WO2024037839A1

WO2024037839A1 - Method for producing metal strips by continuous casting and rolling

Info

Publication number: WO2024037839A1
Application number: PCT/EP2023/070506
Authority: WO
Inventors: Ralf Setzer; Bernhard Ehls; Ingo Schuster; Wolfgang RÖDER
Original assignee: Sms Group Gmbh
Priority date: 2022-08-16
Filing date: 2023-07-25
Publication date: 2024-02-22
Also published as: DE102022208498A1

Abstract

The invention relates to a method for producing metal strips by continuous casting and rolling, in which a slab (3) is first cast in a casting machine (2), wherein the slab (3) is cleaned in a cleaning device (4) placed after the casting machine (2) in the conveying direction, and the slab (3) then undergoes a heat treatment in a heat treatment device (11), wherein, between the cleaning device (4) and the heat treatment device (11), the slab (3) undergoes a smoothing process by means of two interacting smoothing rolls (13, 14). In order to reduce energy and production costs and to improve the surface of the slabs before the first forming process, according to the invention the smoothing process is carried out such that the slab (3) does not undergo a substantial reduction in thickness, and the roughness depth of the smoothed surface of the slab (3) is reduced.

Description

Process for producing metallic strips by casting rolls

The invention relates to a method for producing metallic strips using casting rolls, in which a slab is first cast in a casting machine, the slab being cleaned in a cleaning device in the conveying direction behind the casting machine and the slab is then subjected to a heat treatment in a heat treatment device, the Slab between the cleaning device and the heat treatment device is subjected to a smoothing process by means of two interacting smoothing rollers.

Such a method is disclosed in DE 10 2008 029 581 A1. The casting strand emerging from the casting machine is first descaled and, before entering a furnace, is subjected to a pre-rolling process using a pre-rolling stand, with a first relevant reduction in the thickness of the cast slab (see Figure 6 of the document). After the slab leaves the furnace, further rolling takes place in a rolling mill.

A similar process is described in WO 2008/113848 A1. Other similar and other solutions show the JP 2018 061999 a, the US 2008/251232 A1, the DE 10 2005 059 692 A1, the CN 213495668 U, the US 2010/116380 A1, DE 10 2007 022 931 A1 and DE 101 37 944 A1.

In the previously known solutions relevant to the generic type, the slab is either already in the area of the casting machine, i.e. before it enters the furnace. H. subjected to a relevant thickness reduction when the core of the casting strand is still liquid, or between the casting machine and the furnace in a roughing stand.

With the previously known production method, the following disadvantageous situation arises: If a forming with a significant reduction in thickness of the solidified slab takes place in an oven before homogenization, the temperature differences in the slab can lead to uneven forming, which can occur later Rolling steps have a detrimental effect. Another disadvantage of reducing the thickness is the necessary structural extension of the continuous furnace, which is designed to be a multiple of the length of the slab. The length of the oven not only increases the energy consumption; Prolonged contact between the slab and the furnace rollers also has a negative impact.

Insofar as the previously known solutions do not provide for a reduction in the thickness of the slab, the technological focus here is on improving the profile or geometry of a cast strip or a very thin slab.

The disadvantage of large thickness reductions in front of the furnace is the negative influence on the quality of the lateral slab and strip edge geometry, which leads to higher energy and cost use due to the necessary excess widths in the melting, casting and rolling processes and due to a wider trimming cut that is then necessary .

It has been found that cast slabs, which can be thin, medium or thick slabs, often have an uneven surface due to, among other things, casting marks. With further treatment, e.g. B. in a roller hearth furnace, the slabs rest on these surface tips, which can lead to ruts and unwanted scale rolling in the recesses in the area of the subsequent process, especially when using disk rollers. In addition, a long residence time of the slab in the furnace leads to an increased build-up of scale, which must first be removed before a subsequent rolling step. The scale is difficult to remove from the depressions if the surface is not smoothed.

The problems explained lead to surface impairments in the finished rolled product, which cannot be remedied and, in surface-sensitive applications, may lead to the product being downgraded. The invention is based on the task of developing a method of the type mentioned in such a way that the problem mentioned is eliminated. In particular, energy and production costs should be reduced, which should be achieved by specifically influencing the slab and strip edge geometry. In particular, the surface of the slabs should be improved before the first forming.

The solution to this problem by the invention is characterized in that the smoothing process is carried out in such a way that the slab does not experience a significant reduction in thickness and the roughness of the smoothed surfaces of the slab is reduced.

The average roughness value of the rolled surfaces of the slab after smoothing is preferably at most 10 pm, particularly preferably at most 8 pm. This means that the average roughness value is reduced compared to the usual value when casting from a mold (approx. 11 pm to 14 pm).

The slab is preferably subjected to the smoothing process in a fully solidified state.

The reduction in thickness of the slab during the smoothing process is preferably less than 10%, particularly preferably less than 5% and most preferably less than 3%.

The smoothing process is carried out with two cooperating smoothing rollers, which preferably exert a force acting normally on the slab between 3,000 kN and 5,000 kN, and particularly preferably between 3,500 kN and 4,500 kN.

The smoothing process with the two interacting smoothing rollers is preferably carried out in such a way that smoothing roller diameters between 500 mm and 700 mm, preferably between 550 mm and 650 mm, are provided. The cleaning process in the cleaning device is preferably a descaling process, in particular by fluid descaling or scarfing.

The smoothing rollers can be cooled during the smoothing process.

The smoothing process is preferably carried out at a speed between 1.0 and 6.0 m/min.

The proposed method is therefore used in particular when casting and rolling hot slabs in order to prepare the surfaces of the slab before entering the furnace. The surfaces of the solidified slab that emerges from the casting machine are smoothed.

The central aspect of the invention is the smoothing of the surface of the casting strand or the slab, with cleaning, in particular descaling (e.g. by fluid descaling, flame cleaning or gas cleaning), taking place beforehand and the cleaned slab surface being smoothed by a pair of rollers. There is no relevant reduction in thickness, i.e. H. no penetrating forming and therefore no associated structural transformation from a cast structure to a rolled structure (which only occurs with a corresponding reduction in thickness). Rather, the planned smoothing process (by using the pair of smoothing rollers) only smoothes the surface tips of the slab and thus reduces the surface roughness, so that a surface that is as flat as possible is created.

The material from the “surface peaks” therefore only flows from them into the depressions or “valleys”. This reduces the possible attack surface for the formation of scale and the evener surface scales more evenly in the further process, without forming further surface-damaging peaks and depressions.

The reduction in thickness of the slab resulting from the application of force is less than 10%, preferably less than 5% and particularly preferably less than 3%. In particular, a thickness reduction of less than 1% can be provided during the smoothing process, only an elastic deformation takes place in the slab itself, which, however, causes the desired slight deformation (as explained above) due to the surface peaks there and is limited to the layer of the slab near the edge.

The pair of smoothing rollers used for the smoothing process described can be adjusted to the slab thickness. The applied force can be adjusted using a process model. The parameters for setting the smoothing rollers are transmitted via a control device. The pair of smoothing rollers is therefore not a full-fledged rolling stand with corresponding actuators.

According to a possible design, the pair of smoothing rollers can be moved in and out of the line. However, it can also remain stationary in the system.

The smoothing rollers are preferably cooled. The pair of smoothing rollers can be housed together with a pair of scissors in a common frame. Furthermore, it can be provided that the scale scrubber is also integrated into this common frame.

The invention is preferably used with a slab thickness between 30 mm and 180 mm, particularly preferably with a slab thickness between 50 mm and 150 mm.

The planned preferred pressing force of the smoothing rollers of around 4,000 kN differs significantly from the otherwise planned forces. This force is too low for a desired reduction in the thickness of the slab, but on the other hand it is significantly above the force that is intended for the contact of drive rollers (this is only approx. 20% to 50% of the contact pressure of the intended roller contact pressure of the smoothing rollers). The design of the operating parameters is of course also dependent on the bandwidth.

The preferred diameter of the smoothing rollers (approx. 600 mm) is also significantly larger than the typical drive rollers in the casting machine sector.

The design of the diameter and optionally the shape of the bale also depends on the bandwidth.

The arrangement of the smoothing rollers provided according to the invention is provided close to the outlet of the casting machine and can also be partially located below the casting platform.

The proposed procedure results in significant advantages, which initially lie in the reduction of scale formation, which results from the reduction in surface roughness and thus the avoidance of running marks on the slab.

In particular, this results in quality improvements, especially for surface-sensitive alloys and applications.

Energy can also be advantageously saved because the smaller and simpler scale build-up means that less scale has to be removed or it can be removed more easily. This means that the amount of water required is also lower, so that the cooling of the slab or the pre-strip, which has to be compensated for later, requires less energy. Finally, production costs are reduced because unnecessary excess widths can be avoided.

An exemplary embodiment of the invention is shown in the drawing.

Figure 1 shows a system according to the invention for producing metallic strips by casting rolls, Figure 2 shows an embodiment of a smoothing device,

Figure 3 shows a possible sequence of process steps in the process according to the invention and

Figure 4a and

Figure 4b shows a schematic, greatly enlarged view of the surface structure of a slab that is treated according to the invention.

Figure 1 shows a schematic representation of a front part of the casting-rolling system 1 according to the invention for producing metallic strips, in particular steel strips. The system 1 initially comprises a casting device 2, via which slabs 3 with a thickness of 30 to 150 mm are cast, which are typically formed from the vertical to the horizontal via guide rollers, not shown. The slabs 3 leaving the casting device 2 are so hot that an oxide layer in the form of scale immediately forms upon contact with atmospheric oxygen. This must be removed from the surface of the slabs 3 for the subsequent heat treatment.

For this purpose, the system 1 comprises a cleaning unit 4, which is arranged directly behind the casting device 2 in the strip running direction and has a first upper and a first lower scale washer 5, 6. The majority of the scale that has already formed can be removed from the slab surface via the scale washers 5, 6 arranged above and below the slab 3.

In the strip running direction behind the cleaning unit 4, the system 1 further comprises a separating device 7 with two scissors 8, 9, via which the slab 3 is optionally divided before entering a heat treatment device 11. The heat treatment device 11 is designed here as a roller hearth furnace 11. The roller hearth furnace 11 serves both for reheating and for equalizing the slab temperature.

In order to improve the transport conditions in the roller hearth furnace 11 on the one hand and on the other hand also to remove the part of the part that cannot be removed using the scale washers 5, 6 To remove scale, the system 1 according to the invention comprises a smoothing device 12 arranged between the cleaning device 4 and the separating device 7 with an upper and a lower drivable smoothing roller 13, 14. Both smoothing rollers 13, 14 are spaced apart from one another in such a way that a smoothing stitch is produced on the cleaned slabs 3 is feasible. The smoothing stitch, on the one hand, smoothes the surface of the slab 3 and, on the other hand, effectively breaks up the scale that cannot be removed via the upstream scale washers 5, 6. This is then removed via a second cleaning unit 15, which is connected downstream of the separating device 7 and has a second upper and a second lower scale washer 16, 17, so that an almost scale-free divided slab 10 can be fed to the roller hearth furnace 11.

The distance between the two smoothing rollers 13, 14 is set in such a way that the slabs 3 experience a thickness reduction of at least 3.0% and a maximum of 5.0% according to a possible embodiment of the invention, this being kept constant between the two smoothing rollers 13, 14 throughout the entire process becomes. Furthermore, the system 1 can include a force and/or position control device (not shown), via which a hydraulic and/or mechanical device (not shown) of the casting device 2 can be controlled.

In Figure 2, an embodiment of the smoothing device 12 is shown in a sectional view. The smoothing device 12 comprises the two smoothing rollers 13, 14 arranged in a stand 19 and a force measuring sensor 20 arranged on the operating and drive sides, by means of which the forces across the slab width can be determined. In this way, useful information about the shape of the slabs, such as in particular the thickness and/or the wedgeness, can be obtained at an early stage of the process, which can be forwarded to the casting device 2 and/or to the subsequent rolling train via appropriate signaling systems, to optimize the rolling process overall.

2 also indicates that corresponding control or regulating devices 21 are provided for the position of the smoothing rollers 13, 14 or the force that they exert on the slab. In order to ensure the possibility of retrofitting old systems, the cleaning units 4, 15, the separating device 7 and the smoothing device 12 arranged between them can be designed in the form of a unit 18 (see FIG. 1).

3 shows the sequence of the individual process steps as they can be provided in the process according to the invention. The casting strand or slab is produced in the casting machine in step A. According to step B, inductive heating of the slab can be provided. The slab then enters the cleaning device or the scale washer in step C. According to step D, the slab can then be separated into individual pieces. According to step E, the central smoothing of the surface of the slab according to the invention takes place by means of the smoothing rollers 13 and 14. According to step F, the further transport or heating of the pretreated slabs in the oven then takes place.

A possible alternative to this sequence provides that step E (smoothing) is carried out before step D (separating).

The effect intended according to the invention, which the smoothing stitch is intended to bring about by means of the smoothing rollers 13 and 14, is schematically illustrated in Figures 4a and 4b: In Figure 4a, the slab is schematically sketched with its thickness D, with the “surface mountain range” as usual according to the Pouring in the mold results. It should be noted that with normal care, the average roughness R _a of the surface is typically between 11 pm and 14 pm. After smoothing by means of the smoothing rollers 13 and 14, as sketched in Figure 4b, the slab 10 (divided thin slab) essentially retained its thickness D, ie there was no relevant reduction in thickness. However, the “surface mountains” have been significantly leveled, ie the average roughness value R _a is significantly reduced. This is preferably done to a value below 10 pm, particularly preferably below 8 pm. Smaller values below 6 pm are even cheaper and are aimed for.

The first cleaning unit 4, the separating device 7 and the smoothing device 12 arranged between them are preferably designed as a unit 18. At least One of the two smoothing rollers 13, 14 of the smoothing device 12 can include a force measuring sensor 20 on the operating and/or drive side, by means of which the force across the slab width can be determined.

There is preferably no rolling train provided between the casting device 2 and the heat treatment device 11. The heat treatment device 11 can be designed as a roller hearth furnace and/or as an induction heater.

The slab surface is thus evened out before the separating device or the possible separating step but after the cleaning unit or after the cleaning step by smoothing the two surfaces, i.e. the top and bottom of the slab, using the smoothing stitch. The local roughness peaks are thereby reduced to such an extent that the formation of undesirable track grooves is effectively avoided and the transport processes in the heat treatment device are thus improved. Surprisingly, it has also been shown that the smoothing stitch leads to reduced scale formation on the two surfaces of the slab as soon as it leaves the heat treatment device and is fed to the rolling train. In this respect, it can be assumed that this effect is based on the reduction of the active surface on which the scale preferentially forms. This reduction in scale formation has a positive effect on the output of the system by reducing material losses due to scale formation, which later has to be removed.

By means of the cleaning device, which is designed in the form of scale washers, a large part of the scale that has already formed is removed from the surfaces of the slab before the separating device. The part of the scale that cannot be removed using the scale scrubber can be effectively broken up using the smoothing stitch using the proposed method, which leads to a higher heat transfer and thus a more effective heat treatment process.

The separating device can be in the form of scissors and/or a laser-based cutting device. Depending on the mode of operation, the endless cast Slab divided into individual slabs or passes through the separating device as an endless slab for further processing in subsequent process sections. Both modes of operation can be provided individually or together by the system and the method and are equally suitable for implementing the invention without restrictions.

For the purposes of the present invention, the term “smoothing device” means a device with two driven smoothing rollers, which are arranged at a defined distance from one another. It is therefore preferably provided that the system between the casting device and the heat treatment device does not include a rolling train.

The smoothing stitch is characterized by a particularly small reduction in thickness and can therefore be distinguished from a classic rolled stitch. It is therefore preferably provided that the distance between the two smoothing rollers or the gap between them is designed such that the smoothing stitch has a thickness reduction of a maximum of 5.0% based on the thickness of the incoming slab, more preferably a thickness reduction of 3.0 to 5 .0% based on the thickness of the incoming slab. In other words, the gap between the two smoothing rollers is set so that it is slightly smaller than the incoming slab.

It is therefore particularly preferred that the distance between the two smoothing rollers is constant and also remains constant during the smoothing stitch. For this purpose, the system advantageously comprises a force and/or position control device, via which a hydraulic and/or mechanical device of the casting device can be controlled.

In the embodiment of the invention described above, it is provided that a second cleaning device is arranged between the separating device and the heat treatment device, which is particularly preferably designed in the form of scale washers. The remaining loose scale can be removed via the scale washers arranged behind the separating device in the direction of strip travel Scale is removed from the surface of the slabs before they are then subjected to heat treatment.

In order to ensure the possibility of retrofitting old systems, it is particularly preferably provided that the first cleaning unit, the separating device and the smoothing device arranged between them are designed in the form of a unit.

List of reference symbols:

1 facility

2 casting machine / casting device

3 slab/thin slab

4 first cleaning device / cleaning unit

5 first upper scale scrubber

6 first lower scale washer

7 separation device

8 upper scissors

9 lower scissors

10 divided thin slabs

11 Heat treatment device (roller hearth furnace)

12 smoothing device

13 upper smoothing roller

14 lower smoothing roller

15 second cleaning device/cleaning unit

16 second upper scale scrubber

17 second lower tinder washer

18 unit

19 scaffolding

20 force measuring sensor

21 Control/regulating device for position or force

Claims

Patent claims:

1. A method for producing metallic strips using casting rolls, in which a slab (3) is first cast in a casting machine (2), the slab (3) being cleaned in a cleaning device (4) in the conveying direction behind the casting machine (2) and the slab (3) is then subjected to a heat treatment in a heat treatment device (11), the slab (3) being subjected to a smoothing process between the cleaning device (4) and the heat treatment device (11) by means of two cooperating smoothing rollers (13, 14), thereby characterized in that the smoothing process is carried out in such a way that the slab (3) does not experience any significant reduction in thickness and the roughness depth of the smoothed surfaces of the slab (3) is reduced.

2. The method according to claim 1, characterized in that the average roughness of the smoothed surfaces of the slab (3) after smoothing is at most 10 pm, preferably at most 8 pm.

3. The method according to claim 1 or 2, characterized in that the slab (3) is subjected to the smoothing process in a fully solidified state.

4. Method according to one of claims 1 to 3, characterized in that the reduction in thickness of the slab (3) during the smoothing process is less than 10%, preferably less than 5%.

5. The method according to claim 4, characterized in that the reduction in thickness of the slab (3) during the smoothing process is less than 3%.

6. The method according to one of claims 1 to 5, characterized in that the smoothing process takes place with two cooperating smoothing rollers (13, 14), which exert a force acting normally on the slab between 3,000 kN and 5,000 kN, preferably between 3,500 kN and 4,500 kN.

7. The method according to one of claims 1 to 6, characterized in that the smoothing process takes place with two cooperating smoothing rollers (13, 14), each of which has a roller diameter between 500 mm and 700 mm, preferably between 550 mm and 650 mm.

8. The method according to any one of claims 1 to 7, characterized in that the cleaning process in the cleaning device is a descaling process, in particular by fluid descaling or scarfing.

9. Method according to one of claims 1 to 8, characterized in that the smoothing rollers (13, 14) are cooled during the smoothing process.

10. The method according to any one of claims 1 to 9, characterized in that the smoothing process is carried out at a speed between 1.0 and 6.0 m/min.