Patent Application
20190255602
The invention relates to a method for controlling a continuous casting system, a computer program product and a control device for controlling a continuous casting system.
Continuous casting systems are used for the production of slabs from various materials such as steels, copper alloys or aluminum. A corresponding melt is transported to the continuous casting system and poured from a converter into a casting ladle. Via a bottom outlet the melt then flows from the ladle into a tundish from which the melt can flow into so-called molds. Each mold determines the shape of the strand which is cast. In order to prevent the material from caking on the walls of the mold, the mold is oscillating moved. Due to the cooling of the walls of the mold, the material solidifies at the edges, resulting in a solidified strand shell which is cooled further after leaving the mold. The strand shell or the strand in general is still supported by rollers after leaving the mold in order to prevent the strand from breaking open.
Once the strand has solidified in its cross-section, it can be cut to the desired length by an appropriate cutting system, e.g. a cutting torch or scissors.
As a result, the continuous casting process results in individual slabs which can for example then be further processed in a rolling mill. One possibility, for example, is hot rolling, in which the slabs are heated to a corresponding temperature above the recrystallization temperature and then reduced to the specified thickness in the gap of a hot rolling mill by exerting pressure. Since the volume of the slab remains the same, changes in length and width occur. Due to the rolling process, a slab finally becomes a strip which is wound onto a reel to form a coil.
Continuous casting systems are used in various configurations. So-called multiple strand systems, in which several strands can be cast in parallel and simultaneously, are common. Here, the tundish has the function of distributing the liquid material, such as liquid steel, to the individual molds and thus the individual strands.
EP 1021261 B 1 describes, for example, a process and a system for the production of slabs of various formats. The EP 1658533 B1 reveals a method and a device for controlling a plant for the production of steel.
The invention has as its object to provide for a method for controlling a continuous casting system for the production of slabs, a computer program product and a control device for controlling a continuous casting system for the production of slabs. The object is achieved by the features of the independent patent claims. Preferred embodiments of the invention are given in the dependent claims.
A method for controlling for controlling a continuous casting system for producing slabs from a predetermined material is presented, wherein the continuous casting system has a plurality of molds for forming respective strands, wherein the method comprises:
Embodiments of the invention could have the advantage that the quantity of scrap (i.e. the production of stock slabs not currently included in the orders) could be reduced by the optimized production of the slabs, thus maximizing the casting performance of the continuous casting system. Due to the sorting criteria, the batch purity (one converter filling) of the individual casting orders and thus of the assigned customer orders is also improved, which reduces the sampling effort for these orders, since one sampling per order is required. The latter is relevant because the coils must meet certain quality criteria with regard to the materials used. For this reason, one sample must be taken per batch (i.e. per melt) to check the material quality.
The term “control” of the continuous casting system is generally understood to mean that the continuous casting system receives the continuous casting data from which the actual continuous casting program can be created. The control data contain all information concerning the slabs to be produced with regard to the production sequence as well as their materials and sizes. The continuous casting data thus specify the casting sequence, for example the slab widths and slab lengths to be produced, from which a control program or continuous casting program for the corresponding control of the molds, the transport speed of the strand etc. can then be created in the continuous casting system.
According to an embodiment of the invention, the continuous casting system is a multiple strand system with a plurality of strands arranged in parallel, wherein one of the molds is assigned to each strand, wherein the control is performed for parallel simultaneous production of the slabs to be cast determined in the subsequences. The control data can, for example, specify in which order which slabs with which width are to be produced in parallel and simultaneously.
In this case, the method includes a unique assignment of each of the subsequences to one of the strands, wherein the assignment is carried out in such a way that the average slab width of the slabs to be cast determined in the respective subsequences continuously decreases from the inner strands to the outer strands. This could lead to an increase in the quality of the slabs produced, since the quantities of material flowing out of the tundish are regularly distributed through the corresponding casting tubes into the corresponding molds: in the middle, the largest material discharges take place through the pouring tubes, whereas the material discharges are reduced with respect to the external pouring tubes and molds. All in all, this could prevent corresponding turbulence of the liquid material in the tundish.
According to an embodiment of the invention, due to the uniform partitioning, the number of slabs to be cast determined in the respective subsequences is identical for all subsequences. All casting orders on which the partial sequence formation is based are fully taken into account. By suitable adaptation of the slab lengths, the strand lengths of the individual subsequences can be adjusted to each other without changing the total weight of all partial strands. By the associated shortening of the maximum partial strand length, the total casting time with regard to the casting orders could also be minimized, whereby the overall utilization of the system and thus the casting performance can be further optimized.
It should be noted at this point, that uniform partitioning in the sense of the present description means that segments of the sorted base sequence continue to be used unchanged as subsequences, while the sorting contained within the segments with regard to the slabs is retained. If, for example, the base sequence describes 20 slabs to be cast, a uniform partitioning could be such that slabs 1 to 5 are contained in a first subsequence, slabs 6 to 10 in a second subsequence, slabs 11 to 15 in a third subsequence and slabs 16 to 20 in a fourth subsequence. So to speak, only a photographic cutting of the slabs to be cast, which are described in the sorted basic sequence, takes place.
According to an embodiment of the invention, the method further comprises after the adjusting of the slab widths:
This could help to ensure that the entire target quantity is planned on an order-by-order basis when casting orders are primarily specified and that order-less additional slabs to achieve the target weights are avoided.
This could also help to maximize the casting performance of the system by adhering to and exploiting the tolerance data for casting orders, as the threshold range and target weight can be selected in such a way that the available quantity of material from which the slabs are cast is optimally utilized. For example, the target weight is at least an integer multiple of the weight that can be obtained by supplying the material from a converter. If, for example, the total weight of the slabs to be cast from the adjusted sequences is initially 275 tons, whereas only 270 tons can be obtained with one converter, for example, this would mean that a further casting process would have to be carried out with another converter for the difference of five tons, whereby 265 tons of melt could not initially be used for this purpose. If the tolerance specifications for the casting orders are used and “exploited to the full”, the method described could optimize the dimensioning of the slabs to be produced to such an extent that their total weight lies at the desired 270 tons and thus the casting orders can be fulfilled with just one converter of melt.
The comparison value includes, for example, the quotient of total weight and target weight, whereby the change in slab weight or slab length includes a multiplication of the slab weight or slab length by the quotient. This could make it easy to quickly and purposefully optimize the total weight in one or more iterations. For example, the threshold range could be a deviation of the total weight from the target weight<3%.
According to an embodiment of the invention, the method further comprises after the adjusting of the slab widths for all of the slabs to be cast of all of the adjusted subsequences, changing the slab width of each slab in a similar way with concomitant shortening of its slab length while retaining its slab weight, wherein in case when the thereby changed slab width or the thereby changed slab length violates the tolerance specifications of the associated casting order no change in the slab width or the slab length occurs.
This could have the advantage of reducing casting times by achieving shorter strand lengths with higher widths. If it is assumed that the throughput speed of the strands through the system is constant or that the length of the slab produced per unit of time is constant, this reduction in the slab length while maintaining the slab weight and correspondingly increasing the slab width leads to a reduction in the time required to carry out the casting program.
For instance, the sorting criterion comprises a decreasing order of the slab widths, wherein the changing of the slab width of each slab in a similar way with concomitant shortening of its slab length comprises for all slabs of an adjusted subsequence respectively:
While the first quotient first takes into account the possible tolerances with regard to the slabs, the second quotient ensures that the strand is not set up. Setting up means that in the sequence the successor of the current slab suddenly becomes wider than its predecessor, i.e. suddenly a width adjustment towards larger widths takes place, but this is however not desired. Starting from the initial sorting of the slabs to be cast according to the sorting criterion of the decreasing slab widths, it is desired that the width adjustment always takes place towards smaller widths in order to optimize the casting performance of the system. Finally, the third quotient serves to avoiding a jump in width to the successor, which cannot be performed by the system.
According to an embodiment of the invention, the changing of the slab width of each slab in a similar way with concomitant shortening of its slab length comprises for all slabs of an adjusted subsequence respectively:
By multiplying by the smallest value of the quotients, it could be ensured that the strand widths can actually be varied in an optimized way in such a way that an optimization of the casting sides by short slabs at high widths is actually possible, since the process could then approach the optimal strand widths and strand lengths in small steps without overshooting the target.
According to an embodiment of the invention, the continuous casting system has, for each pair of strands, a common cutting system for the two strands for cutting slabs cast in parallel, wherein, for a pair of adjusted subsequences associated with one of the pairs of strands, the slabs specified at the same position of the respective subsequences form a pair of slabs to be cast in parallel, wherein the determining of the first, second and third quotients is performed for each pair of current slabs of the slabs to be cast in parallel, wherein the changing of the slab width of each slab in a similar way with concomitant shortening of its slab length comprises for all the slabs of all the pairs of the adjusted subsequences respectively:
This could have the advantage that the technical conditions of the system are taken into account, whereby the corresponding cutting system for cutting a strand is only available for a given pair of strands. In practice, however, this means that the two parallel strands can only be cut simultaneously to obtain slabs of identical length. By using the smallest of the quotient values determined for the pair of current slabs, this technical limitation is now taken into account in an optimized step sequence and it is ensured that an optimization of casting times is possible and that strand pairs with the limitation of identical slab lengths are taken into account.
According to an embodiment of the invention, each casting order comprises a KIM weight, wherein the sorting criterion comprises a decreasing order of the slab widths as a primary criterion and the KIM weight as a secondary criterion, wherein the tolerance specifications each comprise a lower limit and an upper limit with respect to the slab widths and the KIM weights.
It should be noted that the use of KIM weights for coils is a standard specification in the processing and production of strip materials such as steel strip. KIM means weight in kilograms per millimeter of coil width. If, for example, the coil width is 570 mm and the coil weight is 10500 kg, this results in a KIM of 18.4 kg/mm. Since the specific weight of the material is now constant, dimensions, weight and KIM can be converted to each other. If, for example, a strip thickness of 3.5 mm and a specific weight of 7.8 kg/dm3 are assumed in the case of strip steel, a corresponding length of strip steel can be calculated from this, namely in the above example the KIM weight of 18.4 kg/mm and a length of 674764 mm. The KIM weight can therefore be used as a width-independent indicator for the slab length, as it can be assumed that the slabs are to be regarded as having a given and constant thickness.
According to an embodiment of the invention, the determining of the set of slabs to be cast comprises for each casting order:
This could have the advantage that the number of slabs corresponding to each casting order can first be determined for each casting order in such a way that there is still sufficient leeway within the given tolerances for the variation of the strand widths or strand lengths for the subsequent optimization steps. All in all, this could guarantee the highest possible flexibility with regard to the execution of the procedure for variation of the continuous casting system.
According to an embodiment of the invention, the adjusting of the slab widths of the slabs to be cast comprises the subsequence:
It is also possible that in this case the reduced width of the current slab violates the associated tolerance specifications, the current slab is set to the minimum permissible width in the tolerance range, and after adjustment of the slab widths for all slabs in the subsequence, the process is repeated in the opposite direction starting from the last or the first slab to be cast.
This could have the advantage that the strand widths are varied in such a way that the width transitions from slab to slab in the subsequence are as compatible as possible. In particular, it could be avoided in this way that width jumps are present which technically cannot be realized at all by the system at the transition from one slab to the next one, so that in this case so-called intermediate slabs or bearing slabs would first have to be inserted into the subsequence in order to realize such width jumps in several steps. However, a bearing slab again means an ineffective utilization of the continuous casting system, since it is uncertain at what point the bearing slab can be used at all. In addition, a storage slab would have to be assigned to another casting order at a later point in time, so that there is no uniform identical quality within the casting order and the resulting slabs.
According to an embodiment of the invention, each casting order comprises a KIM weight, wherein the tolerance specifications each comprise a lower limit and an upper limit with respect to the KIM weights, wherein the continuous casting system has, for each pair of strands, a common cutting system for the two strands for cutting slabs cast in parallel, wherein, for a pair of adjusted subsequences associated with one of the pairs of strands, the slabs specified at the same position of the respective subsequences form a pair of slabs to be cast in parallel, wherein the method further comprises, after the adjusting of the slab widths:
On the one hand, this could ensure that an identical length of the produced slabs can be guaranteed with regard to the parallel lower strands belonging to each other. On the other hand, for this special case of a continuous casting system with pairs of strands, each of which has a common cutting system, it could also be ensured that compatible slab lengths are produced here as effectively as possible. Although the continuous casting system has a common cutting system for each pair of strands and the resulting two parallel strands must have the same length, it could still be ensured that the casting performance of the system is maximized, i.e. in the above example the number of necessary bearing slabs is minimized.
In another aspect the invention relates to a computer program product having processor executable instructions for performing the method described above.
In a further aspect the invention relates to a control device for controlling a continuous casting system for producing slabs from a predetermined material, said continuous casting system comprising a plurality of molds for forming respective strands, said control device comprising a processor and a memory, said memory storing instructions executable by said processor, wherein execution of said instructions by said processor controls said control device to: receive a plurality of casting orders, each casting order comprising a demand quantity of the material, an associated slab width, and tolerance specifications with respect to the casting order, determine, for each of the casting orders, from the respective demand quantity and the respective slab width, a set of slabs to be cast with associated slab weights and slab widths, sort all slabs to be cast of all sets of all casting orders according to a sorting criterion to obtain a sorted base sequence of slabs to be cast, the sorting criterion comprising the slab widths, uniformly partition the sorted base sequence into a number of subsequences, the number of subsequences corresponding to the number of molds, adjust, for each of the subsequences, the slab widths of the slabs to be cast of the subsequence under consideration of the tolerance specifications, wherein as a result of the adjusting of the width changes between two slabs to be cast immediately successively one after the other in the subsequence do not exceed a predetermined step value, wherein adjusted subsequences are obtained as a result of the adjusted slab widths, transmit control data to the continuous casting system for producing the slabs to be cast determined in the adjusted subsequences, wherein in the control data for each of the subsequences the order of production of the slabs corresponds to the order in which the slabs to be cast are determined in the respective adjusted subsequence.
It should be noted that the embodiments and examples described above can be combined in any way as long as these combinations are not mutually exclusive.
In the following, the preferred embodiments of the invention are explained in more detail using the drawings, wherein:
In the following, similar elements are marked with the same reference numbers.
The result in the example of
The important control parameters for the products, i.e. the width of the molds 126 and the slab lengths to be produced by the cutting systems 134 as well as the process of continuous casting, i.e. the movement of the strand, the pouring of the liquid steel into the ladle into the tundish, the movement of the mold 126 etc. are controlled by a continuous casting program which is transmitted to the external system via the interface. Memory 120 of a control computer 114 is included. The control computer 114 also has a processor 118 capable of executing the continuous casting program contained in the memory 120 to control the continuous casting system. The control computer 114 also has an interface 116 through which the control computer can receive control data 112 from a control device 100.
The control data 112 determine the slabs to be produced by the continuous casting system. The control data determine the sequence and distribution of the slabs to the individual strands as well as the geometric dimensions of the slabs in detail.
The control unit 100 has a processor 102, an interface 104 and a memory 106. The interface 104 is used to communicate with the interface 116. The memory 106 contains various casting orders 108 and instructions 110. By executing the instruction 110 by the processor 102, the control device 100 is able to carry out the method for casting orders 108 described in
The implementation of the individual process steps discussed in
The method for controlling the continuous casting system 101 begins in step 200 in
However, the fact that coils are to be produced from the slabs is only to be seen as an example of an application—other processing options for slabs are well known to the skilled person.
For Order 1 the minimum KIM weight is 15 kg/mm and the maximum KIM weight is 20 kg/mm. Based on this, an associated semi-finished product weight of at least 7959 kg and a maximum semi-finished product weight of 10192 kg can be calculated for a rolling width of 520 mm, whereby a yield of 98% is taken into account as an example (e.g. 520×15/0.98). In other words, a slab from which a coil with the said rolling width data and KIM weights is made will have a total weight between 7959 kg minimum and 10192 kg maximum.
Each order therefore specifies a required quantity of material (in the example of
First, for each of the orders, a set of slabs to be cast with the corresponding slab weights and slab widths is determined from the respective required quantities and slab widths. From the minimum and maximum semi-finished product weight (slab weight) determined for each order in
The slabs are then sorted in step 204 to obtain a base sequence. Sorting is carried out according to a sorting criterion, whereby the sorting criterion covers the slab widths. Starting from
Now, in step 206, the sorted base sequence of
After step 206 of partitioning into subsequences, in step 208 each of the subsequences is uniquely assigned to one of the strands, i.e. to one of the molds 126, whereby the assignment is carried out in such a way that the average slab width of the slabs to be cast, determined in the respective subsequence, decreases continuously from the inner strands to the outer strands. As a result, with respect to the continuous casting system of
The result of the assignment of the individual subsequences to the strands or the strand assignment scheme is shown in
Afterwards, in step 210, the slab widths of the slabs to be cast in the subsequences are adjusted for each of the subsequences, taking into account the tolerance specifications. The aim is to keep the width changes between immediately successive slabs to be cast in a subsequence in an interval which corresponds to the permissible specifications for the continuous casting system. In the following, the maximum permissible width difference between two immediately successive slabs is referred to as the “step value”, whereby in the example in
If one now considers sub strand 1 with subsequence T3, there is a width jump between Order 1 and Order 4 in lines 1 and 2 with regard to the slabs in the rolling width from 520 to 470 mm. This clearly exceeds the mentioned 25 mm as step value. The same applies to the jump from Order 4 with a rolling width of 470 mm in line 7 and Order 7 with a rolling width of 430 mm. In order to adjust the slab widths in step 210, the width difference to the width of the following position is checked starting with the first position of the respective sorted subsequences. If the difference is greater than the step value, the width of the current slab or the current position is reduced to such an extent that the resulting difference in width corresponds to the step value. This is repeated cyclically. As a result, there are maximum jumps of 25 mm from the first position to the last position with regard to substrand 1. It should be noted that the exact way in which this adjustment of slab widths is made in order to take into account the maximum step values of the width jumps is possible in many ways. Ultimately, the result is decisive here, namely that the step value is not exceeded in a sequence from one slab to be cast to the next.
Since a special feature of the continuous casting system of
It should also be noted here that it is irrelevant how exactly this mean slab length is calculated. It is possible, for example, that the target length (slab length) for the two slabs is the middle of the tolerance range of the lengths of the two slabs as follows: Target length=Length_min of substrand 1+(Length_max of substrand 2−Length_min of substrand 1)/2.
It should be noted that the minimum and maximum slab lengths can again be calculated using the density of steel, the constant thickness of the slab (e.g. 260 mm) and a certain tolerance deduction of e.g. 2% according to the known formula length=weight/(thickness×width×density).
The determination of the average value with respect to the two minimum and maximum lengths of the slabs and the determination of the length of the two slabs to the average value is carried out in
The method continues in step 218 by adjusting the slab weights to the amount of liquid steel actually available in a converter. If the slab weights resulting from the slab lengths determined in step 216 are summed up in
As an example, this can be realized in step 218, the adjustment of the slab weights, in such a way that a quotient of the resulting total weight and target weight is determined for all slabs of all substrands, whereby the change in the slab weight or slab length of each individual slab involves a multiplication of the slab weight or slab length with this coefficient. The relevant result is shown exemplarily in
After step 218, the casting times are optimized in step 220, whereby the details of step 220 are outlined in steps 222-232. The aim is to increase the strand width while at the same time shortening the strand length in such a way that the weight is maintained and no tolerance violation takes place. The steps for optimizing the casting times are shown in detail in
In
After this calculation in step 222, a further quotient for the slabs of this pair of slabs is calculated in step 224. However, there is no “pre-slab ” here, since the slabs indicated in the first line are the first slabs. In this respect, Q2 does not play a role here. Now the quotient Q3 is calculated in step 226 as the quotient of the width of the next slab plus the step value and the width of the current slab. With regard to substrand 1 this would be 475 mm+25/500 mm =1. After the quotients Q1, Q2 (not available, because there is no pre-slab) and Q3 have been calculated for the first line, the smallest value is now used for substrand 1 and substrand 2 together (since parallel slab) and the quotients calculated in this way are used for the first line (step 230). With this smallest quotient, the width of the current slab in line 1 for substrand 1 and substrand 2 is then multiplied in each case and the length of the current slab divided in each case (step 232).
The same is now done for the next line of substrands 1 and 2, i.e. the next pair of slabs. This time Q2 can be calculated, because e.g. with respect to line 2 of subline 1 the pre-slab has a width of 500 mm and the current slab has a width of 475 mm, so that Q2=500/475.
Ultimately, the steps of determining the different quotients, multiplying the widths and dividing the lengths, i.e. steps 222 to 232, can be performed iteratively, one after the other, for all the slabs of a pair of strands and for all the strands, and, at the end of these steps, this procedure can be repeated several times until either the width of the slabs is no longer changed or a certain number of iterations is reached or exceeded. The result is slabs to be cast which are optimized with regard to casting time by increasing the strand width within the tolerances without any tolerance violations.
The method ends in step 234 in which the control data 112 are transmitted to the continuous casting plant using the interfaces 104 and 116. The control data contain information regarding the sequence in which the slabs are to be produced with the corresponding calculated width and length. The control computer 114 can then control the control system in such a way that the slabs are produced accordingly.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102018202651.3 | Feb 2018 | DE | national |
