EP0929883B1 - Display element for use in a magnetic anti-theft system - Google Patents

Abstract

The invention relates to a medium-hard magnetic alloy for use in magnetic anti-theft systems, containing between 8 and 25 weight % Ni, between 1.5 and 4.5 weight % Al and between 0.5 and 3 weight % Ti, the remainder being made up of Fe. The alloy differs from known, used alloys in that it has excellent magnetic properties and high corrosion resistance. The alloy provided for in the invention is also extremely well suited for cold working before tempering.

Description

1. Einem länglichen, aus einer amorphen ferromagnetischen Legierung bestehenden Alarmstreifen und zumindest

2. einem aus einer halbhartmagnetischen Legierung bestehenden Aktivierungsstreifen.

The invention relates to a display element for use in a magnetic anti-theft system consisting of:

1. An elongated alarm strip made of an amorphous ferromagnetic alloy and at least

2. an activation strip consisting of a semi-hard magnetic alloy.

Such magnetic anti-theft systems and indicators are well known and for example in the EP 0 121 649 B1 or described in detail in WO 90/03652. On the one hand there are magnetoelastic systems in which the activation strip for activating the alarm strip serves by magnetization, on the other hand there are harmonics Systems in which the activation strip according to its Magnetization serves to deactivate the alarm strip.

Alloys with semi-hard magnetic properties, that are used for the bias strips Co-Fe-V alloys known as VICALLOY, Co-Fe-Ni alloys, known as VACOZET, as well as Fe-Co-Cr alloys. These well-known semi-hard magnetic alloys contain high proportions of cobalt, some of them at least 45 wt .-% and are accordingly expensive.

Furthermore, these alloys are magnetically final annealed Condition brittle so that they do not have sufficient ductility, to meet the requirements for the display elements for Anti-theft systems adequately. An important requirement is that these activation strips insensitive to bending or deformation have to be.

Furthermore, there is now a move to incorporate the display elements in theft protection systems directly into the product to be secured (source tagging). This also results in the requirement that the semi-hard magnetic alloys can also be magnetized from a greater distance or with smaller fields. It has been shown that the coercive force H _c must be restricted to values of at most 24 A / cm.

On the other hand, there is also sufficient stability in the opposite field required, causing the lower limit of the coercive force is set. Here are only coercive forces from suitable at least 10 A / cm.

Furthermore, the remanence under bending or tensile load should be as possible be small. As a guideline, a change becomes smaller 20% specified.

The object of the present invention is therefore to begin with mentioned display elements with regard to their bias strips to develop further in that the above Requirements are met.

According to the invention this object is achieved in that the Pre-magnetization strips made from a semi-hard magnetic alloy consist of 8 to 25 wt .-% nickel, 1.5 to 4.5 % By weight aluminum, 0.5 to 3% by weight titanium and balance iron is.

The alloy can also contain 0 to 5% by weight of cobalt and / or 0 up to 3% by weight of molybdenum or chromium and / or at least one of the elements Zr, Hf, V, Nb, Ta, W, Mn, Si in individual Proportions of less than 0.5% by weight of the alloy and in one Total content of less than 1% by weight of the alloy and / or at least one of the elements C, N, S, P, B, H, O in individual proportions of less than 0.2% by weight of the alloy and in a total proportion of less than 1% by weight of the Alloy included.

The alloy is characterized by a coercive force H _c of 10 to 24 A / cm and a remanence B _r of at least 1.3 T (13,000 gaus).

The alloys of the invention are highly ductile and excellent cold workability before starting, so that cross-sectional reductions of more than 90% are also possible are. Magnetic strips can be made from such alloys are produced, in particular by cold rolling, which Have thicknesses of less than 0.05 mm. Also stand out the alloys of the invention by excellent magnetic Properties and characterized by corrosion resistance.

A particularly advantageous alloy is a semi-hard magnetic Iron alloy according to the present invention, the 13.0 to 17.0 wt% nickel, 1.8 to 2.8 % By weight of aluminum and 0.5 to 1.5% by weight of titanium. Reducing the aluminum content can in particular the magnetostriction can be set particularly favorably.

Typically, the bias strips are through Melt the alloy under vacuum and pour into one Cast block made. Then the ingot becomes one Hot rolled strip at temperatures above 800 ° C, then at annealed at a temperature above 800 ° C and then cooled down quickly. After cold working, expediently Cold rolling in accordance with a reduction in cross section 90% is followed by intermediate annealing at approx. 700 ° C. Cold forming then takes place, expediently Cold rolling, corresponding to a reduction in cross section of at least 60%, preferably 75% or higher, instead. As The last step is the cold rolled strip at temperatures tempered from approx. 400 ° C to 600 ° C. After that, the bias strips cut to length.

Figur 1

das Entmagnetisierungsverhalten von Fe-Ni-Al-Ti-Legierungen nach einer Wechselfeldentmagnetisierung bei 4 A/cm in Abhängigkeit von der Koerzitivkraft,

Figur 2

das Entmagnetisierungsverhalten von Fe-Ni-Al-Ti-Legierungen nach einer Wechselfeldentmagnetisierung bei 20 A/cm in Abhängigkeit von der Koerzitivkraft,

Figur 3

die Änderung der Remanenz unter Zugspannung im Vergleich zu einer Legierung nach dem Stand der Technik und

Figur 4

die relative Änderung des magnetischen Flusses in % % bei verschiedenen Koerzitivfeldstärken nach mechanischer Verformung im Vergleich zu einer Legierung nach dem Stand der Technik.

The invention is described in detail below with reference to the drawing. Show:

Figure 1

the demagnetization behavior of Fe-Ni-Al-Ti alloys after an alternating field demagnetization at 4 A / cm depending on the coercive force,

Figure 2

the demagnetization behavior of Fe-Ni-Al-Ti alloys after an alternating field demagnetization at 20 A / cm depending on the coercive force,

Figure 3

the change in the remanence under tension compared to an alloy according to the prior art and

Figure 4

the relative change in the magnetic flux in%% at different coercive field strengths after mechanical deformation in comparison to an alloy according to the prior art.

For the suitability of an alloy for an activation strip in an anti-theft system, especially for So-called "source tagging", the following requirements result:

The change in remanence under bending or tensile load should be as low as possible. As a guideline, a change becomes smaller 20% specified. As can be seen from Figure 3, values with the alloys of the present invention ≤ 10% reached.

From Figure 4 it follows that in addition to the alloy Coercivity and the bending radius change the Determine the river. The alloys according to the present invention achieve with corresponding coercive field strengths Bending radii ≥ 12 mm values <5% or with bending radii ≥ 4 mm Values <10% and thicknesses of approx. 50 µm.

The ratio of the saturation for a given low magnetization field strength of, for example, 40 A / cm to the saturation B _f for a magnetic field in the kOe range should be almost 1, which can be seen from FIG. 3.

The counter-field stability should be such that the remanence B _S still retains at least 80% of its original value after a counter-field demagnetization of a few A / cm.

Finally, after a demagnetization cycle with a given magnetic field, the remanence B _{r should} only keep 20% of the original value.

Specifically, this means that magnetization of the activation strip d. H. an activation / deactivation of the Display element, can also be done on site. Stand there but usually only very small fields are available. The Saturation achieved is said to differ only slightly from the value at high Magnetizing fields differ in order to have the same behavior guarantee the display elements.

The display elements must be such that they do not change their remanence B _r very much in the vicinity of the coils in the detection locks as a result of a field which is elevated there and possibly oriented in the opposite direction. As can be seen from FIG. 1, the alloys according to the invention have such a required counter field stability.

Finally, the display elements need to be relatively small Allow fields to demagnetize, i.e. with magnetoelastic Deactivate display elements or for harmonic display elements activate, leave. Figure 2 illustrates these relationships in the alloys according to the invention.

The simultaneous fulfillment of the last three requirements mentioned results in very strong restrictions for the accessible areas of the coercive forces H _c , since the three requirements are opposed.

The alloys of the present invention are typically by casting a melt from the alloy components in a crucible or oven under vacuum or under a protective gas atmosphere. The temperatures are at about 1600 ° C.

The casting is typically done in a round mold. The Cast ingots made from the present alloys then become typical through hot working, intermediate annealing, cold working and further intermediate annealing. The intermediate glow takes place for the purpose of homogenization, grain refinement, deformation or the development of desirable mechanical properties, especially high ductility.

An excellent structure is, for example, by the following Processing reached:

Heat treatment at preferably temperatures above 800 ° C, rapid cooling and starting. Preferred tempering temperatures are around 400 ° C to 600 ° C and the starting times are typical from one minute to 24 hours. With the invention Alloys are especially cold worked a reduction in cross section of at least 60% before Starting possible.

Through the step of tempering, the coercive force and the squareness of the magnetic B-H loop increases what essential for the requirements for bias strips is.

1. Gießen bei 1600°C

2. Warmwalzen des Gußblocks bei Temperatur oberhalb 800°C

3. Mehrstündiges Zwischenglühen bei größer 800°C mit Abschreckung in Wasser

4. Kaltwalzen entsprechend einer Querschnittsverringerung von ca. 90 %

5. Kaltverformen entsprechend einer Querschnittsverringerung von ca. 90 %

6. Zwischenglühen bei ca. 700°C

7. Mehrstündiges Zwischenglühen bei ca. 700°C

8. Kaltverformen entsprechend einer Querschnittsverringerung von ca. 70 %

9. Mehrstündiges Anlassen bei ca. 480°C

10. Schneiden und Ablängen der Aktivierungsstreifen.

The manufacturing process for particularly good bias strips comprises the following steps:

1. Pour at 1600 ° C

2. Hot rolling the ingot at a temperature above 800 ° C

3. Intermediate annealing at 800 ° C for several hours with quenching in water

4. Cold rolling corresponding to a cross-sectional reduction of approx. 90%

5. Cold forming corresponding to a reduction in cross section of approx. 90%

6. Intermediate annealing at approx. 700 ° C

7. Intermediate annealing at approx. 700 ° C for several hours

8. Cold forming corresponding to a reduction in cross section of approx. 70%

9. Tempering for several hours at approx. 480 ° C

10. Cutting and cutting the activation strips.

With these methods, activation strips were produced which had an excellent coercive force H _c and a very good remanence B _r . The magnetization properties and the counter field stability were excellent.

The production of Fe-Ni-Al-Ti activation strips of the in The type in question is now based on the following examples described in detail:

Example 1:

An alloy with 18.0% by weight of nickel, 3.8% by weight of aluminum, 1.0% by weight of titanium and the rest of iron were melted under vacuum. The resulting cast ingot was hot rolled at about 1000 ° C, annealed at 1100 ° C for one hour and quickly cooled in water. After a subsequent cold rolling with a cross-sectional reduction of 80%, the resulting strip was again annealed at 1100 ° C for one hour and quickly cooled in water. After a further cold working with a cross-section reduction of 50%, the strip was annealed at 650 ° C for four hours. In accordance with a reduction in cross-section of 90%, the strip was then cold rolled and tempered for three hours at 520 ° C. and cooled in air. A coercive force H _c equal to 23 A / cm and a remanence B _r equal to 1.48 T were measured.

Example 2:

An alloy with 15.0% by weight of nickel, 3.0% by weight of aluminum, 1.2% by weight of titanium and the rest of iron was processed as in Example 1, but with a final intermediate annealing at 700 ° C, one last cold deformation corresponding to a cross-sectional reduction of 70% and a final annealing at 500 ° C. A coercive force H _c equal to 21 A / cm and a remanence B _r equal to 1.45 T were measured.

Example 3:

An alloy with 15.0% by weight of nickel, 3.0% by weight of aluminum, 1.2% by weight of titanium and the rest of iron was produced as in Example 2. Deviating from this, the last intermediate annealing was carried out at 650 ° C, the last cold working corresponding to a cross-sectional reduction of 85% and the tempering treatment at 480 ° C. A coercive force H _c equal to 20 A / cm and a remanence B _r equal to 1.53 T were measured.

Example 4:

An alloy with 15.0% by weight of nickel, 3.0% by weight of aluminum, 1.2% by weight of titanium, 2.0% by weight of molybdenum and the rest of iron was produced as in Example 2. After an annealing treatment at 480 ° C, a coercive force H _c equal to 20 A / cm and a remanence B _r equal to 1.56 T were measured.

Example 5:

An alloy with 15.0% by weight of nickel, 2.0% by weight of aluminum, 0.8% by weight of titanium and the rest of iron was melted under vacuum. The resulting cast ingot was hot rolled at about 1000 ° C, annealed at 900 ° C for one hour and quickly cooled in water. After a subsequent cold rolling with a cross-section reduction of 90%, the resulting strip was annealed at 650 ° C for four hours. After a reduction in cross section of 95%, the strip was then cold rolled and tempered for three hours at 460 ° C. and air-cooled. A coercive force H _c equal to 14 A / cm and a remanence B _r equal to 1.46 T were measured.

Example 6:

An alloy with 15.0% by weight of nickel, 2.5% by weight of aluminum, 1.2% by weight of titanium and the rest of iron was produced as in Example 5, but with a cross-sectional reduction of 83% and an annealing treatment at 420 ° C. A coercive force H _c equal to 17 A / cm and a remanence B _r equal to 1.44 T were measured.

A satisfactory result was found in all of the exemplary embodiments Magnetization behavior and a useful counter field stability.

Claims (3)

1. Display element for use in a magnetic anti-theft system consisting of:

   1. an elongated alarm strip consisting of an amorphous ferromagnetic alloy and at least

   2. one activation strip consisting of a medium-hard magnetic alloy,

   characterised in that

   a) the medium-hard magnetic alloy consists of
   8 to 25 % by weight Ni   0.5 to 3 % by weight Ti
   1.5 to 4.5 % by weight Al   with the remainder Fe
   and

   b) the alloy may furthermore contain

   0 to 5 % by weight Co and/or 0 to 3 % by weight Mo or Cr and/or

   at least one of the elements Zr, Hf, V, Nb, Ta, W, Mn and Si with an individual content of less than 0.5 % by weight of the alloys and a total content of less than 1 % by weight of the alloy and/or

   at least one of the elements C, N, S, P, B, H and 0 with an individual content of less than 0.2 % by weight of the alloy and a total content of less than 1 % by weight of the alloy, and

   c) the medium-hard magnetic alloy displays a coercive force H_c of 10 to 24 A/cm and remanence B_r of at least 1.3 T (13 000 gauss).
2. Display element according to claim 1, characterised in that the medium-hard magnetic alloy consists of
   13 to 17 % by weight Ni   0.5 to 1.5 % by weight Ti
   1.8 to 2.8 % by weight Al   with the remainder Fe.
3. Process for the production of an activation strip according to claim 1 or claim 2, characterised by the following steps:

   1. melting the alloy in vacuo or in an inert-gas atmosphere and then casting it to form an ingot;

   2. hot working the ingot to form a strip at temperatures in excess of approximately 800°C;

   3. interannealing the strip at a temperature in excess of approximately 800°C;

   4. rapid cooling;

   5. cold working corresponding to a cross-sectional reduction of approximately 90%;

   6. interannealing at approximately 700°C;

   7. cold working corresponding to a cross-sectional reduction of at least 85 %;

   8. tempering at a temperature of approximately 480°C, and

   9. cutting the activation strips to length.

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