EP3088102B2 - Verfahren zum stranggiessen von verschiedenen stahlqualitäten - Google Patents
Verfahren zum stranggiessen von verschiedenen stahlqualitäten Download PDFInfo
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- EP3088102B2 EP3088102B2 EP13900119.2A EP13900119A EP3088102B2 EP 3088102 B2 EP3088102 B2 EP 3088102B2 EP 13900119 A EP13900119 A EP 13900119A EP 3088102 B2 EP3088102 B2 EP 3088102B2
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- 229910000831 Steel Inorganic materials 0.000 title claims description 632
- 239000010959 steel Substances 0.000 title claims description 632
- 238000000034 method Methods 0.000 title claims description 130
- 238000005266 casting Methods 0.000 title claims description 39
- 238000009749 continuous casting Methods 0.000 claims description 55
- 238000005520 cutting process Methods 0.000 claims description 31
- 238000013213 extrapolation Methods 0.000 claims description 26
- 239000007788 liquid Substances 0.000 claims description 22
- 239000007787 solid Substances 0.000 claims description 10
- 239000002436 steel type Substances 0.000 claims description 3
- 238000004364 calculation method Methods 0.000 description 22
- 239000011651 chromium Substances 0.000 description 12
- 230000005499 meniscus Effects 0.000 description 8
- 239000011572 manganese Substances 0.000 description 7
- 229910052799 carbon Inorganic materials 0.000 description 6
- 230000000694 effects Effects 0.000 description 6
- 229910052748 manganese Inorganic materials 0.000 description 6
- 229910052804 chromium Inorganic materials 0.000 description 5
- 238000007711 solidification Methods 0.000 description 5
- 230000008023 solidification Effects 0.000 description 5
- 238000009826 distribution Methods 0.000 description 4
- 238000004519 manufacturing process Methods 0.000 description 4
- 230000007547 defect Effects 0.000 description 3
- 238000005259 measurement Methods 0.000 description 3
- 229910052751 metal Inorganic materials 0.000 description 3
- 239000002184 metal Substances 0.000 description 3
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 description 2
- 230000003111 delayed effect Effects 0.000 description 2
- 238000001514 detection method Methods 0.000 description 2
- 238000009792 diffusion process Methods 0.000 description 2
- 238000007670 refining Methods 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- PWHULOQIROXLJO-UHFFFAOYSA-N Manganese Chemical compound [Mn] PWHULOQIROXLJO-UHFFFAOYSA-N 0.000 description 1
- 230000002159 abnormal effect Effects 0.000 description 1
- 239000000498 cooling water Substances 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 239000003923 scrap metal Substances 0.000 description 1
- 230000035945 sensitivity Effects 0.000 description 1
- 239000007921 spray Substances 0.000 description 1
- 230000009466 transformation Effects 0.000 description 1
Images
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D11/00—Continuous casting of metals, i.e. casting in indefinite lengths
- B22D11/16—Controlling or regulating processes or operations
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B22—CASTING; POWDER METALLURGY
- B22D—CASTING OF METALS; CASTING OF OTHER SUBSTANCES BY THE SAME PROCESSES OR DEVICES
- B22D19/00—Casting in, on, or around objects which form part of the product
- B22D19/16—Casting in, on, or around objects which form part of the product for making compound objects cast of two or more different metals, e.g. for making rolls for rolling mills
Definitions
- the present disclosure relates to a method of continuous casting heterogeneous steels, and more particularly, to a method of continuous casting heterogeneous steels which may predict and automatically cut off a mixed portion of a strand which is produced by mixing previous steel and subsequent steel in a method of continuous casting different steels.
- a continuous casting operation of heterogeneous steels is an operation of continuous casting by using molten steel of new steel (hereinafter, referred to as "subsequent steel") which has components different from those of molten steel of steel currently being processed (hereinafter, referred to as "previous steel").
- subsequent steel molten steel of new steel
- previous steel molten steel of steel contained in a subsequent ladle
- the molten steel of the subsequent steel contained in a subsequent ladle is supplied to a tundish at the end of the operation of the previous steel.
- the molten steel of the previous steel and the molten steel of the subsequent steel are mixed in the tundish, and the mixed molten steel is injected into a mold through a submerged entry nozzle.
- a mixed portion which is produced by mixing heterogeneous steels, is indispensably generated in some portions of a cast strand, and since the mixed portion does not satisfy compositional specifications of products, the mixed portion is cut off and mostly reused as scrap metal.
- the mixed portion has been cut to a predetermined length on the basis of a meniscus position of the strand.
- a cut position of the mixed portion is not accurate.
- the mixed portion may be cut excessively more than the actual mixed portion so that it may be a cause of reducing productivity, or the mixed portion may be cut less than the actual mixed portion so that the product may be sold in a state in which the mixed portion is mixed.
- the mixed portion was datafied according to types and combination of the previous steel and the subsequent steel to make as a table, and the mixed portion was cut to a cut-off length corresponding to the types and combination of the previous steel and the subsequent steel during the operation of heterogeneous steels.
- the mixed portion was excessively cut so that a region satisfying design specifications may be cut with the mixed portion and discarded, or there were still limitations in that all of the mixed portion may not be cut off and some of the mixed portion may be mixed in the product.
- a mixed concentration of the previous steel and the subsequent steel of a strand during casting was calculated by using operation data, such as a change in ladle weight, a change in tundish weight, and casting speed, of the previous performed operation as disclosed in Korean Patent No. 10-0419886 .
- a mixed portion was determined by using the mixed concentration calculated from hydrodynamic principles and was cut off at both ends thereof.
- the mixed concentration and the mixed portion were predicted without consideration of each position in the cross-section of the strand, i.e., surface and center. Thus, since reliability or accuracy of the prediction of the mixed portion is low, there have still been occasions in which at least a portion of the mixed portion is mixed in the product and delivered to client companies.
- the present disclosure provides a method of continuous casting heterogeneous steels which may predict and automatically cut off a mixed portion of a strand which is produced by mixing previous steel and subsequent steel in a method of continuous casting different steels.
- the present disclosure also provides a continuous casting method which may prevent product failure due to the mixed portion, which is caused by the continuous casting of heterogeneous steels, by calculating the position of the mixed portion of the strand to improve the accuracy of the prediction of the position and length of the mixed portion.
- a method of continuous casting heterogeneous steels includes: obtaining dimensionless relative concentrations of subsequent steel to previous steel respectively at surface and inside of a continuous cast strand in real time; calculating positions in a longitudinal direction of the strand having the dimensionless relative concentrations of the surface and the inside obtained in real time; predicting a mixed portion in the strand by respectively comparing the obtained dimensionless relative concentrations of the surface and the inside with reference concentrations; and cutting off the predicted mixed portion.
- the positions of the strand, from which the dimensionless relative concentrations are obtained, are a surface and a center in a height direction of the strand.
- a method of continuous casting heterogeneous steels includes: obtaining dimensionless relative concentrations of subsequent steel to previous steel respectively at a plurality of positions in a height direction of a strand solidified and continuous cast from a mold in real time by using relative amounts of the previous steel and the subsequent steel in a tundish and relative amounts of the previous steel and the subsequent steel in the mold; calculating positions in a longitudinal direction of the strand having the dimensionless relative concentrations obtained in real time; predicting a mixed portion in the strand by respectively comparing the obtained dimensionless relative concentrations with reference concentrations; and cutting off the predicted mixed portion.
- the plurality of positions in the height direction of the strand, from which the dimensionless relative concentrations are obtained, includes a surface and a center of the strand.
- the method may further include setting the reference concentrations, before the obtaining of the dimensionless relative concentrations of the subsequent steel to the previous steel in the continuous cast strand in real time, wherein the setting of the reference concentrations may include: setting a lowermost limit concentration among upper limit concentrations of each component of the previous steel as a first reference concentration; and setting an uppermost limit concentration among lower limit concentrations of each component of the subsequent steel as a second reference concentration.
- the setting of the first reference concentration and the second reference concentration may include: calculating concentrations of the components of the previous steel as lower limit dimensionless concentrations and upper limit dimensionless concentrations; setting a lowermost limit dimensionless concentration among the upper limit dimensionless concentrations of the each component of the previous steel as the first reference concentration; calculating concentrations of the components of the subsequent steel as lower limit dimensionless concentrations and upper limit dimensionless concentrations; and setting an uppermost limit dimensionless concentration among the lower limit dimensionless concentrations of the each component of the subsequent steel as the second reference concentration.
- the strand may be determined to be in a mixed state when at least one dimensionless relative concentration of the obtained dimensionless relative concentrations of the surface and the center is deviated from the reference concentration, and a position in the longitudinal direction of the strand, in which at least one dimensionless relative concentration of the obtained dimensionless relative concentrations of the surface and the center is deviated from the reference concentration, may be determined as the mixed portion.
- a position in the longitudinal direction of the strand, in which the obtained dimensionless relative concentration of the center reaches the reference concentration, may be determined as a starting point of the mixed portion, and a position in the longitudinal direction of the strand, in which the obtained dimensionless relative concentration of the surface reaches the reference concentration, may be determined as an end point of the mixed portion.
- the method further includes: receiving data of a residual amount of molten steel in the tundish, casting speed, and concentrations of each of the previous steel and the subsequent steel on-line and storing the data; and detecting a subsequent ladle opening signal, before the obtaining of the dimensionless relative concentrations of the subsequent steel to the previous steel.
- the method further includes: obtaining dimensionless relative concentrations of each of the surface and the center of the strand in real time from a time of detecting the subsequent ladle opening signal, and counting a dimensionless concentration acquisition time from the time of detecting the subsequent ladle opening signal to be compared with a reference time in real time; comparing the obtained dimensionless relative concentration of the center with the first reference concentration and comparing the obtained dimensionless relative concentration of the surface with the second reference concentration when the dimensionless concentration acquisition time is the reference time or less; and terminating the acquisition of the dimensionless relative concentrations of each of the surface and the center of the strand when the concentration acquisition time is greater than the reference time.
- the method further includes determining whether or not a type between the previous steel and the subsequent steel is a type that is included in a preset heterogeneous steel cut-off table; cutting the strand to a cut-off length of the corresponding heterogeneous steel type when the type between the previous steel and the subsequent steel subjected to a current operation is the type that is included in the preset heterogeneous steel cut-off table; and cutting the strand to a preset predetermined cut-off length when the type between the previous steel and the subsequent steel subjected to the current operation is not included in the preset heterogeneous steel cut-off table, after the terminating of the acquisition of the dimensionless relative concentrations of each of the surface and the center of the strand.
- the detecting of the subsequent ladle opening signal may include: sending a virtual ladle opening signal; detecting a weight of the tundish in real time, in milliseconds (ms) from a time when the virtual ladle opening signal is sent; calculating the weight of the tundish detected in milliseconds (ms) as an average weight of the tundish at predetermined time intervals in seconds (s); and setting a time of opening the subsequent ladle using a time of continuously increasing the average weight of the tundish.
- t-2* ⁇ t may be determined as the time of opening the subsequent ladle when both of W td (t) - W td (t- ⁇ t) and W td (t) - W td (t-2* ⁇ t) are greater than or equal to "0"
- the dimensionless relative concentrations of each of the surface and the center of the strand may be obtained from t-2* ⁇ t, and the residual-steel amount in the tundish and the casting speed may be stored from t-4* ⁇ t.
- the obtaining of the dimensionless relative concentrations of the subsequent steel to the previous steel at the surface and the center of the strand may include: calculating an inlet volumetric flow (Q td-in ) of the subsequent steel in the tundish; calculating an average dimensionless relative concentration (C td-ave (t+ ⁇ t)) of the molten steel in the tundish at a current time using the inlet volumetric flow (Q td-in ) of the subsequent steel in the tundish; calculating a dimensionless relative concentration (C td-out (t+ ⁇ t)) of the molten steel discharged from the tundish at a current time using the average dimensionless relative concentration (C td-ave (t+ ⁇ t)) of the molten steel in the tundish at a current time; calculating an average dimensionless relative concentration (C md-aver (t+ ⁇ t)) of the molten steel in the mold at a current time using the dimensionless relative concentration (C td-out
- C td-ave (t+ ⁇ t) the average concentration (C td-ave (t+ ⁇ t)) of the molten steel in the tundish at a current time
- C td - ave t + ⁇ t W td t ⁇ C t d - ave t + Q t d - in t ⁇ ⁇ t ⁇ ⁇ L ⁇ C t d - in t W td t + ⁇ t ⁇ Q t d - out t ⁇ ⁇ t ⁇ L ⁇ C t d - out t W td t + ⁇ t
- C td-ave (t) is an average dimensionless relative concentration of the molten steel in the tundish at an earlier time
- Q td-in (t) is an inlet volumetric flow of the molten steel introduced into the tundish at an earlier time
- 4 ⁇ 2 may be applied to the interpolation and extrapolation factor (f td ) of Equation 7, and 0.7 ⁇ 0.4 may be applied to the interpolation and extrapolation factor (f md ) of Equation 9 to calculate the dimensionless relative concentration (C md-out-center ) of the center of the strand.
- 2.2 ⁇ 0.6 may be applied to the interpolation and extrapolation factor (f td ) of Equation 7, and 0.5 ⁇ 0.2 may be applied to the interpolation and extrapolation factor (f md ) of Equation 9 to calculate the dimensionless relative concentration (C md-out-surface ) of the surface of the strand.
- a liquid density of the molten steel may be used as a density ( ⁇ L ) value in Equations 5, 6, and 8, and a value of 7,000 kg/m 3 to 7,400 kg/m 3 may be used as the density of the molten steel.
- the method may further include: setting a position of the strand in which the dimensionless relative concentration of the surface of the strand begins to be obtained; and setting a position of the strand in which the dimensionless relative concentration of the center of the strand begins to be obtained, wherein a position of the strand at the time of opening the subsequent ladle may be set as the position in which the dimensionless relative concentration of the surface of the strand begins to be obtained, and a position of -4 ⁇ 4 m from the position of the strand at the time of opening the subsequent ladle may be set as the position in which the dimensionless relative concentration of the center of the strand begins to be obtained.
- a position of -4 ⁇ 4 m from the position having the obtained dimensionless relative concentration of the surface may be set as the position having the dimensionless relative concentration of the center.
- a region from a point of the strand, in which the real-time obtained dimensionless relative concentration of the center of the strand reaches the first reference concentration, to a point of the strand, in which the real-time obtained dimensionless relative concentration of the surface of the strand reaches the second reference concentration, may be predicted as the mixed portion.
- the method may further include: setting the point of the strand, in which the real-time obtained dimensionless relative concentration of the center of the strand reaches the first reference concentration, as a first cut-off position; setting the point of the strand, in which the real-time obtained dimensionless relative concentration of the surface of the strand reaches the second reference concentration, as a second cut-off position; and cutting off the mixed portion by cutting the strand respectively at the first cut-off position and the second cut-off position.
- the predicting of the mixed portion of the strand and the cutting off of the predicted mixed portion may be performed as an online process.
- dimensionless concentrations of each of surface and center of a strand are obtained, and a position and a length of a mixed portion are derived by using the dimensionless concentrations. That is, the mixed portion is not cut to a predetermined length regardless of heterogeneous steel operating conditions as in the related art, but the dimensionless concentrations of each of the surface and the center of the strand are obtained for each operation of heterogeneous steels, and positions of the strand having the obtained dimensionless concentrations are set to predict the position and the length of the mixed portion.
- the accuracy of the prediction of the position and length of the mixed portion is improved, a decrease in profitability due to excessive cut-off of the mixed portion may be prevented and the shipment of defect products due to less cut-off of the mixed portion to client companies may be prevented.
- strand a solidified object, which is solidified in a mold, drawn or discharged to the outside of the mold, and formed by extending in a casting direction, in a state before cut-off
- slab an object, in which the strand is cut to a predetermined length
- FIG. 1 illustrates general continuous casting equipment.
- FIG. 2 illustrate principal parts of the general continuous casting equipment for describing a process of manufacturing a strand or slab through supply and solidification processes of molten steel.
- the continuous casting equipment includes ladles 100: 110 and 120 which accommodate refined molten steel and are movable, a tundish 200 configured to accommodate the molten steel supplied from the ladles 100: 110 and 120, a mold 300 which produces a strand S having a predetermined shape by receiving and solidifying the molten steel from the tundish 200, a nozzle 400 configured to inject the molten steel in the tundish 200 into the mold by having one end thereof connected to the tundish 200 and having at least a portion of the bottom thereof installed to be inserted into the mold 300, a plurality of rollers 500 configured to transport the strand S drawn from the mold 300 in a casting direction, a plurality of segments 600 configured to spray cooling water to the strand S being transported by the plurality of rollers 500, and a cutter 800 which cuts the strand S continuously produced from the mold 300 to a predetermined size to manufacture a slab 700 having a predetermined shape.
- a gas torch or a hydraulic shear configured to accommodate the molten steel supplied from the
- the tundish 200 has an outlet for supplying the molten steel to the mold 300, wherein the outlet may be provided in plurality depending on continuous casting equipment and the mold 300 is provided in a number corresponding to the number of the outlets.
- the strand S solidified and drawn from the mold 300 becomes a plurality.
- molten steels of different steels having different components are accommodated in the first ladle 110 and the second ladle 120, and when any one ladle 110 or 120 completes the supply of the molten metal to the tundish 200, a ladle turret (not shown) rotates 180 degrees so as to shift the position of the one ladle 110 or 120 with respect to that of the other ladle 110 or 120. Accordingly, the molten steels of the different steels may be alternatinlgy supplied to the tundish.
- casting is first performed by supplying the molten steel contained in the first ladle 110 to the tundish 200, and the molten steel of the second ladle 120 is supplied to the tundish 200 at the end of the casting and cast so that the heterogeneous steels are continuously cast.
- the molten steel of the steel currently being cast and being at the end of the operation (hereinafter, referred to as "previous steel") and the molten steel of the steel subsequently introduced (hereinafter, referred to as “subsequent steel”) are mixed in the tundish 200 and the mold 300, a mixed portion, in which the previous steel and the subsequent steel are mixed and solidified, is generated in the strand S.
- the present disclosure provides a method of continuous casting heterogeneous steels which may improve the accuracy of the prediction of the mixed portion and may automatically cut off the mixed portion by obtaining the concentration of the strand S in real time through an online system, calculating a position of the strand S having the obtained concentration, and predicting a position of the mixed portion in real time by using the calculated position.
- FIG. 3 is a flowchart sequentially illustrating a method of predicting a heterogeneous steel mixed portion of the strand according to an exemplary embodiment and a method of cutting the mixed portion by using the above method.
- FIGS. 4 and 5 are flowcharts specifically illustrating a method of cutting the mixed portion in a continuous casting method according to an exemplary embodiment, and FIGS. 4 and 5 include the method of predicting a mixed portion and the method of cutting the mixed portion of FIG. 3 .
- the method of predicting a heterogeneous steel mixed portion of the strand includes the processes of: storing process variables or process data for continuous casting of heterogeneous steels (S100), detecting a signal of opening a ladle (hereinafter referred to as "subsequent ladle") containing subsequent steel (S200), setting a first reference concentration and a second reference concentration for predicting a heterogeneous steel mixed portion of a strand solidified and drawn from a mold (S300), obtaining dimensionless relative concentrations of the subsequent steel to previous steel at surface and inside of the strand in real time and calculating positions in a longitudinal direction of the strand having the dimensionless relative concentrations at the surface and the inside obtained in real time (S400), comparing the obtained dimensionless relative concentration of the inside of the strand with the first reference concentration in real time and comparing the obtained dimensionless relative concentration of the surface of the strand with the second reference concentration in real time (S600), predicting a mixed portion in the
- the surface and the inside of the strand may be surface and inside in a longitudinal direction (i.e., left and right direction) of the strand or in a vertical direction (or height direction) of the strand which crosses the casting direction, the inside may be the center in the vertical direction (or height direction) of the strand, and the surface may be any one of a top surface and a bottom surface of the strand.
- the dimensionless relative concentration of the subsequent steel to the previous steel is a degree or amount in which the subsequent steel is mixed with respect to the previous steel
- the dimensionless relative concentration in other words, may be a degree in which the previous steel and the subsequent steel are mixed, i.e., "mixed concentration”.
- a dimensionless concentration represents a typical concentration value as a dimensionless ratio or dimensionless value, wherein the dimensionless concentration is a concentration represented by a value of 0 or more or 1 or less.
- the dimensionless relative concentration of the subsequent steel to the previous steel may also be represented by a value of 0 or more or 1 or less.
- a dimensionless concentration of the previous steel is defined as 0 and a dimensionless concentration of the subsequent steel is defined as 1.
- the dimensionless relative concentration it denotes a case in which an amount of the subsequent steel in the molten steel or the strand is 0%, i.e., a case in which there is no inflow of the subsequent steel.
- the dimensionless relative concentration in a case in which the dimensionless relative concentration is 1, it denotes a case in which the amount of the subsequent steel in the molten steel or the strand is 100%.
- the dimensionless relative concentration in a case in which the dimensionless relative concentration is 0.4, it denotes that the previous steel and the subsequent steel in the molten steel or the strand are mixed in a ratio of 60% to 40%.
- the first reference concentration and the second reference concentration which are compared with the dimensionless relative concentrations of each of the center and the surface of the strand obtained in real time, are dimensionless concentration values.
- the method of predicting and cutting a heterogeneous mixed portion as described in FIG. 3 may or may not be used depending on acquisition time of the dimensionless relative concentrations of each of the surface and the center of the strand calculated from a time of opening of the subsequent ladle.
- the concentration acquisition time in which the dimensionless relative concentrations of each of the surface and the center of the strand are obtained, is less than a reference time
- a subsequent process is performed in which a mixed portion is predicted by comparing the obtained dimensionless concentrations of each of the center and the surface with the first and second reference concentrations.
- the concentration acquisition elapsed time of the surface and the center of the strand is greater than the reference time
- the process of obtaining the concentration of each of the surface and the center is terminated.
- the mixed portion is cut off according to a data table, in which cut-off lengths of the mixed portion, which are preset according to types of the previous steel and the subsequent steel, are datafied, or the mixed portion is cut to a predetermined length which is preset regardless of the types of the previous steel and the subsequent steel.
- FIGS. 4 and 5 are flowcharts which include a series of processes, in which the mixed portion is cut off by automatically predicting the position of the mixed portion according to the above-described dimensionless relative concentration acquisition time of each of the surface and the center of the strand, or the mixed portion is cut off by using the mixed portion cut-off length data table which is preset according to the combination of heterogeneous steels, or the mixed portion is cut to a predetermined length.
- the method of continuous casting heterogeneous steels includes the processes of: storing process data according to continuous casting of heterogeneous steels (S100), detecting a subsequent ladle opening signal (S200), setting a first reference concentration and a second reference concentration for predicting a heterogeneous steel mixed portion of a strand solidified and drawn from a mold (S300), obtaining dimensionless relative concentrations of each of surface and center of the strand in real time to calculate positions of the strand having the dimensionless relative concentrations of each of the surface and the center obtained at a current time (S400), and comparing dimensionless relative concentration acquisition time of the surface and the center of the strand with a reference time (S500).
- the setting of the first reference concentration and the second reference concentration for predicting the heterogeneous steel mixed portion of the strand solidified and drawn from the mold (S300) is performed.
- the exemplary embodiment of the present disclosure is not limited thereto, and a sequence of the detecting of the subsequent ladle opening signal (S200) and the setting of the first reference concentration and the second reference concentration for predicting the heterogeneous steel mixed portion of the strand solidified and drawn from the mold (S300) may be changed.
- the method of continuous casting heterogeneous steels includes the processes of: comparing the obtained dimensionless relative concentration of the center of the strand with the first reference concentration in real time and comparing the obtained dimensionless relative concentration of the surface of the strand with the second reference concentration in real time (S600), predicting and determining a position of the mixed portion of the strand according to a comparison result between the obtained dimensionless relative concentrations of the surface and the center and the first and second reference concentrations (S700), and cutting off the predicted mixed portion (S1100).
- the method includes the processes of: terminating the acquisition of the dimensionless relative concentration of each of the surface and the center of the strand (S800), determining whether or not types of heterogeneous steels subjected to a current operation, i.e., the previous steel and the subsequent steel, are types that are included in a preset mixed portion cut-off length table (S900), cutting the mixed portion to a corresponding length by searching a type corresponding to a combination of the previous steel and the subsequent steel subjected to the operation when the combination of the previous steel and the subsequent steel subjected to the current operation is a type that is included in the preset cut-off length table (YES) (S1200), and cutting the mixed portion to a predetermined length, e.g., a maximum length when the combination of the previous steel and the subsequent steel subjected to the current operation is a type that is not included in the preset cut
- a predetermined length e.g., a maximum length when the combination of the previous steel and the subsequent steel subjected to the
- FIG. 6 is a flowchart specifically illustrating a process of detecting a subsequent ladle opening signal according to an exemplary embodiment.
- FIG. 7 is a flowchart illustrating a method of setting the first reference concentration and the second reference concentration for the prediction of the heterogeneous steel mixed portion of the strand as a method according to an exemplary embodiment.
- FIG. 8 is a graph illustrating a dimensionless concentration for each component of previous steel and subsequent steel which is obtained by the method according to the exemplary embodiment.
- FIG. 9 is a graph illustrating a dimensionless concentration distribution of chromium (Cr) in the vertical direction (section thickness) and the casting direction (longitudinal direction) of the strand manufactured by heterogeneous steel continuous casting.
- Cr chromium
- FIG. 10 is images illustrating changes in concentration in the mold over time during a heterogeneous steel continuous casting operation.
- FIG. 11 is the result of calculating a concentration distribution with respect to the longitudinal direction and cross-section of the strand after the completion of final solidification by only considering an effect of the mold without considering an effect of the tundish during the heterogeneous steel continuous casting operation.
- FIG. 12 is a flowchart illustrating a method of obtaining dimensionless concentrations of the surface and the center of the strand according to an exemplary embodiment.
- FIG. 13 is a graph comparing dimensionless concentration data of the surface and the center of the strand obtained according to the exemplary embodiment with results of the measurement of actual components in the longitudinal direction of the cast strand.
- FIG. 14 is a graph comparing data in which the mixed portion is predicted by the prediction method according to the exemplary embodiment and concentrations are measured by collecting the predicted mixed portion.
- heterogeneous steel continuous casting process data (S100) information, such as casting conditions and components of the heterogeneous steels, as variable data for the prediction of the mixed portion of the strand in the heterogeneous steel operation, is stored. That is, a residual amount of the molten steel in the tundish, casting speed, concentrations of components of the molten steel subjected to the current operation (hereinafter, referred to as "previous steel"), and concentrations of components of the molten steel subsequently supplied to the tundish (hereinafter, referred to as "subsequent steel”) are stored. These process data may be initialized for each operation of the heterogeneous steels to be newly set and stored. Also, in the case that the plurality of strands is drawn from the continuous casting equipment, a casting speed for each strand is stored.
- the dimensionless relative concentration of the strand is obtained from the time of opening the subsequent ladle.
- the detecting of the subsequent ladle opening signal (S200) includes the processes of: sending a virtual subsequent ladle opening signal (S210), detecting a weight of the tundish in real time, in milliseconds (ms) from a time when the virtual subsequent ladle opening signal is sent (S220), calculating the weight of the tundish detected in milliseconds (ms) as an average weight of the tundish in second (s) intervals (S230), determining whether or not the average weight of the tundish calculated over time is continuously increased by receiving data of the average weight of the tundish in real time (S240), and setting a time of continuously increasing the average weight of the tundish as a time of opening the subsequent ladle (S250).
- the signal was received and detected as the subsequent ladle opening signal.
- the subsequent ladle opening signal was detected by only sensing an operation of the slide gate even if the molten steel was not discharged from the ladle, its accuracy may be low.
- the weight of the tundish was measured according to the time using a sensor for detecting the weight of the tundish, wherein the weight of the tundish was measured at very short time intervals in milliseconds (ms).
- a sensor for detecting the weight of the tundish wherein the weight of the tundish was measured at very short time intervals in milliseconds (ms).
- ms milliseconds
- a programmable logic system sends a signal that the subsequent ladle is opened.
- the PLC sends a virtual subsequent ladle opening signal according to operating conditions of heterogeneous steels, for example, when the casting speed and the residual amount of the molten steel are reduced and the casting speed and the residual-steel amount in the tundish are predetermined values or less (S210). Thereafter, the weight of the tundish is measured in milliseconds (ms), e.g., 200 ms, from a time when the virtual subsequent ladle opening signal is sent (S220).
- ms milliseconds
- the weight of the tundish measured in milliseconds is calculated as an average weight of the tundish in seconds (s), for example, at predetermined time intervals of 1 second or 2 second (S230), and the calculated average weight of the tundish is analyzed in real time to determine whether or not the weight of the tundish is continuously increased (S240).
- a dimensionless relative concentration of each of the surface and the center of the strand is calculated from t-2* ⁇ t, and, for this purpose, the residual-steel amount in the tundish and the casting speed are stored from t-4* ⁇ t so as to enable the prediction of the mixed portion in real time.
- the first reference concentration and the second reference concentration which are compared with the dimensionless relative concentration of the center and the dimensionless relative concentration of the surface of the strand for the prediction of the mixed portion of heterogeneous steels, are dimensionless concentration values.
- a method of calculating the first and second reference concentrations according to an exemplary embodiment will be described with reference to FIG. 7 .
- a method of setting the first reference concentration and the second reference concentration for the prediction of the heterogeneous steel mixed portion of the strand includes the processes of: receiving concentration data of all components of each of the previous steel and the subsequent steel (S310a and S310b), calculating a lower limit dimensionless concentration and an upper limit dimensionless concentration of each component of the previous steel (S320a), calculating a lower limit dimensionless concentration and an upper limit dimensionless concentration of each component of the subsequent steel (S320b), setting a lowermost limit dimensionless concentration value among upper limit dimensionless concentration values of each component of the previous steel as the first reference concentration (S330a), and setting an uppermost limit dimensionless concentration value among lower limit dimensionless concentration values of each component of the subsequent steel as the second reference concentration (S330b).
- Equation 1 the lower limit dimensionless concentration of each component of the previous steel is calculated by Equation 1, and the upper limit dimensionless concentration of each component of the previous steel is calculated by Equation 2. Also, the lower limit dimensionless concentration of each component of the subsequent steel is calculated by Equation 3, and the upper limit dimensionless concentration of each component of the subsequent steel is calculated by Equation 4.
- Equations 1 to 4 during the calculation of the dimensionless concentration for each component concentration, in a case in which the lower limit dimensionless concentration of the previous steel is greater than the upper limit dimensionless concentration of the previous steel, the lower limit dimensionless concentration value of the previous steel is substituted with the upper limit dimensionless concentration value of the previous steel and the upper limit dimensionless concentration value of the previous steel is substituted with the lower limit dimensionless concentration value of the previous steel.
- the lower limit dimensionless concentration value of the subsequent steel is substituted with the upper limit dimensionless concentration value of the subsequent steel and the upper limit dimensionless concentration value of the subsequent steel is substituted with the lower limit dimensionless concentration value of the subsequent steel in the same manner. This is applied when the component concentration of the previous steel is higher than the component concentration of the subsequent steel.
- a C dimensionless concentration of the previous steel becomes 0 (0.1 to -0.1) when dimensionless transformation is performed. That is, since the upper limit dimensionless concentration of the previous steel becomes -0.1 and the lower limit dimensionless concentration of the previous steel becomes 0.1, these values are substituted with each other.
- the concentration of each component of the previous steel denotes a concentration of each component of molten steel first cast in a current heterogeneous steel operation and is a concentration determined through a refining process before the molten steel is supplied to the tundish, wherein it is a concentration value included in the design specification concentration range of the previous steel.
- the concentration of each component of the subsequent steel denotes a concentration of each component of molten steel subsequently supplied and is also a concentration determined through the refining process before the molten steel is supplied to the tundish, wherein it is a concentration value included in the design specification concentration range of the subsequent steel.
- the lower limit and upper limit dimensionless concentrations of the previous steel and the lower limit and upper limit dimensionless concentrations of the subsequent steel are calculated by using the design specification lower limit concentration of the previous steel, the design specification upper limit concentration of the previous steel, the design specification lower limit concentration of the subsequent steel, the design specification upper limit concentration of the subsequent steel, the concentration of the previous steel, and the concentration of the subsequent steel as described above.
- the lowermost limit dimensionless concentration value among the upper limit dimensionless concentration values of each component of the previous steel is set as the first reference concentration
- the uppermost limit dimensionless concentration value among the lower limit dimensionless concentration values of each component of the subsequent steel is set as the second reference concentration.
- the first reference concentration is a value compared with the dimensionless relative concentration of the center of the strand calculated in real time
- the second reference concentration is a value compared with the dimensionless relative concentration of the surface of the strand calculated in real time.
- FIG. 8 is a graph illustrating the dimensionless concentration for each component of the previous steel and the subsequent steel which is calculated by the method according to the exemplary embodiment.
- C, manganese (Mn), and Cr are included in each of the previous steel and the subsequent steel, and when lower limit dimensionless concentrations and upper limit dimensionless concentrations of C, Mn, and Cr components are calculated by the above-described Equations 1 to 4, the results are as illustrated in FIG. 8 .
- the upper limit dimensionless concentration of Cr is lower than the upper limit dimensionless concentration of C or Mn.
- the upper limit dimensionless concentration of Cr is set as the first reference concentration.
- the lower limit dimensionless concentration of Cr is higher than the lower limit dimensionless concentration of C or Mn.
- the lower limit dimensionless concentration of Cr is set as the second reference concentration. Therefore, according to the example of FIG. 8 , the first reference concentration, as a lowermost limit value of the dimensionless concentration for the prediction of the mixed portion, is 0.07, and the second reference concentration, as an uppermost limit value, is 0.95.
- the dimensionless concentration of the mixed portion is in a range of 0.07 or more to 0.95 or less, and a region from a point where the dimensionless relative concentration of the center of the strand calculated in real time is 0.07 to a point where the dimensionless relative concentration of the surface is 0.95 is predicted as the mixed portion.
- the reason for the comparison of the lowermost limit dimensionless concentration value among the uppermost limit dimensionless concentration values of each component of the previous steel, which is set as the first reference concentration, with the dimensionless relative concentration of the center calculated in real time and the comparison of the uppermost limit dimensionless concentration value among the lowermost limit dimensionless concentration values of each component of the subsequent steel, which is set as the second reference concentration, with the dimensionless relative concentration of the surface calculated in real time is as follows.
- a concentration of one end of the mixed portion of the strand solidified by mixing the previous steel and the subsequent steel satisfies the design specification concentration of the previous steel, and the other end of the mixed portion satisfies the design specification concentration of the subsequent steel.
- a region between the one end and the other end of the mixed portion is outside the design specification concentration range of each of the previous steel and the subsequent steel.
- the concentration is changed along a vertical direction (cross-section thickness direction) and a casting direction (longitudinal direction) of the slab.
- the dimensionless relative concentrations of positions in the vertical direction of the strand i.e., the surface and the center, have a different trend pattern.
- mixing between the previous steel and the subsequent steel occurs in the surface of the strand after the time of opening the subsequent ladle.
- the mixing occurs in the strand before the time of opening the subsequent ladle.
- diffusion of the molten steel mixed and remixed through the tundish and the mold to the center of an unsolidified molten steel layer in the strand occurs due to a concentration gradient. That is, the mixing between the previous steel and the subsequent steel is started in the center of the strand earlier than the surface of the strand.
- the dimensionless relative concentration of the center of the strand obtained in real time reaches the lowermost limit dimensionless concentration value (i.e., the first reference concentration) among the upper limit dimensionless concentration values of each component of the previous steel or is deviated from the lowermost limit dimensionless concentration value (i.e., the first reference concentration)
- the lowermost limit dimensionless concentration value i.e., the first reference concentration
- the dimensionless relative concentration of the surface of the strand calculated in real time reaches the uppermost limit dimensionless concentration value (i.e., the second reference concentration) among the lower limit dimensionless concentration values of each component of the subsequent steel or is deviated from the uppermost limit dimensionless concentration value (i.e., the second reference concentration), it is determined as a state in which the mixing is terminated, and in this case, a position of the strand is determined as a second cut-off position.
- the uppermost limit dimensionless concentration value i.e., the second reference concentration
- the position in the longitudinal direction of the strand, in which the dimensionless relative concentration of the center is the lowermost limit dimensionless concentration among the upper limit dimensionless concentration values of each component of the previous steel, is a starting position of the mixed portion
- the position in the longitudinal direction of the strand, in which the dimensionless relative concentration of the surface is the uppermost limit dimensionless concentration among the lower limit dimensionless concentration values of each component of the subsequent steel is an end position of the mixed portion.
- the lowermost limit dimensionless concentration among the upper limit dimensionless concentration values of each component of the previous steel is named as the first reference concentration and the first reference concentration is compared with the obtained dimensionless relative concentration of the center.
- the uppermost limit dimensionless concentration among the lower limit dimensionless concentration values of each component of the subsequent steel is named as the second reference concentration, and the second reference concentration is compared with the obtained dimensionless relative concentration of the surface to predict as the mixed portion in which heterogeneous steels are mixed. That is, the position in the longitudinal direction of the strand, in which the dimensionless relative concentration of the center obtained in real time reaches the first reference concentration, is determined as the first cut-off position, and the position in the longitudinal direction of the strand, in which the dimensionless relative concentration of the surface reaches the second reference concentration, is determined as the second cut-off position to cut off the mixed portion.
- the mixed portion was predicted without separate consideration of each cross-sectional position, i.e., surface and center, of the strand. That is, typically, a concentration of the strand was obtained under the assumption that concentrations of the surface and the center are the same at one position in the longitudinal direction of the strand. Accordingly, since accuracy of the position of the mixed portion or the prediction of the mixed portion was low, occasions frequently occurred in which the mixed portion was mixed in the product and delivered to client companies.
- the concentrations of the surface and the center are different at one position in the longitudinal direction of the strand as described above, and the dimensionless relative concentrations of each of the surface and the center of the strand are respectively obtained during the continuous casting of heterogeneous steels to predict the mixed portion.
- the subsequent steel when the subsequent steel is supplied to a tundish, the previous steel and the subsequent steel are mixed in the tundish, and, in this case, a portion of the mixed steel is discharged during a process of mixing the previous steel and the subsequent steel and the remainder is continuously remixed while being continuously recycled in the tundish.
- the molten steel mixed and remixed in the tundish is discharged into a mold through a submerged entry nozzle, wherein the molten steel discharged through the submerged entry nozzle has a turbulent flow.
- the mixed molten steel introduced into the mold from the tundish produces a recirculation flow in an upper region due to the turbulent flow of the molten steel in the mold, and accordingly, mixing and remixing phenomena repeatedly occur also in the mold and a concentration in the mold is changed in real time (see FIG. 10 ).
- a mixed portion in which the previous steel and the subsequent steel are mixed, is present in the strand which is solidified and drawn from the mold, and in a case in which a thickness of the slab is 0.4 m when considering only the mold mixing without consideration of the mixing in the tundish, a length of the mixed portion is approximately 4 m.
- the mixed portion was predicted by only considering the mixing in the tundish without consideration of the mixing in the mold, the accuracy of the position of the mixed portion or the prediction of the mixed portion was low, and thus, occasions frequently occurred in which at least a portion of the mixed portion was mixed in the product and delivered to client companies.
- the mixed portion is predicted and cut off by considering the mixing of the heterogeneous steels in the mold as well as the tundish, the accuracy of the cut-off of the mixed portion may be improved.
- the calculating of the dimensionless relative concentrations of each of the surface and center in the strand and calculating the positions in the longitudinal direction of the strand having the corresponding dimensionless relative concentrations includes the processes of: obtaining the dimensionless relative concentrations of each of the surface and center of the strand in real time from a time of detecting the subsequent ladle opening signal (S410) and calculating the positions of the strand having the calculated concentrations of the surface and the center (S420).
- Equation 9 For the calculating of the concentrations of the surface and center of the strand in real time from the time of detecting the subsequent ladle opening signal (S410), the calculation is performed in consideration of the mixing in the mold as described in the present disclosure, and thus, an equation (hereinafter, referring to "Equation 9") for calculating the concentrations of the surface and the center of the strand includes a concentration of the steel discharged from the mold.
- equation 9 "t+ ⁇ t" denotes a current time and "t" denotes an earlier time.
- the obtaining of the concentrations of the surface and the center of the strand is performed by calculating the concentrations according to the following equations.
- the obtaining of the concentrations of the surface and the center of the strand may be expressed, in other words, by "the calculating of the concentrations of the surface and the center of the strand”.
- a change in the amount of the molten steel introduced into the tundish may be expressed by a value in which a change in the weight of the tundish is divided by a change in time ( ⁇ t) and liquid density of the molten steel.
- an inlet volumetric flow (Q td-in ) of the subsequent steel in the tundish is first calculated by using the above-described physical concept of the change in the amount of the molten steel introduced into the tundish (S411).
- the inlet volumetric flow (Q td-in ) of the subsequent steel in the tundish may be calculated by Equation 5 described below.
- Q t d - in W td t + ⁇ t ⁇ W td t ⁇ t ⁇ L + Q t d - out
- W td (t) is a total weight of the molten steel in the tundish at an earlier time
- W td (t+ ⁇ t) is a total weight of the molten steel in the tundish at a current time
- Q td-out is a volumetric flow of the molten steel discharged from the tundish
- ⁇ L is liquid density of the molten steel.
- the total weight (W td (t)) of the molten steel in the tundish at an earlier time and the total weight (W td (t+ ⁇ t)) of the molten steel in the tundish at a current time are measured in real time from a sensor disposed on an outer bottom of the tundish, and the volumetric flow (Q td-out ) of the molten steel discharged from the tundish is calculated as a sum of a product of a cross-sectional size of the mold and casting speed measured from a sensor disposed on one side of the strand.
- a liquid density of the molten steel of 7,000 kg/m 3 to 7,400 kg/m 3 is used instead of a solid density of the molten steel of 7,600 kg/m 3 to 8,000 kg/m 3 .
- a liquid density of the molten steel of approximately 7,200 kg/m 3 is used instead of a solid density of the molten steel of approximately 7,800 kg/m 3 .
- an average dimensionless relative concentration (C td-ave (t+ ⁇ t)) of the molten steel in the tundish is calculated using the calculated inlet volumetric flow (Q td-in ) of the subsequent steel in the tundish (S412).
- a flow of the molten steel generated in the tundish may be classified into a primary flow and a secondary flow including a dead zone, and accordingly, the concentration of the molten steel may be locally different depending on the position of the molten steel in the tundish.
- the average dimensionless relative concentration of the molten steel in the tundish is represented by a specific value without consideration of the local flow, and the specific value is defined as the average dimensionless relative concentration of the molten steel in the tundish.
- the average dimensionless relative concentration (C td-ave (t+ ⁇ t)) of the molten steel in the tundish may be calculated by Equation 6 below.
- C td d - ave t + ⁇ t W td t ⁇ C t d - ave t + Q t d - in t ⁇ ⁇ t ⁇ ⁇ L ⁇ C t d - in t W td t + ⁇ t ⁇ Q t d - out t ⁇ ⁇ t ⁇ ⁇ L ⁇ C t d - out t W td t + ⁇ t
- C td-ave (t+ ⁇ t) is an average dimensionless relative concentration of the molten steel in the tundish at a current time
- W td (t) is a total weight of the molten steel in the tundish at an earlier time
- C td-ave (t) is an average dimensionless relative concentration of the molten steel in the tundish at an earlier time
- Q td-in (t) is an inlet volumetric flow of the molten
- the concentration (C td-in (t)) of the subsequent steel introduced into the tundish at an earlier time is always "1". Also, an initial value of the average dimensionless relative concentration (C td-ave (t)) of the molten steel in the tundish at an earlier time and an initial value of the dimensionless relative concentration (C td-out (t)) of the molten steel discharged from the tundish are set as 0.
- the average dimensionless relative concentration (C td-ave (t+ ⁇ t)) of the molten steel in the tundish at a current time is calculated by using the initial values set as described above.
- Equation 6 a value calculated by Equation 6 is used as the average dimensionless relative concentration (C td-ave (t+ ⁇ t)) of the molten steel in the tundish at a current time, and a value, which is calculated at a current time by Equation 7 to be described later, is used as a dimensionless relative concentration (C td-out (t+ ⁇ t)) of the molten steel discharged from the tundish at a current time.
- the dimensionless relative concentration (C td-out (t+ ⁇ t)) of the molten steel discharged from the tundish at a current time is calculated using the average dimensionless relative concentration (C td-ave (t+ ⁇ t)) (S413).
- the dimensionless relative concentration ((C td-out (t+ ⁇ t)) of the molten steel discharged from the tundish is calculated by the following Equation 7.
- C td d - out t + ⁇ t f td ⁇ C t d - ave t + ⁇ t + 1 ⁇ f td ⁇ C t d - in t + ⁇ t
- C td-out (t+ ⁇ t) is a dimensionless relative concentration of the molten steel discharged from the tundish at a current time
- C td-ave (t+ ⁇ t) is an average dimensionless relative concentration of the molten steel in the tundish at a current time
- C td-in (t+ ⁇ t) is a dimensionless relative concentration of the molten steel introduced into the tundish at a current time.
- the average dimensionless relative concentration (C td-ave (t+ ⁇ t)) of the molten steel in the tundish at a current time is calculated by Equation 6 and used as described above, and the dimensionless relative concentration (C td-in ) of the subsequent steel introduced into the tundish at a current time is 1.
- f td is an interpolation and extrapolation factor, wherein different interpolation and extrapolation factors are respectively used for the calculation of the dimensionless relative concentration of the center of the strand and the dimensionless relative concentration of the surface of the strand.
- an interpolation and extrapolation factor (f td_center ) used for the calculation of the concentration of the center of the strand is 4 ⁇ 2
- an interpolation and extrapolation factor (f td_surface ) used for the calculation of the concentration of the surface of the strand is 2.2 ⁇ 0.6.
- an average dimensionless relative concentration (C md-aver (t+ ⁇ t)) of the molten steel in the mold at a current time is calculated using the dimensionless relative concentration ((C td-out (t+ ⁇ t)) of the molten steel discharged from the tundish at a current time (S414), and is calculated by Equation 8 in the present disclosure.
- the internal cross-sectional area of the mold is the same as the cross-sectional area of the strand.
- a flow of the strand (or steel) discharged from the mold may be calculated as a total sum of a product of the internal cross-sectional area of the mold and the casting speed measured from the sensor disposed on one side of the strand.
- the dimensionless relative concentration (C md-in (t)) of the subsequent steel introduced into the mold at an earlier time is always the same as the dimensionless relative concentration (C td-out (t)) of the subsequent steel discharged from the tundish at an earlier time.
- an initial value of the average dimensionless relative concentration (C md-aver (t)) of the molten steel in the mold at an earlier time and an initial value of the dimensionless relative concentration (C md-out (t)) of the molten steel discharged from the mold are set as 0.
- the average dimensionless relative concentration (C md-aver (t)) of the molten steel in the mold at a current time is calculated using the set initial values.
- Equation 8 a value calculated by Equation 8 is used as the average dimensionless relative concentration (C md-aver (t+ ⁇ t)) of the molten steel in the mold at a current time, and a value, which is calculated at a current time by Equation 9 to be described later, is used as a dimensionless relative concentration (C md-out (t+ ⁇ t)) of the molten steel discharged from the mold at a current time.
- a dimensionless relative concentration (C md-out (t+ ⁇ t)) of the steel (i.e., strand) discharged from the mold at a current time is calculated (S415).
- the dimensionless relative concentration (C md-out (t+ ⁇ t)) of the steel (i.e., strand) discharged from the mold at a current time is calculated by the following Equation 9.
- C md-out (t+ ⁇ t) is a dimensionless relative concentration of the steel (i.e., strand) discharged from the mold at a current time
- C md-aver (t+ ⁇ t) is an average dimensionless relative concentration of the molten steel in the mold at a current time
- C md-in (t+ ⁇ t) is a dimensionless relative concentration of the molten steel introduced into the mold at a current time.
- the dimensionless relative concentration (C md-out (t+ ⁇ t)) of the steel discharged from the mold at a current time is a dimensionless relative concentration of the strand solidified and discharged or drawn from the mold at a current time and is a value to be calculated by Equation 9.
- a value calculated by the above-described Equation 8 is used as the average dimensionless relative concentration (C md-aver (t+ ⁇ t)) of the molten steel in the mold at a current time
- f md is an interpolation and extrapolation factor, wherein different interpolation and extrapolation factors are respectively used for the calculation of the dimensionless relative concentration of the center of the strand and the dimensionless relative concentration of the surface of the strand.
- an interpolation and extrapolation factor (f md_center ) used for the calculation of the dimensionless relative concentration of the center is 0.7 ⁇ 0.4
- an interpolation and extrapolation factor (f md_surface ) used for the calculation of the dimensionless relative concentration of the surface of the strand is 0.5 ⁇ 0.2.
- the dimensionless relative concentration (C md-in (t+ ⁇ t)) of the molten steel introduced into the mold at a current time is the dimensionless relative concentration (C td-out (t+ ⁇ t)) of the steel discharged from the tundish at a current time, wherein a value calculated by the above-described Equation 7 is used. Since the molten steel discharged from the mold is mainly composed of liquid molten steel, a liquid density value of the molten steel of 7,000 kg/m 3 to 7,400 kg/m 3 , for example, approximately 7,200 kg/m 3 is used.
- the dimensionless relative concentrations of each of the surface and the center of the strand are obtained in real time during the heterogeneous steel operation by the above-described method, and the positions in the longitudinal direction (or casting direction) of the strand having the dimensionless relative concentrations of each of the surface and the center obtained in real time are then calculated (S420).
- a process of setting a position in which the dimensionless relative concentration of the surface of the strand begins to be obtained and a position in which the dimensionless relative concentration of the center of the strand begins to be obtained is first performed.
- the reason for this is that, during the continuous casting of heterogeneous steels, the mixed portion between the previous steel and the subsequent steel is present on the surface of the strand after the time of opening the subsequent ladle, but mixing occurs in the center of the strand before the time of opening the subsequent ladle.
- the reason is that the diffusion of the molten steel mixed and remixed through the tundish and the mold to the center of the unsolidified molten steel layer in the strand occurs due to the concentration gradient. Accordingly, the mixing between the previous steel and the subsequent steel occurs in the center of the strand earlier than the surface of the strand, and, in general, the mixing in the center generally occurs at a position of -4 ⁇ 4 m from a position of the strand at the time of detecting the subsequent ladle opening signal.
- the position of the strand at the time of detecting the subsequent ladle opening signal is set as the position in which the dimensionless relative concentration of the surface of the strand begins to be measured.
- the position of -4 ⁇ 4 m from the position of the strand at the time of detecting the subsequent ladle opening signal is set as the position in which the dimensionless relative concentration of the center of the strand begins to be obtained.
- the position of the strand having the calculated dimensionless relative concentration of the center of the strand at a current time and the position of the strand having the calculated dimensionless relative concentration of the surface of the strand at a current time are calculated (S420).
- the position of the strand having the calculated dimensionless relative concentration of the surface may be obtained from a length value which is calculated by dividing a product of a mold discharge volumetric flow (Q md-out ) in the strand and liquid density of the molten steel by a product of a cross-sectional area (A md ) of the strand and solid density ( ⁇ s ) of the molten steel.
- Q md-out a mold discharge volumetric flow
- a md cross-sectional area
- ⁇ s solid density
- the reason for using the solid density (7,600 kg/m 3 to 8,000 kg/m 3 ) of the molten steel as a density value is that a shrinkage in the longitudinal direction due to the solidification of the liquid molten steel is considered.
- the value calculated by Equation 10 is a length value, and a position of a point, which moves as much as the calculated length value based on a position of the meniscus of the strand, is the position of the strand having the corresponding concentration of the surface.
- the position of the strand having the calculated concentration of the center is a position of -4 ⁇ 4 m from the position of the strand having the concentration of the surface obtained at the same time.
- the dimensionless relative concentration of the surface and the dimensionless relative concentration of the center of the strand are obtained by the above-described method, and the positions in the longitudinal direction of the strand having the obtained dimensionless relative concentrations of each of the surface and the center are calculated.
- calculation time is counted from a time of calculating the dimensionless relative concentration of each of the surface and the center of the strand, and the calculation time is compared with the reference time in real time (S500).
- the strand drawn from the mold is transferred in the casting direction, i.e., a direction in which the cutter is disposed, as the casting time has elapsed. Accordingly, the mixed portion generated in the strand is gradually close to the cutter as the operation time has elapsed, and the prediction of the mixed portion must be ended before the mixed portion is disposed under the cutter. In other words, before the actual mixed portion is disposed under the cutter, the calculated dimensionless relative concentration of the center must reach the first reference concentration and the calculated dimensionless relative concentration of the surface must reach the second reference concentration.
- a reference drawn time is set in consideration of the casting speed of heterogeneous steels, wherein the reference time is counted from the beginning of the calculation of the dimensionless relative concentration of each of the surface and the center, and is a time in which the mixed portion does not pass the cutter and reaches a predetermined position in front of the cutter.
- the predetermined position may be changed according to a position of the cutter and operating equipment or operating conditions, and the time required to reach the above-described predetermined position at a casting speed during a typical heterogeneous steel operation may be estimated.
- the reference time may be obtained by using the casting speed and is changed according to the operating equipment or operating conditions as described above.
- An acquisition time is counted in real time while obtaining the dimensionless relative concentration of each of the surface and the center of the strand, and is compared with the reference time in real time (S500), wherein, if the acquisition time is within the reference time (YES), the obtained dimensionless relative concentration of the center is compared with the first reference concentration and the obtained dimensionless relative concentration of the surface is compared with the second reference concentration (S600).
- the position in the longitudinal direction of the strand, in which the dimensionless relative concentration of the center reaches the first reference concentration, is set as a starting point
- the position in the longitudinal direction of the strand, in which the dimensionless relative concentration of the surface reaches the second reference concentration is set as an end point so that a position from the starting point to the end point of the mixed portion is predicted as a position of the mixed portion (S700).
- the cutter cuts off the predicted mixed portion from the strand by cutting the strand at the first cut-off position and the second cut-off position (S1100).
- the obtaining of the dimensionless relative concentrations of each of the surface and the center of the strand (S410) and the calculating of the positions of the corresponding dimensionless relative concentrations (S420) are repeated. Also, for example, in a case in which the dimensionless relative concentration of the center reaches the first reference concentration, but the dimensionless relative concentration of the surface does not reach the second reference concentration, the acquisition of the dimensionless relative concentration of the center is repeated or terminated and the process of the obtaining of the dimensionless relative concentration of the surface and the calculation of the position is again performed.
- the acquisition of the dimensionless relative concentration of the surface is repeated or terminated and the process of the obtaining of the dimensionless relative concentration of the center and the calculation of the position is again performed.
- an acquisition time is counted in real time while obtaining the dimensionless relative concentration of each of the surface and the center of the strand, and is compared with the reference time in real time (S500), wherein, if the acquisition time exceeds the reference time (NO), the acquisition of the dimensionless relative concentration of each of the surface and the center of the strand is terminated (S800).
- it is determined whether or not a combination of the previous steel and the subsequent steel subjected to a current operation is a type that is included in the preset mixed portion cut-off length table (S900).
- the strand is cut to the cut-off length listed in the mixed portion cut-off length table (S1200).
- the strand may be cut to a corresponding cut-off length based on the position of the meniscus of the strand.
- the strand is cut to a maximum cut-off length based on the position of the meniscus of the strand (S1300).
- the position or the cut-off position of the mixed portion calculated by the method of the exemplary embodiment and the position or the cut-off position of the mixed portion detected by direct measurement of the components of the strand coincide with each other. Also, as illustrated in FIG. 14 , when the dimensionless relative concentration of the center reaches the first reference concentration and the dimensionless relative concentration of the surface reaches the second reference concentration, the acquisition of the dimensionless relative concentrations of the surface and the calculation of the position is automatically terminated.
- the method of predicting the mixed portion by obtaining the dimensionless concentrations of the surface and the center in the height direction of the strand has been described. However, the positions of the acquisition of the dimensionless concentrations are not limited to the center and the surface, and the mixed portion may be predicted by obtaining dimensionless concentrations at a plurality of positions in the height direction of the strand or positions having different heights of the strand.
- the casting speed is decreased at an end of operation of the previous steel, and when the residual amount of the previous steel in the tundish is a predetermined amount or less, the programmable logic system (PLC) sends a virtual subsequent ladle opening signal (S200). Thereafter, a weight of the tundish is measured in real time, in milliseconds (ms), for example, 200 ms, from a time when the virtual subsequent ladle opening signal is sent (S220).
- ms milliseconds
- the weight of the tundish detected in milliseconds is calculated as an average weight of the tundish in seconds (s), for example, at predetermined time intervals of 1 second or 2 second (S230), and the calculated average weight of the tundish is analyzed in real time to determine whether the average weight of the tundish is continuously increased or not (S240). That is, t-2* ⁇ t is determined as a time of opening the subsequent ladle when both of W td (t) - W td (t- ⁇ t) and W td (t) - W td (t-2* ⁇ t) are greater than or equal to "0", and thus, a subsequent ladle opening signal is detected (S200).
- the residual-steel amount in the tundish and the casting speed are stored from t-4* ⁇ t so as to enable the prediction of the mixed portion in real time. Also, with respect to continuous casting equipment in which several strands are generated, it is determined whether or not the equipment is operated for each strand, and casting speed of each strand is stored.
- a first reference concentration and a second reference concentration for predicting the heterogeneous steel mixed portion of the strand solidified and drawn from a mold are set by using the stored concentration data of each component of the previous steel and each component of the subsequent steel (S300). Specifically, a lowermost limit dimensionless concentration value among upper limit dimensionless concentration values of each component of the previous steel is set as the first reference concentration. Also, an uppermost limit dimensionless concentration value among lower limit dimensionless concentration values of each component of the subsequent steel is set as the second reference concentration.
- the lower limit dimensionless concentration value of the previous steel is substituted with the upper limit dimensionless concentration value of the previous steel and the upper limit dimensionless concentration value of the previous steel is substituted with the lower limit dimensionless concentration value of the previous steel.
- the lower limit dimensionless concentration value of the subsequent steel is substituted with the upper limit dimensionless concentration value of the subsequent steel and the upper limit dimensionless concentration value of the subsequent steel is substituted with the lower limit dimensionless concentration value of the subsequent steel in the same manner. This is applied when the component concentration of the previous steel is higher than the component concentration of the subsequent steel.
- the first reference concentration and the second reference concentration are reference values for the prediction of the mixed portion, wherein the first reference concentration and the second reference concentration are changed according to the type and combination of the previous steel and the subsequent steel.
- the dimensionless relative concentration of each of the surface and center of the strand is calculated in real time from the time of detecting the subsequent ladle opening signal, i.e., t-2* ⁇ t, and a time for the calculation of the dimensionless relative concentration is counted from the time of detecting the subsequent ladle opening signal (t-2* ⁇ t) (S410). Also, a position of the strand at a time of sending the subsequent ladle opening signal is set as a position in which the dimensionless relative concentration of the surface of the strand begins to be measured. In addition, a position of -4 ⁇ 4 m from the position of the strand at the time of opening the subsequent ladle is set as a position in which the dimensionless relative concentration of the center of the strand begins to be obtained.
- the method of obtaining the dimensionless relative concentrations of the surface and the center includes the processes of: first calculating an inlet volumetric flow (Q td-in ) of the subsequent steel in the tundish using Equation 5 (S411), calculating an average dimensionless relative concentration (C td-ave (t+ ⁇ t)) of the molten steel in the tundish at a current time by applying the calculated inlet volumetric flow (Q td-in ) of the subsequent steel in the tundish to Equation 6 (S412), calculating a dimensionless relative concentration (C td-out (t+ ⁇ t)) of the molten steel discharged from the tundish at a current time by applying the calculated average dimensionless relative concentration (C td-ave (t+ ⁇ t)) at a current time to Equation 7 (S413), calculating an average dimensionless relative concentration (C md-aver (t+ ⁇ t)) of the molten steel in the mold at a current time by
- a dimensionless relative concentration (C md-in (t+ ⁇ t)) of the molten steel introduced into the mold at a current time in Equation 9 is the dimensionless relative concentration ((C td-out (t+ ⁇ t)) of the molten steel discharged from the tundish at a current time
- the dimensionless relative concentration ((C td-out (t+ ⁇ t)) of the molten steel discharged from the tundish at a current time calculated by Equation 7 is applied to the dimensionless relative concentration (C md-in (t+ ⁇ t)) of the molten steel introduced into the mold in Equation 9.
- the dimensionless relative concentration of the surface of the strand may be calculated by applying a value of interpolation and extrapolation factor for the calculation of the surface to an interpolation and extrapolation factor (f) of each of Equation 7 for calculating the dimensionless relative concentration ((C td-out (t+ ⁇ t)) of the molten steel discharged from the tundish at a current time and Equation 9 for calculating the dimensionless relative concentration (C md-out (t+ ⁇ t)) of the steel discharged from the mold at a current time.
- the dimensionless relative concentration of the surface of the strand may be obtained when 2.2 ⁇ 0.6 is applied to the interpolation and extrapolation factor (f) of Equation 7 for calculating the dimensionless relative concentration ((C td-out (t+ ⁇ t)) of the molten steel discharged from the tundish and 0.5 ⁇ 0.2 is applied to the interpolation and extrapolation factor (f) of Equation 9 for calculating the dimensionless relative concentration (C md-out (t+ ⁇ t)) of the steel discharged from the mold.
- the dimensionless relative concentration of the center of the strand may be obtained when 4 ⁇ 2 is applied to the interpolation and extrapolation factor (f) of Equation 7 for calculating the dimensionless relative concentration ((C td-out (t+ ⁇ t)) of the molten steel discharged from the tundish at a current time and 0.7 ⁇ 0.4 is applied to the interpolation and extrapolation factor (f) of Equation 9 for calculating the dimensionless relative concentration (C md-out (t+ ⁇ t)) of the steel discharged from the mold at a current time.
- positions in the longitudinal direction of the strand having the calculated dimensionless relative concentration of the center and the calculated dimensionless relative concentration of the surface are calculated (S420).
- the position of the strand having the calculated dimensionless relative concentration of the surface may be calculated by dividing a product of a mold discharge volumetric flow (Q md-out ) in the strand and liquid density of the molten metal by a product of a cross-sectional area (A md ) of the strand and solid density ( ⁇ s ) of the molten steel as illustrated in Equation 10.
- a solid density of the molten steel of 7,600 kg/m 3 to 8,000 kg/m 3 , for example, approximately 7,800 kg/m 3 is used as a density value.
- the position of the strand having the obtained dimensionless relative concentration of the center is a position of -4 ⁇ 4 m from the position of the strand having the dimensionless relative concentration of the surface calculated at the same time.
- the dimensionless relative concentrations of each of the surface and the center of the strand are obtained by the above-described method, and a time of calculating the concentration is compared with the reference time in real time while the positions in the longitudinal direction of the strand having the obtained dimensionless relative concentrations of each of the surface and the center are calculated (S500). If the calculation time is within the reference time (YES), the calculated dimensionless relative concentrations of each of the center and the surface of the strand are respectively compared with the first reference concentration and the second reference concentration (S600).
- the calculation of the concentration is terminated and the mixed portion is predicted and set (S700). That is, when the dimensionless relative concentration of the center obtained in real time reaches the first reference concentration, the calculation of the position in the longitudinal direction of the strand having the dimensionless relative concentration of the center is terminated, and the position of the strand, in which the dimensionless relative concentration of the center reaches the first reference concentration, is set as a starting position.
- the calculation of the position in the longitudinal direction of the strand having the dimensionless relative concentration of the surface is terminated, and the position of the strand, in which the dimensionless relative concentration of the surface reaches the second reference concentration, is set as an end position.
- a region from the position of the strand in which the obtained dimensionless relative concentration of the center has a first reference concentration value to the position of the strand in which the obtained dimensionless relative concentration of the surface has a second reference concentration value is predicted as the mixed portion.
- the cutter automatically cuts the strand at the starting position and the end position, the heterogeneous steel mixed portion is cut off from the strand (S1100).
- the obtaining of the dimensionless relative concentrations of the surface and the center of the strand (S410) and the calculating of the positions of the corresponding dimensionless relative concentrations (S420) are repeated.
- a time for obtaining the concentration and calculating the position exceeds the reference time (NO)
- the acquisition of the concentrations of the surface and the center of the strand and the calculation of the positions are terminated (S800).
- it is determined whether or not a combination of the previous steel and the subsequent steel subjected to a current operation is a type that is included in a preset mixed portion cut-off length table (S900). For example, in a case in which the combination of the heterogeneous steels subjected to the current operation is a combination that is included in the preset mixed portion cut-off length table, the strand is cut to the cut-off length listed in the mixed portion cut-off length table (S1200).
- the strand may be cut to a corresponding cut-off length based on a position of the meniscus of the strand.
- the strand is cut to a predetermined cut-off length, e.g., a maximum length, based on the position of the meniscus (S1300). After the strand is cut to a predetermined length, the slab before the mixed portion and the slab after the mixed portion are set as abnormal materials and components are verified with a component analyzer.
- FIG. 15 is a graph in which lengths of mixed portions are analyzed by the method of predicting a mixed portion according to the exemplary embodiment for 1 year.
- the length of the mixed portion was varied from 0 m to 23 m according to a real-time operation method and a concentration of the steel. That is, in the present disclosure, since the length and the position of the mixed portion were calculated for each operation of heterogeneous steels without cutting the strand to a predetermined length regardless of operating conditions for each operation of heterogeneous steels as in the related art, the mixed portion was predicted and then cut, and thus, its accuracy was improved. Specifically, the dimensionless relative concentrations of each of the surface and the center of the strand are obtained in real time, and the length and the position of the mixed portion were deduced by using the dimensionless relative concentrations. Thus, in the present disclosure, a decrease in profitability due to excessive cut-off of the mixed portion may be prevented, and the shipment of defect products due to less cut-off of the mixed portion to client companies may be prevented.
- a method of continuous casting heterogeneous steels according to the present disclosure may predict a mixed portion of a strand, which is manufactured by mixing previous steel and subsequent steel, and may automatically cut the mixed portion.
- a decrease in profitability due to excessive cut-off of the mixed portion may be prevented and the shipment of defect products due to less cut-off of the mixed portion to client companies may be prevented. Therefore, there is an effect of improving productivity in which a high-quality slab is manufactured in the continuous casting operation of heterogeneous steels.
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Claims (20)
- Verfahren zum Stranggießen von heterogenen Stählen, wobei das Verfahren umfasst:Erhalten dimensionsloser Relativkonzentrationen von nachfolgendem Stahl zu vorausgehendem Stahl jeweils an der Oberfläche und im Innern eines stranggegossenen Strangs in Echtzeit;Berechnen von Positionen in einer Längsrichtung des Strangs, welche die in Echtzeit erhaltenen dimensionslosen Relativkonzentrationen der Oberfläche und des Innern aufweisen;Vorhersagen eines gemischten Abschnitts in dem Strang durch jeweiliges Vergleichen der erhaltenen dimensionslosen Relativkonzentrationen der Oberfläche und des Innern mit Referenzkonzentrationen; undAbschneiden des vorhergesagten gemischten Abschnitts, wobei die Positionen des Strangs, von denen die dimensionslosen Relativkonzentrationen erhalten werden, eine Oberfläche und eine Mitte in einer Höhenrichtung des Strangs sind,
wobei das Verfahren weiterhin Folgendes umfasst:Online-Empfang von Daten über eine Restmenge an geschmolzenem Stahl in dem Zwischenbehälter, Gießgeschwindigkeit und Konzentrationen des jeweiligen vorausgehenden Stahls und des jeweiligen nachfolgenden Stahls und Speichern der Daten; undErkennung eines Signals der Öffnung der nachfolgenden Gießpfanne vor dem Erhalten der dimensionslosen Relativkonzentrationen des nachfolgenden Stahls zum vorausgehenden Stahl,
wobei das Verfahren weiterhin Folgendes umfasst:Erhalten von dimensionslosen Relativkonzentrationen der jeweiligen Oberfläche und der jeweiligen Mitte des Strangs in Echtzeit ab einem Zeitpunkt der Erkennung des Öffnungssignals der nachfolgenden Gießpfanne, und Zählen einer Erfassungszeit der dimensionslosen Konzentration ab dem Zeitpunkt der Erkennung des Öffnungssignals der nachfolgenden Gießpfanne, die mit einer Referenzzeit in Echtzeit verglichen werden soll;Vergleichen der erhaltenen dimensionslosen Relativkonzentration der Mitte mit der ersten Referenzkonzentration und Vergleichen der erhaltenen dimensionslosen Relativkonzentration der Oberfläche mit der zweiten Referenzkonzentration, wenn die Erfassungszeit der dimensionslosen Konzentration der Referenzzeit entspricht oder kürzer ist; undBeenden der Erfassung der dimensionslosen Relativkonzentrationen der jeweiligen Oberfläche und der jeweiligen Mitte des Strangs, wenn die Konzentrationserfassungszeit länger ist als die Referenzzeit,
wobei das Verfahren weiterhin Folgendes umfasst:Bestimmen, ob ein Typ zwischen dem vorausgehenden Stahl und dem nachfolgenden Stahl ein Typ ist, der in einer vorgegebenen Abschneide-Tabelle für heterogenen Stahl enthalten ist, oder nicht;Schneiden des Strangs auf eine Abschneidelänge des entsprechenden heterogenen Stahltyps, wenn der Typ zwischen dem vorausgehenden Stahl und dem nachfolgenden Stahl, die einem gegenwärtigen Arbeitsgang unterzogen werden, der Typ ist, der in der vorgegebenen Abschneide-Tabelle für heterogenen Stahl enthalten ist; undSchneiden des Strangs auf eine vorgegebene vorbestimmte Abschneidelänge, wenn der Typ zwischen dem vorausgehenden Stahl und dem nachfolgenden Stahl, die dem gegenwärtigen Arbeitsgang unterzogen werden, nicht in der vorgegebenen Abschneide-Tabelle für heterogenen Stahl enthalten ist, nach dem Beenden der Erfassung der dimensionslosen Relativkonzentrationen der jeweiligen Oberfläche und der jeweiligen Mitte des Strangs. - Verfahren zum Stranggießen von heterogenen Stählen, wobei das Verfahren umfasst:Erhalten dimensionsloser Relativkonzentrationen von nachfolgendem Stahl zu vorausgehendem Stahl jeweils an einer Vielzahl von Positionen in einer Höhenrichtung eines erstarrten und aus einer Kokille stranggegossenen Strangs in Echtzeit unter Verwendung relativer Mengen des vorausgehenden Stahls und des nachfolgenden Stahls in einem Zwischenbehälter und relativer Mengen des vorausgehenden Stahls und des nachfolgenden Stahls in der Kokille;Berechnen von Positionen in einer Längsrichtung des Strangs, welche die in Echtzeit erhaltenen dimensionslosen Relativkonzentrationen aufweisen;Vorhersagen eines gemischten Abschnitts in dem Strang durch jeweiliges Vergleichen der erhaltenen dimensionslosen Relativkonzentrationen mit Referenzkonzentrationen; undAbschneiden des vorhergesagten gemischten Abschnitts, wobei die Vielzahl von Positionen in der Höhenrichtung des Strangs, von der die dimensionslosen Relativkonzentrationen erhalten werden, eine Oberfläche und eine Mitte des Strangs umfasst,
wobei das Verfahren weiterhin Folgendes umfasst:Online-Empfang von Daten über eine Restmenge an geschmolzenem Stahl in dem Zwischenbehälter, Gießgeschwindigkeit und Konzentrationen des jeweiligen vorausgehenden Stahls und des jeweiligen nachfolgenden Stahls und Speichern der Daten; undErkennung eines Signals der Öffnung der nachfolgenden Gießpfanne vor dem Erhalten der dimensionslosen Relativkonzentrationen des nachfolgenden Stahls zum vorausgehenden Stahl,
wobei das Verfahren weiterhin Folgendes umfasst:Erhalten von dimensionslosen Relativkonzentrationen der jeweiligen Oberfläche und der jeweiligen Mitte des Strangs in Echtzeit ab einem Zeitpunkt der Erkennung des Öffnungssignals der nachfolgenden Gießpfanne, und Zählen einer Erfassungszeit der dimensionslosen Konzentration ab dem Zeitpunkt der Erkennung des Öffnungssignals der nachfolgenden Gießpfanne, die mit einer Referenzzeit in Echtzeit verglichen werden soll;Vergleichen der erhaltenen dimensionslosen Relativkonzentration der Mitte mit der ersten Referenzkonzentration und Vergleichen der erhaltenen dimensionslosen Relativkonzentration der Oberfläche mit der zweiten Referenzkonzentration, wenn die Erfassungszeit der dimensionslosen Konzentration der Referenzzeit entspricht oder kürzer ist; undBeenden der Erfassung der dimensionslosen Relativkonzentrationen der jeweiligen Oberfläche und der jeweiligen Mitte des Strangs, wenn die Konzentrationserfassungszeit länger ist als die Referenzzeit,wobei das Verfahren weiterhin Folgendes umfasst:Bestimmen, ob ein Typ zwischen dem vorausgehenden Stahl und dem nachfolgenden Stahl ein Typ ist, der in einer vorgegebenen Abschneide-Tabelle für heterogenen Stahl enthalten ist, oder nicht;Schneiden des Strangs auf eine Abschneidelänge des entsprechenden heterogenen Stahltyps, wenn der Typ zwischen dem vorausgehenden Stahl und dem nachfolgenden Stahl, die einem gegenwärtigen Arbeitsgang unterzogen werden, der Typ ist, der in der vorgegebenen Abschneide-Tabelle für heterogenen Stahl enthalten ist; undSchneiden des Strangs auf eine vorgegebene vorbestimmte Abschneidelänge, wenn der Typ zwischen dem vorausgehenden Stahl und dem nachfolgenden Stahl, die dem gegenwärtigen Arbeitsgang unterzogen werden, nicht in der vorgegebenen Abschneide-Tabelle für heterogenen Stahl enthalten ist, nach dem Beenden der Erfassung der dimensionslosen Relativkonzentrationen der jeweiligen Oberfläche und der jeweiligen Mitte des Strangs. - Verfahren nach Anspruch 1 oder 2, weiterhin umfassend das Festlegen der Referenzkonzentrationen vor dem Erhalten der dimensionslosen Relativkonzentrationen des nachfolgenden Stahls zum vorausgehenden Stahl in dem stranggegossenen Strang in Echtzeit,
wobei das Festlegen der Referenzkonzentrationen umfasst:Festlegen einer untersten Grenzkonzentration unter oberen Grenzkonzentrationen jeder Komponente des vorausgehenden Stahls als eine erste Referenzkonzentration; undFestlegen einer obersten Grenzkonzentration unter unteren Grenzkonzentrationen jeder Komponente des nachfolgenden Stahls als eine zweite Referenzkonzentration. - Verfahren nach Anspruch 3, wobei das Festlegen der ersten Referenzkonzentration und der zweiten Referenzkonzentration umfasst:Berechnen von Konzentrationen der Komponenten des vorausgehenden Stahls als dimensionslose untere Grenzkonzentrationen und dimensionslose obere Grenzkonzentrationen;Festlegen einer dimensionslosen untersten Grenzkonzentration unter den dimensionslosen oberen Grenzkonzentrationen der jeweiligen Komponente des vorausgehenden Stahls als erste Referenzkonzentration;Berechnen von Konzentrationen der Komponenten des nachfolgenden Stahls als dimensionslose untere Grenzkonzentrationen und dimensionslose obere Grenzkonzentrationen; undFestlegen einer dimensionslosen obersten Grenzkonzentration unter den dimensionslosen unteren Grenzkonzentrationen der jeweiligen Komponente des nachfolgenden Stahls als zweite Referenzkonzentration.
- Verfahren nach Anspruch 4, wobei das Berechnen der Konzentrationen der jeweiligen Komponente des vorausgehenden Stahls als dimensionslose untere Grenzkonzentrationen und dimensionslose obere Grenzkonzentrationen das Ersetzen eines dimensionslosen unteren Grenzkonzentrationswerts des vorausgehenden Stahls durch einen dimensionslosen oberen Grenzkonzentrationswert des vorausgehenden Stahls und das Ersetzen des dimensionslosen oberen Grenzkonzentrationswerts des vorausgehenden Stahls durch den dimensionslosen unteren Grenzkonzentrationswert des vorausgehenden Stahls umfasst, wenn die dimensionslose untere Grenzkonzentration des vorausgehenden Stahls größer ist als die dimensionslose obere Grenzkonzentration des vorausgehenden Stahls; und
das Berechnen der Konzentrationen der jeweiligen Komponente des nachfolgenden Stahls als dimensionslose untere Grenzkonzentrationen und dimensionslose obere Grenzkonzentrationen das Ersetzen eines dimensionslosen unteren Grenzkonzentrationswerts des nachfolgenden Stahls durch einen dimensionslosen oberen Grenzkonzentrationswert des nachfolgenden Stahls und das Ersetzen des dimensionslosen oberen Grenzkonzentrationswerts des nachfolgenden Stahls durch den dimensionslosen unteren Grenzkonzentrationswert des nachfolgenden Stahls umfasst, wenn die dimensionslose untere Grenzkonzentration des nachfolgenden Stahls größer ist als die dimensionslose obere Grenzkonzentration des nachfolgenden Stahls. - Verfahren nach Anspruch 1 oder 2, wobei der Strang als in einem Mischzustand befindlich bestimmt wird, wenn wenigstens eine dimensionslose Relativkonzentration der erhaltenen dimensionslosen Relativkonzentrationen der Oberfläche und der Mitte von der Referenzkonzentration abgewichen ist, und
eine Position in der Längsrichtung des Strangs, an der wenigstens eine dimensionslose Relativkonzentration der erhaltenen dimensionslosen Relativkonzentrationen der Oberfläche und der Mitte von der Referenzkonzentration abgewichen ist, als der gemischte Abschnitt bestimmt wird. - Verfahren nach Anspruch 6, wobei eine Position in der Längsrichtung des Strangs, an der die erhaltene dimensionslose Relativkonzentration der Mitte die Referenzkonzentration erreicht, als Anfangspunkt des gemischten Abschnitts bestimmt wird, und
eine Position in der Längsrichtung des Strangs, an der die erhaltene dimensionslose Relativkonzentration der Oberfläche die Referenzkonzentration erreicht, als Endpunkt des gemischten Abschnitts bestimmt wird. - Verfahren nach Anspruch 1 oder 2, wobei die Erkennung des Öffnungssignals der nachfolgenden Gießpfanne umfasst:Senden eines virtuellen Gießpfannenöffnungssignals;Erfassen eines Gewichts des Zwischenbehälters in Echtzeit, in Millisekunden (ms) ab einem Zeitpunkt, an dem das virtuelle Gießpfannenöffnungssignal gesendet wird;Berechnen des in Millisekunden (ms) erfassten Gewichts des Zwischenbehälters als Durchschnittsgewicht des Zwischenbehälters in vorbestimmten Zeitintervallen in Sekunden (s); undFestlegen eines Zeitpunkts der Öffnung der nachfolgenden Gießpfanne mittels eines Zeitpunkts der kontinuierlichen Erhöhung des Durchschnittsgewichts des Zwischenbehälters.
- Verfahren nach Anspruch 8, wobei, wenn Wtd(t) ein Gewicht einer Reststahlmenge in dem Zwischenbehälter zu einem gegenwärtigen Zeitpunkt ist und Wdt(t-Δt) ein Gewicht einer Reststahlmenge in dem Zwischenbehälter zu einem früheren Zeitpunkt ist,
t-2∗Δt als der Zeitpunkt der Öffnung der nachfolgenden Gießpfanne bestimmt wird, wenn sowohl Wtd(t) - Wtd(t-Δt) als auch Wtd(t) - Wtd(t-2∗Δt) größer als oder gleich "0" sind,
die dimensionslosen Relativkonzentrationen der jeweiligen Oberfläche und der jeweiligen Mitte des Strangs ab t-2∗Δt erhalten werden, und
die Reststahlmenge in dem Zwischenbehälter und die Gießgeschwindigkeit ab t-4∗Δt gespeichert werden. - Verfahren nach Anspruch 1 oder 2, wobei das Erhalten der dimensionslosen Relativkonzentrationen des nachfolgenden Stahls zum vorausgehenden Stahl an der Oberfläche und in der Mitte des Strangs umfasst:Berechnen eines Eintrittsvolumenstroms (Qtd-in) des nachfolgenden Stahls in dem Zwischenbehälter;Berechnen einer durchschnittlichen dimensionslosen Relativkonzentration (Ctd-ave(t+Δt)) des geschmolzenen Stahls in dem Zwischenbehälter zu einem gegenwärtigen Zeitpunkt mittels des Eintrittsvolumenstroms (Qtd-in) des nachfolgenden Stahls in dem Zwischenbehälter;Berechnen einer dimensionslosen Relativkonzentration (Ctd-out(t+Δt)) des aus dem Zwischenbehälter austretenden geschmolzenen Stahls zu einem gegenwärtigen Zeitpunkt mittels der durchschnittlichen dimensionslosen Relativkonzentration (Ctd-ave(t+Δt)) des geschmolzenen Stahls in dem Zwischenbehälter zu einem gegenwärtigen Zeitpunkt;Berechnen einer durchschnittlichen dimensionslosen Relativkonzentration (Cmd-aver(t+Δt)) des geschmolzenen Stahls in der Kokille zu einem gegenwärtigen Zeitpunkt mittels der dimensionslosen Relativkonzentration (Ctd-out(t+Δt)) des aus dem Zwischenbehälter austretenden geschmolzenen Stahls zu einem gegenwärtigen Zeitpunkt; undBerechnen einer dimensionslosen Relativkonzentration (Cmd-out(t+Δt)) des aus der Kokille austretenden Strangs zu einem gegenwärtigen Zeitpunkt mittels der durchschnittlichen dimensionslosen Relativkonzentration (Cmd-aver(t+Δt)) des geschmolzenen Stahls in der Kokille zu einem gegenwärtigen Zeitpunkt und einer dimensionslosen Relativkonzentration (Cmd-in(t+Δt)) des in die Kokille eingeleiteten geschmolzenen Stahls zu einem gegenwärtigen Zeitpunkt.
- Verfahren nach Anspruch 10, wobei der Eintrittsvolumenstrom (Qtd-in) des nachfolgenden Stahls in dem Zwischenbehälter durch Gleichung 5 berechnet wird,
die durchschnittliche Konzentration (Ctd-ave(t+Δt)) des geschmolzenen Stahls in dem Zwischenbehälter zu einem gegenwärtigen Zeitpunkt durch Gleichung 6 berechnet wird,
wobei Ctd-ave(t) eine durchschnittliche dimensionslose Relativkonzentration des geschmolzenen Stahls in dem Zwischenbehälter zu einem früheren Zeitpunkt ist, Qtd-in(t) ein Eintrittsvolumenstrom des in den Zwischenbehälter eingeleiteten geschmolzenen Stahls zu einem früheren Zeitpunkt ist, Ctd-in(t) eine Eintrittskonzentration (dimensionslose Relativkonzentration) des nachfolgenden Stahls in dem Zwischenbehälter zu einem früheren Zeitpunkt ist, Qtd-out(t) ein Volumenstrom des aus dem Zwischenbehälter austretenden geschmolzenen Stahls zu einem früheren Zeitpunkt ist, Ctd-out(t) eine Konzentration (dimensionslose Relativkonzentration) des aus dem Zwischenbehälter austretenden geschmolzenen Stahls zu einem früheren Zeitpunkt ist und ρL die Flüssigdichte des geschmolzenen Stahls ist,
die Konzentration ((Ctd-out(t+Δt)) des aus dem Zwischenbehälter austretenden geschmolzenen Stahls zu einem gegenwärtigen Zeitpunkt durch Gleichung 7 berechnet wird,
die durchschnittliche Konzentration (Cmd-aver(t+Δt)) des geschmolzenen Stahls in der Kokille zu einem gegenwärtigen Zeitpunkt durch Gleichung 8 berechnet wird,
die Konzentration (Cmd-out(t+Δt)) des aus der Kokille austretenden Strangs zu einem gegenwärtigen Zeitpunkt durch Gleichung 9 berechnet wird, - Verfahren nach Anspruch 11, wobei beim Berechnen der dimensionslosen Relativkonzentration der Mitte des Strangs
4±2 auf den Interpolations- und Extrapolationsfaktor (ftd) von Gleichung 7 angewandt wird, und
0,7±0,4 auf den Interpolations- und Extrapolationsfaktor (fmd) von Gleichung 9 angewandt wird, um die dimensionslose Relativkonzentration (Cmd-out-center) der Mitte des Strangs zu berechnen. - Verfahren nach Anspruch 11, wobei beim Berechnen der dimensionslosen Relativkonzentration der Oberfläche des Strangs
2,2±0,6 auf den Interpolations- und Extrapolationsfaktor (ftd) von Gleichung 7 angewandt wird, und
0,5±0,2 auf den Interpolations- und Extrapolationsfaktor (fmd) von Gleichung 9 angewandt wird, um die dimensionslose Relativkonzentration (Cmd-out-surface) der Oberfläche des Strangs zu berechnen. - Verfahren nach Anspruch 11, wobei eine Flüssigdichte des geschmolzenen Stahls als Dichte(ρL)-Wert in den Gleichungen 5, 6 und 8 verwendet wird, und
ein Wert von 7.000 kg/m3 bis 7.400 kg/m3 als Dichte des geschmolzenen Stahls verwendet wird. - Verfahren nach Anspruch 1 oder 2, weiterhin umfassend:Festlegen einer Position des Strangs, bei welcher die dimensionslose Relativkonzentration der Oberfläche des Strangs beginnt erhalten zu werden; undFestlegen einer Position des Strangs, bei welcher die dimensionslose Relativkonzentration der Mitte des Strangs beginnt erhalten zu werden,wobei eine Position des Strangs zum Zeitpunkt der Öffnung der nachfolgenden Gießpfanne als die Position festgelegt wird, bei welcher die dimensionslose Relativkonzentration der Oberfläche des Strangs beginnt erhalten zu werden, undeine Position -4±4 m von der Position des Strangs zum Zeitpunkt der Öffnung der nachfolgenden Gießpfanne als die Position festgelegt wird, bei welcher die dimensionslose Relativkonzentration der Mitte des Strangs beginnt erhalten zu werden.
- Verfahren nach Anspruch 15, wobei beim Berechnen der Position in der Längsrichtung des Strangs, welche die erhaltene dimensionslose Relativkonzentration der Oberfläche aufweist,
die Position durch Gleichung 10 berechnet wird, in der ein Volumenstrom (Qmd-out) des aus der Kokille austretenden geschmolzenen Stahls durch ein Produkt einer Querschnittsfläche (Amd) des Strangs und einer Festkörperdichte (pS) des geschmolzenen Stahls dividiert wird, - Verfahren nach Anspruch 16, wobei beim Berechnen der Position in der Längsrichtung des Strangs, welche die erhaltene dimensionslose Relativkonzentration der Mitte aufweist,
eine Position -4±4 m von der Position, welche die erhaltene dimensionslose Relativkonzentration der Oberfläche aufweist, als die Position festgelegt wird, welche die dimensionslose Relativkonzentration der Mitte aufweist. - Verfahren nach Anspruch 17, wobei ein Bereich von einem Punkt des Strangs, an welchem die in Echtzeit erhaltene dimensionslose Relativkonzentration der Mitte des Strangs die erste Referenzkonzentration erreicht, bis zu einem Punkt des Strangs, an welchem die in Echtzeit erhaltene dimensionslose Relativkonzentration der Oberfläche des Strangs die zweite Referenzkonzentration erreicht, als der gemischte Abschnitt vorhergesagt wird.
- Verfahren nach Anspruch 17, weiterhin umfassend:Festlegen des Punkts des Strangs, an welchem die in Echtzeit erhaltene dimensionslose Relativkonzentration der Mitte des Strangs die erste Referenzkonzentration erreicht, als eine erste Abschneideposition;Festlegen des Punkts des Strangs, an welchem die in Echtzeit erhaltene dimensionslose Relativkonzentration der Oberfläche des Strangs die zweite Referenzkonzentration erreicht, als eine zweite Abschneideposition; undAbschneiden des gemischten Abschnitts durch jeweiliges Schneiden des Strangs an der ersten Abschneideposition und der zweiten Abschneideposition.
- Verfahren nach Anspruch 1 oder 2, wobei das Vorhersagen des gemischten Abschnitts des Strangs und das Abschneiden des vorhergesagten gemischten Abschnitts als Online-Prozess durchgeführt werden.
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EP3088102B1 (de) | 2017-11-08 |
CN105848808A (zh) | 2016-08-10 |
CN105848808B (zh) | 2018-07-20 |
KR101485913B1 (ko) | 2015-01-26 |
EP3088102A1 (de) | 2016-11-02 |
EP3088102B9 (de) | 2018-02-14 |
JP6220457B2 (ja) | 2017-10-25 |
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