WO1990000453A1 - Process and device for continuous casting of metal strips - Google Patents

Abstract

The invention concerns a process and a device for casting thin metal strips. The molten metal (1) is poured onto at least one of two moving cooling bodies which form an intermediate gap through which the metal flows. A strip (5) with a concave solidification profile is formed on this cooling body (3). The molten metal (6) forms a skin on the other cooling body (8), which in the gap (7) is joined to the partially solidified strip (5) at least on the outer solidified lateral flanks of the latter, and the strip (9) is calibrated to its final dimensions. The strip, which is thereby closed on all sides, is further cooled while its core is still liquid or paste-like until it ultimately solidifies, preferably on the second cooling body (8).

Description

Method and device for the continuous casting of metal strips

The invention relates to a method and an apparatus for the continuous casting of thin metal strips, in particular steel strips with a rectangular cross section.

Methods and devices for the continuous casting of metal strips have been known for a long time. According to the prior art, tapes are usually obtained which are not suitable for immediate further processing. Such

Therefore, strips, also called "pre-strips", have to be re-rolled. The most common reasons why the cast tapes cannot be processed immediately are that an optimal surface on both sides and a void-free core with high dimensional accuracy cannot be achieved for tapes up to about 10 mm thick.

-j ^• f In a first known method (EP 0108926 B1) Molten metal is poured from a pouring nozzle onto a moving heat sink designed as a cooling belt. The molten metal flows from a pouring nozzle onto the cooled belt. The setting of a certain strip thickness is problematic here, especially in the case of strips of several millimeters in thickness. The resulting thin film-like strip has solidified over its entire cross-section before it is brought into contact with a second moving cooling belt, which is pulled against the first cooling belt by magnetic forces and thereby exerts pressure on the cast belt. In practice, this process can only cast tapes up to approx. 0.2 mm thick. Since the side facing away from the heat sink is exposed during solidification, the surface thereof, particularly in the case of thicker strips, is not optimally designed. It is therefore necessary to re-roll such strips.

In another known method (EP 0081175), molten metal is poured onto two heat sinks designed as rollers and forming a vertical passage gap. In such a process, two strips with parallel solidification fronts that grow towards one another form on the heat sinks. These two strips are joined together with their solidification fronts in the passage gap, so that the solidification fronts are welded together. In practice, it has been found that it is difficult to meet the conditions for void-free welding at the joint at a desired specific strip thickness. Blowholes, fluctuations in thickness over the strip width and strip length and longitudinal cracks on the strip surfaces can hardly be avoided. Strips produced in this way are therefore only pre-strips that have to be re-rolled.

In another known one, especially for thicker ones Bands, ie bands over 10 mm thick, suitable process is provided that the molten metal from a

Pouring nozzle is introduced in an essentially horizontal casting gap, which is partially moved into the die by a moving heat sink in the form of a roller having a groove in its jacket and a second heat sink

Trough immersing roller is formed (EP 0154250 B1). The

The feed element for the molten metal has a mouthpiece which projects into the casting gap and which widens in a wedge shape in the running direction of the heat sink

Has mouth. The mouthpiece is designed so that there is a comparatively large one up to the narrowest point of the passage gap for the middle band area

Contact range of the molten metal to the

Chill rolls results while in the far because of the

Passage gap drawn in side flanks of the

Mouthpiece for the side edges of the band on the

Flanges of a cooling roller are only relatively short

Result in contact lengths. For the strip to be cast, this means that in the passage gap, the solidification fronts of the molten metal poured onto the two cooling rollers in the central strip area have progressed relatively far, while a negligibly thin skin has only formed on the side edges. Since such a band does not yet have sufficient inherent rigidity when it leaves the passage gap, it is provided that it be continued in the channel, with it on its

Is held on the outside by a support corset in the channel until the tape is completely solidified. With this support corset, however, a band with optimal

Do not produce the surface and narrow thickness tolerances.

Ripples in the strip cannot be avoided, so that only pre-strips can be produced with this method. j i

Another, the last described method A similar process is used to pour the molten metal onto a heat sink designed as a roller with a channel-like profile (DE 2909848 C2). On a secondary roller that comes into contact with the molten metal later, the strip solidifies on the still molten side facing away from the first cooling roller. With this method, the belt therefore leaves the passage gap between the first cooling roller and the second cooling roller in the solidified state. Since the second cooling roller is supported on the side flanges of the first cooling roller which delimit the trough-shaped profile, the casting parameters must be observed in such a way that the solidification on the second cooling roller ends, since there is otherwise a risk that the strip with a molten core and thinner solidification Outer skin leaves the second cooling roller. As a result, a flawless surface cannot be guaranteed despite support on additional cooling rolls. Therefore ^" such a tape is wavy and can only be used as a supporting tape.

The invention has for its object to provide a method for the continuous casting of thin metal strips that meet the demands on finished strips in terms of thickness tolerances and surface roughness. Another object of the invention is to provide a device for the continuous casting of such metal strips.

The invention relates to a method for the continuous casting of thin metal strips, in particular steel strips with a rectangular cross-section, in which the molten metal is moved on at least one of two in the strip running direction, one between them - 5 -

Desired-band thickness adjustable passage gap forming heat sinks. According to the invention, this process is characterized by the combination of the following process steps:

1. On the first heat sink, a partially solidified strip with a channel-shaped solidification profile is produced, the still molten or pasty core of which lies on the side facing away from the heat sink.

2. The formation of a skin which closes the partially solidified tape on its side with the molten or doughy core takes place on the second heat sink, the resulting skin and the partially solidified tape being joined to the desired tape thickness while deforming the solidified side flanks.

3. The further cooling of the band, which is closed on all sides, with a still molten or doughy core, takes place on the second heat sink for complete solidification.

In the method according to the invention, a thin finished strip with narrow thickness tolerances and a smooth surface can be produced. The partially solidified strip produced on the first heat sink has a sufficient stiffness that there are no changes in the surface a in the further production stages up to solidification. When the skin produced on the second heat sink and the partially solidified strip formed on the first heat sink are joined together, the desired strip thickness can be set precisely without any significant deformation work because of the solidified but still deformable side flanks and during further production up to Maintain rigidity. Since the solidification takes place while the skin, which may not yet have a high degree of rigidity, is held in contact with the second heat sink, it is ensured that the shape given to the strip in the passage gap is also maintained on this side.

Basically, it is possible that the start of the formation of the second skin is delayed to the formation of the partially solidified band with the channel-shaped solidification profile. This type of production will be chosen if tapes under 5 mm are to be cast. If, on the other hand, the strips are to have a greater thickness, in particular up to 10 mm, then it is more advantageous if the second skin is formed on the second heat sink by simultaneously pouring the molten metal onto the second heat sink. In this way, a thicker skin has formed as the one-sided pouring ^'to enter the passage gap.

If molten metal is poured onto both heat sinks at the same time, further cooling to solidification under continuous contact with the second heat sink can even be dispensed with, because in this case the two partially solidified strips already have sufficient inherent rigidity. Nevertheless, it can be advantageous to hold the strip in contact with the second heat sink in order to intensify the solidification.

According to a further embodiment of the method according to the invention, in which molten metal is poured onto both heat sinks at the same time, it is provided that the formation of the second skin in the form of a partially rigid band with a channel-shaped Solidification profile takes place, the still molten doughy core facing the molten or doughy core of the band formed on the first heat sink. It is understood that with this configuration of the band, the solidified side flanks are joined together to the desired band thickness. In order to increase the dimensional rigidity of the strip, which is not yet solidified and leaves the passage gap, which is decisive for the dimensional stability of the strip, it is provided according to the invention that the partially rigid strip on the first heat sink and, if appropriate, on the second heat sink between the side flanks delimiting the grooves has webs corresponding to these side flanks. Like the side flanks, these webs are joined together with the skin or with the corresponding side flanks and webs of the second partially rigid band with a channel-shaped profile.

The formation of the side flanks delimiting the trough of the partially solidified band and, if appropriate, the webs in between can take place by locally more intensive or early cooling of the molten metal in the areas provided for these side flanks and webs compared to the other areas in between.

A hollow band can also be produced with the method according to the invention. For this purpose, only the molten metal needs to be poured onto the heat sink from below and the molten metal is kept downstream of the passage gap below the area in which the strip solidifies.

The known methods for strip casting in the passage gap by displacing the solidified material Elongation with its disadvantages for the dimensional accuracy of a finished tape is largely avoided in the invention, because in the joined areas, i.e. on the side edges of the tape, but also in the area of the webs, material displacement in the transverse direction is possible due to the intermediate, not yet solidified areas is. The thickness of the partially solidified strip or strips can also be reduced in the passage gap in such a way that the transverse shrinkage occurring during the solidification and cooling process is largely compensated for.

The invention further relates to a casting device for metal strips with two heat sinks which can be moved in the strip running direction and form an adjustable passage gap between them, and with a feed element for the molten metal which extends as far as the passage gap. According to the invention, such a casting device is characterized by the combination of the following features:

1. At least one of the two heat sinks and / or the feed element is set up for a more intensive or earlier cooling of the molten metal at the strip edges than in the strip center area.

2. The second heat sink is arranged at such a distance from the first heat sink that strips formed in the passage gap on both heat sinks are joined together at their edges with their solidification fronts to form a belt with solidified shell on all sides.

3. The second heat sink is set up as an after-cooling device for the partially solidified strip until it has completely solidified. The locally more intensive or early cooling of the molten metal on one or both heat sinks can be achieved in various ways. According to a first embodiment, the pouring opening can be U-shaped or comb-like on its side facing the heat sink, the tines of the U or comb profile on the belt being directed against the running direction of the heat sink. However, it is also possible for the heat sink itself to have zones of different cooling intensity, for example due to different heat conductivity of the heat sink.

The delayed cooling on the two heat sinks and thus also the contact length of the molten metal up to the passage gap can be achieved by appropriate design of the feed elements. In this way, one lip can shield the one heat sink far into the passage gap. In the case of a substantially horizontal passage gap, cooling which begins later can also be achieved by the second heat sink in that the feed element is arranged with a substantially horizontal axis and the level of the molten metal determines the location and thus the different times of use, in a substantially horizontal passage gap cooling on the two heat sinks. The feed element is then preferably a channel open at the top.

If the casting device is set up in such a way that the second heat sink and the feed element are set up for simultaneous pouring of the molten metal onto both heat sinks, the device for the second heat sink as after-cooling device for the partially solidified strip can be dispensed with until it has completely solidified. In order to cast strips with a hollow profile, according to one embodiment of the invention, the feed element is attached to the heat sinks on the underside with an essentially vertical passage gap.

The invention is explained in more detail below with reference to a drawing that shows various exemplary embodiments. In detail show:

1 schematically shows a first exemplary embodiment of the strip casting method according to the invention with a first heat sink cast from a pouring spout, a second heat sink and a belt winding device;

FIG. 2 shows a detailed cross section through the pouring spout, the cast-on heat sink and the resulting tape — according to section I-I of FIG. 1;

3 shows a detailed cross section through the strip thickness limiting gap formed between the first and second heat sink with a partially rigid strip cross section, according to section II-II of FIG. 1;

4 shows a detailed cross section through the solidified strip and the second heat sink, according to section III-III of FIG. 1;

Fig. 5 shows a detail section through pouring spout and both heat sinks of the first embodiment

Fig. 1 to 4, showing the solidification lengths and the band thickness limiting gap, according to section IV-IV of Figi 6 ^r ;> 1 1 -

6 shows the pouring spout according to FIG. 5 as a view in the direction X of FIG. 5;

FIG. 7 shows a band cross section open at the top, solidified in a groove-like manner, according to section V-V of FIG. 5;

8 shows a detailed section through a pouring spout and two heat sinks as an embodiment variant of the first exemplary embodiment, showing the solidification lengths and the melt level in the pouring spout, according to section VII-VII of FIG. 9;

9 shows a cross section through the pouring spout with heat sinks behind it and shows the strip thickness limiting gap with the partially solidified strip cross section drawn in, according to section VI-VI of FIG. 8;

Fig. 10 shows another embodiment for the

Belt casting method with a pouring spout for a rectangular melting puddle, with a first cast-on and a second heat sink, the first heat sink having lateral bandwidth limiting flanges, according to section X-X of FIG. 11;

11 shows the top view and the side view of the arrangement and according to FIG. 10, according to section IX-IX or VIII-VIII FIG. 12 of FIG. 10;

FIG. 13 shows a detailed cross section XI-XI according to FIG. 10, with a partially rigid strip cross section in the pouring snout area, pouring snout outlet and limiting flanges on the first heat sink; EP89 / 00769

- 12 -

14 shows a further exemplary embodiment for the strip casting method according to the invention in a modification of the exemplary embodiment of FIG. 10, analogously as a detail cross section XI-XI according to FIG. 10;

15 shows a further exemplary embodiment of the strip casting method according to the invention with two heat sinks cast from a pouring spout, shown according to section XIV-XIV of FIG. 16;

FIG. 16 shows a detailed cross section through the pouring spout, according to section XII-XII of FIG. 15 with the heat sink arranged downstream;

FIG. 17 shows a strip cross section produced according to the exemplary embodiment of FIG. 15 and joined and calibrated in the strip thickness limiting gap according to section XIII-XIII of FIG. 15;

Fi ^• go. 18 a particularly advantageous for wide bands

Belt cross section according to the embodiment of FIG. 15 with a modified pouring spout;

Fig. 19 shows a modified embodiment for

Embodiment of Figure 15, with a first molded heat sink as a cooling roller and a second molded heat sink and Bandlei system.

Fig. 20 in a modified embodiment for

1 with a first cast-on and a second heat sink and strip guide system;

Fig. 21 fine especially for wide bands advantageous band cross-section according to the embodiment of Fig. 1 or 14;

Fig. 22 shows another embodiment of the

Strip casting process in a detail section through a pouring spout and two cast-on heat sinks with representation of the solidification lengths and the strip thickness limiting gap, according to section XV-XV of FIG. 23;

23 shows a pouring spout opening with specification of the shape of the melting puddle on the cast-on heat sinks, according to section XVII-XVII of FIG. 22;

FIG. 24 shows an advantageous strip cross section that can be produced in particular for wide strips with a pouring spout according to FIG. 22, partially rigid and rolled in the strip thickness limiting gap according to section XVI-XVI of FIG. 23;

25 shows a further exemplary embodiment of the strip casting process in a detailed section, with the pouring snout omitted in the drawing, showing the strip / melt solidification form and joining path between two cast-on heat sinks, according to section XIX-XIX of FIG. 26;

Fig. 26 is a puddle shape for generating a

Band solidification form on the two cast heat sinks, according to section XVIII-XVIII of Fig. 25;

Fig. 27 one especially for wide bands

Strip cross section, partially solidified and roll-joined between the two cooling rolls in section XX-XX of FIG. 255 28 schematically shows a last exemplary embodiment for the strip casting method, with two heat sinks cast on from below for producing hollow strip;

29 shows two examples of hollow strip cross sections which can be cast according to the embodiment shown in FIG. 28 and FIG. 30.

1, a first heat sink 3 designed as a cooling roll and a second heat sink 8 designed as a cooling roll form an adjustable passage gap 7, which determines the thickness of the strip to be cast. The first cooling roller 3 is assigned a feed element 2 for molten metal 1, also called "pouring spout". The pouring opening 4 facing the jacket of the cooling roller 3 essentially has a U-profile. For this reason, the solidification begins at the edges of the strip to be cast earlier than in the strip center area, so that a partially solidified strip 5 with a channel-shaped profile is formed. The metal remains molten in the gutter.

As soon as the molten metal comes into contact with the second cooling roller 8, it solidifies into a skin. In the narrowest area of the passage gap, the resulting skin and the partially rigid band 5 are joined with their channel-shaped profile to the desired band thickness, so that the band leaves the passage gap with its final dimensions. The strip 9 is detached from the first cooling roller 3 by means of a wedge 10. It is kept in contact with the second cooling roller 8 until it has solidified. ^" f It is pressed in a guide channel 11 with compressed gas against the second cooling roller 8. After complete solidification, the tape 9 is wound on an ickel device 12.

As the embodiment of FIGS. 1 to 4 shows, the solidification front has advanced so far on the outer edge regions of the partially solidified belt 5 that no contact with the second cooling roller 8 in these areas requires new skin to be formed, but rather on the Solidification front in these areas, doughy material only needs to be cooled further. It is important that these areas at the narrowest point of the passage gap 7 are still sufficiently soft to be able to be reduced to the desired strip thickness so that the calibrated or solidified strip leaving the passage gap has the desired dimensions of the finished strip. The strip thicknesses of the partially solidified strip required in the individual areas can be determined according to the solidification law known in continuous metal casting. Thereafter, the respective strip thicknesses d _ (cf. FIGS. 5 and 6) result according to the selected contact lengths 1, 1 ₂ and the other cooling conditions

wobei d = Banddicke, 1 = Kontaktlänge der Kühlwalze 3 in der Ausgießöffnung 4 in Bandlaufrichtung, v = Bandlauf¬ geschwindigkeit und A s Proportionalitätsfaktor sind. Ein problemloses Zusammenfügen des teilerstarrten Bandes 5 und der entstehenden Haut sowie ein Kalibrieren des Bandes im Durchtrit sspalt läßt sich jedenfalls erreichen, wenn l.. größer/gleich 1₂ plus 1, und 1.. ungefähr gleich 1₂ plus 1, plus 1*, sind, dabei sind: 1^ = Kontaktlänge an den beiden Bandrändern 15, 1₂ = Kontaktlänge im Bandmittenbereich 16 bei einer Breite b«, 1, = Kontaktlänge vom Ende der Ausgießöffnung 4 bis zum Durchtrittsspalt 7, und 1^ = Kontaktlänge des Bandes an der zweiten Kühlwalze 8 vom Durchtrittsspalt 7 bis zur Durcherstarrung.

where d = strip thickness, 1 = contact length of the cooling roller 3 in the pouring opening 4 in the strip running direction, v = strip running speed and A s proportionality factor. A problem-free joining of the partially rigid band 5 and the resulting skin as well as a calibration of the band in the passage gap can be achieved in any case if l .. greater than or equal to 1 ₂ plus 1, and 1 .. approximately equal to 1 ₂ plus 1, plus 1 * , are, where: 1 ^ = contact length at the two band edges 15, 1 ₂ = contact length in the band center area 16 with a width b 1, = contact length from the end of the pouring opening 4 to the passage gap 7, and 1 ^ = contact length of the band at the second Cooling roller 8 from the passage gap 7 to solidification.

The exemplary embodiment of FIGS. 8 and 9 differs from that of FIG. 1 essentially in the design of the pouring spout 17, which is designed here as a channel open at the top. In this embodiment, the level 18 of the molten metal should not fall below the level of the lower edge 19 of the heat sink 8 in the passage gap 19. In this version, the contact length mentioned above does not exist. In this case, the contact and thus also solidification lengths 1 and 1 extend into the passage gap.

By pivoting the heat sink 8 through an angle of up to approximately + 45 ° with respect to the position shown in FIG. 8 while maintaining the pouring angle, there are further possibilities for casting.

The exemplary embodiment in FIGS. 10 to 13 differs from the previous exemplary embodiments in the pouring spout 20 and the first cooling roller 21. The cooling roller 21 has two cooled bandwidth-limiting flanges 22 which prevent the molten metal from flowing out laterally from the pouring spout 20 The pouring spout 20 has a rectangular pouring opening with a contact length 1 and a contact width b. The molten metal solidifies in the whole area of Ausgießδffnung at all cast surfaces of the cooling roller 21, not just on the shell, but also ^'to eng lateral limiting flanges 22. This creates a partially rigid band 23 with a trough-shaped cross section. When leaving the pouring spout 20, the groove of the partially solidified band 23 is filled with molten metal. Laterally pulled down edges of the upper part of the pouring spout 20 extending into the casting gap 25 together with the limiting flanges 22 ensure that no molten metal can flow off laterally. As in the previous exemplary embodiments, a skin is formed on the second cooling roller 26, which is formed when it is formed in the passage gap 25 with the partially rigid band 22. The belt 24 is released from the cooling roller 21 by means of a release wedge 27 and is held in contact with the second cooling roller 27 until it has completely solidified.

The exemplary embodiment in FIG. 14 is modified compared to the exemplary embodiment in FIGS. 10 to 13 in that the more intensive cooling of the band edges is brought about by two laterally arranged cooling zones 30. These cooling zones 30 dissipate the heat better than the central region 28 of the heat sink. The pouring spout 31, which is extended in the upper region in the direction of the passage gap, has pulled-down edges which, together with the solidified side flanks of the partially solidified band 29, prevent the molten metal from flowing off laterally.

The following exemplary embodiments, with the exception of that of FIG. 20, differ from the previously discussed exemplary embodiments primarily in that they are set up in such a way that molten metal is poured onto both cooling bodies designed as cooling rollers at the same time. In the exemplary embodiment in FIGS. 15 to 17, the pouring opening 35 of the pouring spout 32 is designed in such a way that a partially rigid belt 36 with a trough-shaped profile is formed on the lower cooling roller 33 and a band 37 with a rectangular cross section is formed on the upper cooling roller 34. Before the two bands 36, 37 reach the passage gap 38 is so far advanced the solidification front that the two bands are 36 _"37 together with a reduction of the total thickness at the edge regions. As in the previous examples, the tape gets its final shape here. The belt 39 obtained in this way, with a still molten or doughy core 40, is also detached from the cooling roller 33 by means of a detaching wedge 41 and, with continued contact with the second cooling roller 34, is cooled until it solidifies completely.

Since the belt 39 already has a shell of high rigidity on all sides after leaving the passage gap 38, it is also possible not to cool the belt on the cooling roller 34 until it has completely solidified, but to continue straight ahead and to cool it with other coolants. In any case, this is easily possible if the tape is not too wide. However, further cooling on the cooling roller 34 is preferred.

FIG. 18 shows a band in the passage gap, in which webs are formed between the side flanks and divide the channel that extends over the entire width of the band into a plurality of individual channels with molten metal 43 located therein. The partially rigid belt 42 with the many small channels can be formed in that not only at the edge areas, but also at the various areas in between, the contact length on the cooling roller 33 is greater than in the areas where the Gutters are to be formed. Because of the large number of channels, such a belt has a high level of dimensional stability when it leaves the passage gap 33, so that the further cooling until the belt has completely solidified is completely uncritical.

As in the exemplary embodiment in FIGS. 15 and 18, the formation of the outlet opening 4 of the pouring spout 2 in the exemplary embodiment in FIG. 1 enables a partially solidified strip 59 according to FIG. 21 with a plurality of small parallel channels 60, even when the molten metal is poured onto a first heat sink 3 Instead of a band with only one gutter, as shown in Figure 2, generate.

In the exemplary embodiment in FIG. 19, as in the exemplary embodiment in FIG. 15, molten metal is poured onto both heat sinks 45, 46, 47 via a pouring spout 44. The second heat sink is formed by a belt 46 which is guided over two rollers 47 and which keeps the belt 49 calibrated in the passage gap 48 in contact with the first cooling roller 45 until it has completely solidified.

The exemplary embodiment in FIG. 20 represents a modification of the exemplary embodiment in FIG. 1, because the molten metal is brought onto a first heat sink 51, 53 via a pouring spout 50. A second heat sink 52, 54 is only used after the formation of a partially rigid band with a channel-shaped profile. In this exemplary embodiment, the heat sinks consist of cooling belts 51, 52 which run over cooling wheels 53, 54, 55. The cooling wheels 53, 54 with the cooling belts 51, 52 guided above them determine the thickness in the passage gap 57. Following the Passage gap 57, the cooling belts 51, 52 are guided in parallel on support cushions 56. These support the band 58 coming out of the passage gap 57 and are kept in close contact with this band 8 for the purpose of intensive cooling.

The exemplary embodiments in FIGS. 19, 20 are not limited to one form of pouring on, be it only to a first heat sink or simultaneously to both heat sinks. Whether pouring on one or both sides is dependent on the choice of the pouring spout.

The embodiment of Figure 22 differs from that of Figures 15, 16, 18 primarily in that not only on the lower cooling salt 62, but also on the upper cooling roller 63 seen through appropriate design of the outlet opening 64 of the pouring spout 61 over the range there are different contact lengths for the molten metal. The edges 65 of the pouring opening 64 of the pouring spout 61 facing the cooling rollers 62, 63 have a comb-like course. This creates a partially rigid belt 67 on the lower and upper cooling rollers 62, 63 with a plurality of small channels running in the belt running direction. In the passage gap 69, the partially solidified strips are joined to form the strip 70, the molten metal remaining in the grooves 68 solidifying when the strip 70 is preferably in contact with a cooling roller 63 or 63.

The exemplary embodiment of FIGS. 25 to 27 is modified compared to that of FIGS. 22 to 24 in that the cooling rollers 73, 7 are arranged horizontally next to one another with their axes, so that the molten metal is introduced above the passage gap 77 between the two cooling rollers 73, 74 . The molten metal 75 is distributed above the passage gap, for example by the described pouring nozzle of the exemplary embodiment in FIGS. 22, 23. Instead of a pouring spout designed in this way, other melt distributors can also be used here, as in the previous exemplary embodiments. It is important that there are different contact lengths over the width of the tape in the tape running direction. In FIG. 26, line 72 shows the contact limit or start of contact of the molten metal with the cooling salts 73, 74. When the partially rigid strips forming a plurality of parallel channels lying next to one another are joined in the passage gap 77, the strip 71 is calibrated to its final dimension. It is preferably held in contact with one of the two cooling rollers 74 or 73 until it is completely solidified.

The partially solidified tapes with the many parallel small channels of the exemplary embodiment in FIGS. 25 to 27, but also the corresponding tapes of the other exemplary embodiments, are so greatly reduced in thickness when passing through the passage gap 77 in the region of the solidified webs that the deformation caused by the reduced thickness transversely to partially solidified tape, which is significantly counteracted in the solidification and cooling process, at least in the passage gap, impeded transverse shrinkage of the tape. For example, the partially solidified tapes 76 are joined together in the passage gap 77 at the contact points 78 over a length Λ. 1 and a width Δ. b deformed, the lengths 1 preferably greater than the width. b is selected, the deformation results in a material shift mainly in the direction of the bandwidth, as indicated by arrows 79 in Figures 26 and 27. The spread achieved in this way counteracts, as mentioned, at least the width shrinkage of the strip, which is impeded in the joining area, during solidification and cooling. The longitudinal deformation of the strip in the direction of arrow 80, which occurs when the partially solidified strips are joined in the passage gap, is kept small in comparison to the achievable width, so that the solidification process is not disrupted when the strip is formed. A slight longitudinal deformation is not critical because it counteracts a longitudinal shrinkage of the band in the passage gap.

The calibration of the strip thickness in the passage gap is based on the fact that before the partially solidified strips enter the passage gap, the total thickness of the solidified material is greater than the thickness of the calibrated strip leaving the passage gap, so that a deformation process takes place when the partially solidified strips pass through the gap . The required greater thickness of the partially solidified strips can be adjusted by adjusting the casting speed and / or the contact length of the molten metal with the heat sinks. It should be chosen so that calibration to a constant strip thickness is ensured and, on the other hand, so small that there is at least no significant strip elongation during the shaping. With the trough-shaped cross-section of the partially rigid band with webs possibly arranged in the trough, this can be achieved without any problems, because the deformation takes place predominantly in the region of the webs and the side flanks, but hardly on the solidified trough bottom.

Furthermore, the complete solidification of a band

70.75 according to Figure 24.27 with a corresponding adjustment of the

Casting speed and / or the contact lengths 1 i

1 '2 with the heat sinks 62, 63 and 73, 74 set in this way 25 that the solidification of the molten cores 68 has already ended in the joining area 1 according to FIG. 25 until it passes through the narrowest point between the heat sinks.

The exemplary embodiment in FIGS. 28 to 30 differs from all the previous exemplary embodiments in that a hollow band is produced here. As in the previous exemplary embodiment, the cooling rolls 86 are also arranged horizontally next to one another with their axes. In this embodiment, however, the molten metal is introduced into the passage gap 87 from below. For this purpose, the molten metal 81 stored in a melt container 83 is conveyed to a pouring spout 85 by means of a riser pipe 84 under the action of a pressure cushion 42 prevailing in the melt container 83. The pouring spout 85 is designed in the manner described, so that on the two cooling rolls 86 partially rigid bands 89, 90 are formed, each with a single channel or with several small channels. These partially solidified strips 89, 90 are joined in the passage gap 87. The molten metal in the chamber or chambers formed by the channels must be kept at a level in the band 88 at which no complete solidification has yet taken place. Only then can the chambers empty when the belt 88 is transported further.

Claims

I claims 1. Process for the continuous casting of thin metal strips, in particular steel strips with a rectangular cross-section, in which the molten metal is poured onto at least one of two heat sinks that move in the direction of strip travel and form a passage gap between them that can be adjusted to the desired strip thickness, characterized by the combination of the following process steps: 1. A partially solidified strip with a trough-shaped solidification profile is created on the first heat sink, the still molten or doughy core of which lies on the side facing away from the heat sink. 2. The formation of a skin closing the partially solidified strip on its side with the molten or doughy core takes place on the second heat sink, the skin and the partially solidified strip being joined together with deformation of the solidified side flank up to the desired strip thickness. 3. The strip, which is closed on all sides and still has a molten or doughy core, is further cooled until it solidifies completely on the second heat sink. - 2-S-- 2. The method according to claim 1, so that the skin is formed on the second heat sink by pouring the molten metal onto the second heat sink at the same time as the molten metal is poured onto the first heat sink. 3. Process for the continuous casting of thin metal strips, in particular steel strips with a rectangular cross-section, in which the molten metal is poured onto at least one of two heat sinks that move in the direction of strip travel and form a passage gap between them that can be adjusted to the desired strip thickness, characterized by the combination of the following process steps: 1. A partially solidified strip with a trough-shaped solidification profile is created on the first heat sink, the still molten or doughy core of which lies on the side facing away from the heat sink. 2. The formation of a skin closing the partially solidified band on its side with the molten or doughy core is carried out by pouring the molten metal onto the second heat sink at the same time as the molten metal is poured onto the first heat sink, the skin and the partially solidified band being deformed the solidified side flanks can be joined together to the desired strip thickness. 4. The method according to claim 3, characterized in that the further cooling of the Band closed on all sides with a still molten or doughy core until it solidifies completely on the second heat sink. 5. The method according to one of claims 2 to 4, so that the formation of the second skin takes place in the form of a partially solidified band with a trough-shaped solidification profile, the still molten or doughy core of which faces the molten or doughy core of the band formed on the first heat sink . 6. The method according to one of claims 1 to 5, characterized in that the partially solidified strip on the first and optionally second heat sink receives webs between the solidified side flanks delimiting the channel. 7. The method according to one of claims 1 to 6, characterized in that the formation of the side flanks delimiting the groove of the partially solidified strip and, if necessary, the webs in between by locally more intensive or earlier cooling of the molten metal in the areas provided for the side flanks and possibly webs compared to the other areas. 8. The method according to one of claims 1 to 7, so that the molten metal is poured from below onto the heat sink and the level of the molten metal downstream of the passage gap is kept below the area of the solidified strip. 9. Method according to one of claims 1 to 8, - characterized in that the thickness of the partially solidified strip or strips in the passage gap is reduced in such a way that the transverse shrinkage that occurs during the solidification ^ ¹ and cooling process is at least partially compensated. 10. Casting device for metal strips, with two heat sinks moved in the direction of strip travel, which form an adjustable passage gap between them, and with a feed element for the molten metal that reaches up to the passage gap, characterized by the combination of the following features: 1. At least one of the two heat sinks and/or the feed element is set up for more intensive or earlier cooling of the molten metal at the band edges than in the band center area. 2. The second heat sink is arranged at such a distance in front _of the first heat sink that the bands formed on both heat sinks are joined together with their solidification fronts to form a band with a shell solidified on all sides at the side edges. 3. The second heat sink is set up as an after-cooling device for the partially solidified strip until it has completely solidified. 11. Casting device for metal strips, with two heat sinks moving in the direction of strip travel, which form an adjustable passage gap between them, and with a feed element that reaches up to the passage gap -25 - for the molten metal, marked by the combination of the following features: 1. At least one of the two heat sinks and/or the feed element is set up for more intensive or earlier cooling of the molten metal at the band edges than in the band center area. 2. The second heat sink and the feed element are set up for simultaneous pouring of the molten metal onto both heat sinks. 3. The second heat sink is arranged at such a distance from the first heat sink that the bands formed on both heat sinks with their Solidification fronts are joined together to form a band with a solidified shell on all sides at the side edges. 12. Casting device according to claim 11, characterized in that the second heat sink is set up as an after-cooling device for the partially solidified strip until it has completely solidified. 13. Casting device according to one of claims 10 to 12, so that the distance between the heat sinks in the passage gap is smaller than the height of the solidification front at the edges of the partially solidified strip(s). 14. Casting device according to one of claims 10 to 13, characterized in that the pouring opening is designed in a U-shaped or comb-like manner on its side facing the heat sink, with the tines of the U- or comb profile directed against the direction of travel of the heat sink. 15. Pouring device according to one of claims 10 to 13, characterized in that the feed element has a rectangular pouring opening and the heat sink has cooling zones assigned to the band edges, which have a greater thermal conductivity than the zones in between. 16. Pouring device according to one of claims 10 to 15, so that with a substantially horizontal passage gap, the feed element is a channel that is open at the top. 17. Casting device according to one of claims 1 to 15, so that the feed element is attached to the underside of the heat sinks when the passage gap is essentially vertical.