JP2013066905A - Steel billet cutting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel billet cutting method capable of correctly cutting a steel billet to the length of the requested weight.SOLUTION: In the steel billet cutting method, a strand S drawn from a casting mold 14 by a pinch roll 18 by using a continuous casting machine is cut to a steel billet of the requested length having the requested weight which is obtained by correcting the nominal unit weight by the correction coefficient calculated based on information on the casting condition. The continuous casting machine is divided into a plurality of zones along the casting direction, and the corresponding fixed points are set on the terminal end of each zone. The final fixed point is set at the downstream position of the continuous casting machine in which solidification of the entire section of the strand is completed. The zone staying time in which the strand at the position corresponding to the steel billet to be cut stays in each zone is reflected to the calculation of the requested length of the steel billet.

Description

  The present invention relates to a method for cutting a steel slab, and particularly suitable for application to cutting a strand drawn from a mold during continuous casting to an appropriate steel slab length having no variation with respect to a target claimed weight. It relates to a cutting method.

  For convenience, with reference to FIG. 1 to be described later, generally, in a continuous casting facility, when the molten steel conveyed in the ladle 10 is supplied to the tundish 12, it passes through an immersion nozzle 12A at the bottom thereof. It is injected into a mold (mold) 14. Below the bottom portion of the mold 14 is formed a roller apron 16 composed of a vertical portion and a curved portion in which a large number of guide rolls face each other together with a water-cooled spray (not shown), and a horizontal apex that follows the lower end of the curved portion. For example, three pinch rolls 18 are connected in the vicinity of the rear end of the section.

  Downstream of these pinch rolls 18 is disposed a slab cutter 20 for cutting the continuously cast strand S into steel pieces (slabs) of a predetermined length, and the steel pieces (slab pieces) P cut here are further provided. It is conveyed to the weight measuring device (not shown) arrange | positioned downstream and the weight is measured.

  In such a casting facility, the molten steel poured into the mold 14 from the tundish 12 is cooled from the surroundings in the mold 14 and solidified to form a shell, which is drawn from the lower end of the molten steel. While being cooled by the cooling water, it is guided from the straight part (vertical part) to the horizontal part through the curved part, and becomes a flat strand S. The strand S is further sent to the slab cutter 20 by the pinch roll 18 on the downstream side, where it is cut into a slab P having a predetermined length.

  The slab length (slab cutting length) to be cut in such a manufacturing process is obtained from a nominal unit weight and a correction coefficient for correcting the slab length in accordance with the requested weight required in the subsequent process. Here, the nominal unit weight means the weight per unit length of the strand obtained using the cross-sectional area of the mold and the specific gravity determined by the composition of the molten steel. The cross-sectional area of the strand is, for example, drawn from the mold. Since it changes immediately after being cooled and after being cooled, correction is made to the unit weight of the strand immediately before cutting using a correction coefficient to obtain a slab cutting length corresponding to the requested weight, and cutting is performed.

  For example, in Patent Document 1, as a method of cutting a slab manufactured by a continuous casting facility, casting speed, molten steel components, specific water amount are used for the purpose of cutting accurately even if casting conditions during casting vary. By obtaining casting condition information about the slab such as the pinch roll pressing weight, casting time, tundish ΔT, etc., the contribution ratio of the casting condition information to the slab weight correction factor is obtained. It proposes a method of cutting the slab by obtaining the casting weight correction coefficient from the filling condition information.

  However, in the technique disclosed in the above-mentioned Patent Document 1, since all the slabs that have been cut so far are determined for contribution ratios that match them, for example, data on the slab that is to be cut from now on. In the case of slab information in which there is little or the conditions are greatly different, there is a problem that the slab weight after cutting varies with respect to the target value. Therefore, in Patent Document 2, at least one of casting speed, specific water amount, slab surface temperature, and in-machine passage time is set as casting condition information, and an actual input variable representing an operating condition stored in a past actual operating database and , Calculate the similarity with new input variable of continuous cast steel slab, select a predetermined number of data with high calculated similarity, calculate the weighting coefficient for the selected data, and use the selected data A technique for creating a model and calculating a correction coefficient from the created model has been proposed.

JP-A-6-114519 JP 2008-161888

  However, since the slab cutting method disclosed in Patent Document 1 uses a correction coefficient adapted to change in casting conditions during continuous casting, it is also disclosed in Patent Document 2. In the cutting method, since the correction coefficient obtained in consideration of the similarity between past information and new information is used, the accuracy of the cutting length of the slab is improved in any case, There was a problem that it was not always accurate.

  The present invention has been made to solve the above-described conventional problems, and it is an object of the present invention to make it possible to accurately cut a steel piece length corresponding to the weight of the bill.

  As a result of investigating the variation of the billet weight from the target value, the present inventors have found that there is a speed variation in the continuous casting machine as a cause of the variation. A technique for correcting the cutting length of a steel slab by such speed fluctuations has not been seen in the past, including Patent Documents 1 and 2.

  The present invention has been made on the basis of the above knowledge, and using a continuous casting machine, a strand drawn by a pinch roll from a mold is used to obtain a nominal unit weight by a correction coefficient calculated based on casting condition information. In the method for cutting a billet of billet length having a required billing weight obtained by correction, the continuous casting machine is divided into a plurality of regions along the casting direction, and at the end of each region. Sets the corresponding fixing point and sets the final fixing point at the downstream position of the continuous caster where the entire cross section of the strand has been solidified, and for calculating the bill length of the billet, The problem is solved by reflecting the region residence time in which the strands at positions corresponding to the steel pieces to be cut stay in each region.

Here, the reflection of each region residence time is expressed by the following equation: β = Σβ _N
N: Any integer greater than or equal to 2 β _N = a _N · α _N ^m + b _N · α _N ^m-1 + ... + g _N · α _N + h _N
α _N : N-th region residence time (sec.)
a _N , b _N ,..., g _N , h _N : constants
m: Cutting correction coefficient obtained by an arbitrary integer of 1 or more: The following formula multiplied by β Cutting instruction length (hot value) = requested slab length (cold value) × hot correction coefficient × β
It can be realized by hot correction coefficient = hot length / cold length.

  In addition, the strand at the position corresponding to the slab to be cut is subdivided into blocks of a predetermined length, and for each block, the leading end of the block passes through the start end of each region, and the trailing end corresponds. The passage time until passing through the fixed point to be measured is measured, and the average value of the passage times measured for all blocks can be used as the region residence time of the corresponding region of the slab.

  Further, the fixed point of the final region can be the pinch roll or the machine end position.

  According to the present invention, the billing length at the time of cutting is calculated in consideration of the region residence time for each region obtained by dividing the continuous casting machine along the casting direction. It is possible to reflect the speed history for each region, reduce the weight deviation due to the change in solidification completion point and the slab temperature difference, and more accurately cut to the billet length corresponding to the requested weight. It became so.

The schematic diagram which shows the outline | summary of the continuous casting installation with which one Embodiment which concerns on this invention is applied The block diagram which shows the principal part of the control system of the continuous casting installation applied to the said embodiment. Explanatory diagram showing the measurement principle of the slab area residence time, taking the first area as an example Diagram showing the relationship between slab residence time and weight Explanatory drawing which shows concretely calculation method of area residence time of slab The graph which shows the result of an example in contrast with the result of a comparative example Chart showing the effects of the examples Diagram showing how to divide the continuous casting machine and how to determine the cutting correction factor

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 conceptually shows equipment equipped with a vertical-curved type (vertical bending type) continuous casting machine to which a method for cutting a steel piece in continuous casting according to an embodiment of the present invention is applied.

  When the molten steel M supplied from the ladle 10 to the tundish 12 through the long nozzle 10A is injected into the mold (mold) 14 through the immersion nozzle 12A, the molten steel M is cooled and solidified from the surroundings to form a shell. After being formed, it becomes a continuous steel slab (strand) S and is drawn out in a circular arc shape through a roller apron 16 composed of a vertical part and a curved part in which a large number of guide rolls are opposed to each other. It is guided to the downstream side while being cooled by a water-cooled spray (not shown) in the secondary cooling zone disposed along.

  The strand S that has reached the horizontal portion is conveyed to the slab cutter 20 by the pinch roll 18 disposed further downstream from the machine end E corresponding to the final guide roll position, and melted and cut into a slab (slab) having a predetermined weight by the torch. Is done. The cut slab (not shown) is conveyed to a weight measuring device, and an actual weight is measured.

  In the present embodiment, using the continuous casting machine, the strand S drawn by the pinch roll 18 from the mold 14 is obtained by correcting the nominal unit weight with a correction coefficient calculated based on casting condition information. Cut into billet length billets having the required billing weight.

  At that time, the continuous casting machine is divided into a plurality of regions from the first region (one zone in the drawing) to the final region (N zone in the drawing) along the casting direction, and each region corresponds to the end. A fixing point (not shown) to be set, and a final fixing point is set at a downstream position of the continuous casting machine in which solidification of the entire cross section of the strand S is completed, and the billet length of the billet is In the calculation, the region residence time in which the strand S at the position corresponding to the steel piece to be cut stays in each region is reflected. Here, the final fixed point is set to the machine end E.

  The continuous casting equipment of this embodiment is controlled by a continuous casting process computer (also referred to as a continuous casting process computer) 30 constituting a control system schematically shown in FIG. A billing slab length (cold value) and a hot correction coefficient are transmitted as instruction information from a computer (also referred to as a vidicon) 32 and set.

  Further, the process computer 30 is disposed on the inlet side of the slab cutter 20 and the casting speed of the molten steel in the meniscus portion calculated from the flow rate actually measured by a flow meter (not shown) attached to the tundish 12. The casting speed on the outlet side of the continuous casting machine obtained from the measurement result by the measure roll 22 is inputted, and other necessary casting conditions and measurement results are inputted.

  In the present embodiment, in the process computer 30 of FIG. 2, a block of 30A is obtained from the bill slab length (cold value) and the hot correction coefficient corresponding to the corresponding mold size and steel type input from the business computer 32. The cutting length obtained from the cutting instruction calculation formula similar to the conventional one shown is corrected by the cutting correction coefficient β obtained based on the respective region residence times in the plurality of regions obtained for each slab to be cut indicated by the block 30B. Each region residence time is reflected by performing the calculation.

Specifically, as shown in the drawing, the correction coefficient β _N of the Nth region obtained by the following equation (2) is integrated for each region by the following equation (1) with respect to the cutting instruction result of the block 30A. Cutting correction coefficient (parameter): a correction length obtained by multiplying β by the equation (3) is output as a cutting instruction to the slab cutter 20, and the actual length measured by the measure roll 22 matches the correction length by the cutter 20. Control is performed to cut the strand at the length position.

β = Σβ _N (1)
N: Any integer greater than or equal to 2 β _N = a _N · α _N ^m + b _N · α _N ^m-1 + ... + g _N · α _N + h _N (2)
α _N : N-th region residence time (sec.)
a _N , b _N ,..., g _N , h _N : constants
m: Cutting correction coefficient obtained by an arbitrary integer of 1 or more: The following formula multiplied by β Cutting instruction length (hot value) = Requested slab length (cold value) × Hot correction coefficient × β (3)
Hot correction coefficient = Hot length / Cold length (4)

  Here, the bill slab length is obtained by dividing the bill slab weight designed in consideration of the yield after the next step such as the rolling step by the slab width, the slab thickness, and the specific gravity.

Next, a method for obtaining each region residence time α _N of the strand corresponding to the slab to be cut applied to the expression (2) will be described with reference to the image diagram shown in FIG. 3 as a specific example of the first region. . In the second and subsequent regions, the meniscus in the figure becomes the start end of each region (one upstream region fixed point).

  The casting speed of the strand is adjusted so that the melted portion inside the strand is completely solidified at the in-machine position upstream from the machine end E. At that time, since it is necessary to change the casting speed in accordance with the operation state at the time of continuous casting, the staying time in the machine from the mold 14 to the machine end E varies depending on the position in the length direction in the continuously cast strand. .

  Usually, in the continuous casting machine, the guide roller constituting the roller apron 16 following the mold 14 is designed so that the facing distance is narrower toward the downstream.

  As a result, the continuously cast strands are thicker because they are hardened on the upstream side as the casting speed is slower, and are thinner because they are hardened on the downstream side as the speed is faster, so the thickness in the length direction, that is, the weight per unit length. Variation will also occur. FIG. 4 shows an example of the result of actual measurement with the vertical axis representing the ratio of the difference between the slab weight after cutting and the claimed weight. This phenomenon also occurs in each of the first to Nth areas obtained by dividing the cabin into a plurality of areas.

Therefore, as shown in FIG. 3, with respect to the region residence time of the first region of the strand at the position corresponding to the slab to be cut, the entire length of the strand is subdivided into blocks B having a predetermined length. Measured from the time t1 when the tip passes the meniscus surface in the mold (starting end of the first region) to the time tn when the trailing end passes through the fixed point of the first region, the time tn-t1 required for passing the region As the transit time. And passage time is calculated | required about all the blocks corresponding to a slab, respectively, and let the average value be area | region residence time: (alpha) ₁ of the _1st area | region of object slab.

  For example, if the slab billing length is 5 m and the length of one block is 10 cm, the area residence time is obtained for each of the 50 subdivided blocks. By doing so, it is possible to measure the slab-corresponding length within an error range of 10 cm.

  The same measurement as the region residence time for the first region is performed for each region from the second region to the final Nth region. The starting edge after the second area is a fixed point of one upstream area.

As the fixing points of the final region, the positions of the machine end E, the pinch roll 18 and the like, which are positions where the inside of the strand is completely solidified and the outer shape is determined, are set. The area residence times: α _{1 to} α _N of the first region to the Nth region of the slab thus obtained are applied to the equation (2), and the cutting correction coefficient: β is calculated from the equation (1).

When measuring the time for one block whose tip passed through the meniscus surface to pass the fixed point of the corresponding first region at the rear end, the casting length is obtained by calculation based on the rotational speed of the pinch roll 18. The point of the meniscus portion in the casting length is specified, and the information is input to the continuous casting process control 30. Then, the time data when each block reaches the point of the specified meniscus portion and the time data when the block reaches the fixed point of the first region are transmitted to the continuous casting process control 30 in units of blocks, and each time data The area residence time (α ₁ ) of the first area can be obtained from the difference.

  The region residence time will be described more specifically with reference to FIG. FIG. 2A shows an image of the passage time of the first area that is measured and managed for each block for a specific example.

  Usually, the slab cutting schedule in a continuous casting machine is frequently changed by adjustment calculation. Therefore, the slab front end position and rear end position cannot be fixedly determined. Here, as described above, the passage time for each region in the continuous casting machine is managed in units of blocks B at regular intervals (10 cm), and the region residence time for each region is calculated for each slab at the time of preset cutting of the target slab. To do.

1) When the fixed interval position (the tip of the block) reaches the meniscus (starting end of the first region), the passage start time is stored.
2) When the fixed interval position (block tip) reaches the fixed point of the first area, the passage end time of the area is stored, and the elapsed time for each block is calculated.
3) The area passing time of each block is calculated based on the cutting position scheduled to cut the slab and a fixed interval position.

  FIG. 5B shows an image of the concept of the first region residence time of the slab.

Let the average value of the transit time measured about each block in a slab be the 1st field residence time: alpha ₁ of an object slab. That is,
α ₁ = (A + B + C + D) / 4
= (14 + 14 + 15 + 15) ÷ 4
= 14.5 (minutes)
And

  Similar processing is performed for the second and subsequent areas.

  The steel piece cutting method of the present embodiment described above was applied to strands in which the molten steels having the components shown in Table 1 below were cast by a continuous casting machine having the characteristics shown in Table 2.

  At that time, the number of divisions of the continuous casting machine shown in FIG. 1 is N = 3, the vertical region including the mold 14 as the first region, the curved portion as the second region, and the horizontal portion as the third region. Was set respectively. However, it is not limited to this.

At the same time, the following parameter (2-1), (2-2), and (2) are applied to the first area, the second area, and the third area, respectively, as an expression (2) that is applied to the expression (1) for calculating the parameter: β. Each formula of (2-3) is set and each coefficient of a ₁ , b ₁ , c ₁ , a ₂ , b ₂ , c ₂ , a ₃ , b ₃ , c ₃ is a constant determined by regression calculation. Using.

β ₁ = a ₁ · α ₁ ² + b ₁ · α ₁ + c ₁ (2-1)
β ₂ = a ₂ · α ₂ ² + b ₂ · α ₂ + c ₂ (2-2)
β ₃ = a ₃ · α ₃ ² + b ₃ · α ₃ + c ₃ (2-3)

  Here, in the case of the pinch roll segment, the machine is up to the final roll, and when there is a single pinch roll after the segment, the machine is up to the final roll of the final segment before the pinch roll.

  According to this embodiment, when the formulas (2-1), (2-2), and (2-3) are applied, the following formula (5) is used without dividing the continuous casting machine as a comparative example. When applied, the results of the obtained additional weights are shown in comparison with FIG.

  Here, the added weight is given by {(actual weight−claimed weight) / claimed weight} × 100 (%). However, the actual weight is the actual weighed weight.

β = a · α ² + b · α + c (5)

  Here, α is the residence time in the machine until it passes through the full length of the continuous casting machine, and constants determined by regression calculation are similarly used for the coefficients a, b, and c.

  As described above, according to the present invention, it is possible to perform the cutting length correction considering the speed fluctuation for each region divided in the machine, instead of the cutting length correction based on the simple dwell time in the machine. The variation in added weight (σ) can be improved from 0.7% to 0.4% of the comparative example, the variation in added weight can be reduced, and the average value of the added weight can be lowered. It has become possible to improve the yield.

  Next, the improvement effect of the cutting correction coefficient: β by the correction considering the region residence time (speed) fluctuation according to the present invention will be described in more detail with reference to a specific example shown in the chart of FIG.

In the conditions of Table (A), t ₁ , t ₂ , and t ₃ correspond to α ₁ , α ₂ , and α ₃ in the equations (2-1), (2-2), and (2-3), respectively. T corresponds to α in the equation (5). The sections 1 to 3 correspond to the first area to the third area.

In the reference example of Table (B), the following formula (5 ′) corresponding to Formula (5) in Examples (1) to (3) of Table (A) above: β = a · t ² + b · t + c ( 5 ')
The result of the additional weight calculated | required by applying is shown.

In the present invention of Table (C), the following (2-1) respectively corresponding to the formulas (2-1), (2-2), and (2-3) for Examples (1) to (3). The result of the additional weight calculated | required by applying each formula of '), (2-2'), (2-3 ') is shown. In the table, β is β = β ₁ + β ₂ + β ₃ .

β ₁ = a ₁ · t ₁ ² + b ₁ · t ₁ (2-1 ′)
β ₂ = a ₂ · t ₂ ² + b ₂ · t ₂ (2-2 ′)
β ₃ = a ₃ · t ₃ ² + b ₃ · t ₃ + c ₃ (2-3 ')

  From the results of Tables (B) and (C), it can be seen that the variation of the added weight with respect to the target of 2.2% is greatly reduced by the present invention.

  From these results, according to the present invention, it is possible to perform correction in consideration of speed fluctuation for each region, not correction based on simple residence time from the meniscus to the machine end E or the pinch roll 18, and further. It was possible to improve the yield.

  In the above embodiment, an example in which the continuous casting machine is divided into three regions has been described, but it goes without saying that it may be two regions or four regions or more.

  In addition, although the quadratic equation is shown as the equation (2) for obtaining the correction coefficient for each region, the order is not limited to this and is arbitrary. However, in practice, it is preferable to use a linear expression or a quadratic expression for two or more regions.

Here, the dividing method and the cutting correction coefficient β _N of the continuous casting machine can be determined as follows, for example.

The number of combinations to be examined is a combination of dividing No. 1 to No. 13 in FIG. 8 which is a division method of a continuous casting machine into three or two divisions, and β _N (N = 1 to 3) of each section is a quadratic expression. Or it is decided by the combination made into a primary formula, and there are 576 kinds in total. All the additional weight data (in-machine dwell time, target β, etc.) is divided into two, and a certain division method is applied to one of the data to perform regression to calculate the coefficient of β. The obtained regression equation is applied to the other data, the correlation coefficient R value at that time is confirmed, and the division method having the largest R value in all combinations is the mathematically optimal division method and the order of the regression equation. .

  A division method that maximizes the R value may be determined for each type or casting size (strand width, strand thickness). It is preferable to check the correlation coefficient R value in each combination and find a division method that can be used in common and has a large R value.

  What is necessary is just to determine the order of the formula which calculates (beta) for every kind and every casting size (strand width, strand thickness). For example, the primary equation was adopted because the R value of the primary equation was large in the cultivar shown in FIG. 7, but the secondary equation was adopted in the same division method as the cultivar shown in FIG. Since the R value is large in some cases, the quadratic formula was adopted.

10 ... Ladle 12 ... Tundish 14 ... Mold
16 ... Laura apron (guide roll)
18 ... Pinch roll 20 ... Slab cutter 22 ... Major roll 30 ... Process computer

Claims (4)

Using a continuous casting machine, the length of the strand withdrawn from the mold by the pinch roll is obtained by correcting the nominal unit weight by the correction coefficient calculated based on the casting condition information, and having the required billing length In the method of cutting a steel piece to be cut into a steel piece,
The continuous casting machine is divided into a plurality of regions along the casting direction, a corresponding fixing point is set at the end of each region, and the final fixing point is solidified over the entire cross section of the strand. Set at the downstream position of the continuous casting machine,
The method of cutting a steel slab characterized by reflecting the region residence time in which the strands at positions corresponding to the steel slab to be cut stay in each region in calculating the bill length of the steel slab. The reflection of each region residence time is expressed by the following equation: β = Σβ _N
N: Any integer greater than or equal to 2 β _N = a _N · α _N ^m + b _N · α _N ^m-1 + ... + g _N · α _N + h _N
α _N : N-th region residence time (sec.)
a _N , b _N ,..., g _N , h _N : constants
m: Cutting correction coefficient obtained by an arbitrary integer of 1 or more: The following formula multiplied by β Cutting instruction length (hot value) = requested slab length (cold value) × hot correction coefficient × β
It implement | achieves by hot correction coefficient = hot length / cold length, The cutting method of the steel piece of Claim 1 characterized by the above-mentioned.   The strand at a position corresponding to the slab to be cut is subdivided into blocks of a predetermined length, and the fixed end corresponding to the rear end of each block passes through the start end of each area in units of each block. 3. The steel according to claim 1, wherein a passing time until passing through the point is measured, and an average value of the passing times measured for all blocks is set as a region residence time of the corresponding region of the slab. How to cut a piece.   The method for cutting a steel slab according to any one of claims 1 to 3, wherein the fixing point of the final region is the pinch roll or the machine end position.