EP2788133B1 - Process engineering measures in a strand casting machine at the beginning of casting, at the end of casting, and during the manufacturing of a transition piece - Google Patents

Description

Field of engineering

The present invention relates to a method for operating a continuous casting machine at casting start, at the end of casting and at a temporary slowing down of the casting operation.

• Einführen eines Kaltstrangs in die Stranggießmaschine;
• Halten des Kaltstrangs in der Strangführung, wobei ein Kaltstrangkopf die Kokille fluiddicht abschließt;
• Angießen der Stranggießmaschine, wobei flüssiger Stahl in die Kokille gegossen wird und sich dabei ein zumindest teilerstarrter Strang, der einen Stranganfang, einen nachfolgenden Stranganfangsbereich mit einer Länge A, 0,5 < A < 5 m, und nachfolgend einen Stranghauptteil aufweist, ausbildet; und
• Ausziehen des Kaltstrangs, wobei der Kaltstrang in einer Gießrichtung aus der Kokille ausgezogen wird.

On the one hand, the invention relates to a method for operating a continuous casting machine at casting start, wherein the continuous casting machine comprises a mold and a strand guide, and the strand guide comprises at least a pair of engagable strand guide rollers and at least one cooling nozzle, comprising the following method steps:

• Inserting a cold strand into the continuous casting machine;
• Holding the cold strand in the strand guide, wherein a cold strand head, the mold fluid-tightly;
• Casting the continuous casting machine, wherein liquid steel is poured into the mold, thereby forming an at least partially solidified strand having a strand beginning, a subsequent strand starting region having a length A, 0.5 <A <5 m, and subsequently a strand main part; and
• Extracting the cold strand, wherein the cold strand is drawn out of the mold in a casting direction.

• Stranggießen eines Strangs, wobei in der Kokille flüssiger Stahl zu einem zumindest teilerstarrten Strang vergossen wird;
• Stoppen der Zufuhr von flüssigem Stahl in die Kokille, wodurch sich in der Kokille ein Strangende ausbildet, sodass der Strang ein Strangende, einen nachfolgenden Strangendbereich mit einer Länge B, 0,5 < B < 5 m, und nachfolgend einen Stranghauptteil aufweist; und
• Ausziehen des Strangs, wobei der Strang in einer Gießrichtung aus der Kokille ausgezogen wird.

On the other hand, the invention relates to a method for operating a continuous casting machine at the end of casting, wherein the continuous casting machine comprises a mold and a strand guide, and the strand guide comprises at least one pair of engagable strand guide rolls and at least one cooling nozzle, comprising the following method steps:

• Continuously casting a strand, wherein in the mold liquid steel is poured into an at least partially solidified strand;
• Stopping the supply of liquid steel into the mold, whereby a strand end is formed in the mold, so that the strand has a strand end, a subsequent strand region with a length B, 0.5 <B <5 m, and subsequently a strand main part; and
• Extracting the strand, wherein the strand is pulled out of the mold in a casting direction.

• Stranggießen eines Strangs, wobei in der Kokille flüssiger Stahl zu einem zumindest teilerstarrten Strang vergossen wird;
• Ausziehen des Strangs mit einer Geschwindigkeit v, wobei der Strang in einer Gießrichtung mit v im Wesentlichen gleich einer Nenn-Geschwindigkeit v_Nenn aus der Kokille ausgezogen wird;
• Reduzieren einer Zufuhrrate von flüssigem Stahl in die Kokille, wodurch die Ausbildung eines Übergangsstücks beginnt;
• Ausziehen des Strangs mit v < v_Nenn;
• Erhöhen der Zufuhrrate von flüssigem Stahl, wodurch die Ausbildung eines Übergangsstücks beendet wird, sodass der Strang einen unteren Stranghauptteil, ein Übergangsstück und einen oberen Stranghauptteil aufweist;
• Ausziehen des Strangs mit v ≈ v_Nenn.

Finally, the invention relates to a method for operating a continuous casting machine during a temporary deceleration of the casting operation (eg in the course of a ladle change), wherein the continuous casting machine comprises a mold and a strand guide, and the strand guide comprises at least a pair of engageable strand guide rollers and at least one cooling nozzle the following process steps:

• Continuously casting a strand, wherein in the mold liquid steel is poured into an at least partially solidified strand;
• Withdrawing the strand at a speed v, wherein the strand is drawn out of the mold in a casting direction with v substantially equal to a nominal velocity v _nominal ;
• Reducing a supply rate of liquid steel into the mold, thereby starting to form a transition piece;
• Extract the strand with v <v _nominal ;
• Increasing the supply rate of liquid steel, thereby completing the formation of a transition piece such that the strand has a lower strand body, a transition piece, and an upper strand body;
• Extract the strand with v ≈ v _nominal .

State of the art

It is known that the operation of a continuous casting machine at casting start or at the end of casting requires special measures to protect the machine from overload and damage.

From the US 6,779,587 B2 It is known to switch in the event of exceeding a maximum contact force in the employment of engagable strand guide rollers to a strand of a position control to a pressure control. This should prevent damage to the strand guide by the cold strand during casting start. Since, according to the document, the cooling during casting start is not changed compared to the nominal operation, the strand beginning or strand end is cooled "too hard" (ie the strand ends are significantly colder than the strand lying between them). As a result, the quality of the two strand ends is reduced, so that these parts typically have to be separated before a subsequent rolling process. Ultimately, this results in lower productivity of the continuous casting machine and additional effort in the further processing of the strand.

From the US 4,317,482 It is known to continuously monitor the strand extraction forces in a continuous casting machine in order to prevent damage to the continuous casting machine or leakage of liquid metal ("spill-out") from the partially solidified strand. This informs the operating team about imminent problems in the continuous casting machine; However, how these problems can be prevented preventively, the font can not be found.

From the EP 1 697 070 B1 measures are known in a manifold change to keep the entry of foreign particles in the strand low. Furthermore, the casting speed is reduced in the manifold change, forming a so-called transition piece.

Concrete instructions on what measures to protect the continuous casting machine at casting start, at the end of casting or in the creation of a transition piece are made, can not be found in the above writings.

US 4,169,498 A discloses a reduction of the casting speed, the amount of coolant per time in [l / min] and the amount of coolant per strand surface in [l / m ² ] as a function of the time at casting start and casting end.

Summary of the invention Technical task

• die Qualität der Strangenden (des Stranganfangs und Strangendes) verbessert wird, und
• die Stranggießmaschine bei der Anwendung des Verfahrens präventiv vor Beschädigungen geschützt wird.

The object of the invention is to overcome the disadvantages of the prior art and each represent an operating method for a continuous casting at casting start, at the end of casting, and at a slowing of the casting operation, with which

• the quality of strand ends (strand beginning and strand ends) is improved, and
• the continuous casting machine is preventively protected against damage when applying the method.

Technical solution

This object is achieved by a method according to claim 1. Advantageous effects of the invention are the subject of the dependent claims.

• Erfassen einer Position des Stranganfangs in der Strangführung;
• nachdem der Stranganfang, vorzugsweise ein oberes Ende des Stranganfangsbereich, das Paar von anstellbaren Strangführungsrollen passiert hat: Anstellen des Paars an den Strang, sodass das Paar den Strang berührt;
• Kühlen des Stranganfangsbereichs mit Q < Q_Nenn , wobei die Kühldüse eine Kühlmittelmenge Q kleiner einer Nennkühlmittelmenge Q_Nenn auf den Stranganfangsbereich ausbringt;
• Kühlen des Stranghauptteils mit Q ≈ Q_Nenn , wobei die Kühldüse eine Kühlmittelmenge Q im Wesentlichen gleich Q_Nenn auf den Stranghauptteil ausbringt.

Claim 1 relates to a method for operating a continuous casting machine at casting start of the type mentioned, with the additional process steps:

• Detecting a position of the strand start in the strand guide;
• after the strand beginning, preferably an upper end of the strand beginning region, has passed through the pair of engagable strand guide rolls: setting the pair to the strand so that the pair contacts the strand;
• Cooling the strand start region with Q < Q _nominal , the cooling nozzle applying a coolant quantity Q smaller than a _nominal coolant quantity Q _nominal to the strand start region;
• Cooling the strand main part with Q ≈ Q _nominal , wherein the cooling nozzle a coolant quantity Q is substantially equal to Q _rated on the strand main body.

The term continuous casting machine covers all casting machines which are suitable for the continuous production of a strand with a long or flat product cross section from a molten steel.

The invention is based on the recognition that the strand ends, i. the strand beginning and strand end being colder than the intervening strand (hereinafter also referred to as strand main part) which is continuously cast at nominal casting conditions. This is mainly due to the reduced casting speed at the casting start and casting end. In addition, heat is transferred via the cold strand or through the water, which in addition to the strand end or the strand board, i. the end face of the Strangendes, arrives, dissipated. Because of the lower temperature, the strand ends i.A. completely solidified. If these two cold and solidified strand ends are transported through the machine, it can be used especially in the bending and straightening zone (ie in the zones where the strand is bent from the vertical into the arched form or bent back from the arched form into the horizontal) greatly increased roller forces, which are caused by the contact of individual (or at least less) rollers with these strand parts (instead of contact of several roles in one area, so that there is a division of forces). The roller forces can be far above the maximum permissible values of the roller bearings and thus lead to damage of the rollers or the roller position.

According to the invention, after the introduction of the dummy bar, the holding of the dummy bar and the casting of the continuous casting machine, the position of the cold rod head or the strand beginning - which is the cold strand head opposite - when pulling out the cold strand (or the strand, since the strand is connected to the cold strand) in the strand guide temporally discrete or discretized in time (eg at defined sampling times) detected (English "tracked"). After the strand beginning, or preferably the upper end of the strand beginning region having a length of length A, 0.5 <A <5 m, has passed through a pair of engageable strand guide rolls, the pair is turned to the strand so that the pair touches the strand , Furthermore, the strand start region is cooled less by a cooling nozzle than the strand main part, which adjoins the strand start region; Specifically, the strand start region is cooled with a coolant quantity Q <Q _nominal and the strand main part with a coolant quantity Q ≈ Q _nominal . Thus, the strand beginning is "softer cooled" in the language of the art as the strand main part. As a result, the temperature of the strand start region corresponds more closely to the temperature of the strand main part, which is poured continuously at nominal casting conditions. Preferably, only after the strand start has a distance of typically several meters in the casting direction from a pair of opposed strand guide rolls, the pair of opposed strand guide rolls on the strand and the strand through at least one cooling nozzle in the region of the pair of employed strand guide roller with the _nominal coolant quantity Q _Nenn cooled. The fact that at the casting start the actual casting gap between the strand guide rollers and the strand - not technically common - is applied directly to the strand beginning, but only a few meters after the Stranganfang, it is avoided that there is an unwanted contact of the rollers with the dummy strand or Soft Reduction is not used on the cold and therefore very hard strand starting area. Thus, since the strand guide rollers do not touch the strand start region, on the one hand further cooling of the strand by the typically cooled rolls is avoided; On the other hand, damage to the rollers is prevented by the strand starting area preventively and reliably.

In this application, under a engageable strand guide role to both a individually engageable strand guide role (see, eg WO2011 / 095383 ), a strand guide roller of a strand guide segment, which is made by the inclination of the clamping cylinder of the segment, or a strand guide roller, which by a (see, eg WO01 / 94051 ) or two Anstellzylinder is hired to the strand understood.

The rated coolant quantity Q _{Nenn is} preferably dependent on the casting speed, the strand age or particularly preferably on the location-dependent strand temperature. For a casting speed dependent quantity of coolant, Q _{rated is} smaller at a low casting speed than at a higher casting speed. With a nominal coolant quantity Q _Nenn which depends on the strand temperature, the strand temperature can be determined either by measurement (eg by means of a pyrometer) or by online simulation of the strand temperature (eg by the software package Dynacs or Dynacs 3D).

It is advantageous that the amount of coolant Q discharged from the cooling nozzle to the strand start region is increased as a function of a distance between the strand start and the cooling nozzle, where Q ≦ Q _nominal . Increasing the amount of refrigerant causes the temperature of the strand start region to be adjusted reasonably evenly to the temperature of the strand main body continuously poured at nominal casting conditions. The increase in the amount of coolant can be done either continuously or in discrete steps. The distance should be understood as the difference between the so-called metallurgical lengths.

In order to avoid in particular segregations in the strand, it is advantageous if the strand is reduced by the employment of the pair of engagable strand guide rollers to the strand in its thickness.

It is particularly advantageous if the strand has a liquid core in the reduction of its thickness. This will cause u.A. also reduced the forces in the reduction.

The object of the invention is also achieved by a method according to claim 5. Advantageous effects of the invention are the subject of the dependent claims.

• Erfassen einer Position des Strangendes in der Strangführung;
• bevor das Strangende, vorzugsweise ein unteres Ende des Strangendbereichs, das Paar von anstellbaren Strangführungsrollen passiert hat: Zurückziehen des Paars von anstellbaren Strangführungsrollen, sodass das Paar den Strang nicht berührt;
• Kühlen des Stranghauptteils mit Q ≈ Q_Nenn , wobei die Kühldüse eine Kühlmittelmenge Q im Wesentlichen gleich einer Nennkühlmittelmenge Q_Nenn auf den Strangendbereich ausbringt;
• Kühlen des Strangendbereichs mit Q < Q_Nenn, wobei die Kühldüse eine Kühlmittelmenge Q < Q_Nenn auf den Strangendbereich ausbringt;
• Kühlen des Strangendes mit Q ≥ Q_Nenn , wobei die Kühldüse eine Kühlmittelmenge Q ≥ Q_Nenn auf das Strangende ausbringt.

Claim 5 relates to a method for operating a continuous casting at Gießende of the aforementioned type, with the additional steps:

• Detecting a position of the strand end in the strand guide;
• before the strand end, preferably a lower end of the strand area, has passed through the pair of engageable strand guide rolls: retracting the pair of adjoining strand guide rolls such that the pair does not contact the strand;
• Cooling the strand main body with Q ≈ Q _nominal , wherein the cooling nozzle applies a coolant amount Q substantially equal to a rated coolant amount Q _rated to the throat area;
• Cooling the strand area with Q < Q _nominal , the cooling nozzle applying a quantity of coolant Q < Q _nominal to the strand area;
• Cooling the skein end with Q ≥ Q _nominal, wherein the cooling nozzle comprises applying a coolant quantity Q ≥ Q _rated on the strand end.

By introducing the pouring end, a strand end is formed in the mold, followed by a strand region with a length B and a strand main part in the casting direction. At least after the pouring end has been initiated and the supply of molten steel into the mold has been stopped, eg by closing a distributor plug, the position of the strand end in the strand guide is in turn detected. To avoid damage to a pair of engageable strand guide rollers, the pair of engagable strand guide rollers are replaced by the strand end, Preferably, before a lower end of the strand area, the couple has passed, pulled back from the strand, so that the two strand guide rollers no longer touch the strand (positively formulated means that both strand guide rollers spaced from the surface of the strand). The strand body is cooled substantially with the nominal coolant quantity Q _nominal ; the line section is cooled with a coolant Q <Q _Nenn and the end of the line is cooled with coolant Q ≥ Q _Nenn . Weaker cooling of the strand area tends to adjust the temperature of this area to the temperature of the strand body, improving the quality. By strongly cooling the strand end, it is ensured that the strand plate completely solidifies, so that no liquid metal can escape. For many steel grades it is sufficient to apply the strong cooling of the strand end only in the first cooling zones (eg the cooling zones 1 to 3 immediately after the mold).

In order to achieve the most uniform possible temperature of the strand region, it is advantageous if, during cooling of the strand region, the coolant quantity Q discharged from the cooling nozzle is reduced as a function of a distance between the strand end and the cooling nozzle, where 0 <Q <Q _nominal .

In order to avoid a "spill-out" at the end of the casting, it is advantageous if, during cooling of the strand end, the cooling nozzle applies a maximum coolant quantity Q = Q _Max to the strand. As a result, the end plate-at least in the first three cooling zones of the strand guide-is subjected to the maximum water flow rate, so that spill-out is reliably prevented.

In order to reduce the water consumption or to prevent the unwanted cooling of the strand by dripping cooling water, it is advantageous to stop the cooling by the cooling nozzle after the strand end has passed the cooling nozzle. The object of the invention is also achieved by a method according to claim 9. Advantageous effects of the invention are the subject of the dependent claims.

• Erfassen der Positionen eines unteren Endes und eines oberen Endes des Übergangsstücks in der Strangführung;
• bevor das untere Ende des Übergangsstücks das Paar von anstellbaren Strangführungsrollen passiert hat: Zurückziehen des Paars von anstellbaren Strangführungsrollen vom Strang, sodass das Paar das Übergangsstück nicht berührt;
• nachdem das obere Ende des Übergangsstücks das Paar von anstellbaren Strangführungsrollen passiert hat: Anstellen des Paars von anstellbaren Strangführungsrollen an den Strang, sodass das Paar den Strang berührt;
• Kühlen eines Stranghauptteils mit Q ≈ Q_Nenn , wobei die Kühldüse eine Kühlmittelmenge Q im Wesentlichen gleich einer Nennkühlmittelmenge Q_Nenn auf den Stranghauptteil ausbringt;
• Kühlen des Übergangsstücks mit Q < Q_Nenn , wobei die Kühldüse eine Kühlmittelmenge Q < Q_Nenn auf das Übergangsstücks ausbringt

Claim 9 relates to a method for operating a continuous casting machine in a temporary slowdown of the casting operation of the type mentioned, with the additional method steps:

• Detecting the positions of a lower end and an upper end of the transition piece in the strand guide;
• before the lower end of the transition piece has passed the pair of engagable strand guide rollers: retracting the pair of engagable strand guide rollers from the strand such that the pair does not contact the transition piece;
• after the upper end of the transition piece has passed the pair of engagable strand guide rollers: adjusting the pair of engageable strand guide rollers to the strand so that the pair contacts the strand;
• Cooling a strand main body with Q ≈ Q _nominal , wherein the cooling nozzle applies a coolant amount Q substantially equal to a rated coolant amount Q _rated to the strand main body;
• Cooling of the transition piece with Q <Q _nominal, wherein the cooling nozzle is a refrigerant quantity Q <Q _Nominal comprises applying to the transition piece

By reducing the amount of liquid steel supplied and the reduction of the pullout pullout speed resulting from the continuity, a so-called transition piece is formed in the strand, which is considerably colder than the strand main part. Damage to the strand guide is prevented by retracting a pair of engageable strand guide rolls prior to passing the transition piece such that the strand guide rolls do not contact the transition piece. After passing the transition piece, the pair is put back on the strand so that the rolls of the pair touch the strand. Because the transition piece is less strong ("softer") is cooled as the strand main parts, the temperatures of the transition piece and the strand main parts are at least partially adjusted. This increases the quality of the transition piece.

Brief description of the drawings

• Fig 1 eine schematische Darstellung des erfindungsgemäßen Verfahrens beim Gießstart, wobei die unterschiedlichen Phasen in den Subfiguren 1a bis 1d dargestellt sind;
• Fig 2 eine schematische Darstellung des erfindungsgemäßen Verfahrens beim Gießende, wobei die Phasen in den Subfiguren 2a bis 2f dargestellt sind;
• Fig 3 eine schematische Darstellung der Kühlmengenverteilung in einem Stranganfangsbereich;
• Fig 4 eine schematische Darstellung der Kühlmengenverteilung in einem Strangendbereich; und
• Fig 5 eine schematische Darstellung des erfindungsgemäßen Verfahrens bei einer vorübergehenden Verlangsamung des Gießbetriebs, wobei die Phasen in den Subfiguren 5a bis 2f dargestellt sind.

Further advantages and features of the present invention will become apparent from the following description of non-limiting embodiments, reference being made to the following figures, which show the following:

• Fig. 1 a schematic representation of the method according to the invention at the casting start, wherein the different phases are shown in the subfigures 1a to 1d;
• Fig. 2 a schematic representation of the method according to the invention at the end of casting, the phases are shown in the subfigures 2a to 2f;
• Fig. 3 a schematic representation of the cooling amount distribution in a Stranganfangsbereich;
• Fig. 4 a schematic representation of the cooling amount distribution in a strand region; and
• Fig. 5 a schematic representation of the method according to the invention in a temporary slowing down of the casting operation, wherein the phases are shown in the subfigures 5a to 2f.

Description of the embodiments

FIG. 1 shows the inventive method for operating a continuous casting machine at casting start, the method steps are shown in more detail in the subfigures 1a to 1d. The continuous casting machine 1 is in this case as a vertical continuous casting machine with a cooled Run through mold 3 executed, which is designed for the continuous casting of liquid steel to a strand 2 with billet or Vorblockprofilquerschnitt. The strand guide 4 has a plurality of pairs of mutually engageable with the strand 2 strand guide rollers 5 and a plurality of cooling nozzles 10. In the continuous casting operation liquid steel is introduced by means of a dip tube, not shown, in the mold 3, where the molten steel is cooled by a so-called primary cooling and thereby forming a teilerstarrter strand 2 with a thin strand shell.

Fig. 1a shows the situation before the start of pouring, which is referred to in this application as pouring start. After a cold strand 6 has been introduced into the mold 3 from above, the cold strand 6 is held in the strand guide 4, for example by drivable strand guide rollers 8, so that the head of the cold strand (the cold strand head 7) closes the mold fluid-tight.

1b shows the situation when casting the continuous casting machine 1. A casting distributor, not shown, fills molten steel via a dip tube (narrow SEN) in the mold 3, wherein in the mold a casting level (the so-called meniscus 15) is established. As a result of the cooling of the melt in the mold 3, a partially solidified strand 2 is formed, which has a strand beginning 16, a strand starting region 17 having a length A, and a strand main part 20. At the contact surface between the cold strand head 7 and the strand 2, the strand beginning 16 is formed, which is welded to the cold strand head 7. Contrary to the casting direction 9, the strand starting region 17 follows on the strand beginning 16, and the strand main part 20 follows on the strand starting region 17. The at least partially solidified strand 2 is drawn out of the mold 3 and further cooled by means of the cooling nozzles 10 of the secondary cooling. In this embodiment, the strand start region has a length A of 3 m.

Fig. 1c shows the situation when pulling the dummy bar 6 from the mold 3. The mold level 15 in the mold is kept constant by the supply of molten steel, so that by pulling in the casting 9 of the dummy bar 6 - which is connected to the strand 2 - by the drivable strand guide rollers 8 is also pulled out of the mold. For the further method steps, it is crucial that the position of the cold strand head 7 or the position of the strand start 16 in the strand guide is detected. This is done for example by a rotary encoder, which is connected to an employee, driven strand guide roller 8. Of course, the person skilled in the art also knows of other ways in which the position of the cold extruder head can be detected or "tracked". After the strand beginning 16 has passed a pair of engageable strand guide rollers 5, the pair 5 of the opposite strand guide rollers is employed on the strand 2. In the Fig. 1c This is specifically the case with the two upper strand guide rollers 5, the employment of which has been indicated on the strand 2 by an arrow. In addition, it can be seen in this figure that the topmost pair of cooling nozzles 10 delivers a reduced amount of coolant Q <Q _{nominal of} the cooling medium water to the strand start region 17. The reduced amount of refrigerant is represented in the figures by a thin jet of coolant. The strand starting region 17 is defined by the strand beginning 16 and by the length A.

Fig. 1d shows a further situation at the casting start, wherein the strand 2 has been further pulled out of the mold 3. Specifically, the strand beginning 16 has passed the two top pairs of strand guide rollers 5, so that both pairs are employed on the strand 2. The strand starting region 17 with a length of A = 3 m, which is cooled with a reduced amount of coolant is also shown. The uppermost cooling nozzle 10 is already outside the strand start region 17, so that the strand main part 20 of the strand 2 with the nominal coolant quantity Q _Nenn , in concrete Case depends on the casting speed, is cooled. The output of the nominal coolant quantity is shown in the figures by a wide coolant jet.

According to an alternative method, the engageable strand guide rollers 5 are not hired immediately after passing the strand start 16 to the strand, but only after the upper end 17a has passed the rollers 5 and the strand beginning 16 has reached a position that the strand guide roller 5 to a downstream of certain distance A.

According to a further method, the quantity of coolant Q discharged from the cooling nozzle 10 onto the strand starting region 17 is increased as a function of a distance 11 between the strand start 16 and the cooling nozzle 10, where 0 <Q < Q _nominal . Thus, the strand beginning 16 and the strand start region 17 is less cooled than the subsequent strand main piece 20, wherein the amount of coolant Q is continuously or discretely increased to Q _nominal .

gegeben ist. Im Gegensatz dazu folgt die Kühlmittelmengenverteilung entsprechend der strichlierte Linie der Gleichung $Q=\frac{Q_{\mathit{Nenn}}-Q_{\mathit{Min}}}{A}x+Q_{\mathit{Min}},$

wobei Q_Min eine minimale Kühlmittelmenge für den Stranganfang 16 angibt. Fig. 3 shows how the amount of coolant Q discharged from a cooling nozzle 10 onto the strand starting region 17 of length A is determined by the distance x (in FIG Fig. 1d the reference numeral 11, wherein x runs counter to the casting direction 9) is increased between the strand start 16 and the cooling nozzle. The solid line indicates a cooling amount distribution, wherein the refrigerant amount Q by the equation $Q=\frac{Q_{\mathit{nominal}}}{A}x$

given is. In contrast, the coolant quantity distribution follows the dashed line of the equation $Q=\frac{Q_{\mathit{nominal}}-Q_{\mathit{min}}}{A}x+Q_{\mathit{min}}.$

where Q _Min indicates a minimum amount of coolant for strand beginning 16.

The FIG. 2 with the subfigures 2a to 2f show the process steps in Gießende also for the Vertical continuous casting machine for the production of long products according to Fig. 1 ,

Fig. 2a shows the continuous operation of the continuous casting machine 1, wherein all the strand guide rollers 5, 8 of the strand guide are employed on the strand 2 and the strand 2 is cooled by the cooling nozzles 10 with the _nominal coolant quantity Q _Nenn (represented by a wide coolant jet).

Fig. 2b shows the stopping of the supply of liquid steel into the mold 3, whereby the casting mirror or the meniscus 15 with respect to the stationary position of the Fig. 1a something sinks. As a result of the cooling of the molten steel in the mold, a strand end 18 is formed, followed by the strand region 19 in the casting direction 9 with a length B of, for example, 3 m, and the strand main part 20 having an indefinite length. The strand 2 is further drawn out in the casting direction 9 from the mold 3, wherein the position of the strand end 18 is detected in the strand guide 4. Since the top cooling nozzles are outside the strand area 19, the cooling nozzles 10 still bring the nominal coolant quantity Q _Nenn on the strand 2 from.

Fig. 2c Figure 4 shows a position of the strand 2 where, just before the lower end of the strand portion 19a has passed the uppermost pair of engagable strand guide rollers 5, the pair is withdrawn from the strand 2 so that the pair does not touch the strand region, ie the rolls of the pair are spaced apart have transversely to the casting 9 to the strand. Withdrawal is indicated by an arrow.

Fig. 2d shows a further position of the strand 2, wherein the strand portion 19 is cooled by the uppermost cooling nozzles 10 with a reduced coolant quantity Q <Q _nominal .

Fig. 2e shows another position of the strand 2 at the casting end, wherein the top two pairs of strand guide rollers 5 have been withdrawn from the strand. The second row of the cooling nozzles 10 cools the strand region 19 again with a reduced amount of coolant. However, after the strand end 18 has already reached a position at which the cooling region of the uppermost row of cooling nozzles 10 already detects the strand end, the strand end is cooled with the maximum coolant quantity Q = Q _Max .

Fig. 2f Finally, Fig. 3 shows the case where the strand end 18 has already passed the uppermost row of cooling nozzles 10, so that cooling by these cooling nozzles 10 is stopped. In the position shown, the third row of adjustable rollers 5 is withdrawn from the strand 2.

Also, in the casting end process, it is possible that, when cooling the strand portion 19, the amount of coolant Q discharged from a cooling nozzle 10 is reduced depending on a distance 11 between the strand end 18 and the cooling nozzle 10, where 0 <Q <Q _nominal .

gegeben ist. Im Gegensatz dazu ist die Kühlmittelmengenverteilung entsprechend der strichlierte Linie für den Abstand 0 < y < E mit Q = Q_Nenn und für den Abstand E < y < B durch die Gleichung $Q=\frac{Q_{\mathit{Nenn}}}{B-E}y$

gegeben. Fig. 4 shows how the amount of coolant Q discharged from a cooling nozzle 10 onto the stranding region 19 having a length B and to the strand end 18 having a length B is greater than the distance y (see FIG Fig. 2f where y is in the casting direction 9) between the strand end 18 and the cooling nozzle 10 is adjusted. The solid line indicates a cooling amount distribution, wherein for the distance 0 <y <E, the coolant quantity Q = Q _Max and for the distance E <y <B, the coolant quantity by the equation $Q=\frac{Q_{\mathit{nominal}}}{2\left(B-e\right)}y$

given is. In contrast, the coolant quantity distribution corresponding to the dashed line is for the distance 0 <y <E with Q = Q _nominal and for the distance E <y <B by the equation $Q=\frac{Q_{\mathit{nominal}}}{B-e}y$

given.

In Fig. 5 is the method for operating the continuous casting according to Fig. 1 shown at a temporary slowdown of the casting operation.

Fig. 5a shows the continuous operation of the continuous casting machine, wherein in a mold 3 liquid steel is poured into a partially solid strand 2 with billet profile. The strand is guided in the strand guide 4 by the employed strand guide rollers 5 and cooled by the cooling nozzles 10 with cooling water. In this case, the strand 2 is continuously pulled out at a pull-out speed v _nominal by the drivable strand guide rollers 8 in the casting direction 9 from the mold.

Fig. 5b shows the situation in the reduction of the supply rate of liquid steel in the mold 3. By withdrawing the amount of steel supplied to the mold 3, the meniscus 15 drops slightly. At the same time or immediately after the reduction, the pullout pullout speed v is also reduced so that v <v _nominal . By reducing the flow rate of steel into the mold 3 and the reduction of the extraction speed v, the formation of a transition piece 21 is initiated, wherein in the Fig. 5b the lower end 21a of the transition piece is formed.

In Fig. 5c is the reduced inflow rate and the reduced extraction speed v of Fig. 5b maintained, whereby the transition piece 21 further developed. The transition piece in the casting direction 9 subsequent strand part is referred to as the lower strand main piece 20a.

In Fig. 5d the continuous rated operation of the continuous casting machine 1 is restored, wherein the inflow rate and the pullout pullout speed are increased again to the nominal values. In this case, the upper end 21 b of the transition piece 21 is formed, whereby the formation of the transition piece 21 is terminated.

The positions of the upper 21b and lower end 21a of the transition piece 21 are e.g. detected by the driven strand guide rollers 8, so that their positions for the subsequent position of the engageable strand guide rollers 5 and the cooling nozzles 10 can be used.

Fig. 5e shows how the strand 2 with the lower strand main piece 20a, the transition piece 21 and the upper strand main piece 20b, which follows the transition piece, is pulled out of the mold 3 with v _nominal . The uppermost pair of strand guide rollers 5 is immediately before the lower end 21 a of the transition piece 21 passes the pair 5, withdrawn from the strand 2 (shown by arrows), so that the rollers of the pair 5 do not touch the transition piece 21. As a result, the transition piece 21 is cooled less strongly by the cooled strand guide rollers 5 than the strand main pieces 20a, 20b. The uppermost pair of cooling nozzles 10 cools the lower strand main piece 20a of the strand 2 with a coolant quantity Q = Q _nominal .

Fig. 5f shows another situation in the production of the transition piece 21. The strand 2 is further extended, wherein the top pair of strand guide rollers was again turned on the strand 2 and the upper strand main piece 20b. Also, the second pair of strand guide rolls has already undergone this sequence of strand withdrawal and reinstatement to the strand. Also, the uppermost pair of cooling nozzles 10 has undergone a sequence in which the lower and upper strand main pieces 20a, 20b have been cooled with Q = Q _nominal and the intermediate transition piece 21 with Q <Q _nominal . In the figure, a reduced amount of coolant is represented by a thinner coolant jet. The third pair of rollers 5 has been withdrawn from the strand before the lower end 21a of the transition piece 21 passes the rollers, so that the rollers do not touch the transition piece 21. In Fig. 5f the transition piece 21 through the second pair of cooling nozzles 10 cooled with a coolant amount Q <Q _nominal .

Thus, the engageable strand guide rollers 5 are moved according to the position of the transition piece 21, so that the rollers do not touch the transition piece 21. The retraction may be either immediately prior to passing the lower end 21a, or already done a few meters before actually passing. Similarly, the adjustment of the pair of rollers 5 can be done either immediately after passing the upper end 21b of the transition piece, or only a few meters after the actual passing of the transition piece 21st

Although the invention has been illustrated in the embodiments for a vertical continuous casting machine, the invention is by no means limited thereto. Rather, it is fully applicable to vertical, bow and horizontal casters. However, in sheet-fed machines, it should be noted that the distance between two elements (e.g., a strand end and a cooling nozzle) is given by the arc length of a neutral strand fiber between these elements.

While the invention has been further illustrated and described in detail by the preferred embodiments, the invention is not limited by the disclosed examples, and other variations can be derived therefrom by those skilled in the art without departing from the scope of the invention.

List of reference numbers

1

continuous casting

2

strand

3

mold

4

strand guide

5

adjustable strand guide roller

6

dummy bar

7

Dummy bar head

8th

drivable strand guide roller

9

casting

10

cooling nozzle

11

distance

15

meniscus

16

Stranganfang, lower end of the Stranganfangsbereichs

17

Strand initial region

17a

upper end of the strand beginning area

18

strand end

19

Strangendbereich

19a

lower end of the strand area

20

Strand main part

20a

lower strand body

20b

upper strand body

21

Transition piece

21a

lower end of the transition piece

21b

upper end of the transition piece

A

length

Q

Amount of coolant

Q _rated

Nominal amount of coolant

Q _Min

Minimum amount of coolant

Q _Max

Maximum coolant quantity

x, y

distance

Claims (9)

1. Method for operating a strand casting machine (1) at the beginning of casting, wherein the strand casting machine (1) comprises a die (3) and a strand guide (4), and the strand guide (4) comprises at least one pair of deployable strand guide rollers (5) and at least one cooling nozzle (10), having the following method steps:

   - inserting a cold strand (6) into the strand casting machine (1) ;

   - holding the cold strand (6) in the strand guide (4), wherein a cold strand head (7) seals the die (3) in a fluid tight fashion;

   - casting the strand casting machine (1), wherein liquid steel is cast into the die (3) and in the process an at least partially rigid strand (2), which has a strand start (16), a subsequent strand start area (17) with a length A, 0.5 < A < 5m, and subsequently a main strand part (20), is formed;

   - extracting the cold strand (6), wherein the cold strand (6) is extracted from the die (3) in a casting direction (9);

   - detecting a position of the strand start (16) in the strand guide (4);

   - because the strand start (16), preferably an upper end (17a) of the strand start area (17) has passed the pair of deployable strand guide rollers (5); deploy the pair on the strand (2) so that the pair touches the strand (2);

   - cooling the strand start area (17) with Q < Q_Nom , wherein the cooling nozzle (10) yields a coolant quantity Q of less than a nominal coolant quantity Q_Nom onto the strand start area (17);

   - cooling the main strand part (20) with Q ≈ Q_Nom wherein the cooling nozzle (10) yields a coolant quantity Q essentially equal to Q_Nom onto the main strand part (20).
2. Method according to claim 1, characterised in that the coolant quantity Q applied by the cooling nozzle (10) onto the strand start area (17) is increased as a function of a distance (11) between the strand start (16) and the cooling nozzle (10).
3. Method according to claim 1, characterised in that the strand (2) is reduced in terms of thickness (12) by deploying the pair of deployable strand guide rollers (5) on the strand (2).
4. Method according to claim 3, characterised in that the strand (2) has a liquid core by reducing its thickness (12).
5. Method for operating a strand casting machine (1) at the casting end, wherein the strand casting machine (1) comprises a die (3) and a strand guide (4), and the strand guide (4) comprises at least one pair of deployable strand guide rollers (5) and at least one cooling nozzle (10), having the following method steps:

   - strand casting a strand (2), wherein liquid steel is cast into an at least partially rigid strand (2) in the die (3);

   - stopping the supply of liquid steel in the die (3), as a result of which a strand end (18) forms in the die (3) so that the strand (2) has a strand end (18), a subsequent strand end area (19) with a length B, 0.5 < B < 5m and subsequently a main strand part (20);

   - extracting the strand (2), wherein the strand (2) is extracted from the die (3) in a casting direction (9),

   - detecting a position of the strand end (18) in the strand guide (4);

   - before the strand end (18), preferably a lower end (19a) of the strand end area (19), has passed the pair of deployable strand guide rollers (5): retracting the pair of deployable strand guide rollers (5) so that the pair does not touch the strand (2);

   - cooling the main strand part (20) with Q ≈ Q_Nom , wherein the cooling nozzle (10) yields a coolant quantity Q essentially equal to a nominal coolant quantity Q_Nom onto the main strand part (20);

   - cooling the strand end area (17) with Q < Q_Nom , wherein the cooling nozzle (10) yields a coolant quantity Q < Q_Nom onto the strand end area (17);

   - cooling the strand end (18) with Q ≥ Q_Nom , wherein the cooling nozzle (10) yields a coolant quantity Q ≥ Q_Nom onto the strand end (18).
6. Method according to claim 5, characterised in that when cooling the strand end area (19), the coolant quantity Q applied by the cooling nozzle (10) is reduced as a function of a distance (11) between the strand end (13) and the cooling nozzle (10).
7. Method according to claim 5, characterized in that when cooling the strand end (18) the cooling nozzle (10) yields a maximum coolant quantity Q = Q_Max onto the strand (2).
8. Method according to claim 5, characterized in that once the stand end (18) has passed the cooling nozzle (1), the cooling is ended by the cooling nozzle (10).
9. Method for operating a strand casting machine (1) in a temporary slowing-down of the casting operation, wherein the strand casting machine (1) comprises a die (3) and a strand guide (4) and the strand guide (4) comprises at least one pair of deployable strand guide rollers (5) and at least one cooling nozzle (10), having the following method steps:

   - strand casting a strand (2), wherein liquid steel is cast to form an at least partially rigid strand (2) in the die (3),

   - extracting the strand (2) with a speed v, wherein the strand (2) is extracted from the die (3) in a casting direction (9) with v essentially equal to a nominal speed V_Nom;

   - reducing a supply rate of liquid steel, into the die (3), as a result of which the formation of a transition piece (21) begins;

   - extracting the strand (2) with v < V_Nom ;

   - increasing the supply rate of liquid steel in the die (3), as a result of which the formation of a transition piece (21) is ended so that the strand (2) has a lower main strand part (20a), a transition piece (21) and an upper main strand part (20b);

   - extracting the strand (2) with v ≈ V_Nom ;

   - detecting the positions of a lower end (21a) and an upper end (21b) of the transition piece (21) in the strand guide (4);

   - before the lower end of the transition piece (21a) has passed the pair of deployable strand guide rollers (5):

   retracting the pair of deployable strand guide rollers (5) from the strand (2) so that the pair does not touch the transition piece (21);

   - since the upper end (21b) of the transition piece (21) has passed the pair of deployable strand guide rollers (5):

   deploying the pair of deployable strand guide rollers (5) on the strand (2) so that the pair touches the strand (2);

   - cooling a main strand part (20a, 20b) with Q ≈ Q_Nom ,

   wherein the cooling nozzle (10) yields a coolant quantity Q essentially equal to a nominal coolant quantity Q_Nom onto the main strand part (20);

   - cooling the transition piece (21) with Q < Q_Nom , wherein the cooling nozzle (10) yields a coolant quantity Q < Q_Nom onto the transition piece (21).

Images