EP1815925B1 - Method and apparatus for the continuous casting of double-T-bleam blanks - Google Patents

Description

The invention relates to a device and a method for continuous casting of double-T-steel pre-profiles according to the preamble of claim 1.

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.

In the publication JP-A-8294746 there is disclosed a double-T pre-profile die equipped with a pair of static N and S poles on each outside of the flanges and the land area to achieve a defect-free strand surface. These static magnetic poles have the purpose of creating a braking effect just below the two symmetrically arranged inlet tubes. A change in the geometry of the stirring motion is not provided in this stirring device.

The publication JP-A-10230349 discloses an electromagnetic stirring device to a square in cross-section mold format, in which the pole pieces evenly distributed over the circumference are arranged on a circular yoke and with these a rotating stirring motion can be effected.

The present invention has for its object to provide an apparatus and a method can be made with the double-T-steel pre-profiles with improved quality, even if it is a relatively thin web part and / or special steel grades.

This object is achieved according to the invention by devices according to claim 1, 2, 3 or 4 and the method according to claim 7.

Preferred refinements of the device according to the invention and of the method 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 elektromagnetischen Rührer, gemäss Stand der Technik,

Fig. 2:

eine Kokille im Querschnitt mit einem elektromagnetischen Rührer, gemäss Stand der Technik,

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 an electromagnetic stirrer, according to the prior art,

Fig. 2:

a mold in cross-section with an electromagnetic stirrer, according to the prior art,

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 stirrers after 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:

after the stirrer Fig. 10 and the mold in side view,

Fig. 14:

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

Fig. 15

an electrical scheme for the stirrer Fig. 14 ,

Fig. 1 schematically shows 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.

The liquid core of Vorprofilstranges is 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 to the continuous casting and thus the liquid steel in the bottom of the Vorprofilstranges between the flange 2, 3 and the web part 4 replaced.

The in Fig. 1 shown stirrer 10 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.

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

According to Fig. 3 to 6 The mold 1 is associated with an electromagnetic stirrer 30, which has a closed, formed as a rectangular frame yoke 31 surrounding the mold 1, the longitudinal sides of each three distributed over the mold width pole pieces 34, 35, 36 and 37, 38, 39 assigned are, and the narrow sides are each provided with a front on the flange 2, 3 center pole shoe 32, 33 are provided. 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 based on the Fig. 3 to 6 set forth four different operating options in which six of the total of eight pole pieces 32 to 39 are under power.

At the in Fig. 3 The pole shoes 32, 33 in the flange area are switched off 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).

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

At the in Fig. 5 indicated wiring are middle pole pieces 32, 33 in the flange under power, but the middle of the three pole pieces 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 a wiring of the pole pieces 37, 32, 34 and 36, 33, 39 after Fig. 6 can be generated with the stirrer 30 and rotation fields in the opposite direction of rotation in the flange 2, 3.

In FIGS. 7 and 8 a variant is shown in which the mold 1 at its periphery two electromagnetic stirrers 40, 40 'and two in the width direction of the mold 1 separate yokes 41, 41', each with three pole pieces 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 rotation operation can be accomplished or rotation fields can be generated in the flange areas 2, 3, which in turn have the same direction of rotation (FIG. Fig. 7 ) or the opposite direction of rotation ( Fig. 8 ) exhibit.

With the two in the width direction of the mold 1 separate stirrers 40, 40 'and Jochen 41, 41' can thus achieve practically the same effect as with the provided with the closed yoke 31 and after Fig. 5 or 6 switched stirrer 30. 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 in Fig. 9 indicated, wherein the mutual and / or on the mold height related height arrangement of the stirrer 40, 40 'can be preferably adjusted as needed.

The solutions also offer similar advantages 10 to 12 in which the mold 1 in turn has two electromagnetic stirrers 50, 50 '(FIG. Fig. 10 and 13 ) or 60, 60 '( FIGS. 11 and 12 ), which, however, are 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 according to Fig. 10 are the three pole shoes 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 are all three pole pieces 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 a linear stirrer, wherein in the web part 4 opposite flow ( Fig. 10 and 11 ) or a co-current flow ( Fig. 12 ) can be generated.

Finally shows Fig. 14 an electromagnetic stirrer 70 having an 8-pole structure constructed similarly to the stirrer 30 shown in FIG Fig. 3 to 6 (With a designed as a rectangular frame yoke 71, the longitudinal sides, each with three distributed over the mold width pole pieces 74, 75, 76; 77, 78, 79 and its narrow sides, each with a flange on the parts 2, 3 frontally aligned center pole shoe 72, 73 provided are). 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 x 6 pole linear stirrer and the rotation fields using these 2x3-pole rotary stirrers. 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 (12)

1. Apparatus for the continuous casting of steel I-cross-sectional shapes, comprising a continuous mold (1), whose mold cavity cross-section is composed of two flange parts (2, 3) and a web part (4), and a strand guide with secondary cooling devices,
   whereby at least one electromagnetic stirring device (30; 70) disposed outside of the cross section strand respectively the continuous mold (1) comprising a yoke (31: 71) with a number of pole shoes and those surrounding electromagnetic coils for the generation of linearly travelling and/or rotating electromagnetic fields, whereby the direction resp. rotating direction of the fields is definable by a controllable pole interconnection,
   characterized in that
   the stirring device (30; 70) comprises a closed yoke (31; 71), which surrounds the continuous mold (1) and is formed as a rectangular frame, each of their longitudinal sides are provided with three pole shoes (34, 35, 36, 37, 38, 39; 74, 75, 76; 77, 78, 79) distributed over the continuous mold width, and whose narrow sides are each provided with a respective central pole shoe (32, 33; 72, 73) oriented frontally towards the flange parts (2, 3),
   whereby the electric power supply of the pole shoes is switchable, whereby either the central pole shoes (32, 33) associated with the narrow sides or the centrals of the three pole shoes (34, 35, 36, 37, 38, 39), associated with the both longitudinal sides are disconnectable.
2. Apparatus for the continuous casting of steel I-cross-sectional shapes, comprising a continuous mold (1), whose mold cavity cross-section is composed of two flange parts (2, 3) and a web part (4), and a strand guide with secondary cooling devices,
   whereby at least one electromagnetic stirring device (40, 40') disposed outside of the cross section strand respectively the continuous mold (1) comprising a yoke (41, 41') with a number of pole shoes and those surrounding electromagnetic coils for the generation of linearly travelling and/or rotating electromagnetic fields, whereby the direction resp. rotating direction of the fields is definable by a controllable pole interconnection,
   characterized in that
   two stirring devices (40, 40') respective two yokes (41, 41') separated from one another in the width direction of the continuous mold (1), with three respective pole shoes (42, 43, 44; 42', 43', 44'), are associated with the continuous mold (1) at its circumference, whereby each yoke (41, 41') being provided with a central pole shoe (42, 42') oriented frontally towards the respective flange part (2, 3) and with two pole shoes (43, 44; 43', 44') directed towards the flange part (2, 3) from both sides.
3. Apparatus for the continuous casting of steel I-cross-sectional shapes, comprising a continuous mold (1), whose mold cavity cross-section is composed of two flange parts (2, 3) and a web part (4), and a strand guide with secondary cooling devices,
   whereby at least one electromagnetic stirring device (50, 50') disposed outside of the cross section strand respectively the continuous mold (1) comprising a yoke (51, 51') with a number of pole shoes and those surrounding electromagnetic coils for the generation of linearly travelling and/or rotating electromagnetic fields, whereby the direction resp. rotating direction of the fields is definable by a controllable pole interconnection,
   characterized in that
   two stirring devices (50, 50') respective two yokes (51, 51') separated from one another in the thick direction of the continuous mold (1) with three respective pole shoes (52, 53, 54; 52', 53', 54') are associated with the continuous mold (1) at its circumference, whereby the three pole shoes are in each case distributed over the mold width and thereby two of them are directed at the sides towards the flange parts (2, 3) and the central pole shoe (53, 53') projects up to the web part (4).
4. Apparatus for the continuous casting of steel I-cross-sectional shapes, comprising a continuous mold (1), whose mold cavity cross-section is composed of two flange parts (2, 3) and a web part (4), and a strand guide with secondary cooling devices,
   whereby at least one electromagnetic stirring device (60, 60') disposed outside of the cross section strand respectively the continuous mold (1) comprising a yoke (61, 61') with a number of pole shoes and those surrounding electromagnetic coils for the generation of linearly travelling and/or rotating electromagnetic fields, whereby the direction resp. rotating direction of the fields is definable by a controllable pole interconnection,
   characterized in that
   two stirring devices (60, 60') respective two yokes (61, 61') separated from one another in the thick direction of the continuous mold (1) with three respective pole shoes (62, 63, 64; 62', 63', 64') are associated with the continuous mold (1) at its circumference, whereby the three pole shoes are distributed over the web part width.
5. Apparatus according to anyone of the claims 2 to 4, characterized in that the stirrers (40, 40'; 50, 50'; 60, 60') are one to the other disposed staggered in the height of the continuous mold region.
6. Apparatus according to claim 5, characterized in that the height arrangement of the stirrers (40, 40'; 50, 50'; 60, 60') respective the yokes (41, 41'; 51, 51'; 61, 61') is adjustable from one to the other and/or in respect to the mold height.
7. Method for the continuous casting of steel sectional shapes with an apparatus according to anyone of the claims 1 to 6, whereby the molten core is caused to stirring movements transversely to the strand casting direction by the electromagnetically induced forces in the region of the flange parts (2, 3) and/or of the web part (4), and the molten steel is exchanged by the stirring movements in the crater of the sectional shape strand between the flange parts (2, 3) and the web part (4).
8. Method according to claim 7, characterized in that the stirring movements are generated in the region of the continuous mold.
9. Method according to claim 7 or 8, characterized in that the stirring movements are generated in different adjustable heights in the sectional shape strand.
10. Method according to anyone of the claims 7 or 9, characterized in that rotational movements in the same or opposite directions in the molten core are generated by the electromagnetically induced forces in the region of the flange parts (2, 3), in particular in the thickened junction regions of the web.
11. Method according to anyone of the claims 7 or 10, characterized in that linear movements in the same or opposite directions in the molten core are generated by the electromagnetically induced forces in the region of the web part (4).
12. Method according to anyone of the claims 7 or 11, characterized in that the molten steel is supplied over an ingate in the junction region between the web part (4) and one of the flange parts (2, 3) of the cavity asymmetrically into the mold and is distributed in the cavity over its cross section by the stirring movements.

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