Method for producing metal strip by casting rolls - Patent application

Abstract

The present invention relates to a method for producing metal strip by casting rolls, in which a slab (3) is first cast in a casting machine (2), the slab (3) is cleaned in a cleaning device (4) downstream of the casting machine (2) in the conveying direction, the slab (3) then undergoes heat treatment in a heat treatment device (11), and the slab (3) undergoes a smoothing process by two cooperating smoothing rollers (13, 14) between the cleaning device (4) and the heat treatment device (11). In order to reduce energy costs and production costs and to improve the surface of the slab before the initial forming process, the present invention provides that the smoothing process is carried out in such a way that the slab (3) is not significantly reduced in thickness and that the roughness depth of the smoothed surface of the slab (3) is reduced.

Description

[Technical Field]

[0001] The present invention relates to a method for producing metal strip by casting rolls, in which a slab is first cast in a casting machine, the slab is cleaned in a cleaning device downstream of the caster in the conveying direction, the slab is then subjected to heat treatment in a heat treatment device, and the slab is subjected to a smoothing process by two cooperating smoothing rollers between the cleaning device and the heat treatment device. [Background technology]

[0002] Such a method is disclosed in German Patent Application No. DE 10 2008 029 581 A1. The cast strand leaving the caster is first descaled and before entering the furnace undergoes a rough rolling process in a roughing stand, with a first associated reduction of the cast slab (see Figure 6 of the document). After the slab leaves the furnace, further rolling takes place in a rolling mill.

[0003] A similar method is described in WO 2008113848. Further similar and different solutions are shown in JP 2018061999, US 2008251232, DE 102005059692, CN 213495668, US 2010116380, DE 102007022931 and DE 10137944.

[0004] In the case of the hitherto known solutions generally concerned, the slab undergoes an associated reduction in a roughing stand before entering the furnace, either in the area of ​​the caster, when the core of the cast strand is still liquid, or between the caster and the furnace.

[0005] The previously known manufacturing methods have the following disadvantages: if a forming process involving a significant thickness reduction of the solidified slab is carried out before homogenization in the furnace, temperature differences within the slab can lead to uneven forming, which has a negative impact on the subsequent rolling step. Another disadvantage of reduction is the required structural extension of the continuous furnace, which is designed to be a multiple of the slab length. Not only does energy consumption increase with the furnace length, but the longer contact between the slab and the furnace rollers also has a negative effect.

[0006] In hitherto known solutions, where slab reduction is not contemplated, the technical focus is on improving the profile or geometry of the cast strip or very thin slab.

[0007] A disadvantage of large reductions in front of the furnace is the adverse effect on the quality of the transverse slab and strip edge shapes, which results in higher energy and cost consumption due to the necessary excess width in the melting, casting and rolling processes and the wider trimming required thereafter.

[0008] It has been found that cast slabs, which may be thin, medium or thick, often have an uneven surface, particularly due to casting marks. During further processing, for example in a roller hearth furnace, the slabs lie on surface protrusions, which can cause rutting and unwanted scale entrapment in the recesses, especially when using disc rollers in the subsequent process areas. Additionally, the long residence time of the slab in the furnace causes an increase in scale, which must be removed before the subsequent rolling step. Scale is difficult to remove from the recesses if the surface is not smoothed.

[0009] The problems described result in surface damage in the finish rolled product that cannot be repaired and can result in a "downgrade" of the product in surface sensitive applications. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] German Patent Application Publication No. 102008029581 [Patent Document 2] International Publication No. 2008113848 Brochure [Patent Document 3] Japanese Patent Application Publication No. 2018061999 [Patent Document 4] US Patent Application Publication No. 2008251232 [Patent Document 5] DE 102005059692 [Patent Document 6] Chinese Utility Model No. 213495668 [Patent Document 7] US Patent Application Publication No. 2010116380 [Patent Document 8] German Patent Application Publication No. 102007022931 [Patent Document 9] West German Patent Application Publication No. 10137944 Summary of the Invention [Problem to be solved by the invention]

[0011] The object of the present invention is to develop a method of the type mentioned at the beginning so that the problems mentioned are eliminated. In particular, energy and production costs should be reduced, and this should be done by appropriately influencing the edge shape of the slabs and strips. In particular, the surface of the slabs should be improved before the initial forming process. [Means for solving the problem]

[0012] The solution to this problem according to the invention is characterized in that the smoothing process is carried out in such a way that the slab is not subjected to a significant reduction in thickness and the roughness depth of the smoothed surface of the slab is reduced.

[0013] The average roughness value of the rolled surface of the slab after smoothing is preferably at most 10 μm, particularly preferably at most 8 μm, which is reduced compared to the usual values ​​(approximately 11 μm to 14 μm) when cast from a mold.

[0014] The slab is preferably subjected to a smoothing process in a fully solidified state.

[0015] The reduction in thickness of the slab during the smoothing process is preferably less than 10%, particularly preferably less than 5%, very particularly preferably less than 3%.

[0016] The smoothing process is preferably carried out by means of two cooperating smoothing rollers which apply to the slab a force acting perpendicularly to the slab of between 3000 kN and 5000 kN, particularly preferably between 3500 kN and 4500 kN.

[0017] The smoothing process with both smoothing rollers working together is preferably carried out in such a way that smoothing rollers with a roller diameter of 500 mm to 700 mm, preferably 550 mm to 650 mm, are used.

[0018] The cleaning process in the cleaning device is preferably a descaling process, in particular by fluid descaling or flame treatment.

[0019] The smoothing roller may be cooled during the smoothing process.

[0020] The smoothing process is preferably carried out at a speed of 1.0 to 6.0 m / min.

[0021] Therefore, the proposed method is used to prepare the surface of the slab before it enters the furnace, especially during the casting and rolling of hot slabs. The surface of the solidified slab leaving the casting machine is smoothed.

[0022] A central aspect of the present invention is the smoothing of the surface of a cast strand or slab, which has previously been cleaned, in particular descaled (for example by fluid descaling, flame treatment or gas cleaning), and the cleaned slab surface is smoothed by a roller pair. No associated reduction occurs, i.e., no significant deformation occurs, and therefore no accompanying structural change from cast to rolled structure occurs (which occurs only when a corresponding reduction occurs). Rather, the intended smoothing process (by use of a smoothing roller pair) only smooths out the surface protrusions of the slab, thus reducing the surface roughness and thereby producing a surface that is as flat as possible.

[0023] Thus, material from the "surface peaks" flows from these surface peaks into the valleys or "valleys," reducing the available surface area on which scale can form, and allowing the flatter surface to be scaled more uniformly in subsequent processes without forming additional peaks and valleys that damage the surface.

[0024] The reduction of the slab caused by the application of force is less than 10%, preferably less than 5%, particularly preferably less than 3%. In particular, a reduction of less than 1% can be envisaged, with the slab itself only undergoing elastic deformation during the smoothing process, provided that this elastic deformation causes the desired slight deformation (as explained above) due to the surface protrusions therein and is limited to layers near the periphery of the slab.

[0025] The smoothing roller pairs used for the described smoothing process can be adjusted to the slab thickness. The applied force can be adjusted via a process model. The parameters for adjusting the smoothing rollers are transmitted via a control device. That is, the smoothing roller pairs are not regular roll stands with corresponding actuators.

[0026] The smoothing roller pair can, according to one possible embodiment, be moved in and out of the line, but can also remain fixed within the installation.

[0027] Preferably, the smoothing rollers are cooled. The smoothing roller pair can be housed in a common frame together with the shear. It can also be envisaged that the scale washer is also integrated into this common frame.

[0028] The present invention is preferably used for slabs having a thickness of 30 mm to 180 mm, and particularly preferably for slabs having a thickness of 50 mm to 150 mm.

[0029] The intended preferred pressure of the smoothing roller of about 4000 kN differs significantly from the other intended forces: this force is too low for the desired reduction of the slab, but on the other hand it is significantly higher than the intended force for the contact of the drive roller (this force is only about 20% to 50% of the intended roller pressure of the smoothing roller).

[0030] The design of the operating parameters is naturally dependent on the strip width.

[0031] The preferred contemplated diameter of the smoothing roller (approximately 600 mm) is also significantly larger than the diameter of a typical drive roller in the caster area.

[0032] The diameter and optional barrel shape are both designed depending on the strip width.

[0033] The smoothing roller assembly contemplated by the present invention is located adjacent the exit of the casting machine and may be located partially below the casting platform.

[0034] The proposed measures provide significant advantages, which primarily consist in the reduction of scale formation, which is achieved by reducing the surface roughness and thus avoiding running marks on the slabs.

[0035] Thus, improved quality is provided, especially for surface sensitive alloys and applications.

[0036] Advantageously, energy can also be reduced, since due to the smaller and simpler scale structure, less scale needs to be removed or can be removed more easily. This also requires less water, so that the subsequent compensatory cooling of the slab or rough strip requires less energy. Finally, production costs are reduced by being able to avoid unnecessary excess width.

[0037] The drawings illustrate an embodiment of the invention. [Brief explanation of the drawings]

[0038] [Figure 1] Installation according to the invention for producing metal strip by means of casting rolls [Figure 2] One embodiment of the smoothing device [Figure 3] Possible sequences of process steps in the method according to the invention [Figure 4] Schematic enlargement of the surface structure of a slab treated according to the invention (FIGS. 4a and 4b) DETAILED DESCRIPTION OF THE INVENTION

[0039] FIG. 1 shows a schematic diagram of the front end of a casting and rolling plant 1 according to the present invention for producing metal strip, particularly steel strip. Plant 1 includes a casting device 2 through which a slab 3 having a thickness of 30 to 150 mm is cast. The slab is typically moved from vertical to horizontal via guide rollers (not shown). The slab 3 leaving the casting device 2 is hot enough that an oxide layer in the form of scale forms immediately upon contact with atmospheric oxygen. This must be removed from the surface of slab 3 for subsequent heat treatment.

[0040] For this purpose, the installation 1 has a cleaning unit 4 arranged immediately after the casting device 2 in the strip travel direction, which cleaning unit comprises a first upper scale washer 5 and a first lower scale washer 6. By means of the scale washers 5, 6 arranged above and below the slab 3, the majority of the scale already formed can be removed from the slab surface.

[0041] After the cleaning unit 4 in the strip travel direction, the installation 1 further comprises a separating device 7 with two shears 8, 9, via which the slabs 3 are separated as required before entering the heat treatment device 11. The heat treatment device 11 is configured as a roller hearth furnace 11, which is used both for reheating and for equalizing the slab temperature.

[0042] To improve the transport conditions in the roller hearth furnace 11 on the one hand and to remove the parts of the scale that cannot be removed by the scale washers 5, 6 on the other hand, the installation 1 according to the invention has a smoothing device 12 arranged between the cleaning device 4 and the separating device 7, which has drivable upper and lower smoothing rollers 13, 14. The smoothing rollers 13, 14 are spaced apart so that a smoothing pass can be performed on the cleaned slab 3. The smoothing pass smooths the surface of the slab 3 on the one hand and effectively breaks down the scale that cannot be removed by the upstream scale washers 5, 6 on the other hand. The scale is then removed by a second cleaning unit 15 arranged downstream of the separating device 7 and comprising a second upper scale washer 16 and a second lower scale washer 17, so that the divided slab 10, which is almost scale-free, can be fed to the roller hearth furnace 11.

[0043] According to a possible embodiment of the present invention, the distance between the smoothing rollers 13, 14 is set so that the slab 3 is reduced in thickness by a minimum of 3.0% and a maximum of 5.0%, and the distance between the smoothing rollers 13, 14 is kept constant throughout the process. Furthermore, the installation 1 can have a force and / or position control device (not shown), via which the hydraulic and / or mechanical devices (not shown) of the casting device 2 can be controlled.

[0044] 2 shows a cross-sectional view of one embodiment of the smoothing device 12. The smoothing device 12 has two smoothing rollers 13, 14 arranged in a stand 19 and force measuring sensors 20 arranged on the operating side and the drive side, respectively, by means of which the force across the slab width can be determined. This makes it possible to obtain useful information about the slab's shape, in particular its thickness and / or wedge shape, already at an early stage of the process, which can be transmitted via a corresponding signaling system to the caster 2 and / or the downstream rolling mill in order to optimize the rolling process as a whole.

[0045] FIG. 2 also shows that a corresponding control or adjustment device 21 is provided for the position of the smoothing rollers 13, 14 or for the force that the smoothing rollers apply to the slab.

[0046] In order to ensure the possibility of retrofitting old installations, the cleaning units 4, 15, the separating device 7 and the smoothing device 12 arranged therebetween can be made in the form of a unit 18 (see FIG. 1).

[0047] 3 shows a sequence of the individual process steps that can be envisaged in the method according to the invention. A cast strand or slab is produced in a caster in step A. In step B, induction heating of the slab can take place. The slab then passes to a cleaning device or scale washer in step C. In step D, separation of the slab into individual pieces can take place. In step E, smoothing of the slab surface by smoothing rollers 13 and 14, which is central to the invention, then takes place. In step F, further transport or heating of the pre-treated slab in a furnace then takes place.

[0048] A possible alternative to this sequence contemplates that step E (smoothing) is performed before step D (separation).

[0049] The effect intended by the present invention to be brought about by the smoothing pass by the smoothing rollers 13 and 14 is shown diagrammatically in FIGS. 4a and 4b. In FIG. 4a, a slab is shown having a thickness D, and the "surface peaks" are obtained after casting in a mold as usual. It should be noted that, with normal care, the average surface roughness value Ra is typically between 11 μm and 14 μm. After smoothing by the smoothing rollers 13 and 14 as shown in FIG. 4b, the slab 10 (the divided thin slab) essentially maintains its thickness D, i.e., no relevant reduction has taken place. However, the "surface peaks" are significantly leveled, i.e., the average roughness value Ra is significantly reduced. Preferably, this results in a value of less than 10 μm, particularly preferably less than 8 μm. Even smaller values ​​of less than 6 μm are even more preferable and are sought.

[0050] The first cleaning unit 4, the separating device 7 and the smoothing device 12 arranged therebetween are preferably formed as a unit 18. At least one of the two smoothing rollers 13, 14 of the smoothing device 12 can have a force measuring sensor 20 on the operating side and / or on the drive side, by means of which the force across the slab width can be determined.

[0051] Preferably, no rolling mill is provided between the casting device 2 and the heat treatment device 11. The heat treatment device 11 can be configured as a roller hearth furnace and / or an induction heating device.

[0052] Therefore, the slab surface is made uniform by smoothing both surfaces, i.e., the upper and lower surfaces of the slab, by a smoothing pass before the separation device or possible separation step, but after the cleaning unit or cleaning step. This reduces local roughness peaks to such an extent that the formation of undesirable ruts is effectively avoided, thus improving the transport process in the heat treatment device. Furthermore, it has surprisingly been found that the smoothing pass causes a reduction in scale formation on both surfaces of the slab as soon as the slab leaves the heat treatment device and is fed to the rolling mill. In this respect, it can be assumed that this effect is due to a reduction in the active surface on which scale preferentially forms. This reduction in scale formation therefore has a positive effect on the production yield of the equipment by reducing material losses due to scale formation that must be subsequently removed.

[0053] A cleaning device in the form of a scale washer removes most of the already formed scale from the surface of the slab before the separating device. The parts of the scale that cannot be removed by the scale washer can be effectively broken down by the proposed smoothing pass process, which results in a higher heat transfer and therefore a more effective heat treatment process.

[0054] The separating device can be in the form of a shear and / or a laser-based cutting device. Depending on the operating mode, the endlessly cast slab is either divided into individual slabs or passes through the separating device as an endless slab for further processing in the next process section. Both operating modes can be performed individually or together by the installation and method and are likewise suitable without limitation for the implementation of the present invention.

[0055] The term "smoothing device" in the sense of the present invention means a device having two driven smoothing rollers arranged at a predetermined distance from each other. Preferably, therefore, the installation does not have a rolling mill between the casting device and the heat treatment device.

[0056] The smoothing pass is characterized by a particularly small thickness reduction and should therefore be distinguished from a classical rolling pass. Preferably, therefore, the distance between the smoothing rollers or the gap between the smoothing rollers is configured so that the smoothing pass causes a thickness reduction of up to 5.0% of the incoming slab's thickness, more preferably 3.0-5.0% of the incoming slab's thickness. In other words, the gap between the smoothing rollers is set to be slightly smaller than the incoming slab's thickness.

[0057] It is therefore particularly advantageous to provide that the distance between the two smoothing rollers is constant and remains constant during the smoothing pass. For this purpose, the installation advantageously has a force and / or position control device, via which the hydraulic and / or mechanical devices of the casting device can be controlled.

[0058] In the above-described embodiment of the invention, it is provided that a second cleaning device, particularly preferably formed in the form of a scale washer, is arranged between the separating device and the heat treatment device, by means of which loose scale still remaining can be removed from the surface of the slab before it is subsequently fed to heat treatment.

[0059] In order to ensure the possibility of retrofitting old installations, it is particularly advantageously provided for the first cleaning unit, the separating device and the smoothing device arranged therebetween to be formed in the form of a unit. [Explanation of symbols]

[0060] 1 equipment 2 Casting machine / casting equipment 3 Slab / Thin Slab 4. First cleaning device / cleaning unit 5. First upper scale washer 6. First Lower Scale Washer 7 Separation device 8 Upper Shah 9 Lower Shah 10 Divided thin slabs 11 Heat treatment device (roller 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 units 19 Stand 20 Force measurement sensor 21 Position or force control / regulation devices

Claims

1. 1. A method for producing metal strip by casting rolls, in which a slab (3) is first cast in a casting machine (2), the slab (3) is cleaned in a cleaning device (4) downstream of the casting machine (2) in the conveying direction, the slab (3) then undergoes heat treatment in a heat treatment device (11), and the slab (3) undergoes a smoothing process by two cooperating smoothing rollers (13, 14) between the cleaning device (4) and the heat treatment device (11), A method characterized in that the smoothing process is carried out in such a way that the slab (3) is not significantly reduced in thickness and the roughness depth of the smoothed surface of the slab (3) is reduced.

2. 2. The method according to claim 1, characterized in that the smoothed surface of the slab (3) has an average roughness value of at most 10 μm, preferably at most 8 μm, after smoothing.

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

6. 6. A method according to any one of claims 1 to 5, characterized in that the smoothing process is carried out by two cooperating smoothing rollers (13, 14) applying to the slab a force of 3000 kN to 5000 kN, preferably 3500 kN to 4500 kN, acting perpendicularly to the slab.

7. 7. A method according to any one of claims 1 to 6, characterized in that the smoothing process is carried out by two cooperating smoothing rollers (13, 14) each having a roller diameter of 500 mm to 700 mm, preferably 550 mm to 650 mm.

8. 8. The method according to claim 1, wherein the cleaning process in the cleaning device is a descaling process, in particular by fluid descaling or flame treatment.

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

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

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