Method for producing metal strips by continuous casting and rolling

Abstract

A method relates to producing metal strips by casting rolling. A slab (3) is first cast in a casting machine (2). The slab (3) is cleaned in a cleaning device (4) placed after the casting machine (2) in the conveying direction. The slab (3) then undergoes a heat treatment in a heat treatment device (11). 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 prior to the first forming process, 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.

Claims

1. -10. (Canceled)

11. A method for producing metal strips by continuous casting and rolling, comprising: casting a slab (3) in a casting machine (2); cleaning the slab (3) in a cleaning device (4) downstream of the casting machine (2); heat treating the slab (3) in a heat treatment device (11); and smoothing the slab (3) by two interacting smoothing rolls (13, 14) between the cleaning device (4) and the heat treatment device (11) and thereby reducing a roughness depth of surfaces of the slab (3), wherein a reduction in thickness the slab (3) during the smoothing is less than 10%.

12. The method according to claim 11, wherein a mean roughness value of the surfaces of the slab (3) after the smoothing is at most 10 m.

13. The method according to claim 11, wherein a mean roughness value of the surfaces of the slab (3) after the smoothing is at most 8 m.

14. The method according to claim 11, wherein the slab (3) undergoes the smoothing in a fully solidified state.

15. The method according to claim 11, wherein the reduction in thickness of the slab (3) during the smoothing is less than 5%.

16. The method according to claim 11, wherein the reduction in thickness of the slab (3) during the smoothing is less than 3%.

17. The method according to claim 11, wherein the two interacting smoothing rolls (13, 14) exert a force between 3,000 kN and 5,000 kN acting normally on the slab during the smoothing.

18. The method according to claim 11, wherein the two interacting smoothing rolls (13, 14) exert a force between 3,500 kN and 4,500 kN acting normally on the slab during the smoothing.

19. The method according to claim 11, wherein the two cooperating smoothing rolls (13, 14) each have a roll diameter between 500 mm and 700 mm.

20. The method according to claim 11, wherein the two cooperating smoothing rolls (13, 14) each have a roll diameter between 550 mm and 650 mm.

21. The method according to claim 11, wherein the cleaning in the cleaning device is a descaling by fluid descaling or scarfing.

22. The method according to claim 11, further comprising cooling the smoothing rolls (13, 14) during the smoothing.

23. The method according to claim 11, wherein the smoothing is carried out at a speed between 1.0 and 6.0 m/min.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The drawing shows an exemplary embodiment.

[0039] FIG. 1 shows a system for producing metallic strips by casting rolling,

[0040] FIG. 2 shows an embodiment of a smoothing device,

[0041] FIG. 3 shows a possible sequence of method steps, and

[0042] FIG. 4a and FIG. 4b schematically show, in a highly magnified view, the surface structure of a slab treated in accordance with the disclosed method.

DETAILED DESCRIPTION

[0043] FIG. 1 shows a schematic representation of a front part of the casting-rolling system 1 for producing metallic strips, in particular steel strips. The system 1 first comprises a casting device 2, which is used to cast slabs 3 with a thickness of 30 to 150 mm, which are typically formed from the vertical to the horizontal using guide rolls not shown. In doing so, the slabs 3 leaving the casting machine 2 are so hot that an oxide layer in the form of scale forms immediately on contact with atmospheric oxygen. This must be removed from the surface of the slabs 3 for the subsequent heat treatment.

[0044] For this purpose, the system 1 comprises a cleaning unit 4 arranged directly after the casting device 2 in the direction of strip travel, which has a first upper and a first lower descaler 5, 6. The descalers 5, 6 arranged above and below the slab 3 can be used to remove most of the scale that has already formed from the slab surface.

[0045] In the direction of strip travel after the cleaning unit 4, the system 1 also comprises a separating device 7 with two shears 8, 9 via which the slab 3 can be divided prior to entering a heat treatment device 11. In the present case, the heat treatment device 11 is designed as a roller hearth furnace 11. The roller hearth furnace 11 serves both for reheating and for equalizing the slab temperature.

[0046] In order to improve the transport conditions in the roller hearth furnace 11, on the one hand, and to remove the part of the scale that cannot be removed by means of the descalers 5, 6, on the other hand, the system 1 comprises a smoothing device 12 arranged between the cleaning device 4 and the separating device 7 with an upper and a lower drivable smoothing roll 13, 14. Both smoothing rolls 13, 14 are spaced apart such that a smoothing pass can be carried out on the cleaned slabs 3. Due to the smoothing pass, on the one hand, the surface of the slab 3 is smoothed, and on the other hand, the scale that cannot be removed by the upstream descalers 5, 6 is effectively broken up. This is then removed by a second cleaning unit 15 downstream of the separating device 7, which has a second upper and a second lower descaler 16, 17, such that an almost scale-free divided slab 10 can be fed to the roller hearth furnace 11.

[0047] In the present case, the distance between the two smoothing rolls 13, 14 is set such that the slabs 3 undergo a reduction in thickness of at least 3.0% and a maximum of 5.0% in accordance with a possible embodiment, wherein this is kept constant between the two smoothing rolls 13, 14 throughout the entire process. Furthermore, the system 1 can comprise 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.

[0048] FIG. 2 shows a sectional view of an embodiment of the smoothing device 12. The smoothing device 12 comprises the two smoothing rolls 13, 14 arranged in a stand 19 along with a force measuring sensor 20 arranged on the operator and drive side in each case, by means of which the forces across the slab width can be determined. As a result, useful information about the shape of the slabs, such as their thickness and/or wedge shape, can be obtained at an early stage of the process and transmitted via appropriate signaling systems to the casting device 2 and/or the subsequent rolling mill, in order to optimize the rolling process as a whole.

[0049] FIG. 2 also indicates that corresponding control/regulating devices 21 are provided for the position of the smoothing rolls 13, 14/the force that they exert on the slab.

[0050] In order to ensure the option of retrofitting old systems, the cleaning units 4, 15, the separating device 7 along with the smoothing device 12 arranged between them can be designed in the form of a unit 18 (see FIG. 1).

[0051] FIG. 3 shows the sequence of the individual method steps as they may be provided for in the method. The casting strand/slab is produced in step A in the casting machine. In accordance with step B, inductive heating of the slab can be provided. The slab then enters the cleaning device/descaler in step C. In accordance with step D, a separation of the slab into individual pieces can then be provided. In accordance with step E, the central smoothing of the surface of the slab is then carried out by means of the smoothing rolls 13 and 14. In accordance with step F, the further transport/heating of the pretreated slabs in the furnace is then carried out.

[0052] A possible alternative to this sequence is that step E (smoothing) is carried out prior to step D (separating).

[0053] The intended effect, which is to be caused by the smoothing pass by means of the smoothing rolls 13 and 14, is schematically illustrated in FIGS. 4a and 4b: In FIG. 4a, the slab with its thickness D is schematically sketched, wherein the surface mountain range results as usual after casting in the mold. It should be noted that with normal care, the mean roughness value Ra of the surface is typically between 11 m and 14 m. After smoothing by means of the smoothing rolls 13 and 14, as sketched in FIG. 4b, the slab 10 (divided thin slab) has substantially retained its thickness D, i.e., a relevant reduction in thickness has not been carried out. However, the surface mountain range is significantly leveled; i.e., the mean roughness value R.sub.a is significantly reduced.

[0054] Preferably this is carried out to a value below 10 m, particularly preferably below 8 m. Smaller values below 6 m are even more favorable and are aimed for.

[0055] The first cleaning unit 4, the separating device 7 and the smoothing device 12 arranged between them are preferably formed as a unit 18. At least one of the two smoothing rolls 13, 14 of the smoothing device 12 can comprise a force measuring sensor 20 on the operating and/or drive side, by means of which the force over the slab width can be determined.

[0056] Preferably, no rolling mill is 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 an induction heater.

[0057] The slab surface is thus evened out prior to the separating device/the possible separating step but after the cleaning unit/after the cleaning step by smoothing the two surfaces, i.e. the top side and bottom side of the slab, with the smoothing pass. As a result, the local roughness peaks are reduced to such an extent that the formation of undesirable track grooves is effectively avoided, thus improving the transport processes in the heat treatment device. Surprisingly, it has also been shown that the smoothing pass leads to reduced scale formation on both surfaces of the slab as soon as it leaves the heat treatment device and is fed into the rolling mill. In this respect, it can be assumed that this effect is based on the reduction of the active surface on which the scale preferably forms. Thus, this reduction in scale formation has a positive effect on the output of the system by reducing material losses due to scale formation, which in turn has to be removed later.

[0058] By means of the cleaning device, which is designed in the form of descalers, a large part of the scale already formed is removed from the surfaces of the slab prior to the separating device. The part of the scale that cannot be removed by means of the descaler can be effectively broken up by the smoothing pass by means of the proposed method, which leads to a higher heat transfer and thus a more effective heat treatment process.

[0059] The separating device can take the form of a shear and/or a laser-based cutting device. Depending on the mode of operation, the continuous cast slab is divided into individual slabs or passes through the separating device as a continuous slab for further processing in subsequent process stages. Both modes of operation can be provided individually or jointly by the system and the method and are equally suitable for the implementation of the disclosure, without any limitation.

[0060] Within the meaning of the present disclosure, the term smoothing device refers to a device with two driven smoothing rolls that are arranged at a defined distance from one another. Therefore, it is preferably provided that the system does not comprise a rolling mill between the casting device and the heat treatment device.

[0061] The smoothing pass is characterized by a particularly small reduction in thickness and can therefore be distinguished from a classic rolling pass. Therefore, it is preferably provided that the distance between the two smoothing rolls/the gap between them is formed such that the smoothing pass causes a maximum reduction in thickness of 5.0% in relation to the thickness of the incoming slab, more preferably a reduction in thickness of 3.0 to 5.0% in relation to the thickness of the incoming slab. In other words, the gap between the two smoothing rolls is set such that it is slightly smaller than the incoming slab.

[0062] Therefore, it is particularly preferably provided that the distance between the two smoothing rolls is constant and also remains constant during the smoothing pass. 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.

[0063] In the embodiment described above, it is provided that a second cleaning device, which is particularly preferably designed in the form of descalers, is arranged between the separating device and the heat treatment device. The remaining loose scale can be removed from the surface of the slabs via the descalers arranged after the separating device in the direction of strip travel before the slabs are then fed for heat treatment.

[0064] In order to ensure the option 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 formed as a single unit.

LIST OF REFERENCE SIGNS

[0065] 1 System [0066] 2 Casting machine/Casting device [0067] 3 Slab/thin slab [0068] 4 First cleaning device/cleaning unit [0069] 5 First upper descaler [0070] 6 First lower descaler [0071] 7 Separating device [0072] 8 Upper shear [0073] 9 Lower shear [0074] 10 Divided thin slabs [0075] 11 Heat treatment device (roller hearth furnace) [0076] 12 Smoothing device [0077] 13 Upper smoothing roll [0078] 14 Lower smoothing roll [0079] 15 Second cleaning device/cleaning unit [0080] 16 Second upper descaler [0081] 17 Second lower descaler [0082] 18 Unit [0083] 19 Stand [0084] 20 Force measuring sensor [0085] 21 Control/regulating device for position/force