EP2624971B1 - Process for producing a metal strip by casting and rolling - Google Patents

Description

The invention relates to a method for producing a metal strip by casting rolls, in which first in a casting machine a slab of nominal slab thickness is poured by discharging metal at a nominal casting speed from a mold, wherein the slab in the region of a strand guide by a number of roles of a Wherein the slab is subsequently tempered in a furnace of defined length, the slab being rolled behind the furnace in a rolling train and, in particular, the slab behind the casting machine and in front of the furnace in a roughing mill reducing thickness to a nominal reshaped slab thickness or thickness Substrate thickness is subjected.

In cast rolling mills in the form of thin slab plants one can differentiate between batch processes and endless processes.

In batch processes, after casting or casting rolling, the slabs or pre-strips are separated into individual slabs or individual pre-slats so that coils of the desired size are produced after hot-rolling.

Thin slab plants mainly work as a slab process. For the slab process, it is characteristic that the conservation of energy and the required heating of the slab, for example in a roller hearth furnace, which is longer than the maximum slab length. This allows you to separate all slabs so that in a certain period of time, the individual slab is completely in the oven, ie neither in Gießmaschinenbereich is still engaged in the rolling range of the finishing train. Typical thicknesses of the slabs are between 40 mm and 100 mm.

In contrast, the so-called ISP process works with smaller intermediate strip thicknesses, which are typically in the range between 10 and 20 mm. The individual intermediate belts are always engaged either in the casting area or in the rolling area of the finishing train. The intermediate buffering of the pre-bands is carried out by means of two heated coiling ovens, which conserves the temperature of the pre-bands after reheating.

Also known is the so-called ESP process. This is an endless process that originated from the ISP process. Since the ESP process must operate without a thermal intermediate buffer, all distances between the individual devices of the plant must be minimized in order to avoid the unprotected radiation of the heat of the intermediate strips to the environment. This inevitably results in small distances between the facilities. The advantages and disadvantages of the ESP process are as follows:

It is advantageous that uniform continuous rolling conditions can be maintained over several hot strips, which is very favorable, especially for thin hot strips.

The disadvantage, however, is the following: It is difficult to comply with the final rolling temperature, since the rolling speed in the finishing train is directly coupled to the mass flow from the casting machine. This can only be achieved by a consistently high casting performance and by reheating the intermediate belt to very high temperatures after roughing. Furthermore, the required final rolling temperatures can not be achieved for all steel grades, so that certain grades can not be produced in continuous operation. Then it is disadvantageous that in a required roll change, the sequence must be completely stopped. In case of faults, for example, in the casting operation, the endless operation is interrupted, it must then be switched to batch mode. If the ESP process switches to batch mode, then due to the small distances between the caster and the finishing mill only so-called "mini-coils" produced. Since these are not marketable products, their economic use is limited. Their specific coil weight is only about 35% to 40% of the marketable coil size. In order to maintain a consistently high casting performance, a high-performance steelworks is needed, which also can or must work reproducibly at a high level. Disturbances in the steelworks also lead directly to the need to switch from continuous operation to batch operation (too low final rolling temperature) with the disadvantageous consequence that only "mini-coils" can be produced.

In the DE 10 2008 020 412 A1 a method for producing a metal strip by casting rollers is described, in which first a thin slab is cast in a casting machine. This is then rolled in a rolling mill using the primary heat of the casting process. In a first mode of operation can be carried out by direct coupling of the casting machine with the at least one rolling train, a continuous production of the metal strip (endless rolling); In a second operating mode, a discontinuous production of the metal strip can take place by decoupling the casting machine from the at least one rolling train (batch operation). In order to increase the flexibility of the system, it is provided that cast slabs or pre-belts casted behind the casting machine from the main transport line when driving the discontinuous production of the metal strip, stored and later transported back to the main transport line. The removed slabs or pre-bands can be brought to a desired temperature or kept at a desired temperature before being transported back into the main transport line. In order to avoid interruptions in the event of faults or roll changes, an additional slab storage area - accessible by ferry - is thus created next to the main transport line.

A generic method is used in the DE 10 2008 003 222 A1 disclosed. Similar solutions show the WO 2004/004938 A1 and the EP 0 347 662 A2 ,

This makes it possible to solve the problem mentioned, that is to operate a method that overcomes the above-mentioned disadvantages of the ESP process, but the device complexity is high and the Gießwalzvorrichtung correspondingly expensive, d. H. the intermediate storage of the slabs can only be achieved with great effort.

The invention has the object of providing a method of the type mentioned in such a way, with which it is possible, without great effort on the one hand, a sufficient buffer memory in the event of roll interruptions, z. B. due to a roll change, on the other hand to ensure the smallest possible furnace length to work optimally in continuous operation can. Thus, a combined continuous / batch process is to be provided which overcomes the above disadvantages of the ESP process with cost effective means. In particular, additional storage ovens adjacent to the transport line or oven extensions should be avoided.

1. a) Erhöhen der Brammendicke hinter der Gießmaschine durch Verminderung der Dickenreduktion der Bramme im Bereich der Strangführung;
2. b) Absenken der Gießgeschwindigkeit von der nominalen Gießgeschwindigkeit auf einen verminderten Wert;
3. c) Verminderung der Dickenreduktion der Bramme in dem Vorwalzwerk.

The solution of this problem by the invention is characterized in that for the temporary reduction, in particular for temporary interruption, the supply of rolling stock in the rolling mill, a reduction in the thickness reduction of the slab in the roughing mill, wherein the reduction in thickness of the slab in the roughing mill to zero withdrawn or at least two of the measures taken in combination:

1. a) Increase the slab thickness behind the casting machine by reducing the thickness reduction of the slab in the strand guide;
2. b) lowering the casting speed from the nominal casting speed to a reduced value;
3. c) Reduction of the thickness reduction of the slab in the roughing mill.

In conjunction with the temporary reduction in the supply of rolling stock to the furnace, the slab may be cut (separated) on a pair of shears located in front of the furnace.

The inlet velocity of the slab into the furnace is preferably reduced by at least a factor of 2 compared to the nominal value.

The thickness reduction of the slab in the area of the strand guide is preferably reduced by up to 40 mm.

The temporary reduction, in particular the temporary interruption, the supply of rolling stock in the rolling train can be made while in the rolling mill a roll change is made or there is a different production delay in the rolling mill.

After making the temporary reduction in the supply of rolling stock in the rolling mill, the slab can be processed in batch batch operation. This is due to the process for the first slab after a roll interruption.

The slab can, as long as a temporary reduction of the supply of rolling stock in the rolling train is not carried out, be processed in the continuous rolling process. However, the method is applicable to a rolling mill, which is operated in continuous mode or in batch mode.

By means of the above measures a), b) or c), such a buffer time or rolling interruption in the rolling train can be created or made possible, so that no casting breakage must take place in the casting machine, with a short furnace being used in particular.

The slab may also be subjected to heating by means of induction heating in front of or behind the furnace.

The casting rolling plant used to carry out the method, which comprises a casting machine, an oven and a rolling mill connected downstream of the furnace, wherein the furnace has a number of heating elements in order to temper a cast slab, can be characterized in that the furnace has a total length between 30 and 120 m, wherein the heating elements of the furnace, in particular inductive heating elements, are arranged out of the transport line and wherein insulation elements are provided, which can be retracted as needed in the region of the furnace instead of the heating elements.

The furnace is preferably designed as a roller hearth furnace or as roller-skated encapsulation, wherein it preferably has insulated roller conveyor rollers.

In front of the furnace and / or behind the furnace and / or inside the furnace, heating elements for heating the slab may be arranged, in particular inductive heating elements.

Behind the caster, a roughing mill or multiple roughing mills can be arranged.

Thus, the proposed method allows maximizing the slab buffer mass or buffer time in an oven (preferably in a roller hearth furnace or a walking beam oven) by increasing the casting thickness as compared to the (nominal) production thickness. Furthermore, alternatively or additionally, a lowering of the casting speed can be provided in comparison with the (nominal) production speed.

The method further provides, alternatively or in addition, that a reduction in the decrease in an in-line roughing stand or behind the caster and before the furnace in comparison with the (nominal) decrease takes place during regular production.

The method may provide for maximizing the oven bake time (in a hot strip and continuous hot rolling mill) where the feed rate of the slabs into the oven in the buffer phase is at least a factor of 2 over the nominal (normal) feed rate in the case of normal production is reduced.

The change in the thickness decrease at the inline roughing stand is between ε = 0% to 70%. Alternatively or additionally, the casting thickness can be adjusted by LCR (liquid core reduction) of preferably 0 to 40 mm in order to influence the slab segment length in the furnace, preferably with the same ring weight.

Analogous to the change in the oven inlet thickness, the finished strip is changed to a desired practical finished strip thickness.

The method provides buffering time for a roll change or to bridge other production delays.

The casting mill can allow the combined batch and continuous rolling of hot strip. The oven - preferably designed as a roller hearth furnace - is preferably between 30 and 120 m long. The use of an in-line roughing stand is preferred, but not mandatory.

The use of the change in thickness in the caster and in-line scaffolding for the purpose of increasing the buffer time or shortening the kiln length can be provided in a single-strand caster, but also in a multi-strand caster.

In addition, space can be provided for a ferry, as well as an additional logistically required furnace length for handling in the case of a 2-strand operation.

The roller hearth furnace can be designed as a temperature holding furnace or alternatively serve for heating the slabs or intermediate bands. In addition, it is possible, before and / or behind the roller hearth furnace or inductively heat the slab or the pre-band to bring the slab to a temperature between 1050 ° C and 1400 ° C before the scale scrubber of the finishing train.

In special cases, a roller table cover (roller table encapsulation) can also be used partially or instead of a roller hearth furnace. An induction heater, which is preferably arranged behind it, brings the pre-strip or the slab in front of the rolling train to the desired inlet temperature.

The induction heaters can be displaced laterally or upwards out of the line in order to be able to heat at a thin strip and to be able to drive out the induction heaters with a thick strip, in order to replace them with insulation elements (insulating elements, roller shutter encapsulation).

At least one inductive heating can also be provided between the stands of the finishing train.

Thus, despite the use of a short furnace, a buffer time can be created or a rolling interruption can be realized in the rolling train (for example for changing a roller in the finishing train), without a casting demolition must take place in the casting machine.

Fig. 1

schematisch die Seitenansicht einer Gießwalzanlage gemäß einer ersten Ausführungsform,

Fig. 2

in der Darstellung nach Fig. 1 eine Gießwalzanlage gemäß einer alternativen Ausführungsform und

Fig. 3

in der Darstellung nach Fig. 1 eine Gießwalzanlage gemäß einer weiteren alternativen Ausführungsform.

In the drawings, embodiments of the invention are shown.
Show it:

Fig. 1

1 is a schematic side view of a casting and rolling plant according to a first embodiment,

Fig. 2

in the illustration Fig. 1 a casting rolling mill according to an alternative embodiment and

Fig. 3

in the illustration Fig. 1 a casting rolling mill according to another alternative embodiment.

In the FIGS. 1 to 3 in each case a casting rolling plant can be seen, in which a metal strip 1 is produced.

For this purpose, a slab 3, preferably a thin slab with the thickness d, cast first in a conventional casting machine 2 by molten metal from a mold 4 with a casting speed v emerges vertically downwards. The cast strand is deflected by means of a strand guide 5 from the vertical to the horizontal. At the same time there is a reduction in the thickness of the cast slab 3. This is done by rollers which are arranged in the strand guide 5 and exert a normal force on both sides of the slab surface. The slab 3 leaves the casting machine 2 with the nominal thickness d ₀ and speed v ₀ in the belt conveying direction F.

The nominal values for the casting speed v ₀ and the slab thickness d ₀ are those values which are present in the scheduled production of the metal strip 1.

At the end or behind the casting machine 2, an in-line roughing stand 8 (rough rolling mill) is directly arranged, with which the slab 3 is further reduced in thickness. Immediately behind the roughing stand 8 is a pair of scissors 9. Behind the pair of scissors 9, there follows an oven 6, which is designed, for example, as a roller hearth oven. At the position of the furnace 6 is also optionally the arrangement of a roller table cover or encapsulation preferably with insulated roller table rollers conceivable.

Behind the oven is followed by a finishing line 7, in which the strip is rolled to a desired final thickness.

The cast rolling mill still has various other elements, which are shown in the three embodiments.

In Fig. 1 located behind the oven 6, an induction heater 10. This induction heater can optionally be arranged laterally displaceable or heraushebbar from the working position. For thin tapes, the tape can be heated by the induction heater; then be provided with thicker slabs that the induction heater is moved out of the working position and replaced by insulating elements to reduce the heat radiation from the slab.

The exemplary six rolling mills of the finishing train 7 are designated F1 to F6. Within the finishing train 7 further induction heaters 11 may be provided between the rolling stands. Behind the finishing train 7 are a cooling section 12 and reels 13. Further scissors 14 and 15 are provided.

In Fig. 2 be a heat insulation hood in the field of cold strand disposal 16 behind the roughing mill 8 and the scissors 9 mentioned. It can be equipped with a swiveling thermal insulation hood and insulated furnace rollers be. When casting the tape is observable here (pivoting the employment of the framework).

An induction heater 10 is provided here in front of the roller hearth furnace 6.

In the embodiment according to Fig. 3 If no induction heating is provided in the region of the furnace 6, in this embodiment the furnace 6 is made slightly longer.

In the system variants shown - preferably with an inline roughing stand 8, but alternatively also with several of these roughing stands - the intermediate thickness or the inlet thickness in the roller hearth furnace 6 (eg between 20 and 120 mm slab thickness) can be flexibly adjusted.

To produce a time buffer in the roller hearth furnace 6 at a roll interruption and / or in the case of a work roll change, by flexible changing the thickness decrease of the slab 3 on inline roughing 8 (thickness decrease ε = 0 to 70%) and / or by adjusting the casting thickness LCR (Liquid Core Reduction) in the area of strand guide 5 (between 0 and 40 mm) influences the slab length in the furnace. Increasing the intermediate thickness increases the furnace storage capacity or advantageously reduces the necessary furnace length.

If a roll change is planned, the slab 3 deformed on the roughing stand 8 is scooped up on the scissors 9 and then the intermediate thickness is purposefully raised for the following slab segment or for the following segments, specifically via the nominal values (production values). As a result of the lower transport speed, therefore, the oven 6 fills slower. An additional reduction of the casting speed supports this effect.

The following table shows how the aspect ratio of the slab changes (example of a slab for a maximum ring weight of 18 kg / mm): Area Thickness [mm] Length of a slab segment [m] comment mold 110 21.5 Nominal (normal) production condition Outlet casting machine 80 29.6 after LCR Behind inline scaffolding 50 47.4 after thickness reduction Behind inline roughing stand (increased thickness reduction on LCR and roughing stand) 35 67.7 Special case with a short oven: The slab is partially outside the oven and fits between scissors 9 and finishing tipper scrubbers

How fast a roller hearth furnace with a length of, for example, 60 m under different conditions (casting speed 3 or 5 m / min) is filled with and without decrease in the roughing stand 8) is shown in the following table: Thickness [mm] Transport speed behind the roughing stand [m / min] Oven filling time [min] boundary conditions 50 11 5.5 Nominal (normal) production condition with thickness reduction on the roughing stand Conditions for generating a time buffer: 110 5 12.0 No reduction in thickness 110 3 20.0 No reduction in thickness and reduced casting speed

The buffer time results from the Ofenfüllzeit given boundary conditions minus the rolling time in the finishing mill for the previously produced slab minus a reserve distance. Preferably, when rolling in the finishing train before the roll change so selected a final thickness that results in a high feed rate in the finishing train.

If the slab thickness - z. B. in order to increase the buffer time - raised, the finished strip thickness is also increased accordingly to a desired practical finished strip thickness. The finishing train must therefore be prepared for decreases of, for example, H = 110 → 5 mm and H = 50 → 1.0 mm. For this purpose, the stator windows are to be dimensioned sufficiently, it is a large stroke of the thickness adjustment (long-stroke cylinder or additional mechanical employment in the front scaffolding or a wedge adjustment) provided further, the engine speed ranges are provided in the finishing mill accordingly.

The roller hearth furnace is designed for the mode of operation and the maximum and minimum thin slab thicknesses of, for example, 120 or 20 (25) mm, and corresponding roller spacings and diameters are used. The furnace length between the roughing stand 8 and the finishing train 7 is short and is preferably between 30 m and 120 m, depending on the required boundary conditions. Thus, the kiln length is shorter than with conventional CSP plants (where it is between 200 and 240 m). The shorter oven advantageously reduces the energy losses.

The heating of the (transformed) slab 3 can take place with a roller hearth furnace or the roller hearth furnace is operated as a temperature holding furnace and assisted by inductive heating upstream and / or behind or inside the roller hearth furnace (see the three embodiments according to FIG Fig. 1 to 3 ). Parts of the furnace or the entire furnace may alternatively be designed in the form of a roller table cover or encapsulation with insulated roller table rollers.

The above procedure applies to continuous and batch operation in a 1-line system. In order to make better use of the production capacity of the finishing train, it may be useful to integrate a second casting strand in the case of batch operation. In a 2-strand plant, the above procedure of batch operation is also performed on the second strand to reduce the roller hearth furnace length in total. For this purpose, advantageously a flexible two-part ferry can be provided. The half parallel ferry transports the thick slabs and the whole double ferry is intended for the normal thinner, longer slabs. The ring weight of the slabs can be the same.

It should be noted that the slab 3 is understood to be the cast slab behind the casting machine 2 or else the deformed slab behind the rough rolling mill 8.

LIST OF REFERENCE NUMBERS

1

metal band

2

casting machine

3

slab

4

mold

5

strand guide

6

oven

7

Rolling mill (finishing mill)

8th

Pre-rolling mill (inline roughing stand)

9

scissors

10

induction heating

11

induction heating

12

cooling section

13

reel

14

scissors

15

scissors

16

Heat-insulating hood in the area of cold-string disposal

d ₀

nominal slab thickness at the outlet of the casting machine

v ₀

nominal casting speed at the outlet of the casting machine

d

Slab thickness at Kokillenaustritt

v

Casting speed at Kokillenaustritt

F

Slab, pre-strip or belt conveying direction

Claims (9)

1. Method of producing a metal strip (1) by casting and rolling, in which initially a slab (3) with nominal slab thickness (d) is cast in a casting machine (2) by extracting metal at a nominal casting speed (v) from a mould (4), wherein the slab (3) in the region of a strip guide (5) is subjected to a thickness reduction by a number of rollers, wherein the slab (3) is subsequently subjected to temperature influencing in a furnace (6) of defined length, wherein the slab (3) behind the furnace (6) is rolled in a rolling train (7) and wherein, in particular, the slab (3) behind the casting machine (2) and in front of the furnace (6) is subjected in a roughing mill (8) to a thickness reduction to a nominal reshaped slab thickness or pre-strip thickness,
   characterised in that
   for temporary reduction, particularly for temporary interruption, of the feed of rolling stock to the rolling train (7) a decrease of the thickness reduction of the slab (3) in the roughing mill (8) is carried out, wherein the thickness reduction of the slab (3) in the roughing mill (8) is taken back to zero, or at least two of the measures in combination are carried out:

   a) increasing the slab thickness (d₀) behind the casting machine (2) by decreasing the thickness reduction of the slab (3) in the region of the strip guide (5);

   b) lowering the casting speed from the nominal casting speed (v₀) to a decreased value;

   c) decreasing the thickness reduction of the slab (3) in the roughing mill (8).
2. Method according to claim 1, characterised in that in co-operation with carrying out the temporary reduction of the feed of rolling stock to the furnace (6) the slab (3) is cut at shears (9) arranged in front of the furnace (6).
3. Method according to claim 1 or claim 2, characterised in that the entry speed of the slab (3) into the furnace (6) is reduced relative to the nominal value by at least the factor 2.
4. Method according to any one of claims 1 to 3, characterised in that the thickness reduction of the slab (3) in the region of the strip guide (5) is taken back by up to 40 millimetres.
5. Method according to any one of claims 1 to 4, characterised in that the temporary reduction, particularly the temporary interruption, of the feed of rolling stock to the rolling train (7) is carried out while a roll change is carried out in the rolling train (7) or another delay in production is present in the rolling train (7).
6. Method according to any one of claims 1 to 5, characterised in that after carrying out the temporary reduction of the feed of rolling stock to the rolling train (7) the slab (3) is processed in discontinuous batch operation.
7. Method according to any one of claims 1 to 6, characterised in that the slab (3) is processed in the endless rolling method as long as a temporary reduction of the feed of rolling stock to the rolling train (7) does not take place.
8. Method according to any one of claims 1 to 7, characterised in that through the measures a), b) and c) according to claim 1 such a buffer time or rolling interruption in the rolling train (7) is created or made possible that it is not necessary to break off casting in the casting machine, in which case, in particular, a short furnace (6) is used.
9. Method according to any one of claims 1 to 8, characterised in that the slab (3) is subjected to a heating by way of induction heating means (10) in front of or behind the furnace (6).

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