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SEMI-HARD MAGNETIC ALLOY FOR AN ACTIVATION STRIP, DISPLAY ELEMENT, AND METHOD FOR PRODUCING A SEMI-HARD MAGNETIC ALLOY

20210280346 · 2021-09-09

    Inventors

    Cpc classification

    International classification

    Abstract

    A semi-hard magnetic alloy for activation strips in magnetic anti-theft systems is provided. The alloy consists essentially of 5 to 15 wt % Ni, 0.5 to 8 wt % Mn, 0.2 to 4 wt % Cu, 0 to 2 wt % Ai, 0 to 2 wt % Ti, the remainder iron and up to 1 wt % impurities, where 0.5 wt %<(Cu+Al+Ti)<5 wt %.

    Claims

    1. A semi-hard magnetic alloy for an activation strip in magnetic anti-theft systems consisting essentially of 5 to 15 wt % Ni, 0.5 to 8 wt % Mn, 0.2 to 4 wt % Cu, 0 to 2 wt % Al, 0 to 2 wt % Ti, the rest iron and up to 1 wt % impurities, where 0.5 wt %<(Cu+Al+Ti)<5 wt %.

    2. A semi-hard magnetic alloy according to claim 1, wherein the copper content lies between 1.5 wt % and 2.75 wt %.

    3. A semi-hard magnetic alloy according to claim 1, wherein the nickel content lies between 7 wt % and 10 wt %.

    4. A semi-hard magnetic alloy according to claim 1, wherein the manganese content lies between 4 wt % and 6 wt %.

    5. A semi-hard magnetic alloy according to claim 1, where 12 wt %<(Ni+Mn)<15 wt %.

    6. A semi-hard magnetic alloy according to claim 1, wherein the sum of the manganese and nickel contents lies between 13.5 wt % and 14.5 wt %, the copper content lies between 2.75 wt % and 3.25 wt %, the aluminium content is less than 0.1 wt % and the titanium content is less than 0.1 wt %.

    7. A display element for use in a magnetic anti-theft system comprising: at least one elongated alarm strip comprising an amorphous ferromagnetic alloy, and at least one activation strip made of a semi-hard magnetic alloy according to claim 1.

    8. An object having a display element according to claim 7.

    9. An object according to claim 8, the object being a label.

    10. An object according to claim 9, wherein the label has a housing that sheathes the display element.

    11. An object according to claim 10, wherein a layer of adhesive is arranged on at least one side of the housing.

    12. A consumer object with a label having a display element according to claim 7.

    13. A consumer object according to claim 12, wherein the label comprises a housing that sheathes the display element.

    14. A consumer object according to claim 13, wherein a layer of adhesive, by means of which the label is fixed to the consumer object, is arranged on at least one side of the housing.

    15. A packaging for a consumer object having a display element according to claim 7.

    16. A method for producing a semi-hard magnetic alloy for activation strips in magnetic anti-theft systems, the method comprising the following: melting an alloy in a vacuum or a protective gas and its subsequent casting into an ingot, the alloy consisting essentially of 5 to 15 wt % Ni, 0.5 to 8 wt % Mn, 0.2 to 4 wt % Cu, 0 to 2 wt % Al, 0 to 2 wt % Ti, the rest iron and up to 1% w/impurities, where 0.5 wt %<(Cu+Al+Ti)<<5 wt %, hot-forming the ingot to form a strip at temperatures of between 800° C. and 1300° C., intermediate annealing the strip at a temperature above approx. 800° C., rapid cooling at a speed of at least 500K/min; cold-forming to achieve a reduction in cross-section of approx. 90%, intermediate annealing at a temperature of approx. 600° C. to 800° C., cold-forming to achieve a reduction in cross-section of at least 85%, and tempering at a temperature of 350° C. to 550° C.

    17. A method according to claim 15, further comprising: cutting up the strip.

    18. A method according to claim 15, further comprising: cutting an activation strip to length from the strip.

    19. A method for producing a display element for a magnetic anti-theft system comprising the following: providing at least one elongated alarm strip consisting of an amorphous ferromagnetic alloy, providing at least one elongated activation strip consisting of a semi-hard magnetic alloy according to claim 1, arranging of at least one alarm strip on at least one activation strip to produce a display element.

    20. A method according to claim 19, wherein the alarm strip and the activation strip of the display element are arranged in a housing.

    21. A method according to claim 19, wherein the alarm strip and the activation strip of the display element are arranged in the packaging of a consumer object.

    Description

    BRIEF DESCRIPTION OF THE DRAWINGS

    [0032] FIG. 1 shows a display element for a magnetic anti-theft system.

    [0033] FIG. 2 shows a graph of magnetic properties of alloys according to the invention and comparative examples.

    [0034] Table 1 shows the composition and magnetic properties of alloys according to the invention and comparative examples.

    [0035] Table 2 shows the composition and magnetic properties of alloys according to the invention.

    DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

    [0036] FIG. 1 shows a display element 1 consisting of an alarm strip 2 and an activation strip 3. A large-area side of the alarm strip 2 is arranged on a large-area side of the activation strip 3 so as to form a stack. The alarm strip 2 consists of an amorphous ferromagnetic alloy and the activation strip 3 consists of a semi-hard magnetic alloy according to one exemplary embodiment of the invention.

    [0037] In the object shown in FIG. 1, the display element 1 is arranged in a housing 4 made of plastic that has the shape of a label 5. In further exemplary embodiments (not illustrated) the housing 4 is an object, a consumer object or the packaging for a consumer object. In further exemplary embodiments (also not illustrated) the label 5 is arranged on a further object such as a consumer object, for example fixed on the object by means of an adhesive layer.

    [0038] This exemplary embodiment provides for a display element for use in a magnetoelastic anti-theft system. Consequently, the activation strip 3 is magnetised in order to activate the alarm strip 2. The alarm strip 2 oscillates when excited in a detector system (not shown) with a characteristic resonance frequency that is recognised by the detector system as a display element.

    [0039] The activation strip 3 consists of a semi-hard magnetic alloy with 5 to 15 wt % Ni, 0.5 to 8 wt % Mn, 0.2 to 4 wt % Cu, 0 to 2 wt % Al, 0 to 2 wt % Ti, the remainder iron and up to 1 wt % of impurities, where 0.5 wt %<(Cu+Al+Ti)<5 wt %, and can take the form of a thin strip with a thickness of e.g. 50 μm.

    [0040] The activation strip production process consists of melting the semi-hard magnetic alloy at, for example, 1600° C., hot rolling the blocks into slabs at temperatures of above 800° C. and from there into hot strips with a thickness of approx. 3 mm with subsequent heat treatment at temperatures of above 800° C. with quenching. After initial cold-forming comes intermediate annealing at a thickness of approx. 0.25 mm and approx. 700° C., followed by a second cold-forming to the final thickness and finally a tempering treatment at approx. 480° C.

    [0041] Table 1 indicates the compositions and measured magnetic properties of various samples. It also gives the martensite-austenite conversion temperature (Conv.) and the austenite-martensite reconversion temperature (Reconv.). Comparative examples are indicated by an *.

    TABLE-US-00001 TABLE 1 Ni Mn Al Ti Cu Fe Conv. Reconv. Br max. Hc Charge (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) (° C.) (° C.) (T) (A/cm) 81-0616* 13.90 1.68 0.74 Rest 695 412 1.56 13.5 81-0624* 8.95 4.01 1.45 1.68 Rest 710 330 1.54 18.6 81-0622* 8.95 4.01 1.44 0.72 Rest 700 337 1.50 13.0 81-0618* 9.11 3.99 0.41 1.75 Rest 668 320 1.39 17.4 81-0623* 8.98 4.02 0.47 0.70 Rest 657 334 1.37 16.0 81-0617* 6.99 6.02 0.86 1.25 Rest 674 294 1.47 17.3 81-0626 6.95 5.97 2.57 Rest 590 240 1.50 13.6

    TABLE-US-00002 TABLE 2 Ni Mn Al Ti Cu Fe Conv. Re-conv. B.sub.R max. H.sub.C Charge (wt %) (wt %) (wt %) (wt %) (wt %) (wt %) (° C.) (° C.) (T) (A/cm) 93-0270 7.03 5.99 2.08 Rest 605 243 1.48 15.7 93-0271 6.99 5.99 2.59 Rest 589 262 1.50 13.8 93-0272 7.03 5.99 3.14 Rest 595 245 1.52 16.0 93-0273 6.53 5.49 2.61 Rest 605 285 1.51 12.6 93-0274 6.53 6.49 2.62 Rest 600 239 1.48 14.5 93-0275 7.53 6.47 2.62 Rest 582 214 1.51 16.5 93-0276 7.44 5.43 2.55 Rest 616 240 1.51 13.2 93-0277 6.98 5.96 0.92 0.71 2.52 Rest 651 276 1.47 14.0 93-0278 6.98 5.87 1.73 0.73 2.48 Rest 675 285 1.46 16.2 93-0279 6.99 5.99 1.34 0.52 2.51 Rest 656 281 1.46 17.2 93-0280 7.00 6.01 1.35 0.94 2.49 Rest 661 282 1.44 17.1

    [0042] Comparative example 81-0616 represents an alloy that is commercially available under the trade name SENSORVAC. This alloy has 13.90 wt % Ni, 1.68 wt % Al, 0.74 wt % Ti and the rest iron and has a remanence B.sub.rmax of 1.56 T and a coercitivity H.sub.c of 13.5 A/cm.

    [0043] In comparative examples 81-0624, 81-0622, 81-0618, 81-0623 and 81-0617 nickel is partially replaced by manganese and the aluminium and titanium contents vary. In alloy 81-0627 according to the invention Al and Ti are completely replaced by copper, giving the alloy a composition of 6.95 wt % Ni, 5.97 wt % Mn, 2.57 wt % Cu and the rest iron. It has a remanence B.sub.rmax of 1.50 T and a coercitivity H.sub.c of 13.6 A/cm and consequently magnetic properties that make it suitable for use as an activation strip in a display element.

    [0044] FIG. 2 summarises the magnetic results of the examples. As can be seen, magnetic values comparable to the alloy Fe.sub.RestNi.sub.14Al.sub.2Ti.sub.1 are reached if, instead of 14 wt % Ni, the nickel in the alloy is partially replaced by manganese, e.g. if 9 wt % Ni and 4 wt % Mn are used (see examples 81/0616 to 81/0622 and 81/0624). Similarly, results similar to those reached with the addition of Al and Ti are reached with the addition of Cu (see examples 81/0626 to 81/0617).

    [0045] Table 2 shows further examples according to the invention. An alloy with the composition indicated in Table 2 is melted in a vacuum or a protective gas and then cast into an ingot. The ingot is hot-formed into a strip at temperatures of above approx. 800° C., then undergoes intermediate annealing at a temperature of above approx. 800° C. and rapid cooling, e.g. quenching. The strip is then cold-formed to achieve a reduction in cross-section of approx. 90%, undergoes intermediate annealing at approx. 700° C., is cold-formed to achieve a reduction in cross-section of at least 85% and then heat treated at a temperature of approx. 450° C.

    [0046] Examples 93-0270, 93-0271, 93-0272, 93-0273, 93-0274, 93-0275 and 93-0276 each feature Cu in addition to Ni, Mn and Fe and an absence of both Al and Ti. Examples 93-0277, 93-0278, 93-0279 and 93-0280 feature Cu, Al and Ti in addition to Ni, Mn and Fe. In all the examples given in Table 2, the nickel content is below 7.5 wt %.

    [0047] In addition, the martensite-austenite conversion temperature (Conv.) and the austenite-martensite reconversion temperature (Reconv.) are also indicated in Table 2.

    [0048] All the examples in Table 2 have a remanence B.sub.rmax of at least 1.44 T and a coercitivity H.sub.c of at least 12.6 A/cm and, as such, magnetic properties that are suitable for an activation strip in a display element.

    [0049] As a result, on one hand, the Ni content can be reduced, leading to a reduction in cost of the alloy. On the other, the addition of Cu to partially or completely replace Al and/or Ti makes a new family of alloys conceivable for this application.