EP2762251B1 - Method and device for casting a strand - Google Patents

Description

The invention relates to a method and apparatus for casting a strand having a width b and a thickness d, wherein liquid metal in an intermediate container having a drain opening for flowing off the liquid metal with a flow rate V through a pouring tube into a continuous casting mold for casting the strand with a predetermined casting speed v _{cast is} provided. The volume flow V of liquid metal in the pouring tube is measured as actual value V _actual by means of a flow sensor. The Gießspiegelhöhe h of the liquid metal in the continuous casting mold is detected as the actual value H _IST by Gießspiegelmesseinrichtung. The Gießspiegelhöhe h and the volume flow V of the liquid metal are by means of a control device in accordance with the measured actual values h _IST , V̇ _Is to predetermined target values h _SOLL , V _target controlled by driving a closure element, which is arranged at the outlet opening of the intermediate container or in the pouring tube ,

State of the art

In the continuous casting of metals in a continuous caster, the width b of the strand is controlled with adjustable narrow sides. Around Secondary cooling, ie below the continuous casting mold, the strand is guided by means of rollers arranged parallel to the broad side of the strand. This ensures the thickness d of the strand. The narrow sides of the strand have no support in the area below the mold. As a result of the ferrostatic pressure, the strand thus spreads and bulges in the region below the mold in the width direction, ie transversely to the casting direction. The width of the strand can reach several percent of the nominal width.

In the articles " Numerical Simulation of Slab Broadening in Continuous Casting of Steel ", Intech, Chapter 23, 2012 and " Effect of Casting Speed on Slab Broadening in Continuous Casting, "Steel Research Int. 82, No. 11, 2011 by Jian-Xun Fu and Wenig-Sing Hwang Numerical simulations are performed which simulate the continuous casting process in relation to the unwanted spreading of the strand. Results or suggestions for avoiding the spread are, for example, an increase in the continuous casting speed, lower secondary cooling or an increase in the hardness of the steel to be processed. These proposals are usually undesirable in practice, since just soft steel grades are to be processed.

The Japanese Patent Application JP S 61232049 discloses a method for adjusting the width of a continuous casting mold. Specifically, the desired width of the mold, the changes in the mold width at the beginning and at the end of a continuous casting process and the casting speed are entered as parameters in a computing unit, which calculates suitable manipulated variables for adjusting the mold width from these input parameters. As a result, a high-speed casting is possible, in which the variations of the mold width are reduced, even if otherwise the mold width fluctuates greatly during continuous casting.

Furthermore, solutions based on mechanical edge buttons are known; see "Measuring systems for billets and slabs" Brochure published by LAP GmbH, Laserapplikationen, Zeppelinstraße 23, 21337 Lüneburg, Germany. Disadvantages of such systems include mechanical play and the required maintenance of the moving components in an extremely heat-stressed zone.

Furthermore, optical systems, such as laser triangulation (eg LAP laser, LIMAB (SlabProfiler)), for the optical width measurement of the strand are known. Such laser-based measuring systems are used behind the flame cutting machines in a continuous casting plant, since the high material temperature prevents earlier measurement.

In these known systems for measuring the width of the strand, such as the laser measurement, the distance from Kokillenaustritt where the control of the strand width is made and the point at which the optical measuring systems are installed more than 20 meters. This results in a very large dead time for controlling the strand width. This can result in a qualitative downgrade of the cast product.

In the pamphlets DE 10 2009 057 861 and WO2012 / 168005 Devices and methods for measuring the flow of liquid metal are described with a sensor to keep the level of the casting mirror in the continuous casting mold largely constant by means of a regulation and thus to improve the product quality of a strand to be cast.

The object of the invention is to optimize in a known method and a known device for casting a strand, the adjustment of the width of the strand to the effect that an early detection of the spreading of the strand takes place in order to achieve an immediate control of the width of the strand to be cast in order to improve the quality of the product with respect to the precision of the final dimensions of the strand. It is another object of the invention to use existing components of a continuous casting, in particular existing measuring means to save costs.

This object is achieved by the method according to claim 1.

The method is characterized in that a width correction .DELTA.b as a function of a determined volume flow control difference from the measured actual value V̇ _Ist and the predetermined desired value V̇ _{soll of} the volume flow V̇ under Considering the thickness d of the strand to be cast and the casting speed v _{cast is} calculated in a first controller. Subsequently, the calculated width correction .DELTA.b as the first manipulated variable u ₁ (t) to a first actuator for adjusting output of at least one narrow side of the casting mold, so that changing the width b of the article to be cast strand takes place. A height change .DELTA.h of the Gießspiegelhöhe h is calculated as a function of the width correction .DELTA.b and output to a setpoint / actual value comparator of a second control loop. A Gießspiegelhöhenregeldifferenz e ₂ (t) is determined from the measured actual value h _IST , the predetermined setpoint h _SOLL and the calculated height change .DELTA.h the Gießspiegelhöhe h and fed as input to a second controller of the second control loop for controlling the Gießspiegelhöhe h. The volume flow V̇ is controlled taking into account the changed Gießspiegelhöhe h by driving the closure element .

That according to claim 1, a width correction .DELTA.b as a function of a determined volumetric flow control difference from the measured actual value V̇ _{Is t} and a predetermined desired value V̇ _target the volumetric flow V̇ is calculated taking into account the thickness d of the strand to be cast and the casting speed v _cast in a first controller results the advantage that an online calculation is possible.

Advantageously, the calculated width correction .DELTA.b u is ₁ in the form of the manipulated variable (t) to a first actuator for adjusting output of at least one narrow side of the casting mold, so that changing the width b of the article to be cast strand takes place. Due to the fast calculation of the width correction Δb without deadlocking of the system, the width of the strand to be cast undergoes an immediate correction and rejects are avoided. Advantageously, a rapid reaction, so regulation, to the unwanted spreading of the strand to be cast and the current casting width of the continuous casting mold is adjusted.

Advantageously, a height change .DELTA.h of the Gießspiegelhöhe h is calculated as a function of the width correction Δb, which is output to a setpoint / actual value comparator of a second control loop. Advantageously, a Gießspiegelhöhenregeldifferenz e ₂ (t) from the measured actual value h _IST , the predetermined setpoint h _SOLL and the calculated height change .DELTA.h the Gießspiegelhöhe h is determined as input for a second controller of the second control loop for controlling the Gießspiegelhöhe. The changing Gießspiegelhöhe h is corrected in the inner loop promptly.

The fact that the volume flow V̇ is controlled by controlling the closure element taking into account the changed Gießspiegelhöhe , there is the advantage that adjusts the flow on the current casting width and the Gießspiegelhöhe h is kept substantially constant, so that the product quality remains stable.

According to a first embodiment, the desired value V̇ _{soll of} the volume flow V̇ is dependent on the casting speed v _cast , the width b and the thickness d of the strand to be cast (V̇S _oll = v _cast * b * d). Advantageously, this results in a relationship between the volume flow and the width of the strand to be cast.

Characterized in that a volumetric flow control difference e ₁ (t) from the measured actual value V̇ _Ist and the setpoint V̇ _{setpoint of} the volumetric flow V̇ is used as an input variable for the first controller in a first control loop and the width correction Δb is as follows: Δb = e ₁ (t) * 1 / (v _cast * d) is calculated, there is the advantage that the actual width of the strand to be cast does not have to be measured with a complicated additional measuring device and advantageously is not subject to dead-time.

Advantageously, the height change Δh of the casting-mirror height h is calculated as follows: Δh = Δb / b * h _SOLL
This results in the advantage that the height control in the inner second control loop is faster and more accurate.

The above object is further achieved by the claimed device according to claims 6 to 12. The advantages of these solutions correspond to the advantages mentioned above with respect to the method.

Further advantageous embodiments of the device and the method of the invention are specified in the dependent claims.

Figur 1

schematisch eine Stranggießanlage und

Figur 2

ein Regelschema

zeigt.The description is a total of two figures attached, wherein

FIG. 1

schematically a continuous casting and

FIG. 2

a rule scheme

shows.

The device according to the invention and the method according to the invention are described in detail below with reference to the figures.

In FIG. 1 For example, a continuous caster 100 for pouring liquid metal 200 with a controller 300 is shown. The liquid metal 200, ie the melt, is provided in an intermediate container 140 with a discharge opening 130. The drainage opening 130 is preferably closed with a closure element 120 that is adjustable. The closure element 120 is actuated by the regulating device 300 for opening or closing the outflow opening 130 of the intermediate container 140. The closure element 120 is preferably designed as a stopper rod or as a slide and is movable. Thus, the outflow of the liquid metal 200 out of the intermediate container 140 is regulated through a subsequent pouring tube 150 into a continuous casting mold 160. With a flow sensor 440, in particular a Lorentz force anemometer, a volume flow V̇ of liquid metal 200 in the pouring tube 150 is measured and detected as the actual value of the volume flow V̇ _Ist . The continuous casting mold 160 with broad sides and adjustable narrow sides 170 receives the liquid metal 200. In the continuous casting mold 160, the liquid metal 200 forms a casting mirror 210, which has a casting level height h in the continuous casting mold 160. The casting-mirror height h in the continuous casting mold 160 is kept substantially constant with the aid of the regulating device 300 in order to ensure a required product quality. In a known manner, a strand 190 is subsequently produced from the liquid metal 200. The broad sides of the continuous casting mold 160 give the thickness d and the adjustable narrow sides 170 the width b of the strand 190 to be cast. Around Secondary cooling, ie below the continuous casting mold 160, the strand 190 is guided and supported by means of parallel to the broad side of the strand 190 arranged continuous casting 180. Due to these continuous casting rolls 180, the predetermined thickness d of the strand 190 is ensured below the mold.

Such guidance and support is not given on the narrow sides of the strand 190 in the secondary cooling. As a result of the ferrostatic pressure, the strand 190 spreads and bulges in this area in the width direction, ie transversely to the casting direction, and an unwanted spreading of the strand 190 to be cast arises. This occurs in particular for soft steel grades. The spread of the strand 190 can reach several percent of the nominal width b and adversely affects the final product dimension and thus the product quality.

The control according to the invention counteracts this spread.

The control device 300 regulates the volume flow V̇ of liquid metal 200 by outputting corresponding manipulated variables u ₁ (t), u ₂ (t) as actuating signals to the respective actuators 420, 520. In particular, the control device 300 receives as input variables an actual value of the volume flow V̇ _Ist , which is detected by the flow sensor 440, an actual value of the casting mirror height h _IST , which is detected by a Gießspiegelmesseinrichtung 540, and target values of the volume flow V̇ _Soll and the Gießspiegelhöhe h _should from a superior level for monitoring or regulating the casting process. Other variables that are processed by the control device 300 are the width b and thickness d of the strand 190 to be cast and the casting speed v _cast . The control device 300 outputs a first manipulated variable u ₁ (t) to the first actuator 420, preferably a hydraulic cylinder or a Spindle drive to adjust the at least one narrow side 170 of the continuous casting mold 160. A second manipulated variable u ₂ (t) is output from the control device 300 to the second actuator 520 in order to adjust the position of the closure element 120 of the intermediate container 140 and thus to regulate the volume flow through the outflow opening 130.

In FIG. 2 a control scheme of the control device 300 is shown. The control scheme comprises two control loops, which act together as a cascade control. The control variable of a first control loop 400 is the volume flow V̇ of liquid metal 200. The control variable of a second control loop 500 is the casting level h of the liquid metal 200 in the continuous casting mold 160. The second control loop 500 is the inner loop of the cascade control.

For the controlled variable to be controlled primarily, the volume flow V̇ to liquid metal 200, a target value V̇ _{target is} specified by a higher level and performed on a first setpoint / actual value comparator 450 of the first control loop 400. This desired value V̇ _target is dependent on the casting speed v _cast , the width b and the thickness d of the strand 190 according to the following law: V̇ _target = v _cast * b * d. The actual value of the volume flow V̇ _Ist of liquid metal 200 detected by the flow sensor 440 is likewise given to the first setpoint / actual value comparator 450 of the first control loop 400. From the measured actual value V̇ _actual and the predetermined nominal value V̇ _{target of} the volume flow, a volumetric flow control difference e ₁ (t) results as an input variable for a first controller 410 in the first control loop 400. This first controller 410 calculates the latitudinal correction Δb = e ₁ (t) * 1 / (v _cast * d) as manipulated variable u ₁ (t) for the first actuator 420. The first actuator 420 causes the at least one narrow side 170 the continuous casting mold 160 is adjusted on the basis of the calculated width correction .DELTA.b. This correction of the width of the continuous casting mold 160 counteracts the unwanted spreading of the strand 190 to be cast. For example, the narrow sides 170 of the continuous casting mold 160 are set narrower if the actual value of the volume flow V̇ _{Ist is} greater than the setpoint value of the volume flow V̇ _Soll and vice versa.

The adjustment of the at least one narrow side 170 of the continuous casting mold 160 causes a height change .DELTA.h = .DELTA.b / b * h of Gießspiegelhöhe h of the liquid metal 200 in the continuous casting mold 160th This height change .DELTA.h, a predetermined target value of the Gießspiegelhöhe h _SOLL and a detected actual value of the Gießspiegelhöhe h _iS are passed to a second desired-actual value comparator (550) the second control circuit 500, which of these variables, a Gießspiegelhöhenegeldifferenz e ₂ (t) = H _SOLL - forms .DELTA.h that is to pass as an input to a second controller 510 - _H , The second controller 510 calculates a second manipulated variable u ₂ (t) for the second actuator 520, which adjusts the position of the closure element 120, whereupon the volume flow V̇ is regulated .

Due to the adjustment of the narrow sides 170 results in a change in the Gießspiegelhöhe h of the liquid metal 200. The actual value of Gießspiegelhöhe h _IST is detected and the inner loop, so the second control loop 500, controls the Gießspiegelhöhe h to the predetermined setpoint h _SOLL .

LIST OF REFERENCE NUMBERS

100

continuous casting plant

120

closure element

130

drain opening

140

intermediate container

150

casting tube

160

continuous casting

170

narrow side

180

continuous casting

190

strand

200

liquid metal (melt)

210

meniscus

300

control device

400

first control loop

410

first controller

420

first actuator

430

first controlled system

440

Flow Sensor

450

first setpoint / actual value comparator

500

second control loop

510

second controller

520

second actuator

530

second controlled system

540

Gießspiegelmesseinrichtung

550

second setpoint / actual value comparator

V

Volume flow of liquid metal

V̇ _Soll

Setpoint of the volumetric flow

V̇ _is

Actual value of the volume flow

H

casting level

h _SHOULD

Target value of the casting level height

h _IS

Actual value of the pouring height

.delta.h

Height change of the pouring mirror

d

thickness

b

width

.DELTA.b

width correction

V _cast

casting speed

e ₁ (t)

Flow control difference

u ₁ (t)

first manipulated variable

e ₂ (t)

Gießspiegelhöhenregeldifferenz

u ₂ (t)

second manipulated variable

Claims (12)

1. Method of casting a strip (190) with a width b and a thickness d, comprising the following steps:

   providing liquid metal (200) in a tundish (140) with an outflow opening (130) for the outflow of the liquid metal (200) at a volume flow V̇ through a pouring spout (150) into a continuous casting mould (160) for the casting of the strip (190) at a predetermined casting speed v_cast,

   measuring the volume flow V̇ of liquid metal (200) in the pouring spout (150) as actual value V̇_Ist by means of a throughflow sensor (44);

   detecting the casting meniscus height h of the liquid metal (200) in the continuous casting mould (16) as actual value h_IST by means of a casting meniscus measuring device (540); and

   regulating the casting meniscus height h and the volume flow V̇ of the liquid metal (200) by means of a regulating device (300) in accordance with the measured actual values h_ist, V̇_Ist to predetermined target values h_SOLL, V̇_Soll by activating a closure element (120), which is arranged at the outflow opening (130) of the tundish (140) or in the pouring spout (150);

   characterised by

   calculation in a first regulator (410) of a width correction Δb in dependence on a determined volume flow regulating difference e₁(t) from the measured actual value V̇_Ist and the predetermined target value V̇_Soll with consideration of the thickness d of the strip (190) to be cast and the casting speed v_cast;

   issue of the calculated width correction Δb in the form of a setting variable u₁(t) to a first setting element (420) for adjusting at least one narrow side (170) of the continuous casting mould (16) so that a change in the width b of the strip (190) to be cast takes place;

   calculation of a height change Δh of the casting meniscus height h in dependence on the width correction Δb for issue to a second target-value/actual-value value comparator (550) of a second regulating circuit (500);

   determining a casting meniscus height regulating difference e₂(t) from the measured actual value h_IST, the predetermined target value h_SOLL and the calculated height change Δh of the casting meniscus height h as input variable for a second regulator (510) of the second regulating circuit (500) for regulating the casting meniscus height h; and

   regulating the volume flow V̇ with consideration of the changed casting meniscus height h by activating the closure element (120).
2. Method according to claim 1, characterised in that the target value V̇_Soll of the volume flow V̇ is dependent on the casting speed v_cast, the width b and the thickness d of the strip to be cast in accordance with the following law: V̇_Soll = v_cast * b * d.
3. Method according to one of the preceding claims, characterised in that the volume flow regulating difference e1(t) of the measured actual value V̇_Ist and the predetermined target value V̇_Soll of the volume flow V is used as input variable for the first regulator (410) in a first regulating circuit (400).
4. Method according to any one of the preceding claims, characterised in that the width correction Δb is calculated as follows: Δb = e₁(t) * 1/(v_cast * d).
5. Method according to any one of the preceding claims, characterised in that the height change Δh of the casting meniscus height h is calculated as follows: Δh = Δb / b * h_SOLL.
6. Device (100) for casting a strip (190) with a width b and a thickness d, for carrying out the claimed method according to any one of claims 1 to 5, comprising:

   a tundish (10) for providing liquid metal (200), the tundish having an outflow opening (130) for the outflow of the liquid metal (200) at a volume flow V̇ through a pouring spout (150) into a continuous casting mould (160) for the casting of the strip (190) at a predetermined casting speed v_cast;

   a closure element (120) at the outflow opening (130) of the tundish (140) or in the pouring spout (150) for influencing the volume flow V̇ of liquid metal (200);

   a throughflow sensor (440) for measuring the volume flow V̇ of liquid metal (200) in the pouring spout (150) as actual value V̇_Ist;

   a casting meniscus measuring device (540) for detecting the casting meniscus height h of the liquid metal (200) in the continuous casting mould (16) as actual value h_IST; and

   a regulating device (300) for regulating the casting meniscus height h and the volume flow V of the liquid metal (200) in accordance with the measured actual values h_ist, V̇_Ist to predetermined target values h_SOLL, V̇_Soll by activating the closure element (120);

   characterised in that

   a first regulator (410) in the regulating device (300) is constructed for calculating a width correction Δb of the width b of the strip (190) to be cast and for calculating a height change Δh of the casting meniscus height h in dependence on the width correction Δb;

   a first setting element (420) is constructed for adjusting at least one narrow side (170) of the continuous casting mould (160) in response to the width correction Δb in the form of the setting variable u₁(t), wherein a change in the width b of the strip (190) to be cast takes place;

   a second regulator (510) in the regulating device (300)' is constructed for regulating the casting meniscus height h with consideration of the calculated height change Δh; and

   the closure element (120) for regulating the volume flow V̇ is activatable in response to the changed casting meniscus height h.
7. Device according to claim 6, characterised in that the first setting element (420) is constructed in the form of a hydraulic cylinder or a spindle drive.
8. Device according to one of claims 6 and 7, characterised in that the closure element (120) is constructed as a stopper rod or as a slide.
9. Device according to claim 8, characterised in that the stopper rod is arranged to be vertically movable above the outflow opening (130).
10. Device according to claim 8, characterised in that the slide is arranged below the outflow opening (130) of the tundish (140) to be horizontally movable for closing the outflow opening (130).
11. Device according to any one of claims 6 to 10, characterised in that the throughflow sensor (440) is constructed as a Lorentz anemometer.
12. Device according to any one of claims 6 to 11, characterised in that the regulating device (300) can be constructed with at least two regulating circuits (400, 500), which are arranged in cascade form.

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