Method and device for producing soft magnetic strip material for strip ring cores

Abstract

A method producing soft magnetic strip material for roll tape-wound cores with the following steps: preparing a band-shaped material, applying a heat-treatment temperature to the band-shaped material, and applying a tensile force to the temperature-applied band-shaped material in one longitudinal direction of the band-shaped material in order to produce a tensile stress in the band-shaped material, to produce the soft magnetic strip material from the band-shaped material, the method, moreover, comprising determining at least one magnetic measurement value of the soft magnetic strip material that has been produced and controlling the tensile force for setting the tensile stress in a reaction to the determined magnetic measurement value. Furthermore, a device for carrying out the method and a roll tape-wound core produced by means of the method are made available.

Claims

1. A method for producing soft magnetic strip material for roll tape-wound cores comprising: preparing a band-shaped material; heat-treating the band-shaped material at a heat-treatment temperature, wherein the heat-treatment temperature is below a crystallization temperature of the band-shaped material for maintaining an amorphous state of the band-shaped material; applying a tensile force during the heat-treating step to the heat-treated band-shaped material in the longitudinal direction of the band-shaped material in order to produce a tensile stress in the band-shaped material, thereby producing a soft magnetic strip material from the band-shaped material; determining during the step of applying the tensile force, measurement values of the soft magnetic strip material that have been produced, wherein said measurement values include a magnetic saturation flux, an anisotropy field intensity, and a magnetic tape cross-sectional area; and controlling and setting the tensile force during the step of applying the tensile force to the heat-treated band-shaped material and in direct response to the measurement values determined during the step of applying the tensile force, to thereby control the permeability of the soft magnetic strip.

2. The method according to claim 1, wherein the controlling the tensile force comprises varying the tensile force such that the tensile stress in the longitudinal direction of the band-shaped material is kept essentially constant at least in segments along the longitudinal direction, or wherein controlling the tensile force comprises an automatic setting of the tensile stress by a predefined tensile stress setpoint, or both.

3. The method according to claim 1, further comprising applying a magnetic field to the heat-treated band-shaped material.

4. The method according to claim 1, further comprising the winding-on of at least one defined section of the produced soft magnetic strip material for producing at least one annular tape-wound core, following the determining the at least one magnetic measurement value.

5. The method according to claim 4, wherein the winding-on is controlled in response to the at least one magnetic measurement value.

6. The method according to claim 4, wherein the winding-on comprises winding on a pre-determined number of tape layers of the soft magnetic strip material produced for making at least one annular tape-wound core, and pre-determining the number of tape layers in response to the at least one magnetic measurement value.

7. The method according to claim 6, wherein the number of tape layers is varied such that at least one of a cross-sectional area A.sub.Fe1 or a permeability of a first annular tape-wound core and at least one of a cross-sectional area A.sub.Fe2 or a permeability of a second annular tape-wound core are approximately the same.

8. The method according to claim 1, wherein the band-shaped material comprises rapidly solidified magnetic material with at least one component selected from the group consisting of amorphous Co alloys, CoFe alloys, CoNi alloys, Fe alloys, and FeNi alloys, wherein for Co, CoFe and CoNi alloys.

9. The method according to claim 1, comprising the further step of measuring at least one additional magnetic measurement value selected from the group consisting of the permeability, the coercive field intensity, and the remanence ratio of the produced soft magnetic strip material.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) The embodiments of the invention are explained in more detail below using the embodiments shown in the figures of the drawings. Here:

(2) FIG. 1 shows in a schematic the progression of the method according to the invention in accordance with a first embodiment,

(3) FIG. 2 shows in a schematic an exemplary embodiment of a device according to an embodiment of the invention,

(4) FIGS. 3A and 3B show the basics of the tensile stress-induced anisotropy, definition of the mechanical and magnetic terms and in two diagrams the relationship between a tensile stress delivered into a band-shaped material and a resulting anisotropy or permeability,

(5) FIG. 4 shows in a diagram by way of an extract an exemplary thickness characteristic of the band-shaped material in detail,

(6) FIG. 5 shows in a diagram the characteristic shown in FIG. 4 with delineations of regions,

(7) FIG. 6 shows in a diagram the comparison of a hysteresis measured on the unwound soft magnetic strip material to a hysteresis determined on the wound core,

(8) FIG. 7 shows in a diagram the comparison of the respectively attainable permeabilities for a tape according to the state of the art and for a tape that has been produced according to an embodiment of the invention, and

(9) FIG. 8 shows in a diagram exemplary sample dispersions of annular tape-wound cores that have been produced according to an embodiment of the invention.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

(10) FIG. 1 schematically shows an exemplary progression of the method according to the invention for producing soft magnetic strip material for annular tape-wound cores according to a first embodiment. The method comprises making available a band-shaped material, the heat treatment of the band-shaped material at a heat-treatment temperature and the application of a tensile force to the heat-treated band-shaped material in one longitudinal direction of the band-shaped material in order to produce a tensile stress in the band-shaped material. These steps are used to produce the soft magnetic strip material from the band-shaped material. Moreover, the method comprises a determination of at least one magnetic measurement value of the produced soft magnetic strip material and a control of the tensile force for adjusting the tensile stress in reaction to the determined magnetic measurement value (arrow A).

(11) Optionally, the method comprises one step of the winding-on of at least one defined section of the produced soft magnetic strip material for producing at least one annular tape-wound core following the step of determining the at least one magnetic measurement value. For example, the step of winding-on is controlled or adjusted in reaction to the at least one magnetic measurement value (arrow B).

(12) FIG. 2 shows a schematic of a device 20 according to the invention for producing soft magnetic strip material according to one embodiment. The device 20 comprises an entry-side material feed 21 for making available band-shaped material, a heat-treatment device 22 for the heat treatment of the band-shaped material at a heat-treatment temperature, and a clamping device 24 for the application of a tensile force to the band-shaped material for making available a tensile stress in one longitudinal axis of the tape of the band-shaped material at least in the area of the heat-treatment device 22. The clamping device 24 is made adjustable for a variation of the tensile force in the band-shaped material in order to set the desired tensile stress to produce the soft magnetic strip material.

(13) The device 20, moreover, comprises a measurement arrangement 25 for determining at least one magnetic measurement value of the produced soft magnetic strip material and a control unit 26 for controlling the clamping device 24, the control unit 26 being made and connected to the measurement arrangement 25 such that the control of the clamping device 24 comprises controlling the tensile force in reaction to the at least one determined magnetic measurement value. In the illustrated embodiment, the clamping device 24 comprises two S-shaped roller drives that are coupled to one another and a dancer roll control. The roller drives can in addition or alternatively also have different speeds, the roller drive that is first in the direction of movement being able to have a slightly lower drive speed than the following roller drive, as a result of which then an additional tensile force can be produced between the two roller drives. Alternatively, in this case, the first roller can also be braked instead of driven. The dancer roll control can also be used, besides for tensile force generation, to compensate for speed fluctuations. Alternatively or in addition, there can be an oscillation control.

(14) Optionally, the device 20 comprises a device 23 for producing at least one magnetic field for applying the at least one magnetic field to the heat-treated tape material and/or a winding unit 27 with several winding mandrels 28 for winding-on one defined segment of the produced soft magnetic strip material at a time for producing a number of annular tape-wound cores, the winding unit 27 being made and connected to the measurement arrangement 25 such that the winding-on takes place in reaction to the at least one determined measurement value. Likewise, the winding unit 27 optionally comprises an additional S-shaped roller drive 29 for feed of the strip material to the respective winding mandrel 28.

(15) FIGS. 3A and 3B show a relationship between a tensile stress delivered into a band-shaped material 30 by means of a tensile force F and a resulting anisotropy K.sub.u and permeability . A tensile stress prevailing locally in the band-shaped material 30 results from the prevailing tensile force F and a local magnetic cross-sectional area A.sub.Fe (material cross-section):

(16) $=\frac{F}{A_{\mathrm{Fe}}}$
so that an induced anisotropy K.sub.u in the transverse direction to the longitudinally-extended band-shaped material 30 according to the diagram shown in FIG. 3b rises as a function of the tensile stress . A permeability is set via the applied tensile stress and results in the known manner from the average slope of the hysteresis loop and from a magnetic flux density B.sub.s (saturation magnetization) or a magnetic field intensity H (anisotropy field intensity H.sub.a) as well as a magnetic field constant .sub.0 in conjunction with the anisotropy K.sub.u as follows:

(17) $=\frac{1}{2}\frac{B_S^2}{{}_0{K}_U}$

(18) If therefore, for example, there is a fluctuating thickness of the band-shaped material due to production, accordingly when a uniform width is assumed, the local cross-sectional area A.sub.FE and with it, at constant tensile force F, the prevailing tensile stress fluctuate. This in turn causes a corresponding change of the induced anisotropy K.sub.u that via the indicated relationships influences the permeability accordingly so that it also changes over the length of the soft magnetic strip material that has been produced with it from the band-shaped material.

(19) FIG. 3b, moreover, shows a characteristic of the permeability as a function of the tensile stress a for three heat-treatment temperatures.

(20) FIG. 4 shows, by way of an extract, an exemplary characteristic of the thickness of the band-shaped material 30 from FIG. 3, in which local effects in the band-shaped material become noticeable. For this purpose, an extract of the band-shaped material 30 between an axial longitudinal position of l.sub.1=440 m and l.sub.2=640 m is shown, only by way of example, with VITROPERM being used as the material. Within this interval l=200 m, sudden tape thickness changes are shown that are caused by a production process, for example a rapid solidification technology used for this purpose (with any suitable material). Here, for example, local variations of the tape thickness occur and can be ascribed to the production method. The latter move in the illustrated measurements at roughly 1 to 2 m, but conventionally can also be over 3 to 4 m, and thus can cause major sudden changes in a thickness characteristic of the band-shaped material that is used as the initial material for the described method.

(21) FIG. 5 again shows the characteristic of the thickness of the band-shaped material shown in FIG. 4. In the region I of a higher tape thickness (left-hand region), the relationships already presented above, assuming a constant width of the band-shaped material, yield a larger local cross-sectional area A.sub.FE1 of the band-shaped material than a second local cross-sectional area A.sub.FE2 in the adjacent right-hand region II with a smaller tape thickness. This results in that a local tensile stress .sub.1 in the case of a constant tensile force in the left-hand region I is accordingly lower than in the right-hand region II (.sub.2). Since at this point the induced anisotropy and with this also the permeability are a function of the local tensile stress in the band-shaped material, the characteristic of the local permeability will also be varying. To prevent this, according to the described method, it is proposed that the tensile force F not be kept constant, but rather that it be continuously adapted such that the influences and effects caused by the material and the production are compensated by continuous adjustment of the tensile force for setting a constant tensile stress in the band-shaped material.

(22) FIG. 6 shows a comparison of a hysteresis 60 that has been measured on the unwound soft magnetic strip material and a hysteresis 61 that has been determined on the wound core.

(23) In order to prepare from the unwound soft magnetic strip material according to the method in accordance with the invention a wound-on roll tape core that has a permeability as similar as possible or even identical to that of the strip material, the heat-treatment temperature and a passage speed should be adjusted depending on a chosen material or a chosen alloy such that a magnetostriction is near zero in a nanocrystalline state of the strip material.

(24) The product of the bending stresses due to the winding-on of the strip material and the magnetostriction value constitutes an additional anisotropy induced in the wound-on strip material and should therefore be kept as small as possible. Otherwise, the permeability of the core would differ more or less dramatically from that of the unwound strip material.

(25) Thus, it applies that the higher the anisotropy that has been induced when the unwound soft magnetic strip material is produced, the less sensitive the roll tape-wound core becomes against the additional anisotropies that are always uniformly small due to the winding stresses.

(26) As is apparent from the illustrated hysteresis characteristic, there is a permeability in the region of 1,000. This corresponds to a small- to medium-strength induced anisotropy. Except for small defects in one region of a discharge point into magnetic saturation, the two hysteresis characteristics for the unwound soft magnetic strip material 60 and the wound-on roll tape core 61 can be regarded as identical.

(27) For higher anisotropies, and therefore smaller permeabilities, the additional anisotropies due to the winding stresses are thus of subordinate importance.

(28) FIG. 7 shows a characteristic of an attainable permeability for a chosen length segment l=200 m of a first tape of band-shaped material (curve or measurement points A) that was produced with a production method according to the state of the art without tensile force control according to the invention, and a corresponding characteristic of a second tape of band-shaped material (curve B) that was produced with the production method according to an embodiment of the invention. The characteristic of the pertinent average tape thickness is shown as curve C. In order to enable direct comparability, the two tapes were produced from a common tape that had been divided lengthwise, for example by cutting out two adjacent cutting webs from a wide tape. Thus, the two webs have an almost identical tape thickness characteristic. As FIG. 7 furthermore shows, an attained permeability in particular in the region II deviates considerably from a target value Z (in this example at =1,000) when the control according to the invention is not used (curve A). If, conversely, the control according to the invention is used (curve B), the attained permeability in spite of the fluctuations of the tape thickness characteristic can be kept constant with a comparatively very small deviation of roughly +/0.72% over several hundred meters.

(29) FIG. 8 shows by way of example a number of measurement points 80 of roll tape-wound cores that are produced by means of the method according to an embodiment of the invention. As the band-shaped material, tape material of type VP800 with a width of 6.2 mm is used. By means of the described device and using the described method, a permeability with a permeability setpoint of =800 is stipulated, and by means of the control of the tensile force according to embodiments of the invention, a tensile stress is kept almost constant over several hundred meters of the band-shaped material. Each of the roll tape-wound cores that have been wound from it is produced with a predefined core cross-sectional area A.sub.KFe of 13 mm.sup.2. The tape length used per core is thus roughly 8 m. This value fluctuates, however, depending on the local tape thickness (or local cross-sectional area A.sub.Fe) in order to achieve the respectively given predefined core cross-sectional area A.sub.KFe.

(30) Accordingly, therefore, within the scope of the controlled winding-on process depending on the local tape thickness, more or less tape material is wound into a core until the predefined core cross-sectional area A.sub.KFe is reached. The number of correspondingly produced cores shown in FIG. 8 accordingly on average has a permeability of =800.7 with a deviation of 0.44%. A pertinent average core cross-sectional area A.sub.KFe is 13.01 mm.sup.2 and thus has a deviation of only 0.25% compared to the setpoint.

(31) Consequently, cores of soft magnetic strip material with an almost constant permeability characteristic can be produced, and thus a cross-sectional area of the core can be kept as small as possible. The last-mentioned aspect is substantiated in that specific adaptation of a geometry of the individual core based on high dispersion of the permeability in the longitudinal direction of the strip material is not necessary.

(32) For the production of the individual core therefore by means of the method according to embodiments of the invention, a smaller tape length is necessary so that in this way, material can be saved, as a result of which weight and costs of the respective core can, moreover, be reduced. Accordingly, scrap of faulty cores that are somewhat outside of a given specification, such as, for example, due to overly large dimensions or an overly high resulting weight, can be reduced.

(33) The tests underlying FIGS. 6, 7 and 8 were run with VITROPERM 800 as the initial material with a composition of Fe.sub.Rest.Cu.sub.1Nb.sub.3Si.sub.15.5B.sub.6.6. The band-shaped material had a tape width of 6.2 mm at a nominal tape thickness of 19 m. The heat treatment took place in a heat-treatment furnace with a length of 3 m at a heat-treatment temperature of 650 C. and a heat-treatment time in passage of 18 s. For the test results shown in FIGS. 6 and 7, the material was adjusted to a permeability of =1,000. For FIG. 8, a permeability of =800 was assumed, and a total of 63 cores were produced and tested.