Patent Grant
10538822
This US patent application claims priority to German patent application no. 10 2015 102 765.8, filed Feb. 26, 2015, the entire content of which is incorporated herein by reference.
1. Field
The invention relates to a conveyance system for tensioning in order to post-treat a rapidly-solidified metal strip, and to a post-treatment method. For this purpose, the conveyance system comprises a tension roller assembly and a tensioning assembly, between which the metal strip is conveyed in order to be continuously post-treated under a predetermined tensile stress.
2. Related Art
U.S. Pat. No. 7,905,966 B2 discloses a method for producing a strip of nanocrystalline material, wherein the metal strip is conveyed through a continuous furnace under a predetermined tensile stress. In order to obtain this tensile stress in an upright manner, the known conveyance system comprises a roller pair in a direction of conveyance or direction of passage, as a tensioning assembly, at the beginning of the post-treatment region, wherein the two rollers are arranged vertically one above the other, wherein the metal strip to be post-treated rests in the shape of an S on the roller pair.
An additional two rollers of a tension roller pair are arranged vertically one over the other after the post-processing region in the direction of passage, and form a tension roller assembly composed of a drive roller and a pressure roller having dimensions identical to those of the drive roller, for continuous conveyance of the metal strip. The post-treated metal strip is again guided in an S-shaped manner at this tension roller assembly. Therefore, this known conveyance system having a pair of rollers that are arranged vertically one above the other before and after the post-treatment region of the metal strip is called a known S-roller system.
Because the metal strip is conveyed through the system while under tensile stress, cracking may occur in the strip, which is undesirable.
The present invention therefore addresses the problem of providing a conveyance system with which the likelihood that a metal strip could be torn off is reduced.
This problem is solved according to the invention by means of a conveyance system for tensioning in order to post-treat a rapidly-solidified metal strip according to the subject matter of claim 1, as well as by means of a method for post-treating the rapidly-solidified metal strip according to the subject matter of claim 15. Advantageous developments of the invention are made apparent by the accompanying dependent claims and the use claims 13 and 14.
In one embodiment of the invention, a conveyance system for tensioning in order to post-treat a rapidly-solidified metal strip comprises a tensioning assembly and a tension roller assembly, between which the metal strip is conveyed in order to be continuously post-treated under a predetermined tensile stress. The tension roller assembly comprises a single drive roller and a freely-rotating pressing roller. The tensioning assembly may include a braking function. The metal strip is conveyed over an angle of wrap α on the drive roller, and, with respect to the drive roller, the pressing roller is arranged at a contact point of the metal strip that defines one end of an angle of wrap α.
Such a conveyance system for tensioning in order to post-treat a rapidly-solidified metal strip is advantageous in that the arrangement of a freely-rotating pressing roller makes it possible to very precisely adjust the tensile stress acting on the metal strip in the post-treatment region, because the end of the angle of wrap α of the metal strip can be very precisely adjusted via the freely-rotating pressing roller.
If, in one embodiment of the invention, the first contact point of the metal strip on the drive roller corresponds exactly to the end of the angle of wrap α, then the pressing roller is touched by the metal strip only in a line, transversely to the circumference of the drive roller and the pressing roller, at an angle of wrap α=0, such that the tensile force acting on the metal strip to be post-treated is equal to a holding force FA0 at an angle of wrap α=0. If, however, the position of the pressing roller is shifted relative to the first contact point of the metal strip on the drive roller, then an additional static holding force FR is added to the holding force FA0. Only when this additional static holding force FR is overcome does the frictional system transition into sliding friction, such that the required tensile force Fz can no longer be applied through the conveyance system and a “slipping through” of the metal strip is the result, such that it is no longer possible to maintain the adjusted tensile force Fz and thus the required tensile stress in the continuous metal strip.
Another embodiment of the invention provides that the angle of wrap α of the metal strip on the drive roller comprises between 0 and 180°. In the case where the angle of wrap α=180°, the metal strip wraps around half of the circumference of the drive roller, because the pressing roller, relative to the first contact point of the metal strip on the drive roller, is displaced by 180° relative to the first contact point. An S-shaped wrapping around of the metal strip of an S-roller conveyance system—as is illustrated with
Another embodiment of the invention provides limiting the angle of wrap α of the metal strip on the drive roller to up to 40°, because the correspondingly achievable maximum tensile forces of Fz≤120 N are adequate for magnetic applications, and the frequency of breaks in this range is particularly small. For example, for an Fe-based alloy (VP800, FeRest, Cu1, Nb3, Si15.6, B6.6, at %) at a width of 6 to 12 mm, it is possible to achieve a minimum permeability of μ=60 with a continuous heat treatment in the aforementioned angle-of-wrap range of α up to 40°.
In another embodiment of the invention, in contrast to the so-called S-roller system, the pressing roller is arranged so as to freely rotate at a contact point of the metal strip on the end of the angle of wrap α of the metal strip on the drive roller. The pressing roller may then have a significantly smaller radius than the drive roller, as well as a significantly smaller width than the drive roller, in contrast to the S-roller system known in the prior art, with which both the radius and width of the rollers of the respective roller pairs that press onto one another and are frictionally coupled via the metal strip arranged therebetween are equal.
Another embodiment of the invention provides that the drive roller, the pressing roller, and the metal strip have a width bRa, a width bR1, and a width bBand, respectively, and these widths are in the following relationship: bRa>bR1>bBand. Because the pressing roller is freely rotating and need not be wrapped around by the metal strip at an angle of 180°, as would be the case in the prior art, the pressing roller can have an arbitrarily small radius, independently of the minimum allowable radius of curvature of the metal strip; at the pressing roller, it is particularly essential to exactly define the end of the angle of wrap, and this is facilitated by a small radius. In addition, with the conveyance system according to the invention, it is not necessary for the pressing roller to have the same coefficient of friction as the drive roller in order to prevent premature “slipping through” of the strip.
Another embodiment of the invention provides that the pressing roller has a steel alloy in a peripheral region thereof, while the drive roller has a plastic material that is known as FRIBOFLEX in a peripheral region thereof, in order to ensure a suitable coefficient of friction. With an angle of wrap α>0, an additional frictional force FR that acts in the same direction as the holding force FA0 when the angle of wrap α=0 is established or induced in the metal strip. The now effectively acting holding force FA results from the sum:
FA=FA0+FR (1)
where FA is an effectively active force on the metal strip, FA0 is a force on the metal strip when the angle of wrap α=0, and
FR is a static holding force on the metal strip when the angle of wrap α is >0.
The static holding force FR can be calculated by calculating the wrapping friction or cable friction of a flexible traction mechanism. It is also necessary to know the coefficient of sliding friction (η) on the drive roller 13 from, for example, the plastic material FRIBOFLEX for the metal alloy material. For such an assembly, it is possible to experimentally determine a coefficient of sliding friction (η) of, for example, 0.32 for the material combination of the plastic roller and the metal strip. This brings the frictional force of FR to:
FR=Fz(1−1/(eηα[rad]) (2)
Fz then represents the tensile stress in the strip; with α, the angle of wrap in radians is:
α[rad]=α[°]·2π/360 (3)
The additional frictional force thus depends on the tensile stress in the strip and on the angle of wrap α. For α=0°, the frictional force FR disappears. For high α values, FR approaches the tensile force Fz in the strip. Thus, the tensile force Fz in the strip can be increased to an equilibrium state Fz=FA with FA=FA0+FR before there is a “slipping through.” It is thus possible to realize higher tensile forces in the strip, relative to when the angle of wrap α=0; in the case of a magnet, it is also possible to induce higher anisotropies or achieve a lower material permeability. As long as an angle of wrap α that is not too high is selected, there will also be no significant increase in the frequency of breaks in a preferable angle-of-wrap range of up to 40°.
It may furthermore be provided that the tensioning assembly and the tension roller assembly have an identical construction with pressing rollers, and, in place of the drive roller, the tensioning assembly has a brake roller of the same material and of the same size as the drive roller on the other side. Such a conveyance system is extremely cost-efficient, because the construction of the tensioning assembly before the post-treatment region and the tension roller assembly behind or after the post-treatment region is identical, and constructed out of identical materials and components.
In another preferred conveyance system, the pressing rollers have a contact pressure force in the range of 15 to 150 N with surface pressures of 7 to 10 MPa, which act on the drive roller and/or on the brake roller.
Another embodiment of the invention provides arranging an additional deflection roller upwards of the tension roller assembly in the material flow, with which deflection roller the first contact point on the drive roller can be varied, in order to precisely adjust different angles of wrap α of the metal strip on the drive roller. This deflection roller is wrapped around partially by the metal strip, and has a roller radius that is greater than the minimum allowable radius of curvature of the metal strip. In order to adjust the first contact point of the metal strip on the drive roller, the deflection roller 21 therefore has a radius that is significantly greater than that of the pressing roller, which defines the end of the angle of wrap α.
Because the drive roller must also have a greater radius than the minimum allowable radius of curvature of the metal strip, the radius of the deflection roller is equal to the radius of the drive roller in one embodiment of the invention. However, the material of the deflection roller need not correspond to the plastic material of the drive roller, but rather the freely-rotating property of the deflection roller can be supported with a stainless steel roller. Nevertheless, the deflection roller and drive roller do not result in the roller pair of an S-roller system known from the prior art, because both rollers (i.e., the deflection roller and the drive roller) are not pressed onto one another with a force Fs, because this force is applied only by the pressing roller according to the invention at the end of the angle of wrap α.
In another embodiment of the invention, the tensioning assembly has a plurality of deflection rollers, which transfer a gravitational force of a predetermined weight to the metal strip, as a constant tensile force. This embodiment is advantageous in that it is possible to forgo coordinating between the torque of the drive in the tensioning assembly and the torque of the drive in the tension roller assembly, or forgo forming a brake roller in the tensioning assembly. In another embodiment of the invention, the conveyance system made of the tensioning assembly and the tension roller assembly has a tensile stress acting on the metal strip that is up to 1500 MPa, which can be achieved with an angle of wrap α=180°. Such a conveyance system can cooperate with a continuous furnace for heat-treating a rapidly-solidified metal strip, in a manner that is advantageous for post-treating the metal strip, wherein the tensioning assembly is arranged in front of the continuous furnace in the direction of passage and the tension roller assembly is arranged after the continuous furnace.
Further provided is a system for post-treating a metal strip, the system comprising the conveyance system according to one of the preceding embodiments, and a continuous furnace for heat-treating the metal strip, wherein the tensioning assembly is arranged in front of the continuous furnace in the direction of passage (A) and the tension roller assembly is arranged after the continuous furnace.
It is also provided that the conveyance system is used for post-treating a rapidly-solidified metal strip of amorphous or nanocrystalline metal alloys, which are used in magnetic or mechanical applications and are known as VITROVAC, VITROPERM, or VITROBRAZE, or as variants thereof.
The metal strip may comprise an alloy, and a composition may be composed of Fe100-a-b-c-d-x-y-zCuaNbbMcTdSixByZz and up to 1 atom % of impurities, wherein: M is one or more of the elements Mo, Ta, or Zr; T is one or more of the elements V, Mn, Cr, Co, or Ni; and Z is one or more of the elements C, P, or Ge; and wherein 0 atom %≤a<1.5 atom %, 0 atom %≤b<2 atom %, 0 atom %≤(b+c)<2 atom %, 0 atom %≤d<5 atom %, 10 atom %<x<18 atom %, 5 atom %<y<11 atom %, and 0 atom %≤z<2 atom %.
It is also provided that the conveyance system according to the invention is used to achieve an unusually high anisotropy and an unusually low permeability in amorphous or nanocrystalline metal alloys, which are used in magnetic applications.
In one embodiment, the following elements are predetermined: a desired value of the permeability or of the anisotropy field; a maximum value of a remanence ratio Jr/Js, e.g., of less than 0.1 for applications as a flat hysteresis loop and greater than 0.5 for applications as a Z-shaped hysteresis loop; and a maximum value of a ratio of a coercivity field intensity to an anisotropy field intensity Hc/Ha, e.g., an Hc/Ha of less than 10%; as well as an allowable deviation range of each of these values. Magnetic properties of the strip are measured continuously at the exit from the continuous furnace, and when deviations from the allowable deviation ranges of the magnetic properties are found, the tensile stress on the strip is adjusted correspondingly in order to bring the measured values of the magnetic properties back within the allowable deviation ranges.
Another aspect of the invention relates to a method for post-treating a rapidly-solidified metal strip. The first method step relates to inserting the metal strip into a tensioning assembly that is arranged in space and time before a post-treatment region. The next step entails bridging the distance between the tensioning assembly and a tension roller assembly amid the insertion of the metal strip into the tension roller assembly, which is provided in space and in time after a post-treatment region. The metal strip is conveyed between the tensioning assembly and the tension roller assembly, wherein the metal strip is conveyed over an angle of wrap α on the drive roller. The pressing roller is arranged in a contact point of the metal strip with respect to the drive roller, the contact point defining one end of an angle of wrap α. This may be followed by post-treatment of the metal strip under a predetermined tensile stress between the tensioning assembly and the tension roller assembly, with continuous conveyance of the metal strip through the tensioning assembly and the tension roller assembly.
In a start-up phase, a tensile force of the post-treatment method that is greater than a braking action of the braking function of the tensioning assembly is imparted. The braking function of the tensioning assembly may also be entirely omitted in this start-up phase, and a braking action may then be exerted onto the metal strip through the tensioning assembly only in a post-treatment phase. To achieve this braking function of this tensioning assembly, different mechanical scenarios may be applied. One possibility is to provide a brake roller that corresponds in circumference and size as well as in material to the drive roller on the other side, i.e., the tension roller assembly. This brake roller may comprise a variety of braking mechanisms.
It is also possible to provide the brake roller on the side of the tensioning assembly and provide the drive roller on the side of the tension roller assembly with actuators having a torque that differs gradually, so as to exert a braking action on the metal strip. Once a constant conveyance speed is achieved, the braking force and tensile force acting on the metal strip are in equilibrium.
The metal strip is thereby exposed at a constant conveyance speed to a tensile force that induces a tensile stress, wherein the tensile stress results from the quotient of the tensile force and the cross-sectional area of the metal strip. As discussed above, the tensile force depends on one hand on a contact pressure force of a pressing roller at the end of an angle of wrap and an initial holding force resulting from the contact pressure force, and depends on the other hand on the magnitude of the angle of wrap α with which the metal strip follows on the drive roller of the tension roller assembly, under the definition of the end of the angle of wrap, through the pressing roller. There then emerges an additional static holding force that is dependent on this angle of wrap.
In another embodiment of the method, the usability of the conveyance system according to the invention is determined by detecting an optimum range for an angle of wrap α of the metal strip on the drive roller, by means of recording and assessment of a frequency of breaks of the metal strip in relation to the length of the metal strip, which is greater than or equal to 1 km. This determination step gives a clear indication of the productivity, the usability, and the improvement possibilities of the new conveyance method for producing post-treated rapidly-solidified metal alloy strips.
In addition, the method makes it possible to advantageously perform a heat treatment on the metal strip under a predetermined tensile stress in the post-treatment region. With this heat treatment under tensile stress, it is possible to form nanocrystals in a temperature of range of, for example, 670° C. to 690° C., so that a nanocrystalline state is in effect, which is desirable in order to achieve a minimum permeability in the range of μ=60.
In order to vary the passage speeds of the metal strip through the tempering or heat treatment region, it is also possible to use continuous furnaces of different lengths. The effectively active length of continuous furnaces can be between 0.2 and 3 m, such that the metal strip can be moved at throughput speeds of 2 to 30 m/min. The additional variation of the angle of wrap α also makes it possible to cover a broad tensile force range, in order to determine and reduce the optimum number of breaks on the strip lengths in the range of 1000 m.
With a further preferred form of implementation of the method, metal alloy strips of the alloy types of Ni—Fe-based alloys and nanocrystalline Co- or Fe-based alloys are post-treated in the aforementioned tempering temperatures between 670° and 690° C.
In one embodiment, the following elements are predetermined: a desired value of the permeability or of the anisotropy field; a maximum value of a remanence ratio Jr/Js, e.g., of less than 0.11 for applications as a flat hysteresis loop and greater than 0.5 for applications as a Z-shaped hysteresis loop; and a maximum value of a ratio of a coercivity field intensity to an anisotropy field intensity Hc/Ha, e.g. of less than 10%; as well as an allowable deviation range of each of these values. Magnetic properties of the metal strip are measured continuously at the exit from the continuous furnace, and when deviations from the allowable deviation ranges of the magnetic properties are found, the tensile stress on the strip is adjusted correspondingly in order to bring the measured values of the magnetic properties back within the allowable deviation ranges.
In another form of implementation of the method, metal alloy strips having the following composition are post-treated:
Fe100-a-b-c-d-x-y-zCuaNbbMcTdSixByZz
with up to 1 atom % of impurities, wherein: M is one or more of the elements Mo, Ta, or Zr; T is one or more of the elements V, Mn, Cr, Co, or Ni; and Z is one or more of the elements C, P, or Ge; and 0 atom %≤a<1.5 atom %, 0 atom %≤b<2 atom %, 0 atom %≤(b+c)<2 atom %, 0 atom %≤d<5 atom %, 10 atom %<x<18 atom %, 5 atom %<y<11 atom %, and 0 atom %≤z<2 atom %.
The invention shall now be described in greater detail with reference to embodiments depicted in the drawings.
Components of the conveyance systems in the following
The S-roller system for tensioning in order to post-treat a rapidly-solidified metal strip according to a comparative example shall be described in greater detail with reference to
While the roller pair 22 of the tensioning assembly 12 at the beginning of the post-treatment region 20 carry out a braking function with a braking force FB on the metal strip 6 to be post-treated, the roller pair 23 of the tension roller assembly 11 at the end of the post-treatment region generate a driving force FD, which is greater in a start-up phase or acceleration phase at the beginning of conveyance than during the post-treatment phase, during which the metal strip 6 passes through the roller pairs 22 and 23 at a constant speed in the direction of passage A with a tensile force Fz=FD=FB.
Thus, the known S-roller system provides a conveyance system 5 with which it is possible to continuously post-treat metal alloy strips 6 under tensile stresses in the post-treatment region 20 of up to 1500 MPa. The metal strip 6 is then transported at a constant speed VF in the direction A. In a region a between the two roller pairs 22 and 23, the metal strip 6 is subjected to an adjustable tensile stress along the strip axis. The tensile stress in the metal strip 6 then arises from the tensile force Fz and the cross-section ABand of the transported metal strip 6, in the entire post-treatment region 20 between the roller pairs 22 and 23. In the region b outside of the S-roller pairs 22 and 23, almost no tensile stress (or a significantly low tensile stress) predominates in the metal strip 6.
Of the two rollers 13 or 19 of each S-roller pair 22 and 23 is driven by a motor having a gear.
The two rollers 13 and 24 or 19 and 24′ of each S-roller pair 22 and 23 are mounted so as to be displaceable relative to one another in the vertical direction, and pressed together with an adjustable force FS, so as to apply the adjustable force FS to the metal strip 6 needing to be post-treated and transported that is between the rollers 13 and 24 or 19 and 24′. This force FS also acts on the axes of the rollers 24 or 24′. Due to this frictional connection of the two rollers 13 and 24 or 19 and 24′ via the force FS and the metal strip 6 present therebetween, the rollers 24 or 24′ of each S-roller pair 22 and 23 also appear to be driven with this known conveyance system 5 through an angle of wrap of 180° per roller. This angle of wrap of two times 180° is a typical feature of the known conveyance system 5.
The schematic diagram of
The retraction force can be introduced by various methods, such as, for example, one of the methods disclosed in WO 2013/156010 A1. This braking function can be generated by differences in the torque of the drives of the rollers 13 and 19, or by mechanical braking acting adjustably on one of the rollers of the roller pair 22 of the tensioning assembly 12 before the post-treatment region 20.
Due to the double deflection of the metal strip 6 by 180°, the use of S-roller systems leads to a problem in that the metal alloy strips 6, when used, have a higher frequency of breaks. Passage through the S-roller system leads to breaking in particular with the use of very thin, amorphous Fe-based alloys, which are to be transferred into the nanocrystalline state under tensile stress along the strip axis and at temperatures around 700° C., within a tempering or heat treatment region 30 that is confined from the post-treatment region. When rapidly-solidified metal alloy strips 6 are heat-treated under tensile stress, a thermal relaxation occurs in the nanocrystalline strip material in the tempering or heat-treatment region 30. This can lead to brittling of the material as a whole, or to inhomogeneities in the metal alloy material, with an increased brittleness of the metal strip 6.
The nanocrystalline state is thus more brittle in comparison to the amorphous state, such that the metal alloy strips cannot readily be further bent or cut without fragments occurring. On the other hand, the nanocrystalline strip material can be subjected to very high tensile stresses along the longitudinal strip axis.
The freely rotating smaller pressing roller then defines the end of an angle of wrap α of the metal strip 6 on the drive roller 13.
The smaller freely rotating pressing roller 14 is pressed with a force F1 onto the continuous metal strip 6, and thus onto the drive roller 13. The contact pressure force F1 acts constantly, and is not dependent on the position. The contact pressure force F1 is in the range of 15 to at most 150 N, and is adapted to the strip width of the continuous metal strip 6, so that a surface pressure of σ1 of 7 to 10 MPa occurs, where σ1=F1/AAbplattung with a flattening surface from AAbplattung=strip width [m] times a flattening width of 0.001 m, because the flattening of the drive roller 13 is by about one millimeter.
The drive roller 13 is produced at least in a peripheral region 18 thereof from a flexible plastic material such as FRIBOFLEX, with a high hardness (Shore 90A). The smaller pressing roller 14 is made from a comparatively inelastic material, such as stainless steel, at least in a peripheral region 17 thereof.
The width of the pressing roller 14 is selected so as to fulfill the condition bra>br1>bBand, where bra is the width of the drive roller 13, br1 is the width of the pressing roller 14, and bBand is the width of the metal strip 6.
The tensile force Fz is necessary, for example, for adjusting the magnetic properties. Through the contact pressure force F1, the material combination of the roller pairing of the drive roller 13 and the pressing roller 14, and the selection of the above-described width condition, the roller system according to the invention made of the rollers 13 and 14 builds a holding force FA0 that acts opposite to the tensile force Fz and protect the metallic strip from “slipping through” opposite to the direction of travel of the strip. The tensile force Fz can be increased in the strip through a system (not further specified here) up to an equilibrium state Fz=FA0. In the case where Fz>FA0, the metal strip 6 “slips” through the roller pair made of the drive roller 13 and pressing roller 14, and the tensile force Fz in the region a can no longer be kept constant.
The conveyance system 1 illustrated in
In the roller pairing according to the invention, made of the drive roller 13 and the pressing roller 14, the tensile force in the metal strip 6 is formed within a very short range of, for example, 1 mm, and corresponding an angle of wrap α≈0, i.e., without any process to bend or curve the metal strip 6. This results in a very low material strain, which is reflected in an improved frequency of breaks. Table 3 shows the results. However, the maximum holding force FA0 that can be achieved with α=0 and the above-mentioned measures is too low for some applications. With an increase in the angle of wrap α, the holding force FA can be increased, such that it is then possible to have higher strip tensions, as illustrated by the following drawings and depicted by table 3 in relation to the increase in the frequency of breaks.
In
The now effectively acting holding force FA results from the sum:
FA=FA0+FR (1)
The static holding force FR can be calculated with the aid of the equation (2), as described above. It is thus possible to realize higher tensile forces in the metal strip 6 and, in the magnetic case, to also induce a higher anisotropy, or achieve a lower material permeability. As long as an angle of wrap α that is not too high is selected, there will also be no significant increase in the frequency of breaks, as shown in table 3.
In the conveyance system 3 of the third embodiment of the invention, unlike the typical S-roller systems, the range of the very different tension ratios is kept extremely low during the process of bending the metal strip when wrapping around the drive roller 13. Table 1 shows, for example, that the base value of FA0 can be doubled with an angle of wrap α=90°. The effective holding force FA is then about 166 N, thus coming very close to the targeted maximum tensile force value of Fz=170 N.
However, the preferred embodiment range, as already listed above, is at α=0 to about 40°, because the consequently achievable maximum tensile forces Fz of ≤120 N are sufficient for magnetic applications. For example, as shown in table 2, a minimum permeability of μ=60 is achieved for an Fe-based alloy (VP800, FeRest, Cu1, Nb3, Si15.6, B6.6, at %) at a width of 6 to 12 mm and thickness of 19 μm, which is subjected to a continuous heat treatment in the aforementioned tension range. Table 2 below shows further details.
Nevertheless, this fourth embodiment also does not entail a typical S-roller system, because the drive roller 13 and the deflection roller 21 do not touch, and, unlike the typical S-roller systems, the range of the very different tension ratios here is kept extremely low during the process of bending when the metal strip 6 is wrapped around the drive roller 13. In addition, as shown in table 1, the angle of wrap of 180° results in a static holding force of 129 N, such that an effective holding force FA of FA0=80 N+129 N=209 N results, which is well above the desired tensile forces of Fz=120 N for magnetic applications.
It should also be noted that the mechanical post-treatment region 20 for the metal strip 6, in which a tensile stress is induced in the metal strip, as illustrated in
The following tables 1 to 3 show results in relation to a possible increase of the effectively acting holding force, the achievable permeability, and the number of breaks averaged per 1000 m for different angles of wrap α.
Table 1 illustrates the possible increase of the effectively acting holding force FA with the increase in the angle of wrap α. The base value FA0 results from the corresponding contact pressure force F1 exerted by the pressing roller 14 at the end of the angle of wrap on the material combination, namely, from the material combination of the roller pairings made of the drive roller 13 as well as the width condition bra>br1>bBand.
For FA0, a value of 80 N to 100 N is reached at maximum. 170 N is preferable as a maximally necessary tensile force in the strip. This corresponds, for a metal strip 7 that is 6 to 12 mm wide and 19 μm thick, to a tensile stress of 1500 MPa (where σ=F/A; where σ is tensile stress, F is force, and A is cross-sectional area). Fz=170 N was also set as the tensile force for calculating the data in table 1. For the material pairing of the metal strip and the FRIBOFLEX of the drive roller 13, a coefficient of sliding friction of η=0.32 was used.
Table 2 shows the achievable permeability (μ) after a continuous heat treatment under tensile stress (σ) for the alloy VP800 (FeRest, Cu1, Nb3, Si15.6, B6.6, at %) at a width bBand of the metal strip 6 of 6 to 12 mm and a thickness of the metal strip 6 of 19 μm, with a continuous oven or tempering oven temperature of 690° F. and an annealing or tempering time of 4 s. The required tensile force Fz is also shown in the table, and depends on the strip width bBand of the metal strip 6. A tensile stress of 750 MPa already constitutes a borderline material strain in the heat treatment temperatures used. With tensile stresses above there, the material of the metal strip 6 breaks off after previous elastic deformation and constriction.
Table 3 illustrates the probability of a strip break on production lengths of 1 km, on the basis of average numbers of break depending on the angle of wrap α between a first contact point 15 on the drive roller 13 at the beginning of the angle of wrap and a second contact point 16 at the end of the angle of wrap, which is defined by a pressing roller 14. As shown in table 3, the averaged number of breaks per 1000 m clearly falls below 1 as the angle of wrap α decreases, as long as the new conveyance system is used in the preferable angle-of-wrap range of α[°]=0 to α[°]=40°.
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