Combined casting and rolling mill having improved productivity

Abstract

A combined casting and rolling mill is initially operated in continuous operation in a known manner, so that the continuous casting mill and the rolling mill are coupled to one another by the cast metal strand (4). Presently relevant is a special operation which begins when the pouring of the liquid metal (1) into the continuous casting mold (2) is ended. The metal strand (4) is then still drawn off from the continuous casting mold (2), but at a lower draw-off speed (v2) at least at the beginning of the special operation. Furthermore, a last portion (17) of the metal strand (4) which, upon the transition into the special operation, is located in the continuous casting mold (2) and in an adjoining upper region of the strand guide (5) is cooled to a greater extent in the strand guide (5). An adjoining earlier portion (18) of the metal strand (4) is cooled as before or to a slightly lesser extent. The metal strand (4) is cut only after the termination time (t1). The cutting time (t5) is selected such that the remaining portion (23) comprises the last portion (17), which is cooled to a greater extent, and possibly a small part of the immediately preceding portion (18) of the metal strand (4). The entire part of the metal strand (4) lying in front of the cutting point (20) is rolled to form the metal strip with the normal strip thickness (d3N).

Description

[0001] Description

[0002] Title of the invention

[0003] Casting-rolling composite plant with improved productivity

[0004] field of technology

[0005] The present invention is based on an operating method for a combined casting and rolling plant, wherein in normal operation of the combined casting and rolling plant

[0006] - liquid metal is poured into a continuous casting mould of a continuous casting plant of the combined casting and rolling plant,

[0007] - the continuous casting mould is cooled by means of a primary cooling system of the continuous casting plant,

[0008] - the cast metal strand is drawn downwards from the continuous casting mould at a normal withdrawal speed by means of a strand guide of the continuous casting plant arranged downstream of the continuous casting mould and is gradually deflected into the horizontal by means of the strand guide,

[0009] - the cast metal strand is cooled during passage through the strand guide by means of a secondary cooling system of the continuous casting plant with a normal cooling intensity,

[0010] - the cast metal strand, after leaving the strand guide of the continuous casting plant, first passes a separating device of the combined casting and rolling plant and is then rolled into a metal strip with a normal strip thickness in a rear section of a rolling mill of the combined casting and rolling plant comprising at least one rolling stand,

[0011] - the normal cooling intensity is determined in such a way that the cast metal strand is completely solidified before reaching the separating device, and

[0012] - the metal strip is separated from the cast metal strand only after passing through the rear section of the rolling mill, whereby the pouring of the liquid metal into the continuous casting mould is terminated at a final point in time, so that the final point in time represents the transition of the operation of the combined casting and rolling mill from normal operation to special operation.

[0013] State of the art

[0014] Such operating procedures are generally known. For example, see WO 2009 / 141 207 A1.

[0015] Summary of the invention

[0016] Historically, continuous casting and rolling of a cast metal strand were separate processes. A metal strand was continuously cast in the continuous caster. At the end of the continuous caster, sections (slabs) were cut from the cast metal strand, and the cut sections were rolled. Rolling only took place after each slab had been cooled and subsequently reheated. This operation, in which individual slabs are rolled, is called batch operation.

[0017] For several years now, there has been a growing shift to combined casting and rolling plants, in which the slabs are rolled directly from the casting heat. In some cases, the cast metal strand is separated before rolling. This operation, in which individual slabs are rolled from the casting heat, is referred to as batch operation in combined casting and rolling plants. However, combined operation is also known, in which continuous casting and rolling take place while the continuous casting plant and the rolling plant are connected and coupled by the (undivided) metal strand. Any change in the casting speed therefore results in a corresponding change in the rolling speed during rolling in the rolling stands of the rolling plant.

[0018] To maintain such a continuous rolling process, a certain minimum mass flow must be maintained. Only in this way can the required process temperatures be maintained in the rolling mill, so that the rolling mill, given its performance limitations (limited rolling force, limited rolling torque, etc.), is more capable of producing the desired end product (metal strip with the standard strip thickness). Metallurgical properties can also no longer be maintained if the mass flow falls below a certain threshold. If the minimum mass flow is undershot, batch operation must be switched to.

[0019] The term "continuous rolling process" should not be understood as meaning that a metal strand is cast for an indefinite length of time, which is then immediately rolled out of the casting heat and without prior separation into sections in the rolling mill. Rather, the casting process must be interrupted from time to time. The main reasons for such interruptions are planned interruptions, for example, for maintenance or changing equipment such as the tundish and pouring tube, and unplanned interruptions due to disruptions, for example, in the upstream production of liquid metal.

[0020] When the casting process is no longer continued, the pouring of liquid metal into the continuous casting mold is terminated. At this point—hereinafter referred to as the termination point—the casting-rolling plant is operated in a special mode.

[0021] It is known in the art to interrupt the withdrawal of the cast metal strand from the continuous casting mold for some time (usually a few minutes) when transitioning from normal operation to special operation - i.e. immediately upon transition to special operation - in order to ensure that the already cast metal strand has completely solidified. At the same time, i.e. at the final point in time, the metal strand is cut using the cutting device. This also ends continuous operation at this point. The section of the cast metal strand that has already passed the cutting device is rolled to the normal strip thickness (with or without acceleration of the rear section of the rolling mill). The section of the cast metal strand that has not yet passed the cutting device represents scrap, which cannot be further recycled but must be melted down.This approach therefore leads to significant material losses and thus reduced productivity.

[0022] The object of the present invention is to create possibilities by means of which the productivity of the casting-rolling composite plant can be increased.

[0023] The object is achieved by an operating method having the features of claim 1. Advantageous embodiments of the operating method are the subject of dependent claims 2 to 8.

[0024] According to the invention, an operating method of the type mentioned at the outset is designed in that in the special operation of the casting-rolling plant

[0025] - the cast metal strand continues to be drawn downwards from the continuous casting mould by means of the strand guide and is gradually deflected into the horizontal position by means of the strand guide, but the drawing off takes place at a special drawing-off speed which is lower than the normal drawing-off speed, at least during a special period following the completion time,

[0026] - the continuous casting mould is cooled by means of primary cooling at least as long as a part of the cast metal strand is still in the continuous casting mould,

[0027] - a final section of the cast metal strand, which at the time of completion is located in the continuous casting mold and an upper region of the strand guide adjoining the continuous casting mold, is cooled by means of secondary cooling with a special cooling intensity while passing through the strand guide, and a subsequent remaining early section of the cast metal strand, which at the time of completion is located in a remaining lower region of the strand guide, is cooled with a further special cooling intensity while passing through the strand guide, wherein the special cooling intensity is greater than the normal cooling intensity and the further special cooling intensity is equal to or less than the normal cooling intensity,

[0028] - the cast metal strand, after leaving the strand guide of the continuous casting plant, initially continues to pass the separating device and is rolled by means of the rear section of the rolling mill to the metal strip with the normal strip thickness as specified at the completion time, - the cast metal strand is separated by means of the separating device at a separation point related to the cast metal strand at a separation time lying after the completion time, and

[0029] - by means of the rear section of the rolling mill, the section of the cast metal strand which lies before the cutting point is rolled into the metal strip with the normal strip thickness as specified at the time of completion.

[0030] Normal operation, as already mentioned, is generally known and entirely conventional. Due to the cooling of the liquid metal by means of primary cooling, the liquid metal solidifies on the walls of the continuous casting mold to form a metal strand with a strand shell and a still-liquid core. Due to the cooling of the metal strand by means of secondary cooling, the strand shell gradually thickens, so that the liquid core of the metal strand gradually solidifies. The sump tip, i.e. the point on the metal strand where the metal strand has just completely solidified, is still within the continuous casting plant and therefore always in front of the separating device. If a front section of the rolling mill, which includes at least one rolling stand, is arranged between the continuous casting plant and the separating device, the sump tip is usually also in front of the front section of the rolling mill.Because the metal strip is separated from the metal strand only after it has passed through the rolling mill, the metal strand provides a direct link between the continuous casting plant and the rolling mill, particularly with the rear section of the rolling mill. The strip thickness is the thickness of the metal strip after rolling in the rear rolling stands of the rolling mill. Although it can change from time to time, it remains constant for a longer period of time after a change. The metal that is cast into the metal strand and later rolled into the metal strip is often steel. However, it can also be another metal, such as aluminum, copper, or brass.

[0031] The speed at which the metal strand can be withdrawn from the continuous casting mold is considerably lower than the speed at which the cast metal strand could be rolled in the rolling mill. The normal withdrawal speed is therefore the limiting factor for the throughput of the combined casting and rolling plant. For this reason, the normal withdrawal speed is generally selected to be as high as possible. A withdrawal speed below the maximum possible speed is also possible, but only within certain limits. If a certain minimum speed is not met, coupled operation of the continuous casting plant and the rolling plant is no longer possible. In this case, the cast metal strand must be divided into individual slabs before rolling the cast metal strand.This division is avoided in combined operation, where the continuous casting plant and the rolling mill are directly coupled. In special operation, cooling of the continuous casting mold is maintained, at least initially, i.e., as long as there is still metal in the mold. The withdrawal of the cast metal strand is also maintained. However, the withdrawal of the cast metal strand takes place at a lower withdrawal speed. Initially, rolling continues to the normal strip thickness, i.e., the same strip thickness to which the cast metal strand will be rolled at the final stage.

[0032] The term "cooling intensity" is coordinated with the withdrawal speed. This applies equally to normal cooling intensity, special cooling intensity, and further special cooling intensity. Coordination with the withdrawal speed means that, at the same cooling intensity, the amount of heat removed from a specific section of the cast metal strand in the strand guide by secondary cooling is independent of the withdrawal speed at which the section passes through the strand guide. This is explained below using an example.

[0033] Assume that a metal strand is cast at a specific casting speed of, for example, 5 m / min. Upon exiting the continuous casting mold, a section of the cast metal strand of a predetermined length has a thermal energy content of X. On its way through the strand guide, the thermal energy quantity Y is removed from the section by cooling using secondary cooling, so that at the end of the strand guide, the metal strand still has a thermal energy content of Z = X - Y. For cooling, the secondary cooling is operated with a specific coolant quantity per unit of time, which is related only to the time. This coolant quantity defines a specific cooling intensity.

[0034] Now assume that the casting speed is increased from 5 m / min to 5.5 m / min. When it leaves the continuous casting mold, the section of the cast metal strand still has the thermal energy content X. Due to the higher withdrawal speed, the section of the cast metal strand passes through the strand guide in a shorter period of time. At the end of the strand guide, the strand should still have the thermal energy content Z. Consequently, the amount of thermal energy Y must still be extracted from the section of the cast metal strand. For cooling, the secondary cooling must therefore be operated with a certain larger amount of coolant per unit of time, which is only related to time. The cooling intensity, however, remains unchanged, since the amount of thermal energy Y is still extracted from the section of the cast metal strand in the strand guide.

[0035] The additional special cooling intensity is generally set to be as high as the normal cooling intensity. It may be slightly reduced because the longer time a cast section of the metal strand spends in the strand guide can result in greater heat radiation. Due to the cooling of the early section of the cast metal strand with the additional special cooling intensity, the temperature at which the early section is conveyed out of the strand guide remains unchanged, or at least almost unchanged, compared to the temperature at which a comparable section is conveyed out of the strand guide during normal operation. However, due to the more intensive cooling of the late section of the cast metal strand, a type of lid enclosing the liquid core forms comparatively quickly at the upper end of the cast metal strand.The cast metal strand also completely solidifies somewhat earlier. This prevents the liquid core from escaping from the cast metal strand, even when the strand is deflected to a horizontal position.

[0036] The length of the special period can be determined as needed. It will usually be in the range of several minutes. After the end of the special period, the withdrawal speed can either be maintained at the (smaller) value of the special withdrawal speed or increased again, either to the normal withdrawal speed or to a value between the special and normal withdrawal speed.

[0037] The procedure according to the invention makes it possible to continue producing the (correct) metal strip in the rolling mill initially - i.e. up until the time of separation. This alone increases the productivity of the combined casting and rolling plant. By separating the cast metal strand at the separation point, the direct coupling of the continuous casting plant and the rear section of the rolling mill is also eliminated. This makes it possible to also roll the remaining section of the cast metal strand, which has already passed the separation device at the time of separation, to the strip thickness. Any reduction in the temperature of the remaining section can be counteracted by increasing the rolling speed. This increase in rolling speed is possible because, from the separation onwards, there is no longer any direct coupling with the continuous casting plant.Behind the rear section of the rolling mill, the metal strip (rolled to the normal strip thickness) can be further cut as required.

[0038] The procedure according to the invention thus ensures that only the remaining section of the cast metal strand, which essentially consists of the last section of the cast metal strand and a (short) adjoining section of the cast metal strand, can no longer be rolled to the strip thickness and therefore accrues as scrap.

[0039] The procedure according to the invention thus enables a significantly higher material yield. Depending on the specific case, 15 to 80 tons more material can be rolled into the metal strip. Furthermore, correspondingly less scrap is generated, so that the energy required for subsequent remelting is also reduced accordingly. The cutting device itself can be conventional. For example, the cutting device can be designed as a standard pendulum shear.

[0040] The separation point is not related to the combined casting and rolling plant and its components, but to the cast metal strand. It therefore moves along with the metal strand as it is conveyed.

[0041] It is possible for the cast metal strand to be rolled exclusively after passing through the cutting device. In this case, only the rear section of the rolling mill is available. However, it is also possible for the cast metal strand to be rolled into a roughing strip with a standard intermediate thickness in a front section of the rolling mill comprising at least one rolling stand before passing through the cutting device. In this case, the front section of the rolling mill is usually a roughing mill, and the rear section is a finishing mill.If such a division of the rolling mill into a front section and a rear section is provided, with the cutting device arranged between these two sections, in special operation the section of the cast metal strand which lies before the cutting point is preferably rolled by means of the front section of the rolling mill to the preliminary strip with the normal intermediate thickness. However, in special operation the section of the cast metal strand which lies after the cutting point is at least partially rolled by means of the front section of the rolling mill to a special intermediate thickness which is greater than the intermediate thickness. If necessary, the latter section of the cast metal strand can also pass through the front section of the rolling mill without being rolled.

[0042] Similar to rolling to strip thickness, the section of the cast metal strand located before the cut is rolled to the normal intermediate thickness. The thickness of the remaining section, however, is greater than the normal intermediate thickness. Thus, the section behind the cut continues to be scrap, but no longer.

[0043] To optimize productivity, the distance of the separation point from the end of the last section of the metal strand should be kept as short as possible. It is therefore envisaged that the distance of the separation point from the end of the last section of the metal strand is 50% of the metallurgical length or less, preferably 40% of the metallurgical length or less, and in particular 30% of the metallurgical length or less. On the other hand, the distance of the separation point from the end of the last section of the metal strand cannot be arbitrarily reduced. It is therefore envisaged that the distance of the separation point from the end of the last section of the metal strand is 10% of the metallurgical length or more, preferably 15% of the metallurgical length or more, and in particular 20% of the metallurgical length or more. The metallurgical length refers to normal operation. The term is generally known and familiar to those skilled in the art.It is the length of the liquid core of the cast metal strand, seen in the strand direction, i.e. the distance between the sump tip and the casting level.

[0044] Typically, the strand guide has several segments. In this case, the segments are preferably advanced in special operation while the last section of the cast metal strand passes through the respective segment. This increases the thickness of the cast metal strand for the last section of the cast metal strand. By increasing the thickness of the cast metal strand, the casting level drops slightly compared to the upper end of the already solidified strand shell. This reliably prevents any sloshing out of still-molten metal.

[0045] The structure of a strand guide consisting of several segments (often referred to as roller segments) is generally known to those skilled in the art. The adjustment of such segments, particularly using hydraulic cylinder units, is also generally known to those skilled in the art. These facts therefore require no further explanation. Increasing the thickness of the cast metal strand is possible because the metal strand is still very soft immediately after casting, allowing it to follow the segments as they move up.

[0046] Preferably, at a determination time prior to the separation time, the time at which the separation point is within the effective range of the separation device is determined by means of path tracking, and this time is defined as the separation time. Thus, the separation point is determined in advance, and then, by means of path tracking, it is determined when the separation point reaches the separation device. This time is the separation time.

[0047] Preferably, the last section of the cast metal strand is cooled on its top side in addition to its side surfaces, at least after it emerges from the continuous casting mold. This procedure can improve and accelerate the formation of the "lid." This makes the deflection of the last section of the cast metal strand to the horizontal less critical.

[0048] Preferably, the special withdrawal speed, the special cooling intensity, the further special cooling intensity, and the position of the separation point on the cast metal strand are determined taking into account the performance limits of the rolling mill and the changes in the metallurgical properties of the metal strip resulting from the reduction of the special withdrawal speed compared to the normal withdrawal speed and the change in the cooling of the cast metal strand. This allows for optimal matching to the given possibilities. Appropriate models that can be used to determine the resulting effects of cooling and the withdrawal speed on, for example, the temperature and the metallurgical properties of the cast metal strand and the rolled metal strip are known to those skilled in the art.

[0049] Short description of the drawings

[0050] The above-described properties, features, and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more readily understood in connection with the following description of an embodiment, which is explained in more detail in conjunction with the drawings.

[0051] FIG 1 a casting-rolling compound plant,

[0052] FIG 2 a continuous casting mold and part of a metal strand,

[0053] FIG 3 a timing diagram,

[0054] FIG 4 a timing diagram,

[0055] FIG 5 a timing diagram,

[0056] FIG 6 Cooling intensities,

[0057] FIG 7 a timing diagram,

[0058] FIG 8 a timeline,

[0059] FIG 9 a section of a strand guide and a metal strand,

[0060] FIG 10 shows a strip thickness as a function of the location on the metal strand and

[0061] FIG 11 an intermediate thickness as a function of location on the metal strand.

[0062] Description of the embodiments

[0063] FIG. 1 shows a combined casting and rolling plant in normal operation. According to FIG. 1, during normal operation, liquid metal 1 is poured into a continuous casting mold 2, usually from a tundish (not shown). This creates a liquid level 3 in the continuous casting mold 2. The continuous casting mold 2 is cooled by a primary cooling system of the continuous casting plant, as indicated by the symbol "H2O."

[0064] The cast metal strand 4 is drawn downwards from the continuous casting mold 2 by means of a strand guide 5 at a withdrawal speed v. The strand guide 5 has a plurality of rollers by means of which the cast metal strand 4 is supported on both sides. Only a few of the rollers are shown in FIG. 1 at the beginning and end of the strand guide 5. At least some of the rollers are driven. Due to the structural design of the strand guide 5, the strand guide 5 gradually deflects the metal strand 4 into the horizontal position. As it passes through the strand guide 5, the metal strand 4 is cooled by means of a secondary cooling system 6 with a cooling intensity K (see later FIGS. 6 and 7). Cooling is often carried out by means of an atomized water-air mixture. Upon exiting the strand guide 5, the metal strand 4 has a casting thickness d1.

[0065] After emerging from the strand guide 5, the metal strand 4 passes a cutting device 7. The cutting device 7 - for example a conventional pendulum shear - is not active during normal operation. The metal strand 4 therefore passes the cutting device 7 without being cut by the cutting device 7. If necessary, the metal strand 4 can be rolled into a preliminary strip with an intermediate thickness d2 in a front section 8 of a rolling mill before passing the cutting device 7. The front section 8 does not have to be present. If it is present, it comprises at least one rolling stand 9. Of the rolling stands 9, only the work rolls are shown in FIG. 1. The number of two rolling stands 9 shown in FIG. 1 is purely exemplary.

[0066] After passing through the separating device 7, the metal strand 4 is rolled into a metal strip with a strip thickness d3 in a rear section 10 of the rolling mill. The rear section 10 is always present. It also comprises at least one rolling stand 11. Of the rolling stands 11, only the work rolls are shown in FIG. 1. The number of three rolling stands 11 shown in FIG. 1 is purely exemplary.

[0067] Only after passing through the rear section 10 of the rolling mill is the rolled metal strip separated from the cast metal strand 4. For this purpose, a (rear) separating device 12 is arranged after the rear section 10. Thus, the metal strand 4 extends continuously from the continuous casting mold 2 to behind the rear section 10 of the rolling mill.

[0068] Additional devices, such as a cooling section (not shown), can be arranged between the rear section 10 of the rolling mill and the rear separating device 12 as required. Other units can also be present. For example, a cooling device, a descaling device, and / or a continuous furnace can be arranged upstream of the front section 8 of the rolling mill and / or between the front and rear sections 8, 10 of the rolling mill. These devices can optionally be arranged upstream or downstream of the separating device 7. A coiling device is also typically arranged downstream of the rear separating device 12.

[0069] FIG. 2 shows - very schematically - the continuous casting mold 2 and the cast metal strand 4. The strand guide 5 is not shown in FIG. 2 for the sake of clarity. According to FIG. 2, the metal strand 4 initially only has a strand shell 13. Inside, i.e. within the strand shell 13, a core 14 of the metal strand 4 is still liquid. The thickness of the strand shell 13 increases with increasing distance from the continuous casting mold 2 until the metal strand 4 has completely solidified. The point 15 immediately before the point at which the metal strand 4 has first completely solidified is usually referred to as the sump tip 15. The distance L of the sump tip 15 from the meniscus 3 is usually referred to as the metallurgical length L of the cast metal strand 4. The metallurgical length L is often in the range between 12 m and 25 m.

[0070] In the illustration in FIG. 2, the sump tip 15 is located in a region of the cast metal strand 4 that has only slightly deflected from the vertical to the horizontal. In practice, however, the sump tip 15 is located in a region where the deflection to the horizontal is already complete or at least essentially complete.

[0071] As can be seen - see additional FIG. 1 - the sump tip 15 is located within the strand guide 5 and thus in particular (significantly) in front of the separating device 7. The cooling intensity K is thus determined such that the metal strand 4 is completely solidified before reaching the separating device 7. If the front section 8 of the rolling mill is present, the metal strand 4 is generally also completely solidified before reaching the front section 8. Furthermore, the exact position of the sump tip 15 is of secondary importance within the scope of the present invention.

[0072] During normal operation, as already mentioned, liquid metal 1 is continuously poured into a continuous casting mold 2. A dip tube typically used for this purpose is not shown in the figures. Figure 3 shows, as a function of time t, the quantity M of liquid metal 1 that is poured into the continuous casting mold 2 per unit time. According to Figure 4, during normal operation, the withdrawal speed v is at a standard value v1, hereinafter also referred to as the normal withdrawal speed v1.

[0073] Normal operation is carried out according to FIG 3 until a termination time t1. At the termination time t1, the pouring of the liquid metal 1 into the continuous casting mold 2 is terminated. The termination time t1 represents the transition of the operation of the combined casting and rolling plant from normal operation to special operation. During times after the termination time t1, the combined casting and rolling plant is therefore operated in special operation.

[0074] According to FIG 4, even in special operation, the cast metal strand 4 continues to be drawn downwards out of the continuous casting mold 2 by means of the strand guide 5. The metal strand 4 is also gradually deflected into the horizontal by means of the strand guide 5. However, the draw-off speed v is reduced from the normal value v1 to a lower value v2, hereinafter also referred to as the special draw-off speed v2, at least during a special period 16 following the final time t1. At the end of the special period 16, the draw-off speed v can be increased again. The increase can take place, as required, down to the normal draw-off speed v1, to a value that is still below the normal draw-off speed v1, or to a value above the normal draw-off speed v1.

[0075] At the end time t1, a portion of the cast metal strand 4 is still in the continuous casting mold 2. The primary cooling of the continuous casting mold 2 is therefore initially maintained as shown in FIG 5. However, since no more liquid metal 1 is poured into the continuous casting mold 2, the meniscus 3 sinks as the metal strand 4 is withdrawn. When the continuous casting mold 2 is idled or shortly after, i.e. when no more of the cast metal strand 4 is left in the continuous casting mold 2, the primary cooling can be switched off. However, it can also be maintained for a while, for example, to cool the continuous casting mold 2. The primary cooling is switched off at a end time t2 as shown in FIG 5.

[0076] As the individual sections of the cast metal strand 4 pass through the strand guide 5, they are cooled with the cooling intensity K. During normal operation - see FIG 6 left - the sections of the metal strand are cooled with a cooling intensity K1, hereinafter referred to as normal cooling intensity K1. If, on the other hand, a section 17 of the cast metal strand 4 passes through the strand guide 5, the section 17 is also cooled by means of the secondary cooling 6. However, the cooling is - see FIG 6 middle - clearly more intense than the cooling of sections of the metal strand 4 during normal operation. The corresponding cooling intensity K2 is hereinafter referred to as special cooling intensity K2. The special cooling intensity K2 is therefore greater than the normal cooling intensity K1.The section 17 in question, as shown in FIG 2, is the section of the metal strand 4 which, at the completion time t1, is located in the continuous casting mold 2 and in an upper region of the strand guide 5 adjoining the continuous casting mold 2. This section 17 is hereinafter referred to as the last section 17 of the cast metal strand 4. If, however, a section 18 of the cast metal strand 4, which is also located in the strand guide 5 at the completion time t1, but adjoins the last section 17 as shown in FIG 2, passes through the strand guide 5 (more precisely: the remaining part of the strand guide 5), the section 18 is also cooled by means of the secondary cooling 6. The associated cooling intensity K3 can - see FIG 6 on the right - be as great as the normal cooling intensity K1. This is represented by the upper dashed line on the right in FIG 6.Alternatively, the additional special cooling intensity K3 can be smaller than the normal cooling intensity K1. This is indicated by the lower dashed line on the right in FIG 6. The corresponding section 18 is hereinafter referred to as the early section 18 of the cast metal strand 4.

[0077] The situation explained above is explained again below in conjunction with FIG 7 using a specific section of the strand guide 5 as a function of time t. It is assumed here that part of the early section 18 of the metal strand 4 is located in the section of the strand guide 5. Initially - in normal operation - the section of the strand guide 5 is operated with the normal cooling intensity K1. From the completion time t1, the early section 18 of the metal strand 4 is cooled. The associated cooling intensity K2 can be maintained compared to the cooling intensity K1 or - as shown in FIG 7 - slightly reduced. At an entry time t3, the last section 17 of the metal strand 4 enters the corresponding section of the strand guide 5. The cooling intensity K is now increased to the value K3.The special cooling intensity K3 is maintained until the last section 17 of the metal strand 4 exits the corresponding section of the strand guide 5 at an exit time t4.

[0078] The separating device 7 is only activated at a separating time t5 (see FIG. 8). The separating time t5 occurs after the completion time t1. The cast metal strand 4 is only separated by the separating device 7 at the separating time t5. Until the separating time t5, the cast metal strand 4 continues to pass through the separating device 7 without being separated. If present, the cast metal strand 4 also passes through the front section 8 of the rolling mill beforehand. Thus, until the separating time t5, the metal strand 4 extends continuously from the end 19 of the cast metal strand 4 (see FIG. 9) to at least the rear separating device 12. The point 20 at which the metal strand 4 is separated by the separating device 7 is referred to below as the separating point 20. The separating point 20 relates to the cast metal strand 4.

[0079] FIG. 10 shows the strip thickness d3 as a function of the location x on the cast metal strand 4. In the illustration of FIG. 10, the location x refers to the still unrolled metal strand 4. FIG. 10 therefore shows the strip thickness d3 to which a respective location x of the cast, still unrolled metal strand 4 is rolled. According to FIG. 10, the metal strand 4 is first rolled in a section 21 to a value d3N, hereinafter referred to as the normal strip thickness d3N. Section 21 is rolled while the casting-rolling mill is in normal operation.

[0080] According to FIG. 10, the rolling of the metal strand 4 to the normal strip thickness d3N is also maintained for a section 22, which is rolled in the rear section 10 of the rolling mill after the metal strand 4 has been separated by the separating device 7. Section 22 is therefore located, relative to the metal strand 4, in front of the separating device 20. Section 22 is also rolled to the normal strip thickness d3N by means of the rear section 10 of the rolling mill.

[0081] Rolling to the normal strip thickness d3N applies to the entire section 22, i.e., both to the area of ​​the metal strand 4 that is rolled in the rear section 10 of the rolling mill before the metal strand 4 is cut by means of the cutting device 7, and to the area of ​​the metal strand 4 that is rolled in the rear section 10 of the rolling mill after the metal strand 4 has been cut by means of the cutting device 7. Thus, the entire section 22 of the metal strand 4, which lies before the cutting point 20, is rolled into the metal strip with the normal strip thickness d3N by means of the rear section 10 of the rolling mill.

[0082] If the front section 8 of the rolling mill is present, the cast metal strand 4 is rolled in the front section 8 of the rolling mill into a preliminary strip with the intermediate thickness d2. FIG. 11 shows the intermediate thickness d2 as a function of the location x on the cast metal strand 4. In the illustration in FIG. 11 - analogous to the illustration in FIG. 10 - the location x relates to the cast, still unrolled metal strand 4. FIG. 11 therefore shows the intermediate thickness d2 to which a respective location x of the unrolled metal strand 4 is rolled. According to FIG. 11, the metal strand 4 is rolled in section 21 to a value d2N, hereinafter referred to as the normal intermediate thickness d2N. Section 21 is the same section 21 as explained above in connection with FIG. 10.

[0083] The rolling of the metal strand 4 to the normal intermediate thickness d2N is also maintained for section 22 according to FIG. 11. Section 22 is the same section 22 as explained above in connection with FIG. 10. The rolling to the normal intermediate thickness d2N applies to the entire section 22, i.e., the entire area of ​​the metal strand 4 that lies before the cutting point 20. The rolling of the last part of section 22 takes place—as does the rolling of the metal strand 4 in general—before the metal strand 4 is cut by means of the cutting device 7.

[0084] The remainder of the cast metal strand, i.e. the area between the separation point 20 and the end 19 of the metal strand 4, also passes through the front section 8 of the rolling mill. This section - hereinafter referred to as the remaining section 23 - is therefore located after the separation point 20. The remaining section 23 can, as shown in FIG. 11, be rolled by the front section 8 of the rolling mill to an intermediate thickness d2 that is (at least partially) greater than the normal intermediate thickness d2N. The increase to the larger intermediate thickness d2 - hereinafter referred to as the special intermediate thickness - can alternatively occur abruptly or in a ramp-like manner. It is even possible for the remaining section 23 to pass through the front section 8 of the rolling mill without rolling, i.e. continue to have the casting thickness d1.

[0085] The remaining section 23 comprises the last section 17 of the cast metal strand 4 explained above in connection with FIG 2. It can also still comprise a short section of the early section 18 of the cast metal strand 4. In any case, however, the distance a of the separation point 20 from the end 19 of the metal strand 4 (which is identical to the end of the last section 17 of the metal strand 4) is significantly smaller than the metallurgical length L, which is shown in FIG 11 for comparison purposes. In particular, the distance a is generally 50% of the metallurgical length L or less. For example, it can be 40% of the metallurgical length L or less. It is particularly preferred if the distance a is 30% of the metallurgical length L or less. However, the distance a must not be too small. As a rule, the distance a is 10% of the metallurgical length L or more.For example, it can be 15% or more of the metallurgical length L. It is particularly preferred if the distance a is 20% or more of the metallurgical length L. A range between 20% and 30% of the metallurgical length L is therefore particularly preferred.

[0086] As shown in FIG 9, the strand guide 5 has a plurality of segments 24. The segments 24 each have a plurality of rollers with which the segments 24 are positioned against the metal strand 4. The number of roller pairs is usually in the upper single-digit or low double-digit range. The clear width of the segments 24 can be adjusted using appropriate adjustment devices (usually hydraulic cylinder units, not shown). As shown in FIG 9, in special operation the segments 24 are moved up a little while while the last section 17 of the metal strand 4 passes through the respective segment 24. Since the metal strand 4 is still quite soft, at least initially, the casting thickness d1 increases slightly. This causes the casting level 3 to sink slightly below the end 19 of the metal strand 4.This reliably prevents any still liquid metal from spilling out at the end 19 of the metal strand 4.

[0087] Furthermore, the last section 17 of the metal strand 4, at least after it has exited the continuous casting mold 2, can be cooled not only on its sides but also on its top side. This is indicated in FIG. 9 by the arrows labeled "H2O." This allows the thickness of a forming cap 25 to be increased more quickly.

[0088] The combined casting and rolling mill is controlled by a control device (not shown). The control device preferably comprises various models known to those skilled in the art. Using the models, the control device can initially determine—still during normal operation and possibly even before normal operation—the specific withdrawal speed v2, the specific cooling intensity K2, the further specific cooling intensity K3, and the position of the separation point 20 on the metal strand 4. The position of the separation point 20 is generally determined indirectly by the distance a from the end 19 of the metal strand 4.The control device can determine the determination taking into account in particular the performance limits of the rolling mill and the changes in the metallurgical properties of the metal strip resulting from the reduction of the special take-off speed v2 compared to the normal take-off speed v1 and the change in the cooling of the cast metal strand 4.

[0089] During subsequent operation, the control device typically implements, among other things, path tracking. Thus, the control device can use path tracking to determine the time at which the separation point 20 is within the effective range of the separation device 7 at a determination time prior to the separation time. The determination time can be any time between the time at which the control device becomes aware of the termination time t1 and the separation time t5. Thus, once the separation time t5 has been determined, the control device, as far as the separation device 7 is concerned, only needs to wait for the separation time t5 and then control the separation device 7 accordingly.

[0090] The present invention offers many advantages. In particular, in the event of a (planned or unplanned) casting interruption, a significant reduction in rejects / scrap can be achieved, resulting in a significantly improved metal strip yield. The operating method can easily be retrofitted to existing combined casting and rolling plants by appropriately adapting the control software.

[0091] Although the invention has been illustrated and described in detail by the preferred embodiments, the invention is not limited by the disclosed examples and other variations may be derived therefrom by those skilled in the art without departing from the scope of the invention.

[0092] List of reference symbols

[0093] 1 liquid metal

[0094] 2 continuous casting molds

[0095] 3 casting levels

[0096] 4 metal strands

[0097] 5 Strand guide

[0098] 6 Secondary cooling

[0099] 7, 12 Separating devices

[0100] 8, 10 sections of the rolling mill

[0101] 9, 11 rolling stands

[0102] 13 strand shell

[0103] 14 core

[0104] 15 Swamp Peak

[0105] 16 Special period

[0106] 17, 18 sections of the metal strand

[0107] 19 End of the metal strand

[0108] 20 Separation point

[0109] 21 , 22 sections of the metal strand

[0110] 23 remaining section

[0111] 24 segments

[0112] 25 Cover a Distance d1 Casting thickness d2, d2N Intermediate thicknesses d3, d3N Strip thicknesses

[0113] K, K1 , K2, cooling intensities K3 L metallurgical length

[0114] M Amount of liquid metal t Time t1 to t5 Time points v, v1 , v2 Withdrawal speeds x Location on the metal strand

Claims

Claims 1. Operating procedure for a casting-rolling composite plant, - whereby in normal operation of the casting-rolling plant -- liquid metal (1) is poured into a continuous casting mould (2) of a continuous casting plant of the combined casting and rolling plant, -- the continuous casting mould (2) is cooled by means of a primary cooling system of the continuous casting plant, -- the cast metal strand (4) is withdrawn downwards from the continuous casting mould (2) at a normal withdrawal speed (v1) by means of a strand guide (5) of the continuous casting plant arranged downstream of the continuous casting mould (2) and is gradually deflected into the horizontal by means of the strand guide (5), -- the cast metal strand (4) is cooled while passing through the strand guide (5) by means of a secondary cooling system (6) of the continuous casting plant with a normal cooling intensity (K1), -- the cast metal strand (4), after leaving the strand guide (5) of the continuous casting plant, first passes a separating device (7) of the combined casting and rolling plant and is then rolled in a rear section (10) of a rolling plant of the combined casting and rolling plant comprising at least one rolling stand (11) into a metal strip with a normal strip thickness (d3), - the normal cooling intensity (K) is determined such that the cast metal strand (4) is completely solidified before reaching the separating device (7), and -- the metal strip is separated from the cast metal strand (4) only after passing through the rear section (10) of the rolling mill, - wherein the pouring of the liquid metal (1) into the continuous casting mould (2) is terminated at a final time (t1), so that the final time (t1) represents the transition of the operation of the combined casting and rolling plant from normal operation to special operation, - where in the special operation of the casting-rolling plant -- the cast metal strand (4) continues to be withdrawn downwards from the continuous casting mould (2) by means of the strand guide (5) and is gradually deflected into the horizontal by means of the strand guide (5), but the withdrawal takes place at least during a special period (16) following the final time (t) at a special withdrawal speed (v2) which is lower than the normal withdrawal speed (v1), -- the continuous casting mould (2) is cooled by means of the primary cooling at least as long as a part of the cast metal strand (4) is still in the continuous casting mould (2), -- a final section (17) of the cast metal strand (4), which at the final time (t1) is located in the continuous casting mold (2) and an upper region of the strand guide (5) adjoining the continuous casting mold (2), is cooled with a special cooling intensity (K2) by means of the secondary cooling (6) while passing through the strand guide (5), and a subsequent remaining early section (18) the cast metal strand (4), which at the completion time (t1) is located in a remaining lower region of the strand guide (5), is cooled with a further special cooling intensity (K3) while passing through the strand guide (5), wherein the special cooling intensity (K2) is greater than the normal cooling intensity (K1) and the further special cooling intensity (K3) is as great as or less than the normal cooling intensity (K1), -- the cast metal strand (4), after leaving the strand guide (5) of the continuous casting plant, first passes the separating device (7) and is rolled by means of the rear section (10) of the rolling plant into the metal strip with the normal strip thickness (d3N) as specified at the final time (t1), -- by means of the separating device (7), the cast metal strand (4) is separated at a separation point (20) related to the cast metal strand (4) at a separation time (t5) lying after the completion time (t1), and -- by means of the rear section (10) of the rolling mill, that section (22) of the cast metal strand (4) which lies in front of the separation point (20) is rolled into the metal strip with the normal strip thickness (d3) as specified at the completion time (t1).

2. Operating method according to claim 1, characterized in that - that in normal operation, the cast metal strand (4) is rolled into a preliminary strip with a normal intermediate thickness (d2N) in a front section (8) of the rolling mill comprising at least one rolling stand (9) before passing the separating device (7), - that in special operation, that section (22) of the cast metal strand (4) which lies in front of the separation point (20) is rolled by means of the front section (8) of the rolling mill to the preliminary strip with the normal intermediate thickness (d2N) and - that in special operation, that section (23) of the cast metal strand (4) which lies after the separation point (20) is at least partially rolled by means of the front section (8) of the rolling mill to a special intermediate thickness (d2) which is greater than the intermediate thickness (d2N), or passes through the front section (8) of the rolling mill without rolling.

3. Operating method according to claim 1 or 2, characterized in that in normal operation the cast metal strand (4) has a metallurgical length (L) and that the distance (a) of the separation point (20) from the end (19) of the last section (17) of the metal strand (4) is 50% of the metallurgical length (L) or less, preferably 40% of the metallurgical length (L) or less and in particular 30% of the metallurgical length (L) or less.

4. Operating method according to claim 1, 2 or 3, characterized in that in normal operation the cast metal strand (4) has a metallurgical length (L) and that the distance (a) of the separation point (20) from the end (19) of the last section (17) of the metal strand (4) is 10% of the metallurgical length (L) or more, preferably 15% of the metallurgical length (L) or more and in particular 20% of the metallurgical length (L) or more.

5. Operating method according to one of the above claims, characterized in that the strand guide (5) has a plurality of segments (24) and that in special operation the segments (24) are moved up while the last section (17) of the cast metal strand (4) passes through the respective segment (24).

6. Operating method according to one of the above claims, characterized in that at a determination time which lies before the separation time (t5), the time at which the separation point (20) is located in an effective range of the separation device (7) is determined by means of a path tracking, and this time is defined as the separation time (t3).

7. Operating method according to one of the above claims, characterized in that the last section (17) of the cast metal strand (4) is cooled at least after the last section (17) of the cast metal strand (4) has emerged from the continuous casting mold (2) in addition to cooling on the side surfaces also on its upper side.

8. Operating method according to one of the above claims, characterized in that the special withdrawal speed (v2), the special cooling intensity (K2), the further special cooling intensity (K3) and the position of the separation point (20) on the cast metal strand (4) are determined taking into account the performance limits of the rolling mill and the changes in the metallurgical properties of the metal strip resulting from the reduction of the special withdrawal speed (v) compared to the normal withdrawal speed (v1) and the change in the cooling of the cast metal strand (4).

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