EP1369192B1 - Method for determining the position of the liquidus tip of a continuous casting by applying an oscillation - Google Patents

Abstract

To determine the peak of the bottoms in a continuous casting assembly, and register the friction forces between at least two of the elements in the mechanical system, the casting is subjected to an oscillation by one of the mechanical elements e.g. a roll stand. The mechanical rating is divided in a co-ordinate system to give apparent, actual and blind ratings, to give a phase angle (psi) to show the peak of the bottoms. Preferred Features: The oscillation is at a frequency of 0.5-10.0 Hz and preferably 1-4 Hz, and at an amplitude of 0.1-1.0 mm and preferably 0.2-0.4 mm.

Description

The invention relates to a Method for determining the sump tip in the interior of a cast strand its exit from the mold with a core of liquid metal bypassing Strand shell, which as a result of increasing heat release with increasing Thickness reaches to the solidus point of the marsh tip, and then one solidified continuous casting product, in particular a continuous casting slab formed.

In the production of slabs are usually with continuous casting Plattenkokillen used from which the cast strand, the mold with a solidified strand shell of increasing thickness of enclosed liquid melt leaves. A roller stand serves the purpose of not yet completely solidified Strand to support and shape. It is for economic reasons advantageous if possible to set such a high casting speed, that the stiffening of the strand is ideally completed "at the last roll".

If the casting speed is too low, then the length of the system is not sufficient used, productivity is lost; is the casting speed too high, can form a so-called "whale", the slab completely the Form loses and an immediate casting crash would be the result.

The result for the casting operation is the requirement to determine as exactly as possible at which point within a slab the swamp tip lies or where the Position of incipient solidification is located.

On the one hand there are certain empirical values of the plant operators and on the other hand For some time also computer models, with which partly online the situation the sump tip can be calculated by means of current boundary conditions. It has However, it was shown that even powerful, z. Thermal trekking programs, are unable to without the most elaborate optimizations the Location of the sump tip with satisfactory accuracy and spontaneity too determine.

From the document EP 0 980 295 B1 a method for generating is known of slabs of steel, being the guide of a strand with the help of guide rollers is adjusted continuously. The jaw width of the guide rollers is thereby with a predeterminable amplitude oscillating about a centerline when undressing of the strand changed in such a way that the dynamic influences on the leadership roles and the strand shell are negligibly small and no plastic Deformation of the strand shell occurs; the current jaw width is recorded; at the same time, the actuating force of the adjusting elements and the amplitude of the actuating force determines, and with increasing amplitude of the force, the jaw width on set a predetermined amount and / or at least one adjustment controlled by pressure. The course of the force has in a second approximation the Form of a hysteresis, wherein the propagation of the force, relative to an associated Jaw width as a measure of the viscosity of the liquid in the slab Sumpfes, and depending on the determined viscosity conclusions on the Position of the sump tip to be pulled, as well as adjusted the Maulweitenverstellung becomes.

The document EP 0 350 431 B1 describes a method for continuous casting of Slabs with a reduced compared to the cast state thickness, wherein a partially solidified strand between pairs of rollers, driven by means Rolls withdrawn and individual roles against the strand acting deformable are adjustable. For the production of a product with a high proportion of rolled structure, which is coilable, the speed, the current consumption of the driven Rolls and their contact pressure detected and each supplied to a controller. Everyone the Speed of individual driven rollers determining controller is about a parent Regulator adjustable so that by at least one, against stops adjustable, determining the thickness of the strand, on an already solidified Part of the strand deforming acting pair of rollers deform the final dimension and the withdrawal speed of the strand is determined. Upstream or downstream Roles are reflected in the speed and power consumption of their drives depending on the shape change of the strand produced by the rollers adjusted from the measured values current consumption, reaction force of Stranges and the roller clearance determines the location of the sump top and the contact pressures the rollers are adjusted so that the sump tip before at least an adjustable against attacks on a predeterminable distance Role pair lies.

The document DE-OS 25 30 032 discloses a method and an apparatus for Determination of acting on a continuous casting during its solidification Forces in which the cast body emerges from a mold and between passes through several pairs of rolls and in a plane at a distance below the Mold freezes over its entire cross-section. The level of complete solidification is detected by measuring on a plurality of roller pairs Compressive forces and comparing the measured values on different pairs of rolls for Determination of that pair of rollers determined, beyond which no further

Increase of the load takes place.

The document DE-OS 34 23 977 A1 describes a method for non-contact Measurement of the solidified surface layer of a casting of metal with non-solidified Inner core. An alternating magnetic field is applied to the casting, whereby the strength of the eddy currents generated in the casting by a measuring coil means is measured without contact. The thickness of a solidified surface layer is determined by the strength of the eddy currents according to the difference of the specific electrical resistance between a non-solidified molten Part and a solidified part of the casting intended.

Document JP 11083814 A describes a method for determining the state of solidification a casting. It then exists, one with electromagnetic Supersonic acting on a casting element in cooperation with a to provide the supersonic signal receiving switching system, which the Intensity of the propagating ultrasonic waves recorded, evaluated and with each other compares.

The document JP 63174770 describes another method for determining the not solidified end of a cast strand. A variety of roles are at horizontal area of a continuous casting plant and provided with a number of Pressure sensors in the axial direction of the surfaces provided by these rollers. As a result, in the continuous casting process, the lateral pressure in the strand through in the Roller detects existing sensors. In an area where an even more fluid Part of the strand in the interior of which is the lateral compressive force due low elongation recorded. In this way, the position and shape of the not solidified part found in the casting. Based on the aforementioned prior art, the invention has the object underlying to show a method by which the mechanical or dynamic Properties of a forced oscillatory moving system measured and for direct determination of the system status of a cast strand be used to determine the location of the swamp tip exactly.

To solve the problem is proposed according to the invention in a method referred to in the preamble of claim 1, that the strand shell or the continuous casting product with the help of a roller stand of the continuous casting plant, an oscillation is imposed and thereby the applied mechanical power or work in a coordinate system proportionally divided into apparent (P _S ), active (P _W ) and reactive power (P _B ) or work, and from a derivable phase angle (φ) in accordance with these proportions, the position of the sump tip is determined.

In this case, the invention takes advantage of the fact that the mechanical or dynamic Properties of a cast slab depending on its Consistency, e.g. As solid or liquid or mixtures, at the distance of Change the mold outlet to the bottom.

The ratio of active power (work), reactive power (work) changes or apparent power (work) and can be used to determine the phase angle (φ) be evaluated. This then characterizes the current state the consistency of the system or slab. In the process, the determined phase angle becomes evaluated as a significant feature of the mechanical system and the Determination of the position of the swamp tip used.

1. Die Bramme ist durcherstarrt.
Der Strang verhält sich dabei in erster Näherung wie eine Stahlfeder. Durch die Oszillation wird nur in sehr geringem Maße Energie in das System eingebracht und damit auch praktisch keine Wirkleistung benötigt, der Phasenwinkel (ϕ) ist vergleichsweise groß.

2. Die Bramme enthält flüssigen Sumpf.
Dieser Bereich ist geprägt durch einen hohen Anteil an flüssigem Metall. Durch die Oszillation erfolgt im flüssigen Bereich keine elastische Verformung. Für diese nicht elastische Verformung wird im Gegensatz zur Durcherstarrung Wirkleistung benötigt, z. B. für das Hin- und Herpumpen der flüssigen Schmelze.
Der Phasenwinkel (ϕ) ist vergleichsweise klein.

3. Übergangsbereich zur Sumpfspitze.
Da hier sowohl elastische als auch nicht elastische Verformung stattfindet, bewegt sich der Phasenwinkel (ϕ) im mittleren Bereich.

If you force the slab z. B. with the aid of a roller stand an oscillation, so three states can be distinguished:

1. The slab is solidified.
The strand behaves in a first approximation like a steel spring. Due to the oscillation energy is introduced into the system only to a very small extent, and practically no active power is required, the phase angle (φ) is comparatively large.

2. The slab contains liquid sump.
This area is characterized by a high proportion of liquid metal. The oscillation does not cause any elastic deformation in the liquid region. For this non-elastic deformation active power is needed in contrast to the solidification, z. B. for pumping back and forth the liquid melt.
The phase angle (φ) is comparatively small.

3. Transition area to the swamp tip.
Since both elastic and non-elastic deformation takes place here, the phase angle (φ) moves in the middle range.

Thus, the position of the sump tip can be derived from the phase angle (φ).

The invention is described below with reference to the illustrated in the drawings Embodiment explained in more detail.

Figur 1

den Phasenwinkel (ϕ) der Scheinleistung im Koordinatensystem in Abhängigkeit von der Wirkleistung P_W der Abszisse, und der Blindleistung P_B der Ordinate,

Figur 2

den Phasenwinkel (ϕ) in Abhängigkeit von der Durcherstarrung einer Bramme unterhalb einer Kokille.

Show it:

FIG. 1

the phase angle (φ) of the apparent power in the coordinate system as a function of the active power P _{W of} the abscissa, and the reactive power P _{B of} the ordinate,

FIG. 2

the phase angle (φ) as a function of the solidification of a slab below a mold.

In FIG. 1, the coordinate system shows that at maximum reactive power P _B , where the angle of P _S approaches 90 °, the active power P _W decreases towards zero, whereas with a tendency to decrease the reactive power P _B towards zero, the active power P _W approaches a maximum tends.

a) Bramme mit flüssigem Sumpf,

b) Bramme durcherstarrt, und

c) Übergangsbereich zur Sumpfspitze

bei entsprechenden Positionen der Bramme unterhalb der Kokille, sowie die Position der letzten Rolle des Rollengerüstes dargestellt. Das Diagramm zeigt deutlich die Größe des Phasenwinkels ϕ, der den einzelnen Systemzuständen der Bramme entspricht. Mit der Erfindung ergeben sich die folgenden Vorteile:In Figure 2, the system states

a) Slab with liquid sump,

b) slab solidifies, and

c) Transition area to the sump tip

represented at corresponding positions of the slab below the mold, as well as the position of the last roll of the roller stand. The diagram clearly shows the size of the phase angle φ, which corresponds to the individual system states of the slab. The invention provides the following advantages:

Direct measurement of the system status, no indirect calculation. Thereby increased accuracy and reliability.

Depending on the nature of the existing system, this method is without or with only very little mechanical and drive engineering effort feasible (eg CyberLink segments, resonance molds).

• Bei der Strangführung:
  • Die Sumpfspitze kann "bis zur letzten Rolle getrieben werden".
    Das bedeutet eine Maximierung der Produktivität.
  • Die Dynamische Softreduction wird präziser und damit effektiver, da sie genauer in den Bereich der Sumpfspitze gelegt werden kann.
    Das bedeutet eine Verbesserung der Brammenqualität.

The system can be used safely up to limit states:

• In the strand guide:
  • The sump tip can be "driven to the last roll".
    That means maximizing productivity.
  • The Dynamic Softreduction becomes more precise and thus more effective as it can be placed more precisely in the area of the sump tip.
    This means an improvement in slab quality.

Claims (7)

1. Method of determining the end of the liquid phase in the interior of a cast strip after exit thereof from the mould with a strip skin which surrounds a core of liquid metal and which as a consequence of increasing heat delivery reaches with increasing thickness up to the solidus point of the end of the liquid phase, and then forms a continuously cast product, particularly a continuously cast slab, hardened through, charactensed in that an oscillation is imposed on the continuously cast product with the assistance of a roller frame of the continuous casting plant and in that case the mechanical power or work applied is proportionally resolved in a co-ordmate system into apparent power (P_S), effective power (P_W) and reactive power or work (P_B) and the position of the end of the liquid phase is determined from a phase angle (ϕ), which is derivable therefrom, of the co-ordinate system in dependence on these proportions.
2. Method according to claim 1, characterised in that an oscillation frequency between 0.5 and 10 Hz and preferably between 1 and 4 Hz is used.
3. Method according to claim 1, charactensed in that an oscillation amplitude between 0 1 and 1 mm and preferably between 0.2 and 0.4 mm is used
4. Method according to claim 1, charactensed in that oscillation frequency and/or oscillation amplitude is or are modified during the measuring.
5. Method according to one or more of claims 1 to 4, characterised in that the entire segment upper frame of the roller frame is oscillated.
6. Method according to one or more of claims 1 to 5, characterised in that the segment entry or the segment exit of the roller frame is oscillated.
7. Method according to one or more of claims 1 to 6, characterised in that the oscillation energy is introduced directly into the corresponding segments of the roller frame by way of, for example, the hydraulic cylinders thereof.

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