HEATING DEVICE FOR THE INDUCTIVE HEATING OF A FLAT STEEL STRIP IN A HOT ROLLING MILL

Abstract

A heating device and a method for the inductive heating of a flat steel strip in a hot rolling mill. The heating device is between two rolling trains of the hot rolling mill and the flat steel strip runs at a speed through the heating device in a transporting direction. The heating device includes: transverse-field modules arranged one after the other along the transporting direction of the flat steel strip; longitudinal-field modules arranged one after the other along the transporting direction of the flat steel strip and arranged before or after the transverse-field modules along the transporting direction; a first power supply supplying at least one transverse-field module with a first alternating voltage; and a second power supply supplying at least one longitudinal-field module with a second alternating voltage. The power supplies have a converter and an electrically connected capacitor bank with multiple capacitors connected in parallel.

Claims

1-16. (canceled)

17. A heating device for the inductive heating of a flat steel strip in a hot rolling mill, the heating device being arranged between two rolling trains of the hot rolling mill and the flat steel strip runs at a speed through the heating device in a transporting direction, the heating device comprising: a plurality of transverse-field modules arranged one after the other along the transporting direction of the flat steel strip; a plurality of longitudinal-field modules arranged one after the other along the transporting direction of the flat steel strip and are arranged before or after the transverse-field modules along the transporting direction; a first power supply adapted to supply at least one transverse-field module with a first alternating voltage; and a second power supply adapted to supply at least one longitudinal-field module with a second alternating voltage; wherein the power supplies have in each case a converter and an electrically connected capacitor bank with multiple capacitors connected in parallel.

18. The heating device as claimed in claim 17, wherein at least one of the first and the second power supply comprises a frequency input for determining a setpoint frequency and the frequency of the generated alternating voltage follows the setpoint frequency.

19. The heating device as claimed in claim 17, wherein at least one of the first and the second power supply comprises a current input for determining a setpoint current intensity and the current intensity follows the generated alternating voltage of the setpoint current intensity.

20. The heating device as claimed in claim 17, wherein at least one of the first and the second power supply comprises a voltage input for determining a setpoint voltage and the voltage amplitude (U) of the generated alternating voltage follows the setpoint voltage.

21. The heating device as claimed in claim 17, wherein at least one of the first and the second power supply comprises a power input for determining a setpoint power and the heating power of the generated alternating voltage follows the setpoint power.

22. The heating device as claimed in claim 17, further comprising a thrust actuator for changing the width position of at least one coil of a transverse-field module.

23. The heating device as claimed in claim 22, wherein the transverse-field module comprises a width input for determining a setpoint width position and the width position of a coil of the transverse-field module in the direction of the width follows the setpoint width position.

24. The heating device as claimed in claim 17, further comprising a lift actuator for changing the height position of at least one coil of a transverse-field module.

25. The heating device as claimed in claim 24, wherein a transverse-field module comprises a height input for determining a setpoint height position and the height position of a coil of a transverse-field module in the direction of the thickness follows the setpoint height position.

26. The heating device as claimed in claim 17, further comprising an open-loop or closed-loop control device, wherein the open-loop or closed-loop control device comprises at least one output from the group comprising: a frequency output for determining a setpoint frequency of the first alternating voltage; a current output for determining a setpoint current intensity of the first alternating voltage; a voltage output for determining a setpoint voltage of the first alternating voltage; a power output for determining a setpoint power of the first alternating voltage; and the open-loop or closed-loop control device additionally comprises at least one of: a width output for determining a setpoint width position in the direction of the width of a coil of a transverse-field module; and a height output for determining a setpoint height position (sH-Soll) in the direction of the thickness of a coil of a transverse-field module, wherein at least one output from the group comprising the setpoint current intensity, the setpoint frequency, the setpoint voltage, and the setpoint power, and additionally at least one of the setpoint width position and the setpoint height position, are set in dependence on at least one parameter of the flat steel strip from the group comprising the thickness, the width, the speed, the temperature before entering the heating device, and the temperature after leaving the heating device.

27. The heating device as claimed in claim 17, further comprising an open-loop or closed-loop control device, wherein the open-loop or closed-loop control device comprises at least one output from the group comprising: a frequency output adapted to determine a setpoint frequency of the second alternating voltage; a current output adapted to determine a setpoint current intensity of the second alternating voltage; a voltage output adapted to determine a setpoint voltage of the second alternating voltage; and a power output adapted to determine a setpoint power of the second alternating voltage; wherein at least one output from the group comprising the setpoint current intensity, the setpoint frequency, the setpoint voltage, and the setpoint power, is set in dependence on at least one parameter of the flat steel strip from the group comprising the thickness, the width, the speed, the temperature before entering the heating device, and the temperature after leaving the heating device.

28. A method for the inductive heating of a flat steel strip in a hot rolling mill by a heating device as claimed in claim 17, wherein the heating device is arranged between two rolling trains of the hot rolling mill and the flat steel strip runs at a speed through the heating device in a transporting direction, comprising the method steps of: heating the flat steel strip by a plurality of transverse-field modules, which are arranged one after the other along the transporting direction; and heating the flat steel strip by a plurality of longitudinal-field modules, which are arranged one after the other along the transporting direction and are arranged before or after the transverse-field modules along the transporting direction, wherein a power supply for supplying at least one transverse-field module or at least one longitudinal-field module has a converter, which is operated as a load-commutated converter; and wherein the frequency f of the generated alternating voltage is $f=\frac{1}{2\pi \sqrt{L_{\mathrm{Ges}}{C}_{\mathrm{Ges}}}},$ where L.sub.Ges indicates the total inductive load and C.sub.Ges indicates the total capacitive load in the circuit.

29. The method as claimed in claim 28, wherein the heating device is arranged between two rolling trains of the hot rolling mill and the flat steel strip runs at a speed through the heating device in a transporting direction, comprising the method steps of: heating the flat steel strip by a plurality of transverse-field modules, which are arranged one after the other along the transporting direction; and heating the flat steel strip by a plurality of longitudinal-field modules, which are arranged one after the other along the transporting direction and are arranged before or after the transverse-field modules along the transporting direction; wherein a power supply for supplying at least one transverse-field module or at least one longitudinal-field module has a converter, which is operated as an externally commutated converter; and wherein the frequency f of the generated alternating voltage is $f\ne \frac{1}{2\sqrt{L_{\mathrm{Ges}}{C}_{\mathrm{Ges}}}},$ where L.sub.Ges indicates the total inductive load and C.sub.Ges indicates the total capacitive load in the circuit.

30. The method as claimed in claim 28, wherein a transverse-field module is operated with an alternating voltage with a frequency and the frequency is changed during a rolling campaign or between two rolling campaigns.

31. The method as claimed in claim 30, wherein the frequency is set in dependence on the thickness of the flat steel strip.

32. The method as claimed in claim 28, wherein a transverse-field module is operated with a current intensity and the current intensity is set in dependence on at least one parameter of the flat steel strip from the group comprising the thickness, the speed, the temperature before entering the heating device, and the temperature after leaving the heating device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0088] The properties, features and advantages of this invention described above and also the manner in which they are achieved become clearer and more clearly understandable in connection with the following description of exemplary embodiments, which are explained more specifically in conjunction with the drawings, in which:

[0089] FIG. 1 shows a schematic plan view of a first embodiment, not according to the invention, of a heating device for heating a flat steel strip,

[0090] FIG. 2 shows a schematic plan view of a second embodiment, not according to the invention, of a heating device for heating a flat steel strip,

[0091] FIG. 3 shows a schematic plan view of a first embodiment according to the invention of a heating device for heating a flat steel strip,

[0092] FIG. 4 shows a schematic plan view of a second embodiment according to the invention of a heating device for heating a flat steel strip,

[0093] FIG. 5a shows a schematic representation of a transverse-field module for heating a flat steel strip,

[0094] FIG. 5b shows a schematic representation of the current feed and the magnetic field of a transverse-field module for heating a flat steel strip,

[0095] FIG. 6a shows a schematic representation of a longitudinal-field module for heating a flat steel strip,

[0096] FIG. 6b shows a schematic representation of the current feed and the magnetic field of a longitudinal-field module for heating a flat steel strip,

[0097] FIG. 7a shows a front view of a third embodiment according to the invention of a heating device,

[0098] FIG. 7b shows a plan view of the heating device from FIG. 7a,

[0099] FIG. 7c shows a partially sectional representation along the line A-A from FIG. 7b,

[0100] FIG. 8a shows a schematic representation of a first open-loop or closed-loop control device for the heating device of FIG. 7a-FIG. 7c,

[0101] FIG. 8b shows a schematic representation of a second open-loop or closed-loop control device for the heating device of FIG. 7a-FIG. 7c,

[0102] FIG. 9 shows a schematic plan view of a further embodiment according to the invention of a heating device for heating a flat steel strip,

[0103] FIG. 10a . . . c show in each case a schematic representation of a power supply for a heating device according to the invention for heating a flat steel strip.

[0104] Parts that correspond to one another are provided with the same designations in all of the figures.

DETAILED DESCRIPTION

[0105] FIG. 1 shows a schematic view of a first embodiment, not according to the invention, of a heating device 1 for the inductive heating of a flat steel strip 2. The flat steel strip leaves a roughing train, which is not shown, is heated by means of the heating device 1 and, after the heating, enters a finishing train, which is not shown. Optionally, before entering the finishing train, the heated flat steel strip 2 may also be descaled. The heating device 1 comprises eight transverse-field modules 3. A transverse-field module 3 comprises an inductor above and an inductor below the flat steel strip 2, which generate a magnetic field transversely to the transporting direction R, specifically in the direction of the thickness, and consequently perpendicularly to the upper side and underside of the flat steel strip 2, and inductively heat it in this way. In the embodiment shown, eight transverse-field modules 3 are provided, arranged one after the other. However, a greater or smaller number of transverse-field modules 3 may also be provided. The transverse-field modules 3 are operated with alternating voltage of a first frequency f1. The heating device 1 is suitable for example for heating flat steel strips with thicknesses of 6 mm to 17 mm. The flat steel strip 2 can assume different widths b1, b2. In order to prevent overheating of the edge regions of the flat steel strip 2, the inductors of the transverse-field modules 3 can be moved in relation to an edge, for example the upper inductor, arranged above the strip, may be moved in relation to the edge shown at the top and the lower inductor, arranged below the strip, may be moved in relation to the edge shown at the bottom, in each case by means of an actuator.

[0106] FIG. 2 shows a schematic view of a second embodiment, not according to the invention, of a heating device 1 for the inductive heating of a flat steel strip 2, in particular for heating between two rolling trains of a hot rolling mill. The heating device 1 comprises ten transverse-field modules 3. A transverse-field module 3 once again comprises an inductor above and an inductor below the flat steel strip 2, which generate a magnetic field transversely to the transporting direction R, specifically in the direction of the thickness, and inductively heat it in this way. In the embodiment shown, ten transverse-field modules 3 are provided, arranged one after the other. However, a greater or smaller number of transverse-field modules 3 may also be provided. The transverse-field modules 3 are operated with alternating voltage with a switchable frequency, wherein the frequency can assume the value f1 or the value f2, where f2 is greater than f1. The heating device 1 is suitable for example for heating flat steel strips with thicknesses of 6 mm to 15 mm, but with an additional possibility for setting the temperature profile.

[0107] FIG. 3 shows a schematic view of a first embodiment according to the invention of a heating device 1 for the inductive heating of a flat steel strip 2, in particular between two rolling trains of a hot rolling mill. The heating device 1 comprises a number of transverse-field modules 3 and longitudinal-field modules 4, which are arranged one after the other. A transverse-field module 3 comprises one or more inductors, which generate a magnetic field transversely to the transporting direction R, specifically in the direction of the thickness of the flat steel strip 2, and inductively heat it in this way. In the embodiment shown, eight transverse-field modules 3 are provided, arranged one after the other. However, a greater or smaller number of transverse-field modules 3 may also be provided. A longitudinal-field module 4 comprises one or more inductors, which generate a magnetic field in the longitudinal direction, specifically in the transporting direction R, and consequently parallel to the upper side and underside of the flat steel strip 2, and inductively heat it in this way. In the embodiment shown, four longitudinal-field modules 4 are provided, arranged one after the other. However, a greater or smaller number of longitudinal-field modules 4 may also be provided. The transverse-field modules 3 are operated with alternating voltage of a first frequency f1. The heating device 1 is suitable for example for heating flat steel strips with thicknesses of 6 mm to 20 mm.

[0108] FIG. 4 shows a schematic view of a second embodiment according to the invention of a heating device 1 for the inductive heating of a flat steel strip 2, in particular for heating between two rolling trains of a hot rolling mill. The heating device 1 comprises a number of transverse-field modules 3 and longitudinal-field modules 4, which are arranged one after the other. A transverse-field module 3 comprises one or more inductors, which generate a magnetic field transversely to the transporting direction R, specifically in the direction of the thickness of the flat steel strip 2, and inductively heat it in this way. In the embodiment shown, eight transverse-field modules 3 are provided, arranged one after the other. However, a greater or smaller number of transverse-field modules 3 may also be provided. A longitudinal-field module 4 comprises one or more inductors, which generate a magnetic field in the longitudinal direction, specifically in the transporting direction R, and consequently parallel to the upper side and underside of the flat steel strip 2, and inductively heat it in this way. In the embodiment shown, eight longitudinal-field modules 4 are provided, arranged one after the other. However, a greater or smaller number of longitudinal-field modules 4 may also be provided. The transverse-field modules 3 are operated with alternating voltage with a switchable frequency, wherein the frequency can assume the value f1 or the value f2, where f2 is greater than f1. The longitudinal-field modules 4 are operated either with a frequency f3 or f4, where f3>f2 and f4>f2. The heating device 1 is suitable for example for heating flat steel strips with thicknesses of 6 mm to 65 mm.

[0109] FIG. 5a schematically shows a transverse-field module 3 with two coils 5, which are arranged above and below the flat steel strip 2. By feeding current to the coils 5 of the transverse-field module 3, a magnetic field M forms transversely to the transporting direction R in the direction of the thickness of the strip 2. As a result, the flat steel strip 2 with the thickness d and the width b1 is heated. Eddy currents W form on the upper side and the underside of the strip 2.

[0110] In FIG. 5b, the current feed I (currents running into the plane of the drawing are shown by a cross, currents running out of the plane of the drawing are shown by a dot) of the coils 5 and the magnetic flux lines of the magnetic field M for a further transverse-field module 3 are shown.

[0111] FIG. 6a schematically shows a longitudinal-field module 4 with a coil 5, which encloses the flat steel strip 2 transversely to the transporting direction R. By feeding current to the coil 5 of the longitudinal-field module 4, a magnetic field M forms in the transporting direction R parallel to the upper side and the underside of the strip 2. As a result, the flat steel strip 2 with the thickness d and the width b1 is heated. Eddy currents W form parallel to the upper side and the underside of the strip 2.

[0112] In FIG. 6b, the current feed I (currents running into the plane of the drawing are shown by a cross, currents running out of the plane of the drawing are shown by a dot) of the coil 5 and the magnetic flux lines of the magnetic field M for a longitudinal-field module 4 are shown.

[0113] FIGS. 7a and 7b show an elevation and a plan view of a heating device 1 according to the invention in a hot rolling mill. Once the flat steel strip 2 has been rolled in the last stand 9 of a roughing train, the preliminary strip 2 is transported on a roller table, which is not shown any more specifically, to the first stand 10 of the finishing train and is thereby inductively heated by a heating device 1. The heating device 1 comprises six transverse-field modules 3, with a coil 5 above and a coil 5 below the preliminary strip 2 and also two longitudinal-field modules 4, which are arranged behind the transverse-field modules 3. The width b, the thickness d, the speed v and the temperature profile T.sub.1 of the preliminary strip 2 are measured by suitable measuring instruments after the last stand 9 of the roughing train and are fed to an open-loop or closed-loop control device 8 (see FIG. 8a). After passing the heating device 1, the preliminary strip 2 is descaled under high pressure, for example 150 to 400 bar, by two descalers 12. Respectively arranged before and after the descalers is a pair of driver rollers 13 to prevent the escape of pressurized water from the descaling region. Either before or preferably after the descalers, the temperature profile T.sub.2 of the preliminary strip is measured by a pyrometer 11 and likewise fed to the open-loop or closed-loop control device 8. Before the descalers there may optionally be a pyrometer 11, shown by dashed lines, which measures the temperature profile of the preliminary strip 2 before the descalers. The coils 5 of the transverse-field modules 3 are in each case accommodated in a coil car 19 (also see FIG. 7c). The coil car 19 together with the coils 5 above and below the preliminary strip 2 can be moved by means of a thrust actuator 6 in the direction of the width of the preliminary strip. As a result, the width position 5B, i.e. the distance between a side edge of the preliminary strip 2 and the end of the coil 5, can be set. In addition to this, the height position s.sub.H of the coils 5, and consequently the distance between the upper coil 5 and the upper side and also the lower coil 5 and the underside of the preliminary strip 2, can be changed. The changing of the height is performed by multiple lift actuators 7 (also see FIG. 7c). The power supply 14 of one or more transverse-field modules 3 is accommodated in a climatically controlled and clean electrical compartment 20. FIG. 7c schematically shows a section transversely to the transporting direction R along the line A-A from FIG. 7b with a converter 16 for generating an alternating voltage with a specific frequency f and a specific current intensity I, a capacitor bank 17 with multiple capacitors connected in parallel and flexible cables 15, here coaxial cables, for connecting the capacitor bank 17 to the movable coils 5 on the coil car 19. The connection between the converter 16, arranged in a converter cabinet 16a, and the capacitor bank 17 takes place by way of conductor rails 18. If an accidental arc occurs in the region of the power supply 14, the excess pressure in the electrical compartment 20 is discharged to the outside by way of a shaft with an explosion flap 21. This ensures that no harmful gases or vapors get into the hot rolling mill. As schematically shown in FIG. 7b, the power supply 14 has a frequency input for determining a setpoint frequency f.sub.Soll, a current input for determining a setpoint current intensity I.sub.Soll, a width input for determining a setpoint width position s.sub.B-Soll and a height input for determining a setpoint height position s.sub.H-Soll. These inputs can be used to adapt one or more transverse-field modules 3 to the current production conditions with regard to the frequency f and the current intensity I of the alternating voltage and also with regard to the width position s.sub.B and the height position s.sub.H. For reasons of overall clarity, in FIG. 7b only a single power supply 14 is shown. It goes without saying that all of the transverse-field modules 3 are connected to power supplies 14, wherein a power supply 14 can supply one or more transverse-field modules 3. The power supply of the longitudinal-field modules 4 has not been shown.

[0114] FIGS. 8a and 8b each show a diagram of an open-loop or closed-loop control device 8, which is continually fed current data of the production process, such as the width b, the thickness d, the speed v of the preliminary strip and also the temperature profiles T.sub.1 of the preliminary strip 2 before entering the heating device 1 and after leaving the heating device 1. According to FIG. 8a, the open-loop or closed-loop control device 8 calculates from these input variables the setpoint frequency f.sub.Soll and the setpoint current intensity I.sub.Soll for the power supplies 14 and also the setpoint width position s.sub.B-Soll and the setpoint height position s.sub.H-Soll for the coil cars 19 of the transverse-field modules. According to FIG. 8b, the open-loop or closed-loop control device 8 calculates from these input variables the setpoint voltage U.sub.Soll and the setpoint heating power P.sub.Soll for the power supplies 14 of the longitudinal-field modules. The setpoint values are connected in terms of signaling by way of the respective outputs of the open-loop or closed-loop control device 8 to the inputs of the power supply or the inputs on the transverse-field modules. The open-loop or closed-loop control device 8 may be for example a PLC or a process computer. It is also possible that the functionality of the open-loop or closed-loop control device 8 is taken over by the plant controller of the rolling plant.

[0115] FIG. 9 schematically shows a plan view of a heating device according to the invention with four transverse-field modules 3 and four longitudinal-field modules 4 and also the associated power supplies 14a, 14b.

[0116] In FIG. 10a, a first variant of a power supply 14a, 14b is schematically shown. The converter 16 is a load-commutated converter, which sets the frequency f of the generated alternating voltage in dependence on the load, specifically the capacitive load of the capacitor bank 17 and the inductive load of the coils 5. The first capacitor, shown on the left, with the capacitance C can be activated or deactivated by means of a switch, which is switched in dependence on a frequency input 22. In the activated state, the frequency f is obtained as

[00001]$f=f_0=\frac{1}{2\pi \sqrt{L2C}};$

in the deactivated state, the frequency f is obtained as

[00002]$f=f_0=\frac{1}{2\sqrt{LC}}.$

Furthermore, the voltage amplitude U or the setpoint heating power P can be determined for the converter.

[0117] In FIG. 10b, a second variant of a power supply 14a, 14b is schematically shown. The converter 16 is of an identical configuration to the converter from FIG. 10a. The capacitors of the capacitor bank 17 may however not be switched. However, current may be fed to either one or two coils 5. In one case, the frequency f is obtained as

[00003]$f=f_0=\frac{1}{2\sqrt{2L2C}};$

in the deactivated state, the frequency f is obtained as

[00004]$f=f_0=\frac{1}{2\sqrt{L2C}}.$

Again, the voltage amplitude U or the setpoint heating power P can be determined for the converter.

[0118] Of course both inductances and capacitances in a circuit may be activated or deactivated.

[0119] FIG. 10c finally shows a third variant of a power supply 14a, 14b with a non-load-commutated or externally commutated converter 16. The load is 2C for the capacitor bank 17 and L for the coil 5. In the case of a load-commutated converter, the frequency f of the alternating voltage would be obtained as

[00005]$f=f_0=\frac{1}{2\sqrt{L2C}}.$

In contrast to this, the actual frequency f of the alternating voltage may deviate from f.sub.0, because f is determined directly for the converter 16 by a frequency input 22. In the case of the operation of an externally commutated converter, it must be noted that the power supply must feed not only the heating power but also the reactive power to the converter.

[0120] In the description of FIGS. 10a . . . c, f.sub.0 denotes the resonant frequency of a so-called LC resonant circuit.

[0121] The circuits indicated in FIGS. 10a . . . 10c are schematic and do not take into account the magnetic coupling between the coil or the coils 5 and the flat steel strip 2.

LIST OF DESIGNATIONS

[0122]

TABLE-US-00001  1 Heating device  2 Flat steel strip, preliminary strip  3 Transverse-field module  4 Longitudinal-field module  5 Coil  6 Thrust actuator  7 Lift actuator  8 Open-loop or closed-loop control device  9 Stand of the roughing train 10 Stand of the finishing train 11 Thermometer or pyrometer 12 Descalers 13 Driving roller 14, 14a, 14b Power supply 15 Flexible cable 16 Converter 16a Converter cabinet 17 Capacitor bank 18 Conductor rail 19 Coil car 20 Electrical compartment 21 Explosion flap 22 Frequency input 23 Switch b, b1, b2 Width of the flat steel strip C Capacitance d Thickness of the flat steel strip f, f1, f2, f3, f4 Frequency, actual frequency f.sub.0 Resonant frequency of an LC resonant circuit f.sub.Soll Setpoint frequency M Magnetic flux I Current, current intensity, actual current intensity I.sub.Soll Setpoint current L Inductance P Power R Transporting direction S.sub.B Width position of the coil, actual width pos. S.sub.B-Soll Setpoint width position of the coil S.sub.H Height position of the coil, actual height pos. S.sub.H-Soll Setpoint height position of the coil T.sub.1, T.sub.2 Temperature or temperature profile U Voltage v Speed of the flat steel strip W Eddy current