METHOD FOR PRODUCE METALLIC STRIPS BY DISHING ROLLS

Description

[0001] The invention relates to a method for producing metallic strips by means of casting rollers, in which a slab is first cast in a casting machine, wherein the slab is cleaned in a cleaning device in the conveying direction behind the casting machine and the slab is subsequently subjected to heat treatment in a heat treatment device, wherein the slab is subjected to a smoothing process between the cleaning device and the heat treatment device by means of two cooperating smoothing rollers.

[0002] Such a process is disclosed in DE 10 2008 029 581 A1. The casting strand exiting the casting machine is first descaled and, before entering a furnace, subjected to a pre-rolling process using a pre-rolling stand, whereby an initial relevant thickness reduction of the cast slab occurs (see Figure 6 of the document). After the slab exits the furnace, further rolling takes place in a rolling mill.

[0003] A similar procedure is described in WO 2008 / 113848 A1. Further similar and other solutions are shown in DE 10 2008 020 412 A1, WO 2007 / 137740 A1, JP 2018 061999 A, US 2008 / 251232 A1, DE 10 2005 059 692 A1, CN 213495668 U, US 2010 / 116380 A1, DE 10 2007 022 931 A1 and DE 101 37 944 A1.

[0004] In the generically relevant prior known solutions, the slab is subjected to a relevant thickness reduction before entering the furnace, either already in the area of ​​the casting machine, i.e., with the core of the casting strand still liquid, or between the casting machine and the furnace in a pre-rolling stand.

[0005] The previously known manufacturing method presents the following disadvantage: If the solidified slab undergoes a forming process with a significant reduction in thickness before homogenization in a furnace, temperature differences within the slab can lead to uneven forming, which has a detrimental effect in subsequent rolling steps. A further disadvantage of the thickness reduction lies in the necessary structural lengthening of the continuous furnace, which is designed for a multiple of the slab length. With the increased furnace length, not only does energy consumption rise, but the longer contact time of the slab with the furnace rollers also has a negative impact.

[0006] Insofar as no reduction in slab thickness is provided for in the previously known solutions, the technological focus here is on improving the profile or geometry of a cast strip or a very thin slab.

[0007] A disadvantage of large thickness reductions before the furnace is the negative impact on the quality of the lateral slab and strip edge geometry, which leads to higher energy and cost input due to the necessary extra widths in the melting, casting and rolling process and the wider trimming cut that is then required.

[0008] It has been observed that cast slabs, which can be thin, medium, or thick, often exhibit an uneven surface, due in part to casting marks. During further processing, such as in a roller hearth furnace, the slabs rest on these surface peaks, which, particularly when disc rollers are used in the subsequent process, can lead to grooves and unwanted scale buildup in the depressions. Additionally, a long residence time of the slab in the furnace results in increased scale buildup, which must be removed before a subsequent rolling step. Removing the scale from the depressions is difficult when the surface is not smoothed.

[0009] The problems described lead to surface defects in the finished rolled product that cannot be remedied and may lead to a "downgrading" of the product in surface-sensitive applications.

[0010] The invention is based on the Task The underlying principle is to further develop a process of the aforementioned type in such a way as to eliminate the aforementioned problem. In particular, energy and production costs are to be reduced, which is to be achieved through targeted manipulation of the slab and strip edge geometry. Specifically, the surface of the slabs before the first forming process is to be improved.

[0011] The Solution The invention is characterized in that the smoothing process is carried out in such a way that the slab experiences a thickness reduction of less than 10% and the roughness depth of the smoothed surfaces of the slab is reduced.

[0012] The average roughness of the rolled surfaces of the slab after smoothing is preferably at most 10 µm, particularly preferably at most 8 µm. This reduces the average roughness compared to the value usually found when casting from a mold (approx. 11 µm to 14 µm).

[0013] The slab is preferably subjected to the smoothing process in a fully solidified state.

[0014] The thickness reduction of the slab during the smoothing process is preferably less than 5% and particularly preferably less than 3%.

[0015] 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.

[0016] The smoothing process with the two cooperating 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.

[0017] The cleaning process in the cleaning device is preferably a descaling process, in particular by fluid descaling or flame treatment.

[0018] The smoothing rollers can be cooled during the smoothing process.

[0019] The smoothing process preferably takes place at a speed between 1.0 and 6.0 m / min.

[0020] The proposed method is therefore used particularly in the casting and rolling of hot slabs to prepare the slab surfaces before they enter the furnace. This involves smoothing the surfaces of the solidified slab as it emerges from the casting machine.

[0021] The central aspect of the invention is the smoothing of the surface of the casting strand or slab, wherein prior cleaning, in particular descaling (e.g., by fluid descaling, flame treatment, or gas cleaning), takes place, and the cleaned slab surface is smoothed by a pair of rollers. No significant thickness reduction occurs during this process, i.e., no penetrating deformation and thus no associated microstructure transformation from a cast structure to a rolled structure (which only occurs with a corresponding thickness reduction). Rather, the intended smoothing process (using the pair of smoothing rollers) merely smooths the surface peaks of the slab, thereby reducing the surface roughness and resulting in the flattest possible surface.

[0022] The material from the surface peaks simply flows from these into the depressions or valleys. This reduces the potential surface area for scale formation, and the smoother surface scales more evenly in the subsequent process, without developing further surface-damaging peaks and depressions.

[0023] The thickness reduction of the slab resulting from the application of force is less than 10%, preferably less than 5%, and particularly preferably less than 3%. Specifically, a thickness reduction of less than 1% can be provided, whereby only elastic deformation occurs in the slab itself during the smoothing process. However, due to the surface peaks, this deformation causes the desired slight deformation (as explained above) and is limited to the layer of the slab closest to the edge.

[0024] The pair of smoothing rolls used for the described smoothing process can be adjusted to the slab thickness. The applied force can be set via a process model. The parameters for adjusting the smoothing rolls are transmitted via a control unit. Therefore, the pair of smoothing rolls is not a complete rolling mill stand with corresponding actuators.

[0025] Depending on the design, the pair of smoothing rollers can be moved into and out of the line. However, it can also remain stationary within the system.

[0026] Preferably, the smoothing rollers are cooled. The pair of smoothing rollers can be housed together with a pair of shears in a common frame. Furthermore, the scale washer can also be integrated into this common frame.

[0027] The invention is preferably used with a slab thickness between 30 mm and 180 mm, and particularly preferably with a slab thickness between 50 mm and 150 mm.

[0028] The intended preferred contact force of the smoothing rollers, approximately 4,000 kN, differs significantly from the forces otherwise specified. This force is too low for the desired slab thickness reduction, but on the other hand, it is considerably higher than the force specified for the contact of drive rollers (which is only about 20% to 50% of the intended contact force of the smoothing rollers).

[0029] The design of the operating parameters naturally also depends on the bandwidth.

[0030] The preferred diameter of the smoothing rollers (approx. 600 mm) is also significantly larger than that of the typical drive rollers in the casting machine sector.

[0031] The design of the diameter and, optionally, the bale shape also depends on the bandwidth.

[0032] The arrangement of the smoothing rollers provided according to the invention is located close to the outlet of the casting machine and can also be partially located below the casting platform.

[0033] The proposed approach offers significant advantages, primarily in the reduction of scale formation, which results from the reduction of surface roughness and thus the avoidance of running marks on the slab.

[0034] This results in quality improvements, especially for surface-sensitive alloys and applications.

[0035] Energy savings are also advantageous, as the reduced and simpler scale buildup means less scale needs to be removed, or it can be removed more easily. This also reduces the required amount of water, so the subsequent cooling of the slab or strip, which needs to be compensated for, requires less energy. Finally, production costs are reduced because unnecessary overwidths can be avoided.

[0036] The drawing shows an embodiment of the invention. Figure 1 shows a system according to the invention for the production of metallic strips by casting rollers, Figure 2 shows an embodiment of a smoothing device, Figure 3 shows a possible sequence of the process steps in the process according to the invention, and Figures 4a and 4b show schematically enlarged images of the surface structure of a slab treated according to the invention.

[0037] Figure 1Figure 1 shows a schematic representation of a front part of the casting and rolling plant 1 according to the invention for the production of metallic strips, in particular steel strips. The plant 1 initially comprises a casting device 2, over which slabs 3 with a thickness of 30 to 150 mm are cast. These slabs are typically formed from a vertical to a horizontal position by means of guide rollers (not shown). The slabs 3 leaving the casting device 2 are so hot that an oxide layer in the form of scale forms immediately upon contact with atmospheric oxygen. This scale must be removed from the surface of the slabs 3 for subsequent heat treatment.

[0038] For this purpose, the system 1 comprises a cleaning unit 4 arranged in the direction of belt travel directly behind the casting device 2, which has a first upper and a first lower scale washer 5, 6. The majority of the scale already formed can be removed from the slab surface via the scale washers 5, 6 arranged above and below the slab 3.

[0039] In the direction of belt travel downstream of the cleaning unit 4, the system 1 further comprises a separating device 7 with two shears 8, 9 by which the slab 3 is optionally divided before entering a heat treatment unit 11. The heat treatment unit 11 is designed in this case as a roller hearth furnace 11. The roller hearth furnace 11 serves both for reheating and for equalizing the slab temperature.

[0040] To improve the transport conditions in the roller hearth furnace 11 on the one hand and to remove the portion of the scale that cannot be removed by the scale washers 5, 6 on the other, 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 driveable smoothing roller 13, 14. Both smoothing rollers 13, 14 are spaced apart from each other such that a smoothing pass can be performed on the cleaned slabs 3. The smoothing pass smooths the surface of the slab 3 and effectively breaks up the scale that cannot be removed by the upstream scale washers 5, 6. This is then removed via a second cleaning unit 15 downstream of the separating device 7, which has a second upper and a second lower scale washer 16, 17, so that an almost scale-free split slab 10 can be fed to the roller hearth furnace 11.

[0041] The distance between the two smoothing rollers 13, 14 is set such that, according to one possible embodiment of the invention, the slabs 3 experience a thickness reduction of at least 3.0% and at most 5.0%, with this distance between the two smoothing rollers 13, 14 being kept constant throughout the entire process. Furthermore, the system 1 can include a force and / or position control device (not shown) by which a hydraulic and / or mechanical device (not shown) of the casting device 2 can be controlled.

[0042] In Figure 2Figure 12 shows a sectional view of an embodiment of the smoothing device 12. The smoothing device 12 comprises two smoothing rollers 13 and 14 arranged in a frame 19, as well as force measuring sensors 20 located on both the operator and drive sides, by means of which the forces across the slab width can be determined. This allows useful information about the shape of the slabs, such as in particular the thickness and / or the wedge shape, to be obtained at an early stage of the process. This information can be transmitted via appropriate signaling systems to the casting device 2 and / or to the subsequent rolling mill in order to optimize the overall rolling process.

[0043] In Figure 2 It is also indicated that corresponding control devices 21 are provided for the position of the smoothing rollers 13, 14 or the force that these exert on the slab.

[0044] To ensure the possibility of retrofitting existing systems, the cleaning units 4, 15, the separating device 7 and the smoothing device 12 arranged between them can be combined into a single unit 18 (see below). Fig. 1 ) be trained.

[0045] In Figure 3 The sequence of individual process steps is shown as they can be implemented in the process according to the invention. In step A, the casting strand or slab is produced in the casting machine. According to step B, the slab can be inductively heated. Subsequently, in step C, the slab enters the cleaning device or the scale scrubber. According to step D, the slab can then be cut into individual pieces. According to step E, the surface of the slab is then smoothed centrally according to the invention using the smoothing rollers 13 and 14. According to step F, the pretreated slabs are then conveyed further or heated in the furnace.

[0046] One possible alternative to this sequence is to perform step E (smoothing) before step D (separating).

[0047] The effect provided according to the invention, which the smoothing stitch is intended to produce by means of the smoothing rollers 13 and 14, is shown schematically in the Figures 4a and 4b illustrated: In Figure 4a The slab with its thickness D is schematically sketched, with the "surface rock" forming as usual after casting in the mold. It should be noted that, with normal care, the average surface roughness Ra is typically between 11 µm and 14 µm. After smoothing with the smoothing rollers 13 and 14, as in Figure 4bAs outlined, slab 10 (divided thin slab) has essentially retained its thickness D, i.e., no significant thickness reduction has occurred. However, the surface rock is significantly leveled, i.e., the average roughness Ra is considerably reduced. Preferably, this is achieved to a value below 10 µm, particularly preferably below 8 µm. Smaller values ​​below 6 µm are even more advantageous and are the goal.

[0048] 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 operator and / or drive side, by means of which the force can be determined across the slab width.

[0049] Preferably, no rolling mill is provided between the casting unit 2 and the heat treatment unit 11. The heat treatment unit 11 can be designed as a roller hearth furnace and / or as an induction heater.

[0050] The slab surface is thus homogenized before the cutting unit or potential cutting step, but after the cleaning unit or cleaning step, by smoothing both surfaces, i.e., the top and bottom of the slab, through a smoothing pass. This reduces the local roughness peaks to such an extent that the formation of undesirable grooves is effectively prevented, thereby improving the transport processes in the heat treatment unit. 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 unit and is fed into the rolling mill. It can therefore be assumed that this effect is based on the reduction of the active surface area on which scale preferentially forms.This reduction in scale formation thus has a positive effect on the plant's output by reducing material losses due to scale formation, which later has to be removed.

[0051] Using the cleaning device, which takes the form of scale washers, a large portion of the already formed scale is removed from the slab surfaces before they reach the separation unit. The portion of scale that cannot be removed by the scale washers can be effectively broken up using the proposed method of smoothing, resulting in higher heat transfer and thus a more effective heat treatment process.

[0052] The cutting device can be in the form of shears and / or a laser-based cutting device. Depending on the operating mode, the continuous cast slab is either divided into individual slabs or passes through the cutting device as a continuous slab for further processing in subsequent process stages. Both operating modes can be provided individually or together by the system and the process and are equally suitable for implementing the invention without limitations.

[0053] For the purposes of the present invention, the term "smoothing device" refers to a device with two driven smoothing rollers arranged at a defined distance from each other. Therefore, it is preferably provided that the system between the casting device and the heat treatment device does not include a rolling mill.

[0054] The smoothing pass is characterized by a particularly small reduction in thickness and is therefore distinguishable from a conventional rolling pass. Preferably, the distance between the two smoothing rolls, or the gap between them, is designed such that the smoothing pass results in a thickness reduction of a maximum of 5.0% relative to the thickness of the incoming slab, and more preferably a thickness reduction of 3.0 to 5.0% relative to the thickness of the incoming slab. In other words, the gap between the two smoothing rolls is positioned so that it is slightly smaller than the incoming slab.

[0055] It is therefore particularly preferred that the distance between the two smoothing rollers is constant and remains constant even during the smoothing process. For this purpose, the system advantageously includes a force and / or position control device by which a hydraulic and / or mechanical component of the casting device can be controlled.

[0056] In the embodiment of the invention described above, a second cleaning device is arranged between the cutting device and the heat treatment device, preferably in the form of scale washers. The remaining loose scale can be removed from the surface of the slabs by means of the scale washers, which are arranged downstream of the cutting device in the direction of belt travel, before the slabs are subsequently subjected to heat treatment.

[0057] To ensure the possibility of retrofitting existing systems, it is particularly preferred that the first cleaning unit, the separating device and the smoothing device arranged in between are designed in the form of a single unit. Reference symbol list:

[0058] 1 Plant 2 Casting machine / Casting device 3 Slab / Thin slab 4 First cleaning device / Cleaning unit 5 First upper scale washer 6 First lower scale washer 7 Separating device 8 Upper shear 9 Lower shear 10 Split thin slab 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 washer 17 Second lower scale washer 18 Unit 19 Frame 20 Force measuring sensor 21 Control / regulating device for position or force

Claims

1. Method of producing metallic strips by casting and rolling, in which initially a slab (3) is cast in a casting machine (2), wherein the slab (3) is cleaned in conveying direction behind the casting machine (2) in a cleaning device (4) and the slab (3) is subsequently subjected to a heat treatment in a heat treatment device (11), wherein the slab (3) between the cleaning device (4) and the heat treatment device (11) is subjected to a smoothing process by means of two co-operating smoothing rollers (13, 14), characterised in that the smoothing process is carried out in such a way that the slab (3) experiences a decrease in thickness of less than 10% and the surface roughness of the smoothed surfaces of the slab (3) is reduced.

2. Method according to claim 1, characterised in that the mean roughness value of the smoothed surfaces of the slab (3) after the smoothing is at most 10 µm, preferably at most 8 µm.

3. Method according to claim 1 or 2, characterised in that the slab (3) is subjected to the smoothing process in the fully hardened state.

4. Method according to any one of claims 1 to 3, characterised in that the decrease in thickness of the slab (3) in the smoothing process is less than 5%.

5. Method according to claim 4, characterised in that the decrease in thickness of the slab (3) in the smoothing process is less than 3%.

6. Method according to any one of claims 1 to 5, characterised in that the smoothing process is carried out by two co-operating smoothing rollers (13, 14) which exert on the slab a force acting normal to the slab of between 3,000 kN and 5,000 kN, preferably between 3,500 kN and 4,500 kN.

7. Method according to any one of claims 1 to 6, characterised in that the smoothing process is carried out by two co-operating smoothing rollers (13, 14) which each have a roller diameter of between 500 mm and 700 mm, preferably between 550 mm and 650 mm.

8. Method according to any one of claims 1 to 7, characterised in that cleaning process in the cleaning device is a descaling process, particularly by fluid descaling or flame descaling.

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

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