage chokes, single-ended chokes, transductor chokes and total or differential current transformers for RCCBs.

They are set high demands in terms of magnetic properties: Residual current transformer for AC-sensitive residual current circuit breaker, for example, must provide a secondary voltage that is at least sufficient to trigger the magnetic system of the trip relay, which is responsible for the shutdown. Since the most space-saving design of the current transformer is desired, a material for the magnetic core is needed, which in addition to a high induction at the typical operating frequency of 50 Hz above all a maximum permeability μ _r has. The geometry of the magnetic core and the material properties in combination with the technological refinement of the material, for example by a heat treatment, have a major influence on the permeability.

So far, it was necessary to achieve sufficiently high permeability, a smallest possible saturation magnetostriction constant λ _s of | λ _s | <2ppm or even <0.3ppm. In addition, geometric as perfect as possible Bands with as few form errors as possible are an important requirement. However, such a small saturation magnetostriction constant λ _s can easily be achieved only with a few alloys, and it is also almost impossible in an industrial production to achieve an exact alloy composition without impurities.

However, it would be possible to achieve high permeability numbers even with numerous other alloy compositions if the magnetic core were free from mechanical stress. Mechanical stresses are introduced, for example, during winding of the core from one or more bands or during its subsequent handling in the magnetic core. The relationship between the absence of voltage of the magnetic core and high permeability is, for example, in the JP 63-115313 addressed. While stresses that have arisen during winding can usually be greatly reduced in a subsequent heat treatment, the introduction of mechanical stresses due to external influences such as impact or shaking must be avoided as far as possible.

This is for example from the EP 0 509 936 B1 It is known to connect a magnetic core of a nickel-iron alloy by means of a flexible silicone adhesive by a plurality of adhesive dots with a housing. However, this procedure can not be transferred to magnetic cores of a magnetostrictive alloy, because before the complete crosslinking of the silicone adhesive this crawls between the tape layers of the magnetic core due to capillary forces and the dead weight of the magnetic core. Form defects in amorphous and nanocrystalline ribbons still favor the penetration of the adhesive. During curing, tensile stresses then occur at the wetted strip layers and thus deteriorate the magnetic properties of the core. Since the amount of penetration of the silicone adhesive between the tape layers is highly dependent on random shape errors of the tape, this effect is also possible difficult to predict and leads to a strong dispersion of permeability values.

The object of the present invention is therefore to provide a method for producing a magnetic core, wherein the magnetic core is effectively protected from outside introduced mechanical stresses and thus permanently has good magnetic properties.

For example, such a magnetic core may be made of a spirally wound soft magnetic ribbon having a top surface and a bottom surface, the top surface and bottom surface being formed by side surfaces of the soft magnetic ribbon. The magnetic core can be fixed in a protective housing and for fixing the magnetic core, a pressure-sensitive adhesive can be provided between the underside of the magnetic core and a housing inner wall.

zwischen der Permeabilitätszahl µ_r, der Sättigungsmagnetostriktionskonstante λ_s und der mechanischen Spannung o führen solche Verspannungen bei nicht ausreichend kleiner Sättigungsmagnetostriktionskonstante zu zu geringen und außerdem stark streuenden Permeabilitätszahlen.It should be avoided in particular with magnetic cores made of rapidly solidified alloys, a frictional connection between the protective housing and the magnetic core, since these tape layers have a low intrinsic stability, so that caused by volume shrinkage of the adhesive tensile forces inevitably bring mechanical stresses in the magnetic core. It should therefore be prevented impregnation of the magnetic core with the adhesive. A non-positive connection between the magnetic core and the protective housing would have the consequence that differences in the thermal expansion between the material of the magnetic core and that of the housing would be directly noticeable by mechanical tension. Because of the basic relationship $${\mu }_{\mathrm{<figure-callout\; id="1"\; label="r\; \alpha "\; filenames="imgf0001.png,imgf0002.png"\; state="\{\{state\}\}">r\; </figure-callout>}}\alpha \frac{1}{{\lambda }_s\cdot \sigma }$$

between the permeability μ _r , the saturation magnetostriction constant λ _s and the mechanical stress o such strains lead to too small and also strongly scattering permeability figures at not sufficiently small saturation magnetostriction.

Through the use of a pressure-sensitive adhesive, which has a permanently tacky surface after drying, however, a fixation of the magnetic core in the protective housing can be achieved, which is at the same time elastic enough to compensate for stresses. In addition, in the case of a pressure-sensitive adhesive, the penetration of the adhesive between the band layers can be reduced to a minimum, the connection of the magnetic core to the housing taking place almost exclusively via the adhesion of the adhesive to the side surfaces of the individual band layers. Suitable pressure-sensitive adhesives are, for example, flexible, thermoplastic PSAs.

For example, the pressure-sensitive adhesive comprises an acrylate polymer. Compared to other in principle suitable PSAs such as based on rubber, polyvinyl esters, polybutadiene or polyurethane, those based on acrylate polymers have the advantage that they allow the formulation of particularly resistant adhesives.

For example, the pressure-sensitive adhesive has an elongation at break ε _R with ε _R > 250%, preferably> 450%, more preferably> 600%. Such a pressure-sensitive adhesive is sufficiently elastic to prevent unwanted power transmission between the housing and the magnetic core fixed therein. Furthermore, the pressure-sensitive adhesive advantageously has a glass transition temperature T _g with T _G <0 ° C; better T _G <-20 ° C; better T _G <-30 ° C and a melting temperature T _x with T _s > 180 ° C.

The penetration depth t of the pressure-sensitive adhesive between the tape layers of the magnetic core is, for example, t <2 mm, preferably t <0.5 mm and even more preferably t <0.01 mm.

Typically, the finished magnetic core, so the magnetic core after completion of the heat treatment, a nanocrystalline soft magnetic tape on. However, depending on the intended use of the magnetic core, amorphous or crystalline bands are also conceivable.

Various alloy compositions are conceivable for the magnetic core according to the invention. Since a disappearance of the saturation magnetostriction constant is not required, common iron-based alloys can be used, and also residual impurities, which can not be completely avoided in general, are tolerable, without causing undesirable effects on the magnetic properties.

For example, in addition to commercially available impurities of the raw materials or the melt, the soft magnetic strip essentially has the alloy composition

Fe _a Co _b Cu _o SidB _e M _f X _g

in which M is at least one of the elements v, Nb, Ta, Ti, Mo, W, Zr and Hf and X is at least one of the elements P, Ge and C, a, b, c, d, e and f in atomic percent are and 0 ≤ b ≤ 45; 0.5 ≤ c ≤ 2; 6, 5 ≤ d ≤ 18; 5 ≤ e ≤ 14; 1 ≤ f ≤ 6; d + e>16; g <S and a + b + c + d + e + f + g = 100. In this case, cobalt may be wholly or partially replaced by nickel.

For example, the magnetic core has a saturation magnetostriction constant λ _s of λ _s <15 ppm.

The ratio of remanent induction to saturation induction B _R / B _{S of} the magnetic core is advantageously B _R / B _S > 45% and the maximum permeability μ _max > 250,000, for example after a magnetic field-free heat treatment for nanocrystallization. Alternatively, the magnetic core has, for example, a ratio of remanent induction to saturation induction B _R / B _s of B _R / B _s > 50% and a maximum permeability μ _max of μ _max > 150,000. These properties can be achieved, for example, by a longitudinal field treatment following a heat treatment for nanocrystallization. In another alternative embodiment, B _R / B _S > 2% and μ _max > 5,000. These properties can be achieved, for example, by a transverse field treatment following a heat treatment for nanocrystallization.

A method of manufacturing a magnetic core according to the present invention comprises the steps of first providing a magnetic core wound with a soft magnetic ribbon having a top surface and a bottom surface, the top and bottom surfaces being formed by side surfaces of the soft magnetic ribbon. Furthermore, a protective housing for receiving the magnetic core is provided. On a housing inner wall, a pressure-sensitive adhesive is applied, wherein the pressure-sensitive adhesive forms a film on its surface. After forming the film, the magnetic core is inserted into the protective case, and the lower surface of the magnetic core is brought into contact with and adhered to the pressure sensitive adhesive.

In an advantageous embodiment, the pressure-sensitive adhesive is applied to the housing inner wall as an aqueous dispersion. In an alternative embodiment, the pressure-sensitive adhesive is applied as an organic solution. The use of an aqueous dispersion has the advantage that film formation takes place on the surface, while the drying in lower layers of the adhesive takes place over time delayed by diffusion of the water contained in the dispersion through the already formed film.

Advantageously, when the magnetic core is inserted into the protective housing under the film, the pressure-sensitive adhesive has not yet set on its surface. As a result, especially when the pressure-sensitive adhesive has a viscosity v with v <20 Pa · s when inserting the magnetic core into the protective housing, it is ensured that the film on the surface is strong enough on the one hand to rupture the film between the adhesive layers To prevent band layers, while on the other hand, the remaining, still liquid dispersion amount allows deformation of the drop of adhesive under the weight of the magnetic core and a tension-free sinking of the magnetic core in the adhesive.

After application of the pressure-sensitive adhesive is advantageously subjected to drying by hot air or infrared or other heat-generating radiation, wherein the film formation begins at the adhesive surface.

In an advantageous embodiment, when the magnetic core is inserted into the protective housing, the pressure-sensitive adhesive has a solids content of more than 30% by weight and a minimum film formation temperature T _F with T _F <0 ° C.

The magnetic core is typically subjected to a heat treatment prior to insertion into the protective housing. By such a heat treatment on the one hand mechanical stresses resulting from the winding of the magnetic core can be reduced. On the other hand, a nanocrystalline or crystalline structure can be set in the originally amorphous ribbon. The heat treatment is advantageously carried out at a temperature T of 505 ° C ≤ T ≤ 600 ° C. However, to set a nanocrystalline structure are also slightly lower temperatures of 480 ° C, for example. In one embodiment, the heat treatment is performed field-free in the absence of a magnetic field. In order to set desired magnetic properties, however, the magnetic core may also be exposed during the heat treatment to a magnetic field of a certain direction (eg transverse or longitudinal field) and strength.

The magnetic core according to the invention is particularly suitable for use in a residual current circuit breaker, since it provides a sufficiently high secondary voltage due to its high permeability, sufficient to trigger the magnetic system of the trip relay, which is responsible for the shutdown. Also applications, eg. As a current transformer, transformer or chokes with different hysteresis are conceivable.

Figur 1

schematisch ein Ausführungsbeispiel des erfindungsgemäßen Magnetkerns;

Figur 2

anhand eines Diagramms den Einfluss einer unzureichenden mechanischen Stabilisierung bei Magnetkernen mit nichtverschwindender Magnetostriktion;

Figur 3

anhand eines Diagramms den Einfluss einer Fixierung des Magnetkerns mit einem Silikonkautschukkleber;

Figur 4

anhand eines Diagramms den Einfluss einer Fixierung des erfindungsgemäßen Magnetkerns mit einem Acrylathaftkleber und

Figur 5

anhand eines Diagramms den Einfluss einer mechanischen Stabilisierung des erfindungsgemäßen Magnetkerns.

Embodiments of the invention are explained below with reference to the accompanying figures. Show it

FIG. 1

schematically an embodiment of the magnetic core according to the invention;

FIG. 2

a diagram of the influence of insufficient mechanical stabilization in magnetic cores with non-vanishing magnetostriction;

FIG. 3

using a diagram the influence of a fixation of the magnetic core with a silicone rubber adhesive;

FIG. 4

with reference to a diagram, the influence of a fixation of the magnetic core according to the invention with an acrylic pressure-sensitive adhesive and

FIG. 5

a diagram of the influence of a mechanical stabilization of the magnetic core according to the invention.

The magnetic core 1 according to FIG. 1 is designed as a ring band core and wound from a soft magnetic tape. It has a number of band layers 2, which are separated from each other by gaps 3. The end faces 14 and 15 of the band layers 2 form an upper side 4 and a lower side 5 of the magnetic core 1.

The magnetic core 1 is embedded in a protective housing 6, which consists in the embodiment shown of an inner protective trough 7, which is placed over the magnetic core 1, and a protective trough 7 receiving the upper shell 9 and lower shell 8. The magnetic core 1 is protected by the protective housing against external influences that could introduce mechanical tension into the tape layers 2. The upper shell 9 can also be designed as a flat lid.

The magnetic core 1 is fixed in the protective housing 6 by means of a layer of a pressure-sensitive adhesive 11. The pressure-sensitive adhesive 11 is arranged on a housing inner wall 10 and has a permanently tacky surface 12, with which the end faces 15 of the tape layers 2 are in adhesive contact on the underside 5 of the magnetic core. However, the pressure-sensitive adhesive 11 does not penetrate or only very slightly penetrates into the lower region 13 of the intermediate spaces 3. It is also elastic enough so that the transmission of tensile stress caused by the pressure-sensitive adhesive 11 on the tape layers 2 is reliably prevented.

In the embodiment shown, only the underside 5 of the magnetic core 1 is fixed to a housing inner wall 10 by a single adhesive layer. However, it is also possible, for example, to fix the side surfaces 16 and / or the upper side 4 of the magnetic core 1 to the protective housing 6 by means of a pressure-sensitive adhesive layer.

As has been found, in the illustrated type of fixation, an amount of adhesive of 2 drops with a mean diameter of about 1.5 to 3 mm with a dependent on the solids content of the adhesive mass of the drops of at least 0.05 to 0.3 g is sufficient , In typical magnetic cores can thus produce a glue point, not as in FIG. 1 shown covering the entire bottom 5 of the magnetic core 1. The glue point then has an area of at least 15 mm ² and it is possible to achieve adhesive strengths of more than 0.3 N / mm ² , which is sufficient for typical masses of the magnetic core of about 10 to 30 g.

To be fixed magnetic cores made of a nanocrystalline alloy of composition Fe _rest Co _0.11 Ni _0.05 Cu _0.97 Nb ₂ , ₆₃ Si _13.1 B _7.8 C _0.18 with dimensions of 18.5 mm x 13.5 mm x 12 mm were subjected to a heat treatment in a continuous furnace for one hour at 538 ° C under hydrogen atmosphere and then as in FIG. 1 shown embedded in a protective housing. They had a saturation magnetostriction λ _s of 4.3 ppm.

The FIGS. 2 to 5 show the improvement achieved by the fixation of the magnetic properties of the magnetic core according to the invention.

FIG. 2 shows a diagram of the influence of insufficient mechanical stabilization in magnetic cores with non-disappearing magnetostriction according to the prior art. For this purpose, highly permeable magnetic cores of rapidly solidified nanocrystalline alloys with non-vanishing magnetostriction between two punching disks of a very soft, open-cell foam such as polyurethane foam were stored in a plastic housing. The thus protected magnetic cores were dropped from a height of about 10 cm on a hard surface. After the fall, the magnetic characteristics of the magnetic cores such as their permeability at a given field strength such as in R.Boll: "Soft Magnetic Materials", 4th edition, p. 140 et seq. After the measurement, each magnetic core was turned and dropped with its opposite end face from a height of about 10 cm on the hard surface. Its magnetic characteristics were redetermined and this drop test was repeated several times.

In FIG. 2 As a result of this drop test, the measured permeability numbers are plotted against the number of drops. As in FIG. 2 As can be seen, the permeability numbers of the magnetic cores change with the falling events in an unpredictable manner. This can be explained by the fact that the falling or striking of the embedded magnetic core due to the insufficient stabilization by the foam blanking discs leads to an axial displacement of individual tape layers or tape layer packages. This mechanical deformation of the magnetic core along its longitudinal axis changes the mechanical stress state of the individual tape layers and leads to the observed changes in the permeability number.

FIG. 3 shows a diagram of the influence of a fixation of the magnetic core with a silicone rubber adhesive according to the prior art. These were highly permeable magnetic cores after in the EP 0 509 936 B1 described method by means of a soft elastic silicone adhesive by a plurality of adhesive dots connected to the plastic housing. As in FIG. 3 Obviously, the adhesive causes a deterioration in the magnetic properties of the magnetic cores, in particular a reduction in the permeability number.

This is in accordance with the diagram FIG. 3 the permeability of the magnetic cores determined at 50 Hz in the freshly glued state (first measured values with core numbers up to 10) and in the fully cured state of the adhesive (subsequent core numbers).

The cause of the undesirable reduction in the permeability number is presumably that the adhesives used in the non-crosslinked state have typical viscosities between 2 Pa.s and 200 Pa.s and the time until the onset of curing of the adhesive by moisture absorption between 30 and 120 minutes lies. During this time, after the insertion of the magnetic core into the adhesive droplets, an adhesive penetrates between individual band layers of the magnetic core, on the one hand as a result of capillary forces, and on the other hand due to sinking of the magnetic core under its own weight. During the subsequent curing of the adhesive, there is a reduction in volume of the adhesive and thus tensile stresses on the wetted with the adhesive tape layers. If the core had only been used after curing of the adhesive, there would have been no adhesion.

The magnetic cores according to FIG. 3 had relatively high band-fill factors of 83.4% and thus low shape errors and a relatively low saturation magnetostriction λ _s of 2.2 ppm. Nevertheless, the reduction in permeability was about 50%. Such influence by the adhesive is on the one hand undesirably large and on the other hand, as also in FIG. 3 recognizable, not calculable in their concrete amount.

FIG. 4 shows a diagram of the influence of a fixation of the magnetic core of the invention with an acrylate adhesive. This was like the case FIG. 3 described test highly permeable magnetic cores according to an embodiment of the invention with an acrylate adhesive in a plastic housing glued using an aqueous pure acrylate dispersion was used.

The nanocrystalline alloy cores to be fixed of composition Fe _Residual Co _0.11 Ni _0.05 Cu _0.97 Nb _2.63 Si _13.1 B _7.8 C _0.18 with the dimensions 18.5 mm x 13, 5 mm x 12 mm were subjected to a heat treatment in a continuous furnace at 538 ° C for one hour Hydrogen atmosphere exposed and then, as shown in Figure 1, embedded in a plastic housing. Although the saturation magnetostriction λ _{s was} not particularly low at 4.3 ppm, the irreversible deterioration between the unfixed cores (core numbers 1 to 64) and the fixed cores (core numbers 65 to 130) was significantly lower than about 12% due to mechanical stresses in magnetic cores of the prior art. A vibration test carried out on the same cores with a frequency of 50 Hz, an amplitude of 1 mm and a duration of one minute likewise did not lead to any appreciable changes in the parameters such as the permeability number of the magnetic cores (core numbers from 131).

Also in conjunction with FIG. 2 described drop test, as in FIG. 5 shown, only a negligible change in the permeability of the magnetic cores.

LIST OF REFERENCE NUMBERS

1

magnetic core

2

strip position

3

gap

4

top

5

bottom

6

housing

7

protection trough

8th

lower shell

9

upper shell

10

Housing inner wall

11

adhesive

12

Surface of the pressure-sensitive adhesive

13

lower area

14

front sides

15

front sides

16

side surface

Claims (15)

1. A method of producing a magnetic core (1), which includes the following steps:

   - providing a magnetic core (1) wound from a soft magnetic strip with an upper side (4) and a lower side (5), wherein the upper side (4) and the lower side (5) are defined by side surfaces (16) of the soft magnetic strip;

   - providing a protective housing (6) for accommodating the magnetic core (1);

   - applying an adhesive to an inner wall (10) of the housing;

   - inserting the magnetic core (1) into the protective housing (6), whereby the lower side (5) of the magnetic core (1) is brought into contact with the adhesive and adheres to it, characterised in that

   - the adhesive is a pressure sensitive adhesive (11) and

   - the pressure sensitive adhesive (11) forms a film on its surface (12).
2. A method as claimed in claim 1, wherein an acrylate polymer is used as the pressure sensitive adhesive (11).
3. A method as claimed in claim 1 or 2, wherein the pressure sensitive adhesive (11) is applied in the form of an aqueous dispersion or organic solution to the inner wall (10) of the housing.
4. A method as claimed in one of claims 1 to 3, wherein the pressure sensitive adhesive (11) has a viscosity v where u < 20 Pa·s on insertion of the magnetic core (1) into the protective housing (6).
5. A method as claimed in one of claims 1 to 4, wherein the pressure sensitive adhesive (11) has a solid material content of more than 30 percent by weight on insertion of the magnetic core (1) into the protective housing (6).
6. A method as claimed in one of claims 1 to 5, characterised in that the pressure sensitive adhesive (11) has a minimum film formation temperature T_F where T_F < 0°C.
7. A method as claimed in one of claims 1 to 6, wherein the pressure sensitive adhesive 11 has an elongation to rupture ε_R where ε_R > 600%.
8. A method is claimed in one of claims 1 to 7, wherein the pressure sensitive adhesive (11) has a glass transition temperature Tg where Tg < -30°C.
9. A method as claimed in one of claims 1 to 7, wherein the pressure sensitive adhesive (11) has a melting temperature T_s where T_s > 180°C.
10. A method as claimed in one of claims 1 to 9, wherein the pressure sensitive adhesive (11) penetrates between strip layers (2) of the magnetic core (1) to a penetration depth t of t < 2mm, of t < 0.5mm or of t < 0.01mm.
11. A method as claimed in one of claims 1 to 10, wherein the pressure sensitive adhesive (11) is subjected to warm air drying or infrared drying after application to the inner wall (10) of the housing.
12. A method as claimed in one of claims 1 to 11, wherein the pressure sensitive adhesive (11) has not yet set beneath the film on its surface (12) on insertion of the magnetic core (1) into the protective housing (6).
13. A method as claimed in one of claims 1 to 12, wherein the magnetic core (1) is subjected to a heat treatment before being inserted into the protective housing (6), wherein the heat treatment is conducted in a preferably field-free manner in the absence of a magnetic field.
14. A method as claimed in claim 13, wherein the heat treatment is performed at a temperature T where 505°C ≤ T ≤ 600 °C.
15. A method as claimed in claim 14, wherein the heat treatment is performed wholly or intermittently in a magnetic field.

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