DE10114269C1 - Production of a hot strip comprises inserting liquid steel between two opposing rotating casting rollers in a two roller thin strip casting device, solidifying the strand skins to a defined thickness, and deforming to a final thickness - Google Patents

Abstract

Production of a hot strip comprises inserting liquid steel between two opposing rotating casting rollers in a two roller thin strip casting device; solidifying the strand skins to a defined thickness; and deforming to a final thickness. The strand skins are pressed together to form a hot strip with variable material cross-sections. An Independent claim is also included for a device for producing a hot strip. Preferred Features: The strand skins are pressed together in transition regions in point-form, line-form and/or planiform.

Description

The invention relates to a method and an apparatus for producing Hot strip using two-roll thin strip casting machines, with molten steel between two counter rotating casting rolls is introduced and during the Rotational movement of the two casters on the circumferential surface of the same two Stranded skin, each with a thickness "s", which in turn solidifies as a result of Rotational movement moves down and in a so-called kiss point the hot strip are pressed together and then completely solidified hot strip in a rolling mill in one or more passes the finally rolled strip having the desired thickness range is formed becomes.

Thin strip casting plants, especially two-roll Thin strip casting machines for the production of hot broadband in the usual for this Width range from about 800 to 1,400 mm and thickness range from about 2 to 5 mm known, casting rolls with a constant diameter and different Bale lengths are used because the bandwidth is essentially determined by the Bale length of the same is determined.

The casting roll diameter is approximately 0.6 to 1.5 m.

The strand skins solidifying on the two casting rolls, the so-called The kiss point reaching the thickness "s" will become one in this kiss point Hot strip with constant thickness d = 2.s pressed together.

The thickness "d" of the hot strip is subsequently reduced by at least in a rolling mill 5% to a final dimension or the desired final dimension having reduced band.

Furthermore, it has been shown in practice and is confirmed by the technical literature listed below that there are certain limits to the increase in the production throughput "P" of the above conventional thin strip casting installation, since an increase in the cast thickness "d" of the hot strip as a function of the setting time " t "of the skins always a reduction in the casting speed" v "requires:

• 1. Near-dimensional casting of stainless steel, metal, 53rd year No. 6/99
• 2. KTN builds the first industrially operated belt caster in Europe, Press review, 24/1999, Steel Information Service
• 3. State of strip casting of steel, steel and iron 119 ( 1999 ) No. 67
• 4. Strip Casting Trials at Hachinohe (Pacific Metals)
• 5. The 1 ^st International Symposium on Advanced Solidification Processing and it's Application, October 25-28 , 1993
• 6. Properties of directly cast steel strips, produced by the two-roll strip casting process, steel and iron 118 ( 1998 ) No. 8
• 7. Basic investigation on the two-roll casting process at the Max Plank Institute for Iron Research, Steel and Iron 117 ( 1997 ) No. 8
• 8. Direct Strip Casting on the Mysotis industrial pilot plant (in Isbergues plant), MPT International 3/1997

This is where the invention described below comes into play.

The object of the invention is a method and an apparatus for producing To specify hot strip by means of two-roll thin strip casting machines, with which one substantial increase in production throughput "P" over that by the Solidification time "t" of the skins set limits for conventional two-roll Thin strip casting machines is possible.

According to the invention the task is in connection with the features in the preamble of claim 1 solved by a method, the two within the Extruded skins formed in such a way in sections on two-roll thin-strip caster defined to be pressed together or spaced apart from each other Forms hot strip with locally limited and variable material cross-sections.

In an advantageous embodiment of the invention, the hot strip is so formed that it consists of a plurality of merging into one another consist of uniform and / or non-uniform surface elements, whose material cross-section each at least towards the transition areas represents a tapered profile, in the transition areas the strand skins, realizing a firm connection with the thickness d = 2.s, pressed together  and outside the transition areas between the spaced apart Skinned liquid steel is embedded, which subsequently solidifies.

It is also proposed that the skins in the transition areas be punctiform, line and / or surface to compress.

It can also be indicated that the two skins in sections defines to squeeze or space apart that one Hot strip with a plurality of approximately parallel to each other and in Flow direction of the hot strip arranged strip-shaped surface elements formed.

Furthermore, it may be appropriate to section the two strand skins in this way defines to squeeze or space apart that one Hot strip with a plurality of approximately parallel to and around one certain angle "β" pivoted to the flow direction of the hot strip arranged strip-shaped surface elements.

In inventive further training it is further proposed that the individual Surface elements of the hot strip at least in one direction with a maximum extension "b" are formed, which is about 15 times the thickness "s" corresponds to the strand skin.

It is also considered to be according to the invention for the production of the final rolled Strip in a rolling mill to choose the acceptance in the first pass so that both for the thick sections of the hot strip and for the thinnest Sections of the same have a cross-sectional decrease.

It is also proposed that the greatest thickness "d '" of the individual surface elements depending on a factor "a" according to the relationship

d '= ad

to choose, taking the factor "a" of the condition

1 <a <1.8

enough.  

The device for the production of hot strip by means of two-roll Thin strip casting machines are characterized by the fact that for the production of a Hot strip with defined, locally limited and variable material cross sections one of the two or both casting rolls has a peripheral surface structure different and defined changes in diameter "D" exhibit.

A further development of the device according to the invention provides that one of the both or both casting rolls have such a peripheral surface structure that the two skins of the hot strip leaving the kiss point, one A plurality of merging uniformly and / or non-uniformly Forming designed surface elements, pressed together in sections in a defined manner or are spaced from each other.

Furthermore, it is provided that one of the two or both casting rolls is one have such a peripheral surface structure that the material cross section of the individual surface elements to be trained each at least to the Transitional areas towards tapered profile, being in the Transition areas the skins, a firm connection with the thickness d = 2.s realizing, compressed and outside the transition areas liquid steel embedded between the spaced skins which then freezes.

It is also considered to be according to the invention that one of the two or both Casting rolls have such a peripheral surface structure that the strand skins in the transition areas are pressed in a point, line and / or area shape are.

Furthermore, one of the two or both casting rolls can be one Have peripheral surface structure that the leaving the kiss point Hot strip, a plurality of merging and approximately parallel to each other and in the flow direction of the hot strip or by an angle "β" to Flow direction of the hot strip pivoted strip-shaped Includes surface elements.  

Another inventive measure provides that the individual surface elements the hot strip has a maximum extension "b" in at least one direction have about 15 times the thickness "s" of the strand skin.

As the invention also provides, the roll gap of the roll stand in the rolling mill is for set the first rolling pass so that both for the thick sections of the Hot strip as well as for the thinnest sections of the same There is a decrease in cross-section.

As the invention further provides, the greatest thickness "d '" of the individual surface elements is dependent on a factor "a" according to the relationship

d '= ad

chosen, the factor "a" of the condition

1 <a <1.8

enough.

The proposed improvements to a known two-roll Thin strip casting machines make a significant difference to conventional machines higher throughput of hot strip.

Conventional systems that may already be operating in their border areas can also operate through these improvements according to the invention that a more precise adaptation to an upstream steelworks is possible and thus a constant production, accompanied by avoidance artificially extended batch times of the steel mill, and accordingly one economic utilization of the same is guaranteed.

The invention is illustrated below schematically with reference to a in the drawings illustrated embodiment explained in more detail.

Show it:

Fig. 1 is a side view of the device according to the invention in the form of a two-roll thin strip casting,

Fig. 2 shows the detail "Z" of FIG. 1,

Fig. 3 shows the section II by a Gießrollenpaar of Fig. 2 for the preparation of a hot strip according to Fig. 4,

Fig. 4 shows the top view of an invention designed according to the hot strip by means of a Gießrollenpaar of FIGS. 2 and 3,

Fig. 5 shows the section II-II through a hot strip according to Fig. 4 at time T ₁ at the level of the kiss point,

Fig. 6 shows the section III-III through a hot strip according to Fig. 4 at the time T ₂ below the kiss point after solidification,

Fig. 7 is a plan view of the invention designed according to the hot strip in a further embodiment,

Figure 8-11 further material cross-sections. Shown as an example of a hot strip,

Fig. 12 shows the section IV-IV of FIG. 2 by a Gießrollenpaar for producing a hot strip according to Fig. 11.

Referring to FIG. 1, the apparatus for producing hot-rolled strip 1 from a two-roll thin strip casting 2, of a supply device for liquid steel 3 in the form of a turret 4 for receiving the ladle 5 to an intermediate container 6 which, in turn, a dip tube 7 and a not further Plug mechanism shown for the control of the supply of the liquid steel 3 in the vertically arranged under the intermediate container 6 arranged two-roll thin strip caster 2 , is arranged upstream.

Furthermore, in a known embodiment, the two-roll thin-strip casting installation 2 is followed by a discharge part 8 , consisting, for example, of a roller strip guide for the cast hot strip 1 , and a rolling mill 9 and / or at least one reel (not shown in more detail, but known per se).

As can be seen in the present case, the rolling mill 9 can have one roll stand or also a plurality of roll stands.

As shown in Fig. 2 in more detail, the two-roll thin-strip caster 2 consists of two counter-rotating and possibly cooled casting rolls 10 , which form a funnel 11 for receiving the liquid steel 3 by means of lateral seals (not shown in detail), for example in the form of ceramic plates ,

As is known, the liquid steel 3 is fed to the two-roll thin-strip casting installation 2 by means of the immersion tube 7 and, as already mentioned, forms a steel bath 12 with the bath level 13 in the funnel 11 which is closed off at the side, the height of which is also referred to as the solidification length "l" and by the bath level angle " α "is defined (" α "in radians).

During the rotational movement of the casting rolls 10, liquid steel 3 solidifies on the same to form two skins 14 a and 14 b with a respective thickness “s”, which in turn subsequently moves downward by the rotation of the casting rolls 10 and, in conventional two-roll thin strip casting plants 2, on the so-called Kiss point 15 are pressed together over the entire surface to form the hot strip 1 with the thickness d = 2.s.

The hot strip 1 then leaves the two-roll thin strip caster 1 at the casting speed "v", which in turn corresponds to the peripheral speed of the casting rolls 10 .

It is now known in this connection that the Solidification rate for metals at the solid / liquid phase boundary proportional to the temperature gradient in the solidified material at the phase boundary and this in turn is almost equal to the temperature gradient in the solidified layer from the phase boundary to the outer skin (Gröber, Erk, Grigall; The basic laws of heat transfer).

It is also known that in the case of conventional continuous casting, the surface temperature in the solidified strand skin after the initial solidification in a mold is approximately constant. As a result, the temperature gradient in the solidified strand skin and thus also in the phase boundary becomes ever smaller with increasing strand skin thickness. In this case, the law known for conventional continuous casting applies to the relationship between the solidification time "t" and the thickness "s" of the solidified strand skin

s = K.√t,

where "K" is a factor depending on the cooling conditions.

When casting by means of two-roll thin strip casting plants 2 , on the other hand, the surface temperature drops sharply in the short solidification time from the start of solidification in the area of the bath level 13 to the end of solidification at the kissing point 15 , so that the temperature gradient in the solidified strand skin 14 a; 14 b remains approximately constant. For this specific case, the relationship between solidification time "t" and thickness "s" of the solidified strand skin 14 a applies; 14 b the relationship

s = K.t.

For "t" in seconds and "s" in mm, a factor "K" = 2.5 mm / s for the very rapid initial solidification was also evaluated in the evaluation of extensive tests and the specialist literature for thin strip casting in the range of thicknesses of up to 5 mm mentioned in the introduction to the description the skins 14 a, 14 b found.

Now the conditions apply:

s = 2.5.t.

d = 2.s and accordingly

d = 5.t or t = d / 5

As is known, v = l / t applies to the casting speed "v", the solidification length "l" depending on the bath level angle "α" being as follows:

l = D.π.α / 360 °

The casting speed "v" follows from the setting time "t" and the setting length "l", with which a desired thickness "d" of the hot strip 1 , with a given given setting angle "α" and a given diameter "D" of the casting rolls 10 must be poured.

For t = d / 5, "v" results in dm / s and "D" and "d" in dm

v = l / t = (D.π.α / 360 °) / (d / 0.05) = (D.π.α / 360 °). (0.05 / d)

For a certain bandwidth "B" ( FIG. 4) and a specific weight for steel of g = 7.8 kg / dm ³ , the possible production throughput "P" in kg / s follows from the casting speed "v"

P = vdBg = (D.π.α / 360 °). (0.05 / d) .dB7.8 = DBα.0.0034
If a conventional value of 45 ° is used for the mold level angle "α" in the above relationship, this results in "P"

P = D.B.0.153

It has accordingly been demonstrated that in conventional two-roll thin-strip casting plants 2, the production throughput “P” is proportional to the strip width “B” and the diameter “D” of the casting rolls 10 .

According to the prior art, two-roll thin strip casting is thus apparently a relatively "rigid" process in which the production throughput "P" is predetermined within narrow limits by the bandwidth "B" and the diameter "D" of the casting rolls 10 .

Accordingly, for a desired bandwidth "B", the production throughput "P" can apparently only be changed by changing the diameter "D" of the casting rolls 10, apart from small changes which can be achieved by changing the casting level angle "α" and are around 10%.

An increase in the production throughput "P" over the solidification time "t" of the skins 14 a; 14 b set limits for conventional two-roll thin-strip casting systems 2 can now be achieved according to the invention in that the casting rolls 10 are provided with a peripheral surface structure with different and defined changes in diameter "D" (D ₁ -D _n ) ( FIG. 3) ,

As a result, during the casting process, which is carried out in a manner known per se, the two strand skins 14 a; which form on the outer circumference of the casting rolls 10 or on their specially designed circumferential surface structure; 14 b in such a defined manner pressed together or spaced apart in such a way that a hot strip 1 is formed with locally limited and variable material cross sections.

Gem. Fig. 3 can be, for. B. each casting roller 10 on its circumferential surface a plurality of mutually parallel circumferential groove-shaped recesses 16 which, as in the present case, correspond to uniformly shaped groove-shaped recesses 16 of the opposite casting roller 10 .

With the casting rolls 10 in FIG. 3, a hot strip 1 can now be produced according to the invention by adding to a time "T _1" (Fig. 2) in height of the kiss point 15, to which on the circumferential surface structure of the casting rolls 10 each having a strand skin 14 a ; 14 b with the thickness "s", they are pressed together in sections or spaced apart in such a way that a hot strip 1 with a plurality of merging strip-shaped surface elements 17 arranged approximately parallel to one another and in the flow direction thereof is formed ( FIG. 4).

As shown in FIG. 5, the material cross section of each surface element 17 has a profile 19 that tapers at least towards the transition regions 18 . In the present case, the outer contour of this profile 19 describes a circular section, the radius of which can be chosen as desired.

In the transition areas 18 of the individual surface elements 17 , the skins 14 a; 14 b, realizing a firm connection with the thickness d = 2.s, pressed together.

Outside of these transition areas 18 is at the time "T ₁ " between the mutually spaced skins 14 a; 14 b embedded liquid steel 3 , which solidifies during the further guiding of the hot strip 1 at the casting speed "v" at the time "T ₂ " ( FIGS. 2 and 6).

These measures according to the invention described above result from the finding that liquid steel 3 which is between two strand skins 14 a; 14 b is embedded, due to the ferrostatic pressure, the strand skins 14 a; 14 b apart in an uncontrolled manner, in order to break through and leak if necessary.

As a result of the fact that one or more supports between the two skins 14 a; 14 b in the form of pressing them together exclusively in the transition areas 18 , the liquid steel 3 is prevented from breaking through.

In particular, it was found that the skins 14 a; 14 b in the two-roll thin-strip caster 2 in question, in particular, not to be pressed apart when the ratio of the thickness "s" of each strand skin 14 a; 14 b to the so-called span in at least one direction does not exceed 1:15. Accordingly, it is appropriate to form the individual surface elements 17 of the hot strip 1 at least in one direction with a maximum extension "b" ( FIGS. 4 and 6), which is to be equated with the span that is found, which is approximately 15 times the thickness "s" of the strand skin 14 a; 14 b corresponds.

A strand skin 14 a; 14 b with a thickness "s" of 2 mm at the kissing point 15 is thus not pushed apart, let alone broken, at a maximum extension "b" (span) of 30 mm in at least one direction by the liquid steel 3 .

It should also be pointed out that the skins 14 a; 14 b in the transition areas 18 can be pressed in a point, line and / or area shape.

It is certainly easy for the person skilled in the art to understand that the invention is not limited to the exemplary embodiment described above with a plurality of strip-shaped surface elements 17 arranged approximately parallel to one another and in the flow direction of the hot strip 1 , but rather any and suitable arrangement of a plurality of merging uniformly and / or non-uniformly shaped surface elements 17 are also recorded .

For example, it is conceivable that the individual skins 14 a; 14 b are pressed together in sections in such a defined manner or spaced apart that a hot strip 1 is formed with a plurality of strip-shaped surface elements 17 which are arranged approximately parallel to one another and pivoted by a certain angle ".beta." To the flow direction of the hot strip 1 .

Fig. 7 shows such according to the invention produced hot strip 1 in the plan view, wherein an angle "β" has been selected of 90 °.

Furthermore, the invention is not limited to surface elements 17 with profiles 19 that describe a circular section, but also includes any conceivable and suitable profiling.

Selected examples can be seen in FIGS. 8 to 11. FIG. 8 shows, for example, a triangular profile, FIG. 9 an elliptical and FIG. 10 a trapezoidal profile.

The profile according to FIG. 11 differs from all those described above in that only one of the two skins 14 a or 14 b is provided with the profile, and accordingly only one of the two casting rolls 10 is designed with recesses 16 according to the invention ( FIG. 12).

Since the production of thin strip ultimately aims at a flat strip of the same thickness over the entire width, it is necessary that a flat strip 20 with the desired thickness is rolled from the existing uneven strip cross sections.

In order to avoid surface defects in the area of the thinnest sections of hot strip 1 (smallest strip thickness), it was found that the decrease in the first roll pass should be selected so that the roll gap of the roll stand for the first roll pass should be set so that both for the thick ones Sections of the hot strip 1 with the thickness "d '" and the thinnest sections of the same with the thickness "d" ( FIG. 6) show a decrease in cross section.

It is known that the maximum stretching during flat rolling can be approximately 1.8. Accordingly, it must be ensured that the decrease in the first roll pass is selected such that the stretching of the sections of the hot strip 1 with the maximum thickness "d '" does not exceed 1.8.

However, since for the reasons mentioned above the thinnest sections of the hot strip 1 with the thickness "d", which are arranged in the transition regions 18 of the surface elements 17 , are to be deformed in the first stitch, the ratio of "d '" to "d" , which is denoted by "a", be less than 1.8.

The following criteria result:
The greatest thickness "d '" of the individual surface elements 17 depends on a factor "a" according to the relationship

d '= ad

to choose, taking the factor "a" of the condition

1 <a <1.8

enough.

Finally, it should be shown that for a hot strip 1 with a conventional uniform thickness "d" and the width "B", which is cast with casting rolls 10 with the constant diameter "D", the relationship derived above for the production throughput "P"

P = DB0.153

applies, thus for a hot strip 1 with the cross-sectional area F1 = Bd

By contrast, a hot strip 1 produced according to the invention has a cross-sectional area "F2", which in turn is larger than the cross-sectional area "F1". Since the production throughput "P", as stated above, with the same casting speed "v" is proportional to the bandwidth "B" and the diameter "D" of the casting rolls 10 and thus the cross-sectional area "F1", applies to a hot strip 1 produced according to the invention with the Cross-sectional area "F2" the relationship

P = D.B.0,153.F2 / F1 with F1 = B.d

As explained above, the profiling of the surface elements 17 is relatively free to choose and can, for. B. be formed by arcs, ellipses, triangles and / or trapezoids.

With a chosen factor "a" of 1.7, for example for the trapezoid, each results after forming the corners, a ratio of F2: F1 = 1.5 to 1.6 and for a Triangle a ratio of F2: F1 = 1.2 to 1.3.  

As has been demonstrated, the production throughput "P" for a given starting diameter (diameter "D") of the casting rolls 10 for a specific bandwidth "B" when using the profiles according to the invention can thus be at least up to the 1st with a factor a = 1.7 , Increase 6 times the production throughput "P" for conventional, newly formed hot strips 1 .

LIST OF REFERENCE NUMBERS

1

hot strip

2

Two-roll thin strip casting

3

molten steel

4

turret

5

ladle

6

intermediate container

7

dip tube

8th

Ausförderteil

9

rolling mill

10

casting rolls

11

funnel

12

Stahlbad

13

Bathroom mirror
14a; b skins

15

Kusspunkt

16

recesses

17

surface elements

18

Transition areas

19

profile

20

final rolled strip

Claims (17)

1. Process for the production of hot strip by means of two-roll thin strip casting plants, liquid steel being introduced between two counter-rotating casting rolls and solidifying during the rotation of the two casting rolls on the circumferential surface of the latter into two strand skins, each with a thickness "s", which in turn is a result of the rotation movement are moved downwards and pressed together in a so-called kissing point to form the hot strip, and subsequently the completely solidified hot strip is shaped in a rolling mill in one or more rolling passes to form the end-rolled strip having the desired thickness range, characterized in that the two skins ( 14 a ; 14 b) are pressed together in sections in such a defined manner or spaced apart that a hot strip ( 1 ) is formed with locally limited and variable material cross sections. 2. The method according to claim 1, characterized in that the hot strip ( 1 ) is formed such that it is composed of a plurality of merging uniformly and / or non-uniformly shaped surface elements ( 17 ), the material cross-section of which in each case one at least to the transition areas ( 18 ) tapering profile ( 19 ), in the transition areas ( 18 ) the strand skins ( 14 a; 14 b), realizing a firm connection with the thickness d = 2.s, are pressed together and outside the transition areas ( 18 ) between the spaced skins ( 14 a; 14 b) liquid steel ( 3 ) is embedded, which then solidifies. 3. The method according to any one of claims 1 and 2, characterized in that the extruded skins ( 14 a; 14 b) in the transition regions ( 18 ) are pressed together in a point, line and / or area. 4. The method according to any one of claims 1 to 3, characterized in that the two skins ( 14 a; 14 b) are pressed together in sections in such a defined manner or spaced apart that a hot strip ( 1 ) with a plurality of approximately parallel to each other and in Flow direction of the hot strip ( 1 ) arranged strip-shaped surface elements ( 17 ) forms. 5. The method according to any one of claims 1 to 3, characterized in that the two extruded skins ( 14 a; 14 b) are pressed together in sections in such a defined manner or spaced apart that a hot strip ( 1 ) with a plurality of approximately parallel to one another and around forms a certain angle "β" to the direction of flow of the hot strip ( 1 ) pivoted strip-shaped surface elements ( 17 ). 6. The method according to any one of claims 1 to 5, characterized in that the individual surface elements ( 17 ) of the hot strip ( 1 ) are formed at least in one direction with a maximum extent "b" which is approximately 15 times the thickness "s "corresponds to the strand skin ( 14 a; 14 b). 7. The method according to any one of claims 1 to 6, characterized in that for the production of the final rolled strip ( 20 ) in a rolling mill ( 9 ), the decrease in the first pass is selected so that both for the thick sections of the hot strip ( 1 ) there is also a decrease in cross-section for the thinnest sections of the same. 8. The method according to any one of claims 1 to 7, characterized in that the greatest thickness "d '" of the individual surface elements ( 17 ) depending on a factor "a" according to the relationship
d '= ad
is chosen, the factor "a" of the condition
1 <a <1.8
enough. 9. Device for the production of hot strip by means of two-roll thin-strip casting plants, liquid steel being introduced between two counter-rotating casting rolls and solidifying during the rotational movement of the two casting rolls on the circumferential surface of the latter into two strand skins, each with a thickness "s", which in turn is a result of the rotating movement are moved downwards and pressed together in a so-called kissing point to form the hot strip, and subsequently the completely solidified hot strip is shaped in one or more pass passes in a rolling mill to form the end-rolled strip having the desired thickness range, characterized in that for the production of a hot strip ( 1 ) with defined, locally limited and variable material cross sections, one of the two or both casting rolls ( 10 ) have a peripheral surface structure with different and defined changes in diameter "D". 10. Apparatus according to claim 9, characterized in that one or both of the casting rolls (10) have such a circumferential surface structure that the two strand skins (14 a; 14 b) of the kiss point (15) exiting the hot-rolled strip (1), a plurality of surface elements ( 17 ) of uniform and / or non-uniform design which merge into one another, are pressed together in sections in a defined manner or are spaced apart from one another. 11. The device according to one of claims 9 and 10, characterized in that one of the two or both casting rollers ( 10 ) have such a peripheral surface structure that the material cross section of the individual surface elements ( 17 ) to be formed each one at least to the transition areas ( 18 ) tapering profile ( 19 ), wherein in the transition areas ( 18 ) the extruded skins ( 14 a; 14 b), realizing a firm connection with the thickness d = 2.s, are pressed together and outside the transition areas ( 18 ) between the spaced apart Extruded skins ( 14 a; 14 b) liquid steel ( 3 ) is embedded, which subsequently solidifies. 12. Device according to one of claims 9 to 11, characterized in that one of the two or both casting rollers ( 10 ) have such a peripheral surface structure that the strand skins ( 14 a; 14 b) in the transition areas ( 18 ) point, line and / or are pressed together flat. 13. Device according to one of claims 9 to 12, characterized in that one of the two or both casting rollers ( 10 ) have such a peripheral surface structure that the hot strip ( 1 ) leaving the kiss point ( 15 ), a plurality of merging and approximately parallel contains strip-shaped surface elements ( 17 ) arranged to one another and in the flow direction thereof. 14. Device according to one of claims 9 to 12, characterized in that one of the two or both casting rolls ( 10 ) have such a peripheral surface structure that the hot strip ( 1 ) leaving the kiss point ( 15 ), a plurality of merging and approximately parallel contains strip-shaped surface elements ( 17 ) which are pivoted to one another and at an angle "β" to the flow direction of the hot strip ( 1 ). 15. Device according to one of claims 9 to 14, characterized in that the individual surface elements ( 17 ) of the hot strip ( 1 ) have at least in one direction a maximum extension "b" which is approximately 15 times the thickness "s" of Strand skin ( 14 a; 14 b) corresponds. 16. Device according to one of claims 9 to 15, characterized in that the roll gap of the roll stand in the rolling mill ( 9 ) for the first pass is set such that both for the thick sections of the hot strip ( 1 ) and for the thinnest sections thereof there is a decrease in cross-section. 17. Device according to one of claims 9 to 16, characterized in that the greatest thickness "d"'of the individual surface elements ( 17 ) depending on a factor "a" according to the relationship
d '= ad
is selected, the factor "a" of the condition
1 <a <1.8
enough.