Method and device for regulating a strand casting system

Abstract

A method that includes casting liquid metal in the mould of the strand casting system, extracting a metal strand from the mould using rollers of the strand guide of the strand casting system, determining a measurement variable, which correlates to the fluctuation of the casting level in the mould, cyclically changing the spacing of the opposing rollers of the strand guide in directions opposite to the fluctuations of the casting level to reduce fluctuations of the casting level, and detecting casting level fluctuation frequencies and providing at least one observer, which determines the actual value (ACT) of the roller spacing being used as one of the input variables for the observer in order to compensate a phase shift and/or amplitude of the actual value (ACT) of the roller spacing.

1 . A method for regulating a strand casting plant,
 wherein the strand casting plant comprises a mold and a strand guide downstream of the mold,   wherein liquid metal is poured into the mold, in particular via an inflow unit, which liquid metal solidifies on walls of the mold, so that a metal strand having a solidified strand shell and a still liquid core forms,   wherein the metal strand is drawn out of the mold by means of rollers of the strand guide arranged spaced apart,   wherein a measured variable is determined, which correlates with the variation of the casting level forming in the mold, this measured variable is processed with incorporation of at least one computing rule and is used to reduce the variations of the casting level,   wherein the mutual spacing of opposing rollers of the strand guide is cyclically changed before the complete solidification point (D) to reduce the variations of the casting level, namely by cyclic change of the roller spacing, opposing the variations of the casting level, of opposing rollers of the strand guide,   wherein frequencies of the variations of the casting level are detected and at least one observer is provided which, on the basis of these frequencies, determines a compensation value (k′) for a target value (SET) of the roller spacing of the rollers, characterized in that the actual value (ACT) of the roller spacing is used as one of the input variables for this observer, in order to compensate for a phase shift and/or amplitude of the actual value (ACT) of the roller spacing.   
     
     
         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, preferably up to 5 Hz. 
     
     
         3 . The method as claimed in  claim 1 , wherein multiple roller segments each having one or more rollers are arranged on both sides along the strand guide, wherein at least the inner roller segment located closest to the mold is pivoted normally in relation to the strand guide direction about the axis of rotation of a roller of this roller segment located closest to the mold. 
     
     
         4 . The method as claimed in  claim 1 , wherein frequencies of the variations of the casting level in a frequency range from 0 to 5 Hz are detected and the variations are offset by means of cyclic opposing change of the roller spacing of rollers of the strand guide. 
     
     
         5 . The method as claimed in  claim 1 , wherein
 frequencies of the variations of the casting level in a first frequency range are detected and the variations are offset by means of cyclic opposing movements of the inflow unit, further frequencies of the variations of the casting level in a second frequency range are detected and the variations are offset by means of 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,   a first observer is provided which determines a first compensation value (k) for a target position of the inflow unit on the basis of frequencies of the first frequency range, and   a second observer is provided which determines a second compensation value (k′) for a target value (SET) of the roller spacing of the rollers of the strand guide on the basis of frequencies of the second frequency range, wherein the actual value (ACT) of the roller spacing is used as one of the input variables for this second observer.   
     
     
         6 . 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 variations of the casting level, which is connected to a control unit,
 wherein an adjustment device connected to the control unit is provided, which is designed to reduce, in particular offset, variations of the casting level by cyclic change, opposing the variations of the casting level, of the roller spacing of opposing rollers of the strand guide, and wherein the control unit comprises at least one observer which is designed in such a way that, based on frequencies of the variations of the casting level, a compensation value (k′) for a target value (SET) of the roller spacing of the rollers is determined and the actual value (ACT) of the roller spacing is used as one of the input variables for this observer, in order to compensate for a phase shift and/or amplitude of the actual value (ACT) of the roller spacing.   
     
     
         7 . The device as claimed in  claim 6 , wherein the adjustment device is designed for cyclic changes of the roller spacing in a frequency range up to greater than or equal to 0.6 Hz, preferably up to 5 Hz. 
     
     
         8 . The device as claimed in  claim 6 , wherein multiple roller segments each having one or more rollers are arranged on both sides along the strand guide, wherein at least the inner roller segment located closest to the mold is pivotable normally in relation to the strand guide direction by means of the adjustment device about the axis of rotation of a roller of this roller segment located closest to the mold.