JP4414601B2 - Slab compression force control device for continuous casting machine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
It is an object of the present invention to prevent cracking of the inside and surface of a slab by giving an appropriate compressive force to the slab at a correction point from the curved part to the horizontal part in a curved continuous casting machine. The present invention relates to a slab compression force control device for a continuous casting machine.
[0002]
[Prior art]
A conventional compressive force control method will be described with reference to FIG. In the curved continuous casting machine in which molten steel is poured from the mold 1 as shown in FIG. 1, the slab 2 is drawn from the curved portion to the horizontal portion by the pinch rolls 3 and 4. At that time, at the curvature change point P ₁ (correction point 5) in the middle, stress is generated by correcting the arc cast piece horizontally. The direction is tensile stress with respect to the shell on the upper surface (L surface) side of the slab and compressive stress with respect to the shell on the lower surface (F surface) side of the slab. Of these, the tensile stress generated in the upper shell of the slab also affects the inside of the shell and causes internal cracks near the mechanically fragile solidification interface, which also causes surface cracking or promotion on the surface. . Therefore, in order to prevent cracking of the slab 2, a braking force is generated on the driving roll 4 in the horizontal portion so as to eliminate distortion caused by tensile stress at the correction point 5, and the slab 2 is intentionally compressed at the correction point 5. (Hereinafter, this is abbreviated as compression casting).
[0003]
In order to realize compression casting, in the prior art, the drive motor for the pinch roll 3 in the curved portion is controlled by the speed control device 6, and the drive motor for the pinch roll 4 in the horizontal portion is the torque control device 7. Thus, constant torque control is performed.
[0004]
First, the speed control device 6 of the bending portion pinch roll (PR) 3 performs speed control with a drooping characteristic independently for each drive roll 3 with respect to a common speed command value. In order to maintain a uniform load balance, the average of the individual roll speeds is regarded as the overall slab speed (for example, in Japanese Patent Application Laid-Open No. 56-122601, “Control Device for Slab Pulling Device in Continuous Casting Equipment” The result of calculating the roll speed of the bending portion pinch roll 3 by the representative speed calculation unit 8 is regarded as the entire slab speed.) The overall slab speed is fed back to control the speed of the entire slab. The control output is equally distributed to each drive roll 3 as a torque correction command. Here, the representative speed control unit 9 sends a torque correction command to each speed control device 6 based on the result calculated by the representative speed calculation unit 8.
[0005]
On the other hand, the constant torque control of the horizontal portion pinch roll (PR) 4 is set in order to obtain the compression force [ton] generated at the correction point 5, and is divided by the number of horizontal portion driving pinch rolls 4; The torque setting value of each pinch roll 4 is used.
[0006]
[Problems to be solved by the invention]
FIG. 2 is a graph showing a time chart of the bending portion pinch roll generation force when the conventional control is performed. As can be seen from the graph, periodic torque fluctuations occur in the curved portion where the speed control is performed. When frequency analysis (FFT) was performed on this torque fluctuation signal, it was found that the roll rotation period in the horizontal portion was the cause of torque fluctuation.
[0007]
In other words, this is because the fluctuation of the drawing load (resistance) caused by the eccentricity of the roll 4 at the horizontal part, the bending of the roll 4, etc. is controlled by the constant torque control at the horizontal part where the roll occurs. For this reason, it cannot be removed at the horizontal portion, and the bending portion performing the speed control is loaded with the load fluctuation. When this situation is seen by the stress acting on the slab 2, the load fluctuation generated in the individual rolls 4 in the horizontal portion described above is accumulated as the stress fluctuation toward the upstream side, and the speed control execution region and the torque control are accumulated. The maximum stress fluctuation is given in the vicinity of the correction point 5 which is the boundary of the implementation area. This situation is shown in the stress distribution diagram of FIG. This figure is a distribution diagram showing the range of compressive force fluctuation that occurs when the slab 2 is stopped for a certain period of time at a joint between different steel types and then restarted over the entire length of the continuous casting machine. From this, it is understood that the maximum stress fluctuation (about 10 to 20 tons) occurs at the correction point 5 (between the 47th roll and the 57th roll in FIG. 3). At this time, when the compressive force is at the lower limit, the compressive force necessary for canceling the distortion due to the tensile stress generated in the upper shell of the slab at the correction point 5 described above cannot be secured, and the slab 2 is cracked. It is estimated to be. Here, as a countermeasure, a method of increasing the absolute amount as much as possible to secure a sufficiently necessary compressive force even if the compressive force fluctuates is conceivable. The slip limit between the piece 2 and the roll is exceeded, which is impossible.
[0008]
Accordingly, an object of the present invention is to ensure a good slab quality by reducing the above-described fluctuations in the compression force and always applying an appropriate compression force to the slab.
[0009]
[Means for Solving the Problems]
The present invention for achieving the above-described object is to perform control for applying an appropriate compressive force to each part of a slab in a curved continuous casting machine having a roll drive motor and a drive control device for each pinch roll. The slab compressive force control device for each of the pinch rolls , the individual roll speed control means for performing speed control with a drooping characteristic for each pinch roll , and the drawing speed of the entire slab based on the slab transport speed The slab speed control means to be controlled and the plurality of pinch rolls are divided into a plurality of groups, and the estimated value of the pulling resistance generated in each group is output to the output of the slab speed control means and the pinch roll pressure of each group and pullout resistance estimating means for determining, based, externally supplied, the compressive force between the respective groups, and the target value of the distribution in the slab longitudinal direction of the output by the pulling resistance estimating means That the speed of the based on the estimated value of the pull-out resistance generated by the group, define a pinch roll torque target value to be output for each group, the individual roll speed control means corresponding to the pinch roll torque target value Speed correction amount setting means for determining a correction amount.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Below, the slab compression force control apparatus of the continuous casting machine which is one Embodiment of this invention is demonstrated with reference to drawings. FIG. 9 is a diagram showing an overall configuration of a continuous casting machine to which a slab compression force control device according to an embodiment of the present invention is applied. Such a continuous casting machine is a so-called curved type in which molten steel is poured from the mold 1 and the cast piece 2 is pulled out from the curved portion to the horizontal portion by a plurality of pinch rolls 3 and 4. Here, for each of the pinch rolls 3 and 4, a roll drive motor and a drive control device are individually provided. The slab compression force control device of the present embodiment includes a representative speed calculation unit 8, a compression force distribution setting circuit 11, a slab speed control device 23, a drawing resistance estimation device 24, a speed correction amount setting device 25, An individual roll speed control device 26 is provided. In the present embodiment, components having the same functions as those of the conventional ones are denoted by the same reference numerals, and detailed description thereof is omitted.
[0011]
In order to solve the above-described problems, the present invention stops the conventional technique of “constant torque control in a pinch roll group in a horizontal portion”, divides a plurality of pinch roll groups into a plurality of groups, and only a curved portion. In addition, the speed control with drooping characteristics is performed in all the groups including the horizontal part, and the torque (force) generated by each group is controlled using the characteristics, and the torque to be generated for each controllable group ( By appropriately setting (force), control is performed to apply an appropriate compressive force to each part of the slab.
[0012]
Therefore, in the following, first, (1) a method of controlling the torque (force) generated by the motors of each group using the drooping characteristic while performing speed control will be described. Next, (2) a torque (force) setting method to be output by each pinch roll group in order to give an appropriate compressive force according to the site over the entire length of the slab in the continuous casting machine will be described.
[0013]
First, (1) speed control with drooping characteristics and a motor driving force (or torque) control method using the characteristics will be described.
[0014]
FIG. 4 shows a circuit configuration of an individual roll speed control device 26 having a general drooping characteristic (Droop). The individual roll speed control device 26 includes a speed control device 26a and a droop rate control device 26b. In this example, drooping characteristics are realized by returning 10% of the output voltage of the speed control device 26a to the input circuit of the operational amplifier (droop characteristic ratio: droop ratio α = 0.1 = 10%). As described above, in the speed control having the drooping characteristic, when the motor torque command (≈motor torque record) increases to the + side, the speed command is automatically decreased, and conversely, the motor torque command (≈motor torque record) decreases to the − side. When it changes, the circuit automatically increases the speed command. In the control block diagram, the output of the speed control device 26a is negatively fed back by the droop rate control device 26b.
[0015]
Thus, when a single rigid body (in this case, a slab) is transported by a plurality of rolls driven by a plurality of motors due to the characteristics of the circuit that increases or decreases the motor speed command according to the motor torque results, The actual speed is not set to zero for the given speed command, and in the steady state, the force balance between the rolls is achieved, and the speeds of all motors are balanced and matched (in this case, all The matched speed of the motor is the slab conveying speed.)
[0016]
Thus, the drooping characteristic is a method of changing the speed command according to the output torque of the motor and balancing a plurality of motor output torques, but from the opposite view, this method balances the speeds of a plurality of motors. In the balanced state (that is, the steady state), the torque (force) output from each motor can be calculated backward from the speed deviation of each motor. In other words, when a long rigid body is conveyed by a plurality of motors that perform speed control with drooping characteristics as described above, the torque (force) results output by each motor are the speed deviations (= individual speeds) of each motor. Command-conveying speed), droop rate, motor capacity, etc. Specifically, the relationship between the current value I _i indicating the force (torque) generated by the electric motor and the speed record V _i is as shown in FIG.
V _i = V _iSET −α _i · V _0i · (I _i / I _0i ) (1)
It can be expressed as. here,
V _i : i-roll speed [m / sec]
V _iSET : i-roll speed command [m / sec]
α _i : i-roll drive motor droop rate (Drooping coefficient) [−]
V _0i : i-roll drive motor rated speed [m / sec]
I _i : i-roll drive motor current [A]
I _0i : i-roll drive motor rated current [A]
It is. The subscript “i” indicates that the physical quantity relates to the i-th pinch roll.
[0017]
In particular, the line speed V (which is equal to the total roll speed because it is a steady state under this condition) is known under the assumption that “the stretch and shrinkage of the conveyed product and“ roll slip ”are negligibly small”. In this case, since V _i = V (known amount), it is possible to control each roll drive motor generating force by each roll speed command V _iSET .
[0018]
That, i the roll speed deviation V _ISET -V _i needed to generate a force of roll drive motor is F _i, as in the following equation, drooping factor, rated speed, parameters G _i defining the rated output or the like it can be seen that a may be an amount obtained by multiplying the desired driving force F _i. That is,
V _iSET −V _i = G _i · F _i ··· (Equation 2)
G _i = (α _i · V _0i ² ) / P _i ··· (Equation 3)
It becomes. here,
F _i : i-roll drive motor generating force [N]
α _i : i-roll drive motor Droping coefficient [−]
V _0i : i-roll drive motor rated speed [m / sec]
H _fi : A coefficient [N / A] for converting the i-roll drive motor current into the generated force. That is, F _i = H _fi · I _i
P _i : i-roll drive motor rated output [W], that is, P _i = H _fi · I _{0 i} · V _{0 i} . Thus, in the speed control system having the drooping characteristic, the driving force can be controlled by the feedforward control as described above.
[0019]
In the above description, relational expressions in units of rolls are shown. However, these relational expressions can be read as relations in units of roll groups composed of a plurality of roles. In that case, _Pi is the sum of the rated outputs of the roll drive motors included in the group.
[0020]
Next, (2) a method for setting the pinch roll group torque (force) for applying an appropriate compressive force according to the slab part will be described.
[0021]
The local force balance seen directly under any roll or roll group is as shown in FIG.
C _i-1 + τ _i = C _i + L _i (4 formulas)
Can be expressed as here,
τ _i : i group motor generated force (torque)
L _i : Pull-out resistance in i group C _i : Slab compression force between i + 1 roll group and i roll group (i group rear compression force)
It is. When the roll diameter is r, there is a relationship of τ _i = F _i × r between the torque τ _i and the motor generated force F _i . Usually, since the roll diameter r is constant, τ _i and F _i can be regarded as the same. Therefore, in this specification, the torque τ _i is also referred to as “force”.
[0022]
(Formula 4) is transformed into τ _i = C _i −C _i−1 + L _i . At this time, C _i and C _i-1 are regarded as inter-roll group stress (compressive force) set values C _iSET and C _i-1SET respectively, and L _i can be estimated, and the estimated value is defined as L _iEST . Then, if τ _i is _regarded as each i-th roll group driving force setting value (pinch roll torque target value to be output for each group) τ _iSET , (Expression 4) is _expressed as τ _iSET = C _iSET −C _i−1SET + L _iEST (5 formulas)
It becomes possible to grasp like. Thereby, slab stress setting control can be realized in which the slab stress setting value between the i + 1 roll group and the i roll group is C _iSET .
[0023]
At this time, the method of estimating the pullout resistance L _i at the i group is performed as follows. In other words, the explanation so far was based on a balance of local forces around a roll group, but the external force for the entire slab is the sum of all roll driving forces and the sum of all roll pulling resistances. It is obvious from the law of inertia that the sum is zero as long as the slab is cast at a constant speed. That is, Στ _i = ΣL _i (6)
Therefore, the total sum (ΣL _i ) of all roll drawing resistances can be regarded as measurable from measurable τ _i . Therefore, under the assumption that the pulling resistance is proportional to the drag force of the roll against the slab, each L _i can be estimated by proportionally dividing ΣL _i by each measurable pinch roll pressure. Note that the total sum (ΣL _i ) of all roll drawing resistances is equal to the total sum (Στ _i ) of all roll driving forces as shown in (Equation 6). Since this matches the operation output (total torque command), this is used in the implementation.
[0024]
In other words, as described above, the force (torque) τ _iSET to be generated by each pinch roll group is determined based on the concept of (2), and the force τ _iSET is realized by speed control based on the concept of (1). By giving a speed command correction value ΔV _i = V _iSET −V _i to each pinch roll group, it is possible to simultaneously control the force (torque) while performing the speed control.
[0025]
7 and 8 are diagrams illustrating a configuration example of a slab compressive force control device of a continuous casting machine according to an embodiment of the present invention. In this example, the grouping method that has been conventionally divided into two groups of a curved portion and a horizontal portion is reviewed, and a plurality of pinch rolls are subdivided into six groups. In such a slab compressive force control device, as shown in FIGS. 7 and 8, the slab speed signal 21 output from a slab speedometer (rotary speed meter) or the like installed on a non-driven roll is used in accordance with the operating conditions. A deviation from the determined slab speed target signal 22 is input to the slab speed control device 23. The output ΣL _i of the slab speed control device 23 calculated by the PI calculation is input to the drawing resistance estimation device 24.
[0026]
The drawing resistance estimation device 24 apportions the output of the slab speed control device 23 based on the sum of the roll pressure setting values belonging to each group for each group. That is, if the sum of the roll pressure setting values of the i-th group is RP _i ,
K _i = RP _i / ΣRP _i (7)
By applying a pulling resistance distribution ratio K _i to the output .SIGMA.L _i of the slab speed control device 23 for the i-group determined by, for prorated output .SIGMA.L _i of the slab speed controller 23 to the value L _IEST for each group . Each _apportioned value L _iEST is output to the speed correction amount setting device 25. In FIG. 7 and FIG. 8, the suffix “EST” is omitted.
[0027]
The speed correction amount setting device 25 _{obtains the} force τ _iSET to be output by each group based on the balance relationship of the above (4 formula) and (5 formula), and in (2 formula) and (3 formula). Using the conversion coefficient G _i from the i-roll drive motor generated force to the speed deviation in the speed control with the drooping characteristic shown, the speed deviation command (speed correction amount) ΔV _i = V _iSET −V _i to each group is obtained. . That is, from (Equation 5), the force τ _iSET to be output by the i-th group is between the compression force target value C _iSET between the i + _1th group and the ith group and the ith group and the i− _1th group. _Therefore , the target speed compensation amount ΔV _i is calculated by addition / subtraction as shown in FIGS. 7 and 8 because the i-th group pull-out resistance L _iEST is added to the difference from the target compression force value C _i−1SET . It will be. A speed command V _i + ΔV _i for each group corrected by the target speed compensation amount ΔV _i is given to each individual roll speed control device 26, thereby individually controlling the speed of the pinch roll. In this case, V _i = V (total roll speed), and in FIG. 7 and FIG. 8, the subscript “SET” is omitted.
[0028]
FIG. 9 shows a configuration example of the entire continuous casting machine to which the slab compression force control device according to an embodiment of the present invention is applied. As described above, the grouping method that has been conventionally divided into two groups of a curved portion and a horizontal portion is reviewed, and the plurality of pinch rollers 3 are subdivided into six groups. As a result, the compression force setting point (correction point 5), which was 1 point in the past, increased to 5 points from P _{1 to} P ₅ . Conventionally, the pinch roll control has been speed control for the curved portion and torque control for the horizontal portion, but in this embodiment, the pinch roll control is all changed to speed control with drooping characteristics, and speed correction ΔV _{1 to} ΔV ₆ are added.
[0029]
For example, taking the first group as an example, ΔV ₁ is calculated as follows. That is, the target value ΔV ₁ of the first group torque is obtained by adding the drawing resistance distribution ratio K ₁ for the first group to the total torque command ΣL _i that is the output of the slab speed control device (representative speed control device) 23 ( L 1 _EST ) is added with the output value A ₁ of the compression force distribution setting circuit 11 and this addition is multiplied by the conversion factor G ₁ .
[0030]
The compressive force distribution setting circuit 11 calculates A _{1 to} A ₆ as follows. That is, as shown in FIGS. 7 to 9, based on the inter-roll group compressive force setting value C _iSET input from the outside,
A ₁ = Compression force setting value C _1SET
A ₂ = Compression force setting value C _{2SET −Compression} force setting value C _1SET
...
A _i = compression force setting value C _{iSET −compression} force setting value C _i−1SET
...
A ₆ = _{−Compressive} force setting value C _5SET
It becomes. Here, C _iSET is the compression force setting value at point P _i , that is, the compression force setting value between the i group and the i−1 group.
[0031]
Next, the effect of the slab compression force control apparatus of this embodiment will be described with reference to FIGS. FIG. 10 is a diagram showing the compression force fluctuation reducing effect of the slab compression force control device of this embodiment in comparison with the conventional control, and FIG. 11 is a diagram showing the quality improvement effect brought about by this.
[0032]
First, FIG. 10 shows a time chart of fluctuations in compressive force near the correction point before and after the temporary stop time zone due to the joint at the time of continuous casting of different steel types. Here, the third roll group and the first roll The compressive force performance between 4 roll groups is shown. From FIG. 10, it can be seen that the fluctuation of the compression force after the restart is particularly reduced in the new control compared to the conventional control. Thus, since the fluctuation | variation of compressive force was able to be reduced, the distortion which causes the internal crack of a slab can be canceled, and it can be anticipated that the amount of flaws generated is reduced. FIG. 11 shows the result of the investigation related to this.
[0033]
FIG. 11 is a comparison of the amount of wrinkles generated in the same cast when one strand is subjected to conventional control and the other strand is subjected to new control in a two-strand continuous casting machine. From FIG. 11, it was found that the strands introduced with the new control had a reduction in wrinkles as intended, particularly in the vicinity of the correction point (machine length 16 m to 24 m), compared with the strands of the old control method.
[0034]
In addition, this invention is not limited to said embodiment, A various deformation | transformation is possible within the range of the summary.
[0035]
【The invention's effect】
As described above, the slab compressive force control device for a continuous casting machine according to the present invention has a drawing load generated by eccentricity of the drawing roll, bending of the roll, etc. with respect to the slab being cast by the continuous casting machine. Resistance) fluctuation can not be removed at the horizontal part where it is generated, excessive stress (compression force) fluctuation near the correction point can be reduced, and appropriate compression force can always be applied to the slab. Therefore, it is very useful in that it can prevent cracks in the slab and on the surface, and provides essential performance for ensuring good slab quality.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of an entire slab compression force control system according to a conventional method.
FIG. 2 is a time chart of bending portion pinch roll generation force during conventional compression force control.
FIG. 3 is a distribution diagram of fluctuation amounts of compressive force between pinch rolls during conventional compressive force control.
FIG. 4 is a block diagram showing an individual roll speed control circuit with a drooping characteristic.
FIG. 5 is a diagram showing drooping characteristics.
FIG. 6 is a diagram showing a balance of forces immediately below an arbitrary pinch roll.
FIG. 7 is a configuration example of a slab compression force control device of a continuous casting machine according to an embodiment of the present invention.
FIG. 8 is a configuration example of a slab compression force control device of a continuous casting machine according to an embodiment of the present invention.
FIG. 9 is a configuration example of the entire continuous casting machine to which the slab compression force control device is applied.
FIG. 10 is a time chart showing the effect of reducing fluctuations in compressive force by the slab compressive force control device of the present embodiment.
FIG. 11 is a graph showing the quality improvement effect by the slab compressive force control device of the present embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Mold 2 Casting piece 3 Bending part pinch roll 4 Horizontal part pinch roll 5 Correction point 6 Speed control device 7 Torque control device 8 Representative speed calculation part 9 Representative speed control device 11 Compression force distribution setting circuit 21 Casting piece speed signal 22 Casting piece Speed target signal 23 Slab speed control device 24 Drawing resistance estimation device 25 Speed correction amount setting device 26 Individual roll speed control device 26a Speed control device 26b Droop rate control device

Claims (1)

In the bending type continuous casting machine having a roll drive motor and a drive control device individually for each pinch rolls, a cast piece compressive force control device for performing control to impart a proper compressive force on the slab each site,
For all pinch rolls, individual roll speed control means for performing speed control with drooping characteristics for each pinch roll,
A slab speed control means for controlling the drawing speed of the entire slab based on the slab conveyance speed;
A plurality of pinch rolls are divided into a plurality of groups, and a drawing resistance estimation means for obtaining an estimated value of the drawing resistance generated in each group based on the output of the slab speed control means and the pinch roll pressure of each group,
Externally supplied, the compressive force between the respective groups, and the target value of the distribution in the slab longitudinal direction, output by the pulling resistance estimating means, on the basis of the estimated value of the pull-out resistance generated by the group A pinch roll torque target value to be output for each group , a speed correction amount setting means for determining a speed correction amount of the individual roll speed control means corresponding to the pinch roll torque target value;
A slab compressive force control device for a continuous casting machine.

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