JP3063763B1 - Level control method and level control device for continuous casting machine - Google Patents

Abstract

Abstract: PROBLEM TO BE SOLVED: To effectively suppress a periodic fluctuation of a metal level in a mold of a continuous casting machine without forcing a major change of existing equipment. SOLUTION: A promotion index calculating section 80 provided in correspondence with each of the guide rolls 5, 5... Rolled in contact with a slab 3 drawn from a mold 1 is provided with a target level setting section 72.
Using the distance L from the set target level to the guide roll 5, 5 ..., and the fluctuation period T of the detected mold 1 inside the molten steel surface level by variation period detection unit 82, and a casting speed V _c to , Formula L / (V _c × T) = n + α (n: integer, 0 ≦ α <
1) Obtain the promotion index α by. The target change amount determining unit 81 determines the target level change amount such that each of the promotion coefficients α does not fall within a predetermined range including 0.5, and sets a target level setting unit.
Change the target level setting in 72.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a level control method for controlling a level in a mold during a casting operation of a continuous casting machine so as to maintain the level in a mold at a predetermined target level. It relates to a level control device.

[0002]

2. Description of the Related Art A continuous casting machine is operated by pouring (pouring) molten metal (molten metal) into a cylindrical mold having openings at upper and lower sides, bringing the molten metal into contact with a water-cooled inner wall of the mold, and cooling the mold. The outside is formed as a slab covered with a solidified shell, and the slab is guided by a plurality of pairs of guide rolls that are in contact with the outside of the slab and continuously drawn from the lower opening of the mold. Cooled by cooling water injected from the spray band arranged in the path, cut to a predetermined size after the solidification proceeds to the inside of the slab, the product slab to be a raw material of a post-process such as rolling It is performed in the procedure to obtain. The slab is drawn at a predetermined pouring speed by controlling the rotation of one or more pairs of pinch rolls that are in contact with the outside of the slab that has solidified to the inside downstream of the guide roll in the drawing direction. Has been done.

[0003] In such a continuous casting machine, various inconveniences which hinder stable operation such as overflow of molten metal from the upper part of the mold and occurrence of breakout are prevented beforehand, and the production efficiency is improved. In order to stabilize the cooling and solidification state in the mold and improve the quality of the product slab, it is important to maintain the surface level (molten level) of the molten metal staying inside the mold at an appropriate level. The level control is performed to maintain the level inside the mold at a predetermined target level.

[0004] This level control is performed by detecting the level in the mold using an appropriate level meter such as an eddy current level meter.
This detection level is compared with a predetermined target level, and a target operation position of a pouring means (sliding gate, stopper device, etc.) for pouring into a mold is obtained by PID calculation based on a deviation between the two. Actuator (hydraulic cylinder, etc.) of the pouring means to achieve the target operating position
Is operated and feedback control is performed to adjust the amount of molten metal.

[0005]

However, in the operation of a continuous casting machine, various disturbances that cause a change in the level of the molten metal, such as a change in the flow rate gain of the pouring means, a bulging of the slab drawn from the mold, and the like. Is present, and when the level change caused by these disturbances occurs in a specific cycle, there is a problem that the level continues to grow and the level of the level inside the mold fluctuates periodically. there were.

[0006] Since such a periodic level fluctuation has a small fluctuation width, it may cause serious problems such as the above-mentioned overflow of the molten metal and the occurrence of breakout which hinder the stable operation of the continuous casting machine. Although this is small, when this level fluctuation occurs, the following problems occur.

FIG. 7 is an explanatory diagram of a problem caused by periodic fluctuations in the molten metal level. In the figure, reference numeral 1 denotes a cylindrical mold having openings at upper and lower sides. In the mold 1, a molten metal 2 poured from a pouring means (not shown) is retained. Is cooled from the outside by the contact with the water-cooled inner wall and solidified, and becomes a slab 3 whose outside is covered by the solidified shell 3a, and is continuously drawn below the mold 1.

The solidified shell 3a grows from the upper part to the lower part of the mold 1, and in the lower opening of the mold 1, withstands the pressure of the molten metal 2 inside and has a thickness that does not hinder the drawing as a slab 3. However, in the vicinity of the surface of the molten metal 2,
It has only a small thickness and is supported by the molten metal 2 inside.

Here, the surface level of the molten metal 2 in the mold 1 falls from the highest level shown in FIG. 7A to the lowest level shown in FIG. 7B, and then shown in FIG. 7C. When it fluctuates to return to the highest level, the thin solidified shell 3a generated near the surface of the molten metal 2 in the state of FIG.
As shown in FIG. 7B, a phenomenon occurs in which the support of the molten metal 2 on the inner side of the mold 1 is lost with the lowering to the lowest level, and as shown in FIG.

On the other hand, on the surface of the molten metal 2, lubrication called powder is applied to improve the lubricity between the inner wall of the mold 1 and to prevent the surface from being oxidized by contact with outside air. As shown in FIG. 7B, when the agent (not shown) is supplied and the solidified shell 3a falls down, the powder enters the space formed between the solidified shell 3a and the inner wall of the mold 1. Next, when the level of the molten metal rises, the intrusion of the molten metal 2 into the intruded portion of the powder is hindered, and FIG.
As shown in FIG. 3, a recess 3b is formed on the surface of the slab 3.

Therefore, when the fluctuation of the molten metal level occurs periodically as described above, the slab 3 formed during this period includes:
A plurality of recesses 3b arranged at intervals corresponding to the cycle of the fluctuation will be formed on the surface, and a shape defect will occur in the product slab after solidification is completed, and in the vicinity of each recess 3b, Subcutaneous defects are likely to occur due to the entrainment of powder in the above-described production process, and there is a disadvantage that the quality of product slabs is deteriorated. In particular, in a continuous casting machine requiring high product quality, the It is an important issue to suppress periodic fluctuations in the molten metal level.

Various causes have been hitherto described for the cause of such periodic fluctuations in the molten metal level, and at present, as disclosed in Japanese Patent Publication No. 4-65742, It is said that the cause is bulging that occurs in a slab that is drawn below the mold.

[0013] The bulging is performed by the casting 3 during the drawing.
The solidified shell 3a that coats the outside of the slab bulges outward in a “barrel shape” between a plurality of guide rolls for guiding the slab 3 due to the pressure of the unsolidified molten metal contained therein. Yes, if this bulging occurs, the solidified shell
The swelling of 3a increases the internal volume of the slab 3, which lowers the level of the molten metal in the upstream mold 1. When the swelling portion is clamped from the outside by the guide roll, the slab 3 3 decreases, and the molten metal level rises.

In Japanese Patent Publication No. 4-65742, the above-mentioned lowering and rising of the level of the molten metal due to bulging occur repeatedly in a cycle of passing between a plurality of guide rolls. Assuming that the level periodically fluctuates, the pitch (arrangement interval) of the guide rolls arranged below the mold 1 is made non-uniform, and further, by displacing the positions of the guide rolls on both sides of the slab 3, It is stated that the periodic fluctuation of the surface level can be suppressed.

However, when this method is carried out in an existing continuous casting machine, a large-scale equipment change for changing the arrangement of tens of pairs of guide rolls is required, and there is a problem that it is difficult to realize the method. Further, there is a continuous casting machine in which the arrangement intervals of the guide rolls are not uniform from the beginning, but in the operation of this type of continuous casting machine, the periodic fluctuation of the molten metal level may occur as described above, The method disclosed in Japanese Patent Publication No. 4-65742 does not achieve a sufficient effect even if it can be realized.

The present invention has been made in view of such circumstances, and clarifies, from a new point of view, a periodic fluctuation factor of a molten metal level inside a mold of a continuous casting machine, and examines this fluctuation with existing equipment. It is an object of the present invention to provide a method and a device for controlling the level of a continuous caster, which can reduce the amount of change without forcing a large change.

[0017]

SUMMARY OF THE INVENTION According to the present invention, there is provided a method for controlling a surface level of a continuous casting machine, comprising: a plurality of pairs of slabs which are drawn from a mold at a predetermined casting speed; In the method for controlling the level of the molten metal in the continuous casting machine, which controls the level of the molten metal inside the mold during operation of the continuous casting machine guided by the guide rolls, the level is generated inside the mold. The period of the periodic fluctuation of the molten metal level is detected, and the detected fluctuation period T
Using the casting speed V _c and the separation distance L from a predetermined position inside the mold to each of the plurality of pairs of guide rolls, the following formula L / (V _c × T) = n + α (n: integer) , 0 ≦ α <1), and when the promotion index α obtained for each guide roll is within a predetermined range including 0.5, the target level is changed so as to be out of the range. It is characterized by.

Further, in the apparatus for controlling the level of a molten metal in a continuous casting machine according to the present invention, a slab drawn from a mold at a predetermined pouring speed is guided by a plurality of pairs of guide rolls arranged in parallel along the drawing path. During the operation of the continuous casting machine
In a level controller for a continuous casting machine for controlling a level of a metal level inside the mold to be maintained at a predetermined target level, means for detecting a period of a periodic fluctuation of the level of the metal level generated inside the mold. When the fluctuation period T that is detected by said means, said a velocity V _c casting, by using the distance L from a predetermined position within the mold until people said plurality of pairs of guide rolls husband, the formula L / ( V _c × T) = n + α (n: integer, 0 ≦ α <
1) means for calculating the promotion index α according to, means for determining whether the promotion index α obtained by the means is within a predetermined range including 0.5, and determination by the determination means Means for changing the target level according to the following.

In the present invention, a predetermined position inside the mold,
For example, using a target level position set in advance to be a target of the level control, a cycle T of a periodic fluctuation of the level generated in the mold during the operation of the continuous casting machine is detected. Separation distance L between level and guide roll
When the said calculated fractional parts of the quotient obtained by dividing by the product of the period T and the casting speed V _c as conducive index alpha, the facilitator index alpha is in a predetermined danger zone containing 0.5, the It is determined that the periodic fluctuation is in a state of being promoted, the target level of the level control is changed, the separation distance L is increased, and the enhancement index α is out of the danger range. Suppress level fluctuations.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings showing the embodiments. The method for controlling the level of the molten metal in the continuous casting machine according to the present invention (hereinafter referred to as the method of the present invention) is intended to suppress the periodic fluctuation of the level of the molten metal in the mold as described above. In this section, the mechanism of periodic fluctuations in the level of the molten metal is described.

FIG. 1 is an explanatory diagram of a mechanism of generating a periodic level change. In the figure, reference numeral 1 denotes a cylindrical mold having openings at upper and lower sides. In the mold 1, a molten metal 2 poured from a pouring means (not shown) stays.
Is solidified by being cooled from the outside by contact with the water-cooled inner wall of the mold 1, and is continuously drawn out below the mold 1 as a slab 3 whose outside is covered by a solidified shell 3 a.

The slab 3 is pulled out from the slab 3, which is arranged at a sufficient distance below the mold 1 and solidified to the inside thereof, and is brought into contact with the pair of pinch rolls 4 so as to hold both sides of the slab 3. , 4 while maintaining a predetermined casting speed. A plurality of pairs of guide rolls 5, 5,... Are arranged at predetermined intervals between the pinch rolls 4, 4 and the mold 1 along a drawing path. The slab 3 is roll-contacted to the outside of the slab 3 containing the molten metal, and
4 to perform a guiding action.

During the operation of such a continuous casting machine, the mold 1
In the case where the internal level of the molten metal changes, as shown in FIG.
As shown in (b) and (c), a recess is formed in the surface of the slab 3 in contact with the inner wall of the mold 1 due to the fall of the solidified shell 3a generated near the surface of the molten metal 2 when the level of the molten metal lowers. 3b,
3b ... are formed, and the formation portions of such recesses 3b, 3b ...
As the slab 3 is pulled out, the slab moves downward and reaches below the mold 1 to the juxtaposed area of the guide rolls 5, 5,.

Here, if the interval between the formation positions of the recesses 3b in the longitudinal direction of the slab 3 is substantially equal to the juxtaposed interval of the guide rolls 5, 5,. As shown, adjacent guide rolls 5, 5...
... may be in a state of being in contact with each other,
The rolling resistance between each of the guide rolls 5, 5,... And the slab 3 increases.

At this time, the rotation of the pinch rolls 4, 4 arranged below the guide rolls 5, 5,... Is controlled to maintain a constant casting speed. , 5 ..., the rolling torque of the pinch rolls 4, 4 is reduced as shown by the white arrows in the figure to maintain the casting speed against the increased rolling resistance. Increasing control is performed.

As shown in FIG. 1 (b), the rolling resistance between the guide rolls 5, 5 and the slab 3 is reduced by the recesses 3b, 3b falling out of the recesses 3b. The rolls 4 and 4 are in a state having a large rotation torque, and as a result of the rotation speed of the pinch rolls 4 and 4 being increased, the casting speed is increased as shown by the white arrow in the figure, and this speed increase , The level of the molten metal in the mold 1 falls.

When such a decrease in the level of the molten metal occurs,
As shown in FIG. 1 (c), the solidified shell 3a generated earlier falls down on the surface of the molten metal 2, and when the level of the molten metal subsequently rises, a new recess is formed as shown in FIG. 1 (d). A place 3b is formed. The recess 3b formed in this manner is pulled out below the mold 1 with the drawing of the slab 3 and rolled into contact with the guide roll 5, after which the processes of FIGS. 1 (a) to 1 (d) are performed. Since this is repeated, the fluctuation of the surface level of the molten metal 2 in the mold 1 is maintained while maintaining its periodicity and increasing the fluctuation width.

Here, the mechanism of occurrence of the periodic level fluctuation as described above will be verified. The cause of the periodic level fluctuation in the mold 1 is a recess 3b formed on the surface of the slab 3, and the recess 3b is, as shown in FIG. When the surface level of the molten metal 2 falls inside, it occurs when the solidified shell 3a previously formed at a position higher than this level falls down. That is, the recess 3b is
This occurs at the surface position of the molten metal 2 when the level of the molten metal in the mold 1 falls most.

The reason why the recess 3b generated as described above causes a level change is that when the recess 3b reaches the position where the guide roll 5 is provided, the rolling resistance of the guide roll 5 increases. There is such an increase in rolling resistance,
Conditions that promote periodic level fluctuations in the mold (hereinafter referred to as “promotion conditions”) are as follows.
It is considered that the rolling contact between the roll and the guide roll 5 occurs, and the increase in the casting speed according to the rolling contact occurs at the timing of lowering the molten metal surface from the highest position.

Here, the variation cycle of the molten metal level inside the mold 1 is T, and the pouring speed, which is the moving speed of the slab 3, is V _c
Then, the recess formed on the surface of the slab 3 as described above
The parallel pitch of 3b, 3b is ( _Vc × T). At this time, as shown in FIG. 1 (a), the distance from the surface of the molten metal 2 having an appropriate level inside the mold 1 to a predetermined guide roll 5 (the uppermost guide roll 5 in the figure) was L. In this case, when the distance L is an integral multiple of the above ( _Vc × T), the transfer of the recess 3b to the guide roll 5 is performed when the surface level of the molten metal 2 in the mold 1 is at an appropriate level. That is, it occurs at a timing substantially at the center between the highest level and the lowest level, and the above-mentioned promotion condition is not satisfied. In other words, the fractional part of the quotient obtained by dividing the above L by the above ( _Vc × T), that is, α (promoting exponent) given by the following equation is a value close to 0.5. When this happens, the promotion condition is satisfied.

L / (V _c × T) = n + α (1) where n is an integer and 0 ≦ α <1

L in the formula (1) is a value determined from an appropriate molten metal level value inside the mold 1 predetermined as an operating condition of the continuous casting machine and a lower surface of the mold 1 given as equipment specifications of the continuous casting machine. The sum of the separation distances to the guide rolls 5, 5,... Can be obtained in advance for each of the plurality of guide rolls 5, 5,..., And the casting speed V _c is a value determined in advance as the operating condition of the continuous casting machine. is there.

Therefore, the fluctuation period T of the level fluctuation actually occurring inside the mold 1 is detected, and using the detection result, the calculation of the above equation (1) is performed for each of the guide rolls 5, 5,. Of the promotion index α obtained with respect to
By examining whether the value is close to 5 or not, it is determined whether there is a possibility that the currently occurring periodic level fluctuation may be promoted, and this promotion is performed by a plurality of guide rolls 5 and 5.
.. Can be determined.

Here, among the values on the left side of the equation (1), the fluctuation period T of the molten metal level is a value that cannot be directly changed. The casting speed V _c, is capable changed, a predetermined value in accordance with the operating conditions, this change, desirable since it involves a change in the cooling conditions of the slab 3 on withdrawal path Absent.

Therefore, according to the method of the present invention, when it is determined that the promotion index α obtained by the equation (1) is close to 0.5 and it is within the danger range where the periodic level fluctuation can be promoted, the above-mentioned (1) By changing the remaining value L included in the left side of the equation and excluding the promotion index α in the corresponding guide roll 5 from the risk range, periodic level fluctuation is suppressed.

L is a distance between the surface of the molten metal 2 having an appropriate level inside the mold 1 and each of the guide rolls 5, 5,... As described above. It is difficult to change the relative position of
The appropriate level of the surface of the molten metal 2 inside the mold 1, that is, the target level to be kept constant in the mold 1 is changed to suppress periodic level fluctuation. Since this target level is a value which is set in advance so that the cooling of the molten metal 2 in the mold 1 and the formation of the solidified shell 3a can be performed well at the start of the operation of the continuous casting facility, a drastic change is not made. Although it is difficult, since the promotion index α is a decimal part of the quotient obtained by the calculation on the left side of the equation (1), the promotion index α is removed from the risk range by a slight change of the target level. Level fluctuation can be suppressed.

Here, the risk range may be set with an appropriate width before and after 0.5, for example, 0.25 <α <0.75 (2).

As shown in FIG. 1A, recesses 3b, 3b...
5 at the same time, the rolling resistance described above is further increased, so that periodic level fluctuations are further promoted. As shown in the following equation, the distance D between the guide rolls 5, 5,... (See FIG. 1) is determined by the parallel pitch (V _c × T) of the recesses 3b, 3b in the longitudinal direction of the slab 3. ) Occurs when it is an integer (m) times.

D = m × V _c × T (3)

Therefore, for each of the lengths d (= D / m) obtained by dividing the roll interval D by various integers m, when the influence index β obtained by the following equation is close to 0.5, the periodicity It is determined that the level fluctuation is further promoted.

L / d = n + β (4)

In the equation (4), d is a value determined in advance according to the equipment specifications of the continuous casting machine, and it is difficult to change the value. Therefore, the influence index β obtained for each of the guide rolls 5, 5,. It is desirable to change the value of β by changing the distance L when in the danger range close to. This change is performed by setting the target level before the operation of the continuous casting facility by setting the influence index β obtained for each guide roll 5, 5,... Can be realized by not including the

0.25 <β <0.75 (5)

FIG. 2 is a schematic block diagram showing an embodiment of the liquid level control apparatus used for carrying out the method of the present invention as described above. In the figure, reference numeral 1 denotes a cylindrical mold having openings at upper and lower sides. Above the mold 1, a tundish 6 for storing the molten metal 2 is arranged. A pouring nozzle 60 is connected to the lower surface of the tundish 6 and extends to the inside of the mold 1. The molten metal 2 in the tundish 6 is formed by sliding at the base of the pouring nozzle 60. Gate 61
Is poured into the mold 1 and cooled and solidified from the outside by contact with the water-cooled inner wall of the mold 1 to form a slab 3 covered with a solidified shell and continuously below the mold 1. Is pulled out.

The withdrawal of the slab 3 is carried out while maintaining a predetermined casting speed V _c by the rotation control of a pair of pinch rolls 4, 4 which are disposed sufficiently spaced below the mold 1. Also, between the pinch rolls 4, 4 and the mold 1, a plurality of pairs (only four pairs are shown) of guide rolls 5, 5,... The slab 3 drawn from the mold 1 is guided by guide rolls 5, 5... Rolling on the outside thereof and guided to the pinch rolls 4, 4, during which cooling blast injected from a spray band (not shown) is performed. The solidified shell is cooled by water so as to increase the thickness of the solidified shell, and is pinched between the pinch rolls 4 when solidification progresses to the inside.

In the continuous casting machine configured as described above, the surface level control for maintaining the surface level of the molten metal 2 in the mold 1 at a predetermined target level is performed. In this level control, a deviation between the detected level of the level in the mold and the target level is determined, and feedback for changing the opening of the sliding gate 61 as a means for pouring the mold 1 into the mold 1 in order to eliminate the deviation. It is performed by control.

The configuration of the feedback control system will be described. The surface level of the molten metal 2 inside the mold 1 is detected by an eddy current level meter 70 facing the surface, and this detection level is given to an adder 71. The adder 71 includes:
A target level serving as a control target set in the target level setting section 72 is given.The adder 71 calculates a deviation between the detection level and the target level, and outputs a deviation signal corresponding to the determined deviation to a level. An operation for outputting to the control unit 7 is performed.

The level controller 7 uses the input from the adder 71, that is, the deviation between the detection level and the target level, and performs, for example, a PID calculation based on this deviation to determine the target opening of the sliding gate 61. In order to achieve the target opening, an opening / closing command is issued to an actuator (hydraulic cylinder or the like) 62 of the sliding gate 61, and the opening of the sliding gate 61 is adjusted by the operation of the actuator 62 in accordance with the opening / closing command. An operation of adjusting the amount of molten metal poured into the mold 1 is performed.

The illustrated apparatus is provided with a periodic fluctuation control unit 8 which operates to suppress the periodic fluctuation of the molten metal level inside the mold 1 which cannot be eliminated by the above-described feedback control, according to the method of the present invention. . This periodic variation control unit 8
, A boost index calculating section 80 for calculating the boost index α according to the above equation (1), a target change amount determining section 81 for determining the target level change amount based on the calculation results, A fluctuation cycle detection unit 82 extracts a periodic fluctuation component included in the level detected by the level meter 70 and detects the cycle of the fluctuation component.

The fluctuation period detecting section 82 performs, for example, a fast Fourier transform process on the output signal of the eddy current level meter 70,
The level fluctuation occurring on the surface of the internal molten metal 2 is divided into fluctuation components having periodicity, and a period T of a dominant fluctuation component having the maximum amplitude is obtained.
.. To be used in the calculation of the promotion index α according to the above equation (1).

.. Are provided with a plurality of guide rolls 5, 5 arranged in parallel along the drawing path of the slab 3.
Are provided in correspondence with each of..., And the level change period T given as an output of the change period
With a velocity V _c casting, is given a distance L from the surface of the molten metal 2 in the mold 1 to the rolls, by applying these values to the equation (1), each guide roll 5 , 5,... Are given to the target change amount determining unit 81.

[0052] Incidentally, the casting speed V _c can be determined from the results of detection by the rotation detector (not shown) the rotational speed of the pinch rolls 4, 4 for extraction of the slab 3. The distance L can be obtained as a value obtained by adding the current target level given from the target level setting unit 72 and the distances L ₁ , L _2, ... From the lower surface of the mold 1 to each of the guide rolls 5, 5,. The distances L ₁ , L _2, ... Are obtained in advance for the respective guide rolls 5, 5,... According to the equipment specifications of the continuous casting machine, and are stored in the respective promotion index calculating units 80, 80,.

The target change amount determining section 81 includes a promotion index calculating section 8
It is determined whether or not each of the promotion indexes α of the guide rolls 5, 5... Given from 0, 80... Is included in the danger range shown in the above-mentioned equation (2), and the promotion index α is included in the danger range. If the guide roll 5 is present, the amount of change in the target level required to remove the promotion index α from the risk range is determined, and the result is given to the target level setting section 72. The target level setting unit 72 performs an operation of changing the previously set target level according to the input from the target change amount determination unit 81,
Thereafter, the above-described level control is performed by the operation of the level control unit 7 based on the deviation between the changed target level and the detection level of the eddy current level meter 70.

When the target level change amount is determined by the target change amount determining section 81, the promotion index α obtained for each of the guide rolls 5, 5,... Other than the guide roll 5, is also referred to. are performed so that α, α,... do not fall within the danger range after the target level is changed. Also, the influence index β of each of the guide rolls 5, 5,...
If it is included in the risk range shown in the equation, it is desirable to expand the risk range of the promotion coefficient α and determine the amount of change of the target level so as to be as close to 0 as possible.

In the above embodiment, the separation distance L from the target level position set inside the mold 1 to each guide roll 5 is used for the calculation of the promotion index α. It is also possible to use the separation distance L between the predetermined position and each guide roll 5.

Next, an embodiment in which the method of the present invention as described above is applied to the actual level control of a continuous casting machine will be described.

EXAMPLE 1 As shown in FIG. 3, a continuous casting machine having guide rolls 5, 5... of setting a target level that the distance L is 1050mm from the guide roll 5, was operating a casting speed V _c is set to 1.2 m / sec, as shown in FIG. 4, the mold 1 inside the surface level of the molten metal 2 In the detected value, a level fluctuation of a period T = 3 sec occurred.

[0058] Here, in equation (1), since the _{L / (V c × T)} = 1050 / (1200/60 × 3) = 17.5, the facilitator exponent α is 0.5, the equation (2) It is approximately at the center of the indicated danger area.

In the above equation (4), since L / d = 1050/300 = 3.5, the influence index β is also 0.5, and (5)
It is approximately at the center of the danger area shown in the formula.

Therefore, when the continuous casting machine shown in FIG. 3 is operated under the above-mentioned conditions, a level fluctuation having a period of 3 sec is promoted, and this level fluctuation is
As shown in the figure, the fluctuation range was gradually increased and continued, and the fluctuation range after approximately 40 seconds from the point of occurrence reached ± 9 mm.

In the method of the present invention, since both the promotion index α and the influence index β are within the danger range, the change of the target level accompanying the detection of the level fluctuation as described above takes approximately 50 seconds from the time when the level fluctuation occurs. Will be executed after
As shown in FIG. 4, a new target level 30 mm lower than the initial target level was set. As a result, the level fluctuation gradually converged, and the fluctuation width at the time when approximately 50 seconds had elapsed since the setting change, that is, at approximately 100 seconds after the start of the fluctuation, was suppressed to ± 1.6 mm as shown in FIG.

Here, the separation distance L between the newly set target level and the uppermost guide roll 5 is 1020 mm, and when this is used to calculate the above equation (1), L / ( the _{V c × T) = 1020 /} (1200/60 × 3) = 17.

.. With respect to the other guide rolls 5, L / (V _c × T) = (1020 + 300 ×) / (1200/60 ×)
3) = 17 + 5x, and the promotion coefficient α is 0 for each of the guide rolls 5, 5.

[Embodiment 2] As shown in FIG. 5, the second to sixth guide rolls 5, 5,...
Continuous casting machines arranged side by side at unequal intervals of 240 mm, 300 mm, 360 mm, and 420 mm, respectively, were set to a target level at which the distance L from the second guide roll 5 was 1240 mm,
Was operating a speed V _c casting is set to 0.9m / sec,
As shown in FIG. 6, a level variation having a period T = 4 sec occurred in the detected value of the surface level of the molten metal 2 in the mold 1.

Here, when the calculation of the expression (1) is performed for the second guide roll 5, L / (V _c × T) = 1240 / (900/60 × 4) = 20.67, and similarly, 3 to 6 th for each guide roller 5 of _{the, L / (V c × T} ) = (1240 + 240) / (900/60 × 4) = 24.67 L / (V c × T) = (1240 + 540) / (900/60 × 4 _{) = 29.67 L / (V c} × T) = (1240 + 900) / (900/60 × 4) = 35.67 L / (V c × T) = (1240 + 1020) / (900/60 × 4) = 37.67 , and the these Are both 0.67, (2)
It is included in the danger range shown in the formula.

Therefore, when the continuous casting machine shown in FIG. 5 is operated under the above-mentioned conditions, a level fluctuation having a period of 4 sec is promoted, and this level fluctuation is
As shown in FIG. 4, the fluctuation range is gradually increased and continues, and this fluctuation range is approximately 40 seconds from the time of occurrence as in the embodiment shown in FIG.
After ec, it reached ± 9 mm.

In the method of the present invention, since the promotion index α is within the danger range, the level of the level change is approximately equal to the time when the level change occurs.
After 50 seconds, the target level was changed and a new target level was set 30 mm lower than the initial target level. As a result, the level fluctuation gradually converges, and when about 50 seconds have passed since the setting change, that is, 100 seconds after the start of the fluctuation, the fluctuation width is ± 2.8 as shown in FIG.
mm.

Here, by using the newly set target level and calculating the above equation (1) for the second to sixth guide rolls 5, 5,..., L / (V _c × T) = (1240) -30) / (900/60 × 4) = 20.17 L / (V c × T) = (1480-30) / (900/60 × 4) = 24.17 L / (V c × T) = (1780-30 ) / (900/60 × 4) = 29.17 L / (V c × T) = (2140-30) / (900/60 × 4) = 35.17 L / (V c × T) = (2260-30) / (900/60 × 4) = 37.17, which indicates that all the promotion coefficients α are out of the risk range.

[0069]

As described above in detail, in the method and apparatus for controlling the level of a continuous casting machine according to the present invention, the factor of the periodic variation of the level in the casting mold of the continuous casting machine is considered. Due to this variation, a recess formed on the surface of the slab is caused by an increase in rolling resistance generated when passing through each guide roll. When the timing of falling from the level coincides with the timing, it is determined that the fluctuation is promoted, and this state is eliminated by changing the target level which is the target of the level control of the molten metal. Fluctuations can be effectively suppressed without forcing major changes to existing equipment, preventing the occurrence of shape defects and subcutaneous defects in product slabs due to such level fluctuations. Te, etc. good quality becomes possible to manufacture a product slab stably, the present invention provides excellent effects.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a generation mechanism of a periodic molten metal level fluctuation focused on in the present invention.

FIG. 2 is a schematic block diagram showing an embodiment of a molten metal level control device used for carrying out the method of the present invention.

FIG. 3 is a view showing an arrangement of guide rolls in a continuous casting machine used in Embodiment 1 of the method of the present invention.

FIG. 4 is a view showing a state of a change in a molten metal level in the continuous casting machine shown in FIG. 3;

FIG. 5 is a view showing a guide roll arrangement in a continuous casting machine used in Embodiment 2 of the method of the present invention.

FIG. 6 is a view showing a state of a change in a metal surface level in the continuous casting machine shown in FIG. 5;

FIG. 7 is an explanatory diagram of a problem caused by periodic fluctuations of the molten metal level.

[Explanation of symbols]

 Reference Signs List 1 mold 2 molten metal 3 slab 3a solidified shell 3b recess 4 pinch roll 5 guide roll 6 tundish 7 level control unit 8 cycle fluctuation control unit 70 eddy current level meter 72 target level setting unit 80 promotion index calculating unit 81 target change amount determination Unit 82 Fluctuation period detection unit

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Masahiko Oka 4-5-33 Kitahama, Chuo-ku, Osaka-shi, Osaka Sumitomo Metal Industries, Ltd. (56) References JP-A-11-320059 (JP, A) JP-A-8-290251 (JP, A) JP-A-11-333551 (JP, A) JP-A-11-170021 (JP, A) JP-A-10-314911 (JP, A) JP-A-10-146658 (JP JP, A) JP-A-9-29408 (JP, A) JP-A-8-147044 (JP, A) JP-A-7-234705 (JP, A) JP-A-3-1744961 (JP, A) JP Hei 2-169163 (JP, A) JP-A-61-235056 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B22D 11/18 B22D 11/16 104

Claims (2)

(57) [Claims] 1. During the operation of a continuous casting machine in which a slab drawn from a mold at a predetermined casting speed is guided by a plurality of pairs of guide rolls arranged in parallel along the drawing path, the inside of the mold is removed. In a method for controlling a level of a continuous casting machine for controlling a level of a level of a molten metal to be maintained at a predetermined target level, a cycle of a periodic variation of the level of the molten metal occurring inside the mold is detected, and the detected variation cycle using a T, the the velocity V _c casting, and a distance L from a predetermined position within the mold until people said plurality of pairs of guide rolls husband,
The following equation L / (V _c × T) = n + α (n: integer, 0 ≦ α <
1) calculating the promotion index α according to, and when the promotion index α obtained for each guide roll is within a predetermined range including 0.5, the target level is changed so as to be out of the range. A method for controlling the surface level of a casting machine. 2. During the operation of a continuous casting machine in which a slab to be drawn from a mold at a predetermined casting speed is guided by a plurality of pairs of guide rolls arranged in parallel along the drawing path, the inside of the mold is removed. In a level control apparatus for a continuous casting machine for controlling a level of a molten metal to be maintained at a predetermined target level, a means for detecting a period of a periodic fluctuation of a molten metal level generated inside the mold, and by using the detected fluctuation period T, the the velocity V _c casting, and a distance L from a predetermined position within the mold until people said plurality of pairs of guide rolls husband, the formula L / (V _c × T) = N + α (n: integer, 0 ≦ α <
1) means for calculating the promotion index α according to, means for determining whether or not the promotion index α obtained by the means is within a predetermined range including 0.5, and determination by the determination means Means for changing the target level according to the following formula: