EP0557689B1 - Method for manufacturing a magnetic pulse generator - Google Patents

Abstract

In order to produce a pulse generator, in the case of which a voltage pulse, which is independent of the magnetic field change, can be produced by sudden reversal of the magnetisation (Barkhausen effect) when a magnetic field is applied, an iron alloy 2 is used for one of the materials of the composite body, the additional alloying components of which alloy are selected such that a structural transformation takes place, with a volume change, at different temperatures in each case. In order to produce the braced state, heat treatment is then carried out, which includes heating above the upper transition temperature and cooling below the lower transition temperature. This results in considerably higher stresses between the materials of the composite body and hence a pulse behaviour which is considerably better than that known and which can be used for identifying constant or alternating magnetic fields. <IMAGE>

Description

The invention relates to a method for manufacturing one due to sudden magnetic reversal when applied Magnetic field acting pulse generator, which consists of an elongated Composite body made of at least two materials exists, the different thermal expansion behavior and mechanically by heat treatment against each other.

Such a pulse generator as a composite is in the DE-PS 31 52 008 described. This composite body contains a core and a shell, some of whose materials or all made of magnetic materials with different Coercivity can exist. Using two magnetic materials with different Coercivity is for the magnetically harder Material, for example, an alloy in the range of 45 up to 55% by weight cobalt, 30 to 50% by weight iron and 4 to 14 wt .-% (chrome + vanadium) used, while as soft magnetic material nickel is provided. Here is achieved by installing a material component with shape memory or by using materials with different coefficients of thermal expansion a certain stress state through heat treatment manufactured in the braced soft magnetic Component of the composite body when exposed sudden magnetic reversal of an external magnetic field results.

This known composite body lies as an elongated one magnetic switch core.

It is also already known from DE-OS 29 33 337, a composite body consisting of nickel or unalloyed Steel as a bracing component and a cobalt-vanadium-iron alloy as a magnetically active switching component to use. In the manufacture of a Heat treatment carried out. First the wire, from which the composite body preferably consists, so far heated that a material component among the resulting stresses plastically deformed, so that this Tensions are largely reduced. In the following The different coefficients of thermal expansion cause cooling in turn, that mechanical Stresses arise because of the lower temperature no longer lead to plastic deformation and in the magnetically active component - due to their magnetostriction - the sudden magnetic reversal result when a certain magnetic field is applied.

An elongated composite body with a low response field strength of 1.0 Oe (about 0.8 A / cm) is also in US-PS 46 60 025. For example here an elongated, 7.6 cm long wire made of amorphous Material used and it is stated that the Length of this wire can be between 2.5 and 10 cm. Here are those by quenching the material at the Production of the resulting amorphous state internal voltages cause of the magnetic bounce behavior.

DE-OS 34 11 079 is used to manufacture the composite body a combination of hard and soft magnetic Alloys used. From DE-PS 31 52 008 to this known that the hard magnetic component at the same time serve to brace the soft magnetic component can. This construction has the advantage of being a wire with a coat of high strength and that one can provide relatively short wires.

By magnetizing the hard magnetic jacket the magnetization characteristic of a composite body shifts, so that through the flow in the hard magnetic Envelope demagnetization zones on the edge of the strip largely avoided with the result that it is here when remagnetizing in one direction to one sudden magnetic reversal (Barkhausen jump) while this one is reversed in the other Direction is missing. You can use much shorter cores here use as the permanent magnet demagnetization zones largely at the ends of the wire (pulse generator) prevented.

The object of the present invention is a method specify for the manufacture of such a pulse generator, that without additional procedural steps between the Materials of the composite body much higher Voltages and thus significantly higher voltage pulses in the case of sudden magnetic reversal of the active component results. The invention also achieves the object premagnetization in addition to the improved pulse behavior of the magnetically active part of the composite body to be realized with sufficient coercive field strength, without an additional strip of permanent magnetic Material must be provided.

This object is achieved in that an iron alloy is used for one of the materials the additional alloy components are selected in this way are that at different temperatures one Structural transformation with volume change takes place that a elongated composite body made of the materials and that as a heat treatment this composite body first heated above the upper transition temperature and later is cooled below the lower transition temperature.

For example, as a structural transformation with volume change a change in the crystal structure by phase change e.g. from the alpha phase (body-centered cubic grid) in the gamma phase (face-centered cubic lattice) or in understand the epsilon phase (hexagonal grid) and vice versa.

Advantageous developments of the invention are in the Subclaims described.

Fig. 1

zeigt einen drahtförmigen Impulsgeber im Schnitt;

Fig. 2

stellt die Magnetisierungskurve bei kleiner Aussteuerung und nicht magnetisiertem hartmagnetischem Mantel dar;

Fig. 3

zeigt die Magnetisierungskennlinie bei voller Aussteuerung, bei der auch der Mantel des Impulsgebers nach Fig. 1 ummagnetisiert wird;

Fig. 4

zeigt die Magnetisierungskennlinie eines erheblich verkürzten Impulsgebers mit und ohne aufmagnetisiertem Mantel;

Fig. 5

zeigt den damit erzielbaren Spannungsimpuls bei Ummagnetisierung des weichmagnetischen Kerns;

Fig. 6

vergleicht den bei nicht aufmagnetisiertem Mantel erzielten Impuls mit dem bei einem amorphen Draht, der innere Verspannungen aufweist;

Fig. 7

zeigt eine Dilatometer Aufheiz- und Abkühlkurve eines matensitischen Stahles (Zusammensetzung 17Cr 4Ni 4Cu 0,4Nb Rest Eisen; handelsübliche Bezeichung ARMCO 17-4PH);

Fig. 8

zeigt eine Dilatometer Aufheiz- und Abkühlkurve eines extra festen "Maraging"-Stahles mit 250 kp/mm² Zugfestigkeit (18Ni-300 Stahl);

Fig. 9

zeigt eine Dilatometer Aufheiz- und Abkühlkurve eines austenitischen Mangan-Stahles, der außer Eisen im wesentlichen aus Mangan (16 %) besteht.

An embodiment is shown with reference to FIGS. 1 to 6 including the mode of operation of the pulse generator produced by the method according to the invention.

Fig. 1

shows a wire-shaped pulse generator in section;

Fig. 2

represents the magnetization curve with low modulation and non-magnetized hard magnetic jacket;

Fig. 3

shows the magnetization characteristic at full modulation, in which the jacket of the pulse generator according to Fig. 1 is remagnetized;

Fig. 4

shows the magnetization characteristic of a significantly shortened pulse generator with and without a magnetized jacket;

Fig. 5

shows the voltage pulse that can be achieved when magnetizing the soft magnetic core;

Fig. 6

compares the impulse achieved with a non-magnetized sheath with that with an amorphous wire with internal tension;

Fig. 7

shows a dilatometer heating and cooling curve of a matensitic steel (composition 17Cr 4Ni 4Cu 0.4Nb rest iron; commercial name ARMCO 17-4PH);

Fig. 8

shows a dilatometer heating and cooling curve of an extra strong "maraging" steel with 250 kp / mm ² tensile strength (18Ni-300 steel);

Fig. 9

shows a dilatometer heating and cooling curve of an austenitic manganese steel which, apart from iron, consists essentially of manganese (16%).

A wire is shown as a composite body in FIG Core made of a soft magnetic material 1 and its jacket consists of an iron alloy 2. The coercive force the iron alloy 2 is higher than that of soft magnetic material 1. In the exemplary embodiment the soft magnetic material 1 made of an alloy with 75.5 Ni 2.9 Mo 3.0 Ti 1.0 Nb rest Fe. In this alloy the Ti and the Nb serve as a hardening additive to make one slight plastic deformation of the soft magnetic material to exclude. This soft magnetic material has magnetostriction greater than zero, d. H. the material stretches in the direction of magnetization. For this reason the desired jumping behavior is achieved when the manufacture pulse generator of soft magnetic material 1 under Tension is there.

To this tension to a much greater extent than in known To achieve composite bodies, the jacket is made from a Iron alloy manufactured at different Temperatures undergo structural changes. In the embodiment became a martensitic hardening steel Composition 17Cr 4Ni 4Cu 0.4Nb balance iron chosen. Here it is a martensitic curing commercially available Steel as it is known, for example ARMCO 17-4PH is known. For this, refer to the prospectus "PRODUCT DATA" from Armco Steel Corporation, Baltimore, Maryland, No. S-6c. This iron alloy shows - how many other known steels too - structural transformation points between the so-called alpha and gamma structure. The temperature behavior is on page 11 of the mentioned brochure and shown in Fig. 7 of the drawing. You look this diagram that when heating up first a continuous Volume increase up to a temperature of approx 620 'C takes place; from then on the structural transformation begins, those with a volume reduction up to a temperature of about 660 ° C. This increases from here Volume - and thus the length of the jacket according to Fig. 1 - without further conversion or other Abnormality occurs.

After heating this iron alloy over the top The alloy can then also transition temperature be cooled again, which is a continuous Volume reduction according to the dashed line caused up to a temperature of below 200 ° C. Here now begins a back transformation of the structure, the at known steels is used to harden the To achieve steel. The resulting martensite (alpha phase) causes the volume to change with another Cooling has not been reduced further to the extent but here, in contrast, is still expanding how the dashed curve (Product Data, Armco 17-4 PH, Page 11) in the range from 300 to 100 ° C.

According to the invention, this behavior is used to to produce a pulse generator that is particularly high mechanical bracing of the component of a composite body reached that with a certain magnetic field experience sudden magnetic reversal (Barkhausen jump) should. For this purpose, the composite body 3 in the exemplary embodiment 1 to a temperature above 750 ° C. heated and then cooled below 100 ° C. This has the consequence that the soft magnetic material 1 and the iron alloy 2 is initially approximately uniform expand (depending on their coefficient of thermal expansion). If the upper transition temperature of the Iron alloy is reached, the soft magnetic tries Expand material further while the Iron alloy shrinks or expands less. This creates a pressure load in the soft magnetic material 1 and a tensile stress in the iron alloy 2. At high temperature after the consequence of this, however, is that the mechanically much softer material of the core plastically deformed or recrystallized while this at least not in the same for iron alloy 2 Dimensions is the case. It can therefore be assumed that at the heat treatment compensates for the stresses, so that at the beginning of the cooling no tensile or compressive stresses are present between the core and the jacket.

When cooling down, both the volume of the soft magnetic material 1 and that of Iron alloy 2 continuously up to one Temperature below 300 ° C. As with known composite bodies arise - depending on the different Coefficient of thermal expansion of the materials for core and Sheath - certain mechanical stresses that are known in prior Pulse generators for biasing the magnetic active material are used, but not here are essential, although they are supportive can.

If the range between 300 and 100 ° C during the cooling process is passed through, it causes the martensitic Conversion of the iron alloy 2 that this itself suddenly trying to expand strongly while the core continue to shrink from soft magnetic material 1 want. This has the consequence that a considerable tensile stress on the core and a corresponding compressive stress on the Coat works. The mechanical hardness of the core from one soft magnetic material 1 is now chosen so that at this relatively low temperature is not an essential one plastic deformation occurs more, so that high elastic Tensile stresses act in the core. Cause this in connection with the positive magnetostriction of the soft magnetic material 1 an essential faster, sudden magnetic reversal certain magnetic field values than this with less biased Composite bodies in known pulse generators is the case.

Instead of the steel with martensitic transformation chosen as an example in FIG. 1, all other iron alloys which undergo a corresponding transformation can also be used. For example, "RADEX-RUNDSCHAU" 1972, H. 3/4 from page 212 onwards describes "An extra-strong maraging steel with a tensile strength of 250 kp / mm ² ". The word "maraging" here means "martensitic aging hardening" and indicates that these structural changes were used in the known prior art to harden the material in order to obtain particularly strong steels for mechanical applications. The temperature profile of one of the steels described is shown on page 216 in Figure 9 of this literature reference and in Fig. 8 of the drawing, and shows that here too the structural changes lead to an increase in volume after cooling to between 200 and 130 ° C with sufficient heating , which can be used to clamp positive magnetostrictive soft magnetic materials in a pulse generator.

The volume change in the structural transformation of iron alloys for bracing a soft magnetic material It is not absolutely necessary to take advantage of such alloys to choose which when cooling and at relatively lower Temperature no further decrease in volume, but even an increase in volume in a certain temperature range exhibit. It is enough if the normal decrease in volume when cooling changes during the structural change. After cooling below the lower transition temperature is done, there is a subsequent heating below no change in structure to the upper transition temperature Consequence, so that those generated by the structural transformation mechanical stresses are retained.

In addition, you can compressive stresses in a soft magnetic Produce material if you use an iron alloy for bracing used, the volume of which cools below lower transition temperature reduced. For example, this is known for austenitic manganese steels in which not a gamma-alpha conversion, but a gamma-epsilon conversion takes place. This conversion behavior is for example in the Journal of Metallurgy Volume 56, 1965 Book 3, described from page 165. Picture 3 on page 167 of this Magazine and Fig. 9 of the drawing show the change in length in an iron alloy that is essentially except iron Contains 16.4% Mn. The composition is on page 166, left column specified. From picture 3 it can be seen that here in the case of heating (arrow pointing upwards to the right) again a continuous one Volume or length increase takes place at the conversion between about 220 and 280 ° C amplified.

If you make a composite body with this material a pulse generator would be used in heat treatment the composite material again via this transition temperature heat to such an extent that tension compensation by plastic deformation or by recrystallization he follows. Cooling would then cause the material during the reconversion between 100 and 20 ° C contracts much more than this magnetic material 1 is the case, so that here - because the Iron alloy shrinks more than the soft magnetic one Material - this soft magnetic material 1 under Compressive stresses. The iron alloys described here can be used if you have one soft magnetic Wants to use material with negative magnetostriction, a pulse generator with sudden magnetic reversal given a given magnetic field.

It is advantageous if the lower transition temperature is below about 600 ° C, since then it is rather guaranteed is that the stresses brought in by Relaxation processes or plastic deformation reduced will.

It is also possible to use iron alloys at which the lower transition temperature is below the Room temperature. To one with such a material To produce composite bodies with good tension, must at least briefly below this transition temperature be cooled. If the material turns up again Room temperature warmed, but the upper transition temperature not reached, the tension is maintained, since it is similar to the material of the braced soft magnetic material with temperature changes behaves.

Such alloys are in the magazine "METALLURGICAL REVIEWS "126 from page 115. The diagram in Fig. 4 on page 118 shows that the lower transition temperature in the case of an iron alloy with 29.7% Ni and 6% Al after aging annealing at 700 ° C depending on the time of this annealing first below the room temperature is. From the above illustration however, you can see that with a sufficiently long treatment period for example at 700 ° C the lower transition temperature is also above room temperature.

In the example mentioned above with high tension The soft magnetic material 1 is then obtained very good, very rectangular magnetization curve, as Fig. 2 shows. Here's on the ordinate like Induction is common and field strength on the abscissa shown in the range of ± 0.8 A / cm. In this level remains the magnetization of the iron alloy 2 essentially unchanged; and it will be the Magnetic leap in soft magnetic material 1 triggered at approximately ± 0.2 A / cm.

A corresponding magnetization curve is shown in FIG. 3 shown. Here was the field strength control changed between ± 80 A / cm. A field strength that is sufficient around the iron alloy used here as a jacket also completely re-magnetize. You can see here the induction jump at approximately the field strength 0, which by the sudden re-magnetization of the pre-stressed soft magnetic Material 1 takes place and you can see that the for bracing the soft magnetic material 1 serving iron alloy about a coercive force of Has 39 A / cm, as shown by the dashed curve in Fig. 3 shows the hysteresis loop of the under compressive stresses standing iron alloy. This dashed curve was obtained by parallel displacement of the measured curve of the composite body determined.

A comparison with the product brochure "PRODUCT DATA ARMCO 17-4 PH "on page 12 shows that here in the example iron alloy normally used a coercive force of ± 20 Oe = ± 16 A / cm. This substantial increase in the coercive field strength of the iron alloy compared to the usual on the material measured value probably results from the briefly high heating of the material in connection with the compressive stresses that it is part of the composite body in response to the tensile stress of the soft magnetic Experiences material. This shows another essential Advantage of using iron alloys in Combined with a heat treatment that changes the structure with volume change to brace the exploits soft magnetic material, because now not for Generate sufficient bias of the Composite body provided an additional permanent magnet must become.

This additional bias is then advantageous and required if you have short wires as a pulse generator wants to use. With relatively short wires namely the own demagnetizing field strong noticeable as this is in detail in DE-OS 34 11 079 is described. 1 in the composite body hence the one when measuring the hysteresis loops Fig. 2 and 3 selected length from 90 mm to 20 mm and again measured the hysteresis loop. This is in Fig. 4 shown. You can see on the dashed curve (Measurement with demagnetized iron alloy jacket 2) that the edge effects shown in Fig. 2 shown rectangular curve is sheared somewhat. It therefore does not find a sudden magnetic reversal of the core more instead.

However, if the iron alloy is magnetized, it is obtained the solid curve in Fig. 4, on the one hand by the influence of the magnetic field of the iron alloy 2 horizontally shifted and which on the other hand shows that when passing in one direction, again a sudden one Magnetic reversal of the entire soft magnetic Materials 1 takes place because when passing through the Hysteresis loops in this direction the wire ends of the soft magnetic material their direction of magnetization under the influence of the magnetic field of the iron alloy 2 until the outer Magnetic field the sudden reversal of magnetism soft magnetic material 1 enforces.

In Fig. 5 is now the voltage on the ordinate and the Time in microseconds plotted on the abscissa. Here was a composite wire with a length of 20 mm from a winding surrounded with 1000 turns. The magnetic reversal took place through an alternating current at 50 Hz in a separate Excitation coil, which was set so that the field strength was 5 A / cm along the composite wire. One can see that a voltage pulse of approximately 0.95 V can be achieved here, which, however, because of the asymmetry of the hysteresis loop with magnetized iron alloy only in every second half-wave occurs.

6 now shows the voltage pulse of the composite body 1 with a diameter of 0.2 mm and one Length of 90 mm in a coil of 1500 turns and also 90 mm in length after heating the composite body for 6 seconds to 1100 ° C and then cooling. In this state, the composite body can be smaller Level control operated, for example, 0.8 A / cm because the core has a low coercive force of about 0.1 A / cm. The impulse achieved here magnetized iron alloy 2 is shown in Fig. 6 with the amorphous wire compared to US-PS 46 60 025. The Curve 4 gives the voltage pulse of the amorphous wire and the curve 5 again the voltage pulse, which is in the pulse generator produced according to the invention results.

Although in the exemplary embodiment the iron alloy as Jacket and the soft magnetic material as the core of one Wire is used, you can - as with the acquaintance - also use other materials by plating etc. Flat, elongated composite bodies are particularly obtained advantageous by rolling the finished wire before Heat treatment. To use the iron alloy as a jacket offers the advantage of having a solid surface receives. However, it is also possible in principle Iron alloy as the core of a wire or as a middle layer to use a flat composite body.

In the event that you have an even higher coercive force the iron alloy or another improvement in strength wishes, the finished composite wire can after the heat treatment according to the invention for at least 10 minutes at a temperature of 360 anneal to 750 ° C. With the resulting improvement in strength the iron alloy is then also obtained a further increasing coercive field strength. Except the strength-enhancing additives in the soft magnetic Material 1 of the embodiment included can be used to increase strength and / or to improve corrosion resistance Elements Nb, Ti, Al, Cu, Be, Mo, V, Zr, Si, Cr, Mn advantageously add to the iron alloy without whose properties-reversible structural transformations different temperatures with volume change significantly to be influenced.

Because the composite body is only heated for a short time the whole wire is not absolutely necessary or the whole band from which the composite body be produced, stationary heat treatment can be subjected to heating as well Continuous annealing or by passing electrical Make electricity.

Claims (10)

1. Process for producing a pulse generator which acts by means of sudden magnetic reversal under an applied magnetic field and consists of an elongated composite body made of at least two materials (1, 2) which have different coefficients of thermal expansion and are mechanically tensioned against one another by means of a heat treatment, characterized in that, for one of the materials, use is made of an iron alloy (2) whose additional alloy constituents are selected in such a way that, at respective different temperatures, a structural transition involving a change in volume takes place, in that an elongate composite body (3) made of the materials (1, 2) is produced, and in that, for the heat treatment, this elongate composite body (3) is firstly heated to above the upper transition temperature and later cooled to below the lower transition temperature.
2. Process according to Claim 1, characterized in that an iron alloy (2) is used whose lower transition temperature is below 600°C.
3. Process according to Claim 1, characterized in that, as the iron alloy (2), use is made of a maraging steel which expands during the structural transition on cooling.
4. Process according to Claim 1, characterized in that the elongate composite body (3) is produced by drawing a wire core with the casing enclosing the core.
5. Process according to Claim 4, characterized in that, in order for the elongate composite body (3) to be produced by drawing, the wire core consists of a soft magnetic material (1) and the casing consists of the iron alloy (2).
6. Process according to Claim 4, characterized in that the heat treatment is carried out by temporarily heating the elongate composite body (3) to a temperature which is so far above the upper transition temperature of the iron alloy (2) that a reduction in internal stresses takes place by recrystallization of the soft magnetic material (1).
7. Process according to Claim 4, characterized in that the heat treatment of the wire is carried out in the form of continuous annealing.
8. Process according to Claim 4, characterized in that the heat treatment of the wire by temporary heating is carried out by passing an electric current through.
9. Process according to Claim 4, characterized in that, in order to increase the strength of the iron alloy (2) in combination with an increase in the coercive force, the prefabricated composite wire is annealed at a temperature of between 360 and 750°C for at least 10 minutes.
10. Process according to Claim 1, characterized in that use is made of an iron alloy (2) which, in order to increase the strength and/or resistance to corrosion, contains additives such as Nb, Ti, Al, Be, Cu, Mo, V, Zr, Si, Cr, Mn.

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