EP1815925A1 - Method and apparatus for the continuous casting of steel beam blanks, especially double-T-bleam blanks - Google Patents

Abstract

The continuous casting of preliminary double-T steel sections, comprises introducing liquid steel substantially vertically into an open-ended die (1) and supplying partially hardened preliminary section to a strand guide with secondary cooling equipments. The cross section of the cavity of the open-ended die is made up of two flange parts (2,3) and a web part (4) and applied on a liquid strand in the preliminary section over magnet poles of magnetic fields. A 3-phase alternating current is supplied to agitating coils (19) of an agitator over a pole wiring. The continuous casting of preliminary double-T steel sections, comprises introducing liquid steel substantially vertically into an open-ended die (1) and supplying partially hardened preliminary section to a strand guide with secondary cooling equipments. The cross section of the cavity of the open-ended die is made up of two flange parts (2,3) and a web part (4) and applied on a liquid strand in the preliminary section over magnet poles of magnetic fields. A 3-phase alternating current is supplied to agitating coils (19) of an agitator over a pole wiring in dependence of a thickness of the web part, a steel quality and a symmetrical or asymmetrical steel supply with one or two sprue (passage) in such a manner that electromagnetic travelling waves are applied in the liquid strand of the preliminary section with horizontal direction components. The travelling waves are generated in the flange parts with direction components rotating in same- or opposite direction and/or in the web part with linear direction components and/or in the area of the open-ended die and/or in different and adjustable heights in the preliminary section and/or in transition area or area of the web part with direction components rotating in same- or opposite direction. The liquid steel is supplied on the sprue intended symmetrically or asymmetrically in the web part and the distribution of the liquid steel is supported over the cross section of the cavity depending upon casting parameters and/or product parameters by the rotary and/or linear travelling waves. An independent claim is included for a device for continuous casting of preliminary double-T steel sections.

Description

The invention relates to a method for the continuous casting of steel pre-profiles, in particular double-T pre-profiles according to the preamble of claim 1 and an apparatus for carrying out the method.

Steel pre-profiles represent primary material for producing rolled steel profile beams in I, H, U and Z-cross-sectional shape and special sheet pile profiles. A method for continuous casting of such pre-profiles is, for example, in EP-B-1 419 021 disclosed. Continuous casting of pre-profiles was introduced industrially in the 70's and has become increasingly important in recent years as part of the general trend towards so-called near-net-shape casting.

The pre-profiles are usually cast in a double-T cross-sectional shape, wherein the liquid steel is introduced substantially vertically into a so-called "dog-bone" continuous casting mold whose cavity cross section is composed of two flange parts and a web part. From the mold a Vorprofilstrang with liquid core of a strand guide with secondary cooling devices is supplied.

In contrast to the continuous casting of classic, rectangular or round long products, the continuous casting of double-T pre-profiles poses some problems, especially when it comes to pre-profiles with a relatively thin web part, if high-strength special steel grades (CaSi or Alberuhigt and micro-alloyed steels with V, Nb, etc.), or by rapid casting. For reasons of space, but also for economic reasons, the liquid steel is introduced into the mold via only one gate, usually asymmetrically at the transition between the web part and one of the flange parts. As a result, it is particularly difficult to fill the complicated Kokillenhohlraum evenly and without disturbing turbulence and thus to create favorable conditions for initial solidification while avoiding near-surface casting defects (gas bubbles, pin-hols). It is also difficult to have a symmetrical liquid flow within the strand shell and consequently a symmetrical temperature distribution, which ultimately leads to a homogeneous solidification structure to achieve. Equally problematic is to avoid bridge formation during solidification and consequent pore porosity and / or voids in a thin web portion.

The present invention has for its object to provide a method of the type mentioned above and to provide a device for carrying out the method by which steel pre-profiles, which have two flange and a web portion, can be made with improved quality, even if it is is a relatively thin web part and / or special steel grades.

This object is achieved according to the invention by a method according to claim 1 and by a device having the features of claim 7.

Preferred developments of the inventive method and the inventive device form the subject of the dependent claims.

• Stabilisierung des Giessspiegelbereiches durch Unterdrückung der Turbulenzen auch bei wechselnden Prozessparametern wie Giessgeschwindigkeit, Giessspiegelposition (zwecks Vermeidung von nichtmetallischen Einschlüssen sowie Gasblasen in der Strangoberfläche);
• günstige, steuerbare Strömungsverhältnisse mit einem gezielten Flüssigstahlaustausch zwischen den beiden verdickten Hohlraumbereichen durch den dünnen Stegteil, auch bei einem asymmetrischen Einguss, und dadurch die Bildung einer gleichmässig dicken Strangschale mit günstigem Erstarrungsgefüge unter Vermeidung von Lunker und/oder Kernporosität;
• Vermeidung von Brückenbildungen während der Erstarrung trotz engen Verhältnissen im Stegteil des Formhohlraumquerschnittes.

Characterized in that, according to the invention, the liquid core of the Vorprofilstranges is displaced transversely to the continuous casting by using electromagnetically induced forces in the region of the flange and / or the web part in stirring movements and is replaced by the stirring movements of the liquid steel in the bottom of Vorprofilstranges between the flange and the web part , the flow and temperature conditions in the liquid steel sump within the pre-profile strand shell can be actively influenced specifically and thus the following effects can be brought about:

• Stabilization of the Giessspiegelbereiches by suppression of turbulence even with changing process parameters such as casting speed, Giessspiegelposition (in order to avoid non-metallic inclusions and gas bubbles in the strand surface);
• favorable, controllable flow conditions with a targeted liquid steel exchange between the two thickened cavity areas through the thin web portion, even with an asymmetric sprue, and thereby the formation of a uniformly thick strand shell with favorable solidification structure while avoiding cavities and / or core porosity;
• Avoidance of bridge formation during solidification despite narrow conditions in the web portion of the mold cavity cross-section.

Fig. 1:

eine Kokille im Querschnitt mit einem ersten Ausführungsbeispiel eines elektromagnetischen Rührers,

Fig. 2:

eine Kokille im Querschnitt mit einem zweiten Ausführungsbeispiel eines elektromagnetischen Rührers,

Fig. 3 - 6:

ein drittes Ausführungsbeispiel eines elektromagnetischen, einer Kokille zugeordneten Rührers, mit verschiedenen Polschuh-Schaltungen,

Fig. 7 + 8:

eine Kokille mit zwei Rührern in einer vierten Ausführungsform, mit verschiedenen Polschuh-Schaltungen,

Fig. 9:

die Rührer nach Fig. 8 sowie die Kokille in Seitenansicht,

Fig. 10:

eine Kokille mit zwei Rührern in einer fünften Ausführungsform,

Fig. 11 + 12:

eine Kokille mit zwei Rührern in einer sechsten Ausführungsform, mit verschiedenen Polschuh-Schaltungen,

Fig. 13:

den Rührer nach Fig. 10 sowie die Kokille in Seitenansicht,

Fig. 14:

ein siebtes Ausführungsbeispiel eines elektromagnetischen, einer Kokille zugeordneten Rührers und

Fig. 15

ein elektrisches Schema für den Rührer nach Fig. 14.

The invention will be explained in more detail with reference to the drawings. It shows purely schematically:

Fig. 1:

a mold in cross-section with a first embodiment of an electromagnetic stirrer,

Fig. 2:

a mold in cross-section with a second embodiment of an electromagnetic stirrer,

Fig. 3 - 6:

A third embodiment of an electromagnetic, a mold associated stirrer, with different pole shoe circuits,

Fig. 7 + 8:

a mold with two stirrers in a fourth embodiment, with different pole shoe circuits,

Fig. 9:

the stirrer according to FIG. 8 and the mold in side view,

Fig. 10:

a mold with two stirrers in a fifth embodiment,

Fig. 11 + 12:

a mold with two stirrers in a sixth embodiment, with different pole shoe circuits,

Fig. 13:

the stirrer according to FIG. 10 as well as the mold in side view,

Fig. 14:

a seventh embodiment of an electromagnetic, a mold associated stirrer and

Fig. 15

an electrical diagram for the stirrer of FIG. 14.

Fig. 1 shows schematically a mold 1 and its horizontal mold cavity cross-section, which is composed of two flange parts 2, 3 and a web part 4. The mold 1 is intended for continuous casting of double-T pre-profiles. The liquid steel is introduced substantially vertically into this continuous casting mold, in which the strand crust forms, and from which a Vorprofilstrang with liquid core of a strand guide with secondary cooling means is supplied.

According to the invention, the liquid core of the Vorprofilstranges preferably in the region of the mold 1 (theoretically possible would also be directly at the exit from the mold 1) by means of an electromagnetic stirrer 10 using electromagnetically induced forces in stirring movements transversely offset to the continuous casting and thereby the liquid steel in the sump the Vorprofilstranges between the flange 2, 3 and the web part 4 exchanged.

The stirrer 10 shown in Fig. 1 has an annular, the mold 1 in a certain height range surrounding, closed yoke 11 with six pole pieces 12 to 17, wherein each pole piece is surrounded by an electromagnetic coil 19. The pole shoes 12 to 17 are unevenly distributed on the circumference of the yoke 11, such that each pole piece 12, 13 on the flange 2, 3 and two pole pieces 14, 15; 16, 17 are aligned on both sides of the web part 4. The stirrer or rotary stirrer 10 operates on the principle of a 6-pole asynchronous motor in which a traveling field can be generated with the aid of 3-phase current. The correct wiring of the poles is important in order to obtain a linearly moving or rotating field.

In an embodiment shown in Fig. 2, the mold is again in a certain and preferably adjustable height range of an electromagnetic stirrer 20 surrounded by an annular closed yoke 21, on whose circumference in turn six pole pieces 22 to 27 are distributed unevenly, with the difference that all six pole shoes 22 to 27 are aligned with the web part 4.

According to FIGS. 3 to 6, the mold 1 is assigned in each case an electromagnetic stirrer 30 which has a closed yoke 31 surrounding the mold 1 and designed as a rectangular frame whose longitudinal sides each have three pole shoes 34, 35, 36 and 42 distributed over the mold width 37, 38, 39 are assigned, and the narrow sides are each provided with one on the flange parts 2, 3 frontally aligned center pole piece 32, 33. As described below The stirrer 30 can be operated both as a rotary stirrer and as a linear stirrer, depending on the pole circuit, ie, depending on which pole shoes and with which phase sequence (see phase designation U, V, W, U ', V', W ') Power to be set. It will be explained with reference to FIGS. 3 to 6, four different operating options in which six of the total of eight pole pieces 32 to 39 are under power.

In the pole circuit indicated in FIG. 3, the middle pole shoes 32, 33 are switched off in the flange area and the pole shoes 34, 35, 36 are phase-shifted on one longitudinal side of the yoke 31 opposite the pole shoes 37, 38, 39 on the other longitudinal side, whereby a linear, counter-rotating Flow is generated in the web part 4 (2x3-pole linear operation, in opposite directions).

4 also shows a circuit for a linear operation (middle pole shoes 32, 33 switched off in the flange area), without switching the phases on the longitudinal sides, so that in the web part 4 a co-current flow results (2x3-pole linear operation, the same direction).

In the wiring indicated in FIG. 5, middle pole shoes 32, 33 are energized in the flange region, but the middle of the three pole shoes 34, 35, 36; 37, 38, 39, which are assigned to the two longitudinal sides, switched off (pole shoes 35, 38 without power). Thus, rotation fields are generated in the flange areas (2x3-pole rotation operation). With the indicated phase allocation to the pole pieces 37, 32, 34 and 36, 33, 39, the direction of rotation of the rotation fields in the two flange 2, 3 is equal, whereby a flow in the web part 4 is formed, which, however, is less efficient than in the linear operation after Fig. 3.

In the case of a wiring of the pole shoes 37, 32, 34 and 36, 33, 39 according to FIG. 6, it is also possible with the stirrer 30 to generate rotation fields with opposite directions of rotation in the flange parts 2, 3.

FIGS. 7 and 8 show a variant in which the mold 1 has on its circumference two electromagnetic stirrers 40, 40 'or two yokes 41, 41' which are separated from one another in the widthwise direction of the mold 1, each with three pole shoes 42, 43, 44 ; 42 ', 43', 44 'are associated with each yoke 41, 41' with a on the respective flange part 2, 3 frontally aligned middle pole piece 42, 42 'and two on the flange part 2, 3 directed from both sides pole pieces 43, 44; 43 ', 44' is provided. With the two stirrers 40, 40 ', in turn, a 2x3-pole rotational operation can be accomplished or rotational fields can be generated in the flange regions 2, 3, which in turn have the same direction of rotation (FIG. 7) or the opposite direction of rotation (FIG. 8). respectively.

With the two stirrers 40, 40 'or yokes 41, 41' which are separated from one another in the width direction of the mold 1, one can thus achieve practically the same effect as with the stirrer 30 provided with the closed yoke 31 and according to FIG. 5 or 6. In addition, however, this solution brings additional benefits. The electromagnetic stirring can be carried out with two independent stirrers or half stirrers, which can be relatively easily brought from outside to the mold 1 / mounted. The free sector creates a designer's freedom. Not least, this solution also allows the two stirrers 40, 40 'arranged mutually offset in height, as indicated in Fig. 9, wherein the mutual and / or on the mold height related height arrangement of the stirrer 40, 40' can be preferably adjusted as needed.

10 to 12, in which the mold 1 in turn at its periphery two electromagnetic stirrers 50, 50 '(Fig. 10 and 13) or 60, 60' (Fig. 11 and 12) assigned are, however, not in width but in the thickness direction of the mold 1 separate yokes 51, 51 'and 61, 61' have. Each yoke is in each case with three pole shoes 52, 53, 54; 52 ', 53', 54 'and 62, 63, 64, respectively; 62 ', 63', 64 'equipped.

In the embodiment of Fig. 10, the three pole pieces 52, 53, 54; 52 ', 53', 54 'distributed over the entire width of the mold and two of them (pole pieces 52, 54, 52', 54 ') laterally directed to the flange 2, 3, and the middle pole piece 53, 53' projects up to the web part 4.

In the embodiment according to FIGS. 11 and 12, all three pole shoes 62, 63, 64; 62 ', 63', 64 'of the respective stirrer 60, 60' distributed only over the web portion width and protrude to the web portion. 4

The stirrers 50, 50 'and 60, 60' are operated as linear stirrers, whereby opposing flow (FIGS. 10 and 11) or a corotating flow (FIG. 12) can be produced in the web part 4.

Finally, FIG. 14 shows an electromagnetic stirrer 70 with an 8-pole structure, constructed in a manner similar to the stirrer 30 according to FIGS. 3 to 6 (with a yoke 71 formed as a rectangular frame whose longitudinal sides each have three pole shoes 74 distributed over the mold width) , 75, 76; 77, 78, 79 and whose narrow sides are each provided with a center-pole shoe 72, 73 aligned in a frontal manner on the flange parts 2, 3). However, this embodiment does not select between rotational and linear operation by turning off two of the eight poles, but at the same time linear arrays in the ridge portion 4 using a 1x6 pole linear stirrer (pole shoes 74, 75, 76, 77, 78, 79 ) and rotating fields in the flange parts 2, 3 using 2x3-pole rotary stirrers (pole shoes 74, 72, 77 and 76, 73, 79).

FIG. 15 shows an electrical diagram of the stirrer 70 with this 8-pole structure or this 8-pole system, in which the linear fields are simultaneously generated by means of a 1 × 6 pole linear stirrer and the rotation fields using these 2 × 3 pole rotary stirrers become. This electromagnetic stirrer 70 is fed by the network, for example, with three-phase current 50 Hz, by means of lines 81, 82, wherein the lines 81, 82 each lead to a frequency converter 83, 84. These frequency converters 83, 84 are connected to a converter control 85 and the individual phases are set by this to a predetermined frequency.

The control 85 has the task of matching the frequencies of the two converters to one another in order to synchronize the stirring movements generated in the web and in the transition region to the two flange parts. In addition, it should be the appearance of beat phenomena at slightly different Prevent frequencies of the two stirrers. A beating would mean that over time one and the other poles would be under full load at the same time, which would result in a very uneven network load.

Of these frequency converters 83, 84, the individual phases U, V, W of one converter 84 and the phases U ₁ , V ₁ , W _{1 of} the other converter 83 are connected to the pole pieces 74, 75, 76; 77, 78, 79 wound coils guided. The phases U, V, W lead to the coils 77 ', 78', 79 'at the pole shoes 77, 78, 79 in the web portion and further to the symmetrically arranged to these coils 76', 75 ', 74' of the pole pieces 76, 75, 74, wherein the connecting lines of the coils 77 ', 79' over the cross to the coils 76 ', 74' (connected in series) are guided. The lines are led from these coils to the star point 87. The same is provided in the phases U ₁ , V ₁ , W ₁ , which is not explained in detail. In the linear mode, the phase W _{1 is conducted} to the coil 72 'and further to the opposing coil 73' and further to a star circuit 88.

• Stabilisierung des Giessspiegelbereiches durch Unterdrückung der Turbulenzen auch bei wechselnden Prozessparametern wie Giessgeschwindigkeit, Giessspiegelposition (zwecks Vermeidung von nichtmetallischen Einschlüssen sowie Gasblasen in der Strangoberfläche);
• günstige, steuerbare Strömungsverhältnisse mit einem gezielten Flüssigstahlaustausch zwischen den beiden verdickten Hohlraumbereichen durch den dünnen Stegteil, auch bei einem asymmetrischen Einguss, und dadurch die Bildung einer gleichmässig dicken Strangschale mit günstigem Erstarrungsgefüge unter Vermeidung von Lunker und/oder Kernporosität;
• Vermeidung von Brückenbildungen während der Erstarrung trotz engen Verhältnissen im Stegteil des Formhohlraumquerschnittes.

With the electromagnetic stirrers 10 described above; 20; 30; 40, 40 '; 50, 50 '; 60, 60 '; 70 can thus - as already mentioned - the liquid core of Vorprofilstranges using electromagnetically induced forces in the region of the flange and / or the web part in stirring movements transversely offset to the continuous casting and thereby replaced the liquid steel in the bottom of the Vorprofilstranges between the flange and the web part become. As a result, the flow and temperature conditions in the liquid steel sump within the pre-profile strand shell can be actively influenced in a targeted manner and thus the following effects can be brought about:

• Stabilization of the Giessspiegelbereiches by suppression of turbulence even with changing process parameters such as casting speed, Giessspiegelposition (in order to avoid non-metallic inclusions and gas bubbles in the strand surface);
• favorable, controllable flow conditions with a targeted liquid steel exchange between the two thickened cavity areas through the thin web portion, even with an asymmetric sprue, and thereby the formation of a uniformly thick strand shell with favorable solidification structure while avoiding cavities and / or core porosity;
• Avoidance of bridge formation during solidification despite narrow conditions in the web portion of the mold cavity cross-section.

Claims (15)

Method for continuous casting of steel pre-profiles, in particular double-T pre-profiles, wherein the liquid steel is introduced substantially vertically into a continuous casting mold (1), whose hollow space cross-section is composed of two flange parts (2, 3) and a web part (4), and a Vorprofilstrang with liquid core from the mold (1) is fed to a strand guide with secondary cooling means, characterized in that the liquid core using electromagnetically induced forces in the region of the flange (2, 3) and / or the web part (4) in Stirring movements is offset transversely to the continuous casting and is replaced by the stirring movements of the liquid steel in the bottom of the Vorprofilstranges between the flange (2, 3) and the web part (4). A method according to claim 1, characterized in that the stirring movements in the region of the continuous casting mold (1) are generated. A method according to claim 1 or 2, characterized in that the stirring movements are generated in different, adjustable heights in Vorprofilstrang. Method according to one of claims 1 to 3, characterized in that by using electromagnetically induced forces in the region of the two flange parts (2, 3), in particular in thickened transition regions to the web, co-rotating or counterrotating rotational movements are generated in the liquid core. Method according to one of claims 1 to 4, characterized in that by using electromagnetically induced forces in the region of the web part (4) co-rotating or opposite linear movements are generated in the liquid core. Method according to one of claims 1 to 5, characterized in that the liquid steel via an inlet in the transition region between the web part (4) and one of the flange (2, 3) of the mold cavity asymmetrically fed into the continuous mold and on by the stirring movements in the mold cavity its cross section is distributed. Apparatus for carrying out the method according to claim 1, comprising a continuous casting mold (1) whose cavity cross-section comprises two flange parts (2, 3) and a web part (4), and a strand guide with secondary cooling devices, characterized in that at least one electromagnetic stirrer (10; 20; 30; 40, 40 '; 50, 50') is provided on the circumference of the pre-profile strand or continuous mold (1). 60, 60 ', 70) having a yoke (11; 21; 31; 41, 41'; 51, 51 '; 61, 61'; 71) with a number of pole shoes and electromagnetic coils surrounding them for generating comprises linearly traveling and / or rotating electromagnetic fields, the direction or direction of rotation of the fields can be determined by controllable Poleveraltung. Apparatus according to claim 7, characterized in that the stirrer (10; 20) has an annular closed yoke (11; 21) surrounding the continuous casting mold (1), on whose circumference six pole shoes (12, 13, 14, 15, 16 , 17; 22, 23, 24, 25, 26, 27) are distributed unevenly, such that they are aligned with the flange parts and the web part or only on the web part. Device according to claim 7, characterized in that the stirrer (30; 70) has a closed yoke (31; 71) surrounding the continuous casting mold (1) whose longitudinal sides are each provided with three pole shoes distributed over the mold width (FIG. 34, 35, 36, 37, 38, 39, 74, 75, 76, 77, 78, 79) and whose narrow sides each have a center pole shoe (32, 33, 72, 73) which is frontally aligned with the flange parts (2, 3) are provided. Device according to claim 9, characterized in that the power supply of the pole shoes is switchable, wherein either the narrow side associated Mittelpolschuhe (32, 33) or the middle of the three pole pieces (34, 35, 36, 37, 38, 39), the two long sides are assigned, can be disconnected from the power. Apparatus according to claim 7, characterized in that the continuous casting mold (1) has two stirrers (40, 40 ') or two yokes (41, 41') which are separated from one another in the width direction of the continuous casting mold (1), each having three pole shoes (42 , 43, 44; 42 ', 43', 44 '), each yoke (41, 41') having a center pole shoe (42, 42 ') aligned frontally on the respective flange part (2, 3) and two on the Flange part (2, 3) of both sides directed pole pieces (43, 44, 43 ', 44') is provided. Apparatus according to claim 7, characterized in that the continuous casting mold (1) has on its periphery two stirrers (50, 50 ') or two yokes (51, 51') which are separated from each other in the direction of thickness of the continuous casting mold (1), each with three pole shoes (52 , 53, 54; 52 ', 53', 54 ') are arranged, the three pole shoes being distributed over the width of the mold in each case, two of which being laterally applied to the flange parts (2, 3) and the middle pole shoe (53, 53'). directed to the web part (4). Apparatus according to claim 7, characterized in that the continuous casting mold (1) has on its periphery two stirrers (60, 60 ') or two yokes (61, 61') which are separated from one another in the direction of thickness of the continuous casting mold (1), each with three pole shoes (62 , 63, 64, 62 ', 63', 64 '), the three pole shoes being distributed over the web part width. Device according to one of claims 11 to 13, characterized in that the stirrers (40, 40 ', 50, 50', 60, 60 ') or yokes (41, 41', 51, 51 ', 61, 61') mutually offset in height are arranged in the mold area. Device according to claim 14, characterized in that the height arrangement of the stirrer (40, 40 ', 50, 50', 60 ', 60') or yokes (41, 41 ', 51', 51 ') relative to one another and / or the height of the mold is provided ', 61, 61') is adjustable.

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