EP1066898A1 - Process and system for feeding molten metal in a continuous casting machine - Google Patents

Abstract

Initial temperature of melt in the distributor (302) is measured at a first casting speed. The first heat loss rate is measured from melt in the distributor, and also during its residence time between distributor and the casting level in the casting mold. An equivalent liquidus temperature T'liq + 0 is determined as the limiting temperature which will be reached, taking into account the initial liquidus temperature Tliq of melt already in the casting region of the mold, and the given casting speed. Isotherms of the equivalent liquidus temperature T'liq + x are determined as a function of superheating temperatures x, with x greater than zero, the isotherms each relating melting temperatures in the distributor and casting speeds. The initial continuous casting speed is matched to a desired continuous casting speed inside a given window of isotherms, with the lowest boundary lying above the equivalent liquidus temperature curve T'liq + 0. An Independent claim is included for the corresponding casting system.

Description

The invention relates to a method for _guiding the melt in a continuous casting machine, the melt of a specific alloy having a liquidus temperature T _{liq being} poured into a casting mold via a distributor and the strand which has solidified within the casting mold being drawn off, and a system therefor. In addition, the invention relates to a continuous casting machine with a system according to the invention.

The continuous casting processes according to the conventional continuous casting process with one oscillating mold via thin slab casting, strip casting or 2-roll casting with the ever thinning solidification thickness of the Cast product with shorter solidification times and increasing casting speeds precise process control is necessary.

The object of the present invention is to provide a method and a system for To provide melt guidance in a continuous casting machine, with which one precise temperature and casting speed control for a reliable operation and in particular automated casting is possible.

This object is achieved by a method having the features of claim 1 and achieved a system with the features of claim 10. Advantageous further developments are described in the subclaims.

In particular, it is proposed according to the method that the actual temperature of the melt in the distributor is recorded at an actual casting speed, the temperature being measured discontinuously or continuously by means of suitable known temperature recording means, for example thermocouples or temperature sensors. The actual heat loss of the melt in the distributor and during its residence time between the distributor and the casting level in the casting mold, for example an oscillating mold, is determined by taking into account factors which are responsible for the heat loss. Knowing the liquidus temperature T _{liq of} the melt to be cast and the current heat loss, an equivalent liquidus temperature T * _liq (+ 0 ° C) is determined as the limit range for the temperature of the melt in the distributor, at which continuous casting defects occur in the mold. This means that the temperature of the melt in the distributor or the temperature curve is determined via the casting speed at which the melt solidifies in the casting mold at an undesirably early stage, ie in the casting level or in the area of the level. If the liquidus temperature is already reached in the mold level of the mold, there is a risk of bridging in the solidifying structure combined with a strand break through lack of slag lubrication or damaged strand surfaces. The steel temperature in the mold must be chosen so that there is no pre-solidification in the mold level and the mold powder is melted sufficiently to ensure good lubrication and insulation of the strand as it travels through the mold.

The isotherms for this are determined as a function of this limit temperature or the course of the limit, ie the equivalent liquidus temperature _curves T * _liq + x (° C) as a function of the superheating temperature x (° C) with x> 0, in each case as a function of the casting speed . In this way, a grid is created which, using the temperature of the melt in the distributor as a measure, allows a prediction of the temperature conditions in the mold by utilizing the ratio of the melt temperatures in the distributor and the mold via the overheating and the respective casting speed. There follows an adaptation of the actual continuous casting speed to a desired continuous casting speed or also a desired continuous casting speed range within a predetermined isothermal _window , the lowest limit of which runs above the equivalent liquidus temperature _curve T * _liq (+ 0 ° C). This ensures that, at no time, depending on the temperature of the melt in the distributor and the heat loss, the casting speed is used, which could lead to a break in the strand in the mold due to low temperatures.

Overall, the temperature of the melt in the distributor is used as a measure of the prediction the temperature conditions used in the mold. In this way the current temperature conditions in the mold can be predicted or indirectly within an "incubation period" and for adjustment an optimal casting speed or a casting speed range be used. The casting speed is therefore not directly dependent from the temperature of the melt in the mold, but indirectly above the manifold temperature is set.

With this prediction option, the method offers the possibility of an emerging, for example excessive cooling of the melt in the mold level of the mold, which is indicated by the determination of the equivalent T * _liq temperature in the distributor, which is based on the melt _temperature measurement in the distributor to react by a corresponding increase in the casting speed in order to avoid a casting defect in the mold in the form of surface defects on the cast product or a breakthrough. This relatively early recognizable problem or prediction of what is happening in the casting mold or mold becomes particularly clear with the help of a temperature measurement of the melt in the distributor and is based on the long residence time of the steel, for example 8 minutes in the distributor, which is sufficient time for a corresponding Change the casting speed there.

According to the method, data is "online" to achieve good process management be measured, the solidification process in the mold at one of these optimal casting speed and at the same time a reinforcement-free production and ensure good surface quality.

The invention makes it clear that with the detection of the melt temperature in the distributor by discontinuous and / or continuous measurement and by the qualitative "online" detection of the heat losses of the melt in the distributor and between the distributor and the casting mold, an optimal, breakdown-proof and possibly fully automatic melt guidance alone on the data of the melt _temperature in the distributor and the equivalent T * _liq temperature of the melt in the distributor, T * _liq. + 0 ° C and their isotherms +5 to + 20 ° C, preferably in a step interval of 5 ° C each, or the temperature profiles can be ensured via the casting speed to generate an isothermal window.

In order to achieve reliable casting, the casting speed is chosen so that the temperature of the melt in the distributor runs along or above the isotherms of the equivalent liquidus temperature _curve T * _liq + 5 ° C. The temperature of the melt in the distributor should preferably run along or below the isotherms of the equivalent liquidus temperature profile T * _liq + 20 ° C, particularly preferably below the isotherms of the equivalent liquidus temperature profile T * _liq + 15 ° C.

All in all, these determined equivalent liquidus temperature profiles T * _liq + 0 ° C or x ° C of a melt with given isothermal windows should be shown in a manifold temperature / casting speed diagram over the casting time of a melt and made visually visible. In this way, process monitoring is always possible. At the same time, it is proposed that influencing variables flow into this distributor temperature / casting speed diagram, which shifts the distributor temperature / casting speed diagram to higher or lower temperatures and thus changes dynamically. Special influencing variables and their effects are explained in the B figure description.

The residence time of the melt goes into the heat loss of the melt in the distributor in the distributor, the residence time of the melt in the distributor being dependent the casting performance, which in turn is determined by the casting width, the solidification thickness, the casting speed, the current distributor level and the Ratio of distributor surface to its volume or the distributor size, the decrease in the melt weight in the distributor depending on it Surface / volume ratio, the initial heating time of the distributor for setting the equilibrium temperature corresponding to the melt temperature as well as the isolation or the isolation status of the distributor and thus the Heat radiation from the distributor.

The system proposed according to the invention is used in a continuous casting machine with an oscillating stand mold or traveling mold, also in Continuous casting machines with a casting mold that acts as a 2-roller mold (twin roller) or belt mold are formed. Allowed especially in the last two procedures the proposed system at the necessary high casting speeds with shorter solidification times with a smaller solidification thickness one optimal process control.

Fig. 1

schematisch einen Querschnitt eines Ausschnitts einer Stranggießmaschine mit einem Verteiler und einer oszillierenden Kokille;

Fig. 1a

schematisch einen Längsschnitt einer Bandgießanlage mit Bandkokille;

Fig. 1b

schematisch einen Querschnitt einer 2-Rollen-Anlage mit 2-Rollen-Kokille;

Fig. 2a

ein Verteilertemperatur-/Gießgeschwindigkeitsdiagramm bzw. T/v_C-Raster nach der Erfindung;

Fig. 2b

das Verteilertemperatur-/Gießgeschwindigkeitsdiagramm bzw. T/v_c-Raster der Fig. 2a mit eingetragenen äquivalenten T*_liq-Verläufen;

Fig. 3

ein dynamisches Verteilertemperatur-/Gießgeschwindigkeits diagramm (T/v_c-Raster) nach der Erfindung;

Fig. 3a

die schematische Darstellung des Einflusses der Verteilerisolation (E) und der Gießleistung (D) auf das Verteilertemperatur-/Gieß geschwindigkeitsdiagramm;

Fig. 3b

die schematische Darstellung des Einflusses der anfänglichen Aufheizphase des Verteilers zur Einstellung eines Temperatur-Gleichgewichtszustands (A), des Absinkens des Gewichts der Schmelze im Verteiler (B) sowie einer Liquid-Core-Reduction (C);

Fig. 4

dynamisches Verteilertemperatur-/Gießgeschwindigkeitsdiagramm (T/v_c-Raster) mit einer Häufigkeitsverteilung von ordnungsgemäßen Schmelzen und einem Durchbruch über einen Zeitabschnitt;

Fig. 5

eine schematische Darstellung einer Stranggießmaschine mit einer oszillierenden Kokille sowie einer Steuerungs- und Darstellungsein heit.

Further details and advantages of the invention result from the claims and the following description:

Fig. 1

schematically shows a cross section of a section of a continuous casting machine with a distributor and an oscillating mold;

Fig. 1a

schematically shows a longitudinal section of a belt caster with belt mold;

Fig. 1b

schematically shows a cross section of a 2-roll system with 2-roll mold;

Fig. 2a

a manifold temperature / casting speed diagram or T / v _C grid according to the invention;

Fig. 2b

the distributor temperature / pouring rate diagram or T / v _c grid of FIG. 2a with registered equivalent T * _liq curves;

Fig. 3

a dynamic manifold temperature / casting speed diagram (T / v _c grid) according to the invention;

Fig. 3a

the schematic representation of the influence of the distributor insulation (E) and the casting performance (D) on the distributor temperature / casting speed diagram;

Fig. 3b

the schematic representation of the influence of the initial heating phase of the distributor for setting a temperature equilibrium state (A), the drop in the weight of the melt in the distributor (B) and a liquid core reduction (C);

Fig. 4

dynamic distribution temperature / casting speed diagram (T / v _c grid) with a frequency distribution of proper melting and a breakthrough over a period of time;

Fig. 5

is a schematic representation of a continuous casting machine with an oscillating mold and a control and display unit.

Figure 1a schematically represents part of the casting process of a molten steel in a continuous casting machine, while Figure 5 gives an overview of a complete continuous casting machine. For the casting process, the melt is poured via a pan 1 into a distributor 2, from which it then flows into the mold 4 via a dip spout (also SEN) 3. According to the embodiment of the casting method shown in FIG. 1, there is a stationary mold, for example a thin slab mold, which oscillates vertically with respect to the solidifying strand shell 5a, b (see arrows in the mold side walls 6a, b). The outflow speed of the melt from the distributor is regulated by means of a vertically movable plug 7 with a displacement device 7a or a slide 8. The dip tube 3 dips into the mold 4. 9 is the casting mold which is set, 10 is the casting powder or pouring slag. Overall, the casting speed v _c results. X denotes the slab width resulting from the mold dimensions when it emerges from the mold.

The distributor 2 has a thermal radiation in the thermal equilibrium with the melt, here indicated by 11, which can be specified with a skin temperature of, for example, 100 ° C. and which thus leads to a loss of heat in the steel during its dwell time in the distributor. The distributor 2 is further characterized by a maximum weight of the melt with a maximum filling height (h _max ) in relation to the respective actual filling height h _ist .

According to the method, in addition to the measurement of the melt temperature (T _distributor ) in the distributor, here characterized by a measuring device 12, which can be a discontinuous or continuous measurement, the heat losses of the melt in the dip tube (SEN) 3, here indicated by 13, as well as the actual filling height h _{ist of} the distributor, which has a direct influence on the heat loss of the steel in the distributor.

In the further FIGS. 1a and 1b it is clear that the method according to the invention or system is not limited to continuous casting with an oscillating mold is, there are also casting processes using the strip casting process (Fig. 1a), in which the melt from a distributor 102 onto a cooled endless belt 104, which runs around two rollers 114, 115, is cast and drawn off, or for example 2-roll casting (Fig. 1b), in which the melt from one Distributor 202 is cast between two counter-rotating rollers 214, 215 and then subtracted, conceivable.

Starting from the material flow represented by FIG. 1, FIGS. 2 and 2a the relationships between the melt temperature in the distributor or the Overheating of the melt in the distributor (or the heat loss of the melt in the distributor and between the distributor and bath level of the mold) and the casting speed and the utilization of these relationships for the mathematical prediction of the temperature of the melt in the bath level in the mold. FIG. 2a shows a section from FIG. 2 in the casting speed range from 3.5 to 6.0 m / min. The temperature of the is below the manifold temperature Understand melt in the manifold.

From Fig. 2 it can be seen that, for example, with constant casting format, with constant Distribution skin temperature and with a constant distribution volume the loss the heat of a melt of a specific alloy between the distributor and Chill mold at a casting speed of 4 m / min at 30 ° C and at a casting speed of 6 m / min at 20 ° C was determined. The other dependencies are designated by 14. From this the relationship becomes visible, that at lower Pouring speed of the melt in the distributor or between the distributor and the mold more heat is extracted and therefore the overheating of the melt in the Consistently higher must be in order to solidify too early in the Avoid mold and thus bridging. To summarize, it can can be said quantitatively that with half the residence time of the steel melt or when doubling the casting speed or the strand width at constant Solidification thickness and with a constant amount of steel in the distributor the heat loss halved and with a smaller manifold volume the heat loss correspondingly the surface / volume ratio and the total residence time reduced.

The equivalent T * _liq temperature of the melt in the distributor (15) and the equivalent T * _liq temperature curve (T * _liq + 0 ° C) shown in the diagram show the temperature in the distributor at which the steel temperature in the Mold will reach the liquidus temperature. If the liquidus temperature (here about 1500 ° C) in the mold is reached too early, the solidification already takes place in the mold level and not only when it comes into contact with the mold walls to form the desired strand shell, which leads to bridging and thus a breakthrough due to the lack of it Slag lubrication or defective strand surfaces are connected. Safe pouring is only possible if the pouring speed is set so that the temperature of the melt is above the isotherm T * _liq + 0 ° C, in particular above the isotherm T * _liq + 5 ° C. According to the method, it is proposed to enter their isotherms step by step for 5 ° C in this diagram on the basis of this equivalent temperature profile, so that the isotherm _window shown in FIG. 2a with T * _liq + x ° C for x = + 5, +10, +15 and + 20 ° C gives (16). The pouring window then advantageously results with a distributor temperature between T * _liq + 5 ° C and T * _liq + 15 ° C or the corresponding temperature profiles. The preferred pouring window 17 is shown hatched.

The ratio of the temperature of the melt to the casting speed shown in FIGS. 2 and 2a can be influenced by various factors which shift the T / v _c grid to higher or lower temperatures and thus introduce a dynamic. The influence of various factors is shown in Figure 3. The heat loss increases with the drop in the weight of the distributor as a function of the surface / volume ratio of the distributor and the residence time (influence B), as shown schematically in FIG. 3b. The heat loss and thus the necessary overheating due to the so-called "liquid core reduction" also increase, the strand with still liquid sump being reduced from a mold exit thickness x to a smaller solidification thickness y (influence C).

In contrast, the heat loss with greater casting performance is reduced by an initially increasing heating process of the distributor 2 when casting the first melt, the temperature adjusting to an equilibrium temperature after a certain time (cf. FIG. 2b). For example, the time t _{GG is} approximately 20-30 minutes until a temperature equilibrium is established between the distributor and the melt (influence A). In addition, the heat loss decreases with increasing pouring width, shown in Fig. 3a with the ratio D to D1) as well as with increasing solidification thickness (D2) and with improved insulation of the distributor of the distributor lining (influence E, Fig. 3a) or falling outer distributor skin temperature and the Dipping spout.

With these influences A to E, the T / v _C grid becomes dynamic and can be constantly updated during casting with the help of process data recorded online.

4 is in such a dynamic temperature casting rate system the casting properties behavior of a melt reproduced certain composition, the respective casting speed is optimally adapted by the method according to the invention, represented here by 18. Furthermore, the frequency distribution (19) is shown in FIG. the temperatures of the melt in the distributor in the given diagram one here - Monthly production - of good and thus inconspicuous melts entered to to be able to statistically determine an optimization of the melt flow.

A further course of the melt is also shown (20), in which the strand is poured too slowly or has insufficient overheating, and the temperature of the melt is already in the mold level of the mold T _liq. was achieved. The temperature of the melt in the distributor corresponds to the equivalent temperature T * _liq or is less than T * _liq , (21); the strand breaks through a pre-solidification in the mold level and thus the slag lubrication between the strand shell and the mold wall is disturbed and thus rejects.

5 shows an overview of a continuous casting machine with a pan 300 and a holding device 301 receiving the pan 300 and a distributor 302 with corresponding holding device 303. The heat loss of the melt in The distributor is determined by means of suitable measuring devices 304 and the data fed into a computer 307 via corresponding lines 305, 306. It is also conceivable to reduce the heat loss of the melt in the pan to be measured by means of measuring devices 308 and via line 309 into the computer feed. It is also conceivable in a first approximation of a constant Steel temperature in the pan with a temperature drop of, for example 0.1 ° C / min. According to the procedure, the current Overheating in the melt, the more factors can be determined, the more certain are detected, and the liquidus temperature of the alloy is the equivalent liquidus temperature calculated and in the temperature / casting speed diagram represented by a monitor 310. It will now be automatic or semi-automatic or also by operating personnel manually using input means 311 a target casting speed, which is in the isothermal window shown, set, and via a line 312 the slide or plug of the distributor as setting means (315) controlled for the casting speed. After the strand shell solidifies the strand 314 continuously via roller units 313 (bending and straightening units) deducted.

The method and the system are preferably used for thin slab casting. A thin slab of, for example, 50 mm solidification thickness requires a setting time of about 1 min. The events in the Mold at casting speeds of up to 8 m / min so far and in the near future 10 m / min make a precise temperature and Speed control necessary, which is provided according to the invention becomes.

Claims (12)

Process for melt _guidance in a continuous casting machine, the melt of a specific alloy having a liquidus temperature T _{liq being poured} via a distributor (2, 102, 202, 302) into a casting mold (4, 104, 214, 215) and which within the Mold solidified strand (314) is pulled off
marked by Adopting the actual temperature of the melt in the distributor at an actual casting speed, Determination of the actual heat loss of the melt in the distributor and during its dwell time between distributor and casting level (9) in the casting mold, Determining an equivalent liquidus temperature T * _liq +0 (15) as the limit temperature for the temperature of the melt in the distributor, at which the liquidus temperature T _liq is already reached at a given casting speed in the area of the casting mold the isotherms of the equivalent liquidus temperature T * _liq + x as a function of superheating temperatures x with x> 0, the isotherms in each case in relation to the melt temperatures in the distributor and casting speeds, Adjusting the actual continuous casting speed to a target continuous casting speed within a predetermined isothermal window, the lowest limit of which is above the equivalent liquidus temperature _curve T * _liq +0. Method according to claim 1,
characterized, that the isotherms of the equivalent liquidus temperature T * _liq + x are determined step by step at intervals of 5 ° C. The method of claim 1 or 2,
characterized, that the casting speed is chosen so that the temperature of the melt in the distributor runs along or above the isotherms of the equivalent liquidus temperature _curve T * _liq + 5 ° C. The method of claim 1 or 2,
characterized, that the casting speed is chosen so that the temperature of the melt in the distributor runs along or above the isotherms of the equivalent liquidus temperature profile T * _liq + 5 ° C and that the temperature of the melt in the distributor runs along or below the isotherms of the equivalent liquidus temperature profile T * _liq + 20 ° C, preferably + 15 ° C. Method according to one of claims 1 to 4,
characterized, that go into the heat loss of the melt in the distributor: residence time of the melt in the distributor and / or Decrease in the melt weight in the distributor depending on its surface / volume ratio and / or initial heating time of the distributor for setting the temperature corresponding to the melt temperature and / or Isolation or the isolation status of the distributor. Method according to one of claims 1 to 5,
characterized, that in the determination of the heat loss of the melt during their dwell time between the distributor and the casting level in the casting mold, the heat radiation of an immersion spout of the distributor, which dips into the mold as a casting mold, is included. Method according to one of claims 1 to 6,
characterized, that the equivalent liquidus temperature _curves T * _liq +0 and + T * _liq + x of a melt with specified isothermal windows are shown in a manifold temperature / casting speed diagram over the casting time of a melt and are made visually visible. Method according to claim 7,
characterized, that factors that influence heat loss are included in the manifold temperature / casting speed diagram and are displayed visually. Method according to one of claims 1 to 8,
characterized, that the target continuous casting _speed is automatically set within the predetermined isothermal window, the lowest limit of which is above the equivalent liquidus temperature profile T * _liq + 0. System for melt guidance in a continuous casting machine, with a distributor (2, 102, 202, 302) from which the melt is poured into a casting mold (4, 104, 214, 215) from which the solidified strand (314) is drawn off, and with means (315) for adjusting the continuous casting speed, with means (12) for detecting the actual temperature of the melt in the distributor at an actual casting speed, Means (304) for determining the heat loss of the melt in the distributor and during its residence time between the distributor and the casting level in the mold, Control means for the setting means (7, 8) of the continuous casting speed for adapting the actual continuous casting speed to a target continuous casting speed within a predetermined isothermal window, the lowest limit of which is above the equivalent liquidus temperature _curve T * _liq +0, the isothermal _window being determined an equivalent liquidus temperature T * _liq +0 (15) as the limit temperature for the temperature of the melt in the distributor, at which the liquidus temperature T _{liq is reached} at a given casting speed in the area of the casting mold, and the isotherms of the equivalent liquidus Temperature T * _liq + x as a function of superheating temperatures x with x> 0, the isotherms in each case in relation to the melt temperatures in the distributor and casting speeds. System according to claim 10,
characterized by means (310) for the optical representation of the isothermal temperature profiles in a distributor temperature / casting speed diagram and their influencing variables. Continuous casting machine with a system according to one of claims 10 and 11 with an oscillating stand mold (4, 304) or traveling mold or 2-roller mold (214, 215) or belt mold (104) as a casting mold.

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