EP0210944B1 - Process for the horizontal continuous casting of metals, especially steel - Google Patents

Description

The invention relates to a method for the horizontal continuous casting of metals, in particular steel, in which the cast strand is gradually removed from an oscillating horizontal continuous casting mold.

Such a process is carried out with horizontal continuous casting molds, in which the molten metal solidifies in crust rings. Such solidification can e.g. are supported by so-called separating rings (crushing rings) at the entrance of the horizontal continuous casting mold.

The generic method is known from DE-PS 31 37 119. The formation of the ring-shaped crust-like cooling zones with a relatively stationary mold and a moving strand within a so-called drawing length leads to a falling flank in the cross-section of the crust ring. The further course approaches the mold wall, so that with each drawing stroke there is an annular area of liquid metal which is not considered for the transmission of tensile forces. The farther away the liquid ring-shaped area is from the separating ring, the longer holding times must be required to support the desired crust ring formation, with long holding times leading to low output of continuous casting material.

In addition, with a relatively stationary mold and the thinnest crust area located away from the separating ring, there is increased friction between the crust and the mold wall, as a result of which the solidifying cast strand shell tears easily.

On the other hand, it is known from EP-A 0 144 795 to ensure a constant relative movement between the mold and the strand by means of a sinusoidal mold movement at a speed that is faster than the strand withdrawal speed with a continuous strand withdrawal. This also occurs in the case of a stationary mold with intermittent strand withdrawal in accordance with GB-A-2 015 081.

The person skilled in the art was therefore familiar with the fact that the coefficient of friction for static friction is greater than that of smooth friction and this means that higher forces have to be applied in order to overcome a state of rest. Since higher forces can damage the crust area, efforts have been made according to the prior art to avoid phases of a relative movement of zero between the strand and the mold.

The object of the present invention is to take suitable measures to place the crust area at risk of tearing closer to the mold entrance (e.g. separating ring) in order to more easily detach the strand shell that forms from the mold wall with constant friction.

The object is achieved in that, in addition to the reciprocating movement of the horizontal continuous casting mold, the cast strand is conveyed in steps in the direction of the strand running such that the movements of the horizontal continuous casting mold and the strand extracting machine take place synchronously in the strand running direction at the same speed. This not only shifts the ring-shaped crust area closer to the mold entrance (separating ring), but also creates a larger crust thickness in the area mentioned, so that larger pull-out forces or faster application, i.e. faster casting. The otherwise necessary longer holding time is advantageously placed in the synchronous movement of the horizontal continuous casting mold and the extracting machine, since this movement brings about a relative movement between the cast strand and the horizontal continuous casting mold wall equal to zero.

In an improvement of the invention, it is proposed that the cast strand be compressed into the horizontal continuous casting mold outside of the synchronous movements of the horizontal continuous casting mold and the strand pulling machine. This measure additionally increases the thickness of the ring crust.

Such a process step can be carried out in such a way that the horizontal continuous casting mold is pushed against the continuous drawing machine.

A further improvement of the invention is that dwell times of the strand extraction machine are switched on between a recoil and a pulling movement. This measure also means a further strengthening of the strand shells or a better welding of the crust rings which follow one another in the strand running direction.

In this sense it also works that dwell times are inserted between the back and forth movements of the horizontal continuous casting mold. This measure also contributes to strengthening the strand shell or the individual crust rings to be welded.

Several exemplary embodiments of the invention (alternative method steps) are shown in the drawing and are described in more detail below.

• Fig. 1 ein Zeit-Weg-Diagramm für die Bewegungen der Horizontalstranggießkokille und der Ausziehmaschine für einen ersten Zyklus,
• Fig. 2 ein Zeit-Weg-Diagramm zu den Bewegungen der Horizontalstranggießkokille und der Ausziehmaschine für einen zweiten Zyklus,
• Fig. 3 einen Querschnitt durch Horizontalstranggießkokille und Trennring in einem Ausschnitt, wobei die Horizontalstranggießkokille stillsteht und der Strang bewegt wird,
• Fig. 4 einen Querschnitt wie Fig. 3 aufgrund des erfindungsgemäßen Verfahrens und
• Fig. 5 einen Querschnitt wie die Fig. 3 und 4 in vergrößertem Maßstab zur Darstellung der Verfahrensunterschiede zwischen den Vorgängen der Fig. 3 und 4.

Show it:

• 1 is a time-path diagram for the movements of the horizontal continuous casting mold and the pulling machine for a first cycle,
• 2 shows a time-path diagram for the movements of the horizontal continuous casting mold and the pulling machine for a second cycle,
• 3 shows a cross section through the horizontal continuous casting mold and separating ring in a cutout, the horizontal continuous casting mold standing still and the strand being moved,
• Fig. 4 shows a cross section like Fig. 3 due to the inventive method and
• 5 shows a cross section like FIGS. 3 and 4 on an enlarged scale to illustrate the process differences between the processes of FIGS. 3 and 4.

On the abscissa, the mold backward movement 1, the mold forward movement 2 and the forward movement 3 of the pulling machine and the backward movement 4 of the pulling machine are shown. The pouring direction and the product length are also shown in the direction of arrow 5.

After the horizontal continuous casting mold 6 has been moved into its starting position with a mold backward movement 1, an additional shell thickness is formed within a holding time 7 which serves to reinforce the weakest shell point 8. After the stopping time 7 has elapsed, the horizontal continuous casting mold 6 and the pulling machine move in a mold forward movement 2 and a forward movement 3 of the pulling machine absolutely synchronously in the same direction at the same speeds. During the backward movement 4 of the pull-out machine (which is uncoupled from the cast strand), the horizontal continuous casting mold 6 is in the rest position, and a holding time 9 can be inserted. The cycle described then begins again with the mold backward movement 1. The formation of the length of the cast strand can be followed using line 10.

As a following movement, the pull-out machine is then decoupled and returned to the starting position via the backward movement 4. The cycle described then begins, although the holding time 9 could of course also be dispensed with, for example by the retraction of the pull-out machine could take place faster due to the backward movement 4. The holding times 7 and 9 thus mean possible variations in order to reinforce the strand shells or the crust rings.

Compared to FIG. 1, a longer holding time 7 and an increased clamping time 11 are provided in FIG. 2. 2 also shows the course of the length of the cast strand on the line 10a for casting without the invention. A comparison of lines 10a and 10 makes it clear that a higher cast strand production is achieved due to the invention.

According to the conventional horizontal continuous casting process, the formation of the ring crust 12 is made clear in FIG. 3. The strand shell is formed on the inner wall 6a of the horizontal continuous casting mold 6 and on the end face 13a of the separating ring 13 running perpendicular thereto, the horizontal continuous casting mold 6 being kept relatively calm. This creates the weakest shell part 8. The tensile force 14 loads the ring crust 12 inappropriately high.

4 corresponds to the method according to the invention, the horizontal continuous casting mold 6 being moved in the direction 15, i.e. the weakest shell point 8 is located closer to the end face 13a of the separating ring 13. The direction of the metal flow directed into the entrance of the horizontal continuous casting mold 6 is denoted by 16.

• Um ein Zerreißen der Ringkruste 12 an der dünnsten Schalenstelle 8 zu vermeiden, wird die Zugkraft (im bekannten Fall die Reibungslänge 17) über diese dünnste Schalenstelle 8 übertragen. Im Fall der Erfindung hingegen entspricht die Reibungslänge dem Abstand von der dünnsten Schalenstelle 8 bis zur Stirnseite 13a und damit dem Abstand 18.

In order to show the differences between the conventional method and the method according to the invention, the ring crusts 12 from FIGS. 3 and 4 in FIG. 5 are superimposed. The ring crust 12 according to FIG. 4 is drawn in solid lines and the ring crust 12 according to FIG. 3 with a broken line. The weakest shell locations are designated 8. The invention follows the following consideration:

• In order to avoid tearing of the ring crust 12 at the thinnest shell point 8, the tensile force (in the known case the friction length 17) is transmitted via this thinnest shell point 8. In the case of the invention, however, the length of friction corresponds to the distance from the thinnest shell point 8 to the end face 13a and thus the distance 18.

As can be seen from FIG. 5, the ring crust 12 grows at the weakest shell point 8 at a distance 18 by a multiple of the friction length 17.

• s = Ziehlange
• x = Reibungslänge bei nicht synchron bewegter Horizontalstranggießkokille
• y = Reibungslänge bei synchron bewegter Horizontalstranggießkokille
• ty = Zeit in Sekunden bei synchron bewegter Horizontalstranggießkokille

In one example, which is not shown, the friction length 17 equals x and the distance 18 equals y as follows, where:

• s = drawing length
• x = length of friction with horizontal casting mold not moving synchronously
• y = length of friction with synchronously moving horizontal continuous casting mold
• ty = time in seconds with synchronously moving horizontal continuous casting mold

According to the law on shell growth (s = k.y't), the following relationships result according to FIG. 5:

Example values:

With a cycle time of 0.50 s, in the conventional process, 0.27 s are omitted for other process details, which are approximately retained in the synchronous process. This means a cycle time of 0.27 s + 0.08 s = 0.35 s for synchronous operation, i.e. there is an increase in the number of cycles and therefore (with the drawing length remaining the same) a production advantage of around 40%.

Any changes or adjustments to recoil, stopping times and the like are of minor influence. The process is therefore particularly suitable for highly sensitive steels. In most cases, the "shell impact" (or recoil) can be dispensed with.

Another important advantage is the filling process (Figures 3 and 4). In the synchronous process, the solidification gusset 19 between the separating ring 13 and the horizontal continuous casting mold is kept small and hot, so that welding or fusing with the crust rings 12 formed one after the other is not only easier, but also better quality. This also significantly reduces the risk of cracks at this point.

If the so-called shell impact is eliminated (conventional = recoil), the stress on the separating ring 13 is significantly reduced and thus the service life is increased or the feed material becomes cheaper by changing the quality requirement.

Claims (5)

1. A process for the horizontal continuous casting of metals, in particular of steel, in which the cast billet is produced step-wise from an oscillating horizontal continuous casting mould, characterised in that in addition to the backward and forward movement of the horizontal continuous casting mould the cast billet is conveyed in the direction of movement of the billet in steps in such a manner that the movements of the horizontal continuous casting mould and the billet drawing machine in the direction of movement of the billet take place synchronously at the same speed.

2. A process according to Claim 1, characterised in that the cast billet is upset into the horizontal continuous casting mould outside the synchronous movements of the horizontal continuous casting mould and the billet drawing machine.

3. A process according to Claim 2, characterised in that the horizontal continuous casting mould is pushed forward against the billet drawing machine.

4. A process according to Claims 1 to 3, characterised in that holding times of the billet drawing machine are inserted between a recoil and a drawing movement.

5. A process according to one or more of Claims 1 to 4, characterised in that holding times are inserted between the backward and forward movements of the horizontal continuous casting mould.

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