JP3478263B2 - Control method of continuous casting - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control method for continuous casting, in which an unsolidified slab continuously drawn from a mold is rolled down.

[0002]

2. Description of the Related Art As a typical method for producing a thin plate, there is a method of rolling and processing a slab produced by continuous casting in a rolling process. In this method, it is necessary to reheat the air-cooled slab after hot pressing, which is disadvantageous in terms of energy consumption.

In recent years, development of a hot rolling direct-coupling process in which the slabs coming out of the continuous casting machine are supplied to the pressure-rolling machine as they are, has been particularly developed. Efforts have been made to develop a continuous casting technique for thin cast pieces that can be omitted.

As a method for producing a thin slab, a slab drawn from a mold is further cooled while being rolled by a plurality of roll pairs of a drafting device while the unsolidified phase remains in the central portion. There is a non-solidification rolling method for continuously producing. At the start of casting, the dummy bar and the low temperature part at the tip of the slab pass, so the roll pair spacing in each reduction device is set to be equal to the thickness of the mold, but when casting becomes stable, the rolls are rolled sequentially in each reduction device. When the pair spacing is narrowed and the cast piece thickness reaches the target value, thin cast continuous casting is performed with the roll pair spacing maintained at the same value (steady state). The transition from the start of rolling to the target thickness of the slab is called the transient state.

In the unsolidified rolling method, it is important to control the thin slab to a predetermined thickness. The thickness of the thin slab is determined by the spacing between the roll pairs, and the spacing between the rolls is determined by the rolling position of the rolling down device and the deformation of the structure that supports the rolls. Determined by the reaction force (also called the rolling force).

The present inventors have previously disclosed in WO97 / 14522 that a plurality of reduction devices are used to perform reduction, a reference reduction device is defined among these reduction devices, and position control is performed in the reduction device upstream of the reference reduction device. The technique of improving the precision of the thickness control of the thin slab by performing the control of the system and the control of the rolling force control system in the downstream side rolling down device is disclosed.

[0007]

Problems to be Solved by the Invention WO 97/145
In the technique disclosed in Japanese Patent No. 22, the rolling reduction device arranged on the downstream side of the reference rolling reduction device attempts to make the interval between the roll pairs constant by compensating the rolling reaction force received from the slab. In the same technology, the standard reduction device is selected from the reduction devices near the point where the solidified shell thickness (total of both surfaces) of the slab is equal to the target thin slab thickness, but the final solidification position is determined by the casting conditions. Because of the change, the reference reduction device cannot be fixed to the reduction device at a specific location. Therefore, each rolling down device needs to have both the function of the position control system and the function of the rolling down force control system, and it is necessary to switch these at any time. Since the rolling down device of the continuous casting machine is exposed to a very severe environment such as a narrow installation space, high temperature, dripping of cooling water, or dripping of molten iron at breakout, a hydraulic system is favored as the rolling down control device. Therefore, there is a problem that the hydraulic control system (pipe, control valve, switching valve, control device) becomes complicated in order to make the control system capable of switching the two control functions of the pressure reduction control device.

An object of the present invention is to provide a control method for continuous casting, which can realize improvement in thickness control accuracy of thin cast pieces at low cost.

[0009]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventor has conducted studies and obtained the following findings. (1) In order to deal with the problem of complication of the control system disclosed in the above-mentioned WO97 / 14522, each rolling reduction device is controlled only by a position control system, and if the function of the rolling down force control system is omitted, The control system, especially the hydraulic control system, can be simplified. In this case, similarly to the method disclosed in the above-mentioned WO97 / 14522, the rolling-down device at the position closest to the position where the solidified shell thickness of the slab is equal to the thin slab target thickness is defined as the reference rolling-down device and positioned. Take control. In the rolling down device on the upstream side of the reference rolling down device, if the rolling position setting value is set so as to gradually reduce the thickness from the thickness of the mold to the slab thickness at the location of the reference rolling down device, the position control method is controlled. , No unreasonable deformation of the solidified shell in the unsolidified state. Further, in the rolling down device on the downstream side of the reference rolling down device, by controlling the same value as the rolling down position actual value of the reference rolling down device as the rolling down position set value of the rolling down device by the position control method, all the rolling down devices are positioned. It can be a control method.

(2) However, if the position control system control is performed with the reduction position target of the reduction device downstream of the reference reduction device of the above item (1) being the same value as the actual reduction position of the reference reduction device, thin casting is performed. Decrease in thickness accuracy and overpressurization occur. The decrease in the accuracy of the thin slab thickness is due to the elastic deformation of the reduction device and its supporting structure. Also, in the over-pressure reduction, after the start of casting, in the transitional state where the thickness is reduced to the target thin ingot thickness, the solidification completed part cannot be forced when the reduction position is changed or when the casting conditions such as the casting speed change even in the steady state. Due to the reduction. In order to prevent this, it is preferable to add a correction considering the rolling force to the rolling position set value.

(3) As the correction value considering the reduction force, a value considering the rigidity of the reduction device and its supporting structure in the reduction device on the downstream side of the reference reduction device and a predetermined reduction force on the slab. It is the sum of the values specified to be added. The value for applying a predetermined rolling force to the slab, if there is a non-solidified portion, and if there is no non-solidified portion, if the value is different, over-rolling down prevention and thin slab thickness control The accuracy can be improved.

(4) The value of the predetermined rolling force applied to the cast slab is the static pressure of molten iron when a non-solidified portion exists and the value that gives a predetermined rolling force to the solidified portion at the width end of the slab. When there is no solidified portion, it is preferable that the value be such that a predetermined rolling force is applied to the entire width of the slab.

The present invention has been completed based on the above findings, and its gist is as follows. (1) A continuous casting control method for obtaining a thin slab by reducing the unsolidified slab drawn from the mold with a plurality of reduction devices, and the thickness of the solidified portion of the slab among the plurality of reduction devices. Is defined as a reference reduction device at a position close to a position where the target thickness of the thin slab is the target thickness, and for the reference reduction device, a reduction position is set so that a predetermined reduction speed and a target thickness of the thin slab are obtained. Position control is performed by setting a target, and for the rolling down device upstream of the reference rolling down device, a rolling down position target is set and position control is performed so as to obtain a predetermined rolling down speed and rolling down amount of the unsolidified slab. System, and for the rolling down device downstream of the reference rolling down device, a value obtained by adding a correction value based on the rolling down force of the downstream rolling down device to the rolling position actual value of the reference rolling down device. Performing position control system control by setting it as a position target A method for controlling continuous casting, characterized by:

(2) The correction value based on the rolling down force of the downstream rolling down device is a value for compensating the elastic deformation of the rolling down device and its supporting structure, and the uncoagulated portion at the position of the rolling down device. In the existing state, a value based on the sum of the force resulting from the molten iron static pressure of the unsolidified portion of the slab center and the force that gives a predetermined rolling force to the solidified portion of the slab width end, or the rolling down device. The control method for continuous casting according to the above item (1), wherein in a state where there is no unsolidified portion at a location, the sum is a value based on a force that applies a predetermined rolling force to the entire width of the slab.

[0015]

1 is a block diagram of a hydraulic control system of a pressure reducing device. In the figure, reference numeral S is a cast piece, SG is a non-solidified portion of the cast piece S, SS is a solidified portion, 1 is a reduction device, 2 is a reduction position control device, 3 is a reduction cylinder, 31 is a reduction position for detecting a reduction position. A position sensor, 32 is an upper pressure sensor for detecting the pressure on the upper side of the reduction cylinder 3, 33 is a lower pressure sensor, 4 is a piston of the reduction cylinder 3, 5 is a reduction rod, 7 is a hydraulic pressure supply source, and 8 is a servo. Valve, 81
Is a servo amplifier, 82 is a servo position sensor, 15 is a reduction roll, and 16 is a roll. Among the symbols representing the signals between the respective sensors or mutual elements, S _0A is the actual value of the pressure reduction position of the pressure reduction cylinder 3, P _U is the upper pressure value of the pressure reduction cylinder, and P _L
Is a lower pressure value of the reduction cylinder, and S _C is a reduction position target value. Normally, the reduction mechanism is installed on the upper roll,
The roll 16 is fixed along a predetermined curve.

Although the drawing shows only one side (for example, the work side: WS) of the reduction device in detail, the similar reduction device is also present on the drive side (DS), and no inclination appears on both sides of the reduction roll. Controlled as.

A reduction position target value S _C is given to the reduction position control device 2, and the servo valve 8 is opened / closed according to a deviation between the reduction position target value S _C and the reduction position actual value S _0A from the reduction position sensor 31. The pressure oil supplied from the hydraulic pressure supply source 7 with respect to the deviation given to the servo valve 8 is supplied to the upper part or the lower part of the pressure reduction cylinder 3 depending on the valve position of the servo valve 8, and the position of the piston 4 changes. The reduction position sensor 31 detects this change in position, gives a feedback signal to the reduction position control device 2, and positions the piston 4 at the reduction position corresponding to S _C. The interval between the reduction roll 15 and the pair of rolls 16 (hereinafter referred to as the roll pair interval) is not determined only by the positioning of the piston 4, but a structure such as a frame that supports the reduction cylinder 3 by the reduction force ( The roll pair interval is a value obtained by adding a displacement corresponding to the deflection of the piston rod 5 (not shown). That is, even if the rolling position is set according to the target thickness of the cast piece, the cast piece becomes thick due to elastic deformation due to the pressing force.

[0018] The overpressure in the present invention, when viewed slab S in cross section, in FIG. 1, excessively to reduction width equivalent of W _SS width end portion of the slab S, or unsolidified In the state in which the width equivalent part of W _SG disappears, the entire width is excessively reduced, which causes a problem in quality such that a predetermined thin slab thickness cannot be obtained or cracks occur inside the slab. Cause.

Upper pressure sensor 32, lower pressure sensor 33
The function of will be described later. FIG. 2 is a schematic view showing the arrangement of the rolling down device. In the figure, the same elements as those in FIG. 1 are designated by the same reference numerals. The figure shows a steady state, that is, a state in which the target thickness of the thin slab is constantly obtained. The roll pair interval at the position of the reference reduction device 11 is equal to the target thickness of the thin slab, The uncoagulated part is almost absent or completely disappeared. As shown in the figure, in the rolling down devices 12 (plurality) on the upstream side of the reference rolling down device 11, the distance between the roll pairs is from the thickness T _{in of the} mold to the target thin cast piece thickness T _out (in the steady state, the rolling down is performed by the reference rolling down). Each rolling position is set so as to decrease gradually (corresponding to the roll pair distance of the apparatus), but T _in
It is preferable to set the difference between T _out and T _out to be evenly distributed. In the transient state, the reference reduction device 11 performs reduction at a predetermined speed determined by the casting conditions (steel type, casting speed, cooling conditions, etc.), so that the reduction position of the upstream reduction device 12 group also changes with time. To do.

On the other hand, in the reduction devices 13 (plurality) downstream of the reference reduction device 11, the actual reduction value S _0A of the reduction position of the reference reduction device.
Although the same value is given as the rolling position setting value, this rolling position setting value also changes with time. Here, although the unit of the rolling-down device 1 is independent, and the rolling-down position control of one or a plurality of roll pairs can be performed respectively, in the illustrated example, one rolling-down device is provided for each pair of rolls.

FIG. 3 is a schematic diagram showing a transitional state from the start of rolling down the unsolidified portion to the steady state. In the figure, the same elements as those in FIG. 1 or 2 are designated by the same reference numerals. In the figure, as the reference reduction device 11, a reduction device is selected where the total thickness of the solidified shells from both surfaces of the slab is closest to the target slab thickness. The thickness of the solidified shell can be calculated by empirical formula or heat transfer solidification calculation.
It can be determined by a known method.

At the start of casting, each reduction device has a mold thickness T _in
The rolling position is set so as to have the same roll pair interval as. When starting the reduction in order to obtain a thin cast piece having the thickness T _out , it is preferable to perform the reduction at a constant speed until the predetermined reduction position is reached in order to prevent a rapid change in the mold molten metal level. In this transient state, the slab thickness becomes thicker toward the downstream side of the reference reduction device, and the slab thickness also becomes thicker toward the upstream side. In this state, if the reduction position target of the reduction device on the downstream side of the reference reduction device 11 is set to the same value as the actual reduction position value of the reference reduction device, under the position control method, the slab on the downstream side is excessively reduced. As a result, the thickness of the thin slab becomes insufficient and quality problems occur. In addition, an error occurs between the pair of rolls due to elastic deformation of the reduction device and its supporting structure. In order to prevent these, it is necessary to add a correction value based on the reduction force to the reduction position setting value of the reduction device on the downstream side.

FIG. 4 is a block diagram showing the operating principle of the present invention. A control logic corresponding to the block diagram of the figure is included inside the reduction position control device 2 (see FIG. 1). In the figure, a symbol S representing a signal
_0A , P _U , P _L and S _C are the same as those shown in FIG.

In the rolling down device on the upstream side of the reference rolling down device, the ingot thickness is gradually reduced from the thickness T _{in of the} mold to the target thin ingot thickness T _out (for example, the difference between T _in and T _out ). (Equal distribution) Calculate each rolling position S _X. In the transient state, since each S _X is determined according to the reduction speed in the reference reduction device 11 (see FIG. 3), the set value changes with time. Since this S _X is set as the target value for the pressure reduction position, the A side is selected as the pressure reduction position setting switch 26 in FIG. Further, since the slab portion where the unsolidified thickness is sufficiently thick is rolled on the upstream side of the reference drafting device, it is not necessary to compensate the drafting force. Therefore, the pressure reduction compensation switch 25 of FIG. 4 is also selected on the A side, and the pressure reduction correction circuit shown in the upper half of the figure is disconnected. The A side is also selected in the reference reduction device for the same reason.

In the rolling down device on the downstream side of the reference rolling down device, the rolling down force compensation switch 25 is selected on the B side in order to perform the position control in consideration of the rolling down force. The rolling position set value is
The same value (S) as the actual value (measured value) of the reduction position of the reference reduction device
_0A ). Therefore, the rolling position setting switch 26 is selected to the B side.

The slab portion that must be prevented from being over-pressurized is the slab full width when the solidified portion and the solidified portion at both ends of the slab width on the downstream side of the standard reduction device disappear. In the present invention, control of overpressure reduction in the pressure reduction device 13 (see FIG. 3) on the downstream side of the reference pressure reduction device is performed as follows.

When the central portion of the slab is in an unsolidified state at the location of the reduction device, the static molten iron of the unsolidified portion (the width portion corresponding to W _SG in FIG. 1) is included in the reaction force applied to the reduction roll. Pressure P
Regarding the force equivalent to _Fe , it is not necessary to consider overpressure.
Further, in the solidified portion (width portion corresponding to W _SS in FIG. 1), it is desirable to support the slab at a predetermined reduction pressure α that does not result in deformation due to overpressure. Therefore, the reduction force that should be taken into consideration for the overpressure reduction is a force equivalent to the sum Pα of the total pressure of the molten iron static pressure P _Fe of the unsolidified portion and the predetermined reduced pressure α of the solidified portion (force not subject to overpressure compensation). ) Has been deducted.

When there is no unsolidified portion at the center of the slab, it is desirable that the slab is pressed down by a predetermined rolling force required to support the slab and not to cause deformation by rolling. The reduction force to be compensated is obtained by subtracting the reduction force corresponding to the predetermined reduction pressure P ₀ of the solidified portion from the total reduction force.

In FIG. 4, the rolling-down force calculator 21 calculates the rolling-down force F _A applied to the entire rolling-down roll from the hydraulic pressures P _U and P _L applied to the upper and lower sides of the piston and the areas A _U and A _L of the upper and lower surfaces of the piston. Calculate As will be described later, this F _A compensates for the deflection of the reduction cylinder of the reduction device, the piston rod, the reduction roll, and the frame structure supporting them,
Used to accurately set the roll pair spacing.

In the state where there is an unsolidified portion at the center of the slab, the force Fα that is not subject to overpressure compensation is the sum of the molten iron static pressure P _Fe of the unsolidified portion and the predetermined reduced pressure α of the solidified portion Pα, It is the product of the contact area A _S. Therefore, as shown in FIG. 3, when the slab having an unsolidified portion is pressed down, the pressure setting switch 24 of FIG. 4 selects the Pα side (Pα.
= P _Fe + α). In this state, Fα is changed to the effective rolling force adder 22.
The reduction force ΔF, which is the target of overpressure compensation, is subtracted from F _A at
Ask for.

A constant K _g (reciprocal of frame rigidity M: 1 / M multiplied by a correction gain Kα for fine adjustment, that is, K in consideration of elastic deformation of a frame supporting the pressing device, is applied to the pressing force ΔF. _g = Kα / M) to obtain the correction amount of the rolling position. The reduction position set value S _{0A of the} reduction device and the correction amount K _g * ΔF of the reduction position are added by the reduction position correction adder 23 to obtain a reduction position target value S _C.

Here, in the description of the present invention, the reduction position instructed to the reduction position control device 2 from a control computer (not shown) is set to the reduction position set value (S _0A or S _0).
X ), and the reduction position instructed from the reduction position control device 2 to the hydraulic control system shown in FIG. 1 is referred to as the reduction position target value (S _C ).

The P _Fe is the static pressure of the molten iron from the meniscus to the reduction device, and is obtained from the positional relationship between the meniscus and the reduction device. Further, α is a pressure that supports the solidified portion (width corresponding to W _{SS in} FIG. 1) at both ends of the slab as viewed in the cross section and does not deform this portion in a rolling manner, depending on the width and temperature of the solidified portion. Decided. To obtain α, the width and temperature of the solidified portion on both ends of the slab are obtained by solidification model calculation, and the deformation resistance value of this portion may be used for calculation. That is, this is a method in which the rolling force and the plastic deformation of the slab are obtained by a known calculation method known in the theory of rolling of plate materials, the upper limit αmax of the reaction force per unit area is obtained, and α is obtained from this. Alternatively, if the steel type for performing the unsolidified reduction and the cooling conditions are determined, the value obtained by the experiment may be prepared as a table of α according to the position of the reduction device without using the rolling theory or the like. .

When the rolling-down position control device is constructed as shown in FIG. 4, when the rolling-down device rolls down the slab in a transient state, the rolling-down force rises when the rolling-down pressure falls and the rolling-down force is the rolling-down force F of the rolling-down cylinder. Detected as an increase in _A , rolling position set value S _0A
Is corrected so as to decrease, and the target value of the reduction position is obtained to control the position control method. As a result, it is possible to prevent overpressure reduction in the downstream pressure reducing device. On the other hand, since the molten iron static pressure and the predetermined reduction pressure of the solidification portion are subtracted from the overpressure compensation, the reaction force against the molten iron static pressure and the predetermined reduction force required for the width solidification portion are secured. At the same time, the elastic deformation of the rolling-down device and its supporting structure is compensated, and a thin slab with high thickness accuracy can be obtained.

Next, a control method in a state where the unsolidified portion is reduced and the cast piece is solidified and the unsolidified portion disappears will be described. Since there is no unsolidified portion at the portion of the rolling down device downstream of the reference rolling down device, it is not necessary to consider the static pressure of the molten iron. Therefore, in these rolling reduction devices, the distance between the rolls is set to the target slab thickness, and therefore the rolling reduction position may be corrected to compensate the elastic deformation of the rolling reduction device. That is, when the steady state is reached, the input of the pressure setting switch 24 of FIG. 4 is switched to the P ₀ side. P ₀ gives a predetermined reduction pressure in a steady state of the reduction device on the downstream side of the reference reduction device, and can be calculated according to the above-described method of calculating α. With this configuration, it is possible to maintain an appropriate reduction pressure P ₀ while maintaining the reduction position control.

The advantage of using the position control for the pressure reducing device is to switch the input of the pressure setting changeover device 24 from the Pα side to the P ₀ side only by electrical switching inside the pressure reducing position control device 2 or switching of the control logic of the computer. Well, since there is no mechanical switching of the hydraulic control system, the equipment cost can be reduced and the reliability can be improved.

Although the above description has been made on the case where the reduction device is provided for each pair of the upper reduction roll 15 and the lower roll 16, one reduction device is provided for a plurality of roll pairs. The case will be described.

FIG. 5 is a schematic view showing the arrangement of segmented rolling down devices. Reference numeral 17 in the figure is a segment that holds a plurality of reduction rolls. The other same elements are denoted by the same reference numerals as those in FIG.

In FIG. 5, the reference reduction device 11 is a reduction roll (referred to as a reference roll) at a position where the total thickness of the solidified shell is the closest to the target slab thickness among the reduction rolls 15 at the most downstream side of each segment. It is a segment that includes.

There is one pair of reduction cylinders for each segment on one side of the width, and the upstream reduction cylinder 34 in the segmented reduction devices 11, 12, and 13, respectively.
And a downstream side reduction cylinder 35. The reduction position of each reduction roll 15 in the segment can be calculated geometrically from the reduction positions of the upstream reduction cylinder 34, the downstream reduction cylinder 35, and the arrangement state of the reduction roll 15.

As in the case where the reduction roll is an independent type,
In the segmented reduction device, in the segment 12 on the upstream side of the reference reduction device, a reduction position target is provided so that the reduction position of each reduction roll 15 equally distributes the difference between the thickness of the mold and the target thickness of the thin slab. It is preferable to control it.

In the segment 11 which is the reference pressure reducing device,
A reference rolling position is given to the reference roll, and the rolling positions of the other rolling rolls are the same as the rolling rolls of the upstream segment, the thickness of the mold and the thickness of the thin slab (the roll of the reference roll in the transient state. It is preferable to control the rolling position such that the pair interval) is a value that is evenly distributed.

In the segment on the downstream side of the segment of the reference reduction device, the elastic deformation of the support structure of the reduction device and the overpressure compensation are performed. The logic for these compensations can be derived from the block diagram of FIG. 4 where each reduction roll is controlled by an independent reduction device.

As shown in FIG. 4, the inputs P _U and P _L of the reduction force calculator 21 are the upper pressure value and the lower pressure of the upstream side reduction cylinder 34 and the downstream side reduction cylinder 35 (see FIG. 5), respectively. The value is entered. The rolling force F _A is calculated in the rolling force calculator 21 as follows.

F _A = (A _U1 * P _U1 −A _L1 * P _L1 ) + (A _U2 * P _U2 −A _L2 * P _L2 ) where the subscripts 1 and 2 are the upstream and downstream compression cylinders. Where A _U and A _L are the areas of the upper surface and the lower surface of each piston 4. Normally, the mechanical specifications of the upstream and downstream compression cylinders are the same, so A _U1 =
A _U2 , A _L1 = A _L2 . The contact area A _S between the pressing roll and the slab may be the total area of the plurality of rolls of the segment.

If the control system as described above is constructed,
The control method of the present invention can also be applied to a segmented rolling-down device.

[0047]

[Example] (Example 1) The test of the present invention was conducted using a thin cast continuous casting tester. First, a test was conducted on an apparatus in which a reduction device was provided independently for each pair of reduction rolls. The slab was made into a thin slab of 50 mm by pressing down the slab cast in a 90 mm thick mold.

FIG. 6 is a schematic diagram showing the relationship between the roll arrangement in the vicinity of the final freezing point and the unsolidified position. In the figure, the rolling down device 1A, which is the rolling down device closest to the position where the thickness of the solidified portion of the ingot is the target thickness of the thin ingot, is used as the reference rolling down device,
The downstream pressure reducing devices are numbered 1B and 1C, respectively. However, in the same drawing, the reduction position control device, the hydraulic system and the like are omitted, and the drawing of the reduction cylinder shows the reduction device as a representative.

The distance between the rolling rolls 15 at the positions of the rolling devices 1A and 1B is L1, and the distance between the rolls 1B and 1C is L2. The cast S in the figure shows the state before the start of the reduction.

FIG. 7 is a graph showing the temporal change of the rolling position of each rolling device in the vicinity of the final freezing point.
, (B) and (c) show the reduction positions of the reference reduction device 1A and the reduction devices 1B and 1C on the downstream side, respectively.

FIG. 7 (a) shows the transition of the reduction position in the reference reduction device 1A. As shown in FIG. 6, since the unsolidified thickness of the cast slab S is larger than the reduction target value at the reference reduction device, the actual reduction position value (shown by the solid line) follows the target at time t _A. The reduction was completed.

The solid line in FIG. 7B shows the actual rolling position of the rolling device 1B shown in FIG. The reduction position set value for the reduction device 1B is shown by a dotted line, and the same value as the reduction position actual value S _{0A of the} reference reduction device 1A is given (see FIG. 4).

The actual value of the reduction position could follow the set value (indicated by the dotted line) until the time indicated by t _B1 after the start of the reduction, but thereafter, the actual result of the reduction position does not follow the set value. We were able to follow up at time t _B2 . The reason for this is that, until the time t _B1 in the reference reduction device 1B, the unsolidified thickness is larger than the reduction amount, and the reduction progresses according to the set value (same as the actual reduction position actual value of the reference reduction device 1A). _This is because after _B1 , the uncoagulated part disappeared due to the reduction, and only the coagulated part was reduced. That is, from t ₀ to t _B1 , the Pα side is selected by the pressure reduction setting switch 24 (see FIG. 4), but after t _B1, the Pα side is switched to the P ₀ side, and the solidified slab is changed. This is because the over-compression compensation of (1) works and suppresses the compression more than a predetermined compression force based on P ₀ .

Here, when the casting speed is V _c , the time t _B1 at which the reduction target does not follow can be expressed as (t _B1 −t ₀ ) = L ₁ / V _c .

FIG. 7C shows the pressing position of the pressing device 1C shown in FIG. Since solidification of the slab has been completed at the location of the same reduction device, only the solidification portion was reduced, and the actual reduction position was delayed with respect to the reduction position set value (S _0A ). This is because the P ₀ side is selected in the pressure reduction setting switch 24 (see FIG. 4) of the pressure reduction device 1C from the beginning, and overpressure compensation is performed. Further, the time t _C1 at which the reduction position starts to change is a time point at which the portion subjected to the reduction in the preceding reduction device 1B reaches the reduction device 1C, and (t _C1 −t ₀ ) = L ₂ / V _c Can be expressed as

Example 2 The test apparatus described in Example 1 was modified in order to carry out the test of the present invention on the thin cast continuous casting apparatus in which the reduction roll was segmented. A segment was constituted by three sets of rolling rolls for the portion for performing the unsolidified rolling, only the rolling down devices at both ends were operated, and the intermediate rolling down device was used as a dummy.

FIG. 8 is a schematic diagram showing the relationship between the roll arrangement in the vicinity of the final freezing point and the non-solidifying position in a continuous casting machine having a segmented rolling-down device. In the figure, the segment 17A is used as a reference pressure reducing device, the upstream pressure reducing device is denoted by 1A1, and the downstream pressure reducing device is denoted by 1A2. 1B1 for the upstream side reduction device of segment 17B, 1 for the downstream side
B2, and each of segment 17C is 1C1, 1C
Number 2 is attached. In the same figure, the location of the most downstream roll (reference roll) of the segment 17A is the location of the reference reduction device that should achieve the target thickness of the thin slab.

FIG. 9 is a graph showing the time-dependent change in the rolling position of the segmented rolling-down device. In FIG. 9, (a) is the reference rolling-down device, and (b) and (c) are the upstream segments of the downstream segments. The rolling position of the rolling apparatus of the side and the downstream side is shown.

FIG. 9A shows the pressure reducing positions of the pressure reducing devices on the upstream side and the downstream side of the segment 17A (reference pressure reducing device). The downstream side rolling down device 1A2 starts rolling down at t ₀ , and t _A1
The target rolling position was reached at. During this period, the upstream side drafting device 1
Since the reduction position of A1 is a value determined by the geometrical positional relationship between the segment and the reduction cylinder, the reduction position is larger than that of the downstream side reduction device 1A2.

In FIG. 9 (b), since the upstream side rolling down device 1B1 of the segment 17B carries out rolling down of the unsolidified portion, a given rolling down position set value (actual value of the reference rolling down device:
The _rolling position followed as shown in S _0A ). On the other hand, although the same rolling position setting value S _0A was given to the downstream side rolling down device 1B2, the rolling down setting changeover device 24 (see FIG. 4) was initially set to P ₀ because the slab was solidified at that location. It is selected at time t _B1 that the over-compression compensation of the coagulation portion works and the reduction position starts to decrease. The difference between t _B1 and t ₀ corresponds to the moving time of the segment 17B between the upstream reduction roll and the downstream reduction roll, and was (t _B1 −t ₀ ) = (L _B / V _c ).

Similarly, the completion of the reduction by the reduction device 1B2 is delayed by a time corresponding to the moving time between the upstream reduction roll and the downstream reduction roll of the segment 17B, and (t _B2- t _A1 ) = (L _B / V _c ).

In FIG. 9 (c), with respect to the rolling down devices 1C1 and 1C2 of the segment 17C, the rolling down position actual value S _0A of the reference rolling down device is given as the rolling down position set value, but it is the rolling down of the solidification completion portion. Therefore, the pressure reduction setting switch 24
(See FIG. 4) was selected from the beginning on the P ₀ side to compensate for the overpressure reduction of the solidification portion, and the reduction start was delayed by the moving time of the portion reduced by the reduction device 1B2, and the completion of reduction was the same.
That was _{(t C1 -t B1) = (} t C2 -t B2) = (L C / V c).

As described above, in the present invention, both in the continuous casting apparatus having the rolling apparatus in the rolling roll unit and in the segmented continuous casting apparatus, in the rolling down apparatus downstream of the reference rolling apparatus, the reference rolling down apparatus is used. It was found that the rolling reduction was started with a delay from the start of the rolling reduction of the device, and it was possible to prevent overpressure reduction.

In the overpressure reduction prevention method disclosed in the above-mentioned WO97 / 14522, the pressure reduction control system is controlled by the pressure reduction device on the downstream side of the reference pressure reduction device.
The present invention achieves the same effect of preventing overpressurization even though the position control method is used for controlling the pressure reducing devices. In the present invention, the structure of the hydraulic control system can be simplified as compared with the structure according to the method disclosed in the above publication.

[0065]

According to the control method of continuous casting of the present invention, it is possible to continuously cast thin slabs with high precision of thickness of thin slabs and prevent over-pressurization with inexpensive equipment.

[Brief description of drawings]

FIG. 1 is a block diagram of a hydraulic control system of a pressure reducing device.

FIG. 2 is a schematic view showing the arrangement of a rolling down device.

FIG. 3 is a schematic diagram showing a transitional state from the start of reduction of the unsolidified portion to the transition to a steady state.

FIG. 4 is a block diagram showing the operating principle of the present invention.

FIG. 5 is a schematic diagram showing an arrangement of segmented rolling down devices.

FIG. 6 is a schematic diagram showing the relationship between the roll arrangement near the final freezing point and the unsolidified position.

FIG. 7 is a graph showing the temporal change of the rolling position of the rolling device near the final freezing point, and shows the graphs (a), (b) and
(c) shows the reduction positions of the reference reduction device and the reduction device on the downstream side, respectively.

FIG. 8 is a schematic diagram showing a relationship between a roll arrangement in the vicinity of a final freezing point and an unsolidified position in a continuous casting device having a segmented rolling-down device.

FIG. 9 is a graph showing a temporal change of a rolling position of a segmented rolling device, wherein FIG. 9 (a) is a reference rolling device;
(b) and (c) show the reduction positions of the reduction devices on the upstream and downstream sides of the downstream segment, respectively.

[Explanation of symbols]

1, 1A1, 1A2, 1B1, 1B2, 1C1, 1C
2: Reduction device 11: Reference reduction device 12: Upstream reduction device 13: Downstream reduction device 2: Reduction position control device 15: Reduction roll 16: Roll S: Cast slab SG: Unsolidified part SS: Solidified part

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) B22D 11/20 B22D 11/128 350

Claims (2)

(57) [Claims] 1. A continuous casting control method for obtaining a thin slab by reducing a non-solidified slab drawn from a mold with a plurality of reduction devices, wherein a solidification part of the slab is included in the plurality of reduction devices. Is determined as a reference reduction device at a location close to the location where the thickness of the thin cast piece becomes the target thickness, and for the reference reduction apparatus, a predetermined reduction speed and a target thickness of the thin cast piece are obtained. Performing a position control system control by setting a reduction position target, and regarding the reduction device on the upstream side of the reference reduction device,
Perform the position control method control by setting the rolling position target so that the predetermined rolling speed and the rolling amount of the unsolidified slab can be obtained.
For the rolling down device downstream of the reference rolling down device, a value obtained by adding a correction value based on the rolling down force of the downstream rolling down device to the actual rolling down position of the reference rolling down device is set as the rolling down position target. A control method for continuous casting, characterized by controlling a control method. 2. The correction value based on the rolling force of the downstream rolling down device is a value that compensates for elastic deformation of the rolling down device and its supporting structure, and an uncoagulated portion exists at the location of the rolling down device. In the state, the value based on the sum of the force resulting from the molten iron static pressure of the unsolidified portion of the slab center and the force that gives a predetermined rolling force to the solidified portion of the slab width end, or the location of the rolling down device 2. The control method for continuous casting according to claim 1, wherein, in a state where there is no unsolidified portion, the sum is a value based on a force that applies a predetermined rolling force to the entire width of the slab.