WO2014177605A1

WO2014177605A1 - Method and device for controlling the molten metal level in an ingot mold

Info

Publication number: WO2014177605A1
Application number: PCT/EP2014/058802
Authority: WO
Inventors: Heinz-Dieter RUMPLER; Robert ZIRKL; Silvio Cecchini; Andreas DISSAUER
Original assignee: Tbr Casting Technologies Gmbh
Priority date: 2013-05-03
Filing date: 2014-04-30
Publication date: 2014-11-06
Also published as: AT514734A1; EP2991788A1; EP2991788B1

Abstract

The signal obtained by measuring a mold level (5) is analyzed, the occurrence of irregular strand bulges (8) is recognized and the stopper rod movement is boosted and adapted by adding an additional control algorithm to the mold level controller (10) such that the variations of the mold level (5) about the target level can be maintained in a predetermined range of ± 1.0 to ± 3.0 mm.

Description

Method and device for regulating the

Liquid metal mirror in a mold

DESCRIPTION

State of the art

The invention relates to a method for controlling the liquid metal level in a mold, in particular a continuous casting mold, according to the preamble of claim 1. Furthermore, the invention relates to an apparatus for carrying out the method according to the invention.

It is known that in the continuous casting of steels, the level of the mold level in a mold must be kept as constant as possible and variations in the level of the mold level must be avoided to ensure uniform shell growth and the occurrence of strand defects, such as overlaps, inclusions of mold powder, formation of To avoid cracks, etc.

This is generally achieved by a mounted over a spout opening in the manifold or intermediate vessel, vertically movable plug or horizontally movable slide, by the position of the flow rate of the liquid metal is controlled in the mold, and for the adjusting mechanism, the Gießspiegelmessvorrichtung depending on the deviation of Gießspiegels from the setpoint signal. With undisturbed casting and a constant withdrawal speed of the strand from the mold only minor interventions are required, so that a slight fluctuation of the casting mirror occurs around the target position, which is corrected by slight corrections of the stopper (slide) position. In this case, the level of the pouring mirror typically varies ± 1, 5mm to 3mm around the target position, with the disturbances within one Time frame of 0.3sec. to 1, 5sec. can be compensated. However, it can also lead to disturbances in the casting operation, through which the tolerable deviation of the Gießspiegelniveaus is exceeded by the target value and to which the Gießspiegelregelung must respond.

Within the normal casting operation, this includes: changing the casting speed

Wear of plug and spout

Narrowing of the spout opening by deposition

Inclusions known as "clogging"

A change in the casting speed represents a one-time event, which leads to a one-time exceeding the allowable fluctuation range of the Gießspiegel level to the desired position and which is compensated by the Gießspiegelregelung with some minor Nachschwankungen.

A wear of the plug or spout opening leads to a larger flow rate and would result in an increase of the casting level at a constant withdrawal speed. However, such wear ß occurs rather slowly compared to the intervention times of the scheme, so that this effect is generally adjusted continuously without any visible effect on the level of the casting mirror.

A narrowing of the spout opening due to "clogging" also does not occur suddenly and is compensated by the mold level control while maintaining the take-off speed by lifting the plug (or opening the spool) the set withdrawal speed of the strand can no longer be maintained. Then the casting speed has to be reduced or in extreme cases the casting process has to be stopped.

In addition to the above disturbances larger Gießspiegelschwankungen can be effected by so-called strand outbookings, known as a "bulging" effect.

Strand bulging occurs in particular during casting of so-called slab formats due to the effect of ferrostatic pressure on the strand shell at locations where it is not supported, ie immediately after exit from the mold and between the strand guide rolls or support rolls.

The effect of strand bulges, also called strand pumps, on the casting mirror can be illustrated as follows: If, with a uniform take-off speed of the strand from the mold, bulging and widening of the liquid portion of the casting cross-section initially occurs, the casting level would be uniform if metal is fed into the mold decline. If this strand position then returns to the area of a support roll, the solidified strand shell is compressed, whereby an increase in the casting level would be effected. With constant casting speed, constant ferrostatic pressure and constant casting temperature, these two effects compensate each other and there is no influence on the pouring level. One speaks here of a uniform bulge or in the jargon of "steady bulging." Critical is the effect of irregular strand bulges or "unsteady bulging". Here, the volume of the liquid metal within the solidified strand shell changes with uneven strand shell growth. When the convex part of the strand shell is between the support rollers, the mold level sinks as it rises as the concave part passes through the area of the support rollers. Basically, the thinner the strand shell is on exit from the mold or at the beginning of the secondary cooling zone, the more pronounced the effect of strand bulking. This means that a high casting speed and low secondary cooling, apart from the properties of the casting powder used, promote strand bulging. The induced by the irregular Strandausbauchungen Gießspiegelschwankungen have compared to the usual control fluctuations a long period and are in a time frame of 2.5 seconds. to 25 sec. This period is too long to change from the standard controller operating to periods of 0.3sec. to 1, 5sec. is set, recorded and corrected. On the contrary, there is a risk that the system will rocket. Remedy, however, can then be achieved only by switching off the control and restart with modified control parameters or manual operation, which can not be described as a proper control process.

In the relevant literature, the above-mentioned disorders are described, in particular by indirect measuring methods on the occurrence of strand bulges, also referred to as strand pumps, should be closed. Essentially, in these known methods, the measurement of the drive currents of the drive rollers of the trigger mechanism or a measurement of the strand bulge between the strand guide rollers or the measurement of the pressure exerted by the strand shell on the support rollers pressure, methods which sometimes use additional measuring devices, an occurrence of extrusion pumping indirectly, without detecting the actual overshoot or undershoot. All of these methods therefore suffer from the problem of being unable to generate direct manipulated variables for outflow regulation. Disclosure of the invention

At this point, the present invention is based on the objective of automatically deducing the occurrence of strand bulges from the ongoing analysis of the fluctuations in the levels of the casting mirror detected by the casting level measurement without additional devices on the basis of the number and type of exceeding of defined limit values and their effect to avoid the pouring mirror by an adapted, the normal control process superimposed control algorithm.

This task should be done directly by an ongoing evaluation of the data associated with the Gießspiegelregelung Gießspiegelmessung without additional devices to be independent of design features of the system such as distance and arrangement of the support rollers but also operating conditions such as casting speed, secondary cooling, etc. and thus indirect measurement data.

For this purpose, the amplitude of the Gießschwankungenschwankungen is constantly monitored and overruns or falls below an allowable detection limit registered.

The inventively proposed procedure for the detection of irregularities caused by irregular strand bulges is the following:

In the interaction of measuring arrangement and inflow control, different measurement and control parameters are defined as follows. As the range for the detection limits for a positive and / or negative overshoot of the level of the pouring mirror, the amplitude of the allowable Gießspiegelschwankung is set to +1 mm to a maximum of + 6mm.

For example, with a Gießspiegelschwankung of ± 2mm to a fictitious setpoint, a detection threshold between ± 3mm and ± 6mm is selected. These values are therefore outside the normal stability during normal casting, where fluctuations of ± 2, Omm are normal. A non-periodic disturbance, such as a change in casting speed, may result in exceeding the above limit. However, the intervals of such disturbances are shorter than those caused by irregular strand bulges and the number of deviations is limited, so that they can be corrected by the standard Gießspiegelregelung in a short time.

In order to distinguish such disturbances from disturbances caused by irregular strand bulges, the following procedure is proposed according to the invention:

A fault counter is incremented from zero by the number one whenever the positive or negative detection limit is exceeded. Whenever a count is made, a wait time window with a run time of 1. 0sec. up to 3.0sec. open. A further disturbance count is only made if the wait time has expired and it occurs within a certain time window, which is indicative of the effect of irregular string bulges. This collection time frame within which a count is allowed is up to 30.0sec after the wait time.

The setting values of the counter for the detection of "bulging" can be selected with values between 5 and 10, whereby a value of 8 is preferentially selected.If a limit value is exceeded within the waiting time, then no disturbance counting takes place.This function is used to recognize Whether or not a limit value violation is caused by a non-periodic disturbance, in which the period of the oscillations is shorter than that caused by burst bulges, and only if another disturbance occurs up to 30 seconds after the expiry of the waiting time is it counted and the time slots for the waiting time and the acquisition time are reset and start to run again. At each fault count and expiration of the wait time, a deactivation time window is also opened whose period of time is equal to that of the acquisition time frame. If no further fault occurs within this period, all time windows and the fault counter are reset.

This means that no strand bulge was detected. However, if a fault occurs within the set period of time, on the one hand the timers are reset and on the other hand the fault is registered until the fault counter reaches the set value between 5 and 10. When the set number is reached, the counter is set to 0 (zero) and the time window is set to its initial position, ie also 0 (zero). Only after registering a new fault, the time windows are reactivated and the counting process begins again.

The present invention is therefore a method by which increased Gießschwankungenschwankungen attributed to irregular strand bulges ("unsteady bulging") are clearly recognized as such without the use of additional measuring equipment and against other Gießspiegelschwankungen, as for example by a change in the Characteristic features are the acquisition and registration of additional parameters from the existing measurement and control system such as a fault count, by each of which a first following disturbance, the one, within the limits of detects a positive or negative overshoot detection limit set at least ± 3mm to within ± 6mm of the target level of the water level, then increments by 1 if and after a waiting time selected in the range of 1, 0sec to 3.0sec and before expiration of a starting after the end of the waiting time selectable detection period to 30,0sec. a renewed disturbance is registered, whereby counting the disturbance, the waiting period and detection period start to restart and the disturbance counter starts is always reset when a preselectable number between 5 and 10 disturbances, preferably reached 8, or since the last count after the expiry of the waiting time a time of 30.0 seconds has elapsed and in consequence an intervention in the inflow control by connecting a additional control algorithm is triggered, which is characterized in that in a slowly rising Gießspiegelstörung with a comparison with the default increased backlash reaction, wherein in the control system an asymmetric control algorithm is used to preclude a rocking of the system plug position - Gießspiegel.

In the application of the additional control parameters and active active detection of Gießspiegelstörungen following states are possible: The controller settings are correct and by

Detection system will not detect unacceptable bilge disturbances due to irregular strand bulge - no further action

> It will be for the first time or still inadmissible

Disturbances registered, which are returned by the detection system to irregular Strandausbauchungen, so there is automatically a reaction in the sense of an increased response in terms of plug control.

> The pouring level becomes unstable, which suggests

that the reaction of the Gießspiegelreglung is excessive with respect to the plug control, so there is an automatic weakening so retraction of the reaction of the plug control. In the inventive combination of detection system and automatic control or adaptation of the control algorithm of plug control thus succeeds to reduce the effects of irregular Strandausbauchungen ("unsteady bulding") to the level of the casting mirror in the continuous casting mold so far that the casting level within the proposed process-typical fluctuation of ± 2 mm without external intervention.

The invention will be explained below with reference to FIGS. 1 to 6, which illustrate the principles of the present invention.

Fig. 1 shows schematically the structure of a continuous slab caster. From a distribution vessel, not shown, the liquid steel 1 passes through a spout opening 2 with dip tube in the continuous casting mold 3, wherein the metal inflow is controlled by a plug 4 so that the casting level 5 approximately in accordance with the withdrawal speed V caused by the driver rollers not shown here is kept constant. Furthermore, FIG. 1 shows the guided by support rollers 6 strand, which is formed in this area of the fixed strand shell 7 and the existing of liquid steel 1 core.

As shown, the growth of the initial strand shell is not uniform, but may be different depending on the contact with the mold wall, the effect of the secondary cooling, etc.

2 shows the appearance of so-called regular bulges 8, which are caused by the ferrostatic pressure, in the regions where strand support is absent, bulges 8 occur, which then extend in the region of the support rollers 6 The effects of these regular bulges 8 and the subsequent back-compression compensate each other and therefore have no influence on the level of the casting mirror 5. 3 schematically shows the influence of irregular (stranded) bulges 8 on the level of the casting mirror 5. Irregular bulges 8 are characterized in that the maxima of the bulges 8 can be of different heights and also their positions This can lead to volume changes in the liquid metal sump and to an influence on the level of the casting mirror 5, which is not compensated by a casting level control which is also indicated by the arrow, standard settings can be.

FIG. 4 schematically illustrates the behavior of the casting mirror 5 over time when irregular bulges 8 occur using the measurement and control method according to the invention. In the normal, undisturbed casting operation, the standard controller keeps the level of the pouring mirror 5 within a range of ± 1 mm to ± 3 mm. In the event of irregular bulges 8, the standard controller can not control the pouring mirror fluctuations, so that they build up and ultimately exceed the upper and / or lower detection limit.

If such overflows / underflows occur twice or more within a selectable detection period of up to 30.0 seconds after a lapse of a waiting period of time, this is evidence of the occurrence of irregular bulges 8 and the higher order control algorithm is activated. As a result, the stronger Gießspiegelschwankungen caused by the bulges 8 are compensated and the casting level 5 can be maintained within a desired fluctuation range of ± 1 mm to ± 3mm.

Fig. 5 summarizes the basics of the invention detection of irregular bulges 8 from the behavior of the Cast Mirrors 5. The requirement for registration as an irregular bulge 8 is that the level of the pouring mirror 5 is between 5 times and 10 times, typically 8 times the set detection or detection limits, each within a selected detection time frame of up to 30.0 seconds after a waiting time of 1, 0sec- 3.0sec. exceeds.

If the acquisition time frame (EZ) is fully utilized after the waiting time (WZ) without another fault being registered, deactivation takes place. Reset all time frames. If the preselected number of faults reaches from 5 to 10, preferably 8, then the fault counter and all time frames are reset to 0 (zero) and the count of any exceedances starts again with the number 1 with simultaneous activation of the time window for waiting time and detection time, respectively deactivation.

FIG. 6 shows a block diagram of how the adaptation according to the invention of the controller software of a mold level control 10 and of a control algorithm 1 according to the invention adapted to leveling irregularities caused by irregular bulges 8 are compensated. The signal coming from the mold level gauge 9 is analyzed in the "Bulging" detection block 12, as shown in Fig. 4 and Fig. 5. If no disturbance is detected, the controller continues to operate in the standard pouring mode mode If the occurrence of "bulging" can be recognized, the control algorithm 1 1 is changed to an increased intervention, so that these stronger and occurring at longer intervals disturbances are compensated by appropriate influence on the position of the plug 4.

Claims

1 . Method for controlling a level of a casting level (5) in a mold (3) which is constant within a permissible range, from which the metal strand formed by means of an electrically or hydraulically actuated strand extraction device by rollers (6) adjoining the mold (3) at approximately constant speed (V), by controlling the supply of metal from a distributor or tundish by means of a plug or slide control, which receives its actuating signal from a Gießspiegelmesseinrichtung (9), characterized in that on the one hand by analyzing the Gießspiegelmesseinrichtung (9) continuously registered variations of Level of the pouring mirror (5) on the occurrence of irregular strand bulges (8) is closed and on the other hand their influence on the level of the casting level (5) automatically by adjusting a control algorithm (1 1) for the stopper or slide control of the metal inflow into theMold (3) is regulated.

2. The method according to claim 1, characterized in that one of the Gießspiegelmesseinrichtung (9) more than simple alternating and cyclic exceeding or falling below the limits of an allowable bandwidth of at most ± 6mm of the level of the Gießspiegel (5) within a selectable period of from to 30,0sec. after expiry of a waiting time of 1, 0sec following each registered fault. up to 3.0sec. is evaluated as an indication of the occurrence of strand bulges (8) and an additional algorithm for conventional inflow control is activated, that the cycle of impermissible Überbzw. Underrunning of the bandwidth of the level of the casting mirror (5) by an asymmetric countermovement of the position of a plug (4) or slide in the distribution vessel in the sense of less metal supply in excess, more inflow to below and in that corresponding adaptation of the metal feed into the mold (3) is compensated for so far that the pouring mirror (5) is held within the predetermined range of at most ± 3.0 mm, whereby the asymmetry of the movement of the plug (4) or slider is controlled in that a superposition of the frequency of the fluctuation of the casting mirror (5) with the frequency of the control of the stopper (4) or slider is avoided.

3. The method according to claim 1 or 2, characterized in that by an additional algorithm for keeping constant the pouring mirror (5) caused greater fluctuations in the position of the plug (4) or slider as an indicator of the occurrence and the extent of strand bulges (8 ) and registered.

4. The method according to any one of claims 1 to 3, characterized in that a one-time exceeding or falling below the permissible bandwidth of the pouring mirror (5) is not regarded as an indication of strand bulge (8) and thus no additional algorithm for conventional inflow control is activated ,

5. The method according to any one of claims 1 to 3, characterized in that a multiple non-cyclical exceeding or falling below the allowable bandwidth of the pouring mirror (5) is not regarded as an indication of the occurrence of strand bulges (8) and thus no additional algorithm for conventional inflow control is activated.

6. The method according to claims 1 to 5, characterized in that the permissible bandwidth of the fluctuation of the casting mirror (5) ± 2mm.

7. The method according to any one of claims 1 to 6, characterized in that one or more overruns or falls below the allowable bandwidth only as a sign of irregular strand bulge (8) are counted by the fault counter, if after a fault after a waiting time of 1, 0sec. up to 3.0sec. and before expiration of a subsequent acquisition time of up to 30.0sec. a renewed disturbance is registered, wherein the waiting and detection time begin to restart and the disturbance counter is reset when a preselectable disturbance number between five and ten is reached and / or since the last disturbance a deactivation time frame corresponding to the detection time of up to 30.0 Seconds after the waiting time has elapsed.

8. The method according to claim 7, characterized in that preferably a waiting time of 1, 5sec. and a subsequent acquisition time of 20.0sec. and the disable time period corresponding to the detection period and the maximum reset number causing the reset are set to eight.

9. A device comprising a Gießspiegelregelung (10), which operates according to a method according to one of claims 1 to 8.