EP0946318B1 - Method and device for continuous thin slab steel casting - Google Patents

Abstract

The present invention pertains to a method for continuous thin slab steel casting at speeds over 3m/min. in a facility where, above an immersion spout (42) which can be closed by means of a stop element (44), the cast is fed into an ingot mould located downstream from the guide rollers of the strand. Said method comprises the following steps: a) when the slab goes out of the ingot mould, the frozen layer on each of its large sides takes a steady waved form during the plastic adaptation phase, depending on the spacing between the guide rollers on which it takes its bearing; b) thereafter, on the large sides of the slab, the shell featured by the frozen layer takes on its surface a non steady waved form during the plastic adaptation phase, depending on the arrangement of the guide rollers located opposite it; c) when the strand is removed, the transition from plastic to elastic adaptation of the frozen layer is metrologically determined and, with regard to the plastic adaptation of the shell featured by said frozen layer, the slab takes its bearing in such a way that, for a minimum force exerted upon the frozen layer, said slab is routed by the strand guiding part.

Description

The invention relates to a process for the continuous casting of thin slabs Casting speeds greater than 3m / min. in a continuous caster, in which one Immersion spout, which can be closed by a shut-off element, converts the melt into one Mold is passed, followed by a strand guide equipped with rollers is. The invention further relates to a continuous casting plant for performing the Procedure.

Under the ferrostatic pressure of the molten steel, it can be found in the continuous casting of Slabs to bulge the strand, ie. after leaving the The mold shell undergoes a series of bulging and rolling deformations, but the bulging by the support rollers of the mold downstream Strand guide structure is restricted.

According to Stahl und Eisen 99 (1979), No. 19, page 1039-1050 is in an existing Slab caster the secondary cooling the only parameter in connection with the casting speed, which can be adjusted to reduce bulging. It is recommended to optimize the secondary cooling to the internal quality of the Stranges to improve. An indication of the influence of the bulge on the liquid swamp of the strand is not apparent from this article.

In the specialist book "Metallurgy of Continuous Casting, Casting and Solidification of Steel", Verlag Stahl und Eisen, 1992, points out that too strong Bulges segregations page 361, and cause internal cracks. It is shown that Bulges measured in operation on continuous casting machines and theoretically were calculated and examined on bending models. Aim of investigating this mechanical deformations are their influence on surface defects and Internal cracks in the slabs produced on continuous caster.

From EP 0 041 498 is a continuous sheet caster with one below the mold arranged strand guide known, the two opposite roller conveyors has, whose roles are mounted on scaffolding parts and the distance between them opposite scaffolding parts and thus the distance between the roller conveyors accordingly a strand cross section to be adjusted is changeable. For this, at least one of the Roller conveyors on the scaffold part are arranged such that they can be offset in the longitudinal direction of these roller conveyors and fixed to the scaffold part in different positions. By the proposed here Construction should include An inadmissible bulging of the strand shell can be prevented Maintaining the same possible distance between the end rollers of adjacent scaffolding parts. This document therefore deals exclusively with the constructive structure of a Continuous caster.

In continuous casting plants, the melt is usually poured into a headed oscillating mold. The inflow amount is regularly over one at the entrance of the Immersion spout arranged stopper or slide closure set. The level height the melt in the mold is recorded by measuring technology and via an EDP-supported measuring and Control device used to change the stopper position in the closure, which compensates for an up and down movement of the bath surface.

None of the objects that have become known from the documents mentioned becomes a So-called "mold-level hunting", that is, an uncontrolled swinging of the mold level in the mold with amplitudes that no longer guarantee safe casting operation, prevented.

A continuous caster is known from the abstract JP 57209759, in which the rod a plastic zone and an elastic zone and an intermediate one Transition zone is present and roles are provided for strand guidance, which are arranged oppositely offset.

The invention has for its object a method and a system for continuous casting to create thin slabs, through which actively an uncontrolled swinging open of the mold level in the mold and also the slab quality Reduction of mid-segregation is improved.

This object is achieved by the features of Method claim 1 and claim 6 directed to a continuous caster solved. The subclaims indicate advantageous developments of the invention.

According to the strand shell ie. the so-called shell box Leave the stationary mold during the plastic behavior Waveform embossed and after a transition phase during its elastic Behavior impressed an unsteady wavy surface shape. After that after measuring the transition from plastic to elastic Behavior of the strand shell in the area of elastic behavior in such a way supported that the slab produced with minimal force on its broad sides is guided through the strand guide.

The minimal force applied to the upper and lower broad side of the strand shell a slab is achieved in that in the area of elastic behavior Strand shell selected a different arrangement of the opposing roles is considered in the plastic area of the strand shell. This ensures that after the transition phase the increasingly solidifying strand through the Strand guide meanders. This avoids that at the same time on the The top and bottom of the strand shell box are stamped into the strand shells Bulges or indentations at the same time on the supporting ones Meet leadership roles. A simultaneous squeeze of two Bulges would become a "pump" and a simultaneous impact of two Indentations would "suck" what is encased in the strand shell box Lead swamp. Since the only opening of the Strangschalenkastens is located in the mold, there is then the mold level Swing excited.

The displacement of the rollers required to avoid the oscillation lies in the range of a translation a with a size between 0.1 to 0.5 x I _R , where I _{R represents} the roller division in mm.

The change in the oscillating surface structure of the strand shell by Change of the support by the strand guide rollers is after the Transition area from the plastic to the elastic behavior of the strand shell carried out. The setting of the size and position of this transition area is advantageously due to the amount, type and location of external cooling set. Overall, the transition area depends on the casting speed and the temperature profile and moreover from the shell thickness, the swamp length, the Steel grade, ie. their chemical composition, the mold exit dimension and the design of the continuous caster and in particular the width and the Division of roles. The transition area from plastic to elastic behavior the strand shell can be found in any frame of the strand guiding device become.

In a further embodiment of the invention, the strand shell box is proposed in the area of elastic behavior in such a way that a minimal Force on the strand shell is achieved by using actuators Measuring elements for recording the contact pressure or the position of the strand shell in Connected and the pressure of connected to the guide rollers keep the hydraulic elements regulated, so that the strand shell uniform pressure is applied regardless of their shape.

A continuous caster is proposed for carrying out the process the guide frame is divided into three zones, with the guide roles in the Starting zone to each other have a different assignment than in the after Transition zone arranged end zone. The individual zones can already be first scaffold.

In continuous casting plants that have a narrow range of positions, the individual zones of the roll allocation can be permanently installed. However, since the position of the transition zone can change, it is proposed to provide translation elements with which a translation of the opposite guide rollers that can be adjusted to a gap is possible at any point on the strand, the translation a being of the order of magnitude a = 0.1 to 0, 5 x I _R (I _R = division of roles) is provided.

In an advantageous embodiment, the guide frame is in the transition zone structurally designed so that the same in the upper frame and in the lower frame Number of guide rollers is provided and that the positioning of the The guide rollers of the lower frame can be changed continuously along the strand is executed. In a further embodiment, an additional Leadership role should be provided in addition to the existing leadership roles can be positioned in the subframe.

A cooling device is used to limit the location of the transition zone provided that in the area where usually the plastic behavior of the Strand shell occurs, is installed and its cooling medium quantity, shape and temperature is adjustable.

A complete suppression of the uncontrolled swinging up of the casting mirror in the Mold (mold level hunting) is achieved when the stopper regulation is a Has natural frequency that is outside the resonance frequency of the pump frequency Liquid column and thus outside the frequency of pumping the strand shell lies.

Figur 1

eine schematische Ansicht der Stranggießanlage,

Figur 2a,2b

schematische Darstellungen des Bereichs des plastischen Verhaltens der Strangschale

Figur 3a,2b

die Anordnung der Führungsrollen im Bereich des elastischen Verhaltens der Strangschale

Figur 4

eine schematische Darstellung eines Führungsrollenbereiches zur Erläuterung des Änderns der Rollenteilung.

An exemplary embodiment of the invention is shown in the drawing and is described below

Figure 1

a schematic view of the continuous caster,

Figure 2a, 2b

schematic representations of the range of plastic behavior of the strand shell

Figure 3a, 2b

the arrangement of the guide rollers in the area of the elastic behavior of the strand shell

Figure 4

is a schematic representation of a guide roller area to explain the change in role division.

FIG. 1 shows a melt supply vessel 43, the bottom opening of which can be closed by a stopper 44 which is connected to a stopper control 45. An immersion spout 42, which projects into a mold 41, is fastened to the melt supply vessel 43.
The mold 41 is followed by scaffolds 12, 22, 32 having individual segments, corresponding to an initial zone 11, a transition zone 21 and an end zone 31.

The start and transition zones 11 and 21 extend over a relatively wide area, which is connected to the end zone 31. The initial zone 11 and the transition zone 21 can already be present in the first framework, so that the end zone 31 extends over the remaining strand guide area.

The individual stands have guide rollers 13, 23, 33, which are in the upper frame 14, 24, 34 and subframes 15, 25, 35 are arranged (see Fig. 4).

Furthermore, the slab B is shown schematically, the bottom tip S _s of which protrudes beyond the end zone 31. Furthermore, a cooling device 61 is indicated schematically in the end region of the starting zone 11.

FIGS. 2a and 2b show guide rollers 13 in the area of the plastic behavior of the strand shell, in which a stationary waveform is molded. The thickness of the bulge is marked with D, the width of the rollers with d.
In FIG. 2a, the guide rollers 13 are located directly opposite each other with the internal width d and are at a distance from one another on the respective strand side, which is determined by the roller pitch I _R. The strand shell W, which includes the sump S, has indentations and bulges.

In FIG. 2b, in comparison to FIG. 2a, with the same roller pitch I _R and the same mouth width d, the guide rollers 13 are offset from one another by a translation a. Here a = 0.5 x I _R.
Due to the displacement of the guide rollers 13, the bulge D is smaller than the stationary bulge in the case of guide rollers 13 arranged opposite one another according to FIG. 2a.

FIGS. 3a and 3b show the situation in the area of the elastic behavior of the Strand shell with an unsteady undulating surface shape.

In FIG. 3a, a section through the strand shell box is shown schematically, in which the broad sides have indentations and bulges opposite each other in mirror symmetry.
Due to the staggered arrangement of the guide rollers, the strand moves in the strand withdrawal direction through the guide frame in such a way that it meanders through the rollers, which are spaced apart from one another.

In Figure 3b, the strand shell box is shaped like a double-walled corrugated sheet. During the withdrawal process of the strand, it moves in the form of a corrugated sheet Strand shell box through the guide frame so that it is here through the opposite guide rollers meanders.

It does not occur in either of the two forms shown in FIGS. 3a and 3b a crushing of the strand shell box in relation to its Broad sides, and thus not to pump or suck the from Strand shell box enclosed liquid column.

FIG. 4 shows a frame 12, 22, 32 and an upper frame 14, 24, 34 and a lower frame 15, 25, 35 and guide rollers 13, 23, 33. An additional roller 19, 29, 39 is provided on the lower frame 15, 25, 35 which, after a translation of the lower guide rollers 13, 23, 33, can additionally be added to the row of these rollers, as shown in the lower part of FIG. 4, and as a result of which an offset arrangement of the opposite rollers 13, 23, 33 can be achieved . Of course, a translation of the guide rollers is also possible without the addition of a further roller 19, 29, 39, but then there is a gap to be observed in the row of the lower guide rollers.
Means for carrying out the translation a are only indicated in the lower part of FIG. 4 by reference symbols 16, 26, 36

In the upper part of Figure 4 are a measuring element 74 for the pressure and a measuring element 75 shown for the position of the strand shell, which with actuators 71, 72, 73 in Are connected, which in turn act on hydraulic elements 18, 28, 38, by means of which the pressure on affected guide rollers is essentially constant can be held.

Claims (11)

1. Method of continuous casting of thin slabs at casting rates greater than 3m/min. in a continuous casting plant, in which via an immersion nozzle (42), which is closable by a locking element (44), the melt is guided into a mould (41), to which is connected in series a strand guide equipped with rollers, characterised by the following stages:

   a) after the strand has left the mould (41), there is imparted to the strand shell of each wide side of the slab, during its plastic phase and according to the roller spacing of the guide rollers (13, 23, 33) supporting it, a stationary wave shape,

   b) afterwards, on the slab wide sides, a non-stationary wavy surface shape is impressed on the strand shell case during its elastic phase and following the arrangement of the guide rollers disposed opposite one another,

   c) while the strand is being drawn off, the transition from the plastic to the elastic phase of the strand shell is determined with measurement technology, and

   d) in the region of the elastic phase of the strand shell case, the slab is so protected that it is guided through the strand guide with minimal force exerted on the strand shell.
2. Method according to claim 1, characterised in that in order to set the size and position in the strand guide of the transition region from the plastic to the elastic phase of the strand shell, the shell is cooled in a controllable manner.
3. Method according to claim 1 or 2, characterised in that the strand shell case receives in the region of the plastic phase of the strand shell a shape which has bulges and recesses due to the guide rollers (13, 23, 33) supporting the same and in that after the transition phase, in the region of the elastic phase, the shell of the strand shell case is supported by staggered guide rollers (13, 23, 33).
4. Method according to claim 1 or 2, characterised in that the strand shell case receives in the region of the plastic phase of the strand shell the shape of a corrugated sheet due to the staggered guide rollers (13, 23, 33), and in that after the transition phase in the region of the elastic phase of the strand shell, the strand shell case is supported by guide rollers (13, 23, 33) disposed opposite on another at the same height.
5. Method according to claim 3 or 4, characterised in that in the region of the elastic phase of the strand shell, the lower and the upper strand shell of the strand shell case is excited to a pumping frequency (v_S), which behaves as follows: vS = vG/IR where v_G = casting rate
   I_R = roller spacing
   and in that the frequency (vF) of the column of liquid of the sump enveloped by the strand shell case varies according to vF = vG/IR±a where a = translation of the opposite guide rollers (13, 23, 33) in a range a=0.1 to 0.5 x I_R and taking into account of the position of the guide rollers allocated to the respective wide sides of the strand shell case.
6. Continuous casting plant for producing thin slabs at casting rates higher than 3m/min. comprising a mould, into which an immersion nozzle (42) closable by a locking element (44) projects and to which is connected in series a guide stand equipped with rollers, which stand has upper and lower frames (14, 24, 34; 15, 25, 35), which are held via tie rods and has hydraulic elements (18, 28, 38), with which the guide rollers (13, 23, 33) are pressed against the wide sides of the strand shell case, for carrying out the method according to claim 1, characterised in that the guide stand is divided into a starting zone (11), a transition zone (21) and an end zone (31), in that in the starting zone (11) the guide rollers (13) are disposed substantially opposite one another or with a gap and in the end zone (31) the guide rollers (33) are disposed respectively in the opposite manner, in that between the starting zone (11) and the end zone (31) a transition zone is provided, which has a combination of both roller arrangements, and in that actuators (71-73) are provided, which communicate with measuring elements (74) for detecting the contact pressure or measuring elements (75) for determining the position of the strand shell and which according to the frequency of the strand shell (vS) keep the pressure of the hydraulic elements (18, 28, 38) substantially constant.
7. Continuous casting plant according to claim 6, characterised in that translation elements (16, 26, 36) are provided, with which translation (a) of the guide rollers (13, 23, 33), which can be set opposite one another with a gap, can be carried out to a degree a=0.1 to 0.5 x 1.
8. Continuous casting plant according to claim 6, characterised in that the guide stand (22) has in the transition zone (21) in the upper frame (24) and the lower frame (25) the same number of guide rollers (23) and in that the positioning of the guide rollers (23) of the lower frame (25) along the strand is infinitely variable.
9. Continuous casting plant according to claim 8, characterised in that an additional guide roller (26) is provided, which can be positioned in a complementary manner to the available guide rollers (23) in the lower frame (25).
10. Continuous casting plant according to claim 8, characterised in that a cooling device (61) is provided in the zone of the plastic phase of the strand shell, whose quantity, form and temperature of coolant can be set.
11. Continuous casting plant according to claim 6, characterised in that a continuous casting control is provided, which has a natural frequency lying outside the resonance range of the frequency of the liquid column (v_F), wherein v_F corresponds to the frequency v_S (frequency of pumping of the strand shell).

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