Patent Application
20070051152
The invention relates to a device for heating a metal strip and to apparatuses, equipped with a device of this type, for producing hot-rolled metal strip.
In the production of hot-rolled metal strips, there is frequently the problem that the temperature of the stock to be hot-rolled decreases so markedly, prior to the respective hot-rolling passes to be carried out, that the hot-rolling may no longer take place. This problem occurs, in particular, during the treatment of steel, which, below a specific minimum temperature, may not be hot-rolled at all, or may not be hot-rolled with the desired degree of success.
A particularly critical drop in temperature occurs during what is known as Steckel rolling, as during reversing the respective strip end is not jointly heated in the coilbox. But also in the case of direct strip casting with subsequent hot-rolling, the procedural flexibility (scope of application) is crucially dependent on the possibility of a purposeful adjustability of the strip temperature in order to produce a required product mix, including different process parameters (casting rate, degree of deformation, etc), resulting from the need for different steel qualities or strip thicknesses.
A further problem in the production of hot-rolled metal strips consists in the fact that a non-uniform temperature distribution occurs over the cross section of the stock to be hot-rolled. This inhomogeneity may lead, on the one hand, to unflat or askew strips, owing to locally varying flow properties, and, on the other hand, to a non-uniform structure formation. In principle, a non-ideal initial thickness profile (inconstancies) may also cause the above-mentioned unflat or askew strips during hot-rolling, despite the uniform temperature distribution over the strip cross section. This problem is particularly significant if the hot-rolling process is carried out on an initial strip having a thickness of <10 mm, and spreading of the stock is accordingly no longer possible, or is possible only to an insufficient degree. During hot-rolling of directly cast strip, in particular, where irregularities in the thermal camber of the casting roll and intermittent infiltrations in the lateral seals cannot be ruled out, a temperature level differing locally from the remaining temperature profile should therefore be adjustable “on-line”, in order to assist process stability (flat or straight strips).
The article “Bandgieβtechnik—eine Revolution in der Stahlindustrie?” by Claus Hendricks, Stahl und Eisen 115 (1995), No. 3, pages 75 to 81, contains an overview of the above-mentioned rolling processes and the equipment used in the carrying-out of said processes. In the conventional production of hot strip from slabs, the rolling stock accordingly passes prior to the hot-rolling process through a furnace, in which it is brought to the necessary hot-rolling starting temperature. In the production of hot strip from thin slabs, which are supplied to the hot-rolling in a continuous production sequence following the casting of the melt, the thin slabs, before entering the rolling train, pass through a compensation furnace in order to render the temperature distribution over the slab cross section as uniform as possible. Finally, it is known from the field of the in-line production of hot strip from cast strip to guide the cast strip through a conventionally configured induction furnace, before it is rolled to its final thickness in a hot-rolling stand.
The advantage of using an induction furnace for heating or warming the stock to be rolled consists in the fact that the rolling stock may be heated to a relatively precisely predeterminable temperature in a short application time. However, in practical implementation, it was found that even induction furnaces that had, in the past, been provided for this purpose did not yield results that satisfied the increasingly stringent requirements. In the case of the known induction furnaces, it was thus not easily possible to control the temperature distribution in the strip in such a way that the respectively desired temperature profile was reliably achieved. It was also found that the space available in the entry region of the hot-rolling stand was frequently insufficient for fitting a conventional furnace. Moreover, the overall size of conventional continuous furnaces means that there has to be a considerable distance between the outlet of the furnace and the entry region of the hot-rolling stand, so the strip leaving the furnace is again exposed to cooling on its path to the rolling stand.
What are known as “Steckel rolling stands”, such as are disclosed, for example, in DE 195 81 737 T1, are another application in which the overall size of the furnaces used for reheating a rolled product has proven problematic. In the case of rolling stands of this type, which operate in reversing mode, the strip, which is hot-rolled to a specific thickness, is reeled between each rolling step in a furnace, in which it is then maintained at a high temperature, which is optimal for carrying out the following rolling pass.
Starting from the above-described prior art, the object of the invention was to provide a device for heating a metal strip, which device allows the metal strip to be heated precisely and rapidly to a predetermined temperature, while taking up little space. Apparatuses of the above-described type that are intended for producing hot-rolled metal strip, with which apparatuses, despite the small overall space available, optimal heating, in terms of the hot-rolling process, of the rolling stock may be carried out, were also to be specified. This includes the compensation of problems during hot-rolling resulting from the thickness profile, which problems may result in unflat or askew strips.
With respect to the device for heating a metal strip, this object is achieved in that a device of this type is equipped, according to the invention, with an inductively operating heating devices, each of which comprises an inductor inducing an electromagnetic field, which inductor extends over the conveying path of the metal strip to be heated and the position of which is adjustable transversely to the conveying path depending on of the width of the metal strip.
The invention provides at least one heating device, which carries an inductor. This inductor extends, in each case, in the transverse direction over the transportation path, through which the rolling stock to be heated passes. During its transportation, the rolling stock therefore passes through the electromagnetic field generated by the inductor, which field causes a concentrated heating of the rolling stock. At the same time, in the case of a device according to the invention, the inductor of the heating device is adjustable transversely to the conveying direction of the metal strip to be heated. This transverse adjustability allows the position of the inductor to be optimally adapted, in each case, to the course and the width of the metal strip. The invention therefore provides a transverse field heating device that allows concentrated heating of a metal strip to a desired temperature within very short application times, while taking up as little space as is conceivable.
As a result of the small dimensions required for its assembly and its operation, the device according to the invention is particularly suitable for heating steel strips that are hot-rolled immediately after the reheating process. A device according to the invention may therefore be arranged in immediate proximity to a rolling stand, so the temperature losses between the heating process and the hot-rolling process are reduced to a minimum.
A particular advantage of the invention consists in the fact that the precise adjustability of the temperature characteristic allows, as a result of the adjustment of a specific temperature profile over the width of the strip to the rolled, equally specific deformation properties to be adjusted during the rolling process. The predetermined temperature characteristic thus allows unflat strips, directional stability and other geometrical defects of the strip to be minimised, without requiring expensive additional measures or devices.
A configuration of the invention that has in practice proven particularly advantageous is characterised in that it is equipped with at least two inductively operating heating devices arranged in pairs. The heating devices each carry an inductor. On the one hand, a paired arrangement of this type allows increased quantities of heat to be introduced into the rolling stock. At the same time, as a result of a corresponding adjustment of the inductors, the transverse field generated by said inductors may be configured in such a way that it always reliably encompasses the entire width of the strip to be heated.
This may be brought about particularly effectively in that one heating device is arranged laterally of one side of the conveying path and the other heating device is arranged laterally of the other side of the conveying path. This arrangement ensures, even in the case of particularly wide metal sheets, that the inductors cover the total width of the strip, so homogeneous warming of the metal strip may easily be ensured. Practical tests have thus revealed that as a result of the transverse adjustability according to the invention of the inductors, a temperature profile, which exhibits a uniform characteristic over the total width and thickness, including the strip edge regions, may be produced in the respectively heated metal strip.
In addition to the orientation of the inductors, a further possibility for adjusting the temperature profile produced in the heated strip consists in the fact that the inductors carry metal sheets, which influence the orientation and extent of the electromagnetic field generated by the inductors. As a result of a corresponding arrangement of the metal sheets, the transverse field may, for example, if required be configured in such a way that a desired overheating occurs in the region of the strip edges. The metal sheets may also be oriented in such a way that a higher temperature is generated in the region of the strip centre than in the edge regions. It is not necessary to change the metal sheets for each application; rather, the intensity with which the field, which is influenced by the metal sheets, acts on the stock to be heated may in turn be varied by means of a transverse adjustment of the inductors.
A particularly practical configuration of the invention is characterised in that it comprises at least four heating devices. These four heating devices may be arranged in pairs opposing one another in such a way that the heating devices are arranged in alternation laterally of one side and of the other side of the conveying path in the conveying direction of the metal strip. In the case of this arrangement of the heating devices, a particularly uniform effect of the transverse fields induced by the inductors on the stock to be heated is achieved. If, however, it should emerge that uniform heating of the metal strip may not be achieved, this problem may be solved, according to an alternative configuration, in that, in succession in the conveying direction of the metal strip, a first heating device is positioned laterally of one side, two heating devices are positioned laterally of the other side, and the fourth heating device is positioned laterally of the side of the transportation path with which the first heating device is associated.
Current markings on the surface of apparatus components that are exposed to the electromagnetic transverse field generated by the heating devices may be prevented in that the heating devices comprise a respective converter and in that the converters of all of the heating devices are in forced synchronisation. The surface of rolls on which the metal strip passes, for example, on its route through the device according to the invention may in this way be protected from damage. This protection may be additionally improved by means of suitable insulation measures, as a result of which an undesired current flow is prevented.
A further fundamental point for the effect of the device according to the invention is the configuration of the respectively used inductors or the heat conductors thereof. It has thus proven beneficial in practical tests if, in a plan view of the conveying path, the inductors exhibit an elongate, rectangular shape. In the case of this configuration of the inductors, the heat conductors thereof may be arranged in such a way that they cover a large surface extending parallel to the transportation path of the metal strip. Theoretical calculations and practical tests have also revealed, in this connection, that particularly good results may be achieved if the inductors of the heating devices used according to the invention comprise a respective heat conductor, which comprises a first longitudinal portion, which, starting from a connection portion, extends along the outside of one longitudinal side of the respective inductor, a second longitudinal portion, which extends along the outside of the other longitudinal side, a third longitudinal portion, which extends along the inside of the first longitudinal portion, a fourth longitudinal portion, which extends along the inside of the second longitudinal portion and is connected to a second connection portion, a first short portion, which externally connects the end of the first longitudinal portion that is remote from the connection portion to the end of the second longitudinal portion that opposes this end, a second short portion, which connects the other end of the second longitudinal portion to the end of the third longitudinal portion that opposes it, and a third short portion, which internally connects the other end of the third longitudinal portion to the end of the fourth longitudinal portion that opposes it. In order to complete the planar arrangement of the heat conductors, the connection portions and the second short portion should preferably be arranged parallel to one another. It has also proven beneficial if the first and the third short portions are curved in their configuration, so an optimal effect of the electromagnetic field generated is also achieved in the region of the free end of the heat conductor formed by the relevant portions.
As a result of its capacity to generate a precisely predeterminable temperature distribution in the strip and owing to its compactness, the device according to the invention is particularly suitable for heating cast strip, which, after the casting process, is hot-rolled to its final thickness in a hot-rolling stand. With respect to an apparatus for producing hot-rolled metal strip, the abovementioned object is therefore achieved in that it comprises a device for casting a molten metal to form a cast metal strip, a device for hot-rolling the cast metal strip and a device, which is arranged between the device for casting and the device for hot-rolling and is configured according to the invention, for reheating the cast strip prior to the hot-rolling process.
Alternatively, the device according to the invention may also be used in an apparatus for hot-rolling, carried out in a reversing manner, of a metal strip, which apparatus is equipped with a reversing rolling stand and with at least one device configured according to the invention, which device is arranged on one of the entry/exit sides of the reversing rolling stand and by which the stock to be hot-rolled is reheated prior to a rolling pass.
In addition to the heat deformation properties themselves, adherence to a defined temperature is at the same time also of fundamental importance to the configuration of the structure, and therefore the material properties of the hot strip as a finished product or input stock for further processing. It may therefore be beneficial, in the case of narrowly predetermined tolerance limits for the coil temperature, to undertake in the manner according to the invention an additional inductive heating process between the rolling stand and coiler.
The invention will be described below in greater detail with reference a drawing illustrating embodiments. In the drawing:
The apparatus 1 for producing hot-rolled steel strip 2 from cast strip 3 comprises, in succession in the conveying direction F of the cast strip 3, a casting device 4 for casting a molten metal 5 to form the cast strip 3, a rolling unit 6 for guiding the cast strip 3, a device 7 for reheating the cast strip 3, a rolling stand 8 for hot-rolling the cast strip 3 to form the steel strip 2, and a roller table 9, via which the steel strip 2 passes to a reeling device (not shown). The casting device 4 is constructed in the manner of a conventional double roller known from the prior art. The rolling unit 6 and the rolling stand 8 are also configured in a manner known per se.
The device 7 for heating the cast strip 3, which is conveyed to the rolling stand 8, is equipped with four heating devices 10, 11, 12, 13 of substantially identical construction. Each of the heating devices 10, 11, 12, 13 comprises an inductor 14, 15, 16, 17, which has a rectangular, elongate basic shape and extends, in its longitudinal orientation, transversely above the upper side of the conveying path 18 via which the strip 3 is conveyed. A corresponding inductor 14a, 15a, 16a, 17a extends, in each case, in an identical manner transversely to the lower side of the conveying path 18, so the strip 2 passes, in each case, through a coupling gap K formed between the inductors 14, 14a, 15, 15a, 16, 16a, 17, 17a.
The inductors 14 to 17a are each equipped with a heat conductor 19, the course and arrangement of which are selected in such a way that an electromagnetic transverse field, which is optimised with respect to its effect on the strip 3 to be heated passing under the inductors 14 to 17a, is generated. For this purpose, the heat conductors 19 each have a first longitudinal portion 19b, which, starting from a connection portion 19a, extends along the outside of one longitudinal side L1 of the respective inductor 14 to 17a, a second longitudinal portion 19c, which extends along the outside of the other longitudinal side L2 of the inductor 14 to 17a, a third longitudinal portion 19d, which extends along the inside of the first longitudinal portion 19b, and a fourth longitudinal portion 19f, which extends along the inside of the second longitudinal portion 19c and is connected to a second connection portion 19e. The end of the first longitudinal portion 19b that is remote from the connection portion 19a is connected to the end of the second longitudinal portion 19c that opposes this end by means of a first short portion 19g, which is externally arranged and outwardly curved, while the other end of the second longitudinal portion 19c is connected to the end of the third longitudinal portion 19d that opposes it by means of a second, straight short portion 19h. Finally, the other end of the third longitudinal portion 19d is internally connected to the end of the fourth longitudinal portion 19f that opposes it by means of a third short portion 19i, which is guided in a curved manner in a curvature extending parallel to the curvature of the first short portion 19g. The connection portions 19a, 19e and the second short portion 19h are arranged parallel to one another. The individual portions of the respective heat conductors 19 are jointly arranged in a plane extending parallel to the conveying path 18.
The coil end of the inductors 14 to 17a, which is arranged in the region of the housing of the respective heating device 10 to 13, comprises metal sheets (not shown), by means of which the field generated by the inductors 14 to 17a is controlled in such a way that optimal heating, in terms of the particular features of the respectively treated steel material, of the edges 3a, 3b of the cast strip 3 is achieved.
The inductors 14, 14a, 15, 15a, 16, 16a, 17, 17a of each heating device 10 to 13 are carried, in each case, by the piston of an actuating cylinder 20, which, as illustrated for the heating device 10 by means of broken lines, is arranged in the housing of the heating devices 10, 11, 12, 13. Depending on the control signal from a control device (not shown), the actuating cylinders 20 perform, in each case, independently of one another a linear actuating movement, directed transversely to the conveying path 18, by means of which movement the position of the inductor pairs 14, 14a, 15, 15a, 16, 16a and 17, 17a, respectively associated with said cylinders, of the heating devices 10 to 13 is adjusted above the conveying path 18.
The conveying path 18 is formed by rolls 21, which are electrically insulated with respect to their environment or are made of a non-conductive material, in order to prevent undesirable current flows resulting from the electromagnetic fields generated by the inductors 14 to 17a.
The inductors 14 to 17a are supplied with electricity in a manner known per se by means of medium voltage generators, transformers and medium frequency converters (not shown), which are accommodated, in each case, in the housings of the heating devices 10 to 13, which housings are oriented, with respect to the longitudinal orientation of said inductors, transversely to the conveying path 18. In order to prevent current markings from occurring on the rolls 21 of the conveying path 18, the converters are in forced synchronisation, so the occurrence of fields of travelling waves and excessively elevated field strengths is prevented.
In the case of the embodiment illustrated in
In the case of the alternative configuration, illustrated in
As a result of a corresponding transverse adjustment of the inductor pairs 14, 14a, 15, 15a, 16, 16a, 17, 17a, the position of the inductors 14 to 17a is adapted to the width B of the respective strip 3 to be heated. It is thus ensured that as the strip 3 passes through the device 7, the strip 3 is heated to the optimal temperature for the hot-rolling process that is subsequently carried out in the rolling stand 8, a temperature distribution that is as uniform as possible thus being achieved. If the strip edges 3a, 3b are to be overheated during this heating process, the inductors 14 to 17a are accordingly oriented in such a way that their coil ends protrude beyond the strip edge 3a or 3b respectively associated with said inductors. If, on the other hand, a lower temperature is purposefully to be achieved in the region of the strip edges 3a, 3b than in the region of the strip centre, the inductors 14 to 17a are oriented in such a way that their coil ends are set back with respect to the respective strip edge 3a or 3b.
The cast strip 3, which is produced in the casting device 4, issues in the vertical direction from the casting gap in the casting device 5 and is then diverted in a horizontal direction in an arc, is guided onto the conveying path 18 by the rolling unit and then passes through the device 7, in which it is reheated to the required hot-rolling starting temperature. The strip 3 enters the rolling stand 8, in which it is hot-rolled to the final thickness of the obtained steel strip 2, at this temperature.
As a result of the adjustability according to the invention of the inductors 14 to 17a transversely to the conveying path 18 of the strip 3, it is possible in this operation to reheat cast strips 3, the width of which may vary in a wide range. Moreover, as a result of the transverse adjustment of the inductors 14 to 17a, any desired temperature profiles may be produced in the strip 3. It is thus ensured that optimal results are achieved during the hot-rolling process carried out after the reheating process. All of the actuating processes of the device 8 may be automated. Devices according to the invention are therefore particularly suitable for carrying out an operation that proceeds automatically.
By combining an on-line measurement value logging of the strip thickness profile in the entry region of the device 7, the strip temperature transverse profile in the entry and exit regions of the device 7, the strip flatness in the exit region of the rolling stand 8, and the strip position in the entry region of the device 7, it is possible from the outset to prevent unflat or askew strips, and this is of fundamental importance specifically in the case of the direct strip casting method. The corresponding control variable alterations are undertaken in a process-dependent manner by means of a corresponding automation apparatus, by modifying and adapting the parameters within the strip delivery line steering driver, device, hot-rolling stand 8.
It was demonstrated on the basis of various operating tests that a temperature characteristic that results in an optimal form of the hot strip obtained after the hot-rolling process may be adjusted in the cast strip 3 before said strip enters the rolling stand 8, by adjusting the inductors 14 to 17a over the width of the strip 3.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10323796.8 | May 2003 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP04/05569 | 5/24/2004 | WO | 7/31/2006 |
