EP1066898B1 - Process 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 _{carrying out} the melt in a continuous casting machine, wherein the melt of a specific alloy having a liquidus temperature T _{liq is} poured into a casting mold via a distributor and the strand solidified within the casting mold is drawn off.

The continuous casting processes according to the conventional continuous casting with a oscillating mold via thin slab casting, strip casting or 2-roll casting make with the steadily thinning solidification thickness of Casting product with shorter solidification times and increasing casting speeds an exact process control necessary

US Pat. No. 4,235,276 describes a method in which the heat loss of the melt in the Mold, is controlled by regulating the withdrawal speed.

The object of the present invention is to provide a method for To provide melt guide in a continuous casting machine, with which a accurate temperature and casting speed control for a reliable and in particular automatable casting is possible.

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

In detail, the method proposes that the actual temperature of the melt is detected in the distributor at an actual casting speed, wherein the detection of the temperature discontinuously or continuously by means of suitable known temperature receiving means, such as thermocouples or temperature sensors occurs. The actual heat loss of the melt in the distributor and during its residence time between distributor and pouring mirror in the casting mold, for example an oscillating mold, is determined by taking factors 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 melt temperature limit in the distributor at which continuous casting defects occur in the mold. That is, it is the temperature of the melt in the distributor or the temperature profile determined by the casting speed at which the melt in the mold already solidifies in an undesirably early stage, ie in the casting mirror or in the Gießspiegelbereich. If, in fact, the liquidus temperature is already reached in the casting level of the mold, there is a risk of bridging in the solidifying microstructure associated with a strand break through lack of slag lubrication or defective strand surfaces. The temperature in the mold steel temperature must therefore be chosen so that no pre-solidification takes place in the mold and the casting powder is sufficiently melted to ensure good lubrication and insulation of the strand in his journey through the mold.

Depending on this limit temperature or the boundary _curve, the isotherms are determined for this purpose, ie the equivalent liquidus temperature profiles T * _liq + x (° C) as a function of the superheat temperature x (° C) with x> 0, in each case depending on the casting speed , This results in a grid, which allows using the temperature of the melt in the manifold as a measure prediction of the temperature conditions in the mold by the ratio of the melt temperatures in the manifold and the mold on the superheating and the respective casting speed is utilized. This is followed by an adaptation of the actual continuous casting speed to a desired continuous casting speed or else a desired continuous casting speed range within a predetermined isotherm window, the lowest limit of which lies above the equivalent Uquidus temperature profile T * _liq (+ 0 ° C.). This ensures that at no time depending on the temperature of the melt in the manifold and the heat loss is driven at a casting speed, which could lead to a breakthrough of the strand in the mold due to low temperatures.

Overall, therefore, the temperature of the melt in the distributor as a measure of 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 recruitment 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 distributor temperature is set.

By this predictability, the method offers the possibility of indicating, 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 manifold, which is based on the melt _temperature measurement in the manifold to respond by a corresponding Gießgeschwindigkeitserhöhung to avoid a casting disturbance in the mold in the form of surface defects on the cast product or a breakthrough. This relatively early problem or prediction of the events in the mold or mold is particularly clear by means of a temperature-duration measurement of the melt in the manifold and based on the long residence time of the steel, for example, 8 minutes in the manifold, the sufficient time for a corresponding There is a change in the casting speed.

According to the method, to achieve a good process control data "online" are measured, the solidification process in the mold at a optimal casting speed and at the same time a trouble-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 manifold and between distributor and mold optimal, breakthrough-proof and possibly fully automatic melt management 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 its isotherms +5 to + 20 ° C, preferably in a step interval of 5 ° C, respectively, or the temperature curves over the casting speed can be ensured to produce an isothermal window.

In order to achieve a safe pouring, 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. 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.

Altogether, these determined equivalent liquidus temperature profiles T * _liq + 0 ° C. or x ° C. of a melt with predetermined isothermal windows in a distribution temperature / casting speed diagram are to be represented over the casting time of a melt and visualized visually. In this way, a process observation is always possible. At the same time, it is proposed that influence variables be included in this distributor temperature / casting speed diagram, which shifts the distributor temperature / casting speed diagram to higher or lower temperatures and thus changes it dynamically. Special influencing variables and their effects are explained in the description of the figures.

In the heat loss of the melt in the distributor go the residence time of the melt in the distributor, wherein the residence time of the melt in the distributor is dependent the casting capacity, 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 distributor size, the drop in the melt weight in the distributor depending on its Surface / Votum ratio, the initial heating time of the distributor for adjusting the equilibrium temperature corresponding to the melt temperature as well as the insulation or the insulation state of the distributor and thus the Heat radiation of the distributor.

The inventively proposed system is used in a continuous casting machine with an oscillating stand or walking mold, also in Continuous casting machines with a casting mold designed as 2-roller molds (Twin Roller) or band mold are formed. Especially with the last two procedures allowed the proposed system at the necessary high casting speeds with decreasing solidification times at 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/_Vc-Raster der Fig. 2a mit eingetragenen äquivalenten T*_liq-Verläufen;

Fig. 3

ein dynamisches Verteilertemperatur-/Gießgeschwindigkeits diagramm (T/_Vc-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 will become apparent 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 a longitudinal section of a strip casting with band mold;

Fig. 1b

schematically a cross section of a 2-roller system with 2-roller mold;

Fig. 2a

a distributor temperature / casting speed diagram or T / v _c -Raster according to the invention;

Fig. 2b

the distributor temperature / casting speed diagram or T / _Vc -Raster of Figure 2a with registered equivalent T * _liq -Verläufen;

Fig. 3

a dynamic distributor temperature / casting speed diagram (T / _Vc grid) according to the invention;

Fig. 3a

the schematic representation of the influence of the manifold insulation (E) and the casting capacity (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 splitter temperature / casting speed diagram (T / v _c -Raster) with a frequency distribution of proper melts and a breakthrough over a period of time;

Fig. 5

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

Figure 1a schematically illustrates a part of the casting process sequence 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 over a pan 1 in a manifold 2, from which it then flows through a submount (also SEN) 3 in the mold 4. The embodiment of the casting method illustrated in FIG. 1 is a stand-alone mold oscillating in the vertical direction with respect to the solidifying strand shell 5a, b (see arrows in the mold side walls 6a, b), for example a thin-slab mold. The outflow rate of the melt from the distributor is controlled by means of a vertically movable plug 7 with traversing device 7a or a slider 8. The dip tube 3 dips into the mold 4. With 9 is the self-adjusting Gießspiegel, with 10 the casting powder or forming casting slag characterized. Overall, the casting speed v _c . With x is given by the mold dimensions resulting slab width at the exit from the mold.

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

According to the method, in addition to the measurement of the melt temperature (T _distributor ) in the distributor, characterized by a measuring device 12, which may be a discontinuous or continuous measurement, the heat losses of the melt in the dip tube (SEN) 3, here indicated by 13 and possibly the actual filling height h of the manifold _is detected based on the heat loss of the steel in the distributor has an influence directly.

In the further Fig. 1a and 1b it is clear that the inventive method or system is not limited to a continuous casting with an oscillating mold is, there are also casting processes after 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, poured and withdrawn, or For example, the 2-roll casting (Fig. 1 b), in which the melt from a Distributor 202 between two counter-rotating rollers 214, 215 is poured and then subtracted, conceivable.

Starting from the flow of material 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 distributor and bath level of the mold) and the casting speed as well as the utilization of these connections for the mathematical prediction of the temperature of the melt in the bath level in the mold. Fig. 2a shows a detail of Fig. 2 in the casting speed range from 3.5 to 6.0 m / min. Under distribution temperature is in each case the temperature of the Melt in the distributor to understand.

From Fig. 2 it can be seen that, for example, with constant casting format, at a constant Distribution skin temperature and at constant distribution volume the loss the heat of a melt of a specific alloy between distributor and 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 14. From this, the ratio becomes visible that at lower Casting speed of the melt in the distributor or between distributor and mold more heat is withdrawn and therefore the overheating of the melt in the Consequently, distribution must be higher in order to avoid too early solidification in the Mold and thus avoid bridging. If you get together, you can quantitatively speaking, that with half the residence time of the molten steel or when doubling the casting speed or the strand width at a constant Solidification thickness and at a constant amount of steel in the distributor of heat loss halved and with a smaller distribution volume, the heat loss accordingly the surface / volume ratio and the residence time in the sum decreased.

The equivalent T * _liq temperature of the melt in the distributor (15) or the equivalent T * _liq temperature profile (T * _liq + 0 ° C) shown in the diagram show at which temperature in the distributor the steel temperature in the distributor Mold will reach the liquidus temperature. If the liquidus temperature (here about 1500 ° C) is reached too early in the mold, the solidification takes place already in the mold level and not only in contact with the mold walls to form the desired strand shell, creating a bridging and thus a breakthrough by missing Slag lubrication or defective strand surfaces are connected. A safe pouring is only given if the casting speed is adjusted so that the temperature of the melt above the isotherm T * _liq + 0 ° C, in particular above the isotherms T * _liq + 5 ° C, runs. According to the procedure, it is proposed to enter the isotherms stepwise for 5 ° C. into this diagram on the basis of this equivalent temperature profile, so that the isothermal _window shown in FIG. _{2 a} with T * _liq + x ° C. for x = + 5, +10, +15 and + 20 ° C gives (16). Advantageously, then the casting window with a distributor temperature between T * _liq + 5 ° C and T * _liq + 15 ° C or the corresponding temperature _curves . The preferred casting 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 -Raster to higher or lower temperatures and thus bring about a dynamic. The influence of various factors is shown in FIG. Thus, the heat loss increases with the decrease of the distributor weight in function of the top surface / volume ratio of the distributor and the residence time (influence B), as shown schematically in Fig. 3b. Also, the heat loss and thus the necessary overheating by the so-called "Liquid Core Reduction" increases, the strand is reduced with still liquid sump from Kokillenaustrittsdicke x to a smaller solidification thickness y (influence C).

On the other hand, the heat loss decreases with greater casting power due to an initially increasing heating process of the distributor 2 during the casting of the first melt, the temperature being adjusted to an equilibrium temperature after a certain time (see Fig. 2b). For example, the time t _{GG is} about 20-30 minutes, until a temperature equilibrium between distributor and melt is set (influence A). In addition, the heat loss decreases with increasing casting width, shown in Fig. 3a with the ratio D to D1) and with increasing solidification thickness (D2) and with improved insulation of the manifold of the Verteilausausmauerung (influence E, Fig. 3a) or sinking outer distributor skin temperature and immersion nozzle.

With these influences A to E, the T / v _c raster becomes dynamic and can be constantly updated during casting by means of 'online' recorded process data.

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

It is also shown a further course of melt (20), in which the strand cast too slowly or had too low overheating, and the temperature of the melt was reached in the mold level of the mold T _liq . The temperature of the melt in the distributor corresponds to the equivalent temperature T * _liq or is less than T * _liq , (21); It comes to the breakthrough of the strand by a pre-solidification in the casting mirror and thus to a disruption of slag lubrication between strand shell and mold wall and thus to committee.

5 shows an overview of a continuous casting machine with a pan 300 as well a pan 300 receiving fixture 301 and a manifold 302 with appropriate holding device 303. The heat loss of the melt in Distributor is determined by means of suitable measuring devices 304 and the data via corresponding lines 305, 306 fed into a computer 307. It is also conceivable already the heat loss of the melt in the pan Measure by means of measuring devices 308 and via the line 309 in 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 go out. According to the method, when the current Overheating in the melt, the more certain the more factors and the liquidus temperature of the alloy is the equivalent Uquidus temperature calculated and in the temperature / casting speed diagram represented by a monitor 310. It will now be automatic or semi-automatic or by operators manually by input means 311 a target casting speed, which is in the illustrated isothermal window, set, and via a line 312 of the slide or plug of the distributor as adjusting (315) controlled for the casting speed. After solidification of the strand shell is the strand 314 continuously via roller units 313 (bending and straightening units) deducted.

Preferably, the inventive method and the system are used for thin slab casting. A thin slab of, for example 50 mm solidification thickness requires a solidification time of about 1 min. The processes in the Mold at casting speeds of up to now 8 m / min and in the near future 10 m / min make for a reliable temperature and temperature Speed guide necessary, which provided according to the invention becomes.

Claims (9)

1. Method of guiding melt in a continuous casting machine, wherein the melt of a specific alloy is cast at a liquidus temperature T_liq by way of a distributor (2, 102, 202, 302) in a casting mould (4, 104, 214, 215) and the strip (314) hardened within the casting mould is drawn off, characterised by detecting the actual temperature of the melt in the distributor at an actual casting speed, determining the actual heat loss of the melt in the distributor during its dwell time between distributor and casting surface (9) in the casting mould, determining an equivalent liquidus temperature T*_liq + 0 (15) as boundary temperature for the temperature of the melt in the distributor in which the liquidus temperature T_liq is reached already in the casting surface region of the casting mould at a casting speed, as well as the isothermal lines of the equivalent liquidus temperature T*_liq + x in dependence on excess heating temperatures x at x > 0, the isothermal lines respectively in relation to the melt temperatures in the distributor and casting speeds, adapting the actual continuous casting speed to a target continuous casting speed within a predetermined isothermal line window, the lowermost boundary of which lies above the equivalent liquidus temperature path T*_liq+ 0.
2. Method according to claim 1, characterised in that the isothermal lines of the equivalent liquidus temperature T*_liq + x are determined in steps at intervals of 5° C.
3. Method according to claim 1 or 2, characterised in that the casting speed is so selected that the temperature of the melt in the distributor runs along or above the isothermal lines of the equivalent liquidus temperature path T*_liq + 5° C.
4. Method according to claim 1 or 2, characterised in that the casting speed is so selected that the temperature of the melt in the distributor runs along or above the isothermal lines of the equivalent liquidus temperature path T*_liq + 5° C and that the temperature of the melt in the distributor runs along or above the isothermal lines of the equivalent liquidus temperature path T*_liq + 20° C, preferably + 15° C.
5. Method according to one of claims 1 to 4, characterised in that entering into the heat loss of the melt in the distributor are:

   dwell time of the melt in the distributor and/or

   lowering of the melt weight in the distributor in dependence on the surface/volume ratio thereof and/or

   initial heating-up time of the distributor for setting the temperature corresponding with the melt temperature and/or

   insulation or insulation state of the distributor.
6. Method according to one of claims 1 to 5, characterised in that the heat radiation of an immersion outlet of the distributor, which dips into the chill mould as casting mould, enters into the determination of the heat loss of the melt during its dwell time between distributor and casting surface in the casting mould.
7. Method according to one of claims 1 to 6, characterised in that the equivalent liquidus temperature paths T*_liq + 0 as well as + T*_liq + x of a melt are illustrated by predetermined isothermal line windows in a distributor-temperature/casting-speed diagram over casting time of a melt and are made optically visible.
8. Method according to claim 7, characterised in that factors influencing the heat loss enter into the distributor-temperature/casting-speed diagram and are optically illustrated.
9. Method according to one of claims 1 to 8, characterised in that the target continuous casting speed is automatically set within the predetermined isothermal line window, the lowermost boundary of which runs above the equivalent temperature path T*_liq + 0.

Images