Method and device for regulating a continuous casting machine

Abstract

A method and a device for regulating a continuous casting system. The continuous casting system has a mold (1) and a strand guide (8) which is arranged downstream of the mold (1). Molten metal (3) is cast into the mold (1), in particular via an inlet device (4). The molten metal hardens on walls (1a) of the mold (1), such that a metal strand (7) with a hardened strand shell (5) and a still liquid core (6) is formed. The metal strand (7) is drawn out of the mold (1) by mutually spaced rollers (8b) of the strand guide (8), and a measurement variable is ascertained which correlates to the undulation of the casting level formed in the mold. The measurement variable is processed using at least one computing specification and is used to reduce the undulation of the casting level. In order to reduce the undulations of the casting level, the mutual spacing of opposing rollers (8b) of the strand guide is changed cyclically prior to the full hardening point (D).

Claims

1. A method for regulating a continuous casting machine, wherein the continuous casting machine comprises a mold for forming a strand and a strand guide for guiding the strand and metal from the mold downstream of the mold; the method comprising: pouring liquid metal into the mold, via an inflow unit, wherein the liquid metal solidifies on walls of the mold, thereby forming a metal strand having a solidified strand shell and a still liquid core forming within the shell; drawing the metal strand out of the mold by means of rollers of the strand guide, wherein the rollers are arranged spaced apart; determining a measured variable correlated with cyclical variations of a casting level of liquid metal in the mold; processing the measured variable with incorporation of at least one computing rule and using the at least one computing rule to reduce the cyclical variations of the casting level of the liquid metal in the mold; and reducing the cyclical variations of the casting level of the liquid metal in the mold by cyclically changing the mutual spacing of opposing rollers of the strand guide toward or away from the strand before a complete solidification point, whereby the cyclical variations of the casting level of the liquid metal in the mold are opposed by anti-cyclically changing the mutual spacing of opposing rollers of the strand guide toward or away from the strand.

2. The method as claimed in claim 1, wherein the cyclic changes are in a frequency range up to greater than or equal to 0.6 Hz.

3. The method as claimed in claim 1, further comprising: arranging multiple roller segments, each having one or more rollers, on both sides along the strand guide, and adjusting at least one roller segment normally in relation to a strand guide direction.

4. The method as claimed in claim 3, further comprising adjusting at least one roller segment of a first segment.

5. The method as claimed in claim 3, further comprising pivoting at least one roller segment.

6. The method as claimed in claim 3, further comprising adjusting at least one roller segment in parallel alignment in relation to an opposing roller segment.

7. The method as claimed in claim 1, further comprising adjusting at least one roller segment by an adjustment device, which comprises at least one electromechanical or hydraulic actuator.

8. The method as claimed in claim 1, further comprising detecting frequencies of the cyclic variations of the casting level in a frequency range from 0.6 to 5 Hz; and offsetting the cyclic variations by cyclic opposing change of the roller spacing of rollers of the strand guide.

9. The method as claimed in claim 1, further comprising detecting frequencies of first cyclic variations of the casting level in a first frequency range; offsetting the first cyclic variations by cyclic opposing movements of the inflow unit; detecting further frequencies of second cyclic variations of the casting level in a second frequency range; and offsetting the second cyclic variations by cyclic opposing change of the roller spacing of rollers of the strand guide, wherein the second frequency range is greater than the first frequency range.

10. A device for carrying out a method as claimed in claim 1, comprising: means for introducing a metal melt into a mold, a strand guide comprising rollers; a measuring unit for measuring the cyclic variations of the casting level; and an adjustment device connected to a control unit, the adjustment device is configured to reduce and compensate the cyclic variations of the casting level in the mold by anti-cyclic change of the roller spacing of opposing rollers of the strand guide toward or away from the strand for opposing the variations of the casting level.

11. The device as claimed in claim 10, wherein the adjustment device is configured for cyclic changes of the roller spacing in a frequency range up to greater than or equal to 0.6 Hz.

12. The device as claimed in claim 10, wherein the adjustment device comprises at least one hydraulic or electromechanical actuator.

13. The device as claimed in claim 10, wherein the rollers comprise multiple roller segments, each segment having one or more rollers, the roller segments are arranged on both sides along the strand guide, wherein at least one roller segment is adjustable in a direction normal in relation to a strand guide direction by means of the adjustment device.

14. The device as claimed in claim 13, wherein the at least one roller segment is a first roller segment.

15. The device as claimed in claim 13, wherein the at least one roller segment is pivotable.

16. The device as claimed in claim 13, wherein the at least one roller segment is adjustable in parallel alignment in relation to an opposing roller segment arranged along the strand guide.

17. The device as claimed in claim 10, wherein the measuring unit is configured and operable to detect frequencies of the cyclic variations of the casting level in a first frequency range; an inflow unit of the mold is configured and operable to offset cyclic opposing movements of an inflow unit of the mold; the measuring unit being configured and operable to detect further frequencies of the cyclic variations of the casting level in a second frequency range; the cyclic variations of the first and second frequency ranges are offsettable by a cyclic opposing change of roller spacing of the rollers of the strand guide and by the adjustment device; and wherein the second frequency range is greater than the first frequency range.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The invention will be explained in greater detail on the basis of an exemplary embodiment. The drawings are exemplary and are to illustrate the concept of the invention, but are in no way to restrict it or even reproduce it exhaustively.

BRIEF DESCRIPTION OF THE DRAWINGS

(2) FIG. 1 shows a schematic view of a portion of a continuous casing machine according to the invention,

(3) FIG. 2 shows a schematic view of a strand guide according to the invention,

(4) FIG. 3 shows the schematic construction of a control unit of the prior art,

(5) FIG. 4 shows details of the first observer from FIG. 3,

(6) FIG. 5 schematically shows a monitoring loop according to the invention comprising a first and second observer,

(7) FIG. 6 shows the time curve of various variables during the regulation of a continuous casting machine.

EMBODIMENT OF THE INVENTION

(8) According to FIG. 1, a continuous casting machine comprises a mold 1. Liquid metal 3, for example, liquid steel or liquid aluminum is poured into the mold 1 via an immersion pipe 2. The inflow of the liquid metal 3 into the mold 1 is set by means of an inflow unit 4. A design of the inflow unit 4 as a closure plug is illustrated in FIG. 1. In this case, a position p of the inflow unit 4 corresponds to a stroke position of the closure plug. Alternatively, the inflow unit 4 can be designed as a slide. In this case, the closure position p corresponds to the slide position.

(9) The liquid metal 3 located in the mold is cooled by means of cooling units (not shown), so that it solidifies on walls la of the mold 1 and thus forms a strand shell. A core 6 is still liquid, however. It solidifies only later. The strand shell 5 and the core 6 together form a metal strand 7. The metal strand 7 is supported and drawn out of the mold 1 by means of a strand guide 8. The strand guide 8 is downstream of the mold 1. It comprises multiple roller segments 8a, which in turn comprise rollers 8b. Only a few are shown of the roller segments 8a and the rollers 8b in FIG. 1. The metal strand 7 is drawn at a draw-off speed v out of the mold 1 by means of the rollers 8b.

(10) The liquid metal 3 forms a casting level 9 in the mold 1. The casting level 9 is to be kept as constant as possible. Therefore, both in the prior art and also in the present embodiment variant of the invention, the position p of the inflow unit 4 is tracked to set the inflow of the liquid metal 3 into the mold 1 accordingly. A height h of the casting level 9 is detected by means of a measuring unit 10 (known per se). The height h is supplied to a control unit 11 for the continuous casting machine. The control unit 11 determines a manipulated variable S for the inflow unit 4 according to a regulating method, which is explained in greater detail hereafter. The inflow unit 4 is then activated accordingly by the control unit 11. In general, the control unit 11 outputs the manipulated variable S to an adjustment unit 12 for the inflow unit 4. The adjustment unit 12 can be, for example, a hydraulic cylinder unit. Frequencies of the bulging after the mold are detected metrologically and/or determined according to f=v.sub.c/p.sub.Roll*n, wherein v.sub.c corresponds to the draw-off speed of the strand, f corresponds to the bulging frequency, n corresponds to the number of the harmonic frequencies (1, 2, etc.), and p.sub.Roll corresponds to the roller spacings.

(11) The roller spacings, which correspond to the strand thickness d shown, can be intentionally adapted by means of pivot axis 23 and/or adjustment device 24. This can take place, as shown here in FIG. 1, in that in the first segment at least one roller segment 8a comprises a fixed outer frame, for example, the roller segment 8a located on the left directly below the mold 1 here. The opposing roller segment 8a, and/or the inner frame supporting it, is pivotable around a pivot axis 23, which extends normally in relation to the plane of the drawing. The pivot axis 23 can coincide with a rotational axis of a roller 8b, with the rotational axis of the upper roller 8b here, but could also be provided at another point, of course. Due to the pivoting, the roller spacing changes in the lower roller pair of the uppermost roller segment 8a in FIG. 1, while the roller spacing of the upper roller pair remains the same. This is not disadvantageous because the change of the roller spacing due to the method according to the invention is generally only in the range of a few tenths of millimeters up to 2 mm.

(12) Possible guide rollers, which are directly connected to the mold and would be arranged above the uppermost roller segment 8a shown here, are not shown in FIG. 1. These guide rollers are generally not adjustable in relation to one another and normally in relation to the strand guide direction, however.

(13) As an alternative to the pivoting, the left uppermost roller segment 8a, i.e., for example, its outer frame, could be fixed and the right upper roller segment 8a, i.e., for example, its inner frame, could be displaced in parallel normally to the strand guide direction toward the left roller segment 8a and away from it. The roller spacing of all roller pairs thus changes by the same absolute value in each case. This could also be carried out using one or more hydraulic cylinders (distributed along the strand width and/or along the strand guide direction).

(14) In FIG. 2, only one strand guide 8 is shown, which can replace the strand guide 8 in FIG. 1 or also supplement it, after the uppermost segment. In FIG. 2, in each of the three illustrated segments, each roller segment 8a has three rollers 8b on each side. However, there could also be only two or more than three rollers 8b per roller segment 8a. In continuation of FIG. 1, the fixed strand shell 5 and the liquid core 6 of the strand are illustrated here up to the complete solidification point D. Accordingly, adjustment devices 24 are also provided in all segments 8a up to the complete solidification point D. The adjustment devices 24 can adjust each of the roller segments 8a by pivoting or by parallel displacement, as already explained in FIG. 1. In this example, the inner roller segment 8a of the first (uppermost) segment is adjusted by pivoting around the pivot axis 23, and the inner roller segment 8a of the second segment is adjusted by parallel displacement by means of two adjustment devices 24. The connection of the adjustment devices 24 to the control unit 11 is not shown here.

(15) In FIG. 3, the control unit 11 implements inter alia, a casting level regulator 13. The height h of the casting level 9 is supplied to the casting level regulator 13. Furthermore, a target value h* for the height h of the casting level 9 is supplied to the casting level regulator 13. Furthermore, further signals are supplied to the casting level regulator 13. The further signals can be, for example, the width and the thickness of the cast metal strand 7 (or more generally the cross section of the metal strand 7), the draw-off speed v (or its target value), and others. The casting level regulator 13 then determines on the basis of the deviation of the height h of the casting level 9 from the target value h* in particular a preliminary target position p′* for the inflow unit 4. The casting level regulator 13 can use the further signals for its parameterization and/or for determining a pilot control signal pV.

(16) The control unit 11 furthermore implements a first observer 14. The height h of the casting level 9 and its target value h*, the further signals and a final target position p* for the inflow unit 4 are supplied to the first observer 14. The first observer 14 determines a first compensation value k. The first compensation value k is added to the preliminary target position p′* and the final target position p* is thus determined. The manipulated variable S activates the inflow unit 4, and that variable is then determined on the basis of the deviation of the actual setting p from the final target position p*. In general, the control unit 11 implements a lower-order position regulator (not shown) for this purpose.

(17) For the sake of good order, the first and second observers 14, 25 are not persons, but rather function blocks implemented in the control unit 11.

(18) The difference between the preliminary target position p′* and the final target position p* corresponds to the first compensation value k determined by the first observer 14. Since the first compensation value k is determined by the first observer 14 and it is therefore known to the first observer 14, alternatively to the final target position p*, the preliminary target position p′* can also be supplied to the first observer 14. Because of the circumstance that the first compensation value k is known to the first observer 14, the first observer 14 can thus readily determine the final target position p* from the preliminary target position p′*. A tapping point 15, at which the (preliminary or final) target position p′*, p* is tapped can thus be located before or after a node point 16 as needed, at which the first compensation value k is added to the preliminary target position p′*. The tapping point 15 is to be located before a node point 16′, however, at which the pilot control signal pV is added on.

(19) The first observer 14 comprises a determination block 17. The height h of the casting level 9, the further signals, and the final target position p* are supplied to the determination block 17. The determination block 17 comprises a model of the continuous casting machine. By means of the model, the determination block 17 determines on the basis of the further signals and the final target position p* an expected height (i.e., computed with model support) for the casting level 9. On the basis of the expected height, the determination block 17 then determines an expected variation value δh (i.e., computed with model support) for the height h of the casting level 9, i.e., the short-term variation. For example, the determination block 17 can perform averaging of the height h of the casting level 9 and subtract the resulting mean value from the expected height. The determined variation value δh thus reflects the expected variation of the height h of the casting level 9. On the basis of the variation value δh, the determination block 17 then determines the first compensation value k.

(20) The procedure previously explained in conjunction with FIG. 3 corresponds to the procedure of the prior art. It is also used in this embodiment variant of the present invention. The first observer 14 having the determination block 17 is illustrated once again in FIG. 4. In the scope of the present invention, the determination block 17 is merely one of multiple components of the first observer 14 in accordance with the illustration in FIG. 4, however. Thus, for example, the first observer 14 additionally comprises a first analysis element 18. The variation value δh is supplied to the first analysis element 18. The first analysis element 18 determines the frequency components of the variation value δh therefrom. In addition, a second analysis element 19 is preferably also provided. A secondary signal Z is supplied to the second analysis element 19. The second analysis element 19 determines the frequency components of the secondary signal Z therefrom.

(21) The secondary signal Z can be a withdrawal force F. Using that force, the metal strand 7 is withdrawn from the mold 1 by the rollers 8b of the strand guide 8. The withdrawal force F is oriented parallel to the draw-off speed v. Alternatively, it can be the draw-off speed v itself. These two alternatives are preferred. However, it is also possible, for example to use a force signal F′, which is applied to (at least) one of the roller segments 8a of the strand guide 8, as the secondary signal Z. The direction to which the force signal F′ is related is orthogonal to the draw-off speed v. The secondary signal Z can again alternatively be a local strand thickness d, which is measured by means of a measuring unit 21 in the strand guide 8. The first analysis element 18 supplies the frequency components determined thereby to a selection element 22. If it is provided, this also applies in a similar manner to the second analysis element 19. The selection element 22 determines, in conjunction with the draw-off speed v, the associated wavelengths which correspond to the frequency components of the variation value δh and possibly also of the secondary signal Z. The draw-off speed v is supplied for this purpose to the first observer 14 and to the selection element 22 within the first observer 14. The selection element 22 determines the wavelengths at which the associated frequency component of the variation value δh and possibly also the associated frequency component of the secondary signal Z is greater than a threshold value S1, S2. The respective threshold value S1, S2 can be defined individually for the frequency components of the variation value δh, on the one hand, and the frequency components of the secondary signal Z, on the other hand. These wavelengths are preselected by the selection element 22. Within ranges, which are each coherent per se, of preselected wavelengths of the variation value δh, the selection element 22 then determines the wavelengths λi (i=1, 2, 3, . . . ), at which the respective frequency component of the variation value δh assumes a maximum. The number of wavelengths λi is not restricted. The selection element 22 (finally) selects these wavelengths λi. The selection element 22 supplies the selected wavelengths λi to the determination block 17. The determination block 17 carries out a filtering of the height h of the casting level 9 and the final target position p* for the wavelengths λi selected by the selection element 22. The determination block determines the first compensation value k solely on the basis of the filtered height h of the casting level 9 and the filtered final target position p*. The determination block 17 leaves the other frequency components of the height h of the casting level 9 and the final target position p* unconsidered in the scope of the determination of the first compensation value k. Furthermore, predetermined wavelength ranges can be specified to the selection element 22. In this case, the predetermined wavelength ranges represent an additional selection criterion. In particular, wavelengths at which the associated frequency component of the variation value δh and possibly also the associated frequency component of the secondary signal Z are above the respective threshold value S1, S2 are only selected if they are additionally within one of the predetermined wavelength ranges. Otherwise, they are not selected even if the associated frequency component of the variation value δh and possibly also the associated frequency component of the secondary signal Z is greater than the respective threshold value S1, S2.

(22) As already previously mentioned, the second observer 25 comprises identical components as the first observer 14, analyzes frequencies of the bulging after the mold 1, and specifies a second compensation value k′ for the adjustment device 24. A monitoring loop is shown in FIG. 5, which comprises a first and a second observer 14, 25. The first observer 14 specifies a first compensation value k for the inflow unit 4 of the mold 1, whereby the casting level 9 in the mold 1 is regulated. Stated in simplified terms, the first observer 14 and the inflow unit 4 of the mold 1 together represent a standard system for regulating the casting level 9 of the mold 1, which is used for the compensation of frequencies in the first frequency range and thus represents a controller 27 for frequencies of the first frequency range. The second observer 25, which is connected to the adjustment device 24, represents a controller for frequencies of the second frequency range 26 and specifies a second compensation value k′.

(23) Instead of the first observer 14, which controls and/or regulates the inflow unit 4 of the mold 1, another regulating method could be provided, and/or instead of the second observer 25, which controls and/or regulates the adjustment device 24 of the rollers 8b, another regulating method could be provided.

(24) Only a single regulating method could also be provided, which only controls and/or regulates the adjustment device 24 of the rollers 8b, while the inflow unit 4 of the mold 1 is not used at all for adjusting out the variations of the casting level.

(25) This single regulating method could be the second observer 25, or also another control or regulating method. In this case, the second observer or another single control or regulating method would generally cover a greater frequency range than in the case of two regulating methods. This frequency range could then cover, for example, the frequencies from 0 to 0.6 Hz, 0 to 1 Hz, 0 to 2 Hz, 0 to 3 Hz, 0 to 4 Hz, or 0 to 5 Hz.

(26) FIG. 6 shows an example of a suppression of cyclic oscillations. The time t is plotted along the horizontal axis. The position of the inflow unit 4, inscribed with “Pos (4)”, is illustrated along the vertical axis in the first (uppermost) illustration, in the second figure the height of the casting level in the mold 1, inscribed with “M_L”, and in the third figure the steel flow from the mold 1, inscribed with “St_Fl”. For better comprehension, the regulation “Comp” is still deactivated at the point in time t=0 and is then switched on, which is illustrated in the last figure with the states “0” for the deactivated regulation and “1” for the activated regulation. It is well recognizable in the first three illustrations that the position of the inflow unit 4 cyclically changes, and also the height of the casting level and as a result also the steel flow out of the mold. The cyclic variations of the casting level “M_L” are reduced with the activation of the regulation, by changing the position “Pos (4)” of the inflow unit 4 here. In the method according to the invention, additionally or alternatively to changing the position “Pos (4)” of the inflow unit 4, one would cyclically change the mutual spacing of the rollers 8b in the uppermost segment accordingly to reduce the variations of the casting level.

LIST OF REFERENCE SIGNS

(27) 1 mold 1a walls of the mold 2 immersion pipe 3 liquid metal 4 inflow unit 5 strand shell 6 core 7 metal strand 8 strand guide 8a roller segments 8b rollers 9 casting level 10 measuring unit 11 control unit 12 adjustment unit 13 casting level regulator 14 first observer 15 tapping point 16, 16′ node points 17 determination block 18, 19 analysis elements 20 temperature sensor 21 measuring unit 22 selection element 23 pivot axis 24 adjustment device 25 second observer 26 controller for frequencies of the second frequency range 27 controller for frequencies of the first frequency range D complete solidification point d strand thickness F withdrawal force F′ force signal h height of the casting level h* target value for the height of the casting level k first compensation value k′ second compensation value p position of the inflow unit p*, p′* target positions pV pilot control signal S manipulated variable S1, S2 threshold values T temperature v draw-off speed Z secondary signal δh variation value